Growth and physiological responses of Eichhornia crassipes to clonal integration under experimental defoliation

Many notorious invasive plants are clonal, and clonal integration may improve their ability to cope with disturbances such as herbivory. We hypothesize that clonal integration positively affects the growth, physiology and biomass allocation of the invasive aquatic plant Eichhornia crassipes and thus improves its performance in response to defoliation. In a 7-week greenhouse experiment, we subjected E. crassipes ramets to three levels of experimental defoliation, i.e., 20 % (mild), 50 % (moderate) and 80 % (heavy) leaf clipping and an unclipped control, and the stolon connections to the mother plants were either severed or kept intact. Compared with the control, defoliation significantly decreased the growth (total biomass and ramet number), but increased the maximum quantum yield of photosystem II (F (v)/F (m)) and chlorophyll content of the target ramets. Stolon connection (clonal integration) greatly increased the growth, F (v)/F (m) and contents of non-structural carbohydrates (soluble sugar and total non-structural carbohydrates) of E. crassipes, and these effects were larger under heavier defoliation. Moreover, stolon connection significantly reduced the shoot/root ratio of E. crassipes ramets, and such effects were greater under heavier leaf clipping. These results support our hypothesis that E. crassipes can benefit from clonal integration in response to defoliation, suggesting that clonal integration may enhance the invasion potential of E. crassipes and potentially reduce the efficacy of biological control.