Acclimation of photosynthesis to increasing atmospheric CO2: The gas exchange perspective

Abstract

The nature of photosynthetic acclimation to elevated CO2 is evaluated from the results of over 40 studies focusing on the effect of long-term CO2 enrichment on the short-term response of photosynthesis to intercellular CO2 (the A/Ci response). The effect of CO2 enrichment on the A/Ci response was dependent on growth conditions, with plants grown in small pots (< 5 L) or low nutrients usually exhibiting a reduction of A at a given Ci, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given Ci following a doubling or tripling of atmospheric CO2 during growth. Using theoretical interpretations of A/Ci curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/Ci curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO2 enrichment usually had little effect or increased the value of A at all Ci. However, a minority of species grown at elevated CO2 exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO2 and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO2 (the Ci/Ca ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, Ci/Ca exhibited no consistent change in a variety of C3 species, indicating no stomatal acclimation. Under drought or humidity stress, Ci/Ca declined in high-CO2 grown plants, indicating stomata will become more conservative during stress episodes in future high CO2 environments.

Comparison of ROS formation and antioxidant enzymes in Cleome gynandra (C4) and Cleome spinosa (C3) under drought stress

“…C 4 plants, in contrast to C 3 plants, are reported to be better adapted to water stress [10,11] due to its (i) distinctive leaf anatomy (Kranz anatomy) (ii) having two carboxylation pathways (phosphoenolpyruvate carboxylase (PEPC) and RUBISCO) in mesophyll and bundle sheats that limit photorespiration and increase carboxylation efficiency [12] and (iii) requiring a lower CO 2 saturation point for photosynthesis than C 3 plants [13].…”

Intra-specific variation in response of Neem (Azadirachta indica A. Juss) to elevated CO2 levels and biochemical characterization of differently responding plants

“…Moore et al (1998) also reported that short term exposure of elevated CO 2 for plants generally leads to increased rates of leaf-level photosynthesis due to enhanced activity of RuBisCO. On the other hand, photosynthesis down regulation is characterized at the biochemical and leaf levels by reduced chlorophyll content, reduced RuBisCO content and activity and decreased leaf nitrogen concentration on a leaf mass basis (Sage 1994, Tissue et al 1995. It warrants further research to understand the reason for higher leaf N in some species and lower N levels in leaf in other species when plants are exposed to elevated CO 2 .…”

Plant responses to elevated CO2 concentration at different scales: leaf, whole plant, canopy, and population

“…To use nitrogen efficiently, nitrogen should be reallocated from non-limiting to limiting processes (Evans 1989;Hikosaka and Terashima 1995). It has been suggested that nitrogen reallocation from RuBP carboxylation to the RuBP regeneration processes would increase photosynthetic nitrogen use efficiency at elevated CO 2 (Sage 1994;Webber et al 1994;Medlyn 1996). Using a theoretical model of nitrogen partitioning in the photosynthetic apparatus, Hikosaka and Hirose (1998) suggested that nitrogen reallocation to RuBP regeneration in the doubled CO 2 level would increase photosynthesis by 20%.…”

“…It is still increasing at a rate of 1.5 lmol mol À1 per year and may reach 700 lmol mol À1 at the end of this century (IPCC 2001). Because CO 2 is a substrate for photosynthesis, an increase in atmospheric CO 2 concentration stimulates photosynthetic rates in C 3 plants (Kimball 1983;Cure and Acock 1986;Bazzaz 1990;Poorter 1993;Sage 1994;Curtis 1996;Ward and Strain 1999). However, the effect of elevated CO 2 on growth and reproduction is often much weaker than that predicted by the photosynthetic response.…”

“…However, the effect of elevated CO 2 on growth and reproduction is often much weaker than that predicted by the photosynthetic response. It also differs considerably between species and between plants grown under different conditions (Bazzaz 1990;Arp 1991;McConnaughay et al 1993;Sage 1994;Farnsworth and Bazzaz 1995;Makino and Mae 1999;Ward and Strain 1999;Jablonski et al 2002). Nutrient availability has been considered one of the key factors for the variation in plant responses to elevated CO 2 (e.g.…”