Fig 1.
Growing season average monthly precipitation (mm) from 1963 to 2012 (a), and daily precipitation (mm) and daily mean air temperature (°C) from April 1th to October 31th in 2012 (b).
The shaded area in panel b denotes the field sampling period.
Table 1.
Information on species studied.
List of plant species studied, and their photosynthetic pathway, classification and phenological phase.
Table 2.
Maximum leaf net CO2 assimilation rate (Amax, μmol m-2 s-1), mean leaf net CO2 assimilation rate (Mean A, μmol m-2 s-1), maximum stomatal conductance (gsmax, mol m-2 s-1), mean ratio of intercellular air space to ambient CO2 concentration (Mean Ci/Ca), and nighttime mean respiratory rate (Mean R, μmol m-2 s-1) of the species studied. Data are reported as mean ± 1 SE.
Table 3.
The df and P values from the photosynthetic pathway and the plant functional type differences in the maximum leaf net CO2 assimilation rate (Amax, μmol m-2 s-1), the mean leaf net CO2 assimilation rate (Mean A, μmol m-2 s-1), maximum stomatal conductance (gsmax, mol m-2 s-1), mean ratio of leaf internal to ambient CO2 concentration (Mean Ci/Ca), nighttime mean respiration rate (Mean R, μmol m-2 s-1), magnitude of nocturnal shift in δ13CR (Variation in δ13CR), and respiratory apparent 13C/12C fractionation (‰) comparative to biomass (ΔR, biomass), soluble carbohydrates (ΔR, sugar), starch (ΔR, starch) and lipids (ΔR, lipid) at 8 pm and 4 am, respectively.
Table 4.
The C isotope composition (‰) of leaf-respired CO2 (δ13CR), leaf soluble carbohydrates (δ13Csugar), leaf starch (δ13Cstarch) and leaf lipids (δ13Clipid) at 8 pm and 4 am, respectively. The carbon isotope composition of leaf bulk tissue (δ13Cbiomass) was measured once at 8 pm. The amplitude of the nighttime variation in δ13CR (Variation in δ13CR) was estimated as δ13CR-8pm—δ13CR-4am. Differences in the δ13CR between the samples collected at 8 pm and 4 am were assessed by One-way analysis of variance (ANOVA) and the P values are presented.
Fig 2.
Dependence of the amplitude of the variations in δ13C of leaf-respired CO2 (δ13CR, ‰) on the amount of cumulative carbon assimilation (mol CO2 m-2 d-1).
The data contains 19 of the 22 studied species, the exceptions being Chenopodium glaucum, Saussurea amara and Xanthium sibiricum. The r2 and P values are provided. The data are reported as mean ±1 standard error (n = 5).
Fig 3.
Plant functional type differences in respiratory apparent fractionation comparative to leaf bulk materials (ΔR, biomass), soluble carbohydrates (ΔR, sugar), starch (ΔR, starch) and lipids (ΔR, lipid) at 8 pm and 4 am, respectively.
Data are reported as mean ± 1 standard error (n = 5). The different letters within each panel indicate the significant differences (P <0.05) among the plant functional types.
Table 5.
Respiratory apparent fractionation.
Respiratory apparent 13C/12C fractionation (‰) of the nighttime leaf-respired CO2, comparative to biomass (ΔR, biomass), soluble carbohydrates (ΔR, sugar), starch (ΔR, starch) and lipids (ΔR, lipid) at 8 pm and 4 am, respectively.