Münzbergová Z, Skálová H. & Hadincová V. Genetic diversity affects productivity in early but not late stages of stand development. Basic and Applied Ecology. 10: 411-419.

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Münzbergová Z, Skálová H. & Hadincová V. Genetic diversity affects productivity in early but not late stages of stand development. Basic and Applied Ecology. 10: 411-419.

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  Basic and Applied Ecology  ]  ( ]]]] )  ]]]  –  ]]] Genetic diversity affects productivity in early but not late stagesof stand development Zuzana M u¨ nzbergov a´ a,b,  , Hana Sk a´ lov a´ a , V eˇ ra Hadincov a´ a a Institute of Botany, Academy of Sciences of the Czech Republic, Zamek 1 CZ-252 43 Pru˚ honice, Czech Republic b Department of Botany, Faculty of Science, Charles University, Bena´ tska´  2, CZ-128 01 Praha 2, Czech Republic Received 10 May 2008; accepted 22 October 2008 Abstract Recent declines in the genetic diversity of populations have stimulated research on the importance of geneticdiversity for the functioning of natural communities. Current studies on this topic are based on the exploration of alimited number of clones and do not allow distinctions to be made between the effects of genetic identity and geneticdiversity per se and to evaluate the effects of genetic diversity in genetically diverse communities. Also, mostinformation comes from short-term studies, which are insufficient for evaluating the long-term effects relevant inrelatively undisturbed communities of perennial species.We explored the importance of clone diversity vs. clone identity for stand productivity and the changes of thepattern over time. We used 18 clones of a perennial grass,  Festuca rubra , to establish a set of communities composed of 1, 6 or 18 clones in two environments and studied the effects of genetic diversity on stand productivity over 3 years.Genetic diversity had a significant effect on stand productivity in the 1st year but not in the 2nd or 3rd year. In mostcases, the observed yield was not significantly different from the total expected yield. The biomass of the mixtures neveroutperformed the biomass of the most productive clone, suggesting that clone identity is an important determinant of total biomass.The results indicate that the effects of genetic diversity on stand productivity may be transient and suggest that theconclusions of short-term studies on diversity effects should be evaluated carefully. They also suggest that individualclones are not complementary and that the properties of the stands are mainly additive results of the properties of theconstituent clones. r 2008 Gesellschaft f  u¨ r  O¨  kologie. Published by Elsevier GmbH. All rights reserved. Zusammenfassung Die derzeitige Abnahme der genetischen Diversit a¨ t von Populationen hat die Forschung  u¨ ber die Wichtigkeit dergenetischen Diversit a¨ t f  u¨ r die Funktionsf  a¨ higkeit von nat u¨ rlichen Gemeinschaften stimuliert. Aktuelle Studien indiesem Bereich beruhen auf Untersuchungen einer begrenzten Anzahl von Klonen und erlauben keineUnterscheidungen zwischen den Auswirkungen der genetischen Identit a¨ t und der genetischen Diversit a¨ t per se undkeine Evaluation der Auswirkung von genetischer Diversit a¨ t in genetisch diversen Gemeinschaften. Auch kommen diemeisten Informationen aus kurzfristigen Untersuchungen, die ungeeignet sind, um die langfristigen Auswirkungen zu ARTICLE IN PRESS www.elsevier.de/baae1439-1791/$-see front matter r 2008 Gesellschaft f  u¨ r  O¨  kologie. Published by Elsevier GmbH. All rights reserved.doi:10.1016/j.baae.2008.10.005  Corresponding author. Institute of Botany, Academy of Sciences of the Czech Republic, Zamek 1 CZ-252 43 Pr u˚ honice, Czech Republic.Tel.: +420271015456; fax: +420267750031. E-mail address:  zuzmun@natur.cuni.cz (Z. M u¨ nzbergov a´ ).Please cite this article as: M u¨ nzbergov a´ , Z., et al. Genetic diversity affects productivity in early but not late stages of stand development.  Basic and Applied Ecology  (2009), doi:10.1016/j.baae.2008.10.005  bewerten, die in relativ ungest o¨ rten Gemeinschaften perennierender Arten von Bedeutung sind. Wir untersuchten dieBedeutung der Klondiversit a¨ t vs. Klonidentit a¨ t f  u¨ r die Bestandsproduktivit a¨ t und die Ver a¨ nderungen der Muster mitder Zeit. Wir nutzten 18 Klone des perennierenden Gras  Festuca rubra  um in zwei verschiedenen UmweltenGemeinschaften einzurichten, die aus 1, 6 oder 18 Klonen zusammengesetzt waren, und wir untersuchten dieAuswirkungen der genetischen Diversit a¨ t auf die Bestandsproduktivit a¨ t  u¨ ber drei Jahre.Die genetische Diversit a¨ t hatte einen signifikanten Effekt auf die Bestandsproduktivit a¨ t im ersten, aber nicht imzweiten und dritten Jahr. In den meisten F a¨ llen unterschied sich die beobachtete Ernte nicht signifikant von derinsgesamt erwarteten Ernte. Die Biomasse der Mischungen  u¨ bertraf niemals die Biomasse des produktivsten Klons undl a¨ sst vermuten, dass die Klonidentit a¨ t eine wichtige Determinante der Gesamtbiomasse ist. Die Ergebnisse weisendarauf hin, dass die Auswirkungen der genetischen Diversit a¨ t auf die Bestandsproduktivit a¨ t kurzlebig sein k o¨ nntenund lassen erkennen, dass die Schlussfolgerungen aus kurzfristigen Untersuchungen zur genetischen Diversit a¨ tvorsichtig bewertet werden sollten. Sie lassen ebenfalls erkennen, dass die individuellen Klone nicht austauschbarsind und die Eigenschaften der Best a¨ nde haupts a¨ chlich additive Ergebnisse aus den Eigenschaften der beteiligtenKlone sind. r 2008 Gesellschaft f  u¨ r  O¨  kologie. Published by Elsevier GmbH. All rights reserved. Keywords:  Clonal grass; Complementarity; Diversity-productivity relationship; Ecosystem function; Experiment; Genotypes; Redfescue; Sampling effect; Stability; Transient effects Introduction Recent studies on the importance of species diversityfor community structure and function have shown thathigher species diversity can lead to higher overallproductivity and higher efficiency of resource capture(e.g., Johnson, Vogt, Clark, Schmitz, & Vogt 1996; Waide, Willig, Steiner, Mittelbach, Gough et al. 1999).This can be due to two basic mechanisms – samplingeffect and complementarity (including facilitation)between species (Fridley 2001; Hooper & Vitousek 1997; Lep sˇ , Brown, Len, Gormsen, Hedlund et al.2001). Sampling effect might explain the higher pro-ductivity of a mixture because increasing diversity alsoincreases the probability of including the most produc-tive species of the system. Complementarity, on theother hand, describes a situation in which each speciesoccupies a different niche or the presence of one speciesfacilitates the growth of another, resulting in mostspecies gaining higher biomass than would be expectedin a monoculture (Loreau 2000; Loreau & Hector 2001). In a pioneering study, Aarssen and Turkington (1985)showed that the outcome of interactions between twoneighbouring species depended on genotype. Followingthis finding, several studies demonstrated that geneticdiversity within species might also have importantconsequences for community structure and function(e.g., Booth & Grime 2003; Fridley, Grime, & Bilton 2007; Gamfeldt, Wallen, Jonsson, Berntsson, & Havenhand 2005; Hughes & Stachowicz 2004; Johnson, Lajeunesse, & Agrawal 2006). Specifically, these studies have shownthat communities with higher within-species geneticdiversity have higher productivity, are less susceptible todisturbance (Reusch, Ehlers, H a¨ mmerli, & Worm 2005), have different litter decomposition rates (Schweitzer,Bailey, Hart, & Whitham 2005) and are more productive and less variable across environments (Bell 1991) thancommunities with less within-species diversity. Thegenetic diversity of a population also has a significantimpact on other trophic levels, affecting, for example,arthropods (Crutsinger, Collins, Fordyce, Compert,Nice et al. 2006; Johnson et al. 2006; Wimp, Young, Woolbright, Martinsen, Keim et al. 2004) or fungaldiseases (Zhu, Chen, Fan, Wang, Li et al. 2000). Ithas also been shown that genetic diversity withinspecies affects species diversity and species interactionswithin the same trophic level (Fridley et al. 2007;Whitlock, Grime, & Booth 2007). This suggests it is necessary to consider conservation of intra-specificgenetic diversity to be as important as conservation of species diversity.Most studies comparing stands of different geneticdiversity within species are dealing with the overall effectsof genetic diversity. However, Madritch, Donaldson andLindroth (2006) suggested that not only the geneticdiversity, but also the genetic identity of individuals, hasa decisive role in community structure and function.Several studies have tested the effect of genotype oncommunity properties. In most cases, the genetic diversityof the simulated communities was low (e.g., eight genets inHughes & Stachowicz 2004 and in Johnson et al. 2006, five in Madritch et al. 2006, and six in Reusch et al. 2005). Studies on the effect of genetic diversity in communitieswith high small-scale genetic diversity are missing.Furthermore, published studies on the effects of genetic diversity on ecosystem productivity lasted from5 months in (Reusch et al. 2005) to 10 months in(Hughes & Stachowicz 2004).  While this is not aproblem in studies from highly disturbed environmentssuch as coastal sea grass communities (Hughes &Stachowicz 2004), it may be a problem in relativelyundisturbed communities of perennial species such as ARTICLE IN PRESS Z. M u¨ nzbergov a´  et al. / Basic and Applied Ecology  ]  ( ]]]] )  ]]]  –  ]]] 2Please cite this article as: M u¨ nzbergov a´ , Z., et al. Genetic diversity affects productivity in early but not late stages of stand development.  Basic and Applied Ecology  (2009), doi:10.1016/j.baae.2008.10.005  grasslands or forests. Huston (1997) suggested thatdiversity–productivity relationships in short-term stu-dies in such relatively undisturbed communities of perennial species might be due to transient samplingeffects resulting from the random selection of specieswith higher initial individual growth rates in higherdiversity plots, and that these effects may disappear overtime. Research over longer time periods is thus neededto evaluate whether genetic diversity has long-termeffects on the structure of natural relatively undisturbedcommunities of perennial species since it is only in thiscase that genetic diversity can be expected to haveimportant effects on the function of ecosystems.Complementarity effects occur when the resourcebase is used more efficiently. It can thus be expected thatthe relationship between diversity and productivitymight depend on the nutrient status of the soil (Fridley2002). The effects of nutrient status on the geneticdiversity–productivity relationship has, however, beenexplored only rarely, and thus we do not know howthese effects generalize across different environment.We explored the effects of the genetic diversity of  Festuca rubra  on grassland productivity. This perennialgrass was chosen as the model species since it isdominant in many mesophytic grasslands in thetemperate zone, and the productivity and stability of these grasslands thus has important effects on ecosystemfunctions on larger spatial scales.  F. rubra  waspreviously shown to be a highly variable species withclones differing in their morphological parameters andin their response to competition by other species(Herben, Krahulec, Hadincov a´ , & Pech a´cˇ kov a´  2001).Also, this species exhibits high genetic diversity on asmall spatial scale (Suzuki, Herben, Krahulec,  Sˇ torch-ov a´ , & Hara, 2006). Strong differences in morphology and plasticity between clones suggest that differentclones differ in their use of space, and the differentclones might be expected to show complementaritywhen grown together. This would lead to increasedstand productivity as the genetic diversity of the standincreases. Specifically, we ask the following questions: (i)what is the effect of genetic diversity on overallproductivity, (ii) what are the mechanisms driving thegenetic diversity–productivity relationship, (iii) do theconclusions differ between environments with differentnutrient availability, and (iv) do the conclusions dependon time since establishment of the experiment? Material and methods Study species F. rubra  L. is a common perennial grass species of temperate grasslands in Europe. We used  F. rubra  ssp. rubra,  a widespread hexaploid type from the  F. rubra complex. It reproduces vegetatively as well as by seeds.Clones of   F. rubra  possess considerable variability andplasticity (Herben et al. 2001). The clones for this studywere collected in the Krkono sˇ e Mountains (CzechRepublic) in the Janovy boudy settlement (50 1 41 0 28 00 N,15 1 47 0 35 00 E, 880masl) at the meadow traditionallymanured every 2–4 years, mown in summer and grazedon or mown late in autumn ( Sˇ tursov a´  &  Sˇ tursa 1982).Nowadays, the meadow is mown once a year (June) andmanured only rarely. Such meadows are characterizedby fine scale vegetation and environment patterns,resulting in high heterogeneity within a few centimetresand very low variation on a larger spatial scale (Herben,Krahulec, Hadincov a´ , & Sk a´ lov a´  1993; Sk a´ lov a´ , Krahulec,During, Hadincov a´ , Pech a´cˇ kov a´  et al. 1999, B r ˇ ezinaunpublished). Clone selection and multiplication Eighteen  F. rubra  ramets were sampled randomlyfrom a plot of 100m  100m. This was done by selectingrandom points within the plot and collecting the rametclosest to the point. If there was no  F. rubra  rametwithin 10cm of the random point, the point wasskipped. The collected plants can be safely assumed tobelong to different clones (genets), as Suzuki et al.(2006) showed that the probability of   F. rubra  rametsbeing genetically identical decreases as ramet distanceincreases, approaching zero at a distance of 20cm, withan average genet size of 4–5.3cm. From autumn 2002,the 18 clones were cultivated in an experimental gardenand multiplied vegetatively. Experimental design The experiment was carried out in an experimentalgarden of the Institute of Botany, Academy of Sciencesof the Czech Republic, Pr u˚ honice (50 1 0 0 7.11 00 N,14 1 33 0 20.66 00 E, 350masl). Thirty-six ramets wereplanted in each square pot of 19cm  19cm  19cm ina grid of 3cm in a common garden. This distancecorresponds to approximately the distance betweenneighbouring clones of   F. rubra  in the studied locality(Suzuki et al. 2006). The ramets srcinated from 1, 6 or18 clones, so each clone was replicated 36, 6 or 2 timeswithin individual stands, respectively. The exact positionof each clone in each stand was set randomly anddiffered between replicates. The same design was used intwo nutrient treatments designed to compare standswith the same clone composition but different soilresources. For each nutrient treatment, there were 54one-clone stands (  ¼  three replicates per clone) and 18six-clone stands, with each clone present in each of sixrandomly selected stands, and nine pots of 18-clone ARTICLE IN PRESS Z. M u¨ nzbergov a´  et al. / Basic and Applied Ecology  ]  ( ]]]] )  ]]]  –  ]]]  3Please cite this article as: M u¨ nzbergov a´ , Z., et al. Genetic diversity affects productivity in early but not late stages of stand development.  Basic and Applied Ecology  (2009), doi:10.1016/j.baae.2008.10.005  stands with two ramets of each clone. Thus, 81 standswere planted per nutrient treatment. The density of clones planted in the multi-clone mixtures correspondedroughly to the estimated genetic diversity per 1m 2 (231–968 clones) in the locality studied (Suzuki et al.2006). The planted ramets were between one and sixmonths old. The experiment was initiated in May 2005.The ramets were cut from tussocks and rooted in waterfor 20 days before planting.To ensure that all ramets survived the initialmanipulation, the ramets were checked at weeklyintervals, and dead ramets were replaced by new ones.All ramets were successfully established after 2 months,so no ramets were replaced after this time.In the first nutrient treatment, the ramets were plantedinto a garden soil. The garden soil was compost from anexperimental garden, containing 0.2% N and 2.22% Cand 70.4mg/1000g PO 4  in dry matter. It contained thenatural soil microorganisms. It was watered regularly withnutrient-rich water from a local pond, and fertilized inJune, July and August with N, P, K and Mg (2.5g N and1g for the other nutrients per m 2 ).In the second nutrient treatment, the ramets wereplanted into a nutrient-poor soil (the common garden soilmixed with sand in a 1:1 ratio) and watered regularly withtap water with a low nutrient concentration. Bothtreatments also received natural rainfall. After the 2 yearsof the experiment, the high nutrient soil had 2.9 timesmore total available phosphorus than the soil in the lownutrient treatment. There was, however, no significantdifference in the amount of nitrogen and in the C/N ratiobetween the two nutrient treatments (not shown).Aboveground biomass was harvested at 3cm height.It was harvested for the first time at the end of September 2005; the timing of the harvest correspondedto the 2nd harvest in the original locality. In thefollowing years, the aboveground biomass was har-vested twice, in the peak of flowering in June and againin September. Biomass of the flowering shoots from theJune harvest was treated separately. We thus obtainedinformation about not only the extent to which speciesoccupied space by vegetative growth, but also thepotential of the species to spread further away andexamine differences in the reproductive allocationbetween treatments. The biomass was dried to aconstant weight at 60 1 C and weighted. Since the datafrom September in the 2nd and 3rd year showedqualitatively the same patterns as data from June, onlythe June data from the 2nd and 3rd year are presented. Data analysis We used the data to calculate the over-yielding index,defined as OI   ¼  Y  = max ð M  i  Þ where  Y   is the yield of a mixture and  M  i   is the biomassof the  i  th clone grown in monoculture (Lanta & Lep s 2006; equivalent to  D max  of  Loreau 1998). OI 4 1indicates transgressive over-yielding (sensu Loreau1998) providing evidence of complementarity (includingfacilitation). OI o 1 does not necessarily mean that theclones are not complementary (Hector 2006), becauseeven in this case most of the clones can have theirbiomass in the mixture higher than it would be expectedfrom their biomass in monoculture.An alternative way to separate complementarity andsampling effects is to calculate the total expected yield of the mixture (sensu Loreau & Hector 2001) and compare it to the observed yield. Higher than expected observedyield would indicate non-transgressive over-yielding,and higher yield of the mixture than of the mostproductive monoculture would indicate transgressiveover-yielding. Non-transgressive over-yielding can meansignificant complementarity or may indicate that themore productive clones are out-competing the lessproductive ones. Without clone-based data, however,it is not possible to decide which of these alternativesis true.We used analysis of variance to test differences inbiomass and over-yielding index between differentdiversity treatments. Number of clones was treated asa continuous variable; treating it as a factor did notaffect the conclusions (not shown). The biomass datawere square root transformed, and the over-yieldingindex was log transformed before the analyses to achievenormality. We used two sided  t -tests to compareobserved yield with expected yield and the yield of themost productive clone.Because the one-clone stands within nutrient treat-ments were identical, the three replicates per clone wereaveraged for all analyses to reduce the number of degrees of freedom. All tests were performed usingS-PLUS (2000) and used type III sums of squares. Results The total biomass of the stands increased significantlywith the number of clones in the 1st year, but not in the2nd or 3rd year (Fig. 1, Table 1). When the data from different years were combined, the effect of number of clones ( F  1,86  ¼  0.27,  p  ¼  0.77) and interaction betweennumber of clones and year ( F  1,258  ¼  0.40,  p  ¼  0.67) werenot significant. Similar to the total biomass, the numberof clones did not have any significant effect on thebiomass of flowering shoots (Table 1). In all years, therewas a significant effect of nutrient treatment on totalbiomass (with lower biomass in high nutrient treatmentin the 3rd year), but there was no significant interactionbetween nutrient treatment and number of clones, ARTICLE IN PRESS Z. M u¨ nzbergov a´  et al. / Basic and Applied Ecology  ]  ( ]]]] )  ]]]  –  ]]] 4Please cite this article as: M u¨ nzbergov a´ , Z., et al. Genetic diversity affects productivity in early but not late stages of stand development.  Basic and Applied Ecology  (2009), doi:10.1016/j.baae.2008.10.005  suggesting that the effect of the number of clones wasthe same in both nutrient treatments (Table 1).The over-yielding index was never higher than 1 and itwas higher in the six-clone stands than in the 18-clonestands in all cases (Figs. 2 and 3). When testing the over-yielding index based on total biomass from the 3 yearstogether, there was no significant interaction betweenyear and number of clones ( F  1,154  ¼  0.16,  p  ¼  0.68,Fig. 2). For the biomass of flowering shoots, the over-yielding index was significantly higher in the lownutrient treatment in both the 2nd and 3rd years(Table 2). In the 3rd year, there was also an interactionbetween nutrient level and number of clones (Table 2,Fig. 3), with less difference between six-clone and18-clone stands in the low nutrient treatment.The observed yield of the six-clone stands wassignificantly higher than the total expected yield onlyin the 1st year and for the low nutrient treatment(Appendix A). In all other years and treatments, it wasnot significantly different. In the 18-clone stands, the ARTICLE IN PRESS Fig. 1.  Effect of number of clones, nutrient level and year on total biomass of the stands. Table 1.  Effect of number of clones, nutrient level and their interaction on total biomass and biomass of flowering shoots in the 1st,2nd and 3rd years of the experiment.Stem biomassAll FloweringYear1st year 2nd year 3rd year 2nd year 3rd year F p F p F p F p F p No. of clones 5.17  0.025  0.25 0.621 0.12 0.89 0.33 0.566 0.17 0.842Nutrient level 156.63  o 0.001  109.73  o 0.001  418  o 0.001  9.36  0.003  465.7  o 0.001 No. clones  nutrient l. 2.44 0.122 0.67 0.415 0.43 0.651 0.33 0.569 0.2 0.817 DF error  ¼  86. Significant values are in bold.Z. M u¨ nzbergov a´  et al. / Basic and Applied Ecology  ]  ( ]]]] )  ]]]  –  ]]]  5Please cite this article as: M u¨ nzbergov a´ , Z., et al. Genetic diversity affects productivity in early but not late stages of stand development.  Basic and Applied Ecology  (2009), doi:10.1016/j.baae.2008.10.005
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