Biology subjects

Dawson, H. R.

Publications and source records attributed to Dawson, H. R..

4 recordsLinked to original sources

bioRxiv2022

Local and regional scale mycorrhizal network assembly in an experimental prairie-pasture system

Arbuscular mycorrhizal (AM) symbioses between plants and fungi are essential to the functioning of terrestrial ecosystems through maintaining soil stability, controlling nutrient cycles (e.g. C, N, P and K), and influencing competitive dynamics in plant communities. Despite the importance of AM symbioses, the ecological coassembly patterns of AM fungi-plant partners are not well characterized across environmental gradients. Further, it is unclear whether fungi forming associations with several plants of the same or different species - forming common mycorrhizal networks (CMNs) - preferentially allocate limiting resources within natural plant communities at the local-scale. We used an experimental prairie-pasture grassland system in three sites along a latitudinal gradient ranging from cool/wet to warm/dry climates to investigate how environmental conditions, local plant diversity and drought shift AM fungal composition and plant-fungal coassembly patterns across spatial scales. We show that plant-AM fungal assembly patterns are hierarchically structured, with environmental variables driving differences in AM fungal communities at the largest spatial scale (across sites), and plant host identity and diversity governing AM assembly at the local scale (within plot). Bipartite interaction networks revealed evidence for preferential partner selection between plants and fungi, while there was no evidence for nested assembly of plant-fungal partners. At the plot-level, we applied stable isotopes (13C and 15N) to illustrate CMN assembly and nutritional function. There was no significant correlation between increased resource transfer among plants in a plot that shared more AM fungal partners; however, we identified specific AM fungi that were indicator taxa for increased plant isotope enrichment. Further research integrating stable isotope probing of fungal DNA in plant roots is necessary to more clearly illustrate the form and function of CMNs in grasslands under different environmental and plant diversity conditions.

ecology↗

bioRxiv2022

Agnostic fungi: plant traits and tissue stoichiometry explain nutrient transfer in common arbuscular mycorrhizal networks of temperate grasslands

Plants and mycorrhizal fungi form mutualistic relationships that affect how resources flow between organisms and within ecosystems. Common mycorrhizal networks (CMNs) could facilitate preferential transfer of carbon and limiting nutrients, but this remains difficult to predict. Do CMNs favor fungal resource acquisition at the expense of plant resource demands (a fungi-centric view), or are they passive channels through which plants regulate resource fluxes (a plant-centric view)? We used stable isotope tracers (13CO2 and 15NH3), plant traits, and mycorrhizal DNA to quantify above- and belowground carbon and nitrogen transfer between 18 plant species along a 520-km latitudinal gradient in the Pacific Northwest, USA. Plant functional type and tissue stoichiometry were the most important predictors of interspecific resource transfer. Of "donor" plants, 98% were 13C-enriched, but we detected transfer in only 2% of "receiver" plants. However, all donors were 15N-enriched and we detected transfer in 81% of receivers. Nitrogen was preferentially transferred to annuals (0.26 {+/-} 0.50 mg N per g leaf mass) compared to perennials (0.13 {+/-} 0.30 mg N per g leaf mass). This corresponded with tissue stoichiometry differences. Our findings suggest that plants and fungi that are located closer together in space and with stronger demand for resources over time are more likely to receive larger amounts of those limiting resources.

ecology↗

bioRxiv2022

Leaf traits predict water-use efficiency in U.S. Pacific Northwest grasslands under rain exclusion treatment

Does drought stress in temperate grasslands alter the relationship between plant structure and function? Here we report data from an experiment focusing on growth form and species traits that affect the critical functions of water- and nutrient-use efficiency in prairie and pasture plant communities. A total of 139 individuals of 12 species (11 genera and four families) were sampled in replicated plots maintained for three years across a 520 km latitudinal gradient in the Pacific Northwest, USA. Rain exclusion did not alter the interspecific relationship between foliar traits and stoichiometry or intrinsic water-use efficiency. Rain exclusion reduced intrinsic water-use efficiency in grasses, an effect was primarily species-specific, although leaf morphology, life history strategy, and phylogenetic distance predicted intrinsic water-use efficiency for all twelve species when analyzed together. Variation in specific leaf area explained most of the variation in intrinsic water-use efficiency between different functional groups, with annual forbs and annual grasses at opposite ends of the resource-use spectrum. Our findings are consistent with expected trait-driven tradeoffs between productivity and resource-use efficiency, and provide insight into strategies for the sustainable use and conservation of temperate grasslands. Plain language summaryScientists have previously shown that plant leaf form (e.g., shape, width, size) has a predictable relationship to leaf function (e.g., how it can perform biological processes). When we deprive plants of water, does this relationship break down? We grew prairie and pasture plants at three sites in Oregon and Washington, USA, spanning a broad range of climate and water availability. At each site, we built shelters over half our plots to keep out some of the rain, reducing how much water our plants received. Leaf form-function relationships did not change between plots with more or less water. However, each species had a different water use efficiency and nutrient content, and some grasses had an unusual response, that is, they became less efficient at using water under less rain. Overall, we were pretty good at predicting water and nutrient use based on leaf form, whether plants were annual or perennial, and how related they were. Our findings match expectations about leaf structure-function relationships and people who manage temperate grasslands can use our results to decide which plants will work best for using and conserving their systems. Key pointsO_LIFoliar structure-function relationships did not change under experimental drought. C_LIO_LILeaf morphology, life history, and phylogenetics predicted resource-use for 12 species. C_LI

plant biology↗

bioRxiv2022

Quantifying climate change impacts on plant functional composition and soil nitrogen fixation in Mediterranean grasslands

The projected increase in warming and drought severity (i.e., hotter and drier summers) in the U.S. Pacific Northwest (PNW) may negatively impact grassland plant composition and ecosystem function, with further implications for sustainable land management in the region. To test the vulnerability of Mediterranean grassland function to climate change, we quantified the response of grassland communities to multiannual warming (+2.5{degrees}C) and drought (-40% precipitation) by quantifying plant species diversity, legume cover, and biogeochemical controls on and patterns of soil asymbiotic nitrogen fixation (ANF). We hypothesized that the effects of warming on plant functional diversity would increase soil ANF inputs by decreasing legume cover and soil nitrogen availability. Given that asymbiotic N fixers can increase soil organic carbon (C) and nitrogen (N) availability under drought, we hypothesized that the effect of drought on grassland plant cover correlated with increased soil ANF. We surveyed the vegetation and collected composite soil samples from five co-located plots under control (ambient), drought and warming conditions during the fall and spring seasons. In control and drought plots, we quantified the moderator effect of plant composition by comparing low-diversity (unmanipulated plant composition) and high-diversity (manipulated composition) grassland plots. We used a point intercept technique to survey plot-level plant community composition and calculate Shannons diversity index and percent cover of legumes (members of Fabaceae according to the Integrated Taxonomic Information System). We measured ANF by incubating collected soils with N-labeled dinitrogen (15N2), and quantified total soil C, total and available N, available phosphorus (P) and iron (Fe) pools, pH, and soil water holding capacity. Plant species diversity decreased significantly with warming and along the drought severity gradient. ANF response to warming varied by season and site, with rates increasing along the drought severity gradient in the fall but decreasing in the spring. Total soil inorganic N was the strongest predictor of ANF response to warming in the spring but not in the fall. Soil ANF response to drought increased with drought intensity; while soil ANF increased nearly twofold in the southernmost (warm and dry) site, ANF decreased in the northernmost (cool and wet) site. ANF response to drought also varied depending on plant diversity, where low-diversity grasslands had more predictable response to drought than high-diversity grasslands. Soil P availability and pH were the most important variables explaining ANF variability across vegetation types and sites. Our study highlights the importance of using soil-plant-atmosphere interactions to assess grassland ecosystem resilience to drought and warming in the PNW.

ecology↗