亚热带常绿阔叶林根系生物量和形态特征对长期施氮的响应

Response of Root Biomass and Root Morphology to Long-term Nitrogen Application in Subtropical Evergreen Broad-leaved Forest

摘要:

为探究森林生态系统在环境变化中的生存策略，预测植物根系在长期氮沉降背景下的响应模式，在亚热带天然常绿阔叶林中设置对照和施氮[80 kg N/(hm²·a)] 2个处理，研究长期氮添加对根系生物量、比根长、比表面积和组织密度等的影响。结果表明，长期的氮添加没有对根系生物量及其根系生物量消减系数β产生显著影响(P>0.05)，即根系生物量的垂直分布特征并没有发生显著变化(即在不同土层积累的生物量之间没有明显差异)，对照和氮处理下的不同径级的根系生物量密度随土层变化的趋势相同，但是土层和径级的交互作用会对根系生物量产生显著影响；长期氮添加显著增加0~1 mm的细根比根长；但是长期的氮添加显著降低了组织密度且不受径级的影响；而氮添加对根系比表面积无显著影响，这种变化是在群落水平上的一种整体的变化趋势。在群落水平上，长期的氮添加对亚热带常绿阔叶林根系生物量及垂直分布无显著影响，这正与土壤总碳氮磷的含量随土层变化一致。但11 a的氮添加会增加比根长而降低组织密度，一些物种的根系资源获取策略会变为快速获取型策略。因此，长期的氮沉降背景下根系会通过增加比根长，降低组织密度来响应养分变化。

Abstract:

In order to explore the survival strategies of forest ecosystems under environmental change and predict the response mode of roots under the background of long-term nitrogen (N) deposition, two treatments, including control and N addition [80 kg N/(hm²·a)], were set up in subtropical natural evergreen broad-leaved forest to study the effects of long-term N addition on root biomass, specific root length, specific surface area and tissue density. The results showed that long-term N addition had no significant effect on root biomass and its root biomass reduction coefficient β (P>0.05), the vertical distribution characteristics of root biomass did not change significantly (there was no significant difference between biomass accumulated in different soil layers). The root biomass density of different diameter classes under control and N addition showed the same trend with soil layer, but the interaction between soil layer and diameter class had a significant effect on root biomass. Long-term N addition significantly increased 0-1 mm fine specific root length. However, long-term N addition significantly decreased the tissue density and was not affected by diameter class. However, N addition had no significant effect on the specific surface area of roots, and this change was an overall trend at the community level. At the community level, long-term N addition had no significant effect on the root biomass and vertical distribution of subtropical evergreen broad-leaved forest, which was consistent with the changes in total carbon (C), N and phosphorus (P) contents in soil with soil layer. However, N addition for 11 years increased the specific root length and decrease the tissue density, and the root resource acquisition strategy of some species changed to a rapid acquisition strategy. Therefore, under the background of long-term N deposition, roots would respond to nutrient changes by increasing specific root length and decreasing tissue density.