The Phosphorus Activation In Black Soil By Exogenous Activators At Low Temperature And Its Possible Mechanisms

Following up on screening experiments, we investigated the phousphorus-activation efficacy of the targeted exogenous activators in a black soil at low temperature (10℃) and its possible mechanisms. The major results are presented as follows:Screening experiments using phosphurus activation coefficient as an indicator showed that fulvic acid (FA), organic manure (OM) and malic acid (MA) were the best to mobilize phosphorus. A new combination activator (Activator Ⅰ) was developed composed of FA, OM and MA at a proper ratio and this new activator exhibited best activation efficacy. FA, OM and Activator I were used for the subsequent incubation and pot experiments. The results aslo show that the best soil moisture content is50%of the maximum water holding capacity.The results of incubation experiments show that the content of soil Olsen-P, organic phosphorus and total phosphorus in the treatment with FA, OM and Activator I were higher than in the control with the best efficacy observed in the Activator I treatment. The same is true for acidic phosphatase activity. We extracted soil DNA at30days after incubation to analyze soil bacterial and fungal community structure. The results show that significant differences in bacterial community structure were found between the FA treatment and the OM treatment under no P fertilization, while no significant differences were observed under P fertilization, suggesting that P fertilizer may have impacts on bacteria. Significant differences were found in bacterial community structure among all the treatments, suggesting that bacterial activities were impacted by the additives used. The bacterial community structure in the treatment with Activator I was clearly different from that in the other treatments, suggesting that both soil microbial abundance and diversity were improved by Activator I.The results from both plate and shaking culture show that the transparent circle diameter and the D/d value were larger in the treatments with additives than in the control, suggesting that the phosphate-solubilizing bacteria were more abundant with higher phosphate-solubilizing rates in the treatments with additives. The total phosphorus content in bacterial suspension of the treatments with additives is7-10times as high as that of the control. The highest content of soluble phosphorus was found in the bacterial suspension of Activator I. The soluble phosphorus content in the treatment with Activator I was507μg·ml-1(16.5times as high as in the control) under phosphorus fertilization, and was525μg·ml-1(15.6times as high as in the control) under no phosphorus fertilization. The DGGE profles show that significant differences were found in soil phosphate-solubilizing bacterial community between the Activator I treatment and either of the other treatments with additives under P fertilization. Under no P fertilization significant differences were also found in soil phosphate-solubilizing bacterial community among the control, FA, OM and Activator I treatments.The results from the pot experiments show that chlorophyll content, plant height, fresh and dry weight of maize grown on soils amended with FA, OM and Activator I were all higher than those of the control, irrespective of P fertilization. The chlorophyll content increment percentage was higher under no P fertilization than under P fertilization.The T4treatment produced the largest rise in plant height with41%of plant height rise over the control. All the treatments with different additives could increase total plant nitrogen, phosphorus and potassium. Exogeous additives are conducive to the enhancement of shoot nitrogen and phosphorus under no phosphorus fertilization but to the enhancement of root nitrogen and phosphorus under phosphorus fertilization. The total plant potassium content was higher in shoots than in roots.