胶农林复合系统土壤水分运移行为对植物水分来源的调控

Rubber tree (Hevea brasiliensis), the single viable source of natural rubber, shows strong synchronicity for flushing and shedding, displaying a very different phenology to the native vegetation in Xishuangbanna. As a tree native to the tropical rainforest of the Amazon Basin, its ideal habitat is characterized by small variations in air temperature and precipitation throughout the year. Plants water access strategies are affected by the distribution ration of water between matrix flow region and preferential flow region, which is an urgently problem in rubber-based agroforestry systems. In this study, based on some selected rubber-based agroforestry systems characteristics of different root system features, such as the depth root and shallow root, taproot and lateral root, pure rubber forestry serve as control plots. In this study, we will conduct several key techniques in field experiments, such as double ring infiltration, dyeing tracer, solute breakthrough curve, electron microscope scanning and three-dimensional reconstruction techniques were conducted to analyze the water infiltration characteristics (infiltration rate and infiltration amount, etc.), the water migration behavior (matrix flow, preferential flow and lateral flow, etc.), water distribution pattern (depth and width, etc.), water storage time in matrix flow region and preferential flow region, the soil microstructure; stable isotope technique (stable hydrogen, oxygen) is used to tracer the source and ratio of plants water which from preferential flow zone and matrix flow zone, and stable carbon isotopes technique is also adopted to calculate the water use efficiency by plant. This project aims to reveal the main influence factors which soil water flow behavior would affect water distribution and utilization of agroforestry system, and to explicate the difference of composite system in regulating water allocation and in improving water use efficiency. Meanwhile, we will compare the water use efficiency for the limited source-water between plants, the differential water resources among plants, and hydraulic redistribution of soil water under the different rubber agroforestry systems. The objective of this study is to select some suitable intercropping patterns among the established rubber agroforestry systems in this region, which would provide more favorable strategy of distribution and utilization of water. Our results should be offering some important references for the local rubber-based agroforestry systems planters and smallholders. These results would be useful on the improvement of adhesive garden ecological environment, not only on the building of the sustainable utilization of ecological garden pattern, but also on the providing the theoretical basis and practical reference.

针对分布于土壤基质流区和优先流区的不同含量水分如何影响植物水分获取的问题，以具有不同根系特征（深浅、主侧等）的胶农林复合系统为研究对象，以纯橡胶林为对照，采用双环入渗、染色示踪、溶质穿透曲线、电镜扫描和土壤三维结构重建等技术来分析土壤水分入渗特性（入渗速率、入渗量等）、运移行为（基质流、优先流、侧流等）、分布格局（深度、宽度等）、水分在基质流区和优先流区的储存时间、土壤微观结构，并用氢（δD）氧（δ18O）稳定同位素示踪橡胶和间作植物对优先流区和基质流区水分的利用比例，及用碳（δ13C）稳定同位素研究植物水分利用效率。揭示胶农林复合系统内土壤水分运移行为对水分在分布和利用之间的影响因子，明确调节水分分配、提高水分利用率的主要因子，为遴选一些具有良好水分分配和利用策略的复合系统、改善胶园生态环境、营造可持续利用的生态胶园模式，提供理论依据和切实参考。

土壤水分分配格局和储存能力与植物的水分利用密切相关，这种关系在具有不同根系特征的胶农林复合系统中更加复杂。揭示影响水分分配和利用效率的主要因子，为改善胶园生态环境提供理论依据和切实参考。本项目在纯橡胶林和多种胶农复合系统内建立样地，采用双环入渗、染色示踪、CT扫描等技术来分析土壤水分的入渗能力、运移行为、分布格局，土壤孔隙三维结构及其水分储存能力。结果表明，(1)单作橡胶林的管理方式会增加土壤容重，降低雨水入渗速率，雨水大多以地表径流形式流走；但在细根系处的土壤饱和导水率（Ks）、非毛管孔隙度则分别增加了96%、234%，且细根系诱导大量雨水快速入渗进入土壤内部，尔后通过水分交互作用储存于土壤孔隙中。（2）样地尺度上，Ks呈现出极高的空间异质性，间作植物区域的Ks均显著高于橡胶种植区域。（3）剖面尺度上，水分入渗具有明显的侧流、快速下移的湿润峰，这种水分运移模式对土壤水分进行了有效补给。（4）根据根系分布范围将剖面分类成优先流域和非优先流域，在降雨时期，水分优先进入优先流域，同时在深层剖面中有水分从优先流域侧向流入和保存到非优先流域；在排水阶段，优先流域水分优先排完，非优先流域的水分向优先流域补充；在无雨或干旱时期，非优先流域的毛管水向优先流域补给，满足橡胶树的水分需求。因此，两域间物理和水文性质相反，功能互补。橡胶林的不同水域组合有利于多雨时期雨水的入渗和保存，也有助于干旱时期有效水的补给。总之，纯橡胶林土壤容重高、孔隙度低、土壤水分匮缺。间作植物后，土壤有机质和全氮含量增加、土壤容重降低、土壤团聚体稳定性增强、大孔隙度和Ks均显著增加，大量优先流的发生和不同水域的组合使得土壤水分的深层入渗和补给得到了保障。