AMMONIFICATION OF COMPLEXES PREPARED FROM GELATIN AND AQUEOUS EXTRACTS OF LEAVES AND FRESHLY-FALLEN LITTER OF TREES ON DIFFERENT SOIL TYPES

The rates of decomposition of polyphenol-gelatin complexes were studied in two sets of experiments. In the first set, ammonification rates of complexes formed from aqueous extracts of green, pre-dehiscent leaves and from aqueous extracts of freshly-fallen litter of a range of tree species and one shrub were determined using a standard soil inoculum and the unspecialized microflora of distilled water. The second set of experiments investigated the rates of ammonification of complexes prepared from green, pre-dehiscent leaves of a smaller range of species, using inocula prepared from the soils beneath the trees from which the leaves had been collected and with the medium buffered to the appropriate soil pH. The quantity of polyphenol-gelatin complex formed differed between species, within species between green pre-dehiscent leaves and freshly-fallen litter, and in the case of birch, sycamore, oak, and hybrid larch, within species between sites. Aqueous extracts of both green, pre-dehiscent leaves and fresh litter of elm, ash, and beech did not form precipitates with gelatin. Six of the 14 complexes formed from aqueous extracts of green, pre-dehiscent leaves were ammonified to some extent by the unspecialized microflora in unsterilized distilled H2O, which suggests that the complexes have a relatively low resistance to ammonification. Complexes formed from leaves of hybrid larch at Grizedale forest, Sitka spruce, western hemlock, and grand fir, released no more mineral N with the soil inoculum than with microbial inhibitors, which suggests that those complexes are very resistant to ammonification. Complexes formed from aqueous extracts of freshly-fallen litter released more N in the presence of the soil inoculum than did complexes formed from aqueous extracts of green, pre-dehiscent leaves of the same species. In general, the release of mineral N from the complexes was fitted well by double exponential regressions, with R2 values between 68 and 94%. From these regressions, the time taken for half of the N in a complex to be released ranged from 2 days (complex prepared from leaves of sycamore on a brown earth of high base status) to 56 weeks (complex prepared from leaves of birch growing on a brown podzolic soil). The regressions showed that complexes prepared from green, pre-dehiscent needles of western hemlock, Norway spruce, and Sitka spruce would never release 50% of their N in the experimental conditions.