<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Hussain, M Z</style></author><author><style face="normal" font="default" size="100%">Otieno, D O</style></author><author><style face="normal" font="default" size="100%">Mirzae, H</style></author><author><style face="normal" font="default" size="100%">Li, Y L</style></author><author><style face="normal" font="default" size="100%">Schmidt, M W T</style></author><author><style face="normal" font="default" size="100%">Siebke, L</style></author><author><style face="normal" font="default" size="100%">Foken, T</style></author><author><style face="normal" font="default" size="100%">Ribeiro, N.a.</style></author><author><style face="normal" font="default" size="100%">Pereira, J S</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">CO2 exchange and biomass development of the herbaceous vegetation in the Portuguese montado ecosystem during spring</style></title><secondary-title><style face="normal" font="default" size="100%">Agriculture, Ecosystems &amp; Environment</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Ecosystem productivity</style></keyword><keyword><style  face="normal" font="default" size="100%">Environmental regulators</style></keyword><keyword><style  face="normal" font="default" size="100%">Herbaceous layer</style></keyword><keyword><style  face="normal" font="default" size="100%">montado</style></keyword><keyword><style  face="normal" font="default" size="100%">Net ecosystem CO2 exchange</style></keyword><keyword><style  face="normal" font="default" size="100%">Soil moisture</style></keyword><keyword><style  face="normal" font="default" size="100%">Spring period</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2009</style></year></dates><volume><style face="normal" font="default" size="100%">132</style></volume><pages><style face="normal" font="default" size="100%">143-152</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Montado are spatially heterogeneous ecosystems that are economically important for the production of cork and herbaceous biomass that provide fodder for animals. Understanding of how trees and the herbaceous layer interact to determine pasture yield and the overall CO2 exchange of the herbaceous layer is crucial. Portable chambers were used to study CO2 exchange by the herbaceous layer component of the montado ecosystem in southern Portugal. Biomass, Net herbaceous layer CO2 exchange (NEE) and respiration (Reco) were measured in the open and understory locations between March and May, during the active growing period. Parameter ﬁts on the NEE data were performed using empirical hyperbolic light response model, while ecosystem respiration (Reco) data were ﬁtted with a two-parameter exponential model. Annual green biomass productions were 405.8 9.0 and 250.6 6.3 g m2 in the open and the understory, respectively. The respective maximum NEE during the day were 24.0 2.9 and 9.6 2.2 mmol m2 s 1 while maximum Reco were 20.6 2.2 and 10.0 1.6 mmol m2 s 1 , occurring in April. Photosynthetic photon ﬂux density (PPFD) explained more that 70% of variations in daytime NEE while soil temperature at 10 cm depth (Tsoil ) explained &gt;50% of the variations in Reco under non-limiting soil moisture conditions. Both the herbaceous layer communities shared similar plant functional types and no signiﬁcant difference in nutrient nitrogen (N) occurred between them. The two herbaceous layer components shared similar physiological characteristics and differences that arose in their CO2 uptake capacities and green biomass production were the result of microclimatic differences created by tree shading</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Otieno, D O</style></author><author><style face="normal" font="default" size="100%">Kurz-Besson, C</style></author><author><style face="normal" font="default" size="100%">Liu, J</style></author><author><style face="normal" font="default" size="100%">Schmidt, M W T</style></author><author><style face="normal" font="default" size="100%">Do, R Vale-Lobo</style></author><author><style face="normal" font="default" size="100%">David, T S</style></author><author><style face="normal" font="default" size="100%">Siegwolf, R</style></author><author><style face="normal" font="default" size="100%">Pereira, J S</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Seasonal Variations in Soil and Plant Water Status in a Quercus suber L. Stand: Roots as Determinants of Tree Productivity and Survival in the Mediterranean-type Ecosystem</style></title><secondary-title><style face="normal" font="default" size="100%">Plant and Soil</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Drought stress</style></keyword><keyword><style  face="normal" font="default" size="100%">leaf water potential</style></keyword><keyword><style  face="normal" font="default" size="100%">osmotic adjustment</style></keyword><keyword><style  face="normal" font="default" size="100%">oxygen isotope</style></keyword><keyword><style  face="normal" font="default" size="100%">root distribution</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2006</style></year></dates><volume><style face="normal" font="default" size="100%">283</style></volume><pages><style face="normal" font="default" size="100%">119-135</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Studies were conducted to examine changes in soil (Ys) and plant water status during summer in a 16-year old Quercus suber plantation in southern Portugal. Continuous measurements were conducted between May 2003 and August 2004, while discontinuous measurements were conducted on a monthly basis between May and September 2003 and repeated between March and September 2004. Intensive measurements were conducted on ﬁve trees with mean height and DBH of 5.3 m and 11.6 cm, respectively, growing at close proximity to each other. Weather conditions and soil water potential (Ys) at the rhizosphere of each of the trees measured at 0.3 and 1 m soil depth were continuously monitored. Predawn (Ypd) and midday (Ymd) leaf water potentials were determined every month. Soil and plant samples were also collected in June and September from diﬀerent locations within the study site for d 18 O isotope composition analysis. Pressure–volume (p–v) curves were constructed from plant shoots at diﬀerent times during the vegetative period to determine osmotic potential at full saturation (P 100 ), water potential at turgor loss point (Ytlp), relative water content at turgor loss point (R*tlp) and bulk modulus of elasticity (e). Signiﬁcant P &lt; 0.05 decline in Ys occurred between May and September, the lowest value recorded being –2.0 MPa. Decline in soil moisture aﬀected tree water status, but decline in leaf water potential varied signiﬁcantly (P &lt; 0.05) among the trees. At the end of summer drought, lowest Ypd measured was –1.7 MPa while the highest measured during this time was –0.8 MPa. Diﬀerences among trees were attributed to diﬀerences in rooting depth, as shown by regression analysis of 18 O isotopes. Radial stem growth ceased when Ys within the upper 0.3 m depth approached –1.5 MPa. The upper soil layers contributed approximately 33% of the total tree water requirement, between spring and mid summer when drought was experienced by trees. Deep soil layers however, supplied most of the water required during drought and no growth was recorded during this time. Stressed trees increased solute concentration of their tissues by a Magnitude of 0.7 MPa while bulk tissue elastic modulus increased by about 17 MPa. The study emphasizes the signiﬁcance of roots as determinants of tree productivity and survival in the Mediterranean ecosystems.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Niinemets, Ü</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author><author><style face="normal" font="default" size="100%">Canta, N R</style></author><author><style face="normal" font="default" size="100%">Chaves, M M</style></author><author><style face="normal" font="default" size="100%">Faria, T</style></author><author><style face="normal" font="default" size="100%">Pereira, J S</style></author><author><style face="normal" font="default" size="100%">Reynolds, J F</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Interactive effects of nitrogen and phosphorus on the acclimation potential of foliage photosynthetic properties of cork oak, Quercus suber, to elevated atmospheric CO2 concentrations</style></title><secondary-title><style face="normal" font="default" size="100%">Global Change Biology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">nitrogen</style></keyword><keyword><style  face="normal" font="default" size="100%">nutrient imbalances</style></keyword><keyword><style  face="normal" font="default" size="100%">phosphate limitation</style></keyword><keyword><style  face="normal" font="default" size="100%">phosphorus nutrition</style></keyword><keyword><style  face="normal" font="default" size="100%">photosynthetic electron transport</style></keyword><keyword><style  face="normal" font="default" size="100%">Rubisco</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1999</style></year></dates><publisher><style face="normal" font="default" size="100%">Blackwell Science Ltd</style></publisher><volume><style face="normal" font="default" size="100%">5</style></volume><pages><style face="normal" font="default" size="100%">455-470</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Leaf gas-exchange and chemical composition were investigated in seedlings of Quercus suber L. grown for 21 months either at elevated (700 μmol mol–1) or normal (350 μmol mol–1) ambient atmospheric CO2 concentrations, [CO2], in a sandy nutrient-poor soil with either ‘high’ N (0.3 mol N m–3 in the irrigation solution) or with ‘low’ N (0.05 mol N m–3) and with a constant suboptimal concentration of the other macro- and micronutrients. Although elevated [CO2] yielded the greatest total plant biomass in ‘high’ nitrogen treatment, it resulted in lower leaf nutrient concentrations in all cases, independent of the nutrient addition regime, and in greater nonstructural carbohydrate concentrations. By contrast, nitrogen treatment did not affect foliar N concentrations, but resulted in lower phosphorus concentrations, suggesting that under lower N, P use-efficiency in foliar biomass production was lower. Phosphorus deficiency was evident in all treatments, as photosynthesis became CO2 insensitive at intercellular CO2 concentrations larger than ≈ 300 μmol mol–1, and net assimilation rates measured at an ambient [CO2] of 350 μmol mol–1 or at 700 μmol mol–1 were not significantly different. Moreover, there was a positive correlation of foliar P with maximum Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) carboxylase activity (Vcmax), which potentially limits photosynthesis at low [CO2], and the capacities of photosynthetic electron transport (Jmax) and phosphate utilization (Pmax), which are potentially limiting at high [CO2]. None of these potential limits was correlated with foliar nitrogen concentration, indicating that photosynthetic N use-efficiency was directly dependent on foliar P availability. Though the tendencies were towards lower capacities of potential limitations of photosynthesis in high [CO2] grown specimens, the effects were statistically insignificant, because of (i) large within-treatment variability related to foliar P, and (ii) small decreases in P/N ratio with increasing [CO2], resulting in balanced changes in other foliar compounds potentially limiting carbon acquisition. The results of the current study indicate that under P-deficiency, the down-regulation of excess biochemical capacities proceeds in a similar manner in leaves grown under normal and elevated [CO2], and also that foliar P/N ratios for optimum photosynthesis are likely to increase with increasing growth CO2 concentrations. Symbols: A, net assimilation rate (μmol m–2 s–1); Amax, light-saturated A (μmol m–2 s–1); α, initial quantum yield at saturating [CO2] and for an incident Q (mol mol–1); [CO2], atmospheric CO2 concentration (μmol mol–1); Ci, intercellular CO2 concentration (μmol mol–1); Ca, CO2 concentration in the gas-exchange cuvette (μmol mol–1); FB, fraction of leaf N in ‘photoenergetics’; FL, fraction of leaf N in light harvesting; FR, fraction of leaf N in Rubisco; Γ*, CO2 compensation concentration in the absence of Rd (μmol mol–1); Jmax*, capacity for photosynthetic electron transport; Jmc, capacity for photosynthetic electron transport per unit cytochrome f (mol e–[mol cyt f]–1 s–1); Kc, Michaelis-Menten constant for carboxylation (μmol mol–1); Ko, Michaelis-Menten constant for oxygenation (mmol mol–1); MA, leaf dry mass per area (g m–2); O, intercellular oxygen concentration (mmol mol–1); [Pi], concentration of inorganic phosphate (mM); Pmax*, capacity for phosphate utilization; Q, photosynthetically active quantum flux density (μmol m–2 s–1); Rd*, day respiration (CO2 evolution from nonphotorespiratory processes continuing in the light); Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase; RUBP, ribulose-1,5-bisphosphate; Tl, leaf temperature (°C); UTPU*, rate of triose phosphate utilization; Vcmax*, maximum Rubisco carboxylase activity; Vcr, specific activity of Rubisco (μmol CO2[g Rubisco]–1 s–1] *given in either μmol m–2 s–1 or in μmol g–1 s–1 as described in the text.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Sala, A</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Simulations of canopy net photosynthesis and transpiration in Quercus ilex L. under the influence of seasonal drought</style></title><secondary-title><style face="normal" font="default" size="100%">Agricultural and Forest Meteorology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">canopy net photosynthesis</style></keyword><keyword><style  face="normal" font="default" size="100%">Empirical model (voyant)</style></keyword><keyword><style  face="normal" font="default" size="100%">Stomatal conductance</style></keyword><keyword><style  face="normal" font="default" size="100%">water use</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1996</style></year></dates><volume><style face="normal" font="default" size="100%">1</style></volume><pages><style face="normal" font="default" size="100%">203-222</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">A mechanistically based C 3 leaf photosynthesis model combined with an empirical stomatal model and a canopy model of light interception and microclimate was used to simulate Quercus ilex canopy net photosynthesis and transpiration at l'Avic watershed (NE Spain). The model takes into account the sun-shade leaf differentiation of photosynthetic characteristics as affected by depth within the canopy. Based on field studies, simulations were carried out for two locations within the watershed along a gradient in elevation, microclimate and forest structure. Effective predictions of diurnal and seasonal courses of stomatal conductance of sun and shade leaves for different days during the year were obtained by changing a single model variable termed gF- The value of gF determined from least squares of observed vs. simulated time courses was linearly related to pre-dawn xylem water potential over critical ranges of the response curve. Response to gF in the model may to a great extent be thought of as the integrated expression of canopy response to root system generated signals or control mechanisms. For development of predictive capability, gF is extremely useful because it allows seasonal assessments of water use and carbon dioxide uptake with differing patterns in water availability. Based on simulated responses on representative clear, overcast and variable days throughout the year, only small differences in annual totals for net photosynthesis and transpiration were found between the two sites, despite large differences in soil drying. Annual estimates of canopy water loss were in close agreement with independent estimates of evapotranspiration using the hydrological input/output method.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Sala, A</style></author><author><style face="normal" font="default" size="100%">Sabate, S</style></author><author><style face="normal" font="default" size="100%">Gracia, Carlos</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Canopy structure within a Quercus ilex forested watershed: variations due to location, phenological development, and water availability</style></title><secondary-title><style face="normal" font="default" size="100%">Trees-Structure and Function</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Canopy structure</style></keyword><keyword><style  face="normal" font="default" size="100%">leaf area index</style></keyword><keyword><style  face="normal" font="default" size="100%">Mediterranean sclerophylls</style></keyword><keyword><style  face="normal" font="default" size="100%">Quercus ilex</style></keyword><keyword><style  face="normal" font="default" size="100%">water deficit</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1994</style></year></dates><pages><style face="normal" font="default" size="100%">254-261</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Spatial and temporal changes in canopy structure were studied in 1988 and 1989 in a Mediterranean Q u e r c u s ilex forest in north-eastern Spain. Due to differences in precipitation patterns the 1989 growing season was drier than the 1988 growing season. Sampling was conducted in parallel at two sites which represent endpoints along a slope gradient within a watershed (ridge top at 975 m, and valley bottom at 700 m). At both sites, similar inter-annual changes in canopy structure were observed in response to differences in water availability. Samples harvested in the upper 50 cm of the canopy during 1989 exhibited a de- crease in both average leaf size and the ratio of young to old leaf and stem biomass relative to samples obtained in 1988. At the whole canopy level, a decrease in leaf pro- duction efficiency and an increase in the stem to leaf bio- mass ratio was observed in 1989. Temporal changes in canopy leaf area index (LAI) were not statistically sig- nificant. Average LAI values of Q. ilex at the two sites were not significantly different despite differences in tree stature and density (4.6 m 2 m -2 at the ridge top, and 5.3 m 2 m -2 at the valley bottom). Vertical distribution of leaves and stems within the canopy was very similar at the two locations, with more than 60% of the total LAI in the uppermost metre of the canopy. The possible significance of such an LAI distribution on the canopy carbon budget is discussed.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Castell, Carles</style></author><author><style face="normal" font="default" size="100%">Terradas, Jaume</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Water relations, gas exchange, and growth of resprouts and mature plant shoots of Arbutus unedo L. and Quercus ilex L.</style></title><secondary-title><style face="normal" font="default" size="100%">Oecologia</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Growth</style></keyword><keyword><style  face="normal" font="default" size="100%">photosynthesis</style></keyword><keyword><style  face="normal" font="default" size="100%">Resprouts</style></keyword><keyword><style  face="normal" font="default" size="100%">Sclerophyll shrubs and trees</style></keyword><keyword><style  face="normal" font="default" size="100%">water relations</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1994</style></year></dates><volume><style face="normal" font="default" size="100%">98</style></volume><pages><style face="normal" font="default" size="100%">201-211</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Resprout and mature plant shoot growth, leaf water status and gas exchange behavior, tissue nutrient content, flowering, and production were studied for co- occurring shallow-rooted (Arbutus unedo L.) and deep- rooted (Quercus ilex L.) Mediterranean tree species at the Collserola Natural Park in Northeast Spain. Resprouts showed higher growth rates than mature plant shoots. During fall, no differences in eco-physiological perfor- mance of leaves were found, but mobilization of carbo- hydrates from burls strongly stimulated growth of fall re- sprouts compared to spring resprouts, despite low expo- sed leaf area of the fall shoots. During summer drought, resprouts exhibited improved water status and carbon fixation compared to mature plant shoots. Shoot growth of Q. iIex was apparently extended due to deep rooting so that initial slower growth during spring and early summer as compared to A. unedo was compensated. Tis- sue nutrient contents varied only slightly and are postula- ted to be of minor importance in controlling rate of shoot growth, perhaps due to the relatively fertile soil of the site. Fall flowering appeared to inhibit fall shoot growth in A. unedo, but did not occur in Q. ilex. The results de- monstrate that comparative examinations utilizing vege- tation elements with differing morphological and physio- logical adaptations can be used to analyze relatively complex phenomena related to resprouting behavior. The studies provide an important multi-dimensional back- ground framework for further studies of resprouting in the European Mediterranean region.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author><author><style face="normal" font="default" size="100%">Lange, O L</style></author><author><style face="normal" font="default" size="100%">Gebel, J</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Changes in photosynthetic capacity, carboxylation efficiency, and CO 2 compensation point associated with midday stomatal closure and midday depression of net</style></title><secondary-title><style face="normal" font="default" size="100%">Planta</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Carboxylation efficiency</style></keyword><keyword><style  face="normal" font="default" size="100%">Compensation point (CO2)</style></keyword><keyword><style  face="normal" font="default" size="100%">Photosynthesis (temperature- humidity)</style></keyword><keyword><style  face="normal" font="default" size="100%">Quercus</style></keyword><keyword><style  face="normal" font="default" size="100%">Sclerophyll</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1984</style></year></dates><volume><style face="normal" font="default" size="100%">162</style></volume><pages><style face="normal" font="default" size="100%">193-203</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The carbon-dioxide response of photo- synthesis of leaves of Quercus suber, a sclerophyl- lous species of the European Mediterranean re- gion, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a &quot;standard&quot; time course for temperature and hu- midity, which resembled natural conditions, was imposed on the leaves, and the CO 2 pressure exter- nal to the leaves on subsequent days was varied. The particular temperature and humidity condi- tions chosen were those which elicited a strong sto- matal closure at midday and the simultaneous de- pression of net CO 2 uptake. Midday depression of CO 2 uptake is the result of i) a decrease in CO2- saturated photosynthetic capacity after light satu- ration is reached in the early morning, ii) a de- crease in the initial slope of the CO 2 response curve (carboxylation efficiency), and iii) a substantial in- crease in the CO 2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in pho- tosynthesis, the internal leaf CO 2 pressure re- mained essentially constant despite stomatal clo- sure. The effects on capacity, slope, and compensa- tion point were reversed by lowering the tempera- ture and increasing the humidity in the afternoon. Constant internal CO 2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible tem- perature, humidity, and hormonal effects on pho- tosynthesis.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author><author><style face="normal" font="default" size="100%">Lange, O L</style></author><author><style face="normal" font="default" size="100%">Braun, M</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Midday Stomatal Closure in Mediterranean Type Sclerophylls Under Simulated Habitat Conditions in an Environmental Chamber II. Effect of the Complex of Leaf Temperature and Air Humidity on Gas Exchange of Arbutus unedo and Quercus ilex</style></title><secondary-title><style face="normal" font="default" size="100%">Oecologia</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">midday stomatal closure</style></keyword><keyword><style  face="normal" font="default" size="100%">net photosynthetic rate (voyant)</style></keyword><keyword><style  face="normal" font="default" size="100%">transpiration rate</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1981</style></year></dates><volume><style face="normal" font="default" size="100%">50</style></volume><pages><style face="normal" font="default" size="100%">5-11</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Shrubs of the Mediterranean sclerophyllous species Arbutus unedo and Quercus ilex were studied under simulated habitat conditions in an environmental chamber. Temperature, humidity, and light intensity were altered stepwise to simulate diurnal changes in conditions similar to those measured in an evergreen macchia in Sobreda, Portugal. Leaves were enclosed in cuvettes which reproduced the growth chamber climate and which allowed measurement of gas exchange. Increasing atmo- spheric stress in the form of higher temperature and lower humid- ity on successive days gradually results in midday depression of transpiration rate and net photosynthesis rate of leaves due to midday stomatal closure.</style></abstract></record></records></xml>