植物多样性与生态系统土壤保持功能关系及其生态学意义

THE RELATIONSHIP OF PLANT SPECIES DIVERSITY TO ECOSYSTEM FUNCTION IN RELATION TO SOIL CONSERVATION IN SEMI-HUMID EVERGREEN FORESTS, YUNNAN PROVINCE,CHINA

测定物种丰富度呈梯度变化的半湿润常绿阔叶林不同次生演替阶段小区地表径流、土壤侵蚀和总磷流失及影响这些过程的植物群落郁闭度、个体密度、胸高断面积、植物叶吸附水,分析物种多样性与生态系统土壤保持功能、稳定性及直接影响土壤保持功能的群落结构、树冠截留间的关系。结果表明,在降雨、坡度、坡向、坡位、土壤类型等水土保持影响因子相同条件下,随着各小区物种多样性的增加,地表产流次数不断下降;在3个降雨季节,物种多样性最低的小区产生地表径流77次,而物种多样性最高小区产生地表径流才9次;系列小区地表径流、土壤侵蚀和总磷流失随着物种多样性增加呈幂指数下降;物种多样性最低的小区地表径流、土壤侵蚀和总磷流失分别为960.20m3·hm-2·a-1,11.4t·hm-2·a-1,127.69kg·hm-2·a-1,而物种多样性最高的小区为75.55m3·hm-2·a-1、0.28t·hm-2·a-1、4.71kg·hm-2·a-1,分别相差12、50和25倍;地表径流、土壤侵蚀和总磷流失变异系数也呈幂指数下降,物种多样性最高的小区地表径流、土壤侵蚀和总磷流失的变异系数分别为57.93、187.94和59.2,而物种多样性最低的小区变异系数高达287.6、534.21、315.47,分别相差4、3和5倍。物种多样性与影响土壤保持功能的群落郁闭度、密度和胸高断面积呈正相关关系。不同演替阶段植物叶吸附水量差异显著,吸附水量最高的演替阶段是次生半湿润常绿阔叶林,为12.28t·hm-2·a-1,最低是云南松(Pinusyunnanensis)林,为4.15t·hm-2·a-1。“植物多样性_土壤保持功能相关群落结构因子及树冠截留效应_生态系统土壤保持功能”的耦合关系表明了植物多样性通过植物群落结构削弱了降雨动能,减少了地表径流,减轻了土壤及营养元素的流失,以间接方式调控生态系统土壤保持功能,维持系统营养的持续性,在不同尺度上实现生态系统生产力。物种多样性的提高,促进了生态系统土壤保持功能的稳定性。植物多样性_生态系统土壤保持过程的研究可能是生态系统稳定性研究的好方法。用植物叶吸附水测定可评价群落树冠截留效应。由于植物多样性与生态系统土壤保持功能间存在相关关系,基于植物多样性对生态系统土壤保持功能作用模式,可增进对生命系统和地球系统界面间相互作用关系的了解。

In recent years, the relationship of biodiversity to ecosystem stability, productivity and other ecosystem functions have been researched by using theoretical approaches, experimental investigations and observations in natural ecosystems, however, results have been controversial. For example, simple systems were more stable than complex systems in theoretical studies, higher productivity was observed in man-made ecosystems with poorer species composition than in natural ecosystems with more diverse assemblages, etc. The role of biodiversity in ecosystem functioning, such as its influence on sustainability, stability, and productivity, still is not understood. Because accelerated soil erosion in various ecosystems has caused a decrease in ecosystem primary productivity, a logical way to study the relationship between biodiversity and ecosystem function will be to study the relationship between plant species diversity and soil conservation. In addition, biodiversity is a product of evolutionary history and soil erosion is a key factor controlling the evolution of the modern environment on the surface of the Earth. A study on the relationships between biodiversity and soil erosion processes could help to understand the environmental evolution of Earth and predict the future changes. To test this, fifteen 10 m×40 m standard runoff plots were established to measure surface runoff, soil erosion and total P leaching in different secondary communities of semi-humid evergreen broad-leaved forests that varied in composition, diversity and level of disturbance and soil erosion. The following five communities were studied： AEI （Ass. Elsholtzia fruticosa ＋ Imperata cylindrical ）, APMO （Ass. Pinus yunnanensis ＋ Myrsine africana ＋ Oplismenus compsitus ）, APLO （Ass. Pinus yunnanensis ＋ Lithocarpus dealbatus ＋ Oplismenus compsitus ）, AEME （Ass. Eucalyptus smith ＋ Myrsine africana ＋ Eupatorium enophorum ） and ACKV （Ass. Cyclobalanopsis glaucoides ＋ Keteleeria evelyniana ＋ Viola duelouxii ） in central Yunnan Province of China （101°28＇18＂ E, 25°24＇09＂ N, 1 950-2 015 m）. Tree density, the diameter of trees at breast height and the hygroscopic volume of plant leaves were determined in each plot in order to analyze the relationship between plant species diversity and ecosystem function related to soil conservation and community structure. The degraded AEI, APMO, APLO and ACKV communities were restored naturally and the AEME was restored using plantation trees of E. smith and E. maidenii at AEI. The sequence of the successional phases were： 1 ） AEI AEME ACKV; 2） AEI APMO APLO ACKV. The slope degree, slope position and soil types of all plots were similar so that the results of these plots could be compared based on differences in diversity and composition only. The results indicated that surface runoff, soil erosion and total P leaching decreased according to a power function as plant species diversity increased and the three year average was 960.20m^3·hm^-2·a^-1,11.4t·hm^-2·a^-1,127.69kg·hm^-2·a^-1 in the plot with the lowest species diversity and 75.55m^3·hm^-2·a^-1、0.28t·hm^-2·a^-1、4.71kg·hm^-2·a^-1 in the plot with the highest species diversity. The low species plot was 12, 50 and 25 times, respectively, higher than in the high species plot. Soil conservation was enhanced with increasing plant species diversity. The coefficient of variation of surface runoff, soil erosion and total P leaching also followed a power function decreasing with increasing plant species diversity from 2001 to 2003. The coefficient of variation was 287.6,534.21, 315.47, respectively, in the lowest species diversity plot and 57.93, 187.94 and 59.2 in the highest species diversity plot, which was 4, 3 and 5 times greater in the low- est species plot. Enhanced soil conservation maintained greater stability with increased plant species diversity. Plant individual density increased linearly and the degree of closeness and basic coverage increased logarithmi- cally with increasing plant species diversity. The hydrological function of the leaves of the plant communities was strongest in ACKV, poorest in APMO, and intermediate in the AEME, APLO and AEI communities. The hydrological function of the leaves was enhanced as the plant species diversity increased. There were obviously relationships between plant species diversity with rainfall interception, coverage, plant individual density and they were related to soil conservation once more in the five successional forest communities. The complex relationships of plant species diversity with aboveentioned ecological processes indicated that plant species diversity was an important factor influencing the interception of rainfall reducing soil erosion and enhancing the stability of soil conservation, but the causal mechanism is not known. This experiment showed that plant species diversity promoted soil and nutrient conservation and was able to predict primary productivity of the ecosystem, and was thus a good way to study the relationship between biodiversity and ecosystem stability. Rainfall interception could be assessed easily using the hygroscopic volume of plant leaves of the plant community. Because there were strong correlations between plant species diversity and ecosystem functioning as related to soil conservation, the patterns of plant species diversity will show a certain level of predictability on the interactions of life systems with surface processes of the Earth.