Assessing the Impact of Pteropyrum Aucheri Species on Particulate Organic Matter and Soil Aggregate Dispersion

In order to assess the impact of Pteropyrum aucheri on soil organic matter components and the soil aggregate dispersion, as the sensitive index of grassland management changes, soil samples were taken from two locations in area rangelands representing the Pteropyrum aucheri - Astragalus microcephalus vegetation types with similar physical properties (Slope, Aspect, Elevation) and dominance of Pteropyrum aucheri species but with different coexisting species in the species composition. For this purpose, in each location regarding the vegetation distribution and physical characteristics of the ranges under study, 6 transects that were 100 meters long were placed systematically in vegetation types while 4 of them were parallel to slope and 2 of them were perpendicular to the slope. Soil samples were taken with three replicates from surface horizons (depth of 0-15 cm) and lower horizons (depth of 15-30 cm) of drilled profiles at the beginning, middle, and end of transects. Then, the values of soil characteristics, including carbon, particulate organic matter carbon (POM-C), nitrogen, particulate organic matter nitrogen (POM-N), micro-aggregate, macro-aggregate, and the Carbon in the aggregate, were measured. The information related to the vegetation of selected areas inside one-squared meter plots (60 plots) with 10 meters long intervals deployed along the transects were recorded, and based on this information, numerical indices of diversity and evenness in the selected areas were calculated. The results of the ANOVA test of soil samples revealed that there is a significant difference between index values at different soil horizons of studied areas, and in all of the cases, excluding the amount of the micro-aggregate, the indices values (Including; C, N, POM-C, POM-N, Macro-aggregate, C-associated with macro and micro- aggregates) are more in surface horizons than the lower ones. Moreover, the values of each of the indices in number 1 grassland location was more than number 2 location since number 1 location has a better species diversity. This suggests that the physical components of soil organic matter justifies the changes resulted from the Pteropyrum aucheri species impact on the quantity and quality of soil organic matter. Furthermore, the above results confirm the hypothesis suggesting the rapid emergence of management changes in the components of nitrogen and unstable carbon. The results also prove the sensitivity of soil particulate organic matter to the pasture management changes. Therefore, having information regarding the changes of particulate organic matter and soil aggregate dispersion would be beneficial for the pasture ecosystem management.