Abstract. In the quest to understand how biotic interactions respond to climate change, one area that remains poorly explored is how interactions involving organisms other than vascular plants will respond. However the interactions between plants and biological soil crusts (BSCs) are relevant in many ecosystems and they will likely respond uniquely to climate change. Simultaneous considerations of both plant–plant and plant–BSC interactions may substantially improve our understanding of this topic. The aim of this study is to assess whether water availability differentially affects the biotic effects of BSCs and pioneer shrubs on the early life-history stage of tree seedling growth. We conducted a greenhouse factorial experiment with soil surface cover (bare soil, soil covered by a creeping shrub and BSC covered soil) and water regime (control and drought) as factors. We monitored Nothofagus pumilio (a native tree species of ecological and economic relevance) seedling water status and growth as well as changes in soil water content and soil properties. The shrub cover had a positive effect on soil water conservation and on the water balance of seedlings under water stress. However, its effect was negative for seedling growth under both water conditions. The BSC also contributed to soil water conservation and apparently added nutrients to the soil. The net effect of the BSC on seedling growth was negative under full-watering conditions but positive under water stress conditions. This result highlights how the studied biotic interactions, and especially interactions involving BSCs, depend on changes in water availability.

中文翻译：

---

温带森林生态系统中水介导的植物-植物和生物土壤地壳-植物相互作用的变化

摘要。在寻求了解生物相互作用如何应对气候变化的过程中，一个仍未得到充分探索的领域是涉及维管植物以外的生物体的相互作用将如何反应。然而，植物和生物土壤结皮 (BSC) 之间的相互作用在许多生态系统中是相关的，它们可能会对气候变化做出独特的反应。同时考虑植物-植物和植物-BSC 相互作用可能会大大提高我们对这一主题的理解。本研究的目的是评估水的可用性是否对 BSC 和先锋灌木在树木幼苗生长的早期生命史阶段的生物效应有不同的影响。我们进行了土壤表层覆盖（裸土、匍匐灌木覆盖的土壤和 BSC 覆盖的土壤）和水分状况（控制和干旱）作为因素。我们监测了 Nothofagus pumilio（一种与生态和经济相关的本地树种）幼苗的水分状况和生长情况，以及土壤含水量和土壤特性的变化。灌木覆盖对土壤水分保持和水分胁迫下幼苗的水分平衡具有积极作用。然而，在两种水条件下，其对幼苗生长的影响都是负面的。BSC 还有助于保持土壤水分，并明显地向土壤中添加了养分。BSC 对幼苗生长的净影响在全浇水条件下为负，但在水分胁迫条件下为正。这一结果突出了所研究的生物相互作用，特别是涉及 BSC 的相互作用，