Hypothesis 4: Autotrophic respiration

While models of photosynthesis are complex and well-tested, modelling of the fate of fixed C in plants is much weaker, due to difficulties in separating plant and microbial contributions to soil effluxes, and in measuring root allocation and exudates. Many models use simple empirical factors that relate respiration of recently assimilated (<1 week) C directly to photosynthesis (Waring et al., 1998), but this relationship has not been widely tested in arctic vegetation. Indeed, empirical data are lacking on the fate of recently fixed C in arctic plants.

H4a: Autotrophic respiration is a fixed fraction of gross C fixation over daily timescales.

H4b: More new C will be turned over at less fertile sites (low LAI, low available N) due to high allocation to soil microbial populations (either direct to mycorrhizas or via root exudates).

WP1 will use pulse labelling with 13C to track the fate of recently fixed C, and harvests to determine biomass accumulation in plants, while WP3 will provide chamber and branch bag estimates of gross primary production. WP7 will provide estimates of C allocation and turnover via modelling and assimilation of flux data.

Outcome: Improved modelling of the fate of recently fixed C.