Intercropping maize and common bean enhances microbial carbon and nitrogen availability in low phosphorus soil under Mediterranean conditions

European Journal of Soil Biology 80 (2017) 9e18

Contents lists available at ScienceDirect

European Journal of Soil Biology journal homepage: http://www.elsevier.com/locate/ejsobi

Original article

Intercropping maize and common bean enhances microbial carbon and nitrogen availability in low phosphorus soil under Mediterranean conditions Mourad Latati a, *, Adel Aouiche b, Sihem Tellah a, Abdelkader Laribi a, Samia Benlahrech a, Ghiles Kaci a, Faiza Ouarem a, Sidi Mohamed Ounane a a Ecole Nationale Sup
erieure Agronomique, D
epartement de Productions V
eg
etales, Laboratoire d'am
elioration int
egrative des productions v
eg
etales (LAIPV), Avenue Hassane Badi, El Harrach, 16200 Algiers, Algeria b Ecole Pr
eparatoire en science de la Nature et de la vie d'Alger, Avennue Ahmed Hamidouch Route de Beaulieu, El Harrach, 16200 Algiers, Algeria

a r t i c l e i n f o

a b s t r a c t

Article history: Received 10 August 2016 Received in revised form 3 March 2017 Accepted 14 March 2017

The beneficial effect of intercropping system under low phosphorus (P) conditions has already been reported in previous works. The aim of this study was to test the hypothesis that intercropping (common bean - maize) in P-deficient soil can enhance the carbon (C) and nitrogen (N) stocks from the microbial biomass (MB). The field experiment was conducted in Setif province in a northern Algerian agroecosystem with a Mediterranean climate. The nodule N storage in intercropped common bean was 60% higher than for sole crops and was highest in a P-deficient soil in the second year. The carbon stock from the microbial biomass of the soil (MBC) was higher with intercropping than for sole crops and fallow and was even higher in P-deficient (23%) soils as compared to P sufficient (17%) conditions. There was a strong correlation between C stock from nodule (NC) and MBC stock for intercropping in either Pdeficient (r2 ¼ 0.80***; p < 0.001) or P-sufficient soils (r2 ¼ 0.69**; p < 0.01). P-deficient conditions gave the highest total soil respiration (1.68 g C-CO2 m2 days1) and the lowest MB C:N ratio (10.3 and 12.2 for common bean and maize, respectively) in intercrops system. This study showed that, in a P-deficient soil, intercropping is a good solution for increasing the rhizosphere MB through C and N partitioning between root nodules and rhizosphere microbial community, which is responsible for improving soil fertility and recycle mineral elements. © 2017 Elsevier Masson SAS. All rights reserved.

Handling Editor: Christoph Tebbe Keywords: Intercropping P deficiency Microbial biomass Carbon Nitrogen Agroecosystem

1. Introduction A high soil quality improves agroecosystem services and sustains biological productivity which promotes plant growth and increases bioavailability of essential nutrients [1,2]. Species diversity has a beneficial effect through both functional complementarity and facilitation between plants which improves productivity as well as increases C and N stocks in the soil, the microbial biomass and the crop residues [3,4]. High C and N stocks in the soil are correlated with soil productivity. The soil organic matter (SOM) stock is a key biological factor and is one of the biological and chemical indicators that need to be evaluated in a soil fertility analysis [5]. In Algeria, the restoration of soils with low

* Corresponding author. Revolution Street, Collo, Skikda, Algeria. E-mail address: [email protected] (M. Latati). http://dx.doi.org/10.1016/j.ejsobi.2017.03.003 1164-5563/© 2017 Elsevier Masson SAS. All rights reserved.

SOM has become a strategic necessity for food security, given the current economic situation [2,7]. Most studies on legume-cereal intercropping system have shown the efficient use of environmental resources by stimulating plant growth and yield in calcareous and P-deficient soils [2,8,9], compared with fallow-cereal rotation practice. The legumes could increase the availability of nutrients such as N [10] and P [11] in the rhizosphere of the intercropped cereals, improving grain yield, nutrient uptake and efficiency in use of rhizobial symbiosis (EUR), especially in low P conditions [2]. Intercropping can also improve growth and nutrient use efficiency through the stimulation of biological N2 fixation by nodules of the intercropped legumes [12]. Recent studies suggest that N storage in legume-cereal intercropping is greater as a result of a higher EURS in a P-deficient soil than in a P-sufficient soil [2]. Changes in the C:N ratio of soil microorganisms (fungi and bacteria) have also been attributed to the relative demand of soil microbes for C and N [20]. These changes

10

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

may have a major effect on N and C cycling. Despite extensive literature on intercropping, little information is available on the effects of cereal-legume intercropping on microbial mediated processes and the relationship between intercropping and biological N2 fixation by the legumes. Microbial biomass (MB) is one of the most important biological indicators for monitoring environmental change. It is also considered as important for planning appropriate land use and for the management of agriculture practices [1]. The carbon (MBC), nitrogen (MBN) and phosphorous (MBP) stock from the microbial biomass of the soil depends on the composition and structure of the microbial community [13], the growth stage of microorganisms and the environmental conditions [14]. In the rhizosphere, microorganisms assimilating C from rhizodeposits need P to satisfy their growth requirements and may, therefore, compete with plants for soil P. However, it has also been suggested that MBP is another pool of soil P that is potentially available to plants through the decomposition of dead microbial cells [13]. The MB pool can be a substantial source of available nutrients, such as C, N and P, for plant growth [1,16]. Furthermore, soil can be managed to improve either MBC or MBN stock by introducing crop management practices such as intercropping of cereals and legumes in agroecosystems [1,15]. Recent studies have reported an increase in microbial activity with higher SOM and MBC stock in intercropping systems than in corresponding sole cropping systems [17]. Tang et al. [16] observed a significant increase in MBC and MBP stock in the rhizosphere of intercropped legumes in a P-deficient soil. In order to ensure food security in Algeria with the current economic crisis and declining oil prices, the development and intensification of local farming practices has become a strategic necessity. However, most northern Algerian soils are alkaline (pH varying from 7.5 to 8.5) [42], which is considered to be a limiting factor for the growth and nodulation of legumes [7]. In addition, fallow-cereals rotation is the most common system in Algeria for crop production [2]. There are two types of fallows in Algeria, one that is used to control weeds, store water and weakly enrich the soil with nutrients. However in the second fallow type; the soils were only plowed without any treatment such as fertilizer and irrigation. The latter is the most used for ecological intensification of agriculture in Algeria. In both cases, this practice is not profitable and does not allow either to satisfy the needs of the Algerian population or to ensure a good restoration of the fertility of the Algerian soils. This deprives the country's economy from freeing itself from dependence on food imports [42,45]. Finding solutions for the Algerian soil problems to replace fallow systems by more profitable agricultural practices is, therefore, currently a major concern. The effects of intercropping on agroecosystem productivity and on C and N storage have been well documented for both the shortterm and the long-term [1,16,17]. The C input into the soil through root residues, for both legumes and cereals, has been shown to be higher in intercropping than in monoculture systems [18,19]. Among possible interspecific interactions (complementarity and facilitation) between intercropped cereals and legumes; little information is available in the literature on the effect of this intercropping on changes in MBC:N ratio, soil respiration and nodule C (NC) and N (NN) stocks sequestered by root nodules. A previous study reported that intercropping common bean and maize might be an alternative agronomical practice that is currently rarely used in north-east Algerian agroecosystems under low P conditions [2,11]. In the studies reported here, our first objective was to study, under P-deficient and P-sufficient conditions, the effects of intercropping common bean with maize on i) nodule C and N sequestration, ii) C and N stocks from the microbial

biomass of the soil and iii) soil respiration. Our second objective was to attempt to explain the links between these effects. 2. Material and methods 2.1. Experimental sites and field plot design The study was performed in 2012 and 2013 at the same two experimental sites (P-deficient) S1 (35 58, 110 N and 514, 900 E) and (P-sufficient) S2 (35 53, 370 N and 5 37, 010 E) as in our previous study [2]. These sites are located in the Setif agroecosystem (300 km east of Algiers) where maize and common bean are widely cultivated as intercrops. The previous study confirmed that these sites have very different soil P availability and EURS [2]. The soil physical and chemical properties for the P-deficient and P-sufficient sites were determined by standard sampling of the top layer (0e30 cm) at the sowing stage during the 2012 growing season. There were no significant differences for clay, loam and sand content between the two study sites. However, the chemical properties (total N, total P and bioavailable P) of the sites had been significantly affected by the land management. The P-deficient site had lower levels of N (0.7 g kg1) and P (total P: 71,7 ppm; OlsenP:4.6 ppm) than the P-sufficient site (N:1.9 g kg1;total P: 187.5 ppm and Olsen-P: 19.4 ppm). The CaCO3 content in both sites varied from 22.5% to 25% with a relatively high pH of 8.3 in Pdeficient and 7.7 in P-sufficient sites, respectively. The study was carried out with one common bean cultivar (Phaseolus vulgaris cv. El Djadida) and one maize cultivar (Zea mays cv. Filou) which are the most common cultivars grown by farmers in Algerian agroecosystems. The experimental design was a split plot with four replicates. Each sub-plot was cultivated with common bean as sole crop, maize as sole crop, maize-common bean intercrop and fallow (uncultivated plot) (4 cropping systems x 4 replicates). The planting density was that commonly used by farmers: 24 plants m2 for common bean and 15 plants m2 for maize as sole crops, and 12 plant m2 for each species intercropped. All crop management such as sowing, amendment and irrigation was carried out by farmers. The soil in the fallow plot was ploughed and left unplanted according to local farming practices (with the same interventions which are applied in crop treatment such as irrigation and weeding). The soils from the fallow were taken as a control as well as from the rhizosphere of each species in crop system. While the same type of fallow treatments was practiced in the experiment field according to farmers' practices. 2.2. Nodule harvest and rhizosphere soil sampling Seventy days after sowing, corresponding to the full flowering stage, soil samples were taken from the rhizosphere of each species and the fallow plot. The rhizospheres of each of the maize and common bean roots were bulked for each replicate in all cropping systems. The rhizosphere samples were then stored at 4  C for 72 h before analysis. The nodules were separated from the common bean roots, dried and weighed separately. For the soil samples during first growing season (2012), the total P concentration was determined using the malachite green method after digestion by nitric and perchloric acid [21]. The soil P availability was determined by NaHCO3 extraction (Olsen method, [22]) and the rhizosphere pH was measured in soil suspended in purified water with a soil: water ratio of 1: 2.5 [23]. The calcium carbonate (CaCO3) concentration was determined in the laboratory by measuring the volume of CO2 evolved using the Horton and Newson method.

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

11

Fig. 1. C (A) and N (B) stock (g m2) in common bean nodules (CN and NN) as sole crop and intercrop in P-sufficient and P-deficient soil. Values correspond to the mean calculated with 4 replicates. Bars indicate standard errors. For each crop, Letters show significant differences between cropping systems within a same level of P and a same year (p < 0.05).

For the soil and nodule samples taken at the flowering stage, the N concentration was determined using the Kjeldahl method and the total organic C concentrations in both soil and nodules were determined using the Walkley-Black method. The total microbial and root respiration (CO2-C fluxes from the soil) for intercropping, sole cropping and fallow were evaluated at full flowering (70 days after sowing). The respired CO2-C was estimated by CO2 absorption for one day in 20 mL of NaOH solution inside PVC cylinders, precipitating the carbonates and titrating the remaining NaOH with a standard 0.25 mol L1aqueous solution of HCl [6]. The CO2-C fluxes were estimated in mg m2 day1 [24].

fumigated) for 1 h with 0.05 and 0.5 M K2SO4 (30 ml) for C and N respectively. The extracted solutions were then centrifuged at 4000 rpm for 10 min and filtered using sterilized filters with 0.2 mm pore size. Finally, the liquid filtrates were stored at 4  C before the total organic C (TOC) and total N (TN) were determined using a TOC analyzer (TOC-V CSH, Shimadzu). The MBC and MBN stock were determined by calculating the difference between the TOC and TN of the fumigated and control soil samples. The final values of microbial biomass were obtained by dividing by extraction factors: kEC ¼ 0.45 for MBC and kEN ¼ 0.54 for MBN, respectively [27,28]. 2.4. Calculations and statistical analysis

2.3. Soil microbial biomass The MBC and MBN stock were measured by the laboratories at the National Institute of Agronomy Research (INRA, Montpellier, France). They were determined by a chloroform fumigationextraction method derived from the Brookes and Jenkinson methods [25,26]. Ten grams of fresh soil sample were fumigated with chloroform for one day in sealed desiccators. C and N were extracted from the fumigated soil samples and controls (un-

For comparison, all C and N concentrations (g plant1 and mg ml1 for plant and soil, respectively) in both rhizosphere soil and nodule were converted to stocks (g m2 C and N: g of C and N stocks in one square meter that is really occupied by plants) on the 0e30 cm soil layer. Indeed, the corrective factor 2 was used data to calculate all C and N stock in g m2. The C and N stocks from either common bean nodules (NC and NN) or the microbial biomass of the soil (MBC or MBN) were calculated as follows (Eq. (1) and Eq. (2))

12

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

Fig. 2. MBC stock (g m2) in the rhizosphere of common bean and maize as sole crop and intercrop and in the fallow in P-sufficient (A) and P-deficient (B) soil. Values correspond to the mean calculated with 4 replicates. Bars indicate standard errors. For each crop, letters show significant differences between cropping systems within a same level of P and a same year (p < 0.05).

according to Ibrahim et al. [46,47]:

  NC ðor NNÞ stock ¼ nodule C ðor NÞ content in g g1  d  mP MBC ðor MBNÞ stock ¼ vme  st  bd  MBC ðor MBNÞ  ð1  WpÞð1  Cf Þ=mS

Where

(2)

(1)

Where MBC (or MBN) stock ¼ C and N stock of the soil microbial biomass (in g m2) vme is the volume of microbial extract (in ml, here: 30 ml) St is the soil thickness (in m, here: 0.3 m) bd is the soil bulk density (in g cm3) mS is the soil sub-sample mass (in g) Wp is the water content (in w/w) Cf is the coarse gravel fraction (in %) Wp and Cf were measured for each field plot.

NC and NN stocks is C and N stocks, respectively in common bean nodules (in g m2) mp is the nodules biomass of each sampled plant (in g plant1) d ¼ density of common bean plants (in plant m2). One-way ANOVA (analysis of variance) with the cropping system as a factor (p value ¼ 0.05) was carried out on the CN and NN stock, MBC stock, MBN stock and soil respiration (g C-CO2 m2 day1). Significant differences between mean values were determined by Tukey's multiple comparison tests at a level of significance of 0.05. All statistical analyses were performed with STATISTICA (8.5).

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

13

Fig. 3. MBN stock (g m2) in the rhizosphere of common bean and maize as sole crop and intercrop and in the fallow in P-sufficient (A) and P-deficient (B) soil. Values correspond to the mean calculated with 4 replicates. Bars indicate standard errors. For each crop, letters show significant differences between cropping systems within a same level of P and a same year (p < 0.05).

3. Results 3.1. Nodule carbon and nitrogen stocks In both years, NC and NN stocks of common bean grown as either intercrops or sole crops were substantially affected by the P level in the soil (Fig. 1). In the second year, the C storage in the nodules was significantly lower in the intercropping than in the sole crop, while there was no significant difference between two cropping systems in the first year (Fig. 1A). The effect was more pronounced for the P-deficient soil (-P, 46%) than for the P-sufficient soil (þP, 21%). Conversely, N storage in the nodules of intercropped common bean was significantly greater than in the sole crop (Fig. 1B): in the first growing season, the difference was similar (þ60%) at both sites and, in the second growing season, the difference was even greater (þ150%). 3.2. Nitrogen and carbon in the soil microbial biomass For common bean, the MBC stock was significantly greater in the

rhizosphere of both intercropped and sole cropped common bean than in fallow soil (Fig. 2). In the first year, MBC stock was significantly higher in the intercrop than the fallow (þ62% for -P soil and þ43% for þ P soil) whereas for the sole crop the increase was smaller (þ45% for -P soil and 20% for þ P soil), while there was no significant difference between cropping systems during the second year. On the other hand, rhizosphere of intercropped common bean showed an even more pronounced increase in MBC stock under -P (23%) as compared to þ P (17%) conditions. For maize, MBC stock in the rhizosphere was significantly higher in the intercrop than in either the sole crop or fallow only for -P soil (Fig. 2B) and not for þ P soil (Fig. 2A). The difference was greater in the second year (þ40% relative to sole crop and þ23% relative to fallow) than in the first year (þ20% and þ14%, respectively). For common bean, MBN stock was significantly higher for intercropping than sole crop and fallow soil with a greater effect for -P soils (þ25% in the first year and þ10% in the second year) than for þ P soils (þ16% and þ7%, respectively) (Fig. 3A and B). However, for maize, MBN stock was significantly higher in the rhizosphere of intercropped maize than in the fallow only in -P soils (þ26% in the

14

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

Fig. 4. MBC:N ratio for common bean and maize as sole crop and intercrop and in the fallow in P-sufficient (A) and P-deficient (B) soil. Values correspond to the mean calculated with 4 replicates. Bars indicate standard errors. For each crop, letters show significant differences between cropping systems within a same level of P and a same year (p < 0.05).

first year and 41% in the second year) (Fig. 3B). Furthermore, MBN stock was higher in the fallow soil than in the sole crop, but this was only significant in the second year (þ7% for -P soil and þ19% for þP soil).

intercropping than for sole crops, except for maize in -P soil in the first year (Fig. 5B) where the intercrop had significantly higher respiration (þ43%) than as a sole crop. However, the soil respiration in intercropped common bean was significantly higher than in sole crop for both -P soil (þ27% in the first year and þ52% in the second year) and þP soil (þ42% and 55%, respectively).

3.3. Carbon-to-nitrogen ratio (C:N) of the microbial biomass and soil respiration The soil microbial C:N ratio was significantly lower in both sole crops and intercrops than in the fallow (Fig. 4A and B). There were significant differences between intercrops and sole crops only in -P soil (P-deficient: Fig. 4B). The C:N ratio was lower in the rhizosphere of intercropped maize than in the sole crop (0.7 in the first year and 1 in the second year) and lower in intercropped common bean than in the sole crop (1.3 and 0.8, respectively). For both common bean and maize, the total soil respiration in both years was higher in-P soil (between 0.7 and 1.75 g C-CO2 m2 day1) than in þP soil (between 0.55 and 1.2 g C-CO2 m2 day1), with the respiration being greater than that of the fallow (Fig. 5A and B). For maize, the soil respiration was significantly lower in

3.4. Nodule C and N stocks and relationship with soil microbial biomass The correlations between NN stocks and MBN stock (Fig. 6A and B) were dependent on the cropping system and soil P content. The correlations were positive and were only significant (p  0.01) for intercropped common bean grown in either -P (r2 ¼ 0.80***) or þ P (r2 ¼ 0.69**) soil. There was no significant correlation for sole crops. The same result was found for correlations between NC stocks and MBC stock, with a stronger correlation for -P soil (r2 ¼ 0.75**) than for þ P soil (r2 ¼ 0.56*) (Fig. 6C and D).

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

15

Fig. 5. Soil and root respiration (g C-CO2 m2 day1) in the rhizosphere of common bean and maize as sole crop and intercrop and in the fallow in P-sufficient (A) and P-deficient (B) soil. Values correspond to the mean calculated with 4 replicates. Bars indicate standard errors. For each crop, letters show significant differences between cropping systems within a same level of P and a same year (p < 0.05).

3.5. Soil respiration to nodule C stock The relationship between soil respiration and NC stock was determined by linear regression (Fig. 7A and B). There was a strong dependence on cropping system and soil P level. For intercropped common bean, there was a strong positive relationship between soil respiration and NC stock which was higher in P-deficient soil (r2 ¼ 0.97***; p < 0.001) than in P-sufficient soil (r2 ¼ 0.6*; p < 0.05). However, for sole cropped common bean, soil respiration was positively correlated (r2 ¼ 0.74**; p < 0.01) with NC stock in Pdeficient soil, while there was no significant correlation for sole crop in P-sufficient soil (Fig. 7A). 4. Discussion This study showed that NN stock in intercropped common bean was significantly higher compared to the sole crop in both years (Fig. 1). This agrees with the results of Zhang et al. [29], Betencourt et al. [30], and Latati et al., [2,10]. The results also showed that NN stocks were higher in -P soil than in þP soil, suggesting greater

symbiotic N2 fixation under these conditions. Previous studies [2,16] showed that under P-deficient conditions intercropping increased P availability in the soil. Under these conditions, plants are stressed, driving an increase in symbiotic N2 fixation which is accompanied by an increase in proton release from the roots, which acidifies the rhizosphere and increases the P availability in the soil by transforming P into a form that can be directly assimilated by the plants [2,30,45]. The NC stock was lower in the -P soil than in the þP soil, this may be explained by the C transfer from the nodules to the atmosphere as CO2 during the respiration which is necessary to provide the energy for plant growth. Several studies have shown the relationship between nodule respiration and nodule biomass. The NC may also be transferred from the nodules to the rhizosphere where the microorganisms feed on them to grow. This constitutes an NC stock in the rhizosphere MB. Previous studies have shown the beneficial effects of intercropping common bean and maize in P-deficient soils in northeastern Algerian agroecosystems. In fact, this study showed that MBN stock was much higher for intercrops than for the

16

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

Fig. 6. Relationship between NN stock and MBN stock (A and B) and between NC and MBC stock (C and D) for intercrop (open circle) and sole crop (solid circle) in P-sufficient and Pdeficient soil. All linear regression functions (intercropping: light gray text and sole crop: dark gray text) were established from 10 samples of either rhizospheric soil or plant and *, ** and*** denote significant differences at p < 0.05, p < 0.01 and p < 0.001, respectively.

corresponding sole crops and fallow (Fig. 3). This result is very interesting particularly as fallow-crop rotation is currently a widespread practice in Algeria. The nitrogen stock from the microbial biomass of the soil is strongly positively correlated with the NN stocks for intercropping in P-deficient soils (Fig. 6). That suggests that N is transferred from the nodules to the rhizosphere benefitting the rhizosphere microorganisms after nodule senescence. The rhizosphere MBN stock was significantly higher in intercropping under P-deficient conditions in both years. This was confirmed in this study by the effect of intercropping on MB in Pdeficient soil. Indeed, the low MBN stock of the soil observed in the fallow plots may be mainly explained by the type of fallow practiced by farmers, for which the soil was unseeded and weeded without organic matter supply. It may also be explained by the short duration over which the fallow system is practiced by farmers in experiment field. The carbon of the soil from the microbial biomass was higher in intercropping than in sole crops and fallow and even more in Pdeficient soil for intercropped maize. Carbon is a major factor limiting the growth and development of microorganisms while for plants the limiting factor is nitrogen [31]. Tang et al. [16], showed that the carbon stock of the rhizosphere microbial biomass was higher in intercropping than in monoculture. As stated above, under P-deficient conditions, plants are stressed, driving an increase

in the rate of symbiotic fixation N2, especially through increasing of P availability as was confirmed in our previous studies [2]. This could enrich the soil microbial biomass after the senescence of the nodules. This strongly affects the metabolism of plants, from the regulation of gene expression to the production of biomass [32,33]. However, microorganisms can stimulate rhizodeposition from plants, providing organic matter, especially carbon that is easily assimilated by microorganisms in the rhizosphere [34,35]. In addition, the MBC stock can also occur as a consequence of enzyme activities (eg. cellobiohydrolase, chitinase and phosphatase activities), as a result of an increase of P availability in agroecosystems [36]. The MBC stock in this study was strongly positively correlated with the NC stock for intercropping in P-deficient soils. This suggests that the microbial biomass is enriched by the transfer of carbon from the roots to the rhizosphere, through various pathways (rhizodeposition, respiration or root senescence). Concerning total soil respiration (Fig. 5), it has been long known that increased biomass production contributed to the enhanced respiration [37,38]. The C:N ratio of the microbial biomass is an important indicator of the nutritional balance of the microorganisms. If C:N is high, nitrogen becomes limiting factor for the microorganisms so that they compete with the plants for nitrogen [39]. In the case of our study (Fig. 4B), this shows that the nitrogen needs, not only for

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18

17

biomass and its C:N ratio in the fallow soil, whereas more complex processes, such as predation or phage dynamics, may also have been involved in the rhizosphere, especially in the case of intercrops. However, for legume species, enzyme activities hold an important role in the mobilization of both MBC and MBN stock and subsequent increase P availability for plant acquisition, either via the nitrification or the mineralization processes [43,45]. It is wellknown that microorganisms that utilize rhizodeposits can cause a priming effect in the rhizosphere, increasing SOM mineralization and thereby releasing C and N as well as nutrients such as P [44]. The microorganisms in the rhizosphere can also be a major sink, attracting the C and N of both plant and nodules. Microorganisms in turn stimulate rhizodeposition and in this case, the C which is most readily available, is transferred to the rhizosphere so that it is assimilated by the microorganisms [35]. 5. Conclusion

Fig. 7. Relationship between NC stocks and soil respiration in intercrop (open circle) and sole crop (solid circle) in P-sufficient (A) and P-deficient (B) soil. All linear regression functions (intercropping: light gray text and sole crop: dark gray text) were established from 10 samples of either rhizospheric soil or plant and*, **, ***, denote significant differences at p < 0.05, p < 0.01 and p < 0.001, respectively.

adequate respiration of the microbial biomass decomposing organic matter but also for plant growth, are covered under these conditions. Under the low-P conditions of our soil, these results suggest that soil respiration can also occur as a consequence of microbial activity simulations, as a result of a shift in the nutritional (eg. C and N) balance of the microorganisms. Thus, the soil microbial community in return provides the plants with mineral elements, made available by microbial activities (mineralization, storage and recycling). Recent studies suggest that other mechanism patterns, i.e. enzyme activity, may show at least similar increases in soil respiration as those found in this study, through their effect on either soil functions (e.i. C, N and P mobilization abilities) or soil properties [40]. An important finding of this work is related to the relationship between soil respiration and NC stock (Fig. 7B). This can be explained, first, improved efficiency in use of environmental resources by intercrops, eventually resulting in a stimulating of plant growth under low P conditions and, second, increased nodule permeability to oxygen [41] by common bean when intercropped with maize as a result of low P availability in the soil [42]. On the other hand, rhizosphere microorganisms may have greater respiration resulting from growth stimulation in P-deficient soils. Resource availability may have determined the microbial

In conclusion, this study has highlighted the impact of intercropping in Algerian P-deficient soils on the enrichment of the rhizosphere in organic matter that could restore the fertility of Algerian soils and consequently have an effect on the yield of agricultural production and the economy of the country. Indeed, the main results showed that, in P-deficiency conditions, intercropping gave the highest increases in MBC and MBN stock than in sole crops and fallow. In the same conditions, the highest total soil respiration in the rhizosphere was noted and the C:N ratio of the microbial biomass was lower in the rhizosphere of intercropped maize than in the sole crops. Also, one of the important results found is the strong correlation established between C stock from nodule (NC) and MBC stock in intercropping, especially in P-deficient soils. P deficiency could cause a stress in the plant inducing probably an increase in symbiotic nitrogen fixation which in turn increases P availability in the soil. This could probably enrich the rhizosphere of legumes with organic matter thereby increasing MBC and MBN stock. The enriched rhizosphere microbial community contributes to SOM mineralization, which in turn could stimulate rhizodeposition and plant growth. The relationships between biological N2 fixation and the microbial soil respiration appeared to be complex and could be further elucidated as a function of nutrient application rate, such as in a P fertilization gradient. We can conclude that in low P soils conditions, intercropping could be an effective solution and could replace fallow system in Algeria, which is not currently practiced as a traditional fallow that can improve the soil with input of organic matter. Acknowledgements This work was funded by the CNEPRU F04020110004 project of the Ministry of Higher Education and Scientific Research and the AUF-PCSI 63113PS012 Algeria-France cooperation framework and the FABATROPIMED Great Federative Project of the Agropolis Foundation, reference ID 1001-009. The authors would like to ^le et de Certification des thank the “Centre National de Contro Semences” (CNCC) in Algiers for providing the common bean cultivar. We thanks also the farmers of Setif region for supporting research collaboration. References [1] W.F. Cong, E. Hoffland, L. Li, J. Six, J.H. Sun, X.G. Bao, F.S. Zhang, W. Van Der Werf, Intercropping enhances soil carbon and nitrogen, Glob. Change Biol. 21 (2015) 1715e1726. [2] M. Latati, A. Bargaz, B. Belarbi, M. Lazali, S. Benlahrech, S. Tellah, G. Kaci, J.J. Drevon, S.M. Ounane, The intercropping common bean with maize

18

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

M. Latati et al. / European Journal of Soil Biology 80 (2017) 9e18 improves the rhizobial efficiency, resource use and grain yield under low phosphorus availability, Eur. J. Agr 72 (2016 a) 80e90. R.M. Callaway, Direct mechanisms for facilitation, in: R.M. Callaway (Ed.), Positive Interactions and Interdependence in Plant Communities, Springer, Dordrecht, The Netherlands, 2007, pp. 15e59. S. Steinbeiss, H. Bessler, C. Engels, V.M. Temperton, N. Buchmann, C. Roscher, Y. Kreutziger, J. Baade, M. Habekost, G. Gleixner, Plant diversity positively affects short-term soil carbon storage in experimental grasslands, Glob. Change Biol. 14 (2008) 2937e2949. M. Pansu, Y. Martineau, B. Saugier, A modelling method to quantify in situ the input of carbon from roots and the resulting C turnover in soil, Plant Soil 317 (2009) 103e120. M. Latati, D. Blavet, N. Alkama, H. Laoufi, M. Pansu, J.J. Drevon, F. Gerard, S.M. Ounane, The intercropping cowpea-maize improves soil phosphorus availability and maize yields in an alkaline soil, Plant Soil 385 (2014) 181e191. N. Alkama, G. Ounane, J.J. Drevon, Is genotypic variation of Hþ efflux under P deficiency linked with nodulated-root respiration of N2 fixing common-bean (Phaseolus vulgaris L.)? J. Plant Physiol. 169 (2012) 1084e1089. G. Corre-Hellou, Y. Crozat, Assessment of root system dynamics of species grown in mixtures under field conditions using herbicide injection and 15N natural abundance methods: a case study with pea, barley and mustard, Plant Soil 276 (2005) 177e192. L. Li, D. Tilman, H. Lambers, F.S. Zhang, Plant diversity and over yielding : insights from belowground facilitation of intercropping in agriculture, New Phytol. 203 (2014) 63e69. M. Latati, M. Pansu, J.J. Drevon, S.M. Ounane, Advantage of intercropping maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) on yield and nitrogen uptake in Northeast, Int. J. App. Sci. 01 (2013) 23e29. M. Lazali, S. Brahimi, C. Merabet, M. Latati, C. Benadis, R.T. Maougal, D. Blavet, J.J. Drevon, S.M. Ounane, Nodular diagnosis of contrasting recombinant inbred lines of Phaseolus vulgaris in multi-local field tests under Mediterranean climate, Eur. J. Soil Biol. 73 (2016) 100e107.
rard, Root induced processes conN. Devau, P. Hinsinger, E. Le Cadre, F. Ge trolling phosphate availability in soils with contrasted P-fertilized treatments, Plant Soil 348 (2011) 203e218. E. Bünemann, B. Prusisz, K. Ehlers, Characterization of phosphorus forms in soil microorganisms, in: E. Bünemann, A. Oberson, E. Frossard (Eds.), Phosphorus in Action, Springer, Berlin Heidelberg, 2011, pp. 37e57. J.V. Cotner, D.L. Montoya, K.O. Winemiller, Seasonally variable riverine production in the Venezuelan llanos, J. North Amer. Benthol. Soc. 206 (2006) 171e184. J.T. Scott, J.B. Cotner, T.M. La Para, Variable stoichiometry and homeostatic regulation of bacterial biomass elemental composition, Fron. Microb. 3 (2012) 1e8. X. Tang, L. Bernard, A. Brauman, T. Daufresne, P. Deleporte, D. Desclaux, G. Souche, S.A. Placella, P. Hinsinger, Increase in microbial biomass and phosphorus availability in the rhizosphere of intercropped cereal and legumes under field conditions, Soil Biol. Biochem. 75 (2014) 86e93. M.S. Verma, P.Z. Chena, L. Jonesa, F.X. Gu, Chemical nose for the visual identification of emerging ocular pathogens using gold nanostars, Bios. Bioelect 61 (2014) 386e390. M. Yang, G. Ding, L. Shi, J. Feng, F. Xu, J. Meng, Quantitative trait loci for root morphology in response to low phosphorus stress in Brassica napus, Theo. App. Gen. 121 (2010) 181e193. Q.Z. Li, J.H. Sun, X.J. Wei, P. Christie, F.S. Zhang, L. Li, Over yielding and interspecific interactions mediated by nitrogen fertilization in strip intercropping of maize with faba bean, wheat and barley, Plant Soil 339 (2011) 147e161. X. Xu, P.E. Thornton, W.M. Post, A global analysis of soil microbial biomass carbon, nitrogen and phosphorus in terrestrial ecosystems, Glob. Ecol. Biogeo 22 (2013) 737e749. G.R. Valizadeh, Z. Rengel, A.W. Rate, Response of wheat genotypes efficient in P utilization and genotypes responsive to P fertilization to different P banding depths and watering regimes, Aus. J. Agri. Res. 54 (2003) 59e65. S.R. Olsen, C.V. Cole, F.S. Watanabe, L.A. Dean, Estimation of Available Phosphorus in Soil by Extraction with Sodium Bicarbonate, USDA, Washington DC, USA, 1954. A.L. Shen, X.Y. Li, T. Kanamori, T. Arao, Effect of long-term application of compost on some chemical properties of wheat rhizosphere and nonrhizosphere soils, Pedosphere 6 (1996) 355e363. T. Chevallier, E. Blanchart, E. Albrecht, J.L. Chotte, V. Eschenbrenner, M. Voltz,

[25]

[26] [27] [28] [29]

[30]

[31] [32] [33] [34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43] [44] [45]

[46]

[47]

M. Mahieu, Restoration of C content andearth worm population in a vertisol under pasture (Martinique), in: World Congress of Soil Science, Proceedings, Montpellier, 1998, 8pp. P.C. Brookes, J.F. Kragt, D.S. Powlson, D.S. Jenkinson, Chloroform fumigation and the release of soil nitrogen : the effects of fumigation time and temperature, Soil Biol. Biochem. 17 (1985) 831e835. D.S. Jenkinson, P.C. Brookes, D.S. Powlson, Measuring soil microbial biomass, Soil Biol. Biochem. 36 (2004) 5e7. R.G. Joergensen, The fumigation-extraction method to estimate soil microbial biomass: calibration of the KEC value, Soil Biol. Biochem. 28 (1996a) 25e31. R.G. Joergensen, The fumigation-extraction method to estimate soil microbial biomass: calibration of the KEN value, Soil Biol. Biochem. 28 (1996b) 33e37. F. Zhang, S. Zhang, J. Zhang, R. Zhang, F. Li, Nitrogen fertilization on uptake of soil inorganic phosphorus fractions in the wheat root zone, Soil Sci. soci. Amer. J. 68 (2004) 1890e1895. E. Betencourt, M. Duputel, B. Colomb, D. Desclaux, P. Hinsinger, Intercropping promotes the ability of durum wheat and chickpea to increase rhizosphere phosphorus availability in a low P soil, Soil Biol. Biochem. 46 (2012) 21e33. J.P. Kaye, S.C. Hart, Competition for nitrogen between plants and soil microorganisms, Tree 12 (1997) 139e143. H. Marschner, Mineral Nutrition of Higher Plants, second ed., Academic Press, London, 1995. M. Stitt, Nitrate regulation of metabolism and growth, Curr. Opin. Plant Biol. 2 (1999) 178e186. A. Hodge, J. Stewart, D. Robinson, B.S. Griffiths, A.H. Fitter, Competition between roots and soil micro-organisms for nutrients from nitrogen-rich patches of varying complexity, J. Ecol. 88 (2000) 150e164. S. Bazot, J. Mikola, C. Nguyen, C. Robin, Defoliation-induced changes in carbon allocation and root soluble carbon concentration in field-grown Lolium perenne plants: do they affect carbon availability, microbes and animal trophic groups in soil? Funct. Ecol. 19 (2005) 886e896. K.Z. Mganga, B.S. Razavi, Y. Kuzyakov, Microbial and enzymes response to nutrient additions in soils of Mt. Kilimanjaro region depending on land use, Eur. J Soil Biol. 69 (2015) 33e40. A.H.C.M. Schapendonk, P. Dijkstra, J. Groenwold, C.S. Pot, S.C. Van de Geijn, Carbon balance and water use efficiency of frequently cut Lolium perenne L. swards at elevated carbon dioxide, Glob. Change Biol. 3 (1997) 207e216. E. Casella, J.F. Soussana, Long-term effect of CO2 enrichment and temperature increase on the carbon balance of a temperate grass ward, J. Exp. Bot. 48 (1997) 1309e1321. D.L. Jones, P.R. Darrah, Re-sorption of organic components by roots of Zea mays L. and its consequences in the rhizosphere. I. Re-sorption of 14C-labelled glucose, mannose and citric acid, Plant Soil 143 (1992) 259e266. B.S. Razavi, M. Zarebanadkouki, E. Blagodatskaya, Y. Kuzyakov, Rhizosphere shape of lentil and maize: spatial distribution of enzyme activities, Soil Biol. Biochem. 96 (2016) 229e237. M. Lazali, J.J. Drevon, The nodule conductance to O2 diffusion increases with phytase activity in N2-fixing Phaseolus vulgaris L, Plant Physiol. Biochem. 80 (2014) 53e59. N. Alkama, B.I. Bolou, E. Bolou, H. Vailhe, L. Roger, S.M. Ounane, J.J. Drevon, Genotypic variability in P use efficiency for symbiotic nitrogen fixation is associated with variation of proton efflux in cowpea rhizosphere, Soil Biol. Biochem. 41 (2009) 1814e1823. S. Liang, J. Grossman, W. Shi, Soil microbial responses to winter legume cover crop management during organic transition, Eur. J Soil Biol. 65 (2014) 15e22. Y. Kuzyakov, Review: factors affecting rhizosphere priming effects, J. Plant Nutr. Soil Sci. 165 (2002) 382e396. M. Latati, S. Benlahrech, M. Lazali, Tellah Sihem, G. Kaci, R. Takouachet, N. Alkama, F.Z. Hamdani, E.A. Hafnaoui, B. Belarbi, G. Ounane, S.M. Ounane, Intercropping promotes the ability of legume and ccereal to facilitate phosphorus and nitrogen acquisition through root- induced processes, in: Aakash Kumar Goyal (Ed.), Grain Legumes, E-Publishing Intech, Croitia, 2016b, pp. 127e139, http://dx.doi.org/10.5772/63438. H. Ibrahim, A. Hatira, M. Pansu, Modeling the functional role of microorganisms in the daily exchanges of carbon between atmosphere, plants and soil, Proc. Env. Sci. 19 (2013) 96e105. H. Ibrahim, M. Pansu, D. Blavet, A. Hatira, P. McDonald, M. Bernoux, J.J. Drevon, Modeling the continuous exchange of carbon between living organisms, the soil and the atmosphere, Plant Soil (2015), http://dx.doi.org/10.1007/s11104015-2665-4.