亚热带杉木和米老排人工林土壤呼吸对凋落物去除和交换的响应

Contrasting responses of soil respiration to litter manipulation in subtropical Mytilaria laosensis and Cunninghamia lanceolata plantations

在我国亚热带地区米老排(Mytilaria laosensis)和杉木(Cunninghamia lanceolata)人工林中设置去除凋落物、交换凋落物和对照3种处理,利用LI-8100对不同处理土壤呼吸速率进行为期14个月的连续观测。结果表明:与对照相比,去除和交换凋落物导致米老排人工林CO2年排放量显著减少29.8%和14.2%,杉木人工林则分别减少6.1%和增加37.8%。两种林分交换凋落物处理产生了不同程度的激发效应,米老排凋落物相对于杉木凋落物具有更大的激发效应。不同处理土壤呼吸速率均与土壤温度呈显著指数关系,与土壤含水量呈负相关,土壤温度和含水量的回归模型可以分别解释米老排人工林中去除、交换和对照处理土壤呼吸速率的68.9%、77.0%和69.6%,杉木人工林的53.0%、36.2%和63.8%。两种林分不同处理土壤呼吸速率与土壤可溶性有机碳含量、微生物生物量碳含量以及主要微生物种群生物量显著相关。米老排人工林去除和交换凋落物处理均降低了土壤呼吸的温度敏感性Q10值,而杉木林中仅去除凋落物降低了Q10值。研究表明,土壤呼吸对凋落物输入方式改变的响应因树种而异,这种差异与凋落物输入的数量和质量及其对土壤易变性有机碳含量和微生物生物量的影响有关。

Future climate change is expected to alter the primary productivity of forest ecosystems, and thus potentially change the quality and quantity of aboveground litter inputs which could affect soil carbon emission and sequestration. A litter manipulation experiment was carried out in 19-year-old Mytilaria laosensis and Cunninghamia lanceolata plantations replanted in C. lanceolata woodland in subtropical China between January 2012 and February 2013. Three treatments including litter exclusion, reciprocal litter transplant and control were conducted within 2 m x2 m plots in randomized block design. Soil respiration rate （R,） were measured monthly by Li-Cor 8100 and soil temperature and soil moisture were also monitored. The results showed that Rs subject to three treatments exhibited similar seasonal patterns in M. laosensis andC.lanceolata plots. The average Rs in litter exclusion, litter transplant and control treatments were 1.79, 2.18, 2.45μmol CO2 m-2 s-1 in M.laosensis plots and 1.77, 2.29, 1.90μmol CO2 m-2 s-1 in C.lanceolata plots, respectively. Overall, litter exclusion and transplant significantly decreased the annual fluxes under M. laosensis plots by 29.8% and 14.2%, respectively. Litter exclusion caused a slight decline in annual flux but litter transplant markedly increased the annual flux by 37.8% in C.lanceolata plots. Using the decay constants of the two litter species in a reciprocal litter transplant decomposition experiment, priming effects were calculated as the amount of litter-derived respiration minus decomposed carbon from litter. Results showed that M. laosensis litter aroused higher priming effect than C. lanceolata litter, suggesting that the quantity and quality of litter input caused by different tree species could result in different below-ground responses. Correlations showed that Rs were exponentially correlated with the soil temperature and negatively correlated with the soil moisture under both M.laosensis and C.lanceolata plots. Non-liner regressions of soil temperature and soil moisture together accounted for 68.9%--77.0% and 36.2%--63.8% of monthly variation in soil respiration in M. laosensis and C.lanceolata plots, respectively, indicating that other factors were responsible for interpreting variations in Re. The average R2 was significantly correlated to soil dissolved organic carbon concentration （P = 0. 019 ） and microbial biomass carbon concentration （P = 0.037）, which suggests that litter manipulation induced changes in soil labile carbon caused significant effects on R. A one time-point measured soil PLFA profiles showed that the average Rs was significantly correlated with the biomass of main signature PLFAs such as fungi （18：1 w9c, 18：2 w6,9c）, which may imply that the high quality of litter input could alter soil microbial biomass and thus affect R. The temperature sensitivity （Q10） of R, decreased to 1.86 and 2. 05 in the litter exclusion and transplant plots compared to 2.14 in the control plots under M. laosensis plantations. However, the Q10 in the litter exclusion, litter transplanting and control plots were 1.40, 1.52 and 1.52 in C. lanceolata plantations, respectively, which are lower than other studies in subtropical China. In summary, we concluded that the effects of litter manipulation on Rs were dependent on tree species, the contributions of litter to R~. can be attributed to the quantity and quality of litter input, the changes in soil labile carbon and soil microbial biomass in subtropical forest plantations.