Potential Photosynthetic Capacity Research Articles

Leaf and stand-level carbon uptake of a Mediterranean forest estimated using the satellite-derived reflectance indices EVI and PRI

Various aspects of global environmental change affect plant photosynthesis, the primary carbon input in ecosystems. Thus, accurate methods of measuring plant photosynthesis are important. Remotely sensed spectral indices can monitor in detail the green biomass of ecosystems, which provides a measure of potential photosynthetic capacity. In evergreen vegetation types, however, such as Mediterranean forests, the amount of green biomass changes little during the growing season and, therefore, changes in green biomass are not responsible for changes in photosynthetic rates in those forests. This study examined the net photosynthetic rates and the diametric increment of stems in a Mediterranean forest dominated by Quercus ilex using three spectral indices (normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and photochemical reflectance index (PRI)) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. Average annual EVI accounted for 83% of the variability of the diametric increment of Q. ilex stems over a 10 year period. NDVI was marginally correlated with the diametric increment of stems. This study was the first to identify a significant correlation between net photosynthetic rates and radiation use efficiency at the leaf level using PRI derived from satellite data analysed at the ecosystem level. These results suggest that each spectral index provided different and complementary information about ecosystem carbon uptake in a Mediterranean Q. ilex forest.

Assessing the use of camera-based indices for characterizing canopy phenology in relation to gross primary production in a deciduous broad-leaved and an evergreen coniferous forest in Japan

Recent studies have reported that seasonal variation in camera-based indices that are calculated from the digital numbers of the red, green, and blue bands (RGB_DN) recorded by digital cameras agrees well with the seasonal change in gross primary production (GPP) observed by tower flux measurements. These findings suggest that it may be possible to use camera-based indices to estimate the temporal and spatial distributions of photosynthetic productivity from the relationship between RGB_DN and GPP. To examine this possibility, we need to investigate the characteristics of seasonal variation in three camera-based indices (green excess index [GE], green chromatic coordinate [rG], and HUE) and the robustness of the relationship between these indices and tower flux-based GPP and how it differs among ecosystems. Here, at a daily time step over multiple years in a deciduous broad-leaved and an evergreen coniferous forest, we examined the relationships between canopy phenology assessed by using the three indices and GPP determined from tower CO2 flux observations, and we compared the camera-based indices with the corresponding spectra-based indices estimated by a spectroradiometer system. We found that (1) the three camera-based indices and GPP showed clear seasonal patterns in both forests; (2) the amplitude of the seasonal variation in the three camera-based indices was smaller in the evergreen coniferous forest than in the deciduous broad-leaved forest; (3) the seasonal variation in the three camera-based indices corresponded well to seasonal changes in potential photosynthetic activity (GPP on sunny days); (4) the relationship between the three camera-based indices and GPP appeared to have different characteristics at different phenological stages; and (5) the camera-based and spectra-based HUE indices showed a clear relationship under sunny conditions in both forests. Our results suggest that it might be feasible for ecologists to establish comprehensive networks for long-term monitoring of potential photosynthetic capacity from regional to global scales by linking satellite-based, in situ spectra-based, and in situ camera-based indices.

不同产地披针叶茴香光合特性对水分胁迫和复水的响应

Low availability of soil moisture is considered a major limiting factor for plant growth and crop yield worldwide,and global change will likely aggravate water shortage and make water availability an even greater limitation to plant productivity across an increasing amount of land.The Chinese anise(Illicium lanceolatum),a traditional medicinal plant in China,has high content of shikimic acids which have effects of antiphlogosis and analgesis,and can reduce platelet aggregation and suppress vascular and cerebral thrombosis.Shikimic acid can also be an intermediate for antivirus and anticancer drugs.Scattering in its natural habitats,I.lanceolatum resources have experienced a rapid decline due to overexploitation.Therefore,it is necessary to study the protection and development strategies of I.lanceolatum resources.Until now,there is no study on the mechanism of this species responds to water and light conditions.In this paper,we reported the effects of drought stress on photosynthesis of varied ecotypes of Illicium lanceolatum.One year old potted seedlings of four ecotypes,respectively ecotypes from Linan Zhejiang(LA),Kaihua Zhejiang(KH),Wuning Jiangxi(WN) and Nanping Fujian(NP),were treated with different level of drought stress and their photosynthetic parameters were measured.The results showed that photosynthetic parameters differed significantly between the ecotypes during the drought stress and the recovery period.As the drought stress progressed,the light saturation points(LSP) and the light compensation point(LCP) declined for the four ecotypes.The maximum photosynthetic rate(Pmax) increased initially and decreased rapidly later during the drought treatment period,however the relative changes in Pmax induced by water stress differed from each other among the four ecotypes.The apparent photon quantum yield(AQY) increased as drought stress progressed.Significant differences in LSP,LCP,AQY and Pmax,were found before and after water stress was released,but the margin of the difference was affected by the ecotypes.After rewatering,the LSPs of WN,KH and LA ecotypes increased,the LCP recovered rapidly,and AQY also remained at a high level.The Pmax increased for KH and WN ecotypes,but decreased for LA and NP ecotypes after the water stress was released,implying a difference in the sensitivity to light intensity and water stress among the four ecotypes.The WN ecotype seedlings grew well in a wide range of light intensity and water conditions,presenting a good adaptability to various changing environments.NP ecotype was another one with higher adaptability to light and water stress.The KH and LA ecotypes from Zhejiang province exhibited stricter requirements for soil moisture content.The ecotypic differences existed in rates of recovery of photosynthesis during drought stress.Photosynthesis rate under drought stress was rapidly recovered until one day after re-watering only for WN ecotypes.The photosynthetic response curve also changed in response to drought stress.The light response of net photosynthetic rate(Pn) was affected by soil water content under low light intensity(≤200 μmol · m-2 · s-1).However,the negative effect of light intensity exceeded that of water stress as the light intensified.Studies revealed synergistic effects of water stress and light intensity on the potential photosynthetic capacity of I.lanceolatum.The growth of I.lanceolatum requires an environment with adequate soil moisture as well as suitable light intensity.When soil water condition becomes poor,the light intensity should be reduced by shading or other measures,thus to reduce the negative impacts on plant growth.This study showed that the interaction of genetic background(ecotypes) and environmental factors(drought and light intensity) should be taken into consideration when introducing the plant species to different climate conditions,and developing water management shading strategy for high-efficiency intensive culture.

Effect of water stress on leaf photosynthesis, chlorophyll content, and growth of oriental lily

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P n), stomatal conductance (g s), intercellular CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P max) and dark respiration rates (R D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P n, E, g s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P n)-PAR response curve. Drought stress increased LCP and R D and decreased LSP and P max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.

Responses of photosynthetic capacity to soil moisture gradient in perennial rhizome grass and perennial bunchgrass.

BackgroundChanging water condition represents a dramatic impact on global terrestrial ecosystem productivity, mainly by limiting plant functions, including growth and photosynthesis, particularly in arid and semiarid areas. However, responses of the potential photosynthetic capacity to soil water status in a wide range of soil moisture levels, and determination of their thresholds are poorly understood. This study examined the response patterns of plant photosynthetic capacity and their thresholds to a soil moisture gradient in a perennial rhizome grass, Leymus chinensis, and a perennial bunchgrass, Stipa grandis, both dominant in the Eurasian Steppe.ResultsSevere water deficit produced negative effects on light-saturated net CO2 assimilation rate (Asat), stomatal conductance (gs), mesophyll conductance (gm), maximum carboxylation velocity (Vc,max), and maximal efficiency of PSII photochemistry (Fv/Fm). Photosynthetic activity was enhanced under moderate soil moisture with reductions under both severe water deficit and excessive water conditions, which may represent the response patterns of plant growth and photosynthetic capacity to the soil water gradient. Our results also showed that S. grandis had lower productivity and photosynthetic potentials under moderate water status, although it demonstrated generally similar relationship patterns between photosynthetic potentials and water status relative to L. chinensis.ConclusionsThe experiments tested and confirmed the hypothesis that responsive threshold points appear when plants are exposed to a broad water status range, with different responses between the two key species. It is suggested that vegetation structure and function may be shifted when a turning point of soil moisture occurs, which translates to terms of future climatic change prediction in semiarid grasslands.

Photosynthetic, biochemical, and ultra-structural changes in the chloroplasts of two ginkgo (Ginkgo biloba L.) cultivars during leaf development

SummaryChanges in chlorophyll fluorescence, leaf biochemistry, and ultra-structure were studied in 10-year-old female ginkgo trees (Ginkgo biloba L.) cvs. Dafozhi and Qixingguo, from April to October in Jiangdu, Jiangsu Province, P. R. China. The maximum quantum efficiency (Fv / Fm)of PS II and the potential photosynthetic capacity (Fv / Fo) of PS II peaked in June and July, then declined. Changes in the concentrations of chlorophyll a and total chlorophyll followed these patterns, whereas changes in the concentrations of chlorophyll b andtotal carotenoids were less dramatic or had no clear trend. Changes in electron transport activities (PS II, PS I, and the whole chain) followed the same pattern as total chlorophyll content, with increases up until June, then a decline. Changes in the biochemistry of photosynthesis were associated with changes in the ultra-structure of the chloroplasts. Initially, the chloroplasts had tightly-stacked thylakoids with distinctive starch grains. However, as the leaves senesced, the chloroplast membranes began to degrade, the thylakoids became disorganised, and there was a large increase in the number of osmiophilic granules. Overall, there were only small differences in chlorophyll fluorescence and leaf biochemistry between the two cultivars. These results show that ginkgo leaves reached their full photosynthetic capacity in June, when they were fully expanded. Photosynthetic capacity declined as the leaves began to senesce in September, with the decline possibly being accelerated by lower temperatures and water deficits at this time of year. Senescence may be the result of active adaptation by leaves to changes in the external environment.

Changes of photosynthetic activities of maize (Zea mays L.) seedlings in response to cadmium stress

Maize (Zea mays L.) seedlings were grown in nutrient solution culture containing 0, 5, and 20 μM cadmium (Cd) and the effects on various aspects of photosynthesis were investigated after 24, 48, 96 and 168 h of Cd treatments. Photosynthetic rate (P N) decreased after 48 h of 20 μM Cd and 96 h of 5μM Cd addition, respectively. Chl a and total Chl content in leaves declined under 48 h of Cd exposure. Chl b content decreased on extending the period of Cd exposure to 96 h. The maximum quantum efficiency and potential photosynthetic capacity of PSII, indicated by Fv/Fm and Fv/Fo, respectively, were depressed after 96 h onset of Cd exposure. After 48 h of 5μM Cd and 24 h of 20 μM Cd treatments, the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.39) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in the leaves started to decrease, respectively. We found that the limitation of photosynthetic capacity in Cd stressed maize leaves was associated with Cd toxicity on the light and the dark stages. However, Cd stress initially reduced the activities of Rubisco and PEPC and subsequently affected the PSII electron transfer, suggesting that the Calvin cycle reactions in maize plants are the primary target of the Cd toxic effect rather than PSII.

Constraints on physiological function associated with branch architecture and wood density in tropical forest trees

This study examined how leaf and stem functional traits related to gas exchange and water balance scale with two potential proxies for tree hydraulic architecture: the leaf area:sapwood area ratio (A(L):A(S)) and wood density (rho(w)). We studied the upper crowns of individuals of 15 tropical forest tree species at two sites in Panama with contrasting moisture regimes and forest types. Transpiration and maximum photosynthetic electron transport rate (ETR(max)) per unit leaf area declined sharply with increasing A(L):A(S), as did the ratio of ETR(max) to leaf N content, an index of photosynthetic nitrogen-use efficiency. Midday leaf water potential, bulk leaf osmotic potential at zero turgor, branch xylem specific conductivity, leaf-specific conductivity and stem and leaf capacitance all declined with increasing rho(w). At the branch scale, A(L):A(S) and total leaf N content per unit sapwood area increased with rho(w), resulting in a 30% increase in ETR(max) per unit sapwood area with a doubling of rho(w). These compensatory adjustments in A(L):A(S), N allocation and potential photosynthetic capacity at the branch level were insufficient to completely offset the increased carbon costs of producing denser wood, and exacerbated the negative impact of increasing rho(w) on branch hydraulics and leaf water status. The suite of tree functional and architectural traits studied appeared to be constrained by the hydraulic and mechanical consequences of variation in rho(w).

Effect of Methanol on Photosynthesis and Chlorophyll Fluorescence of Flag Leaves of Winter Wheat

Photosynthesis and chlorophyll a fluorescence parameters, photochemical efficiency of PS II (Fv/Fm), photochemical quenching of PS II (qP), nonphotochemical quenching of PS II (NPQ), maximum activity of PS II (Fv/Fo) as well as electron transport rate (ETR), and quantum yield of PS II (ΨPS II) were measured on flag leaves of the winter wheat treated by methanol at different concentrations. The results revealed that photosynthesis was greatly improved by methanol, as indicated by higher photosynthetic rates and stomatal conductance. The enhancement effect of methanol on photosynthesis was maintained for 3–4 days. Different methanol concentration treatments also increased intercellular CO2 concentration and transpiration rates. No significant decline was found in Fv/Fm, Fv/Fo, and ΨPS II, which revealed no photoinhibition during methanol application in different methanol concentrations. Methanol showing no apparent inhibitory effects indicated higher potential photosynthetic capacity of flag leaves of winter wheat. However, the increase in photosynthesis was not followed by an increase in the photosynthetic activity (Fv/Fm), and fluorescence parameters did not indicate an improvement in intercellular CO2 concentration and PS II photochemical efficiency compared with the control, thereby encouraging us to propose that lower leaf temperatures caused by applied methanol would reduce both dark respiration and photorespiration (most importantly), thus, increasing net CO2 uptake and photosynthetic rates.

Growth yield of Vicia faba L in response to microbial symbiotic associations

A multifactor experiment was undertaken to investigate the influence of Rhizobium and arbuscular mycorrhizal fungi (AMF) on biomass production, leaf area generation, whole plant photosynthetic and respiration rates, growth yield and maintenance respiration in Vicia faba L under low phosphorus (P) supply. Treatments consisted of low (LN) or high nitrogen (HN) supply with or without microbial symbiont(s). Plants were harvested at 54 (T 1) and 63 (T 2) days after planting. In all instances, plants colonized with both microbial symbionts had significantly higher total biomasses, leaf areas, whole plant photosynthesis and respiration rates than plants with only one or no microbial symbionts. Similarly, plants with both microbial symbionts also had significantly higher (≥ 0.7) growth yield ( Y g) values than all the other treatments. There were no significant differences in Y g values between harvest intervals within individual treatments. Maintenance respiration rates were also highest in plants with two microbial symbionts (> 30 CO 2 (g DM) − 1 d − 1 ). In LN plants colonized by both microbial symbionts there was evidence of compensatory increases in the photosynthetic rates in response to the carbon sink demands of the microbial symbionts. Finally, the results of this investigation are consistent with the hypothesis that the plant potential photosynthetic capacity exceeds the carbon demand of the Rhizobium–AMF symbiotic complex.

Toward Synthesis of Relationships among Leaf Longevity, Instantaneous Photosynthetic Rate, Lifetime Leaf Carbon Gain, and the Gross Primary Production of Forests

The assimilation of carbon by plant communities (gross primary production [GPP]) is a central concern in plant ecology as well as for our understanding of global climate change. As an alternative to traditional methods involving destructive harvests or time-consuming measurements, we present a simple, general model for GPP as the product of the lifetime carbon gain by a single leaf, the daily leaf production rate, and the length of the favorable period for photosynthesis. To test the model, we estimated leaf lifetime carbon gain for 26 species using the concept of mean labor time for leaves (the part of each day the leaf functions to full capacity), average potential photosynthetic capacity over the leaf lifetime, and functional leaf longevity (leaf longevity discounted for periods within a year wholly unfavorable for photosynthesis). We found that the lifetime carbon gain of leaves was rather constant across species. Moreover, when foliar biomass was regressed against functional leaf longevity, aseasonal and seasonal forests fell on a single line, suggesting that the leaf production rate during favorable periods is not substantially different among forests in the world. The gross production of forest ecosystems then can be predicted to a first approximation simply by the annual duration of the period favorable for photosynthetic activity in any given region.

Apparent carboxylation efficiency and relative stomatal and mesophyll limitations of photosynthesis in an evergreen cerrado species during water stress

Miconia albicans, a common evergreen cerrado species, was studied under field conditions. Leaf gas exchange and pre-dawn leaf water potential (Ψpd) were determined during wet and dry seasons. The potential photosynthetic capacity (PNpmax) and the apparent carboxylation efficiency (e) dropped in the dry season to 28.0 and 0.7 %, respectively, of the maximum values in the wet season. The relative mesophyll (Lm) and stomatal (Ls) limitations of photosynthesis increased, respectively, from 24 and 44 % in the wet season to 79 and 57 % at the peak of the dry season when mean Ψpd reached −5.2 MPa. After first rains, the PNpmax, e, and Lm recovered reaching the wet season values, but Ls was maintained high (63 %). The shallow root system growing on stonemason limited by lateral concrete wall to a depth of 0.33 m explained why extreme Ψpd was brought about. Thus M. albicans is able to overcome quickly the strains imposed by severe water stress.

Toward Synthesis of Relationships among Leaf Longevity, Instantaneous Photosynthetic Rate, Lifetime Leaf Carbon Gain, and the Gross Primary Production of Forests

The assimilation of carbon by plant communities (gross primary production [GPP]) is a central concern in plant ecology as well as for our understanding of global climate change. As an alternative to traditional methods involving destructive harvests or time‐consuming measurements, we present a simple, general model for GPP as the product of the lifetime carbon gain by a single leaf, the daily leaf production rate, and the length of the favorable period for photosynthesis. To test the model, we estimated leaf lifetime carbon gain for 26 species using the concept of mean labor time for leaves (the part of each day the leaf functions to full capacity), average potential photosynthetic capacity over the leaf lifetime, and functional leaf longevity (leaf longevity discounted for periods within a year wholly unfavorable for photosynthesis). We found that the lifetime carbon gain of leaves was rather constant across species. Moreover, when foliar biomass was regressed against functional leaf longevity, aseasonal and seasonal forests fell on a single line, suggesting that the leaf production rate during favorable periods is not substantially different among forests in the world. The gross production of forest ecosystems then can be predicted to a first approximation simply by the annual duration of the period favorable for photosynthetic activity in any given region.

Heat and Drought Influence Photosynthesis, Water Relations, and Soluble Carbohydrates of Two Ecotypes of Redbud (Cercis canadensis)

Net photosynthesis (Pn) of two ecotypes of redbud (Cercis canadensis L.) was studied following growth under high temperatures and increasing drought. Although mexican redbud [C. canadensis var. mexicana (Rose) M. Hopkins] exhibited greater Pn than eastern redbud (C. canadensis var. canadensis L.), Pn decreased at a similar rate under water deficit stress for both ecotypes. Mexican redbud also had greater instantaneous water use efficiency [net photosynthesis: transpiration (WUE)] than eastern redbud. Differences in both Pn and WUE might have been due to differences in leaf thickness. The optimum temperature for potential photosynthetic capacity (37 °C) was unaffected by irrigation or ecotype. Tissue osmotic potential at full turgor was more negative in eastern redbud, but was unaffected by drought stress in either ecotype. Soluble carbohydrate content was higher in eastern redbud, and in both ecotypes, d-pinitol was the major soluble carbohydrate and was considerably more abundant in the water-stressed plants. Total polyol content (myo-inositol + ononitol + pinitol) was also greater in the water-stressed plants. Both ecotypes were very tolerant of high temperatures and drought.

Photosynthesis, Chlorophyll Fluorescence, and Carbohydrate Content of Illicium Taxa Grown under Varied Irradiance

Tolerance to high solar irradiation is an important aspect of stress tolerance for landscape plants, particularly for species native to understory conditions. The objective of this study was to evaluate differential tolerance to high solar irradiation and underlying photosynthetic characteristics of diverse taxa of Illicium L. grown under full sun or 50% shade. Eleven commercially available taxa of Illicium were evaluated for light tolerance by measuring light-saturated photosynthetic capacity (Amax), dark-adapted quantum efficiency of photosystem II (Fv/Fm), and relative chlorophyll content using a SPAD chlorophyll meter. Comparisons of Amax indicated that three of the 11 taxa (I. anisatum L., I. parviflorum Michx. ex Vent., and I. parviflorum `Forest Green') maintained similar rates of light-saturated carbon assimilation when grown in either shade or full sun. All other taxa experienced a significant reduction in Amax when grown in full sun. Chlorophyll fluorescence analysis demonstrated that Fv/Fm was similar between sun and shade plants for the same three taxa that were able to maintain Amax. These taxa appeared to experience less photoinhibition than the others and maintained greater maximum photochemical efficiency of absorbed light. SPAD readings were not significantly reduced in these three taxa either, whereas most other taxa experienced a significant reduction. In fact, SPAD readings were significantly higher in I. parviflorum `Forest Green' when grown under full sun, which also maintained the highest Amax of all the taxa. These results suggest that there is considerable variation in light tolerance among these taxa, with I. parviflorum `Forest Green' demonstrating superior tolerance to high light among the plants compared. A more rigorous examination of I. parviflorum `Forest Green' (high light tolerance) and I. floridanum Ellis (low-light tolerance) demonstrated that I. parviflorum `Forest Green' had a considerably higher Amax, a higher light saturation point, greater potential photosynthetic capacity, reduced susceptibility to photoinhibition as indicated by superior PSII efficiency following light exposure, greater capacity for thermal de-excitation as indicated by a higher rate of nonphotochemical quenching (NPQ) under full sun, greater apparent electron transport rate (ETR) at mid-day, and higher concentrations of the free-radical scavenger myo-inositol. All of these factors contribute potentially to a greater capacity to use light energy for carbon fixation while minimizing photodamage.

Studies on Photosynthetic Characteristics and Adaption to Environment of Some Alpine plants in Qinghai-Xizang Plateau

Mainly the alpine plants in Qinghai?Xizang plateau including Salix gilashanica, Salix pilosomicrophylla, Rhododendron coriaceum, Rhododendron faucium, Rhododendron nivale, Quercus aquifolioides were compared with the same genera, non-alpine plants including Salix babyleuica, Salix matsudana, Rhododendron maoronulatum, Quercus liaotangensis for studying their photosynthetic characteristics and photosynthetic adaptability to high mountain environment. The results showed that chlorophyll content of the leaves and chloroplasts tended to be lower in alpine plants than in non-alpine, but the chlorophyll a to b ratio and the carotenoid relative content were higher in alpine plants than non-alpine plants. The decreased trends of Fv/Fm and Fv/Fo (parameter of kinetics of Chl a fluorescence induction) of detached leaves indicated that the potential photosynthetic capacity of alpine plants did not be higher than those non-alpine plants. But that the PSI/PSII ratio was low and related content of PSII in the chloroplasts was high from alpine plant as indicated by fluorescence spectra. Separation and quantification of the various carotenoids was completed by the high performance liquid chromatography. The results show that the chloroplast of S. gilashanica and Q. aquifolioides contained greater amounts of the components of the xanthophyll cycle than the same genera, non-alpine plants S. matsudana and Q. liaotangensis. But the content of the components of the xanthophyll cycle in the chloroplast of R. coriacenm and R. nivale were lower than the same genera non-alpine plants R. macronulatum. The results showed the xanthophyll cycle may be very important in adaptation of the partial alpine plants to high light radiation.

Foliar Heat Tolerance of Three Holly Species (Ilex spp.): Responses of Chlorophyll Fluorescence and Leaf Gas Exchange to Supraoptimal Leaf Temperatures

Temperature sensitivity of CO2 assimilation (ACO2), dark respiration, and chlorophyll fluorescence was evaluated among three taxa of hollies including I. aquifolium L., I. cornuta Lindl. & Paxt., and I. rugosa Friedr. Schmidt. Variations in foliar heat tolerance among these species were manifested in temperature responses for ACO2. Temperature optima of ACO2 for I. rugosa, I. cornuta, and I. aquifolium were 22.0, 26.3, and 27.9 °C, respectively (LSD0.05 = 2.9). Temperature responses of respiration were similar among taxa and did not appear to be contributing factors to variations in ACO2. At 40 °C, potential photosynthetic capacity, measured under saturating CO2, was 4.1, 9.4, and 14.8 μmol·m-2·s-1 for I. rugosa, I. aquifolium, and I. cornuta, respectively (LSD0.05 = 5.1). Variations in the relative dark-acclimated fluorescence temperature curves were used to assess thresholds for irreversible heat injury. The critical fluorescence temperature threshold (TC) was similar (48.0 °C) for all taxa. The fluorescence temperature peaks (TP) were 52.0, 52.8, and 53.5 °C for I. rugosa, I. cornuta, and I. aquifolium, respectively (LSD0.05 = 0.9). Based on these results, I. rugosa was the most heat-sensitive species, followed by I. aquifolium and I. cornuta. Ilex cornuta also had substantially greater potential photosynthetic capacity than the other species at 40 °C, indicating superior metabolic tolerance to high temperatures.

Evaluation of Heat and Flood Tolerance among Diverse Taxa of Hollies (Ilex)

Temperature sensitivity of net photosynthesis (PSN), dark respiration, and chlorophyll fluorescence was evaluated among three taxa of hollies including I. aquifolium, I. cornuta, and I. rugosa. Variations in foliar heat tolerance among these species were expressed as differential temperature responses for PSN. Temperature optima for PSN was 22.0, 26.3 and 27.9 umol·m–2·s–1 for I. rugosa, I. cornuta, and I. aquifolium, respectively. Differences in temperature optima for PSN and thermotolerance of PSN appeared to result from a combination of stomatal and nonstomatal limitations. At 40°C, potential photosynthetic capacity, measured under saturating CO2, was 4.1, 9.4, and 14.8 μmol·m–2·s–1 for I. rugosa, I. aquifolium, and I. cornuta, respectively. Based on these results, I. rugosa was identified as the most heat-sensitive species followed by I. aquifolium then I. cornuta. Comparative tolerance to root-zone inundation was evaluated among 14 holly taxa. Following 8 weeks of flooding, four of the taxa: I. cornuta `Burfordii', I. × `Nellie R. Stevens', I. cassine, and I. × attenuata `Foster's #2' performed remarkably well during and after flooding with photosynthetic rates > 40% of the controls, root ratings >75% of the controls, <5% of the foliage showing deterioration, and 100% survival. Conversely, I. crenata `Convexa', Ilex × meserveae `Blue Princess', I. rugosa and I. aquifolium `Sparkler' did not tolerate flooding well as indicated by severely depressed photosynthetic rates, deterioration of foliage and roots, and decreased survival. The remaining taxa were intermediate.0

Investigations on the photosynthetic system of spruce affected by forest decline and ozone fumigation in closed chambers

Investigations using chlorophyll fluorescence induction kinetics provide the parameters R fd , L and A p to characterize different specifications of the photosynthetic system (PS). The application of ozone, with concentrations between 100 μg m −3 and 2000 μg m −3 to spruce in closed chambers yields a reduction of R fd between 6% and 23% for the current year's needles, which indicates a reduced potential photosynthetic capacity. Further measurements on the current year's needles of spruce of the damage classes SO/S1, S2 and S3 show also a reduction of R fd of between 7% and 14% in 2 successive years. In addition, the parameter L increases for damaged trees by between 11% and 49%, indicating a change of the chlorophyll content and of the internal energy distribution between PSI and PSII. As no effect of L can be observed with ozone fumigation, it is concluded that the change of some specifications of the PS can be simulated well by ozone fumigation (e.g. R fd ) while other specifications cannot (e.g. L).

The Potential Role of Rime Ice Defoliation in Tree Mortality of Wave- Regenerated Balsam Fir Forests

(1) Overstorey mortality occurs rapidly and synchronously within the dieback zones of subalpine, wave-regenerated balsam fir (Abies balsamea (L.) Mill.) forests (fir waves) of the north-eastern United States. (2) Reductions in leaf area associated with dieback zone formation may cause increases in within-canopy windspeeds and rime ice deposition rates during winter storms, resulting in further foliage loss. (3) Field measurements in a fir wave on Mt Moosilauke, New Hampshire, U.S.A., showed that rime ice deposition during winter storms and cumulative winter needle litterfall were greatest in the dieback zone. (4) One-year-old foliage had 56%, lower photosynthetic capacity than current-year foliage. (5) Using reasonable assumptions, it was estimated that during the course of a single winter, the loss of stand-level potential photosynthetic capacity increased from 2 1 %/, in a 13-year-old sapling stand to 7 5%/o in a 75-year-old dieback zone stand. (6) Repeated defoliation each winter may contribute to tree death by reducing wholetree photosynthetic capacity.