Interactions between temperature and intercellular CO2 concentration in controlling leaf isoprene emission rates

Abstract

Plant isoprene emissions have been linked to several reaction pathways involved in atmospheric photochemistry. Evidence exists from a limited set of past observations that isoprene emission rate (I_s ) decreases as a function of increasing atmospheric CO₂ concentration, and that increased temperature suppresses the CO₂ effect. We studied interactions between intercellular CO₂ concentration (C_i ) and temperature as they affect I_s in field-grown hybrid poplar trees in one of the warmest climates on earth - the Sonoran Desert of the southwestern United States. We observed an unexpected midsummer downregulation of I_s despite the persistence of relatively high temperatures. High temperature suppression of the I_s :C_i relation occurred at all times during the growing season, but sensitivity of I_s to increased C_i was greatest during the midsummer period when I_s was lowest. We interpret the seasonal downregulation of I_s and increased sensitivity of I_s to C_i as being caused by weather changes associated with the onset of a regional monsoon system. Our observations on the temperature suppression of the I_s :C_i relation are best explained by the existence of a small pool of chloroplastic inorganic phosphate, balanced by several large, connected metabolic fluxes, which together, determine the C_i and temperature dependencies of phosphoenolpyruvate import into the chloroplast.

Keywords: abiotic; hot; model; ozone; photosynthesis; stress; terpene; thermotolerance.