Belowground clonal expansion and biomass allocation of Phragmites australis along a sand burial gradient in mobile dunes

Background and aims Sand burial is a dominant physical disturbance in arid dune ecosystems, profoundly altering soil moisture, temperature regimes and mechanical resistance, and thereby constraining belowground plant growth. Rhizomatous clonal plants are particularly dependent on belowground strategies to persist and expand under such conditions, yet how sand burial regulates rhizome expansion and biomass allocation remains poorly understood.Methods We combined two complementary field components in an active dune system in the Ulan Buh Desert, northwestern China. First, rhizome extension of Phragmites australis was monitored descriptively across three burial-depth categories. Second, rhizome traits, ramet recruitment and biomass allocation were examined across three dune microhabitats: interdune lowland, transition zone and windward slope.Results Rhizomes in deeper burial categories showed greater extension rate and total expansion length than those in shallow burial. Rhizome morphology exhibited strong habitat-dependent variation: internode length and cross-sectional area were greater on windward slopes and transition zones, while rhizomes in interdune lowlands displayed higher length-to-width ratios. Ramet recruitment pathways also shifted spatially, with rhizome-derived ramets dominating in lowlands and tiller-derived ramets prevailing on windward slopes. Biomass allocation further reflected this gradient, with greater vertical investment in lowlands and increasing horizontal allocation toward windward slopes over the growing season.Conclusion These results show that P. australis exhibits substantial variation in rhizome expansion, clonal traits and biomass allocation across heterogeneous dune environments. Descriptive observations suggest contrasting rhizome expansion under different burial conditions, while habitat-scale patterns reveal variation in clonal organization and biomass allocation. The observed variations in rhizome traits and biomass allocation help explain how clonal plants persist under disturbance in mobile dunes.