The Response of Soil CO2 Fluxes to Progressively Excluding Vertebrate and Invertebrate Herbivores Depends on Ecosystem Type

Abstract

Grasslands support large populations of herbivores and store up to 30% of the world's soil carbon (C). Thus, herbivores likely play an important role in the global C cycle. However, most studies on how herbivory impacts the largest source of C released from grassland soils-soil carbon dioxide (CO 2) emissions-only considered the role of large ungulates. This ignores all other vertebrate and invertebrate herbivores and their collective effects on ecosystem properties. We progressively excluded large, medium, and small vertebrates and invertebrates from two subalpine grasslands (productive, heavily grazed short-grass; less productive, lightly grazed tall-grass) using size-selective fences, assessed the impact on soil CO 2 emissions and related biotic and abiotic variables. Exclusion resulted in significant changes in soil CO 2 emissions in both vegetation types. Short-grass soil CO 2 emissions progressively increased when large and medium mammals were excluded. However, no difference was detected among plots were all or no herbivores grazed. In contrast, tall-grass soil CO 2 emissions were not affected by mammal exclusion, but excluding all herbivores lead to reduced emissions. Soil micro-climatic parameters best predicted the patterns of soil CO 2 emissions in short-grass vegetation, whereas root biomass was the best predictor of CO 2 release in tall-grass vegetation. Our results showed that diverse herbivore communities affect soil respiration differently than assumed from previous studies that only excluded large ungulates. Such information is important if we are to understand how changes in herbivore species composition-as could happen through altered management practices, extinction or invasion-impact grassland C storage and release.

Aboveground vertebrate and invertebrate herbivore impact on net N mineralization in subalpine grasslands

“…; 30-100 g), and invertebrates (e.g., grasshoppers, caterpillars, leafhoppers, ,5 g). Ungulates consume the largest proportion of available biomass, closely followed by invertebrates: medium and small mammals consume the least (Risch et al 2013).…”

“…A detailed description of our experimental setup and fence construction can be found in Risch et al (2013) and Haynes et al (2014). Briefly, we selected 18 subalpine grassland sites (nine short-grass, nine tallgrass vegetation) distributed over six subalpine grasslands throughout the park.…”

“…The ''All'' plot (not fenced) was located at least 5 m away from the 2.1 m tall and 7 3 9 m main electrical fence that enclosed the other four exclosure types (ET). Within each main fence, we randomly established four plots: (1) the ''Marmot, Mice, Invertebrates'' plots (unfenced; access for all but ungulates); (2) the ''Mice, Invertebrates'' plots (electrical fence), which excluded all medium-sized mammals; (3) the ''Invertebrates'' plots (metal mesh), which excluded all mammals; and (4) the ''None'' plots (mosquito net covered with a roof ), which excluded all herbivores (for details on fence construction, see Risch et al 2013, Haynes et al 2014). In addition, we established six ''microclimate control'' exclosures to assure that the ''None'' exclosure construction (mesh and roof ) did not affect the microclimatic conditions within the plots and therefore the results.…”

A meta-analysis of soil biodiversity impacts on the carbon cycle

“…While laboratory manipulations can provide useful information about potential controls over ecological processes, these manipulations are by necessity short-term (range: 35 days-52 weeks for the studies we compiled) and may include only a subset of the complex food webs and biogeochemical processes that occur in natural field settings (Hol et al, 2010). Furthermore, diversity effects may become more apparent over time as functional redundancy declines (Reich et al, 2012).…”

“…These body size classes typically are useful functional groupings as they correlate with metrics such as metabolic rate, generation time, and food size (Peters, 1983). Estimates suggest that 1 g of soil can harbor tens of thousands of bacterial taxa; up to 200 m of fungal hyphae; and a wide range of micro-, meso-, and macrofauna (Roesch et al, 2007;Bardgett, 2005). This complex soil community plays an important role in determining the magnitude and direction of C fluxes between the atmosphere and terrestrial ecosystems, controlling soil C mineralization and promoting plant growth by regulating soil nutrient availability (e.g., De Deyn and Fitter et al, 2005;Wall et al, 2010;de Vries et al, 2013).…”