Würth Mirjam K R, Winter Klaus, Körner Christian
Institute of Botany, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland e-mail:
Smithsonian Tropical Research Institute, Ap. 2072, Balboa, Panamá, , , ,.
Oecologia. 1998 Aug;116(1-2):18-25. doi: 10.1007/PL00013821.
The accumulation of non-structural leaf carbohydrates is one of the most consistent plant responses to elevated CO. It has been found in both fast-and slow-growing plants and is largely independent of the duration of exposure. Changes in leaf quality are thus to be expected, irrespective of other plant responses to atmospheric CO enrichment. However, there is no experimental evidence from tropical forests, the biome with the largest biomass carbon pool. Here we report in situ mesophyll responses of mature tropical trees to a doubling of CO. Individually CO-enriched leaves on 25 to 35-m-tall forest trees living at 26-35°C can be assumed to experience little sink limitation, and so, may be expected to exhibit no or very little carbohydrate accumulation. We tested this hypothesis using the leaf cup method on leaves accessible via the canopy crane of the Smithsonian Tropical Research Institute in a semi-deciduous tropical forest in Panamá. We also investigated the influence of the leaf-specific light regime, another possible environmental determinant of leaf carbon gain and mobile leaf carbohydrates. Total non-structural carbohydrates (TNC) reached a new steady state concentration after less than 4 days of exposure to twice ambient CO concentration. Against expectation, all four tree species investigated (Anacardium excelsum, Cecropia longipes, C. peltata, Ficus insipida) accumulated significant amounts of TNC (+41 to +61%) under elevated CO. The effect was stronger at the end of the daylight period (except for Ficus), but was still significant in all four species at the end of the dark period. In contrast, neither artificial nor natural shading affected leaf TNC. Taken together, these observations suggest that TNC accumulation reflects a mesophyll-bound tissue response specific to elevated CO, presumably unrelated to sink limitations. Thus, leaves of tropical forests seem not to be an exception, and will most likely contain more non-structural carbohydrates in a CO-rich world.
叶片中非结构性碳水化合物的积累是植物对二氧化碳浓度升高最一致的反应之一。在快速生长和缓慢生长的植物中均有发现，且很大程度上与暴露时间无关。因此，无论植物对大气中二氧化碳浓度升高的其他反应如何，叶片质量的变化都是可以预期的。然而，在拥有最大生物量碳库的热带森林生物群落中，尚无实验证据。在此，我们报告了成熟热带树木叶肉对二氧化碳浓度翻倍的原位反应。生活在26 - 35°C、树高25至35米的森林树木上，单独的二氧化碳富集叶片可被认为几乎没有库限制，因此，预计不会或仅有极少的碳水化合物积累。我们在巴拿马一个半落叶热带森林中，利用史密森热带研究所树冠起重机可触及的叶片，采用叶杯法对这一假设进行了测试。我们还研究了叶片特定光照条件的影响，这是叶片碳获取和可移动叶片碳水化合物的另一个可能的环境决定因素。在暴露于两倍环境二氧化碳浓度不到4天后，总非结构性碳水化合物（TNC）达到了新的稳态浓度。与预期相反，在所研究的四种树木（腰果、长柄蚁栖树、盾叶蚁栖树、无味榕）中，在二氧化碳浓度升高的情况下，所有树种都积累了大量的TNC（增加了41%至61%）。在白天结束时这种效应更强（除了榕属植物），但在黑暗期结束时，所有四个树种中这种效应仍然显著。相比之下，人工遮光和自然遮光均未影响叶片的TNC。综合这些观察结果表明，TNC积累反映了对二氧化碳浓度升高的叶肉组织特异性反应，可能与库限制无关。因此，热带森林的叶片似乎也不例外，在一个二氧化碳丰富的世界中很可能含有更多的非结构性碳水化合物。
