Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), leaf water potential (ψleaf), leaf nitrogen content, and photosynthetic nitrogen use efficiency (PNUE) were compared between a typical C4 plant, Agriophyllum squarrosum and a C3 plant, Leymus chinensis, in Hunshandak Sandland, China. The plant species showed different diurnal gas exchange patterns on June 12-14 when photosynthetic photon flux density (PPFD), air temperature (Tair), and water potential were moderate. PN, E, and
gs of A. squarrosum showed distinct single peak while those of L. chinensis were depressed at noon and had two peaks in their diurnal courses. Gas exchange traits of both species showed midday depression under higher photosynthetic photon flux density (PPFD) and T air when Ψleaf was significantly low down on August 6-8. However, those of A. squarrosum were depressed less seriously. Moreover, A. squarrosum had higher PN, Ψleaf, water use efficiency (WUE), and PNUE than L. chinensis. Thus A. squarrosum was much more tolerant to heat and high irradiance and could utilise the resources on sand area more efficiently than L. chinensis. Hence species like A. squarrosum may be introduced and protected to reconstruct the degraded sand dunes because of their higher tolerance to stress and higher resource use efficiency. and S. L. Niu ... [et al.].
Only three tree species, i.e. Ulmus pumila, Malus baccata, and Prunus padus, are distributed in Hunshandak Sandland (HS) in Inner Mongolia, China. Field studies of gas exchange and chlorophyll (Chl) fluorescence of these three tree species were conducted in three arid periods of growth season 2002. Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and Fv/Fm of U. pumila were higher than in M. baccata and P. padus, especially in the midday. Hence M. baccata and P. padus were more sensitive to high temperature and irradiance than U. pumila in HS. This may be a reason for wide distribution of U. pumila in HS. M. baccata and P. padus are adapted to the back slope of fixed dune, because the micro-habitat is relatively cool and less irradiated than the slope facing sun. Water use efficiency (WUE) of U. pumila was lower than that of M. baccata and P. padus, and thus U. pumila does not form forests in this region, because the soil is dry. and Y. G. Li ... [et al.].
Three winter wheat (Triticum aestivum L.) cultivars, representatives of those widely cultivated in Beijing over the past six decades, were grown in the same environmental conditions. Net photosynthetic rate (PN) per unit leaf area and instantaneous water use efficiency (WUE) of flag leaves increased with elevated CO2 concentration. With an increase in CO2 concentration from 360 to 720 µmol mol-1, PN and WUE of Jingdong 8 (released in 1990s and having the highest yield) increased by 173 and 81 %, while those of Nongda 139 (released in 1970s) increased by 88 and 66 %, and Yanda 1817 (released in 1945, with lowest yield) by 76 and 65 %. Jingdong 8 had the highest PN and WUE values under high CO2 concentration, but Yanda 1817 showed the lowest PN. Stomatal conductance (gs) of Nongda 139 and Yanda 1817 declined with increasing CO2 concentration, but gs of Jingdong 8 firstly went down and then up as the CO2 concentration further increased. Intercellular CO2 concentration (Ci) of Jingdong 8 and Nongda 139 increased when CO2 concentration elevated, while that of Yanda 139 increased at the first stage and then declined. Jingdong 8 had the lowest Ci of the three wheat cultivars, and Yanda 1817 had the highest Ci value under lower CO2 concentrations. However, Jingdong 8 had the highest PN and lowest Ci at the highest CO2 concentration which indicates that its photosynthetic potential may be high. and H. Q. Liu ... [et al.].
Gas exchange, photochemical efficiency, and leaf water potential (Ψl) of Salix matsudana (non-indigenous species), S. microstachya and S. gordejevii (indigenous species) were studied in Hunshandak Sandland, China. Ψl of all the three species decreased from 06:00 to 12:00, and increased afterwards. S. matsudana showed higher values of Ψl than others. Net photosynthetic rate (PN) and stomatal conductance (gs) of S. matsudana were the lowest among all, with the maximum PN at 10:00 being 75% of that of S. gordejevii. Compared with the indigenous species, the non-indigenous S. matsudana had also lower transpiration rate (E) and water use efficiency (WUE). The values of Fv/Fm in all the species were lower from 06:00 to 14:00 than those after 14:00, indicating an obvious depression in photochemical efficiency of photosystem 2 in both non-indigenous and native species. However, it was much more depressed in S. matsudana, the non-indigenous tree. PN was positively correlated to gs and negatively related to Ψl. The relationship between gs and vapour pressure difference (VPD) was exponential, while negative linear correlation was found between gs and Ψl. and M. Z. Liu ... [et al.].