Evolutionary lineages of Phragmites australis in China.

(A) Bayesian clustering analysis based on 42 nuclear microsatellites at the optimal genetic cluster number K = 2. (B) Principal coordinate analysis (PCoA) based on Bruvo’s genetic distance. Colors indicate chloroplast haplotypes, where P_r denotes P-related haplotypes and “Unknown” refers to samples without haplotype data. Shapes denote geographical origins: circles (northern China, CN_N), squares (southern China, CN_S), and triangles (northwestern China, CN_W). (C) Geographical distribution of sampling locations for each genetic lineage by PCoA or/and chloroplast haplotypes. (D) Bioclimatic variable differences among lineages. Bio1, annual mean temperature; bio2, mean diurnal range; bio3, isothermality; bio4, temperature seasonality; bio8, mean temperature of wettest quarter; bio14, precipitation of driest month; bio15, precipitation seasonality; bio18, precipitation of warmest quarter. Significance levels are indicated as: * p < 0.05, ** p < 0.01, *** p < 0.001.

Admixture and introgression between CN and FEAU lineages revealed by STRUCTURE.

(A) Scatter plot of individual ancestry coefficients for the two ancestral components (CN and FEAU). Dashed lines indicate the 0.2 and 0.8 thresholds used to define pure and admixed individuals. Points are colored by admixture group. STRUCTURE is used here to detect hybridization, not to define lineages (see Figure 1). (B) Histograms of CN ancestry values across three geographic regions: Northern China, Southern China, and Northwestern China. (C) Geographic distribution of admixture groups across Chinese provinces. Pie charts show the relative proportions of pure CN (blue), pure FEAU (orange), and mixed (red) individuals in each province. (D) Relationship between latitude and log-transformed admixture level. Points are colored by admixture group. The regression line (solid if p < 0.05, dashed if p > 0.05) and p-value (from linear mixed-effects model with Province as random effect) are shown. The admixture level for each individual was calculated as 1 - 2 × |CN−0.5|, where CN is the ancestry coefficient of the CN lineage (range 0 - 1). This value approaches 1 when CN = 0.5 (high admixture) and approaches 0 when CN is near 0 or 1 (near-pure ancestry). To improve visualization, we plotted log (admixture level + 1), which ranges from 0 (pure) to log (2) ≈ 0.69 (maximally admixed). (E) Relationship between longitude and log-transformed admixture level. Visualization follows the same conventions as panel D. Pure individuals are defined as having > 80% ancestry from one component; individuals with 20-80% ancestry from each component are classified as mixed.

Comparative growth performance and heat tolerance of the CN and FEAU lineages of Phragmites australis across common garden environments.

(A) Geographic locations of the four common garden sites (Panjin, Jinan, Qingdao, Shanghai) overlaid on the mean annual temperature (Bio1) raster map of eastern China. Color gradient represents annual mean temperature (℃). (B-E) Comparison of four growth traits between lineages across four common garden locations: (B) Total Biomass, (C) Shoot Height, (D) Density, and (E) Specific Leaf Area (SLA). Bar heights represent mean values, and error bars indicate the standard error of the mean. (F) Comparison of key heat tolerance parameters (Tcrit, T50 and T95) between the CN and FEAU lineages. Significance levels from pairwise t tests within each garden (B-E) and unpraised t tests for heat tolerance parameters (F) are denoted by asterisks: * p < 0.05, ** p < 0.01, *** p < 0.001; “ns” indicates not significant.

Predicted potential distribution of three Phragmites australis lineages (CN, FEAU, and SW) in China under current and future climate scenarios.

The first row (A, B, C) shows the results for the CN lineage, the second row (D, E, F) for the FEAU lineage, and the third row (G, H, I) for the SW lineage. Columns represent different time periods: current distribution (A, D, G), and projected distributions for 2061–2080 under the low-emission scenario SSP1-2.6 (B, E, H) and the high-emission scenario SSP5-8.5 (C, F, I). Predictions were generated using the Maximum Entropy (MaxEnt) model. The depth of color (color intensity) corresponds to the level of habitat suitability, ranging from dark blue (unsuitable) to bright yellow (highly suitable).