Successful inoculation of biocrust on gypsum soils does not influence vascular plant establishment

Background/Question/Methods

Large scale disturbances are spreading across the Mojave Desert as urban sprawl, energy development, and resource extraction increase. These developments have impacted, among other ecosystems, the gypsum soils in southern Nevada. Gypsum soils have hydrological, physical, and chemical properties which leads to unique: assemblages of vascular plants, biological soil crust (biocrust) organisms, and restoration challenges. Biocrusts, the community of lichens, bryophytes, cyanobacteria, and algae. which coat the soil surface, stabilize soil against wind and water erosion and influence vascular plant success. To identify the most effective restoration treatments for gypsum soils, we conducted a randomized complete block experiment on disturbed public lands near Las Vegas. We hypothesized that 1) Biocrust inoculation increases biocrust cover 2) Increased biocrust cover will increase plant establishment and 3) Plant based soil tackifiers would aid both biocrust and plant establishment. In January 2018, we monitored initial soil stability and then applied factorial combinations of biocrust inoculation, and endemic species seeding to 2x2m plots which were then split, half of each plot receiving psyllium husk as a soil stabilizing amendment. We monitored soil surface covers and vascular plants for 2.5 years.

Results/Conclusions

We analyzed our data through a series of linear mixed effects models, holding block and plot as random effects. Biocrust percent cover was six times higher in inoculated plots than control plots (12.9 ± 1.7 versus 2.0 ± 0.5, ) but was not influenced by any other treatments (shrub planting, seedings, psyllium). Plots with higher pre-treatment soil aggregate stability ratings tended to have higher biocrust cover. While the biocrust treatment was successful, neither biocrust nor seeding treatment increased vascular plants. However, there was a positive relationship between higher penetrometer readings (measure of surface crust strength) and both vascular plant numbers and diversity (R2=0.20). Endemic seeded species (6 Arctomecon californica; 45 Enceliopsis argophyla) established only in seeded plots. However, establishment was too low to consider successful. Longer term monitoring is needed to fully assess, as many Mojave plants require climactic germination conditions which do not occur every year. Overall, we had very limited success with reestablishing plants of interest, but we were able to boost biocrust cover on highly disturbed gypsum soils through inoculation. This is promising because increasing biocrust cover is important for restoring soil health, preventing erosion, and may still have long term benefits for plant communities.