Elevated CO2 and tree root growth: contrasting responses in Fraxinus excelsior, Quercus petraea and Pinus sylvestris.

Root growth and respiration in elevated CO2 (700 μmol mol-1 ) was studied in three tree species, Fraxinus excelsior L., Quercus petraea. L. and Pinus sylvestris L. grown in open-top chambers (OTCs) during a long-term exposure (20 months), during which root systems were allowed to develop without restriction imposed by pots. Root growth, measured as root length using root in-growth bags was increased significantly in trees exposed to elevated CO2 , although the magnitude of the response differed considerably between species and with time of sampling, the greatest effect observed after 6 months in ash (ratio of elevated: ambient, e∶a; 3·40) and the smallest effect observed in oak (e∶a; 1·95). This was accompanied by changes in specific root length, with a significant decrease in all species after 6 months, suggesting that root diameter or root density were increased in elevated CO2 . Increases in root length might have resulted from an acceleration in root cell expansion, since epidermal cell size was significantly increased in the zone of elongation in ash root tips (P<0·05). Contrasting effects of elevated CO2 were observed for root carbohydrates, with significant increases in soluble sugars for all species (P<0·05), but both increases and decreases in starch content were observed, depending on species, and producing a significant interaction between species and CO2 (P<0·001). Exposure to elevated CO2 increased the total root d. wt for whole trees of all three species after 8 months of exposure, although the magnitude of this effect, in contrast to the root in-growth study, was greatest in Scots pine and smallest in ash. No significant effect of elevated CO2 was observed on the root∶shoot ratio. Further detailed analysis of whole root systems after 20 months confirmed that species differences in root responses to elevated CO2 were apparent, with increased coarse and fine root production in elevated CO2 for Scots pine and ash respectively. Lateral root number was increased in elevated CO2 for all species, as was mean root diameter. Root respiration rates were significantly reduced in elevated CO2 for all three species. These results provide firm evidence that exposure of trees to future CO2 concentrations will have large effects on root system development, growth, carbohydrate status and respiration. The magnitude and direction of such effects will differ, depending on species. The consequences of such responses for the three species studied are discussed.

[1]  M. Ribas-Carbó,et al.  Direct Inhibition of Plant Mitochondrial Respiration by Elevated CO2 , 1996, Plant physiology.

[2]  M. G. Ryan,et al.  Foliage, fine-root, woody-tissue and stand respiration in Pinus radiata in relation to nitrogen status. , 1996, Tree physiology.

[3]  C. Nietch,et al.  Increased growth efficiency of Quercus alba trees in a CO2 -enriched atmosphere. , 1995, The New phytologist.

[4]  G. Taylor,et al.  Elevated CO2 and hybrid poplar: a detailed investigation of root and shoot growth and physiology of Populus euramericana, ‘Primo’ , 1995 .

[5]  P. Curtis,et al.  Atmospheric CO2, soil nitrogen and turnover of fine roots , 1995 .

[6]  P. Kuikman,et al.  Carbon allocation and water use in juvenile Douglas fir under elevated CO2. , 1995, The New phytologist.

[7]  G. Taylor,et al.  Effects of elevated CO2 on cellular mechanisms, growth and development of trees with particular reference to hybrid poplar , 1995 .

[8]  Reinhart Ceulemans,et al.  Tansley Review No. 71 Effects of elevated atmospheric CO2on woody plants , 1994 .

[9]  S V Krupa,et al.  Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere. , 1994, Environmental pollution.

[10]  H. Rogers,et al.  Response of plant roots to elevated atmospheric carbon dioxide , 1992 .

[11]  J. Houghton,et al.  Climate change 1992 : the supplementary report to the IPCC scientific assessment , 1992 .

[12]  F. A. Bazzaz,et al.  Plant life in a CO2 - rich world , 1992 .

[13]  F. I. Woodward,et al.  The root system architecture and development of Senecio vulgaris in elevated CO_2 and drought , 1992 .

[14]  M. L. Williams,et al.  The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source‐sink relations and respiration , 1991 .

[15]  E. Kanemasu,et al.  Root growth of winter wheat under elevated carbon dioxide and drought. , 1990 .

[16]  J. Guehl,et al.  Differential growth response to atmospheric carbon dioxide enrichment in seedlings of Cedrusatlantica and Pinusnigra ssp. Laricio var. Corsicana , 1989 .

[17]  R. Norby,et al.  Effects of Atmospheric CO(2) Enrichment on the Growth and Mineral Nutrition of Quercus alba Seedlings in Nutrient-Poor Soil. , 1986, Plant physiology.

[18]  R. B. Burnett,et al.  Effect of carbon dioxide on sorghum yield, root growth, and water use , 1986 .

[19]  K. Vogt,et al.  Production, Turnover, and Nutrient Dynamics of Above- and Belowground Detritus of World Forests , 1986 .

[20]  H. Lambers,et al.  Respiration of crop species under CO2 enrichment , 1985 .

[21]  J. Farrar.  Allocation of carbon to growth, storage and respiration in the vegetative barley plant , 1980 .

[22]  H. Lyr,et al.  Growth Rates and Growth Periodicity of Tree Roots , 1967 .

[23]  F. Smith,et al.  Colorimetric Method for Determination of Sugars and Related Substances , 1956 .