Effect of Organic and Inorganic Carbon on Extracellular Enzyme Activity of Acid Phosphatase and Proteases in Three Kinds of Fungal Hyphae Dynamics of nitrogen and phosphorus concentrations and nitrate reductase and acidic phosphatase activities in Imperata cylindrica on copper mine tailings Mechanism of fulvic acid- and organic manure-mediated phosphorus mobilization in black soil at low temperature