DO FUNGI TRANSPORT 10Be DURING WOOD DEGRADATION?
Decayed organic matter in soils and sediments contains high concentrations of 10Be of up to 109-1010 atoms/g (1). Yet, living trees contain only 106 atoms/g (2). The driving question for this study is how 10Be becomes bound to decayed organic matter. A possibility is that fungi transports 10Be. Wood-degrading fungi are known to transport and bioaccumulate metals from large areas, facilitated by acids such as oxalic acid in the fungal hyphae.
To test the hypothesis that fungi transport 10Be, we analyzed both intact and fungally degraded wood of oak, hickory, and hemlock. From these data, we reached two conclusions:
Oak has a 10Be concentration of about 2x106 at/g, similar to that observed by Klein et al. (2). Hickory has a much higher concentration of about 3x107 atoms/g, confirming observations that hickory bioaccumulates Be. The inventory of 10Be in a temperate forest is expected to be about 6x106 atoms/cm2 equivalent to only a few years of fallout.
We observed two patterns of metal accumulation by wood-degrading fungi. One group of samples showed enrichment in Mn, Fe, and Cr, but showed no enrichment in 10Be. Another group showed enrichment primarily in Al and Ti, and a five-fold enrichment in 10Be.
Neither group showed fungal enrichment of 10Be sufficient to account for the 1000-fold difference between living trees and soil organic matter. To constrain the annual flux of 10Be of the system, leaves and nuts are being analysed. It is expected the nuts and leaves will have a negligible amount that will not account for the 1000-fold difference.
1. Lundberg, L., et al. (1983). JGR 88(C7):4498-4504
2. Klein, J, et al. (1982). Nucl. Instr. Meth., 193:601-616