Application of a rapid thin section method for observations on decomposing litter in mor humus form in a subalpine coniferous forest

Morphological changes in the decomposing litter of Abies spp. and Betula spp. in a mor humus form were studied by a rapid thin section method. According to the morphological characteristics, the epidermis, mesophyll and vascular bundle of Abies needle litter were classified into four types: (i) newly fallen; (ii) slightly decomposed; (iii) moderately decomposed; and (iv) greatly decomposed. The distribution of these tissue types along the profile of the forest floor was then investigated. The morphological changes in other litter types, such as branches, scales and Betula leaves during decomposition were observed directly with microscope and electron microscope. Five vertical thin sections and 80 horizontal thin sections were used for these observations and investigations. The decomposition of Abies litter was slower than that of Betula litter. The relative decomposition rate of the tissues was in the order of mesophyll > vascular bundle > epidermis in Abies needles; mesophyll greater than or equal to epidermis > vascular bundles in Betula leaves; and inner bark > xylem > outer bark in both Abies and Betula branches. The last remains of the litter were usually stomata, segments of seminiferous scale and outer bark of Abies. The decomposition of plant litter occurred mainly within the L and F layers of the soil (0-5 cm in depth). Abies needles and Betula leaves completely disappeared at. depths of 0-6 cm and 0-4 cm, respectively, Branches disappeared within the top of 5 cm and 6-8 cm for Betula and for Abies, respectively. The scales of Abies were most slowly decomposed in the soil layers.