Soil nitrogen utilisation for growth and gas exchange by grapevines in response to nitrogen supply and rootstock

This study investigated the response to nitrogen (0 or 100 kg N/ha) of fiel d-grown Muller-Thurgau grapevines grafted on six rootstocks (Kober 5BB, Tel eki 5C, Teleki 8B, Selection Oppenheim 4, Couderc 3309, Ruggeri 140). Half the nitrogen was applied four weeks pre-flowering and half at the end of fl owering. Glutamine accounted for over 85% of xylem nitrogen, indicating tha t most soil nitrogen was assimilated by way of vine root metabolism. Nitrog en supply increased the translocation of glutamine, glutamate, NO3-, NH4+, K+, Ca2+, Mg2+ and PO43- in the xylem sap and decreased the ratio of organi c to inorganic nitrogen, V. berlandieri x V. riparia crosses generally resu lted in higher xylem solute concentrations compared with other rootstocks, but were less effective in total nitrogen assimilation. High soil nitrogen increased vine leaf area by stimulating lateral-shoot growth, increased lea f chlorophyll, photosynthesis, transpiration and stomatal conductance, and delayed leaf senescence. There was no difference among rootstocks in scion leaf area, but rootstocks affected scion response to soil nitrogen level in terms of leaf chlorophyll content and leaf gas exchange; SO4 induced the s trongest reaction to soil N, whereas Ru-140 elicited the least reaction. Ch lorophyll content was highest for vines grafted on 5BB and lowest for C-330 9. Photosynthesis response to both nitrogen and rootstock was regulated at the mesophyll level. There were few interactions between nitrogen and roots tocks, and their contribution to total variance was small relative to main effects. Thus, with the exception of SO4, differences due to rootstocks wer e mostly unaffected by soil nitrogen level.