Testing unified theories for ozone response in C₄ species

Abstract

There is tremendous interspecific variability in O 3 sensitivity among C 3 species, but variation among C 4 species has been less clearly documented. It is also unclear whether stomatal conductance and leaf structure such as leaf mass per area (LMA) determine the variation in sensitivity to O 3 across species. In this study, we investigated leaf morphological, chemical, and photosynthetic responses of 22 genotypes of four C 4 bioenergy species (switchgrass, sorghum, maize, and miscanthus) to elevated O 3 in side-by-side field experiments using free-air O 3 concentration enrichment (FACE).The C 4 species varied largely in leaf morphology, physiology, and nutrient composition. Elevated O 3 did not alter leaf morphology, nutrient content, stomatal conductance, chlorophyll fluorescence, and respiration in most genotypes but reduced net CO 2 assimilation in maize and photosynthetic capacity in sorghum and maize. Species with lower LMA and higher stomatal conductance tended to show greater losses in photosynthetic rate and capacity in elevated O 3 compared with species with higher LMA and lower stomatal conductance. Stomatal conductance was the strongest determinant of leaf photosynthetic rate and capacity. The response of both area-and mass-based leaf photosynthetic rate and capacity to elevated O 3 were not affected by LMA directly but negatively influenced by LMA indirectly through stomatal conductance. These results demonstrate that there is significant variation in O 3 sensitivity among C 4 species with maize and sorghum showing greater sensitivity of photosynthesis to O 3 than switchgrass and miscanthus. Interspecific variation in O 3 sensitivity was determined by direct effects of stomatal conductance and indirect effects of LMA. This is the first study to provide a test of unifying theories explaining variation in O 3 sensitivity in C 4 bioenergy grasses. These findings advance understanding of O 3 tolerance in C 4 grasses and could aid in optimal placement of diverse C 4 bioenergy feedstock across a polluted landscape.

The leaf economics spectrum of triploid and tetraploid C4 grass Miscanthus x giganteus

“…M.× giganteus genotypes also tended to have a higher A m at a given N m or P m when compared to the Glopnet species, in agreement with the observations of higher A N and A P in M.× giganteus (Table 1 1; Figure 1) (Ferguson et al, 2021). In other studies, the lowest reported A a , A m and N m values for five genotypes of sorghum were 44.3 µmol m −2 s −1 , 1426.7 nmol g −1 s −1 and 3.76% (Li et al, 2019(Li et al, , 2021 (Li et al, 2019(Li et al, , 2022. A recent study also revealed broad variation in leaf morphology across switchgrass genotypes in common garden experiments (Lovell et al, 2021).…”

“…Concerning LMA, the highest value for sorghum was 35.3 g m −2 , which is much lower than the lowest values of 41.0 g m −2 in M .× giganteus . However, switchgrass ( Panicum virgatum ; three genotypes) had a similar mean LMA value with M .× giganteus (67.4 vs. 67.1 g m −2 ), but displayed overall higher mean values for A a (30.6 vs. 23.7 µmol m −2 s −1 ), A m (456.6 vs. 369.8 nmol g −1 s −1 ), and N m (3.37 vs. 2.20%) (Li et al, 2019 , 2022 ). A recent study also revealed broad variation in leaf morphology across switchgrass genotypes in common garden experiments (Lovell et al, 2021 ).…”

“…Higher activity of PEPCase effectively concentrates CO 2 , leading to a high CO 2 /O 2 ratio around Rubisco, thereby increasing photosynthetic efficiency and decreasing photorespiration (Ehleringer & Monson, 1993 ). C 4 species typically exhibit superior efficiencies of carbon fixation, water and nutrient use, and increased resistance to environmental stress compared to C 3 species (Ehleringer & Monson, 1993 ; Leakey et al, 2019 ; Li et al, 2022 ; Montes et al, 2022 ). As a result, multivariate correlations among leaf functional traits in C 4 species may not be consistent or may differ greatly from the general trends observed in the global fundamental leaf trait relationships.…”

Implementation of trait-based ozone plant sensitivity in the Yale Interactive terrestrial Biosphere model v1.0 to assess global vegetation damage

“…In reality, there are hundreds and thousands of plant species in each PFT and they usually have large variation in biophysical parameters including LMA and O3 sensitivities. The LMA-based approach takes advantage of the newly revealed unifying concept in O3 sensitivity (Feng et al, 2018;Li et al, 2016;Li et al, 2022) and the recent development in a trait-based LMA global map (Fig. S1a).…”

“…Recent observations revealed a uniform plant sensitivity to O3 if stomatal O3 flux is expressed based on leaf mass rather than leaf area (Feng et al, 2018;Li et al, 2016;Li et al, 2022). The trait of leaf mass per area (LMA) is an important metric linking leaf area to mass.…”