Interacting effects of soil fertility and atmospheric CO₂ on leaf area growth and carbon gain physiology in Populus×euramericana (Dode) Guinier

Abstract

SUMMARYTwo important proeesses whieh may limit produetivity gains in forest eeosystems with rising atmospheric CO, are reduction in photosynthetie capacity following prolonged exposure to high CO, and diminution of positive growth responses when soil nutrients, particularly N, are limiting. To exan-iine the interacting effects of soil fertility and CO^ enrichment on photosynthesis and growth in trees we grew hybrid poplar {Populus x euramericana) for 158 d in the field at ambient and twice ambient CO,^ and in soil with low or high N availability. We measured the timing and rate of eanopy development, the seasonal dynamies of leaf level photosynthetie capacity, respiration, and N and carbohydrate concentration, and final above-and belowground dry weight.Single leaf net CO,^ assimilation (A) increased at elevated CO,, over the majority of the growing season in both fertility treatments. At high fertility, the maximum size of individual leaves, total leaf number, and seasonal leaf area duration (LAD) also increased at elevated CO,, leading to a 49 % increase in total dry weight. In contrast, at low fertility leaf area growth was unaffeeted by COj treatment. Total dry weight nonetheless increased 25 % due to COg effeets on A. Photosynthetic capacity (A at constant internal p(CO,2), (C,)) was reduced in high CO,, plants after 100 d growth at low fertility and 135 d growth at high fertility. Analysis of A responses to changing C, indicated that this negative adjustment of photosynthesis was due to a reduetion in the maximum rate of CO fixation by Rubisco. Maximum rate of electron transport and phosphate regeneration capacity were either unaffected or declined at elevated CO,. Carbon dioxide effects on leaf respiration were most pronounced at high fertility, with increased respiration mid-season and no change (area basis) or reduced (mass basis) respiration lateseason in elevated compared to ambient CO, plants. This temporal variation correlated with changes in leaf N concentration and leaf mass per area. Our results demonstrate the importance of considering both structural and physiological pathways of net C gain in predicting tree responses to rising CO, under conditions of suboptimal soil fertility.

Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO2 and soil N availability

“…Elevated CO # has a direct effect on photosynthetic efficiency because it increases the diffusion gradient of CO # into leaves, and increases leaf N-use efficiency and the efficiency of photosynthetic enzymes (Drake & Gonza ' lez-Meler, 1997). This CO # -stimulation of A decreased following budset, possibly through carbohydrate feedback inhibition of photosynthesis, as seen in other Populus species before and after budset (Bosac et al, 1995 ;Curtis et al, 1995).…”

“…This was unexpected because several studies demonstrated substantial increases in stem height (c. 7-90 %), leaf area (c. 10-50 %), and above-ground biomass (c. 25-47 %) in five Populus hybrids in elevated CO # (Radoglou & Jarvis, 1990 ;Bosac et al, 1995 ;Curtis et al, 1995 ;Pregitzer et al, 1995 ;Ceulemans et al, 1996). However, Populus grandidentata, another naturally occurring species, had no significant height or leaf area response to elevated CO # (Curtis et al, 1994).…”

“…This study is one in a series of experiments to examine the interactions between elevated atmospheric CO # and soil N availability on tree growth, and to study how trees mediate the cycling of C and N in forest ecosystems (Curtis & Teeri, 1992 ;Zak et al, 1993 ;Curtis et al, 1994Curtis et al, , 1995Pregitzer et al, 1995 ;Kubiske et al, 1997). The purposes of the present study were to measure the effect of elevated atmospheric CO # and soil N availability on the production and turnover of fine roots, and to determine the extent to which differences in autumnal leaf-fall phenology of Populus tremuloides genotypes might influence late-season C allocation to fine roots under elevated atmospheric CO # .…”

Growth performance of Populus exposed to "Free Air Carbon dioxide Enrichment" during the first growing season in the POPFACE experiment

“…In fact poplars are the most promising trees for "short rotation intensive culture" (SRIC) [15]. In recent years several experiments were already carried out on the effects of atmospheric CO 2 on poplars [1,3,7,14,20,31,32,39], most of them for a limited duration of treatment (less than one year) and/or on individual plants.…”

Photosynthesis, Rubisco activity and mitochondrial malate oxidation in pedunculate oak (Quercus robur L) seedlings grown under present and elevated atmospheric CO2 concentrations

“…A higher CO 2 concentration may also affect leaf respiration directly by as yet unknown modifications of the respiratory biochemistry (Amthor, 1991;Wullschleger et al, 1994) and indirectly through changes in growth rate and tissue composition (sugars, nitrogen) (Wullschleger et al, 1992a;Curtis et al, 1995). In trees, the CO 2 enrichment usually induced a reduction in leaf dark respiration (EI Kohen et al, 1991;Wullschleger et al, 1992b;Reid and Strain, 1994;Teskey, 1995 (Bradford, 1976 (Sheen, 1994 (Bonner, 1967;Laties, 1974).…”