The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source‐sink relations and respiration

Abstract

Abstract. Herbaceous C3 plants grown in elevated CO2 show increases in carbon assimilation and carbohydrate accumulation (particularly starch) within source leaves. Although changes in the partitioning of biomass between root and shoot occur, the proportion of this extra assimilate made available for sink growth is not known. Root:shoot ratios tend to increase for CO2‐enriched herbaceous plants and decrease for CO2‐enriched trees. Root:shoot ratios for cereals tend to remain constant. In contrast, elevated temperatures decrease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root: shoot ratios due to elevated CO2 show no alteration in the whole‐plant partitioning of biomass. Little information is available for interactions between temperature and CO2. Cold‐adapted plants show little response to elevated levels of CO2, with some species showing a decline in biomass accumulation. In general though, increasing temperature will increase sucrose synthesis, transport and utilization for CO2‐enriched plants and decrease carbohydrate accumulation within the leaf. Literature reports are discussed in relation to the hypothesis that sucrose is a major factor in the control of plant carbon partitioning. A model is presented in support.

Acquisition and allocation of carbon and nitrogen by Danthonia richardsonii in response to restricted nitrogen supply and CO2 enrichment

“…Allometric analysis was used to elucidate allocation patterns by removing plant dry weight effects (Troughton 1955;Hunt 1978;Farrar & Williams 1991). The function y = bx k , linearized to lny = lnb + klnx, was fitted to the data, where x and y are the attributes of the plant fractions.…”

“…Watson & Graves 1993), but declines with increasing plant dry weight as plants move out of the exponential phase of growth (Ballard et al 1936;Evans 1993;Gifford et al 1996). Indeed, many characteristics of plants, such as dry matter distribution change with age and with increases in plant dry weight (Ballard et al 1936;Evans 1972;Farrar & Williams 1991). It has been hypothesized that some of the common responses to CO 2 enrichment, such as the decrease in total plant nitrogen concentration may result solely from changes in plant dry weight (Coleman, McConnaughay & Bazzaz 1993).…”

“…To understand, model and predict the physiological response of plants to CO 2 increase, it is important to separate real CO 2 effects on allocation and function from those related to changes in ontogeny or plant dry weight (Loehle 1995). Thus, allometric relationships were used to test for actual differences between CO 2 treatments in dry weight and nitrogen allocation (Troughton 1955;Hunt 1978;Farrar & Williams 1991), as opposed to changes in distribution (root dry weight or nitrogen ratio, the mass of root dry weight or N as fraction of total plant dry weight or N) at harvest that are due to changes in plant mass. This paper addresses, for an Australian native grass, the following hypotheses related to growth over the first 37 d from seed imbibition.…”

“…The statistically significance of differences in growth analysis parameters was determined using ANOVA. Average RGR for the period from seed imbibition to the first harvest was calculated assuming an average seed mass of 0·70 mg (n = 100).Allometric analysis was used to elucidate allocation patterns by removing plant dry weight effects (Troughton 1955;Hunt 1978;Farrar & Williams 1991). The function y = bx k , linearized to lny = lnb + klnx, was fitted to the data, where x and y are the attributes of the plant fractions.…”

Growth responses of Quercus petraea, Fraxinus excelsior and Pinus sylvestris to elevated carbon dioxide, ozone and water supply

“…Only the natural CO # springs in Italy represent a long-term natural elevated CO # experiment (Tognetti et al, 1998), although even here problems associated with large, rapid variations in CO # concentrations are apparent. In many of the traditional growth and open-top chamber experiments, the observed down regulation or acclimation of the photosynthetic apparatus might be attributable to reduced rooting volume (Farrar & Williams, 1991 ;Thomas & Strain, 1991 ;Curtis & Wang, 1998). The use of potted trees within open-top and growth chambers might also lead to increased root temperature during the summer, further affecting the source-sink relationship through respiratory C loss.…”