Crous Kristine Y, Walters Michael B, Ellsworth David S
School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI 48109-1115, USA.
Tree Physiol. 2008 Apr;28(4):607-14. doi: 10.1093/treephys/28.4.607.
To investigate whether long-term elevated carbon dioxide concentration ([CO(2)]) causes declines in photosynthetic enhancement and leaf nitrogen (N) owing to limited soil fertility, we measured photosynthesis, carboxylation capacity and area-based leaf nitrogen concentration (N(a)) in Pinus taeda L. growing in a long-term free-air CO(2) enrichment (FACE) facility at an N-limited site. We also determined how maximum rates of carboxylation (V(cmax)) and electron transport (J(max)) varied with N(a) under elevated [CO(2)]. In trees exposed to elevated [CO(2)] for 5 to 9 years, the slope of the relationship between leaf photosynthetic capacity (A(net-Ca)) and N(a) was significantly reduced by 37% in 1-year-old needles, whereas it was unaffected in current-year needles. The slope of the relationships of both V(cmax) and J(max) with N(a) decreased in 1-year-old needles after up to 9 years of growth in elevated [CO(2)], which was accompanied by a 15% reduction in N allocation to the carboxylating enzyme. Nitrogen fertilization (110 kg N ha(-1)) in the ninth year of exposure to elevated [CO(2)] restored the slopes of the relationships of V(cmax) and J(max) with N(a) to those of control trees (i.e., in ambient [CO(2)]). The J(max):V(cmax) ratio was unaffected by either [CO(2)] or N fertilization. Changes in the apparent allocation of N to photosynthetic components may be an important adjustment in pines exposed to elevated [CO(2)] on low-fertility sites. We conclude that fundamental relationships between photosynthesis or its component processes with N(a) may be altered in aging pine needles after more than 5 years of exposure to elevated atmospheric [CO(2)].
为了探究长期升高的二氧化碳浓度([CO₂])是否会因土壤肥力有限而导致光合增强和叶片氮(N)含量下降,我们在一个氮素受限的地点,对生长在长期开放式空气CO₂富集(FACE)设施中的火炬松(Pinus taeda L.)的光合作用、羧化能力和基于面积的叶片氮浓度(Nₐ)进行了测量。我们还确定了在升高的[CO₂]条件下,最大羧化速率(Vcmax)和电子传递速率(Jmax)如何随Nₐ变化。在暴露于升高的[CO₂] 5至9年的树木中,1年生针叶的叶片光合能力(A净 - Ca)与Nₐ之间关系的斜率显著降低了37%,而当年生针叶则未受影响。在升高的[CO₂]中生长长达9年后,1年生针叶中Vcmax和Jmax与Nₐ关系的斜率均下降,同时分配给羧化酶的氮减少了15%。在暴露于升高的[CO₂]的第9年进行氮肥施用(110 kg N ha⁻¹),使Vcmax和Jmax与Nₐ关系的斜率恢复到对照树(即处于环境[CO₂]中的树)的水平。Jmax:Vcmax比值不受[CO₂]或氮肥施用的影响。在低肥力地点,氮向光合组分的表观分配变化可能是松树对升高的[CO₂]的一种重要适应性调整。我们得出结论,在暴露于升高的大气[CO₂]超过5年后,衰老松针中光合作用或其组成过程与Nₐ之间的基本关系可能会发生改变。