ObjectivePhysiological mechanism of salt tolerance in Ginkgo biloba is not only helpful to solve the problem that snow melting agent and other salts leading to weakened growth of Ginkgo biloba, but also useful for fine species breeding and plant area enlargement of Ginkgo biloba.

MethodIn this study, the three-year-old Ginkgo biloba potted seedlings were used as plant material to explore physiological characteristics. By conditional control method, the concentrations of NaCl were set as 0, 0.2%, 0.4%, 0.6%, 0.8% and 1.0%, respectively. The changes of the growth, anatomic structure of tissue, photosynthesis in Ginkgo biloba were observed under NaCl stress.

ResultThe survival rate was 100% in the 0.2%-0.8% NaCl treated group on the 64th day of salt stress, the relative growth yield of plant height and ground diameter in Ginkgo biloba seedlings under 0.2% NaCl treatment group had no significant difference compared with the control, but they were severely restrained under high concentration of NaCl(0.6%-1.0%)treatment group(P < 0.05). It indicated that Ginkgo biloba seedlings in our study can grow normally when the salt concentration was below 0.44%. From the result of noninvasive scanning electron microscope observation, we found that a great number of pores existed on leave hypodermis, stoma closure time and extent were uneven, the sink of guard cells and the upheaval of subsidiary cells occurred. The leaf cuticle was thickened, and the leaf surface was covered by tubular wax crystal. A great deal of salt cluster crystal was observed in stem parenchymal cell, and little was found in root and stipe, suggesting that the Ginkgo biloba seedlings had certain ability of salt reservation in stem. These anatomical characteristics of Ginkgo biloba seedlings were related to their salt tolerance. The diurnal variations of photosynthesis(P_n、G_s、T_r、WUE)in the treatment group showed bimodal curves, C_i showed fall-rise and L_s showed rise-fall trend, respectively. The peak and valley values of P_n in the 0.2% treatment group were very significantly higher than other groups(P < 0.01). With the increase of treatment time, value of P_n decreased, while the values of G_s、C_i、T_r showed rise-fall trends. The P_n of the 0.2% treatment group was very significantly higher than the other groups before the processing of the former 35 days(P < 0.01), while lower than the other groups after that(P < 0.01), these could be resulted from stomatal limitation. The P_n of the 0.4%-1.0% treatment groups was very significantly lower than the control during the whole processing of salt(P < 0.01), and the decrease of P_n value in medium concentration(0.4%)treatment group was mainly resulted from stomatal limitation before the processing of the former 2-7 days, while that in the higher concentration(0.6%-1.0%)treatment group was mainly resulted from non-stomatal limitation in the same period, the decrease of P_n value in 0.4%-1.0% treatment groups was mainly resulted from non-stomatal limitation on the first day and in the lately stages of processing (the 35th day of stress), putatively resulting from emergency response of Ginkgo biloba and decrease of photosynthetic activity in high concentration in mesophyll cell.

ConclusionIt can be seen that this Ginkgo biloba species has certain salt tolerance and can be planted under 0.44% NaCl in soil. Photosynthesis parameters are sensitive to salt stress, and this can be useful to monitor and estimate salinity tolerance of Ginkgo biloba.