Kálmán Szente

Reconstitution of chlorophylls and photosynthetic CO2 assimilation upon rehydration of the desiccated poikilochlorophyllous plant Xerophyta scabrida (Pax) Th. Dur. et Schinz

Resynthesis of the photosynthetic apparatus and resumption of CO2 assimilation upon rehydration is reported for the monocotyledonous and poikilochlorophyllous desiccation-tolerant (PDT) plant Xerophyta scabrida (Pax) Th. Dur. et Schinz (Velloziaceae). During desiccation there was a complete breakdown of chlorophylls whereas the total carotenoid content of air-dried leaves was reduced to about 22% of that of functional leaves. The prerequisites for the resynthesis of photosynthetic pigments and functional thylakoids were the reappearance of turgor and maximum leaf water content at 2 and 10 h after rehydration, respectively. The period of increased initial respiration after rewetting leaves (rehydration respiration) lasted up to 30 h and was thus 6 to 10 times longer than in homoiochlorophyllous desiccation-tolerant plants (HDTs) in which chlorophylls are retained during desiccation. Accumulation of chlorophylls a + b and total carotenoids (xanthophylls and βcarotene) started 10 h after rehydration. Normal levels of chlorophyll and carotenoids were obtained 72 h after rehydration. Values for the variable-fluorescence decrease ratio (Rfd690 values), an indicator of photochemical activity, showed that photochemical function started 10 h after rehydration, but normal values of 2.7 were reached only 72 h after rehydration. Net CO2 assimilation started 24 h after rewetting and normal rates were reached after 72 h, at the same time as normal values of stomatal conductance were obtained. The increasing rates of net CO2 assimilation were paralleled by decreasing values of the intercellular CO2 concentration. All photosynthetic parameters investigated showed values normal for functional chloroplasts by 72 h after the onset of rehydration. Fully regreened leaves of the presumed C3 plant X. scabrida exhibited a net CO2 assimilation rate which was in the same range as that of other C3 plants and higher than that of recovered HDT plants. The fundamental difference between air-dried PDT plants, such as X. scabrida, which have to resynthesize the photosynthetic pigment apparatus, and air-dried HDT plants, which only undergo a functional recovery, is discussed.

Response of Photosynthesis, Stomatal Conductance, Water Use Efficiency and Production to Long-Term Elevated CO2 in Winter Wheat

Summary Responses of photosynthesis, stomatal conductance, water use efficiency (at the beginning of flowering) and production allocation (at full ear/grain ripening) to long-term elevated CO2 were assessed in winter wheat (Triticum aestivum L. cv. MV16). Plants were grown in open top chambers under a temperate-continental climate from germination at ambient (350 μmol mol-1) and elevated (700 μmol mol-1) CO2 concentrations. High CO2 plants displayed a decreased initial slope of the A/Ci response curve, with the assimilation rate (A) continuing to increase above 400 μmol mol-1 internal CO2 concentration (C). A in the ambient plants showed P regeneration limitation while RuBP regeneration appeared to be limiting A in the high CO2 treatment. Variable fluorescence ratios (Rfd 690) were lower in the high CO2 plants indicating a lower potential photochemical activity. The increase in the values for the chlorophyll fluorescence ratio F690/F735 in the high CO2 plants was in agreement with the lower chlorophyll a+b concentrations. The high CO2 plants had higher concentrations of starch in their leaves and roots that the ambient plants. Stomatal conductance (gs) was lower in the high CO2 plants at every CO2 concentration (Ca) and Ci and the Ci-dependent gs response had a large influence on the A/gs function. The higher water use efficiency (WUE) values (at Cas>350 μmol mol-1) in the high CO2 wheat plants were the result of a larger decrease in transpiration rate (E) in the high CO2 plants than in the ambient plants, and of a simultaneous larger increase in A in the range of Ca above 350 μmol mol-1 CO2. The integrated and combined effect of the photosynthetic and stomatal acclimation to elevated CO2 produced a higher C-assimilation in high CO2 plants at elevated CO2 than in the ambient plants, however, this was not followed by an acclimation in C-allocation. These were reflected in a slightly increased (6.7 %) overall dry matter production and lower reproductive allocation (RA).

Responses of CO2 assimilation, transpiration and water use efficiency to long-term elevated CO2 in perennial C3 xeric loess steppe species

Summary CO 2 assimilation (A), transpiration (E), water use efficiency (WUE), leaf-nitrogen and carbohydrate responses to 11 months elevated (700 μmol mol -1 ) CO 2 exposure in four perennial C 3 species ( Festuca rupicola, Dactylis glomerata, Filipendula vulgaris, Salvia nemorosa ) from a xeric temperate loess steppe are reported. The responses in the species varied greatly owing to their differing acclimation. The acclimation of photosynthesis was somewhat downward in F. rupicola , fully downward in D. glomerata , and upward in S. nemorosa and F. vulgaris . The reduction in the initial slope of the A/q response curve in F. rupicola and D. glomerata suggested a decrease in Rubisco capacity. Net CO 2 assimilation at 700 μmol mol -1 CO 2 c a in the high CO 2 F. rupicola was higher than in those grown at present (350 μmol mol -1 ) CO 2 ; there was no difference in D. glomerata . The initial slope of the A/c i curve indicated an increased Rubisco capacity in high CO 2 F. vulgaris and S. nemorosa . Their net CO 2 assimilation was higher in the plants grown in the high CO 2 treatment at c i s ovet 200 μmol mol -1 than that in the plants grown at present CO 2 . The A/c i response curves, which were saturated in all species grown at present CO 2 , did not reach saturation in the plants grown at elevated CO 2 , reflecting that the Pi limitation of CO 2 assimilation was alleviated in the plants grown at high CO 2 . Transpiration decreased with an increase in q in both the present and elevated CO 2 F. rupicola and D. glomerata . In F. vulgaris , an increase in q caused a reduction in transpiration in the plants grown at high CO 2 only. Transpiration rate in both the present and elevated CO 2 S. nemorosa was not affected by any change in c i . It is suggested then that long-term exposure to high CO 2 causes a similar acclimation of stomatal regulation and transpiration to that of photosynthesis. High CO 2 caused a significant decrease in protein-nitrogen content only in D. glomerata . Starch increased in F. rupicola and D. glomerata and soluble sugar content was higher in all species grown at high CO 2 than at ambient. Instantaneous WUE significantly increased in all species grown at elevated CO 2 .

Limitations of net CO2 uptake in plant species of a temperate dry loess grassland

Abstract Possible limitations of net CO 2 assimilation (P N ) in four drought stressed loess grassland species ( Festuca rupicola, Salvia nemorosa, Euphorbia pannonica , all three C 3 plants, and Bothriochloa ischaemum , a C 4 plant) were characterised using data from measurements of CO 2 gas exchange (P N , intercellular CO 2 concentration C i and stomatal conductance G s ) and the slow kinetics of chlorophyll fluorescence (variable Chl fluorescence decrease ratio, Rfd). The limitation imposed by Rubisco capacity was estimated from P N /C i curves. In leaves of the C 3 plant F. rupicola , P N was mainly limited by the mesophyll diffusion resistance, most probably due to its sclerophyllous leaf structure. In S. nemorosa (C 3 ) leaves, P N was significantly affected by all investigated factors with well balanced weights. In E. pannonica (C 3 ), the order of limitations was stomatal-mesophyll without a photochemical limitation. In the C 4 -plant B. ischaemum , the limitation of P N was mesophyll-stomatal including a significant photochemical limitation. The most characteristic difference in the limitation of P N by the factors considered occurred in species in which photochemical reactions (Rfd-values) were not limiting ( F. rupicola ) or only to a small extent ( E. pannonica ) and where either mesophyll ( F. rupicola ) or stomatal ( E. pannonica ) limitations of P N were decisive. These species had either very low or very high CO 2 assimilation rates and are either the maintainer of the original grassland vegetation ( F. rupicola ) or represent species associated with the degradation of the grassland ( E. pannonica, B. ischaemum ). Plant species with either a deep root system and succulent leaves ( E. pannonica ) or with the traits, such as high water use efficiency (WUE) associated with C 4 photosynthesis ( B. ischaemum ), might be successful in an increasingly arid and disturbed environment. Photochemical limitation was significant in the invader B. ischaemum and the characteristic species S. nemorosa . These species exhibited their tolerance through a coordinated stomatal mesophyll and photochemical control.

Winter photosynthetic activity of twenty temperate semi-desert sand grassland species

The winter photosynthetic activity (quantified by net CO(2) assimilation rates and chlorophyll (Chl) a fluorescence parameters) of 20 plant species (including two lichens and two mosses) of a Hungarian temperate semi-desert sand grassland was determined on one occasion per year in 1984, 1989 and 1994. Throughout winter, the overwintering green shoots, leaves or thalli were regularly exposed to below zero temperatures at night and daytime temperatures of 0-5 degrees C. In situ tissue temperature varied between -2.1 and +6.9 degrees C and the photosynthetic photon flux density (PPFD) between 137 and 351 micromol m(-2)s(-1). Under these conditions 18 of the grassland species exhibited photosynthetic CO(2) uptake (range: vascular plants ca. 0.2-3.8 micromol m(-2)s(-1), cryptogams 0.3-2.79 micromol kg(-1)s(-1)) and values of 0.9-5.1 of the Chl fluorescence decrease ratio R(Fd). In 1984, Festuca vaginata and Sedum sexangulare had net CO(2) assimilation at leaf temperatures of -0.85 to -1.2 degrees C. In 1989, all species except Cladonia furcata showed net CO(2) assimilation at tissue temperatures of 0 to +3.3 degrees C, with the highest rates observed in Poa bulbosa and F. vaginata. The latter showed a net CO(2) assimilation saturation at a PPFD of 600 micromol m(-2)s(-1) and a temperature optimum between +5 and +18 degrees C. At the 1994 measurements, the photosynthetic rates were higher at higher tissue water contents. The two mosses and lichens had a net photosynthesis (range: 1.1-2.79 micromol CO(2)kg(-1)s(-1)) at 2 degrees C tissue temperature and at 4-5 degrees C air temperature. Ca. 80% of the vascular grassland plant species maintained a positive C-balance during the coldest periods of winter, with photosynthetic rates of 1.5-3.8 micromol CO(2)m(-2)s(-1). In an extremely warm beginning March of the relatively warm winter of 2006/2007, the dicotyledonous plants had much higher CO(2) assimilation rates on a Chl (range 6-14.9 micromol g(-1)Chl s(-1)) and on a dry weight basis (9-48 micromol kg(-1)dw s(-1)) than in the cold winter of 1994. However, the assimilation rates of the three investigated cryptogams (Tortula and two Cladonia) and the two grasses Festuca and Poa were not affected by this increase. The results indicate that the photosynthetic activity of temperate semi-desert sand grassland species can help somewhat in slowing the general CO(2) rise in winter and function as a potential carbon sink of the investigated semi-desert Hungarian grassland species.

Modelling Net Photosynthetic Rate of Winter Wheat in Elevated Air CO2 Concentrations

Winter wheat plants were grown in open top chambers either at 365 µmol mol−1 (AC) or at 700 µmol mol−1 (EC) air CO2 concentrations. The photosynthetic response of flag leaves at the beginning of flowering and on four vertical leaf levels at the beginning of grain filling were measured. Net photosynthetic rates (PN) were higher at both developmental phases in plants grown at EC coupled with larger leaf area and photosynthetic pigment contents. The widely accepted Farquhar net photosynthesis model was parameterised and tested using several observed data. After parameterisation the test results corresponded satisfactorily with observed values under several environmental conditions.

Enhanced Water Use Efficiency in Dry Loess Grassland Species Grown at Elevated Air CO2 Concentration

Net CO2 assimilation rate (PN), stomatal conductance (gs), transpiration rate (E), and water use efficiency (WUE) in four perennial C3 species (grasses: Dactylis glomerata, Festuca rupicola, dicots: Filipendula vulgaris, Salvia nemorosa) grown for 231 d in open-top chambers at ambient (CA, 350 µmol mol-1) or elevated (CE, 700 µmol mol-1) CO2 concentrations were compared. When measured at CE, PN was significantly higher in CE plants of all four species than in the CA ones. The increase in PN was less prominent in the two grasses than in the two dicots. The E was significantly higher in the CE-grass F. rupicola and CE-dicot F. vulgaris than in the CA plants. There was no change in E owing to CE in the other grass and dicot. The gs in F. vulgaris and F. rupicola increased, while there was a decrease in D. glomerata and no change in S. nemorosa. WUE increased in all species grown in CE: four- to five-fold in the dicots and less than two-fold in the grasses. The increase in WUE was primarily due to an increase in PN and not to a decrease in E.