三峡库区森林凋落叶化学计量学性状变化及与分解速率的关系

凋落物分解是森林生态系统生物元素循环和能量流动的重要环节,其过程是植物与土壤获得养分的主要途径。为了量化凋落叶化学计量学性状变化过程对分解的影响及对凋落物-土壤生物化学连续体的深层理解,用凋落物分解袋法研究了不同林型各自凋落叶化学计量学性状变化及与分解速率关系,结果表明:林下各自凋落叶分解速率是马尾松林栓皮栎林马尾松-栓皮栎混交林,马尾松林、栓皮栎林、马尾松-栓皮栎混交林凋落叶分解50%和95%的时间分别是2.11 a和9.15 a,1.93 a和8.45 a,1.76 a和7.77 a;凋落叶分解过程中,化学计量学性状变化明显,分解450 d后马尾松-栓皮栎混交林碳释放最快,栓皮栎林最慢;3种凋落叶起始N含量是栓皮栎林最高,马尾松林最低,分解450 d后马尾松林、栓皮栎林和马尾松-栓皮栎混交林N含量分别增加了66.67%、44.91%和44.52%,而P含量分别释放了30.80%、38.89%和42.29%。凋落物不同化学计量学性状与分解速率关系不同,3种林型凋落叶分解速率均与N含量呈正相关(P0.01),与C含量(P0.01)、C/N比(P0.01)呈负相关,与N/P比呈负二次函数关系(P0.01),而P含量与3种林型关系不同,与栓皮栎林(P0.01)和马尾松林(P0.05)呈负线性关系,与马尾松-栓皮栎混交林呈负二次函数关系(P0.05)。研究表明,不同林型凋落叶分解中的养分动态趋向利于分解变化,N、P养分动态是生态系统碳平衡和凋落物分解速率的主要因素,混交林中混合凋落物的养分迁移是分解相对较快的原因。

Dynamic of leaf litter stoichiometric traits dynamic and its relations with decomposition rates under three forest types in Three Gorges Reservoir Area

Litter decomposition is an important link between bioelement cycles and energy flow in the forest ecosystems, and the main source of nutrients for plants and soil. The relationships were studied between leaf litter stoichiometric traits dynamic and decomposition rate under different forest types using litter bag method in this paper to quantify the effects of stoichiometric traits dynamic on leaf litter decomposition and to get a better understanding to the biochemistry of litter-soil continuum. The results were showed as follows: the sequence of litter decomposition rate for the three forest types was Pinus massoniana stand (PM)< Quercus variabilis stand (QV)< P. massoniana-Q.variabilis mixed stand (PQ) and the litter decomposition rate was more and more significant with time. The remaining dry mass of litter in PM, QV and PQ were 67.59%, 64.75% and 62.13%, respectively after 450 d decomposition. The predicated period of litter decomposition 50% and 95% for PM, QV and PQ was 2.11 a and 9.15 a, 1.93 a and 8.45 a, as well as 1.76 a and 7.77 a, respectively. In these forest types, the concentration of C and P in decomposing litter decreased while N concentration increased with not significant. Leaf litter element dynamic was significantly different. The sequence of the initial C concentration was PQ< QV P<0.01), negatively with C concentration (P<0.01), C/N ratio (P<0.01), and negative quadratic function with N/P ratio (P<0.01). P concentration was different in three stands, and negatively linearly related to the decomposition rate for QV (P<0.01) and PM (P < 0.05), and negative quadratic related for PQ (P < 0.05). The decomposition rate and leaf litter stoichiometry was different among the three stands. The dynamic of C, C/N ratio and N/P ratio in the three stands were similar showing a significant positive correlation with N concentration. The possible reason for this may be that the plants in high latitudes are more susceptible to N restrictions, while those in low latitudes are more susceptible to P restrictions. Whether the plant is limited by N or P, the stoichiometry for different plants is influenced by different environmental factors. This study indicated that the nutrient dynamic during the decomposition of litter leaf under different forest types tend to help itself decompose. The concentration dynamic for N and P was the major factors in regulating carbon balance of ecosystem and litter decomposition, nutrient transfer in mixed litter is the reason for decomposition acceleration.