NSFDEB-NERC:Tropical deadwood carbon fluxes: Improving carbon models by incorporating termites and microbes

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Objectives of this project are to measure rates of tropical deadwood (coarse woody debris;CWD) turnover and identify mechanisms that determine fates of CWD carbon (C) under currentand future climates. Woody plants are the largest aboveground terrestrial biotic C store,and CWD biomass is likely substantial but poorly estimated. Much of our knowledge of turnovercomes from temperate systems, where CWD is thought to be slow cycling. Less is known abouttropical CWD pools and turnover, despite large living tree biomass. Due to differences inclimate (warmer temperatures and sometimes greater precipitation), wood construction, andloss pathways (increasing role of termites), it is likely that CWD is dynamic in tropicalsystems. This project combines field, molecular, and modeling approaches in tropical Australia,where termites and fungi are key agents of wood turnover. A continuous belt of forest fromrainforest to savanna with existing long-term data and infrastructure makes it an ideal location.Three questions will be addressed: Q1. What controls rates of CWD C turnover? Turnover rateswill be determined by termite and fungal activity, which are dependent on climate and woodconstruction. Warmer and wetter conditions should increase turnover, but termites should increaseturnover relatively more in dry conditions as they have water conservation strategies. Densehighly lignified wood should decay more slowly. Q2. What controls fates of C from CWD? C fates(CO2, CH4, organic residues) will depend on stage of decay and functional composition of termiteand microbial communities. Later stages of decay, increased methanogens, decreased methanotrophsand changes in termite species should result in greater CH4:CO2. Greater organic residue formationwill occur when C loss is via termites. Q3. How do mechanisms of wood turnover scale up toaffect ecosystem-level C fluxes under climate change? Climate warming in Northern Australiawill increase turnover rates and alter C fates of wood. To date, CWD is poorly parameterizedin Earth system models (e.g., CWD decays only via physical fragmentation). Field data fromQ1 and Q2 will be used to drive new predictive models of wood turnover and greenhouse gas(GHG) production under climate change. To test Q1 and determine relative saprobic microbeand termite decay rates in response to precipitation variation, blocks of a novel substrate(Pinus radiata) known to attract termites will be placed at 6 sites (Rainfall gradient experiment).Blocks will be enclosed in fine-mesh with or without holes manipulating termite access; blockswill be harvested at end of wet and dry seasons for 4 years. To determine influence of woodconstruction on decay, replicate logs of 10 species/site similarly enclosed will be placedat rainforest and savannah sites (Common garden experiment). Logs will be harvested at endof 2 wet and 2 dry seasons. For logs/blocks, initial and final mass, density and chemistrywill be measured. Local weather stations will provide climate data. To test Q2, wood subsamplesand termites in wood will be collected to determine termite community, microbial communityand functional gene composition, and organic residue formation. CO2 and CH4 will be measuredfor harvested logs/blocks. As some termites live in mounds, experimental mounds (Termite mesocosmexperiment) will be established and mound diel CO2 and CH4 fluxes will be measured monthlyfor 1 yr. To test Q3, field data will be incorporated into woodCLM, an ecosystem model derivedfrom the Community Land Model. Results from the modified and original models will be compared.Using woodCLM, wood dynamics and GHG emissions will be simulated under future climate scenarios