我国西南山地喀斯特植被的根系生物量初探

在贵州茂兰喀斯特森林国家自然保护区内,选取2种立地条件上(岩石和土壤分别占优势)的5个植被恢复阶段(草本群落、灌草群落、灌木群落、次顶极常绿落叶阔叶林和顶极常绿落叶阔叶林)共10个样地,利用平均标准木机械布点法对根系进行采集,分析了其生物量总量、不同根系径级的分配格局和地下空间的分布规律。结果表明:1)喀斯特植物群落的正向植被恢复进程极显著地增加了地下生物量(p0.001),从草本群落的2.63Mg·hm–2增加到顶极森林群落的58.15Mg·hm-2;同一恢复阶段的石生和土壤立地上根系生物量的差异不显著(p0.05),在顶极和次顶极常绿落叶阔叶林阶段,石生立地的根系生物量高于土壤立地,而灌木、灌草和草本群落阶段则相反。2)同一恢复阶段的石生立地的粗根生物量均高于土壤立地,但差异不显著(p0.05),而细根和小根生物量则从石生到土壤立地显著增加(p0.05);随着喀斯特植被的恢复,石生和土壤立地上粗根占总根系生物量的比例均逐渐增加。3)石生立地根系的分布以水平扩散和穿梭为主,无垂直层次分布;而土壤立地各恢复阶段的根系生物量主要集中在地面到地下10cm的垂直空间内;在不同的土层深度,粗根占所有根径级生物量的80%,且随土层加深,其比例降低。该研究不仅填补了喀斯特植被根系生物量观测的空白,为估算我国西南喀斯特地区植被的总生物量和生产力提供了本底数据,也为进一步研究喀斯特森林稳定性维持机制和喀斯特石漠化防治与植被适应性修复奠定了基础。

Root biomass of karst vegetation in a mountainous area of southwestern China

Aims The karst vegetation in southwestern China, growing in a harsh environment, is a specific ecosystem that can lead to land degrActation and rocky desertification under human disturbances. The root biomass (RB) of the karst vegetation is very difficult to measure due to the karst geomorphology and rigorous habitat and is therefore rarely reported. However, RB is a key factor in understanding ecosystem stability in this region and is an indicator of vegetation restoration in different rocky desertification stages. Our objective was to estimate the RB of karst plant communities in each restoration stage in Maolan National Natural Reserve of Guizhou Province, southwest-ern China.Methods We investigated 40 plots. The karst vegetation was divided into five restoration stages according to its community physiognomy, dominant species, habitat types, mean tree diameter at breast height (DBH), mean tree height and tree density, as well as disturbances of rocky desertification: herb community, herb-scrub community, scrub-shrub community, sub-climax community and climax community of evergreen-deciduous broadleaved mixed forests. We divided the karst plant communities into rock-dominated and soil-dominated stands. We measured root biomass in different soil layers and in various root diameter classes and estimated it in 10 representative plots using the Specific Sampling Method of Averaged Standard Tree.Important findings Forward restoration of karst vegetation significantly increases its RB from 2.63 Mg·hm~(-2) in rock-stand herb community to 58.15 Mg·hm~(-2) in rock-stand climax evergreen-deciduous broadleaved mixed forest (p < 0.001). In the same restoration stage, RB of rock-stands and RB of soil-stands are not significantly different (p > 0.05). Total RB in rock-stand climax and sub-climax communities are higher than that in soil-stand ones, but it is reversed in the other three restoration stages. In the same restoration stage, coarse RB in the rock-stand community is not significantly different from soil-stand community (p > 0.05). The fine and small RB in the soil-stand community is significantly higher than in the rock-stand community (p < 0.05). The biomass ratio of coarse versus total roots in rock-stand and soil-stand communities increases gradually with forward restoration. The RB of rock-stand communities is mainly distributed on the rock surface or in the rock gaps, and has no obvi-ous vertical pattern of distribution. The distribution of RB in soil-stand communities, however, is concentrated in the top 10 cm of the soil. In different soil layers the ratio of coarse to total RB is ca. 80%; it decreases with in-creasing soil depth.