| Abstrakt: |
Effects of nitrogen (N) supply on biomass distribution as well as N effects on NO3“assimilation, were examined in two‐year‐old graftlings of Vitis viniferaL. cv. Cabernet Sauvignon on five rootstocks. Whole‐plant biomass in all graftlings more than doubled with increased N supply in solution from 0.25 to 8 mM. Whole plant biomass was also affected by rootstock genotype, but to a lesser extent than by N supply. Biomass allocation to roots declined with increased N supply for all stock‐scion combinations, but the magnitude of that response varied with rootstock genotype. Nitrate reductase activity (NRA) in leaves increased with increased N supply for all stock‐scion combinations, whereas root NRA increased only up to 1 mM N supply, dropping markedly with additional N. NRA in leaves was one to two orders of magnitude higher than NRA in roots ‐ a difference that increased steadily with increased N supply. By implication, grapevine leaves have a much higher capacity for NO3‐‐reduction than do grapevine roots, and any contribution by roots to whole‐vine NO3‐‐assimilation declines even further as NO3‐‐availability increases. |
