Investigation of the relationships between tree-specdes diversity and the functions of tropical rain forests

本研究的目的是了解树种多样性对热带雨林功能的控制。为了实现这一目标，我们采取了一种创新的方法，我们比较了两个自然物种丰富的(马来西亚)和物种贫乏的(夏威夷)热带雨林地区。工作假设是，更大的物种池(即区域物种多样性)可以提供更多养分利用效率较高的物种，从而减少养分可获得性，而贫穷物种库将提供养分利用效率较低的物种，从而减少养分可获得性，从而导致生物量随养分可用性的变化而发生时间变化。为了验证这一工作假说，我们在每个地区建立了一个土壤时间序列，沿着该序列，土壤养分有效性因土壤老化和相关的地球化学过程而变化。我们调查了每个地区主要树种的地上净第一性生产力和养分利用情况。通过重复测量林木次生生长量加上每两周测定一次的枯枝落叶率来估算地上净第一性生产力。采集各采样点主要树种的完整叶片，湿法消化，分析叶片矿物质含量。在夏威夷，区域物种丰富度(即种库)很小，地上净初级生产力和生物量随着土壤氮素有效性的增加而增加，接近土壤氮和磷丰富的高峰期，随后是土壤磷有效性下降的突然下降阶段。相比之下，马来西亚没有出现这种突然的变化，因为更多的磷利用高效物种用土壤磷有效性不断下降的土壤磷有效性取代了低效物种。因此，我们的工作假设被接受了。

The objectives of this study are to understand the control of the functions of tropical rain forests by tree-species diversity. In order to achieve this goal, we took an innovative approach in that we compared two naturally species-rich (Malaysia) versus species impoverished (Hawaii) tropical rain-forest regions. The working hypothesis was that a greater species pool (i.e. regional species diversity) could provide more nutrient-use efficient species to reduced nutrient availability while a impoverished species pool would provide lesser nutrient-use efficient species to reduced nutrient availability leading to a temporally variable biomass in response to nutrient availability. To test this working hypothesis, we set up one soil chronosequence in each region, along which soil nutrient availability changed due to soil aging and associated geochemical processes. We investigated the above-ground net primary productivity and nutrient-use of the major tree species in each region. The adove-ground net primary productivity was estimated by repeated measures of secondary growth of trees plus litter-fall rate which was measured bi-weekly. The intact leaves were collected from the major trees in each site and wet-digested to analyze foliar minerals. In Hawaii where regional species richness (i.e. species pool) was small, above-ground net primary productivity and biomass increased with increasing soil nitrogen availability towards a peak stage where soil nitrogen and phosphorus were abundant, followed by an abrupt decline phase where soil phosphorus availability declined. By contrast, such an abrupt change did not occur in Malaysia because more phosphorus-use efficient species replaced inefficient species with declining soil-phosphorus availability. Thus our working hypothesis was accepted.