Long term effects of naturally elevated CO2 on mediterranean grassland and forest trees
Long term effects of naturally elevated CO2 on mediterranean grassland and forest trees
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自然升高的二氧化碳对地中海草原和林木的长期影响
作者：
C. Körner;F. Miglietta
我们调查的碳供应状况物种丰富的地中海植物群落生长在一个碗状的1公顷的“二氧化碳泉”附近的锡耶纳，意大利地区。只要有历史记录，地热“石灰窑”就为这些社区提供了纯二氧化碳，在树冠层与环境空气混合，白天平均为500-1000 ppm二氧化碳。在春季区域之外，相似的植物群落生长在相似的基质上，在相同的气候条件下，但在大约1000年的时间里，355 ppm二氧化碳。我们没有发现任何证据表明二氧化碳春季地区的植物生长更快，开花更早或更大。然而，我们发现非常大的差异，组织质量之间的40个物种研究内部和外部的春季地区。根据天气条件，总的非结构性碳水化合物（TNC，糖和淀粉）在草本植物叶片的平均浓度是38-47%，在春季地区。生长在春季区内外的花园土壤上的快速生长的杂草表现出相同的反应。在树木中，落叶栎叶片内的TNC含量是喷口区外的两倍，而常绿栎叶片内的TNC含量是喷口区外的两倍。冬青叶无显著差异。分支木材中的TNC水平和叶片值。阴生叶的TNC也较高。CO2浓度升高对糖组分没有影响，因此TNC的差异是由于淀粉积累造成的。CO2浓度升高会降低叶片氮浓度。这些观察结果表明，通常报道的TNC积累和N耗尽在CO2浓度升高的情况下生长的叶子不限于短期CO2富集实验的人工条件下，但持续很长一段时间。如果大气中的CO2水平继续上升，预计其他植物群落也会发生组织组成的这种变化。可能对食物网和养分循环产生影响。
We investigated the carbon supply status in species-rich mediterranean plant communities growing in a bowl-shaped 1-ha “CO2 spring” area near Sienna, Italy. A geothermic “lime-kiln” has provided these communities, for as long as historical records are available, with pure CO2 that mixes with ambient air at canopy level to daytime means of 500–1000 ppm CO2. Immediately outside the spring area similar plant communities are growing on similar substrate, and in the same climate, but under ca. 355 ppm CO2. We found no evidence that plants in the CO2 spring area grow faster, flower earlier or become larger. However, we found very large differences in tissue quality among the 40 species studied inside and outside the spring area. Depending on weather conditions, the mean concentration of total non-structural carbohydrates (TNC, sugars and starch) in leaves of herbaceous plants was 38–47% higher in the spring area. Fast growing ruderals growing on garden soil inside and outside the spring area show the same response. Among trees, leaves of the deciduousQuercus pubscens contain twice as much TNC inside as outside the vent area, whereas evergreenQ. ilex leaves show no significant difference. TNC levels in branch wood paralleled leaf values. TNC in shade leaves was also higher. Elevated CO2 had no effect on the sugar fraction, therefore differences in TNC are due to starch accumulation. Leaf nitrogen concentration decreases under elevated CO2. These observations suggest that the commonly reported TNC accumulation and N depletion in leaves growing under elevated CO2 are not restricted to the artificial conditions of short-term CO2 enrichment experiments but persist over very long periods. Such an alteration of tissue composition can be expected to occur in other plant communities also if atmospheric CO2 levels continue to rise. Effects on food webs and nutrient cycling are likely.