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One-year-old jack pine ( Pinus banksiana  Lamb.) and current-year white birch ( Betula papyrifera  Marsh.) seedlings were grown in ambient (360 ppm) or twice ambient (720 ppm) atmospheric CO 2  concentration ([CO 2 ]) and at three soil temperatures ( T  soil  = 7, 17 and 27 °C initially, increased to 10, 20 and 30 °C two months later, respectively) in a greenhouse for 4 months. In situ foliar gas exchange, in vivo carboxylation characteristics and chlorophyll fluorescence were measured after 2.5 and 4 months of treatment. Low  T  soil  suppressed net photosynthetic rate ( P  n ), stomatal conductance ( g  s ) and transpiration rate ( E ) in jack pine in both CO 2  treatments and  g  s  and  E  in white birch in ambient [CO 2 ], but enhanced instantaneous water-use efficiency (IWUE) in both species after 2.5 months of treatment. Treatment effects on  g  s  and  E  remained significant throughout the 4-month study. Low  T  soil  reduced maximal carboxylation rate ( V  cmax ) and PAR-saturated electron transport rate ( J  max ) in jack pine in elevated [CO 2 ] after 2.5 months of treatment, but not after 4 months of treatment. Low  T  soil  increased actual photochemical efficiency of photosystem II (PSII) in the light (Δ F / F  m  ′ ) in jack pine, but decreased Δ F / F  m  ′  in white birch after 4 months of treatment. In response to low  T  soil , photosynthetic linear electron transport to carboxylation ( J  c ) decreased in jack pine after 2.5 months and in white birch after 4 months of treatment. Low  T  soil  increased the ratio of the photosynthetic linear electron transport to oxygenation ( J  o ) to the total photosynthetic linear electron transport rate through PSII ( J  o / J  T ) in both species after 2.5 months of treatment, but the effects became statistically insignificant in white birch after 4 months of treatment. High  T  soil  decreased foliar N concentration in white birch. Elevated [CO 2 ] increased  P  n , IWUE and  J  c  but decreased  J  o / J  T  in both species at both measurement times except  J  c  in white birch after 2.5 months of treatment. Elevated [CO 2 ] also decreased  g  s  and  E  in white birch at high  T  soil ,  V  cmax  in both species and triose phosphate utilization in white birch at low  T  soil  after 4 months of treatment, and Δ F / F  m  ′  in white birch after 2.5 months of treatment. Elevated [CO 2 ] also increased foliar N concentration in both species. Low  T  soil  caused no permanent damage to PSII in either species, but jack pine responded and acclimated to low  T  soil  more quickly than white birch. Photosynthetic down-regulation and a decrease in photosynthetic electron transport to photorespiration occurred in both species in response to elevated [CO 2 ].

tree physiology

Effects of soil temperature and elevated atmospheric CO 2  concentration on gas exchange, in vivo carboxylation and chlorophyll fluorescence in jack pine and white birch seedlings