MICROBIAL RESPONSE TO FREEZE-THAW CYCLES IN TUNDRA AND TAIGA SOILS

Four tundra and taiga soils were experimentally subjected to three fre eze-thaw cycles (5 days each at -5 degrees C and +5 degrees C). After each thaw, there was an initial pulse (<24 h) in microbial respiration . The total amount of C respired in each thaw period was largest durin g the first cycle and decreased in successive cycles. Three cycles cau sed a net increase in total respired C relative to the +5 degrees C co ntrol in wet meadow tundra soil, a reduction in birch soil, and had no net effect in either alder-poplar or tussock tundra soil. These diffe rent patterns apparently resulted from differences in the quality of t he soil organic matter and the relative activity of the microbial biom ass. Net N mineralization was generally enhanced relative to the +5 de grees C controls in the first cycle, but was inhibited in the third cy cle, similar to what was observed with C. Over multiple freeze-thaw cy cles, the initial response of C and N mineralization appear to be driv en by release from the microbial biomass, while over the longer-term, the response is driven by the reduction in attack on soil organic matt er resulting from a reduced microbial population. Copyright (C) 1996 E lsevier Science Ltd