Understanding soil treatment effectiveness in dryland restoration: ecological barriers, contexts, and baseline conditions
Date
2023
Authors
Kimmell, Louisa, author
Havrilla, Caroline, advisor
Cotrufo, M. Francesca, committee member
Sueltenfuss, Jeremy, committee member
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Abstract
Land degradation is one of the greatest environmental issues our planet faces today, with over 33% of Earth's soils currently degraded. Drylands are especially vulnerable to soil degradation given their history of intensive land use and desertification. However, dryland restoration can be very difficult, and often fails when seeding is used as a sole treatment. Soil-based restoration, which includes abiotic treatments like organic amendments and water collection pits, and biotic treatments like microbial inoculation, may be needed for ecosystem recovery in drylands. Compared to plant-based restoration, however, less is known about how and when to use active soil restoration for optimal results. To improve our understanding of how to best use active soil restoration to restore degraded drylands, we conducted two research studies: (1) a global meta-analysis of dryland soil restoration treatment effectiveness across environmental gradients (Chapter 1), and (2) a regional field study comparing microbial communities across degraded, intact, and revegetated dryland sites to understand baseline conditions and when active soil restoration (e.g., inoculation) may be needed to improve soil conditions (Chapter 2). For project 1, we generated a global database from 155 publications and 1,403 unique studies of responses of soil health variables [i.e., aggregate stability, bulk density, soil moisture, soil organic carbon, soil nitrogen, mycorrhizal colonization, and basal respiration] to soil restoration relative to untreated controls. We then used quantitative meta-analysis techniques to analyze soil restoration effect sizes. In Chapter 2, we collected soil samples from paired reference, degraded, and revegetated plots across seven different dryland sites across the southwestern United States, sequenced the 16S and ITS rRNA gene regions from extracted DNA for bacteria/archaeal and fungal communities (respectively), and analyzed differences in microbial community composition among samples. Results from the meta-analysis suggested that active soil restoration generally improves soil health and is most effective in arid, fine-textured soils. Organic amendments were most effective at increasing soil organic carbon, while fungi inoculation treatments were most effective at increasing mycorrhizal colonization. From the regional microbiome study, we found that soil microbial communities differ between paired degraded and intact sites, and that degraded sites have lower abundances of biocrust-forming bacteria and dark septate endophytic fungi, which are both indicative of reference/intact conditions, making these taxa potential targets for inoculation treatments. However, we found that microbial communities do not differ between degraded and revegetated sites, suggesting that degraded sites may require active interventions beyond revegetation, such as direct microbial inoculation, to replenish microbial communities. These findings advance understanding of the effects of dryland degradation and restoration on soil health and have actionable implications for improving restoration decision-making, and thus improve outcomes in dryland restoration.
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Subject
meta-analysis
restoration
dryland
soil health
microbial communities