The total soil organic carbon (SOC) in the northern permafrost zone is estimated to be more than twice as much C as is in the atmosphere. The accumulation of this SOC is driven by the cold climate limiting decomposition. Climate models predict that the Arctic will warm over the next century, therefore accelerating microbial decomposition of SOC is one of the most significant potential greenhouse gas release feedbacks from terrestrial ecosystems to the atmosphere. Winter snow cover and spring thaw are particularly important in influencing decomposition. Few studies, however, have explored how long-term warming will affect the seasonality of soil biogeochemical dynamics. To address this knowledge gap, this research project uses a greenhouse experiment initiated in 1988 at the Toolik, AK Long Term Ecological Research site to explore the consequences of long-term warming on Arctic soil microbial dynamics and nutrient cycling through repeated sampling across seasons and soil horizons. Bacterial and fungal communities? DNA will be studied, to characterize phylogenetically how different organisms respond to long-term warming across seasons and soil horizons. This work is being used to develop and parameterize a mechanistic model of tundra soils? responses to warming.
Broader impacts: The data and model that grows from them are part of a multi-institute collaborative effort supported by the Arctic System Science Program's ?Changing Seasonality in the Arctic System initiative.? The model directly links the structure and activity of the Arctic microbial community to C and nutrient cycling, increasing our ability to predict how biogeochemical cycling in this system will respond to rapid climate warming. Additionally, any pyrosequencing-derived sequences generated through this project will be added into the NIH GenBank database. In addition to scientific collaborations, this project will foster the development of several students in the biogeochemical sciences, including two female undergraduates and a minority high school student, as well as supported participation in several science outreach projects targeted to the local K-12 community. The NSF DDIG grant will enhance the completion of a doctoral dissertation by a female scientist, as well as promoting continued outreach efforts in global change science education and cross-disciplinary research.
The total soil organic carbon (SOC) in the northern permafrost zone is estimated to be more than twice as much C as is in the atmosphere. This accumulation of Arctic SOC is driven by the cold climate limiting microbial decomposition (which releases carbon to the atmosphere in the forms of carbon dioxide and methane). The Arctic is the most rapidly warming biome on earth and climate models predict that it will continue to rapidly warm over the next century. Therefore, warming-driven acceleration of microbial decomposition of SOC represents one of the most significant potential greenhouse gas release feedbacks from terrestrial ecosystems to the atmosphere. The extent of winter snow cover and spring thaw are particularly important regulators of Arctic decomposition. Few studies, however, have explored how long-term warming will affect the seasonality of soil biogeochemical dynamics. To address this knowledge gap, this research project used a greenhouse whole ecosystem warming experiment initiated in 1988 at the Toolik, AK Long Term Ecological Research site to explore the consequences of long-term warming on Arctic soil microbial dynamics and nutrient cycling through repeated sampling across seasons and soil depth. This experiment is the longest-running warming study in the Arctic, and therefore of particular scientific significance, because plant-soil-microbial feedbacks can take many years to develop. As such, this information can help to inform our understanding of terrestrial feedbacks to increasing atmospheric CO2 concentration. The major goals of this project were to identify how over two decades of experimental whole ecosystem warming affected tundra biogeochemical cycling, microbial extracellular enzyme activity (which is the rate-limiting step in decomposition), and microbial community structure. We also wanted to identify whether these responses varied across season and soil depth. We found that peak soil nutrients, microbial biomass, and hydrolytic enzyme activities all occurred from the late winter through thaw in both the warmed and control soils. In contrast, peak oxidative enzyme activities occurred during the summer, suggesting that decomposer communities maintain a seasonal niche separation in this system. Warming amplified this natural seasonal pattern of extracellular enzyme activities. Soil depth also was correlated with variation in decomposer response to warming. Extracellular enzyme activities in the deeper soil horizons were more sensitive to warming than at the surface. Direct greenhouse warming during the summer months did not strongly stimulate decomposition: only oxidative enzyme activities in the surface horizon increased in the July sampling period. Surprisingly, we observed the most robust treatment effects at depth in the mineral horizon from the late winter through thaw (before the greenhouse treatment was directly active). This effect declined during senescence and was reversed in early winter, suggesting that negative biotic-abiotic feedbacks may curtail increased decomposer activity in warming arctic systems.
