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The Potential for advanced snowmelt timing to decouple plant and mycorrhizal fungal phenology and biogeochemical cycling

Active Dates 8/15/2021-8/14/2024
Program Area Environmental Systems Science
Project Description
As climate changes, snowpack is expected to diminish, and snowmelt timing is expected to advance. Shifts in snow quantity and melt dates are especially relevant in mountain ecosystems, which provide 50% of the Earth’s fresh water. As snowmelt advances, the phenology (e.g., timing of growth and life history events) of organisms that rely on the water and nutrient pulses provided at snowmelt may also change. However, all organisms may not respond the same ways to advanced snowmelt. If previously interacting organisms shift their phenologies in different ways, previously synchronous interactions may become asynchronous with climate change (i.e., phenological mismatch).

   Nowhere is the threat of temporal interaction decoupling more relevant than among plants and associated mycorrhizal and decomposer fungi. Decomposer fungi mineralize soil organic compounds into plant-available nutrients. Arbuscular mycorrhizal (AM) fungi then provide plants with these nutrients, up to 80% of their required nutrients. While belowground plant growth has been observed under snow, the timing and magnitude of this plant root growth is largely understudied. Decomposer and AM fungal growth under snowpack has not been addressed. Snowmelt date can vary by two months at our study site. If plants and fungi respond to different cues (e.g., plants respond to temperature, but fungi respond to soil moisture), then their growth may become decoupled. If this occurs, nutrients that would have been mineralized by decomposer fungi and acquired by AM fungi and shunted to fuel plant productivity could instead be leached from soil into the underlying hydrological system. If this occurs consistently, plant productivity will decrease and watershed nutrient loads will increase in a warmer climate.    Our project links with the existing LBNL Watershed SFA to assess the potential for climate-induced temporal disruption of plant and fungal exchange of nutrients and consequences on watershed biogeochemical nutrient cycling with shifts in the magnitude of snowpack and snowmelt timing. We will evaluate temporal decoupling of plant – AM fungal symbioses and decomposer fungi using observational elevational gradients that capture both local and regional snowmelt heterogeneity, (AIM I), and in paired early and late snowmelt plots (AIM II) and connect these to functional consequences by modeling soil biogeochemical fluxes at the watershed scale (AIM III). We will first determine plant and fungal growth belowground by installing ingrowth cores at 8 time points in each of three years at 4 elevations (2500 – 3900 m) that vary in length of the growing season, soil nutrients, climate, and snowmelt date. We will then explicitly determine how snowmelt timing affects belowground plant and fungal growth by installing ingrowth cores into early snowmelt manipulations at one elevation (2900 m) at 8 time points in each of three years. In all of these sites and times, we will also measure soil nutrient concentrations within the rooting zone and below the rooting zone (to assess leaching). During the growing season, we will also assess plant productivity (e.g., NDVI) and nutrient acquisition traits (e.g. SLA, tissue stoichiometry) to understand if particular plant and fungal traits are selected for across ecosystems that vary in snowmelt timing and soil nutrient concentrations. All data will be integrated into structural equation models to understand plant versus fungal control on soil nutrient retention at the watershed scale. Finally we will parameterize E3SM model runs with collected phenological and biogeochemical data across the RMBL watershed.
Award Recipient(s)
  • University of Tennessee Knoxville (PI: Kivlin, Stephanie)