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Photosynthesis of birch (Betula pendula) is sensitive to springtime frost and ozone

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Abstract:

Impacts of springtime frost and ozone enrichment, alone and in combination, on six birch (Betula pendula Roth) genotypes regenerated from a naturally occurring birch stand in southeastern Finland were studied. The seedlings were exposed to 65 ppb ozone (AOT40 (accumulated over a threshold of 40 ppb) exposure of 10.7 ppm·h) over 62 d in climate chambers, simulating spring conditions, and to –2 °C over two consecutive nights 33 d after the start of the experiment. The plants were measured for net photosynthesis, stomatal conductance, and concentrations of photosynthetic pigments, Rubisco, soluble proteins, carbohydrates, and macronutrients. Frost treatment caused a rapid 60%–77% decline in net photosynthesis and stomatal conductance rates. Recovery of net photosynthesis from frost was not complete during the subsequent 14 d, mainly because of impaired light capture through significant pigment loss and structural injuries. Concomitant ozone enrichment exacerbated the negative effect of frost on pigments and stomatal conductance. Both frost and ozone caused nutrient imbalance and increase in soluble proteins in leaves, whereas metabolism of carbohydrates was disturbed only when ozone was present. Responses to ozone and frost varied greatly among the genotypes, suggesting that there is a high capacity within the birch population to adapt to climate change through "preadapted" individuals.

Les impacts d'un gel tardif et d'un enrichissement en ozone, seuls et combinés, ont été étudiés sur six génotypes de bouleau (Betula pendula Roth) régénérés à partir d'un peuplement naturel de bouleau dans le sud-est de la Finlande. Les semis furent exposés à 65 ppb d'ozone (AOT40 exposition de 10,7 ppm·h) pendant 62 j dans des chambres à atmosphère contrôlée pour simuler des conditions printanières et à –2 °C pendant deux nuits consécutives 33 j après le début de l'expérience. Les mesures comprenaient la photosynthèse nette, la conductance stomatale et la concentration de pigments photosynthétiques ainsi que la rubisco, les protéines solubles, les hydrates de carbone et les macronutriments. Le gel a entraîné une diminution rapide (60 % – 77 %) des taux de photosynthèse nette et de conductance stomatale. La récupération de la photosynthèse nette après un gel n'était pas complète pendant les 14 j subséquents, surtout à cause du processus de capture de la lumière qui était perturbé par une perte importante de pigments et des dommages structuraux. L'enrichissement concomitant en ozone a aggravé l'effet négatif du gel sur les pigments et la conductance stomatale. Tant le gel que l'ozone ont causé un déséquilibre nutritif et une augmentation des protéines solubles dans les feuilles tandis que le métabolisme des hydrates de carbone a été perturbé seulement en présence d'ozone. Les réactions à l'ozone et au gel ont beaucoup varié selon le génotype indiquant qu'il y a une grande capacité d'adaptation au changement climatique dans la population de bouleau par le biais d'individus pré-adaptés.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2005

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  • Published since 1971, this monthly journal features articles, reviews, notes and commentaries on all aspects of forest science, including biometrics and mensuration, conservation, disturbance, ecology, economics, entomology, fire, genetics, management, operations, pathology, physiology, policy, remote sensing, social science, soil, silviculture, wildlife and wood science, contributed by internationally respected scientists. It also publishes special issues dedicated to a topic of current interest.
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