Anatomical and physiological responses of two kiwifruit cultivars to bicarbonate

Bicarbonate-induced chlorosis is a common agricultural problem that affects both the quantity and quality of fruit crops grown on calcareous soils. However, little is known about the responses of kiwifruit to bicarbonate stress. In the present study, we investigated the anatomical and physiological responses of two kiwifruit cultivars ('Nongdajinmi' and 'Xuxiang') grafted onto the same rootstock ('Qinmei') to bicarbonate (0.50 g/L CaCO3 and 0.84 g/L NaHCO3) under sand culture. After 35 days, bicarbonate-treated vines exhibited yellowing symptoms and decreased chlorophyll content in new expanded leaves. Bicarbonate imposition decreased N and Cu concentration in new leaves and P in old leaves. Moreover, bicarbonate decreased the dry weight of the new leaves and twigs and degenerated the chloroplast, particularly in 'Nongdajinmi', suggesting that 'Nongdajinmi' is more sensitive to bicarbonate than 'Xuxiang'. However, bicarbonate treatment thickened palisade tissue and decreased the phenolic content in 'Nongdajinmi' and lowered the organic acid content and stomatal length, width and aperture size in 'Xuxiang'. Interestingly, bicarbonate raised Ca concentration in new leaves and reduced Mg in old leaves of 'Nongdajinmi', but the opposite was true for 'Xuxiang'. These results implied that the two cultivars adopted two different mechanisms in response to bicarbonate stress. Our study contributes to better understanding the responsive mechanisms of kiwifruit to bicarbonate and the cultivar selections for kiwifruit orchards established on calcareous soils.