Allocation Of Photosynthesized Carbon To Rice-Soil-Microbial Community System Under Nitrogen Application

Carbon cycling of soil is a critical process of the flow of matter and energy in terrestrial ecosystems, in which the agricultural soil carbon cycling which is closely related to human activity has been more concerned. As an important source of farmland soil organic carbon, the production, input to soil, allocation and fixed of photosynthesized carbon deserved deep investigation. Nitrogen (N) is the one of nutrition elements affecting photosynthesized carbon input and distribution which make great sense in crop growth and production. In order to clearly understand the influence of N application in photosynthesized carbon input and distribution, find process of farmland soil carbon cycling, we determined Allocation of photosynthesized carbon to Rice-Soil-Microbial Community System under Nitrogen Application.A13C-labelled microcosm experiment was carried out to quantify the input of photosynthesized carbon into soil and allocation in soil active carbon pool, soil aggregate fractionation, chemical fractionation of soil humus and soil microbial communities in a rice-soil system during tillering stage. Growing rice (Oryza sativa L.) was continuously fed13C-labeled CO2(13C-CO2) in a closed chamber without nitrogen (NO), or at different rates of nitrogen application (10,20,40,60mg N kg-1soil (N10, N20, N40or N60)). The main research results are as follows.(1) Nitrogen levels significantly affected the growth of rice plant and the input of photosynthesized carbon in rice-soil system. After cultivation of18-day-labeled, N levels made significant different in rice plant biomass, which the amount of shoots and roots were1.58～4.35g·plot-1and1.05-2.44g·plot-1, respectively, and increased with the N levels increase. Labeled13C input into shoots and roots were44.0～157.6g·plot-1and8.3～49.4g·plot-1respectively. The total labeled13C input into rice-soil system was63.4～233.0mg·kg-1showed that N application enhance the process. The percentage of13C incorporation in shoot, roots and soil in the rice-soil system were68.0～71.4%,11.8～21.4%and10～20%, as the percentage of13C incorporation in shoot had nothing significant with N levels.(2) Photosynthesized carbon allocation in soil activated carbon pool (DOC, MBC), soil aggregate fractionations (2-0.25mm,0.25-0.053mm,<0.053mm) and chemical fractionation of soil humus (FA, HA, Hu) were significantly influenced by N application. The amount of13C-DOC and13C-MBC in soil was4.82々14.51ug·kg-1and540.04～1484.40μg·kg-1, which showed that photosynthesized carbon input increase the amount of soil activated carbon pools. The13C-DOC,13C-MBC as proportions of total DOC, MBC respectively, were0.08～0.25%and0.04-0.11%under five N levels, obviously, the13C-MBC’s is more than the13C-DOC’s. N application levels affects allocation of13C in2-0.25mm and0.25-0.053mm soil aggregate fractionations, but did not make different in <0.053mm. The amount of13C in2-0.25mm,0.25-0.053mm and <0.053mm soil aggregate fractionations were1.32～7.00mg·kg-1,2.02‖4.13mg·kg-1and0.48～1.14mg·kg-1, respectively, the<0.053mm’s was smaller than other two. The distribution of photosynthesized carbon in HA, Hu, FA soil humus followed the sequence as13C-HA<13C-Hu<13C-FA, the amount were0.23～0.46mg·kg-1,1.87-5.89mg·kg-1, and3.24～8.43mg·kg-1.(3) The increase of N levels promoted soil microbial communities, mainly the increase of total PLFA and Fungi PLFA. The13C-PLFA of soil microbial communities followed a sequence as Fungi>G+>G->Actinomycetes>AM Fungi, N levels enhanced the ability of soil microbial communities use the13C, especially Fungi, G+and G". The amounts of13C-MBC and13C-PLFA showed the same trend with the increase of N application, it indicated that MBC and PLFA express the activity of soil microbial communities in coherence. We found that13C-Root/13C-Shoot value significantly influence the formation of soil microbial communities in Rice-Soil system.Analyzed the correlation of photosynthesized carbon allocation in rice, soil, microbial communities comprehensively, we found that rice biomass,13C in plant,13C-SOC,13C in soil aggregate fractionations (2-0.25mm,0.25-0.053mm,<0.53mm),13C in soil humus (FA、HA),13C in soil activated carbon pool (DOC, MBC) and soil microbial communities are different significant positive correlations. The correlation number of13C-Hu with other parts is lower than0.5, showed no correlation because of it’s character. N application levels significantly influenced the input and allocation of photosynthesized carbon into plant-soil-microbial community system, and they show differences on account of different location and formation.