Microbial communities and functions of greenhouse-cultivated and field-cultivated biological soil crust inocula for dryland restoration

Background/Question/Methods

Biological soil crusts (biocrust) are photosynthetic soil surface communities of moss, lichen, and cyanobacteria that thrive in drylands and influence ecosystem functions like soil stability, fertility, and hydrology. Biocrusts are vulnerable to soil compaction (e.g., grazing, energy development and recreation) which can result in land degradation. Efforts to restore biocrust include cultivating moss, lichen, and cyanobacteria in the laboratory or greenhouse and then inoculating soils in situ where biocrust cover has been lost. In order to cultivate biocrust inoculum at scales large enough for land restoration, field-cultivation may be required. This study compares biocrust cultivation in side-by-side greenhouse and field-trials. Source materials were obtained from the Colorado Plateau and Mojave Deserts, inocula were cultivated for four months in the greenhouse and for one year in the field, and then transferred to a degraded site and monitored for survival and function. Our objectives were to: 1) compare microbial and fungal community composition of greenhouse- and field-cultivated inocula to degraded site controls, 2) assess the impact of inoculation and cultivation method on cyanobacterial biocrust function (e.g., soil stability and photosynthetic potential).

Results/Conclusions

Five months after inoculation at the restoration site, the microbial composition of inoculated plots did not differ from uninoculated controls. In particular, the relative abundance of cyanobacteria genera declined through cultivation and inoculation. At the five-month checkpoint, only one cyanobacteria genera, Tychonema, was measured in inoculated and control plots, while source materials contained more than ten genera. These results indicate that survival of biocrust cyanobacteria within the inocula was poor, with greenhouse-cultivated inocula slightly outperforming field-cultivated inocula. Inoculation also did not improve the function of degraded soils in their photosynthetic activity (chlorophyll a content) or soil stability (slake test and exopolysaccharide content). There were no differences in these functions for plots inoculated with greenhouse- or field-cultivated inocula. In conclusion, microorganism survival remains a challenge for biocrust restoration via inoculation. Large-scale cultivation of biocrust inoculum should consider cyanobacterial composition in addition to moss and lichen abundance for assessing inocula viability, while also addressing more functional metrics like potential photosynthetic activity, exopolysaccharide content, or soil stability.