Abstract
Glomalin-related soil protein (GRSP) is a specific glycoprotein secreted into the soil by hyphae and spores of arbuscular mycorrhizal fungi that have many potential functions. It is not clear whether exogenous GRSP has an effect on plant growth and soil properties or whether the effects are related to the type of GRSP used. In this study, trifoliate orange (Poncirus trifoliata L. Raf.) seedlings were used to analyze the effects of easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) at a quarter-, half-, and full-strength concentration on shoot and root biomass as well as soil properties The results showed that, at different strengths, exogenous EE-GRSR significantly increased shoot and root biomass compared to the control, which displayed the most significant effects from the half-strength EE-GRSP. In contrast, DE-GRSP, at various strengths, significantly reduced shoot and root biomass. Furthermore, the application of exogenous EE-GRSP stimulated soil water-stable aggregate (WSA) content at 2–4 mm and 0.5–1 mm sizes, while DE-GRSP strongly reduced WSA content at the 2–4 mm, 1–2 mm, 0.5–1 mm, and 0.25–0.5 mm sizes, consequently leading to an increase or decrease in the WSA stability, according to the mean weight diameter. However, exogenous EE-GRSP decreased soil pH and DE-GRSP increased it, which was related to WSA stability. Exogenous EE-GRSP almost significantly increased soil acidic, neutral, and alkaline phosphatase activity at different strengths, while exogenous DE-GRSP, also at different strengths, significantly inhibited soil acidic phosphatase activity. The application of both exogenous EE-GRSP and DE-GRSP increased the organic carbon content of the soil. This study concluded that exogenous GRSP exerted differential effects on plant biomass and soil properties, and EE-GRSP can be considered as a soil stimulant for use in citrus plants. To our knowledge, this is the first report on the negative effects of exogenous DE-GRSP on plant biomass and soil properties.
Highlights
The beneficial effects of mycorrhizal symbiosis are partly attributed to the production of a specific glycoprotein, glomalin, which is secreted by the hyphae and spores of Arbuscular mycorrhizal fungi (AMF) [8,9,10]
A total of 39% and 19% of the shoots and roots received a quarter-strength of EE-glomalin-related soil protein (GRSP) application, 52% and 53% received a half-strength extractable GRSP (EE-GRSP) application, and 49% and 34% received a full-strength EE-GRSP application, respectively (Figure 1a)
Different concentrations of difficultly extractable GRSP (DE-GRSP) all significantly reduced shoot and root biomass production with increased concentrations, implying that exogenous DE-GRSP negatively affects the growth of trifowhich had functions in improving plant growth [30]
Summary
Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with approximately. After colonizing the roots of host plants, AMF develop mycorrhizal extraradical hyphae, which extend into the soil beyond the root, increasing the root surface area of the plant and its contact with the soil/rhizosphere [1,2]. Arbuscular mycorrhizas promote the growth and development of the host plant by improving the fruit quality, water, and nutrient acquisition, in addition to increasing its stress resistance [2,3,4,5,6,7]. The beneficial effects of mycorrhizal symbiosis are partly attributed to the production of a specific glycoprotein, glomalin, which is secreted by the hyphae and spores of AMF [8,9,10]. Rillig [11] proposed the term glomalin-related soil protein (GRSP)
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