赣南低效飞播马尾松林对土壤水分变化的响应机制研究

Improving the quality of forest resource is the eternal theme of forest management. Aerially seeded Pinus Massoniana plantations (AS) is one of the main forest resource in southern Jiangxi province, which accounts for 21.4% of total forest land area. However, quite a few AS are growing worse, the understory vegetation are scarce, and stand functions decline, influenced by main effects of seasonal drought stress and soil degradation along with soil moisture capacity decreased under the background of severe soil erosion. Therefore, aimed at the possibility of extreme drought or increase of precipitation under the background of global climate change, this project takes the low-efficiency AS in Xingguo county of southern Jiangxi province as the research object, and then carry out kinds of experiments, such as measures of improving the soil moisture reserve and water-holding capacity, increasing the precipitation, and rainfall exclusion experiment, by integrating theories and methods of ecology, forest management, soil science, soil and water conservation, etc. In this project, we can expound the change of soil moisture and the coupling relationship between changes of soil properties and soil moisture, explore the temporal-spatial variations of soil moisture response to growth of plant roots, plant growth and understory vegetation restoration, through experimental field survey, monitoring and sample determination. In addition, based on the comprehensive analysis of soil moisture-vegetation- precipitation system, we can reveal the basic mechanism of plant-soil interaction caused by soil moisture change, which can provide scientific basis for improvement of low-efficiency AS in southern Jiangxi province as well as research of revealing the mechanism of degraded forest ecosystem that influenced by seasonal drought stress in South China.

提高森林资源质量是森林经营的永恒主题。飞播马尾松林是赣南主要森林资源之一，其面积占有林地总面积的21.4%，但因受季节性干旱胁迫的主要影响及严重水土流失背景导致的土壤退化、持水性能下降，不少飞播林林木长势差、林下植被稀少、林分功能低下，因此，本项目针对全球性气候变暖可能造成极度干旱或降雨量增加的背景下，以赣南兴国县的低效飞播马尾松林为研究对象，集成生态学、森林经营学、土壤学、水土保持学等学科的理论与方法，开展提高土壤蓄水保水能力、降水排斥和增加降水等措施的试验，通过对试验地的调查与样品测定，阐明土壤水分变化及其与土壤性质变化的耦合关系，探明植物根系、林木生长、林下植被恢复对土壤水分时空变化的响应，并通过土壤水分-植物-降雨系统的综合分析，揭示土壤水分变化对植物-土壤交互作用的基本机制，为赣南低效飞播马尾松林经营改造及进一步揭示我国南方季节性干旱胁迫对退化森林生态系统的影响机理提供科学依据。

飞播马尾松林是赣南主要森林资源之一，因受季节性干旱胁迫的影响及严重水土流失背景导致的土壤退化、持水性能下降，其不少飞播林林木长势差、林下植被稀少、林分功能低下，如何提高其林分质量是当前亟待解决的问题。项目揭示了飞播马尾松林土壤水分与植被、土壤、地形因子的耦合机制，阐明了低效马尾松林对土壤水分变化及改造措施的响应，从区域尺度上探明了降水量等因子对碳密度的影响。重要结果：飞播马尾松林平均土壤含水量、田间持水量分别为14.5%和13.6%，均随土层深度的增加而增大；土壤水分主要受土壤容重、毛管孔隙度等土壤因子的影响，其次为草本盖度、枯落物厚度、地被盖度等植被因子，地形因子的影响最小；土壤因子是影响土壤水分变异的主要因子，其单独解释率占总解释率的46.6%，次要因子为植被因子的独立作用及其与其他因子的交互作用，其中植被与地形因子主要是通过影响土壤因子作用于土壤水分。试验表明林木细根生长与土壤水分呈显著相关，间伐或补植阔叶树均能有效提高低效林的质量，随着与木荷混交比例的增加，马尾松种内平均竞争指数逐渐减小，其竞争压力主要来自种内，大于20 cm时受到的竞争压力变化较小且维持在较低水平。飞播马尾松林随着龄级的增大，其田间持水量、毛管持水量以及土壤质量综合指数均逐渐增大，且不同龄级间均存在显著性差异；灌木层和草本层的物种数均呈先增大后减小的变化趋势，林下植被Patrick丰富度、Shannon-Wiener指数、Pielou均匀度等指数随龄级的变化不尽相同。马尾松林植被（乔木层、林下植被层、凋落物层）及生态系统（植被和土壤层）碳密度的平均值分别为52.02 t•hm-2和122.33 t•hm-2，其植被碳密度与林龄、年均降水量、海拔、林分密度呈极显著正相关，与坡度、年均温度呈极显著负相关，而对生态系统碳密度影响显著的因子为海拔、坡度、土层厚度、胸径、年均温度和年均降水量；碳密度在空间上存在中等程度的相关性。研究成果可为低效飞播马尾松林提质增效经营措施的制订及马尾松林碳汇林业经营规划等提供科学依据。