Atmospheric CO₂ enrichment increases growth and photosynthesis of Pinus taeda: a 4 year experiment in the field

Abstract

Forest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long-term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size-dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these difterences were greater in the summer (60-130% increase) than in the winter (14-44% increase), refiecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non-structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy-level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then

Effects of lifelong [CO2] enrichment on carboxylation and light utilization of Quercus pubescens Willd. examined with gas exchange, biochemistry and optical techniques

“…Mousseau 1993;Tissue et al 1993Tissue et al , 1999Lewis et al 1996;Tissue, Thomas & Strain 1997, Rey & Jarvis 1998Spunda et al 1998;Turnbull et al 1998; also see review by Medlyn et al 1999). For example, A max did not differ for new Q. ilex leaves but was downregulated for 1-year-old leaves at the Laiatico CO 2 spring compared to a control site (C. Cario et al unpublished results).…”

“…Indeed, many other studies have reported no change or an increase in leaf area index with elevated [CO 2 ] (e.g. Tissue et al 1997; also see reviews by Saxe et al 1998 andNorby et al 1999).…”

Photosynthetic adjustment in field-grown ponderosa pine trees after six years exposure to elevated CO{sub 2}

“…In most trees, net photosynthesis was stimulated 40-80% by growth in elevated CO,, with the lowest stimulation for non-shade grown trees being 20% in Mangifera indica (Goodfellow et al 1997). In loblolly pine (Pinus taeda), net photosynthesis of trees grown in the field in conditions that did not limit rooting volume was also stimulated by growth in elevated CO, (Ellsworth et al 1995, Liu and Teskey 1995, Teskey 1995, Lewis et al 1996, even after four years of CO1exposure (Tissue et al 1997). In general, net photosynthesis is enhanced in trees grown in elevated CO1 and that enhancement is maintained for long periods.…”

“…Seasonal effects have been shown to influence the photosynthetic response to elevated COZ (El Kohen and Mousseau 1994, Curtis et al, 1995Lewis et al 1996, Tissue et al 1997, Rey and Jarvis 1998. In two deciduous trees, C'astanea sativa (El Kohen and Mousseau 1994) and Betula pendzda (Rey and Jarvis 1998), photosynthetic adjustment to elevated C02 increased as the growing season progressed.…”

Connecting silvan and lacustrine ecosystems: transport of carbon from forests to adjacent water bodies

“…The increased concentration of atmospheric CO 2 could enhance photosynthesis, since the uptake of CO 2 will become easier (Tissue et al 1997, Kirschbaum 2011. This might lead to a reduced ne e d f o r w a t e r. A s a re s u l t o f w a rm e r a n d l o ng e r g ro w i ng s e a s o ns , t he a m o u nt o f assimilated CO 2 could increase.…”