Abstract: We examined root exudation rate and rhizosphere effect of four arbuscular mycorrhizal (AM;Amygdalus triloba, Acer negundo, Viburnum opulus subsp. calvescens, and Armeniaca sibirica) and three ectomycorrhizal tree species (ECM; Picea koraiensis, Betula platyphylla, and Pinus sylvestris var.mongolica), to determine the differences of different mycorrhizal associations of tree species and to evaluate their improvement on soil quality in the black soil at Keshan Farm in Heilongjiang, China. The results showed that root exudation rate of the seven tree species was significantly different (P<0.05), with that of the ECM tree species being significantly higher than that of AM tree species (P<0.05). The pH of Viburnum sargenti, Armeniaca sibirica andAcer negundo rhizosphere soil was 0.3%-5.9% higher than the bulk soil. In contrary, it was1.9%-5.1% lower in Amygdalus triloba, Picea koraiensis, Betula platyphylla, and Pinus sylvestris var.mongolica rhizosphere soil. Rhizosphere effects on soil total organic carbon (TOC), total nitrogen (TN), alkalihydrolyzed nitrogen (AHN), total phosphorus (TP), and available phosphorus (AP) in the rhizosphere soil of the seven tree species were 22.1%-250.4%, 9.9%-146.9%, 5.5%-23.8%, 3.8%-48.8% and 23.6%-189.1% higher compared to bulk soil, respectively. The rhizosphere effects of the ECM tree species on TOC, TN, and AHN were greater than that of the AM tree species, while that on soil TP and AP was lower than the AM tree species. Compared to the bulk soil, the abundance of bacteria and actinomycetes in the rhizosphere soil of the seven tree species was increased by 42.9%-309.6% and 13.3%-134.7%, respectively. The abundance of fungi in the rhizosphere soil of Armeniaca sibirica and Amygdalus triloba was decreased by 21.6% and 8.6%, respectively, but increased by 43.5%-215.4% in the rhizosphere soil of other tree species. The rhizosphere effect on the abundance of bacteria and fungi in the ECM tree species was greater than that of the AM tree species (P<0.05), while the rhizosphere effect on actinomycetes was not different between the AM and ECM species (P>0.05). The correlation among root exudation rates, microbial quantity, and soil chemical properties in AM species was significantly greater than that in the ECM species. The effect of ECM tree species on soil improvement was stronger than that of AM tree species.

Key words: rhizosphere effect, root exudates, arbuscular mycorrhizae, ectomycorrhizae, soil microorganism, soil chemistry.