In the present study, we conducted a field experiment along a temporal rainfall gradient for five consecutive years, in order to investigate interactions in a shrub-herbaceous plant community at the southern edge of the Badain Jaran Desert, and, more specifically, investigated the effects of Calligonum mongolicum, a dominant shrub species, on both abiotic environmental variables and the performance of sub-canopy plant species. We found that shrubs can improve sub-canopy water regimes, soil properties, plant biomass, density, cover, and richness and, more importantly, that the positive effect of shrubs on sub-canopy soil moisture during the summer diminishes as rainfall decreases, a pattern that partly explains the collapse of the positive interaction between shrubs and their understory plants. These results provide empirical evidence that the positive effect of shrubs on understory plant communities in extreme arid environments may decline and become neutral with increasing drought stress.
In early July 2013–2016, 25 similar-sized C. mongolicum shrubs were randomly selected from a permanent sample plot (100×200 m) and marked accordingly. Calligonum mongolicum was the dominant species in the sample plot, and all the sub-canopy species (target species) were annuals. In September of each year, a single 1×1 m quadrat was established under the canopy of each selected shrub, and an open-area quadrat was placed in shrub interspaces, extending from 5 to 8 m for each selected shrub. Then the above-ground biomass, individual density, total cover, and species richness of the understory vegetation were measured within each of the quadrats. In late September of 2012, we randomly selected 19 shrubs from the permanent sample plot and measured the individual density, total cover, and species richness of understory plants within quadrats (1×1 m) that were established both underneath the shrubs and within shrub interspaces. The total cover of understory species was estimated using the Braun–Blanquet scale (Westhoff and Van der Maarel 1978), and aboveground biomass of the understory species was measured using an electronic balance, after oven-drying at 80°C for 48 h. Due to rodent and pest damage, the samples of six and four of the shrubs selected in 2013 and 2015 were eliminated before analysis.
Linear mixed-effects model (LMM) that was fitted using maximum likelihood estimation was used to measure the effects of growing-season rainfall on abiotic factors modulated by shrubs. To analyse the effect on SWC, the rainfall of each growing season and habitat type (quadrats beneath shrubs or in open areas) and months (when soil moisture was investigated) were included as fixed terms, with paired shrubs as random terms.
Generalized linear mixed-effect model (GLMM) was used to measure the effects of growing-season rainfall and soil moisture on sub-canopy plant communities. To analyse the effect of rainfall on the understory plants modulated by shrubs, rainfall and habitat were included as fixed terms, with paired shrubs as random terms.
In addition to affecting the soil moisture of drylands, shrubs can also affect other abiotic factors in their understory microhabitats. Our results indicated that evaporation, irradiance, soil organic matter, and bulk density are all modulated beneathCalligonum mongolicum shrubs. They have facilitative effects in underproductive ecosystems, generally benefiting their neighbours, and contributing to positive plant–plant
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CSTR:11738.11.NCDC.ZENODO.DB3959.2023
10.5061/dryad.hd53q