Ecophysiological responses of Phragmites australis populations to a tidal flat gradient in the Yangtze River Estuary, China

Abstract

Phragmites australis is a prevalent species in the Chongming Dongtan wetland and is capable of thriving in various tidal flat environments, including high salinity habitats. P. australis population displays inconsistent ecological performances, highlighting the need to uncover their survival strategies and mechanisms in tidal flats with diverse soil salinities. Upon comparing functional traits of P. australis at multiple tidal flats (low, middle, and high) and their responses to soil physicochemical properties, this study aimed to clarify the salt-tolerant strategy of P. australis and the corresponding mechanisms. These results showed that leaf characteristics, such as specific leaf area and leaf dry matter content, demonstrated more robust stability to soil salinity than shoot height and dry weight. Furthermore, as salt stress intensified, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxisome (POD) in P. australis leaves at low tidal flat exhibited an increased upward trend compared to those at other tidal flats. The molecular mechanism of salt tolerance in Phragmites australis across various habitats was investigated using transcriptome sequencing. Weighted correlation network analysis (WGCNA) combined with differentially expressed genes (DEGs) screened out 3 modules closely related to high salt tolerance and identified 105 core genes crucial for high salt tolerance. Further research was carried out on the few degraded populations at low tidal flat, and 25 core genes were identified by combining WGCNA and DEGs. A decrease in the activity of ferroptosis marker gonyautoxin-4 and an increase in the content of Fe³⁺ in the degenerated group were observed, indicating that ferroptosis might participate in degradation. Furthermore, correlation analysis indicated a possible regulatory network between salt tolerance and ferroptosis. In short, this study provided new insights into the salt tolerance mechanism of P. australis population along tidal flats.

Keywords: Phragmites australis; ferroptosis; salt tolerance; transcriptome; wetland ecosystem.

Figure 1

Study area and different sampling locations. H, high tidal flat; M, mid-tidal flat; L, low tidal flat outside the dike; L(IN), low tidal flat inside the dike.

Figure 2

Soil salinity at different tidal flats. (A) and (B) represented 0-10cm and 10-20cm soil layers respectively. L, low tidal flat outside the dike; IN, low tidal flat inside the dike; M, mid-tidal flat; H, high tidal flat. Letters indicate significant groupings of soil salinity at different tidal flats from LSD test (P ≤ 0.05). Mean ± SD, n = 15(L), n = 5(IN), n = 10 (M and H, respectively).

Figure 3

Correlation analysis of functional traits and antioxidant enzyme activity of P. australis under different tidal flats.

Figure 4

Principal component analysis of functional traits (A) and redundancy analysis of plant functional traits and soil physical and chemical properties (B) of P. australis at different tidal flats. SH, shoot height; BD, base diameter of P. australis; DW, total aboveground dry weight; FW, total aboveground fresh weight; SPAD, relative chlorophyll content; LDMC, leaf dry matter content; SLA, specific leaf area; POD, peroxidase; CAT, catalase; SOD, superoxide dismutase; AVP, Available phosphorus; TN, Total nitrogen; TP, Total phosphorus; C/N, Carbon nitrogen ratio; C/P, Carbon phosphorus ratio; N/P, Nitrogen phosphorus ratio. The number after different physical and chemical properties of soil represented different soil layers, 1 mean 0-10 cm soil layer and 2 mean 10-20 cm soil layer.

Figure 5

Antioxidant enzyme activities of P. australis leaves at different tidal flats. (A) superoxide dismutase activity; (B) catalase activity; (C) peroxidase activity. Letters indicate significant groupings from LSD post hoc tests (P ≤ 0.05). Mean ± SD, n = 3.

Figure 6

Network analysis of the salt tolerance genes. The thickness and thinness of the lines represented the high and low correlations, respectively, the red lines represented the positive correlation, and the blue lines represented the negative correlation. The blue circle represented salt tolerance genes from WGCNA and DEG, and the red circle represented the gene having GO annotation information. The orange circle represented the gene having GO annotation information that was not screened by WGCNA and DEG.

Figure 7

Screening plant growth and degeneration core gene set by DEG and WGCNA analysis. (A) The common intersection of 8 groups under the DEGs analysis method (compare with group E). (B) The common intersection of growth and degeneration genes under the DEGs and WGCNA analysis method. (C) The heat map showed the expression of the 25 shared genes. (D) Network analysis of the growth and degeneration genes. The thickness and thinness of the lines represented the high and low correlations, respectively, the red lines represented the positive correlation, and the blue lines represented the negative correlation. The blue circle represented growth and degeneration genes from WGCNA and DEG, and the red circle represented the gene having GO annotation information. The orange circle represented the gene having GO annotation information that was not screened by WGCNA and DEG.

Figure 8

Situation of ferroptosis-related factors in the shoot of P. australis in (E) at low tidal flat: iron content, (A); GPX enzyme activity, (B); above ground dry weight, (C); shoot height, (D). Mean ± SD, n = 5. Significant Duncan test differences: *< 0.05, **< 0.01, ***< 0.001. ns (not significant).

Figure 9

Network analysis of the growth & degeneration with salt tolerance genes. (A) Network analysis of the growth & degeneration with salt tolerance genes. (B) Network analysis of the ferroptosis with salt tolerance genes. (C) The heat map showing the expression of the shared genes in network analysis of the ferroptosis with salt tolerance genes.