中国科学院西双版纳热带植物园机构知识库

西双版纳最显著的土地利用变化就是大面积的热带森林被结构单一的纯橡胶林所替代，由此导致的生态环境恶化问题日益凸显（生物多样性降低、水土流失和土壤退化等）。因此，橡胶种植业面临严峻挑战，亟待优化其单一的种植方式和发展友好型生态胶园模式。胶农复合系统被认为是改善橡胶单一栽培下土壤性质和整体生态环境质量的较佳途径，但亟需通过量化各胶农复合系统和单层橡胶林的土壤质量指标确定间作模式。其次，橡胶林下分布着大量的白蚁种群，其搬运、筑巢、觅食等行为显著影响土壤状况，通过研究白蚁活动和白蚁巢穴行为对橡胶林土壤营养元素循环和生态水文特征的影响有助于进一步了解白蚁在热带森林系统的作用。本研究通过选取中科院西双版纳热带植物园内的单层橡胶林和橡胶-咖啡、橡胶-可可、橡胶-大叶千斤拔、橡胶-龙血树胶农复合系统为研究对象，采用湿筛法、环刀法等研究方法，测定了各胶园土壤团聚体、理化性质和水文特征，旨在优化现存的生态胶园栽培模式；选取橡胶林下不同类型的白蚁堆（原生、次生和遗弃白蚁堆）及对照自然土壤为研究对象，采用化学分析法和染色示踪法测定了白蚁堆和自然土壤的营养元素和水文特征，探讨了白蚁在橡胶林土壤的功能作用。结果表明：（1）胶农复合系统显著提高了土壤水稳定大团聚体（> 0.25 mm）含量和土壤团聚体稳定性（MWD）；土壤有机碳和氮含量与土壤团聚体稳定性呈显著正相关关系；团聚体嵌合的有机碳和氮含量随土壤团聚体粒径的增大而增高，胶农复合系统团聚体嵌合的有机碳和氮含量显著高于单层橡胶林；胶农复合系统显著提高了与土壤团聚体稳定性显著相关的土壤有机碳、植物细根、凋落物和土壤粘粒的含量。在湿筛过程中，土壤有机碳和氮流失比率和原土有机碳和氮含量，以及和土壤团聚体稳定性显著负相关；胶农复合系统较高的土壤团聚体稳定性，能够减缓团聚体内有机碳和氮的流失，促进胶林土壤有机碳和氮的固定（2）与热带自然雨林相比，单一橡胶种植的土壤退化较为严重，导致胶园水分短缺、土壤结构不稳定、养分流失和土壤渗透缓慢。构建胶农复合系统以后，土壤质量显著改善，胶农复合系统恢复了土壤物理性质（增加了土壤总孔隙度、毛细管孔隙度、增强土壤团聚体稳定性和减少土壤紧实度）；改善了土壤化学性质（土壤有机碳、氮、磷、钾、钙、镁等元素）；提高了土壤水文特征（增加土壤水分渗透、提高土壤含水量和田间持水量等）。（3）林下不同发育程度的白蚁堆（原生、次生和遗弃白蚁堆）通过固定和重新分配营养物质，影响橡胶林土壤系统的发育；白蚁利用深层土壤颗粒营造原生白蚁堆，相比较对照自然土壤白蚁堆NO3-含量显著增加，但有机C和N含量显著减少；白蚁堆被遗弃后，白蚁堆Corg和N含量显著增加，但NH4+和NO3-含量显著下降；当白蚁堆被重新启用后，其顶部新鲜土壤营养元素含量与周围自然土壤差异显著、与原生白蚁堆相近，其侧面原位土壤营养元素含量与遗弃白蚁堆相近；由于侵蚀风化等自然因素，白蚁堆营养元素循环周转到对照自然土壤，能够增加橡胶林土壤营养元素（Corg、N、NH4+和NO3-）含量。（4）白蚁堆结构和白蚁活动显著影响白蚁堆和对照自然土壤的水文特征。在雨季，白蚁堆呈现的教堂状能够将雨水快速排到对照自然土壤，增加橡胶林土壤排水压力。白蚁堆夯实敦厚的外墙可以减缓水分的入渗，但也会减少水分进入胶林土壤；白蚁在白蚁堆和自然土壤上修建大量的通道，能够增加优先流路径，促进土壤水分的入渗及运移；在极端缺水的干季，紧实的土堆墙可以有效减少水分蒸发，加上白蚁从深层土壤水源主动运输水分，可以提高白蚁堆含水量，维持适宜的小环境气候。白蚁活动及其建筑的白蚁堆结构不仅可以维持白蚁堆内稳定的水分含量，还可以促进胶林土壤排水能力和抵御极端干旱的能力。基于以上结论，胶农复合系统，尤其是橡胶-可可、橡胶-大叶千斤拔和橡胶-龙血树复合系统，能够显著改善橡胶林土壤的理化性质，缓解土壤退化；橡胶林下白蚁堆呈现显著的养分时空异质性，并且通过白蚁堆结构及白蚁活动调节内部水分环境，其在生态系统养分固定、再分配和物质循环扮演着重要的角色。

The transformation from both primary and secondary forests to rubber plantations, most of which are rubber monoculture, has resulted in numerous negative environmental consequences, particularly reduction of biodiversity, soil erosion and environmental degradation. Rubber-based agroforestry (Hevea brasiliensis) systems are considered the best way to improve soil properties and the overall environmental quality of rubber monoculture. However, it is urgently needed to examine the changes of soil physico-chemical properties and their related interactions to evaluate the improvement of the soil physico-chemical properties by the rubber-based agroforestry systems. In addition, there are a large number of termites in the rubber plantations, whose behaviors such as nesting and foraging significantly affect the soil systems. Therefore, it is important to examine the influence of the termite activities and their nests on the soil systems in the rubber plantations. In order to evaluate the improvement of the soil physico-chemical properties in the rubber plantations, this study used the cutting ring method and wet sieving method to examine the soil aggregate, soil structure, soil nutrients and soil hydrological properties in the monoculture rubber plantation, the rubber-based agroforestry systems (H. brasiliensis–C. arabica, H. brasiliensis–T. cacao, H. brasiliensis–F. macrophylla and H. brasiliensis–D. cochinchinensis) and the natural rainforest. In addition, this study used chemical analysis method and dye tracer method to investigate the effects of the termite nests and the termite activities on soil nutrient properties and hydrological chrematistics through the chronological development of termite mounds (primary, secondary-occupied and abandoned mounds) in the rubber plantations. This study mainly make the following conclusions: (1) The rubber-based agroforestry systems significantly enhanced the formation of macroaggregate (> 0.25 mm) and increased soil aggregate stability (MWD) compared to the rubber monoculture. Soil organic matter (SOC) and N contents were shown to have significantly positive correlations with the MWD. The macroaggregate fractions contained more organic carbon and nitrogen than the microaggregate fractions. SOC and N contents in all water-stable aggregate fractions were significantly higher in the rubber-based agroforestry systems (except CAAs) compared to the rubber monoculture. The rubber-based agroforestry systems increased soil organic carbon and nitrogen, improved plant roots and litters, and enhanced soil clay contents; these factors significantly affected the stability of soil aggregates. The proportions of C and N loss from slaking and sieving were shown to have significantly negative correlations with the MWD and the SOC and N concentrations in bulk soil. The rubber-based agroforestry systems helped improve soil aggregation, decreased carbon and nitrogen loss, and ultimately improved the carbon and nitrogen accumulation rates. (2) Soils in the rubber plantations suffered serious degradation (limited soil moisture, poor soil structure, depleted nutrients and serious soil erosion) after the conversion from the tropical rainforest to the rubber monoculture. However, the rubber-based agroforestry systems could evidently improve the soil properties, including improved the physical properties (increased soil total and capillary porosity, improved soil MWD and reduced soil density), enriched the soil nutrients (enhanced soil organic matter, nitrogen, P, K, Ca, Mg, etc.), and improved the soil hydrological properties (increased soil infiltration, improved soil water content and field capacity). (3) The nutrient concentrations changed through the chronological development of termite mounds (primary, secondary and abandoned mounds), which affected soil ecosystem processes through the stabilization and redistribution of nutrients. The concentration of NO3-in the primary mound increased, while organic carbon (Corg) and total N decreased compared to natural control soils. The nutrients in the mounds recycled in soils due to the natural factors such as erosion and weather, thus increasing the nutrient contents (Corg, N, NH4+ and NO3-) in the natural control soils. The mean concentrations of nutrients were significantly different between fresh parts (sampling locations 1–3) and old parts (locations 4–6) of the secondary-occupied mounds. The nutrients in the fresh parts of the mound approached the values in the primary mound; whereas the nutrients in the old part of the mound approached the values in the abandoned mound. (4) Termite significantly affected the hydrological characteristics in the termite mounds and the natural surrounding soils. During the rainy season, the cathedral-shaped mound can quickly deliver rainwater into the natural surrounding soils, increasing the drainage pressure in the soils in rubber plantations. The compacted outer walls can decrease water infiltration into the mound, and also reduce the water into the soils in rubber plantations. A large number of channels created by termites in the termite mound and the natural surrounding soils can increase the preferential flow paths and promote soil water infiltration and transportation. During the dry season, the high-density mound wall effectively reduced evaporation, and the termites could actively transport water to maintain favourable microclimatic conditions. Not only could the activities of termites and their nests keep the moisture levels within tolerable ranges, but also enhance soil ecosystem resistance to extreme drought in the rubber plantations. In conclusions, the rubber-based agroforestry systems, especially the H. brasiliensis–T. cacao, H. brasiliensis–F. macrophylla and H. brasiliensis–D. cochinchinensis agroforestry systems, can significantly improve the physico-chemical properties and alleviate soil degradation in the rubber plantations. It is remarkable spatio-temporal variations of the nutrients in the termite mounds in the rubber plantations. Moreover, the mound structures and termite activities can regulate the internal water environment, which plays an important role in nutrient stabilization and redistribution, material circulation in the ecosystem. Key Words: Soil aggregate stability, physico-chemical properties, hydrological characteristics, termite activities，dye tracer