改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。

Changes of above- and belowground carbon input affected soil microbial biomass and community composition in two tree species plantations in subtropical China

We employed Detritus Input and Removal Experiment (DIRT) to examine the effects of carbon (C) input on soil microbial biomass and community composition in 19-year-old Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) and Mytilaria laosensis forests in subtropical China. The treatments included:(1) reciprocal litter transplant; (2) litter removal; (3) no inputs (litter removal+ root trenching); and (4) control. Each treatment had four 2 m×2 m plots. From January to December 2012, we collected the top 5 cm soil layer samples monthly from C. lanceolata and M. laosensis plots. Chloroform fumigation-extraction was used to determine the soil microbial biomass C and nitrogen (N) contents. Phospholipid fatty acid (PLFA) analysis was used to characterize the microbial community composition in soil samples collected in June 2012. Results suggested that the C input manipulations induced differences in soil microbial biomass and community composition were dependent on tree species. C input manipulations had no significant effects on soil microbial biomass C and N under M. laosensis. However, the concentrations of microbial biomass C and N seemed to increase under C. lanceolata. PLFA analysis showed that M. laosensis litter significantly increased the contents of bacterial PLFAs, fungal PLFAs and actinomycetes, and significantly enhanced the percent abundance of gram-negative bacteria and arbuscular mycorrhizal fungi under C. lanceolata. Litter removal significantly increased the contents of gram-positive bacteria, gram-negative bacteria, arbuscular mycorrhizal fungi, actinomycetes and fungi by 22%, 29%, 44%, 25% and 52%, respectively, and also increased the fungi to bacteria ratio by 21% compared with the control in C. lanceolata soil. However, litter removal and root trenching did not change soil microbial community composition in C. lanceolata and M. laosensis soils. Seasonal patterns of microbial biomass C and N were different between C. lanceolata and M. laosensis plantations. Nutrient availability rather than soil temperature, moisture or fresh litter input, may determine seasonal fluctuation of soil microbial biomass in this study. Our results suggested that further studies are required to confirm the relative contribution of above- and belowground C inputs in different tree species plantations in subtropical China.