Climaite.dk

RAIN project (Wright et al., 1993), the European EXMANand NITREX projects (Wright & Rasmussen, 1998) the Gårdsjøn roof project in Sweden (Hultberg & Skeffington,1998), and the whole watershed manipulations in the US at the Bear Brook Watershed in Maine (Norton & Fernandez,1999) and the Fernow Experimental Forest in West Virginia Over the years, the whole-ecosystem approach has proved particularly valuable and unique as a tool for investigating On the bookshelf above my head I can see the book Biogeo- complex cause-effect relationships in ecosystem internal chemistry of a forested ecosystem (Likens et al., 1977). It is in a processes in natural environments (Beier & Rasmussen, 1994).
pretty bad shape, worn out after intensive use for many Despite the complexity and spatial/temporal variability of years. The book describes the ecosystem studies in Hubbard ecosystem processes, field-scale manipulation experiments coupled with process, species, community and ecosystem level this was the first practical example and pioneer of a true studies have become an important tool for generating multidisciplinary ‘whole-ecosystem’ approach to study and knowledge about ecosystem processes and responses. Further- understand ecosystem processes and functioning. Investigating more, ecosystem manipulation experiments are unique for the effects of external impact factors on the ecosystem by validating and testing dynamic model predictions. If a conducting a full-scale manipulation experiment and sub- model is applied to the untreated control situation at the site sequently follow the consequences at various scales – it has and subsequently used to predict the effects of the applied been a strong inspiration to me ever since. In this issue manipulations, the model output can be evaluated by com- of New Phytologist, a range of research studies addressing parison with the measured responses in the treatment (Ferrier, ecosystem-level studies are showcased, and critical reviews 1998; Beier et al., 2003). This provides much stronger con- cover FACE (Free Air CO Enrichment) experiments to fidence in the model’s ability to predict effects of environ- study elevated CO and effects of elevated CO and clima- mental changes compared to a ‘standard’ situation where the tic change on overall ecosystem functioning (Norby & Luo, dynamic behaviour of the model can only be evaluated from pp. 281–293), phenology (Badeck et al. pp. 295–309) and below-ground processes (Pendall et al. pp. 311–322).
Ecosystem experiments and climate change
Climate change is another large-scale threat to the environment, ‘The few examples of combinations of CO and and one that has gained increasing scientific and politicalattention over the past two decades. Climate change is warming point in all directions and results are not particularly complex compared with other previous regional predictable based on the individual effects’ and global environmental changes because it involvessimultaneous increases in atmospheric CO and temperature (IPCC, 2001), coupled with altered precipitation (Weltzin &Tissue, 2003). Together these are among the most importantfactors directly involved in regulating biological and chemicalprocesses and can cause a whole cascade of effects from theindividual organism all the way up to the ecosystem scale. In The ecosystem approach
order to understand and predict the potential effect of this com- Hubbard Brook is still going strong, but it is no longer plexity of changes a large number of research projects have alone. Many ecosystem studies have been conducted since then.
been carried out involving studies of climate driven changes In particular, this ecosystem approach took a major step at all ecosystem scales and involving all levels from single forward during the ‘acid rain’ era, where many ecosystem process studies in laboratories and controlled environments to studies including acid and nutrient manipulations were full-scale ecosystem studies in natural environments. Ultimately, conducted in Europe and the USA. These experiments this should provide the necessary background needed to pre- included large-scale manipulation projects such as the Norwegian dict long-term ecosystem responses to climate change.
New Phytologist (2004) 162: 243 – 251
Because of the complexity and costs for large-scale ecosystem production and net primary productivity (NPP) in the eco- studies, the majority of these have focused on single factors.
system, all combinations of elevated CO with the other For example, a large number of warming studies were treatments dampened the increase (Shaw et al., 2002).
carried out by various techniques in the 1990s (synthesisedby Rustad et al., 2001) and a number of large scale CO2 Climate change and ecosystem research – our
enrichment studies have been carried out by the FACE future challenge
technique, synthesised in this issue by Nowak et al. Thesestudies have together provided an important input to our The research in this issue suggests a general consensus that understanding of how biological processes will respond to a combination of ecosystem-scale experiments and model- predicted climatic changes (Shaver et al., 2000). The bulk of ling is needed. At the same time opinions are mixed these research projects have also underscored the fact that regarding the relative importance of these elements.
ecosystem responses to changes in climatic and environmental Dynamic ecosystem models will be useful for integrating factors are highly variable and complex. Furthermore, it is our understanding from the individual process studies and clear that these single or few-factor experiments may not thereby provide common tools for forecasting future short- provide a comprehensive understanding of how ecosystems and long-term changes in ecosystem functioning as claimed behave when all factors change simultaneously.
by Norby & Luo. On the other hand, this is still a majorchallenge and will only be useful if the general under-standing of how the individual factors interact is good enough.
A multifactor world, a multifactor problem
For this, multifactor experiments at the ecosystem scale Together, the papers in this issue clearly illustrate the value are crucial both to generate the knowledge needed to of a mechanistic understanding of how changes in the build the models and to test and validate the results. A way various climatic factors will affect specific ecosystem processes.
to optimise the resource use and improve the generality is to However, they also clearly illustrate the difficulty of obtaining combine experiments and gradients by conducting the same a true functional understanding of ecosystem responses based ecosystem experiments at different or comparable ecosystems on single factor and single process studies alone. The effects along climatic gradients. This will contrast or combine the of CO alone and to a lesser extent warming alone each short-term effects obtained through experiments at any show some general and consistent patterns, but the few particular site with knowledge of long-term differences and examples of combinations point in all directions and results stability of the ecosystem processes along the climatic or are not predictable based on the individual effects. The environmental gradient. This will further provide insight complexity and unpredictability becomes even worse into the route the ecosystem and ecosystem processes will when we realise that important effects may be driven by take moving from the present to the future state. This changes in off-season processes, seasonality and extreme strategy was used in the European CLIMOOR and events – as illustrated in the paper by Loik et al. (pp. 331– VULCAN projects (Beier et al., 2004) and shows how 341) showing how warming affects the freezing tolerance for variable effects of droughts and warming are among sites under different climatic conditions (Emmett et al., 2004; Obviously, the solution to this problem may include two important elements: multifactor experiments and modelling.
The problem is that multifactor experiments at the To date, very few ecosystem experiments have been conducted ecosystem scale are generally extremely resource demand- involving combinations of all or several climate change ing, particularly if they are to be continued for sufficient parameters. The CLIMEX project conducted in Norway in time to provide information about the longer-term 1995 –1999 (Wright, 1998) was the first full-scale ecosystem responses. Furthermore, as Norby & Luo state: they will experiment in which a complete boreal forest catchment was always be case studies. On the other hand, do we have exposed to simultaneously elevated CO and temperature, an alternative? I doubt it. I do not believe that any and showed changes in N mineralisation processes and N model alone or any single factor experiment will provide leaching (Wright et al., 1998).
the answers we need to predict long-term ecosystem Recently, results from the climate change experiment at responses to future changes in climatic and environmental Jasper Ridge, CA, USA have clearly demonstrated how complex and unpredictable ecosystem responses may be in There is a crucial need to conduct long-term ecosystem-scale a multifactor world. The annual grassland was exposed to multifactor experiments including changes in the main combinations of elevated CO and temperature, and changes drivers we know are going to change in the future and to in precipitation and nitrogen deposition. The results show do this across ecosystems and climatic zones. This is a that while all treatments involving increased temperature, multidisciplinary challenge and each study should involve precipitation or N deposition (alone or in combination) as scientists covering all the ecosystem scales from individual well as CO alone tended to promote the above ground biomass processes to ecosystem structure and function.
www.newphytologist.org New Phytologist (2004) 162: 243–251
Acknowledgements
Likens GE, Bormann FH, Pierce RS, Eaton JS, Fohnson NM.
1977. Biogeochemistry of a forested ecosystem. New York, USA:
A number of the papers in this issue, and discussed here, stemmed from a workshop, ‘Interactions between CO and Loik ME, Still CJ, Huxman TE, Harte J. 2004. In situ photosynthetic
warming’, sponsored by the US National Science Founda- freezing tolerance for plants exposed to a global warming manipulation tion’s global change network, TERACC (Terrestrial Ecosystem in the Rocky Mountains, Colorado, USA. New Phytologist 162:
Research and Atmospheric and Climatic Changes), the goal Norby RJ, Luo Y. 2004. Evaluating Ecosystem Responses to Rising
of which is to integrate results and experiences across Atmospheric CO and Global Warming in a Multi-Factor World. scientific projects and communities. Such integrated networks New Phytologist 162: 281– 293.
are vital to create interdisciplinary and international colla- Norton SA, Fernandez IJ, eds. 1999. The Bear Brook Watershed in Maine
boration/integration. I am grateful to Richard F. Wright and (BBWM) – A Paired Watershed Experiment: The First Decade (1987–97). Lindsey Rustad for valuable comments on the manuscript.
Special Volume (55) of Environ. Monit. Assess. Dordrecht, the Netherlands: Kluwer Academic Publishers.
Nowak RS, Ellsworth DS, Smith SD. 2004. Functional responses
Claus Beier
of plants to elevated atmospheric CO – Do photosynthetic and productivity data from FACE experiments support early predictions? Plant Research Department, Risoe National Laboratory, New Phytologist 162: 253 – 280.
Pendall E, Bridgham S, Hanson PJ, Hungate B, Kicklighter DW,
Johnson DW, Law BE, Luo Y, Megonigal JP, Olsrud M, Ryan MG,
(fax +45 46774160; email [email protected]) Wan S. 2004. Belowground Process Responses to Elevated CO and
Temperature: A Discussion of Observations, Measurement Methods, References
and Models. New Phytologist 162: 311– 322.
Peñuelas J, Gordon C, Llorens L, Nielsen T, Tietema A, Beier C,
Badeck F-W, Bondeau A, Böttcher K, Doktor D, Lucht W, Schaber J,
Bruna P, Emmet BA, Estiarte M, Gorissen T. 2004. Non-intrusive
Sitch S. 2004. Responses of plant phenology to climate change.
field experiments show different plant responses to warming and drought New Phytologist 162: 295 – 309.
among sites seasons and species in a North-South European gradient. Beier C, Emmett B, Gundersen P, Tietema A, Penuelas J, Estiarte M,
Gordon C, Gorissen A, Llorens L, Roda F, Williams D. 2004.
Rustad LE, Campbell JL, Marion GM, Norby RJ, Mitchel MJ, Hartley AE,
Novel approaches to study climate change effects on terrestrial Cornelissen JHC, Gurevitch J. 2001. A meta-analysis of the response of
ecosystems at the field scale-drought and passive night time warming. soil respiration, net nitrogen mineralization, and aboveground plant growth to experimental ecosystem warming. Oecologia 126: 543 –562.
Beier C, Moldan F, Wright RF. 2003. Terrestrial ecosystem recovery –
Shaver GR, Canadell J, Chapin FS, Gurevitch J, Harte J, Henry G,
Modelling the effects of reduced acidic inputs and increased inputs Ineson P, Jonasson S, Melillo J, Pitelka L, Rustad L. 2000. Global
of sea-salts induced by global change. AMBIO 32: 275 –282.
warming and terrestrial ecosystems: a conceptual framework for analysis. Beier C, Rasmussen L. 1994. Effects of whole-ecosystem manipulations
Bioscience 50: 871– 882.
on ecosystem internal processes. Trends in Ecology and Evolution 9:
Shaw MR, Zavaleta ES, Chiariello NR, Cleland EE, Mooney HA,
Field CB. 2002. Grassland responses to global environmental changes
Emmett BA, Beier C, Estiarte M, Tietema A, Kristensen HL,
suppressed by elevated CO . Science 298: 1987–1990.
Williams D, Penuelas J, Schmidt IK, Sowerby A. 2004. The response
Weltzin JF, Tissue DT. 2003. Resource pulses in arid environments –
of soil processes to climate change: Results from manipulation studies patterns of rain, patterns of life. New Phytologist 157: 167–173.
across an environmental gradient. Ecosystems (In press.) Wright RF. 1998. Effect of increased CO and temperature on rnoff chem-
Ferrier RC. 1998. The DYNAMO project: An introduction. Hydrological
istry at a forested catchment in southern Norway (CLIMEX project). Earth Systematic Science 2: 375 –383.
Ecosystems 1: 216 –225.
Gilliam FS, Adams MB, Yurish BM. 1996. Ecosystem nutrient responses
Wright RF, Beier C, Cosby BJ. 1998. Effects of nitrogen deposition
to chronic nitrogen inputs at Fernow Experimental Forest, at the and climate change on nitrogen runoff at Norwegian boreal forest Fernow Experimental Forest, West Virginia. Forest Ecology and catchments: the MERLIN model applied to the RAIN and CLIMEX Management 95: 79 – 91.
projects. Hydrological Earth Systematic Science 2: 399 – 414.
Hultberg H, Skeffington R, eds. 1998. Experimental reversal of acid
Wright RF, Lotse E, Semb A. 1993. RAIN project: Results after 8 years
rain effects: the Gårdsjön Roof Project. Chinchester, UK: John Wiley of experimentally reduced acid deposition to a whole catchment. Canadian Journal of Fisheries and Aquatic Sciences 50: 258 –268.
IPCC (2001) Climate Change 2001: The Scientific Basis. Contribution
Wright RF, Rasmussen L. 1998. Introduction to the NITREX and
of Working Group I to the Third Assessment Report of the EXMAN projects. For Ecological Manage 101: 1–7.
Intergovernmental Panel on Climate Change (eds. J.T. Houghton
et al.). Cambridge University Press, Cambridge, UK and New York,
Key words: Ecosystem manipulation, interaction, multifactor,
New Phytologist (2004) 162: 243 – 251
The previous demonstration of the NO· production by theenzyme nitrate reductase ( Dean & Harper, 1988; Yamasaki oxide in plant cells – beyond et al., 1999) was one possibility (García-Mata & Lamattina, 2003). However, recently an unexpected alternative enzy- matic source of NO· was described. A variant of the P pro-tein of the mitochondrial glycine descarboxylase complex(GDC) was demonstrated to be a pathogen-inducible plant In the mid 1970s it was reported that plants can emit nitric NOS (Chandok et al., 2003; Wendehenne et al., 2003).
oxide (NO·) (Klepper, 1979) and nowadays the generation Additionally, another recent report has shown the presence of NO· in plant cells is well established (Leshem, 2000; of an NOS gene (AtNOS1 ) in Arabidopsis. AtNOS1 turned Lamattina et al., 2003; Neill et al., 2003). In plants, like in out to be a protein very similar to a group of bacterial animal systems, the gaseous free radical NO· has been shown proteins with putative GTP-binding or GTPase domains to play a role as a signal molecule in diverse important (Guo et al., 2003). Surprisingly, both the variant P protein physiological processes (Delledonne et al., 1998; Wendehenne and the purified AtNOS1 protein did not have sequence et al., 2001; Lamattina et al., 2003; Neill et al., 2003).
However, the enzymatic source and site of NO· synthesis However, apart from these cases, there are still other in plant cells has been the subject of much debate and potential enzymatic sources of NO· generation in plants that must be considered (Table 1). The production of NO· by In the past decade, many plant biologists searched horseradish peroxidase from hydroxyurea and H O (Huang intensively for an enzyme similar to any of the isoforms of et al., 2002) is an example of how plant cells can have nitric oxide synthase (NOS) identified in mammalian alternative sources of NO· making use of the widespread systems (Alderton et al., 2001), in the hope of finding the and physiologically important enzymes peroxidases (Huang gene responsible for the ‘plant NOS’. A significant number et al., 2002). Other enzymatic sources that must be taken of reports showed the presence of NOS-like activity in into account are xanthine oxidoreductase and cytochrome several plant tissues which had some similiarities with mam- P450 which are present in plants and have been shown to malian NOS, such as sensitivity to well characterized NOS generate NO· in animal systems (Boucher et al., 1992a; inhibitors and cross-reactivity with several antibodies against Millar et al., 1998; Harrison, 2002; Mansuy & Boucher, mammalian NOS proteins. But following the publication of 2002). Moreover, it has been proposed that hemeproteins the Arabidopsis genome, not a single gene or protein with are good candidates for the enzymatic generation of NO· sequence similarity to the animal NOSs could be identified from N-hydroxyarginine (NOHA) (Boucher et al., 1992b).
( The Arabidopsis genome initiative, 2000). Therefore, Additionally, a plasma membrane-bound enzyme was shown alternative enzymatic sources of NO· had to be considered.
to catalyze the formation of NO· from nitrite in tobacco Table 1 Some established and potential enzymatic sources of NO· in plant cells
Crude extracts and cell organelles (NOS-like activity) Sen & Cheema (1995); Cueto et al. (1996); Ninnemann & Maier (1996); Delledonne et al. (1998); Durner et al. (1998); Ribeiro et al. (1999); Barroso et al. (1999); Modolo et al. (2002) Variant P protein of the GDC (‘plant iNOS’) Dean and Harper (1988); Yamasaki et al. (1999) Millar et al. (1998); Harrison (2002) Boucher et al. (1992b); Huang et al. (2002) Boucher et al. (1992a); Mansuy & Boucher (2002) www.newphytologist.org New Phytologist (2004) 162: 243–251
roots (Stöhr et al., 2001). Taken together, this suggests that Boucher JL, Genet A, Vadon S, Delaforge M, Mansuy D. 1992b.
in plants the enzymatic NO· production, either constitutive Formation of nitrogen oxides and citrulline upon oxidation of or induced by different biotic/abiotic stresses, may be a much Nw-hydroxy-L-arginine by hemeproteins. Biochemical and more common event than was initially thought.
Biophysical Research Communications 184: 1158–1164.
These examples show that the dated concept of one Chandok MR, Ytterberg AJ, van Wijk KJ, Klessig DF. 2003. The
pathogen-inducible nitric oxide synthase (iNOS) in plants is a protein–one function is too simplistic as far as NO· genera- variant of the P protein of the glycine decarboxylase complex. Cell tion is concerned. To improve our understanding of the 113: 469– 482.
physiological function of NO· in the different plant cell Cueto M, Hernández-Perera O, Martín R, Bentura ML, Rodrigo J,
compartments, we must realize that plant cells may not Lamas S, Golvano MP. 1996. Presence of nitric oxide synthase
possess a unique enzymatic source of this versatile molecule activity in roots and nodules of Lupinus albus. FEBS Letters 398:
but multiple generating systems. It appears that in plants there is a battery of multifunctional enzymes, able to pro- Dat J, Vandenabeele S, Vranová E, Van Montagu M, Inzé D,
duce NO· catalytically, which are structurally unrelated to Van Breusegem F. 2000. Dual action of the active oxygen species
mammalian NOS. The burst of publications on ‘plant NOS during plant stress responses. Cellular and Molecular Life Sciences 57:
activity’ over recent years, and the special interest in demon- strating that the origin of NO was due to a unique constitutive Dean JV, Harper JE. 1988. The conversion of nitrite to nitrogen
oxide (s) by the constitutive NAD (P) H-nitrate reductase enzyme or inducible mammalian-type NOS, brings into the memory from soybean. Plant Physiology 88: 389–395.
the discovery of the generation in biological systems of Delledonne M, Xia YJ, Dixon RA, Lamb C. 1998. Nitric oxide
another important free radical, the superoxide anion (O . –) functions as a signal in plant disease resistance. Nature 394:
(McCord & Fridovich, 1968). It was then thought that O . – radicals were only produced by the mammalian oxidative Durner J, Wendehenne D, Klessig DF. 1998. Defense gene induc-
enzyme xanthine oxidase. Today it is known that there are tion in tobacco by nitric oxide, cyclic GMP, and cyclic ADP-ribose. many proteins and enzymes producing these radicals in many Proceedings of the National Academy of Sciences, USA 95: 10328–
compartments of animal and plant cells, as a consequence of normal aerobic metabolism, and it is well established that García-Mata C, Lamattina L. 2003. Abscisic acid, nitric oxide and
the generation of O . – radicals may be induced by different stomatal closure – is nitrate reductase one of the missing links? pathological or stress conditions (Bolwell, 1999; Dat et al., Trends in Plant Science 8: 20–26.
Guo F-Q, Okamoto M, Crawford NM. 2003. Identification of a
2000; Halliwell & Gutteridge, 2000; del Río et al., 2003).
plant nitric oxide synthase gene involved in hormonal signaling. In a similar way, concerning the enzymatic production of Science 302: 100–103.
NO· in plants, perhaps we are just starting to see the tip of Halliwell B, Gutteridge JMC. 2000. Free Radicals in Biology and
Medicine. Oxford University Press: Oxford, UK.
Harrison R. 2002. Structure and function of xanthine oxidoreductase:
F. Javier Corpas*, Juan B. Barroso and Luis A. del Río
where are we now? Free Radical in Biology and Medicine 33:
774 –797.
Departamento de Bioquímica, Biología Celular y Molecular Huang J, Sommers EM, Kim-Shapiro DB, King SB. 2002.
de Plantas, Estación Experimental del Zaidín, CSIC, Apdo.
Horseradish peroxidase catalyzed nitric oxide formation from hydroxyurea. Journal of the American Chemical Society 124:
Klepper L. 1979. Nitric oxide and nitrogen dioxide (NO ) emissions
from herbicide- treated soybean plants. Atmospheric Environment 13:
537–542.
References
Lamattina L, García-Mata C, Graziano M, Pagnussat G. 2003. Nitric
oxide: the versatility of an extensive signal molecule. Annual Review Alderton WK, Cooper CE, Knowles RG. 2001. Nitric oxide
of Plant Biology 54: 109–136.
synthases: structure, function and inhibition. Biochemical Leshem YY. 2000. Nitric oxide in plants. Occurrence, function and use.
Journal 357: 593–615.
Dordrecht, The Netherlands: Kluwer Academic Publishers.
Barroso JB, Corpas FJ, Carreras A, Sandalio LM, Valderrama R,
Mansuy D, Boucher J-L. 2002. Oxidation of N-hydroxyguanidines by
Palma JM, Lupiáñez JA, del Río LA. 1999. Localization of
cytochromes P450 and NO-synthases and formation of nitric oxide. nitric-oxide synthase in plant peroxisomes. Journal of Biological Drug Metabolism Review 34: 593–606.
Chemistry 274: 36729–36733.
McCord JM, Fridovich I. 1968. The reduction of cytochrome c by
Bolwell G. 1999. Role of reactive oxygen species and NO in plant
milk xanthine oxidase. Journal of Biological Chemistry 243: 5753 –
defence responses. Current Opinion in Plant Biology 2: 287–294.
Boucher JL, Genet A, Vadon S, Delaforge M, Henry Y, Mansuy D.
Millar TM, Stevens CR, Benjamin N, Eisenthal R, Harrison R,
1992a. Cytochrome P450 catalyzes the oxidation of Nw-hydroxy-L-
Blake DR. 1998. Xanthine oxidoreductase catalyses the
arginine by NADPH and O to nitric oxide and citrulline. reduction of nitrates and nitrite to nitric oxide under hypoxic Biochemistry and Biophysics Research Communications 187: 880–886.
conditions. FEBS Letters 427: 225–228.
New Phytologist (2004) 162: 243 – 251
Modolo LV, Cunha FQ, Braga MR, Salgado I. 2002. Nitric oxide
immunoreactivity in plant embryonic tissue. Biochemical synthase-mediated phytoalexin accumulation in soybean cotyledons Archives 11: 221–227.
in response to the Diaporthe phaseolorum f. sp. meridionalis elicitor. Stöhr C, Strube F, Marx G, Ullrich WR, Rockel P. 2001. A plasma
Plant Physiology 130: 1288–1297.
membrane- bound enzyme of tobacco roots catalyses the formation Neill SJ, Desikan R, Hancock JT. 2003. Nitric oxide signalling in
of nitric oxide from nitrite. Planta 212: 835–841.
plants. New Phytologist 159: 11–35.
The Arabidopsis Genome Initiative. 2000. Analysis of the genome
Ninnemann H, Maier J. 1996. Indications for the occurrence of
sequence of the flowering plant. Nature 408: 796 – 815.
nitric oxide synthases in fungi and plants and the involvement in Wendehenne D, Lamotte O, Pugin A. 2003. Plant iNOS: conquest of
photoconidiation of Neurospora crassa. Photochemistry and the holy grail. Trends in Plant Science 8: 465–468.
Photobiology 64: 393–398.
Wendehenne D, Pugin A, Klessig DF, Durner J. 2001. Nitric oxide:
Ribeiro EA Jr., Cunha FQ, Tamashiro WMSC, Martins IS. 1999.
comparative synthesis and signalling in animal and plant cells. Growth phase-dependent subcellular localization of nitric oxide Trends in Plant Science 6: 177–183.
synthase in maize cells. FEBS Letters 445: 283–286.
Yamasaki H, Sakihama Y, Takahashi S. 1999. An alternative pathway
del Río LA, Corpas FJ, Sandalio LM, Palma JM, Barroso JB. 2003.
for nitric oxide production in plants: new features of an old enzyme. Plant peroxisomes, reactive oxygen metabolism and nitric oxide. Trends in Plant Science 4: 128–129.
IUBMBI Life 55: 71–81.
Sen S, Cheema IR. 1995. Nitric oxide synthase and calmodulin
Key words: nitric oxide, NO·, signalling, nitric oxide synthase, NOS.
mission of Southern Connections is to ensure that scientificgeneralizations and theory genuinely address both hemispheres.
Notwithstanding the common Gondwanan past of their respective lands, and the resulting biotic affinities, there are other issues that unite the scientists involved. Many of thesecountries are facing similar issues arising from rapid changes inland use, massive introduction of alien species and declining IV Southern Connections Conference: Towards a
native biodiversity. Although a wide range of topics in eco- southern perspective, Cape Town, South Africa,
logy, biogeography and systematics were presented at the IV January 2004
Southern hemisphere ecologists and biogeographers have tradi- conferences/sc2004), below we concentrate on some of the tionally looked northward for stimulus and ideas. Southern major issues in plant ecology addressed at the meeting.
Cose fromthe recent realization that there was also much to be gained bylooking east and west. This organization has held meetings every3 – 4 yr since 1994, providing a unique interdisciplinary forum ‘Are southern hemisphere ecosystems susceptible to invasion for whole-organism biologists working in the southern hemi-sphere. One speaker at an earlier meeting commented on how by Eurasian taxa because northern hemisphere plants refreshing it was not to begin by virtually apologising forhis subject (terrestrial mammal pollination in Proteaceae) as he would in a northern hemisphere forum, where suchmechanisms might be viewed as curiosities or, at worst, freakshows. At Southern Connec-tions he could take it for grantedthat many would be conversant with his subject, whichcould then be discussed in more depth.
Invasive plants – correlates and consequences
The mood generates a healthy iconoclasm about ‘unifying schemes’ served up mainly from Europe and North America.
Huge numbers of exotic plant species have been introduced Widely read texts were derided for presenting ‘laughable’ to southern hemisphere countries. Duane Peltzer (Landcare generalizations, many of which have to be unlearned by Research, Lincoln, New Zealand) showed us an extreme case southern hemisphere ecologists and biogeographers. Thus, a in New Zealand, where naturalized exotic vascular plants now www.newphytologist.org New Phytologist (2004) 162: 243–251
outnumber natives. Although by no means all naturalized southern temperate forests than in their northern counterparts plants can be classed as invasive, it is therefore no surprise (Armesto et al., 1996; Willson et al., 1996). This dependence that the ecology of invasions is a big research topic in the is even higher on some tropical Pacific islands such as Tonga and New Caledonia (McConkey & Drake, 2002). Community Are southern hemisphere ecosystems susceptible to invasion structure and ecosystem function are therefore likely to be by Eurasian taxa because northern hemisphere plants are particularly sensitive to extinctions in these systems.
simply ‘better’? This idea, referred to by Ian Radford (Otago Alastair Robertson (Massey University, New Zealand) University, New Zealand) as the ‘biological cringe’, was not reviewed collapsing plant–bird mutualisms on Pacific supported by an analysis of 233 invasive plant species in islands, where human settlement has resulted in dozens of South Africa, carried out by Lesley Henderson (Agricultural bird extinctions, including many frugivores (Steadman, 1995).
Research Council, Pretoria, South Africa). She found that exotics New Zealand has lost 13 frugivorous birds since human originating from the northern and southern temperate zones arrival during the last millennium (Worthy & Holdaway, had identical average rates of expansion in that country.
2002). Although this is not known to have caused the Peter Williams (Landcare Research, Nelson, New Zealand) extinction of any plant species to date, a dozen large-seeded highlighted the importance of propagule pressure and suit- woody plants now depend on a single vector, the pigeon ability of the abiotic environment in determining naturaliza- Hemiphaga novaezelandiae (Clout & Hay, 1989), whose tion success of plants in Australia and New Zealand. The populations have dwindled in the face of depredation current prevalence of Eurasian species in New Zealand’s by introduced mammals as well as humans. Similarly, the register of exotic plants therefore reflects the persistent efforts extinction of four pigeon species (Ducula spp.) in Tonga has of 19th century colonists to create a “Better Britain” in the left plants with diaspores larger than c. 28 mm in diameter Antipodes’, as well as an influx of Eurasian stowaways. Suit- without any known seed disperser (McConkey & Drake, 2002).
ability of environment was also a good predictor of which Pollination mutualisms are also vulnerable throughout the species invade successfully in different parts of South Africa Pacific region, as a result of recent declines in abundance of im- (Mathieu Rouget, Kirstenbosch Botanic Gardens, South portant vertebrate pollinators such as honeyeaters and bats.
Africa). However, the case of Eucalyptus shows that massive Robertson quantified the effects of local extinction or propagule pressure and suitable abiotic environments won’t decline of mutualists on seed dispersal and set of several turn all exotics into invasives. Dave Richardson (University plant species in New Zealand. Reproductive success was of Cape Town, South Africa) showed that despite widespread consistently poorer in plant populations on mainland New plantings around the world, most Eucalyptus species scarcely Zealand than on small islands where conservation pro- naturalise and very few are aggressive invaders.
grammes have retained dense populations of pollinators In many cases, invasive plants are most prominent in early and seed dispersers. Similarly, Anton Pauw (University of Cape successional communities, eventually giving way to late- Town, South Africa) made use of spatial and temporal com- successional natives. However, in those cases where their parisons to show how orchid pollination in South Africa has functional traits differ from those of competing native been impaired by declines in abundance of oil-collecting bees.
pioneers, their influence on ecosystem properties such as soil Although most previous studies have focused on the nutrient availability could leave a persistent legacy. Duane vulnerability of plants to loss of their pollinators or dispersers, Peltzer and Peter Bellingham (Landcare Research, Lincoln, Cecilia Smith-Ramirez (Universidad Católica de Chile, New Zealand) described successions in New Zealand, where Santiago) reminded us not to overlook the situation of spe- exotic pioneer shrubs such as Buddleja davidii and Ulex cialist pollinators. Her analysis of the pollinator assemblage of europaeus produce more nutrient-rich leaf litter than their the Chilean rainforest tree Eucryphia cordifolia (currently a nearest native equivalents such as Coriaria arborea and Kunzea common species) revealed 15 species of Diptera which have ericoides. Elizabeth Lindsay and Tanya Mason (University of not been reported visiting flowers of any other plant.
Wollongong, Australia) presented similar results fromcontrasting the exotic shrub Chrysanthemoides molinifera andnative species such as Banksia integrifolia. Successional trajec-tories are in some cases quite different under exotic and native ‘25% of the Earth’s vegetation is fire-maintained’ shrub canopies, and as many of the species regeneratingbeneath them live for several centuries, the impact on vege-tation composition at landscape level could be appreciable.
Mutualism collapse
Fire – controlling global vegetation patterns
The proportion of woody plants dependent on vertebrates Studies of South African and Australian ecosystems have for pollination and seed dispersal is generally higher in produced novel perspectives on the role of fire as a driver of New Phytologist (2004) 162: 243 – 251
plant evolution, and as a control on global vegetation patterns.
such as lignotubers in central Chilean matorral (Montenegro It has long been recognized that adaptations facilitating et al., 1983). We know little about prehuman fire regimes in regeneration after fire are common in some floras. A more temperate South America, but Mauro González (Universi- recent suggestion is that flammability can be advantageous dad Austral de Chile, Valdivia), Donaldo Bran (INTA EEA, to a given genotype if it promotes the spread of fire to Bariloche, Argentina) and Tom Veblen (University of Colo- neighbours lacking sprouting or seeding responses that rado, Boulder, CO, USA) showed how present vegetation permit rapid recapture of the site (Bond & Midgley, 1995).
patterns in some parts of the region have been shaped by fire.
The Sheffield Dynamic Global Vegetation Model (SDGVM: González also pointed out that fuel loads associated with Woodward et al., 1995) generates the provocative prediction synchronous flowering and death of Chusquea bamboos that 25% of the Earth’s vegetation is fire-maintained. The promote rapid spread of forest fires, whether of human or SDGVM uses physiological criteria to predict spatial and temporal variation in broad vegetation types on the basis of Whether as a result of climate or isolation from evolutionary climate, soil and atmospheric CO concentration. William innovations, fire seems to have made fewer inroads in New Bond (University of Capetown, South Africa) showed that Zealand than in any of the major southern landmasses. Geoff the model grossly overpredicts global forest cover, unless a Rogers (Department of Conservation, Dunedin, New fire module is incorporated in simulations. Without fire, Zealand) estimated prehuman fire return intervals of > 1000 yr forest cover is predicted for Mediterranean-type climates, in the eastern South Island, attesting to the low flamm- implying that widespread heathlands and shrublands in ability of vegetation even in this relatively dry district of those regions are fire-maintained. When fire is added to the the country. Although human arrival greatly increased fire model, the predicted global vegetation map coincides closely frequency, most native plants lack the ability to recapture with current patterns, although deciduous forest is still sites rapidly through sprouts or seed banks.
incorrectly predicted for maritime temperate climates inChile, New Zealand and the Pacific North-west.
The future
Long-term fire exclusion experiments in South African savannas support model predictions (Bond et al., 2003). Sites While ‘Towards a southern perspective’ may be a reasonable receiving > 650 mm rainfall show succession to forest when short-term goal of Southern Connections, the real issue is fire is excluded, whereas arid savanna sites (predicted to remain that due consideration of both hemispheres means a better as savanna), although showing some increase in tree biomass, understanding of ecological processes and the evolution of do not develop closed forest. An analysis of Tasmanian the biosphere as a whole. Perhaps the clearest case is the work landscapes by Ross Bradstock (NSW National Parks & by South African and Australian ecologists on fire, which, Wildlife Service, Hurstville, Australia) developed the inter- although spurred mainly by studies of their own particularly esting related point that low site fertility can promote fire fire-prone systems, may force a rethink on the part of plant by prolonging dominance of flammable early successional ecologists and biogeographers the world over.
Another worthwhile aim must be to improve the rep- When and why did fire become so important? Bond et al.
resentation of some of the smaller southern hemisphere countries (2003) argue that the spread of fire as a major ecological at future conferences. Perspectives from New Caledonia and force can be linked to the advent of a new fuel type: the C Madagascar were sorely missed, and efforts must be made to grasses which proliferated under the falling CO levels of the persuade delegates from these remarkable Gondwanic frag- late Miocene. The combination of rapid growth and pro- ments to attend the next meeting in 2007 in Adelaide.
duction of slow-decaying litter by many C grasses results in Southern Connections is a ‘must attend’ forum for southern rapid buildup of inflammable material, enabling these plants hemisphere whole-organism biologists that northern hemi- to carry fire into mesic habitats (D’Antonio & Vitousek, sphere scientists might also do well to attend, to help a flow 1992). Ensuing changes in disturbance regimes may have of ideas across the divide. Perhaps there is also a need for triggered the evolution of fire-adapted traits in other taxa.
‘Northern Connections’ ensuring east–west interchange and Has fire split southern biotas? David Bowman (Charles inclusion of east Asian and Russian input to ecological and Darwin University, Australia) argued that the ecological and evolutionary impact of fire in Australian landscapes pre-dates human arrival by millions of years (contra Flannery, Chris Lusk1,* and Peter Bellingham2
1994), as is also clearly so in South Africa. Peter Clarke(University of New England, Armidale, Australia) showed 1Departamento de Botánica, Universidad de Concepción, that fire stimulated recruitment of > 80% of taxa even on Casilla 160-C, Concepción, Chile; 2Landcare Research, P.O.
relatively mesic sites in New South Wales. Although fire seems Box 69 Lincoln, New Zealand (*Author for correspondence: to have played a lesser role in the evolution of South American tel + 41 56 203418; fax + 41 56 246005; email vegetation, some plants show probable fire adaptations, www.newphytologist.org New Phytologist (2004) 162: 243–251
Flannery TF. 1994. The future eaters: an ecological history of the Australasian
Acknowledgements
lands and people. Sydney, Australia: Reed.
We thank Jeremy Midgley, Elizabeth Dankwertz and the McConkey KR, Drake DR. 2002. Extinct pigeons and declining bat
populations: are large seeds still being dispersed in the tropical Pacific?. organising committee for making the IV Southern Con- In: Levey D, Silva W, Galetti M, eds. Frugivory and seed dispersal: evolutionary and conservation perspectives. Wallingford, UK: CAB International, 381– 395.
Montenegro G, Avila G, Schatte P. 1983. Presence and development
References
of lignotubers in shrubs of the Chilean matorral. Canadian Journal of
Botany 61: 1804 –1808.
Armesto JJ, Smith-Ramirez C, Sabag C. 1996. The importance of
Steadman DW. 1995. Prehistoric extinctions of Pacific Island birds:
plant-bird mutualism in the temperate rainforest of southern South biodiversity meets zooarchaeology. Science 267: 1123 –1131.
America. In: Lawford RG, Alaback P, Fuentes ER, eds. High latitude Willson MF, De Santo TL, Sabag G, Armesto JJ. 1996. Avian
rainforests and associated ecosystems of the west coast of the Americas: communities of temperate rainforests of North and South America. climate, hydrology, ecology and conversation. Berlin, Germany: In: Lawford RG, Alaback P, Fuentes ER, eds. High latitude rainforests and associated ecosystems of the west coast of the Americas: climate, Bond WJ, Midgley JJ. 1995. Kill thy neighbour: an individualistic
hydrology, ecology and conversation. Berlin, Germany: Springer-Verlag, argument for the evolution of flammability. Oikos 73: 79 – 85.
Bond WJ, Midgley GF, Woodward FI. 2003. What controls South
Woodward FI, Smith TM, Emanuel WR. 1995. A global land primary
African vegetation – climate or fire? South African Journal of Botany productivity and phytogeography model. Global Biogeochemical Cycles 9:
69: 79 – 91.
Clout MN, Hay JR. 1989. The importance of birds as browsers,
Worthy TH, Holdaway RN. 2002. The lost world of the Moa.
pollinators and seed dispersers in New Zealand forests. NZ Journal of
Ecology 12: 27–32.
Bloomington, IN. USA: Indiana University Press.
D’Antonio CM, Vitousek PM. 1992. Biological invasions by exotic
grasses, the grass/fire cycle, and global change. Annual Review of Ecology Key words: fire ecology, flammability, invasive plants, plant–bird
and Systematics. 23: 67– 87.
mutualisms, southern hemisphere ecosystems.
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