Project Summary:

        The primary objective of this study is to test whether increased nitrogen (N) fertility mitigates ozone injury to ponderosa pine. The response of this common western conifer to oxidant exposure has been well described and plant responses to N fertility are generally understood, but the combined effects of elevated N deposition and oxidant exposure have not been tested. Nitrogen induced mitigation of foliar ozone injury will be evaluated by a multivariate assessment of visible foliar injury and associated characteristics. A collection of biochemical attributes which play a role in foliar carbon acquisition (CO₂ fixation) and export (via translocation), and N metabolism and storage will be tested as indicators of changes in forest health.

        Ozone concentrations frequently reach or exceed 100 ppb in mid-elevation forests in Sequoia/Kings Canyon National Park, California. Nitrogen deposition, however, has been estimated for only a few sites in the Sierra Nevada. Ozone and nitrogenous pollutants are believed to be the major pollutant types in the west-side mid-elevation forests of the Sierra Nevada and are usually co-occurring. Only one study, to date, has addressed the combined effects of these co-occurring pollutants on mature trees in situ. In that study two mid-elevation mixed conifer sites in the San Bernardino Mountains with differing ozone levels have been exposed to background N deposition, or fertilized with 50 or 150 kg ha^-1 of slow release urea (USDA funding awarded to Mark Ferm, Mark Poth, and Paul Miller; ongoing). The study proposed here will replicate the San Bernardino work using background N deposition levels and the lower fertilization treatment (+50 kg ha^-1).

        This will provide additional information regarding the responses of a Sierran mixed conifer ecosystem to similar ozone exposures. This work will extend beyond the San Bernardino data set by using a design that includes two levels of soil moisture availability.

        Ponderosa pine trees growing in mesic and xeric microsites at similar elevations will be selected for this study. The differences in summer water availability will be used to drive differences in ozone uptake. The mesic sites will extend stomatal opening later on both a diurnal and seasonal basis, thus increasing ozone uptake as compared to the xeric microsites. Within each microsite, five blocks of ten trees will be fertilized at the rate of 50 kg ha^-1 and five blocks will receive no fertilizer. Background N deposition levels have been estimated to be approximately 9 kg ha^-1 yr^-1. Statistical comparisons of tree response variables will be made within a soil moisture level across fertilizer treatments (background and elevated N), and between soil moisture levels in unamended blocks. The proposed study would make a major contribution in evaluating whether N deposition, at current and potentially higher future levels mitigates a known environmental stressor (oxidant pollution) in the Sierran mixed conifer zone.

        An additional supporting objective is to quantify and determine the extent to which ozone exposure and N deposition co-vary at four sites along an elevational gradient in the Sequoia/Kings Canyon National Park from 580 m to 2900 m.

        The specific objectives of the study are to (1) test whether N deposition mitigates foliar oxidant injury and associated tree response variables in ponderosa pine at two different levels of ozone, (2) describe the effects of soil moisture availability and N amendment on available soil N forms (ammonium and nitrate) and on various foliar N attributes, and (3) quantitatively correlate nitrogen deposition with ozone exposure along an elevational transect.

 

FINAL REPORT: Does nitrogen mitigate ozone injury in Jeffrey pine?

Other Nancy Grulke Publications

Grulke NE 2003 Physiological basis of ozone injury assessment in Sierra Nevadan conifers. In: Bytnerowicz A, Arbaugh M, Alonso R. Assessment of ozone distribution and its effects on Sierra Nevada ecosystems. Elsevier Publishers, The Hague, Netherlands (in press).

2002 Sequoia-Kings Canyon PRIMENet Meeting Presentation handout

2001 PRIMENet Meeting Presentation: Canopy transpiration of Jeffrey pine in mesic and xeric microsites: Implications for O3 uptake (Nancy Grulke)

Grulke, N. E., R. Johnson, et al. (2003). "Variation in morphological and biochemical O3 injury attributes of mature Jeffrey pine within canopies and between microsites." Tree Physiology 23: 923-929.

Tausz, M., K. Herbinger, et al. (2002). "Antioxidant status of Pinus jeffreyi needles from mesic and xeric microsites in early and late summer." Phyton 42(3): 201-207.

Grulke, N. E. (2003). The physiological basis of ozone injury assessment attributes in Sierran conifers. Ozone air pollution in the Sierra Nevada: distribution and effects on forests. A. Bytnerowicz, M. J. Arbaugh and R. Alonso. New York, Elsevier.

Grulke, N. E., R. Johnson, et al. (2003). "Canopy transpiration of Jeffrey pine in mesic and xeric microsites: O3 uptake and injury response." Trees 17: 292-298.

Grulke N. E., Johnson R, Monschein S, Nikolova P, Tausz M 2003 Variation in morphological and biochemical ozone injury attributes of mature Jeffrey pine within canopies and between microsites. Tree Physiology 23:923-929.