Climate-change effects on bryophyte carbon balances in the warm tropics: a rainforest experiment complemented by simulation modelling

气候变化将影响全球植物的生长和分布，但准确的预测是困难的。对于热带树木和作物，报告对变暖的反应不一致，而对于其他植物，这种信息基本上不存在。苔藓植物（苔藓和地钱），热带森林的一个重要组成部分，在丰富性和多样性方面表现出强烈的海拔梯度，是我们DFG资助的项目全球变暖对热带苔藓植物的影响：负碳平衡会把热带低地变成一个苔藓沙漠吗？我们解决了一个以温度为中心的假设，该假设将温暖低地中的Brittites的缺乏与由于温暖夜晚的高呼吸率和每日碳收益低而难以获得正碳平衡联系起来。我们还研究了未来变暖的影响，暗示在这个假设中，山地britonites。我们最重要的发现是：1。光合作用和呼吸作用的温度响应似乎很好地适应当前的当地条件，因此，CO2交换率本身不能解释海拔brittite丰度模式。2.移植到较低的，温暖的海拔山地bratelites没有明显的适应CO2交换，这是由不同物种的样品的长期生存形成对比。因此，驯化结果不具有决定性。3.干燥耐受性高，以及在山地和低地brittites，不能解释海拔模式，不应该成为温和的气候变化下的限制。我们的结论是，无论是干燥耐受性，也没有代谢温度的反应可以解释目前在热带地区的bratonite丰度模式。更有可能的是，苔藓水合作用的时间和持续时间是低地和山地生境之间的主要区别。然而，我们的研究结果不允许预测超出目前的气候范围。气候变化的影响将取决于水化模式的变化和驯化，但这些过程的信息是完全缺乏的低地britonites。因此，这些问题是拟议项目的主要重点。我们的目标是研究气候变化对热带低地briterites的影响与新的现场和模型实验。在野外试验中，在森林下层原位的开顶室中加热和CO2施肥，持续18个月。我们将确定二氧化碳交换率，活动模式，生长和生存的变化。同时，将开发一个模型，以实测或模拟的小气候数据为输入，计算基于环境响应曲线的碳平衡。该模型的目的是更好地解释实地数据，并研究水化模式变化和其他气候变化对长期碳平衡的影响。该模型的未来用途还包括探索热带地区海拔梯度和其他生物地理模式的解释。

Climate change will affect plant growth and distributions globally, but accurate predictions are difficult. For tropical trees and crops, inconsistent responses to warming are reported, while for other plants such information is largely non-existent. Bryophytes (mosses and liverworts), an important component of tropical forests showing strong elevational gradients in abundance and diversity, were the focus of our DFG-funded project Global warming effects on tropical bryophytes: will negative carbon balances turn the tropical lowlands into a bryophyte desert? We addressed a temperature-centred hypothesis which links the paucity of bryophytes in the warm lowlands to difficulties in gaining a positive carbon balance due to high respiration rates in warm nights and low daily carbon gains. We also studied the effects of future warming, implied in this hypothesis, for montane bryophytes. Our most important findings were: 1. Temperature responses of photosynthesis and respiration appear well-adapted to current local conditions, so that CO2-exchange rates per se cannot explain the elevational bryophyte abundance pattern. 2. Montane bryophytes transplanted to lower, warmer elevations did not measurably acclimatize CO2-exchange, which was contrasted by long-term survival of samples from various species. Results on acclimation were thus not conclusive. 3. Desiccation tolerance was high in montane as well as lowland bryophytes and cannot explain elevational patterns and should not become limiting under mild climate change. We conclude that neither desiccation tolerance nor metabolic temperature responses can explain current bryophyte abundance patterns in the tropics. More likely, the timing and duration of moss hydration are the main distinction between lowland and montane habitats. However, our results do not allow projections beyond the current range of climates. Climate-change effects will depend on changes in hydration patterns and on acclimation, but information about these processes is lacking completely for lowland bryophytes. These issues are therefore the main foci in the proposed project. We aim to study climate-change effects on tropical lowland bryophytes with novel field- and model-experiments. In the field experiment, bryophytes are warmed and CO2-fertilized in open-top chambers in situ in the forest understorey for 18 months. We will determine changes in CO2-exchange rates, activity patterns, growth and survival. Simultaneously, a model will be developed, calculating carbon balances of bryophytes based environmental response curves, with measured or simulated microclimatic data as the input. The aims of the model are to better interpret the field data and to study the effects of changes in hydration patterns and other climatic changes on long-term carbon balances. Future uses of this model also include exploring explanations for the elevational gradients in the tropics and other biogeographical patterns in bryophyte abundance.