The interactive effects of nitrogen and calcium on photosynthetic characteristics and chlorophyll fluorescence parameters of nectarine under pototected culture

The interactive effects of nitrogen and calcium on leaf chlorophyll content, photosynthetic characteristics and chlorophyll fluorescence parameters of nectarine in protected cultivation were studied by using 3-yearsold nectarine (prunus persica var. nectariana cv. Zhongyou 5 ) trees which were watered by mixed solution of nitrogen and calcium at different levels. The results show that under different nitrogen levels, the chlorophyll contents, net photosynthetic rates (Pn), stomatal conductances (Gs), transpiration rates (Tr), intercellular CO2 concentrations (Ci), maximal photochemical efficiencies of PSⅡ(Fv/Fm), photochemical quenching coefficients (qP), apparent photosynthetic electron transfer rates (ETR), and quantum yields of PSⅡ electron transport(￠PSⅡ) are increased firstly and then decreased with the increase of calcium levels, while the minimal fluorescence values (F0) and nonphotochemical quenching coefficients (NPQ) are decreased firstly and then increased. Under the low nitrogen level (5 mmol/L) the interactive effects of nitrogen and calcium on photosynthesis are the best with 4 mmol/L calcium level, which has significant differences (P0.05) compared with other calcium levels. Under the high nitrogen level (25 mmol/L) the interactive effects of nitrogen and calcium on photosynthesis are the best with 8 mmol/L calcium level, which has significant differences (P0.05) compared with other calcium levels.