The outcome of plant-plant interactions depends on environmental (e.g. grazing, climatic conditions) and species-specific attributes (e.g. life strategy and dispersal mode of the species involved). However, the joint effects of such factors on pairwise plant-plant interactions, and how they modulate the role of these interactions at the community level, have not been addressed before. We assessed how these species-specific (life strategy and dispersal) and environmental (grazing and rainfall) factors affected the co-occurrence of 681 plant species pairs on open woodlands in south-eastern Australia. Species-specific attributes affected the co-occurrence of most species pairs, with higher co-occurrence levels dominating for drought-intolerant species. The dispersal mechanism only affected drought-tolerant beneficiaries, with more positive co-occurrences for vertebrate-dispersed species. Conversely, the percentage of facilitated species at the community scale declined under higher rainfall availabilities. A significant grazing × rainfall interaction on the percentage of facilitated species suggests that grazing-mediated protection was important under low to moderate, but not high, rainfall availabilities. This study improves our ability to predict changes in plant-plant interactions along environmental gradients, and their effect on community species richness, by highlighting that: 1) species-specific factors were more important than environmental conditions as drivers of a large amount (~30%) of the pairwise co-occurrences evaluated; 2) grazing and rainfall interaction drive the co-occurrence among different species in the studied communities, and 3) the effect of nurse plants on plant species richness will depend on the relative dominance of particular dispersal mechanisms or life strategies prone to be facilitated.

中文翻译：

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护理植物对旱地植物物种丰富度的影响：放牧、降雨和物种特异性的作用。

植物-植物相互作用的结果取决于环境（例如放牧、气候条件）和特定物种的属性（例如所涉及物种的生活策略和传播模式）。然而，这些因素对成对植物-植物相互作用的联合影响，以及它们如何在群落层面调节这些相互作用的作用，以前没有得到解决。我们评估了这些特定物种（生活策略和扩散）和环境（放牧和降雨）因素如何影响澳大利亚东南部开阔林地中 681 种植物对的共生。物种特异性属性影响了大多数物种对的共现，较高的共现水平在不耐旱物种中占主导地位。分散机制仅影响耐旱受益者，对于脊椎动物分散的物种有更多积极的共现。相反，在较高的降雨可用性下，群落规模的促进物种百分比下降。对促进物种百分比的显着放牧×降雨相互作用表明，放牧介导的保护在低到中等但不高的降雨可用性下很重要。这项研究提高了我们预测植物-植物相互作用沿环境梯度变化的能力，以及它们对群落物种丰富度的影响，强调：1）物种特异性因素比环境条件更重要，因为它是大量驱动因素（~30 %) 评估的成对共现；2）放牧和降雨相互作用推动了研究群落中不同物种之间的共存，