Greenway Ken J, Macdonald S Ellen, Lieffers Victor J
Department of Forest Science, University of Alberta, T6G 2H1, U, Edmonton, Alberta, Canada.
Oecologia. 1992 Aug;91(2):184-191. doi: 10.1007/BF00317782.
This study evaluated the contribution of different ages of foliage to the nutrient and carbon balance of black spruce (Picea mariana (Mill.) B.S.P.) from a nutrient-poor peatland in Alberta. Seasonal patterns of foliar nitrogen and phosphorus concentration and content were examined in six needle cohorts up to 10 years old. Trees were treated to simulate excess nutrient deficiency (removal of all one-year-old foliage), nutrient excess (fertilized with 250, 50, 100 kg ha NPK split application in June and July), or left as controls. Gas exchange (net assimilation-Na, stomatal conductance-g, mesophyll conductance-g, water-use efficiency-WUE, dark respiration-RS) was measured on six different needle cohorts in several control trees in 1989 and 1990. Nitrogen and phosphorus concentration decreased with needle age. Foliar nutrient concentration fell from April to June and then was stable until September except for the fertilized trees where it increased. There was no evidence of greater than normal retranslocation of nutrients from older needles for defoliated trees or greater than normal nutrient loading in older needles of fertilized trees. NA, g, g, WUE, and RS were similar for all needles up to six or eight years old, these older needles having NA of 65% of current needles and similar RS. The results do not support to conclusion that older needles of black spruce are retained as an adaptation to nutrient stress. It does not appear that older needles serve as a nutrient storage site in conditions of excess nutrient availability or a greater than normal nutrient source during times of excess nutrient deficiency. It appears that the maintenance of long-livedfoliage in black spruce does not provide for greater flexibility in tree nutrient allocation. Their contribution to the carbon balance of the tree seems to be sufficient to explain their retention.
本研究评估了来自艾伯塔省一个营养贫瘠泥炭地的黑云杉（Picea mariana (Mill.) B.S.P.）不同树龄叶片对养分和碳平衡的贡献。研究了六个树龄达10年的针叶组中叶片氮和磷浓度及含量的季节性模式。对树木进行处理以模拟养分极度缺乏（去除所有一年生叶片）、养分过剩（6月和7月分施250、50、100千克/公顷氮磷钾）或作为对照。1989年和1990年在几棵对照树的六个不同针叶组上测量了气体交换（净同化率-Na、气孔导度-g、叶肉导度-g、水分利用效率-WUE、暗呼吸-RS）。氮和磷浓度随针叶年龄增长而降低。叶片养分浓度从4月到6月下降，然后一直稳定到9月，但施肥树木除外，施肥树木的养分浓度有所增加。对于落叶树木，没有证据表明老叶中养分的再分配高于正常水平；对于施肥树木，也没有证据表明老叶中的养分负载高于正常水平。六岁或八岁以下的所有针叶的Na、g、g、WUE和RS相似，这些老针叶的Na为当前针叶的65%，RS相似。结果不支持黑云杉老叶被保留是为适应养分胁迫这一结论。在养分供应过剩的情况下，老叶似乎不是养分储存部位；在养分极度缺乏时，老叶也不是高于正常水平的养分来源。黑云杉中长寿叶片的维持似乎并未为树木养分分配提供更大的灵活性。它们对树木碳平衡的贡献似乎足以解释它们被保留的原因。
