Nitrogen source effects on black walnut seedling physiology

Michael A Nicodemus, Purdue University

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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