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Browsing by Author "Havrilla, Caroline, advisor"

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    Exploring interactions among biological soil crusts, plant germination, and morphological seed traits: implications for plant community assembly and dryland restoration
    (Colorado State University. Libraries, 2023) Bacovcin, John, author; Havrilla, Caroline, advisor; Ocheltree, Troy, committee member; Wrighton, Kelly, committee member; Paschke, Mark, committee member
    Arid and semi-arid (dryland) ecosystems make up over 40% of our plant's terrestrial surface and are incredibly vulnerable to land degradation. To combat dryland degradation, active plant and soil restoration is often needed and the role of plant-soil microbe interactions can be key to dryland restoration trajectories. Within drylands, biological soil crusts (biocrusts), collections of cyanobacteria, algae, lichen, and moss are key surface communities that influence soil processes (e.g., stability, nutrient cycling, hydrology) and can thereby strongly influence recruitment of dryland plants. These biocrusts may interact with plant functional traits (i.e., seed morphological traits), and these interactions can influence germination. However, much is still unknown about mechanisms that underlie these interactions and how plant functional traits mediate effects of biocrusts on plant germination. To investigate these knowledge gaps, I conducted two studies: (Chapter 1) a global meta-analysis of the role of morphological seed traits in determining biocrust effects on germination, and (Chapter 2) a full-factorial greenhouse study examining the effects of biocrust inoculum cover treatments and plant functional traits on plant recruitment to investigate questions about how biocrust heterogeneity and biotic components of biocrusts in the context of restoration. To explore effects of morphological seed traits on plant germination responses to biocrusts (Ch. 1), we compiled a global database of 491 studies of biocrust effects on plant germination encompassing 101 unique plant species and their associated morphological seed traits. For the greenhouse study (Ch. 2) we seeded two seed mixes on three different inoculum cover treatments (i.e., 0%, 30%, and 100%) using both biologically active (live) and autoclaved biocrust inoculum, to assess effects of cover heterogeneity, biological biocrust activity, and plant functional traits on percent germination. Results from the meta-analysis showed that morphological seed traits do mediate plant germination responses to biocrusts, and that, in general, germination of smaller seeded species with appendages was increased by biocrusts. Results from the greenhouse study showed that, in a restoration context, increasing cover of biocrust inoculum increases plant germination, and that these effects were explained by physical rather than biotic effects of inoculum on germination. As in Chapter 1, we found that biocrusts effect on germination differed across plant functional groups and that seed traits also influenced germination responses to biocrust inoculum cover treatments. Together, both studies showed that morphological seed traits mediate effects of biocrusts on plant germination. These findings increase understanding of the role of biocrusts in determining dryland plant community assembly and have implications for dryland restoration.
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    Understanding soil treatment effectiveness in dryland restoration: ecological barriers, contexts, and baseline conditions
    (Colorado State University. Libraries, 2023) Kimmell, Louisa, author; Havrilla, Caroline, advisor; Cotrufo, M. Francesca, committee member; Sueltenfuss, Jeremy, committee member
    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.