Multiple resource limitation of dryland soil microbial carbon cycling on the Colorado Plateau

Abstract

Understanding interactions among biogeochemical cycles is increasingly important as anthropogenic alterations of global climate and of carbon (C), nitrogen (N), and phosphorus (P) cycles interactively affect the Earth system. Ecosystem processes in the dryland biome, which makes up over 40% of Earth's terrestrial surface, are often distinctively sensitive to small changes in resource availability, likely because levels of many resources are low. However, data also suggest that simultaneous changes in the availability of multiple resources may be necessary to affect a response in these low‐resource systems, offering an opportunity to test patterns and controls of co‐limitation, serial limitation, and individual limitation in soil environments. While drylands may play a governing role in key aspects of Earth's C cycle, and while an improved understanding of resource limitation could substantially improve our forecasts of dryland responses to change, our understanding of interacting controls on soil C cycle processes remains notably poor in these dry systems. Here, we address multiple fundamental hypotheses of resource controls over ecosystem function to test how water, C, N, and P regulate soil C cycling individually and interactively in a dryland ecosystem on the Colorado Plateau. Using a series of laboratory incubations, we found that, while water, C, and N limited C cycling through serial limitation, water alone resulted in an extremely small respiratory response from target organisms, whereas water + C resulted in a dramatic increase in soil C cycling, suggesting a degree of functional co‐limitation. Nitrogen additions alone resulted in no changes to soil C cycling, but when N was added in concert with water and C, N greatly increased soil C cycling rates relative to additions of water and C without N. Phosphorus additions had no effect on the C cycle either alone or synergistically. These patterns were consistent with the stoichiometry of the system and interactions among resources were surprising in ways that inform our understanding of critical theories in ecology, such as the Transient Maxima Hypothesis, supporting the suggestion that multiple resource limitation explains pulse‐dynamic C cycling in drylands better than water limitation alone.

Biogeochemical and ecosystem properties in three adjacent semi‐arid grasslands are resistant to nitrogen deposition but sensitive to edaphic variability

“…The addition of water alone increased heterotrophic respiration rates (Figure 3). However, this increase in microbial activity was not associated with changes in microbial biomass over the 7‐day period of the incubation, suggesting that the growth of the microbial community was not limited by water or N. A soil incubation study focused on multiple resource limitation at the finest‐textured site suggested that C may also be needed to stimulate soil microbial community growth (Choi et al, 2022).…”

“…Relative to water, few data are available regarding the nature of C and nutrient limitation in drylands. Choi et al (2022) directly tested the potential for multiple resource limitation on microbial activity in soils from the fine‐textured site. Water independently increased heterotrophic respiration rates (as it did in our incubation experiment), but the addition of C with water increased CO 2 fluxes by an order of magnitude relative to the addition of water alone, signalling functional co‐limitation of water and C. Nitrogen alone had no effect on heterotrophic respiration rates (as we observed in our field experiment and laboratory incubation), but the addition of N with water and C increased CO 2 fluxes an additional order of magnitude, suggesting functional serial limitation of water, C and N. Together, these findings indicate that multiple resources (water and C) may be required in addition to N inputs to affect soil ecosystem properties at these sites, highlighting the importance of the timing of N deposition and its relationship to precipitation and the release of C into the soil (e.g.…”

Response of soil carbon dioxide efflux to temporal repackaging of rainfall into fewer, larger events in a semiarid grassland

“…Dryland ecosystems have high spatial heterogeneity in soil properties and vegetation distribution, which presents challenges for understanding ecosystem responses to changes in climate, including rainfall size and frequency (Osborne et al, 2022). Because we observed large variability in seasonal total F s for the many/small regime (Table 2), future research should examine how spatial heterogeneity and colimitation of multiple resources (e.g., water, carbon, nutrients) mediate carbon cycling responses to rainfall repackaging (Choi et al, 2022;Osborne et al, 2022). There is also a Frontiers in Environmental Science frontiersin.org need to better understand how soil texture shapes F s responses to rainfall repackaging.…”

The consequences of climate change for dryland biogeochemistry

“…The classic water‐limitation model of drylands offers important insights into ecosystem function, but multiple resources (e.g. water, C, nutrients) often are scarce simultaneously in drylands, increasing the occurrence of co‐ and serial limitation (Austin, 2011; Choi et al ., 2022). High levels of spatial and temporal heterogeneity compound this complexity.…”

“…Instead, in some long‐term experiments, drylands behave as if they were saturated with N – losing N during periods when N availability increases without a concomitant increase in biological N demand (Homyak et al ., 2016; Phillips et al ., 2021). This may reflect co‐ or serial limitation of N with other resources like water and/or C (Choi et al ., 2022). Improving our understanding of multiple resource dynamics by using multifactorial experiments with regression designs and isotope tracers, for example, may help improve our ability to predict and mitigate the biogeochemical consequences of climate change in drylands and across other diverse ecosystem types.…”