桂西北喀斯特森林植物-凋落物-土壤生态化学计量特征

探明我国西南喀斯特生态脆弱区植被恢复重建背景下, 森林植物、凋落物与土壤碳(C)、氮(N)、磷(P)化学计量特征有助于深入地认识喀斯特森林生态系统养分循环规律和系统稳定机制。该文选取桂西北典型喀斯特地区域3个原生林群落和3个自然恢复28年的次生林群落, 研究其“植物-凋落物-土壤”连续体的C、N、P化学计量学特征及其内在关联。结果表明: 1)圆果化香树(Platycarya longipes)、伞花木(Eurycorymbus cavaleriei)和青檀(Pteroceltis tatarinowii)以及圆叶乌桕(Sapium rotundifolium)、八角枫(Alangium chinense)和黄荆(Vitex negundo) 6种植物的C、N、P平均含量分别为427.5、21.2、1.2 mg·g^-1; 凋落物C、N、P平均含量分别为396.2、12.7、0.9 mg·g^-1, 而表层土壤(0-10 cm) C、N、P平均含量分别为92.0、6.35和1.5 mg·g^-1。2)原生林N再吸收率(平均值为42.7%)高于次生林(平均值为36.5%), P再吸收率(20.4%)显著低于次生林(32.3%) (p < 0.05); 6个森林群落N的再吸收率均大于P的再吸收率。3)不同群落凋落物的C:N值差异不显著, 原生林植物的C:N值小于次生林、土壤C:N显著大于次生林; 原生林土壤C:P与次生林无显著差异, 植物与凋落物C:P小于次生林; 原生林凋落物与土壤N:P值小于次生林, 植物N:P比平均值均为17.4。4)研究区典型森林群落植物中N和P含量呈显著的正相关关系, 植物C:N与N:P、C:P与N:P比值均无明显相关关系; 经过对数变换后的土壤C:N与N:P呈显著负相关关系, 凋落物的C:P与N:P值呈极显著正相关关系。研究结果可为我国西南典型喀斯特脆弱生态区的生态功能恢复与植被重建提供科学依据。

Stoichiometric characteristics of plants,litter and soils in karst plant communities of Northwest Guangxi

The objectives of this study were to characterize the C:N:P stoichiometry of the “plant-litter-soil” continuum and to better understand nutrient cycling and stability mechanisms in karst forest ecosystems in Southwest China. Three representative forest sites were selected for each of the primary and secondary communities (28 years of natural restoration) in Northwest Guangxi, and measurements were made on carbon (C), nitrogen (N), and phosphorus (P) contents in plants, litter and soils. Compared with other regions, the plants in karst forest ecosystems had relatively lower C content and higher N content, with a lower C:N ratio in consistency with the characteristics of plants. After 28 years of natural recovery, N and P absorption in secondary forests were at a relatively stable state compared with the primary forest communities. The values of N:P ratio varied from a range of 16-19 in the primary forest communities to 17-19 in the secondary forest communities, without apparent difference in the mean vale between the two contrasting community types. Soil organic C, N and P in karst forests occurred primarily in the top 0-10 cm soil layer, at 92.0 mg·g^-1 C, 6.35 mg·g^-1 N, and 1.5 mg·g^-1 P, respectively. In contrast, the nutrient utilization efficiency and nutrient resorption rate were lower in karst forest plants than in other plant types, with karst forest plants exhibiting a relatively rapid nutrient turnover rate. The N resorption rate was lower, and the P resorption higher, in the primary forest communities than in the secondary forest communities, indicating that the higher N deficiency and lower P deficiency of the primary forest communities compared with the secondary forest communities. Determination of the C:N:P stoichiometric characteristics in the plant-litter-soil continuum in this study provides a scientific guidance for restoration of the vulnerable karst ecosystem in Southwest China.