Typical Rhizomatous Clonal Grass Psammochloa villosa Changes Resource Allocation During Clonal Expansion to Fit Arid...

Rhizomatous plants forming patchy expansions show high potential for sand fixation in mobile dunes with heterogeneous resources, yet resource allocation strategies among different plant parts and reproductive methods during patch expansion remain poorly understood. This study investigated the growth dynamics and allocation of key morphological traits (plant height, leaf area, and rhizome length) of Psammochloa villosa across clonal patches of different sizes in the desert-oasis ecotone of Northwest China. Results revealed that aboveground traits exhibited rapid unimodal growth, peaking in the order of plant height followed by leaf area, whereas rhizomes showed prolonged bimodal growth (approximately 8 months) with delayed peak phases. During clonal expansion from micro to medium patches, asexual clusters decreased the growth rate and increment of leaf area per ramet but markedly increased that of rhizome length, reflecting a shift from photosynthetic to clonal investment. The ratio of belowground to aboveground growth and their allometric relationship both shifted when patch size reached an lg-transformed area of 2-3, while sexual reproduction occurred exclusively in large patches (lg-transformed area more than 4). The maximum growth increment of aboveground traits in sexual clusters was more than double that in asexual clusters, indicating a high energy cost associated with sexual reproduction. This was supported by increased aboveground allocation in asexual ramets alongside reduced absolute rhizome growth, despite elevated relative rhizome growth rates. Consequently, sexual reproduction occurs at the expense of rhizome expansion, requiring extensive clonal expansion to accumulate resources in the resource-limited environment. P. villosa thus adapts to arid sandy habitats through stage-specific resource reallocation during patch expansion, with long-term spatial occupation via rhizomes preceding the costly sexual reproduction. These insights elucidate the persistence mechanisms of sand-fixing rhizomatous herbs and highlight the need to quantify threshold patch sizes and ages to enable sexual reproduction across environmental gradients.