Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (12 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2012)

Abiotic and biotic land surface properties are often highly heterogeneous but can assemble in a repetitive manner forming landform mosaics at a mesoscale (ten to hundreds of meters). Nonetheless, we still do not fully understand their interactions or the mechanisms involved that change these properties during landscape evolution. The goal of this work was to relate land surface properties to functional group diversity of biological soil crusts and vascular plants, ecosystem functions and pedogenesis within a Mojave Desert landscape. Seven mosaic types were visually identified that occurred on three geomorphic-aged surfaces: young bars and swales, intermediate-aged flattened bars, flattened swales and bioturbation units, and old desert pavement and shrub zones. Sixty-three randomly selected landform mosaics served as study plots. In each plot a suite of morphometrical, physical and biological variables were determined. Multivariate analysis revealed that landform mosaics are statistically distinct according to specific sets of abiotic and biotic land surface properties. Within each landform type I also detected significant differences in functional group diversity of plants and biological soil crusts. The aggregate stability, nitrogen and carbon fixation of crusts were measured. An area based quality index (ABQI) was developed to evaluate these microbial communities based on ecological functions. The ABQI was computed for each landform mosaic and statistically compared. The ABQI was highest for bars and lowest for desert pavements.

Two landform evolutionary trajectories were identified: an abiogenic and a biogenic tract. In the abiogenic track, vegetation contracted and the surface increased in physical components. In the biogenic track vegetation diversity and abundance increased, and crust cover and diversity was high. Both of these trajectories were linked to different pedogeneses. Abiogenic soils promoted vesicular and calcic horizon development, as well as sodicity and alkalinity. Organic carbon and total nitrogen decreased. Biogenic soils were well mixed. No vesicular horizon could develop and calcic horizons were weakly expressed. Furthermore, these soils increased in organic carbon and total nitrogen.

Overall, this work showed that desert landscapes are highly diverse in landform mosaics defined by abiotic and biotic land surface properties at the mesoscale. Moreover, strong linkages and feedbacks occur between physical, biotic and pedologic landscape components that over time result in quite contrasting surface features.

    Cover page: Effects of Land Surface Characteristics on Pedogenesis, Biological Soil Crust Community Diversity, and Ecosystem Functions in a Mojave Desert Piedmont Landscape
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2020)

    Biocrusts are the living skin of drylands, comprising diverse microbial communities that are essential to desert ecosystems. Despite extensive knowledge on biocrust ecosystem functions and lichen and moss biodiversity, little is known about factors structuring diversity among their microbial communities. We used amplicon-based metabarcode sequencing to survey microbial communities from biocrust surface and subsurface soils at 4 sites located within the Mojave Desert. Five biocrust types were examined: Light-algal/Cyanobacteria, Cyano-lichen, Green-algal lichen, Smooth-moss, and Rough-moss crust types. Microbial diversity in biocrusts was structured by several characteristics 1) central versus southern Mojave sites displayed different community signatures, 2) indicator taxa of plant associated fungi (plant pathogens and wood saprotrophs) were identified at each site, 3) surface and subsurface microbial communities were distinct, and 4) crust types had distinct indicator taxa. Network analysis ranked bacteria-bacteria interactions as the most connected of all within-domain and cross-domain interaction networks in biocrust surface samples, with Actinobacteria, Proteobacteria, Cyanobacteria, and Ascomycota as hubs among all phyla. Specifically, the genera with highest node degree was Pseudonocardia sp. (Pseudonocardiales, Actinobacteria) in bacteria and Alternaria sp. (Pleosporales, Ascomycota) among fungal genera. Our findings provide crucial insights for dryland microbial community ecology, conservation, and sustainable management.

      Cover page: Insights into drylands biocrust microbiome: geography, soil depth, and crust type affect biocrust microbial communities and networks in Mojave Desert, USA.
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2020)

      Biocrusts are the living skin of drylands, comprising diverse microbial communities that are essential to desert ecosystems. Despite extensive knowledge on biocrust ecosystem functions and lichen and moss biodiversity, little is known about factors structuring diversity among their microbial communities. We used amplicon-based metabarcode sequencing to survey microbial communities from biocrust surface and subsurface soils at 4 sites located within the Mojave Desert. Five biocrust types were examined: Light-algal/Cyanobacteria, Cyano-lichen, Green-algal lichen, Smooth-moss, and Rough-moss crust types. Microbial diversity in biocrusts was structured by several characteristics 1) central versus southern Mojave sites displayed different community signatures, 2) indicator taxa of plant associated fungi (plant pathogens and wood saprotrophs) were identified at each site, 3) surface and subsurface microbial communities were distinct, and 4) crust types had distinct indicator taxa. Network analysis ranked bacteria-bacteria interactions as the most connected of all within-domain and cross-domain interaction networks in biocrust surface samples, with Actinobacteria, Proteobacteria, Cyanobacteria, and Ascomycota as hubs among all phyla. Specifically, the genera with highest node degree was Pseudonocardia sp. (Pseudonocardiales, Actinobacteria) in bacteria and Alternaria sp. (Pleosporales, Ascomycota) among fungal genera. Our findings provide crucial insights for dryland microbial community ecology, conservation, and sustainable management.

        Cover page: Insights into drylands biocrust microbiome: geography, soil depth, and crust type affect biocrust microbial communities and networks in Mojave Desert, USA.
        • Article
        • Peer Reviewed
        UC Riverside Previously Published Works (2023)
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2014)
          Terrestrial ecosystems can be more holistically understood by investigating the morphology of landscape mosaics, the assemblage of their ecological communities, and the linkages and feedbacks between the mosaics and communities. The overarching objectives of this study were to: (1) study the abiotic and biotic configurations of landform units as mosaics within a Mojave Desert chronosequence; and (2) elucidate their potential feedbacks, interactions, and dynamics during landform evolution. Seven landform units distributed over three geomorphic ages were identified, including: young bars and swales; intermediate-aged flattened bars, flattened swales, and bioturbation units; and old desert pavements and shrub zones. These landform units were characterized according to abiotic and biotic land surface properties. Landform units were statistically distinct and predictable based on a specific suite of abiotic and biotic properties. Vascular plant functional group and biological soil crust community diversity varied with geomorphology, with greatest diversity associated with bars and shrub zones and lowest diversity associated with desert pavements. Biological soil crust communities were controlled by geomorphic age, surface rock size, and protruding rocks with young bar units having the highest abundance and diversity. Perennial forbs were observed in old shrub zones with small rocks and few protruding rocks. A high clast density and a finer-sized clast distribution were found particularly in desert pavements and flattened swales, and generally inhibited biological soil crust and plant cover. Evolutionary trajectories for landforms of a lower piedmont landscape can be dominated by either abiotic and biotic landform processes. These two trajectories are distinctly different and are associated with their own unique linkages, feedbacks, and dynamics of abiotic and biotic land surface properties, producing a highly diverse desert landscape. © 2013 Elsevier B.V.
            Cover page: Biogeomorphology of a Mojave Desert landscape — Configurations and feedbacks of abiotic and biotic land surfaces during landform evolution
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2023)
            INTRODUCTION: In dryland systems, biological soil crusts (biocrusts) can occupy large areas of plant interspaces, where they fix carbon following rain. Although distinct biocrust types contain different dominant photoautotrophs, few studies to date have documented carbon exchange over time from various biocrust types. This is especially true for gypsum soils. Our objective was to assess the carbon exchange of biocrust types established at the worlds largest gypsum dune field at White Sands National Park. METHODS: We sampled five different biocrust types from a sand sheet location in three different years and seasons (summer 2020, fall 2021, and winter 2022) for carbon exchange measurements in controlled lab conditions. Biocrusts were rehydrated to full saturation and light incubated for 30 min, 2, 6, 12, 24, and 36 h. Samples were then subject to a 12-point light regime with a LI-6400XT photosynthesis system to determine carbon exchange. RESULTS: Biocrust carbon exchange values differed by biocrust type, by incubation time since wetting, and by date of field sampling. Lichens and mosses had higher gross and net carbon fixation rates than dark and light cyanobacterial crusts. High respiration rates were found after 0.5 h and 2 h incubation times as communities recovered from desiccation, leveling off after 6 h incubation. Net carbon fixation of all types increased with longer incubation time, primarily as a result of decreasing respiration, which suggests rapid recovery of biocrust photosynthesis across types. However, net carbon fixation rates varied from year to year, likely as a product of time since the last rain event and environmental conditions preceding collection, with moss crusts being most sensitive to environmental stress at our study sites. DISCUSSION: Given the complexity of patterns discovered in our study, it is especially important to consider a multitude of factors when comparing biocrust carbon exchange rates across studies. Understanding the dynamics of biocrust carbon fixation in distinct crust types will enable greater precision of carbon cycling models and improved forecasting of impacts of global climate change on dryland carbon cycling and ecosystem functioning.
              Cover page: Biocrust carbon exchange varies with crust type and time on Chihuahuan Desert gypsum soils.
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2013)
              Soil stability, nitrogen and carbon fixation were assessed for eight biological soil crust community types within a Mojave Desert wilderness site. Cyanolichen crust outperformed all other crusts in multi-functionality whereas incipient crust had the poorest performance. A finely divided classification of biological soil crust communities improves estimation of ecosystem function and strengthens the accuracy of landscape-scale assessments.
                Cover page: Biological soil crust community types differ in key ecological functions
                • Article
                • Peer Reviewed
                UC Riverside Previously Published Works (2023)

                Introduction

                Soil microbial communities, including biological soil crust microbiomes, play key roles in water, carbon and nitrogen cycling, biological weathering, and other nutrient releasing processes of desert ecosystems. However, our knowledge of microbial distribution patterns and ecological drivers is still poor, especially so for the Chihuahuan Desert.

                Methods

                This project investigated the effects of trampling disturbance on surface soil microbiomes, explored community composition and structure, and related patterns to abiotic and biotic landscape characteristics within the Chihuahuan Desert biome. Composite soil samples were collected in disturbed and undisturbed areas of 15 long-term ecological research plots in the Jornada Basin, New Mexico. Microbial diversity of cross-domain microbial groups (total Bacteria, Cyanobacteria, Archaea, and Fungi) was obtained via DNA amplicon metabarcode sequencing. Sequence data were related to landscape characteristics including vegetation type, landforms, ecological site and state as well as soil properties including gravel content, soil texture, pH, and electrical conductivity.

                Results

                Filamentous Cyanobacteria dominated the photoautotrophic community while Proteobacteria and Actinobacteria dominated among the heterotrophic bacteria. Thaumarchaeota were the most abundant Archaea and drought adapted taxa in Dothideomycetes and Agaricomycetes were most abundant fungi in the soil surface microbiomes. Apart from richness within Archaea (p = 0.0124), disturbed samples did not differ from undisturbed samples with respect to alpha diversity and community composition (p ≥ 0.05), possibly due to a lack of frequent or impactful disturbance. Vegetation type and landform showed differences in richness of Bacteria, Archaea, and Cyanobacteria but not in Fungi. Richness lacked strong relationships with soil variables. Landscape features including parent material, vegetation type, landform type, and ecological sites and states, exhibited stronger influence on relative abundances and microbial community composition than on alpha diversity, especially for Cyanobacteria and Fungi. Soil texture, moisture, pH, electrical conductivity, lichen cover, and perennial plant biomass correlated strongly with microbial community gradients detected in NMDS ordinations.

                Discussion

                Our study provides first comprehensive insights into the relationships between landscape characteristics, associated soil properties, and cross-domain soil microbiomes in the Chihuahuan Desert. Our findings will inform land management and restoration efforts and aid in the understanding of processes such as desertification and state transitioning, which represent urgent ecological and economical challenges in drylands around the world.
                  Cover page: Landscape characteristics shape surface soil microbiomes in the Chihuahuan DesertCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC Riverside Previously Published Works (2024)
                  We present eight metatranscriptomic datasets of light algal and cyanolichen biological soil crusts from the Mojave Desert in response to wetting. These data will help us understand gene expression patterns in desert biocrust microbial communities after they have been reactivated by the addition of water.
                    Creative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Riverside Previously Published Works (2024)
                    We present six whole community shotgun metagenomic sequencing data sets of two types of biological soil crusts sampled at the ecotone of the Mojave Desert and Colorado Desert in California. These data will help us understand the diversity and function of biocrust microbial communities, which are essential for desert ecosystems.
                      Top