典型喀斯特峰丛洼地植被群落凋落物C∶N∶P生态化学计量特征

Litter C∶N∶P ecological stoichiometry character of plant communities in typical Karst Peak-Cluster Depression

为了解典型喀斯特峰丛洼地植被群落凋落物养分空间分异以及其生态化学计量特征,分析了4个不同演替阶段植被凋落物现存量、C、N、P含量及C、N、P元素比值关系在不同坡位间的差异。结果表明:(1)不同演替阶段群落凋落物现存量和C、N、P含量、N∶P值随植被正向演替而升高;C∶N值和C∶P值随植被正向演替而下降。(2)凋落物C含量、C∶N值、C∶P值和N∶P值在不同坡位表现为上坡位较高、下坡位较低;P含量的变化规律与之相反,N含量则没呈现很明显的规律性(P<0.05)。典范对应分析(CCA)结果表明演替阶段和坡位对凋落物积累、养分分布和存储影响最大,坡度、坡向和裸岩率也有较大影响。(3)N∶P值是制约凋落物分解和养分循环的重要因素。凋落物在P素较低的情况下具有较高的N及木质素含量(即较高的N∶P值),分解速率较低,较低的N∶P值使凋落物更易分解。N素在3个坡位的不显著差异以及P素的显著差异反映了P含量波动对喀斯特峰丛洼地植被凋落物N∶P值和分解速率变化的影响。推测下坡位及幼龄林群落由于具有较低的N∶P值,其凋落物分解速率相对较快,养分的存储量较少。因此,上坡位、成熟林群落的凋落物有利于积累养分。

Ecological stoichiometry theory,which was put forward to investigate nutrient cycling of marine ecosystem by Reiners,has been incorporated successfully into many research fields such as decomposition dynamics,nutrient cycling and biology ecological response to global change and so on.The ratio of carbon∶nitrogen∶phosphorus（C∶N∶P） in planktonic biomass was found to be well-constrained in marine ecosystem.Some analyses indicated the existence of analogous ratios in plants,suggesting that the theory may be applicable in terrestrial ecosystems.Here we tested if the ecological stoichiometry theory is applicable to the typical Karst Peak-Cluster Depression,where our previous studies showed that soil nutrient in the upward slope was higher than in the downward slope.It was speculated that the possible reason could be that the litter carbon,nitrogen,phosphorus and carbon： nitrogen： phosphorus（C∶N∶P） ratio were the same as soil nutrient.It was also inferred that litter C∶N∶P ratio could play an important role in the decomposition and nutrient cycling of Karst forested ecosystems.In this study,the slope gradients of litter carbon,nitrogen,phosphorus and their mass ratio in four vegetation succession stages was analyzed in order to understand the spatial differentiation and ecological stoichiometry trail of litter nutrient of plant communities in the typical Karst Peak-Cluster Depression.The results of this study showed that（1） carbon,nitrogen,phosphorus and N∶P ratio in litter standing crops increased from the early to the later succession stages,while the ratio of C：∶N and C∶P decreased.（2） The content of litter carbon,ratio of C∶N,C∶P and N∶P in upward slope were larger than that in downward slope,while the reverse trend was exhibited in phosphorus content and no significantly different nitrogen content was observed among slopes（P0.05）.The result of Canonical Correspondence Analysis（CCA） showed that the succession stages and slope position had greater impact on the litter accumulation,nutrient distribution and storage,compared to that of slope and bare rock.（3） It is known that the litter decomposition and nutrient cycling is mainly constrained by the N∶P ratio.Previous research indicated that litter P concentrations and low N∶P ratio did not limit decomposition,but litter N concentrations and high N∶P ratios showed contrary results.The lack of significant differences among N elements among slopes and significant difference of P elements reflected that the fluctuations of P content affected vegetation litter N∶P ratio and the changing decomposition rate in typical Karst Peak-Cluster Depression.Lower N and high lignin content（namely higher N∶P ratio） under the case of low P leading decomposition rate become lower,thus lower N∶P ratio is easy for litter decomposition.It is presumed that litter decomposed faster in the downward slope and in young-growth plant communities than that in the upward slope and in old-growth plant communities due to the lower N∶P ratio.As a result,less litter nutrient was stored in the downward slope and in young-growth plant communities.Therefore,litter in the upward slope,old-growth forests were conducive to the accumulation of nutrients.