Spatial and temporal fluctuation in biomass, nitrogen mineralizing reactions and mineral nitrogen in a soil cropped to barley

Abstract

We compared changes in components of the N-mineralization cascade ranging from the very specific, such as a deaminase, to the highly integrated, such as biomass in a Black Chernozemic seeded to barley (Hordeum vulgare L.) under field conditions at Edmonton. Changes in enzyme content were related to soil [Formula: see text] to determine if the microbial environment changed sufficiently to exert feedback control on N mineralizing reactions and thereby to be detected. Histidase and protease were chosen as model systems for depolymerization and deamination respectively because information exists on their control in pure culture studies, on histidine content and control of histidase in soil, and assay procedures are available for soils. We observed an inverse relationship of labile histidase activity with [Formula: see text] in soils with high [Formula: see text] content and low [Formula: see text] ratio. This relationship provides indirect evidence for [Formula: see text] control of histidase content, but emphasizes that it is only one element of a complex control mechanism. Conversely, enzyme content was not rate limiting to net N mineralization, or sensitive to common control mechanisms. Biomass-C, an integrative measure of substrate supply, potential biological activity and enzymatic activity, describes net mineral-N production better than do indices of any single step. Regular spatial variability is exhibited by [Formula: see text] (and [Formula: see text]). [Formula: see text] is a product of mineralization; a substrate for immobilization, nitrification, plant uptake, and other reactions; and may also be a regulator of activity, or synthesis, of some enzymes. It is intriguing that none of the variables that influence mineral N, such as enzyme activity, biomass, or respiration, varied spatially in a statistically identifiable manner, yet [Formula: see text] did. Key words: Nitrogen mineralization, enzyme content, biomass, protease, histidase, ammonium regulation