Changes In Photosynthetic Capacity Research Articles

Changes in photosynthetic capacity during leaf senescence of Liquidambar formosana

In this study, the photosynthetic light response curves were measured for Liquidambar formosana during the leaf senescence from October to December in 2014. The measurements were simulated by a photosynthetic light response model (Ye model) and the conventional non-rectangular hyperbola model, in order to understand the photosynthetic capacity of senescing leaves of L. formosana. The results showed that the light sensitivity of the net photosynthetic rate decreased gra-dually during the leaf senescence. The measured maximum net photosynthetic rate was about 2.88 μmol CO2·m-2·s-1 when the leaf color just turned yellow, and dropped to 0.95 μmol CO2·m-2·s-1 in the later stage of leaf senescence (8th December). The two photosynthetic light-response models performed well in fitting the observation data, with Ye model being slightly better. Parameters estimated from the two models, such as the maximum net photosynthetic rate, the appa-rent quantum yield, the quantum yield at the light compensation point and the dark respiration rate, all gradually decreased with time, quantitatively describing the decrease in the photosynthetic capacity during the leaf senescence for L. formosana. The senescing leaves of L. formosana maintained positive net photosynthesis rates during the whole senescence, which had positive impact on carbon assimilation in the study area.

After more than a decade of soil moisture deficit, tropical rainforest trees maintain photosynthetic capacity, despite increased leaf respiration.

Determining climate change feedbacks from tropical rainforests requires an understanding of how carbon gain through photosynthesis and loss through respiration will be altered. One of the key changes that tropical rainforests may experience under future climate change scenarios is reduced soil moisture availability. In this study we examine if and how both leaf photosynthesis and leaf dark respiration acclimate following more than 12 years of experimental soil moisture deficit, via a through‐fall exclusion experiment (TFE) in an eastern Amazonian rainforest. We find that experimentally drought‐stressed trees and taxa maintain the same maximum leaf photosynthetic capacity as trees in corresponding control forest, independent of their susceptibility to drought‐induced mortality. We hypothesize that photosynthetic capacity is maintained across all treatments and taxa to take advantage of short‐lived periods of high moisture availability, when stomatal conductance (g s) and photosynthesis can increase rapidly, potentially compensating for reduced assimilate supply at other times. Average leaf dark respiration (R d) was elevated in the TFE‐treated forest trees relative to the control by 28.2 ± 2.8% (mean ± one standard error). This mean R d value was dominated by a 48.5 ± 3.6% increase in the R d of drought‐sensitive taxa, and likely reflects the need for additional metabolic support required for stress‐related repair, and hydraulic or osmotic maintenance processes. Following soil moisture deficit that is maintained for several years, our data suggest that changes in respiration drive greater shifts in the canopy carbon balance, than changes in photosynthetic capacity.

A comparative analysis of transcriptomic, biochemical, and physiological responses to elevated ozone identifies species-specific mechanisms of resilience in legume crops.

Current concentrations of tropospheric ozone ([O3]) pollution negatively impact plant metabolism, which can result in decreased crop yields. Interspecific variation in the physiological response of plants to elevated [O3] exists; however, the underlying cellular responses explaining species-specific differences are largely unknown. Here, a physiological screen has been performed on multiple varieties of legume species. Three varieties of garden pea (Pisum sativum L.) were resilient to elevated [O3]. Garden pea showed no change in photosynthetic capacity or leaf longevity when exposed to elevated [O3], in contrast to varieties of soybean (Glycine max (L.) Merr.) and common bean (Phaseolus vulgaris L.). Global transcriptomic and targeted biochemical analyses were then done to examine the mechanistic differences in legume responses to elevated [O3]. In all three species, there was an O3-mediated reduction in specific leaf weight and total non-structural carbohydrate content, as well as increased abundance of respiration-related transcripts. Differences specific to garden pea included a pronounced increase in the abundance of GLUTATHIONE REDUCTASE transcript, as well as greater contents of foliar glutathione, apoplastic ascorbate, and sucrose in elevated [O3]. These results suggest that garden pea may have had greater capacity for detoxification, which prevented net losses in CO2 fixation in an elevated [O3] environment.

Photosynthetic traits of tree species in response to leaf nutrient content in the central Amazon

Rainforest tree species are often found on poor soils where essential nutrients may be in low concentrations. Here, we determine the effect of nutrients (N, P, Ca, Mg and K) in photosynthetic traits in five rainforest tree species from central Amazonia. Gas exchange parameters were measured with an infrared gas analyzer in four saplings (1–3 m tall) per species using two leaves per plant. Data on gas exchange and leaf nutrient content (N, P, K, Ca and Mg) were collected between August and November, 2010. Specific leaf area (SLA) and leaf thickness (L T) were also determined. Potential photosynthesis per unit mass (A pot-mass), maximum carboxylation velocity of Rubisco (V c-max) and electron transport rate (J max) were responsive to variation in leaf nutrient content per unit mass. On a mass basis, P content was positively correlated with N, Mg, and K content; Mg content was positively correlated with K content. However, no correlation was found between the content of P, Mg, K and Ca, or between Ca, Mg, K and N. SLA and L T were strongly related to A pot-area, V c-max and J max (per unit area). Our study shows in situ evidence on the effect of leaf nutrients on A pot-mass, V c-max and J max (per unit mass) of tree saplings in the central Amazon. The magnitude of changes in photosynthetic capacity of juvenile trees in the forest understory depends not only on N and P use efficiency, but also on the availability of K, Mg and Ca, in decreasing order.

Biochemical and molecular characteristics of leaf photosynthesis and relative seed yield of two contrasting rice cultivars in response to elevated [CO₂

Understanding the basis for intraspecific yield variability may be important in elucidating biological mechanisms that are associated with superior yield performance in response to projected increases in carbon dioxide concentration, [CO₂]. Using a free-air CO₂ enrichment (FACE) facility, two rice lines, S63 and W14, which differed consistently in their enhancement of seed yield when grown at elevated [CO₂] in multiple field trials, were examined. To determine if the different cultivar responses were linked to changes in photosynthetic characteristics at elevated [CO₂], spatial and temporal changes in photosynthetic stimulation and the occurrence of down-regulation, or acclimation, in relation to panicle sink development were quantified for the uppermost canopy leaves. Changes in photosynthetic capacity were determined by quantifying changes in the sink:source ratio, leaf nitrogen (N) content, the concentration and mRNA expression of the large Rubisco subunit, and changes in V c,max, the maximum ribulose bisphosphate (RuBP)-saturated rate of carboxylation. For the W14 cultivar, significant reductions in photosynthesis at the elevated, relative to ambient [CO₂], signalling photosynthetic acclimation, were observed following panicle initiation. The observance of photosynthetic acclimation was consistent with significant reductions in N, Rubisco content and expression, and V c,max. In contrast, for the cultivar S63, elevated [CO₂] resulted in increased spikelet number and grain weight, increased sink:source ratios, and continued stimulation of photosynthesis up to grain maturity. Overall, these data suggest that the greater response of the S63 line to elevated [CO₂] may be associated with enhanced carbon sinks relative to sources, and the ability to maintain photosynthetic capacity during grain development.

Effects of nitrogen additions on biomass, stoichiometry and nutrient pools of moss Rhytidium rugosum in a boreal forest in Northeast China

Global nitrogen (N) deposition has been enhanced with anthropogenic N emissions, and its impacts on mosses are receiving more and more attention. This study investigates how N deposition influence the biomass and stoichiometry of moss Rhytidium rugosum, using a 3-year N enrichment experiment with 0, 2, 5 and 10 g N m−2 yr−1 in a boreal forest in Northeast China. Low N additions caused an N redundancy and moderate to high N additions resulted in a biomass loss. N additions reduced biomass ratios of green to brown tissues and increased N and phosphorus (P) contents, suggesting changes in photosynthetic capacity and litter decomposition. Biomass N pools showed a unimodal response to the N additions, and P pools decreased under moderate and high N additions. Our findings indicate significant stoichiometric and biomass changes caused by N deposition may lead to a substantial carbon and nutrient loss in boreal moss carpets.

Cotton radiation use efficiency response to plant growth regulators

SUMMARYPlant growth regulators are widely used in cotton production to improve crop management. Previous research has demonstrated changes in crop growth, dry matter (DM) partitioning and lint yield of cotton after the application of plant growth regulators. However, no reports are available demonstrating the effect of plant growth regulators on light interception and radiation use efficiency (RUE). Field studies were conducted in Fayetteville, Arkansas, USA in 2006 and 2007. RUE was estimated for the period between the pinhead square stage (PHS) of growth and 3 weeks after first flower (FF+3) from plots receiving three applications of the nitrophenolate and mepiquat chloride with Bacillus cereus plant growth regulators (Chaperone™) at 7·19 g a.i./ha and Pix Plus® at 41·94 g a.i./ha compared with an untreated control. No differences between the Chaperone treatment and the untreated control were found in the present study. However, Pix Plus significantly reduced plant height (both 2006 and 2007) and leaf area (2007 only), and altered the canopy structure of the crop as recorded by increased values of canopy extinction coefficient. Although DM accumulation was found not to be affected by plant growth regulator treatments, RUE was significantly increased after Pix Plus application, by 33·2%. RUE was increased because less light was intercepted by the Pix Plus treatment for the same biomass production, and this is probably a result of changes in photosynthetic capacity of the leaves and changes in light distribution throughout the canopy.

In situ examination of the relationship between various vegetation indices and canopy phenology in an evergreen coniferous forest, Japan

We examined the relationship between four vegetation indices and tree canopy phenology in an evergreen coniferous forest in Japan based on observations made using a spectral radiometer and a digital camera at a daily time step during a 4 year period. The colour of the canopy surface of Japanese cedar (Cryptomeria japonica) changed from yellowish-green to whitish-green from late May to July and turned reddish-green in winter. The normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and plant area index (PAI) showed no seasonality. In contrast, the green–red ratio vegetation index (GRVI) increased from March to June and then decreased gradually from July to December, resulting in a bell-shaped curve. GRVI revealed seasonal changes in the colour of the canopy surface. GRVI correlated more positively with the evaluated maximum photosynthetic rate for the whole forest canopy, A max, than did NDVI or EVI. These results suggest the possibility that GRVI is more useful than NDVI and EVI for capturing seasonal changes in photosynthetic capacity, as the green and red reflectances are strongly influenced by changes in leaf pigments in this type of forest.

Variation in water potential, hydraulic characteristics and water source use in montane Douglas-fir and lodgepole pine trees in southwestern Alberta and consequences for seasonal changes in photosynthetic capacity

Tree species response to climate change-induced shifts in the hydrological cycle depends on many physiological traits, particularly variation in water relations characteristics. We evaluated differences in shoot water potential, vulnerability of branches to reductions in hydraulic conductivity, and water source use between Pinus contorta Dougl. ex Loud. var. latifolia Engelm. (lodgepole pine) and Pseudotsuga menziesii (Mirb.) Franco (interior Douglas-fir), and determined the consequences for seasonal changes in photosynthetic capacity. The Douglas-fir site had soil with greater depth, finer texture and higher organic matter content than soil at the lodgepole pine site, all factors that increased the storage of soil moisture. While the measured xylem vulnerability curves were quite similar for the two species, Douglas-fir had lower average midday shoot water potentials than did lodgepole pine. This implied that lodgepole pine exhibited stronger stomatal control of transpiration than Douglas-fir, which helped to reduce the magnitude of the water potential gradient required to access water from drying soil. Stable hydrogen isotope measurements indicated that Douglas-fir increased the use of groundwater during mid-summer when precipitation inputs were low, while lodgepole pine did not. There was a greater reduction of photosynthetic carbon gain in lodgepole pine compared with Douglas-fir when the two tree species were exposed to seasonal declines in soil water content. The contrasting patterns of seasonal variation in photosynthetic capacity observed for the two species were a combined result of differences in soil characteristics at the separate sites and the inherent physiological differences between the species.

Variações na anatomia foliar de videira Niagara em diferentes sistemas de condução

Alterações na anatomia de folhas são causadas por diversos fatores ambientais, principalmente a disponibilidade de radiação, podendo causar mudanças na capacidade fotossintética e afetando a produção final. Este trabalho objetivou identificar alterações na estrutura anatômica de folhas de videiras 'Niagara Rosada' e 'Niagara Branca' em três diferentes sistemas de condução: espaldeira (ESP), manjedoura em 'Y' (Y) e manjedoura em 'Y' coberto com plástico (YPLA). Os estudos anatômicos foram realizados em folhas, externas em relação ao dossel, retiradas em três diferentes alturas da planta (superior, mediana e inferior). Para a caracterização anatômica, as amostras foram fixadas em FAA, emblocadas em parafina, seccionadas em micrótomo e coradas com safranina e azul de alciã. As lâminas foram analisadas com o auxílio de um microscópio óptico acoplado a uma câmera de captura de imagens. As espessuras da epiderme das faces adaxial e abaxial, dos parênquimas paliçádico e esponjoso, da espessura total da folha e da razão entre parênquimas paliçádico e esponjoso foram estimadas em uma amostra ao acaso de dez segmentos de cada tratamento, totalizando 1800 observações. Realizaram as análises de variância pelo teste F, sendo as médias dos tratamentos comparadas pelo Tukey a 5% de probabilidade. Observaram-se nas cultivares Niagara Branca e Niagara Rosada conduzidas em ESP uma espessura média de limbo maior, porém foram menos produtivas, quando comparados com Y e YPLA; folhas expostas a maiores intensidades luminosas tiveram limbo mais espesso devido ao maior desenvolvimento do parênquima paliçádico, independentemente do sistema de condução.

Quantifying the effect of nitrogen-induced physiological and structural changes on poplar growth using a carbon-balance model

We evaluate the importance of changes in photosynthetic capacity, respiration rates, root shoot ratio, pipe model parameters and specific leaf area in the early-growth response of hybrid poplar to nitrogen availability. Juvenile growth simulations for trees with three different levels of leaf nitrogen concentration (N(leaf)) (low (1.2%), medium (2.4%) and high (3.6%)) were conducted with the carbon-balance model CROBAS. Five-year growth simulations showed the diameter and height of poplar trees to be, respectively, four and three times larger in plants with 2.4% N(leaf) compared with those with 1.2% N(leaf). Increasing N(leaf) from 2.4 to 3.6% resulted in 34 and 16% higher diameter and height growth of trees. According to the model, changes in the photosynthetic capacity accounted for most of the differences in growth between trees with different levels of N(leaf); the other parameters were much less influential. This suggests that in fast-growing early-successional broadleaved species such as poplars, physiological rather than allocational and morphological traits predominate in determining growth, at least under non-limiting light conditions.

What is the proximate cause for size-dependent ecophysiological differences in vascular epiphytes?

Size-related variation in physiological parameters as diverse as photosynthetic capacity, abscisic acid relationships or the relative water deficit at stomatal closure have been reported for a large number of vascular epiphytes, but the proximate mechanism behind these observations has not been identified. We test four possible reasons for size-related changes in photosynthetic capacity, leaf-N content and specific leaf area: (i) plant size itself, (ii) plant age or developmental stage, (iii) previous nutrition, or (iv) previous water regime. A suite of study species and approaches were used: a 'natural experiment' with the orchid Polystachya foliosa; an experimental field study with another orchid, Dimerandra emarginata; and a study under controlled conditions with the tank bromeliad, Vriesea sanguinolenta. Neither size, age nor differences in water supply caused differences in leaf N and photosynthetic capacity, while low supply of nutrients yielded, and high supply with nutrients completely removed, size-related trends. The observed size-related trends are thus a consequence of in situ differences in nutrient acquisition. Arguably, the improved nutrient status of larger plants under natural conditions results from larger tanks, holding moisture for increasingly longer intervals, which allows longer periods of decomposition of detritus and of nutrient uptake.

Photosynthetic acclimation in relation to nitrogen allocation in cucumber leaves in response to changes in irradiance

Leaves deep in canopies can suddenly be exposed to increased irradiances following e.g. gap formation in forests or pruning in crops. Studies on the acclimation of photosynthesis to increased irradiance have mainly focused on the changes in photosynthetic capacity (A(max)), although actual irradiance often remains below saturating level. We investigated the effect of changes in irradiance on the photosynthesis irradiance response and on nitrogen allocation in fully grown leaves of Cucumis sativus. Leaves that fully developed under low (50 µmol m⁻² s⁻¹) or moderate (200 µmol m⁻² s⁻¹) irradiance were subsequently exposed to, respectively, moderate (LM-leaves) or low (ML-leaves) irradiance or kept at constant irradiance level (LL- and MM-leaves). Acclimation of photosynthesis occurred within 7 days with final A(max) highest in MM-leaves, lowest in LL-leaves and intermediate in ML- and LM-leaves, whereas full acclimation of thylakoid processes underlying photosystem II (PSII) efficiency and non-photochemical quenching occurred in ML- and LM-leaves. Dark respiration correlated with irradiance level, but not with A(max). Light-limited quantum efficiency was similar in all leaves. The increase in photosynthesis at moderate irradiance in LM-leaves was primarily driven by nitrogen import, and nitrogen remained allocated in a similar ratio to Rubisco and bioenergetics, while allocation to light harvesting relatively decreased. A contrary response of nitrogen was associated with the decrease in photosynthesis in ML-leaves. Net assimilation of LM-leaves under moderate irradiance remained lower than in MM-leaves, revealing the importance of photosynthetic acclimation during the leaf developmental phase for crop productivity in scenarios with realistic, moderate fluctuations in irradiance that leaves can be exposed to.

Análises de fluorescência e consumo de água em Brachiaria decumbens após aplicação de herbicidas em pós-emergência

A análise da fluorescência da clorofila vem sendo largamente utilizada no entendimento dos mecanismos da fotossíntese propriamente dito, bem como na avaliação da capacidade fotossintética alterada com a aplicação de herbicidas. O consumo de água pelas plantas é uma maneira também de avaliar a atuação dos herbicidas nas plantas daninhas. O objetivo deste trabalho foi avaliar a fluorescência através da taxa de transporte de elétrons, consumo de água e fitointoxicação de Brachiaria decumbens após aplicação de quatro herbicidas de diferentes mecanismos de ação. Aos 30 dias após a semeadura de B. decumbens, as plantas foram arrancadas dos tubetes e preparadas para os tratamentos. Elas tiveram o sistema radicular colocado em tubos falcon preenchidos com água, e a superfície dos falcon foi isolada com papel-alumínio, para evitar evaporação do sistema. Os herbicidas aplicados foram: glyphosate, haloxyfop-methyl, diuron e amicarbazone. A aplicação foi feita com um pulverizador estacionário instalado em laboratório; após a aplicação dos tratamentos, as plantas foram mantidas em casa de vegetação. Foi avaliada a taxa de transporte de elétrons (ETR), o consumo de água e a fitointoxicação das plantas em vários períodos após o início do experimento. Os dados de ETR e fitointoxicação foram expressos em porcentagem da testemunha e submetidos à análise de variância e à comparação das médias. Para o consumo de água, os dados foram acumulados e ajustados por modelos de regressão. Assim, pode-se dizer que as plantas de B. decumbens tiveram respostas diferentes aos herbicidas aplicados, e o consumo de água das plantas está relacionado diretamente com o transporte de elétrons. A metodologia fundamentada no fluorômetro mostrou-se adequada para verificar a intoxicação antecipada em B. de cumbens submetidas ao amicarbazone e diuron antes mesmo da verificação visual de intoxicação.

Modeling acclimation of photosynthesis to temperature in evergreen conifer forests

• In this study, we used a canopy photosynthesis model which describes changes in photosynthetic capacity with slow temperature-dependent acclimations. • A flux-partitioning algorithm was applied to fit the photosynthesis model to net ecosystem exchange data for 12 evergreen coniferous forests from northern temperate and boreal regions. • The model accounted for much of the variation in photosynthetic production, with modeling efficiencies (mean > 67%) similar to those of more complex models. The parameter describing the rate of acclimation was larger at the northern sites, leading to a slower acclimation of photosynthesis to temperature. The response of the rates of photosynthesis to air temperature in spring was delayed up to several days at the coldest sites. Overall photosynthesis acclimation processes were slower at colder, northern locations than at warmer, more southern, and more maritime sites. • Consequently, slow changes in photosynthetic capacity were essential to explaining variations of photosynthesis for colder boreal forests (i.e. where acclimation of photosynthesis to temperature was slower), whereas the importance of these processes was minor in warmer conifer evergreen forests.

PGRL1 Participates in Iron-induced Remodeling of the Photosynthetic Apparatus and in Energy Metabolism in Chlamydomonas reinhardtii

PGRL1 RNA and protein levels are increased in iron-deficient Chlamydomonas reinhardtii cells. In an RNAi strain, which accumulates lower PGRL1 levels in both iron-replete and -starved conditions, the photosynthetic electron transfer rate is decreased, respiratory capacity in iron-sufficient conditions is increased, and the efficiency of cyclic electron transfer under iron-deprivation is diminished. Pgrl1-kd cells exhibit iron deficiency symptoms at higher iron concentrations than wild-type cells, although the cells are not more depleted in cellular iron relative to wild-type cells as measured by mass spectrometry. Thiol-trapping experiments indicate iron-dependent and redox-induced conformational changes in PGRL1 that may provide a link between iron metabolism and the partitioning of photosynthetic electron transfer between linear and cyclic flow. We propose, therefore, that PGRL1 in C. reinhardtii may possess a dual function in the chloroplast; that is, iron sensing and modulation of electron transfer.

Carbon and oxygen isotope analysis of leaf biomass reveals contrasting photosynthetic responses to elevated CO<sub>2</sub> near geologic vents in Yellowstone National Park

Abstract. In this study we explore the use of natural CO2 emissions in Yellowstone National Park (YNP) in Wyoming, USA to study responses of natural vegetation to elevated CO2 levels. Radiocarbon (14C) analysis of leaf biomass from a conifer (Pinus contortus; lodgepole pine) and an invasive, non-native herb (Linaria dalmatica; Dalmation toadflax) was used to trace the inputs of vent CO2 and quantify assimilation-weighted CO2 concentrations experienced by individual plants near vents and in comparable locations with no geologic CO2 exposure. The carbon and oxygen isotopic composition and nitrogen percent of leaf biomass from the same plants was used to investigate photosynthetic responses of these plants to naturally elevated atmospheric CO2 concentrations. The coupled shifts in carbon and oxygen isotope values suggest that dalmation toadflax responded to elevated CO2 exposure by increasing stomatal conductance with no change in photosynthetic capacity and lodgepole pine apparently responded by decreasing stomatal conductance and photosynthetic capacity. Lodgepole pine saplings exposed to elevated levels of CO2 likewise had reduced leaf nitrogen concentrations compared to plants with no enhanced CO2 exposure, further suggesting widespread and dominant conifer down-regulated photosynthetic capacity under elevated CO2 levels near geologic vents.

Stomatal and non‐stomatal limitations of photosynthesis in trees of a tropical seasonally flooded forest

Trees in the flooded forest of the Mapire River in Venezuela suffer a decrease in photosynthetic rate (A) when flood begins, which is reverted at maximum flood. Changes in A are accompanied by similar changes in stomatal conductance (g(s)), and the possibility of changes in photosynthetic capacity is not ruled out. In order to understand how relative stomatal and non-stomatal limitations of photosynthesis are affected by flooding, we studied the seasonal changes in A and its response to intercellular CO(2) concentration in trees of Campsiandra laurifolia, Symmeria paniculata, Acosmium nitens and Eschweilera tenuifolia. Flooding caused in trees of C. laurifolia and S. paniculata a reduction in A, g(s), carboxylation efficiency and total soluble protein (TSP), whereas gas exchange in A. nitens and E. tenuifolia was more sensitive to drought. Under flooding, relative stomatal limitation (L(s)) was on average half the highest, and relative non-stomatal limitation (L(ns)) increased from the dry season to flooding. Under full flood, A, g(s) and TSP regained high values. A was positively correlated to light-saturated electron transport rate, suggesting that part of the decrease in A under flooding was due to impairment of photosynthetic capacity. Under flooding, not only stomatal closure but also increased L(ns) causes a reduction in photosynthesis of all four species, and a process of acclimation as flooding progresses allows gas exchange and related variables to regain high values.

Changes in photosynthetic capacity and antioxidant enzymatic systems in micropropagated Zingiber officinale plantlets during their acclimation

Ginger (Zingiber officinale Rosc.) plantlets were propagated in vitro and acclimated under different photosynthetic photon flux densities (60 and 250 µmol m-2 s-1 = LI and HI, respectively). Increases in chlorophyll (Chl) content and Chl a/b ratio were found under both irradiances. In vitro plantlets (day 0) exhibited a low photosynthesis, but chloroplasts from in vitro leaves contained well developed grana and osmiophillic globules. Photoinhibition in leaves formed in vitro was characterized by decrease of photochemical efficiency and quantum efficiency of photosystem 2 photochemistry in HI treatment during acclimation. The new leaves formed during acclimation in both treatments showed a higher photosynthetic capacity than the leaves formed in vitro. Also activities of antioxidant enzymes of micropropagated ginger plantlets changed during acclimation.

The boreal dwarf shrub Vaccinium vitis-idaea retains its capacity for photosynthesis through the winter

The ability to retain their photosynthetic capacity through the winter may be important for plants in boreal conditions, where the growing season is relatively short and winter temperatures fluctuate from severe freezing up to near 0 °C. The snow cover is an important protector for field-layer plants against both extreme freezing and excessive light, both of which could damage the photosynthetic apparatus. To understand the importance of wintertime photosynthetic activity for evergreen boreal dwarf shrubs, the photosynthesis of Vaccinium vitis-idaea L. was monitored in field conditions for one year. A dynamic model was used to determine the relative effect of temperature on the photosynthetic capacity. Our results show that V. vitis-idaea retains its photosynthetic capacity throughout the winter: its average photosynthetic capacity in winter was almost 25% of the yearly maximum measured. Changes in photosynthetic capacity over the year reflect the changes in air temperature with a certain delay, except in summer. Concentrations of soluble sugars remained high during the winter months, probably as a consequence of CO2 uptake under the snow cover. Our measurements indicated no significant damage to the leaf tissue over the winter, but suggest that photoinhibition may occur immediately after snowmelt.