Soil nitrogen and chronic ozone stress influence physiology, growth and nutrient status ofPinus taedaL. andLiriodendron tulipiferaL. seedlings

Abstract

SUMMARYThe effects of soil nitrogen availability and chronic ozone stress on carbon and nutrient economy were investigated in loblolly pine {Pinus taeda L,) and yellow-poplar {Liriodendron tulipifera L.). One-year-old seedlings were planted individually in pots in forest soil of low (58/ig g"'), medium (96/ig g"') or high (172/fg g"^) initial concentrations of soluble nitrogen. The seedlings were exposed to ozone in open-top 6eld chambers at sub-ambient (charcoalfiltered air), ambient, and elevated (ambient+ 60 nl T^ O3) (32, 56, 108 nl 1"' O3, 7 h seasonal mean, respectively) levels for 18 weeks. At final harvest loblolly pine dry matter increased by 50"0 at the highest soil N level relative to the iow with the largest gains in new needle biomass. Elevated ozone reduced the biomass of current-year needles by 20% in plants grown at the highest N level. Higher soil N supply increased the concentration of nitrogen in needles, stimulated current-year needle photosynthesis and increased needle and whole-plant wateruse efficiencies. Ozone treatment had no significant effect on photosynthesis or water-use efficiency in either species, although ozone exposure tended to reduce stomatal conductance in loblolly pine. The low N treatment increased the proportion of dry matter allocated to fine roots in yellow-poplar, but whole-plant dry weight had not responded to N fertilization at the final harvest, suggesting other limitations on growth. Ozone exposure increased leaf abscission and doubled leaf turnover in yellow-poplar. Although yellow-poplar was highly sensitive to ozoneinduced leaf abscission, final whole-plant dry weights were not aFfected. The indeterminate growth habit of yellow-poplar permitted compensatory leaf growth which may have ameliorated effects of chronic ozone stress on biomass gain. Ozone exposure also decreased shoot weight more than root weight, resulting in higher root:shoot ratios in loblolly pine and a similar trend in higher fine root:leaf ratios in yellow-poplar. Greater proportional allocation of carbon to roots in response to nutrient deficiency may preclude an increased allocation to shoots often observed in response to air pollution stress. Interspecific differences in growth response to chronic ozone and nutrient stress may be influenced by differences in leaf growth habit.

Nitrogen allocation in ponderosa pine seedlings exposed to interacting ozone and drought stresses

“…Taylor et al (1993) discussed another possible source of N enrichment in remaining foliage of O.,-injured plants, that of deposition of N-containing compounds co-generated with O., in O., generators using air as the source gas. Although this possibility cannot be dismissed (see Brown & Roberts, 1988;Tjoelker & Luxmoore, 1991), in our study the contribution of co-generated N compounds to the N economy of trees in the O^-added treatment was small. The concentration of co-generated N compounds (principally N.^O, in the gas phase, converted to HNO., in the aqueous phase) was estimated to be 4 mol per 100 mol of O3 generated (Harris et al, 1982).…”

The effects of nutrient limitation on the response of Plantago major to ozone

“…Such a tend has been documented previously (Paakonen et al, 1995) but the converse, an increase in sensitivity under a highnutrient regime, is more frequently reported (Cowling & Koziol, 1982 ;Pell et al, 1990 ;Tjoelker & Luxmoore, 1991). The difference might be due to the relative degree of nutrient limitation.…”

“…Older reports are reviewed by Cowling & Koziol (1982). More recently, a number of studies have shown that plants grown under a high-nutrient regime are more sensitive to ozone (Pell et al, 1990 ;Tjoelker & Luxmoore, 1991), but in contrast, Paakonen, Holopainen & Karenlampi (1995) reported greater sensitivity of birch trees under nutrient deficiency. Heagle (1979) found greater sensitivity to ozone in plants supplied with moderate amounts of nutrients than in those with a very low or high supply.…”

Ambient ozone effects on forest trees of the eastern United States: a review

“…Ozone did not affect leaf net photosynthesis and stomatal conductance of waterstressed or well-watered yellow-poplar, but reductions in root biomass were observed in response to an ozone concentration of 0n07 µl l −" in droughtstressed seedlings (Cannon, Roberts & Barger, 1993). Foliar N did not affect leaf net photosynthesis and biomass response to ozone in loblolly pine and yellow-poplar (Tjoelker & Luxmoore, 1991). Similarly, the influence of ozone on foliar carbohydrates of red spruce saplings was not modified by foliar N (Amundson, Kohut & Laurence, 1995).…”

“…Whereas leaf net photosynthesis and biomass of quaking aspen, a shade-intolerant species, were reduced by ambient ozone profiles commonly found in aspen's natural range (Coleman et al, 1995), ambient and twiceambient concentrations of ozone did not reduce leaf net photosynthesis or biomass of shade-intolerant yellow-poplar (Tjoelker & Luxmoore, 1991).…”