Distribution, genetic diversity and compositional variation of wetwood prokaryote communities within and among two native California Populus species

Wetwood is a chronic condition of many tree species characterized by water-soaked and stained wood, high internal gas pressures, elevated pH, bleeding from stem junctions and wounds, branch die-back and canopy decline. Wetwood often supports communities of anaerobic fermentative and methanogenic prokaryotes. The spatial distribution of prokaryotes, host tissue damage, and wetwood symptoms including staining and elevated pH were determined within the trunk of Populus baslamifera ssp. trichocarpa. A conical area of wetwood, widest at ground level, tapers to a point in the upper trunk. Unstained sapwood is slightly acid, whereas wetwood is slightly alkaline, and pH changes abruptly at the unstained sapwood-wetwood boundary. Scanning electron microscopy revealed prokaryotes within vessels of wetwood in contact with degraded vessel-to-ray pit membranes. They are most abundant in interior wetwood and not seen in unstained sapwood. Vessel-to-ray pit membranes are intact in unstained sapwood, degraded at the wetwood boundary and destroyed in interior wetwood.; I identified prokaryotic 16S rDNA from wetwood of Populus balsamifera ssp. trichocarpa and P. fremontii ssp. fremontii. In one hundred eighty-seven prokaryotic DNA sequences, diversity includes the genera Bacteroides, Cytophaga, Clostridium, Sporomusa, Termitobacter, Desulfosporosinus, Desulfotomaculum, Sinorhizobium, Pseudomonas and Methanobacterium. I report Cytophaga, Sporomusa, Termitobacter, Desulfosporosinus, Desulfotomaculum, Sinorhizobium and Methanobacterium in wetwood for the first time. All the taxa delineated have at least some ability to grow anaerobically and most are obligate anaerobes. Most Eubacteria found are from fermentative taxa, which occurred in all trees examined. All Archaeal sequences belong to methanogenic taxa. Sulfate reducing prokaryotes are identified in wetwood for the first time, as well as denitrifiers and nitrogen fixers.; I compared community composition within and among individual hosts, sites, and two cottonwood species (Populus balsamifera ssp. trichocarpa and P. fremontii ssp. fremontii) from four wild populations in California, using denaturing gradient gel electrophoresis (DGGE). Density plots of denaturing gradient gel electropherograms were compared using Bray-Curtis ordination to reveal patterns of similarity among wetwood communities. Wetwood Eubacterial community composition varies within individual hosts with height, but does not vary among core samples within individual hosts at the same height. Community composition varies among hosts, stands, sites and hosts species.