Natural fallow alleviates carbon and nitrogen limitation of microorganisms and plants in paddy fields

Carbon (C), nitrogen (N), and phosphorus (P) serve as critical limiting
factors for plant-microbe colonization and growth in agroecosystems, while
simultaneously functioning as key regulatory controls for soil C
emissions. Here, we investigated plant-microbial nutrient limitation under
two states of paddy fields (cultivation state and fallow state), assessing
synchronization patterns through combined analysis of plant resorption
efficiency and microbial ecoenzyme stoichiometry. We found that there was
a consistent pattern of N (25.00%) and P (44.44%) limitation between
plant-microbial communities. Plant-microbial communities were mainly
N-limited in the rice cultivation stage and P-limited in the fallow stage.
Nutrient limitation of plant-microbial communities was regulated by soil
C:N:P stoichiometry: the increase in available soil N:P led to P
limitation in plant communities, which enhanced the secretion of
organoheterocyclic compounds and organometallic compounds. This change
increased the relative abundance of Chloroflexi and Ascomycota, thereby
exacerbating microbial P limitation. Notably, the direct effect of
available soil N:P on microbial N:P limitation was as important as the
indirect effect through plant communities. The increased available soil
C:N exacerbated microbial C limitation primarily through changing
microbial composition. Overall, variations in stoichiometry of available
soil nutrients drove a transition from N to P limitation in
plant-microbial communities during fallow periods. We highlight that
fallowing is an important compensatory process to alleviate the C and N
limitation of plant-microbial communities resulting from long-term
agricultural monoculture patterns.