Biological soil crust and vascular plant interactions in Western Myall (Acacia papyrocarpa) open woodland in South Australia

Abstract

Aim: Biological soil crust (BSC) is a key component of arid environments and plays a major role in determining ecological structure and function. Our research aim was to examine several mechanisms that contribute to BSC–plant interactions at species and community levels, to increase our understanding of plant community dynamics. Location: Yellabinna Regional Reserve, South Australia (30°50′17.99″ S, 132°12′10.37″ E). Methods: We used seed extraction techniques to examine soil seed banks beneath patches with and without BSC, and field and glasshouse experiments to study the effects of crust presence and disturbance on seedling emergence and survival. We also explored the influence of chemical leachates from BSC on seed germination. Results: Biological soil crust plays a pivotal role in influencing spatial patterns in soil seed bank composition. Our results showed less propagules accumulate in soils beneath crust when compared with patches without crust, and that propagule size is a contributing factor to determining their distribution between patch types. We found that late‐stage BSC physically inhibited seedling emergence, which increased when the BSC was disturbed in field experiments. Low seedling survivorship in both patch types suggests that although BSC may suppress recruitment in favourable years, it is low precipitation levels that have the over‐riding impact on recruitment success. Finally, leachates from late‐stage BSC were found to inhibit germination in three annual plant species, whilst early‐stage BSC accelerated germination in one annual plant. This clearly shows that leachate effects on seed germination vary according to plant species and crust successional stage. Conclusion: Overall, we identified several mechanisms through which BSC has complex effects on the annual and short‐lived perennial plant guilds of arid lands. These mechanisms contribute to species diversity through the creation of spatial heterogeneity in soil seed bank structure and emergence opportunities.