Journal of Plant Ecology Advance Access published online on March 13, 2008
Journal of Plant Ecology, doi:10.1093/jpe/rtn004
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Nutrient-patch contrast in relation to clonal integration, with special reference to Glechoma longituba
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
* Correspondence address. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China. Tel: 86-10-82595899; Fax: 86-10-82595899; E-mail: weiminghe{at}ibcas.ac.cn.
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Abstract |
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If clonal integration is dependent on source-sink relationships within a clone, then increased nutrient-patch contrast might enhance integration. To test this we conducted an experiment in which Glechoma longituba was subjected to contrasting patch contrasts. The findings that physiological and growth traits varied with nutrient-patch contrast suggest that patch contrast may play an important role in determining integration intensity and direction.
Keywords: nutrient-patch contrast • clonal integration • Glechoma longituba
Patch contrast, defined as the difference between patches, is among the basic traits of environmental heterogeneity (Kolasa and Pickett 1991; Stuefer 1996). Clonal plants, especially those with long spacers, usually experience certain patches with different nutrient-patch contrasts (de Kroon et al. 2005; Stuefer 1996). Clonal integration has been recognized as a basic strategy, by which clonal plants can effectively cope with patchy resources and increase their fitness in such habitats (de Kroon et al. 2005; Zhang et al. 2007). Glechoma longituba is distributed in a wide range of habitats (Wu and Chen 1974). Thus, it appears to be most likely that G. longituba plants grow in habitats with different nutrient-patch contrasts. Given that integration is highly dependent on source-sink relationships within a clone (Pitelka and Ashmun 1985), we hypothesize that increased nutrient-patch contrast might enhance clonal integration within a clone. To test this hypothesis, we conducted a garden experiment, in which G. hederacea was subjected to four levels of patch contrast.
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Methods |
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Glechoma longituba L. is a perennial stoloniferous herb (Wu and Chen 1974). All G. longituba materials used in the experiment were propagated vegetatively. We made 48 growth containers (60 cm long, 20 cm wide and 25 cm deep), and filled them with pure river-sand. A couple of growth containers were put together to create a habitat. Similar-sized fragments were chosen; one ramet was planted in one growth container and the other ramet in another (Fig. 1). One growth container received high nutrient supply and the other received low nutrient supply. A water-soluble fertilizer was employed to achieve different nutrient supplies. The concentration of the nutrient solution applied in the original patches was 0.45%, and the concentrations of the nutrient solution applied in the target patches were 0.45, 0.40, 0.35 and 0.30%, respectively (Fig. 1). The nutrient solution was applied once a week, and water was supplied when necessary. Six replicates for each treatment were randomly arranged, and this experiment ran from 15 July 2005 through 5 October 2005.
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Similar-sized leaves were chosen for measurements of midday leaf water potential, gas exchange and chlorophyll fluorescence. The detailed method was described in our previous study (Zhang et al. 2007). At the end of the experiment, fragments were harvested and separated into roots and shoots. Finally, all the plant materials were dried at 85°C for two consecutive days and then weighed. One-way analysis of variance was employed to test the effect of nutrient-patch contrast on the physiology and growth of G. longituba. Square-root transformed data were used in the analysis when necessary.
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Results |
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Clonal integration in gas exchange, water potential and chlorophyll fluorescence varied along the gradient of nutrient-patch contrast; higher nutrient-patch contrast yielded smaller integration intensity in both gas exchange and fluorescence response and greater integration intensity in leaf water potential (Fig. 2). The direction of clonal integration for some characteristics also differed among nutrient-patch contrasts, indicating that the threshold of nutrient-patch contrast might play a role in determining integration direction. At the whole-plant level, total biomass remained unchanged along the gradient of nutrient-patch contrast when original and target fragments were considered together (data not shown). Given that biomass is a good indictor for the fitness of plants, the fitness in clones of G. longituba could not decrease with decreased total nutrient availability in habitats.
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Discussion |
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In this study, all the original fragments experienced the same nutrient-rich patches, but target fragments did more unfavorable nutrient patches with increasing nutrient-patch contrast. Interestingly, root morphology and its biomass allocation in target fragments remained unchanged along the gradient of nutrient-patch contrast; biomasses of target fragments did not decrease with decreasing nutrient availability. On the other hand, biomass of original fragments connected to target fragments in nutrient-poor patches did not decrease either. Therefore, the total biomass of a whole plant was not significant reduced by increased nutrient-patch contrast. These findings show that clonal integration supports the growth of target fragments, but this support does not reduce the growth of original fragments. Thus, nutrient integration may be beneficial to the fitness of whole plants. Clonal integration modifies response at one level but not at another level (He et al. 2004). This phenomenon was found in our study. For example, clonal integration affected certain traits at the fragment level, but not at the whole-plant level. Clonal integration in different environments has importantly evolutionary and ecological consequences (de Kroon et al. 2005; Hutchings and Wijesinghe 1997).
In conclusion, our findings are showing that nutrient-patch contrast intensity may modify the pattern of clonal integration (intensity and direction), which can shape the phenotypic plasticity of clonal plants. Compared to plasticity of clonal plants to patches, the consequences of patch contrast have been overlooked. To better understand the ecological and evolutionary implications of patch contrast, we should pay more attention to the following four aspects: (i) cost-benefit analysis of the contrast-induced consequences, (ii) the role of changing patch contrast in the life history of plants, (iii) the relative importance of patch contrast in inter- and intra-specific relationships and (iv) effects of patch contrast on ecosystem diversity and stability.
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Acknowledgements |
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We are grateful to M Dong, F Yu, S Li, P Fan, Q Cui, R Li, S Zhang, J Du, F Liu, H Yu and N Wang for their help. This study was supported by grants from the National Natural Science Foundation of China (30300043 and 30330130).
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References |
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de Kroon H, Huber H, Stuefer JF, et al. A modular concept of phenotypic plasticity in plants. New Phytologist (2005) 166:73–82.[CrossRef][ISI][Medline]
He WM, Zhang H, Dong M. Plasticity in fitness and fitness-related traits at ramet and genet levels in a tillering grass Panicum miliaceum under patchy soil nutrients. Plant Ecol (2004) 172:1–10.[CrossRef]
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Kolasa J, Pickett STA. Ecological Heterogeneity (1991) New York: Springer-Verlag.
Pitelka LF, Ashmun JW. Physiology and integration of ramets in clonal plants .In. In: Population Biology and Evolution of Clonal Organisms—Jackson JBC, Buss L, Cook RE, eds. (1985) New Haven, CT: Yale University Press. 399–435.
Stuefer JF. Potential and limitations of current concepts regarding the response of clonal plants to environmental heterogeneity. Vegetatio (1996) 127:55–70.[CrossRef][ISI]
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Zhang LL, Dong M, Li RQ, et al. Nutrient patch contrast modifies clonal integration in Glechoma longituba: intensity and direction. J Plant Ecol (2007) 31:567–72. (in Chinese with English abstract).
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