Post-fire co-stimulation of gross primary production and ecosystem respiration in a meadow grassland on the Tibetan Plateau

Predicting post-fire ecosystem CO2 exchange requires an explicit understanding of the sensitivity of gross primary production (GPP), ecosystem respiration (ER) and net ecosystem exchange (NEE) to post-fire conditions. However, the simultaneous effects of fire on GPP, ER and NEE are rarely evaluated. We established a three-year manipulative fire experiment in a meadow grassland on the Tibetan Plateau to investigate the responses of GPP, ER and NEE to prescribed fire. We found that fire on average increased GPP by 13% and ER by 9%, leading to an increase in NEE by 20% across the three years. There was no clear relationship between post-fire changes in soil temperature and ecosystem CO2 exchange, yet reductions in soil volumetric moisture were positively related to changes in GPP, ER and NEE. These results suggest that post-fire stimulation of GPP, ER and NEE cannot be fully explained by changes in soil temperature and soil moisture. Besides, changes in GPP, ER and NEE were positively related to fire-induced increases in graminoid biomass, legume biomass and soil inorganic nitrogen. Taken together, our results suggest the interwoven control of biotic and abiotic factors on post-fire GPP, ER and NEE, yet also that shifts in plant functional type biomass may outweigh the negative effects of reduced soil moisture on ecosystem CO2 exchange. These results underscore how simultaneous documentation of GPP, ER and NEE dynamics can advance a mechanistic understanding of CO2 exchange under fire disturbance.

Automated summary

A three-year manipulative fire experiment in a meadow grassland on the Tibetan Plateau showed that fire increased GPP and ER, leading to an increase in NEE. Changes in plant functional type biomass post-fire may outweigh the negative effects of reduced soil moisture on ecosystem CO2 exchange.