Drivers of C cycling in three arctic-alpine plant communities

Abstract

Recent vegetation changes in arctic-alpine tundra ecosystems may affect several ecosystem processes that regulate microbe and soil functions. Such changes can alter ecosystem carbon (C) cycling with positive feedback to the atmosphere if plant C uptake is less than the amount of soil C released. Here, we examine how differences in plant functional traits, microbial activity, and soil processes within and across Salix-dominated shrub, dwarf shrub-dominated heath, and herband cryptogam-dominated meadow communities influence C cycling. We develop a hypothesized framework based on a priori model selection of variation in daytime growing season gross ecosystem photosynthesis (GEP) and above-and belowground respiration. The fluxes were standardized to light and temperature. Gross ecosystem photosynthesis was primarily related to soil moisture and secondarily to plant functional traits and aboveground biomass, and belowground respiration was dependent on the community weighted mean of specific leaf area (SLA CWM). Similarly, microbial activity was linked with SLA CWM and was highest in meadows, and carbon-degrading microbial activity decreased with vegetation woodiness. These results suggest that shrub expansion may influence summer C cycling differently depending on plant community, as belowground respiration might increase in the heath and decrease in the meadow communities.

Statistical upscaling of ecosystem CO2 fluxes across the terrestrial tundra and boreal domain: Regional patterns and uncertainties

“…The lack of this relationship might be due to annual ER models not covering the full range of conditions represented by the annual NEE models, or spurious causal relationships being identified by the relatively poorly performing NEE models. The importance of land cover was expected as it summarizes many key processes related to carbon cycling (e.g., the carbon uptake capacity, temperature sensitivity, as well as quantity and quality of carbon inputs into the soil; Sørensen et al, 2019) and other environmental characteristics (e.g., soil moisture is likely higher in wetlands than in sparse vegetation).…”

“…Mean annual NEE derived by subtracting annual ER (ecosystem respiration) from GPP (gross primary production) in this study (a), from a global upscaling product FLUXCOM (b), and from a process model ensemble CMIP5 (Coupled Model Intercomparison Project Phase 5) (c), and the standard deviation of these and the independently modeled annual NEE in this study (visualized in Figure 3c) (d). A regional-scale example of the spatial variation of annual NEE in our prediction in northern Alaska, with black outlines depicting the size of the pixel in one of the highest resolution (smallest pixel size) models in the CMIP5 ensemble (1.92 × 1.5°) (e) [Colour figure can be viewed at wileyonlinelibrary.com] cover was expected as it summarizes many key processes related to carbon cycling (e.g., the carbon uptake capacity, temperature sensitivity, as well as quantity and quality of carbon inputs into the soil; Sørensen et al, 2019) and other environmental characteristics (e.g., soil moisture is likely higher in wetlands than in sparse vegetation).…”

“…Finally, many of the recent upscaling studies have relied on EC flux measurements only, neglecting chamber measurements despite their importance as additional data sources (with exception of Natali et al, 2019). Chambers are useful especially in remote, sparsely measured treeless tundra where they can capture the entire ecosystem CO 2 balance and directly measure NEE and ER (Sørensen et al, 2019). Thus, a compilation of both EC and chamber flux measurements and the comparison of available modeling techniques is clearly required to ensure accurate CO 2 flux estimates from existing data and models.…”

Relationships between aboveground plant traits and carbon cycling in tundra plant communities

“…Today, this hypothesis is most often operationalized using abundance-weighted average trait values (Garnier et al 2004) . In the tundra, photosynthesis and ecosystem respiration have been shown to correlate positively with fast leaf economics, indicated by, for example, high average SLA (Sørensen et al 2019) . Plant size is often described using biomass or its proxies, such as total plant cover or leaf area index (LAI) (Oberbauer et al 2007;Street et al 2007;Shaver et al 2007;Marushchak et al 2013) .…”

“…It is unclear how such changes in vegetation will influence the carbon stocks and balance of these ecosystems. On one hand, the expansion of larger plants might increase net carbon uptake (Cahoon et al 2012; Sørensen et al 2019). On the other hand, vegetation-driven changes in soil conditions and microorganisms might accelerate decomposition and, in turn, increase carbon losses to the atmosphere (Parker, Subke, and Wookey 2015; Vowles and Björk 2018).…”