亚热带不同植被恢复阶段生态系统N、P储量的垂直分配格局

Vertical distribution pattern of N and P storage of ecosystem at different vegetation restoration periods in the subtropical region of China

氮(N)、磷(P)是影响生态系统生产力的主要养分因子,为科学评估植被恢复对生态系统N、P积累、分配及其耦合关系的影响,采用时空互代法,以湘中丘陵区地域相邻、环境条件基本一致,且处于不同恢复阶段的4个植物群落(4—5年灌草丛、10—12年灌木林、45—46年马尾松针阔混交林和>90年常绿阔叶林)作为一个恢复序列,设置固定样地,采用收获法和建立主要树种各器官生物量相对生长方程估算群落生物量,采集植被层(叶、枝、干、根)、凋落物层(未分解层、半分解层、已分解层)、土壤层(0—10、10—20、20—30、30—40 cm)样品,测定全N、全P含量,估算生态系统各组分(植被层、凋落物层、土壤层)全N、全P储量。结果表明:植被层全N、全P储量均随植被恢复增加,全N储量增长速率呈先慢后快的特征,而全P储量则呈慢—快—慢增长,地上(叶、枝、干)、地下(根)部分表现为异速增长;随植被恢复,凋落物层全N、全P储量先增加后下降,增长速率为先快后慢,4—5年灌草丛全N、全P储量最低;土壤层全N、全P储量随植被恢复显著增加(P<0.05),全N储量增长速率呈快-慢-快特征,而全P储量呈先慢后快特征;从4—5年灌草丛到>90年常绿阔叶林,生态系统全N、全P储量分别增加了6031.5、454.7 kg/hm^(2),增幅分别为231.5%、41.1%;不同恢复阶段生态系统全N、全P均主要存储于土壤中,分别占生态系统全N、全P储量的87.3%—99.0%、96.5%—99.9%;生态系统全N、全P储量的垂直分配格局随植被恢复而变化,植被层全N、全P储量贡献率增加,而土壤层全N、全P储量贡献率下降,凋落物层变化较小;植被层、凋落物层、土壤层全N、全P含量之间呈极显著正相关关系(P<0.01),随植被恢复,植被层、凋落物层、土壤层N、P含量协同发展,P变化滞后于N。因此,可通过合理的经营管理措施促进植被恢复,提高植被层生物量以及N、P间的耦合协调性,以提高生态系统养分固持潜力和促进养分间的高效协调利用。

Nitrogen(N) and phosphorus(P) are the main nutrient factors affecting ecosystem productivity. This study investigated the response of coupling relationship between N and P to environmental change during vegetation restoration, and assessed the effects of vegetation restoration on N and P accumulation and distribution in ecosystem. According to the restoration gradient, four fixed plots were respectively established in four distinct plant communities: 4—5 years scrub-grassland, 10—12 years shrubs, 45—46 years Pinus massoniana coniferous and broadleaved mixed forest, and >90 years evergreen broad-leaved forest by using the space-for-time substitution method. The community biomass was estimated by using the total harvesting method to establish the relative growth equation of organ biomass of main tree species. The samples of vegetation layer(leaves, branches, stems and roots), litter layer(un-decomposed, semi-decomposed and decomposed), and soil layer(0—10, 10—20, 20—30, 30—40 cm) were collected to determine total N and total P contents, and estimated the N and P storage of each component of ecosystem. The results showed that the N and P storage in vegetation layer increased with vegetation restoration, in which the growth rate of N storage was slow first and then fast, while the P storage presented slow-fast-slow. The aboveground(leaves, branches, stems) and underground(roots) parts showed allometric growth. As vegetation restoration, the N and P storage in litter layer increased first and then decreased, and the growth rates were fast first and then slow. The N and P storage in soil layer increased significantly with vegetation restoration(P<0.05), in which the growth rate of N storage showed fast-slow-fast, while the P storage was slow first and then fast. From 4—5 years scrub-grassland to >90 years evergreen broad-leaved forest, ecosystem N and P storage increased by 6031.5 kg/hm^(2) and 454.7 kg/hm^(2), with the increase ranges of 231.5% and 41.1%, respectively. In different restoration periods, soil N and P storage were the primary component in ecosystem, accounting for 87.27%—98.99% and 96.5%—99.9% of N and P storage in ecosystem, respectively. The vertical distribution pattern of N and P storage in ecosystem varied with vegetation restoration, among which the contribution rate of N and P storage in vegetation layer increased, but that in soil layer decreased, and that in litter layer changed little. The contents of total N and total P in vegetation layer, litter layer and soil layer had significantly positively correlation(P<0.01). During vegetation restoration, N and P contents in vegetation layer, litter layer and soil layer developed synergistically, but the change of P lagged behind that of N. Therefore, reasonable management measures can be adopted to promote vegetation restoration, improve the biomass of vegetation layer and the coupling and balance of N and P, so as to enhance the nutrient fixation potential of ecosystem, and facilitate the efficient and coordinated utilization of nutrients.