Department of Biology and Geology, Rey Juan Carlos University, Madrid, Spain.
PLoS One. 2012;7(7):e41270. doi: 10.1371/journal.pone.0041270. Epub 2012 Jul 27.
The study of species coexistence and community assembly has been a hot topic in ecology for decades. Disentangling the hierarchical role of abiotic and biotic filters is crucial to understand community assembly processes. The most critical environmental factor in semi-arid environments is known to be water availability, and perennials are usually described as nurses that create milder local conditions and expand the niche range of several species. We aimed to broaden this view by jointly evaluating how biological soil crusts (BSCs), water availability, perennial species (presence/absence of Stipa tenacissima) and plant-plant interactions shape a semi-arid annual plant community. The presence and cover of annual species was monitored during three years of contrasting climate. Water stress acted as the primary filter determining the species pool available for plant community assembly. Stipa and BSCs acted as secondary filters by modulating the effects of water availability. At extremely harsh environmental conditions, Stipa exerted a negative effect on the annual plant community, while at more benign conditions it increased annual community richness. Biological soil crusts exerted a contradictory effect depending on climate and on the presence of Stipa, favoring annuals in the most adverse conditions but showing repulsion at higher water availability conditions. Finally, interactions among co-occurring annuals shaped species richness and diversity of the final annual plant assembly. This study sheds light on the processes determining the assembly of annual communities and highlights the importance of Biological Soil Crusts and of interactions among annual plants on the final outcome of the species assembly.
物种共存和群落组装的研究是生态学中几十年来的热门话题。解析非生物和生物过滤器的层次作用对于理解群落组装过程至关重要。在半干旱环境中，最关键的环境因素通常被认为是水分可用性，多年生植物通常被描述为护士，它们创造了更温和的局部条件，并扩大了几种物种的生态位范围。我们旨在通过联合评估生物土壤结皮（BSC）、水分可用性、多年生物种（存在/不存在芨芨草）和植物-植物相互作用如何塑造半干旱一年生植物群落，来拓宽这一观点。在三年的对照气候条件下，监测一年生物种的存在和覆盖情况。水分胁迫是决定植物群落组装可用物种库的主要过滤器。芨芨草和 BSCs 通过调节水分可用性的影响充当二级过滤器。在极其恶劣的环境条件下，芨芨草对一年生植物群落产生负面影响，而在条件更温和的情况下，它增加了一年生植物群落的丰富度。生物土壤结皮的作用取决于气候和芨芨草的存在，在最不利的条件下有利于一年生植物，但在水分可用性较高的条件下表现出排斥作用。最后，共同出现的一年生植物之间的相互作用塑造了物种丰富度和最终一年生植物组合的多样性。本研究揭示了决定一年生植物群落组装过程的过程，并强调了生物土壤结皮和一年生植物之间相互作用对物种组装最终结果的重要性。
