Leaf and canopy responses of Lolium perenne to long-term elevated atmospheric carbon-dioxide concentration

Abstract

The relationship between leaf photosynthetic capacity (p n, max), net canopy CO2- and H2O-exchange rate (NCER and E t, respectively) and canopy dry-matter production was examined in Lollium perenne L. cv. Vigor in ambient (363±30 μl· l(-1)) and elevated (631±43 μl·l(-1)) CO2 concentrations. An open system for continuous and simultaneous regulation of atmospheric CO2 concentration and NCER and E t measurement was designed and used over an entire growth cycle to calculate a carbon and a water balance. While NCERmax of full-grown canopies was 49% higher at elevated CO2 level, stimulation of p n, max was only 46% (in spite of a 50% rise in one-sided stomatal resistance for water-vapour diffusion), clearly indicating the effect of a higher leaf-area index under high CO2 (approx. 10% in one growing period examined). A larger amount of CO2-deficient leaves resulted in higher canopy dark-respiration rates and higher canopy light compensation points. The structural component of the high-CO2 effect was therefore a disadvantage at low irradiance, but a far greater benefit at high irradiance. Higher canopy darkrespiration rates under elevated CO2 level and low irradiance during the growing period are the primary causes for the increase in dry-matter production (19%) being much lower than expected merely based on the NCERmax difference. While total water use was the same under high and low CO2 levels, water-use efficiency increased 25% on the canopy level and 87% on a leaf basis. In the course of canopy development, allocation towards the root system became greater, while stimulation of shoot dry-matter accumulation was inversely affected. Over an entire growing season the root/shoot production ratio was 22% higher under high CO2 concentration.

Nonlinear dynamics in ecosystem response to climatic change: Case studies and policy implications

“…Separate from the greenhouse effect of CO 2 on atmospheric temperatures and moisture, it is well established that atmospheric CO 2 enrichment has a fertilizing effect on most herbaceous plants by enhancing photosynthesis and water-use efficiency (Acock et al, 1985;Nijs et al, 1989;Allen et al, 1988;Rabbinge et al, 1993;IPCC, 1996;Anderson et al, 2001). Growth in woody species is also stimulated by increases in CO 2 , but there is a wide range of responses among deciduous and coniferous species (Eamus and Jarvis, 1989;NCASI, 1995).…”

Effects of Climate Change on Plant Respiration

“…Ryan, personal observation). Atmospheric C02• -Long-term exposure to [C02] > 350 ~tUL can either decrease respiration Stevens 1984, Gifford et al 1985 [wheat], Reuveni andGale 1985, Bunce 1990) or increase respiration (Gifford 1977, Azcon-Bieto and Osmond 1983, Gifford et al 1985, Poorter et al 1988, Nijs et al 1989. Decreased plant respiration may account for increased net carbon flux into tundra ecosystems fertilized with C02 at 510 and 680 ~tUL (Hilbert et al 1987), although the effect declined in year 2 and was nearly absent in year 3 of chronic fertilization .…”

Stomatal regulation in a changing climate: a field study using Free Air Temperature Increase (FATI) and Free Air CO2 Enrichment (FACE)

“…Stomatal conductance was determined with a diffusion porometer Mk-II (Delta-T, Burwell, UK) on 15, 16 and 17 August. Only adaxial g^ was sampled because abaxial values are =4 times smaller (Nijs et al 1989). Daily profiles were obtained by continuous sampling throughout the day, alternating between the four treatments.…”

“…Most of these studies were concerned with rising concentrations of atmospheric COo and have demonstrated that the antitranspirant potential of this greenhouse gas is also effective in long-term experiments (Radoglou et al 1992;Morgan et al 1994). An increase in leaf area tends to offset this antitranspirant effect in many species, but even then the benefit of enhanced water use efficiency often remains at the canopy level (Morison & Gifford 1984a,b;Nijs, Impens & Behaeghe 1989). Climate warming, on the other hand, has received less attention, presumably because consequences for transpiration seem straightforward to predict (higher water loss at higher leaf temperature Ty}.…”