黄土丘陵区退耕地先锋群落演替过程中细根特征的变化

采用空间序列取代时间序列的方法,对退耕时间分别为2、4、6和8年的退耕地群落细根特征进行了分析,以探讨退耕地植被演替过程中细根特征在土壤剖面上的变化及其在演替过程中的作用.结果表明:(1)群落细根根长密度和根面积密度随植被演替显著增加;比根长、比根面积和地下/地上生物量也有增加趋势;细根平均直径随植被演替波动,但有减少趋势;(2)在土壤剖面上根长密度、根面积密度和根系生物量均随土壤深度的增加而降低.其中超过63%的根长、61%的根面积和72%的生物量分布在0～20cm的表层土壤中;(3)根径级统计表明,多数细根直径在0～0.5和0.5～1.0mm之间,这两级细根长度占细根总长度的80%以上;(4)逐步回归分析表明,植被演替过程中细根特征的变化主要与土壤有效氮(第2年)、有效磷(第2～8年)和土壤水分(第8年)的含量有关,且随着植被演替,2～6年退耕地中细根特征与土壤资源正相关,而第8年中二者呈负相关.这可能与植物生长对资源的需求与土壤提供资源的能力之间的平衡有关.研究表明,退耕地植被演替过程对土壤资源有一定影响,尤其是土壤水分含量显著减少;而土壤水分等土壤资源的变化又对群落产生影响,导致茵陈蒿先锋群落向地带性...

Primary succession of algal community structure in desert soil

The microbiotic crust study is among new focuses in investigating on the desertification control. Based on determination of algal crusts with different successive ages (4-, 8-, 17-, 34-, 42-year-old) and unconsolidated sand in the desert area, species composition and clustering analyses were carried out in this study. Results on successional orientation revealed that (1) the abundance of Cyanophyta, specially of Scytonema javanicum gradually decreased; (2) the abundance of Chlorophyta, Bacillariophyta and a species of Cyanophyta, Phormidium tenue increased; (3) the biodiversity increased gradually with the community succession; and (4) biomass of microalgae increased at the early stage, but decreased at the later stage due to the abundance of lichens and mosses. But, the speed of natural succession was so slow that the community-building species was still the first dominant species after 42 years, except that its dominant degree decreased just slightly. However, successive speed and trend were affected by water, vegetation coverage, terrain, time and soil physico-chemical properties as well, especially Mn content in the soil appeared to have a threshold effect.

The effect of land management on plant community composition, species diversity, and productivity of alpine Kobersia steppe meadow

Grassland degradation is widespread and severe on the Tibet Plateau. To explore management approaches for sustainable development of degraded and restored ecosystems, we studied the effect of land degradation on species composition, species diversity, and vegetation productivity, and examined the relative influence of various rehabilitation practices (two seeding treatments and a non-seeded natural recovery treatment) on community structure and vegetation productivity in early secondary succession. The results showed: (1) All sedge and grass species of the natural steppe meadow had disappeared from the severely degraded land. The above-ground and root biomass of severely degraded land were only 38 and 14.7%, respectively, of those of the control. So, the original ecosystem has been dramatically altered by land degradation on alpine steppe meadow. (2) Seeding measures may promote above-ground biomass, particularly grass biomass, and ground cover. Except for the grasses seeded, however, other grass and sedge species did not occur after seeding treatments in the sixth year of seeding. Establishment of grasses during natural recovery treatment progressed slowly compared with during seeding treatments. Many annual forbs invaded and established during the 6 years of natural recovery. In addition, there was greater diversity after natural recovery treatment than after seeding treatments. (3) The above-ground biomass after seeding treatment and natural recovery treatment were 114 and 55%, respectively, of that of the control. No significant differences in root biomass occurred among the natural recovery and seeded treatments. Root biomass after rehabilitation treatment was 23-31% that of the control.