A detailed assessment of ecosystem carbon dynamics along an elevation transect in the Andes

热带山地森林是最迷人但研究最少的陆地生态系统之一。在生态系统科学方面，它们结合了温带森林(低年平均温度)和低地热带森林(缺乏温度季节性)的一些属性，从而为我们对气候控制生态系统碳和养分循环的理解提供了重要的考验。除了在土壤中拥有大量的碳储备外，它们还拥有全球生物多样性的很大一部分。因此，热带山地森林生态系统的变化可能对全球生物多样性和全球碳循环产生深远影响。当一个人在潮湿的热带地区攀登海拔梯度时，生态系统特性的两个趋势变得突出：地上生产力(木材和树叶的生产)明显下降，土壤和死生物质有机储量增加，而活的生物质减少。然而，尽管这些趋势有很好的记录，但关于这些趋势的原因仍然存在相当大的争论。我们将集中在辩论的三个方面：-地下根生产力是与地上生产力同时下降，还是实际上增加(最近的一项研究表明)，导致总生产力几乎没有随海拔变化的趋势？-低地热带森林是否比热带山地或温带森林通过呼吸损失更多的碳，这种比例损失的幅度是否与环境温度有关？-凋落物质量是完全由温度解释的，还是凋落物质量是重要因素？在这项提案中，我们将通过对安第斯山脉垂直样带上四个地点的植物、凋落物和土壤碳动态进行详细测量，来探索这两种趋势的原因。这将建立在我们目前在秘鲁低地亚马逊地区进行的类似测量的基础上，并对其进行补充。我们于2003年建立了实地考察场地，我们将：(I)对地上和地下的生产力进行详细的观察，测量木材、树叶和根的产量。(2)对树叶、木材和树根以及凋落物和土壤中腐烂的有机物质的呼吸二氧化碳排放量进行量化。(3)量化凋落物和土壤池中的C、N和P的存量和流动。(4)量化温度、凋落物质量和降雨对凋落物、木质碎屑、腐殖质和土壤有机质衰减率的影响，方法是进行一项迁移实验，将凋落物、枯木和土壤的样本在样带的不同海拔之间交换，并随时间监测材料的衰减率。

Tropical montane forests are amongst the most fascinating yet least studied of terrestrial ecosystems. In terms of ecosystem science, they combine some of the attributes of temperate forests (low mean annual temperature) with those of lowland tropical forests (lack of temperature seasonality), and thereby provide an important test of our understanding of climatic controls on ecosystem carbon and nutrient cycling. In addition to holding large stocks of carbon in their soils, they host a large fraction of global biodiversity. Hence changes in tropical montane forest ecosystems could have a profound effect on global biodiversity and the global carbon cycle. As one climbs an elevation gradient in the wet tropics, two trends in ecosystem properties stand out: an apparent decline in above-ground productivity (the production of wood and leaves), and an increase in soil and dead biomass organic stocks at the expense of live biomass. However, although these trends are well-documented, there is still considerable debate as to the causes of these trends. We will focus on three aspects of the debate: - does below-ground root productivity decline in parallel with above-ground productivity, or does it actually increase (as indicated by a recent study), resulting in little trend in total productivity with elevation ? - do lowland tropical forests lose more carbon through respiration than tropical montane or temperate forests, and is the magnitude of this proportional loss related to ambient temperature ? - is the decline in decay rates with increasing elevation entirely explained by temperature, or is litter quality and important factor ? In this proposal we will explore the causes of both these trends, by conducting detailed measurements of plant, litter and soil carbon dynamics at four sites along an altitudinal transect in the Andes. This will build upon and complement similar measurements that we are currently conducting in the lowland Peruvian Amazon. We established the field study site in 2003 We will: (i) Conduct detailed observation of above- and below-ground productivity, measuring the production of wood, leaves and roots. (ii) Quantify respiratory CO2 emissions from leaves, wood and roots, and from decaying organic matter in litter and soils. (iii) Quantify the stocks and flows of C, N and, P in litter and soil pools. (iv) Quantify the the effects of temperature, litter quality and rainfall on the decay rates of leaf litter, woody debris, humic material and soil organic matter, by conducting a translocation experiment, where samples of litter, dead wood and soil with be swapped between different elevations along the transect, and the decay rates of material monitored over time.