中国北部半干旱区乔木、灌木和草本3种不同生活型植物的氮素回收特征

Nitrogen Resorption of Three Life-forms (Trees,Shrubs and Grasses) in the Semi-Arid Region of North China

在位于中国北部半干旱区的多伦县选择 3种不同生活型的植物 ,每种生活型各选取 3种有代表性的植物 :3种落叶乔木白桦 Betula platyphylla 、山定子 Malus baccata 、山杏 Prunus armeniaca ,3种落叶灌木黄柳 Sal-ix flavida 、山刺玫 Rosa davurica 、羊柴 H edysarum laeve 和 3种多年生草本地榆 Sanguisorba officinalis 、菊叶委陵菜 Potentilla tanacetifolia 、叉分蓼 Polygonum divaricatum ,对它们的氮素回收特征进行了研究 .结果表明 :乔木、灌木及草本 3种不同生活型植物的氮素回收效率分别为 4 3.4 2 %、5 8.84 %、73.76 % ,氮素回收水平分别为 12 .4 m g· g- 1、10 .7mg· g- 1和 8.2 m g· g- 1 .两种深根系生活型植物 乔木、灌木 的枯叶具有较高的氮素浓度 即回收水平低 ,并且成熟绿叶与枯叶中的氮素浓度差异较小 即回收效率低 ,与之相比 ,浅根系的多年生草本植物的枯叶具有较低的氮素浓度 即回收水平高 ,并且成熟绿叶与枯叶中的氮素浓度差异较大 即回收效率高 .不同生活型植物氮素回收能力的差异说明了不同生活型植物对生境具有不同的氮素适应策略 ,另一方面 ,氮素回收效率和氮素回收水平可作为衡量植物氮素回收能力的两个重要参数 .

Nitrogen resorption from senescing leaves,by minimizing N losses,could be just as uptake in determining N balance.It can increase plant N use efficiency,and may be an adaptation to N limitation.To explore the dynamics of nutrient conservation in this assemblage of plants,the main plant strategies to conserve N,i.e.N resorption efficiency and proficiency,in nine species in the semi-arid region in northern China were analyzed.It was hypothesized that the three main life-forms (trees,shrubs,and grasses) display different mechanisms of N conservation relating to their structural and functional characteristics.Three deciduous trees (Betula platyphylla,Malus baccata and Prunus armeniaca),three deciduous shrubs (Salix flavida,Rosa davurica and Hedysarum laeve) and three perennial grasses (Sanguisorba officinalis,Potentilla tanacetifolia and Polygonum divaricatum) were chosen.N resorption efficiency averaged 43.42%,(58.84%) and 73.76% for trees,shrubs and grasses,respectively,and N resorption proficiency averaged (12.4) mg·g^(-1),10.7 mg·g^(-1) and 8.2 mg·g^(-1),respectively.However,resorption varied significantly among the life-forms.The two deep-rooted life-forms (tree and shrub) displayed high N concentration in senescing leaves (low resorption proficiency) and small differences in N concentration between mature and senescing leaves (low N resorption efficiency).In contrast,shallow-rooted perennial grasses showed high N resorption proficiency (low N concentration in senescing leaves) and high N resorption efficiency (high differences in N concentration between mature and senescing leaves).Additionally,P.tanacetifolia was individually more proficient at resorbing N than any of the other eight species.Significant differences in resorption among life-forms suggested that evolutionary history and habitat specificity be added to the list of factors known to have influence on resorption.The patterns of resorption in all species strongly indicated that efficiency and proficiency were good complementarily estimators for measuring resorption.