Introduction of earthworms into mycorrhizosphere of white clover facilitates N storage in glomalin-related soil protein and contribution to soil total N

Abstract

Either arbuscular mycorrhizal (AM) fungi or earthworms as soil organisms promote plant growth, while their interaction on nitrogen (N) content in plants, soil, and glomalin-related soil protein (GRSP) is not known. In this study, an AM fungus (Funneliformis mosseae) and an earthworm (Pheretima guillelmi), either in single or in combination, were introduced into soil growing white clover to analyze their effects on plant growth, chlorophyll, soluble protein, N contents in leaves, roots, GRSP, and soil, and the contribution of N in purified GRSP to soil total N. The four-week introduction of earthworms significantly increased root mycorrhizal colonization rate, and accelerated an improved AM effect on chlorophyll and plant growth. The single introduction of earthworms significantly increased root N and soil total N contents, while the single introduction of AM fungi distinctly elevated N contents in leaves, roots, easily extractable GRSP, and soil (nitrate N and total N). The N in total GRSP was 5.78–7.70 mg g−1, accounting for 3.46 %–5.45 % of the soil total N, of which the contribution of N from easily extractable GRSP and difficult-to-extract GRSP was 1.84 %–3.07 % and 1.34 %–2.39 %, respectively. AM fungi, but not earthworms, significantly increased the contribution of N in GRSP to soil total N, and the introduction of earthworms further accelerated the increased effect of mycorrhizas on the contribution of N in easily extractable and total GRSP to soil total N. These results demonstrated that the introduction of earthworms into mycorrhizosphere can facilitate N storage in GRSP and thus a contribution to soil total N.