Search

Background and aims: Livestock grazing and climate change are two of the most important global change drivers affecting ecosystem functioning in drylands. Grazing and climate are known to influence the cover and composition of biocrusts, which are substantial components of dryland soils globally. Much less is known, however, about how these global change drivers affect the functional diversity of biocrust communities in these ecosystems.Methods: Here, we evaluate the role of increasing aridity and grazing intensity in driving the functional diversity of biocrusts. We collected data on multiple biocrust functional traits and community composition, recent and historic grazing intensity, and vascular plants at 151 sites from drylands in eastern Australia. We then used structural equation modelling and a fourth corner analysis to examine the combined effects of aridity and grazing on biocrust functional diversity and individual functional traits.Results: Aridity had a significant direct suppressive effect on biocrust functional diversity. Effects of grazing by livestock, kangaroos and rabbits on functional diversity were predominantly indirect and suppressive, mediated by a reduction in biocrust cover. Grazing did, however, promote functional diversity via an increase in vascular plant richness, with a concomitant increase in biocrust richness. The overall effect of grazing on biocrust functional diversity however was negative. Fourth corner analyses revealed that livestock grazing had a significant negative effect on the ability of biocrusts to stabilise the soil. Aridity had strong negative effects on biocrust height and their ability to absorb water and capture sediment. Few significant relationships were detected between enzyme-related traits and environmental variables.Conclusions: Our findings provide novel evidence that the combination of increasing aridity and intensified livestock grazing will reduce the functional diversity and capabilities of biocrust communities, with resultant declines in ecosystem functioning. [ABSTRACT FROM AUTHOR]

Background and aims: Functional traits are increasingly being used to assess the degree to which ecosystems maintain key processes. The functional traits of vascular plants are well-documented but those of non-vascular plants are poorly known. We describe a comprehensive methodology to measure the functional traits of soil-borne lichens, mosses and liverworts making up biocrust (biological soil crust) communities. Methods: We collected 40 biocrust taxa from across 10,000 km of eastern Australia, and measured eight functional traits using a combination of mensurative studies and laboratory-based experiments. These traits were sediment capture, absorptivity, root (or rhizine) length, height, and the activity of four enzymes involved in key nutrient cycles; β-glucosidase, β-D-cellobiosidase, N-acetyl-β-glucosaminidase and phosphatase. Results: Taxa were distributed across a broad range of trait values. Sediment capture values ranged from 2 % in the crustose lichen Diploschistes thunbergianus to 83 % in the tall moss Triquetrella papillata. The highest absorptivity value was observed in the moss Bartramia hampeana ssp. hampei, which was able to absorb 12.9 times its dry mass in water, while the lowest value, 0.3, was observed in Diploschistes thunbergianus. Multivariate analyses revealed that biocrust morphological groups differed significantly in their functional profiles. Conclusions: Our results indicate that biocrust taxa vary greatly in their functional traits and that morphological groups explain, in part, the ability of biocrusts to sequester resources (sediment, moisture) and to undertake key processes associated with the cycling of carbon, nitrogen and phosphorus. This methodology will enhance our understanding of ecosystem functioning in drylands where biocrusts make up a large component of the surface cover and provide a range of ecosystem goods and services. [ABSTRACT FROM AUTHOR]