DO FUNGI TRANSPORT 10Be DURING WOOD DEGRADATION?

Meteoric cosmogenic ¹⁰Be is used as a tracer of soils to determine erosion and soil transport rates. However, there is experimental evidence that beryllium (Be) mobilized in soils is complexed with organic acids. It is not known to what extent biological Be transport affects the calculated transport rates.

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:

1. 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.

2. 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.

References

1. Lundberg, L., et al. (1983). JGR 88(C7):4498-4504

2. Klein, J, et al. (1982). Nucl. Instr. Meth., 193:601-616