Effects Of Patch Contrast On The Benefits Of Clonal Integration Of Invasive Plant Alternanthera Philoxeroides(Mart.) Griseb.and Its Related Species

Plant invasion has posed a great threat to the biodiversity,environment and economy both globally and locally.Many of the world’s worst invasive alien plants are clonal and able to share resources within clones(clonal integration),particularly in heterogeneous environments.Environmental heterogeneity is widespread in nature,an important element of heterogeneity is contrast,i.e.,the degree to which different patches differ quantitatively with respect to certain environmental factors.The size of the contrast in environmental heterogeneity will enhance or diminish the transport of substances defined by the source-sink relationship of the plant body itself.However,it is unclear whether the effect of patch contrast on the benefits of clonal integration of clonal plants differs between invasive alien and native plants.To investigate whether the increase in patch contrast could improve the benefits of clonal integration and whether this pattern was more significant in invasive alien plants,we conducted controlled experiments using the malignant invasive plant Alternanthera philoxeroides and its native plant A.sessilis of the same genus.The main results as follows:(1)Effects and differences of patch contrast on the benefits of clonal integration of A.philoxeroides and A.sessilis in a heterogeneous soil nutrient environment: The experiment was set up with three soil nutrient heterogeneous environments with different patch contrast sizes,and keeping the total nutrient content exactly the same.The clonal fragments of A.philoxeroides and A.sessilis were treated with severing(blocking clonal integration)and keeping connection(allowing clonal integration),respectively.The results showed that the biomass of A.philoxeroides was always significantly higher than that of A.sessilis without considering the effects of clonal integration and patch contrast.Clonal integration significantly increased the biomass of the whole clonal fragment of A.philoxeroides and A.sessilis,and the benefits of clonal integration increased with increasing patch contrast.More importantly,the positive effect of patch contrast on the benefits of clonal integration was more pronounced in the invasive species A.philoxeroides relative to A.sessilis.(2)Effects and differences of patch contrast on the benefits of clonal integration of A.philoxeroides and A.sessilis in a resource-reciprocal environment: The experiment was conducted by manipulating the light and nutrient levels of each pair of ramets to place connected and disconnected pairs of A.philoxeroides and A.sessilis in control,low and high patch contrast environments,respectively.The results showed that clonal integration significantly enhanced the growth performance of A.philoxeroides and A.sessilis in a high patch contrast environment,benefiting from the resource-specific uptake of the ramets.The results also showed that A.philoxeroides benefited more from clonal integration than A.sessilis.Clonal integration had no significant effect on plant growth in the control and low patch contrast environments.(3)Effects and differences of patch contrast on the benefits of clonal integration of A.philoxeroides and A.sessilis in a competitive environment: The experiment was conducted to simulate a competitive environment by constructing populations of L.peploides,while keeping the soil nutrient content constant in the competitive patches(apical ramet)and controlling the availability of soil nutrients in the blank patches(basal ramet)to adjust the size of the patch contrast.The clonal fragments of the two subject species were subjected to severing and maintaining connection treatments.The results showed that clonal integration significantly alleviated the competitive pressure on the apical ramets of both A.philoxeroides and A.sessilis in all patch contrast treatments.The positive effects of clonal integration were more pronounced as the patch contrast increased.Invasive plant A.philoxeroides benefited more from clonal integration than A.sessilis,and this difference was more pronounced in the high patch contrast treatment.In summary,an increase in patch contrast can improve the benefits of clonal integration.This positive effect was more pronounced in the invasive alien plant A.philoxeroides relative to the native plant A.sessilis.