Effects of ozone on foliar nitrogen metabolism of Pinus taeda L. and implications for carbohydrate metabolism

Abstract

SUMMARYDose-response relationship of ozone effects on foliar nitrogen metabolism of two half-sib families of Pinus taeda L. was studied. Trees were exposed to six ozone concentrations, ranging from 0 2 to 3 times the ambient, for two consecutive growing seasons (1988 and 1989) in open-top chambers. Content of total chlorophyll, soluble protein and soluble amino acids, and activities of glutamine synthetase and glutamate dehydrogenase, were measured in second-flush needles of 1989, harvested in November of 1989. Root collar diameter growth rate was also determined. Variation in depth to soil mottling, an indicator of changing redox conditions, significantly affected tree growth and nitrogen metabolism. Therefore depth to soil mottling was used as a covariate and dose-response curves were provided with adjusted means. A decline of root collar diameter growth rate and foliar chlorophyll content was found at the highest ozone level. However, both these parameters were affected much more by soil conditions than by ozone. Glutamine synthetase, glutamate dehydrogenase and amino acids, especially glutamate and glutamine, increased by approx. 2-fold and 3-fold, respectively, at two and three times ambient ozone. However, soluble protein content was only affected at the highest ozone concentration, showing a 2-5-fold increase. Nitrogen metabolism was more influenced by ozone than by the variation in edaphic conditions. No consistent ozone X family interaction on nitrogen metabolism could be found, but the two half-sib families significantly differed in glutamate dehydrogenase activity and the contents of glutamate and glycine, indicating a regulatory function of this enzyme between nitrogen and carbon metabolism. The increase of amino-N turnover and the following rise in soluble protein content are explained by the strategy of the plant to reallocate the nutrients from needles subjected to accelerated senescence by ozone. Possible implications of this process in carbohydrate metabolism and carbon partitioning are discussed.

Ozone-induced microscopical changes and quantitative carbohydrate contents of hybrid poplar (Populus � euramericana)

“…Spence et al (1990) reported a reduction in the rate of phloem transport as well as in phloem photosynthate concentration and total carbon transport to the roots. However, Manderscheid et al (1992) concluded from their results with ozone-stressed Pinus taeda L. seedlings that the reduction of carbon allocation to the roots is not due to an inhibited mechanism of phloem loading, but may be explained with the partitioning model postulated by Reynolds and Thornley (1982). According to this model, root growth is favoured by a high ratio of total nonstructural carbohydrates to free amino acids, whereas a low ratio stimulates shoot growth.…”

Interactions between exposure to O3 and nutrient status of trees: effects on nutrient content and uptake, growth, mycorrhiza and needle ultrastructure

“…Probably also growtb of short roots and formation of mycorrhiza were enhanced to supply enough N for growth and repairing of O3 induced disturbances m protein metabolism (Pell & Dann, 1991). Enhanced N metabolism oi Pinus taeda needles alter exposure to O3 for two growing seasons has been observed by Manderscheid, Jager & Kress (1992), who suggested that nitrogen reallocation occurs to support new growth. Results of the present study suggest that N reallocation tnay be one of the earliest signs of metabolic disturbances caused by Enlarged starcb grains in the needles of fumigated seedlings observed in this experiment may be a sign of initially increased photosynthetic rate (Eanius et al, 1990: Bevers, Riecbers & Temple, 1992, altered carbobydrate metabolism or impaired translocation due to damage of phloem cells caused by Mg deficiency (Eink, 1991), also observed in this study.…”

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

“…Increased N in remaining leaves has also been observed in clonal poplars (PO/)M/)V.V spp.) (Ballach,Oppenheimer&Moori, 1992) and Loblolly pine {Pinus taeda) (Tjoelker & Luxmoore, 1991;Manderscheid, Jager & Kress, 1992) with O.,-induced premature foliar senescence. What is the source of the additional N in these leaves?…”

“…What is the source of the additional N in these leaves? Both Ballach et al (1992) and Manderscheid et al (1992) reported evidence of increased proteolytic activity and increased concentrations of soluble amino acids, particularly glutamate and glycine, in O.,-induced senescing leaves. Increased rates of protein turnover in prematurely senescing foliage would increase the availability of N for reallocation to actively growing parts of the plant (Peoples & Dalling, 1988), and would account for the reduced concentration of N in litter from Oa-injured pine seedlings.…”