喀斯特林地细根碳氮磷生态化学计量特征的季节变化及其影响因子

Seasonal variation of ecological stoichiometric characteristics of C,N and P in fine roots from karst forest and its influencing factors

植物细根养分生态化学计量特征是植被适应土壤环境的一种策略。为了解喀斯特地区不同林地类型细根碳(C)氮(N)磷(P)的生态化学计量比值的季节变化及其影响因素,该文研究了喀斯特地区灌木林和乔木林活细根和死细根的C、N、P含量和比值及其与环境因子的关系。结果表明:(1)总体上乔木林两类细根C、N、P含量高于灌木林,表明乔木物种细根对养分的吸收和储存比灌木物种更强。另外,两种林地类型活细根C含量显著高于死细根(P<0.05),而活细根N、P含量则低于死细根。(2)两种林地类型的两类细根C含量在雨季均低于旱季;灌木林活细根N、P含量在雨季高于旱季,而乔木林相反。灌木林活细根C∶N、C∶P和N∶P比值在雨季均低于旱季;乔木林两类细根的C∶N和C∶P比值在雨季高于旱季,而N∶P比值则是雨季低于旱季。雨季较低的活细根N∶P比值,表明灌木林和乔木林的植物在雨季的P限制程度较低。(3)两种林地类型上坡两类细根的C含量均高于中坡和下坡,而灌木林下坡N、P含量相对较高,乔木林中坡N、P含量相对较高;灌木林上坡两类细根C∶N、C∶P、N∶P比值相对较高,乔木林下坡两类细根的C∶N比值高于其他坡位而C∶P和N∶P比值是上坡高于其他坡位,表明两种林地中的植物在上坡受P限制影响较强,在中下坡受影响较弱。(4)冗余分析表明,林地类型、有效磷、季节是细根C、N、P养分含量及比值的主要影响因子,它们的单独解释量分别为18.8%、6.6%、6.5%。上述结果表明,在人工促进植被恢复时应考虑适当的林地类型、季节以及坡位差异造成的N∶P比值变化的影响,以便加快喀斯特生态系统的恢复。

The ecological stoichiometry of fine root carbon(C),nitrogen(N),and phosphorus(P)is considered to reflect the strategies whereby plants adapt to the soil environment.In order to gain an understanding of the seasonal variation in fine root C∶N∶P ratios in different forest types of karst ecosystem,we measured the C,N,and P contents and ratios of living and dead fine roots in shrubland and arbor forest,as well as the influence of abiotic and biotic factors.The results were as follows:(1)C,N,and P contents in the fine roots of arbor forest were higher than those of shrubland,thereby indicating that the fine roots of arbors may by characterized by a stronger absorption and storage of nutrients than those of shrubs.In addition,the contents of C in living fine roots were significantly higher than those in dead fine roots(P<0.05),but N and P contents in living fine roots were lower than those in dead fine roots.(2)It was found that the contents of C in the living and dead fine roots of the two forest types were lower during the rainy season than during the dry season.The N and P contents of living fine roots of shrubs were higher during the rainy season than those in dry season,the opposite pattern was observed for the living fine roots of arbors.During the rainy season,the C∶N,C∶P,and N∶P ratios of living fine roots in shrubland were lower than the values obtained during the dry season.Conversely,the C∶N and C∶P ratios of the living and dead fine roots of arbors were higher during the rainy season than in the dry season,whereas the values for the N∶P ratio were lower during the rainy season than during the dry season.The lower N∶P ratios of rainy season tended to indicate that plants in shrubland and arbor forest may be less P restricted during this season.(3)It was found that for both the living and dead fine roots of the two forest types,C contents were higher in trees growing on the upper slopes than in those growing on the middle and lower slopes,whereas the contents of N and P were higher in shrubs growing on the lower slopes and in arbors growing on the middle slopes.Furthermore,the C∶N,C∶P,and N∶P ratios of living and dead fine roots were found to be relatively higher in shrubs growing on the upper slopes.In the case of arbor forest,the C∶N ratios of living and dead fine roots in trees growing on the lower slopes were higher than other slopes,however the C∶P and N∶P ratios in trees growing on the upper slopes were higher than those of trees growing at other slopes,indicating that trees under these two forest types were strongly influenced by P limitation in the upper slopes,but only weakly affected on the middle and lower slopes.(4)Redundancy analysis revealed that forest type,available phosphorus,and season were the main factors influencing the contents and ratios of C,N,and P nutrients in fine roots,and could explain 18.8%,6.6%,and 6.5%of the observed variation,respectively.These findings indicate that the effects of changes in the N∶P ratio associated with differences in forest type,season,and slope should be taken into consideration when vegetation restoration is promoted,which will contribute to accelerating the restoration of karst ecosystems.