The Effects of Different Nitrogen Nutrition Forms on Photosynthetic Characteristics in Wheat Leaves

In three different nitrogen treatments, the chlorophyll content(Ch1), photosynthetic rate (Pn), RuBPcase initial activity, RuBPcase content, mesophyll conductance (gm), carbonic anhydrase (CA) activity, PS I activity and PS Ⅱ activity of leaves were the highest in the mixture treatment of NHt4++NO3-, then were in the NO3- treatment and the lowest were in NH4+ treatment. No evident differences were found in RuBPcase specific activity among treatments. There was little difference on stomatol conductance (gs) between different treatments and CK. Nitrogen nutritions decreased the intercellular CO2 concentration (Ci). There were similarly changing trends between gm, CA activity and photosynthetic rate (Pn) in different treatments, which showed the conductivity of CO2 in liquid part of mesophyll cell having probably important influence on photosynthesis of leaves. Compared to NH4+ treatment, NO3- treatment increased the photorespiration rate, the ratio of photorespiration rate to photosynthetic rate and nitrate reductase(NR) activity in wheat leaves. The increase of photosynthetic rate in mixture treatment NHk4++ NO3- was mainly correlated to the higher RubisCO activity, higher photosynthetic electron conductivity and the improvment of CO2 conductivity in liquid phase of mesophall cell.