Nutrient stoichiometry of a plant-microbe-soil system in response to cover crop species and soil type

Plant Soil https://doi.org/10.1007/s11104-021-04853-9 REGULAR ARTICLE Nutrient stoichiometry of a plant-microbe-soil system in response to cover crop species and soil type Luca Bragazza & Mario Fontana & Thomas Guillaume & Kate M. Scow & Sokrat Sinaj Received: 16 October 2020 / Accepted: 18 January 2021 # The Author(s) 2021 Abstract Aims The theory of ecological stoichiometry mostly builds on studies of natural terrestrial ecosystems, whereas only limited stoichiometry information is available in response to agronomic practices. Methods We 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. Results Nutrient 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 sandyrich soil. A greater microbial cumulative respiration in clay soils, where a higher microbial biomass C at the Responsible Editor: Yolima Carrillo L. Bragazza (*) : M. Fontana : T. Guillaume : S. Sinaj Agroscope, Field-Crop Systems and Plant Nutrition, Research Division Plant Production Systems, Route de Duillier 50, P.O. Box 1012, CH-1260 Nyon, Switzerland e-mail: K. M. Scow Land, Air and Water Resources Department, UC Davis, One Shields Avenue, Davis, CA 95616, USA beginning of the incubation was observed, suggested a major role of soil type, compared to cover crop identity, in affecting microbial metabolism. Conclusions By 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. Keywords Agricultural soil . Ecological stoichiometry . Soil texture . Metabolic quotient . Cumulative soil respiration . Homeostasis Introduction Cover crops, also known as green manure crops, represent an important management component of conservation agriculture in association with crop rotation and notillage (Hobbs et al. 2008). Cover crops are typically used between two cash crops (i.e. main crops) as single species or a mixture of species in order to provide various ecological and agronomical benefits. Indeed, cover crops can, for example, protect the soil from erosion, reduce water and nutrient losses, improve soil organic matter content, promote soil biological activity, stabilize cash crop yields, and control weeds (e.g. Abdalla et al. 2019; Büchi et al. 2020; Finney et al. 2017; Martínez-García et al. 2018; McDaniel et al. 2014; Smith et al. 2008; Vukicevich et al. 2016; Wittwer et al. 2017). However, to optimize the benefits provided Plant Soil by cover crops, management practices must be adapted to local soil and climatic conditions (Abdalla et al. 2019; Romdhane et al. 2019). Different studies have shown that cover crops can increase soil microbial biomass and modify the structure of microbial communities (Buyer et al. 2010; Finney et al. 2017; Hontoria et al. 2019; Martínez-García et al. 2018; Schmidt et al. 2019). Accordingly, 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;). To this aim, the application of ecological stoichiometry concepts to the plant-microbe-soil system can provide helpful insights on how soil type, in combination with cover crop diversity, can affect not only the nutrient balance but also the functions of soil microbes and, ultimately, nutrient cycling in agroecosystems (Bertrand et al. 2019). This is particularly important if we want to optimize microbial and plant performances not only to secure crop yields, but also to improve soil carbon (C) sequestration and, more broadly, to properly adopt ecologically sustainable agricultural practices (Kallenbach et al. 2019; Ptacnik et al. 2005). The theory of ecological stoichiometry focuses on the balance of elements (i.e. the nutrient ratio) from individual-scale to ecosystem-scale in relation to available resources. The founding biogeochemical principles of ecological stoichiometry assume that organisms have consistent nutrient ratios, in particular C to nitrogen (N) to phosphorus (P), and that the abundance of nutrients in a system is regulated by the interactions between organisms and their environment (Elser et al. 1996; Sterner and Elser 2002). Stoichiometric homeostasis is defined as the degree to which the organism, or system, can maintain a relatively stable chemical composition (i.e. nutrient ratios) in response to variations in the composition and availability of external resources (Spohn 2016). For terrestrial ecosystems, it has been shown that, at global scale, autotrophic organisms (plants) are generally rather plastic (i.e. they have a greater stoichiometric flexibility) in terms of nutrient ratios compared to heterotrophs (e.g., soil organisms) that generally show more constrained nutrient ratios, i.e. they tend to be more homeostatic (Cleveland and Liptzin 2007). Ecological stoichiometry represents a helpful conceptual framework to understand the cycling of C, N and P nutrients at different spatial scales (Buchkowski et al. 2019; Sterner and Elser 2002). Currently most of ecological stoichiometry studies focus on aquatic ecosystems or natural terrestrial ecosystems with few studies relating ecological stoichiometry of crops, soil, and microbes to agricultural practices (Bertrand et al. 2019). To fill this knowledge gap, we designed a greenhouse experiment to understand the interactions between soil type (a clay versus a sandy soil), cover crop identity (four different species widely used in conservation agriculture) and soil microbes to answer the following questions: 1) How do plant and microbial stoichiometry vary in relation to soil type? 2) To what extent does the identity of cover crops affect soil microbial stoichiometry? 3) How do plant species and soil type interact in affecting microbial me (...truncated)