How do silicious trichomes influence leaf decomposition by meso- and macrofauna?

Decomposition of plant leaves is influenced by multiple traits, however, discrete structures of Si such as silicious trichomes on the leaf surface have been overlooked, although similarly to defense against insect herbivores, trichomes are thought to protect leaves from decomposers. This study hypothesized that silicious trichomes slow down leaf decomposition by soil meso- and macrofauna. We used two mesh bags (<0.2 mm and 5 mm) and examined ash-free mass loss of green leaves of Broussonetia papyrifera and Morus australis, closely related Moraceae species apparently different in trichome size and density, after 25 days of decomposition in a common garden. We also measured 10 traits of initial leaves and performed microscopic observation of the leaf surface with an energy dispersive X-ray analyzer. Of the leaf traits, trichome density on the lower leaf surface differed greatly between the two species. Our microscopic observation showed that short trichomes densely arranged on the lower leaf surface of B. papyrifera were highly silicified and that some of long trichomes were also composed of calcium. Ash-free mass loss of M. australis was greater in 5-mm mesh bag than in <0.2-mm mesh bag, while that of B. papyrifera did not differ by mesh size, which represents a suppressive effect of silicious trichomes on decomposition by meso- and macrofauna. The trichomes of B. papyrifera remained apparently intact on the decomposed surface, supporting a view of their continuously deferring influence on the large decomposers during the experimental period. For the meso- and macro-detritivore community, three taxa (Acari, Collembola and Isopoda) showed high population density in the common garden. Overall, our results suggest that distinct forms of Si bodies in plants such as trichomes are worth considering in better understanding of leaf decomposition by meso- and macrofauna.