宁夏回族自治区沙坡头地区半荒漠土壤中藻类的垂直分布

Vertical distribution of algae in semi-desert soil of Shapotou area,Ningxia Hui Autonomous Region

对沙坡头地区半荒漠土壤中藻类植物的垂直分布进行了为期一年多的采样、分析 ,结果发现结皮层有藻类植物 2 4种 ,蓝藻及其丝状种类的比例最大 ;结皮下 0～ 5 0 mm和 5 0～ 1 0 0 mm层次分别有 1 5种、1 0种 ,且都以硅藻及单细胞种类最丰富 ;深层次出现的种类在浅层次都出现 ;1 0 0 mm以下层次没有任何藻种发现。生物量从表及里随深度的增加而锐减 ,99%的分布在结皮层 ;就结皮层中 78%的在 0～ 0 .1 mm层次 ,96%在 0～ 1 .0 mm深度。种类数变化在结皮层和结皮下 0～ 5 0 mm层次都与降水量相关 ,而结皮下 5 0～ 1 0 0 mm层次基本不变。

Shapotou (37°27′N, 104°57′E) is located in the southeast of Tegger Desert, Zhongwei County, Ningxia Hui Autonomous Region of China. The average annual precipitation is ca.186 mm (mainly in summer), evaporation more than 2900 mm. The windy days (>5 m/s) are more than 200 days each year. Forty five years ago there was only shifting sand dunes. Since 1956 drought-resistant trees are batch planted each several years under irrigation and non-irrigation conditions. Now the stable algal crusts had formed on the topsoil of those sand dunes. And due to ecological roles in reducing soil erosion degree, algal crusts had been widely investigated from many perspectives. However, no study has proposed algal distribution in the whole soil layer of desert and semi-desert environment, which actually distribute in the deeper layer and affect soil structure and formation. The purposes of this research are to determine the depth of algae distribution in this semi-desert soil, and also to examine the regularities of their distribution and possible mechanism on soil amelioration. Therefore the algal crusts, soil samples of 0～50 mm, 50～100 mm, 100～150 mm and 150～500 mm depths below the crusts from the surface to lower levels were separately collected and analyzed at the interval of every two months from May 1997 to October 1998. All data were analyzed by statistical software (Statistica 6.0) The results showed that 24 taxa were found in the crust layer, 15 and 10 taxa separately in 0～50 mm and 50～100 mm depth of below the crusts, no algae in the ranges of below 100 mm depth. Among them the widespread species were Nostoc sp, Microcoleus vaginatus, Navicula cryptocephala, Chlorella vulgaris, Euglena sp, Lyngbya cryptovaginatus, Phormidium tenue, Scytonema javanicum, Desmococcus olivaceus and Chlorococcum humicola in the crust layer, but blue-green algae and filamentous species were the most abundant. In 0～50 mm and 50～100 mm depth diatoms and unicellular species dominated, namely Hantzschia amphioxys, N. cryptocephala and Diatoma vulgare var. ovalis often distributed in 0～50 mm depth, while H. amphioxys and N. cryptocephala in 50～100 mm ranges. In addition to all species that appeared in the lower layers they could be found in the upper ones as well. And the global distribution mechanism of algae in the arid and semi-arid environments was discussed as well. The vertical distribution of algal biomass dramatically decreased with the soil depths from the surface to lower levels, and more than 99% biomass concentrated in the crust layer. Within crust 78% biomass distributed in 0.1 mm upper depth, 96% in the 1.0 mm upper depth. The reason was that there was not enough oxygen and light intensity for alage growth in below 1.0 mm depth.Seasonal variance of species number in the crusts layers and 0～50 mm ranges was closely related to local precipitation, and the highest value occurred in the rain most abundance season (August), but it was basically stable in deeper layer (50～100 mm depth). This was attributed to rainwater seep. During the relative rainy season those species with small volume and easy motion were oozed down from the upper layers, and concentrated in the deeper layer. After their long-term metabolic activities the soil of deeper layer will be improved.