Application of response surface methodology and ANOVA to detect pollution effects on photosynthetic response under varying temperature and light regimes

Studies of air pollution effects on plant physiological responses to diurna l changes in environmental conditions are complex, and thus, require effici ent statistical design and valid data analysis. Here, we aim at demonstrati ng the use of a response-surface methodology (RSM) including least square r egression and canonical analyses in combination with a two-way ANOVA to qua ntify net photosynthetic (A(n)) response of ponderosa pine (Pinus ponderosa Dougl. ex Laws) seedlings to different levels of rain acidity, ozone, temp erature, and light conditions. Seedlings were exposed to four combinations of two rain (pH 5.1 and 3) and two ozone (ambient, and twice-ambient) regim es. The rain treatment was applied to foliage only on a weekly basis from J anuary to April 1992. The ozone treatment was applied from September 1991 t o November 1992. A(n) responses of current- and 1-year-old foliage to nine combinations of three temperatures (18, 25, 32 degreesC) and three light re gimes (250, 500, 1000 mu mol photons m(-2) s(-1)) were measured between 080 0 and 1900 h from 18 August to 7 September 1992. A completely randomized de sign, replicated twice, was used for the assignment of rain-by-ozone combin ations (main plots). Foliage age classes were sub-plots within the main plo ts, temperature levels were sub-plots within foliage age classes, and light levels were sub-plots within temperature levels. Response surface models o f A(n) response to temperature and light levels were constructed per rain-b y-ozone combination for each foliage age. beta (Temp), beta (Temp2), beta ( Light), A(n mean), A(n max), temperature at A(n max), and light at A(n max) were calculated or estimated. The effects of rain pH and ozone on these va riables were then quantified using a two-way ANOVA. No significant rain-by- ozone or ozone effect was detected for any response. Rain of pH 3 decreased A(n mean) in current-year foliage only. (C) 2001 Elsevier Science B.V. All rights reserved.