Arbuscular mycorrhizal fungal community was affected by tillage practices rather than residue management in black soil of northeast China

Soil & Tillage Research 198 (2020) 104552

Contents lists available at ScienceDirect

Soil & Tillage Research journal homepage: www.elsevier.com/locate/still

Arbuscular mycorrhizal fungal community was affected by tillage practices rather than residue management in black soil of northeast China

T

Siyu Gu, Shuai Wu, Yupeng Guan, Cheng Zhai, Zehui Zhang, Ayodeji Bello, Xingjun Guo, Wei Yang* College of Resources and Environment, Northeast Agricultural University, Harbin, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Tillage practices Residue management Arbuscular mycorrhiza Black soil

Arbuscular mycorrhizal (AM) fungi are one of the most important soil microbes in an agrarian ecosystem, and consequently affected by various agricultural practices. To elucidate the effects of tillage practices and residue management on AM fungi, a field trial was conducted on the Songnen Plain, Northeast China. We examined the effects of different tillage practices including no-tillage (NT), rotary tillage (RT), subsoil tillage (ST) and deep tillage (DT) on the AM fungal biomass, diversity and community under residue removal and residue retention. AM root colonization and extraradical hyphal (ERH) density were significantly higher in DT treatment compared with NT treatment, whereas an opposite trend was observed for AM fungal spore density. Structural equation modeling indicated that AM fungal spore density was directly affected by tillage practices. Albeit, the effect of tillage practices on ERH density was mainly mediated through root length of maize. By Miseq sequencing of 18S rDNA, 66 AM fungal operational taxonomic units (OTUs) were identified and Glomeraceae was the most abundant group in this study. AM fungal OTU richness was highest in treatment NT, and significantly higher than that in treatment DT. Non-metric multidimensional scaling analysis indicated that treatment DT and ST induced a distinct AM fungal community composition compared with treatment NT. On the other hand, residue did not significantly influence AM fungal biomass, OTU richness and community composition. Overall, our findings indicated that tillage practice is a stronger determinant than residue management in AM fungal development and community composition in black soil on the Songnen Plain.

1. Introduction Black soil is regarded as one of the most productive soils in China. It occupies approximately 20 % of the national arable land and contributes to 30 % of the grain yield (Xu et al., 2018; Yin et al., 2015). Due to the increasing demands for grains, the use of different tillage systems (rotary tillage, subsoil tillage and deep tillage) has been widely conducted in the black soil region for decades (Zhang et al., 2015a). However, the excessive and unsuitable tillage practices have induced serious soil erosion and fertility deterioration (Liu et al., 2010). Because of concerns regarding soil erosion and degradation, conservation tillage practices, especially no tillage was proposed in this region recently (Zhang et al., 2015a). No tillage systems not only improve soil fertility (Zhang et al., 2015b), reduce soil erosion (Peigne et al., 2007), but also have several advantages such as enhancement in soil microbial activity and diversity (Sun et al., 2016), and less need of energy and labor (Arvidsson, 2010). However, it was sometimes reported that no tillage practice will harden the top soil layer and fail to control weeds and soil⁎

borne pathogens. This might hamper the plant growth and yield (Galvez et al., 2001). Therefore, uncertainties still remain about the influence of no tillage practice on the agricultural ecosystem especially the microbial component. Arbuscular mycorrhizae (AM) are mutualistic symbiosis formed between terrestrial plant roots and soil fungi of Glomeromycota (Smith and Read, 2008). The large majority of agricultural crops (95 %), such as wheat, rice, and maize can form a symbiosis with AM fungi (Hijri, 2016). In this association, AM fungi benefit the host plant by increasing nutrient (e.g. N and P) uptake (Marx, 2004), and also improve their resistance to pathogen and environmental stress (Smith and Read, 2008). More importantly, AM fungi can improve soil structure and soil aggregation through the production of glomalin related protein (GRSP), and thus contribute greatly to soil quality and health (Rillig, 2004). In this view, AM fungi are considered to be one of the most important microorganisms in the sustainability of agricultural ecosystem. AM fungi are influenced by various agricultural management practices, including tillage, fertilization and residue management (Säle

Corresponding author. E-mail address: [email protected] (W. Yang).

https://doi.org/10.1016/j.still.2019.104552 Received 29 June 2018; Received in revised form 5 November 2019; Accepted 18 December 2019 0167-1987/ © 2019 Elsevier B.V. All rights reserved.

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

481 mm. The soil at this study site is classified as Mollisol (according to USDA soil taxonomy), with soil organic matter (SOM) of 34.96 g·kg-1, total nitrogen (TN) of 1.51 g·kg-1, total phosphorus (TP) of 0.60 g·kg-1, available phosphorus (AP) of 53.69 mg kg-1, available potassium (AK) of 0.23 g·kg-1, and pH of 5.74. The field trial plots were established in 2015 with tillage practices and residue management as main factors. One factor contained 4 types of tillage practices: (1) no tillage (NT), (2) rotary tillage (RT), (3) subsoil tillage (ST), and (4) deep tillage (DT). The field was ploughed to the depth of 15 cm in the RT treatment, ploughed with a vertical blade to the depth of 30 cm (non-soil-turning) in the ST treatment, and ploughed to the depth of 30 cm (soil turning) in the DT treatment. The second factor contained two treatments: maize residue removal (-R) or retention (+R). The maize residues were cut into pieces (ca. 5 cm) after harvest. In the NT + R plot, the maize residues were retained on the soil surface after harvest; while maize residues in RT + R, ST + R and DT + R treatment were incorporated into soils together with tillage practices after harvest. Each treatment had three replicates, resulting in a total of 24 plots (8 treatments × 3 replicates). There were nine rows in each plot with row lengths of 40 m, and two-row separations from each other. Maize (Zea Mays L.), genotype Hongshuo 616 was planted at a density of 45,000 plants ha−1 in early May and harvested at the end of September in 2016 and 2017. All the tillage practices were conducted after maize harvest in autumn. Mineral fertilizers were applied twice on 12 May (N: 117 kg/ha, P: 23.58 kg/ha, K: 26.14 kg/ha) and on 29 June (N: 139.2 kg/ha), in 2016 and 2017, respectively.

et al., 2015; Yang et al., 2018). Previous studies have shown that conventional tillage generally decreased AM fungal abundance in comparison with no tillage system (Jansa et al., 2006 ; Brito et al., 2012 ; Säle et al., 2015), mainly due to the disruption in AM fungal hyphal network (Jansa et al., 2006). Also, it has been reported that the negative effect of tillage practices on AM fungi could be mediated by changes in the nutrient availability, weed communities, as well as other soil microorganisms associated with tillage practices (Jansa et al., 2002). Nevertheless, both the positive and neutral effects of tillage practices on AM fungi were sometimes reported (Curaqueo et al., 2011; Duan et al., 2011; Hu et al., 2015). For instance, AM fungal spore density or extraradical hyphal (ERH) density were unaffected by conventional tillage practices in a Mediterranean agroecosystem (Curaqueo et al., 2011). On the other hand, AM species vary tremendously in functional traits (Mensah et al., 2015; Veresoglou et al., 2011), therefore insight to the diversity and community composition of AM fungi is critical for the understanding of its ecological function in agroecosystems (Njeru et al., 2015). Previous studies showed that intensive tillage imposed strong filters on AM fungi and thus induced a marked shift in AM fungal community composition (Alguacil et al., 2014; Säle et al., 2015). AM fungal richness was observed to be reduced by conventional tillage in several long term field studies (Brito et al., 2012; Säle et al., 2015), whereas it was unaffected by conventional tillage in 4-year maize-wheat rotation systems in Northern China (Hu et al., 2015). These contradicting results indicated that the effect of different tillage practices on AM fungi still need better understanding through further investigations. In addition to tillage practices, residue retention is another important agricultural practice (Qiu et al., 2016). The black soil region is generating large amounts of straw residues, most of them are burned and thereby cause a serious threat to the environment (Yang et al., 2018). Residue retention is an effective strategy for straw waste recycling and beneficial practice for improving soil health. It is widely recognized that long term residue retention can ameliorate soil wateruse efficiency, enhance soil fertility and crop productivity (Guo et al., 2015). Although AM fungi have no saprophytic capacity, some studies have shown that AM fungi can directly take advantage of organic matter (Govindarajulu et al., 2005; Hodge et al., 2001). For instance, some field studies showed that organic fertilization (e.g. animal manure) tend to improve AM fungal growth and sporulation in agricultural systems (Yang et al., 2018). However, there is a dearth of information on how residue retention will influence the AM fungi in agroecosystems (Alguacil et al., 2014). Especially, as the conservation tillage and residue retention were two main advocated agricultural practices in black soil region (Shen et al., 2018), it will be crucial to emphasize the interactive effect of tillage practices and residue management on the AM fungi. To better understand the effect of tillage practice, residue management and their interaction on soil fertility, AM fungal biomass, diversity and community composition, a field study was conducted in a maize agroecosystem on the Songnen Plain, Northeast China in 2015. We hypothesized that: (1) AM root colonization, ERH density, spore density and diversity will be enhanced by no tillage practices and residue retention; (2) different tillage practices and residue management will induce a shift in AM fungal community composition; (3) the effects of tillage practices and residue management on AM fungal community will be mediated through soil and plant variables.

2.2. Soil and root sampling Both soil and root samples were collected on 26th June 2017. Briefly, five soil cores (20 cm deep, 5 cm diameter) and maize roots from each plot were randomly sampled and mixed as one composite sample. In total, 24 soil and root samples were collected, then packed in an ice box and transported to the laboratory. Fresh soil samples were divided into two parts. Subsamples for DNA extraction and AM hyphal measurement were sieved (1 mm) and stored at −80 °C until analysis. Subsamples for physiochemical properties, GRSP and AM fungal spore measurements were air-dried and sieved (0.25 mm and 1 mm), then stored at room temperature until analysis. Fine maize roots (< 1 mm diameter) were washed with sterilized deionized water and dried up with filter paper. Fresh soil and root samples were then stored at −80 °C for further analyses. 2.3. Soil and plant variables Soil pH was determined with the combination glass electrode, based on a water - soil ratio of 2.5:1. Soil moisture was by drying at 105 °C for 48 h. SOM content was analyzed with the potassium dichromate oxidation-ferrous sulfate titrimetry (Walkley and Black, 1934). TN was determined as ammonium-N by steam distillation after digestion with H2SO4 (Bremner and Mulvaney, 1982). TP was measured by digesting soil using the H2SO4−HClO4 method and then measured using the Mo–Sb colorimetry method (Murphy and Riley, 1962); AP was extracted using 0.5 mol/L NaHCO3 solution and determined as described above. AK was extracted with NH4OAc and determined by flame atomic absorption spectrometry (Schollenberger and Simon, 1945). Soil compaction (SC) was measured with a hand-held cone penetrometer (Field Scout SC 900, SpectrumTechnologies, IL, USA) to record the resistance over a 0–45 cm depth. Root length, root biomass, shoot biomass, shoot height and root/shoot ratio were measured according to Guo et al. (2018, Table A1).

2. Materials and methods 2.1. Field experiment design The study was carried out under field conditions at Shuangcheng, the central part of Songnen Plain, Northeast China (45°45′ N, 126°55′ E). This region has a typical monsoon climate, with annual average temperature of about 4.4 °C, and an annual mean precipitation of

2.4. AM root colonization, ERH density and spore density Fifty fine root fragments (ca. 1 cm long) of each sample were stained with trypan blue and the percentage of AM root colonization was 2

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

OTUs were calculated using the ‘rarefy’ function in the package Vegan (Oksanen et al., 2016) in R (R core team, 2013).

determined by the magnified line-intersect method (McGonigle et al., 1990) at 200-fold magnification. Total AM root colonization was determined as the percentage of root length colonized by AM fungi. AM extraradical hyphae were extracted from 2 g soil samples using a modified membrane filter technique (Rillig et al., 1999). Hyphal length was recorded in 25 random fields of view per filter. The length of stained hyphae on the filters was determined by the grid line intercept method at 200-fold magnification. AM fungal spores were extracted from 10.0 g air-dried soil of each sample with deionized water using wet-sieving and decanting method and counted under 50-fold magnification (Daniels and Skipper, 1982). Then the AM fungal ERH density and spore density were expressed on a dry weight basis.

2.8. Data analysis Two-way ANOVAs were used to examine the effects of tillage practices, residue management and their interaction on AM root colonization, spore density, ERH density, OTU richness, Pielou evenness and Shannon diversity indices. All data were tested for normality and homogeneity of variance before two-way ANOVA. Differences among treatments were tested by a Tukey’s HSD post-hoc test at P < 0.05. The relative abundance of prevalent AM fungal families did not meet the homogeneity of variance and was subjected to Kruskal - Wallis test. SEM is an advanced and robust multivariate statistical method that allows for hypotheses causal relationships among variables in a path diagram, and considers both direct and indirect effects of variables on one another (Malaeb et al., 2000). We used SEM to detect the direct and indirect effect of tillage practices on AM fungal ERH density and spore density using AMOS 22.0 (Arbuckle, 2011). We assumed a priori model based on our knowledge of soil ecological causal relationships. Model adequacy was determined by χ2 tests (P > 0.05), goodness-of-fit index (GFI > 0.9), Akaike Information Criteria (AIC), and root square mean errors of approximation (RSMEA < 0.05, Hooper et al., 2008). The AM fungal community composition was ordinated using nonmetric multidimensional scaling (NMDS) with the dissimilarity matrices using the ‘metaMDS’ function in the Vegan package (Oksanen et al., 2016). Using the ‘envfit’ function of the Vegan package with 999 permutations, the soil and plant variables were fitted as vectors to the ordination graphic. Moreover, the ‘varpart’ function in the Vegan package was used to partition the variation of AM fungal community dissimilarity by tillage practice, residue management, soil variables, and plant variables. In order to determine AM fungal indicator species for different treatments, we conducted indicator species analysis (species with Indval values > 0.3 and P < 0.05 are strong indicators) using the function ‘indval’ in the labdsv package (Roberts, 2010). The analyses above were carried out in R (v.3.1.1) (R Core Team, 2013).

2.5. GRSP content GRSP content was measured as easily extracted GRSP (EE-GRSP) according to Wright and Upadhyaya (1998). The EE-GRSP was extracted from 1 g soil with 8 mL sodium citrate (20 mM, pH 7.0) at 121 °C in an autoclave for 30 min. Extracts from each sample were then centrifuged at 10000 × g for 6 min to remove soil particles. EE-GRSP in the supernatant was analyzed using the Bradford assay with bovine serum albumin as the standard. 2.6. Miseq sequencing Genomic DNA was extracted from 0.25 g fresh soils with a PowerSoil DNA Isolation Kit (MoBio Laboratories, Inc., Carlsbad, CA, USA) following the manufacturers’ instruction. An approximately 334 bp region of the 18S rDNA gene was amplified with two-step PCR. Briefly, the extracted DNA was diluted 10 times and amplified with GeoA-2 (Schwarzott and Schüßler, 2001) / AML2 (Lee et al., 2008) in the first amplification. The PCR product was then diluted 10 times and amplified with NS31 (Simon et al., 1992) / AMDGR (Lumini et al., 2010) in the second amplification. The primer NS31 was modified with a unique 12 nt barcode at the 5′end. The final PCR products from all samples were mixed and then subjected to Illumina Miseq platform at Environmental Genome Platform of Chengdu Institute of Biology, Chinese Academy of Sciences. The raw sequence data had been accessioned in the Sequence Read Archive of National Center for Biotechnology Information, USA (accession No：SRP151204). More details about the PCR conditions and quality assessment were provided in the Supplementary Information.

3. Results 3.1. Soil chemical and physical variables The soil chemical and physical variables were presented in Table 1. Two-way ANOVA analysis indicated that pH and SC were significantly affected by tillage practices and interaction between tillage practices and residue management; TN content was significantly affected by an interactive effect; whereas, SOM, TP, AP, AK content and SM were unaffected by any factor (Table A2). The highest pH value was observed in treatment NT, which was significantly higher (9.6 %, P = 0.005) than that in treatment RT under residue removal (Table 1). Compared with the residue removal treatment, residue retention caused a 10 % increase in pH value in treatment RT (P = 0.005), but not in NT, ST and DT treatment (Table 1). Under residue retention, treatment DT significantly decreased SC by 43.6 % and 34.6 % compared with treatment NT (P = 0.008) and RT (P = 0.004), respectively, but not under residue removal (Table 1).

2.7. Bioinformatics analysis Raw sequences with low quality (length < 250 bp, with ambiguous base ‘N’, and average base quality score < 20) were removed using QIIME Pipeline Version 1.8.0 (Caporaso et al., 2010) before further analysis. Potential chimeras were discarded using the 'chimera.uchime' command in Mothur (Schloss et al., 2009), using both no external database and the MaarjAM 18S rRNA gene reference database (Öpik et al., 2010). The remaining nonchimeric sequences were clustered into different operational taxonomic units (OTUs) with 97 % similarity level using USEARCH v8.0 (Edgar, 2013) after dereplication and discarding all singletons. The representative sequences of each OTU were blasted against the NCBI nt database (Altschul et al., 1990) to remove non-AM fungal OTUs. Then the AM fungal OTUs were confirmed by a 'blastn' search in the MaarjAM 18S rRNA gene database using an E value less than 1e−50 as a significant matching criterion (Öpik et al., 2010). To account for the variation in read numbers among samples, the number of sequences per sample was normalized to the smallest sample size using the ‘normalized.shared’ command in Mothur (Schloss et al., 2009). We then constructed a neighbor joining tree including certain taxa of Glomeromycota from GenBank in MEGA v5 (Tamura et al., 2011) to identify AM fungal OTUs. The tree was then visualized with iTOL (Letunic and Bork, 2016). Accumulative numbers of AM fungal

3.2. AM root colonization, ERH density, spore density and GRSP content Two-way ANOVA analysis revealed that AM root colonization, ERH density and spore density were significantly influenced by tillage practices, but unaffected by residue management (Table A2). In addition, AM root colonization was significantly influenced by the interactive effect between tillage practices and residue management, but ERH and spore density were unaffected (Table A2). Compared with treatment NT, ST and DT significantly enhanced AM root colonization by 62.0 % (P = 0.04) and 72.2 % (P = 0.001), respectively (Fig. 1A). 3

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

Table 1 Soil organic matter (SOM), total N (TN), total P (TP), available P (AP), available K (AK), pH, soil moisture (SM) and soil compaction among treatments.

NT-R NT + R RT-R RT + R ST-R ST + R DT-R DT + R

SOM (g/kg)

TN (g/kg)

34.1 37.6 33.7 42.1 35.0 33.8 35.0 43.4

1.20 1.07 1.10 1.18 1.12 1.21 1.17 1.07

± ± ± ± ± ± ± ±

5.9 a 9.1 a 2.9 a 4.3 a 5.9 a 2.5 a 1.9 a 14.3 a

± ± ± ± ± ± ± ±

0.01 0.08 0.10 0.05 0.07 0.06 0.03 0.04

TP (g/kg) a a a a a a a a

0.53 0.56 0.60 0.55 0.57 0.39 0.57 0.56

± ± ± ± ± ± ± ±

0.03 0.05 0.07 0.06 0.06 0.14 0.00 0.06

a a a a a a a a

AK (mg/kg)

AP (mg/kg)

pH

SM (%)

SC (pa)

180.7 179.6 202.3 193.5 173.0 205.6 178.9 179.2

43.4 ± 6.1 a 56.5 ± 11.3 a 60.2 ± 2.2 a 56.4 ± 29 a 54 ± 23.6 a 56.7 ± 6.7 a 52.2 ± 6.2 a 45 ± 18.3 a

5.7 ± 0.2 a 5.4 ± 0.1 ab 5.2 ± 0.2 b 5.7 ± 0.2 a 5.4 ± 0.1 ab 5.4 ± 0.2 ab 5.57 ± 0 ab 5.68 ± 0.1 a

18.2 ± 0.2 a 17.2 ± 0.9 a 16.6 ± 0.3 a 17.83 ± 0.4 a 18.01 ± 0.6 a 18.0 ± 1.1 a 17.2 ± 0.5 a 17.5 ± 0.9 a

862.0 ± 276.0 ab 1080.7 ± 87.1 a 931.3 ± 34.5 a 1126.7 ± 155.3 a 1000.3 ± 34.5 a 793.0 ± 69.0 ab 850.7 ± 52.9 ab 609 ± 143.6 b

± ± ± ± ± ± ± ±

22.1 a 0.6 a 11.9 a 23.1 a 30.8 a 18.0 a 10.0 a 27.4 a

Abbreviations: NT, no tillage; RT, rotary tillage; ST, subsoil tillage; DT, deep tillage; -R, residue removal; +R, residue retention. Values are means (n = 3) ± SD. Shared letters denote no significant difference among treatments, as indicated by Tukey-HSD test at P < 0.05.

3.3. Miseq sequencing and identification of AM fungi

Besides, treatment DT exhibited a significantly higher AM fungal ERH density than NT (60.5 %, P = 0.03) and RT (39.5 %, P = 0.03), respectively (Fig. 1B). Moreover, AM fungal spore density was significantly decreased by treatment ST (38.1 %, P = 0.04) and DT (66.8 %, P < 0.001) compared with NT (Fig. 1C). But, treatment RT did not cause a significant shift in AM root colonization, ERH density and spore density in comparison with NT (Fig. 1A, B, C, all P > 0.05). However, soil GRSP content was unaffected by tillage practices, residue management and their interaction (Table A2, Fig. 1D) We next used SEM to assess the direct and indirect effects of tillage practices on AM fungal ERH and spore density (Fig. 2). The final SEM met our significance criteria (χ2 = 3.78, df = 4, P = 0.44, RMSEA < 0.001, GFI = 0.95, AIC = 37.78) and was able to explain 46 % of AM fungal ERH density, and 60 % of spore density. AM fungal spore density was directly affected by tillage practices, whereas, the effect of tillage practices on ERH density was mainly mediated through root length (Fig. 2).

A total of 2,415,284 reads were obtained after a quality control procedure, from which 115,689 potential chimeras were removed. The remaining 2,299,595 non-chimeric reads were assigned to 279 operational taxonomic units (OTUs) based on a 97 % sequence similarity. Of these 279 OTUs, 66 (2,048,541 reads) belonged to AM fungi. The number of AM fungal reads ranged from 27,861 to 231,351 among the samples, the read numbers were then normalized to 27,861, resulting in a normalized dataset containing 66 AM fungal OTUs (668,664 reads). Of these 66 AM fungal OTUs, 50 frequent OTUs occurred in ≥ 12 (50 %) soil samples (Fig. A1). The first 18 abundant OTUs (relative abundance > 1 %) accounted for 93.0 % of the total AM fungal reads, and the remaining 48 OTUs accounted for 18.2 % (Fig. A1). Among these 66 AM fungal OTUs, 28 belonged to Glomeraceae, 18 to Claroideoglomeraceae, four to Paraglomeraceae, three to Ambisporaceae, two to Archaeosporaceae, two to Diversisporaceae, one to Acaulosporaceae, Pacisporaceae, Gigasporaceae and Sacculosporaceae, five to unidentified OTUs (Fig. A2). Rarefaction analysis showed that all rarefaction curves for observed AM fungal Fig. 1. Arbuscular mycorrhizal fungal root colonization (A), ERH density (B), spore density (C) and glomalin related soil protein (GRSP, D) content among treatments. Shared letters denote no significant difference among different tillage practices according to TukeyHSD test at P < 0.05. Gray color represents for residue removal; black color represents for residue retention. Abbreviations: NT, no tillage; RT, rotary tillage; ST, subsoil tillage; DT, deep tillage; T, tillage practice; R, residue management.

4

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

Fig. 2. (A) Structural equation modelling (SEM) showing the direct and indirect effects of tillage practices on the arbuscular mycorrhizal (AM) spore density and extraradical hyphal (ERH) density. Values above the line represent the path coefficients. Values above the text box represent the residuals. Solid and dashed lines indicate significant and non-significant pathways, respectively (***P < 0.001; ** P < 0.01; * P < 0.05). (B) Impact of tillage practices on AM spore density and ERH density assessed by SEM including direct, indirect and total effect coefficients based on hypothesized causal relationships.

Fig. 3. The relative abundance of prevalent arbuscular mycorrhizal fungal families among treatments. Abbreviations: NT, no tillage; RT, rotary tillage; ST, subsoil tillage; DT, deep tillage. (color should be used).

OTUs reached the saturation platform, indicating that sequencing effort was sufficient to identify the most AM fungi in this study (Fig. A3). 3.4. AM fungal community At the family level, five families including Glomeraceae, Claroideoglomeraceae, Paraglomeraceae, Gigasporaceae and Ambisporaceae were predominant, and accounted for 99.6 % of the total AM fungal sequences (Fig. 3). We next investigated changes in relative abundance patterns of AM fungal families associated with tillage and residue practices. The most striking change observed was the reduction for Ambisporaceae in ST and DT treatment in comparison with treatment NT and RT (Fig. 3, Table A2). However, the relative abundance of Glomeraceae, Claroideoglomeraceae, Gigasporaceae and Paraglomeraceae did not exhibit significant variations among treatments (Fig. 3, Table A3). For the combined “top 20” abundant OTUs, most were classified as Glomeraceae, followed by Claroideoglomeraceae, and then Paraglomeraceae (Fig. 4). Among these OTUs, indicator species analysis showed that OTU39 (Rhizophagus sp.) was indicator in the RT treatment, while OTU3 (Septoglomus sp.) was indicator in the + R treatment (Fig. 4, Table A4). However, other abundant OTUs did not exhibit obvious variations among treatments (Fig. 4). Tillage significantly affected AM fungal OTU richness, marginally affected AM fungal Shannon diversity index and Pielou evenness index (Table A2). Treatment DT exhibited the lowest AM fungal OTU richness, and was significantly lower than that in treatment NT (Fig. 5A, P = 0.03). In addition, treatment NT caused a significant reduction in Pielou evenness index in comparison with treatment RT (Fig. 5C, P = 0.04). However, AM fungal OTU richness, Shannon diversity index and Pielou evenness index were unaffected by residue management and the interactive effect (Table A2). NMDS analysis showed that AM fungal community composition was significantly affected by tillage practices ( r2 = 0.40, P = 0.005), but

Fig. 4. The combined ‘top 20′ arbuscular mycorrhizal (AM) fungal OTUs visualized in a bootstrapped neighbor-joining tree. The tree is surrounded by an additional heatmap representing the relative abundance of each AM fungal OTU. The OTUs in red indicate indicator OTUs. Color gradients indicate the relative abundance of OTUs, with blue colors indicating high abundant taxa and white colors indicating low abundant taxa in soil. Green, Claroideoglomeraceae; yellow, Ambisporaceae; purple, Paraglomeraceae; red, Gigasporaceae; blue, Diversisporaceae; orange, Glomeraceae. Abbreviations: NT, no tillage; RT, rotary tillage; ST, subsoil tillage; DT, deep tillage; -R, residue removal; +R, residue retention. (color should be used).

unaffected by residue management ( r2 = 0.03, P = 0.77). The AM fungal community composition in treatment NT was distinguished from treatment DT and ST, whereas overlapped with treatment RT (Fig. 6). 5

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

Fig. 5. Arbuscular mycorrhizal fungal OTU richness (A), Shannon diversity index (B) and Pielou evenness index (C) among treatments. Abbreviations: NT, no tillage; RT, rotary tillage; ST, subsoil tillage; DT, deep tillage. Shared letters denote no significant difference among treatments, as indicated by Tukey-HSD test at P < 0.05.

Fig. 6. Non-metric multidimensional scaling (NMDS) of arbuscular mycorrhizal fungal community composition. Circles with dashed line are 95 % confidence ellipses of no tillage, conventional tillage, subsoil tillage and deep tillage treatment. Square, no tillage; triangle, rotary tillage; diamond, subsoil tillage; circle, deep tillage. Abbreviations: TP, total phosphorus; AP, available phosphorus; SC, soil compaction; RS, root/shoot ratio; RL, root length. † P < 0.10; * P < 0.05; ** P < 0.01.

Fig. 7. Variation partitioning analysis showing the effects of tillage practices, residue management, soil and plant variables on arbuscular mycorrhizal fungal community. Numbers inside circles indicate the proportion of explained variation.

Furthermore, the AM fungal community composition was significantly related to soil compaction ( r2 = 0.38, P = 0.008), TP ( r2 = 0.27, P = 0.04) and root/shoot ratio ( r2 = 0.36, P = 0.003). Variation partitioning showed that total 25 % of variation in AM fungal community composition was explained (Fig. 7). Of these variations, 23 % were explained by tillage practices, 15 % by residue management, 35 % by soil variables, and 21 % by plant variables (Fig. 7).

all treatments. On the other hand, it was reported that deep tillage could break root-restricting soil layers, improve soil porosity and water availability, thus enhance root growth (Schneider et al., 2017). Therefore, AM fungi will proliferate when more carbon was allocated to plant roots, leading to an increase in AM fungal hyphal growth in the DT system, which was confirmed by SEM analysis. Second, it was proposed that the soil microbe might be resilient and have the potential to recover from disturbance quickly (Allison and Martiny, 2008), highlighting the importance of sampling time. In the present study, we sampled in mid-August, three and half months after planting, which enabled the reconstruction of the AM hyphal network. Had the samples been taken earlier, a negative or neutral effect of tillage practices on AM fungal growth might have been observed. Our assumption was confirmed by Kabir et al. (1997), who showed an initially low abundance of soil external hyphae after tillage but a rapid increase in AM fungal hypha at the end of the growing season. Furthermore, the test crop (maize) in the present study, is a good host for AM growth and development (Jansa et al., 2002). Owing to the above mentioned reasons, the AM fungal growth recovered from the soil disturbance quickly. In support of our first hypothesis, our results clearly indicated that subsoil and deep tillage significantly decreased AM fungal spore density compared with no tillage. Similarly, a field study conducted in a Mollisol observed a reduction in AM fungal spore density in conventional tillage systems in Central Chile (Curaqueo et al., 2011). This

4. Discussion Previously published literature has established that no-tilled soil had more AM fungal external mycelium and higher AM root colonization than tilled soil (Jasper et al., 1989; Jansa et al., 2006; Balota et al., 2016; Wang et al., 2016), due to maintaining AM fungal hyphal network in no tillage systems. However, our results revealed that tillage practices enhanced AM root colonization and external hyphal growth. Especially, treatment DT exhibited the largest increase in ERH density compared with the NT treatment. Two mechanisms could be responsible for these results. First, time of ploughing: we ploughed the field in the autumn (after maize harvest), which was followed by an extremely cold and long winter in Northeast China. Although the AM fungal mycelium in tilled soil was destroyed, most of the AM mycelium in the no tillage system may not survive due to the low temperature (Addy et al., 1994). Therefore, we theoretized that the initial amount of active AM fungal external hyphae may be similar after soil thawing in 6

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

consequentially, the host plant provides the photosynthetic product for AM fungi (Smith and Read, 2008). It is confirmed that the host plant allocates more carbon to AM fungi when soil is deficient in P, at the same time reducing allocation to AM fungi when soil is rich in P. Consequently, the soil P level would influence AM community by mediating its growth. Furthermore, root/shoot ratio and root length were also observed to be related to AM fungal community composition in the present study. Indeed, ST and DT practices loosened the soil structure and benefit the root growth, thus induced more carbon allocation to maize roots. In the AM association, AM fungal growth mainly depended on the carbon provided by host plant, and the plant performance could thus affect AM fungal community (Smith and Read, 2008; Liu et al., 2012). Our hypothesis that residue management would influence AM fungal biomass was upheld. In addition, residue retention did not alter AM fungal community composition in the present study. This confirms Borie et al. (2002) and Duan et al. (2011), who reported no significant effect of residue application on AM colonization or ERH density in a pot experiment. Likewise, Alguacil et al. (2014), comparing different agricultural practices in a Mediterranean soil also reported that oats straw addition together with ploughing did not significantly affect AM fungal community as compared with ploughing alone. In contrast with our findings, Sheldrake et al. (2017) reported that litter removal significantly affected the AM fungal community composition after nine years. It was suggested that organic matter including litter and residue affect AM growth and community mainly by changing soil nutrient availability or by altering soil microbial community composition (Herman et al., 2012). In this study, however, soil nutrient contents (e. g. N, P, K) were scarcely affected by residue management, possibly due to the short duration or the deficiency of water and heat in the black soil region. As reported previously, the positive effect of residue retention on soil variables was usually not apparent in the short-term study (Peng et al., 2016). Therefore, there remains the need to investigate the long-term effect of residue retention on AM. In conclusion, we investigated the effect of tillage practice, residue management on AM root colonization, ERH density, spore density, OTU richness and community composition in black soil of Northeast China. Compared with no tillage, two years with deep tillage significantly enhanced AM fungal growth in both soil and maize roots, while it decreased AM fungal spore density and OTU richness in soil. Moreover, both subsoil tillage and deep tillage altered AM fungal community composition in comparison with no tillage. Our findings indicated that tillage practice is a stronger determinant than residue management in AM fungal development and community composition.

observation is also in accordance with the results observed by Jansa et al. (2002) and Säle et al. (2015) in the wheat agroecosystem. Deep tillage turns soil horizons and results in complete or semi-complete inversion of the soil layers, with subsoil ending up at the soil surface and topsoil buried in the deep soil (Schneider et al., 2017). Meanwhile, a large number of researches have reported a decreasing trend of AM fungal spore density along with the increase in soil depth (Kabir, 2005; Säle et al., 2015). Consequently, the deep tillage was thought to reduce AM fungal spore density simply by mixing topsoil and subsoil layers. In addition, although subsoil tillage did not invert soil layers, it could dilute AM fungal spores in the root zone (Säle et al., 2015). AM fungal species vary tremendously in functional traits, including colonization strategy, carbon fixation from plants and nutrient utilization (Mensah et al., 2015; Veresoglou et al., 2011). Therefore, a more diverse AM fungal community would indicate a greater ecosystem function. In this study, richness of AM fungal OTUs in no-tilled soil was greater than in tilled soil, indicating a positive effect of no tillage on agroecosystem functions. Our result was in accordance with Brito et al. (2012) and Säle et al. (2015) who reported a decreased AM fungal richness under conventional tillage as compared to the reduced or notillage system. Likewise, a meta-analysis based on 239 articles reported a 11 % increase in AM fungal OTU richness (Bowles et al., 2017) in notillage systems. In addition to the shift in vertical distribution of AM fungal population, the niche separation would be another reason (Bowles et al., 2017). It was proposed that lower intensity tillage such as no tillage creates more niche space in the root zone for AM fungi (Balota et al., 2016), while higher intensity tillage induced narrowing of niche width and loss of AM fungal species sensitive to disturbance. It was noted that both subsoil tillage and deep tillage altered AM fungal community composition in comparison with no tillage in a relative short-term (2 year) field study, indicating that intensive tillage is important in shaping AM fungal community composition. Previous studies comparing tillage and no tillage systems in other regions also reported a shift of AM fungal community composition in response to tillage practices de Pontes et al. (2017d); Säle et al., 2015). It was reported that different AM fungal species exhibited different tolerance to soil disturbance (Jansa et al., 2002). For instance, members in Scutellospora were observed to be very sensitive to tillage practices and prevalent in no-till system, while species in the genus formerly known as Glomus were reported to be dominant in tilled fields (Jansa et al., 2002). In the present study, Rhizophagus sp. (former Glomus, Krüger et al., 2012) was quite abundant in the rotary tillage system but not in other treatments, indicating low tolerance to soil disturbance. Ambisporaceae, generally rare components of the AM fungal groups in agricultural system (Alguacil et al., 2014), were found to be dominant in NT or RT treatment, but scarcely found in high intensity tillage system (e.g. ST and DT) in this study. Similarly, Ambispora species are regularly absent in intensified fertilization and cultivation practices (Oehl et al., 2015). By fitting soil variables with AM fungal community composition, we observed that soil compaction was significantly related with AM fungal community composition. Soil compaction has been reported to limit hyphal development of certain AM fungal isolates (Entry et al., 2002), reducing the competition and encouraging the occurrence of other better performing isolates. The effect of soil compaction on AM fungal community was possibly mediated by soil water and O2 availability (Epelde et al., 2017). In accordance with previous studies, we observed that soil compaction was highest in NT treatment, which will limit soil O2 and water supply for AM fungi. While DT and ST practices ameliorate the soil compaction and provide better condition for the AM fungal growth, leading to distinct AM fungal community composition. Other soil factors such as soil total P and available P, which are recognized as one of the most important drivers for shaping AM fungal community in terrestrial ecosystems (Xiang et al., 2014), was observed to be significantly (P < 0.05) or marginally (0.05 < P < 0.01) related with AM fungal community as revealed by NMDS analysis. AM fungi assist their host mainly by increasing uptake of P (Marx, 2004),

Declaration of Competing Interest The authors declared that they have no conflicts of interest to this work. We declared that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted Acknowledgments This work was supported by National Key Research and Development Program of China (2017YFD0300502-2); Young Innovative Talents of Heilongjiang Province (Grant number: UNPYSCT2018172); postdoctoral scientific research developmental fund of Heilongjiang Province (Grant number: LBH-Q18016), and Open Foundation of the Key Laboratory of Soil Quality, Chinese Academy of Agriculture Science (201701). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.still.2019.104552. 7

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

References

Jansa, J., Mozafar, A., Anken, T., Ruh, R., Sanders, I., Frossard, E., 2002. Diversity and structure of AMF communities as affected by tillage in a temperate soil. Mycorrhiza 12, 225–234. Jansa, J., Wiemken, A., Frossard, E., 2006. The effects of agricultural practices on arbuscular mycorrhizal fungi. Geol. Soc. Lond. Spec. Publ. 266, 89–115. Jasper, D., Abbott, L., Robson, A., 1989. Soil disturbance reduces the infectivity of external hyphae of VA mycorrhizal fungi. New Phytol. 112, 93–99. Kabir, Z., 2005. Tillage or no-tillage: impact on mycorrhizae. Can. J. Plant Sci. 85, 23–29. Kabir, Z., O’Halloran, I.P., Fyles, J.W., Hamel, C., 1997. Seasonal changes of arbuscular mycorrhizal fungi as affected by tillage practices and fertilization: hyphal density and mycorrhizal root colonization. Plant Soil 192, 285–293. Krüger, M., Krüger, C., Walker, C., Stockinger, H., Schüßler, A., 2012. Phylogenetic reference data for systematics and phylotaxonomy of arbuscular mycorrhizal fungi from phylum to species level. New Phytol. 193, 970–984. Lee, J., Lee, S., Young, J.P.W., 2008. Improved PCR primers for the detection and identification of arbuscular mycorrhizal fungi. Fems Microbiol. Ecol. 65, 339–349. Letunic, I., Bork, P., 2016. Interactive tree of life (iTOL) v3: an online tool for the display and annotation of phylogenetic and other trees. Nucleic Acids Res. 44, W242–W245. Liu, X.B., Zhang, X.Y., Wang, Y.X., Sui, Y.Y., Zhang, S.L., Herbert, S.J., Ding, G., 2010. Soil degradation: a problem threatening the sustainable development of agriculture in Northeast China. Plant Soil Environ. 56, 87–97. Liu, Y.J., Shi, G.X., Mao, L., Cheng, G., Jiang, S.J., Ma, X.J., An, L.Z., Du, G.Z., Johnson, N.C., Feng, H.Y., 2012. Direct and indirect influences of 8 yr of nitrogen and phosphorus fertilization on Glomeromycota in an alpine meadow ecosystem. New Phytol. 194, 523–535. Lumini, E., Orgiazzi, A., Borriello, R., Bonfante, P., Bianciotto, V., 2010. Disclosing arbuscular mycorrhizal fungal biodiversity in soil through a land-use gradient using a pyrosequencing approach. Environ. Microbiol. 12, 2165–2179. Malaeb, Z.A., Summers, J.K., Pugesek, B.H., 2000. Using structural equation modeling to investigate relationships among ecological variables. Environ. Ecol. Stat. 7, 93–111. Marx, J., 2004. The roots of plant-microbe collaborations. Science 304, 234–236. McGonigle, T.P., Miller, M.H., Evans, D.G., Fairchild, D.L., Swan, J.A., 1990. A new method which gives an objective-measure of colonization of roots by vesicular arbuscular mycorrhizal fungi. New Phytol. 115, 495–501. Mensah, J.A., Koch, A.M., Antunes, P.M., Kiers, E.T., Hart, M., Bucking, H., 2015. High functional diversity within species of arbuscular mycorrhizal fungi is associated with differences in phosphate and nitrogen uptake and fungal phosphate metabolism. Mycorrhiza 25, 533–546. Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27, 31–36. Njeru, E.M., Avio, L., Bocci, G., Sbrana, C., Turrini, A., Barberi, P., Giovannetti, M., Oehl, F., 2015. Contrasting effects of cover crops on’ hot spot’ arbuscular mycorrhizal fungal communities in organic tomato. Biol. Fert. Soils 51, 151–166. Oehl, F., Sanchez-Castro, I., Palenzuela, J., da Silva, G.A., 2015. Palaeospora spainii, a new arbuscular mycorrhizal fungus from Swiss agricultural soils. Nova Hedwigia 101, 89–102. Oksanen, J., Blanchet, F.G., Kindt, R., Legendre, P., Minchin, P.R., O’Hara, R.B., Simpson, G.L., Solymos, P., Stevens, M.H.H., Wagner, H., 2016. Vegan: Community Ecology Package. https://CRAN.R-project.org/package=vegan. Öpik, M., Vanatoa, A., Vanatoa, E., Moora, M., Davison, J., Kalwij, J.M., Reier, U., Zobel, M., 2010. The online database MaarjAM reveals global and ecosystemic distribution patterns in arbuscular mycorrhizal fungi (Glomeromycota). New Phytol. 188, 223–241. Peigne, J., Ball, B.C., Roger-Estrade, J., David, C., 2007. Is conservation tillage suitable for organic farming? A review. Soil Use Manage. 23, 129–144. Peng, C., Lai, S., Luo, X., Lu, J., Huang, Q., Chen, W., 2016. Effects of long term rice straw application on the microbial communities of rapeseed rhizosphere in a paddy upland rotation system. Sci. Total Environ. 557–558, 231–239. Qiu, S.J., Gao, H.J., Zhu, P., Hou, Y.P., Zhao, S.C., Rong, X.M., Zhang, Y.P., He, P., Christie, P., Zhou, W., 2016. Changes in soil carbon and nitrogen pools in a Mollisol after long-term fallow or application of chemical fertilizers, straw or manures. Soil Till. Res. 163, 255–265. R Core Team, 2013. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org/. Rillig, M.C., 2004. Arbuscular mycorrhizae, glomalin, and soil aggregation. Can. J. Soil Sci. 84, 355–363. Rillig, M.C., Field, C.B., Allen, M.F., 1999. Soil biota responses to long-term atmospheric CO2 enrichment in two California annual grasslands. Oecologia 119, 572–577. Roberts, D.W., 2010. LABDSV: Ordination and Multivariate Analysis for Ecology. http:// cran.r-project.org/web/packages/labdsv/labdsv.pdf. Säle, V., Aguilera, P., Laczko, E., Mäder, P., Berner, A., Zihlmann, U., van der Heijden, M.G.A., Oehl, F., 2015. Impact of conservation tillage and organic farming on the diversity of arbuscular mycorrhizal fungi. Soil Biol. Biochem. 84, 38–52. Schloss, P.D., Westcott, S.L., Ryabin, T., Hall, J.R., Hartmann, M., Hollister, E.B., Lesniewski, R.A., Oakley, B.B., Parks, D.H., Robinson, C.J., Sahl, J.W., Stres, B., Thallinger, G.G., Van Horn, D.J., Weber, C.F., 2009. Introducing mothur: opensource, platform-independent, community-supported software for describing and comparing microbial communities. Appl. Environ. Microb. 75, 7537–7541. Schneider, F., Don, A., Hennings, I., Schmittmann, O., Seidel, S.J., 2017. The effect of deep tillage on crop yield - what do we really know? Soil Till. Res. 174, 193–204. Schollenberger, C.J., Simon, R.H., 1945. Determination of exchange capacity and exchangeable bases in soil by ammonium acetate method. Soil Sci. 59, 13–24. Schwarzott, D., Schüßler, A., 2001. A simple and reliable method for SSU rRNA gene DNA extraction, amplification, and cloning from single AM fungal spores. Mycorrhiza 10, 203–207. Sheldrake, M., Rosenstock, N.P., Revillini, D., Olsson, P.A., Mangan, S., Sayer, E.J.,

Addy, H.D., Schaffer, G.F., Miller, M.H., Peterson, R.L., 1994. Survival of the external mycelium of a VAM fungus in frozen soil over winter. Mycorrhiza 5, 1–5. Alguacil, M.M., Torrecillas, E., Garcia-Orenes, F., Roldan, A., 2014. Changes in the composition and diversity of AMF communities mediated by management practices in a Mediterranean soil are related with increases in soil biological activity. Soil Biol. Biochem. 76, 34–44. Allison, S.D., Martiny, J.B.H., 2008. Resistance, resilience, and redundancy in microbial communities. P. Natl. Acad. Sci. USA 105, 11512–11519. Altschul, S.F., Gish, W., Miller, W., Myers, E.W., Lipman, D.J., 1990. Basic local alignment search tool. J. Mol. Biol. 215, 403–410. Arbuckle, J.L., 2011. IBM SPSS Amos 20 User’s Guide. IBM Corporation, New York. Arvidsson, J., 2010. Energy use efficiency in different tillage systems for winter wheat on a clay and silt loam in Sweden. Eur. J. Agron. 33, 250–256. Balota, E.L., Machineski, O., Honda, C., Yada, I.F.U., Barbosa, G.M.C., Nakatani, A.S., Coyne, M.S., 2016. Response of arbuscular mycorrhizal fungi in different soil tillage systems to long-term swine slurry application. Land Degrad. Dev. 27, 1141–1150. Borie, F., Redel, Y., Rubio, R., Rouanet, J., Barea, J., 2002. Interactions between crop residues application and mycorrhizal developments and some soil-root interface properties and mineral acquisition by plants in an acidic soil. Biol. Fert. Soils 36, 151–160. Bowles, T.M., Jackson, L.E., Loeher, M., Cavagnaro, T.R., 2017. Ecological intensification and arbuscular mycorrhizas: a meta-analysis of tillage and cover crop effects. J. Appl. Ecol. 54, 1785–1793. Bremner, J.M., Mulvaney, C.S., 1982. Methods of soil analysis, part 2, chemical and microbiological properties. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Nitrogen Total. American Society of Agronomy, Madison, pp. 595–624. Brito, I., Goss, M.J., de Carvalho, M., Chatagnier, O., van Tuinen, D., 2012. Impact of tillage system on arbuscular mycorrhiza fungal communities in the soil under Mediterranean conditions. Soil Till. Res. 121, 63–67. Caporaso, J.G., Kuczynski, J., Stombaugh, J., Bittinger, K., Bushman, F.D., Costello, E.K., Fierer, N., Pena, A.G., Goodrich, J.K., Gordon, J.I., Huttley, G.A., Kelley, S.T., Knights, D., Koenig, J.E., Ley, R.E., Lozupone, C.A., McDonald, D., Muegge, B.D., Pirrung, M., Reeder, J., Sevinsky, J.R., Tumbaugh, P.J., Walters, W.A., Widmann, J., Yatsunenko, T., Zaneveld, J., Knight, R., 2010. QIIME allows analysis of highthroughput community sequencing data. Nat. Methods 7, 335–336. Curaqueo, G., Barea, J.M., Acevedo, E., Rubio, R., Cornejo, P., Borie, F., 2011. Effects of different tillage system on arbuscular mycorrhizal fungal propagules and physical properties in a Mediterranean agroecosystem in central Chile. Soil Till. Res. 113, 11–18. Daniels, B.A., Skipper, H.D., 1982. Methods for the recovery and quantitative estimation of propagules from soil. In: Schenck, N.C. (Ed.), Methods and Principles of Mycorrhizal Research. American Phytopathological Society, St. Paul, Minn., USA, pp. 29–35. de Pontes, J.S., Oehl, F., Pereira, C.D., Machado, C.T.D., Coyne, D., da Silva, D.K.A., Maia, L.C., 2017d. Diversity of arbuscular mycorrhizal fungi in the Brazilian’s Cerrado and in soybean under conservation and conventional tillage. Appl. Soil Ecol. 117, 178–189. Duan, T.Y., Facelli, E., Smith, S.E., Smith, F.A., Nan, Z.B., 2011. Differential effects of soil disturbance and plant residue retention on function of arbuscular mycorrhizal (AM) symbiosis are not reflected in colonization of roots or hyphal development in soil. Soil Biol. Biochem. 43, 571–578. Edgar, R.C., 2013. UPARSE: highly accurate OTU sequences from microbial amplicon reads. Nat. Methods 10, 996. Entry, J., T Rygiewicz, P., S Watrud, L., K Donnelly, P., 2002. Influence of adverse soil conditions on the formation and function of Arbuscular mycorrhizas. Adv. Environ. Res. 7, 123–138. Epelde, L., Lanzen, A., Mijangos, I., Sarrionandia, E., Anza, M., Garbisu, C., 2017. Shortterm effects of non-grazing on plants, soil biota and aboveground-belowground links in Atlantic mountain grasslands. Sci. Rep. 7, 15097. Galvez, L., Douds, D.D., Drinkwater, L.E., Wagoner, P., 2001. Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize. Plant Soil 228, 299–308. Govindarajulu, M., Pfeffer, P.E., Jin, H.R., Abubaker, J., Douds, D.D., Allen, J.W., Bucking, H., Lammers, P.J., Shachar-Hill, Y., 2005. Nitrogen transfer in the arbuscular mycorrhizal symbiosis. Nature 435, 819–823. Guo, L.J., Zhang, Z.S., Wang, D.D., Li, C.F., Cao, C.G., 2015. Effects of short-term conservation management practices on soil organic carbon fractions and microbial community composition under a rice-wheat rotation system. Biol. Fert. Soils 51, 65–75. Herman, D.J., Firestone, M.K., Nuccio, E., Hodge, A., 2012. Interactions between an arbuscular mycorrhizal fungus and a soil microbial community mediating litter decomposition. Fems Microbiol. Ecol. 80, 236–247. Hijri, M., 2016. Analysis of a large dataset of mycorrhiza inoculation field trials on potato shows highly significant increases in yield. Mycorrhiza 26, 209–214. Hodge, A., Campbell, C.D., Fitter, A.H., 2001. An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material. Nature 413, 297–299. Hooper, D., Coughlan, J., Mullen, M.R., 2008. Structural equation modeling: guidelines for determining model fit. Elect. J. Bus. Res. Methods 6, 53–60. Hu, J., Yang, A., Wang, J., Zhu, A., Dai, J., Wong, M.H., Lin, X., 2015. Arbuscular mycorrhizal fungal species composition, propagule density, and soil alkaline phosphatase activity in response to continuous and alternate no-tillage in Northern China. Catena 133, 215–220.

8

Soil & Tillage Research 198 (2020) 104552

S. Gu, et al.

China. Soil Till. Res. 155, 54–61. Wright, S.F., Upadhyaya, A., 1998. A survey of soils for aggregate stability and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi. Plant Soil 198, 97–107. Xiang, D., Verbruggen, E., Hu, Y., Veresoglou, S.D., Rillig, M.C., Zhou, W., Xu, T., Li, H., Hao, Z., Chen, Y., Chen, B., 2014. Land use influences arbuscular mycorrhizal fungal communities in the farming-pastoral ecotone of Northern China. New Phytol. 204, 968–978. Xu, L.X., Yi, M., Yi, H.L., Guo, E.H., Zhang, A.Y., 2018. Manure and mineral fertilization change enzyme activity and bacterial community in millet rhizosphere soils. World J. Microb. Biot. 34, 8. Yang, W., Gu, S., Xin, Y., Bello, A., Sun, W., Xu, X., 2018. Compost addition enhanced hyphal growth and sporulation of arbuscular mycorrhizal fungi without affecting their community composition in the soil. Front. Microbiol. 9, 169. Yin, C., Fan, F.L., Song, A.L., Cui, P.Y., Li, T.Q., Liang, Y.C., 2015. Denitrification potential under different fertilization regimes is closely coupled with changes in the denitrifying community in a black soil. Appl. Microbiol. Biot. 99, 5719–5729. Zhang, S., Li, Q., Lü, Y., Sun, X., Jia, S., Zhang, X., Liang, W., 2015a. Conservation tillage positively influences the microflora and microfauna in the black soil of Northeast China. Soil Till. Res. 149, 46–52. Zhang, Z.Y., Zhang, X.K., Jhao, J.S., Zhang, X.P., Liang, W.J., 2015b. Tillage and rotation effects on community composition and metabolic footprints of soil nematodes in a black soil. Eur. J. Soil Biol. 66, 40–48.

Wallander, H., Turner, B.L., Tanner, E.V.J., 2017. Arbuscular mycorrhizal fungal community composition is altered by long-term litter removal but not litter addition in a lowland tropical forest. New Phytol. 214, 455–467. Shen, Y., McLaughlin, N., Zhang, X.P., Xu, M.G., Liang, A.Z., 2018. Effect of tillage and crop residue on soil temperature following planting for a Black soil in Northeast China. Sci. Rep. 8, 4500. Simon, L., Lalonde, M., Bruns, T.D., 1992. Specific amplification of 18S fungal ribosomal genes from vesicular-arbuscular endomycorrhizal fungi colonizing roots. Appl. Environ. Microb. 58, 291–295. Smith, S.E., Read, D.J., 2008. Mycorrhizal Symbiosis. Academic Press, London. Sun, B.J., Jia, S.X., Zhang, S.X., McLaughlin, N.B., Zhang, X.P., Liang, A.Z., Chen, X.W., Wei, S.C., Liu, S.Y., 2016. Tillage, seasonal and depths effects on soil microbial properties in black soil of Northeast China. Soil Till. Res. 155, 421–428. Tamura, K., Peterson, D., Peterson, N., Stecher, G., Nei, M., Kumar, S., 2011. MEGA5: molecular evolutionary genetics analysis using maximum likelihood, evolutionary distance, and maximum parsimony methods. Mol. Biol. Evol. 28, 2731–2739. Veresoglou, S.D., Shaw, L.J., Sen, R., 2011. Glomus intraradices and Gigaspora margarita arbuscular mycorrhizal associations differentially affect nitrogen and potassium nutrition of Plantago lanceolata in a low fertility dune soil. Plant Soil 340, 481–490. Walkley, A., Black, I.A., 1934. An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Sci. 37, 29–38. Wang, P., Wang, Y., Wu, Q.S., 2016. Effects of soil tillage and planting grass on arbuscular mycorrhizal fungal propagules and soil properties in citrus orchards in southeast

9