Abstract The diversification of agroecosystems with shade trees has a complex role in climate change adaptation. Multiple interactions among shade tree composition, heterogeneous soil conditions, and resulting microclimate modifications makes reproducible evaluations of agroforestry as a climate change adaptation practice challenging. In this study we systematically investigate soil water and nutrient acquisition strategies in cocoa (Theobroma cacao) along a climatic and diversity gradient in Ghana, West Africa. We adopted a functional trait-based approach to comparatively examine cocoa root strategies in monoculture or in agroforestry with a single species of shade tree (Terminalia ivorensis) across two precipitation regimes (optimal and suboptimal dry), and in contrasting edaphic conditions (sandy and loam). Variance decomposition indicated that shade trees explained 20 % of the variability in absorptive root trait covariation in cocoa. However, shade tree effects on trait expression were not systematic and depended on climatic and edaphic conditions. Notably, effects of shade trees were amplified on fine-textured soils, with significantly higher conservative trait values of cocoa absorptive roots when in agroforestry within a suboptimal precipitation regime. Transport root traits (root tissue density, diameter) associated with water and solute transport strongly varied among contrasting climate and edaphic conditions. Structural equation models indicated that soil texture played a critical role in regulating transport root trait expression. In agroforestry, clay content improved soil moisture levels, and, in suboptimal climate, fine root growth rates were positively affected by specific leaf area while being significantly controlled by soil texture. Results describe the importance of soil texture in controlling the effect of shade trees on cocoa cultivated in suboptimal precipitation regimes. Thus, agroforestry success as a climate change adaptation strategy in cocoa systems requires detailed assessments of crop strategies in different climatic conditions, as well as identification of soil-mediated filters on crop function.

中文翻译：

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土壤质地在跨气候梯度的农林复合系统中调节根系功能性状

摘要 具有遮荫树的农业生态系统多样化在适应气候变化方面具有复杂的作用。遮荫树组成、异质土壤条件和由此产生的小气候变化之间的多重相互作用使得对农林业作为气候变化适应实践的可重复评估具有挑战性。在这项研究中，我们系统地调查了可可（可可可可）中沿气候和多样性梯度在西非加纳的土壤水分和养分获取策略。我们采用了一种基于功能性状的方法，在两种降水状况（最佳和次优干燥）以及对比土壤条件（沙质和壤土）中，在单一栽培或农林业中使用单一树种（Terminalia ivorensis）比较检查可可根策略。 ）。方差分解表明，遮荫树解释了可可吸收根性状共变中 20% 的变异性。然而，遮荫树对性状表达的影响不是系统的，取决于气候和土壤条件。值得注意的是，遮荫树对细质地土壤的影响被放大，在次优降水情况下的农林业中可可吸收根的保守性状值显着更高。与水和溶质运输相关的运输根特征（根组织密度、直径）在对比气候和土壤条件下差异很大。结构方程模型表明土壤质地在调节运输根系性状表达中起关键作用。在农林业中，粘土含量提高了土壤水分含量，并且在次优气候下，细根生长率受特定叶面积的积极影响，同时受土壤质地的显着控制。结果描述了土壤质地在控制遮荫树对在次优降水条件下种植的可可的影响方面的重要性。因此，农林业作为可可系统中气候变化适应策略的成功需要对不同气候条件下的作物策略进行详细评估，并确定土壤介导的作物功能过滤器。