Growth Light Environment Research Articles

Impact of growth light environment on oxygen sensitivity in rice: Pseudo-first-order response of photosystem I photoinhibition to O2 partial pressure.

Photosynthetic organisms generate reactive oxygen species (ROS) during photosynthetic electron transport reactions on the thylakoid membranes within both photosystems (PSI and PSII), leading to the impairment of photosynthetic activity, known as photoinhibition. In PSI, ROS production has been suggested to follow Michaelis-Menten- or second-order reaction-dependent kinetics in response to changes in the partial pressure of O2 . However, it remains unclear whether ROS-mediated PSI photoinhibition follows the kinetics mentioned above. In this study, we aimed to elucidate the ROS production kinetics from the aspect of PSI photoinhibition in vivo. For this research objective, we investigated the O2 dependence of PSI photoinhibition by examining intact rice leaves grown under varying photon flux densities. Subsequently, we found that the degree of O2 -dependent PSI photoinhibition linearly increased in response to the increase in O2 partial pressure. Furthermore, we observed that the higher photon flux density on plant growth reduced the O2 sensitivity of PSI photoinhibition. Based on the obtained data, we investigated the O2 -dependent kinetics of PSI photoinhibition by model fitting analysis to elucidate the mechanism of PSI photoinhibition in leaves grown under various photon flux densities. Remarkably, we found that the pseudo-first-order reaction formula successfully replicated the O2 -dependent PSI photoinhibition kinetics in intact leaves. These results suggest that ROS production, which triggers PSI photoinhibition, occurs by an electron-leakage reaction from electron carriers within PSI, consistent with previous in vitro studies.

Terrestrial and Floating Aquatic Plants Differ in Acclimation to Light Environment.

The ability of plants to respond to environmental fluctuations is supported by acclimatory adjustments in plant form and function that may require several days and development of a new leaf. We review adjustments in photosynthetic, photoprotective, and foliar vascular capacity in response to variation in light and temperature in terrestrial plants. The requirement for extensive acclimation to these environmental conditions in terrestrial plants is contrasted with an apparent lesser need for acclimation to different light environments, including rapid light fluctuations, in floating aquatic plants for the duckweed Lemna minor. Relevant features of L. minor include unusually high growth rates and photosynthetic capacities coupled with the ability to produce high levels of photoprotective xanthophylls across a wide range of growth light environments without compromising photosynthetic efficiency. These features also allow L. minor to maximize productivity and avoid problems during an abrupt experimental transfer of low-light-grown plants to high light. The contrasting responses of land plants and floating aquatic plants to the light environment further emphasize the need of land plants to, e.g., experience light fluctuations in their growth environment before they induce acclimatory adjustments that allow them to take full advantage of natural settings with such fluctuations.

Effect of growth unit characteristics and light environment on leaf fall in the evergreen mango tree

Effect of growth unit characteristics and light environment on leaf fall in the evergreen mango tree

Lemna as a Sustainable, Highly Nutritious Crop: Nutrient Production in Different Light Environments

Development of a nutritious, sustainable food source is essential to address worldwide deficiencies in human micronutrients. Aquatic floating plants (e.g., species in the family Lemnaceae, duckweeds) are uniquely suited for area-efficient productivity with exceptionally high rates of growth and nutritional quality. Here, we provide an overview of the role of dietary micronutrients (with a focus on carotenoids) in human health and the promise of Lemnaceae as sustainable crops. We examine the effect of growth light environment on plant biomass production and levels of the carotenoids zeaxanthin, lutein, and pro-vitamin A (β-carotene), as well as the antioxidant vitamin E (α-tocopherol), and protein. Data on each of these nutrients are reported on a plant dry biomass basis (as relevant for nutrition) as well as relative to the required input of light energy (as relevant to resource-use efficiency).

Red:Blue LED light proportion affects biomass accumulation and polyamine metabolism in Anoectochilus roxburghii studied by nano-electrospray ionization mass spectrometry

Light quality affects the plant growth, physiology, and polyamine (PA) metabolism. Anoectochilus roxburghii is an ornamental, medicinal, and culinary perennial herb in many countries. In this study, we identified the optimal light environment for enhancing the growth of A. roxburghii in vitro, and analyzed PA metabolism under blue (B), three red:blue combinations at different proportions of the total incident photon flux density (R1B2: the ratio of 1: 2, R1B1: the ratio of 1: 1, and R2B1: the ratio of 2: 1, respectively), red (R), and white light (W) environment for 120 days. The biomass accumulation and stomata characteristics were evaluated, as well as total phenolic, total flavonoids, soluble sugars, and soluble proteins. Besides, nine PA compounds were quantitatively analyzed by nano-electrospray ionization mass spectrometry (nano-ESI-MS) without complex sample pretreatment. The results showed that the biomass, total phenolic, total flavonoids, soluble sugars, and soluble proteins were significantly higher in the R1B1 group, which was more conducive to stomata opening. The accumulation of the nine PA compounds increased significantly in the B and R groups, compared with W group, but decreased in the combinations of red and blue lights, especially in the R1B1 group, which A. roxburghii showed better growth. We conclude that the R1B1 could be used as the optimal growth light environment of A. roxburghii tissue culture. Nano-ESI-MS could be used as a rapid and sensitive method to quantify PAs, providing new data for enhancing our understanding about the functions of PAs in plant-light environment interactions.

Estimating Light Acclimation Parameters of Cucumber Leaves Using Time-Weighted Averages of Daily Photosynthetic Photon Flux Density.

Leaves acclimate to day-to-day fluctuating levels of photosynthetic photon flux density (PPFD) by adjusting their morphological and physiological parameters. Accurate estimation of these parameters under day-to-day fluctuating PPFD conditions benefits crop growth modeling and light environment management in greenhouses, although it remains challenging. We quantified the relationships between day-to-day PPFD changes over 6 days and light acclimation parameters for cucumber seedling leaves, including leaf mass per area (LMA), chlorophyll (Chl) a/b ratio, maximum net photosynthetic rate (Pnmax), maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Vcmax), and maximum rate of electron transport (Jmax). The last two parameters reflect the capacity of the photosynthetic partial reactions. We built linear regression models of these parameters based on average or time-weighted averages of daily PPFDs. For time-weighted averages of daily PPFDs, the influence of daily PPFD was given a specific weight. We employed three types of functions to calculate this weight, including linear, quadratic, and sigmoid derivative types. We then determined the trend of weights that estimated each parameter most accurately. Moreover, we introduced saturating functions to calibrate the average or time-weighted averages of daily PPFDs, considering that light acclimation parameters are usually saturated under high PPFDs. We found that time-weighted average PPFDs, in which recent PPFD levels had larger weights than earlier levels, better estimated LMA than average PPFDs. This suggests that recent PPFDs contribute more to LMA than earlier PPFDs. Except for the Chl a/b ratio, the average PPFDs estimated Pnmax, Vcmax, and Jmax with acceptable accuracy. In contrast, time-weighted averages of daily PPFDs did not improve the estimation accuracy of these four parameters, possibly due to their low response rates and plasticity. Calibrating functions generally improved estimation of Chl a/b ratio, Vcmax, and Jmax because of their saturating tendencies under high PPFDs. Our findings provide a reasonable approach to quantifying the extent to which the leaves acclimate to day-to-day fluctuating PPFDs, especially the extent of LMA.

Acclimation to Fluctuating Light Impacts the Rapidity of Response and Diurnal Rhythm of Stomatal Conductance.

Plant acclimation to growth light environment has been studied extensively; however, the majority of these studies have focused on light intensity and photo-acclimation, with few studies exploring the impact of dynamic growth light on stomatal acclimation and behavior. To assess the impact of growth light regime on stomatal acclimation, we grew Arabidopsis (Arabidopsis thaliana) plants in three different lighting regimes (with the same average daily intensity), fluctuating with a fixed pattern of light, fluctuating with a randomized pattern of light (sinusoidal), and nonfluctuating (square wave), to assess the effect of light regime dynamics on gas exchange. We demonstrated that gs (stomatal conductance to water vapor) acclimation is influenced by both intensity and light pattern, modifying the stomatal kinetics at different times of the day and resulting in differences in the rapidity and magnitude of the gs response. We also describe and quantify the response to an internal signal that uncouples variation in A and gs over the majority of the diurnal period and represents 25% of the total diurnal gs This gs response can be characterized by a Gaussian element and when incorporated into the widely used Ball-Berry model greatly improved the prediction of gs in a dynamic environment. From these findings, we conclude that acclimation of gs to growth light could be an important strategy for maintaining carbon fixation and overall plant water status and should be considered when inferring responses in the field from laboratory-based experiments.

Morphological and physiological acclimation of Catalpa bungei plantlets to different light conditions

This study was performed to evaluate the ecophysiological acclimation of Catalpa bungei plantlets to different light conditions. We hypothesized that the acclimation of old and newly developed leaves to both increasing and decreasing irradiance should follow different patterns. The growth, photosynthesis, chlorophyll (Chl) content, and Chl fluorescence response were examined over a range of light treatments. The plants were grown under fixed light intensities of 80% (HH), 50% (MM), 30% (LL) of sun light and transferring irradiance of 80% to 50% (HM), 80% to 30% (HL), 30% to 50% (LM) and 30% to 80% (LH). For old leaves, light-saturation point, photosynthetic capacity, dark respiration rate of LH were lower than that of HH, while HL were higher than LL, indicating that light-response parameters were affected by the original growth light environment. Initial fluorescence increased and variable fluorescence decreased in LH and LM after transfer, and the PSII damage was more serious in LH than that in LM, and could not recover within 30 d. It suggested that the photoinhibition damage and recovery time in old leaves was related to the intensity of light after transfer. For the newly emerged leaves with leaf primordia formed under the same light environment, a significant difference was observed in leaf morphology and pigment contents, suggesting that previous light environment exhibited carry-over effect on the acclimation capacity to a new light environment. Our result showed that thinning and pruning intensity should be considered in plantation management, because great changes in light intensity may cause photoinhibition in shade-adapted leaves.

Evaluation of genotypic variation during leaf development in four Cucumis genotypes and their response to high light conditions

Physiological responses to differences in light intensity were studied in four genotypes of Cucumis with differences in leaf greenness. The four genotypes were C. ×hytivus (synthesized allotetraploid, yellow-green); its parents, C. hystrix (wild Cucumis species, dark green) and BeijingJietou (cultivated cucumber, green); and M1 (a chlorophyll deficient mutant of cultivated cucumber, yellow-green). The plants were subjected to a photosynthetic photon flux density (PPFD) of either 800μmolm−2s−1 or 200μmolm−2s−1 in climate chambers for 20 days. Plant growth, chlorophyll (Chl) content, gas exchange, Chl fluorescence parameters and carbohydrate partitioning in the four genotypes were studied. The four genotypes showed different amounts of Chl accumulation and the genotypic differences led to divergent photosynthetic capabilities, carbohydrate partitioning and photosynthetic responses to high light. The original natural habitat characteristics of the two species may also play an important role in the divergence. Moreover, the ability of the yellow-green M1 to slowly increase the leaf Chl content during leaf development was aligned with a long leaf life span, maintaining high levels of photosynthesis, which was not the case in the yellow-green C.×hytivus. In addition, Fv/Fm is such a sensitive parameter that it should not be evaluated alone for high light stress without the context of the prevailing growth light environment.

Growth irradiance affects ureide accumulation and tolerance to photoinhibition in Eutrema salsugineum (Thellungiella salsuginea)

Plants are able to acclimate to their growth light environments by utilizing a number of short- and long-term mechanisms. One strategy is to prevent accumulation of excess reactive oxygen species that can lead to photoinhibition of photosynthesis. Ureides, generated from purine degradation, have been proposed as antioxidants and involved in certain abiotic stress responses. Eutrema salsugineum (Thellungiella salsuginea) is an extremophilic plant known to exhibit a high degree of tolerance to a variety of abiotic stresses that invariably generate reactive oxygen species. In the present study we have investigated the possible role of the ureide metabolic pathway during acclimation to growth irradiance and its conference of tolerance to photoinhibition in Eutrema. Ureide accumulation was greater under high light growth which also conferred tolerance to photoinhibition at low temperature as measured by the maximal quantum yield of PSII photochemistry. This may represent an adaptive plastic response contributing to the extreme tolerance exhibited by this plant. Our results would provide evidence that ureide accumulation may be involved in abiotic stress as another defence mechanism in response to oxidative stress.

Rate Constants of PSII Photoinhibition and its Repair, and PSII Fluorescence Parameters in Field Plants in Relation to their Growth Light Environments.

The extent of photoinhibition of PSII is determined by a balance between the rate of photodamage to PSII and that of repair of the damaged PSII. It has already been indicated that the rate constants of photodamage (kpi) and repair (krec) of the leaves differ depending on their growth light environment. However, there are no studies using plants in the field. We examined these rate constants and fluorescence parameters of several field-grown plants to determine inter-relationships between these values and the growth environment. The kpi values were strongly related to the excess energy, EY, of the puddle model and non-regulated energy dissipation, Y(NO), of the lake model, both multiplied by the photosynthetically active photon flux density (PPFD) level during the photoinhibitory treatment. In contrast, the krec values corrected against in situ air temperature were very strongly related to the daily PPFD level. The plants from the fields showed higher NPQ than the chamber-grown plants, probably because these field plants acclimated to stronger lightflecks than the averaged growth PPFD. Comparing chamber-grown plants and the field plants, we showed that kpi is determined by the incident light level and the photosynthetic capacities such as in situ rate of PSII electron transport and non-photochemical quenching (NPQ) [e.g. Y(NO)×PPFD] and that krec is mostly determined by the growth light and temperature levels.

Differences in light-harvesting, acclimation to growth-light environment, and leaf structural development between Swedish and Italian ecotypes of Arabidopsis thaliana.

Leaf morphological differences have an impact on light distribution within the leaf, photosynthesis, and photoprotection in Arabidopsis thaliana ecotypes from near the limits of this species' latitudinal distribution in Europe. Leaf morphology, photosynthesis, and photoprotection were characterized in two Arabidopsis ecotypes from near the limits of this species' latitudinal distribution in Europe (63°N and 42°N). The Swedish ecotype formed thicker leaves and upregulated photosynthesis more substantially than the Italian ecotype in high-light environments. Conversely, the smaller rosette formed, and lesser aboveground biomass accumulated, by the Swedish versus the Italian ecotype in low growth-light environments is consistent with a lesser shade tolerance of the Swedish ecotype. The response of the thinner leaves of the Italian ecotype to evenly spaced daily periods of higher light against a background of otherwise non-fluctuating low light was to perform the same rate of photosynthesis with less chlorophyll, rather than exhibiting greater rates of photosynthesis. In contrast, the thicker leaves of the Swedish ecotype showed elevated photosynthetic performance in response to daily supplemental higher light periods in a low-light growth environment. These findings suggest significant self-shading in the lower depths of leaves of the Swedish ecotype by the chloroplasts residing in the upper portions of the leaf, resulting in a requirement for higher incident light to trigger photosynthetic upregulation in the lower portions of its thicker leaves. Conversely, photoprotective responses in the Italian ecotype suggest that more excess light penetrated into the lower depths of this ecotype's leaves. It is speculated that light absorption and the degree of utilization of this absorbed light inform cellular signaling networks that orchestrate leaf structural development, which, in turn, affects light distribution and the level of absorbed versus photosynthetically utilized light in a leaf.

Light-induced plasticity in leaf hydraulics, venation, anatomy, and gas exchange in ecologically diverse Hawaiian lobeliads.

Leaf hydraulic conductance (Kleaf ) quantifies the capacity of a leaf to transport liquid water and is a major constraint on light-saturated stomatal conductance (gs ) and photosynthetic rate (Amax ). Few studies have tested the plasticity of Kleaf and anatomy across growth light environments. These provided conflicting results. The Hawaiian lobeliads are an excellent system to examine plasticity, given the striking diversity in the light regimes they occupy, and their correspondingly wide range of Amax , allowing maximal carbon gain for success in given environments. We measured Kleaf , Amax , gs and leaf anatomical and structural traits, focusing on six species of lobeliads grown in a common garden under two irradiances (300/800μmolphotonsm(-2) s(-1) ). We tested hypotheses for light-induced plasticity in each trait based on expectations from optimality. Kleaf , Amax , and gs differed strongly among species. Sun/shade plasticity was observed in Kleaf , Amax, and numerous traits relating to lamina and xylem anatomy, venation, and composition, but gs was not plastic with growth irradiance. Species native to higher irradiance showed greater hydraulic plasticity. Our results demonstrate that a wide set of leaf hydraulic, stomatal, photosynthetic, anatomical, and structural traits tend to shift together during plasticity and adaptation to diverse light regimes, optimizing performance from low to high irradiance.

A Study on Crop Growth Environment Control System

The concept of Plant factory could realize the multiple targets of high yield, high quality, high efficiency and security. It had become the trend of agricultural development. It solved the growing contradiction between people's increasing demand for green, organic food and the diminishing agricultural arable area in China. According to the research on the key technologies of plant factory, a small simulated environment for crop growth (i.e., a growth cabinet) was designed. The growth cabinet used the light-emitting diode (LED) light source as crop growth light and simulated ecological environment artificially based on the requirement of crop growth and development. The crop can obtain suitable environmental conditions for growth and development in anti-season and non-suitable environmental conditions by using the sensor and embedded technology. The results of experiments showed that the crop growth cabinet’s structure design was reasonable and had the advantages such as reliable performance, low-carbon, intelligence and security.

Increased nutritional quality of plants for long-duration spaceflight missions through choice of plant variety and manipulation of growth conditions

Low levels of radiation during spaceflight increase the incidence of eye damage and consumption of certain carotenoids (especially zeaxanthin), via a whole-food-based diet (rather than from supplements), is recommended to protect human vision against radiation damage. Availability of fresh leafy produce has, furthermore, been identified as desirable for morale during long spaceflight missions. We report that only trace amounts of zeaxanthin are retained post-harvest in leaves grown under conditions conducive to rapid plant growth. We show that growth of plants under cool temperatures and very high light can trigger a greater retention of zeaxanthin, while, however, simultaneously retarding plant growth. We here introduce a novel growth condition—low growth light supplemented with several short daily light pulses of higher intensity—that also triggers zeaxanthin retention, but without causing any growth retardation. Moreover, two plant varieties with different hardiness exhibited a different propensity for zeaxanthin retention. These findings demonstrate that growth light environment and plant variety can be exploited to simultaneously optimize nutritional quality (with respect to zeaxanthin and two other carotenoids important for human vision, lutein and β-carotene) as well as biomass production of leafy greens suitable as bioregenerative systems for long-duration manned spaceflight missions.

Modeling the environmental response of leaf net photosynthesis in Pinus pinea L. natural regeneration

Environmental factors as incident light, temperature and soil water content mainly determine the dynamics of growth and survival of natural forest regeneration in Mediterranean forests. The complex interactions among these factors highlight the need for physiology-based models which describe seedling and sapling performance under current and changing climatic conditions. These models should be flexible enough to take into account the effect of growth light environment changes on physiological processes and, therefore, to assist in the decision-making process on different silvicultural management alternatives under climatic uncertainty. In the present work the net photosynthesic rate of Pinus pinea L. natural regeneration is modeled as a function of light irradiance using the non-rectangular hyperbola function. The model fit was carried out following a two-step procedure, where the parameters of the original function were expanded over the most influential factors: leaf temperature, soil moisture, global site factor and needle type. The developed model allows defining the optimal niche conditions for the natural regeneration of the species and permits identifying the most limiting conditions which prevent natural regeneration. Regeneration niche was assessed by using the model to simulate net CO2 assimilation of a seedling over twelve contrasting light environments during both a normal and an extremely dry vegetative period. The model predicts that the most favorable carbon balance would be found in mid-shaded expositions, while fully exposed plants at midday during summer would exhibit longer periods of negative assimilation rates, especially on severe dry years.

Recovery kinetics of photochemical efficiency in winter stressed conifers: the effects of growth light environment, extent of the season and species

Evergreens undergo reductions in maximal photochemical efficiency (F(v)/F(m)) during winter due to increases in sustained thermal energy dissipation. Upon removing winter stressed leaves to room temperature and low light, F(v)/F(m) recovers and can include both a rapid and a slow phase. The goal of this study was to determine whether the rapid component to recovery exists in winter stressed conifers at any point during the season in a seasonally extreme environment. Additional goals were to compare the effects of species, growth light environment and the extent of the winter season on recovery kinetics in conifers. Four species (sun and shade needle) were monitored during the winter of 2007/2008: eastern white pine (Pinus strobus), balsam fir (Abies balsamea), Taxus cuspidata and white spruce (Picea glauca). F(v)/F(m) was measured in the field, and then monitored indoors at room temperature and low light for 6 days. The results showed that all species showed a rapid component to recovery in early winter that disappeared later in the season in sun needles but was present in shade needles on most days monitored during winter. There were differences among species in the recovery kinetics across the season, with pine recovering the most slowly and spruce the most quickly. The results suggest an important role for the rapidly reversible form of energy dissipation in early winter, as well as important differences between species in their rate of recovery in late winter/early spring which may have implications for spring onset of photosynthesis.

Effects of flooding and shading on growth and gas exchange of Vochysia divergens Pohl (Vochysiaceae) of invasive species in the Brazilian Pantanal

Vochysia divergens Pohl (commonly known as cambara) is a pioneer tree species that is native to the Amazon Basin but has been invading the seasonally flooded wetlands of the Brazilian Pantanal, forming monospecific communities. The physiological aspects associated with cambara invasion, including the effects of flooding and shading on growth and leaf gas exchange, are unknown but may shed light on why cambara is able to invade this novel habitat so rapidly. Thus, we conducted a manipulative experiment to quantify the effects of shading and flooding on the growth, gas exchange and leaf nutrient content of V. divergens saplings. Based on previous research we hypothesized that (1) experimental flooding would have no effect on the growth and gas exchange of V. divergens,and (2) experimental shading would reduce the growth and gas exchange of V. divergens regardless of the water treatment plants are subjected. Our data indicate that shading significantly increased the height, stomatal conductance (gs), and transpiration (T) of V. divergens saplings, especially for plants exposed to normal irrigation. Experimental flooding significantly reduced rates of leaf production, plant height, and gas exchange; however, shaded plants exposed to flooding had a higher water use efficiency than plants exposed to full sun and flooding, because Twas more depressed than net photosynthesis (A) in flooded plants exposed to full sun. Despite the inhibitory effects of flooding and shading, V. divergenssaplings exhibited positive growth and C gain, regardless of the growth light environment or water level, indicating that the growth and leaf gas exchange of species is tolerant to both flooding and shading. Such tolerance to a wide variety of hydrological and growth light conditions presumably explains the ability of cambara to invade, and ultimately form dense, monospecific stands in the Brazilian Pantanal.

Photosynthesis-Dependent and -Independent Responses of Stomata to Blue, Red and Green Monochromatic Light: Differences Between the Normally Oriented and Inverted Leaves of Sunflower

The effects of growth light environment on stomatal light responses were analyzed. We inverted leaves of sunflower (Helianthus annuus) for 2 weeks until their full expansion, and measured gas exchange properties of the adaxial and abaxial sides separately. The sensitivity to light assessed as the increase in stomatal conductance was generally higher in the abaxial stomata than in the adaxial stomata, and these differences could not be completely changed by the inversion treatment. We also treated the leaves with DCMU to inhibit photosynthesis and evaluated the photosynthesis-dependent and -independent components of stomatal light responses. The red light response of stomata in both normally oriented and inverted leaves relied only on the photosynthesis-dependent component. The blue light response involved both the photosynthesis-dependent and photosynthesis-independent components, and the relative contributions of the two components differed between the normally oriented and inverted leaves. A green light response was observed only in the abaxial stomata, which also involved the photosynthesis-dependent and photosynthesis-independent components, strongly suggesting the existence of a green light receptor in sunflower leaves. Moreover, acclimation of the abaxial stomata to strong direct light eliminated the photosynthesis-independent component in the green light response. The results showed that stomatal responses to monochromatic light change considerably in response to growth light environment, although some of these responses appear to be determined inherently.

Recovery kinetics of winter stressed conifers: The effects of growth light environment, extent of the season, and species.

AbstractEvergreens undergo a dramatic reduction in their maximal photochemical efficiency (measured as Fv/Fm) during winter, which is largely due to increases in a sustained form of thermal energy dissipation. Upon removing winter-stressed leaves to room temperature and low light, Fv/Fm recovers over several days and can include both a rapid phase (reversing in minutes) and a slow phase (reversing over days). Both phases are associated with reversal of sustained energy dissipation. Preliminary examination of recovery of evergreens monitored in January in Minnesota showed an absence of the rapid component to recovery. Our goal was to monitor recovery kinetics of sun and shade evergreens in Minnesota throughout winter in order to assess whether the rapid phase of recovery exists early in the winter and converts to the slowly reversible form as winter progresses. Four species of conifers (sun and shade needles) were monitored during the winter of 2007/08: eastern white pine (_Pinus strobus_ L.), balsam fir [Abies balsamea (L.) P. Mill], Taxus cuspidata (L.) and blue spruce (Picea pungens Engelm.). Fv/Fm was measured on dark acclimated needles in the field, twigs were collected, brought indoors and maintained at room temperature and low light where Fv/Fm was monitored for six days.The results demonstrated that all species, and both sun and shade needles, showed a rapidly reversible component to recovery in early winter (November). In the sun needles this component was rarely present later in the season, while in the shade needles it was present (although only a small fraction of the total sustained energy dissipation) on most days monitored during winter. The slowly reversible component to sustained energy dissipation was present in both sun and shade needles of all species beginning in November. In all cases, shade needles recovered significantly faster than sun needles. There was a significant slowing of recovery (the slowly reversible component) as winter progressed in both sun and shade needles, and significant differences between species in their recovery response. The results indicate a relatively small contribution of the rapidly reversible component of sustained energy dissipation compared with earlier studies on evergreens growing in the milder winter conditions of Colorado. The results also provide evidence that the rapid component to recovery diminishes as the season progresses, particularly in needles growing in full sun where the slowly reversible component of sustained energy dissipation accounts for most or all of the observed sustained energy dissipation.