Geology topics

Amber C. Churchill

Publications and source records attributed to Amber C. Churchill.

5 recordsLinked to original sources

USGS2026

Growth form and lifespan of herbaceous species mediate the role of traits in short-term drought response

Increased climate variability is expected to intensify short-term drought events. Plants have evolved stress tolerance strategies involving trade-offs in resource conservation, mycorrhizal collaboration and plant size, yet how these strategies promote drought resistance across different herbaceous plant groups remains unknown. Leveraging 63 globally distributed grassland and shrubland sites from the International Drought Experiment, we identified plant traits linked to drought resistance in 661 populations of 421 species after 1 year of extreme drought. We assessed how traits, site precipitation and drought severity affected cover change across growth forms and lifespans, and how trait–environment interactions influenced drought resistance. Across all species, leaf N (an acquisitive trait) was associated with drought resistance, whereas in forbs, drought resistance was also associated with a conservative root trait and plant size. In addition, interactions among traits mediated drought resistance; root traits predicted performance only in concert with other traits. Environmental variables influenced trait effects on drought resistance, notably for annuals in wetter sites, suggesting that drought-escape strategies in annuals may be advantageous only under mild stress. Our study highlights variability in traits that predict drought resistance across herbaceous plant groups, emphasizing the importance of species context, environmental stress and the selection of traits in research and management.

Nature Ecology and Evolution↗

USGS2025

Drought intensity and duration interact to magnify losses in primary productivity

As droughts become longer and more intense, impacts on terrestrial primary productivity are expected to increase progressively. Yet, some ecosystems appear to acclimate to multiyear drought, with constant or diminishing reductions in productivity as drought duration increases. We quantified the combined effects of drought duration and intensity on aboveground productivity in 74 grasslands and shrublands distributed globally. Ecosystem acclimation with multiyear drought was observed overall, except when droughts were extreme (i.e., ≤1-in-100-year likelihood of occurrence). Productivity losses after four consecutive years of extreme drought increased by ~2.5-fold compared with those of the first year. These results portend a foundational shift in ecosystem behavior if drought duration and intensity increase, from maintenance of reduced functioning over time to progressive and profound losses of productivity when droughts are extreme.

Science↗

USGS2024

Aridity drives the response of soil total and particulate organic carbon to drought in temperate grasslands and shrublands

The increasing prevalence of drought events in grasslands and shrublands worldwide potentially has impacts on soil organic carbon (SOC). We leveraged the International Drought Experiment to study how SOC, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) concentrations, responds to extreme drought treatments (1-in-100-year) for 1 to 5 years at 19 sites worldwide. In more mesic areas (aridity index > 0.65), SOC and POC concentrations decreased by 7.9% (±3.9) and 15.9% (±6.2) with drought, respectively, but there were no impacts on MAOC concentrations. However, drought had no impact on SOC, POC, or MAOC concentrations in drylands (aridity index < 0.65). The response of SOC to drought varied along an aridity gradient, concomitant with interannual precipitation variability and standing SOC concentration gradients. These findings highlight the differing response magnitudes of POC and MAOC concentrations to drought and the key regulating role of aridity.

Science Advances↗

USGS2014

Response of plant community structure and primary productivity to experimental drought and flooding in an Alaskan fen

Northern peatlands represent a long-term net sink for atmospheric CO 2 , but these ecosystems can shift from net carbon (C) sinks to sources based on changing climate and environmental conditions. In particular, changes in water availability associated with climate control peatland vegetation and carbon uptake processes. We examined the influence of changing hydrology on plant species abundance and ecosystem primary production in an Alaskan fen by manipulating the water table in field treatments to mimic either sustained flooding (raised water table) or drought (lowered water table) conditions for 6 years. We found that water table treatments altered plant species abundance by increasing sedge and grass cover in the raised water table treatment and reducing moss cover while increasing vascular green area in the lowered water table treatment. Gross primary productivity was lower in the lowered treatment than in the other plots, although there were no differences in total biomass or vascular net primary productivity among the treatments. Overall, our results indicate that vegetation abundance was more sensitive to variation in water table than total biomass and vascular biomass accrual. Finally, in our experimental peatland, drought had stronger consequences for change in vegetation abundance and ecosystem function than sustained flooding.

Alaska↗

USGS2012

Bacterial and enchytraeid abundance accelerate soil carbon turnover along a lowland vegetation gradient in interior Alaska

Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the 13C isotopic composition of SOM and respired CO 2 to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in saturated systems, which has been often ignored.

Soil Biology and Biochemistry↗