Drought Sensitivity of the Carbon Isotope Composition of Leaf Dark-Respired CO2 in C3 (Leymus chinensis) and C4 (Chloris virgata and Hemarthria altissima) Grasses in Northeast China

Abstract

Whether photosynthetic pathway differences exist in the amplitude of nighttime variations in the carbon isotope composition of leaf dark-respired CO2 (δ13Cl) and respiratory apparent isotope fractionation relative to biomass (ΔR,biomass) in response to drought stress is unclear. These differences, if present, would be important for the partitioning of C3-C4 mixed ecosystem C fluxes. We measured δ13Cl, the δ13C of biomass and of potential respiratory substrates and leaf gas exchange in one C3 (Leymus chinensis) and two C4 (Chloris virgata and Hemarthria altissima) grasses during a manipulated drought period. For all studied grasses, δ13Cl decreased from 21:00 to 03:00 h. The magnitude of the nighttime shift in δ13Cl decreased with increasing drought stress. The δ13Cl values were correlated with the δ13C of respiratory substrates, whereas the magnitude of the nighttime shift in δ13Cl strongly depended on the daytime carbon assimilation rate and the range of nighttime variations in the respiratory substrate content. The ΔR,biomass in the C3 and C4 grasses varied in opposite directions with the intensification of the drought stress. The contribution of C4 plant-associated carbon flux is likely to be overestimated if carbon isotope signatures are used for the partitioning of ecosystem carbon exchange and the δ13C of biomass is used as a substitute for leaf dark-respired CO2. The detected drought sensitivities in δ13Cl and differences in respiratory apparent isotope fractionation between C3 and C4 grasses have marked implications for isotope partitioning studies at the ecosystem level.

Nitrogen Addition Increases the Sensitivity of Photosynthesis to Drought and Re-watering Differentially in C3 Versus C4 Grass Species

“…However, this was not observed in the C 3 grass L. chinensis , for which both sugar and starch decreased (Chaves, 1991) between day 1 and 7 of drought (Table 2). These results are consistent with our previous study of drought impacts on dark respiration in these three species, in which starch content decreased both in the C 3 and C 4 grasses and sugar content increased in the C 4 grasses but not in the C 3 grass L. chinensis (Zhong et al, 2017).…”

“…The experiment was conducted in an open greenhouse at the Grassland Ecological Research Station of the Northeast Normal University, China (44°32′N, 123°40′E, 138–167 masl). The research area has a semi-arid, continental climate with a mean annual temperature of 6.3°C (1950–2014) and annual precipitation ranges from 280 to 644 mm (1950–2014) with over 70% of the precipitation occurring from June to August (Zhong et al, 2017). Potential evapotranspiration is approximately three times that of the annual precipitation (Qu and Guo, 2003).…”

Arbuscular Mycorrhizal Fungi Alleviate Drought Stress in C3 (Leymus chinensis) and C4 (Hemarthria altissima) Grasses via Altering Antioxidant Enzyme Activities and Photosynthesis

“…(Zhang et al, 2016). The soil is classified as chernozem and has a soil organic carbon content of 2.0% and a soil total nitrogen content of 0.15% (Zhong et al, 2017; Shi et al, 2019).…”

Effects of Nitrogen Addition on the Drought Susceptibility of the Leymus chinensis Meadow Ecosystem Vary with Drought Duration

“…Leymus chinensis , the dominant species of the Songnen meadow steppe, is a rhizomatous grass that uses the C 3 photosynthetic pathway ( Zhong et al, 2017 ). To avoid summer high temperatures, it has a relatively short growing season and completes its breeding season before July.…”