Effect of N and P fertilization on the allocation and fixation of photosynthesized carbon in paddy soil

Abstract

ABSTRACT Photosynthetically fixed carbon (C) plays a crucial role in regulating soil organic carbon (SOC) sequestration in ecosystems. However, its allocation and fixation in SOC fractions in response to nitrogen (N) and phosphorus (P) application in paddy soil remains unclear. Thus, Potted rice seedlings independently treated with N, P, and NP were continuously 13CO2 labeled to investigated the influence of N and P application on the contribution of newly photosynthesized C to the rhizosphere versus bulk soil and particulate organic matter (POM) versus mineral fraction (MIN). N and NP enhanced net assimilated 13C on day14 (D14) (3.28 and 4.81 g13C m−2, respectively), with maximum C assimilation (16.64 g 13C m−2) occurring on day22 (D22) under NP. Aboveground biomass retained more 13C than belowground biomass for all treatments (55-77% vs 25-44 %). 13C incorporation into the rhizosphere exceeded that in bulk soil, with the maximum (6-10 %) found under N addition. The amount of newly assimilated 13C incorporated into POM increased in the rhizosphere under N and NP conditions, whereas MIN remained largely unaffected. 13C-MBC proportion in the total microbial biomass C (MBC) pool revealed that N and NP stimulated microbial activity to a greater degree than P. The main portion of 13C in the rhizosphere and bulk soil was found in POM on D14, which decreased over time due to microbial utilization. Contrastingly, root-derived 13C in the MIN remained unchanged between sampling days, which indicates that the stabilization of rhizodeposits in this fraction might be the potential mechanism underlying SOM sequestration in paddy soils.