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营养循环可能会减少它们获取基岩中所含养分的需要，特别是在日益风化向更潮湿的气候发展的情况下。此外，营养循环还受到更高营养水平的影响，即食草性。然而，气候，特别是降雨，如何与草食动物相互作用影响养分循环和凋落物分解几乎是未知的。我们的总体目标是剖析生物因素(植物、微生物、草食动物)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上的过程进行深入研究，并通过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，将生物和地球化学过程直接联系起来。我们扩大了最初的重点，即植物-土壤-地质学的反馈，包括向下和向上的与凋落物相关的反馈。具体地说，我们将集中于a)植物和土壤微生物的营养限制和营养效率，以及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空间换时间方法与现场操纵气候条件的机械定向野外实验相结合。通过这种方法，我们解决了以下主要问题：空间气候梯度，即地球表面长期气候影响的结果，是否可以作为短期到中期时间气候变化的代理？哪些过程(绿色、棕色和灰色)最能用空间梯度来描述？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，并辅之以创新的稳定同位素示踪剂。通过阐述一整套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EarthShape的支柱。此外，我们的研究是智利第一次使用大型野外实验来调查气候变化对生态系统过程的影响。

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.