大型生态学控制实验----降雨季节格局改变平台简介 未来全球气候变化势必对森立生态系统结构和功能产生重大影响，而这些影响会反过来影响生态系统的服务能力，即关系到了人类福祉。已有不少研究表明降水会变得越来越分布不均，如在华南地区呈现“干季更干、湿季更湿”的特点。在每年的1-3月和10-12月这两段干季的降雨近年来越来越少，而湿季的4-9月份暴雨和特大暴雨越来越频繁。同时，也有很多模型预测到了这种极端的降雨分布模式。因此，认识和了解在极端降雨条件的森林生态系统响应机制可以帮助人们采取合理的森林经营措施，从而避免森林生态系统的衰退和最大化地提高其服务功能。然而，目前这方面的研究十分匮乏。 利用大型生态学控制实验平台可以帮助人们详细测量植物生理的各项参数，从而认识生态系统过程对极端降水事件的响应。早在2012年，中科院华南植物园的研究人员就开展了“降水季节变化(Precipitation Seasonal Distribution Change, PSDC)”的试验（PI： 申卫军研究员），以期解释森林生态系统的响应。具体试验设计是：把干季的穿透水隔除，在湿季加入等量的穿透水在同样的样方， 保持全年降水总量不变 ，即“干季更干、湿季更湿”（Drier dry season and wetter wet season，缩写DD）的处理；延长干季的处理，把干季10-3月延长到10-5月，增加两个月的干旱处理，即模拟春旱，把隔除等量的雨水在湿季加入到同样的样方，同样 保持全年降雨总量不变 ，即“干季更干、延长干季”（Extended dry season and wetter wet season，缩写ED）的处理；没有做任何处理的对照(Ambient control，缩写AC)，样方接受正常的大气降水。 此大型野外生态学控制实验从2012年10月开始实施，到2014年9月告一段落，已经完整地进行了两个整年（或水文年）。在此平台开展的试验或测试的变量包括但不局限于：土壤呼吸、土壤微生物多样性、细根动态和周转、凋落物分解、土壤养分、树木蒸腾或树干液流等。相信在大家共同的努力下定会揭示出有趣的生态学规律、发现有意思的生态学现象和回答重要的基础生态学问题。那么，哪些是这个耗资巨大的试验需要回答的科学问题呢？我觉得可以是： 1）森林生态系统功能和过程能否对极端降雨产生一定的抵抗力？它的阈值在哪里？2）降雨季节分配格局改变能否改变物种（如树木）的种类和组成？哪些是敏感种？哪些是耐受种？3）物种，如树种对降雨季节格局改变的生理学响应能在多大程度上帮助人们预测未来的生态系统结构和功能？ 研究样地位于广东省鹤山市境内(Heshan National Field Research Station of Forest Ecosystem, Chinese Academy of Sciences)，东经112°54′，北纬 22°41′ ，平均海拔高度47m。属南亚热带粤中丘陵地区，历史上为森林地带，顶级群落是亚热带季风常绿阔叶林，但由于人类活动的干扰，造成了植被退化、水土流失和土壤贫瘠。年平均气温21. 92 ºC，年均降雨量1580.43mm。 穿透雨隔除样地 乔木 有藜蒴锥、阴香、 木荷 （优势种！）、 火力楠 （优势种！）、尖叶杜英、山苍子、红鳞蒲桃、红锥、马尾松、枫香、野漆、等； 灌木 有银柴、九节、梅叶冬青、三叉苦、竹节树、鬼灯笼、 乌桕、 米碎花、玉叶金花、 桃金娘等； 草本 有海金沙、淡竹叶、 拔葜、酸藤子、乌毛蕨、小花露籽草、雪下红、异叶鳞始蕨、山菅兰、芒萁、地稔、火炭母、青江藤等。乔木林木密度为1019株/ha，林龄为25年左右 。 广东鹤山降水和气温特征，降水系1985-2014年30年平均值，气温系1998-2014年17年平均（未发表数据） 鹤山站森林生态系统 远观PSDC平台，总共4个区组 挡雨布关闭时的情形，以及大量隔除穿透雨的支架和挡雨布 挡雨布（较为干净透明）打开后并未能影响到林下植被 土壤呼吸测定装置 树干液流测定系统 凋落物收集网 排水管和人工挖的隔离槽，隔离槽大约0.5米深，且用塑料板隔开（排除样方之间的相互干扰） 供水装置 湿季加水时的情形，水雾漂浮，如同仙境 林下植被较为丰富 近在咫尺（不足100米）的全天候气象站
Abstract: The purpose of this study is to investigate geochemical process and driving forces of soil major chemical elements in the forest-dominated Jinshui River basin, tributary of the upper Hanjiang River. We carry out investigations on soil major chemical elements distribution and transport patterns and driving forces by integrated analysis of natural environmental factors and human activities. In order to achieve these goals, we further employ efficient approaches including field investigation, laboratory testing and GIS spatial simulation. Through this research work, following findings are achieved. Firstly, general soil weathering process of Jinshui River Basin basically evolves from Ca, Na stages to K stage. Ca, Na decreased rapidly, and silicate weathering process evolved gradually. Major ions of water are subject to carbonate dissolution, about 2 / 3 of the soil in the basin are alkaline (pH7) which provide good condition for mineralization of organic nitrogen. Chemical index of alteration (CIA) gradually increase from south to north, initially decrease from east to west and increase eventually. Predominant major elements in the upper stratum of soil are oxides of Si, Al, Fe and Ca, which account for about 78.1% of the total. Secondly, specific soil weathering process differs in spatial patterns and elements transport which is driven by integrated interior forces (e.g., mineral materials) and external forces (e.g., temperature, precipitation, wind and the gravity). Original mineral materials are changed into soils with different physical properties (soil texture, mechanical composition) and chemical components (organic matter). Upstream original mineral materials have been transported, accumulated and deposited in the downstream, which are driven by forces of gravity, water transport, glacial effects, and wind. Key ecological factors of plant growth change greatly which are caused by integrated environmental effects such as climatic conditions, sunlight, nutrients and soil biological characteristics. Organic matters accumulate in forest covered belts of Jinshui River while inorganic weathering processes are dominated by decomposition and eluviation of silicate minerals. In the vertical section, within all vegetation types, soil moisture storage capacity and saturation decrease with an increase in depth. Forest soil has better conditions of physical properties and chemical characteristics than those of wasteland and farmland. Mixed coniferous soil reserves the most water than other vegetation types, followed by coniferous forest, chestnut forest and shrub. Thirdly, land use and cover is one of key contributors to determine geochemical patterns of soil organic matters. Land use and cover types greatly impact on volumes of standing deadwood, particulate organic carbon content and Na / K value. Soil particulate organic carbon and Na / K are in good correlation, especially in dry land and bamboo areas. Intensity of mineral weathering process decreases with the decrease of biomass which follows the sequences, dry land bamboo paddy soil shrub coniferous forest mixed forest deciduous forest. Improper human activities decreased soil organic matters, and thus had negative impacts on agriculture. However, it helps to prevent the loss of N, P if effective countermeasures are adopted to develop a vegetation buffer zone along riversides, especially in residential areas. The overall investigation of this study suggests that protection of forestry ecosystem and proper human activities are important for improvement of water quality and soil erosion. Key words: Geochemical transport of soil chemical elements; soil weathering; forestry ecosystem; Hanjiang River Basin; Jinshui River
标签: 森林生态系统
