LTREB: Sustainability of Soil Fertility in Reconstructed Tropical Ecosystems

小行星9318403 保持土壤肥力是湿热带森林恢复和可持续发展面临的一项重大挑战，在那里，有机物迅速分解，矿物质风化迅速，大量降雨会沥滤植物生长所必需的养分。 在控制土壤肥力的许多因素中，有两个可能非常重要：植物生命形式（树木、棕榈树、灌木、藤蔓等）的数量，以及植物群落被收获或干扰的频率。 1991年在哥斯达黎加的La Selva生物站建立了由快速生长的热带树种（Hyeronima、Cordia和Cedrela）组成的复制种植园，将用于研究这两个因素对土壤肥力的控制。 在一些种植园中，树木以单一栽培方式生长;这些树木将每隔1年、4年和16年收获并重新种植。 其他种植园包含树木和其他生命形式的植物，如棕榈树和香蕉类草药。 淋溶是通过表征土壤水的化学性质，并通过将水中营养物质的浓度乘以其向下移动的速度来确定的。 向下运动将根据水平衡模型进行估算，该模型包括土壤蒸发和蒸腾作用，后者来自能量平衡测量（太阳辐射、风速）、植物通过叶片传递水分的能力（气孔导度）和空气蒸发能力（来自树冠的温度和湿度测量）。 随着轮作间隔时间的增加和植物生命形式的多样性增加，预计沥滤率会降低。 植物群落利用土壤资源的有效性对维持土壤肥力也很重要，而且也可能随着生物复杂性和收获或干扰的频率而变化。 为了评估这种有效性，将通过测量植物和土壤中养分储存和周转的变化来获得养分吸收、回收和利用的效率。 再加上养分淋溶数据，这些效率之间的林分的比较将提供生态上合理的热带森林恢复和热带土壤的可持续利用的指导。

9318403 Ewel Maintenance of soil fertility is a major challenge to forest restoration and sustainable development in the humid tropics, where organic matter breaks down quickly, weathering of mineral matter is fast, and high rainfall leaches nutrients essential for plant growth. Among the many factors that control soil fertility, two are likely to be of great importance: the number of plant life forms (trees, palms, shrubs, vines, etc.), and the frequency with which the plant community is harvested or disturbed. Replicated plantations consisting of fast-growing tropical tree species (Hyeronima, Cordia,and Cedrela), established in 1991 at La Selva Biological Station in Costa Rica, will be used to study the controls that these two factors exert on soil fertility. In some of the plantations, the trees are grown in monoculture; these will be harvested and replanted at intervals of 1, 4, and 16 years. Other plantations contain the trees plus plants of other life forms, such as palms and banana-like herbs. Leaching is determined by characterizing the chemistry of soil water and by multiplying the concentrations of nutrients in the water by the rate of its downward movement. Downward movement will be estimated from a water-balance model that incorporates evaporation from the soil and transpiration, which is derived from energy balance measurements (solar radiation, wind speed), the ability of the plants to pass water through their leaves (stomatal conductance), and the evaporative power of the air (from temperature and humidity measurements in the tree canopies). Leaching rates are expected to diminish with increasing time intervals between rotations and with increasing diversity of plant life forms. The effectiveness with which plant communities exploit soil resource is also important to sustaining soil fertility, and it, too, is likely to vary with biotic complexity and frequency of harvest or disturbance. To assess this effectiveness, efficiencies of nutrient uptake, recovery, and us e will be obtained from measures of changes in nutrient storage and turnover in both plants and soil. Coupled with the nutrient leaching data, comparison of these efficiencies among stands will provide ecologically sound guides to tropical forest restoration and the sustainable use of tropical soils.