Vizoso Seraphine, Gerant Dominique, Guehl Jean Marc, Joffre Richard, Chalot Michel, Gross Patrick, Maillard Pascale
Génomique Ecophysiologie et Ecologie fonctionnelles, 54506 Vandoeuvre, France.
Tree Physiol. 2008 Nov;28(11):1729-39. doi: 10.1093/treephys/28.11.1729.
Soil nitrogen can alter storage and remobilization of carbon and nitrogen in forest trees and affect growth responses to elevated carbon dioxide concentration ([CO(2)]). We investigated these effects in oak saplings (Quercus robur L.) exposed for two years to ambient or twice ambient [CO(2)] in combination with low- (LN, 0.6 mmol N l(-1)) or high-nitrogen (HN, 6.1 mmol N l(-1)) fertilization. Autumn N retranslocation efficiency from senescing leaves was less in HN saplings than in LN saplings, but about 15% of sapling N was lost to the litter. During the dormant season, nonstructural carbohydrates made up 20 to 30% of the dry mass of perennial organs. Starch was stored mainly in large roots where it represented 35-46% of dry mass. Accumulation of starch increased in large roots in response to LN but was unaffected by elevated [CO(2)]. The HN treatment resulted in high concentrations of N-soluble compounds, and this effect was reduced by elevated [CO(2)], which decreased soluble protein N (-17%) and amino acid N (-37%) concentrations in the HN saplings. Carbon and N reserves were labeled with (13)C and (15)N, respectively, at the end of the first year. In the second year, about 20% of labeled C and 50% of labeled N was remobilized for spring growth in all treatments. At the end of leaf expansion, 50-60% of C in HN saplings originated from assimilation versus only 10-20% in LN saplings. In HN saplings only, N uptake occurred, and some newly assimilated N was allocated to new shoots. Through effects on the C and N content of perennial organs, elevated [CO(2)] and HN increased remobilization capacity, thereby supporting multiple shoot flushes, which increased leaf area and subsequent C acquisition in a positive feedback loop.
土壤氮素可改变森林树木中碳和氮的储存与再分配，并影响其对二氧化碳浓度升高（[CO₂]）的生长响应。我们对橡树幼苗（Quercus robur L.）进行了研究，这些幼苗在环境[CO₂]或两倍环境[CO₂]条件下，结合低氮（LN，0.6 mmol N l⁻¹）或高氮（HN，6.1 mmol N l⁻¹）施肥处理两年。与LN幼苗相比，HN幼苗衰老叶片中秋季氮素再转运效率较低，但约15%的幼苗氮素流失到凋落物中。在休眠季节，非结构性碳水化合物占多年生器官干重的20%至30%。淀粉主要储存在大根中，占大根干重的35 - 46%。LN处理使大根中淀粉积累增加，但升高[CO₂]对其无影响。HN处理导致氮溶性化合物浓度较高，而升高[CO₂]可降低这种影响，降低了HN幼苗中可溶性蛋白氮（-17%）和氨基酸氮（-37%）的浓度。在第一年结束时，分别用¹³C和¹⁵N标记碳和氮储备。在第二年，所有处理中约20%的标记碳和50%的标记氮被重新分配用于春季生长。在叶片伸展结束时，HN幼苗中50 - 60%的碳来自同化作用，而LN幼苗中仅为10 - 20%。仅在HN幼苗中发生了氮素吸收，一些新同化的氮被分配到新梢中。通过对多年生器官碳和氮含量的影响，升高[CO₂]和HN增加了再分配能力，从而支持多次新梢萌发，这增加了叶面积并随后通过正反馈回路增加了碳的获取。
