Dry matter and leaf area partitioning, bud fertility and second season growth of <i>Vitis vinifera</i> L.: Responses to notrogen supply and limiting irradiance

Abstract

Potted Vitis vinifera L. plants were grown under controlled environmental conditions at five different levels of nitrogen (0, 1, 5, 10, 100 mM NH₄NO₃) in combination with two different levels of irradiance (30 and 140 µmol m^-2 s^-1 PAR, respectively) during bloom. The immediate, whole season and second year effects on vegetative growth were assessed, and bud fertility and rate of development were evaluated. The optimum N addition level was 1 mM NH₄NO₃ for root growth and 5 mM for shoot growth, respectively, both after bloom and at the end of the first growing season. This growth response to N supply became apparent only in the higher light treatment and was mainly due to an N-induced enhancement of leaf and lateral shoot growth. Low-light stress also strongly enhanced the number of new leaves and laterals, but total dry matter production was reduced and did not respond to N nutrition. Light restriction increased the specific leaf area by 52 % and the leaf area ratio by 37 % but did not affect the leaf weight ratio. The leaves of N-deficient vines, in particular in combination with light stress, senesced earlier than those of vines with sufficient or excessive N availability. The light effect on shoot growth in the second season was inverted compared with the first season, and the peak response to N supply was shifted towards 100 mM NH₄NO₃. Limiting light conditions during inflorescence initiation severely reduced the bud fertility but advanced the date of bud break and enhanced the rate of development of the new shoots in the subsequent season. The optimum N supply rate for both bud fertility and development was 5 mM NH₄NO₃. Bud mortality was not affected by either treatment factor. These data indicate that the bloom period is critical for reproductive development of grapevines, with high sensitivity to environmental stress. They also emphasize the importance of nutrient reserves in the permanent structure for both compensatory and early season growth.