Fig. 4: Plant biomass across treatments and experimental rounds.

Filled circles with error bars represent estimated marginal means of total plant dry biomass (g) per plant (±95% confidence intervals), derived from generalized linear models (quasipoisson, log link). Estimates are shown for each chamber type (Donor = red, Receiver = blue), treatment (Permeable, Impermeable, Axenic), and experimental round (Main, Follow-Up). Semi-transparent x-marks show individual plant biomass values. Significance of pairwise contrasts between chambers within each treatment is indicated (*p < 0.05, **p < 0.01, ***p < 0.001), based on back-transformed comparisons. Sample sizes (number of paired donor-receiver samples) are shown below each treatment group. Treatments with fewer than two replicates were excluded from statistical analyses and are shown only as individual points without summary statistics.