Nitrogen source effects on black walnut seedling physiology
Abstract
Nitrogen (N) is the primary nutrient element that limits plant productivity in most ecosystems and its uptake and assimilation may be influenced by N source and level, and by nitrate reductase activity (NRA). Location of NO 3- assimilation dictates which source of N is more favorable for plant energy consumption as related to investment in metabolic processes and in growth. Information on how these factors interact to affect N uptake and assimilation processes in woody angiosperms is limited. One-year-old halfsib black walnut (Juglans nigra L.) seedlings were fertilized with ammonium (NH4+) (as (NH4)2 SO4), nitrate (NO3-) (as NaNO 3) or a mixed N source (NH4NO3) at several levels for two months in a series of experiments. This was done to assess impacts of N source and level on C and N metabolism, gas exchange parameters, xylem exudate N composition, and on NRA. Regardless of N source, N fertilization increased the proportion of amino acids in xylem exudate, inferring greater NRA in roots, which implicates greater energy costs to plants. Decreased growth noted in NaNO3 fed plants on a medium with sufficient amounts of other nutrients suggests that more C was allocated to NRA in roots than to seedling growth. By contrast, deleterious effects noted at increasing NaNO 3 in a nutrient sterile sand culture study may be explained by presence of Na in medium. Net photosynthesis was better correlated with NRA than with N concentration, suggesting the latter could serve as a useful alternative to predict plant vigor. Black walnut seedling growth and metabolism were generally favored by the mixed-N source over NO3- or NH 4+ alone. Thus, the mixed-N source could potentially maximize growth in this species. My study results indicate that juvenile black walnut responses to N source and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms.
Degree
Ph.D.
Advisors
Jacobs, Purdue University.
Subject Area
Forestry|Plant biology
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