Growth responses of seedlings of sixBetula pubescensEhrh. Provenances to six ozone exposure regimes

Abstract

Growth responses of seedlings of six Betula pubescens Ehrh. provenances to six ozone exposure regimes. Seedlings of six provenances of Betula pubescens Ehrh. from different latitudes (59-70°N) were grown under six ozone exposure regimes by combining different concentrations and daily exposure periods. The different treatments at increasing O 3 exposure over 40 nmol mol -1 (AOT40 given in parentheses) were: 19 nmol mol -1 /24 h day -1 (0.1 μmol mol -1 -h), 42 nmol mol -1 /12 h day -1 (2.5 μmol mol -1 -h), 44 nmol mol -1 /24 h day -1 (7.1 μmol mol -1 -h), 76 nmol mol -1 /6 h day -1 (9.4 μmol mol -1 -h), 75 nmol mol -1 /12 h day -1 (17.8 μmol mol -1 ) and 116 nmol mol -1 /6 h day -1 (19.8 μmol mol -1 ) for 40 days at a 24 h day -1 photoperiod in growth chambers placed in a greenhouse. The effect of increasing the O 3 exposure from 19 nmol mol -1 /24 h (0.1 μmol mol -1 -h AOT40) to 42 nmol mol -1 /12 h (2.5 μmol mol -1 -h AOT40) was a decrease in root but not shoot dry weight. A further increase in the exposure to 44 nmol mol -1 /24 h (7.1 μmol mol -1 -h AOT40) also decreased the shoot dry weight. An increase in the O 3 concentration to 75 (9.4-17.8 μmol mol -1 -h AOT40) and 116 nmol mol -1 (19.8 μmol mol -1 -h AOT40) further decreased shoot and root dry weights. A moderate O 3 exposure (42 nmol mol -1 /12 h = 2.5 μmol mol -1 -h AOT40) increased the plant height and leaf size, while a further increase in O 3 concentration and exposure time decreased both of these variables. The birch provenances generally had a similar response to the O 3 treatments. The accumulated O 3 exposure over the 0, 10, 20, 30, 40 and 50 nmol mol -1 concentrations (AOT0, AOT10, AOT20, AOT30, AOT40 and AOT50, respectively) was calculated for all O 3 treatments. The shoot and root dry weights were correlated best with AOT40 and AOT30, and were estimated to decrease by 10% at an AOT40 of 7.0 and 5.5 μmol mol -1 -h, respectively. The development of O 3 injury (yellow stipples/chlorosis) was most marked when correlated with AOT40.

Below‐ground responses of silver birch trees exposed to elevated CO2 and O3 levels during three growing seasons

“…2). Present coarse and fine root results agree with previous O 3 studies, where mild O 3 stress has affected root growth before any effect on shoot growth is detectable (Cooley & Manning, 1987;Coleman et al, 1996;Mortensen, 1998).…”

Responses to ozone in 12 provenances of European beech (Fagus sylvatica): genotypic variation and chamber effects on photosynthesis and dry‐matter partitioning

“…responded even later and less, in agreement with Lippert et al (1996). Ozone sensitivity in trees typically depends upon genotype (Pa$ a$ kko$ nen et al, 1993 ;Mortensen, 1994 ;Taylor, 1994), but different genotypes sometimes seem to have similar responses (Kelly et al, 1993 ;Mortensen, 1998). When variation in ozone sensitivity among a large number of genotypes is tested, the importance of a few extremes is minimized and the statistical test may turn out to be non-significant.…”

Source–sink balance and carbon allocation below ground in plants exposed to ozone

“…However, measurable effects on roots may occur before effects on shoots are observed since shoots have immediate access to carbon for repair and compensation. Mortensen (1998) found decreased root but not shoot growth in Betula pubescens at exposures of 42 nMol mol‐1 (applied 12 h d −1 ), whereas both root and shoot growth were reduced at higher exposures. Chromosomal aberrations were found in root tips of Norway spruce exposed to O 3 , even in the absence of biochemical changes in needles (Wonisch, 1999).…”