Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts? An Implication for Biocontrol

Field studies have shown that native, parasitic plants grow vigorously on invasive plants and can cause more damage to invasive plants than native plants. However, no empirical test has been conducted and the mechanism is still unknown. We conducted a completely randomized greenhouse experiment using 3 congeneric pairs of exotic, invasive and native, non-invasive herbaceous plant species to quantify the damage caused by parasitic plants to hosts and its correlation with the hosts' growth rate and resource use efficiency. The biomass of the parasitic plants on exotic, invasive hosts was significantly higher than on congeneric native, non-invasive hosts. Parasites caused more damage to exotic, invasive hosts than to congeneric, native, non-invasive hosts. The damage caused by parasites to hosts was significantly positively correlated with the biomass of parasitic plants. The damage of parasites to hosts was significantly positively correlated with the relative growth rate and the resource use efficiency of its host plants. It may be the mechanism by which parasitic plants grow more vigorously on invasive hosts and cause more damage to exotic, invasive hosts than to native, non-invasive hosts. These results suggest a potential biological control effect of native, parasitic plants on invasive species by reducing the dominance of invasive species in the invaded community

Effect of carbon assimilation on dry weight production and partitioning during vegetative growth

Potassium deficiency is known to deeply impact dry matter yield through a lower photoassimilates production. The objectives of this study were to find out and classify the principal mechanisms that accounted for the reduction in plant stature. Our approach used the framework of interception-conversion modelling, with focuses on photosynthesis (gas exchange analysis, Farquhar model), plant-water relations (water potential components), and soluble sugars in leaves. Cotton plants were grown during 7 weeks under glasshouse hydroponic conditions and 4 increasing levels of potassium nutrition (K0, K1, K2 and K3). Sugar started to accumulate in mature leaves of K deficient plants at 20 days after emergence (DAE). This was mainly interpreted as the consequence of a low phloem loading for sucrose. At 40 DAE, leaf area and dry weight were reduced in K0 and K1 treatments compared to K2 and K3. Specific leaf weight was much higher in K deficient plants then in non deficient ones. Photosynthesis was reduced but only for severe deficient treatments (K0) and at the last measuring dates (50 DAE). We venture the hypothesis that sugar accumulation may be the key factor affecting nutrition of the growing organs, and photosynthetic capacity of the unfolded and mature leaves