连续三年夜间增温和施氮对云杉外生菌根及菌根真菌多样性的影响

以西南亚高山针叶林建群种粗枝云杉(Picea asperata)为研究对象,采用红外加热模拟增温结合外施氮肥(NH₄NO₃ 25 g N m^-2 a^-1)的方法,研究连续3a夜间增温和施肥对云杉幼苗外生菌根侵染率、土壤外生菌根真菌生物量及其群落多样性的影响。结果表明:夜间增温对云杉外生菌根侵染率的影响具有季节性及根级差异。夜间增温对春季(2011年5月)云杉1级根,夏季(2011年7月)和秋季(2010年10月)云杉2级根侵染率影响显著。除2011年7月1级根外,施氮对云杉1、2级根侵染率无显著影响。夜间增温对土壤中外生菌根真菌的生物量和群落多样性无显著影响,施氮及增温与施氮联合处理使土壤中外生菌根真菌生物量显著降低,但却提高了外生菌根真菌群落的多样性。这说明云杉幼苗外生菌根侵染率对温度较敏感,土壤外生菌根真菌生物量及其群落多样性对施氮较敏感。这为进一步研究该区域亚高山针叶林地下过程对全球气候变化的响应机制提供了科学依据。

Effects of 3-year continuous night-time warming and nitrogen fertilization on ectomycorrhizae of Picea asperata and the ectomycorrhizal fungal diversity

Global climate changes have become hot topics in ecological research filed in last decade. Picea asperata, the constructive species of the Southwest subalpine coniferous forest which is well known for its sensitivity to climate changes in China, is a typical ectomycorrhizal species. Ectomycorrhizal fungi play an important role in the forest system by enhancing the ability of host trees which form ectomycorrhizal symbionts with them to uptake nutrient and water, promoting seedling establishment and improving nutrient cycling in the forest by the mycorrhizal networks belowground. Many scientists have already studied the effects of warming and nitrogen deposition on Picea asperata''s physiology and phenological phenomenon. But how ectomycorrhizal symbionts and ectomycorrhizal fungal community associated with Picea asperata respond to warming and nitrogen deposition in this area is lack of research. To simulate the effects of warming and nitrogen deposition, we conducted an experiment with the infrared radiator and NH₄NO₃ 25 g N m^-2 a^-1 fertilizing. And we evaluated the effects of 3-year continuous night-time warming and nitrogen fertilization on the ectomycorrhizal colonization rate of Picea asperata seedlings, soil ectomycorrhizal fungal biomass and the diversity of soil ectomycorrhizal fungal community. The experimental results clearly showed that the effects of night-time warming on the ectomycorrhizal colonization rate were varied seasonally in different root orders. In spring (May, 2011) night-time warming significantly affected the ectomycorrhizal colonization of first-order roots, however, in summer (July, 2011) and autumn (Oct, 2010) the ectomycorrhizal colonization rate of second-order roots were changed significantly. Nitrogen fertilization didn''t dramatically affect the ectomycorrhizal colonization rate of first-order and second-order roots except for the colonization rate of first-order roots in July 2011. There were no significant effects of night-time warming on soil ectomycorrhizal fungal biomass and the diversity of ectomycorrhizal fungal community. But we found that nitrogen fertilization and the interaction of the two treatments affected them significantly: the soil ectomycorrhizal fungal biomass was decreased while the diversity of ectomycorrhizal fungal community was increased. These results indicated that the ectomycorrhizal colonization rate of Picea asperata seedlings was sensitive to warming, however, the soil ectomycorrhizal fungal biomass and the diversity of ectomycorrhizal fungal community was sensitive to nitrogen fertilization. The primary effect of night-time warming was to increase the ectomycorrhizal colonization rate, but there was negligible or insignificant effect on diversity of soil ectomycorrhizal fungal community. On the contrary, nitrogen fertilization directly and significantly affected the diversity of soil ectomycorrhizal fungal community rather than the ectomycorrhizal colonization rate of Picea asperata seedlings. The different response of different ectomycorrhizal fungus to the global climate change and long-term experiments simulated natural climate change will be considered in the following studies. The findings of our research provide the scientific basis for further studying the response mechanism of below-ground of southwest subalpine coniferous forest to global climate changes in this region.