Ultraviolet-B radiation and nitrogen affect the photosynthesis of maize: a Mediterranean field study

Abstract

The effects of UV-B radiation on the gas exchange rates, chlorophyll fluorescence, pigmentation, soluble sugars, starch, soluble proteins and carboxylating enzyme activities of maize ( Zea mays L.) were investigated at four levels of applied nitrogen (0, 100, 200 and 300 kg ha −1 of N) under Mediterranean field conditions. The experiment simulated a 20% stratospheric ozone depletion over Portugal. Supplementary UV-B radiation and N deficiency reduced photosynthetic and transpiration rate, stomatal conductance, total chlorophyll, total carotenoids, soluble sugars and UV-B absorbing compounds concentration, as well as the pool size of the electron acceptors in PSII and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPCase) activities. Enhanced UV-B and N deficiency increased minimal and maximal chlorophyll fluorescence. The effect of additional UV-B on maize photosynthesis was dependent on the plant nutritional status, since the lower reduction of net photosynthetic rate occurred in N-stressed plants. At the same time, photosynthesis was less affected by N nutrition under high UV-B. Similar results were obtained for RuBisCO and PEPCase activities. N-starved plants had higher amounts of soluble proteins at high UV-B as compared to ambient UV-B. The starch concentration of N-deprived plants at ambient UV-B was higher than all other treatments. The underlying mechanisms for these results are discussed.