Weak Evidence of Regeneration Habitat but Strong Evidence of Regeneration Niche for a Leguminous Shrub

Abstract

The identification of an ecological niche specific to the regeneration phase has mobilised significant attention. However, the importance of the regeneration niche concept remains unclear. Our main objective was to study the existence of such a regeneration niche for a leguminous shrub, Ulex europaeus. This study was carried out in southwest France in the context of water and nutrient stresses (mainly phosphorus limitation) due to the presence of nutrient-poor sandy soils. We analysed the regeneration of the species from the germination of seeds and emergence of new seedlings until the seedlings reached young shrub size. Our design included a P fertilisation treatment. We also investigated microsite characteristics (micro-topography and vegetation development) as they can interact with meteorological conditions and determine water availability for seeds and seedlings. We found that P availability controlled seedling growth and the time necessary to reach young shrub size. Water availability appeared to impact the species germination and seedlings survival. We also found that P and water availability depended on the interactions between microsite characteristics and climatic variations. Finally we found evidence that P and water availability are important ecological factors shaping the regeneration niche of the species, but we found weak evidence that any microsite would be appropriate for the regeneration of the species in the long term. Future studies regarding regeneration niches need to distinguish more clearly the ecological factors important for regeneration (the regeneration niche per se) and the physical world where the seedlings appear and develop (the regeneration habitat).

Shift from short‐term competition to facilitation with drought stress is due to a decrease in long‐term facilitation

“…Thus, in our study short‐term interactions shifted from negative to positive with increasing drought stress from spring to summer seasons, as found by other authors assessing the effects of drought stress on plant–plant interactions along temporal gradients (Greenlee and Callaway 1996, Sthultz et al 2007, Delerue et al 2015). This increase in short‐term facilitation with increasing stress, supporting the SGH theory (Bertness and Callaway 1994), was due to an environmental‐severity effect.…”

“…In contrast, when nurses are shrubs, like in the study of Sthultz et al (2007) or ours, short-term effects are very unlikely to become more negative with increasing drought stress (Michalet 2007), likely because the increase in water competition does not outweighs the benefit of shading for microclimate stress mitigation (Holmgren et al 1997, Gómez-Aparicio et al 2005, Muhamed et al 2013. Thus, in our study short-term interactions shifted from negative to positive with increasing drought stress from spring to summer seasons, as found by other authors assessing the effects of drought stress on plant-plant interactions along temporal gradients (Greenlee and Callaway 1996, Sthultz et al 2007, Delerue et al 2015. This increase in short-term facilitation with increasing stress, supporting the SGH theory (Bertness and Callaway 1994), was due to an environmental-severity effect.…”

Response of soil and vegetation in a warm-temperate Pine forest to intensive biomass harvests, phosphorus fertilisation, and wood ash application

“…The increase of the N-fixer shrub was expected as we are used to observing a positive response of this leguminous species to P fertilisation ( e.g . Delerue et al (2015)), but although the N-fixers abundance was increased by P fertilisation, it was relatively low compared with previous experiments (Augusto et al 2005; Vidal et al 2019), and lower than results after the wood ash application. This ash effect may be the positive consequence of reducing the ambient acidity on the symbionts of the leguminous species (Slattery and Coventry 1995).…”

Direct litter interference and indirect soil competitive effects of two contrasting phenotypes of a spiny legume shrub drive the forb composition of an oromediterranean community

“…We did not directly assess these mechanisms in our study but our measurements of soil moisture strongly suggest that water availability was a crucial factor in this interaction. The high hydrophobicity of organic surfaces likely decreases water availability for herbaceous species on the soil of the tight phenotype as compared to the soil of the loose phenotype (Borken and Matzner ), as also observed in wetter climate conditions in a Pinus maritima community developed on highly organic podzolic soil (Delerue et al ). Furthermore, the higher direct negative soil effect of the tight phenotype observed in south than in north exposure supports the hypothesis of a primary influence of decreasing water availability for forbs in this interaction.…”