Q.D. Zhang's research while affiliated with Chinese Academy of Sciences and other places

Variables of gas exchange of flag leaves and grain yield potentials of five representative winter wheat (Triticum aestivum L.) cultivars varied greatly across different development stages under the same management and irrigation. The cultivars with high yield potential had higher net photosynthetic rate (P N), PPFD (photosynthetic photon flux density) saturated photosynthetic rate (P sat), stomatal conductance (g s), and maximum apparent quantum yield of CO2 fixation (Φm,app) than those with low grain yield, but their dark respiration rate (R D) and compensation irradiance (I c) were remarkably lower. Compared with overall increase of yield potential of 71 % from low yield cultivars to high yield ones, P N, P sat, Φm,app, and g s were 13, 19, 57, and 32 % higher, respectively; but R D and I c decreased by 19 and 76 %, respectively. Such difference was evidently large during anthesis stage (e.g., P N by 33 %), which indicated that this period could be the best for assisting further selection for better cultivars. However, transpiration rate (E) and water use efficiency (WUE) differed only little. At different development stages, especially at anthesis, P N and P sat were positively correlated with Φm,app, g s, and yield potential, and negatively correlated with R D and I c. Thus the high-yield-potential winter wheat cultivars possess many better characters in photosynthesis and associated parameters than the low-yield cultivars. apparent quantum yield of CO2 fixation–compensation irradiance–cultivars with high and low yield potentials–dark respiration–flag leaf–net photosynthetic rate–stomatal conductance–transpiration–water use efficiency

Super-rice hybrids are two-line hybrid rice cultivars with 15 to 20 % higher yields than the raditional three-line hybrid rice cultivars. Response of photosynthetic functions to midday photoinhibition was compared between seedlings of the traditional hybrid rice (Oryza sativa L.) Shanyou63 and two super-rice hybrids, Hua-an3 and Liangyoupeijiu. Under strong midday sunlight, in comparison with Shanyou63, the two super-rice hybrids were less photoinhibited, as indicated by the lower loss of the net photosynthetic rate (P N), the quantum yield of photosystem 2 (ΦPS2), and the maximum and effective quantum yield of PS2 photochemistry (Fv/Fm and Fv′/Fm′). They also had a much higher transpiration rate. Hence the super-rice hybrids could protect themselves against midday photoinhibition at the cost of water. The photoprotective de-epoxidized xanthophyll cycle components, antheraxanthin (A) and zeaxanthin (Z), were accumulated more in Hua-an3 and Liangyoupeijiu than in Shanyou63, but the size of xanthophyll cycle pool of the seedlings was not affected by midday photoinhibition. Compared to Shanyou63, the super-rice hybrids were better photoprotected under natural high irradiance stress and the accumulation of Z and A, not the size of the xanthophyll pool protected the rice hybrids against photoinhibition.

PS II photochemistry and xanthophyll cycle during photoinhibition (exposed to strong light of 2 000 μmol photons·m-2·s-1) and the subsequent restoration were compared between two superhigh-yield rice hybrids (Liangyoupeijiu and Hua-an 3, the newly developed rice hybrids from two parental lines) and the traditional rice hybrid Shanyou 63 developed from three parental lines. The results showed that the maximal efficiency of PS II photochemistry (Fv/Fm), the efficiency of excitation energy capture by open PS II centers (Fv' / Fm'), and the yield of PS II electron transport (ΦPSII) of the three rice hybrids decreased during photoinhibition. However, a greater decrease in Fv / Fm, Fv'/Fm', and ΦPSII was observed in Shanyou 63 than in Liangyoupeijiu and Hua-an 3. At the same time, the components of xanthophyll cycle, antherxanthin (A) and zeathanxin (Z) increased rapidly while violaxanthin (V) decreased considerably. Both the rate of accumulation and the amount of A and Z in the two superhigh-yield rice hybrids were higher than that in Shanyou 63. The de-epoxidation state (DES) of xanthophyll cycle increased rapidly with the fast accumulation of A and Z, and reached the maximal level after first 30 min during photoinhibition. Of the three hybrids, the increasing rate of DES in Liangyoupeijiu and Hua-an 3 was higher than that in Shanyou 63. After photoinhibition treatment, the plant materials were transferred to a dim light (70 μmol photons·m-2·s-1) for restoration. During restoration, both chlorophyll fluorescence parameters and xanthophyll cycle relaxed gradually, but the rate and level of restoration in the two superhigh-yield rice hybrids were higher than those in Shanyou 63. Our results suggest that Liangyoupeijiu and Hua-an 3 had higher resistance to photoinhibition and higher capacity of non-radiative energy dissipation associated with xanthophyll cycle, as well as higher rate of restoration after photoinhibition, than Shanyou 63 when subjected to strong light.

Three winter wheat cultivars (Triticum aestivum L.), representatives of those widely cultivated in Beijing over the past six decades, were grown in the same environmental condition, and their physiological features were investigated. Daily changes of net photosynthetic rate (Pn), transpiration (Tr) in different growth stages were measured in order to find the relationship between leaf photosynthesis and yield. Instantaneous water use efficiency (WUE) of leaf was calculated from Pn/Tr. It is suggested that relationship between photosynthetic rate and yield changed with the developing stages of wheat. High yield wheat cultivar Jingdong 8 (released in the 1990s) had a higher photosynthetic rate (the maximal Pn increased by 77%) and transpiration rate (the maximal Tr increased by 69%), but a lower WUE than the low yield cultivar Yanda 1817 (released in the 1940s) during the day time at stem elongation stage. However, difference of Pn among the three cultivars changed with wheat growth process. Before 10 o'clock Pn in leaves of Jingdong 8 usually was the highest of the three cultivars, but Pn of Yanda 1817 was the highest after 10 o'clock. At dough ripe stage, Pn in leaves of Yanda 1817 was the highest among the three cultivars during the whole day. The difference of changing trend of transpiration in three wheat cultivars was similar to Pn, but WUE of Yanda 1817 was the highest in those three cultivars, indicating that the higher yield of Jingdong 8 was achieved via a greater consumption of water. Contrary to the cultivars released in the later period, midday depression of photosynthesis was small in Yanda 1817, which might suggest that Yanda 1817 was resistant to photoinhibition. It is possible that photosynthetic potential in leaves of wheat increased as wheat cultivars was improved over the past six decades. However, it became less resistant to photoinhibition.

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 (P N) 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 mol mol–1, P N 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 P N and WUE values under high CO2 concentration, but Yanda 1817 showed the lowest P N. Stomatal conductance (g s) of Nongda 139 and Yanda 1817 declined with increasing CO2 concentration, but g s of Jingdong 8 firstly went down and then up as the CO2 concentration further increased. Intercellular CO2 concentration (C i) 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 C i of the three wheat cultivars, and Yanda 1817 had the highest C i value under lower CO2 concentrations. However, Jingdong 8 had the highest P N and lowest C i at the highest CO2 concentration which indicates that its photosynthetic potential may be high.

Effects of photoinhibition and its recovery on photosynthetic functions of winter wheat (Triticum aestivum L.) under salt stress were studied, The results showed that several parameters associated with PS II functions, e.g. Fv/Fo, Fv/Fm and qP were not influenced by lower salt concentration (200 mmol/L NaCl) while CO2 assimilation rate decreased significantly. When exposed to higher salt concentration (400 mmol/L NaCl), PS II functions were significantly inhibited which led to the decrease of carbon assimilation. These results suggest that different concentrations of salt stress affected photosynthesis by different modes. Salt stress made photosynthesis more sensitive to strong light and led to more serious photoinhibition. Under lower concentration of salt stress, the Q(B)-non-reductive PS II reaction centers formed at the beginning of photoinhibition could be effectively used to compose active PS II reaction center (RC) and repair the reversible inactivated PS II RC. Under higher concentration of salt stress, PS II reaction centers were seriously damaged during photoinhibition, the Q(B)-non-reductive PS II RC could only be partly effective at the early time of photoinhibition, thus led to the accumulation of Q(B)-non-reductive PS II RC in the course of restoration under dim light.