MICROBIAL FUNCTIONAL DIVERSITY CAN BE INFLUENCED BY THE ADDITION SIMPLE ORGANIC SUBSTRATES TO SOIL

The influence of the composition of added organic C on microbial funct ional diversity was investigated in an arable soil. Soil was treated w ith single large additions of organic C compounds (asparagine, gluconi c acid, glutamic acid, mannose, methyl-glucamine and urocanic acid) or repeated additions of compounds (asparagine, glucosamine, alpha-ketov aleric acid or urocanic acid) over 4 d. The effects on microbial funct ional diversity were assessed by measurement of patterns of in situ ca tabolic potential (ISCP) in each experiment at 1, 7 and 20 weeks, and 1, 4 and 7 d, respectively. Microbial biomass C was generally increase d by the substrate additions in both experiments and remained greater than the control over 7 d in the repeated-addition experiment. After 2 0 weeks, however, only the microbial biomass C in the asparagine and m annose treatments remained increased in the single-addition experiment . The direction of changes in the patterns of ISCP were distinctly dif ferent between most treatments in both the single- and repeated-substr ate addition experiments. Over 20 weeks, factor analysis showed that t he patterns of ISCP in the glutamic acid, mannose, methyl-glucamine an d urocanic acid treatments tended to converge with that in the non-ame nded treatment. The changes in patterns of ISCP were also different af ter repeated additions of different substrates. However, respiration r esponses to the added substrate in each of the treatments were not spe cifically increased relative to the respiration responses to other org anic C compounds. These results support the hypothesis that addition o f different types of organic C can influence patterns of ISCP. However , it is difficult to distinguish the direct effects of the added compo unds on the respiration response to individual substrates. (C) 1998 El sevier Science Ltd. All rights reserved.