[Effect of nitrogen additions on soil pH, phosphorus contents and phosphatase activities in grassland]. / æ°®æ·»åŠ å¯¹è‰åœ°ç”Ÿæ€ç³»ç»ŸåœŸå£¤pHã€ç£·å«é‡å’Œç£·é ¸é ¶æ´»æ€§çš„å½±å“.

Phosphorus is a key nutrient for all plant species and a limiting factor for grassland ecosystem function. In recent years, in response to the rapid increase of global nitrogen deposition, soil phosphorus contents and phosphatase activities changed to varying degrees in grassland ecosystems. We conducted a meta-analysis to examine the responses of soil pH, total phosphorus (TP), available phosphorus (AP), as well as activities of alkaline phosphatase (AlP) and acid phosphatase (AcP) in soils to nitrogen addition amount, nitrogen type, experimental duration, and sampling depth. The correlation between soil pH and phosphatase response ratio was investigated. The results showed that nitrogen addition significantly reduced soil pH, TP and AlP activity, while significantly increased AcP activity, but had no significant effect on AP. Soil pH and AlP activity significantly decreased under nitrogen addition >5 g·m-2·a-1, and AcP activity significantly increased under high nitrogen addition (>10 g·m-2·a-1). The contents of TP and AP significantly decreased when nitrogen addition was 5-10 g·m-2·a-1. NH4NO3 treatment significantly reduced soil TP and increased AcP activity, while urea treatment significantly reduced soil pH and AlP activity. Across all nitrogen addition amounts, when the experiment duration was 3 to 10 years, soil TP content and AlP activity were significantly reduced. Soil pH was significantly reduced after three years nitrogen addition, and AcP activitiy was significantly increased after 10 years nitrogen addition. In the 0-10 cm soil layer, the TP content and AlP activity significantly decreased, while the AP content significantly increased. In >10 cm soil layer, the AP content was significantly decreased. The significant negative correlation between soil pH and AcP activity indicated that change in soil pH caused by nitrogen addition may be an important factor for the variation of soil phosphatase activity.

[Responses of soil intracellular and extracellular urease activities to carbon additions in chernozem].

Urease in soil, as the most important enzyme catalyzing urea hydrolysis, plays an important role in nitrogen supply of grassland ecosystems. While the effects of different carbon additions on extracellular urease in grassland soil are well understood, their effects on soil intracellular urease remain unknow. Moreover, whether the responses of intracellular and extracellular urease to carbon additions are consistent need to be clarified. With a field experiment in Hulun Buir grassland of Inner Mongolia, we investigated soil intracellular and extracellular urease activities in chernozem under four treatments, including carbon-free (C0), 250 (C250), and 500 (C500) kg C·hm-2·a-1, using glucose as carbon source. Further, we analyzed their relationships with soil properties. Carbon additions significantly increased soil intracellular urease activity and its ratio to total urease activities and total urease activity, but did not affect soil extracellular urease activities. There was significant positive correlation between soil intracellular urease activity and microbial biomass, suggesting that the increases of soil intracellular urease activities were mainly caused by the increases of microbial biomass. Results of structural equation modeling (SEM) analysis showed that carbon additions indirectly increased soil intracellular urease activities by affecting microbial biomass.