Background and aims

Positive plant-plant interactions (i.e. facilitation) often occur under stressful environments and regulate population and community dynamics. However, the relative importance of shoot vs. root facilitation in determining plant size inequality (coefficient of variation for biomass among individuals) remains poorly understood.

Methods

We used a two-layer “zone-of-influence” model to explore the effects of competitive size-asymmetry and facilitation on size inequality along stress gradients.

Results

Stress level alone (without plant-plant interactions) had little influence on size inequality. When facilitation was not present, shoot, root, and shoot + root competition intensity generally decreased with increasing stress. Accordingly, size inequality under most interaction scenarios decreased with increasing stress. Size inequality was higher under asymmetric shoot competition (the largest individual obtains all the contested resources) than under completely-symmetric root competition. When either shoot or root facilitation was present, corresponding net effects of shoot or root interactions were positive at high stress levels. Facilitation led to larger size inequality under these interaction scenarios because larger plants tend to overlap more with and thus benefit more from neighbors. Furthermore, size inequality with shoot facilitation was greater than that with root facilitation, possibly because the former is generally size-asymmetric (i.e. larger shoots obtain disproportionately more benefits from overlapping areas), while the latter is more likely to be symmetric.

Conclusion

Our results highlight the role of shoot facilitation in amplifying plant size inequality. Agricultural and forest management in harsh environments may attempt to manipulate aboveground plant-plant interactions to achieve desired production goals.

中文翻译：

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在环境胁迫下，芽的促进作用超过根的促进作用对植物大小不平等的贡献：来自两层影响区模型的理论见解

 背景和目标

积极的植物-植物相互作用（即促进）通常发生在压力环境中，并调节种群和群落动态。然而，shoot 与根系促进性在确定植物大小不等性（个体间生物量的变异系数）方面仍然知之甚少。

 方法

我们使用两层“影响区”模型来探索竞争性大小不对称和便利化对沿应力梯度的大小不等性的影响。

 结果

单独的胁迫水平（没有植物-植物相互作用）对大小不平等几乎没有影响。当不存在便利时，芽、根和芽 + 根的竞争强度通常随着胁迫的增加而降低。因此，在大多数交互情景下，大小不等式随着压力的增加而减小。在不对称芽竞争 （最大的个体获得所有竞争资源） 下的大小不等性高于完全对称根竞争下。当存在地上部或根系的便利时，地上部或根系相互作用的相应净效应在高胁迫水平下是正的。在这些交互情景下，便利化导致了更大的大小不平等，因为较大的植物往往与邻居重叠更多，从而从邻居中受益更多。此外，芽促进的大小不等性大于根促进性，这可能是因为前者通常是大小不对称的（即较大的芽从重叠区域获得不成比例的更多好处），而后者更有可能是对称的。

 结论

我们的结果强调了芽便利化在放大植物大小不平等中的作用。恶劣环境中的农业和森林管理可能会试图操纵地上植物与植物的相互作用，以实现预期的生产目标。