Comparison of Photosynthetic Characteristics of Grafted and Ownroot Seedlings of Cucumber under Low Temperature Circumstances

Abstract

The study probed the relations of the net photosynthetic rates (Pn),apparent quantum yields (AQY), stomatal conductance (Gs), transpiration rates (Tr) and intercellular CO_(2) concentrations (Ci) with the photosynthetic flux densities (PFD) of grafted and own-root seedlings (35 days after sowing) of greenhouse-planted cucumber under long-time low-temperature circumstances. The results showed that at different photosynthetic flux densities (PFD),grafted and own-root seedlings suffering long-time low temperature significantly decreased in light compensation point,apparent quantum yield, Pn,Gs and Tr compared with those growing at normal temperature,but grafted seedlings decreased at a low rate and by a smaller range than own-root seedlings, the Ci of both grafted and own-root seedlings declined with increased photosynthetic flux density (PFD) at normal temperature;at low temperature,the Ci of grafted seedlings rose with increased photosynthetic flux densities (PFD) whereas the Ci of own-root seedlings kept at a high level no matter how much the photosynthetic flux density (PFD) increased;those above show that under long-time low temperature circumstances ,both grafted and own-root seedlings suffered stamatal limitation but grafted seedlings maintained a higher level in stomatal conductance,photosynthetic and assimilation efficiencies,produced a smaller amount of surplus excitation energy,suffered lighter damage to their photosynthetic organs thereby having stronger adaptability to low temperature ,compared with own-root seedlings.