平茬年限和林龄对沙冬青叶片功能性状及土壤化学计量特征的影响

Effects of time after rejuvenation pruning and stand age on leaf functional traits of Ammopiptanthus mongolicus and stoichiometric characteristics of rhizosphere soil

为阐明平茬年限和林龄对沙冬青叶片功能性状及灌丛下土壤碳(C)、氮(N)、磷(P)化学计量特征的影响,采用方差及相关性分析方法研究沙冬青被平茬后更新恢复生长的机理和策略,探讨C、N、P化学计量特征对沙冬青种群生长及恢复的指示意义,从而更好地解释平茬复壮后植物补偿性生长机理与持续年限,以期在理论与技术上解决孑遗植物种质资源的保存与修复,为天然沙冬青种群在生态系统中演变特征进行预测和评估提供基础资料。结果表明:1)沙冬青经平茬处理后,叶片面积显著增大(P<0.05)。平茬恢复生长1年的沙冬青比叶面积、叶片N含量、叶片P含量显著升高(P<0.05),且随平茬年限和林龄的增加呈下降趋势,叶片干物质含量变化趋势与比叶面积相反,叶片碳含量在不同平茬年限和林龄下无显著差异(P>0.05)。叶片N含量与叶片P含量、比叶面积呈极显著正相关,叶片干物质含量与比叶面积呈极显著负相关,且与叶片N含量、叶片P含量呈显著负相关。2)叶片与土壤中的C、N、P化学计量特征对平茬年限和林龄变化的响应不完全一致。平茬年限和林龄对沙冬青灌丛下土壤有机碳含量产生显著影响(P<0.05),但对土壤P含量无显著影响(P>0.05),仅林龄对土壤全N含量影响显著(P<0.05)。随着平茬年限和林龄的增加,土壤C、N含量呈上升趋势,土壤P含量呈下降趋势。3)在叶片C、N、P化学计量特征中,叶片P与C∶P对平茬年限和林龄变化反应最为敏感,对于沙冬青更新恢复生长及种群动态变化规律具有指示意义。平茬恢复1、3和8年的沙冬青叶片N∶P平均值分别为14.79、15.77、17.81,幼龄林、中龄林和成熟林沙冬青叶片N∶P平均值分别为15.32、18.23、21.76,可见随着平茬年限和林龄的增加,沙冬青生长由N、P共同限制逐渐转向更受P的限制。

Carbon(C),nitrogen(N),and phosphorus(P)stoichiometry are critical indicators of biogeochemical coupling in terrestrial ecosystems.Therefore,nutrient stoichiometry has been used as an indicator of community succession and vegetation restoration in recent years.The aim of this study was to clarify the effects of time elapsed after pruning and shrub age on leaf functional traits and on the chemical characteristics of C,N,and P in leaves of Ammopiptanthus mongolicus.Variance and correlation analyses were used to detect the adaptive strategies of shrubs during restoration and growth after a pruning treatment.This information is helpful to solve technical conservation problems and for the development of germplasm resources in theory and in practice.The results provide basic data for the prediction and evaluation of the natural population of A.mongolicus in this ecosystem.The results showed that:1)The leaf area of A.mongolicus increased significantly after a rejuvenation pruning treatment(P<0.05).Specific leaf area,leaf N content,and leaf P content were significantly increased by 1 year after rejuvenation pruning(P<0.05).They declined during subsequent years after pruning and with shrub age.Leaf dry matter content showed the opposite trend to that of specific leaf area.The C content of leaves did not differ significantly(P>0.05)with age or among different years after the pruning treatment.The leaf N content was significantly positively correlated with leaf P content and specific leaf area.Leaf dry matter content was significantly negatively correlated with specific leaf area,and significantly negatively correlated with leaf P content and specific leaf area.2)The responses of C,N,and P contents and stoichiometric ratio to shrub age and the number of years after the pruning treatment were not exactly the same between leaves and soil.The number of years after the pruning treatment and shrub age significantly affected soil C content under the shrubs(P<0.05),but not the P content in soil(P>0.05).Only shrub age significantly affected the N content in soil.With prolonged time after the pruning treatment and increasing shrub age,the soil C and N contents increased,but the soil P content showed a downward trend.3)For the leaf C,N,and P and stoichiometric ratio,P and C∶P were most sensitive to the number of years after the pruning treatment and the age of A.mongolicus,implying that these indices can reflect the regeneration,growth,and the dynamic changes in this population.The average N∶P of the leaves at 1,3,and 8 years after the pruning treatment were 14.79,15.77,and 17.81,respectively.The average N∶P ratios of the leaves of the young,middle-aged,and mature shrubs were 15.32,18.23,and 21.76,respectively.These results suggest that with increasing time after the pruning treatment and with increasing plant age,the growth of A.mongolicus gradually shifted from being restricted by N and P to being more restricted by P.