Regulating Mechanism Of Carbon Sequestration By C: N: P Stoichiometry In Soil Under Conversion Of Cropland To Forest In Loess Hilly Region

Not only vegetation restoration is the main measures to restoration and reconstruction of soil ecosystem, but also the carbon sequestration benefits is key factors to estimate the effects of vegetation restoration. This study based on Green to Green Program(GTGP), through the methods of combining the historical data collection and field investigation, field experiment and indoor analysis, to study carbon sequestration benefits evolution process and its mechanism during ecological restoration and reconstruction, and analysis the change of carbon storage, C:N, C:P and N:P ration after GTGP. We were also using the typical sample sites to study carbon fractions and mechanism between carbon storage and soil stoichiometry. Illustrate their interactions after GTGP and analysis the regulatory mechanism between them. The main results are as follows:(1)‘GTGP’ Program in China plays a significant role in increasing soil carbon storages. Restoration age and vegetation types were the main factor affecting the present soil carbon sequestration.SOC sequestration due to GTGP was estimated to be 14.46 TG C/year(a rate of 0.54 Mg C/ha/year). The SOC sequestration significantly increased in forest lands(P<0.05), which was greater 18.7% and 42.9% than in shrub lands and grasslands, respectively. SOC sequestration increased with annual average precipitation. SOC sequestration significantly increased after 20 years later, however, the average rate of SOC accretion was highest before 10 years. Therefore GTGP resulted in increased SOC storage, making significant contribution to carbon sequestration in China.(2) The combined C, N and P stoichiometry in soil affect after GTGP, and affected by annual temperature and precipitation.The frequency distribution of the soil C:N, C:P, and N:P values reveal that the soil C:N, C:P, and N:P values were 8–16, 16–32, and 0–2, respectively. Vegetation types significantly affected the soil C:N, C:P, and N:P values and annual temperature and precipitation significantly affected the soil C:N, C:P, and N:P values all restoration stage. In addition, ‘‘Redfield–like’’ interactions between C, N and P in the soil may exist. A linear regression revealed significant positive correlations between the C:N, C:P, and N:P values and the restoration age, temperature, and precipitation after a change in land use. Therefore, large–scale changes in land use under the ‘GTGP’ program might significantly affect the C:N, C:P and N:P ratios in soil.(3) Topsoil C, N and P storage increased after ‘GTGP’, however the C, N and P storage in deep cannot be ignored. And the vegetation types greatly affect the C, N and P stoichiometry.soil C, N and P storage in 40–100 cm and 100–200 cm soil layer was increased 17.56–32.96% and 21.05–43.75%, 22.47–44.83% and 12.02–42.42%,10.34–33.00% and 27.86–59.46%. Indicate that vegetation restoration could significantly affect soil C, N and P storage in deep soil. C:P and N:P ration decreased with soil layer except C:N ration. And the C:N, C:P and N:P ration under vegetation types were higher than slope cropland.(4) Vegetation restoration was affected the carbon fractions in 0–200 cm soil layerThe dissolved organic carbon(DOC), particle organic carbon(POC), active organic carbon(LOC) were increased 23.52–64.28%,12.50–60.00%,0.52–38.35% and 1.18–24.70% in 0–10 cm,10–40 cm,40–100 cm and 100–200 cm soil layer; The light fraction organic carbon(LOFC) was increased 60.92–85.60%,5.97–30.38% and 7.77–10.82% in 0–10 cm,10–40 cm,40–100 cm soil layer; The microbial biomass carbon(MBC) was in creased 27.59–66.88%,22.25–41.21% and 6.39–32.85% in 0–10 cm,10–20 cm,20–30 cm soil layer. It is infer that as major factors, the carbon fractions in deep cannot be ignored.(5) The C, N and P stoichiometry and carbon fractions were characterization of each other, and both them could regulate the carbon storage.Vegetation restoration could affect the light fraction organic carbon(LOFC), the microbial biomass carbon(MBC) and active organic carbon(LOC) in 0–200 cm soil layer. Illustrate that vegetation restoration lead to different carbon sensitivity under different vegetation types and soil layers. C:N could greatly affect particle organic carbon(POC2–53μm), however, C:P and N:P could affect microbial biomass carbon(MBC) and active organic carbon(LOC). Meanwhile, there were the similarity among C:N, C:P and N:P ration under different vegetation types. It is indicated that The C, N and P stoichiometry and carbon fractions were characterization of each other, and both them could regulate the carbon storage.