Arbuscular mycorrhizal fungi (AMF) enhance nutrient provision in exchange for carbon. However, a shift from nutrient to carbon limitation, induced by repeated or intense defoliation, can represent a trade-off between plant regrowth and the maintenance of mycorrhiza. The combined effects of AMF, phosphorus and defoliation on growth of Agropyron elongatum (C₃ grass, low mycorrhizal responsiveness) and Brachiaria brizantha (C₄ grass, high mycorrhizal responsiveness) were explored. Each species was subjected to a manipulative experiment with AMF inoculation (non-inoculated, inoculated), soluble P supply (low, high) and defoliation (non-defoliated, 60% defoliated). In A. elongatum, at low P supply, mycorrhizal plants showed increased growth rates following defoliation without substantial changes in AMF colonization. At high P supply instead, we found a clear trade-off between regrowth and the maintenance of mycorrhiza evidenced by growth depression (biomass and tillers) and lower AMF activity (reduction of arbuscules). In contrast, in B. brizantha, defoliation effects on plant regrowth were independent from AMF at any P supply (no trade-off). This indicates that cost-benefit relationship in defoliated plants is highly context-dependent and may vary with mycorrhizal responsiveness of species. This variation of responses can play a decisive role on plant recovery in pastures and natural grasslands subjected to herbivory.

丛枝菌根真菌（AMF）可以增加碳的营养供应。然而，由反复或强烈的脱叶引起的从养分向碳限制的转变，可能代表了植物再生长和菌根维持之间的权衡。AMF，磷和脱叶的上生长的组合效应甲gropyron 麦草（C ₃草，低菌根响应性）和乙rachiaria brizantha（C ₄草，高菌根响应性）进行了探讨。对每种物种进行了AMF接种（未接种，接种），可溶性磷供应（低，高）和脱叶（无脱叶，60％脱叶）的操作实验。在伸长的A. elongatum菌根植物在落叶后表现出增加的生长速率，而AMF菌落没有明显变化。相反，在高磷供应下，我们发现生长恢复（生物量和分ers）和较低的AMF活性（减少丛枝）证明了再生长和菌根维持之间的明显权衡。相反，在B. brizantha中，在任何磷供应下，落叶对植物生长的影响均独立于AMF（无权衡）。这表明，落叶植物的成本效益关系高度依赖于上下文，并且可能随物种的菌根响应而变化。响应的这种变化可以对草食性牧场和天然草原中的植物恢复起决定性作用。