Can grafting in watermelon plants enhance tolerance to bicarbonate in nutrient solution?

A greenhouse experiment was carried out to determine growth, and mineral composition of watermelon plants, either ungrafted or grafted onto two commercial bottle gourd rootstocks and two commercial Cucurbita hybrid rootstocks, grown in a closed-loop system with nutrient solutions having two levels of pH (6.0 or 8.1). The high pH nutrient solution had the same basic composition plus an additional of 10 mM NaHCO3 and 0.5 g L-1 CaCO3. Significant depression of shoot, root biomass production, and leaf macro- and micro elements (N, P, K, and Fe) under high pH level was observed in both grafted and ungrafted plants. At high pH level, the percentage of shoot biomass weight reduction was significantly lower in plants grafted onto pumpkins rootstocks in comparison to those grafted onto the bottle gourd rootstocks and the ungrafted plants. The Fe concentration in leaves was significantly higher in plants grafted onto pumpkin rootstocks (avg. 0.109 mg g-1) in comparison to that of bottle gourd rootstocks and ungrafted plants (avg. 0.087 mg g-1). For plants grafted onto bottle gourd rootstocks and ungrafted plants the high pH level (8.1) in the nutrient solution caused significant decrease in macronutrient leaf concentration especially for P compared to plants grafted onto pumpkin rootstocks. The improved crop performance of grafted plants in particular pumpkin rootstocks was attributed to the better uptake and translocation of mineral elements in particular iron and phosphorus to the shoot.