不同菌根类型的森林净初级生产力对气温变化的响应

Responses of net primary productivity to air temperature change in forests dominated by different mycorrhizal strategies

菌根是由土壤中的菌根菌与植物根系形成的互惠共生体,在植物生产力和生态系统碳循环过程中发挥着重要的作用。该文基于全球森林数据库,建立了包括全球森林菌根类型、净初级生产力(net primary productivity,NPP)和年平均气温等指标的新数据库。在此基础上,分析了6种菌根类型(丛枝菌根(arbuscular mycorrhiza,AM)、AM+外生菌根(ectomycorrhiza,ECM)、AM+ECM+内外生菌根(ectendomycorrhiza,EEM)、ECM、ECM+EEM和ECM+EEM+无菌根(nonmycorrhiza,NM))森林的总NPP、地上和地下NPP、树木主干NPP、树叶NPP,以及树木细根NPP对年平均气温变化的响应。结果表明,不同菌根类型的森林总NPP、地上和地下NPP虽然都随气温的升高呈现上升的趋势,但其响应程度因菌根类型的不同而有所差异。除AM和AM+ECM+EEM类型的森林外,其他4种菌根类型的森林总NPP都随年平均气温的增加而显著增加;随着菌根类型的不同,地上和地下NPP对年平均气温变化的响应程度也存在差异,在AM+ECM类型的森林中,气温对地上NPP变异的解释率最高,达到57.27%,而地下NPP仅在ECM类型和ECM+EEM类型的森林中呈现出与年平均气温显著的回归关系。树木主干、树叶和细根的NPP则随菌根类型的不同而变化,与气温变化呈现正、负相关关系。从AM与ECM类型的森林的NPP来看,无论是总NPP还是各个组成部分的NPP,ECM类型的森林的NPP对气温的响应总是较AM类型更为敏感。可见,不同类型的菌根通过影响森林不同部分的NPP对气温变化的响应程度而影响到森林NPP对气温变化的响应。这表明菌根类型是预测气温变化对森林NPP影响的重要指标。

Aims Mycorrhizae, as the symbiotic associations between plant roots and mycorrhizal fungi, are almost ubiqui- tous. Mycorrhizal fungi play a crucial role in the regulation of terrestrial net primary production carbon dioxide （CO2） fluxes and respond strongly to climatic changes in temperature. Our objective was to explore how interan- nual variations in air temperature influence net primary productivity （NPP） in global forest ecosystems that are classified by the mycorrhizae of the dominant plants. Methods A new database was established including NPP and mean annual air temperature （MAT） of forests dominated by different mycorrhizal strategies based on an existing global forest database. We used this new data- base to study the responses of NPP of forests dominated by different mycorrhizal strategies to air temperature change. Important findings Total NPP, aboveground NPP and belowground NPP increased with the increase of MAT, although the slopes were different in forests dominated by different mycorrhizal types. Total NPP increased with the rise of MAT in forests dominated by all mycorrhizal strategies out of arbuscular mycorrhiza （AM） and AM ＋ ectomycorrhiza （ECM） ＋ ectendomycorrhiza （EEM）. The responses of above- and below-ground NPP of forests to the variation of MAT changed depending on mycorrhizal strategies of dominate forest tree species. The MAT explained 57.27% of the variation of aboveground NPP in AM ＋ ECM forest. Significant regressions between belowground NPP and MAT were observed in ECM and ECM ＋ EEM forests. NPP values of main stem, tree leafand fine root tended to either increase or decrease with the increase of MAT in the different forests. As far as the comparison between AM and ECM forest was concerned, the NPP, including total NPP and each part, was more sensitive to air temperature change in forest dominated by ECM than forest dominated by AM. We conclude that different mycorrhizae affected the responses of forest NPP to air temperature change by influencing the extent of response of various parts of forest NPP to air temperature change. The mycorrhizal symbiosis makes this vital for accurate prediction of future changes of forest NPP with change of air temperature.