TRACING THE CARBON FLOW FROM PLANTS TO SOIL

This goal of this project is to quantify the effect of carbon allocation to different plant tissues, symbionts and exudates on its turnaround and resilience in the ecosystem.This study will validate the estimates of carbon allocation to belowground root and mycorrhizal growth, respiration, exudation, and storage carbohydrates using a novel Temporally Integrating Mass Balance Carbon Allocation (TIMBCA) model against existing and new field observations, and the implication of carbon allocation for soil carbon dynamics. It will (i) quantify the uncertainties of allocation estimates associated with parameter and input flux variability using sensitivity analysis, and (ii) constrain current uncertainties in input fluxes using independent and additional measurements. The mass balance model provides a novel and powerful method for deriving carbon allocation to different tissues, the biomass production efficiencies of different compartments, and storage carbohydrate dynamics from observable or commonly estimable fluxes (gross and net primary productivity, and auto- and heterotrophic respiration). The proposed study will (1) estimate these and other plant carbon allocation metrics from existing data, (2) validate difficult to measure fluxes with independent measurements, and (3) assess the relationship between belowground allocation and soil carbon balance. The findings test the "surplus carbon" hypothesis, whereby carbon retention in the ecosystem arises from resource limitation and competition between different fungal guilds in the soil that have different access to plant-derived carbon.The key component in the TIMBCA model is the storage carbohydrateterm, allowing temporal decoupling between photosynthetic carbon gain and biomass production. We will partition this term between non-structural storage carbohydrate pool and mycorrhizal and exudation dynamics using direct measurements of carbohydrate concentration in plant tissues and soil, and fatty acid methyl ester (FAME) concentrations, chitinase, alpha- and betaglycosidase and cellobiohydrolase activities in the soil.