Soil Respiration Of Different Ecosystems And Its Influencing Factors In Loess Plateau

Soil respiration is the key ecological process, and plays an important role in carbon cycle of terrestrial ecosystem. Gullied Loess Plateau was with fragmented topographies, diverse land use cover. Understanding soil respiration under different landuses conditions is critical to estimate carbon cycle at regional scale in Loess Plateau of China. At the present study, soil CO2emission in cropland, grassland and woodland ecosystem was measured by an automated soil CO2system (Li-8100, Li-COR, Lincoln, NE, USA) in the Loess Plateau. The relations of soil CO2emission to soil moisture, and soil temperature were explored among the three ecosystems of cropland, grassland and woodland. Our objectives at the present study are as follows:First, study the contribution of aboveground litter in the black Locust Plantation.Second, in cropland and its adjacent grassland, we determined if landuse change could alter soil CO2efflux under similar edaphic and climate conditions with conversion of arable land into grassland or forest land.Third, what are the effects of water and temperature on soil respiration when arable land is converted into grassland or forest land.The main results of this study are as follows:Aboveground litter accumulation can affect soil respiration and the carbon accumulation of the terrestrial ecosystems. DL significantly increased Rs in CK by26%(p=0.091) while NL significantly decreased Rs in CK by22%(p=0.099). The cumulative CO2-C emissions from NL, CK and DL were631,787and973g C m-2year-1, respectively. And annual mean contribution rate of aboveground litter to soil respiration was20%. The aboveground litterfall was 213g C m-2year-1, which was greater than the release of C from the respiration caused by aboveground litter (156g C m-2year-1). This result has strong implications for soil C storage, indicating that aboveground litter accumulation in this young black locust plantation may be expected to continue contribute the carbon pool in the ecosystem undergoing vegetation restoration and soil conservation measures on the Loess Plateau, at least in the near future.In cropland and its adjacent grassland, landuse change could alter soil CO2efflux under similar edaphic and climate conditions. We found marked differences in soil respiration related to different landuse:the mean cropland soil respiration (1.35μmol m-2s-1) averaged24%less than paired grassland soil respiration (1.67μmol m-2s-1)(p<0.05) during the period of experiment. The extent of soil respiration of cropland varied from-0.02to3.41μmol m-2s-1and its mean value was1.67μmol m-2s-1. The grassland was varied from0.12to3.83μmol m-2s-1, and its mean value was1.67μmol m-2s-1. The difference was occurred in summer and autumn, which was higher. In summer and autumn, the mean values of soil respiration of cropland was2.19and1.18μmol m-2s-1, which grassland was25%and32%higher than the values of cropland. And the cumulative CO2-C emission in grassland (856g C m-2) was23%higher than that in cropland (694g C m-2).The effects soil water or temperature on soil respiration under the conditions of environmental change. In woodland ecosystem, the temperature of different treatments showed an order of DL> NL> CK, but there was no significant difference among them. Like soil temperature, soil moisture increased with time going on. The moisture had a significant difference among these treatments (p<0.01). The Rs of NL, CK and DL had significant exponential correlation (R2=0.81to0.90; p<0.0001) with soil temperature but had unclear relationships with soil moisture. The temperature sensitivity of soil respiration, Q10, in NL, CK and DL was1.92,2.29and2.31, respectively. Correlation analysis showed that litter contribution on every measurement day had significant positive correlativity with soil temperature (r=0.54, p<0.05) or moisture (r=0.68,p<0.05)In cropland and grassland ecosystem, soil temperature at5cm was2.5℃higher in grassland during the period of experiment (p<0.05). The moisture of cropland was15.5%, grassland14.4%, that is, there was no significant between them. Regression of soil temperature vs. soil respiration indicated significant exponential relationships both in grassland and cropland, explaining79%of the variation in soil respiration in grassland, compared to82%in cropland. Besides, there were intrinsic differences in response of soil respiration to temperature between the cropland and grassland ecosystems:grassland and cropland respiration response was significantly different at the a=0.05level, also expressed by a higher temperature sensitivity of soil respiration (Q10) in cropland (2.13) relative to grassland (1.81). Soil temperature difference between cropland and grassland can explain the Rs difference caused by landuse change, which was confirmed by the validation results. But soil moister that have unclear relationship with soil respiration cannot explain.