توصيفگر ها :
مرتع , چرخه انجماد-ذوب , چرخه خشك-مرطوب شدن , تغييرات اقليمي , پتاسيم توده زنده ميكروبي , توليد و دوام آنزيم اوره آز
چكيده انگليسي :
Rangelands are among the most important ecosystems on the earth, which cover a large area of the earth. Today, climate changes are evident all over the world, and rangelands are not excluded from the impact of this global phenomenon. Global warming is a phenomenon that has caused more freeze-thaw and dry-rewet cycles in soil ecosystems and Rangelands. The occurrence of these cycles occurs more in areas with moderate climate. In this research, which includes two studies, by applying 1, 3 and 5 freeze-thaw cycles in the first study and 1, 3 and 5 dry-rewet cycles in the second study, in two Rangeland soils located in Chalgerd city, Chaharmahal O Bakhtiari province, which are facing the north and south aspects of a rangeland hill, some important biological characteristics, various chemical forms of potassium and microbial biomass potassium have been measured. The changes in urease enzyme activity compared to the situations of 1, 3 and 5 freeze-thaw cycles in soils did not have a statistically significant difference, but of the trait related to the slope aspect; In this way, in the north-facing slope soil, urease enzyme activity was 1.3 times that of the south-facing slope soil, which was also statistically significant. Examining the various forms of potassium in the first study showed that the occurrence of the cycle caused an increase of 1.2 and 1.013 times in the amount of soluble and exchangeable potassium, respectively, while the non-occurrence of the cycle had an increase of 1.1 times on the non-exchangeable potassium, which all three were statistically significant. The occurrence of 1 freeze-thaw cycle showed 2.01 times increase in soluble potassium compared to the 3 and 5 cycle situations, which was statistically significant. Also, the soluble potassium in the soil of the north-facing slope was 1.4 times that of the south slope, while the exchangeable and non-exchangeable potassium in the soil of the south slope was 1.02 times and 1.5 times more than the soil facing the north slope, respectively, which are all statistically significant. After 5 freeze-thaw cycles microbial biomass potassium was statistically increased 1.1 times than 3 cycles and 1.032 times than 1 cycle. Also, microbial biomass potassium in the north-facing soil compared to the south-facing soil showed a statistically significant increase of 1.027 times. In the second study, the two traits of induced microbial respiration and microbial biomass carbon after the first dry-rewet cycle, showed a statistically significant increase equal to 1.3 times and 2.026 times, respectively, compared to conditions 3 and 5; Also, the lowest amount of induced microbial respiration and microbial biomass carbon showed a statistically decrease in the situation of 5 drying-reweting cycles, compared to other two situations. Measuring the net activity of urease enzyme in both the first and second studies, the net activity of urease enzyme after applying 5 times freeze-thaw cycle and dry-rewet in the north-facing slope soil on the 0, 1, 2, 3, 4, 5, 7, 9, 11, 13, 15, and 20 days of incubations were done so that the index of enzyme production and persistence measured in them. In the first study, according to the process of net activity of urease enzyme, the production index was equal to 33.79 and the persistence index was equal to 7.39. The production index was higher than the control sample that did not receive 5 freeze-thaw cycles, and the persistence index was lower than the control sample, which indicates the negative effect of the freeze-thaw cycle on the net urease enzyme activity. In the second research, net activity of urease enzyme was carried out under the same conditions as the first research, except the freeze-thaw cycle, and instead of the freeze-thaw cycles, drying-rewetting cycles were applied.
