Growth Of Soil Algae On Different Substrates-An Ecosystem Approach To Soil Crusts

In the experiments of the thesis, the growth of filamentous green algae and cynobacteria in two kinds of soil was studied:sand from Eerduosi desert (Inner Mongolia) and washed sand from Northern Germany. Four kinds of additives was added to these two soils to find out if the growth of algae would be affected. The four additives were:clay, biochar, organic matter and geohumus. And the best quantity of these additives which could help for algal growth was tried to find out. So 30% and 10% of clay,30% and 10% of organic matter,30% and 10% of biochar,1% of geohumus and a combination of all (clay:organic matter:biochar:geohumus= 10:10:10:1) were prepared. Before adding the algae to the soil, the water holding capacity and soil pH were tested. The results showed that the water holding capacity of Mongolian soil was higher than that of washed sand. And when 30% of the organic matter added to the soil, the water holding capacity was greatly improved.The green algae Klebsormidium flaccidum used in experiments were from Goettingen University EPSAG experimental institution. Algae were cultured in agar with BBM+V medium at the beginning, and then transferred them to liquid BBM+ SE medium. Incubation temperature was 25℃, light intensity was 5000 lux with 16 hours light and 8 hours dark. Green algae were transplanted to the soil in flower pots (100mL) after growing in the liquid medium about one month.The wild algae used in experiments were collected from the sandy part of the ReviTec experimental field at the University of Bremen. They were studied under the light microscope:the co mmunity consists mainly of cyanobacteria, as well as of small amounts of filamentous green algae and single-cell algae. For the flower pot experiments, the wild algae were separated and enriched from the soil with a floatation device. The pots were cultured in the greenhouse and watered every three days. After 3 months, the experiments were ended. Soil pH was measured with the pH meter and soil crust stability with the penetrometer. The abundance of soil algae was assessed with the fluorescence microscope. A new indirect counting method was developed:from each sample (treatment),15 slides were prepared and 20 microscope fields (magnification 10 x 40) were read according to a virtual grid. The algae in each field were identified (cyanobacteria, filamentous green algae, single cell green algae). To analyze the data, the General Linear Model from SPSS was used.The results show a better growth of green algae Klebsormidium flaccidum than that of the wild algae in general and a better growth of algae in washed sand than in Mongolian sand. When using biochar and clay as additives, the abundance of green algae was increased significantly. The addition of geohumus was best for the growth of wild algae. The growth of algae changed the soil pH significantly. The pH values of washed sand and Mongolian sand were both around 7.3 at the start of the experiment, before the growth of algae. After the experiments, pH of both kinds of soil is lower: Mongolian sand's pH was around 6.7 and the pH of washed sand was around 6.4. The results of soil crusts showed that the crust in Mongolian sand was stronger than that in washed sand. When adding clay and biochar, the strength of soil crust was increased. However, when adding organic matter, the soil crust was least developed, even less than in the control:organic matter helps the soil to become loose and soft.The correlation model of SPSS was used to analyze the relationship between soil crusts, soil pH and abundance of green algae and wild algae. The results showed that the pH of the soil and the strength of crust were influenced greatly by abundance of green algae. When the abundance of green algae increased, the strength of soil crust increased. The abundance of green algae was highest when the soil pH was around 6.8-6.9. However, the abundance of wild algae does neither correlate with the strength of the soil crust nor with pH.My experiments showed that biochar and clay as soil amendments can improve the performance of soil algae. They will play an important role in combating desertification. From the view of algae, green algae grow better in moist condition and it is not clear how the performance of both will be in real desert condition.