Effects of clonal integration, nutrients and cadmium on growth of the aquatic macrophyte Pistia stratiotes

Aims Many wetlands are polluted with both nutrients and toxic metals and vegetated largely by clonal plants.We hypothesized that eutrophication and clonal integration can increase phytoremediation of toxic metal pollution by increasing plant growth,even under the stress imposed by toxicity.Methods To test this hypothesis,single ramets of the common,widespread,floating,stoloniferous plant Pistia stratiotes L.,were grown for 42 days at two levels of nutrient availability with and without 0.6 mg L^(-1) cadmium.Ramets were either severed from their vegetative offspring to prevent clonal integration or left connected,and severed offspring were either removed to eliminate intraclonal competition or left in place.Important Findings Plants subjected to cadmium addition accumulated almost twice as much dry mass if given the higher nutrient level,due mainly to a doubling of the number of clonal offspring.Severance had little effect on the final mass of the parent plus offspring ramets.Removing offspring following severance had no effect on the final mass of the parental ramet in the presence of added cadmium,but it did increase the final mass of the parent in the absence of cadmium.These results support the hypothesis that eutrophication can increase remediation of toxic metal pollution by aquatic macrophytes but provided no evidence that clonal integration can affect remediation.Species such as P.stratiotes may help remediate co-pollution of wetlands with toxic metals and nutrients,and fragmentation of clones may not affect their remediation capacity.

Genotypic differences in response to different patterns of clonal fragmentation in the aquatic macrophyte Pistia stratiotes

Connected individuals(ramets)of clonal plants are frequently fragmented due to disturbance,and such clonal fragmentation may influence their growth.However,it is unclear whether different patterns of clonal fragmentation produce differential effects on plant growth and whether such differences vary with genotypes.We collected one group of connected ramets of the stoloniferous floating invasive macrophyte Pistia stratiotes from each of six provinces(Guangdong,Guangxi,Hubei,Jiangsu,Sichuan and Yunnan Provinces)of China,and assumed that these ramets belonged to different genotypes.After several generations of vegetative propagation to remove potential parental effects,new ramets(hereafter referred to as parent ramets)from each of these assumed genotypes were subjected to four patterns of clonal fragmentation,i.e.,all offspring ramets produced during the experiment remained connected to their parent ramet(control),or the primary(1°),secondary(2°)or tertiary(3°)offspring ramets were disconnected from their parent ramet.We found significant growth differences among the assumed genotypes,confirming that the ramets sampled from these six provinces were from different genotypes.Compared with the control,disconnecting the 1°,2°or 3°ramets did not significantly affect biomass of the whole clone(i.e.,the parent ramet plus all offspring ramets)of P.stratiotes.Disconnecting the 1°ramets significantly increased biomass of the parental ramet of all six genotypes compared with the control.However,disconnecting the 2°or 3°ramets had little effect on biomass of the parent ramet for all genotypes except the Guangxi genotype,for which disconnecting the 2°ramets decreased biomass of the parent ramet.Disconnecting the 1°,2°or 3°ramets had no impact on biomass or number of the 1°or the 3°ramets for any of the genotypes.However,disconnecting the 1°ramets decreased biomass of the 2°ramets for the Guangdong and Yunnan genotypes,but had no effect for the other four genotypes.We conclude that different patterns of clonal fragmentation can have different impacts on parent and offspring ramets of P.stratiotes and such an impact may vary with genotypes.