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.

许多湿地同时遭受养分和有毒金属的污染,其植被多数为克隆植物。我们假设,富养化和克隆整合可以通过增加植物的生长来提高对有毒金属污染的植物修复能力,即使在毒性胁迫环境下也是如此。为验证此假说,我们将常见、广布的匍匐茎漂浮植物大薸(Pistia stratiotes L.)的单个分株种植在两种不同的养分条件下和两种镉污染处理(无镉或含0.6 mg L^(-1)的镉)中42天。通过保持或切断母株与其后代分株之间的连接来维持或阻止克隆整合,并通过保留或移除切断后的后代分株来控制克隆内竞争的有无。由于高养分条件下克隆后代分株的数量增加了一倍,因此镉处理下大薸的生物量在高养分条件下几乎是在低养分条件下的两倍。切断匍匐茎连接对整个克隆(母株和后代分株的总和)的生物量没有影响。切断连接后去除后代分株对镉污染下母株的生物量没有显著的影响,但却显著增加了无镉污染下母株的生物量。这些研究结果支持富养化可以提高水生植物对有毒金属污染的修复能力这一假说,但并不支持克隆整合有利于植物修复的假说。因此,水生植物(如大薸)可能有助于对同时遭受有毒金属和养分污染的湿地进行修复,但克隆片段化对植物的这种修复能力可能没有显著影响。