Photosynthetic Ability and Mineral Concentrations in Xylem Exudate of Grafted and Non-Grafted Watermelon Seedlings

Grafting as an effective method to overcome soilborne pathogens is widely performed in watermelon (Citrullus Lanatus Mansfeld) production in China. To evaluate physiological characteristics of the grafted plants, taking watermelon 'Jingxin 1' as the scion and Cucurbita ficifolia as rootstock for grafting, growth, photosynthetic ability and mineral concentrations in xylem exudate were investigated in comparison of non-grafted and grafted watermelon seedlings. The results showed the grafted seedlings grew faster. In the grafted seedlings, the plant height, number of leaves, the area of the largest leave, shoot dry weight, root dry weight and ratio of R/T were significantly higher than those of non-grafted seedlings. Chlorophyll content, stomatal conductance (Gs), intercellular CO2 concentration (Ci) and net photosynthetic rate (Pn) were also significantly higher in grafted seedlings leaves. The grafted seedlings yielded much more xylem exudate. The concentration of NO3- -N in the exudates of grafted seedlings was about 2 times of the non-grafted seedlings. NO3- -N was the main form of nitrogen in both grafted and non-grafted seedlings xylem exudates. Concentrations of P, Ca and Mg were also higher but K was lower in the exudate of grafted seedlings. These results indicated that the grafted seedlings had higher photosynthetic ability and higher root absorption capacity for NO3- -N, P, Ca and Mg, but lower absorption capacity for K.