Practice question

Total ecosystem respiration, RE, is the combined carbon dioxide release from autotrophic respiration, RA, and heterotrophic respiration, RH. Autotrophs respire to maintain and build plant, algal, or microbial tissues; heterotrophs—including animals, fungi, and many bacteria—respire while consuming living or dead organic matter. Adding these fluxes gives RE = RA + RH. Gross primary productivity removes CO2 from the atmosphere or water through carbon fixation, whereas ecosystem respiration returns CO2 through oxidation of organic carbon. Their difference defines net ecosystem production: NEP = GPP − RE. At the producer level, NPP = GPP − RA, so GPP − NPP can estimate RA but not total ecosystem respiration because it omits RH. Subtracting GPP from NPP reverses the carbon balance, and subtracting heterotrophic respiration from autotrophic respiration has no meaning as the total. Measurements may combine chamber data, eddy covariance, oxygen fluxes, and models. The sum applies because both biological sources contribute simultaneously to ecosystem-wide respiratory carbon loss.