Data from: Simplification of shade tree diversity reduces nutrient cycling resilience in coffee agroforestry

1. Agroforestry systems are refuges for biodiversity and provide multiple ecosystem functions and services. Diverse multispecies shade tree canopies are increasingly replaced by monospecific shade, often dominated by non-native tree species. The loss of tree diversity and the nature of the dominating tree can have strong implications for ecosystem functions, e.g. nutrient cycling ultimately reducing crop production. 2. To understand direct and indirect impacts of shade trees on nutrient cycling and crop production, we studied coffee agroforestry systems in India along a gradient from native multispecies canopies to Grevillea robusta (Proteaceae) -dominated canopy cover. We identified 25 agroforests, across a broad rainfall and management gradient and assessed litter quantity and quality, decomposition, nutrient release, soil fertility and coffee nutrient limitations. 3. Increasing G. robusta dominance affected nutrient cycling predominantly by; (1) changing of litter phenology, (2) reducing phosphorus (P), potassium (K), magnesium (Mg), boron (B), and zinc (Zn) inputs via litterfall, decelerated litter decomposition and immobilization of P and Zn due to low quality litter, (3) reducing soil carbon (C) and micronutrients (especially sulphur (S), Mg and B). Coffee plants were deficient in several nutrients (nitrogen (N), calcium (Ca), manganese (Mn), Mg and S in organic and B in conventional management). (4) Overall G. robusta dominated agroforests were characterized by a reduction of P cycling due to low inputs, strong immobilization while decomposition and antagonistic effects on its release in litter mixtures with coffee. 4. Synthesis and applications. The conversion of shade cover in coffee agroforestry systems from diverse tree canopies to canopies dominated by Grevillea robusta (Proteaceae) reduces the inputs and cycling of several micro- and macronutrients. Soil fertility is therefore expected to decline in G. robusta dominated systems, with likely impacts on coffee production. These negative effects might increase under the longer dry periods projected by regional climate change scenarios due to the pronounced litter phenology of G. robusta. Maintaining diverse shade canopies can more effectively sustain micro- and macronutrients in a more seasonal climate.

1. 农林业系统（Agroforestry systems）是生物多样性的天然庇护所，同时可提供多种生态系统功能与服务。当前，多样的多物种遮荫林冠正日益被单一物种遮荫林冠取代，这类单一林冠往往由外来树种主导。树木多样性的丧失以及优势树种的特性，会对生态系统功能产生显著影响——例如养分循环过程受损最终会导致作物产量下降。
2. 为探明遮荫树木对养分循环与作物产量的直接及间接影响，我们针对印度的咖啡农林业系统开展了研究，采样梯度涵盖了从本土多物种林冠到以银桦（Grevillea robusta，山龙眼科（Proteaceae））为主导的林冠覆盖类型。本研究共纳入25处农林业样地，覆盖跨度较大的降雨与管理强度梯度，并对凋落物数量与质量、分解过程、养分释放、土壤肥力以及咖啡植株的养分限制状况进行了系统评估。
3. 银桦优势度的提升主要通过以下途径影响养分循环：(1) 改变凋落物物候；(2) 通过减少凋落物输入降低磷（P）、钾（K）、镁（Mg）、硼（B）与锌（Zn）的输入量，同时因凋落物质量低下导致分解速率减缓，并加剧磷与锌的养分固持；(3) 降低土壤碳（C）与微量营养元素含量，尤其是硫（S）、镁（Mg）与硼（B）。咖啡植株存在多种养分缺乏状况：有机种植模式下植株缺乏氮（N）、钙（Ca）、锰（Mn）、镁（Mg）与硫（S），常规种植模式下则缺乏硼（B）；(4) 整体而言，以银桦为主导的农林业系统的磷循环表现为：输入量不足导致循环强度下降，且分解过程中存在强烈的固持效应，同时与咖啡凋落物混合后会对磷的释放产生拮抗作用。
4. 总结与应用。将咖啡农林业系统的遮荫林冠从多样树种结构转换为以银桦（Grevillea robusta，山龙眼科（Proteaceae））为主导的结构，会降低多种微量与大量营养元素的输入与循环效率。因此，以银桦为主导的农林业系统的土壤肥力预计会出现下降，进而可能对咖啡产量造成负面影响。由于银桦具有显著的凋落物物候特征，在区域气候变化情景预测的更长干旱期背景下，这类负面影响可能会进一步加剧。在季节性更为明显的气候条件下，维持多样的遮荫林冠能够更有效地维系土壤中的微量与大量营养元素含量。