O₃ uptake and drought stress effects on carbon acquisition of ponderosa pine in natural stands

Abstract

• The effect of O₃ exposure or uptake on carbon acquisition (net assimilation (A) or gross photosynthesis (P_g)), with and without drought stress, is reported here in 40-yr-old-ponderosa pine (Pinus ponderosa) trees. • Maximum daily gas exchange was measured monthly for 12 trees at four sites differing in pollutant exposure over two growing seasons with above- and below-average annual precipitation. Gas exchange measures were estimated between sampling periods using a generalized additive regression model. • Both A and P_g generally declined with cumulative O₃ exposure or uptake at all sites. As a response variable, P_g was slightly more sensitive than A to cumulative O₃ exposure. As a metric, O₃ uptake vs exposure permitted slightly better statistical resolution of seasonal response between sites. • The effect of late summer drought stress was statistically significant only at the moderate pollution site, and combined synergistically with O₃ exposure or uptake to reduce P_g. The general additive model allows the user to define a deleterious level of cumulative O₃ exposure or uptake, and to quantitatively assess biological response.

Citation

Grulke, N.E.; Preisler, H.K.; Rose, C.; Kirsch, J.; Balduman, L. 2002. O₃ uptake and drought stress effects on carbon acquisition of ponderosa pine in natural stands. New Phytologist. 154: 621-631.