Root Exudates Response of Mycorrhizal Pinus massoniana Seedlings Under Drought Stress

Pinus massoniana Lamb. (P. massoniana) grown under water-deficient conditions displays a series of coordinated adaptive responses. Although ectomycorrhizal (ECM) fungi can enhance plant adaptation to water deficiency, the research of ECM fungi colonization and water stress intensity induce P. massoniana seedlings root exudates to resist is no depth. One-year-old P. massoniana seedlings without inoculation (St1) and inoculated with Suillus luteus (St2, St3) were studied under no water stress 70-80% (Wt1), mild stress 60-70% (Wt2), moderate stress 50-60% (Wt3), and severe stress 35-50% (Wt4), respectively. The root exudates of seedlings were extracted by organic extraction method and identified by gas chromatography-mass spectrometry (GC-MS). The results show that root exudates variety and contents of different seedlings decreased as drought stress increased. Except for St1 under Wt1 treatment, other seedlings root secreted mono (2-ethylhexyl) phthalate (MEHP). Under the same water treatment, MEHP content of seedlings was Wt2: St1 (17.74%) < St3 (21.04%) < St2 (23.67%), Wt3: St1 (76.46%) < St2 (77.35%) < St3 (77.82%), and Wt4: St1 (0%) < St3 (56.71%) < St2 (61.65%). The content of MEHP in mycorrhizal P. massoniana seedlings was higher than that of un-inoculated seedlings. Therefore, drought can reduce root exudates richness of P. massoniana seedlings and the more obvious difference was that ECM fungi can increase the content of MEHP in seedlings significantly. The change was likely an important feature of mycorrhiza P. massoniana seedlings to adapt to drought stress.