Plant intraspecific competition and growth stage alter carbon and
nitrogen mineralization in the rhizosphere
Plant roots interact with rhizosphere microbes to accelerate soil
organic matter (SOM) mineralization and promote nutrient acquisition.
Root-mediated changes in SOM turnover largely depend on root-C input and
soil nutrient availability. Hence, interspecific competition and
nutrient uptake dynamics over plant development stages as well as
spatiotemporal variability in C input may modify SOM turnover. To
investigate the effect of intraspecific competition on SOM
mineralization at three growth stages (heading, flowering and ripening),
we grew maize (C4 plant) under three planting densities on a C3 soil.
13C-natural abundance and 15N-pool dilution were applied in situ to
determine C- and N-mineralization rates. Soil C- and N-mineralization
rates were tightly coupled and peaked at maize flowering. However, the
C-to-N-mineralization ratio increased with N, indicating that microbes
mineralize N-rich components to mine SOM for N. Furthermore,
intraspecific competition did not affect root biomass; instead, plants
shaped root morphology towards higher specific root length as an
efficient strategy competing for nutrient. Hence, root morphologic
traits rather than root biomass per se were positively related to C- and
N-mineralization. Overall, plant competition for nutrients controlled
the intensity and mechanisms of soil C- and N-turnover by the adaptation
of root traits and nutrient depletion.