Research progress on spatial expansion of clonal plants and its utilization for restoring degraded ecosystems

The spatial expansion ability of clonal plants can help them successfully colonize adverse habitats and make efficient use of patchily distributed resources, which is crucial for growth and adaptation of such plants. Spatial expansion characteristics of clonal plants also hold considerable potential for restoration of degraded ecosystems. One important characteristic of clonal plants is physiological integration, which consitutes resource translocation and sharing between ramets (i.e., potentially physiologically independent units or individuals) connected by horizontal structures such as rhizomes, stolons, and horizontally growing roots. In this review, adaptive strategies of clonal plants to colonize heterogeneous habitats are summarized. Based on physiological integration, clonal plants enhanced the division of labor by modifying phenotypic plasticity, foraging behavior, and the tradeoff of biomass allocation; thus, ramets in heterogeneous patches performed “specialization for abundance”, which substantially improved resource use efficiency and adaption potential. Moreover, based on the “C–S–R (competition–stress–ruderal)” life history strategy theory, effects of environmental factors including disturbance, stress, and competition on spatial expansion of clonal plants are discussed, and the driving mechanisms of expansion were also revisited. We assumed that intermediate disturbance (e.g., grazing, mowing, etc.) may improve spatial expansion of clonal plant populations. Furthermore, we summarized the application potential of expansion of clonal plants for the restoration of degraded ecosystems. Clonal plants produce large and dense multilayered rhizomes/roots during the expansion process which increases soil consolidation and sand fixation, improves water conservation capacity, and thus ameliorates the soil environment. Moreover, propagules of clonal plants play a pioneering role in colonizing poor or bared habitats, which is important for species diversity regeneration, community structure variation, and productivity in degraded ecosystems. Based on their expansion functions in both above- and below-ground environmental recovery, clonal plants improve the restoration succession of degraded ecosystems. It is suggested that future research should focus on spatial expansion of clonal plants from the perspective of restoration of degraded environments in order to increase knowledge on the overlapping fields of clonal plant biology and restoration ecology and to provide a new research ideas for the restoration and management of degraded grasslands.