[Characteristics and Factors of Soil Enzyme Activity for Different Plant Communities in Yellow River Delta]

Soil enzymes play key roles in the construction and succession of coastal wetland communities, while the driving mechanism of their activities under water and salt stress conditions is still unclear. The activities and distributions of sucrase, phosphatase, catalase, and urease in the rhizosphere and non-rhizosphere soils of Suaeda salsa, Phragmites australis, and Tamarix chinensis communities were studied in the Yellow River Delta. Moreover, the changes in soil enzyme activities and their influencing factors during the succession of halophytic plant communities were discussed in combination with changes in the physicochemical properties of soil. The results showed significantly higher soil enzyme activities and soil fertility parameters in the rhizosphere soils of S. salsa, P. australis, and T. chinensis communities than those in the non-rhizosphere soils (P<0.05). In the rhizosphere soils, the activities of phosphatase and catalase increased in the order of S. salsa < P. australis < T. chinensis, while they increased in the order of T. chinensis < S. salsa < P. australis for sucrase activity, and S. salsa < T. chinensis < P. australis for urease activity. Further, significant differences were found in the physicochemical properties of rhizosphere soils between different halophyte communities (P<0.05), which indicated that plant types and their rhizosphere effects could affect soil enzyme activities and fertility characteristics. Furthermore, a two-way analysis of variance showed that the rhizosphere effect was greater than that of vegetation type. The soil sucrase activity was significantly positively correlated with available potassium (AK), available phosphorus (AP), and ammonium nitrogen (NH₄⁺-N) (P<0.05). Meanwhile, urease activity was significantly positively correlated with total nitrogen (TN), organic matter (SOM), AK, AP, NH₄⁺-N, and nitrate nitrogen (NO₃^--N) (P<0.01). Both of the two enzymes were negatively correlated with soil electrical conductivity (EC) (P<0.01). The phosphatase and catalase activities were found to be significantly positively correlated with soil water content (MC), total carbon (TC), TN, total phosphorus (TP), SOM, AK, and NH₄⁺-N (P<0.05). Additionally, parameters of pH, total potassium (TK), and NO₃^--N were also significantly associated with catalase activity. Finally, the redundancy analysis (RDA) revealed that main factors affecting the overall soil enzyme activity were TC (P<0.01), SOM (P<0.01), MC (P<0.01), TN (P<0.05), NH₄⁺-N (P<0.05), and EC (P<0.05). The findings suggested that soil fertility, water, and salinity are the most influential factors of soil enzyme activity in different halophytic plant communities of the Yellow River Delta.