Publication Date:
2012-10-18
Description:
Impacts of elevated ground-level ozone (O 3 ) on nitrogen (N) uptake and allocation were studied on mature European beech ( Fagus sylvatica L.) and Norway spruce ( Picea abies [L.] Karst.) in a forest stand, hypothesizing that: (i) chronically elevated O 3 limits nutrient uptake, and (ii) beech responds more sensitively to elevated O 3 than spruce, as previously found for juvenile trees. Tree canopies were exposed to twice-ambient O 3 concentrations (2 x O 3 ) by a free-air fumigation system, with trees under ambient O 3 serving as control. After 5 years of O 3 fumigation, 15 NH 4 15 NO 3 was applied to soil, and concentrations of newly acquired N (N labelled ) and total N (N total ) in plant compartments and soil measured. Under 2 x O 3 , N labelled and N total were increased in the bulk soil and tended to be lower in fine and coarse roots of both species across the soil horizons, supporting hypothesis (i). N labelled was reduced in beech foliage by up to 60%, and by up to 50% in buds under 2 x O 3 . Similarly, N labelled in stem bark and phloem was reduced. No such reduction was observed in spruce, reflecting a stronger effect on N acquisition in beech in accordance with hypothesis (ii). In spruce, 2 x O 3 tended to favour allocation of new N to foliage. N labelled in beech foliage correlated with cumulative seasonal transpiration, indicating impaired N acquisition was probably caused by reduced stomatal conductance and, hence, water transport under elevated O 3 . Stimulated fine root growth under 2 x O 3 with a possible increase of below-ground N sink strength may also have accounted for lowered N allocation to above-ground organs. Reduced N uptake and altered allocation may enhance the use of stored N for growth, possibly affecting long-term stand nutrition.
Print ISSN:
0829-318X
Electronic ISSN:
1758-4469
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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