Abstract:

This study explored the effects of different degraded grasslands on soil physicochemical properties and enzyme activities in the Songnen Plain, to provide a reference basis for the improvement of degraded grassland and ecological restoration. Taking the Songnen Plain of Heilongjiang Province as an example, the variation patterns and correlation of soil water content (SWC), pH, soil organic carbon (SOC), total nitrogen (TN), alkali hydrolyzed nitrogen (AN), ammonium nitrogen (NH₄⁺-N), total phosphorus (TP), available phosphorus (AP), soil β-glucosidase (BG), sucrase (SC), urease (UE) and alkaline phosphatase (AKP) were analyzed in slightly (LD), moderately (MD) and severely (SD) degraded grasslands. The results showed that the soil pH in the 0-10 and 10-20 cm soil layers showed an upward trend with the intensification of degradation. The SWC showed a decreasing trend in the 0-10 and 10-20 cm soil layers with the intensification of degradation, while the SWC increased with the increase of soil depth in the same degree of degradation. The only exception was that TP content in the 10-20 cm soil layer showed no significant difference in different degrees of degradation, other soil nutrients showed no significant differences among the soil layers in the same degraded grassland. In different degrees of degradation, they generally showed a downward trend with the intensification of degradation. The activities of the four soil enzymes (BG, SC, UE and AKP) in the 0-10 and 10-20 cm soil layers showed a decreasing trend with the intensification of degradation degree, and there were significant differences among the degradation degrees. The results of correlation analysis showed that the SWC was significantly positively correlated with SC in 0-10 cm soil layer (P<0.05). The TN content was significantly positively correlated with the UE (P<0.01), and significantly positively correlated with the BG and AKP (P<0.05). In 10-20 cm soil layers, the SWC was positively correlated with the SC and AKP (P<0.05). TN content was significantly positively correlated with the AKP (P<0.05), while the pH was negatively correlated with the AKP (P<0.05). The results of principal component analysis showed that the cumulative explanation rate of the selected environmental factors was 88.3%. In conclusion, it was believed that although soil physicochemical properties and enzyme activities showed certain correlations in different degraded grasslands, only pH had a stable negative correlation with soil enzyme activities. Therefore, it could be used to indicate the changes in soil enzyme activity characteristics of degraded grasslands.

Key words: Songnen Plain, grassland, degradation, soil enzyme activity, physical and chemical properties