土壤氮磷养分对植物生长的限制性可通过植被的N:P化学计量特征来反映。该研究以常绿阔叶林演替系列为对象,将N:P作为诊断指标,揭示常绿阔叶林次生演替过程中植物群落的N:P化学计量特征和养分限制作用。结果显示:1)物种水平的N:P大小不一,但演替系列总体的变化特征表现出了较高的一致性。2)在群落水平上,次生演替初期的灌草丛N:P极小(7.38),远远低于14,当演替进入灌丛阶段,N:P显著增高到19.96,在进入演替中期的针叶林(14.29)和针阔混交林(14.21)时,N:P显著下降到14~16之间,演替中后期的木荷(Schima superba)群落(18.77)和栲树(Castanopsis fargesii)群落(20.13)的N:P发生了显著的升高过程。根据以往对N:P临界值的确定,可以认为,常绿阔叶林次生演替初期的植物群落生产力主要受到氮素的限制作用;演替中期的针叶林和针阔混交林主要受氮磷的共同限制,但以氮素的限制作用更为强烈;演替中后期植物群落主要受到土壤磷素的限制作用。

Aims It is well documented that nitrogen (N) and phosphorus (P) are the two main growth-limiting nutrients for plants in many natural environments. Plant N:P ratio has proved useful as an indicator of shifts from N (P) to P (N) limitation because it is easily determined and compared. However, little is known about the plant N:P ratio in evergreen broad-leaved forests (EBLF), particularly the pattern along secondary succession. Therefore, our goal was to examine the relationship between the form of nutrient limitation and secondary successional stage by using the N:P ratio of plant leaves (ratio of N to P concentration) as an indicator.
Methods The research was completed in Tiantong National Forest Park (29°52' N, 121°39' E, 200 m elevation), Zhejiang Province, East China. Leaf N and P concentrations of dominant tree species along a secondary succession gradient of EBLF were quantified to provide canopy N:P ratios for different communities. Leaf N and P concentrations of common plant species in a given community were then determined to emphasize the relationships between differences in the N:P ratios among species at each successional stage.
Important finding Shifts in the N:P ratios of species were consistent along the successional series, although the N:P ratios of different species in a given community varied considerably. At the community level, the lowest N:P ratio (7.38) was found in grassland, which was usually considered a primary stage of EBLF succession. Thereafter, the N:P ratio increased to 19.96 in the shrub stage, declined to an average of 14-16 in the mid-stages of succession, including coniferous forest and coniferous-broadleaved mixed forest, and increased at the end stages of succession (e.g. 18.77 in the Schima superba community and 20.13 in the Castanopsis fargesii community). These results suggest that the productivity of vegetation in the Tiantong region is N-limited in the primary stages of succession, N- and P-limited in the mid-succession stages and probably P-limited in the shrub and mature EBLF stages.