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Aboveground litter is a key factor for carbon sequestration in territorial ecosystems as well as soil conservation in erosion-derived,degraded areas.On the Loess Plateau,understanding aboveground litter contribution to soil respiration(LC) enhances the investigation of soil C dynamics as a consequence of litter accumulation accompanying vegetation restoration.Aboveground litter manipulation was carried out in a 26-year-old black locust plantation(Robinia pseudoacacia) in the Wangdong catchment in the gully region of the Loess Plateau.Litter treatments consisted of no litter(NL,aboveground litter excluded from plots),control(CK,normal litter inputs allowed),and double litter(DL,aboveground litter doubled by adding litter removed from NL plots).There were three plots in each treatment,and the plot size was 1.5 m×1.5 m.Three polyvinyl chloride(PVC) collars were installed along the diagonal in each plot.Soil respiration rates(Rs) were measured approximately once every two weeks in 2009 decreasing to once every four weeks in 2010 during the period of April to October in both years using a Li-8100 closed chamber system(Li-COR,Lincoln,NE,USA).In total,Rs was measured on 19 occasions during the two-year period.Concurrent with each respiration measurement,soil temperature at the 5-cm depth was measured using a Li-Cor thermocouple while soil moisture content at the 5-cm depth was also measured using a hand-held frequency-domain reflectometer(ML2x,Delta-T Devices Ltd,UK) at five locations close to the outer edge of each PVC collar.During the experimental period,the mean Rs in CK was 3.23 μmol m-2 s-1.DL significantly increased Rs in CK by 26%(P = 0.091) while NL significantly decreased Rs in CK by 22%(P=0.099).The maximum difference between the Rs of DL(or NL) and the Rs of CK occurred from July to September when air temperatures were high and rainfall was sufficient.Soil temperatures showed no treatment differences(P=0.48) but the difference of soil moisture contents within treatments was significant(P 0.01).The cumulative CO2-C emissions from NL,CK and DL were 631,787 and 973 g C m-2 a-1,respectively.The Rs of NL,CK and DL had significant exponential correlation(R2=0.81 to 0.90;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 was 1.92,2.29 and 2.31,respectively.And annual mean contribution rate of aboveground litter to soil respiration was 20%.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).The aboveground litterfall was 213 g C m-2 a-1,which was greater than the release of C from respiration caused by aboveground litter(156 g C m-2 a-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 contributing to the carbon pool in the ecosystem undergoing vegetation restoration and soil conservation measures on the Loess Plateau,at least in the near future. |
