| Biological soil crust (biocrusts) that constituted by pioneer organismes such as algae,cyanobacteria, mosses and lichens extensively developed in the Loess Plateau region after the“Grain for Green” eco-project was implementated in the region. So far, studies on speciescomposition and distribution of cyanobacteria in the biocrusts in the Loess Plateau region werefresh. In the paper, diversity charecteristic of cyanophytes was studied in biocrusts under differentenvironment conditions on the Loess Plateau region. Cyanobacteria in the biocrusts from theLoess Plateau region was cultured, observed and identified. In addition, we analyzedShannon-Weiner diversity index, species richness, dominant species and biomass in the biocrustsunder field and laboratory conditions so as to determine the influencing factors of thetemporal-spatial distribution characteristics of cyanophytes. The paper was aimed atunderstanding ecological restoration effects of cyanophytes further, including soil fixation andsuccession mechanism in this region, also providing the scientific evidence for soil and watererosion as well as desertification control. As far as our knowledge, the paper was the one of theearliest studies on diversity characteristic of cyanophytes in the Loess Plateau region. The main resultsare as follows.(1) We found76species of cyanophytes in the biocrusts of the Loess Plateau region,which belongs to13genera and5families. In the study area, dominant familiy and genuswere evident which were Oscillatoriaceae and Oscillatoria, respectively. Filamentouscyanobacteria were the dominant species in cyanophytes which accounted for87%. Familiesand genera were Chroococcaceae, Scytonemataceae, Rivulariaceae, Oscillatoriaceae, Nostocaceaeand Chroococcus, Synechocystis, Tolypothrix, Scytonema, Raphidiopsis, Symploca, Lyngbya,Oscillatoria, Phormidium, Microcolus, Nostoc, Anabaena. (2) In the study area, Shannon-Weiner diversity index of cyanobacteria and algaebiomass were ranged in the order of water-wind erosion crisscross region> water erosionregion> wind erosion region. In same erosion region, Shannon-Weiner diversity index ofcyanobacteria on the shady slopes were greater than that on the sunny slopes, whileShannon-Weiner diversity index gradually ascended from higher to lower positions on thesame aspect. In the soil profiles, Shannon-Weiner diversity index of cyanobacteria weredecresing against the increase of soil depth, dominanted cyanobacteria species were mainlyin the0-2cm layers and seldom exist in the lower layers. Futhermore, cyanobacteria speciesin the0-0.5cm layer accounts for85%of that in all layers. In different erosion regions,Shannon-Weiner diversity index of cyanobacteria presented as that: water-wind erosion crisscrossregion> water erosion region> wind erosion region, they were2.22bit,2.20bit and2.14bitseparately. No significant difference was found between the cyanobacteria diversity ofwater-wind erosion crisscross region and water erosion regions, while diversity in the winderosion region was significantly lower than that in the water erosion region or that in thewind-water crisscross erosion region. In addition, richness and the dominant species weredifferent in the three erosion regions. Cyanobacteria richness was greatest (39) in the water-winderosion crisscross region, followed by the water erosion region (26) and the wind erosion region(20). The dominant cyanobacteria species in the water-wind erosion crisscross region, watererosion and wind erosion region were Lyngbya allorgei, Phormidium calciola and Oscillatoriagranulate, respectively. Variation trend of algal biomass were the same as that of Shannon-Weinerdiversity index in the three erosion regions. Dominant cyanobacteria species on the shady slpoesand the sunny slopes were Phormidium angustissimum and Lyngbya allorgei, respectively. In soilprofiles, Cyanobacteria diversity showed descending trend with the increase of soil depth,dominant cyanobacteria species are mainly in the0-2cm layers and seldom exist in lower layers,among them, cyanobacteria species in the0-0.5cm layer accounts for85%of that in all layers.(3) Cyanophyte diversity was influenced by the age of development and the seasons.Shannon-Weiner diversity index were increasing before stabilizing with years of biocrustsdevelopment, when the age of development was over8years, Shannon-Weiner diversityindex were gradually stable. Shannon-Weiner diversity index of cyanobacteria should beranged in the order of rain season> before rain season> after rain season. In the area,significant differences were found in Shannon-Weiner diversity index between other years of development and farmland. Among richness of cyanobacteria in different years of biocrusts,cyanobacteria richness in8years of biocrusts was the highest, and that in farmland was lowest.The first half year of development was the fastest growth stage of cyanobacteria. Shannon-Weinerdiversity index in different seasons were showed as rainy season> before rainy season> afterrainy season, they were2.96bit,2.85bit and2.66bit, separately; Shannon-Weiner diversity indexof cyanobacteria at rainy reason was significantly higher than those after rainy season. Thevariation trend of cyanobacteria richness at different seasons was in accordance with that ofShannon-Weiner diversity index, they were35,32and26. Dominant cyanobacteria species beforerainy season was Phormidium angustissimum, which was the same with that after rainy season,Lyngbya allorgei was the dominant species in the rainy season. Algae biomass was showed in theranged of before rainy season> rainy season> after rainy season.(4) Cyanophyte diversity was related to moisture and tempreture of the environment.The result showed that precipitation was the prime and vital influencing factor on thediversity of Cyanophyte. There was a negative correlation between precipitation andShannon-Weiner diversity index and richeness of Cyanophyte. Tempreture was the secondmost important factor. The correlation analysis indicated that soil total nitrogen and phosphorusand available phosphorus were relevant to diversity of cyanobacteria, among them, diversity ofcyanobacteria has a significantly negative correlation with soil total nitrogen, but a significantlynegative correlation with soil total phosphorus and available phosphorus. Different cyanobacteriaspecies influenced by different environment facters have different ecological suitability. |
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