Document: DOU-3-34-69

Nitrogen availability affects ozone-induced accelerated leaf senescence.

BIELENBERG, D.G.*, J.P.LYNCH and E.J.PELL

The Pennsylvania State University, University Park, PA 16802 USA 1

Abstract:
O3 induces accelerated foliar senescence in many plants; in indeterminate species as the older leaves senesce more rapidly, younger leaves show stimulation of [Rubisco] and Pnet. We tested the hypothesis that a decrease in N availability would increase O3-induced accelerated senescence. We also hypothesized that increases in total soluble protein (TSP) and Rubisco content in the younger foliage result from remobilized N provided by foliage undergoing O3-induced accelerated senescence. Hybrid poplar, Populus trichocarpa x maximowizii clone '245', cuttings were grown in open top chambers with a sand solution culture providing 50ppm N. Air in all chambers was charcoal-filtered, with or without 0.08ppm O3 8h/d for 70 days. After approx. 4 wks of O3 exposure, N levels in the solution culture were withdrawn to 10ppm in half of the trees. Whole-plant harvests to determine biomass and total N content were conducted 6 times during the O3 exposure; independently leaves 6 and 21 from the base were repeatedly harvested to determine TSP and Rubisco content. [TSP] and [Rubisco] of leaf 6 decreased in response to O3 in both N treatments. N withdrawal led to an increase in [TSP] and [Rubisco] in the younger O3 exposed leaves; no differences were observed for constant N between air treatments. Increased [TSP] in the younger leaves of O3 exposed N withdrawn plants coincided with low or negative N flux (mg N d-1) to older, senescing leaves. 15N labeling of the nutrient supply determined that the relative contribution of remobilized N to new growth was not increased appreciably in response to senescence of older leaves. However, the partitioning of newly acquired N shifted in response to O3 exposure to favor new leaf growth; in the N withdrawal and O3 exposed treatment newly acquired N was also preferentially partitioned to the roots.

Keywords: ozone, accelerated leaf senescence, nitrogen

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This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.