胶农复合林植物水分来源与水分利用效率的关联性研究

Rubber plantation has gradually replaced as much as 500, 000 hectares of the native tropical rainforest over the last 50 years, which represented more than 20% of the total land area of Xishuangbanna. The transformation of the vast tracts of tropical rainforest to rubber monoculture has induced a series of ecological environment problems. Rubber monoculture has significantly increased the regional water resource shortages, and aggravated the soil compaction and erosion, which also has to be faced the seasonal drought in this area. In this study, we mainly focus on 6 kinds of rubber-based agroforestry systems (e.g. rubber-coffee, rubber-cacao, rubber-tea, rubber-amomum, rubber-macrophylla and rubber-grapefruit) subjected to seasonal drought in Xishuangbanna in Yunnan Province. Furthermore, the pure rubber plantation is served as control plot. Based on the isotope ratio mass spectrometry and the isotope ratio infrared spectroscopy systems, the stable isotopes of hydrogen and oxygen (δD and δ18O) in plant xylem water, soil water and precipitation will be continuously sampled and analyzed. Combining with the MixSIAR model, water sources of different plants in the rubber-based agroforestry systems (especially those influenced by soil water stress) can be quantified. Meanwhile, the seasonal dynamics of plant water use efficiency (WUE) of different plants can be illuminated through the stable isotopes of oxygen and carbon (δ18O and δ13C) in plant leaves. Then, the impacts of mixed plantation effects on the water sources of rubber trees, as well as the “conservative” or “opportunistic” water use strategies for rubber trees can be investigated. Through analyzing the influences of changing plant water sources and interspecific water competition on the WUE of rubber trees, this study will provide scientific data and references for ameliorating water stress for rubber plantation and promoting the appropriate rubber-based agroforestry systems.

近50年来，西双版纳橡胶林的种植面积（约50万hm2）已超过该区土地总面积的20%。针对大面积单一橡胶林导致的区域水资源短缺以及遭受的干旱（11-4月）胁迫等现状，拟选取该地区广泛种植的6种胶农复合林为研究对象，以纯橡胶林为对照，以稳定同位素质谱和红外光谱技术为基础，通过对植物茎秆水、土壤水和降水氢氧稳定同位素（δD和δ18O）的连续采集和测定，结合MixSIAR模型明确干旱胁迫下不同复合林内的植物水分来源，阐明复合模式对橡胶树水分来源的影响；通过对植物叶片氧碳稳定同位素（δ18O和δ13C）的连续采集和测定，揭示不同复合林内的植物水分利用效率（WUE），阐明复合林内橡胶树的“保守/耐旱”或“投机/避旱”型水分利用策略；综合分析不同复合林内橡胶树的水分来源及种间水分竞争关系变化对其WUE的影响。为缓解橡胶树在旱季遭受水分胁迫以及选择适宜推广的胶农复合栽培模式供科学依据和切实参考。

近50年来，西双版纳地区橡胶种植面积（约50万公顷）已超过该区土地总面积的20%，也有研究预测橡胶种植在未来将进一步扩展到高海拔（> 600 m）山地。针对西双版纳大面积种植单一（纯）橡胶林所导致的区域水资源短缺以及频繁发生的季节性（11月-次年4月）干旱等胁迫，本项目选取该区广泛种植的六种胶农复合林（橡胶-砂仁、橡胶-益智、橡胶-高良姜、橡胶-咖啡、橡胶-茶叶、橡胶-可可）和橡胶纯林（对照）作为研究对象，基于氢（δ2H）氧（δ18O）碳（δ13C）稳定同位素和根系调查等方法，重点开展了作物固态样品（全叶和叶片纤维素）和液态水（茎秆水、土壤水、地下水和降水）的连续采集（2017-2018）和测定分析。主要的研究结果包括：（1）“水分补偿”学说在橡胶树与间作作物之间难以成立，橡胶树与作物之间的水分竞争明显，二者均非常依赖（平均利用比例40.5-69.1%）浅层0-20 cm土壤水分；胶农复合林内橡胶树与作物的种间水分竞争在旱季更为突出，相似的水分来源与他们的浅根系特征一致。（2）虽然间作作物会加剧复合林内的浅层土壤水分消耗，与此同时部分间作作物通过保水效应反而提高土壤含水量；权衡作物水分竞争和保水作用的强弱，可从水分关系视角审视构建胶农复合林的合理性。(3) 面向未来，本项目将为缓解西双版纳地区橡胶树在旱季遭受水分胁迫以及选择适宜推广的胶农复合栽培模式提供科学依据和切实参考。