An official website of the United States government
Global change drivers that modify the quality and quantity of litter inputs to soil affect greenhouse gas fluxes, and thereby constitute a feedback to climate change. Carbon cycling in the Yukon-Kuskokwim (Y-K) River Delta, a subarctic wetland system, is influenced by landscape variations in litter quality and quantity generated by herbivores (migratory birds) that create ‘grazing lawns’ of short stature, nitrogen-rich vegetation. To identify the mechanisms by which these changes in litter inputs affect soil carbon balance, we independently manipulated qualities and quantities of litter representative of levels found in the Y-K Delta in a fully factorial microcosm experiment. We measured carbon dioxide (CO2) fluxes from these microcosms weekly. To help us identify how litter inputs influenced greenhouse gas fluxes, we sequenced soil fungal and bacterial communities, and measured soil microbial biomass carbon, dissolved carbon, inorganic nitrogen, and enzyme activity. We found that positive correlations between litter input quantity and CO2 flux were dependent upon litter type, due to differences in litter stoichiometry and changes to the structure of decomposer communities, especially the soil fungi. These community shifts were particularly pronounced when litter was added in the form of herbivore feces, and in litter input treatments that induced nitrogen limitation (i.e., senesced litter). The sensitivity of carbon cycling to litter quality and quantity in this system demonstrates that herbivores can strongly impact greenhouse gas fluxes through their influence on plant growth and tissue chemistry.
more »
« less
Herbivores influence biogeochemical processes by altering litter quality and quantity in a subarctic wetland
Abstract Global change drivers that modify the quality and quantity of litter inputs to soil affect greenhouse gas fluxes, and thereby constitute a feedback to climate change. Carbon cycling in the Yukon–Kuskokwim (Y–K) River Delta, a subarctic wetland system, is influenced by landscape variations in litter quality and quantity generated by herbivores (migratory birds) that create ‘grazing lawns’ of short stature, nitrogen-rich vegetation. To identify the mechanisms by which these changes in litter inputs affect soil carbon balance, we independently manipulated qualities and quantities of litter representative of levels found in the Y–K Delta in a fully factorial microcosm experiment. We measured CO2fluxes from these microcosms weekly. To help us identify how litter inputs influenced greenhouse gas fluxes, we sequenced soil fungal and bacterial communities, and measured soil microbial biomass carbon, dissolved carbon, inorganic nitrogen, and enzyme activity. We found that positive correlations between litter input quantity and CO2flux were dependent upon litter type, due to differences in litter stoichiometry and changes to the structure of decomposer communities, especially the soil fungi. These community shifts were particularly pronounced when litter was added in the form of herbivore feces, and in litter input treatments that induced nitrogen limitation (i.e., senesced litter). The sensitivity of carbon cycling to litter quality and quantity in this system demonstrates that herbivores can strongly impact greenhouse gas fluxes through their influence on plant growth and tissue chemistry. Graphical abstract
more »
« less
- Award ID(s):
- 1932889
- PAR ID:
- 10473997
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Biogeochemistry
- Volume:
- 166
- Issue:
- 2
- ISSN:
- 0168-2563
- Format(s):
- Medium: X Size: p. 67-85
- Size(s):
- p. 67-85
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Herbivory can have strong impacts on greenhouse gas fluxes in high-latitude ecosystems. For example, in the Yukon-Kuskokwim (Y-K) Delta in western Alaska, migratory goose grazing affects the magnitude of soil carbon dioxide (CO2) and methane (CH4) fluxes. However, the underlying drivers of this relationship are unclear, as few studies systematically tease apart the processes by which herbivores influences soil biogeochemistry. To examine these mechanisms in detail, we conducted a laboratory incubation experiment to quantify changes in greenhouse gas fluxes in response to three parameters altered by herbivores in situ: temperature, soil moisture content, and nutrient inputs. These treatments were applied to soils collected in grazing lawns and nearby ungrazed habitat, allowing us to assess how variation in microbial community structure influenced observed responses. We found pronounced differences in both fungal and prokaryotic community composition between grazed and ungrazed areas. In the laboratory incubation experiment, CO2 and CH4 fluxes increased with temperature, soil moisture, and goose fecal addition, suggesting that grazing-related changes in the soil abiotic environment may enhance soil C losses. Yet, these abiotic drivers were insufficient to explain variation in fluxes between soils with and without prior grazing. Differences in trace gas fluxes between grazed and ungrazed areas may result both from herbivore-induced shifts in abiotic parameters and grazing-related alterations in microbial community structure. Our findings suggest that relationships among herbivores and soil microbial communities could mediate carbon-climate feedbacks in rapidly changing high-latitude ecosystems.more » « less
-
Abstract Permafrost thaw is a major potential feedback source to climate change as it can drive the increased release of greenhouse gases carbon dioxide (CO2) and methane (CH4). This carbon release from the decomposition of thawing soil organic material can be mitigated by increased net primary productivity (NPP) caused by warming, increasing atmospheric CO2, and plant community transition. However, the net effect on C storage also depends on how these plant community changes alter plant litter quantity, quality, and decomposition rates. Predicting decomposition rates based on litter quality remains challenging, but a promising new way forward is to incorporate measures of the energetic favorability to soil microbes of plant biomass decomposition. We asked how the variation in one such measure, the nominal oxidation state of carbon (NOSC), interacts with changing quantities of plant material inputs to influence the net C balance of a thawing permafrost peatland. We found: (1) Plant productivity (NPP) increased post‐thaw, but instead of contributing to increased standing biomass, it increased plant biomass turnover via increased litter inputs to soil; (2) Plant litter thermodynamic favorability (NOSC) and decomposition rate both increased post‐thaw, despite limited changes in bulk C:N ratios; (3) these increases caused the higher NPP to cycle more rapidly through both plants and soil, contributing to higher CO2and CH4 fluxes from decomposition. Thus, the increased C‐storage expected from higher productivity was limited and the high global warming potential of CH4contributed a net positive warming effect. Although post‐thaw peatlands are currently C sinks due to high NPP offsetting high CO2release, this status is very sensitive to the plant community's litter input rate and quality. Integration of novel bioavailability metrics based on litter chemistry, including NOSC, into studies of ecosystem dynamics, is needed to improve the understanding of controls on arctic C stocks under continued ecosystem transition.more » « less
-
Abstract AimsHerbivores create large differences in litter decomposition rates, but identifying how they do this can be difficult because they simultaneously influence both biotic and abiotic factors. In the Yukon-Kuskokwim (Y-K) River Delta in western Alaska, geese are dominant herbivores in wet-sedge meadows, where they create ‘grazing lawns’ that have nutrient-rich litter and an open habitat structure. To understand how geese affect decomposition, we tested the effects of litter quality and habitat type on litter decomposition over one year. MethodsWe performed a litter bag study in which we collected two litter types representing grazed and ungrazed vegetation conditions (high quality litter similar to grazed litter, and lower quality senesced, ungrazed litter), then incubated them in ‘grazing lawn’ and ungrazed meadows. Litter mass loss, carbon, nitrogen, cellulose and lignin content were measured after 3, 6, 9, and 52 weeks. We also monitored abiotic conditions (i.e., soil temperature, UV radiation, throughfall, and soil moisture content) in each habitat type. ResultsHigh-quality litter (lower lignin:N ratios) lost more mass than low-quality ungrazed litter over the whole study. However, at different times during the decomposition process, lower quality litter decomposed faster in grazed habitat, whereas higher quality litter decomposed faster in ungrazed habitat. This occurred despite abiotic conditions in grazed habitat that generally promote faster decomposition. ConclusionResults suggest that herbivore-induced increases in litter quality increase decomposition rates, and that the accumulation of the low-quality litter in ungrazed habitats is partly due to slow decomposition rates. While herbivores influence habitat conditions, the effects of habitat on decomposition differed across litter qualities, which suggests that other variables, such as differing microbial communities, play a role in decomposition processes. Graphical abstractmore » « less
-
Forest ecosystems are important global soil carbon (C) reservoirs, but their capacity to sequester C is susceptible to climate change factors that alter the quantity and quality of C inputs. To better understand forest soil C responses to altered C inputs, we integrated three molecular composition published data sets of soil organic matter (SOM) and soil microbial communities for mineral soils after 20 years of detrital input and removal treatments in two deciduous forests: Bousson Forest (BF), Harvard Forest (HF), and a coniferous forest: H.J. Andrews Forest (HJA). Soil C turnover times were estimated from radiocarbon measurements and compared with the molecular‐level data (based on nuclear magnetic resonance and specific analysis of plant‐ and microbial‐derived compounds) to better understand how ecosystem properties control soil C biogeochemistry and dynamics. Doubled aboveground litter additions did not increase soil C for any of the forests studied likely due to long‐term soil priming. The degree of SOM decomposition was higher for bacteria‐dominated sites with higher nitrogen (N) availability while lower for the N‐poor coniferous forest. Litter exclusions significantly decreased soil C, increased SOM decomposition state, and led to the adaptation of the microbial communities to changes in available substrates. Finally, although aboveground litter determined soil C dynamics and its molecular composition in the coniferous forest (HJA), belowground litter appeared to be more influential in broadleaf deciduous forests (BH and HF). This synthesis demonstrates that inherent ecosystem properties regulate how soil C dynamics change with litter manipulations at the molecular‐level. Across the forests studied, 20 years of litter additions did not enhance soil C content, whereas litter reductions negatively impacted soil C concentrations. These results indicate that soil C biogeochemistry at these temperate forests is highly sensitive to changes in litter deposition, which are a product of environmental change drivers.more » « less
