Functional genes abundance and association with the bacterial communities Using the microcosm setup, we detected major shifts in the bacterial community composition (T-RFLP, Fig. 2; 16S NGS, Figs. 3 and 4). Additionally, nifH (a gene associated with nitrogen fixation) and nosZ (a gene associated with denitrification) were found to correlate strongly with the bacterial community pattern (Table 2). The nifH gene depicts the presence of nitrogen-fixing or diazotrophic communities while the nosZ gene represents denitrifying bacteria. In this study, a positive correlation between nifH transcripts and temperature was detected in microcosms having a high abundance of Firmicutes. The ability of the diazotrophic community to thrive in anoxic condition (Kathiresan and Bingham, 2001) provided support to our finding of high abundance of nifH gene in the high water (HW) treatments. Furthermore, high copies of nifH gene detected in microcosms incubated at 35 C (Supplementary materials Table S3)demonstrated a positive response of nitrogen
fixers towards temperature upshifts.