Abstract
Abstract Understanding the importance of biotic interactions in driving the distribution and abundance of species is a central goal of plant ecology. Early vascular plants likely colonized land occupied by biocrusts — photoautotrophic, surface‐dwelling soil communities comprised of cyanobacteria, bryophytes, lichens and fungi — suggesting biotic interactions between biocrusts and plants have been at play for some 2,000 million years. Today, biocrusts coexist with plants in dryland ecosystems worldwide, and have been shown to both facilitate or inhibit plant species performance depending on ecological context. Yet, the factors that drive the direction and magnitude of these effects remain largely unknown. We conducted a meta‐analysis of plant responses to biocrusts using a global dataset encompassing 1,004 studies from six continents. Meta‐analysis revealed there is no simple positive or negative effect of biocrusts on plants. Rather, plant responses differ by biocrust composition and plant species traits and vary across plant ontogeny. Moss‐dominated biocrusts facilitated, while lichen‐dominated biocrusts inhibited overall plant performance. Plant responses also varied among plant functional groups: C4 grasses received greater benefits from biocrusts compared to C3 grasses, and plants without N‐fixing symbionts responded more positively to biocrusts than plants with N‐fixing symbionts. Biocrusts decreased germination but facilitated growth of non‐native plant species. Synthesis. Results suggest that interspecific variation in plant responses to biocrusts, contingent on biocrust type, plant traits, and ontogeny can have strong impacts on plant species performance. These findings have important implications for understanding biocrust contributions to plant productivity and community assembly processes in ecosystems worldwide.
Highlights
Understanding the predictors of species distribution and abundance has long been a central goal of ecology (e.g. Callaway, 2007; Oosting, 1948)
Plant responses varied among plant functional groups: C4 grasses received greater benefits from biocrusts compared to C3 grasses, and plants without N‐fixing symbionts responded more positively to biocrusts than plants with N‐fixing symbionts
Our results indicate that the overall neutral responses of plants to biocrusts are driven by interspecific variation in plant responses to biocrusts that vary depending on plant and biocrust characteristics and trade‐offs in biotic interaction outcomes across different stages of plant ontogeny
Summary
Understanding the predictors of species distribution and abundance has long been a central goal of ecology (e.g. Callaway, 2007; Oosting, 1948). Biocrusts modify soil microclimate via alteration of soil hydrology (Belnap, 2006; Chamizo, Belnap, Eldridge, Cantón, & Issa, 2016; Concostrina‐Zubiri, Molla, Velizarova, & Branquinho, 2017; Faist, Herrick, Belnap, Van Zee, & Barger, 2017) and surface temperature (Concostrina‐Zubiri et al, 2017; Couradeau et al, 2016) Given this wide range of soil modifications, biocrusts can strongly impact the recruitment and performance of plant species with which they coexist (Belnap, Prasse, & Harper, 2003; Zhang, Aradottir, Serpe, & Boeken, 2016). We tested the propositions that (a) biocrust community composition mediates the direction and strength of plant responses to biocrusts, (b) biocrust effects on plants are not uniformly experienced by all plant types but vary depending on plant characteristics and functional traits, and (c) plant responses to biocrusts shift depending on abiotic environmental conditions (e.g. organisms’ ecosystem of origin, disturbance) Results from this meta‐analysis are expected to have broad implications for understanding the effects of biocrusts on plant species performance. Given that global landcover of biocrust communities is expected to decline 20%–40% within the 65 years in response to climate change and land use intensification (Rodriguez‐Caballero et al, 2018), and local biocrust community structure may shift in response to climate change (Ferrenberg, Reed, & Belnap, 2015; Reed et al, 2012), we believe it is critical and timely to examine relationships between biocrusts and plant communities to better understand how the ecosystems in which they co‐occur will respond to global change
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