68-Interactive-effects-of-N-and-P-on-growth--nutrient-allocation-and-NH4-uptake-kinetics-by

J.A.Romeroetal./AquaticBotany64(1999)369–380373Table2ResultsofANOVA(P-values)forgrowthandbiomasspartitioningofP.australisgrownattwoPandthreeNlevelsfor5weeksaSourceofvariationRGRRWRRhWRLWRN0.006b0.8920.2330.149P0.9110.4080.6090.816N×P0.1020.4030.0850.220aRGR:Relativegrowthrate;RWR:Rootweightratio;RhWR:Rhizomeweightratio;LWR:Leafweightratio.bFiguresinboldindicatestatisticallysignificantvaluesatthe0.05probabilitylevel.2.5.RootrespirationRootrespirationwasmeasuredbyincubatingthreerootsfromeachplant(approx.0.2gfreshweight)in33.5mlincubationflasksmountedonarotatingwheelinathermostated(25◦C)waterbath.Respirationwasestimatedasproductionofdissolvedinorganiccarbon(DIC)overtimeintheincubationflasks.ConcentrationsofDICweremeasuredon100�lsubsamplesthatwereacidifiedandspargedwithN2gastocarryallCO2intoaninfraredgas-analyser(ADC225-MK-3,UK)connectedtoanintegrator(ChromatopacC-R3A,Shi-madzuCorp.,Kyoto,Japan).2.6.StatisticsDatawereanalysedbyanalysisofvariance(ANOVA)usingTypeIIIsumofsquareswiththesoftwareStatgraphicsversion3.1(StatisticalGraphicsCorp.,USA).MultiplecomparisonsofmeanswereperformedusingFisher’sLSDprocedureatthe0.05significancelevel.AlldataweretestedfornormaldistributionandforhomogeneityofvariancebyCochran’stest.3.Results3.1.PlantgrowthandbiomassallocationTheestimatedgrowthrateswereerraticduringtheinitialtwoweeksoftheincubationperiodprobablybecauseofdyingofrootsandacclimationtotheexperimentalconditions.However,aftertwoweeksthegrowthratesbecamestableandaveraged0.033±0.008perday(RGR,mean±SD)foralltreatments.NitrogenlevelintherootsolutionsignificantlyaffectedRGR,theratebeingloweratlowN(0.026perday)thanatintermediate(0.035perday)andhighN(0.037perday).PhosphoruslevelhadnoeffectontheRGR,andnosignificantinteractiontermbetweenNandPwasfound(Table2).TheN:PratiointhegrowthmediumsignificantlyaffectedRGR,theratesbeinghighestatmolarN:Pratiosbetween10and33(Fig.1).Therelativeallocationofbiomasstoroots(11.1±2.6%),rhizomes(27.3±12.6%),stems(33.4±6.1%)andleaves(28.2±7.3%)wasunaffectedbytrea