Changes in Arenosol Nematode Abundance and Trophic Composition as Influenced by Different Faidherbia albida (Delile) A. Chev. Tree Stand Ages in Northern Ethiopia

Faidherbia albida (Delile) A. Chev., hereafter F. albida is an important agroforestry tree species in the semi-arid highlands of Tigray, northern Ethiopia. The paper analyses how different stand ages of the tree could influence nematodes' abundance, trophic composition and selected community index values. A total of 40 composite soil samples were collected from out-canopies and under-canopies of different tree stand age classes designated as young (15–20 years), medium age (35–40 years) and older (> 60 years). Nematodes were extracted following the Baermann funnel technique, identified and counted under an inverted Olympus microscope according to their trophic groups. The highest total count of nematodes and relative abundance of fungivores, omnivores and predatory nematode trophic groups were counted from soil samples influenced by older F. albida trees. The relative abundance of bacterivores and plant parasitic nematodes was low. The nematode channel ratio became lower in soils as influenced by older trees while the Wasilewska index was significantly high. The age difference of the trees influenced the abundance of the soil nematode feeding groups and their ecological index values. Moreover, the results have shown the enhancement of nematode trophic diversity. Redundancy analysis showed that tree age significantly influenced the relationships of nematode trophic groups with the studied soil bio-physicochemical properties. Generally, the findings indicate that the soil food web becomes more complex and functional under the older trees.