Carswell F E, Grace J, Lucas M E, Jarvis P G
Institute of Ecology and Resource Management, University of Edinburgh, UK.
Tree Physiol. 2000 Aug;20(14):977-86. doi: 10.1093/treephys/20.14.977.
Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and elevated CO2 concentrations ([CO2]) for 119 days, using small fumigation chambers. A solution containing macro- and micronutrients was supplied at two rates. The 5% rate (high rate) was designed to avoid nutrient limitation and allow a maximum rate of growth. The 1% rate (low rate) allowed examination of the effect of the nutrient limitation-elevated CO2 interaction on carbon assimilation. Root growth was stimulated by 23% in elevated [CO2] at a high rate of nutrient supply, but this did not lead to a change in the root:shoot ratio. Total biomass did not change at either rate of nutrient supply, despite an increase in relative growth rate at the low nutrient supply rate. Net assimilation rates and relative growth rates were stimulated by the high rate of nutrient addition, irrespective of [CO2]. We used a biochemical model of photosynthesis to investigate assimilation at the leaf level. Maximum rate of electron transport (Jmax) and maximum velocity of carboxylation (Vcmax) did not differ significantly with CO2 treatment, but showed a substantial reduction at the low rate of nutrient supply. Across both CO2 treatments, mean Jmax for seedlings grown at a high rate of nutrient supply was 75 micromol m(-2) s(-1) and mean Vcmax was 27 micromol m(-2) s(-1). The corresponding mean values for seedlings grown at a low rate of nutrient supply were 36 micromol m(-2) s(-1) and 15 micromol m(-2) s(-1), respectively. Concentrations of leaf nitrogen, on a mass basis, were significantly decreased by the low nutrient supply rate, in proportion to the observed decrease in photosynthetic parameters. Chlorophyll and carbohydrate concentrations of leaves were unaffected by growth [CO2]. Because there was no net increase in growth in response to elevated [CO2], despite increased assimilation of carbon at the leaf level, we hypothesize that the rate of respiration of non-photosynthetic organs was increased.
利用小型熏蒸箱，在环境二氧化碳浓度和升高的二氧化碳浓度（[CO₂]）条件下，对洋椿（楝科）幼苗的碳同化进行了为期119天的研究。以两种速率供应含有大量和微量营养素的溶液。5%的速率（高速率）旨在避免养分限制并允许最大生长速率。1%的速率（低速率）用于研究养分限制 - 升高的二氧化碳相互作用对碳同化的影响。在高养分供应速率下，升高的[CO₂]使根系生长受到23%的刺激，但这并未导致根冠比发生变化。尽管在低养分供应速率下相对生长速率有所增加，但在两种养分供应速率下总生物量均未改变。无论[CO₂]如何，高养分添加速率均刺激了净同化率和相对生长速率。我们使用光合作用的生化模型来研究叶片水平的同化作用。最大电子传递速率（Jmax）和最大羧化速率（Vcmax）在不同二氧化碳处理下没有显著差异，但在低养分供应速率下显著降低。在两种二氧化碳处理中，高养分供应速率下生长的幼苗的平均Jmax为75微摩尔·米⁻²·秒⁻¹，平均Vcmax为27微摩尔·米⁻²·秒⁻¹。低养分供应速率下生长的幼苗的相应平均值分别为36微摩尔·米⁻²·秒⁻¹和15微摩尔·米⁻²·秒⁻¹。以质量计，低养分供应速率使叶片氮浓度显著降低，与观察到的光合参数下降成比例。叶片的叶绿素和碳水化合物浓度不受生长[CO₂]的影响。由于尽管叶片水平的碳同化增加，但对升高的[CO₂]没有生长净增加，我们推测非光合器官的呼吸速率增加了。
