Reed decomposition under Bacillus subtilis addition conditions and the influence on water quality

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Reed decomposition under Bacillus subtilis addition conditions and the influence on water quality Jiexiu Zhai, Lamei Jiumu, Ling Cong, Yanan Wu, Liyi Dai, Zhenming Zhang∗, Mingxiang Zhang

Q1

College of Nature Conservation, Beijing Forestry University, Beijing 100083, China

a r t i c l e

i n f o

Article history: Received 26 June 2019 Revised 1 October 2019 Accepted 16 November 2019 Available online xxx Keywords: Litter Decomposition Process Bacteria Water Quality Litter Quality

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a b s t r a c t In order to explore the effects of bacterial on the decomposition processes and water environmental conditions, we used litter bag method and compare reed litter decomposition rates under different Bacillus subtilis addition treatments. Neither mesh size nor bacterial treatment have significant effects on the decomposition rates in the earlier phase. But in last three retrieves, the decomposition rates of litter bags with Bacillus subtilis addition were significantly (p = 0.012) higher than that without Bacillus subtilis addition treatment. As for bacterial influence water parameters, aquatic environmental markers ammonianitrogen (NH3 -N), total phosphorus (TP), dissolved oxygen (DO), and chemical oxygen demand (COD) didn’t show significant difference between different Bacillus subtilis addition treatments. The decomposition rates were affected by litter quality and water parameters. Furthermore, the N/P and C/P ratios of litter were good predictors for litter decomposition. Our findings suggested that the bacterial inoculation could be an excellent approach to facilitate the decomposition processes and nutrient cycles in the wetland ecosystems, but it might require more than 45 days to see the positive effects. © 2019 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.

1. Introduction Wetland can provide many ecosystem functions which supported by the web of interacting forces (Bai et al., 2015; Bai et al., 2012), wetland plant litter decomposition is a part of this web and it can influence many wetland processes (Zhai et al., 2019). Wetland litter decomposition consisted of complex physical, chemical, and biological processes and it is an important aspect in biological and geochemical cycles in wetland ecosystem. Litter and its decomposition are a nexus that links vegetation and soil, and plant-litter-soil constitute a microscopic ecosystem (Zhao et al., 2015, Yun et al. 2015) . Litter has indispensable functions in maintaining ecosystem productivity, ∗

Corresponding author. E-mail addresses: [email protected] [email protected] (M. Zhang).

(Z.

Zhang),

carbon fixation and community succession. It can improve the physiochemical characteristics and hydrological conditions of soil, and improve water quality during decomposition (Atkinson and Cairns 2001). Litter decomposition is a process that is often affected by many factors (Webster and Benfield 1986). Several studies have shown that litter decomposition in an aquatic environment is affected by nutrients (Yin et al., 2019; Rejmánková and Sirová 2007), electron acceptor supply (Li et al., 2010), temperature and pH (Sun et al., 2013), stoichiometric ratios of carbon, nitrogen and phosphorus in litter (Güsewell and Gessner 2009), and metabolic activities of microbiota (Fonseca et al., 2016). Litter decomposition rates and nutrient dynamics are affected by litter mass and environmental conditions (Zhai et al., 2019). In contrast, litter mass is more correlated with decomposition rate (Bijayalaxmi Devi and Yadava 2010; Chen et al., 2001). Decomposition is affected by internal factors

https://doi.org/10.1016/j.ecohyd.2019.11.003 1642-3593/© 2019 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Please cite this article as: J. Zhai, L. Jiumu and L. Cong et al., Reed decomposition under Bacillus subtilis addition conditions and the influence on water quality, Ecohydrology & Hydrobiology, https://doi.org/10.1016/j.ecohyd.2019.11.003

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Fig. 1. The operating conditions for different decomposition experiments.

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(Gessner and Chauvet 1994) such as initial oxygen content, lignin content, the ratio of lignin to nitrogen (L/N), and external factors (Jackson and Vallaire 2007) including water temperature, dissolved oxygen, hydrological conductivity and pH. Biotic factors are dominant factors (Findlay et al., 2002) and play extremely important roles in the litter decomposition processes. Currently, several studies have been conducted to investigate the effects of the biotic factors such as microorganisms (fungi, bacteria) and soil invertebrates on the decomposition in a wetland ecosystem (Zhang et al., 2019; Gingerich et al., 2015; Rejmánková and Sirová 2007). Bacteria and fungi produce extracellular enzymes such as celluloses that degrade lignocellulose (Kuehn et al., 2011), thereby affecting litter decomposition rates (Schimel 2003). Previous studies have reported that microbial communities can affect decomposition rate through total phosphorous (TP) and ammonia-nitrogen (NH3 –N) migration between water bodies and litter (Wu et al., 2017). However, only a few indoor well-controlled simulation studies have been conducted to study the effects of bacteria addition on litter decomposition. In this study, we employed litter bags with two different mesh sizes and Bacillus subtilis as a control treatment to examine the effects of bacteria and different mesh sizes on litter decomposition rates and water parameters. The aims of this study are to investigate the effects of adding microorganisms on litter decomposition by examining: 1) whether there are differences in litter decomposition rates under different litter bag mesh sizes; 2) whether bacteria will affect aquatic environmental markers. Microbial communities play a major role in decay of litter nutrient chemicals in the aquatic environment and nitrogen (N) and phosphorus (P) content have a direct influence on the litter decomposition. Further, the interactions between these factors can reflect the feedback mechanism of litter decomposition toward changes in environmental markers.

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2. Materials and methods

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2.1. Experimental materials

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In this study, we selected reed litter from the Yellow River delta as a study subject. To ensure that the litter used in the experiments is from the same source, all of the litter was collected from the same region. Following that, the

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litter was brought back to the laboratory to wash off surface mud before being cut into 10 cm sections and dried to a constant weight at 65 °C. Different mesh size litter bags (litter bags were constructed by vinyl-coated fiberglass window mesh) have long been used to create a micro environment that was different from the external environment and study the role of invertebrate biomass on decomposition. Using varied mesh sizes litter bags to determine the “arthropod effect” of animals on litter decomposition rates that exclude animals on the basis of body size. The fine mesh had a greater hydrophobic effect (easier water entry for the fine than the coarse mesh bags) than the coarse mesh and dunking the bags helped remove the effect and the potential bias it created. In previous studies, litter bag pore sizes were: 1) micromesh (0.04 - 0.2 mm), 2) mesomesh (1 – 3 mm), 3) macromesh (4 – 5 mm) (Ágoston-Szabó et al., 2016; Bokhorst and Wardle 2013; Wang et al., 2010; Zhai et al., 2019). In this study, we selected litter bags with fine mesh size (0.2 mm) and coarse mesh size (2.8 mm), specification of 15 × 20 cm, and were each filled with 10 g of litter.

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2.2. Experimental design

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In this study, all the litter bags were dunked to completely wet the surface and then submerged under water and placed into plastic crate (610 × 420 × 195 mm) to simulate the decomposition process. A layer of 2 cm thick sandy soil was placed at the bottom as the decomposition matrix, and the substrate was collected in greenhouse where the experiment conducted. Each plastic box was seen as a plot, and the water level in each plastic box was about 16 cm during all the experiment period. Next, we added the Bacillus subtilis culture solution to every box, and each treatment was in an independent box. To examine the effects of microorganisms on litter decomposition, the decomposition box was divided into two groups as shown in Fig. 1; one group is the experimental group in which Bacillus subtilis was added to the litter bag, while the other group is the blank control group. Two hundred milligrams of Bacillus subtilis culture solution (Gingerich et al., 2015) was added to every litter bag in the experimental group with triplicates. The litter bags were collected on day 2, 4, 6, 8, 10, 17, 47, 77, 112 of decomposition process. During each retrieve, water samples were collected from every decomposition box and brought back along with the litter bags to the laboratory for treatment and analysis. Mud

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and other debris were removed from the litter in the litter bag and the litter was washed with deionized water, dried at 65 °C until at a constant weight, and weighed to determine the decomposition rates with the procedures described below. The dried litter samples were crushed using a plant pulverizer and passed through a 0.149-mm sieve. The stored samples were used for quantitation of total carbon, total nitrogen, and total phosphorus content. The total carbon content in the litter was measured using the potassium dichromate-external heating method, and the total nitrogen was measured using the Kjeldahl method (KDY-9830, KETUO). Digestion was used for total phosphorous measurement, and total phosphorus content was measured by vanadate-molybdate colorimetry (UV-2450 ultraviolet spectrophotometry) (Xiang et al., 2015). Water temperature, pH, dissolved oxygen (DO), chemical oxygen demand (COD), total phosphorous (TP), and ammonianitrogen (NH3 –N) were simultaneously monitored in each experimental box. These parameters were measured according to the Chinese national standard methods (State Environmental Protection Administration of China, Monitoring and Analysis Methods of Water and Wastewater, Fourth Ed., China) (Zhai et al., 2019) . In addition, pH and water temperature were monitored using a pH meter and a digital thermometer, respectively. All measurements were taken with three replicates.

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2.3. Date analysis

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The decomposition rate constant k was obtained using Olson’s exponential decay model and k was calculated uswt ing w = e(−kt ) . o In the equation, wt is the decomposition residue of the litter after time t(d) in g, w0 is the starting mass of the litter in g, k is the decomposition rate constant, and t is the decomposition time in days. The nutrient accumulation index (NAI) is used to express the accumulation or release of elements during litter decomposition.

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NAI = (Mt ·Xt ) / (M0 ·X0 ) × 100% (Zhai et al., 2019) In the above equation, Mt is the dry mass of the litter at time t; Xt is the element concentration in the litter at time t in g/kg; M0 is the initial dry mass of the litter, and X0 is the initial concentration of the element in litter in g/kg. When NAI<100%, the element is released during litter decomposition, and when NAI>100%, the element undergoes net accumulation during litter decomposition. In this study, all stoichiometric ratios used are molar ratios of elements. Sigma plot and SPSS 19.0 were used for organization and analysis of all measurement data. Means and standard deviations are used to express all statistical data. One-way ANOVA was performed to test for differences in litter decomposition rates and stoichiometric ratios under different conditions (whether Bacillus subtilis was added or not). Two-way ANOVA was used to examine whether different litter bag mesh size and bacteria have significant effects on water quality, litter decomposition rates, and litter stoichiometric ratios.

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Fig. 2. Dynamic changes of litter decomposition rate during the decomposition process. A. coarse litter bag with Bacillus subtilis added, B. coarse litter bag without Bacillus subtilis added, C. fine litter bag with Bacillus subtilis added D. fine litter bag without Bacillus subtilis added).

3. Results

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3.1. Dynamic change of litter decomposition rate

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As shown in Fig. 2, decomposition rate increases as decomposition time increases. Only during the last retrieve decomposition rate decreased (0.00262d−1 ). As decomposition time increased, residual content of reed litter gradually decreased. After 112 days of decomposition, the residual rate decreased from 100% to 52.44%. The addition of Bacillus subtilis did not show any significant effects on the decomposition rates (p = 0.326, p > 0.05). However, in the last three litter bags retrieve, the decomposition rates of litter bags with Bacillus subtilis added were (p = 0.012) higher than that without Bacillus subtilis treatment. Our results also suggested that there was no significant difference in litter decomposition rates between litter bags with different mesh sizes (p = 0.384, p > 0.05). In 2nd, 4th, 8th retrieve days, litter decomposition rate was the fastest in fine litter bag without Bacillus subtilis added. In the 15th, 45th, 75th retrieve days, the decomposition rates of litter were the fastest in fine mesh size litter bags that contained Bacillus subtilis. In the last 4 retrieves, litter decomposition rate was the fastest in the litter bags with Bacillus subtilis added whether in coarse or fine mesh size litter bag.

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3.2. Dynamic changes of water parameters during decomposition process

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The Fig. 3 showed the dynamic changes in DO, COD, TP and NH3 -N during litter decomposition process. The concentration of COD, TP and NH3 -N gradually decreased, but DO concentration showed fluctuation changes. Whether in coarse or fine mesh size litter bags, if Bacillus subtilis added, DO concentration all raised at first then decreased and ascend at last. In the last 6 retrieves, in fine litter bags without Bacillus subtilis added treatments, DO concentration showed first decrease and then increase. As for coarse litter bags without Bacillus subtilis added treatments, DO

Please cite this article as: J. Zhai, L. Jiumu and L. Cong et al., Reed decomposition under Bacillus subtilis addition conditions and the influence on water quality, Ecohydrology & Hydrobiology, https://doi.org/10.1016/j.ecohyd.2019.11.003

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Fig. 3. Dynamic changes of water quality during the decomposition process. (A. coarse litter bag with Bacillus subtilis added, B. coarse litter bag without Bacillus subtilis added, C. fine litter bag with Bacillus subtilis added D. fine litter bag without Bacillus subtilis added).

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concentration showed a cyclic pattern which increased first then decreased during all the decomposition process. Under coarse litter bag treatment, the concentration of TP (p = 0.001, p < 0.001) was significantly higher than that in the without B. subtilis added, but NH3 -N, DO and COD didn’t show significant difference between different bacteria adding treatment. The concentration of NH3 -N, DO, TP and COD didn’t show significant difference between the presence and absence of Bacillus subtilis added under fine litter bag treatment. 3.3. Relationship between stoichiometric ratio (C/N, C/P and N/P) and litter decomposition rate during decomposition process Litter C/N and C/P ratios are common markers of litter decomposition quality, and the N/P ratio is an important marker for nutrient limit during litter decomposition. As shown in the Fig. 4, the dynamic changes in reed litter nutrients showed a fluctuating variation. Litter C/N showed an increasing trend at the initial stage and reached its peak on Day 75. During the last retrieve, C/N showed a decreasing trend except the treatment of coarse litter bag without Bacillus subtilis added. Under 4 different conditions, a marked degree of variation in C/P during the entire study period was not observed, and C/P all exceed 15. N/P

shows a large fluctuating trend during the entire period and reached its peak on Day 75. At the last retrieve, N/P showed a decreasing trend and lied between 15 and 30. Overall, litter C/N first increased before decreasing while the C/P and N/P fluctuated. Fig. 5.

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3.4. Litter nutrient dynamics and release during decomposition process

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During the 112-day decomposition period, phosphorus concentration in reed litter showed fluctuating changes, which appeared as a decrease in the early stage followed by an increase at the later stage. In this period, the maximum phosphorus concentration was 0.7436 g/kg and decomposition rate was the highest in the last 4 retrieves in the coarse pore litter bags in which Bacillus subtilis was added. The range of nitrogen concentration was 3.760– 15.125 g/kg. The changes in carbon concentrations also fluctuated; during the entire study period, the total carbon content in reed litter first increased with local fluctuations, before decreasing at the late stage of decomposition. The NAI values of nitrogen were lower than 100% and therefore a net release occurred for nitrogen. Under the 4 treatment conditions, the NAIs of phosphorus all showed a decreasing trend. However, NAI increased during the last retrieve. Only the first retrieve had an NAI greater than

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Fig. 4. Dynamic changes of C/N, C/P, N/P of the litter during the decomposition process. (A. coarse litter bag with Bacillus subtilis added, B. coarse litter bag without Bacillus subtilis added, C. fine litter bag with Bacillus subtilis added D. fine litter bag without Bacillus subtilis added).

ing the decay process (Barik et al., 20 0 0; Battle and Mihuc 20 0 0). Microbes colonized the plant litter, releasing nutrients and facilitating decomposition. Once most nutrients have been decomposed and utilized, the effect of microbes diminished.

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100% for phosphorus and the NAI values for all treatment conditions were lower than 100% in subsequent retrieves. The NAI of carbon was greater than 100% only in the coarse mesh size litter bags in which Bacillus subtilis was added.

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4. Discussion

4.2. Effect of bacterial addition on water parameters

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4.1. Effect of litter bag mesh size and bacterial addition on decomposition rate

The overall changes in dissolved oxygen first increased, then decreased, and again increased. These changes may due to the fluctuations caused by slow oxygen consumption during microbial decomposition of substances that are resistant to degradation (Battle and Mihuc 20 0 0). In the last 4 retrieves, except for the last one, the dissolved oxygen contents in litter bags with bacteria added were low. The reason for this is that bacteria simultaneously consume oxygen in the water body while decomposing litter (BROCK 1984). The dissolved oxygen content in the last retrieve was increased, possibly because this experiment was conducted from June to October, the last retrieve was in late autumn and the temperature is much lower than June, this result a low decomposition rate. Therefore, oxygen consumption from the water body is reduced during decomposition and the dissolved oxygen content is increased. Under the 4 treatment conditions, whether in different mesh size litter bag, the addition of bacteria resulted in higher TP content. This may be because bacteria can promote litter decomposition to release organic phosphorus and phosphate salt, thereby causing TP content to be higher (Gamage and Asaeda 2005). The trend for chem-

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Our findings suggested that neither mesh size nor bacterial treatment have significant effects on the decomposition rates. In this study, proportion of mass remaining in the fine mesh (x = 6.8, SE = 1.8) and coarse-mesh (x = 6.6, SE = 1.7) bags was similar (p = 0.79, p > 0.05). Different mesh size litter bags have long been used to create a micro environment that was different from the external environment and study the role of invertebrate biomass on decomposition. Previous studies also have shown that the different litter bag mesh size did not affect litter decomposition rate (Gingerich et al., 2015; Zhai et al., 2019). A possible reason for this is that minor changes in temperature or water body can result in variability in litter decomposition (Bokhorst and Wardle 2013) and that the effects of bacteria on litter decomposition are small (Ágoston-Szabó et al., 2016; Gingerich et al., 2015). During early phases of decomposition, it has been found that fungi tend to be dominant and bacteria are important in later stages, and bacteria were the primary decomposers dur-

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Fig. 5. Dynamic changes of C/N, C/P, N/P of the litter during the decomposition process. (A. coarse litter bag with Bacillus subtilis added, B. coarse litter bag without Bacillus subtilis added, C. fine litter bag with Bacillus subtilis added D. fine litter bag without Bacillus subtilis added).

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ical oxygen demand showed an overall decrease. This is possibly because Bacillus subtilis can decompose organic matter during decomposition (Wang 2011), thereby causing COD content to decrease. Whether litter bag with different mesh size, higher NH3 -N content was founded in which Bacillus subtilis was added. This may be because the addition of Bacillus subtilis promotes the decomposition of nitrogen-containing organic matter, causing ammonianitrogen released from litter to the water body and resulting in a higher ammonia-nitrogen content. However, the bacterial treatment had no significant effects on the water quality parameters in this study, including NH3 -N, TP, DO and COD. One possible reason is that the

effect of Bacillus subtilis is marginal compared to other factors affecting litter decomposition. In addition, our study only measured corresponding environmental factors during the retrieve of litter bags, and the density of measurement time points are insufficient. Additionally, the retrieve frequency at the start was higher and the effects of Bacillus subtilis may not have appeared then. Therefore, we were unable to represent environmental conditions during the various study periods and the effects of Bacillus subtilis on water quality are not clear. Table 1 clearly indicates that water parameters significantly affect the decomposition process. Based on correlation analyses, decomposition rate showed highly

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J. Zhai, L. Jiumu and L. Cong et al. / Ecohydrology & Hydrobiology xxx (xxxx) xxx Table 1 Correlation coefficients between water parameters and decomposition rate during the decomposition process. Decomposition rate NH3 –N DO COD TP Notes:

∗∗

0.575∗∗ 0.155∗∗ 0.360∗∗ 0.437∗∗

NH3 -N

DO

0.148∗ 0.642∗∗ 0.576∗∗

COD

0.047 0.052

TP

0.562∗∗

1

means p < 0.01,∗ means p < 0.05.

Table 2 Correlation coefficients between water parameters and litter nutrient dynamics during the decomposition process. NH3 -N N/P C/P C/N N-NAI P-NAI C-NAI Notes:

∗∗

DO ∗∗

−0.218 −0.212∗∗ −0.150∗∗ 0.221∗∗ 0.262∗∗ 0.416∗∗

COD

TP ∗∗

−0.105 −0.027 0.058 0.053 0.064 0.131∗

−0.205 −0.249∗∗ −0.199∗∗ 0.094 0.147∗ 0.299∗∗

−0.045 −0.287∗∗ −0.311∗∗ 0.132∗ 0.178∗∗ 0.314∗∗

means p<0.01,∗ means p<0.05.

Table 3 Correlation coefficients between litter nutrient dynamics and decomposition rate during the decomposition process. Decomposition C/N Rate Decomposition Rate N-NAI 0.289∗ ∗ P-NAI 0.342∗ ∗ C-NAI −0.121 Notes:

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∗∗

−0.066 −0.242∗∗ −0.212∗∗ −0.144∗

C/P

N/P

−0.209∗ ∗ −0.219∗ ∗ −0.270∗ ∗ −0.221∗ ∗

−0.347∗ ∗ −0.058 −0.242∗ ∗ −0.186∗ ∗

means p < 0.01,∗ means p < 0.05.

significant positive correlation with NH3 -N, DO, TP, and COD. Also, there was a significant correlation between water parameters. NH3 -N had a significant positive correlation with DO, COD and TP (p<0.01), and it had a significant negative correlation with COD and TP (p < 0.01). Tables 2 and 3. 4.3. Correlation between litter nutrient dynamics and water parameters There is a significant correlation between water parameters and litter nutrient dynamics. NH3 -N had a significant positive correlation with N-NAI, C-NAI and P-NAI (p < 0.01), and it had a significant negative correlation with N/P, C/P and C/N (p < 0.01). DO had a significant positive correlation with C–NAI (p < 0.05). COD had a significant positive correlation with C-NAI (p < 0.01) and P-NAI (p < 0.05). In addition, COD had a significant negative correlation with N/P, C/P and C/N (p < 0.01). TP had a significant positive correlation with C-NAI,P-NAI (p < 0.01) and N-NAI (p < 0.05), and it had a significant negative correlation with C/P and C/N (p < 0.01). NH3 -N had significant correlations with all the litter nutrient indicators, TP concentration had a significant correlation with litter quality stoichiometry about element P, this could reflect an important interactive mechanism between hydroperid and processes in nutrient-deficient

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in litter, and this might cause nutrient element transfer between aquatic environment and litter plant (Jia et al., 2018). In general, the difficulty during the litter decomposition process is initially determined by its chemical composition and its inner biological and physical structure. After the Bacillus subtilis addition, the absorb effect of NO3 − -N and TN transfer from water to plant litter might strengthened. The rapid release of organic P and phosphate from the decomposition process resulted in the rapid decrease in TP concentrations in water; moreover, the higher TP values observed in the added fungi treatments might have been the result of uptake by decomposing bacteria and fungi (Zhai et al., 2019; Wu et al., 2017).

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4.4. The effect of litter quality on decomposition rate

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Generally, litter decomposition is mainly affected by litter quality. Nitrogen content, phosphorus content, lignin content, vitamin and hemicellulose content, lignin/N, and C/P are markers that are often used to describe litter quality (Wu et al., 2006; Wu et al., 2017). Decomposition rate shows a negative correlation with C/N, C/P, and N/P and a significantly negative correlation with C/N and C/P. In our experiment, the initial C/N of litter is low and C/N did not show any significant correlation with decomposition rate. During litter decomposition, C/N may not accurately reflect litter decomposition rate. Previous studies have shown that the relationship between C/N and litter decomposition rate is not significant (Brinson et al., 1981; Ouyang et al., 2013). However, it is generally believed that a higher C/N will result in slower litter decomposition (Elder and Mattraw 1984). When C/N is very high, decomposition rate will decrease (Aerts and de Caluwe 1997). In our experiment, decomposition rate showed a significant negative correlation with C/P. During decomposition, C/P showed fluctuating changes. This may be because phosphorus mainly exists as phosphate ions or compounds and large amounts are released during decomposition, and the percentage of P and C in litter fluctuated, resulting in changes of C/P ratios. During decomposition process, litter decomposition rate showed a significant negative correlation with N/P. During decomposition, microorganisms need to consume a large amount of adenosine triphosphate (ATP) to generate energy. Therefore, when phosphorus is limited during litter decomposition, decomposition rate decreases (Lin-hai et al., 2012). In addition to C/N and C/P, the N/P ratio of litter can be used to characterize litter decomposition rate. Many studies have shown that litter decomposition can also be controlled by P-related chemicals. N/P values are important for the short-term litter decomposition. Decomposition was N-limited at low N: P supply ratios and Plimited at high N: P supply ratios. During N/P > 14, litter decomposition is affected by P. When N/P < 10, litter decomposition is affected by N (Aerts R, 1992; Güsewell and Gessner, 2009). Compared with nitrogen, which is mainly affected by biotic factors, phosphorus is mainly affected by both physical and biotic factors (Güsewell andGessner 2009). In our experiment, the initial N/P value was 16–25. Therefore, litter decomposition was not affected by phosphorus supply for microbial nutrient demand.

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5. Conclusions

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In general, litter decomposition rates were much quicker under Bacillus subtilis addition treatment in the later part of decomposition phase, but litter decomposition rates were similar among different litter bag mesh sizes. Also, the decomposition rate has a positive correlation with water parameters, litter quality. This correlation ship between litter decomposition rate and water parameters, litter quality represents large portions of decomposition dynamic that involves a complex web of interacting forces, of which bacterial comprise only a small part, though in later phase we found low measurable influence of Bacillus subtilis addition on decomposition, it is likely that the influence of it was more significant than the link between abiotic factors, microbial communities, invertebrates, and other environmental factors and decomposition rate under various simulating treatments. Further studies are needed to more assess the relationship between the substantial factors and litter decomposition.

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Uncited references

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Koerselman and Meuleman (1996), Tessier and Raynal (2003).

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Conflict of Interest

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None. Ethical statement The research was done according to ethical standards.

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Acknowledgement

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This research was supported by the National Key Research and Development Plan of China (2017YFC0505903).

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Funding body

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The work submitted was supported by the National Key Research and Development Plan of China (2017YFC0505903).

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In this study, litter decomposition rate had a significant positive correlation with P-NAI and N-NAI (p<0.01), and had a negative correlation with C-NAI. N/P had no relationship with N-NAI, N/P, C/P and C/N all had significant positive correlations with P-NAI, N-NAI and C-NAI.

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Please cite this article as: J. Zhai, L. Jiumu and L. Cong et al., Reed decomposition under Bacillus subtilis addition conditions and the influence on water quality, Ecohydrology & Hydrobiology, https://doi.org/10.1016/j.ecohyd.2019.11.003

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