黄土高原刺槐人工林地表凋落物对土壤呼吸的贡献

于黄土高原沟壑区王东沟小流域26年刺槐人工林(Robinia pseudoacacia)中,设置对照(CK)、去除凋落物(no litter, NL)和倍增凋落物(double litter, DL)3个处理,利用Li-8100系统测定各处理的土壤呼吸速率。结果表明,添加或去除凋落物显著影响土壤呼吸(P = 0.091-0.099),与对照(CK)的土壤呼吸速率(3.23 μmol m^-2 s^-1)相比,添加凋落物(DL)使土壤呼吸速率增加26%,去除凋落物(NL)使土壤呼吸速率减少22%。NL、CK和DL的累积土壤呼吸分别为631、787和973 g C m^-2a^-1。各处理土壤呼吸速率与土壤温度呈显著的指数关系(R²=0.81-0.90,P < 0.0001),但与土壤水分的关系不明显。NL、CK和DL的Q₁₀依次为1.92、2.29和2.31。地表凋落物对土壤呼吸年平均贡献量为20%。相关性分析表明,各测定日地表凋落物贡献与土壤温度(r=0.54,P < 0.05)或土壤水分关系显著(r=0.68, P < 0.05)。刺槐人工林地表凋落物的输入量为213 g C m^-2a^-1,大于凋落物引起的呼吸量156 g C m^-2a^-1。在黄土区通过植被恢复治理水土流失过程中,随着地表凋落物的积累,林地生态系统的碳汇功能将逐步得到加强。

Aboveground litter contribution to soil respiration in a black locust plantation in the Loess Plateau

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.