Effects Of Fertilization And Understory Vegetation Management On Soil Labile Carbon Pools And Soil Greenhouse Gas Emissions In Chinese Chestnut Stands

Management practices of plantation have a significant influence on the carbon (C) cycling in ecosystems and global climate change. Researches on the effects of management practices on soil C pools and soil greenhouse gas (GHG) emissions would have a vital significance for revealing the response of ecosystems to forest management practices and associated mechanisms, and scientific estimates of C sequestration function of plantation ecosystems. Chinese chestnut (Castanea mollissima) is one kind of very important economic forest tree species in China and widely distributed in26provinces and cities, accounted for approximately38%of the total world cultivation area and75%of the total world production. With the industrial structure adjustment, adoption of intensive management, mainly including chemical fertilizer application and understory vegetation removal, is becoming more and more common in the Chinese chestnut stands, which would probably have a significant effect on the soil C pools and GHG emissions. In our study, the effects of different fertilizers and understory vegetation managements on soil C dynamics in Chinese chestnut stands were investigated from June2011to June2012in Lin’an, Zhejiang Province. Soil GHG emission fluxes were analyzed by the method of static closed chamber/GC technique, and soil temperature, soil water content, and concentrations of WSOC and MBC were determined as well. On this basis, we had investigated the response of the soil C pools and GHC emission fluxes to different forest management practices and explored the relationships between soil GHC emissions and various environmental factors.The main results obtained from this study were as follows:(1) Forest management practices have not changed the seasonal variations of soil greenhouse gas (GHG) emissions in the Chinese chestnut stands, with the highest rates of soil CO2and N2O fluxes appeared in summer, the lowest in winter; and with the uptake maximum of soil CH4fluxes in the early autumn, the minimum in the late winter or the early spring season;(2) In the fertilization treatments, annual accumulative of soil CO2, N2O and CH4fluxes were27.71t CO2hm-2yr-1,1.91kg N2O hm-2yr-1and-3.09kg CH4hm-2yr-1, respectively, in CK treatment, whereas the annual accumulative of soil CO2and N2O emissions were29.48%and69.34%,46.98%and104.43%,50.73%and92.59%, respectively, higher and the annual accumulative of soil CH4uptake fluxes were7.02%,1.65%and4.38%, respectively, lower in IF, OF and OIF treatments compared with the CK treatment (P<0.05); Additionally, soil WSOC and MBC concentrations were37.22%and13.90%,73.69%and35.48%,58.23%and44.57%higher in IF, OF and OIF treatment, respectively, compared with CK treatment (76.58and253.42mg kg-1, respectively)(P<0.05).(3) In the understory management treatments, compared with CK treatment (the annual accumulative of soil CO2, N2O and CH4fluxes were35.65t CO2hm-2yr-1、3.28kg N2O hm-2yr-1and-2.90kg CH4hm-2yr-1, respectively), understory removal (UR) can significantly increase the soil CO2emission and the soil CH4uptake fluxes.while decreasing the soil N2O emission fluxes (P<0.05); Medicago sativa L.(MS) and Lolium perenne L.(LP) plantation had significantly increasing effects on soil CC2and N2O emissions (P<0.05) and had a significant inhibitory effect on soil CH4uptake (P<0.05). Soil WSOC and MBC concentrations, compared with CK treatment (109.69and298.45mg kg-1, respectively), increased by24.64%and16.59%,18.01%and22.43%, respectively, in MS and LP treatments, while had no significant effects in UR treatment. In addition, there was no significant difference on soil labile carbon pools and GHG emissions between MS and LP treatments;(4) In the Chinese chestnut stands, soil CO2emission fluxes had a significant positive exponential relationship with soil temperature at depth of5cm (P<0.01), while soil N2O emission and soil CH4uptake fluxes had significant positive linear correlations with soil temperature at depth of5cm (P<0.05); In addition, soil GHG emissions had significant correlations with soil WSOC concentrations (P<0.05), while had no significant relationships with soil water contents and soil MBC concentrations.