Plants of pepper (Capsicum amuum L.) were grown in controlled environment chambers at ambient (360 pmol mol"*) and fluctuating pulse-enriched CO2 concentrations (700 pmol mol"* daily average, ranging from 500 to 3500 pmol mol"* = ECO2) under two water regimes. A decrease in plant growth and yield together with frequent visual injuries was found in plants growing under ECO2. Root/shoot ratio was greater, chlorophyll concentration and respiration rates were lower, and stomatal conductance and relative importance of alternativě pathway respiration were higher under ECO2. The negative effects of ECO2 were more intense under high water availability. The symptoms produced by ECO2 were similar to those of resource limitation, and were alleviated with increased nutrient supply. Constant elevated CO2 concentrations (700 pmol mol"*) increased pepper production and did not produce any of the injuries described for this erratic ECO2 treatment. Thus, it is probably the erratic nátuře of the CO2 concentration and not the gas itself that was causing the injiuy.
The influence of air humidity on leaf-air gas exchange and leaf water potential (4^) was investigated during daily courses in control and water stressed potted young plants of Copaifera langsdorffii. When leaf-air water vapour concentration difference (AW) increased during the day, stomatal conductance (g^) and net photosynthetic rate (P]vj) decreased under both soil moistures. Moderate AW induced lower values of g^ and Pn unwatered than control plants, High AW in atmosphere produced strong depression in g^ (from 0.22 to 0,01 mol m'^ s’’) and (from 6.5 to 0.7 pmol m'2 s'*) in control plants around midday, with recuperation of T'. Expected conductance tese) was calculated as fimction of AW, which was useful for discriminating soil to atmosphere water stress. In špite of momentary T or soil water stress, P^, g^, and water use efficiency decreased when AW increased during day course.
Diurnal and seasonal fluctuation in ambient CO2 concentration (C^) of more than 100 cm^ m‘3 in urban areas is an important abiotic factor influencing photosynthetic activity. This was shown in a young poplar tree under controlled environmental conditions. Here, the short-term rise in from 320 to 360 cm^ m‘3 during a day resulted in a 10 % higher CO2 gain. This variation in also influenced the interpretation of CO2 exchange data. Calculation of the intemal CO2 concentration in a leaf, Q, on the basis of an assumed mean value of atmospheric CO2 of 340 cm^ m'^ led to a possible 8 % divergence ffom the actual Cj in our experiments and thus also to a falše interpretation of the results, as it concealed the photosynthetic response to a rise or decline of Cg. Additionally, the changing CO2 concentration directly influenced the measurement by the infrared gas analyzer, because of its nonlinear response. Lack of compensation for this can lead to an additional inaccuracy of 3 to 8 % in the calculation of net photosynthetic rate and Q.
Within each mango (Mangifera indica L.) tree there is a diversity in flowering ability among its terminál branches. Significant variations in net photosynthetic rate (Pn), transpiration rate, stomatal conductance (gj) and mesophyll efficiency (mesophyll capacity to fix CO2) were observed generally among the productive branches. However, the extent of variation was more pronounced in trees with irregular bearing habits (cv. Langra) as compared to regular bearers (cv. Romani). In generál, correlation coefficients indicated that variations in among n5 branches were mainly due to the mesophyll efficiency and g^, In regular bearing trees, the narrow range of variation in was related to a better mesophyll capacity. This in tum might result in higher carbon build-up of 05 branches which would háve helped them to flower regularly with minimum branch to branch variations.
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.