In situ methods of plant-microbial interactions for nitrogen in rhizosphere

Nitrogen (N) is an essential element for plants and microorganisms. In most terrestrial ecosystems, N is a major nutrient limiting plant growth, leading to strong competition for N between roots and rhizosphere microorganisms. Given the importance of N, investigations of plant-microbial competition for N over time and space are a prerequisite for better understanding of net primary production, nutrient cycling and root-microbial interactions. Here we proposed an in situ approach using stable isotopes (15N and 13C) to quantify plant-microbial N and C flows. The approach is based on 15N and 13C partition between plants and microorganisms and allows to investigate the chemical (N forms), spatial (labeling depths) and temporal (seasons) parameters for better understanding ecological functions of belowground systems. In this method, quadrats are selected and labeled with 15N tracers (organic N forms also labeled with 13C), i.e., introducing 15N labeled NH4 + or NO3 −, or 15N and 13C dual labeled amino acids allows to quantifying uptake preferences by plants and/or microorganisms. Detailed calculations of the amount of 15N and 13C label are presented. Such approach is necessary for comparisons between studies, and to advance our knowledge of rhizosphere interactions in terrestrial ecosystems.