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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. • Effects of earthworms and AMF on N content of soil and plants were studied. • Dual earthworms and AMF addition recorded higher plant growth and chlorophyll than single addition. • Earthworms increased root N and soil total N, while AMF elevated N in plants, EE-GRSP, and soil NO 3 −−N and total N. • Dual addition recorded higher N contents in GRSPs than single addition. • Earthworm accelerated the AMF effect on the contribution of N in EE-GRSP and T-GRSP to soil total N. [ABSTRACT FROM AUTHOR]

Earthworms and arbuscular mycorrhizal fungi (AMF) are beneficial organisms in the soil and play an important role in improving soil fertility and plant growth. The objective of this study was to analyze the response of single versus dual inoculation of earthworms (Pheretima guillelmi) and AMF (Funneliformis mosseae) on mycorrhizal growth, root morphology, and rhizosphere properties of white clover (Trifolium repens). Addition of earthworms significantly increased the degree of root AMF colonization, while decreased hyphal length and spore number in the soil. Single or dual inoculation of F. mosseae and P. guillelmi significantly increased root traits (total length, area, volume, and average diameter), soil phosphatase activities (acid, neutral, and alkaline), easily extractable and total glomalin-related soil protein content, the percentage of soil water-stable aggregates at the size of 2–4 mm, 1–2 mm and 0.5–1 mm, aggregate stability, Bray-P, and soil organic carbon (SOC) contents. Among them, the dual inoculation further amplified the effect on glomalin production, phosphatase activity, and aggregate stability, but did not show a superposition effect on root improvement, Bray-P, and SOC. Our study, hence, suggested that AMF and earthworms have synergistic roles in elevating rhizosphere properties vis-à-vis agronomic responses of white clover. • Effects of earthworm-AMF (singly and in combination) on rhizosphere environment and crop response were studied. • Earthworms increased root AMF colonization, but reduced hyphae and spores in soils. • AMF or earthworms singly improved root traits, Bray-P, and soil organic carbon contents, but dual application of AMF and earthworms did not show a major effect than single application. • Single AMF or earthworms increased aggregation, phosphatase, GRSP, and dual addition amplified these responses. [ABSTRACT FROM AUTHOR]