Schäppi Bernd, Körner Christian
Botanisches Institut der Universität Basel, Schönbeinstrasse 6, CH-4056, Basel, Switzerland.
Oecologia. 1996 Jan;105(1):43-52. doi: 10.1007/BF00328790.
Alpine plant species have been shown to exhibit a more pronounced increase in leaf photosynthesis under elevated CO than lowland plants. In order to test whether this higher carbon fixation efficiency will translate into increased biomass production under CO enrichment we exposed plots of narrow alpine grassland (Swiss Central Alps, 2470 m) to ambient (355 μl l) and elevated (680 μl l) CO concentration using open top chambers. Part of the plost received moderate mineral nutrient additions (40 kg ha year of nitrogen in a complete fertilizer mix). Under natural nutrient supply CO enrichment had no effect on biomass production per unit land area during any of the three seasons studied so far. Correspondingly, the dominant species Carex curvula and Leontodon helveticus as well as Trifolium alpinum did not show a growth response either at the population level or at the shoot level. However, the subdominant generalistic species Poa alpina strongly increased shoot growth (+47%). Annual root production (in ingrowth cores) was significantly enhanced in C. curvula in the 2nd and 3rd year of investigation (+43%) but was not altered in the bulk samples for all species. Fertilizer addition generally stimulated above-ground (+48%) and below-ground (+26%) biomass production right from the beginning. Annual variations in weather conditions during summer also strongly influenced above-ground biomass production (19-27% more biomass in warm seasons compared to cool seasons). However, neither nutrient availability nor climate had a significant effect on the CO response of the plants. Our results do not support the hypothesis that alpine plants, due to their higher carbon uptake efficiency, will increase biomass production under future atmospheric CO enrichment, at least not in such late successional communities. However, as indicated by the response of P. alpina, species-specific responses occur which may lead to altered community structure and perhaps ecosystem functioning in the long-term. Our findings further suggest that possible climatic changes are likely to have a greater impact on plant growth in alpine environments than the direct stimulation of photosynthesis by CO. Counter-intuitively, our results suggest that even under moderate climate warming or enhanced atmospheric nitrogen deposition positive biomass responses to CO enrichment of the currently dominating species are unlikely.
研究表明，与低地植物相比，高山植物物种在二氧化碳浓度升高时叶片光合作用的增加更为显著。为了测试这种更高的碳固定效率是否会在二氧化碳浓度增加的情况下转化为生物量的增加，我们使用开顶式气室，将狭窄的高山草地（瑞士中部阿尔卑斯山，海拔2470米）的样地暴露于环境二氧化碳浓度（355微升/升）和升高的二氧化碳浓度（680微升/升）下。部分样地添加了适量的矿质养分（在完全肥料混合物中每年每公顷施氮40千克）。在自然养分供应条件下，到目前为止所研究的三个季节中的任何一个季节，二氧化碳浓度升高对单位土地面积的生物量生产均无影响。相应地，优势物种弯叶苔草、瑞士狮牙草以及高山车轴草在种群水平或地上部分均未表现出生长响应。然而，次优势的广布物种高山早熟禾的地上部分生长显著增加（+47%）。在调查的第二年和第三年，弯叶苔草的年根系产量（在根生长芯中）显著提高（+43%），但所有物种的大量样本中的根系产量没有变化。施肥从一开始就普遍刺激了地上生物量（+48%）和地下生物量（+26%）的生产。夏季天气条件的年变化也强烈影响地上生物量的生产（温暖季节的生物量比凉爽季节多19 - 27%）。然而，养分有效性和气候对植物的二氧化碳响应均无显著影响。我们的结果不支持这样的假设，即高山植物由于其更高的碳吸收效率，在未来大气二氧化碳浓度增加的情况下会增加生物量生产，至少在这样的晚期演替群落中不会。然而，正如高山早熟禾的响应所示，会出现物种特异性响应，从长远来看，这可能会导致群落结构改变，甚至可能影响生态系统功能。我们的研究结果进一步表明，可能的气候变化对高山环境中植物生长的影响可能比二氧化碳直接刺激光合作用的影响更大。与直觉相反，我们的结果表明，即使在适度的气候变暖或大气氮沉降增加的情况下，目前占主导地位的物种对二氧化碳浓度升高的生物量正响应也不太可能出现。
