Analysis of the relationships among O3 uptake, conductance, and photosynthesis in needles of Pinus ponderosa

Abstract

We studied the effects of O(3) uptake on conductance (g(wv)) and photosynthesis (A) in needles of ponderosa pine (Pinus ponderosa Laws.) seedlings exposed for 70 days to one of three O(3) regimes-Low-O(3) (0.1 micro mol mol(-1) daily peak), High-O(3) (0.2 micro mol mol(-1) daily peak), and Low/High-O(3) (alternating 2 days Low-O(3) and 2 days High-O(3)). Seedlings exposed to charcoal-filtered air served as controls. Total O(3) exposures, expressed as ppm-h (the sum of the average hourly concentration in ppm ( micro mol mol(-1)) over the exposure period), were 77, 135, 105 and 4 for the Low-O(3), High-O(3), Low/High-O(3) and control treatments, respectively. Conductance (g(wv)) declined to about 60% of the value in control seedlings by Day 6 in seedlings in the High-O(3) treatment and by Day 37 in seedlings in the Low/High-O(3) treatment, but g(wv) did not decline at all in seedlings in the Low-O(3) treatment. At the end of the 70-day experiment, cumulative O(3) uptake, calculated from measured g(wv) values and assuming an internal O(3) concentration of zero, was 12.2, 13.5, and 14.7 mmol m(-2) for seedlings in the Low-O(3), Low/High-O(3), and High-O(3) treatments, respectively; however, O(3) uptake was reduced by 0, 24, and 36%, respectively, from that expected if there had been no decline in g(wv). With increasing total O(3) exposure, A declined, but the reduction was not strictly cumulative, i.e., A measured on Days 49 and 70 was similar for a given treatment even though both total O(3) exposure and uptake had increased. At the end of the experiment, A at near saturating CO(2) (1000 micro mol mol(-1)) and saturating photosynthetic photon flux density was reduced by about 25, 40 and 50% in seedlings in the Low-O(3), Low/High-O(3) and High-O(3) treatments, respectively, compared to the control seedlings. The ratio of internal to external CO(2) concentrations, an indicator of relative change in stomatal limitation of A, did not change over time and did not differ among treatments, suggesting that A and g(wv) decreased in parallel. After 40-60 days without O(3), A of seedlings in all O(3) treatments was not significantly different. Our data indicate that O(3)-induced stomatal closure was a result of reduced A and that decreased g(wv) reduced O(3) uptake to a rate that needles of ponderosa pine could tolerate without exhibiting further reductions in gas exchange capacity.

Effects of Elevated Ozone on Photosynthetic CO2 Exchange and Chlorophyll a Fluorescence in Leaves of Quercus mongolica Grown in Urban Area

“…These results indicate that the partial closure of stomata can be induced by elevated O 3 to reduce further ozone uptake. Many researches suggested that stomata closure is not a direct response to O 3 insult, but a reaction to an increased internal CO 2 concentration resulted from the inhibition of carbon assimilation (Reich 1987;Weber et al 1993). However, in our study, there was nearly no increase but decrease, some times significantly decrease in intercellular CO 2 concentration of leaves detected in the O 3 elevated environment compared with control when stomata conductance (gs) of leaves had decreased to minimum (Figs.…”

Regional levels of ozone in the troposphere over eastern Mediterranean

“…A recent review of records of impacts of ambient ozone on crops in the Mediterranean concluded that there is evidence of visible injury on 24 different agricultural and horticultural crops [ Fumagalli et al , 2001]. It should be noted that plants have a number of protective reactions that might increase tolerance to ozone, such as increase in antioxidant levels [ Nouchi , 1993] and stomatal closure [ Weber et al , 1993]. The latter response might be triggered also by meteorological conditions such as high wind speeds and drought conditions.…”

Growth, photosynthesis and ozone uptake of young beech ( Fagus sylvatica L.) in response to different ozone exposures

“…Weber et al (1993) supported the hypothesis of a threshold uptake rate, but concluded that it is uncertain whether the threshold is controlled entirely by the rate of uptake or includes cumulative uptake. It seems that to assess exposure-response relationships the rate as well as the total amount absorbed have to be considered.…”