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A Regional Assessment of Changes in Plant–Plant Interactions Along Topography Gradients in Tunisian Sebkhas
Ecosystems ( IF 3.7 ) Pub Date : 2020-10-06 , DOI: 10.1007/s10021-020-00567-8
Ghassen Chaieb , Chedly Abdelly , Richard Michalet

Facilitation among plants in dry ecosystems is crucial for diversity and ecosystem functioning and stability. However, the importance of facilitation in extremely stressful conditions is highly debated. We attempt to separate the effects of direct non-resource and resource stress factors on plant–plant interactions by assessing changes in facilitation and competition along salinity gradients at two contrasting levels of aridity. We selected eight saline depressions (hereafter sebkhas) in the wet and dry Mediterranean arid climate of North Africa, from central Tunisia to the Libyan border 500 km south-eastward. In each sebkha, we transplanted at four positions along the salinity gradient induced by topography, both in open areas and below dominant shrubs, three target species with contrasting tolerances to salinity stress. Target plant survival, soil electrical conductivity and moisture were recorded before and after the dry summer season in all treatments. Shrubs decreased salinity and drought stresses in all treatments, and facilitation was the dominant interaction. However, we found a strong collapse of facilitation along the salinity gradient, due to a dramatic mortality of the three target species both with and without neighbours above their threshold of salinity tolerance. Increasing aridity induced an earlier collapse of facilitation along the gradient. The three target species had contrasting responses to neighbours, with the least stress-tolerant species being facilitated and the two most stress-tolerant ones negatively affected by neighbours. Our study shows that disentangling resource and non-resource stresses along gradients and controlling for target species effects help understanding variation in plant–plant interactions under highly stressful conditions.



中文翻译:

突尼斯塞布哈斯州植物与植物相互作用沿地形梯度变化的区域评估

干旱生态系统中植物之间的便利化对于多样性以及生态系统功能和稳定性至关重要。但是,在极端压力的条件下进行便利化的重要性受到了广泛的争论。我们试图通过评估干旱在两个相对干旱水平上沿盐度梯度的促进和竞争变化,来分离直接的非资源和资源胁迫因素对植物-植物相互作用的影响。在突尼斯中部到东南500公里的利比亚边界,我们在北非潮湿干燥的地中海干旱气候中选择了8个盐洼(以下称sebkhas)。在每个sebkha中,我们沿着地形诱导的盐度梯度在开放区域和优势灌木以下的四个位置移植了三个目标物种,它们对盐胁迫的耐受性相反。目标植物存活率 在所有处理中,均在夏季干燥前后记录土壤电导率和水分。在所有处理中,灌木都降低了盐度和干旱胁迫,而促进作用是主要的相互作用。但是,我们发现沿盐度梯度的促进作用极大地崩溃,这是由于三个目标物种在有或没有其邻域的情况下均超过其耐盐性阈值而导致极大的死亡率。干旱加剧导致沿梯度的便利化较早崩溃。这三个目标物种对邻居的反应截然不同,其中最不容易忍受压力的物种得到了促进,而最容易忍受的两个物种受到邻居的负面影响。

更新日期:2020-10-07
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