Tjoelker M G, Oleksyn J, Reich P B
Department of Forest Resources, University of Minnesota, 1530 Cleveland Ave. N, St. Paul, MN 55108, USA.
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New Phytol. 1998 Oct;140(2):197-210. doi: 10.1046/j.1469-8137.1998.00272.x.
We tested the extent to which growth responses to elevated carbon dioxide (CO ) are temperature-dependent and change through early seedling ontogeny among boreal tree species of contrasting relative growth rates (rgr). Populus tremuloides Michx, Betula papyrifera Marsh, Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., and Picea mariana (Mill.) B.S.P. were grown from seeds for 3 months in controlled-environment chambers at two CO concentrations (370 and 580 μmol mol ) and five temperature regimes of 18/12, 21/15, 24/18, 27/21 and 30/24°C (light/dark). Growth increases in response to CO enrichment were minimal at the lowest temperature and maximal at 21/15°C for the three conifers and at 24/18°C or higher for the two broadleaved species, corresponding with differences in optimal temperatures for growth. In both CO treatments, rgr among species and temperatures correlated positively with leaf area ratio (lar) (r⩾0·90, P<0·0001). However, at a given lar, rgr was higher in elevated CO , owing to enhanced whole-plant net assimilation rate. On average in all species and temperatures at a common plant mass, CO enrichment increased rgr (9%) through higher whole-plant net assimilation rate (22%), despite declines in lar in high CO (11%). Reductions in lar are thus an important feedback mechanism reducing positive plant growth responses to CO . Proportional allocation of dry mass to roots did not vary between CO treatments. Early in the experiment, proportional increases in plant dry mass in elevated CO were larger in faster-growing Populus tremuloides and B. papyrifera than in the slower-growing conifers. However, growth increases in response to CO enrichment fell with time for broadleaved species and increased for the conifers. With increasing plant size over time, compensatory adjustments to CO enrichment in the factors that determine rgr, such as lar, were much larger in broadleaves than in conifers. Thus, the hypothesis that faster-growing species are more responsive to elevated CO was not supported, given contrasting patterns of growth response to CO with increasing plant size and age.
我们测试了北方不同相对生长速率（rgr）的树种对二氧化碳（CO₂）浓度升高的生长响应在多大程度上依赖于温度以及在幼苗早期个体发育过程中如何变化。将颤杨（Populus tremuloides Michx）、纸皮桦（Betula papyrifera Marsh）、落叶松（Larix laricina (Du Roi) K. Koch）、班克松（Pinus banksiana Lamb.）和黑云杉（Picea mariana (Mill.) B.S.P.）的种子在可控环境舱中培养3个月，设置两种CO₂浓度（370和580 μmol mol⁻¹）以及18/12、21/15、24/18、27/21和30/24°C（光照/黑暗）五种温度处理。对于三种针叶树，在最低温度下，CO₂浓度升高引起的生长增加最小，在21/15°C时最大；对于两种阔叶树种，在24/18°C及以上时最大，这与生长的最适温度差异相对应。在两种CO₂处理中，物种间和温度间的rgr与叶面积比（lar）呈正相关（r⩾0·90，P<0·0001）。然而，在给定的lar下，由于整株植物净同化率提高，CO₂浓度升高时rgr更高。在所有物种和温度下，以相同植物质量为基础平均来看，尽管高CO₂浓度下lar有所下降（11%），但CO₂浓度升高通过提高整株植物净同化率（22%）使rgr提高了9%。因此，lar的降低是一种重要的反馈机制，会降低植物对CO₂的正向生长响应。CO₂处理间干物质向根部分配的比例没有变化。在实验早期，CO₂浓度升高时，生长较快的颤杨和纸皮桦的植物干物质比例增加幅度大于生长较慢的针叶树。然而，阔叶树种对CO₂浓度升高的生长增加随时间下降，而针叶树则增加。随着时间推移植物大小增加，阔叶树中决定rgr的因素（如lar）对CO₂浓度升高的补偿性调整比针叶树大得多。因此，考虑到随着植物大小和年龄增加，对CO₂浓度升高的生长响应模式不同，生长较快的物种对CO₂浓度升高更敏感这一假设未得到支持。
