Optimum Temperature For Photosynthesis Research Articles

Interactive Effects of Temperature, Water Regime, and [CO2] on Wheats with Different Heat Susceptibilities

Plants’ response to single environmental changes can be highly distinct from the response to multiple changes. The effects of a single environmental factor on wheat growth have been well documented. However, the interactive influences of multiple factors on different wheat genotypes need further investigation. Here, treatments of three important growth factors, namely water regime, temperature, and CO2 concentration ([CO2]), were applied to compare the response of two wheat genotypes with different heat sensitivities. The temperature response curves showed that both genotypes showed more variations at elevated [CO2] (e[CO2]) than ambient [CO2] (a[CO2]) when the plants were treated under different water regimes and temperatures. This corresponded to the results of water use efficiency at the leaf level. At e[CO2], heat-tolerant ‘Gladius’ showed a higher net photosynthetic rate (Pn), while heat-susceptible ‘Paragon’ had a lower Pn at reduced water, as compared with full water availability. The temperature optimum for photosynthesis in wheat was increased when the growth temperature was high, while the leaf carbon/nitrogen was increased via a reduced water regime. Generally, water regime, temperature and [CO2] have significant interactive effects on both wheat genotypes. Two wheat genotypes showed different physiological responses to different combinations of environmental factors. Our investigation concerning the interactions of multi-environmental factors on wheat will benefit the future wheat climate-response study.

Uncoupling of stomatal conductance and photosynthesis at high temperatures: mechanistic insights from online stable isotope techniques.

The strong covariation of temperature and vapour pressure deficit (VPD) in nature limits our understanding of the direct effects of temperature on leaf gas exchange. Stable isotopes in CO2 and H2 O vapour provide mechanistic insight into physiological and biochemical processes during leaf gas exchange. We conducted combined leaf gas exchange and online isotope discrimination measurements on four common European tree species across a leaf temperature range of 5-40°C, while maintaining a constant leaf-to-air VPD (0.8 kPa) without soil water limitation. Above the optimum temperature for photosynthesis (30°C) under the controlled environmental conditions, stomatal conductance (gs ) and net photosynthesis rate (An ) decoupled across all tested species, with gs increasing but An decreasing. During this decoupling, mesophyll conductance (cell wall, plasma membrane and chloroplast membrane conductance) consistently and significantly decreased among species; however, this reduction did not lead to reductions in CO2 concentration at the chloroplast surface and stroma. We question the conventional understanding that diffusional limitations of CO2 contribute to the reduction in photosynthesis at high temperatures. We suggest that stomata and mesophyll membranes could work strategically to facilitate transpiration cooling and CO2 supply, thus alleviating heat stress on leaf photosynthetic function, albeit at the cost of reduced water-use efficiency.

Interannual variation in gross ecosystem production and evapotranspiration in a temperate semiarid grassland undergoing vegetation recovery

Carbon gains (gross ecosystem production, GEP) and water losses (evapotranspiration, ET) are critical for assessing vegetation recovery potential in drylands. However, large uncertainties remain regarding the controlling factors that regulate GEP and ET in semiarid grasslands, especially during periods of vegetation re-establishment and succession. Using the eddy-covariance technique, we assessed the interannual variability and key biophysical controls of carbon (C) and water vapor (H2O) fluxes in a semiarid grassland ecosystem in northern China from 2012 to 2020. After years of being subjected to heavy grazing and with a recent ban, the shrub-to-herb ratio at the site increased from 0.5 in 2014 to 0.63 in 2020. Associated with decreasing soil water availability (∼4.0% year−1), canopy transpiration and light use efficiency also decreased at rates of about 3.3% and 6.2% year−1, respectively. Multi-year means of GEP and ET were 166.6 ± 20.1 g C m−2 (mean ± SD) and 190.2 ± 21.8 mm, respectively. Interannual variability in GEP was mostly driven by variation in summer GEP, which for the most part was limited by mid-summer air temperature (Ta), particularly when exceeding the plants’ optimal temperature for photosynthesis. Interannual variability in ET was predominantly caused by variation in spring ET, which was mostly affected by spring vapor pressure deficit (VPD) and associated reductions in canopy stomatal conductance. Synchronous changes in GEP and ET resulted in a relatively stable annual water use efficiency (WUE) of 0.97 ± 0.13 g C kg−1 H2O. This stability is indicative of the shrubs’ capabilities to acclimate to arid conditions. Our results suggest that temperature and atmospheric aridity have important roles in regulating C gains and H2O losses in recovering dryland vegetation, respectively. Future increases in climatic variability anticipated with global climate change may augment the regional transition from grass to shrub cover.

Analysis of the optimal photosynthetic environment for an alpine meadow ecosystem

The changes in the carbon sink function of sensitive and fragile alpine ecosystems under climate change are widely concerned. Radiation, temperature, and water resources play important roles in regulating carbon assimilation. Therefore, it is important to detect the optimal configuration of environmental factors for the photosynthesis of alpine meadow ecosystems. In this study, based on 10-year flux and corresponding environmental observations in a typical alpine meadow ecosystem, the optimal environmental configuration that could realistically occur in the natural world for photosynthesis was detected. The results indicated that the temperature and water conditions were the primary limiting factors, as radiation resources are abundant on the Tibetan Plateau. The optimal temperature for photosynthesis (TAopt) was determined to be 11.92 ℃ based on the entire observation dataset, with a maximum photosynthetic capacity (GPPmax) of 0.20 mg CO2 m−2 s−1. However, the TAopt and the corresponding GPPmax could be elevated when the soil water content (SWC) was abundant. When SWC exceeded 0.26 m3 m−3, TAopt increased to 13.41 ℃, and the corresponding GPPmax reached as high as 0.30 mg CO2 m−2 s−1, which is the maximum the ecosystem could reach. Thus, the optimal environmental configuration for photosynthesis that could realistically occur in the natural world in this alpine meadow was air temperature (TA)=13.41 ℃, SWC=0.28 m3 m−3, vapor pressure deficit (VPD)=0.61 kPa, net radiation (RN)=411.53 J m−2 s−1. According to this study, it could be inferred that within a reasonable range, higher temperatures and VPD would benefit photosynthesis in this alpine meadow as long as the soil water supply is sufficient. The climate on the Tibetan Plateau is arid with high VPD and is experiencing warming due to climate change. Consequently, alpine ecosystems situated in relatively humid regions with sufficient soil water resources may exhibit greater potential for carbon sequestration than previously estimated.

Combining local model calibration with the emergent constraint approach to reduce uncertainty in the tropical land carbon cycle feedback

Abstract. The role of the land carbon cycle in climate change remains highly uncertain. A key source of the projection spread is related to the assumed response of photosynthesis to warming, especially in the tropics. The optimum temperature for photosynthesis determines whether warming positively or negatively impacts photosynthesis, thereby amplifying or suppressing CO2 fertilisation of photosynthesis under CO2-induced global warming. Land carbon cycle models have been extensively calibrated against local eddy flux measurements, but this has not previously been clearly translated into a reduced uncertainty in terms of how the tropical land carbon sink will respond to warming. Using a previous parameter perturbation ensemble carried out with version 3 of the Hadley Centre coupled climate–carbon cycle model (HadCM3C), we identify an emergent relationship between the optimal temperature for photosynthesis, which is especially relevant in tropical forests, and the projected amount of atmospheric CO2 at the end of the century. We combine this with a constraint on the optimum temperature for photosynthesis, derived from eddy covariance measurements using the adjoint of the Joint UK Land Environment Simulator (JULES) land surface model. Taken together, the emergent relationship from the coupled model and the constraint on the optimum temperature for photosynthesis define an emergent constraint on future atmospheric CO2 in the HadCM3C coupled climate–carbon cycle under a common emissions scenario (A1B). The emergent constraint sharpens the probability density of simulated CO2 change (2100–1900) and moves its peak to a lower value of 497 ± 91 compared to 607 ± 128 ppmv (parts per million by volume) when using the equal-weight prior. Although this result is likely to be model and scenario dependent, it demonstrates the potential of combining the large-scale emergent constraint approach with a parameter estimation using detailed local measurements.

Limited effects of shade on physiological performances of cocoa (Theobroma cacao L.) under elevated temperature

Shade is one of the recommended management solutions to mitigate the effects of heat stress, which is a major challenge for cocoa production globally. Nevertheless, there are limited studies to verify this hypothesis. Here, we evaluate the effects of heat and shade on cocoa physiology using experimental plots with six-month old potted seedlings in a randomized complete block design. Infrared heaters were applied for one month to increase leaf temperatures by an average of 5–7 ºC (heat treatment) compared with no heat (unheated treatments), and shaded plants were placed under a shade net removing 60% of the light compared with no shade (sun treatments). Plants under heat treatments in sun and in shade showed severe reduction in photosynthesis. Measurements of chlorophyll fluorescence and photosynthetic light response curves indicated that heat caused damages at photosystem II and additionally resulted in lower rates of maximal photosynthesis. Temperature optima for photosynthesis were at 31–33 ºC with only small differences between treatments, and as light saturation was reached at low PAR levels of 325 – 380 µmol m −2 s −1 in shade and 427 – 521 µmol m −2 s −1 in sun, ambient rates of photosynthesis were comparable between sun and shade treatments. Heat treatments resulted in decreased concentrations of chlorophyll and changed pigment composition, reduced specific leaf areas, and plant biomass. While shade may benefit cocoa seedlings, our results indicate that the positive effects may not be sufficient to counteract the negative effects of increased temperatures on cocoa physiology. • Heat is imposed on six-month old cocoa seedlings and shade is provided. • Heat treated plants show severe reduction in photosynthesis and damages at photosystem II. • Heat decreases chlorophyll concentrations and pigment composition. • Shade improves cocoa physiology but has limited effects on heat.

Effect of temperature and osmotic stress during somatic embryogenesis on phenology and physiology of abies nordmanniana emblings

Epigenetic modification induced during embryogenesis can serve as a mechanism for rapid adaptation of plants to climate change, especially for long living organisms such as trees. Here, we test if temperature and osmotic stress during embryogenesis influences spring and autumn phenology, photosynthesis rate, growth and water stress tolerance in Abies nordmanniana. Somatic embryogenic plants (emblings) were developed under different temperatures to test if temperature influences the spring phenology. Our results show that 9 °C higher temperature during somatic embryogenesis advanced budburst by an average of 4 days, but with significant differences among different genotypes in their response. This reveals genetic variation in the observed phenological response to temperature during somatic embryogenesis. However, we did not observe an effect of differences in osmotic stress during somatic embryogenesis on the response of the emblings to water stress. Optimum temperatures for photosynthesis and maximal photosynthetic rates were not found to be influenced by the temperature during somatic embryogenesis. Both height and autumn senescence were significantly different among the genotypes, but the temperature during somatic embryogenesis did not affect these traits. The observed responses in our study complement findings from other species and support that epigenetic modification in phenology may help the species to cope with fluctuations in temperatures in future climate, and may have practical applications for reducing spring frost risk in plantations of the species.

Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes.

Evergreen species are widespread across the globe, representing two major plant functional forms in terrestrial models. We reviewed and analysed the responses of photosynthesis and respiration to warming in 101 evergreen species from boreal to tropical biomes. Summertime temperatures affected both latitudinal gas exchange rates and the degree of responsiveness to experimental warming. The decrease in net photosynthesis at 25°C (Anet25 ) was larger with warming in tropical climates than cooler ones. Respiration at 25°C (R25 ) was reduced by 14% in response to warming across species and biomes. Gymnosperms were more sensitive to greater amounts of warming than broadleaved evergreens, with Anet25 and R25 reduced c. 30-40% with > 10°C warming. While standardised rates of carboxylation (Vcmax25 ) and electron transport (Jmax25 ) adjusted to warming, the magnitude of this adjustment was not related to warming amount (range 0.6-16°C). The temperature optimum of photosynthesis (ToptA ) increased on average 0.34°C per °C warming. The combination of more constrained acclimation of photosynthesis and increasing respiration rates with warming could possibly result in a reduced carbon sink in future warmer climates. The predictable patterns of thermal acclimation across biomes provide a strong basis to improve modelling predictions of the future terrestrial carbon sink with warming.

Thermal Acclimation of Foliar Carbon Metabolism in Pinus taiwanensis Along an Elevational Gradient.

Climate change could negatively alter plant ecosystems if rising temperatures exceed optimal conditions for obtaining carbon. The acclimation of plants to higher temperatures could mitigate this effect, but the potential of subtropical forests to acclimate still requires elucidation. We used space-for-time substitution to determine the photosynthetic and respiratory-temperature response curves, optimal temperature of photosynthesis (Topt), photosynthetic rate at Topt, temperature sensitivity (Q10), and the rate of respiration at a standard temperature of 25°C (R25) for Pinus taiwanensis at five elevations (1200, 1400, 1600, 1800, and 2000 m) in two seasons (summer and winter) in the Wuyi Mountains in China. The response of photosynthesis in P. taiwanensis leaves to temperature at the five elevations followed parabolic curves, and the response of respiration to temperature increased with temperature. Topt was higher in summer than winter at each elevation and decreased significantly with increasing elevation. Q10 decreased significantly with increasing elevation in summer but not winter. These results showed a strong thermal acclimation of foliar photosynthesis and respiration to current temperatures across elevations and seasons, and that R25 increased significantly with elevation and were higher in winter than summer at each elevation indicating that the global warming can decrease R25. These results strongly suggest that this thermal acclimation will likely occur in the coming decades under climate change, so the increase in respiration rates of P. taiwanensis in response to climatic warming may be smaller than predicted and thus may not increase atmospheric CO2 concentrations.

Experimental warming across a tropical forest canopy height gradient reveals minimal photosynthetic and respiratory acclimation.

Tropical forest canopies cycle vast amounts of carbon, yet we still have a limited understanding of how these critical ecosystems will respond to climate warming. We implemented in situ leaf-level + 3°C experimental warming from the understory to the upper canopy of two Puerto Rican tropical tree species, Guarea guidonia and Ocotea sintenisii. After approximately 1 month of continuous warming, we assessed adjustments in photosynthesis, chlorophyll fluorescence, stomatal conductance, leaf traits and foliar respiration. Warming did not alter net photosynthetic temperature response for either species; however, the optimum temperature of Ocotea understory leaf photosynthetic electron transport shifted upward. There was no Ocotea respiratory treatment effect, while Guarea respiratory temperature sensitivity (Q10 ) was down-regulated in heated leaves. The optimum temperatures for photosynthesis (Topt ) decreased 3-5°C from understory to the highest canopy position, perhaps due to upper canopy stomatal conductance limitations. Guarea upper canopy Topt was similar to the mean daytime temperatures, while Ocotea canopy leaves often operated above Topt . With minimal acclimation to warmer temperatures in the upper canopy, further warming could put these forests at risk of reduced CO2 uptake, which could weaken the overall carbon sink strength of this tropical forest.

Adaptation of a marine diatom to ocean acidification and warming reveals constraints and trade-offs

Ocean acidification and warming are recognized as two major anthropogenic perturbations of the modern ocean. However, little is known about the adaptive response of phytoplankton to them. Here we examine the adaptation of a marine diatom Thalassiosira weissflogii to ocean acidification in combination with ocean warming. Our results show that ocean warming have a greater effect than acidification on the growth of T. weissflogii over the long-term selection experiment (~380 generations), as well as many temperature response traits (e.g., optimum temperatures for photosynthesis, maximal net photosynthetic oxygen evolution rates, activation energy) in thermal reaction norm. These results suggest that ocean warming is the main driver for the evolution of the marine diatom T. weissflogii, rather than oceanacidification. However, the evolution resulting from warming can be constrained by ocean acidification, where ocean warming did not impose any effects at high CO2 level. Furthermore, adaptations to ocean warming alone or to the combination of ocean acidification and warming come with trade-offs by inhibiting photochemical performances. The constrains and trade-offs associated with the adaptation to ocean acidification and warming demonstrated in this study, should be considered for parameterizing evolutionary responses in eco-evolutionary models of phytoplankton dynamics in a future ocean.

Photosystem II heat tolerances characterize thermal generalists and the upper limit of carbon assimilation.

The heat tolerance of photosystem II (PSII) may promote carbon assimilation at higher temperatures and help explain plant responses to climate change. Higher PSII heat tolerance could lead to (a) increases in the high-temperature compensation point (Tmax ); (b) increases in the thermal breadth of photosynthesis (i.e. the photosynthetic parameter Ω) to promote a thermal generalist strategy of carbon assimilation; (c) increases in the optimum rate of carbon assimilation Popt and faster carbon assimilation and/or (d) increases in the optimum temperature for photosynthesis (Topt ). To address these hypotheses, we tested if the Tcrit , T50 and T95 PSII heat tolerances were correlated with carbon assimilation parameters for 21 plant species. Our results did not support Hypothesis 1, but we observed that T50 may be used to estimate the upper thermal limit for Tmax at the species level, and that community mean Tcrit may be useful for approximating Tmax . The T50 and T95 heat tolerance metrics were positively correlated with Ω in support of Hypothesis 2. We found no support for Hypotheses 3 or 4. Our study shows that high PSII heat tolerance is unlikely to improve carbon assimilation at higher temperatures but may characterize thermal generalists with slow resource acquisition strategies.

Volatile organic compound emission in tundra shrubs – Dependence on species characteristics and the near-surface environment

Temperature is one of the key abiotic factors during the life of plants, especially in the Arctic region which is currently experiencing rapid climate change. We evaluated plant traits and environmental variables determining leaf temperature in tundra shrubs and volatile organic compound (VOC) emissions with field measurements on deciduous tundra shrubs, Salix myrsinites and Betula nana, and evergreen Cassiope tetragona and Rhododendron lapponicum. Higher leaf-to-air temperature difference was observed in evergreen, compared to deciduous shrubs. Evergreen shrubs also showed continuously increasing photosynthesis with increasing temperature, suggesting high thermal tolerance. For the deciduous species, the optimum temperature for net photosynthesis was between our measurement temperatures of 24 °C and 38 °C. Air temperature and vapor pressure deficit were the most important variables influencing leaf temperature and VOC emissions in all the studied plants, along with stomatal density and specific leaf area in the deciduous shrubs. Using climate data and emission factors from our measurements, we modelled total seasonal tundra shrub VOC emissions of 0.3–2.3 g m−2 over the main growing season. Our results showed higher-than-expected temperature optima for photosynthesis and VOC emission and demonstrated the relative importance of plant traits and local environments in determining leaf temperature and VOC emissions in a subarctic tundra.

A Multiyear Gridded Data Ensemble of Surface Biogenic Carbon Fluxes for North America: Evaluation and Analysis of Results

AbstractAccurate and fine‐scale estimates of biogenic carbon fluxes are critical for measuring and monitoring the biosphere's responses and feedback to the climate system. Currently available data products from flux towers and model‐intercomparison projects struggle to adequately represent spatiotemporal dynamics of surface biogenic carbon fluxes, and to quantify their uncertainties, which also are crucial to atmospheric inversion systems. To address these gaps, we introduce a new perturbed‐parameter model ensemble with the CASA model to estimate surface biogenic carbon fluxes at monthly and 3‐hourly scales for North America at ~500‐m and 5‐km resolutions. We first use the Extended Fourier Amplitude Sensitivity Testing to choose the three most sensitive parameters to be perturbed, maximum light use efficiency (Emax), optimal temperature of photosynthesis (Topt), and temperature response of respiration (Q10). The initial range for each parameter is broadly sampled for the L1 ensemble, but then we pruned Emax with site‐level primary productivity to derive an L2 ensemble with narrower uncertainty ranges. Ensembles are strongly correlated with site‐level results at both monthly and 3‐hourly scales, and the spread across L1/L2 ensemble members encompasses the range of AmeriFlux observations. Monthly variability in the L2 ensemble mean is 85% of the observed variability. The L2 ensemble outperforms diverse data products with the highest Taylor skill scores at diurnal to annual scales. The ensemble's seasonality agrees well with other models for most biome types and in high and middle latitudes, but inconsistencies are found in subtropical and tropical ecoregions and for annual totals over North America.

Optimum temperature for photosynthesis: from leaf- to ecosystem-scale

Optimum temperature for photosynthesis: from leaf- to ecosystem-scale

Eddy covariance measurements of CO2 exchange from agro-ecosystems located in subtropical (India) and boreal (Finland) climatic conditions

Climate impacts agriculture in various complex ways at different levels and scales depending on the local natural crop growth limitations. Our objective in this study, therefore, is to understand how different is the atmosphere–biosphere exchange of CO2 under contrasting subtropical and boreal agricultural (an oilseed crop and a bioenergy crop, respectively) climates. The oilseed crop in subtropical climate continued to uptake CO2 from the atmosphere throughout the year, with maximum uptake occurring in the monsoon season, and drastically reduced uptake during drought. The boreal ecosystem, on the other hand, was a sustained, small source of CO2 to the atmosphere during the snow-covered winter season. Higher rates of CO2 uptake were observed owing to greater day-length in the growing season in the boreal ecosystem. The optimal temperature for photosynthesis by the subtropical ecosystem was close to the regional normal mean temperature. An enhanced photosynthetic response to the incident radiation was found for the boreal ecosystem implying the bioenergy crop to be more efficient than the oilseed crop in utilizing the available light. This comparison of the CO2 exchange patterns will help strategising the carbon management under different climatic conditions.

Variation in Responses of Photosynthesis and Apparent Rubisco Kinetics to Temperature in Three Soybean Cultivars.

Recent in vivo assays of the responses of Rubisco to temperature in C3 plants have revealed substantial diversity. Three cultivars of soybean (Glycine max L. Merr.), Holt, Fiskeby V, and Spencer, were grown in indoor chambers at 15, 20, and 25 °C. Leaf photosynthesis was measured over the range of 15 to 30 °C, deliberately avoiding higher temperatures which may cause deactivation of Rubisco, in order to test for differences in temperature responses of photosynthesis, and to investigate in vivo Rubisco kinetic characteristics responsible for any differences observed. The three cultivars differed in the optimum temperature for photosynthesis (from 15 to 30 °C) at 400 μmol mol−1 external CO2 concentration when grown at 15 °C, and in the shapes of the response curves when grown at 25 °C. The apparent activation energy of the maximum carboxylation rate of Rubisco differed substantially between cultivars at all growth temperatures, as well as changing with growth temperature in two of the cultivars. The activation energy ranged from 58 to 84 kJ mol−1, compared with the value of 64 kJ mol−1 used in many photosynthesis models. Much less variation in temperature responses occurred in photosynthesis measured at nearly saturating CO2 levels, suggesting more diversity in Rubisco than in electron transport thermal properties among these soybean cultivars.

Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale.

The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common-garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.

Limitations to winter and spring photosynthesis of a Rocky Mountain subalpine forest

Temperate and boreal conifer forests are dormant for many months during the cold season. Climate change is altering the winter environment, with increased temperature, altered precipitation, and earlier snowmelt in many locations. If significant enough, these changes may alter patterns of dormancy and activity of evergreens. Here we studied the factors limiting photosynthetic activity of a high-elevation subalpine forest that has undergone substantial warming in recent decades. We tested the hypothesis that this warming has been significant enough to allow photosynthesis during sunny warm days in winter. Using thermal imagery, we found that foliage in winter was sometimes near the temperature optimum for photosynthesis, but no net carbon gain occurred for most of the cold season. Water transport was limited by blockage of sap transport by frozen boles, but not by frozen soils. Foliar carotenoid content was much higher during winter, driven largely by increases in the pool size of the photoprotective xanthophyll cycle. There was no seasonal change in chlorophyll or lutein content. Net carbon uptake began only as boles thawed, with no difference in timing among tree species, and the spring increase in canopy-level photosynthetic capacity occurred before sap transport was detected. The seasonality of gross primary productivity (GPP) was strongly linked to seasonality of xanthophyll cycle deepoxidation state in all species. Seasonality of GPP was detectable with two metrics of canopy color – the Green Chromatic Coordinate and Green-Red Vegetation Index (a proxy for the newly proposed MODIS-based chlorophyll/carotenoid index or CCI). Both indices were significantly correlated with GPP. Together these results indicate the potential for airborne or near-surface remote sensing of leaf color to serve as a metric of photosynthetic activity in evergreen forests, and to monitor physiological changes associated with the progression in and out of winter dormancy.

Altered morphologies and physiological compensation in a rapidly expanding dwarf bamboo in alpine ecosystems

ABSTRACT Dwarf bamboos are evergreen woody grasses that produce large clonal patches and dominate the understories of the montane to subalpine zones of northern Japan. Recently, dwarf bamboos have expanded their distribution to above the treeline and into alpine meadows. To clarify the mechanism of rapid invasion into the alpine, we compared the morphological performance, biomass allocation, photosynthetic activity, CO2 fixation ability, and sensitivity to temperature of dwarf bamboos in their native montane and expanding alpine sites in the Taisetsu Mountains. Alpine bamboo produced shorter but denser aboveground structures, where leaves were smaller and branching was more frequent. The total biomass of alpine bamboo was nearly half of that produced by montane bamboo. Montane bamboo produced more stems, while alpine bamboo invested more carbon in belowground structures. CO2 fixation per land area by alpine bamboo was 1.3 times higher than rates observed in montane bamboo. Optimal temperatures for photosynthesis were lower in alpine bamboo (15–20°C) than in montane bamboo (20–25°C), probably because of the rapid decrease in stomatal conductance at higher temperatures (>20°C) observed in the alpine site. Overall, leaf transpiration rates were higher in alpine bamboo, but water-use efficiency was similar between sites. A high flexibility in both morphological and physiological characteristics enabled dwarf bamboos to expand into alpine environments in response to recent climate change.