Assessing soil microbial community after long term 2,4-D application in the field

Abstract

2,4-dichlorophenoxyacetate was used as a model carbon substrate and applied to field plots at four different rates, 0X- control, 1X (the normal field rate of application of 1.1 kg/ha), 10X and 100X for ten consecutive years to assess the long-term effect on soil microbial community structure and the impact on carbon and nitrogen cycling. With 2,4-D application, decrease in the PLFA signatures such as the monoenoics, branched monoenoics, and the eukaryote were observed especially in the 100X treatment whilst increases in the PLFA signatures such as normal saturates, mid chain branch saturates also occurred. The Shannon Weiner Diversity index was 1.6 for almost all the treatments and the Jaccard evenness ranged from 0.856-0.998 for all the treatments reflecting the evenness of all the treatment plots. No major shift in microbial community was observed in all the treatment plots according to PLFA analysis. Biomass PLFA and microbial biomass carbon by chloroform fumigation declined with 2,4-D application, p< 0.031and p< 0.14 respectively. Generally, carbon mineralization was significantly depressed whilst nitrogen mineralization was not significantly depressed with increase in 2,4-D application. Increase in the cis fatty acid to the trans fatty acid and cis fatty acid to the monoenoic precursor was observed for the 100X treatment plots indicating the stressed state of the Gram negative bacteria.