Plant-Soil interactions control CNP coupling and decoupling processes in agroecosystems with perennial vegetation

In terrestrial ecosystems, plants are the transducers that provide the energy for microbial metabolism through root exudation, cell sloughing, and the input of leaf and root litter. They have profound impacts on biogeochemical cycles and are pivotal control points in the soil for the regulation of ecosystem biogeochemistry. Plant biomass is composed of C-, N-, and P-containing molecules, which are synthesized during plant growth after assimilation of atmospheric CO2 and mineral nutrients, thus leading to coupling of elemental cycles. Plant-derived litter compounds will undergo different fates depending upon their properties, their localization, and availability to the soil microbial biomass. Microbial degradation leads to decoupling of C, N, and P cycles, and it results in CO2 emission and nutrient release. Soluble N and P forms are susceptible to be lost from the system if not taken up by plants or microorganisms. On the other hand, microbial activity stimulated by plant-derived organic matter input may also reuse these mineral N and P and recouple them with C. All three processes may be influenced by plant activity. Plants are able to control microbial processes by exudation of signalling molecules and to closely interact with rhizosphere microorganisms. In addition, CNP coupling and decoupling may be controlled by plants through their symbiosis with mycorrhizal fungi. The aim of this chapter is to shed light on plants' impact on the processes involved in the coupling and decoupling processes, which control stoichiometric relationships in different ecosystems, and to show how they control carbon sequestration and other ecosystem services. By understanding the plants' control on CNP cycles, important advances for the understanding of biogeochemical feedbacks, which may ultimately constrain long-term ecosystem responses to global change, can be achieved.