Analysis of aspen foliage exposed to multiple stresses: ozone, nitrogen deficiency and drought

Abstract

Sl'MMARYTwo field experiments were conducted to examine the impact nf a foliar stress (ozone, O.,), alone or in combination with u resource stress, on cavbon giiin of aspen {Populin^ Iremuioidus MicVis.), The tirst experiment involved nitrogen deficiency, and the second, drought stress.The patterns of change in icaf area, photosynthetic rate and carbon gain with leaf position from root to apex were altered by O^ alone. Net photosynthesis and car boxy iation capaeity of older leaves decreased, and of younger leaves increased, in response to O^, Thus younger leaves partially compensated for the decreased photosynthetic capacity nf older leaves. Physiological maturity and senescence were accelerated by O.,. Whole plant carbon gain declined with O3 due-to reductions in both leaf urea and photosynthetk rate.Nitrogen deficiencv-alone decreased carbon gain via reductions in both leaf area and photosyntheric rate across leaf position. The effects of O., and nitrogen deficiencv together on hoth leaf area and phntosyntht'tic rate were additive. Aspen seedlings compensated to O,, stress regardkss of nitrogen level. Plant responses to both of these stresses may have been mediated by ribulose bisphosphate carboxylase/oxygenase iRubisco) content or activity, and thus indirectly by nitrogen content.ln the second expenment, seedlings were subjected to drought during the first six weeks of exposure to O.,, and were measured several weeks after termination cf the drought treatment. Drought caused aspen seedlings to produce fewer and smaller leaves. After termination of drought, they produced larger new leav'es, and net photosynthesis af most leaves was greater than in continuously well-watered plants. In plants not exposed to O^, enhanced photosynthetic rate partially compensated for the smaller leaf area. ()., generallv decreased leaf area and photosynthesis, and hence carhon gain. The effects of prior exposure to drought and O., together were additive for whnle-plant photosynthetic rate, but less than additive for whole-plant kaf area.Key words: Nitrogen, drought, ozone, photosynthesis. Popidiis tn-mulGides (aspen).parameters, leaf number and area, and carbon allocation to roots and shoots (reviewed by Mooney, Resource and foliar stresses .,,,. j r) n inoi^ r> ^-' . . . ' •' Winner & Pell, 1991). Compensation mtnimizes Plants commonly grow in environments where reductions in whole-plant carbon gain caused by natura) stresses such as deficiency of water or stress. For example, plants growing under nitrogen nutrients are encountered. Chapin (1991) distindeficiency (Marschner, 1986) or drought conditions guishes between stresses caused by insufficient (Sharp & Davies, 1989) increase root: shoot ratios resources and those caused by direct physiological and thereby increase the capacity to obtain nutrients damage due to disruption of metabolism. Plants and water from soils. With increased ability to gain respond to resource stresses by altering gas exchange below-ground resources, more of these resources can be allocated to leaf tis...

Aspen mortality in the Colorado and southern Wyoming Rocky Mountains: Extent, severity, and causal factors

“…For example, tropospheric ozone, O 3 , has been shown to alter leaf surface characteristics in Populus tremuloides Michx., and increased concentrations of ground-level ozone may make trembling aspen more susceptible to fungal attack (Karnosky, et al, 2002). Like many other tree species, ozone accelerates maturation and foliage senescence in P. tremuloides (Greitner, et al, 1994).…”

“…Soil nutrient deficiency can have variety of impacts on aspen. For example, aspen tend to respond to nitrogen deficiency by producing smaller leaves, which results in a decrease in net photosynthesis (Greitner, et al, 1994). Burks (1994) theorizes that nitrogen deficiency may also increase the severity and incidence of cankers caused by Cytospora chrysosperma (Pers.:Fr.)…”

Nitrogen supply as a limiting factor determining the sensitivity of Populus tremuloides Michx. to ozone stress

“…Seeds were germinated as described by Greitner, Pell & Winner (1994). When seedlings were 5-6 wk old they were transplanted into 6 I containers of Metromix* 500 (W. R. Grace & Co., Cambridge, MA, USA).…”

Elevated ozone negatively affects photosynthesis of current-year leaves but not previous-year leaves in evergreen Cyclobalanopsis glauca seedlings

“…For hybrid poplar and Aspen, elevated O 3 concentrations altered the patterns of change in leaf area, photosynthetic rate and carbon gain with leaf position from root to apex and the older leaves were more sensitive to O 3 than younger leaves (Bagard et al, 2008;Greitner et al, 1994). At the canopy level, ambient O 3 concentrations caused reductions in both light-saturated photosynthesis rate (A sat ) and g s of the lower canopy that were about 30% more than those of the upper canopy in black poplar (Populus nigra L.) species (Novak et al, 2005).…”