施氮对不同龄级油松针叶氮磷化学计量的影响

Effects of nitrogen fertilization on nitrogen and phosphorus nutrient stoichiometry in needles of Pinus tabuliformis at different ages

【目的】探究缺氮地区油松(Pinus tabuliformis)人工林碳、氮、磷生态化学计量特征,及养分在树体内的重吸收、利用效率的变化情况,揭示各指标随油松龄级变化的规律及对梯度氮添加的响应差异。【方法】试验在山西省朔州市金沙滩林场进行,选择Ⅱ~Ⅴ龄级油松人工林,每个林下设置5个施氮梯度:0、5、10、15、20 g/m^(2),分别模拟对照以及低、适宜、中高、高氮水平。在生长盛期(7月),采集表层土壤和当年新生枝条上的成熟针叶样品,测定碳、氮、磷含量,计算化学计量比,分析油松氮、磷重吸收效率(NRE、PRE)、氮磷养分利用效率(NNUE、PNUE)和氮磷内稳态指数(HN、HP)。【结果】土壤全氮含量影响着各龄级油松新生叶全碳(TC)、全氮(TN)含量及碳氮比(C/N)、碳磷比(C/P),峰值或谷值均出现在土壤全氮含量为0.8~1.0 g/kg范围内。各龄级油松新生叶氮磷比(N/P)随龄级升高呈增加趋势,叶片全磷(TP)含量与土壤氮水平呈显著正相关。各龄级油松新生叶NRE随土壤全氮含量增加而下降,NNUE则随土壤全氮含量的增加总体呈上升趋势;PRE较为稳定,但Ⅴ龄级油松PRE随土壤全氮含量的升高变化较为明显;PNUE随土壤全氮含量的增加缓慢减小。各龄级油松内稳态指数(H)拟合效果均达到显著水平(P<0.10),且HN均>4,呈稳定状态,除Ⅴ龄级油松HP值为0.999,处于敏态,其余各龄级HP值多在1.951附近浮动,处于弱稳态。【结论】Ⅱ龄级油松对土壤氮含量的变化反应敏感,而较高林龄的油松磷含量变化更显著。各龄级油松氮内稳态指数均大于4,处于稳态,充足的氮养分可以巩固油松氮的稳定性。Ⅲ、Ⅳ龄级油松调节体内营养再吸收利用的能力较强,氮、磷内稳性均较高,而Ⅱ龄级油松对氮的强吸收能力降低了磷的稳定性,Ⅴ龄级油松对磷的再吸收和利用能力较低,Ⅱ、Ⅴ龄级油松磷内稳态指数呈现弱稳态和敏态。因此,土壤氮素水平变化后,应注意幼龄和老龄级油松的磷素营养。

【Objectives】We explored the ecological stoichiometric characteristics of carbon(C),nitrogen(N),and phosphorus(P),the reutilization and utilization efficiency of nutrients in Pinus tabuliformis plantations in different ages in nitrogen deficient areas,to reveal the responses of various indicators to nitrogen addition gradient.【Methods】The survey was conducted in Jinshatan artificial forest farm,Shuozhou City,Shanxi Province,the tested pine(Pinus tabulaeformis)plantations were atⅡtoⅤage groups,respectively.Nitrogen fertilizer was applied at gradients of 0 g/m^(2),5 g/m^(2),10 g/m^(2),15 g/m^(2),and 20 g/m^(2),to assimilate control,and low,suitable,moderate high,and high soil N levels.At the full growing stage in July,the mature needle leaves on the newly grown branches were sampled for determination of total C,N,and P content,and the surface soil was sampled for the measurement of available N and P contents.The N and P reabsorption efficiency(NRE,PRE),nitrogen and phosphorus nutrient utilization efficiency(NNUE,PNUE),and nitrogen and phosphorus homeostasis index(HN,HP)of pine trees were calculated.【Results】The total carbon(TC)and nitrogen(TN)content,C/N and C/P ratio of leaves in various age groups of Chinese pine plantations showed a unimodal trend with the increase of soil N levels,both the peak and foot values occurred between 0.8−1.0 g/kg of soil total N content.The leaf N/P ratio gradually increased fromⅡtoⅤage groups,and the leaf P content was positively correlated with soil total N.The NRE of new leaves of different age groups decreased,while the NNUE showed an overall upward trend with the increase of soil total N content.PRE was relatively stable in age group ofⅡto IV,but the PRE at age group V changed significantly with the increase of soil total N level;PNUE decreased slowly with the increase of soil total N level.The fitting effects of homeostasis indexes(H)of pine plantations at all age groups reached significant level(P<0.1),and HN was all higher than 4,showing a stable state,however,the HP value at ageⅤwas 0.999,indicating a sensitive state.And the fitting result for the HP of majority aged pine plantations was floating around 1.951,which was in a weak but steady state.【Conclusions】Ⅱage grade Pinus tabulaeformis is sensitive to soil N change,while the change of P content in the other age grades are more stronger.The N homeostasis indices in all age grades are higher than 4,being stable state,and sufficient nitrogen supply strengths the stability.Ⅲ,andⅣage grade Pinus tabulaeformis are strong in regulating the reabsorption and reutilization of nutrients,leading to high homeostasis stability in both N and P.WhileⅡage grade Pinus tabulaeformis shows lower P homeostasis stability due to high uptake of nitrogen,andⅤage grade Pinus tabulaeformis shows low P homeostasis stability due to the weak reabsorption and reutilization of P.So,when the soil nitrogen level changes,more attention should be paid on the P nutrition of young and old Pinus tabulaeformis plantations.