Arbuscular mycorrhizal fungi affect the expression of PxNHX gene family, improve photosynthesis and promote Populus simonii× P. nigra growth under saline-alkali stress

Abstract

Introduction: Saline-alkali stress seriously endangers the normal growth of Populus simonii×P. nigra. Arbuscular mycorrhizal (AM) fungi can enhance the saline-alkali tolerance of plants by establishing a symbiotic relationship with them.

Methods: In this study, a pot experiment was conducted to simulate a saline-alkali environment where Populus simonii×P. nigra were inoculated with Funneliformis mosseae to explore their effects on the saline-alkali tolerance of Populus simonii×P. nigra.

Results and discussion: Our results show that a total of 8 NHX gene family members are identified in Populus simonii×P. nigra. F. mosseae regulate the distribution of Na+ by inducing the expression of PxNHXs. The pH value of poplar rhizosphere soil is reduced, result in the promote absorption of Na⁺ by poplar, that ultimately improved the soil environment. Under saline-alkali stress, F. mosseae improve the chlorophyll fluorescence and photosynthetic parameters of poplar, promote the absorption of water, K⁺ and Ca²⁺, thus increase the plant height and fresh weight of aboveground parts, and promote the growth of poplar. Our results provide a theoretical basis for further exploring the application of AM fungi to improve the saline-alkali tolerance of plants.

Keywords: Funneliformis mosseae; NHX gene family; Populus simonii×P. nigra; arbuscular mycorrhizal fungi; saline-alkali stress.

Figure 1

AM fungal infection photos and changes of AM fungal infection rate under saline-alkali stress. (A) AM fungal infection photos; (B) Changes of AM fungal infection rate under saline-alkali stress. AMN means inoculation with F. mosseae without saline-alkali stress; AMS means inoculation with F. mosseae and application of saline-alkali stress. Bars indicate mean ± standard error (n = 3). Different lowercase letters indicate significant differences between the means by Tukey’s test (P < 0.05).

Figure 2

Effects of AM fungal inoculation and saline-alkali stress on soil pH. NMN means no F. mosseae inoculation and no saline-alkali stress; AMN means inoculation with F. mosseae without saline-alkali stress; NMS means application of saline-alkali stress without F. mosseae inoculation; AMS means inoculation with F. mosseae and application of saline-alkali stress. Bars indicate mean ± standard error (n = 3). Different lowercase letters indicate significant differences between the means by Tukey’s test (P < 0.05). Significant effect of two-way ANOVA analysis: “*” indicates P < 0.05, “**” indicates P < 0.01.

Figure 3

Effects of AM fungal inoculation and saline-alkali stress on plant height and fresh weight of P. simonii×P. nigra. (A) Photos of P. simonii×P. nigra growth status after saline-alkali stress and AM fungus inoculation for 8 weeks; from left to right, AMN, AMS, NMN and NMS. (B) Plant height histogram of P. simonii×P. nigra, bars indicate mean ± standard error (n = 18). (C) The fresh weight histogram of the aboveground part of P. simonii×P. nigra, bars indicate mean ± standard error (n = 3). (D) The fresh weight histogram of the underground part of P. simonii×P. nigra, bars indicate mean ± standard error (n = 3). NMN means no F. mosseae inoculation and no saline-alkali stress; AMN means inoculation with F. mosseae without saline-alkali stress; NMS means application of saline-alkali stress without F. mosseae inoculation; AMS means inoculation with F. mosseae and application of saline-alkali stress. Different lowercase letters indicate significant differences between the means by Tukey’s test (P < 0.05). Significant effect of two-way ANOVA analysis: “**” indicates P < 0.01; “NS” indicates no interaction (P ≥ 0.05).

Figure 4

Effects of AM fungal inoculation and saline-alkali stress on gas exchange parameters. (A) Effects of AM fungal inoculation and saline-alkali stress on P_n value; (B) Effects of AM fungal inoculation and saline-alkali stress on g_s value; (C) Effects of AM fungal inoculation and saline-alkali stress on C_i value; (D) Effects of AM fungal inoculation and saline-alkali stress on E value. NMN means no F. mosseae inoculation and no saline-alkali stress; AMN means inoculation with F. mosseae without saline-alkali stress; NMS means application of saline-alkali stress without F. mosseae inoculation; AMS means inoculation with F. mosseae and application of saline-alkali stress. P_n means net photosynthetic rate, g_s means stomatal conductance, C_i means intercellular CO₂ concentration, and E means transpiration rate. Bars indicate mean ± standard error (n = 5). Different lowercase letters indicate significant differences between the means by Tukey’s test (P < 0.05). Significant effect of two-way ANOVA analysis: “*” indicates P < 0.05, “**” indicates P < 0.01; “NS” indicates no interaction (P ≥ 0.05).

Figure 5

Effects of AM fungal inoculation and saline-alkali stress on chlorophyll fluorescence. (A) Effects of AM fungal inoculation and saline-alkali stress on Fv/Fm value; (B) Effects of AM fungal inoculation and saline-alkali stress on NPQ value; (C) Effects of AM fungal inoculation and saline-alkali stress on ФPSII value; (D) Effects of AM fungal inoculation and saline-alkali stress on qN value; (E) Effects of AM fungal inoculation and saline-alkali stress on qP value; (F) Effects of AM fungal inoculation and saline-alkali stress on ETR value. Fv/Fm means maximal photosystem II quantum yield; NPQ means non-photochemical quenching; ФPSII means the efficiency of photosystem II; qN means non-photochemical quenching coefficient; qP means photochemical quenching coefficient; ETR means relative electron transfer rate. NMN means no F. mosseae inoculation and no saline-alkali stress; AMN means inoculation with F. mosseae without saline-alkali stress; NMS means application of saline-alkali stress without F. mosseae inoculation; AMS means inoculation with F. mosseae and application of saline-alkali stress. Bars indicate mean ± standard error (n = 5). Different lowercase letters indicate significant differences between the means by Tukey’s test (P < 0.05). Significant effect of two-way ANOVA analysis: “*” indicates P < 0.05, “**” indicates P < 0.01; “NS” indicates no interaction (P ≥ 0.05).

Figure 6

The evolutionary tree of the NHX gene family of P. simonii×P. nigra, Arabidopsis thaliana, P. trichocarpa and Zea mays.

Figure 7

Expression thermogram of NHX gene family in P. simonii×P. nigra. (A) Expression thermogram of NHX gene family in aboveground part of P. simonii×P. nigra. (B) Expression thermogram of NHX gene family in underground part of P. simonii×P. nigra. NMN means no F. mosseae inoculation and no saline-alkali stress; AMN means inoculation with F. mosseae without saline-alkali stress; NMS means application of saline-alkali stress without F. mosseae inoculation;AMS means inoculation with F. mosseae and application of saline-alkali stress. The colour scale represents the log2 value of the gene expression (n = 3). From red to blue, the expression level was from high to low. Different lowercase letters indicate significant differences between the means by Tukey’s test (P < 0.05). “NS” indicates no interaction (P ≥ 0.05). The results of two-way ANOVA for each gene are presented in the Supplementary Table 3 .

Figure 8

Thermogram of Pearson’s correlation between AM fungal infection and different parameters in aboveground part. TWC, tissue water content; RWC, relative water content; Fv/Fm, the maximum quantum yield of PSII; ETR, photosynthetic electron transport rate, qN, non-photochemical quenching, qP, photochemical quenching, NPQ, non-photochemical quenching coefficient according to the following formulas; ФPSII, PSII actual photon quantum efficiency; P_n , net photosynthetic rate; g_s , stomatal conductance; C_i , intercellular CO₂ concentration; E, transpiration rate; FW, fresh weight. Each circle indicates the Pearson’s correlation coefficient of a pair of parameters. “*” indicates P < 0.05, “**” indicates P < 0.01.

Figure 9

Thermogram of Pearson’s correlation between AM fungal infection and different parameters in underground part. FW, fresh weight. Each circle indicates the Pearson’s correlation coefficient of a pair of parameters. “*” indicates P < 0.05, “**” indicates P < 0.01.