东北次生林生态系统关键种对土壤有机质的调控作用及机制

Secondary forests have been the major forest resources, especially in northeast China. To meet the growing demands for timber, extensive areas of theses secondary forests have been replaced by plantations predominantly of larch species. Thus, larch plantations intersperse with the remnant secondary forests to form mosaic of plantation/secondary forest landscapes (i.e., the secondary forest ecosystem). Previous studies in the secondary forest ecosystem suggested that the quality of litter, as the critical biotic factor, could affect soil organic matter accumulation and stabilization, and then influence timber production and ecological functions. However, the effects of dominant tree species litters on accumulation and stability of soil organic matter in the secondary forest ecosystem are poorly understood. The dominant tree species studied in this project included Juglans mandshurica, Quercus mongolica, Fraxinus rhynchophylla, Fraxinus mandshurica, Acer mono, and Larix gmelinii in the secondary forests and larch plantations. The analysis methods of the isotope and microbiological analysis will be used in this study. The specific objectives of this project are as follows: 1) to explore the mechanism of soil organic matter decomposition and turnover rates in the dominant tree species; 2) to determine the relationships between the decomposition of dominant tree species litters and microbial communities, enzyme activities and soil organic matter chemical properties; 3) to explicit the mechanisms of accumulation and stability of soil organic matter and their dependence on litter qualities; 4) to find out the main tree species to promote soil organic matter stabilization in the secondary forest ecosystem. The results obtained in this project will provide scientific basis and strategies for promoting the restoration of secondary forests and reasonable management of plantations in northeast China.

次生林已成我国森林资源主体，东北尤为如此。由于次生林不能满足木材生产，因此，大面积次生林被人工林取代，形成次生林和人工林镶嵌分布独特的次生林生态系统。前期研究表明，凋落物品质是影响土壤有机质积累和稳定性、进而影响次生林生态系统木材生产和生态功能可持续经营的关键，但其机制不清。本项目以东北次生林生态系统主要林型：次生林和落叶松人工林为对象，以影响有机质积累和稳定性的关键树种凋落物为核心，通过长期野外定位监测、控制和室内培养试验相结合手段，利用同位素和土壤微生物学技术，重点探讨关键树种及其组合凋落物对土壤有机质的分解动态和周转速率的作用机制；确定凋落物分解特征与微生物群落组成、酶活性、有机质化学结构变化的关系；明确凋落物品质对土壤有机质稳定性的影响机制；提出促进次生林生态系统土壤有机质积累和稳定性的关键树种优化方案。研究结果为次生林恢复和人工林合理经营提供科学依据与对策。

次生林已成我国森林资源主体，东北尤为如此。由于次生林不能满足木材生产，因此，大面积次生林被人工林取代，形成次生林和人工林镶嵌分布独特的次生林生态系统。前期研究表明，凋落物品质是影响土壤有机质积累和稳定性、进而影响次生林生态系统木材生产和生态功能可持续经营的关键，但其机制不清。本项目以东北次生林生态系统主要林型：次生林和落叶松人工林为对象，以影响有机质积累和稳定性的关键树种凋落物为核心，通过长期野外定位监测、控制和室内培养试验相结合手段，利用同位素和土壤微生物学技术，重点研究：（1）次生林生态系统关键树种凋落物对土壤有机质积累的影响；（2）次生林生态系统关键树种对土壤有机质稳定性的影响；（3）土壤惰性碳库对关键树种凋落物输入的敏感性。通过对三方面内容的研究，结果表明：（1）次生林转变为落叶松人工纯林改变了凋落物-土壤-根系碳和养分的分布格局，水曲柳土壤与碳循环相关的酶活性酚氧化酶、外切葡聚糖酶、β-葡聚糖酶高于其他树种，这一结果表明水曲柳土壤碳循环较其他阔叶树种快；（2）落叶松凋落物分解速率仅为次生林主要阔叶树种（色木槭、胡桃楸、蒙古栎）凋落物的53-66%，落叶松与阔叶树种凋落物混合改变了分解速率，落叶松与色木槭混合凋落物分解具有非加和的正效应；凋落物基质的Mg含量、木质素/P是影响落叶松、阔叶树种及其混合凋落物分解的关键要素；通过对2万余条细菌和真菌群落序列分析发现，细菌不是影响凋落物分解速率的主要因素，微生物腐生真菌功能群是控制凋落物分解的关键；（3）和根系相比，叶片凋落物输入如花曲柳、胡桃楸、水曲柳更有利于土壤惰性碳库的循环，这三类树种叶片凋落物归还土壤中，更有利于土壤有机质的稳定性。上述研究结果为次生林恢复和人工林合理经营提供科学依据与对策。