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Unraveling the Isotopic Signatures and Effects of Soil Chemistry on Different Biocrust Types in Drylands of Central Texas

Session: New Voices in Geobiology

Presenting Author:

Tabinda Athar

Authors:

Athar, Tabinda¹, Fulton, James², Ford, Josh³, Kirpal, Gita Meera ⁴

(1) Department of Geosciences, Baylor University, Waco, Texas, USA, (2) Department of Geosciences, Baylor University, Waco, Texas, USA, (3) Department of Geosciences, Baylor University, Waco, Texas, USA, (4) Department of Biology, Baylor University, Waco, Texas, USA,

Abstract:

Globally, drylands comprise more than 45% of total land, and this extent is steadily increasing due to global warming and climate change. Drylands are heterogeneous ecosystems and have both biotic and abiotic components. Biocrusts cover more than 70% of the living cover in drylands and offer a multiscale contribution to ecosystem functioning and balance throughout the world. Biocrusts are poikilohydric communities having associations between liverworts, mosses, lichens, cyanobacteria, bryophytes, eukaryotic algae, and soil particles growing together as heterotrophic and autotrophic microbial communities in faunal food webs. Although smaller in size, numerous biocrust types (such as cyanobacteria, lichens, and mosses) greatly influence the microbial community composition, soil stability, and biogeochemical nutrient cycling, particularly in terms of C and N elemental cycling. This research presents a comprehensive biogeochemical analysis of different biocrust types from numerous sampling points across the Doeskin and the Flying X ranch sites in the Balcones Canyonlands Wildlife Refuge, Austin, Texas, in 2024. Based on their morphological characteristics, we have characterized them into different classes, such as bare soil, chlorolichens, cyanobacterial mats, and moss-dominated species. We have analyzed key variables including nutrients (phosphates, ammonium, nitrites, and nitrates), total C and N contents, C/N ratios, pH, and δ¹³C and δ¹⁵N isotopic signatures. The results have shown biogeochemical heterogeneity among different biocrust types due to differences in moisture stress, UV stress, soil chemistry, microbial respiration, photosynthetic pathways, slope, and underlying geology. A wide range of δ¹⁵N values revealed the complex N cycling due to mineralization, biological fixation, and external inputs as well. δ¹³C values also showed distinct respiration, photosynthetic pathways, and C cycling under the influence of different dominant microbial taxa. Temporal changes, such as the transition of bare soil to cyanobacterial, lichen, and hairy moss communities, reveal successional progress and environmental stabilization. These findings highlight the importance of the ecological diversity of biocrusts to regulate surface biogeochemical processes. Our future work includes studying the pigments and lipid profiles and conducting metagenomic studies to explore complex pathways and shifts in biocrust community composition.