Browsing by Author "Hayer, Michaela"
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Item Decreased growth of wild soil microbes after 15 years of transplant-induced warming in a montane meadow(2022) Purcell, Alicia M.; Hayer, Michaela; Koch, Benjamin J.; Mau, Rebecca L.; Blazewicz, Steven J.; Dijkstra, Paul; Mack, Michelle C.; Marks, Jane C.; Morrissey, Ember M.; Pett-Ridge, Jennifer; Rubin, Rachel L.; Schwartz, Egbert; van Gestel, Natasja C. (TTU); Hungate, Bruce A.The carbon stored in soil exceeds that of plant biomass and atmospheric carbon and its stability can impact global climate. Growth of decomposer microorganisms mediates both the accrual and loss of soil carbon. Growth is sensitive to temperature and given the vast biological diversity of soil microorganisms, the response of decomposer growth rates to warming may be strongly idiosyncratic, varying among taxa, making ecosystem predictions difficult. Here, we show that 15 years of warming by transplanting plant–soil mesocosms down in elevation, strongly reduced the growth rates of soil microorganisms, measured in the field using undisturbed soil. The magnitude of the response to warming varied among microbial taxa. However, the direction of the response—reduced growth—was universal and warming explained twofold more variation than did the sum of taxonomic identity and its interaction with warming. For this ecosystem, most of the growth responses to warming could be explained without taxon-specific information, suggesting that in some cases microbial responses measured in aggregate may be adequate for climate modeling. Long-term experimental warming also reduced soil carbon content, likely a consequence of a warming-induced increase in decomposition, as warming-induced changes in plant productivity were negligible. The loss of soil carbon and decreased microbial biomass with warming may explain the reduced growth of the microbial community, more than the direct effects of temperature on growth. These findings show that direct and indirect effects of long-term warming can reduce growth rates of soil microbes, which may have important feedbacks to global warming.Item Life history strategies among soil bacteria—dichotomy for few, continuum for many(2023) Stone, Bram W.G.; Dijkstra, Paul; Finley, Brianna K.; Fitzpatrick, Raina; Foley, Megan M.; Hayer, Michaela; Hofmockel, Kirsten S.; Koch, Benjamin J.; Li, Junhui; Liu, Xiao Jun A.; Martinez, Ayla; Mau, Rebecca L.; Marks, Jane; Monsaint-Queeney, Victoria; Morrissey, Ember M.; Propster, Jeffrey; Pett-Ridge, Jennifer; Purcell, Alicia M. (TTU); Schwartz, Egbert; Hungate, Bruce A.Study of life history strategies may help predict the performance of microorganisms in nature by organizing the complexity of microbial communities into groups of organisms with similar strategies. Here, we tested the extent that one common application of life history theory, the copiotroph-oligotroph framework, could predict the relative population growth rate of bacterial taxa in soils from four different ecosystems. We measured the change of in situ relative growth rate to added glucose and ammonium using both 18O–H2O and 13C quantitative stable isotope probing to test whether bacterial taxa sorted into copiotrophic and oligotrophic groups. We saw considerable overlap in nutrient responses across most bacteria regardless of phyla, with many taxa growing slowly and few taxa that grew quickly. To define plausible life history boundaries based on in situ relative growth rates, we applied Gaussian mixture models to organisms’ joint 18O–13C signatures and found that across experimental replicates, few taxa could consistently be assigned as copiotrophs, despite their potential for fast growth. When life history classifications were assigned based on average relative growth rate at varying taxonomic levels, finer resolutions (e.g., genus level) were significantly more effective in capturing changes in nutrient response than broad taxonomic resolution (e.g., phylum level). Our results demonstrate the difficulty in generalizing bacterial life history strategies to broad lineages, and even to single organisms across a range of soils and experimental conditions. We conclude that there is a continued need for the direct measurement of microbial communities in soil to advance ecologically realistic frameworks.