茂兰喀斯特区68种典型植物叶片化学计量特征

研究茂兰喀斯特区不同功能(类)群植物叶片的养分含量及化学计量特征,揭示其在时间和空间尺度上的变化规律,阐明碳(C)、氮(N)、磷(P)、钾(K)等养分含量与C∶N∶P间的相互关系,探讨N∶P对该区域植物生长的指示作用,以期能够更深入的了解其养分利用状况及适生性,为喀斯特森林的稳定性及维持机制提供理论依据。以茂兰喀斯特区68种典型植物为研究对象,分别测定不同生长阶段植物叶片的C、N、P和K含量,并计算其化学计量比。结果表明:研究区68种植物分属40科62属;其叶片C、N、P和K含量的几何平均值分别为445.87 g/kg、17.32 g/kg、1.35 g/kg和9.86 g/kg,C∶N的算术平均值为26.93,C∶P、C∶K、N∶P、N∶K和P∶K的几何平均值分别为330.93、45.22、12.85、1.76和0.137;C与N呈极显著负相关,N与P、K以及P与K均呈极显著正相关,N与C∶P和C∶K、P与C∶N、C∶K和N∶K以及K与C∶N、C∶P和N∶P均呈极显著负相关,且它们之间均具有二次函数、指数函数或幂函数的非线性耦合关系;从变异程度来看,C含量为弱变异,N、P、K含量及各元素的化学计量比则均属中等变异或强变异。从植物不同生活型来比较,各生长阶段的C含量均表现为灌木乔木草本,N、P和K含量均为草本灌木乔木,各元素的化学计量比则均为乔木灌木草本。从植物不同系统发育来分析,各生长阶段蕨类植物的N、P、K含量均要高于种子植物,而各元素的化学计量比则正好相反。从不同生长阶段来看,各功能(类)群植物生长期(或生长盛期)的养分含量均要高于落叶期(或生长末期);乔木、灌木和草本等不同生活型植物落叶期的C∶P、C∶K、N∶P和N∶K均要高于生长期;蕨类植物各元素的化学计量比不同生长阶段间差异都不显著;而种子植物的C∶P、C∶K、N∶P和N∶K则均表现为落叶期生长期。对比我国其他地区及全国和全球尺度上的研究结果,该区域植物的生长发育易受N和P素的双重限制,但又因功能(类)群及生长阶段的不同其受限的养分元素也存在一定差异,体现了对高度异质的喀斯特生境不同的适应策略;而植物体内较高的K含量则可能是提高其自身抗性、适应恶劣环境的重要因素。减少人为干扰、加之适当的保护,在植物生长期配以适量的N素添加,有利于其更好的生长发育,有助于提高喀斯特森林生态系统的稳定性和抗干扰性。研究结果揭示了喀斯特森林植物的适生机制,对喀斯特森林的保护具有重要的指导意义。

Leaf stoichiometric characteristics of 68 typical plant species in Maolan National Nature Reserve, Guizhou, China

The aim of this study is to better understand the nutrient utilization strategies and adaptations of plants, the spatio-temporal variation of leaf stoichiometric characteristics, and leaf nutrient contents. We explored the correlations between leaf nutrient contents and leaf carbon/nitrogen, carbon/phosphorus, and nitrogen/phosphorus ratios, and discussed the influence of nitrogen/phosphorus ratios on plant growth, which could provide a theoretical reference for maintaining ecosystem stability in the karst regions. In this study, we measured the following leaf traits: leaf carbon content (LC), leaf nitrogen content (LN), leaf phosphorus content (LP), and leaf potassium content (LK) in 68 species (belonging to 40 families and 62 genera) coexisting in Maolan karst forests. We also considered the influence of species'' taxonomic affiliation and calculated stoichiometry ratios for each plant species. The geometric averages of LC, LN, LP, and LK in the karst forests were 445.87, 17.32, 1.35, and 9.86 g/kg, respectively. The arithmetic average of leaf carbon/nitrogen ratio (C:N) was 26.93 and the geometric averages for leaf carbon/phosphorus ratio (C:P), leaf carbon/potassium ratio (C:K), leaf nitrogen/phosphorus ratio (N:P), leaf nitrogen/potassium ratio (N:K), and leaf phosphorus/potassium ratio (P:K) were 330.93, 45.22, 12.85, 1.76, and 0.137, respectively. There was a significantly negative correlation between LC and LN, while LP was positively correlated with LK. The LN was positively correlated with LP and LK, but negatively associated with C:P and C:K. Similarly, LP was positively correlated to LK, but negatively correlated with C:N, C:K, and N:K. However, LK was negatively associated with C:N, C:P, and N:P. Interestingly, all leaf stoichiometric characteristics, including C:N, C:P, C:K, N:K, and N:P, responded non-linearly (which could be expressed approximately as the quadratic function, exponential function, or power function) to LN, LP, and LK. Among all leaf traits, LC had a smaller coefficient of variance than LN, LP, LK, and the leaf stoichiometric ratios. In different growth phases, LC displayed the highest value in shrubs but the lowest in herbs. Herbs also displayed the highest LN, LP, and LK values, while trees displayed the lowest values of these three variables. Among all stages of plant growth, leaf stoichiometric ratios (including C:N, C:P, C:K, N:K, and N:P) were highest in trees and lowest in herbs. It is worth noting that LN, LP, and LK in ferns were greater than those in spermatophytes. On the contrary, leaf stoichiometric ratios in ferns were lower than those in spermatophytes. In each functional group of plants (including trees, shrubs and herbs), leaf nutrient contents were higher during the peak periods of plant growth than at the end of the growth period. Inversely, the C:P, C:K, N:P, and N:K ratios were greater in the later growth period than those in early growth periods in all karst forest species. In ferns, there were no statistically significant differences in leaf stoichiometric ratios between the early stage of growth and the later period of growth. However, the leaf stoichiometric ratios (C:P, C:K, N:P, and N:K) of spermatophytes were higher during the defoliating periods than those during the early stage of growth. Compared with previous studies of the local and global researchers, the growth of trees, shrubs, and herbs at different growth stages was easily influenced by the highly heterogenous nitrogen and phosphorus supply in the karst region. Especially, the higher potassium contents in plants from the karst forests might increase plant ability to adapt to the unfavourable environment. Therefore, it is necessary to provide enough protection with lower anthropogenic disturbances and add extraneous nitrogen in the growth stage, in order to promote plant growth and enhance ecosystem stability and plant resistance. The study also suggested that several forest plant strategies existed for survival in a karst environment, and the results provided an important reference for forest management and conservation in karst areas.