Coupling and Synergistic Relationships Between Soil Aggregate Stability and Nutrient Stoichiometric Characteristics under Different Microtopographies on Karst Rocky Desertification Slopes

Various microtopographical features are formed by exposed bedrock and surrounding soil in karst rocky desertification areas. These microtopographical features significantly change the aggregate stability and nutrient stoichiometric ratios, thereby affecting soil quality. However, little research has been conducted on the effects of microtopography on soil aggregates and nutrient stoichiometric ratios in karst regions and on soil quality in micro-habitats. In this study, aggregates and nutrients in the soils of six typical microgeomorphological units from karstic rocky desertification slopes were experimentally analysed. A degree of coupling model was employed to reveal the coupling and synergy relationships between soil aggregates and the stoichiometric ratios of carbon, nitrogen and phosphorus for different microtopographical features. The results showed that microtopography significantly affected on the distribution of soil aggregates and soil carbon, nitrogen and phosphorus contents. The soil aggregate stability (based on the mean weight diameter (MWD)) was the highest in stone nests and the lowest on the soil surface. Stone crevice soil had the highest soil organic carbon (SOC), hydrolytic nitrogen (HN) and total nitrogen (TN) contents. The available phosphorus (AP) content of soil surface was significantly greater than that of stone crevices, stone caves, stone ditches, stone surfaces and stone nest soils. Correlation analyses showed that silt had a positive effect on aggregate stability and soil organic carbon. The coupling synergy degree between soil aggregates and nutrient stoichiometric ratios were lowest for the soil surface soils, and much lower than for the stone nest and stone crevice soils. The above results show that microtopography is the dominant factor affecting soil aggregate stability and soil nutrient characteristics in karst slopes, and can serve as a reference for the ecologically sound management of rocky desertification areas.