In environments with water and nutrient constraints, some early successional shrub/tree species may promote facilitation by ameliorating the microclimate and increasing resource availability. We ask whether early successional semi-arid shrub/tree species have facilitation effects for other woody species and if they do, which mechanisms are involved and how they affect the water status of juvenile plants. Three early successional woody species; Combretum leprosum, Cenostigma bracteosum and Mimosa tenuiflora, were chosen for investigation. The richness of regenerating woody species and their leaf water potential were used as response variables, while air and soil temperature, leaf area index, humidity and soil attributes were used as explanatory environmental variables. Species growing under the canopy of C. leprosum had better water status and growth at higher soil moisture and lower thermal and solar radiation stress, receiving a facilitative effect. The lower leaf area index, higher radiation and more negative soil water content under the canopy of C. bracteosum in comparison to C. leprosum may have a small negative effect on species richness. M. tenuiflora did not reduce environmental stress, and the species associated with it had low water potential, thus no increase in species richness was detected under its canopy. C. leprosum and C. bracteosum improve the environmental conditions under their canopies and provide favourable microsites for the establishment of other species. The positive effects may be generated by functional traits that modify microclimatic characteristics under the nurse species' canopy and lead to a higher water status of the juveniles growing under it.

中文翻译：

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半干旱地区三种早期演替灌木/乔木树种的微场地非生物条件和幼年反应

在水和养分限制的环境中，一些早期演替灌木/乔木物种可能通过改善小气候和增加资源可用性来促进促进。我们询问早期演替半干旱灌木/乔木物种是否对其他木本物种有促进作用，如果有，涉及哪些机制以及它们如何影响幼苗的水分状况。三个早期演替木本物种；麻风鸡血藤_ _ _, 被选中进行调查。以再生木本物种的丰富度及其叶水势作为响应变量，以空气和土壤温度、叶面积指数、湿度和土壤属性作为解释环境变量。C. leprosum树冠下生长的物种在较高的土壤湿度和较低的热和太阳辐射胁迫下具有更好的水分和生长，收到了促进作用。与C. leprosum相比，C . bracteosum冠层下较低的叶面积指数、较高的辐射和更多的负土壤含水量可能对物种丰富度产生较小的负面影响。M.tenuiflora没有减少环境压力，并且与之相关的物种具有低水势，因此在其树冠下没有检测到物种丰富度的增加。C. leprosum和C. bracteosum改善了其冠层下的环境条件，并为其他物种的建立提供了有利的微型场所。积极影响可能是由改变护士物种树冠下的小气候特征的功能性状产生的，并导致生长在树冠下的幼鱼的水分状况更高。