Connecting the green and the grey world: an experimental approach to separating climate, vegetation, and geochemical effects on nutrient cycling along a climate gradient

生物群可能塑造地球表面的一个因素与它们作为“风化引擎”的积极作用有关。然而，植物和土壤微生物的有效养分循环可能会减少它们对基岩中所含养分的需求，特别是在气候越来越潮湿的情况下。此外，营养循环受到更高营养水平的影响，即草食性。然而，气候，特别是降雨，如何与草食相互作用，影响养分循环和凋落物分解，实际上是未知的。我们的总体目标是剖析生物（植物、微生物、食草动物）和非生物因素（地质、气候）在与风化和生物地球化学养分循环相关的过程中的相对重要性。我们将通过以下方式直接将生物和地球化学过程联系起来：a)在第一阶段奠定的基础上，对绿色、棕色和灰色世界之间的界面过程进行深入研究；b)对这些数据和一个大型跨学科联盟在我们的干旱实验中合作收集的新数据进行综合分析。我们将最初的重点扩展到与凋落物“向下”和“向上”相关的植物-土壤-地质反馈。具体来说，我们将关注a)植物和土壤微生物的营养限制和营养效率，b)草食对凋落物分解的影响，这两者都可能影响生物地球化学岩石风化。为此，我们将EarthShape的时空方法与机械导向的现场实验相结合，以操纵现场气候条件。通过这种方法，我们解决了以下首要问题：空间气候梯度，即对地球表面的长期气候影响的结果，能否作为中短期时间气候变化的代理？哪些过程（“绿色vs棕色vs灰色”）可以用空间梯度来最好地描述？我们将能够根据实地观察和实验以及温室中的植物和草食实验来回答这些问题。为了评估养分循环，我们将测量植物、土壤和土壤微生物中的养分，并辅以创新的稳定同位素示踪剂。通过解决整个生物群在营养循环中的明确作用，我们将揭示它们作为“风化引擎”的潜在作用，这是地球形状的支柱。此外，我们的研究是智利第一个利用大型野外实验调查气候变化对生态系统过程影响的研究。

One component why biota might shape the Earth’s surface is related to their active role as “weathering engine”. However, efficient nutrient cycling of both plants and soil microorganisms might reduce their need to access nutrients contained in bedrock especially under increasingly progressed weathering towards more humid climate. In addition, nutrient cycling is affected by even higher trophic levels i.e., herbivory. However, it is virtually unknown how climate, especially rainfall, interacts with herbivory in affecting nutrient cycling and litter decomposition.Our overall goal is to dissect the relative importance of biotic (plants, microorganisms, herbivores) and abiotic factors (geology, climate) on processes related to weathering and biogeochemical nutrient cycling. We will directly link biological and geochemical processes by a) doing in-depth studies on processes at the interface between the green, the brown, and the grey world that build on the foundations laid in Phase 1, and by b) doing integrated analyses of this data and of new data collected by a large interdisciplinary consortium collaborating in our drought experiment.We expand our initial focus on plant-soil-geology feedbacks related to litter both ‘downwards’ and ‘upwards’. Specifically, we will focus on a) nutrient limitation and nutrient efficiency of plants and soil microorganisms, and b) the influence of herbivory on decomposability of litter that both potentially affect biogeochemical rock weathering. To that end, we combine the EarthShape space-for-time approach with mechanistically orientated field experiments that manipulate climate conditions on-site. With this approach, we address the following overarching questions: Can spatial climate gradients, i.e. the result of long-term climatic impact on the earth surface, serve as proxy for short- to medium-term temporal climatic changes? Which processes (‘green vs. brown vs. grey’) can be best described by spatial gradients? We will be able to answer these questions based on observations and experiments in the field as well as plant and herbivory experiments in the greenhouse. To assess nutrient cycling, we will measure nutrients in plants, soil and soil microorganisms complemented by innovative stable isotope tracers. By addressing the explicit role of a whole suite of biota in nutrient cycling, we will reveal their potential role as “weathering engine” which is a backbone of EarthShape. Additionally, our study is the first in Chile to investigate climate change impacts on ecosystem processes using large field experiments.