Soil nitrogen and ozone effects on growth, physiology and nutrition of loblolly pine and yellow-poplar seedlings

Author

Mark G. Tjoelker

Date of Award

12-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Botany

Major Professor

O. J. Schwarz

Committee Members

Larry Jones. Bob Luxmoore

Abstract

The interactions of soil nitrogen level and chronic ozone (O₃) stress on carbon and nutrient economy were investigated in loblolly pine (Pinus taeda L.) and yellow-poplar (Liriodendron tulipifera L.). The objectives of the study were: 1) to compare the growth and biomass partitioning in seedlings in response to varied low-nitrogen forest soil treatments in combination with chronic ozone levels over one growing season and 2) to investigate seedling physiological responses, including water use efficiency (WUE), photosynthesis, fine root and leaf nitrate reductase activity (NRA), nutrient concentration, nutrient uptake, and nutrient use efficiency (NUE). One-year-old seedlings were planted individually in a forest soil in 3.5-L pots containing one of three initial soil soluble N levels of 58, 96, and 172 μg/g. The seedlings were fumigated in open-top field chambers at subambient (charcoal-filtered air), ambient, and elevated (ambient + 60 nL O₃/L) (32, 56, 108 nL O₃/L, 7 h seasonal mean, respectively) ozone levels for 18 weeks. Each of the nine ozone x nitrogen combinations had six replicates.

Growth of loblolly pine as measured by stem volume, shoot relative growth rate, and whole-plant dry weight increased with higher N level with the largest gains in new needle biomass. Higher soil N supply stimulated current needle photosynthesis and increased both instantaneous and whole-plant WUE in loblolly pine. Greater soil N level increased nutrient uptake and increased NUE for P, in K, Ca, Mg, and B, whose whole-plant concentrations were diluted by new growth. Both species were N-deficient at the lower soil N levels. Low soil N level increased the proportion of biomass partitioned to fine roots in yellow-poplar, but whole-plant growth did not respond to N treatment, suggesting other limitations on growth.

Ozone fumigation accelerated and increased leaf abscission in both species after 8 weeks of exposure. Only loblolly pine previous-year needles were abscised, and higher soil N level appeared to predispose the plants to greater abscission. Although yellow-poplar appeared more sensitive to ozone-induced leaf abscission, final leaf and whole-plant dry weight were not affected. Compensatory leaf growth may have ameliorated chronic ozone stress in yellow-poplar. A significant ozone x nitrogen interaction was observed for new needle biomass and NRA. Higher ozone levels reduced the new needle growth response to N, whereas NRA was elevated in the high ozone and low nitrogen treatment combination. Elevated ozone exposure increased fine root NRA in loblolly pine. Chronic ozone exposure increased new needle N and S concentrations and caused apparent declining trends in NUE. In general, ozone exposure decreased shoot weight more than root weight, resulting in higher root/shoot ratios. At low soil N levels, particularly when N is a growth-limiting factor, N stress may counteract the effects of chronic ozone stress on biomass partitioning. Chronic ozone stress response in tree seedlings may be mediated by soil N supply.

Recommended Citation

Tjoelker, Mark G., "Soil nitrogen and ozone effects on growth, physiology and nutrition of loblolly pine and yellow-poplar seedlings. " Master's Thesis, University of Tennessee, 1988.
https://trace.tennessee.edu/utk_gradthes/13356