Effects of tannins on the decomposition of Chinese tallow leaves by terrestrial and aquatic invertebrates

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Abstract
The hypothesis of this study was that tannins from Chinese tallow leaves have a negative effect upon terrestrial and aquatic reducer organisms and thereby may affect the overall rate of tallow litter decomposition. Species diversity and population size of aquatic reducers was lower in forest than adjacent grassland ponds; litter bags showed no difference in weight loss between bags which excluded reducers and those which did not. Differences in physical factors between habitats did not explain the paucity of reducers although rainfall permitted emigration of grassland organisms to forest ponds, yielding a temporary decrease in diversity. Tannin concentration in ephemeral ponds was altered by rainfall but leaching from leaves and soil continuously maintained tannin in ponds. Laboratory experiments showed that tannin was not directly toxic but inhibition of feeding caused high mortality in Asellus militaris and Crangonyx shoemackerii. Population density and reproduction of the terrestrial reducer (Armadillidium vulgare) was asynchronous with autumn leaf fall. Ground, leached leaves were consumed at much greater rate in laboratory experiments than unground, unleached leaves; in addition, mortality from starvation on the latter was high. These results suggest tallow leaves are not utilized by reducers until tannins are leached and the physical structure altered by rainfall and/or microbial action. Aquatic reducers are relatively unimportant in processing autumn leaf fall due to continual tannin leaching into ephemeral ponds from surrounding soil. Physical and microbial condition of leaves and leaching of tannin preceed spring and summer utilization by terrestrial isopods.