Arbuscular mycorrhizal fungus (AMF) is widely viewed as an ecosystem engineer to help plants adapt to adverse environments. However, a majority of the previous studies regarding AMF's eco-physiological effects are mutually inconsistent. To clarify this fundamental issue, we conducted an experiment focused on wheat (Triticum aestivum L.) plants with or without AMF (Funneliformis mosseae) inoculation. Two water regimes (80% and 40% field water capacity, FWC80 (CK) and FWC40 (drought stress) and four planting densities (6 or 12 plants per pot as low densities, 24 or 48 plants per pot as high densities) were designed. AMF inoculation did not show significant effects on shoot biomass, grain yield, and water use efficiency (WUE) under the low densities, regardless of water regimes. However, under the high densities, AMF inoculation significantly decreased shoot biomass, grain yield and WUE in FWC80, while it significantly increased these parameters in FWC40, showing density and/or moisture-dependent effects of AMF on wheat performance. In FWC40, the relationships between reproductive biomass (y-axis) vs. vegetative biomass (x-axis) (R-V), and between grain biomass (y-axis, sink) vs. leaf biomass (x-axis, source) fell into a typical allometric pattern (α > 1, P < 0.001), and the AMF inoculation significantly increased the values of α. Yet in FWC80, they were in an isometric pattern (α ≈ 1, P < 0.001) and AMF addition had no significant effects on α. Similarly, AMF did not significantly change the isometric relationship between leaf biomass (i.e., metabolic rate) and shoot biomass (body size) in FWC80, while it significantly decreased the α of allometric relationship between both of them in FWC40 (α > 1, P < 0.001). We therefore, sketched a generalized model of R-V and sink-source relationships as affected by AMF, in which AMF inoculation might enhance the capabilities of sink acquisition and utilization under drought stress, while having no significant effect under the well watered conditions. Our findings demonstrate dual density- and moisture-dependent effects of AMF on plant development and provide new insights into current ecological applications of AMF as an ecosystem engineer.

中文翻译：

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丛枝菌根对小麦干旱适应的密度和水分依赖性影响

丛枝菌根真菌 (AMF) 被广泛视为帮助植物适应恶劣环境的生态系统工程师。然而，先前关于 AMF 的生态生理效应的大多数研究是相互矛盾的。为了澄清这个基本问题，我们进行了一项针对有或没有 AMF ( Funneliformis mosseae ) 的小麦 ( Triticum aestivum L.) 植物的实验。) 接种。设计了两种水分状况（80% 和 40% 田间蓄水量，FWC80 (CK) 和 FWC40（干旱胁迫））和四种种植密度（每盆 6 或 12 株植物为低密度，每盆 24 或 48 株植物为高密度） . AMF 接种对低密度下的枝条生物量、粮食产量和水分利用效率 (WUE) 没有显着影响。然而，在高密度下，AMF 接种显着降低了枝条生物量、粮食产量和 WUE在 FWC80 中，而在 FWC40 中显着增加了这些参数，显示了 AMF 对小麦性能的密度和/或水分依赖性影响。在 FWC40 中，生殖生物量（y轴）与营养生物量（x轴）之间的关系（ RV），以及谷物生物量（y轴，汇）与叶片生物量（x轴，源）落入典型的异速生长模式（α > 1，P  < 0.001），AMF 接种显着增加了 α 值。然而在 FWC80 中，它们处于等距模式（α ≈ 1，P  < 0.001），并且 AMF 添加对 α 没有显着影响。同样，AMF 没有显着改变 FWC80 中叶片生物量（即代谢率）和枝条生物量（体型）之间的等长关系，而显着降低了 FWC40 中两者之间的异速关系α（α > 1，P < 0.001)。因此，我们绘制了一个受 AMF 影响的 RV 和库源关系的广义模型，其中 AMF 接种可能会提高干旱胁迫下库的获取和利用能力，而在充分浇水的条件下没有显着影响。我们的研究结果证明了 AMF 对植物发育的双重密度和水分依赖性影响，并为 AMF 作为生态系统工程师的当前生态应用提供了新的见解。