Turnbull Matthew H, Whitehead David, Tissue David T, Schuster William S, Brown Kim J, Engel Victor C, Griffin Kevin L
Department of Plant and Microbial Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Landcare Research, P.O. Box 69, Lincoln, New Zealand.
Oecologia. 2002 Feb;130(4):515-524. doi: 10.1007/s00442-001-0842-z. Epub 2002 Feb 1.
Photosynthesis and related leaf characteristics were measured in canopies of co-occurring Quercus rubra L. (red oak), Quercus prinus L. (chestnut oak) and Acer rubrum L. (red maple) trees. Mature (20+ m tall) trees were investigated at sites of differing soil water availability within a catchment (a drier upper site and a wetter lower site). Leaf photosynthetic characteristics differed significantly between species and in response to site and position in the canopy. Photosynthetic capacity (A ) was significantly greater at the wetter site in all canopy strata in A. rubrum but not in Q. rubra or Q. prinus. Our findings for A. rubrum are generally consistent with those predicting that species with higher specific leaf area (SLA) will have higher A per unit leaf nitrogen (N) and that species with leaves with lower SLA (e.g. Q. rubra and Q. prinus) will have shallower slopes of the A -N relationship. Importantly, the relationships between A and N (and by implication photosynthetic nitrogen-use efficiency, PNUE) differed in A. rubrum between the sites, with PNUE significantly lower at the drier site. The lower photosynthetic capacity and PNUE must substantially reduce carbon acquisition capacity in A. rubrum under these field conditions. Maximum stomatal conductance (g ) differed significantly between species, with g greatest in Q. rubra and Q. prinus. In Q. rubra and Q. prinus, g was significantly lower at the upper site than the lower site. There was no significant response of g to site in A. rubrum. These stomatal responses were consistent with the C /C ratio, which was significantly lower in leaves of Q. rubra and Q. prinus at the upper site, but did not differ between sites in A. rubrum. Leaf δC was significantly lower in A. rubrum than in either Q. rubra or Q. prinus at both sites. These findings indicate differences in stomatal behaviour in A. rubrum which are likely to contribute to lower water use efficiency at both sites. Our results support the hypothesis that the two Quercus species, in contrast to A. rubrum, maintain photosynthetic capacity at the drier site whilst minimising transpirational water loss. They also suggest, based primarily on physiological evidence, that the ability of A. rubrum to compete with other species of these deciduous forests may be limited, particularly in sites of low moisture availability and during low rainfall years.
在共生的红栎（Quercus rubra L.）、栗栎（Quercus prinus L.）和红花槭（Acer rubrum L.）树木的树冠层中测量了光合作用及相关的叶片特征。在一个集水区内不同土壤水分可利用性的地点（一个较干燥的上游地点和一个较湿润的下游地点）对成熟（树高20米以上）树木进行了调查。叶片的光合特征在物种之间以及对地点和树冠层位置的响应上存在显著差异。在红花槭的所有树冠层中，较湿润地点的光合能力（A）显著更高，但在红栎和栗栎中并非如此。我们对红花槭的研究结果总体上与预测结果一致，即比叶面积（SLA）较高的物种每单位叶片氮（N）的光合能力（A）会更高，而SLA较低的物种（如红栎和栗栎）的A-N关系斜率会更平缓。重要的是，红花槭在不同地点之间的A与N的关系（进而意味着光合氮利用效率，PNUE）有所不同，在较干燥地点PNUE显著更低。在这些田间条件下，较低的光合能力和PNUE必然会大幅降低红花槭的碳获取能力。最大气孔导度（g）在物种之间存在显著差异，红栎和栗栎的g最大。在红栎和栗栎中，上游地点的g显著低于下游地点。红花槭的g对地点没有显著响应。这些气孔响应与C3/C4比率一致，红栎和栗栎在上游地点叶片中的该比率显著更低，但在红花槭中不同地点之间没有差异。在两个地点，红花槭叶片的δ13C均显著低于红栎或栗栎。这些发现表明红花槭的气孔行为存在差异，这可能导致其在两个地点的水分利用效率都较低。我们的结果支持以下假设：与红花槭相比，两种栎属物种在较干燥地点维持光合能力的同时，将蒸腾失水降至最低。它们还主要基于生理学证据表明，红花槭与这些落叶林其他物种竞争的能力可能有限，特别是在低水分可利用性地点和低降雨年份。
