Soybean [Glycine max (L.) cv. Jack] grown in open top chambers under controlled laboratory and field conditions was ušed to study the acclimation of leaf gas exchange processes to CO2 enrichment. Air inside the open top chambers was maintained at either 700-800 or 350-400 pmol(C02) mol'^(air). Leaf gas exchange rates were measured for some plants switched between treatments. When measmed in the C02-emiched atmosphere, stomatal conductances (gg) were higher in leaves grown in C02-enriched atmospheres than in those grown under ambient conditions, and the lower gg values for plants in the C02-enriched atmospheres were limiting to leaf net photosynthetic CO2 exchange rates (Pn). of enriched leaves was higher than those of the ambient Controls when measured at elevated CO2 levels in both controlled environment and field studies, while it was depressed in enriched leaves when measured imder ambient CO2 conditions, and this drop in Pn did not recover until 6-15 d after plants were placed back in ambient conditions.
The most representative evergreen shrub species growing in the low mediterranean maquis modified their leaf characteristics during the year, but the response to climate varied among the species. The reál sclerophyllous species, Quercus ilex L., Phillyrea latifolia and Pistacia lentiscus, showed a convergence in higher leaf thickness and lower net photosynthetic rate (P^) compared with Arhuíus unedo L. and Cistus incanus L. Under summer stress they maintained a substantial positive carbon balance. Pistacia was one of the most tolerant species to the drought, it maintained a substantial positive balance over a wide range in temperature. Arhutus and Cistus had relatively thin leaves with a higher succulence index and higher ihe more characteristic sclerophyllous species. The superiority of Cistus in carbon uptake over all the spacies was maintained throughout most of the year by its morphological leaf properties: low leaf thickness, high chlorophyll contents. Besides, Cistus shed most of its leaves before summer, thus reducing its evaporative surface.
We studied the responses of gas exchange, leaf morphology, and growth to irradiance in Taihangia rupestris, a naturally rare herb inhabiting only vertical cliff faces. In low irradiance (LI, 10 % of full sun) T. rupestris had lower net photosynthetic rate (PN) and produced much less leaves, total leaf area, and biomass than in high (HI, full sun) or medium irradiance (MI, 50 % of full sun). PN of T. rupestris was higher in HI than in MI on August 8, but lower in HI than in MI on September 22. T. rupestris had shorter petioles and lower leaf area ratio, and produced more but smaller and thicker leaves in HI than in MI. In HI the fast production of new leaves may guarantee T. rupestris to maintain higher PN at the whole plant level and thus accumulate more biomass at harvest, although the single-leaf PN may become lower as found on September 22. Hence T. rupestris possesses a latent capacity to acclimate and adapt to full sun. Irradiance, therefore, may not be a responsible factor for the restricted distribution of T. rupestris on vertical cliffs. and Min Tang ... [et al.].
Temperature responses of carbon assimilation processes were studied in four dominant species from mountain grassland ecosystem, i.e. Holcus mollis (L.), Hypericum maculatum (Cr.), Festuca rubra (L.), and Nardus stricta (L.), using the gas exchange technique. Leaf temperature (TL) of all species was adjusted within the range 13-30 °C using the Peltier thermoelectric cooler. The temperature responses of metabolic processes were subsequently modelled using the Arrhenius exponential function involving the temperature coefficient Q10. The expected increase of global temperature led to a significant increase of dark respiration rate
(RD; Q 10 = 2.0±0.5), maximum carboxylation rate (VCmax; Q10 = 2.2±0.6), and maximum electron transport rate (J max; Q 10 = 1.6±0.4) in dominant species of mountain grassland ecosystems. Contrariwise, the ratio between Jmax and VCmax linearly decreased with TL [y = -0.884 TL + 5.24; r2 = 0.78]. Hence temperature did not control the ratio between intercellular and ambient CO2 concentration, apparent quantum efficiency, and photon-saturated CO2 assimilation rate (Pmax). Pmax primarily correlated with maximum stomatal conductance irrespective of TL. Water use efficiency tended to decrease with TL [y = -0.21 TL + 8.1;
r2 = 0.87]. and O. Urban ... [et al.].
The effects of varying leaf temperature (T1) on some ecophysiological characteristics of photosynthesis for Quercus liaotungensis Koiz. under ambient radiation stress around midday on clear summer days were investigated using an IRGA equipped with a temperature-controlled cuvette. Net photosynthetic rate (PN) decreased as T1 increased from 30 to 35 °C as a result of stomatal closure, whereas non-stomatal limitation led to decreased PN in the T1 range of 35-45 °C. Decreased transpiration rate (E) and stomatal conductance (gs) at leaf temperatures above 30 °C were interpreted as a combined 'feedward' effect as a result of enhanced leaf-air vapour pressure deficit (VPD) and stomatal closure. Changes in E from T1 30 to 20 °C depended on VPD when gs was maintained constant. Water use efficiency (WUE) varied inversely with T1 by following a hyperbola. A decrease in intercellular CO2 concentration (Ci) occurred as a result of stomatal closure and a relatively high carboxylation capacity, whereas inactivation of mesophyll carboxylation in combination with photorespiration might be associated with the observed increase in Ci in the T1 range of 40 to 45 °C. and Shouren Zhang ... [et al.].
Short-term (2 h) treatment with 10 µM abscisic acid decreased stomatal conductance and net photosynthetic rate, and increased carbonic anhydrase activity in pea seedlings. The treatment with 10 µM methyl jasmonate did not significantly affect these parameters. and G. N. Lazova, M. I. Kicheva, L. P. Popova.
Water-withholding for 5 to 7 weeks and subsequent re-watering were made on potted plants of two epiphytic (E) and two terrestrial (T) fern species, which were collected from a seasonal tropical rainforest and had been grown in a screenhouse with 5 % irradiance for 4 months. During the water stress, the two E species completely closed stomata when frond relative water content (RWC) reached about 70 % with fairly constant maximum photochemistry efficiency (Fv/Fm), while the two T species kept partial stomata opening until RWC reached 45 % and reduction in Fv/Fm at the late stage. Also, chlorophyll content as indicated by a spectral reflectance index was gradually reduced in three species. Physiological recovery was completed after 3-d re-watering for the E species, which was more rapid than for the T species. The gas exchange measurements and regression analyses indicated higher photosynthetic water use efficiency in the E species than in the T species. and Q. Zhang ... [et al.].
The optimum temperature for photosynthetic CO2 assimilation of A. mangium phyllodes was 30-32 °C. Photosystem 2 (PS 2) exhibited high tolerance to high temperature. Gas exchange and the function of PS2 of A. mangium were adapted to the temperature regime of the tropical environment and this might be the contributing factor to their fast growth under tropical conditions. and Hua Yu, Bee-Lian Ong.
Of the four tested sweet potato cultivars having different features in growth and yield, cv. Koganesengan (KOG) was sustainable in photosynthetic activity through young to aged leaves under drought. One of the causes for this phenomenon may be stomatal conductance (g s) of this cultivar that was relatively high in both aged and drought-imposed leaves. In these leaves the non-photochemical quenching (NPQ) was low and the quantum yield of photosystem 2 (Φe) was high, compared to those of the other cultivars. This helps to prevent excessive accumulation of chemical energy in leaves and a decrease in photoinhibition damage to the photosynthetic function, by which KOG sustains a relatively high photosynthetic activity under the drought and alleviates functional deterioration caused by leaf age. and Haimeirong, F. Kubota.
Photosynthetic induction responses to a sudden increase in photosynthetic photon flux density (PPFD) from lower background PPFD (0, 25, 50, and 100 μmol m-2 s-1) to 1 000 μmol m-2 s-1 were measured in leaves of Fagus crenata, Acer rufinerve Siebold & Zucc., and Viburnum furcatum growing in a gap and understory of a F. crenata forest in the Naeba mountains. In the gap, A. rufinerve exhibited more than 1.2-fold higher maximum net photosynthetic rate (PNmax) than F. crenata and V. furcatum. Meanwhile, in the understory F. crenata exhibited the highest PNmax among the three species. The photosynthetic induction period required to reach PNmax was 3-41 min. The photosynthetic responses to increase in PPFD depended on the background PPFD before increase in PPFD. The induction period required to reach PNmax was 2.5-6.5-fold longer when PPFD increased from darkness than when PPFD increased from 100 μmol m-2 s-1. The induction period was correlated with initial PN and stomatal conductance (gs) relative to maximum values before increase in PPFD. The relationship was similar between the gap and the understory. As the background PPFD increased, the initial PN and gs increased, indicating that the degrees of biochemical and stomata limitations to dynamic photosynthetic performance decreased. Therefore, photosynthetic induction responses to increase in PPFD became faster with the increasing background PPFD. The differences in time required to reach induction between species, as well as between gap and understory, were mainly due to the varying of relative initial induction states in PN and gs at the same background PPFD. and M. Naramoto, Q. Han, Y. Kakubari.