Potential of a dust grain in a nitrogen plasma with a condensed disperse phase at room and cryogenic temperatures

The first numerical study is presented of the self-consistent potential of a dust grain in a nitrogen plasma with a condensed disperse phase at room and cryogenic temperatures and at high gas pressures for which the electron and ion transport in the plasma can be described in the hydrodynamic approximation. It is shown that the potential of the dust grain is described with good accuracy by the Debye potential, in which case, however, the screening radius turns out to be larger than the electron Debye radius. The difference between the radii is especially large in a plasma with high ionization rates (about 10¹⁶–10¹⁸ cm^?3 s^?1) at room temperature. It is found that, in a certain range of the parameters of a nitrogen dusty plasma, the parameter describing the interaction between the grains exceeds the critical value above which one would expect the formation of plasma-dust structures such as Coulomb crystals. For a plasma at cryogenic temperature (T=77 K), this range is significantly wider.     

Effects of experimental N addition on plant diversity in an old‐growth temperate forest

Temperate forest ecosystems have experienced mounting negative effects due to increasing levels of nitrogen (N) deposition. We examined the effects of experimental N addition on plant diversity in an old‐growth temperate forest to test the following hypothesis: Long‐term excessive N addition decreases plant diversity by affecting the growth of plants, which results from changes in the soil nutrient content and a decrease in the soil pH in temperate forests. Experimental N additions were administered at the following levels since 2008: control (0 kg N ha^?1 year^?1), low N (30 kg N ha^?1 year^?1), medium N (60 kg N ha^?1 year^?1), and high N (120 kg N ha^?1 year^?1). Additionally, plant diversity was studied from 2014 to 2016. The results showed that the experimental N additions had significant effects on plant diversity and soil properties in an old‐growth temperate forest. The high‐N treatment decreased the density, cover, and diversity of understory plants, and some herbs even appeared to undergo premature aging, whereas the species diversity of herbs and ferns in the low‐N treatment plots showed a slight increasing tendency. This may have been because the old‐growth temperate forest is an N‐limited ecosystem, so the moderate N input did not show a large influence on plant diversity. However, the long‐term high‐N treatment ultimately reduced plant diversity by changing the soil nutrient contents, decreasing the pH values, and damaging plant growth. Our results suggested that the long‐term excessive N addition negatively affected the forest ecosystem in an N‐limited temperature forest.     

Optimization of indole acetic acid production by isolated bacteria from Stevia rebaudiana rhizosphere and its effects on plant growth

The ability to synthesize Indole-3-acetic acid (IAA) is widely associated with the plant growth promoting rhizobacteria (PGPR). The present work deals with isolation and characterization of such bacteria from the rhizosphere of medicinal plant Stevia rebaudiana and optimization of IAA production from its isolates. The optimization of IAA production was carried out at different pH and temperature with varied carbon and nitrogen sources of culture media. Out of different isolates obtained, three of them were screened as efficient PGPRs on the basis of different plant growth promoting attributes. Isolates CA1001 and CA2004 showed better production of IAA at pH 9 (91.7?µg?ml^?1) and at temperature 37?°C (81.7?µg?ml^?1). Dextrose (1%) was found to be the best carbon source for isolate CA1001 with 104?µg?ml^?1 IAA production. Isolate CA 2004 showed best production of IAA 36?µg?ml^?1 and 34?µg?ml^?1 at 1.5% and 1% Beef extract as nitrogen source respectively. Isolate CA 1001 showed 32?µg?ml^?1 IAA production at 0.5% nicotinic acid concentration. From the current study, CA1001 and CA2004 emerged as noble alternatives for IAA production further which also resulted in root and shoot biomass generation in crop plants, hence can be further used as bio-inoculants for plant growth promotion.     

Numerical modelling of conductive and convective heat transfers in retinal laser applications

The control of the temperature increase is an important issue in retinal laser treatments. Within the fundus of the eye heat, generated by absorption of light, is transmitted by diffusion in the retinal pigment epithelium and in the choroid and lost by convection due to the choroidal blood flow. The temperature can be spatially and temporally determined by solving the heat equation. In a former analytical model this was achieved by assuming uniform convection for the whole fundus of the eye. A numerical method avoiding this unrealistic assumption by considering convective heat transfer only in the choroid is used here to solve the heat equation. Numerical results are compared with experimental results obtained by using a novel method of noninvasive optoacoustic retinal temperature measurements in rabbits. Assuming global convection the perfusion coefficient was evaluated to 0.07 s^?1, whereas a value of 0.32 s^?1 – much closer to values found in the literature (between 0.28 and 0.30 s^?1) – was obtained when choroidal convection was assumed, showing the advantage of the numerical method. The modelling of retinal laser treatment is thus improved and could be considered in the future to optimize treatments by calculating retinal temperature increases under various tissues and laser properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural studies of bacteriophage lambda heads and proheads by small angle X-ray diffraction.

We have examined a series of lambda proheads and mature structures by small angle X-ray diffraction. This technique yields spherically averaged density distributions and some information about surface organization of particles in solution.We find that gpE ² of proheads and heads forms shells with one of two radii; A^?, B^?, groE^?, and Nu3^? proheads have shells of radius 246 Å, while mature heads, urea-treated A^? proheads and C^? proheads have a radius of 300 Å. The expansion of proheads to mature heads is accompanied by a corresponding decrease in the thickness of the shell. groE^? proheads contain a core. This core is lost spontaneously from the structure and is only observed if the structures are fixed with glutaraldehyde prior to examination by X-ray diffraction or electron microscopy.C^? proheads expand to mature head size spontaneously. A preparation of C^? proheads which was fixed with glutaraldehyde at an early stage of the purification had the smaller, prohead radius. Unfixed particles from this preparation expanded to the mature head size after further purification and standing in the cold for several days. This result suggests that gpC may be involved in regulating head expansion.The radii of the protein shells of mature heads are identical for a series of phages that contain between 78% and 105% of the wild-type complement of DNA, and this radius is the same as that of proheads expanded in the absence of DNA. These results with phage lambda indicate that assembly of a double shell structure composed of coat and scaffolding protein, followed by expansion to a larger shell containing only coat protein is a general feature of the morphogenesis of dsDNA phages.     

Effect of Dimensional Changes on Plasma Characteristics in Electrothermal Capillary Discharges for Optimized Performance in Fusion Pellet Injection

Geometrical changes in capillary discharges influence the plasma properties and can control exit parameters to certain desired values. For a fixed capillary radius of 2 mm and a 72-μs 43.9-kA peak discharge current, the plasma temperature is about 2.7 eV for different capillary lengths due to the constant input energy, while the number densities tend to saturate for capillary lengths greater than 12 cm. The electrical conductivity reaches 4.02 × 104 Ω^?1 m^?1 and then tends to saturate for 9-cm capillary length. The maximum bulk velocity at the capillary exit slightly increases with the increase in the capillary length from 6.15 to 6.26 km/s for lengths below 18 cm and decreases to 5.88 km/s for longer capillaries due to the higher amount of ablated mass and increased drag forces. For a 9-cm length with the same 72-μs 43.9-kA peak discharge current, the increase in the capillary radius reduces the energy density, which in turn reduces the total ablate mass, plasma density, electrical conductivity, and exit pressure. It is shown that the plasma temperature decreases from 4.6 to 2.1 eV by increasing the capillary radius and radiant heat flux also drops from 463 to 18.1 GW/m². The exit bulk velocity drops from 8.7 to 5.3 km/s as the radius increases from 0.5 to 3.6 mm, respectively. The design features of a capillary discharge can be adjusted for the radius and length, to produce specific plasma parameters for desired applications. Scaling laws relating exit peak plasma parameters to radius and length are obtained to facilitate quick estimate of plasma parameters. The validation of this model has been confirmed by confronting with experimental measurements.     

Radiation transfer and heat budget during the ice season in Lake Pääjärvi, Finland

Lake Pääjärvi, a boreal Finnish lake, was investigated in winter for weather conditions, structure and thickness of ice and snow, solar radiation, and under-ice current and temperature. Heat budget of Lake Pääjärvi in January–March was governed by terrestrial radiation losses of 20–35 W m^?2 recompensed by ice growth of 0.5–1.0 cm day^?1. In April, snow melted, albedo decreased from 0.8 to <0.1, and the mean ice melt rate was 1.5 cm day^?1. Internal melting and surface melting were about equal. The mean turbulent heat loss was small. The heat flux from the water to ice was about 5 W m^?2 in winter, increasing to 12 W m^?2 in the melting season. The light attenuation coefficient was 1.1 m^?1 for the congelation ice (black ice) in winter, compared with 1.5 m^?1 for the lake water, and it was up to 3 m^?1 for candled congelation ice in spring, and about 10 m^?1 for superimposed ice (white ice) and snow. Gas bubbles were the main factor that reduced the transparency of ice. The radiation penetrating the ice heated the water body causing convective currents and horizontal heat transfer. This increased the temperature of the water body to about 3°C before the ice break-up. After the snow had melted, the euphotic depth (the depth of 1% surface irradiance) was estimated as 2.0 m, only two-thirds that in summer.     

Apple (Malus pumila var. domestica) phenology is advancing due to rising air temperature in northern Japan

Recent studies show advancing onset of plant growing season in many regions for the last several decades. With the well‐established dependence of plant phenology on temperature, these trends are interpreted as an indication of global warming. For several decades, however, other determinants of plant phenology, e.g. varieties and trends in managed systems, may have changed and confounded the phenological trends. In this study, we tested if long‐term changes in phenology of apple (Malus pumila var. domestica) are attributable to long‐term changes in temperature by comparing the phenological response to long‐term trend in air temperature, which is of our interest, with that to year‐to‐year fluctuation in air temperature, which should represent the real effect of temperature on phenology. We collected records of air temperature and phenological events (budding and flowering) in apple from 1977 to 2004 at six locations in Japan. Linear trends in flowering showed advancing rate in the range from 0.21 to 0.35 day yr^?1, statistically significant at three locations (P<0.05). We also found a warming trend in mean air temperature throughout March and April, with which flowering was closely correlated, in the range from 0.047 to 0.077 °C yr^?1, statistically significant at five locations (P<0.05). We separated the temperature time‐series into two components: a long‐term trend and a year‐to‐year fluctuation, by fitting smoothing spline to the trend and taking the residuals as the anomaly. We then fit a multiple regression model of phenological response to air temperature with separate coefficients for long‐term trend and anomaly. Flowering date responded to the long‐term trend at ?3.8 day °C^?1 and to the anomaly at ?4.6 day °C^?1. The temperature coefficients were not statistically different from each other or among locations, suggesting that the advance of apple phenology has predominantly been caused by the temperature increase across the locations studied. The same result was also observed with budding.     

Estimates of soil respiration and net primary production of three forests at different succession stages in South China

Soil respiration (heterotropic and autotropic respiration, R_g) and aboveground litter fall carbon were measured at three forests at different succession (early, middle and advanced) stages in Dinghushan Biosphere Reserve, Southern China. It was found that the soil respiration increases exponentially with soil temperature at 5 cm depth (T_s) according to the relation R_g=a exp(bT_s), and the more advanced forest community during succession has a higher value of a because of higher litter carbon input than the forests at early or middle succession stages. It was also found that the monthly soil respiration is linearly correlated with the aboveground litter carbon input of the previous month. Using measurements of aboveground litter and soil respiration, the net primary productions (NPPs) of three forests were estimated using nonlinear inversion. They are 475, 678 and 1148 g C m^?2 yr^?1 for the Masson pine forest (MPF), coniferous and broad‐leaf mixed forest (MF) and subtropical monsoon evergreen broad‐leaf forest (MEBF), respectively, in year 2003/2004, of which 54%, 37% and 62% are belowground NPP for those three respective forests if no change in live plant biomass is assumed. After taking account of the decrease in live plant biomass, we estimated the NPP of the subtropical MEBF is 970 g C m^?2 yr^?1 in year 2003/2004. Total amount of carbon allocated below ground for plant roots is 388 g C m^?2 yr^?1 for the MPF, 504 g C m^?2 yr^?1 for the coniferous and broad‐leaf MF and 1254 g C m^?2 yr^?1 for the subtropical MEBF in 2003/2004. Our results support the hypothesis that the amount of carbon allocation belowground increases during forest succession.     

Plant-mediated CH4 transport and C gas dynamics quantified in-situ in a Phalaris arundinacea-dominant wetland

Northern peatland methane (CH₄) budgets are important for global CH₄ emissions. This study aims to determine the ecosystem CH₄ budget and specifically to quantify the importance of Phalaris arundinacea by using different chamber techniques in a temperate wetland. Annually, roughly 70?±?35% of ecosystem CH₄ emissions were plant-mediated, but data show no evidence of significant diurnal variations related to convective gas flow regardless of season or plant growth stages. Therefore, despite a high percentage of arenchyma, P. arundinacea-mediated CH₄ transport is interpreted to be predominantly passive. Thus, diurnal variations are less important in contrast to wetland vascular plants facilitating convective gas flow. Despite of plant-dominant CH₄ transport, net CH₄ fluxes were low (–?0.005–0.016 μmol m^?2 s^?1) and annually less than 1% of the annual C-CO₂ assimilation. This is considered a result of an effective root zone oxygenation resulting in increased CH₄ oxidation in the rhizosphere at high water levels. This study shows that although CH₄, having a global warming potential 25 times greater than CO₂, is emitted from this P. arundinacea wetland, less than 9% of the C sequestered counterbalances the CH₄ emissions to the atmosphere. It is concluded that P. arundinacea-dominant wetlands are an attractive C-sequestration ecosystem.     

Key parameters for outdoor biomass production of Scenedesmus obliquus in solar tracked photobioreactors

The biomass productivity of Scenedesmus obliquus was investigated outdoors during all seasons in solar tracked flat panel photobioreactors (PBR) to evaluate key parameters for process optimization. CO₂ was supplied by flue gas from an attached combined block heat and power plant. Waste heat from the power plant was used to heat the culture during winter. The parameters pH, CO₂, and inorganic salt concentrations were automatically adjusted to nonlimiting levels. The optimum biomass concentration increased directly with the photosynthetic active radiation (PAR) from 3 to 5 g dry weight (DW)?L^?1 for a low PAR of 10 mol photons m^?2 day^?1 and high PAR of 40–60 mol photons m^?2 day^?1, respectively. The annual average biomass yield (photosynthetic efficiency) was 0.4?±?0.5 g DW mol^?1 photons. However, biomass yields of 1.5 g DW mol^?1 photons close to the theoretical maximum were obtained at low PAR. The productivity (including the night biomass losses) ranged during all seasons from ?5 up to 30 g DW m^?2 day^?1 with a mean productivity of 9?±?7 g DW m^?2 day^?1. Low night temperatures of the culture medium and elevated day temperatures to the species-specific optimum increased the productivity. Thus, continuous regulation of the biomass concentration and the culture temperature with regard to the fluctuating weather conditions is essential for process optimization of outdoor microalgal production systems in temperate climates.     

Linking Belowground Carbon Allocation to Anaerobic CH4 and CO2 Production in a Forested Peatland,New York State

Heterotrophic soil microorganisms rely on carbon (C) allocated belowground in plant production, but belowground C allocation (BCA) by plants is a poorly quantified part of ecosystem C cycling, especially, in peat soil. We applied a C balance approach to quantify BCA in a mixed conifer-red maple (Acer rubrum) forest on deep peat soil. Direct measurements of CH₄ and CO₂ fluxes across the soil surface (soil respiration), production of fine and small plant roots, and aboveground litterfall were used to estimate respiration by roots, by mycorrhizae and by free-living soil microorganisms. Measurements occurred in two consecutive years. Soil respiration rates averaged 1.2 bm μmol m^{? 2} s^{? 1} for CO₂ and 0.58 nmol m^{? 2} s^{? 1} for CH₄ (371 to 403 g C m^{? 2} year^{? 1}). Carbon in aboveground litter (144 g C m^{? 2} year^{? 1}) was 84% greater than C in root production (78 g C m^{? 2} year^{? 1}). Complementary in vitro assays located high rates of anaerobic microbial activity, including methanogenesis, in a dense layer of roots overlying the peat soil and in large-sized fragments within the peat matrix. Large-sized fragments were decomposing roots and aboveground leaf and twig litter, indicating that relatively fresh plant production supported most of the anaerobic microbial activity. Respiration by free-living soil microorganisms in deep peat accounted for, at most, 29 to 38 g C m^{? 2} year^{? 1}. These data emphasize the close coupling between plant production, ecosystem-level C cycling and soil microbial ecology, which BCA can help reveal.     

Purification and biochemical characterization of phytocystatin from Brassica alba

Phytocystatins belong to the family of cysteine proteinases inhibitors. They are ubiquitously found in plants and carry out various significant physiological functions. These plant derived inhibitors are gaining wide consideration as potential candidate in engineering transgenic crops and in drug designing. Hence it is crucial to identify these inhibitors from various plant sources. In the present study a phytocystatin has been isolated and purified by a simple two‐step procedure using ammonium sulfate saturation and gel filtration chromatography on Sephacryl S‐100HR from Brassica alba seeds (yellow mustard seeds).The protein was purified to homogeneity with 60.3% yield and 180‐fold of purification. The molecular mass of the mustard seed cystatin was estimated to be nearly 26 000 Da by sodium dodecyl sulfate polyacrylamide gel electrophoresis as well as by gel filtration chromatography. The stokes radius and diffusion coefficient of the mustard cystatin were found to be 23A° and 9.4 × 10^?7 cm²s^?1 respectively. The isolated phytocystatin was found to be stable in the pH range of 6–8 and is thermostable up to 60 °C. Kinetic analysis revealed that the phytocystatin exhibited non‐competitive type of inhibition and inhibited papain more efficiently (K_i = 3 × 10^?7 M) than ficin (K_i = 6.6 × 10^?7 M) and bromelain (Ki = 7.7 × 10^?7 M respectively). CD spectral analysis shows that it possesses 17.11% alpha helical content. Copyright © 2016 John Wiley & Sons, Ltd.     

Cd AND Zn TOLERANCE AND ACCUMULATION BY SEDUM JINIANUM IN EAST CHINA

Field survey, hydroponic culture, and pot experiments were carried out to examine and characterize cadmium (Cd) and zinc (Zn) uptake and accumulation by Sedum jinianum, a plant species native to China. Shoot Cd and Zn concentrations in S. jinianum growing on a lead/Zn mine area reached 103–478 and 4165–8349 mg kg^?1 (DM), respectively. The shoot Cd concentration increased with the increasing Cd supply, peaking at 5083 mg kg^?1 (DM) when grown in nutrient at a concentration of 100 μmol L^?1 for 32 d, and decreased as the solution concentration increased from 200 to 400 μmol L^?1. The shoot-to-root ratio of plant Cd concentrations was > 1 when grown in solution Cd concentrations ≤ 200 μmol L^?1. Foliar, stem, and root Zn concentrations increased linearly with the increasing Zn level from 1 to 9600 μmol L^?1. The Zn concentrations in various plant parts decreased in the order roots > stem > leaves, with maximum concentrations of 19.3, 33.8, and 46.1 g kg^?1 (DM), respectively, when plants were grown at 9600 μmol Zn L^?1 for 32 d. Shoot Cd concentrations reached 16.4 and 79.8 mg kg^?1 (DM) when plants were grown in the pots of soil with Cd levels of 2.4 mg kg^?1 and 9.2 mg kg^?1, respectively. At soil Zn levels of 619 and 4082 mg kg^?1, shoot Zn concentrations reached 1560 and 15,558 mg kg^?1 (DM), respectively. The results indicate that S. jinianum is a Cd hyperaccumulator with a high capacity to accumulate Zn in the shoots.     

Acclimatization of K+ uptake to changes in root temperature: experiments with oilseed rape and barley in flowing solution culture

Abstract Changes in the net uptake rate of K⁺ and in the average tissue concentration of K⁺ were measured over 14 d in response to changes in root temperature with oilseed rape (Brassica napus L. cv. Bien venu) and barley (Hordeum vulgare L. cv. Atem). Plants were grown in flowing nutrient solutions containing 2.5 mmol m^?3 K⁺ and were acclimatized over 49 d (rape) or 28 d (barley) to low root temperature (5°C) prior to steady–state treatments at root temperatures between 3 °C and 25 °C, with common air temperature. Uptake of K⁺ was monitored continuously over 14 d and nitrogen was supplied as NH₄⁺+ NO^?₃ or NH⁺₄ or NO^?₃. Unit absorption rates of K⁺ increased with time and with root temperature up to Day 4 or 5 following the change in root temperature. Thereafter they usually approached steady-state, with Q₁₀? 2.0 between 7 °C and 17°C, although rates became similar between 7 °C and 13°C. Uptake of K⁺ by rape plants was invariably greater under NO^?₃ nutrition compared with NH⁺₄. The percentage K⁺ in the plant dry matter increased with temperature from 2% at 3 °C to 4% at 25 °C in rape, but there was less effect of temperature on the average concentrations of K⁺ in the plant fresh weight or plant water content. Concentrations of K⁺ in the leaf water fraction of rape plants decreased with increasing root temperature, but in barley they increased with increasing root temperature. Concentrations of K⁺ in the root water fraction were relatively stable with respect to root temperature. The results are discussed in terms of compensatory changes in K⁺ uptake following a change in root temperature and the relationships between growth, shoot: root ratio and K⁺ composition of the plant.     

How in vitro light affects growth and survival of ex vitro cassava

Cassava is one of the most important food crops in Africa. Meristem culture is an effective method of eliminating viruses and other systemic diseases spread through the vegetative propagation of stems. However, in semi‐arid conditions, survival of ex vitro plants in the field is often disappointing. When an increasing range of light regimes in vitro was provided, the fresh and dry masses more than doubled their values between 29 and 369 mmol s^?1 m^?2 PPFDs. Increases in numbers of senescent leaves and stem thickness were also recorded with increasing PPFD. However, PPFD above 101 mmol s^?1 m^?2 resulted in 30–70% reduction in plant survival, with the thin plants with the smallest fresh and dry masses being the ones with highest survival rates. High light and temperature levels in the greenhouse were also found to be critical for plant survival. It was also shown that transpirational loss from detached leaves and epicuticular wax deposits were not good indicators for predicting survival of ex vitro cassava plantlets during acclimatisation.     

The effect of temperature of the rate of photosynthetic electron transfer in chloroplasts of chilling-sensitive and chilling-resistant plants

1. Photochemical activities as a function of temperature have been compared in chloroplasts isolated from chilling-sensitive (below approximately 12 °C) and chilling-resistant plants.2. An Arrhenius plot of the photoreduction of NADP⁺ from water by chloroplasts isolated from tomato (Lycopersicon esculentum var. Gross Lisse), a chilling-sensitive plant, shows a change in slope at about 12 °C. Between 25 and 14 °C the activation energy for this reaction is 8.3 kcal·mole^?1. Between 11 and 3 °C the activation energy increases to 22 kcal·mole^?1. Photoreduction of NADP⁺ by chloroplasts from another chilling-sensitive plant, bean (Phaseolus vulgaris var. brown beauty), shows an increase in activation energy from 5.9 to 17.5 kcal·mole^?1 below about 12 °C.3. The photoreduction of NADP⁺ by chloroplasts isolated from two chilling-resistant plants, lettuce (Lactuca sativa var. winter lake) and pea (Pisum sativum var. greenfeast), shows constant activation energies of 5.4 and 8.0 kcal·mole^?1, respectively, over the temperature range 3–25 °C.4. The effect of temperature on photosynthetic electron transfer in the chloroplasts of chilling-sensitive plants is localized in Photosystem I region of photosynthesis. Both the photoreduction of NADP⁺ from reduced 2,6-dichlorophenol-indophenol and the ferredoxin-NADP⁺ reductase (EC 1.6.99.4) activity of choroplasts of chilling-sensitive plants show increases in activation energies at approximately 12 °C whereas Photosystem II activity of chloroplasts of chilling-sensitive plants shows a constant activation energy over the temperature range 3–25 °C. The photoreduction of Diquat (1,1′-ethylene-2,2′-dipyridylium dibromide) from water by bean chloroplasts, however, does not show a change in activation energy over the same temperature range. The activation energies of each of these reactions in chilling-resistant plants is constant between 3 and 25 °C.5. The effect of temperature on the activation energy of these reactions in chloroplasts from chilling-sensitive plants is reversible.6. In chilling-sensitive plants, the increased activation energies below approximately 12 °C, with consequent decreased rates of reaction for the photoreduction of NADP⁺, would result in impaired photosynthetic activity at chilling temperatures. This could explain the changes in chloroplast structure and function when chilling-sensitive plants are exposed to chilling temperatures.     

Raising the Maximum Permissible Air Velocity in Controlled Environment Plant Growth Chambers

Phaseolus vulgaris L. plants were grown in two naturally lighted, outdoor controlled environment plant growth chambers. The approach velocity to the plant growing zone was 75 cm s^?1 in one chamber and 225 cm s^?1 in the other. The lower air velocity represents the presently considered maximum permissible air velocity in controlled environment plant growth chambers. The humidity in both chambers was near saturation. After three weeks' growth in these chambers, there were no significant differences in fresh or dry weights of the plants or any parts thereof. The high air velocity reduced the transpiration rate as predicted by energy budget considerations and significantly lowered the average leaf temperature of the crop by three degrees. The data strongly support the hypothesis that the maximum permissible air velocity in controlled environment plant growth chambers can be raised considerably if the humidity is maintained high.     

AN ALTERNATE GROWTH PATTERN FOR LAMINARIA LONGICRURIS1,2

A population of Laminaria longicruris de la Pylaie was followed for a year at Bic Island, Quebec, Canada where nutrient levels in the seawater were elevated throughout the year. Tagged kelp were measured each month for growth and analyzed for alginic acid, laminaran, mannitol, carbon, nitrogen, and nitrate. Maximum growth (3.5 cm · d^?1) was observed in June, and minimal growth (0.18 cm · d^?1) from December to February, when ice cover limited light levels. No reserves of carbon or nitrate were formed. Laminaran levels remained below 2.7% dry weight while tissue nitrate did not exceed 0.75 μmol · g^?1 dry weight. Total carbon produced per plant was 40 g C · yr^?1. Nutrient availability enables the kelp to take advantage of summer light and temperature conditions to grow rapidly.     

Application of the Entropy-Enthalpy Relationship in Water Transport through Plant Roots

Water transport through plant roots is determined by a single layer of cells, so that water passes through a plasmamembrane-cytoplasm-plasmamembrane system. The water transport shows an exponential relationship with temperature in two phases with an abrupt transition. The Arrhenius activation parameters log A and E are calculated for the two phases of water transport below and above the transition temperature. Between log A and E two linear and parallel relationships are observed, one for each phase of water transport. The difference of log A between these two relationships is a measure for a change in entropy in cell water structure at the transition temperature. The change in entropy was small (13.4 J · mol^?1· K^?1) in comparison to the difference in activation energy E for water transport above and below the transition temperature. The role of the plasmamembrane and cytoplasm in determining the cell water structure is discussed.