Print PageSoil Ca depletion due to acidic deposition and related soil chemistry changes has lead to decline of forest productivity and carbon sequestration. In 1999, watershed WS1 at the Hubbard Brook Experimental Forest (HBEF), NH, USA was amended with Ca-silicate to restore soil Ca pools. Since then, several studies have been published on the effects of Ca supplementation at WS1 on changes in mycorrhizal fungi, foliar physiology of red spruce, sugar maple and other mixed hardwood species, stream water, and N mineralization and cycling in the soil. Ca supplementation lead to increase in Ca and P, and decrease in Al and acidity of organic and mineral soil horizons as compared to a reference watershed, WS3. We hypothesized that these observed changes in various aboveground forest functions in response to Ca addition is correlated with significant shifts in soil microbial community structure in both the organic and the mineral soil horizons at this site. In the present study, changes in bacterial communities were studied using three different complimentary approaches:Denaturing Gradient Gel Electrophoresis (DGGE), PhyloChip microarrays, and clone library sequencing of the 16S rRNA genes. PhyloChip, a high-density 16S rRNA gene-based microarray, is a powerful and sensitive tool that allows the detection of about 8450 bacterial taxa simultaneously.
Results/Conclusions
The results show that overall bacterial community structure in the reference and the Ca-treated soils was different, and that shifts related to Ca treatment were more pronounced in the mineral soil horizon. While the DGGE analysis indicated gross significant differences between the Ca-treated and reference soils, G2 PhyloChip microarray data showed that the bacterial community structure at family level was significantly affected (P < 0.05). The relative abundance of families such as Acidobacteriaceae, Methylocystaceae, Methylococcaceae (contain some carbon cycling and methane oxidizing genera), Pseudomonadaceae and Comamonadaceae (contain some denitrifiers) declined in response to Ca in both mineral and organic horizons, while for Desulfobacteraceae (sulfate rreducers)and Geobacteraceae (contain some metal reducing genera) it increased in both organic and mineral soils. Some functionally important groups such as Nitrosomonadaceae (comprised of many ammonia-oxidizing genera) decreased in the organic horizon but increased in the mineral horizon. Consistent with prior analyses of acidic soils, at HBEF also, Acidobacteria were dominant as indicated by sequencing of clone libraries of the 16S rRNA gene. The changes in the bacterial communities within specific families and the role they play in the aboveground ecosystem functions are yet to be explored.
