Curtis Peter S, Vogel Christoph S, Pregitzer Kurt S, Zak Donald R, Teeri James A
Department of Plant Biology, The Ohio State University, Columbus, Ohio 43210, USA.
School of Natural Resources and Environment, University of Michigan, Ann Arbor, Michigan 48109, USA.
New Phytol. 1995 Feb;129(2):253-263. doi: 10.1111/j.1469-8137.1995.tb04295.x.
Two important processes which may limit productivity gains in forest ecosystems with rising atmospheric CO are reduction in photosynthetic capacity following prolonged exposure to high CO and diminution of positive growth responses when soil nutrients, particularly N, are limiting. To examine the interacting effects of soil fertility and CO enrichment on photosynthesis and growth in trees we grew hybrid poplar (Populus × euramericana) for 158 d in the field at ambient and twice ambient CO and in soil with low or high N availability. We measured the timing and rate of canopy development, the seasonal dynamics of leaf level photosynthetic capacity, respiration, and N and carbohydrate concentration, and final above- and belowground dry weight. Single leaf net CO assimilation (A) increased at elevated CO over the majority of the growing season in both fertility treatments. At high fertility, the maximum size of individual leaves, total leaf number, and seasonal leaf area duration (LAD) also increased at elevated CO , leading to a 49% increase in total dry weight. In contrast, at low fertility leaf area growth was unaffected by CO treatment. Total dry weight nonetheless increased 25% due to CO effects on A. Photosynthetic capacity (A at constant internal p(CO ), ((C )) was reduced in high CO plants after 100 d growth at low fertility and 135 d growth at high fertility. Analysis of A responses to changing C indicated that this negative adjustment of photosynthesis was due to a reduction in the maximum rate of CO fixation by Rubisco. Maximum rate of electron transport and phosphate regeneration capacity were either unaffected or declined at elevated CO . Carbon dioxide effects on leaf respiration were most pronounced at high fertility, with increased respiration mid-season and no change (area basis) or reduced (mass basis) respiration late-season in elevated compared to ambient CO plants. This temporal variation correlated with changes in leaf N concentration and leaf mass per area. Our results demonstrate the importance of considering both structural and physiological pathways of net C gain in predicting tree responses to rising CO under conditions of suboptimal soil fertility.
随着大气中二氧化碳浓度升高，可能限制森林生态系统生产力增长的两个重要过程是：长期暴露于高浓度二氧化碳后光合能力下降，以及当土壤养分（特别是氮）有限时，正生长响应减弱。为了研究土壤肥力和二氧化碳浓度升高对树木光合作用和生长的交互作用，我们在田间将杂交杨树（Populus × euramericana）种植了158天，设置了环境二氧化碳浓度和两倍环境二氧化碳浓度的处理，以及低氮或高氮有效性的土壤处理。我们测量了树冠发育的时间和速率、叶片水平光合能力、呼吸作用、氮和碳水化合物浓度的季节动态，以及最终的地上和地下干重。在两种肥力处理下，单叶净二氧化碳同化率（A）在生长季节的大部分时间里，在二氧化碳浓度升高时均有所增加。在高肥力条件下，单个叶片的最大尺寸、总叶片数和季节性叶面积持续时间（LAD）在二氧化碳浓度升高时也增加，导致总干重增加49%。相比之下，在低肥力条件下，叶面积生长不受二氧化碳处理的影响。尽管如此，由于二氧化碳对A的影响，总干重仍增加了25%。在低肥力条件下生长100天和高肥力条件下生长135天后，高二氧化碳浓度处理的植株光合能力（在恒定胞内二氧化碳分压（(C))下的A）降低。对A对变化的C的响应分析表明，光合作用的这种负向调节是由于Rubisco固定二氧化碳的最大速率降低。电子传递的最大速率和磷酸再生能力在二氧化碳浓度升高时要么不受影响，要么下降。二氧化碳对叶片呼吸的影响在高肥力条件下最为明显，与环境二氧化碳浓度的植株相比，高二氧化碳浓度处理的植株在生长季中期呼吸增加，后期呼吸无变化（以面积计）或降低（以质量计）。这种时间变化与叶片氮浓度和单位面积叶质量的变化相关。我们的结果表明，在土壤肥力次优的条件下，预测树木对二氧化碳浓度升高的响应时，考虑净碳增益的结构和生理途径都很重要。
