Mycorrhizal efficacy of trifoliate orange seedlings on alleviating temperature stress

Citrus plants often suffer from temperature stress, which seriously inhibits tree growth and even results in tree death. The present experiment was conducted to evaluate the effects of Glomus mosseae on growth, root morphology, superoxide dismutase (SOD) and catalase (CAT) activities, and soluble protein content of trifoliate orange (Poncirus trifoliata) seedlings at low (15°C), optimum (25°C) and high (35°C) temperatures. Sixty-eight days after temperature stresses, mycorrhizal colonization and number of both entry points and vesicles were significantly inhibited by low or high temperature. Mycorrhizal seedlings recorded significantly higher growth characteristics than non-mycorrhizal seedlings at both optimum and high temperatures, but the beneficial effects were almost lost at low temperature. Generally, mycorrhizal seedlings presented notably higher root traits (projected area, surface area, number of forks and volume) than non-mycorrhizal seedlings regardless of temperature levels. Mycorrhizal colonization significantly increased SOD and CAT activities and soluble protein content at high temperature, increased only SOD activity at optimum temperature, and decreased only soluble protein content at low temperature. It suggests that mycorrhizal alleviation of temperature stress in trifoliate orange seedlings was at high temperature, but the alleviation was obviously weakened at low temperature.