Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Growth Respiration, Maintenance Respiration and Structural-Carbon Costs for Roots of Three Desert Succulents

P. S. Nobel, D. M. Alm and J. Cavelier
Functional Ecology
Vol. 6, No. 1 (1992), pp. 79-85
DOI: 10.2307/2389774
Stable URL: http://www.jstor.org/stable/2389774
Page Count: 7
  • Read Online (Free)
  • Download ($18.00)
  • Subscribe ($19.50)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Growth Respiration, Maintenance Respiration and Structural-Carbon Costs for Roots of Three Desert Succulents
Preview not available

Abstract

Water and nutrient uptake are provided at a cost of the carbon incorporated structurally into roots as well as that used for respiratory activities supporting root growth and maintenance. Gas-exchange and dry weight measurements on growing attached roots of Agave deserti indicated a respiratory CO2 requirement of 6.8±0.6 mol CO2 per kg dry weight for newly elongating nodal roots emanating from the stem and 7.2±0.9 for lateral roots occurring as fine branches on the nodal roots. Similar gas-exchange measurements indicated a growth respiration of 9.4±1.4 mol CO2 kg-1 for new roots of Ferocactus acanthodes and 8.7±0.7 for Opuntia ficus-indica. Root growth respiration was also estimated using the heat of combustion of dried root material, which was assumed to contain 47% carbon in the non-ash fraction. For roots 1-20 weeks of age, growth respiration based on the heat of combustion averaged 9.4, 8.4 and 7.7 mol CO2 kg-1 for A. deserti, F. acanthodes, and O. ficus-indica, respectively, averaging 0.7 mol CO2 kg-1 higher for 1-week-old roots. The direct measurements of CO2 evolution and the indirect estimate of growth respiration both indicate that the roots of desert succulents have low respiratory costs for growth compared with other species. The carbon incorporated into the dry weight of the roots averaged 38 mol kg-1 for the three species. Thus, the carbon costs for new roots of these desert succulents represented mainly carbon incorporated structurally into the roots, not growth respiration, and such total carbon costs can become similar to carbon expended by maintenance respiration after about 3 months under wet conditions at 20C. For A. deserti under conditions appropriate to the Sonoran Desert, the water acquired from the soil per unit carbon expended was over twice as high for the drought-deciduous lateral roots and for nodal roots in their second year compared with first-year nodal roots.

Page Thumbnails

  • Thumbnail: Page 
79
    79
  • Thumbnail: Page 
80
    80
  • Thumbnail: Page 
81
    81
  • Thumbnail: Page 
82
    82
  • Thumbnail: Page 
83
    83
  • Thumbnail: Page 
84
    84
  • Thumbnail: Page 
85
    85