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<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 2: Spartina Distribution and Spreadwater supply is not limiting, photosyn<strong>the</strong>sis in C4 plants iscarbon dioxide saturated. However higher atmosphericcarbon dioxide is likely to increase photosyn<strong>the</strong>sis, andhence growth, in C3 plants such as Puccinellia due to higherconversion efficiency.The different effects <strong>of</strong> elevated temperatures andcarbon dioxide on <strong>the</strong> two species were modelled by Long(1990). The model predicts <strong>the</strong> primary production <strong>of</strong>Spartina and Puccinellia to be expected in <strong>the</strong> year 2050,assuming a 3 degree rise in temperature and a doubling <strong>of</strong>atmospheric carbon dioxide. It was validated by comparing<strong>the</strong> predictions <strong>of</strong> production under 1978 conditions wi<strong>the</strong>mpirical field data. The increase in annual net production <strong>of</strong>Spartina from 1.3 kilograms per square meter (kg/m 2 ) in1978 to 2.1 kg/m 2 in 2050 was largely attributable totemperature-driven increases in leaf area, enabling <strong>the</strong> pointwhere <strong>the</strong> leaf area index is sufficient to intercept 30% <strong>of</strong> <strong>the</strong>incoming solar radiation to be reached 50 days earlier. Theincrease in Puccinellia, from 1.4 kg/m 2 in 1978 to 2.5 kg/m 2in 2050, was largely attributed to higher conversionefficiency in a high carbon dioxide environment but <strong>the</strong>model indicated that Puccinellia would gain from highertemperatures in spring and autumn.Long’s model, as he acknowledges, excludes severalfactors which may change with climate and will impact onplant growth. These include salinity, nutrient availability andwater level. Also excluded is a consideration <strong>of</strong> <strong>the</strong>competitive interactions between <strong>the</strong> two species underchanging conditions.A COMPETITION EXPERIMENT BETWEEN THE TWO SPECIESIn order to gain insight into how changing climate mayaffect <strong>the</strong> distribution <strong>of</strong> Spartina and Puccinellia <strong>the</strong> twospecies were grown in a competition experiment undercontrolled conditions <strong>of</strong> carbon dioxide and temperature.The experiment and full results are described in Gray andMogg (2001) and only a summary is given below.Plants <strong>of</strong> <strong>the</strong> two species were originally sampled froma salt marsh in Morecambe Bay (at 54° 10’ N) and grown incommon conditions for 18 weeks before 160 tillers <strong>of</strong> eachspecies were removed, size-matched and transplanted intopots containing standard soils. The experimental design wasa replacement series (de Wit 1960), each series comprisingfive pots <strong>of</strong> four tillers (4 Spartina, 3 Spartina + 1Puccinellia, 2 Spartina + 2 Puccinellia, 1 Spartina + 3Puccinellia, and 4 Puccinellia). Eight series were set up inlarge pots and eight in smaller pots to give two density levelsand, following a three-week establishment period, <strong>the</strong> potswere transferred to <strong>the</strong> experimental conditions. Thesecomprised eight hemispherical glasshouses (<strong>the</strong>‘solardomes’) in which atmosphere and temperature arecontrolled to a high degree <strong>of</strong> precision. The eight domesallowed two replicates <strong>of</strong> each treatment and <strong>the</strong> fourtreatments were: ambient temperature + ambient CO 2 ;ambient temperature + a CO 2 concentration <strong>of</strong> 340 parts permillion; temperature elevated by 3° C and trackedcontinuously above ambient + ambient CO 2 ; and elevatedtemperature + elevated CO 2 . The pots were maintained withnon-limiting water supplies, fertilized, and harvested after 11months growth when each plant was separated into aboveand below ground material before weighing. The results aresummarized in Table 1.The main conclusions to be drawn from <strong>the</strong> experimentare (1) most yield variables were significantly affected bytreatment, ei<strong>the</strong>r by temperature or carbon dioxide level or<strong>the</strong> interaction between <strong>the</strong>se treatments and density(Spartina height and inflorescence number beingexceptions), (2) <strong>the</strong> main competitive interaction effectswere due to <strong>the</strong> competitive superiority <strong>of</strong> Puccinellia,which had a significant negative effect on Spartina’s heightand above ground weight and displayed strong intraspecificcompetitive effects on tiller number and biomass, (3)Spartina responded to higher temperature as predicted, butalso, at low plant density, to carbon dioxide concentration.In both cases <strong>the</strong> response was mainly an increase in belowgroundgrowth including rhizomes, (4) Puccinelliaresponded to higher atmospheric carbon dioxide and highertemperature mainly by increasing above-ground growth, (5)Spartina had an unexplained poor performance in <strong>the</strong> ++treatment, an effect seen at low density and <strong>the</strong>reforeunlikely to be explained by competition with Puccinellia,Table 1. Individual plant means for six yield variables at final harvest.Trait Species Amb +T +CO 2 ++ Sig mn effectsSpa 4.10 6.17 6.00 3.48 D*, CT*Till no.Pucc 31.46 17.69 25.76 25.98 P**, CTD*Fl. TillHt(cm)S wt(g)BG wt(g)Biom(g)Spa 0.13 0.11 0.28 0.01 nsPucc 1.79 0.42 1.34 1.53 D***, DP*Spa 15.37 16.69 19.98 17.88 P*Pucc 44.47 44.08 48.24 54.98 D***, CD*Spa 0.45 0.70 0.89 0.37 D*, P*Pucc 1.77 1.28 1.61 2.70 D***, CDT**Spa 0.61 0.97 1.38 0.60 CT*, CTD**Pucc 0.42 0.24 0.36 0.37 CTP**Spa 1.04 1.67 1.98 0.97 CT**, CTD**Pucc 2.19 1.53 1.97 3.08 D***, CTP*The treatments (see text) were: Amb = ambient temperature and CO 2 , +T =elevated temperature and ambient CO 2 , +CO 2 = ambient temperature andelevated CO 2 , ++ = elevated temperature and elevated CO 2 . The variableswere: Till no. = number <strong>of</strong> tillers, Fl. Till = number <strong>of</strong> flowering tillers,Ht(cm) = plant height, S wt(g) = shoot weight, BG wt(g) = weight <strong>of</strong>below-ground material, Biom(g) = total biomass. The significance levelsare from a generalised ANOVA <strong>of</strong> log transformed values in which D =effect <strong>of</strong> density (pot size) (1df), C = effect <strong>of</strong> elevated CO 2 (1df), T =effect <strong>of</strong> elevated temperature (1df), and P = effect <strong>of</strong> <strong>the</strong> proportion <strong>of</strong>Puccinellia (which is a measure <strong>of</strong> competitive interaction effects) (3df).Only main interaction effects are given. Significance * p
Chapter 2: Spartina Distribution and Spread<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive Spartinaand (6) <strong>the</strong> pervasive effects <strong>of</strong> plant density on mostvariables underlines <strong>the</strong> importance <strong>of</strong> varying density insuch experimental designs (Gibson et al. 1999).A comparison <strong>of</strong> plant growth in ambient conditionswith that in <strong>the</strong> ++ treatment provides broad agreement withLong’s (1990) model predictions. The mean biomass <strong>of</strong>individual Puccinellia plants increased by about 100% inpure stands, a similar order <strong>of</strong> magnitude to <strong>the</strong> 80%increase in cumulative net primary production in <strong>the</strong> model.Increases in Spartina yield <strong>of</strong> 72% and 95% in elevatedtemperature and carbon dioxide respectively comparefavourably with <strong>the</strong> model prediction <strong>of</strong> 62%, but <strong>the</strong> smallincrease in ++ conditions (+5%) was unexpected. Theresponse <strong>of</strong> Puccinellia is broadly in line with that found ino<strong>the</strong>r C3 species (Bazzaz 1990) as is Spartina’s response toelevated temperature. However <strong>the</strong> increased yield <strong>of</strong>Spartina in higher carbon dioxide is at variance with o<strong>the</strong>rwork on C4 grasses, including Spartina patens (Curtis et al.1989).DISCUSSION AND SPECULATIONAs mentioned earlier, plant performance will be affectedby several o<strong>the</strong>r factors related to projected climate change,some <strong>of</strong> which are difficult to predict, and it is generallyrisky to make predictions on <strong>the</strong> basis <strong>of</strong> photosyn<strong>the</strong>ticpathway or CO 2 response alone (Dukes and Mooney 1999).Never<strong>the</strong>less it is interesting to speculate on <strong>the</strong> implications<strong>of</strong> <strong>the</strong> above experiment for <strong>the</strong> future changes in Spartinadistribution. Indeed <strong>the</strong>re are some aspects <strong>of</strong> <strong>the</strong> interactionbetween Spartina and Puccinellia which encourage us tobelieve that our predictions have a better than averagechance <strong>of</strong> being somewhere near <strong>the</strong> mark – a relativelysimple two-species system, predominately vegetativecompetition related to elevation as a resource, a strongseasonal element, wide dispersal <strong>of</strong> propagules, locallyshared resource levels and so on (see Gray and Mogg 2001for a fuller discussion).Locally, competition will be influenced by <strong>the</strong> balancebetween increasing temperatures and carbon dioxideconcentration. The average global warming <strong>of</strong> 1 to 3.5° Cover <strong>the</strong> next century predicted as a result <strong>of</strong> increasedgreenhouse gases is likely to vary spatially and to be higherin nor<strong>the</strong>rn latitudes in winter (Houghton 1996). In generalhowever we may expect Spartina to extend its rangenorthwards <strong>of</strong> 57° N as temperatures and carbon dioxiderise. Seed set in nor<strong>the</strong>rn populations, which is currentlylimited by <strong>the</strong> length <strong>of</strong> <strong>the</strong> growing season (for Spartinathis is <strong>the</strong> number <strong>of</strong> days above 9° C) may also increase andadd to <strong>the</strong> plant’s capacity to colonize new mudfats. Theincreased biomass below ground should enable <strong>the</strong> speciesto survive in <strong>the</strong> lower parts <strong>of</strong> its elevational niche.However, it seems likely that <strong>the</strong> competitively superiorPuccinellia will replace Spartina at appropriate elevations. Itis even possible that <strong>the</strong> high performance <strong>of</strong> Puccinelliaunder elevated temperature and carbon dioxide indicates thatit will replace Spartina at lower elevations in nor<strong>the</strong>rnlatitudes. The future management <strong>of</strong> nor<strong>the</strong>rn marshes,especially <strong>the</strong> extent to which <strong>the</strong>y are grazed (a processwhich favours Puccinellia over Spartina) will influence <strong>the</strong>interaction between <strong>the</strong> two species.In conclusion, our experiment suggests that changingclimatic conditions could kick-start Spartina’s stalledinvasion, enabling it to colonize mudflats and marshesnorthwards <strong>of</strong> its present distribution. Much will depend onchanges in o<strong>the</strong>r ecosystem processes and on o<strong>the</strong>r features<strong>of</strong> <strong>the</strong> changing climate. Higher rainfall, through its effect onsalinity, and changes in storm frequency and wind directionare likely to be important factors. A key factor will be <strong>the</strong>impact <strong>of</strong> rising relative sea levels and <strong>the</strong>ir influence onlocal sediment availability and accretion.ACKNOWLEDGMENTSWe are grateful to Les Jones and <strong>the</strong> staff at CEHBangor who manned <strong>the</strong> solardomes and to Ralph Clarke forstatistical advice. AJG wishes to acknowledge <strong>the</strong> input over<strong>the</strong> years <strong>of</strong> <strong>the</strong> many students who have contributed to <strong>the</strong>Spartina work, in particular Paul Adam, Colin Ferris, AlanRaybould , John Thompson and Liz Warman.REFERENCESBazzaz, F.A. 1990. The response <strong>of</strong> natural ecosystems to <strong>the</strong> risingglobal CO 2 levels. Annual Reviews <strong>of</strong> Ecology and Systematics.21: 167-196.Charman, K. 1990. The current status <strong>of</strong> Spartina anglica in GreatBritain. In: Gray, A.J. and P.E.B. Benham, eds. Spartina anglica– a Research Review, 11-14. HMSO, London.Curtis, P.S., B.G. Drake, and D.F. Whigham 1989. Nitrogen andcarbon dynamics in C3 and C4 estuarine marsh plants grownunder elevated CO 2 in situ. Oecologia. 78:297-301.De Wit, C.T. 1960. On competition. Verslagen van LandbouwkundigeOnderzoekinge., 66:1-82.Dukes, J.S. and H.A. Mooney. 1999. Does global change increase<strong>the</strong> success <strong>of</strong> biological invaders? TREE., 14:135-139.Dunn, R., S.P. Long, and S.M. Thomas. 1981. The effects <strong>of</strong>temperature on <strong>the</strong> growth and photosyn<strong>the</strong>sis <strong>of</strong> <strong>the</strong> C4 grassSpartina townsendii. In: Grace J., E.D. Ford, and P.G. Jarvis,eds. Plants and <strong>the</strong>ir atmospheric environment, 301-311. Blackwell,Oxford.Ferris, C., R.A. King, and A.J. Gray. 1997. Molecular evidence for<strong>the</strong> maternal parentage in <strong>the</strong> hybrid origin <strong>of</strong> Spartina anglicaCE Hubbard. Molecular Ecology. 6:185-187.Gibson, D.J., H. Connolly, D.C. Hartnett, and J.D. Weidenhamer.1999. Designs for greenhouse studies <strong>of</strong> interactions betweenplants. Journal <strong>of</strong> Ecology. 87:1-16.Gray, A.J. and R.J. Mogg. 2001. Climate impacts on pioneersaltmarsh plants. Climate Research. 18: 105-112.Gray, A.J. and A.F. Raybould. 1997. The history and evolution <strong>of</strong>Spartina anglica in <strong>the</strong> British Isles. <strong>Proceedings</strong> 2nd <strong>International</strong>Spartina <strong>Conference</strong>, 13-16. Washington State University,Olympia.Gray, A.J., D.F. Marshall, and A.F. Raybould. 1991. A century <strong>of</strong>evolution in Spartina anglica. Advances in Ecological Research.21:1-61.- 106 -
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FORWARD & ACKNOWLEDGEMENTSThe <stro
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Community Spartina Education and St
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CHAPTER ONESpartina Biology
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Chapter 1: Spartina Biology
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