Interaction of temperature and irradiance effects on photosynthetic acclimation in two accessions of Arabidopsis thaliana

The effect of temperature and irradiance during growth on photosynthetic traits of two accessions of Arabidopsis thaliana was investigated. Plants were grown at 10 and 22 °C, and at 50 and 300 μmol photons m(−2) s(−1) in a factorial design. As known from other cold-tolerant herbaceous species, growth of Arabidopsis at low temperature resulted in increases in photosynthetic capacity per unit leaf area and chlorophyll. Growth at high irradiance had a similar effect. However, the growth temperature and irradiance showed interacting effects for several capacity-related variables. Temperature effects on the ratio between electron transport capacity and carboxylation capacity were also different in low compared to high irradiance grown Arabidopsis. The carboxylation capacity per unit Rubisco, a measure for the in vivo Rubisco activity, was low in low irradiance grown plants but there was no clear growth temperature effect. The limitation of photosynthesis by the utilization of triose-phosphate in high temperature grown plants was less when grown at low compared to high irradiance. Several of these traits contribute to reduced efficiency of the utilization of resources for photosynthesis of Arabidopsis at low irradiance. The two accessions from contrasting climates showed remarkably similar capabilities of developmental acclimation to the two environmental factors. Hence, no evidence was found for photosynthetic adaptation of the photosynthetic apparatus to specific climatic conditions

Метод коррекции для параллелизации численных моделей гидродинамики водоемов со свободной поверхностью

В роботi запропоновано метод перетворення послiдовних алгоритмiв моделей гiдродинамiки резервуарiв з вiльною поверхнею в паралельнi, використовуючи MPI та розбивку розрахункової областi на пiдобластi, перевагою якого є відносна простота реалізації, обумовлена потребою тільки у додаткових процедурах корекції замість значних перетворень існуючих програм послідовного розрахунку. Дослiджується вплив рiзноманiтних факторiв на ефективнiсть методу в термінах зменшення тривалості розрахунків зі збільшенням числа застосованих процесорів.В работе предложен метод преобразования последовательных алгоритмов моделей гидродинамики резервуаров со свободной поверхностью в параллельные, используя MPI и разбивку расчётной области на подобласти, преимуществом метода является относительная простота реализации, обусловленная потребностью только в дополнительных процедурах коррекции вместо значительных преобразований существующих программ последовательного расчёта. Исследуется влияние различных факторов на эффективность метода в терминах уменьшения длительности параллельных расчётов с увеличением числа используемых процессоров.This paper proposes a technique using MPI and domain decomposition to transform serial algorithms of numerical models for hydrodynamics simulations in the water reservoirs with free surface into parallel algorithms. The advantage of the proposed technique is a comparatively simple realization due to the necessity of only additional correction procedures instead of significant transformations of existing serial program code. The impacts of various factors on the method of efficiency are studied in terms of the speedup of computations with the increase of number of utilized processors

Leaf-scale quantification of the effect of photosynthetic gas exchange on δ ¹⁷O of atmospheric CO ₂

Understanding the processes that affect the triple oxygen isotope composition of atmospheric CO2during gas exchange can help constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions using three plant species. The experiments were conducted at two different light intensities and using CO2with different δ17O. We directly quantify the effect of photosynthesis on δ17O of atmospheric CO2for the first time. Our results demonstrate the established theory for δ18O is applicable to δ17O.CO2/at leaf level, and we confirm that the following two key factors determine the effect of photosynthetic gas exchange on the δ17O of atmospheric CO2. The relative difference between δ17O of the CO2entering the leaf and the CO2in equilibrium with leaf water and the back-diffusion flux of CO2from the leaf to the atmosphere, which can be quantified by the cm=ca ratio, where ca is the CO2mole fraction in the surrounding air and cm is the one at the site of oxygen isotope exchange between CO2and H2O. At low cm=ca ratios the discrimination is governed mainly by diffusion into the leaf, and at high cm=ca ratios it is governed by back-diffusion of CO2that has equilibrated with the leaf water. Plants with a higher cm=ca ratio modify the 117O of atmospheric CO2more strongly than plants with a lower cm=ca ratio. Based on the leaf cuvette experiments, the global value for discrimination against δ17O of atmospheric CO2during photosynthetic gas exchange is estimated to be-0:57±0:14% using cm=ca values of 0.3 and 0.7 for C4and C3plants, respectively. The main uncertainties in this global estimate arise from variation in cm=ca ratios among plants and growth conditions.</p

Exploring the potential of Δ¹⁷O in CO₂ for determining mesophyll conductance

Mesophyll conductance to CO2 from the intercellular air space to the CO2–H2O exchange site has been estimated using δ18O measurements (gm18). However, the gm18 estimates are affected by the uncertainties in the δ18O of leaf water where the CO2–H2O exchange takes place and the degree of equilibration between CO2 and H2O. We show that measurements of Δ17O (i.e. Δ17O = δ17O − 0.528 × δ18O) can provide independent constraints on gm (gmΔ17) and that these gm estimates are less affected by fractionation processes during gas exchange. The gm calculations are applied to combined measurements of δ18O and Δ17O, and gas exchange in two C3 species, sunflower (Helianthus annuus L. cv. ‘sunny’) and ivy (Hedera hibernica L.), and the C4 species maize (Zea mays). The gm18 and gmΔ17 estimates agree within the combined errors (P-value, 0.876). Both approaches are associated with large errors when the isotopic composition in the intercellular air space becomes close to the CO2–H2O exchange site. Although variations in Δ17O are low, it can be measured with much higher precision compared with δ18O. Measuring gmΔ17 has a few advantages compared with gm18: (i) it is less sensitive to uncertainty in the isotopic composition of leaf water at the isotope exchange site and (ii) the relative change in the gm due to an assumed error in the equilibration fraction θeq is lower for gmΔ17 compared with gm18. Thus, using Δ17O can complement and improve the gm estimates in settings where the δ18O of leaf water varies strongly, affecting the δ18O (CO2) difference between the intercellular air space and the CO2–H2O exchange site.</p

Exploring the potential of Δ17O in CO2 for determining mesophyll conductance

Mesophyll conductance to CO2 from the intercellular air space to the CO2–H2O exchange site has been estimated using δ18O measurements (gm18). However, the gm18 estimates are affected by the uncertainties in the δ18O of leaf water where the CO2–H2O exchange takes place and the degree of equilibration between CO2 and H2O. We show that measurements of Δ17O (i.e. Δ17O = δ17O − 0.528 × δ18O) can provide independent constraints on gm (gmΔ17) and that these gm estimates are less affected by fractionation processes during gas exchange. The gm calculations are applied to combined measurements of δ18O and Δ17O, and gas exchange in two C3 species, sunflower (Helianthus annuus L. cv. ‘sunny’) and ivy (Hedera hibernica L.), and the C4 species maize (Zea mays). The gm18 and gmΔ17 estimates agree within the combined errors (P-value, 0.876). Both approaches are associated with large errors when the isotopic composition in the intercellular air space becomes close to the CO2–H2O exchange site. Although variations in Δ17O are low, it can be measured with much higher precision compared with δ18O. Measuring gmΔ17 has a few advantages compared with gm18: (i) it is less sensitive to uncertainty in the isotopic composition of leaf water at the isotope exchange site and (ii) the relative change in the gm due to an assumed error in the equilibration fraction θeq is lower for gmΔ17 compared with gm18. Thus, using Δ17O can complement and improve the gm estimates in settings where the δ18O of leaf water varies strongly, affecting the δ18O (CO2) difference between the intercellular air space and the CO2–H2O exchange site

Ontogenetic changes in leaf traits of tropical rainforest trees differing in juvenile light requirement

Relationships between leaf traits and the gap dependence for regeneration, and ontogenetic changes therein, were investigated in juvenile and adult tropical rainforest tree species. The juveniles of the 17 species included in the study were grown in high light, similar to the exposed crowns of the adult trees. The traits were structural, biomechanical, chemical and photosynthetic. With increasing species gap dependence, leaf mass per area (LMA) decreased only slightly in juveniles and remained constant in adults, whereas punch strength together with tissue density decreased, and photosynthetic capacity and chlorophyll increased. Contrary to what has been mostly found in evergreen tropical rainforest, the trade-off between investment in longevity and in productivity was evident at an essentially constant LMA. Of the traits pertaining to the chloroplast level, photosynthetic capacity per unit chlorophyll increased with gap dependence, but the chlorophyll a/b ratio showed no relationship. Adults had a twofold higher LMA, but leaf strength was on average only about 50% larger. Leaf tissue density, and chlorophyll and leaf N per area were also higher, whereas chlorophyll and leaf N per unit dry mass were lower. Ranking of the species, relationships between traits and with the gap dependence of the species were similar for juveniles and adults. However, the magnitudes of most ontogenetic changes were not clearly related to a species’ gap dependence. The adaptive value of the leaf traits for juveniles and adults is discussed