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

热带山地森林是陆地生态系统中最迷人但研究最少的。在生态系统科学方面，他们结合了温带森林的一些属性（年平均温度低）和低地热带森林的一些属性（缺乏温度季节性），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测试。除了在土壤中储存大量碳之外，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。在潮湿的热带地区，随着海拔梯度的上升，生态系统特性的两个趋势会很突出：地上生产力（木材和树叶的生产）的明显下降，以及土壤和死生物量有机储量的增加，而活生物量的减少则是代价。然而，尽管这些趋势是有据可查的，但关于这些趋势的原因仍然存在相当大的争论。我们将关注辩论的三个方面：地下根系生产力是否与地上生产力同时下降，或者它是否实际上增加了（正如最近的一项研究表明的那样），导致总生产力随海拔的变化几乎没有趋势？-低地热带森林通过呼吸损失的碳是否比热带山地或温带森林多？这种比例损失的幅度是否与环境温度有关？-腐烂率随海拔升高而下降是否完全由温度解释，还是凋落物质量是一个重要因素？在这个建议中，我们将通过在安第斯山脉沿高度样带的四个地点对植物、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。这将建立和补充我们目前在秘鲁亚马逊低地进行的类似测量。我们于2003年建立了实地研究地点。我们将：(i)对地上和地下生产力进行详细观察，测量木材、树叶和根的产量。量化来自树叶、木材和根系以及凋落物和土壤中腐烂有机物的呼吸性二氧化碳排放。（iii）量化凋落物和土壤库中碳、氮、磷的储量和流量。量化温度、凋落物质量和降雨对凋落叶、木屑、腐殖质和土壤有机质腐烂率的影响，方法是进行一项迁移实验，在样带沿线不同海拔之间交换凋落叶、枯木和土壤样本，并长期监测材料的腐烂率。

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.