Norby Richard J., Pastor John, Melillo Jerry M.
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Tree Physiol. 1986 Dec;2(1_2_3):233-241. doi: 10.1093/treephys/2.1-2-3.233.
The responses of forest trees to atmospheric CO(2) enrichment will depend in part on carbon-nutrient linkages. Insights into the possible long-term ecological consequences of CO(2) enrichment can be gained from studying physiological responses in short-term experiments. One-year-old white oak (Quercus alba L.) seedlings were grown in unfertilized forest soil for 40 weeks in controlled-environment chambers with ambient (362 microl l(-1)) or elevated (690 microl l(-1)) CO(2). As previously reported, seedling dry weight was 85% greater in the elevated CO(2) environment, despite severe nitrogen deficiency in all seedlings. The increase in growth occurred without a concomitant increase in nitrogen uptake, indicating an increase in nitrogen-use efficiency in elevated CO(2). The weight of new buds was greater in elevated CO(2), suggesting that shoot growth in the next year would have been enhanced relative to that of seedlings in ambient CO(2). However, there was less translocatable nitrogen in perennial woody tissue in elevated CO(2); thus, further increases in nitrogen-use efficiency may not be possible. The leaves that abscised from seedlings in elevated CO(2) contained higher amounts of soluble sugars and tannin and a lower amount of lignin compared with amounts in abscised leaves in ambient CO(2). Based on lignin:N and lignin:P ratios, the rates of litter decomposition might not be greatly affected by CO() enrichment, but the total amount of nitrogen returned to soil would be lower in elevated CO(2).
林木对大气中二氧化碳浓度升高的响应部分取决于碳-养分联系。通过短期实验研究生理响应，可以深入了解二氧化碳浓度升高可能产生的长期生态后果。一年生白栎（Quercus alba L.）幼苗在未施肥的森林土壤中，于可控环境舱内培养40周，二氧化碳浓度分别为环境浓度（362 μl l⁻¹）或升高浓度（690 μl l⁻¹）。如先前报道，尽管所有幼苗都严重缺氮，但在二氧化碳浓度升高的环境中，幼苗干重仍高出85%。生长增加的同时氮吸收并未相应增加，这表明在二氧化碳浓度升高时氮利用效率有所提高。二氧化碳浓度升高时新芽重量更大，这表明相对于处于环境二氧化碳浓度下的幼苗，来年的枝条生长会得到增强。然而，在二氧化碳浓度升高的情况下，多年生木质组织中可转运的氮较少；因此，氮利用效率可能无法进一步提高。与环境二氧化碳浓度下脱落的叶片相比，二氧化碳浓度升高时幼苗脱落的叶片含有更多的可溶性糖和单宁，而木质素含量较低。基于木质素与氮、磷的比例，二氧化碳浓度升高可能不会对凋落物分解速率产生太大影响，但在二氧化碳浓度升高时返还到土壤中的总氮量会更低。
