Forest harbors the largest carbon reservoir in the terrestrial ecosystems. The conversion of forest types may lead to significant changes in soil carbon pools and carbon mineralization. We collected soil samples at 0-10 cm depth converted from Castanopsis carlesii natural forests (NF) to C. carlesii plantations (CC) and Cunninghamia lanceolata plantations (CF) at both Chenda and Xinkou sites in Sanming, Fujian Province to analyze the differences in soil organic carbon mineralization among the three forest types by laboratory incubation. We examined the effects of abiotic variations caused by forest conversion on soil organic carbon (SOC) mineralization, including SOC, total nitrogen (TN), iron and aluminum oxides, mean weight diameter (MWD) of aggregates, and particle size composition. The results showed that the contents of SOC, TN, and MWD differed significantly among the three forest types at both sites, which followed the order of NF>CC>CF. The iron and aluminum oxide contents in CF were significantly lower than those in NF and CC. The sand content in NF was significantly higher than those in CC and CF, while the silt content showed an inverse pattern. The clay content in CC was significantly higher than those in NF and CF. The cumulative carbon mineralization per unit soil (Cm-soil) was significantly affected by stand type, with the Cm-soil in CC and CF stands being 11.3% and 23.3% lower than in NF stands, respectively. The cumulative carbon mineralization per unit soil organic carbon (Cm-SOC) was significantly affected by the interaction between forest types and sites, in that the Cm-SOC in NF stands was 32.8% lower than that in CF at the Chenda site but without differences among forest types at Xinkou site. The Cm-soil positively and significantly correlated with SOC content at both sites, with MWD on the Chenda site, with iron oxide on the Xinkou site, respectively. However, the correlations between Cm-soil and MWD or iron oxides became no significance after introducing SOC as the controlling factor in partial correlation analysis, which suggested that the SOC mediated the relationships between Cm-soil and MWD or iron oxides at both sites. Overall, the conversion of natural forest to plantations could decrease soil C mineralization, due to the decline of SOC content. The effect of aggregate stability, iron and aluminum oxides on soil carbon mineralization varied depending on the site.
森林碳库是陆地生态系统最大的碳库,森林类型转换会引起土壤碳库及碳矿化的显著变化。本研究采用室内培养法分析了福建三明陈大站点和莘口站点的米槠天然林(NF)及由米槠天然林转换而来的米槠人工林(CC)和杉木人工林(CF)0～10 cm表层土壤有机碳矿化的差异,探究了土壤有机碳(SOC)、总氮(TN)、铁铝氧化物、团聚体平均重量直径(MWD)、颗粒组成等非生物因素变化对SOC矿化的影响。结果表明: 两处站点不同林分间SOC、TN含量和MWD均表现为NF>CC>CF,两两差异显著;CF的铁、铝氧化物含量均显著低于NF和CC;NF砂粒含量显著高于CC和CF,而粉粒含量显著低于CC和CF,CC的黏粒含量显著高于NF和CF。单位土壤累积碳矿化量(Cm-soil)受林分类型的显著影响,CC和CF林分的Cm-soil分别比NF林分降低11.3%和23.3%;单位有机碳的累积碳矿化量(Cm-SOC)受林分类型与站点交互作用的显著影响,陈大站点内NF林分的Cm-SOC比CF林分降低32.8%,而莘口站点内各林分间则无显著差异。相关分析表明,两处站点的Cm-soil均与SOC呈极显著正相关;陈大站点Cm-soil与MWD呈显著正相关,莘口站点Cm-soil与氧化铁呈显著正相关,但以SOC为控制变量的偏相关分析则显示,Cm-soil与MWD或氧化铁的相关性均不显著,表明SOC介导了不同站点MWD或氧化铁对Cm-soil的影响。综上,天然林转换为人工林会降低土壤碳矿化,主要受森林转换引起的SOC含量下降的影响,而团聚体稳定性和铁铝氧化物对土壤碳矿化的影响因站点而异。.
Keywords: aggregate stability; humid subtropics; iron and aluminum oxide; land use; soil organic carbon mineralization.