C 4 photosynthesis, atmospheric CO 2 , and climate

Abstract

The objectives of this synthesis are (1) to review the factors that influence the ecological, geographical, and palaeoecological distributions of plants possessing C photosynthesis and (2) to propose a hypothesis/model to explain both the distribution of C plants with respect to temperature and CO and why C photosynthesis is relatively uncommon in dicotyledonous plants (hereafter dicots), especially in comparison with its widespread distribution in monocotyledonous species (hereafter monocots). Our goal is to stimulate discussion of the factors controlling distributions of C plants today, historically, and under future elevated CO environments. Understanding the distributions of C/C plants impacts not only primary productivity, but also the distribution, evolution, and migration of both invertebrates and vertebrates that graze on these plants. Sixteen separate studies all indicate that the current distributions of C monocots are tightly correlated with temperature: elevated temperatures during the growing season favor C monocots. In contrast, the seven studies on C dicot distributions suggest that a different environmental parameter, such as aridity (combination of temperature and evaporative potential), more closely describes their distributions. Differences in the temperature dependence of the quantum yield for CO uptake (light-use efficiency) of C and C species relate well to observed plant distributions and light-use efficiency is the only mechanism that has been proposed to explain distributional differences in C/C monocots. Modeling of C and C light-use efficiencies under different combinations of atmospheric CO and temperature predicts that C-dominated ecosystems should not have expanded until atmospheric CO concentrations reached the lower levels that are thought to have existed beginning near the end of the Miocene. At that time, palaeocarbonate and fossil data indicate a simultaneous, global expansion of C-dominated grasslands. The C monocots generally have a higher quantum yield than C dicots and it is proposed that leaf venation patterns play a role in increasing the light-use efficiency of most C monocots. The reduced quantum yield of most C dicots is consistent with their rarity, and it is suggested that C dicots may not have been selected until CO concentrations reached their lowest levels during glacial maxima in the Quaternary. Given the intrinsic light-use efficiency advantage of C monocots, C dicots may have been limited in their distributions to the warmest ecosystems, saline ecosystems, and/or to highly disturbed ecosystems. All C plants have a significant advantage over C plants under low atmospheric CO conditions and are predicted to have expanded significantly on a global scale during full-glacial periods, especially in tropical regions. Bog and lake sediment cores as well as pedogenic carbonates support the hypothesis that C ecosystems were more extensive during the last glacial maximum and then decreased in abundance following deglaciation as atmospheric CO levels increased.

Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience

“…Edwards and Still (2008) found that the distribution of C4 grasses on Hawaii correlated with areas of lower mean annual precipitation compared to their C3 counterparts. The lower proportion of C4 plants in modern soils within manavai and rock garden soils inferred from δ 13 C values therefore is consistent with higher soil moisture contents in agricultural soils that affect C3/C4 plant ratios (Edwards & Still, 2008; Ehleringer, Cerling, & Helliker, 1997). Historical land use changes, such as extensive sheep farming from ca.…”

Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

“…There is currently little consensus, however, regarding physiological constraints on C 4 plant distribution in cold climates. Dissociation of the C 4 enzymes pyruvatephosphate dikinase and PEP carboxylase (Long, 1983;Potvin et al, 1986), Rubisco limitation (Long 1999;Kubien et al, 2003), and lower quantum yield of C 4 versus C 3 grasses (Ehleringer et al, 1997) at lower temperatures have all been proposed as explanations for the scarcity of C 4 species in cold environments. Most of these studies have focused on low temperatures during the growing season, but our results suggest that winter temperatures may be equally important in limiting C 4 grasses.…”

“…However, this low temperature limit may have been altered during the late Pleistocene due to shifts in dominance between C 3 and C 4 species. The higher quantum yield of C 3 species at low temperatures may limit C 4 grass distribution at sites with cooler growing season temperatures via competitive exclusion (Ehleringer et al, 1997). During the late Pleistocene, however, C 4 photosynthesis may have been favored at lower summer temperatures when reduced crossover temperatures (the mean monthly temperature at which C 4 plants have a higher quantum yield than C 3 plants) resulted from decreased atmospheric CO 2 concentration (Ehleringer et al, 1997;Koch et al, 2004).…”

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].…”