[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.

Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems.

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Impact of long-term phosphorus fertilizer inputs on bacterial phoD gene community in a maize field, Northeast China.

The bacterial phoD gene encodes alkaline phosphomonoesterase, an enzyme which plays an important role in the release of plant-available inorganic phosphorus (P) from organic P in soil. However, the relationships between phoD gene community, alkaline phosphomonoesterase activity, and P availability in soil are poorly understood. In this study, we investigated how alkaline phosphomonoesterase activity, phoD gene abundance, and community structure are influenced by plant-available P using soils (0-10, 10-20 and 20-40 cm) from a long-term field trial in which a continuous maize (Zea mays L.) crop had received different levels of P fertilizer inputs (30, 60 kg P ha-1 year-1) for 28 years. Quantitative PCR and high-throughput sequencing were used to analyze phoD gene abundance and community composition. Alkaline phosphomonoesterase enzyme activity was negatively correlated with soil available P, which was reflected in corresponding data for phoD gene abundance. On the other hand, positive correlations were determined between phoD gene α-diversity and available P, while shifts in phoD gene community structure were related to changes in soil pH and P availability. The relative abundance of Pseudomonas was negatively correlated with P availability and positively correlated with alkaline phosphomonoesterase activity, suggesting that Pseudomonas may play an important role in soil organic P mineralization. The findings of this study demonstrated that changes of soil P availability as a result of long-term P fertilizer inputs significantly affected alkaline phosphomonoesterase activity by regulating phoD gene abundance, diversity, as well as altering the phoD gene community composition.

[Distribution and enrichment characteristics of organic carbon and total nitrogen in mollisols under long-term fertilization].

The characteristics and changes of soil organic carbon (SOC) and total nitrogen (TN) in different size particles of soil under different agricultural practices are the basis for better understanding soil carbon sequestration of mollisols. Based on a 31-year long-term field experiment located at the Heilongjiang Academy of Agricultural Sciences (Harbin) , soil samples under six treatments were separated by size-fractionation method to explore changes and distribution of SOC and TN in coarse sand, fine sand, silt and clay from the top layer (0-20 cm) and subsurface layer (20-40 cm). Results showed that long-term application of manure (M) increased the percentages of SOC and TN in coarse sand and clay size fractions. In the top layer, application of nitrogen, phosphorus and potassium fertilizers combined with manure (NPKM) increased the percentages of SOC and TN in coarse sand by 191.3% and 179.3% compared with the control (CK), whereas M application increased the percentages of SOC and TN in clay by 45% and 47% respectively. For subsurface layers, the increase rates of SOC and TN in corresponding parts were lower than that in top layer. In the surface and subsurface layers, the percentages of SOC storage in silt size fraction accounted for 42%-63% and 48%-54%, TN storage accounted for 34%-59% and 41%-47%, respectively. The enrichment factors of SOC and TN in coarse sand and clay fractions of surface layers increased significantly under the treatments with manure. The SOC and TN enrichment factors were highest in the NPKM, being 2.30 and 1.88, respectively, while that in the clay fraction changed little in the subsurface layer.