ANATOMICAL AND FUNCTIONAL HETEROGENEITY AMONG DIFFERENT ROOT ORDERS OF PHELLODENDRON AMURENSE

Abstract

Aims Fine roots are the primary organs for nutrient and water uptake in trees. The growth and turnover of fine roots significantly influence productivity and matter cycles in forest ecosystems. Our objective was to elucidate the basic structure, function and allocation of fine roots in Phellodendron amurense. Methods We made paraffin slices stained by safranin and fast green to observe anatomical structures (such as diameter, cortex, number of passage cells, development of vascular bundle, mycorrhizae of roots, etc.) of the first five orders of roots of P. amurense. Bright-light and fluorescence microscopes were used to observe and take photos. Important findings Root diameter (R), vascular bundle diameter (V) and V/R increased as root order increased. The thickness and layers of cortex were similar in the first three orders. Few cortical cells were in fourth-order roots and almost none in fifth-order roots. There were higher mycorrhizae infections in the first three order roots than the last two orders, and the later had almost no fungi. Primary growth occurred in all first-and second-order roots, an secondary growth occurred in all fourth and fifth order roots. Some third-order roots had only primary growth, but some had secondary growth with inconsecutive phellogen. All results suggested that the ability of roots to absorb nutrients and water decreased but transport ability and longevity increased as root orders increased. According to the relation- ships among anatomical characteristics, diameters and root orders, the fine roots of P. amurense should be involved in the first three orders at most; these have passage cells but lack successive phellogen and have diameters less than 0.8 mm.