Biocrusts and their disturbance mediate the recruitment of native and exotic grasses from a hot desert ecosystem

摘要

In dryland ecosystems, biocrusts coexist in patchy mosaics with vascular plants and can influence plant performance through modifications of soil stability, hydrology, microclimate, and fertility. Biocrusts often have species‐specific effects on vascular plant recruitment and hypothesized to promote native over exotic plant establishment. While there is considerable interest in potential contributions of biocrusts to the biotic resistance of plant communities, relatively few studies have investigated this relationship. Particularly, we have a limited understanding of how biocrusts may impact exotic plant recruitment in hot desert ecosystems and how these relationships may be affected by biocrust disturbance. In a greenhouse setting, we investigated the effects of two biocrust types (cyanobacteria‐ and lichen‐dominated) from the hot, Chihuahuan Desert and their removal on the emergence, survival, growth, and overall recruitment performance of three perennial bunchgrasses: native species Aristida purpurea (Nutt.) and Bouteloua eriopoda (Torr.), and exotic Eragrostis lehmanniana (Nees.). Specifically, we tested two hypotheses: (1) Intact biocrusts offer favorable microhabitats for increased performance of native vascular grass species but decrease performance and recruitment of exotic species E.?lehmanniana, and (2) biocrust removal increases the recruitment of E. lehmanniana . Overall, we found cyanobacteria‐dominated biocrusts decreased seedling performance, while lichen‐dominated biocrusts increased performance. While biocrusts promoted E.?lehmanniana emergence over that of the two natives, conversely, native species survival and growth responded more positively to biocrusts than the exotic. Biocrust removal increased E.?lehmanniana recruitment, but had mixed effects on the two natives. These results indicate the importance of biocrusts and biocrust disturbance in shaping dryland plant community structure and generate interesting questions about possible contributions of biocrusts to the biotic resistance of plant communities.