Effects of elevated CO₂ and temperature on growth and allometry of five native fast‐growing annual species

Abstract

Whereas much is known of the short-term growth response to elevated atmospheric CO # concentrations, [CO # ] elev , there is relatively little information on how the response of native species is modified by temperature, despite the fact that an increase in global mean temperature is expected to accompany the rise in [CO # ]. In this study, five functionally related annual native species were exposed to different combinations of ambient and elevated [CO # ] and temperatures in order to assess their response in terms of growth and allometry. Fast-growing annuals were selected for the study because their growth responses could be assessed over a major portion of the plant's life cycle and in as short a period as 8 wk. Plants were grown in eight hemi-spherical glasshouses, programmed to track outside ambient conditions and provide a replicated experimental design. increased total plant biomass by 25 % (P l 0n005) at 56 d, reflecting a proportionally greater increase in leaf and stem mass relative to root weight. Elevated [CO # ] had no effect on leaf area, either at the individual species level or overall. Elevated T mC, by contrast, had little effect on shoot growth but increased root mass on average by 43 % and leaf area by 22 %. Few interactions between elevated [CO # ] and T mC were observed, with the CO # response generally greater at elevated than ambient T mC. Both [CO # ] elev and T mC elev resulted in a transient increase in relative growth rate, (), during the first 14 d exposure and a 3 mC increase in temperature had no effect on the duration of the response. CO # stimulation of growth operated through a sustained increase in net assimilation rate. (), although the potential benefit to  was offset by a concurrent decline in leaf area ratio (), as a result of a decrease in leaf area per unit leaf mass (). The response to T mC elev was generally opposite of that to [CO # ] elev . For example, T mC elev increased  through an increase in  and this, rather than any effect on , was the major factor responsible for the stimulation of . Allometric analysis of CO # effects revealed that changes in allocation observed at individual harvests were due solely to changes associated with plant size. Elevated T mC, by contrast, had a direct effect on allocation patterns to leaves, with an increase in leaf area expansion relative to whole plant mass during the initial stages of growth and subsequent increased allocation of biomass away from leaves to other regions of the plant. No change in the allometric relation between roots and shoots were observed at either elevated [CO # ] or T mC. We conclude, therefore, that allocation of biomass and morphological characteristics such as , are relatively insensitive to [CO # ], at least when analysed at the whole-plant level, and where changes have been observed, these are the product of comparing plants of the same age but different size.

Effects of tree size and temperature on relative growth rate and its components of Fagus sylvatica seedlings exposed to two partial pressures of atmospheric [CO2]

“…As found for several other species (Gebauer et al, 1996 ;Groninger et al, 1996 ;Tissue et al, 1997 ;Stirling et al, 1998 ;Tjoelker et al, 1998 ;Centritto et al, 1999) most of the effects of [CO # ] and temperature regime on dry matter allocation and various plant dimensions disappeared when adjustments were made for differences in size. Analysis of allometric coefficients show that only at low [CO # ] were the stems longer at a given diameter at the higher temperature regimes.…”

Elevated Atmospheric CO2 Magnifies Intra-specific Variation in Seedling Growth of Honey Mesquite: An Assessment of Relative Growth Rates

“…For each family and CO 2 treatment, we also calculated allometric coefficients to describe variation in the biomass of leaves or roots with changes in the total biomass of seedlings (e.g., Stirling et al 1998). The allometric coefficient was calculated as the slope of the linear regression between the natural logarithm of the biomass of leaves or roots and the natural logarithm of total biomass.…”

Leaf‐Level Physiology, Biomass, and Reproduction of Phytolacca americana under Conditions of Elevated CO2 and Altered Temperature Regimes

“…The effects of rising atmospheric CO 2 and temperature on plants and ecosystems have been investigated in a number of experiments (Ackerly et al 1992;Hunt et al 1996;Stirling et al 1998;Tjoelker et al 1998;Wayne et al 1998;Loiseau and Soussana 2000;Lee et al 2001;Lewis et al 2001;Luomala et al 2003; see reviews by Rawson 1992;Saxe et al 1998;Morison and Lawlor 1999;Amthor 2001;Norby and Luo 2004;Pendall et al 2004). However, the warming treatments in most of the elevated CO 2 and temperature studies have not considered how changing aspects of the daily temperature regime may affect plants and ecosystems.…”

“…Increasing atmospheric CO 2 concentration and air temperature are both important factors affecting plant physiology, growth, development, and reproduction (Stirling et al 1998;Morison and Lawlor 1999). The concentration of atmospheric CO 2 has increased during the past 250 yr from ca.…”