不同密度下沙地樟子松碳、氮、磷化学计量及养分重吸收特征

以樟子松纯林为对象,研究了6种密度(490、750、1110、1550、1930、2560株·hm^-2)下不同器官(当年生叶、一年生叶、当年生枝、一年生枝和细根)的C、N、P化学计量特征及叶片N、P重吸收效率。结果表明:随着林分密度增加,当年生和一年生叶C含量及当年生和一年生枝P含量呈降低趋势(1550株·hm^-2除外),当年生枝、一年生枝和细根C含量、各器官N含量及当年生叶、一年生叶和细根P含量呈先升高后降低趋势,在1550株·hm^-2密度下最高;当年生叶、一年生叶和细根C∶N、当年生叶和枝C∶P以及当年生叶、当年生和一年生枝N∶P呈先降低后升高趋势,一年生叶和枝C∶P呈升高趋势;凋落叶C含量先增加后降低,N含量呈升高趋势,P含量先降低后升高;叶片N重吸收效率下降,P重吸收效率先升高后降低,N重吸收效率:P重吸收效率呈下降趋势。因此,随樟子松林分密度增加,N限制减弱,P限制增强。当林分密度为1550株·hm^-2时,养分更多分配到叶片和细根,促进高生长,为樟子松人工林适宜经营密度。

Carbon,nitrogen and phosphorus stoichiometry and nutrient resorption of Pinus sylvestris var.mongolica under different densities

We examined the carbon(C),nitrogen(N)and phosphorus(P)stoichiometry in different organs(current-year needle,one-year-old needle,current-year branch,one-year-old branch,and fine root)along with the N and P resorption efficiencies in needles of Pinus sylvestris var.mongolica in pure forest with six densities(490,750,1110,1550,1930 and 2560 trees·hm^-2).The results showed that C concentrations in the current-year and one-year-old needles and P concentrations in the current-year and one-year-old branches exhibited downward trends with increasing stand density,except for the 1550 trees·hm^-2stand.With the increases of stand density,C concentrations in current-year branch,one-year-old branch and fine root,the N concentrations in all organs,and P concentrations in current-year needle,one-year-old needle and fine root tended to increase and then decrease,with the highest values in the 1550 trees·hm^-2stand.The C∶N in current-year needle,one-year-old needle and fine root,C∶P in current-year needle and branch,and N∶P in current-year needle,current-year and one-year-old branches displayed decreasing and then increasing trends with increasing stand density,whereas C∶P in one-year-old needle and branch showed an upward trend.With increasing stand density,C concentrations in leaf litter increased and then decreased,N concentrations exhibited an increasing trend,and P concentrations decreased and then increased.With increasing stand density,N resorption efficiency and the ratio of N resorption efficiency to P resorption efficiency decreased,and P resorption efficiency increased and then decreased.These findings indicated that N limitation weakened but P limitation enhanced with increasing stand density.The optimal management density for P.sylvestris var.mongolica stand should be 1550 trees·hm^-2,in which more nutrients are allocated to needles and fine roots and thus contribute to high growth rate.