Short-term effects of sewage sludge application on phosphatase activities and available P fractions in Mediterranean soils

The aim of this study was to investigate factors regulating phosphatase activities in Mediterranean soils subjected to sewage sludge applications. Soils originating from calcareous and siliceous mineral parent materials were amended with aerobically digested sewage sludge, with or without physico-chemical treatment by ferric chloride. Sludge amendments, ranging from 6.2 to 10 g kg⁻¹ soil, were carried out in order to provide soil with a P total quantity equivalent to 0.5 g P₂O₅ per kg of soil. Bacterial density, phosphatase activities (i.e. acid and alkaline phosphomonoesterases and phosphodiesterases) and available P (i.e. P Olsen and P water) were measured after 25 and 87 days of incubation. Results showed significant effects of sewage sludge application and incubation period. Sewage sludge effect resulted in an increase in phosphatase activities, microbial density and available P. Incubation period increased available P while decreasing phosphatase activities. This study also revealed that the origin of sludge and its chemical characteristics may show different effects on certain variables such as phosphodiesterases or bacterial density, whereas mineral parent materials of soils did not show any significant effects.     

Effects of organic and mineral amendments on available P and phosphatase activities in a degraded Mediterranean soil under short-term incubation experiment

The aim of this study was to determine the effects of mineral and organic-P-fertilizers on soil P availability, bacteria densities and phosphatase activities, in a degraded Mediterranean soil characterized by low level in soil organic matter and nutrients. A typical degraded Mediterranean soil, originating from a siliceous mineral parent material, was amended with different organic or mineral P-sources: aerobically digested sewage sludge (SS), with or without physico-chemical treatment by ferric chloride; sewage sludge compost (SSC); Na or K mineral P-salts (Pi-salts). All the amendments were carried out in order to provide soil with a P total quantity equivalent to 0.5 g P₂O₅/kg of soil. Bacterial density, phosphatase activities (i.e. acid (APH) and alkaline (BPH) phosphomonoesterases and phosphodiesterases), BPH/APH ratio, and available P (P Olsen) were measured after 25 and 87 days of incubation. Results showed that all the P-sources used to fertilize soil during this study resulted in significant increase in P concentration. However, different responses in phosphatase activities and bacterial densities were obtained with regards to the amendment applied to soil. Indeed, it appeared clearly that sewage sludge (SS) considerably stimulated soil biological activity, and more especially the different kinds of phosphatases involved in P mineralization and P turn-over. On the contrary, sewage sludge compost (SSC) as well as P-salts amendments did not affected these parameters in most cases. Results showed also that the incubation time influenced almost all the biological and chemical parameters investigated during this study. As a consequence, P availability was considerably improved in the amended soils between the two sampling dates.     

Changes of adenyl cyclase and phosphodiesterase activities at different time point in hypothalamus of rats with fever and hypothermia

AIM: To observe the changes of adengl cyclase (AC) and phosphodiesterase (PDE) activities of at different time point in hypothalamus of rats with fever and hypothermia. METHODS: Radioisotope method was used to measure the activity of AC and PDE. RESULTS: The fresh yeast caused rats fever after subcutaneous injection 4 h (P<0.01). AC activity reached a peak value at 3rd h after making model (P<0.05), and PDE activity increased slightly in the full process of experiment action; Aminopyrine induced rats hypothermia stat15 min after peritoneal injection (P<0.01). AC activity was higher than normal animal a 15th minute after the injection of aminopyrine. But subsequently AC activity decreased rapidly with the lowest value at 45th minute after the injection (P<0.05). PDE activity fluctuated slightly within normal range in the full course of experiment. CONCLUSION: In fever model, it might be important cause of febrile response that AC activity in hypothalamus increased markedly, while PDE might be the factor causing long-term febrile response. In hypothermia model, the obvious decrease in AC activity indicating that cAMP content in hypothalamus might be related to hypothermia status.