Abstract
AimsThe theory of ecological stoichiometry mostly builds on studies of natural terrestrial ecosystems, whereas only limited stoichiometry information is available in response to agronomic practices.MethodsWe designed a greenhouse experiment in order to disentangle the specific role of cover crop identity and soil characteristic in affecting nutrient stoichiometry of a plant-microbe-soil system.ResultsNutrient ratios of cover crop biomass were species-specific and the growth rate explained, for most species considered, the stoichiometric differences in response to soil type. In contrast, the nutrient stoichiometry of soil microbes was more homeostatic and did not respond to either cover crop identity or soil type. Compared to bare soil, the presence of cover crop enhanced microbial phosphorus immobilization in the clay-rich soil, whereas it promoted microbial carbon biomass and microbial nitrogen immobilization in the sandy-rich soil. A greater microbial cumulative respiration in clay soils, where a higher microbial biomass C at the beginning of the incubation was observed, suggested a major role of soil type, compared to cover crop identity, in affecting microbial metabolism.ConclusionsBy understanding the stoichiometric constraints in the plant-microbe-soil system, our findings can help to implement agro-ecological practices by selecting appropriate cover crop species in relation to soil type in order, for example, to avoid nutrient limitation due to microbial nutrient immobilization.
Highlights
Cover crops, known as green manure crops, represent an important management component of conservation agriculture in association with crop rotation and notillage (Hobbs et al 2008)
In the case of soil microbial biomass, there was a positive correlation between microbial C and N concentration in both clay and sandy soil (Pearson’s r > 0.65, p < 0.01, n = 16), but no correlation was found between microbial C and P or between microbial N and P concentration (p > 0.15)
By comparing the same plant species treatment between the two soil types, we found that nutrient ratios of microbial biomass did not differ in response to B. juncea, A. strigosa, and L. albus, whereas with P. sativum the microbial biomass C:N ratio was higher in clay soil (Table 2)
Summary
Known as green manure crops, represent an important management component of conservation agriculture in association with crop rotation and notillage (Hobbs et al 2008). The selection of certain cover crop species can provide a tool for steering soil microbial composition in order to assure an adequate nutrient availability for subsequent cash crops (Bender et al 2016; Mariotte et al 2018; Verzeaux et al 2017; Vukicevich et al 2016) Such a management strategy must rely on an accurate knowledge of plant-microbe-soil interactions, in particular considering that microbial metabolism can be affected by root exudates of cover crops, nutrient demands of cover crops, soil type and local climatic conditions (Bell et al 2014; Carrillo et al 2017; Kim et al 2020; Mukumbareza et al 2016; Rosenzweig et al 2017;). This is important if we want to optimize microbial and plant performances to secure crop yields, and to improve soil carbon (C) sequestration and, more broadly, to properly adopt ecologically sustainable agricultural practices (Kallenbach et al 2019; Ptacnik et al 2005)
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