东北地区森林凋落叶分解速率与气候、林型、林分光照的关系

在东北长白山、张广才岭、小兴安岭、大兴安岭的主要森林类型中设置26块样地,进行为期3a(2004—2006年)凋落叶分解实验,以研究气候、林型、林冠透光率对凋落叶分解速率的相对影响大小。结果表明,不同林型凋落叶分解速率依次为:落叶阔叶林针阔叶混交林落叶针叶林常绿针叶林岳桦林。对分解速率影响因素的分析表明,气候因子(热量和水分)对分解速率有较强的解释力,分别解释了分解常数k和分解95%所需时间(t95%)的55.5%和65.0%的变异。但是,气候对分解速率的影响在很大程度上是通过与林型、林冠透光率的协同作用而实现的,其独立解释力并不大(9%)。气候的变化导致林型(物种组成)的变化、进而影响分解速率,这一因素解释了分解参数变异的46.8%(k)和56.8%(t95%)。与此同时,气候和林型的变化还导致林冠透光率的变化,随着热量水平的上升林冠透光率下降、间接提高分解速率。这一因素分别解释了k值和t95%变异的23.9%和22.3%。研究结果表明,气候对凋落叶分解的影响主要是通过对物种组成、林冠结构(影响透光率)等生物因素的间接作用实现的。忽视这些生物因素、简单研究气候和分解速率的关系可能难以正确预测未来气候变化对凋落物分解的影响。

Effects of climate, forest type and light availability on litter decomposition rate in forests of Northeast China

Decomposition of plant litter is a key process in nutrient and carbon cycling in terrestrial ecosystems. Disentangling the relative effects of different factors, including climate, local environmental factors, and species identities (which determine litter quality), on leaf litter decomposition rate provides insight into forest carbon cycles. In this study, we conducted a three-year decomposition experiment of leaf litter in 26 plots across Northeast China (Changbai, Zhuangguangcai, Xiaoxing''an, and Daxing''an Mountains) to examine the relative effects of climate, forest type, and gap fraction on leaf litter decomposition rate. The leaf litter decomposition rate differed among forest types in the following order: deciduous broadleaf forest > deciduous broadleaf and needle-leaf mixed forest > deciduous needle-leaf forest > evergreen needle-leaf forest > Betula ermanii forest. A multivariate analysis showed that climate factors (energy and water availability) were strong predictors of the leaf decomposition rate, which explained 55.5% and 65.0% of the variation in decomposition coefficient (k) and the time required for decomposition of 95% of the litter (t_95%), respectively. However, the independent effect of climate on decomposition was weak, and most of the variation was attributed to the joint effect of climate variables with forest type and light availability (< 9%). Climate drives changes in forest types (species composition), which in turn affects the leaf decomposition rate. This joint effect explained 46.8% (k) and 56.8% (t_95%) of the total variation in leaf decomposition rate. Moreover, changes in climate and forest types can affect under-canopy light availability (measured using the gap fraction), which declined with increasing temperature and indirectly improved leaf decomposition rate. The joint effects of climate, forest type, and light availability explained 23.9% and 22.3% of the variation in k and t_95%, respectively. Our results indicate that climate affects litter decomposition mainly through its indirect effects on biological factors such as species composition and canopy structure, which influence litter quality and light availability. It is necessary to understand the interactions of climate with these biological factors for predicting changes in litter decomposition in response to future climate change.