Data from: Can intercropping with the world’s three major beverage plants help improve the water use of rubber trees?

1. The dramatic expansion of rubber plantations in mainland Southeast Asia and Southwest China has caused many eco-environmental problems, especially negative hydrological consequences. These problems have gradually worsened and pose formidable threats to rubber agriculture, especially in light of increasingly frequent extreme weather events. Although rubber-based agroforestry systems are regarded as the best solution for improving the sustainability of rubber agriculture and environmental conservation, plant water use and related interactions have rarely been examined in such systems.
2. We primarily used stable isotope (δD, δ18O, and δ13C) methods to test whether intercropping could improve the water use and extreme weather tolerance (extreme cold and drought in our study) of rubber trees in three types of promising agroforestry systems (i.e. rubber with tea, coffee, and cocoa) in Xishuangbanna, China.
3. We found that the rubber tree is a drought-avoidance plant with strong plasticity with respect to water uptake. This characteristic is reflected by its ability to cope with serious seasonal drought, allowing it to avoid interspecific competition for water. The rubber trees showed wasteful water behaviour unless they were intercropped with tea or coffee. However, these intercropped species exhibited drought-tolerance strategies and maintained lower water use efficiencies to strengthen their competitive capacity for surface soil water. The stable δ13C values of the intercrop leaves indicated that all the agroforestry systems have stable internal microclimatic environments or higher resistance.
4. Synthesis and applications. This study suggests that interspecific competition for water can enhance the water use efficiency of drought-avoidance plants (i.e. rubber trees) and lead to complementarity between the root distributions of plants in rubber agroforestry systems (i.e. rubber with tea, coffee, and cocoa). All agroforestry systems have higher resistance, but tea was the most suitable intercrop in terms of water use because the interspecific competition for water was moderate and the agroforestry system retained much more soil water and improved the water use efficiency of the rubber tree. Considering the root characteristics of the tea trees, we suggest that the crops selected for intercropping with rubber trees should have short lateral roots and a moderate amount of fine roots that overlap with the roots of the rubber trees in the shallow soil layer.

1. 东南亚大陆与中国西南地区的橡胶种植园大幅扩张，引发了诸多生态环境问题，尤以负面水文效应最为突出。此类问题持续恶化，叠加极端天气事件愈发频发的背景，对橡胶种植业构成了严峻威胁。尽管橡胶基农林复合系统被视作提升橡胶种植可持续性与生态保护成效的最优解决方案，但该类系统中植物水分利用及其相关相互作用却极少得到研究关注。
2. 本研究以中国西双版纳地区三种极具应用前景的橡胶基农林复合系统（橡胶-茶、橡胶-咖啡、橡胶-可可）为研究对象，主要采用稳定同位素（stable isotope，δD、δ18O及δ13C）分析方法，旨在探究间作能否改善橡胶树的水分利用状况与极端天气耐受能力（本研究中特指极端低温与干旱胁迫）。
3. 研究发现，橡胶树属于具有较强水分吸收可塑性的干旱规避型植物，这一特性使其能够应对严重的季节性干旱，从而避免与间作植物发生水分竞争。未实施间作的橡胶树呈现出水分利用低效的特征，而与茶叶或咖啡间作的橡胶树则不存在该问题。此外，各间作物种均演化出干旱耐受策略，通过维持较低的水分利用效率来强化其在表层土壤水分竞争中的竞争力。间作植物叶片的稳定δ13C值特征显示，所有受试农林复合系统均拥有稳定的内部微气候环境，或具备更强的环境抗性。
4. 综合分析与实践启示。本研究表明，橡胶农林复合系统（橡胶-茶、橡胶-咖啡、橡胶-可可）中，水分的种间竞争能够提升干旱规避型植物（即橡胶树）的水分利用效率，并促成植物根系分布的生态位互补效应。所有受试农林复合系统均具备更高的环境抗性，但从水分利用角度来看，茶叶是最适配的间作作物：其与橡胶树的水分种间竞争程度适中，该复合系统可留存更多土壤水分，同时提升橡胶树的水分利用效率。结合茶树的根系特征，本研究建议，橡胶树间作作物应选择具备短侧根与适量细根、且在浅层土壤中与橡胶树根系存在分布重叠的物种。