Long-term phosphorus addition alters soil enzyme kinetics with limited impact on their temperature sensitivity in an...

The soil enzymes excreted by soil microorganisms and plant roots are essential for decomposing organic matter and regulating ecosystem function. However, phosphorus (P) deposition effects on the kinetics and thermodynamics of soil enzymes remain poorly understood. Here, an 11-year, multi-level P addition experiment was conducted in the alpine meadows of the Qinghai-Tibet Plateau, a region known as one of the most sensitive to global changes. We measured V_max, K_m and their temperature sensitivities (Q₁₀) for six hydrolytic enzymes, along with soil properties and microbial community composition. P addition significantly reduced total soil organic C (SOC) and soil available N (NH₄⁺-N and NO₃^--N), but increased dissolved organic N (DON), soil total P (TP) and available P (AP). Furthermore, P addition markedly decreased the abundance of Ascomycota, while increased that of Basidiomycota. However, the abundance of bacterial phyla remained unaffected by P addition. We found that P addition significantly increased the V_max of β-glucosidase (BG), β-xylosidase (BX), cellobiohydrolase (CBH) and N-acetyl-glucosaminidase (NAG), but decreased that of acid phosphatase (APA) and L-leucine-aminopeptidase (LAP). P addition had no effect on K_m of BX and CBH, but significantly lowered it for other enzymes. Specifically, P addition significantly reduced the V_max-Q₁₀ of BG and BX, but did not affect that of other enzymes. Conversely, P addition significantly increased the K_m-Q₁₀ of BG, while decreased the K_m-Q₁₀ of NAG, with no change in other enzymes. Variation partitioning analysis confirmed that microbial biomass and fungal community composition are crucial in influencing V_max, K_m, as well as their temperature sensitivities. This study highlights the critical influence of P addition on soil enzyme kinetics and temperature sensitivity and their relationships with microbial community, enhancing predictions of how microbial community and substrate availability interact to regulate the soil nutrient cycle under global environmental changes.