Effects of atmospheric humidity on net photosynthesis,transpiration, and stomatal resistance

Rhizomes ofHydrocotyle plants from three contrasting habitats were cloned and the ramets grown under controlled environmental conditions. Measurements of net photosynthesis, transpiration, and total leaf diffusion resistance were used to examine possible physiological adaptations to specific field environments. Increasing dryness of the growth chamber environment had large effects on gas exchange (CO₂ and water vapor) and on total diffusion resistance of plants from a pond, moderate effects on plants from a mesic forest, but plants from a coastal sand dune were unaffected by the experimentally imposed dryness. Thus the 3 Hydrocotyle types demonstrated adaptive physiological reponses to their specific field habitats. Periodic stomatal oscillations were induced in ramets from the pond by sharply increasing irradiance, but the adaptiveness of the oscillations cannot be determined with the evidence at hand.No stomatal closure could be induced by atmospheric dryness alone as long as soil and plant dessication were prevented. There were no observable differences in stomatal response to increasing atmospheric vapor pressure deficits.     

Apparent responses of stomata to transpiration and humidity in a hybrid poplar canopy

It has been proposed that the stomatal response to humidity relies on sensing of the transpiration rate itself rather than relative humidity or the saturation deficit per se. We used independent measurements of stomatal conductance (g_s), transpiration (E), and leaf-to-air vapour pressure difference (V) in a hybrid poplar canopy to evaluate relationships between g_s and E and between g_s and V. Relationships between E, V and total vapour phase conductance or crown conductance (g_c) were also assessed. Conductance measurements were made on exposed and partially shaded branches over a wide range of incident solar radiation. In exposed branches, g_s appeared to decline linearly with increasing E and increasing V at both high and low irradiance. However, in a partially shaded branch, a bimodal relationship between g_s and E was observed in which g_s continued to decrease after E had reached a maximum value and begun to decrease. The relationship between g_s and V for this branch was linear. Plots of g_c against E always yielded bimodal or somewhat variable relationships, whereas plots of g_c against V were invariably linear. It was not possible to derive a unique relationship between conductance and E or V because prevailing radiation partially determined the operating range for conductance. Normalization of data by radiation served to linearize responses observed within the same day or type of day, but even after normalization, data collected on partly cloudy days could not be used to predict stomatal behaviour on clear days and vice versa. An additional unidentified factor was thus also involved in determining operating ranges of conductance on days with different overall radiation regimes. We suggest that the simplest mechanism to account for the observed humidity responses is stomatal sensing of the epidermal or cuticular transpiration rate rather than the bulk leaf or stomatal transpiration rate.     

The competitive status of trees determines their responsiveness to increasing atmospheric humidity – a climate trend predicted for northern latitudes

The interactive effects of climate variables and tree–tree competition are still insufficiently understood drivers of forest response to global climate change. Precipitation and air humidity are predicted to rise concurrently at high latitudes of the Northern Hemisphere. We investigated whether the growth response of deciduous trees to elevated air humidity varies with their competitive status. The study was conducted in seed‐originated silver birch and monoclonal hybrid aspen stands grown at the free air humidity manipulation (FAHM) experimental site in Estonia, in which manipulated stands (n = 3 for both species) are exposed to artificially elevated relative air humidity (6–7% over the ambient level). The study period included three growing seasons during which the stands had reached the competitive stage (trees were 7 years old in the final year). A significant ‘treatment×competitive status’ interactive effect on growth was detected in all years in birch (P < 0.01) and in one year in aspen stands (P = 0.015). Competitively advantaged trees were always more strongly affected by elevated humidity. Initially the growth of advantaged and neutral trees of both species remained significantly suppressed in humidified stands. In the following years, dominance and elevated humidity had a synergistic positive effect on the growth of birches. Aspens with different competitive status recovered more uniformly, attaining similar relative growth rates in manipulated and control stands, but preserved a significantly lower total growth yield due to severe initial growth stress. Disadvantaged trees of both species were never significantly affected by elevated humidity. Our results suggest that air humidity affects trees indirectly depending on their social status. Therefore, the response of northern temperate and boreal forests to a more humid climate in future will likely be modified by competitive relationships among trees, which may potentially affect species composition and cause a need to change forestry practices.     

Ectopic expression of a horseradish peroxidase enhances growth rate and increases oxidative stress resistance in hybrid aspen

We previously demonstrated that overexpression of the horseradish (Armoracia rusticana) peroxidase prxC1a gene stimulated the growth rate of tobacco (Nicotiana tabacum) plants. Here, the cauliflower mosaic virus 35S::prxC1a construct was introduced into hybrid aspen (Populus sieboldii x Populus grandidentata). The growth rate of these transformed hybrid aspen plants was substantially increased under greenhouse conditions. The average stem length of transformed plants was 25% greater than that of control plants. There was no other obvious phenotypic difference between the transformed and control plants. Fast-growing transformed hybrid aspen showed high levels of expression of prxC1a and had elevated peroxidase activities toward guaiacol and ascorbate. However, there was no increase of the endogenous class I ascorbate peroxidase activities in the transformed plants by separate assay and activity staining of native polyacrylamide gel electrophoresis. Furthermore, calli derived from the transformed hybrid aspen grew faster than those from control plants and were resistant to the oxidative stress imposed by hydrogen peroxide. Therefore, enhanced peroxidase activity affects plant growth rate and oxidative stress resistance.     

北半球高纬度地区气候变化对植被的影响途径和机制

根据标准化植被指数（ＮＤＶＩ）探讨了植被功能的地带特征及其与温度梯度的关系。结果表明在北半球高纬度地区ＮＤＶＩ的年最大值以及该值出现的时间与温度之间存在密切的相在,但共定量关系因纬度而异,在较高纬度地带,两个参数对温度的反应更为敏感,由于这种温度作用的不均衡,气温的增加将可能导致较高纬度地带的植被在物候和生产力上更加接近较低纬度带上的植被,其结果是使大气ＣＯ２季节振幅增大,同时季节谷值出现的时间提     

The effect of atmospheric humidity on photosynthesis,transpiration and water use efficiency of leaves of several plant species

The effect of humidity on the gas exchange of leaves of the dicotyledons soybean (Glycine max (L.) Merrill), sunflower (Helianthus annuus L.), jojoba (Simmondsia chinensis (L.) Schneider), and saltbush (Atriplex halimus L.) and the monocotyledons wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) sorghum (Sorghum bicolor (L.) Moench) and barnyard grass (Echinochloa crus-galli (L.) Beauv.) was examined under conditions of adequate soil moisture in a controlled environment. Photosynthesis and stomatal and internal diffusion resistances of whole, attached, single leaves were not affected by changes in humidity as the vapour pressure deficit between the leaf and atmosphere ranged from 8 to 27 mb. Transpiration increased linearly with increasing vapour pressure deficit. Whole plants of barley exhibited a different response. As humidity was increased, photosynthesis increased, transpiration expressed per unit of vapour pressure difference increased, and diffusion resistances became smaller. Reasons for the different behaviour of single leaves and whole plants are suggested. An index for water use efficiency, expressed per millibar of vapour pressure deficit, was calculated for single leaves of each species used in the experiments. This showed that water use efficiency was highest in the C₄ xerophytes and lowest in the C₃ mesophytes. The effect of environment on water use efficiency is examined using data from the literature.     

Climate, food, density and wildlife population growth rate

1. The aim of this study was to derive and evaluate a priori models of the relationship between annual instantaneous population growth rate (r) and climate. These were derived from the numerical response of annual r and food, and the effect of climate on a parameter in the numerical response. The goodness of fit of a range of such deductive models to data on annual r of Soay sheep and red deer were evaluated using information-theoretic (AICc-based) analyses. 2. The analysis for sheep annual r showed negative effects of abundance and negative effects of the interaction of abundance and climate, measured as March rainfall (and winter NAO) in the best fitting models. The analysis for deer annual r showed a negative effect of deer abundance and a positive effect of climate measured as March rainfall (but a negative effect of winter NAO), but no interaction of abundance and climate in the best fitting models. 3. There was most support in the analysis of sheep dynamics for the ratio numerical response and the assumption that parameter J (equilibrium food per animal) was influenced by climate. In the analysis of deer dynamics there was most support for the numerical responses assuming effects of food and density (Ivlev and density, food and density, and additive responses) and slightly less support for the ratio numerical response. The evaluation of such models would be aided by the collection of and incorporation of food data into the analyses.     

Climate and forest management affect 15N-uptake,N balance and biomass of European beech seedlings

We investigated the effect of (a) different local climate and (b) thinning of the forest canopy on growth and N status of naturally regenerated European beech seedlings in a beech forest on shallow rendzina soil in southern Germany. For this purpose, a ¹⁵N-tracing experiment was conducted during the growing season of the year 2000 with beech seedlings growing on a warm, dry SW-exposed site and a cooler, moist NE-exposed site, and in a thinned and a control stand at each site. Biomass, ¹⁵N uptake and partitioning and total N concentrations of beech seedlings were determined. Site and thinning produced clear differences, particularly at the end of the growing season. Biomass and cumulative ¹⁵N uptake of beech seedlings then increased due to thinning on the NE site and decreased on the SW site. Total N concentrations in leaves, roots and stems of beech seedlings responded similarly. Therefore, growth and N status of beech seedlings are found to be favoured by thinning under cool-moist conditions. However, under higher temperature and reduced water availability—conditions that are prognosticated in the near future—thinning reduces N uptake and plant N concentration and, thus, impairs N balance and growth of beech regeneration.     

Climate change and freshwater biodiversity: detected patterns, future trends and adaptations in northern regions

Current rates of climate change are unprecedented, and biological responses to these changes have also been rapid at the levels of ecosystems, communities, and species. Most research on climate change effects on biodiversity has concentrated on the terrestrial realm, and considerable changes in terrestrial biodiversity and species’ distributions have already been detected in response to climate change. The studies that have considered organisms in the freshwater realm have also shown that freshwater biodiversity is highly vulnerable to climate change, with extinction rates and extirpations of freshwater species matching or exceeding those suggested for better‐known terrestrial taxa. There is some evidence that freshwater species have exhibited range shifts in response to climate change in the last millennia, centuries, and decades. However, the effects are typically species‐specific, with cold‐water organisms being generally negatively affected and warm‐water organisms positively affected. However, detected range shifts are based on findings from a relatively low number of taxonomic groups, samples from few freshwater ecosystems, and few regions. The lack of a wider knowledge hinders predictions of the responses of much of freshwater biodiversity to climate change and other major anthropogenic stressors. Due to the lack of detailed distributional information for most freshwater taxonomic groups and the absence of distribution‐climate models, future studies should aim at furthering our knowledge about these aspects of the ecology of freshwater organisms. Such information is not only important with regard to the basic ecological issue of predicting the responses of freshwater species to climate variables, but also when assessing the applied issue of the capacity of protected areas to accommodate future changes in the distributions of freshwater species. This is a huge challenge, because most current protected areas have not been delineated based on the requirements of freshwater organisms. Thus, the requirements of freshwater organisms should be taken into account in the future delineation of protected areas and in the estimation of the degree to which protected areas accommodate freshwater biodiversity in the changing climate and associated environmental changes.     

Experimental studies on Vaccinium myrtillus and Vaccinium vitis-idaea in relation to air pollution and global change at northern high latitudes: A review

The aim of this paper is to review the experimental studies performed with two important species (i.e. Vaccinium myrtillus and Vaccinium vitis-idaea) of the shrub layer of boreal forests. The focus is on ecophysiology and stress tolerance under conditions of air pollution and global change. Our objective was to make an overview of studies of abiotic stress related to global change on the above species, and discuss the reported effects of these environmental factors. These issues include nitrogen, heavy metals, radionuclides, salt, ozone, carbon dioxide, warming climate, declining snow cover, periodic droughts, fire and elevated UV radiation. The findings suggest that both species are relatively tolerant to many abiotic environmental stresses: increased nitrogen and metal supply have negligible impacts on these species, as the atmospheric gaseous compounds reported. In some cases the effects are even positive, since extra nitrogen may improve the frost hardiness of V. vitis-idaea, and V. myrtillus may even benefit from elevated CO₂. Both species also seem to recover well from fires. However, the reports demonstrated that both have species-specific areas of weakness: (1) V. myrtillus is susceptible to stress caused by warming winter, and (2) frost hardiness of V. vitis-idaea may be reduced under enhanced UV radiation.     

Acclimation of isoprene emission and photosynthesis to growth temperature in hybrid aspen: resolving structural and physiological controls

Acclimation of foliage to growth temperature involves both structural and physiological modifications, but the relative importance of these two mechanisms of acclimation is poorly known, especially for isoprene emission responses. We grew hybrid aspen (Populus tremula x P. tremuloides) under control (day/night temperature of 25/20 °C) and high temperature conditions (35/27 °C) to gain insight into the structural and physiological acclimation controls. Growth at high temperature resulted in larger and thinner leaves with smaller and more densely packed chloroplasts and with lower leaf dry mass per area (M_A). High growth temperature also led to lower photosynthetic and respiration rates, isoprene emission rate and leaf pigment content and isoprene substrate dimethylallyl diphosphate pool size per unit area, but to greater stomatal conductance. However, all physiological characteristics were similar when expressed per unit dry mass, indicating that the area‐based differences were primarily driven by M_A. Acclimation to high temperature further increased heat stability of photosynthesis and increased activation energies for isoprene emission and isoprene synthase rate constant. This study demonstrates that temperature acclimation of photosynthetic and isoprene emission characteristics per unit leaf area were primarily driven by structural modifications, and we argue that future studies investigating acclimation to growth temperature must consider structural modifications.     

Large‐scale variations in the vegetation growing season and annual cycle of atmospheric CO2 at high northern latitudes from 1950 to 2011

We combine satellite and ground observations during 1950–2011 to study the long‐term links between multiple climate (air temperature and cryospheric dynamics) and vegetation (greenness and atmospheric CO₂ concentrations) indicators of the growing season of northern ecosystems (>45°N) and their connection with the carbon cycle. During the last three decades, the thermal potential growing season has lengthened by about 10.5 days (P < 0.01, 1982–2011), which is unprecedented in the context of the past 60 years. The overall lengthening has been stronger and more significant in Eurasia (12.6 days, P < 0.01) than North America (6.2 days, P > 0.05). The photosynthetic growing season has closely tracked the pace of warming and extension of the potential growing season in spring, but not in autumn when factors such as light and moisture limitation may constrain photosynthesis. The autumnal extension of the photosynthetic growing season since 1982 appears to be about half that of the thermal potential growing season, yielding a smaller lengthening of the photosynthetic growing season (6.7 days at the circumpolar scale, P < 0.01). Nevertheless, when integrated over the growing season, photosynthetic activity has closely followed the interannual variations and warming trend in cumulative growing season temperatures. This lengthening and intensification of the photosynthetic growing season, manifested principally over Eurasia rather than North America, is associated with a long‐term increase (22.2% since 1972, P < 0.01) in the amplitude of the CO₂ annual cycle at northern latitudes. The springtime extension of the photosynthetic and potential growing seasons has apparently stimulated earlier and stronger net CO₂ uptake by northern ecosystems, while the autumnal extension is associated with an earlier net release of CO₂ to the atmosphere. These contrasting responses may be critical in determining the impact of continued warming on northern terrestrial ecosystems and the carbon cycle.     

Greater temperature sensitivity of plant phenology at colder sites: implications for convergence across northern latitudes

Warmer temperatures are accelerating the phenology of organisms around the world. Temperature sensitivity of phenology might be greater in colder, higher latitude sites than in warmer regions, in part because small changes in temperature constitute greater relative changes in thermal balance at colder sites. To test this hypothesis, we examined up to 20 years of phenology data for 47 tundra plant species at 18 high‐latitude sites along a climatic gradient. Across all species, the timing of leaf emergence and flowering was more sensitive to a given increase in summer temperature at colder than warmer high‐latitude locations. A similar pattern was seen over time for the flowering phenology of a widespread species, Cassiope tetragona. These are among the first results highlighting differential phenological responses of plants across a climatic gradient and suggest the possibility of convergence in flowering times and therefore an increase in gene flow across latitudes as the climate warms.     

The influence of humidity on growth rate and feed utilization of swine

No statistically significant differences in weight gains or feed consumption were found in swine raised from about 30 to 100 kg at relative humidities of 45, 70, 95 percent and at temperatures that were optimum for production. The trend of the data, however, indicated that there might be a six to eight percent decrease in average daily gain with an increase in relative humidity from 45 to 95 percent.This change is in line with that which might be inferred from the change in the temperature-humidity index developed from consideration of human comfort and from published data on swine heat and moisture loss.

---

Zusammenfassung Es wurden keine signifikanten Unterschiede in Zuwachs und in der Futteraufnahme bei der Aufzucht von Schweinen von 30 bis 100 kg beobachtet, wenn die rel. Feuchte bei den für die Produktionen optimalen Temperaturen von 45 auf 70 und 95 % erhöht wurde. Die Verschiebung der Weerte zeigt jedoch, dass mit ansteigender RH in der täglichen Körpergewichtszunahme ein Abfall von 6 bis 8 % zu bestehen scheint. Diese Reaktion ist in Übereinstimmung mit der, die nach dem Temperatur-Feuchte Index für den Menschen und nach Unterlagen über den Wärme- und Feuchtigkeitsverlust von Schweinen zu erwarten ist.

---

Résumé On ne trouve pas de différences significatives de l'augmentation de poids ou de la consommation en fourrage de porcs de 30 à 100 kg si, par température optimum pour la production, on fait passer l'humidité relative de 45 à 70 ou 95 %. Il semble cependant que cette augmentation de l'humidité relative s'accompagne d'une diminution de la croissance journalière de 6 à 8 %. Cette réaction correspond à celle qui découlerait de l'indice température/humidité chez l'homme ou des conditions de déperdition de chaleur et d'humidité chez le porc.

---

---

This paper was presented at the Fourth International Biometeorolocical Congress, New Brunswick, N.J., 26 August – 2 September 1966.     

秦岭北麓油松径向生长对气候变化的响应

以秦岭北麓南五台油松为样本,建立油松树轮宽度标准化年表(STD),研究油松径向生长与气候因子之间的相关性。结果表明: 秦岭北麓油松径向生长与前一年9月及当年5月水分因子呈显著正相关,与前一年11月温度因子呈显著正相关,与前一年10月、当年5月温度因子呈显著负相关。油松径向生长对不同气候因子响应均存在明显的滞后效应。油松径向生长与PDSI干旱指数具有较好的相关性,特别是与前一年9—12月、当年5月PDSI呈显著正相关。回归模型能较好地模拟树轮宽度指数与PDSI之间的关系,油松极宽窄轮的形成主要是干旱作用的结果。综合各种气候指标,PDSI能更好地反映研究区油松径向生长的特征。     

Influence of light intensity,temperature and humidity on photosynthesis and transpiration ofSasa nipponica andArundinaria pygmaea

Photosynthesis and transpiration were simultaneously measured under different light intensity, temperature and humidity conditions inSasa nipponica andArundinaria pygmaea grown in exposed and shaded habitats. Both species showed a saturated light curve for photosynthetic rate. The saturation point was lower in shaded plants. The apparent quantum yields were larger inS. nipponica and in shaded plants, while the maximum photosynthesis was higher inA. pygmaea and exposed plants. The temperature response of photosynthesis showed an optimum curve in both species. The optinum temperatures were 20 C inS. nipponica and 25 C inA. pygmaea. The influence of humidity on photosynthesis was insignificant for both species. The responses of transpiration to light intensity and relative humidity showed a saturated curve and an optimal one, respectively. There was a significant relationship between transpiration and stomatal frequency, both of which were higher inS. nipponica, while water use efficiency was higher inA. pygmaea. These results suggest thatS. nipponica adapts itself better to shaded, low temperature and less water stress habitats as compared withA. pygmaea.