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1.
Abstract

The effects of blue light supplementation to red light on growth, morphology and N utilization in rice plants (Oryza sativa L. cv. Sasanishiki and Nipponbare) were investigated. Plants were grown under two light quality treatments, red light alone (R) or red light supplemented with blue light (RB; red/blue-light photosynthetic photon flux density [PPFD] ratio was 4/1), at 380 mol m?2 s?1 PPFD. The biomass production of both cultivars grown under RB conditions was higher than that of plants grown under R conditions. This enhancement of biomass production was caused by an increase in the net assimilation rate (NAR). The higher NAR was associated with a higher leaf N content per leaf area at the whole-plant level, which was accompanied by higher contents of the key components of photosynthesis, including Rubisco and chlorophyll. In Sasanishiki, preferential biomass investment in leaf blades and expansion of wider and thinner leaves also contributed to the enhancement of biomass production. These morphological changes in the leaves were not observed in Nipponbare. Both the changes in physiological characteristics, including leaf photosynthesis, and the changes in morphological characteristics, including leaf development, contributed to the enhancement of biomass production under RB conditions, although the extent of these changes differed between the two cultivars.  相似文献   

2.
The coupled heat and mass transfer in soil can be analysed by examining the temperature dependence of thermal conductivity. We have measured the thermal conductivity of two kinds of soil (Ando soil and Red Yellow soil) as a function of both temperature (5–75°C) and water content by the twin heat probe method. From our results we concluded that the thermal conductivity resulting from the latent heat transfer can be separated from the apparent thermal conductivity by subtracting the thermal conductivity at a temperature near 0°C from that at a higher temperature. The relation between the phenomenological enhancement factor (β) and the volumetric air‐filled porosity was divided into two parts: β increases linearly as the volumetric air‐filled porosity increases from zero (that is, water saturation), to the point at which soil water potential corresponds to ?320 J kg?1; from that point to oven‐dry condition, β decreased logistically with the volumetric air‐filled porosity. From these results, we could generalize the behaviour of β.  相似文献   

3.
One of the best ways to evaluate the coupled heat and mass transfer in soil is to measure the heat flux and water distribution simultaneously. For this purpose, we developed an apparatus for measuring the one‐dimensional steady‐state heat flux and water distribution in unsaturated soil under reduced air pressure. The system was tested using four samples with known thermal conductivity (0.6–8.0 W m?1 K?1). We confirmed that the system could measure the one‐dimensional steady‐state heat flux under a fixed temperature difference between ends of the samples over a wide range of thermal conductivity values. Time domain reflectometry was used to measure the water distribution with a repeatability of less than ± 1.0%. We used the apparatus to measure the soil heat flux and distribution of water content and temperature under steady‐state conditions with reduced air pressure. The initial volumetric water content, θini, of the soil samples was set at 0.20 and 0.40 m3m?3. For a θini of 0.20, the heat flux was not significantly affected by air pressure, and the water content on the hot side decreased whilst that on the cold side increased, i.e. a pronounced water content gradient was formed. For a θini of 0.40, the heat flux increased sharply with reduced air pressure, and the water content did not change, i.e. a homogeneous water distribution was observed. The increase in the heat flux with air pressure reduction is caused by the vapour transfer in soil pores. We found that a large vapour transfer took place in the soil with the homogeneous water distribution, and that the vapour transfer was less in the soil with the pronounced water content gradient. These experimental facts were entirely different from the traditional knowledge of vapour transfer in soil under temperature gradients. A lack of data on heat flux must have resulted in the previously incorrect conclusions. The new apparatus will serve to clarify the intricate phenomena of thermally induced vapour transfer in unsaturated soil in further experiments.  相似文献   

4.
The transition of grasslands to forests influences many ecosystem processes, including water and temperature regimes and the cycling of nutrients. Different components of the carbon biogeochemical cycle respond strongly to woody plant encroachment; as a consequence, the carbon balance of the invaded grasslands can change markedly. In our research, we studied the response of soil respiration (RS) to natural succession of calcareous grassland. We established two research sites, called grassland and invaded site, at each of which eddy flux measurement were also performed. Within these sites, triplicate plots were fenced for soil flux measurements. At the invaded site, measurements were performed for forest patches and grassy spaces separately. Soil respiration was strongly dependent on temperature and reached 8–12 µmol CO2 m?2 s?1 in mid‐summer; it was greater at the grassland than at the invaded site. RS dependence on temperature and soil water content was similar between the different vegetation covers (grassland, gaps and forest patches). At a reference temperature of 10°C, the average RS was 2.71 µmol CO2 m?2 s?1. The annual sums of RS were also similar between years and sites: 1345 ± 47 (2009) and 1150 ± 37 g C m?2 year?1 (2010) for grassland and 1324 ± 26 (2009) and 1268 ± 26 g C m?2 year?1 (2010) for the invaded site, which is at the upper range of the values reported in the literature. Cumulative RS peaked in July, with about 200 g C m?2. Large mid‐summer RS rates rely on strong biological activity supported by high, but non‐extreme soil temperatures and by regular summer precipitation. A coupling of photosynthesis and RS was revealed by a 24‐hour measurement, which showed asymmetrical clockwise hysteresis patterns.  相似文献   

5.
The aim of the present experiments was to study the effect of growth-related nutrient demand on Ca2+ translocation from roots to shoot of maize (Zea mays L.). The plants were grown under controlled environmental conditions in nutrient solution with constant Ca2+ supply. The growth-related demand for Ca2+ and other nutrients was modified by growing the plants with their apical shoot meristem either at air temperature (24°C/20°C day/night) or at 14°C. Reduction of the shoot meristem temperature (SMT) to 14°C decreased shoot growth without affecting root growth in the first five days, which diminished the growth-related demand of the shoot for nutrients per unit of roots. This decrease in shoot demand led to a reduction not only of Ca2+ translocation rates in intact transpiring plants but also of Ca2+ fluxes in the xylem exudate of decapitated plants. This indicates that the decrease in xylem flux of Ca2+ at low SMT was not only the result of low transpiration-related water flux, and thus possibly low apoplasmic bypass transport of Ca2+ into the stele. In decapitated plants precultured at low SMT, the water flux through the roots was diminished even more than Ca2+ flux, leading to a significant increase in the Ca2+ concentration of the exudate, and thus presumably an increase in the Ca2+ gradient between cytosol and apoplast of stelar parenchyma cells. When the osmotically driven water flux was reduced by addition of mannitol to the nutrient solution, Ca2+ concentration in the exudate markedly increased, whereas Ca2+ translocation was only slightly affected. From these results it is suggested that the decrease in Ca2+ translocation rates at low shoot demand was not related to low water flux but to direct effects on the capacity of Ca2+ transport mechanisms in the roots.  相似文献   

6.
The growth of sesame (Sesamum indicum L.) was studied at three root temperature regimes (25/25, 20/10 and 15/15°C day/night) factorially combined with three NO3 ‐: NH4 + ratios (mM ratios, 10:0, 8:2, or 6:4), as a source of nitrogen (N), in the irrigation solution. The air temperature was kept constant at 30°C. Transpiration, nutrient composition, and level of root‐born cytokinins and gibberellins in the xylem exudate were monitored. The two low root temperature regimes, 15/15 and 20/10°C, restricted the growth of sesame, reduced transpiration and increased the accumulation of soluble carbohydrates in the shoot and in the roots compared to the 25/25°C regime. The NO3:NH4 + ratios had no effect on growth. Nutrient contents in the shoot at low root temperatures, particularly K+, NO3 ‐, and H2PO4 ‐ were decreased markedly, but Na+ increased relative to it's content in the 25/25°C regime. Increasing NH4 + proportion in the irrigation solution raised total N concentration in the plant tissues at all root temperatures. The amounts of cytokinins and gibberellins in the xylem exudate decreased at the low root temperature regimes relative to the 25/25°C regime. Low root temperature reduced xylem transport of nutrients and root born‐phytohormones, most probably because of reduced water flow through the plant relative to the 25/25°C regime.  相似文献   

7.
Measurement of soil respiration to quantify ecosystem carbon cycling requires absolute, not relative, estimates of soil CO2 efflux. We describe a novel, automated efflux apparatus that can be used to test the accuracy of chamber‐based soil respiration measurements by generating known CO2 fluxes. Artificial soil is supported above an air‐filled footspace wherein the CO2 concentration is manipulated by mass flow controllers. The footspace is not pressurized so that the diffusion gradient between it and the air at the soil surface drives CO2 efflux. Chamber designs or measurement techniques can be affected by soil air volume, hence properties of the soil medium are critical. We characterized and utilized three artificial soils with diffusion coefficients ranging from 2.7 × 10?7 to 11.9 × 10?7 m2 s?1 and porosities of 0.26 to 0.46. Soil CO2 efflux rates were measured using a commercial dynamic closed‐chamber system (Li‐Cor 6400 photosynthesis system equipped with a 6400‐09 soil CO2 flux chamber). On the least porous soil, small underestimates (< 5%) of CO2 effluxes were observed, which increased as soil diffusivity and soil porosity increased, leading to underestimates as high as 25%. Differential measurement bias across media types illustrates the need for testing systems on several types of soil media.  相似文献   

8.
CO2 exchange was measured on the forest floor of a coastal temperate Douglas-fir forest located near Campbell River, British Columbia, Canada. Continuous measurements were obtained at six locations using an automated chamber system between April and December, 2000. Fluxes were measured every half hour by circulating chamber headspace air through a sampling manifold assembly and a closed-path infrared gas analyzer. Maximum CO2 fluxes measured varied by a factor of almost 3 between the chamber locations, while the highest daily average fluxes observed at two chamber locations occasionally reached values near 15 μmol C m−2 s−1. Generally, fluxes ranged between 2 and 10 μmol C m−2 s−1 during the measurement period. CO2 flux from the forest floor was strongly related to soil temperature with the highest correlation found with 5 cm depth temperature. A simple temperature dependent exponential model fit to the nighttime fluxes revealed Q10 values in the normal range of 2–3 during the warmer parts of the year, but values of 4–5 during cooler periods. Moss photosynthesis was negligible in four of the six chambers, while at the other locations, it reduced daytime half-hourly net CO2 flux by about 25%. Soil moisture had very little effect on forest floor CO2 flux. Hysteresis in the annual relationship between chamber fluxes and soil temperatures was observed. Net exchange from the six chambers was estimated to be 1920±530 g C m−2 per year, the higher estimates exceeding measurement of ecosystem respiration using year-round eddy correlation above the canopy at this site. This discrepancy is attributed to the inadequate number of chambers to obtain a reliable estimate of the spatial average soil CO2 flux at the site and uncertainty in the eddy covariance respiration measurements.  相似文献   

9.
An apparatus was developed for the quantitative collection of volatile sulfur compounds released by intact plants and was used to study the effects of leaf temperature and stomatal aperture on the amount and pattern of release.

An air stream sweeps volatiles released by the plants through a water‐cooled condenser system in which the air is dried prior to trapping the volatile sulfur compounds on activated carbon. Tests with 35S‐labelled 1‐butanethiol gave a mean recovery of 95.8 ± 4.3%.

The yield of volatile sulfur compounds increased greatly when air flow rate increased from 1 to 2 1 min‐1 , but was independent of flow rate over the range 2 to 6 1 min‐1. About 93% of the trapped activity originated from plant shoots, about 1% from stem bases and roots and about 4% from culture solutions.

Release of volatile sulfur compounds from intact plants followed a diurnal pattern, maximum rates occurring around midday and minimum rates overnight. Maximum rates of release ranged from 30 to 41 ng S g dry weight of shoots‐1 2 hr ‐1, while minimum rates ranged from 1.5 to 2.1 ng S g dry weight of shoots‐1 2hr‐1. Leaf temperature rather than stomatal aperture seemed to be the major factor controlling rate of release of volatile sulfur compounds. The rate of release was almost doubled by an increase of 7–9°C in leaf temperature.  相似文献   


10.
Abstract

The hilly terrain of the Appalachian region creates an environment in which large differences in soil temperature occur over a very short distance on the landscape. The ability of a grass to display adequate growth over a range of temperatures would greatly enhance its adaptability and use as a forage or for soil conservation. A growth chamber experiment was conducted to evaluate the influence of temperature on the growth of six bermudagrass [Cynodon dactylon (L.) Pers.] selections from the Appalachian region. Midland, a cold tolerant bermudagrass, was included in the study for comparison purposes. The grasses were grown under a 14 hour day length with three day/night temperature regimes: 18°C/13°C, 27°C/21°C, and 35OC/29°C. Two of the selections had significantly higher dry matter production than Midland over the range of temperatures.

This effect was especially pronounced at 35°C where the top growth of Quicksand common and Selection 13 exceeded that of Midland by 206% and 158%, respectively. The higher yielding selections were comparable to the other bermudagrasses when mineral concentrations, neutral detergent fiber, acid detergent fiber and acid detergent lignin levels were considered. Both Quicksand common and Selection 13 seem to have the potential to be particularily useful on south facing slopes where elevated soil temperatures are encountered.  相似文献   

11.
Time domain reflectometry (TDR), while widely used to measure volumetric water content (θ) and bulk electrical conductivity (BEC) in unsaturated granular soils, remains less studied in peat than mineral soils. Empirical models commonly used in mineral soils are not applicable to peat for accurate determination of θ from measured apparent dielectric permittivity (?). Past studies for peat report highly variable calibrations, and suggest differences in origin of organic matter, degree of decomposition and bound water to explain such variability. This study shows that bound water appears to have minimal impact on calibration because of its negligible volumetric fraction at the low bulk densities of peat. Increased volumetric air fraction at the same θ values attributed to high porosity of peat makes the ?‐θ relationships of mineral soils inapplicable. Temperature effects on ? resulted in a correction factor for θ. The temperature correction factor decreased with decreasing θ and was determined experimentally to lie between ?0.0021 m3 m?3 per °C for θ≥ 0.79 m3 m?3 and ?0.0005 m3 m?3 per °C for θ = 0.35 m3 m?3. The decreasing value of the correction factor with θ can be explained by dependence of the ?‐θ relationship on properties of free water alone. Temperature dependence of BEC was close to that of soil solution. Maxwell‐De Loor's four‐phase mixing model (MDL) based on physical properties of the multiphase soil system can efficiently simulate the effect of increased air volume and varying soil temperature on the ?‐θ relationship in peat. In addition, linear ?‐θ calibration in peat can be improved when BEC is included in the calibration equation.  相似文献   

12.
Formation of ordered structures from disordered amylose is practically important. The thermal behavior of high-amylose maize starches was studied during cooling, following heating, and during subsequent reheating. Four commercial high-amylose genotype maize starches with varying amylose contents (ae du, ae su2, and ae [nominally both 50 and 70% amylose]) were heated to either 120, 140, 160, or 180°C, cooled to 5°C, and reheated to 180°C in a differential scanning calorimeter. Each starch was studied with its native lipid, as well as in reduced-lipid and lipid-free form. On cooling of lipid-containing starches, two distinct exotherms were observed and attributed to amylose-lipid complex formation and to amylose chain association. A distinct exotherm at ≈75°C was attributed to amylose-lipid complex formation. The exotherm attributed to amylose chain association on cooling varied according to the initial heat treatment, lipid level, and starch type. Starches with higher amylose contents showed larger exotherms on cooling. For initial heat treatments to 120 or 140°C, a broad exotherm beginning at ≈95°C was observed on cooling. In contrast, for initial heat treatments to 160 and 180°C, a sharper exotherm with a peak temperature below ≈55°C was observed. Upon reheating, samples that had been initially heated to 120 or 140°C showed a peak at >140°C that was attributed to the melting of ordered amylose. Starches initially heated to 160 or 180°C did not show this peak. This work illustrates that initial heating temperature, as well as lipid content and amylose content, all affect amylose chain association during cooling. Thus, this work suggests strategies for controlling ordering of amylose during processing.  相似文献   

13.
Oilseed rape (Brassica napus L.) response to root temperature regimes (20/20, 16/8 and 12/12°C day/night) at constant 20°C air temperature was studied. At each regime, three NO3 ‐:NH4 + ratios (10:0, 8:2, or 6:4), at constant 10 mM N, in the irrigation solution were tested. Plant growth, transpiration, ionic composition and level of cytokinins and gibberellins in the xylem exudate were monitored. The two low root temperature regimes, 12/12 and 16/8°C, reduced rape shoot growth by 28 and 22%, and increased the accumulation of soluble carbohydrates by 42 and 26% in the roots, respectively, as compared to the 20/20°C regime. Low root temperatures reduced plants transpiration. The NO3 ‐:NH4 + ratios had no effect on rape growth. At low root temperatures NO3 ‐contents increased in the shoot and decreased in the roots. The sum of cations and that of anions at 12/12 and 16/8°C root temperatures decreased significantly as compared to 20/20°C. The presence of NH4 + in the irrigation solution decreased the concentrations of Ca2+ and Mg2+ in the shoots and roots and increased that of Cl‐ in the shoots and of H2PO4 ‐ in the roots at all root temperatures. Cytokinins and gibberellins contents in the xylem exúdate decreased at the low root temperature regimes. Low root temperature reduced total upward transport of the mineral nutrients and phytohormones, most probably because of reduced water flow through the plant.  相似文献   

14.
Aerated solution culture is frequently used for studying plant growth. Few comparisons have been made of root growth in solution with that found in soil. The objective of this study was to compare root growth and root hair development in these two mediums. Corn (Zea mays L.) grown in aerated solution at two temperatures (18 and 25°C) and three P concentrations (2, 10, and 500 μmol L‐1) was compared with that in three soils, Raub (Aquic Argiudoll) and two Chalmers (Typic Haplaquoll) silt loams, in a controlled climate chamber over 21d. Corn plant weight and root growth were similar in solution culture and Raub soil when grown at an air and soil temperature of 18°C. At 25°C both yield and root growth were greater in Raub soil, even though P uptake by corn was 7‐fold greater in solution culture. The same difference was found when corn grown at 25°C in solution culture at 3 different P concentrations was compared with that grown in Chalmers soil at two P levels. Percentage of total root length with root hairs, root length and density and consequently root surface area, were all greater in the Chalmers soil than in solution culture. An increase in soil P, resulted in a decrease in root hair growth. No such relationship was found in solution culture. Although the recovery and measurement of plant roots and root hairs is more convenient in solution culture, results from this study indicate that the usefulness of solution culture for determining those factors which control root growth and root hair development in soil is limited.  相似文献   

15.
The effects of temperature and water potential on nitrification were investigated in two Iowa soils treated with Stay‐N 2000. The soils were incubated at 10, 20, and 30 °C after soil water potentials of ?1, ?10, or ?60 kPa were applied to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K max), duration of lag period (t′), period of maximum nitrification (Δt), and termination period of nitrification (t s). The highest K max were 18 and 24 mg kg?1 d?1 nitrate (NO3 ?)–nitrogen (N), respectively, at 30 °C and ?10 kPa in both the Nicollet (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll) and Canisteo (fine‐loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) soils and reduced to 4 and 16 mg kg?1 d?1 NO3 ?‐N when Stay‐N 2000 was added. The extension of t′ due to the addition of Stay‐N 2000 was as high as 7 d in the Nicollet soil at 10 °C and ?1 kPa and as little as 2 d in the Canisteo soil at 20 °C and ?10 kPa.  相似文献   

16.
The browning indicators furosine and color were determined in infant cereals and infant cereals containing powdered milk to evaluate the utility of these parameters for monitoring storage. Studies were made on seven infant cereal samples including both gluten and gluten‐free products. Samples were stored under laboratory conditions at 28°C for four or 16 weeks; or under modified water activity conditions at 25°C or 55°C for one, two, three, or four weeks; or under industrial conditions in air or nitrogen atmospheres at 32°C or 55°C for one, three, six, or 12 months. Furosine levels increased during the storage of infant cereals containing powdered milk under all time, temperature, and water activity (aw) conditions assayed, except drastic conditions (55°C, aw = 0.65). Color values increased in infant cereals with gluten (7‐cereal and 8‐cereal samples), regardless of milk content, when they were stored under drastic conditions (55°C or 25°C with normal or modified water activity). However, the gluten‐free infant cereals (rice‐corn and rice‐corn‐soy samples) that have a characteristic yellow color showed no increase in color during storage. The extent of the Maillard reaction was greatest in the infant cereals that included milk in their formulation.  相似文献   

17.
Abstract

The volume of soil treated with P fertilizer affects P uptake by the crop. Earlier studies have shown that the stimulation of root growth in P‐fertilized soil was similar for both corn (Zea mays L.) and soybean (Glycine max L. Merr). The objective of this research was to determine the effect of fertilizer P placement on P uptake and shoot and root growth of spring wheat (Triticum vulgare L.). Wheat was grown for 34 days in Raub silt loam (Aquic Argiudolls) in a controlled climate chamber. One rate of phosphate per pot, 150 mg P per three kg of soil, was mixed with 2, 5, 10, 20, 40 and 100% of the soil in the pot. The P was equilibrated with moist soil for 5 days at 70°C followed by 21 days at 25° C before transplanting 8‐day‐old wheat plants into each 3 L pot. The P stimulation of root growth in the P‐treated soil was similar to that for corn and soybeans. The effect could be described by the equation y = x0.7 where y is the fraction of the root system in the P‐fertilized soil where P is mixed with x fraction of the soil. The greatest P uptake and plant growth occurred when added P was mixed with 20% of the soil.  相似文献   

18.
A modified differential scanning calorimeter procedure was used to determine the relationship between temperature and unfrozen water content (UWC) in seven clays between 0°C and – 15°C to – 24°C. The procedure, which involved nucleation by a cooling followed by a rapid warming to – 0.l°C, avoided the difficulty of supercooling. Problems caused by temperature lag between the sample and its holder and by slowness of water movement within the sample, important even when cooling clay samples of about 17 mm3 at a rate of 0.31 K min?1, were overcome by cooling in a stepwise fashion which allowed time for equilibration between each temperature step. The clays studied included sodium and calcium Wyoming bentonites, < 1 μm and 1–2 pm fractions of St Austell kaolinite and three subsoil clays from England. After nucleation and as temperature fell below OT, water froze in two stages in most of the clays. UWCs at the minimum temperatures reached were up to 38% for the bentonites, between 9% and 20% for the subsoil clays and <4% for the kaolinites.  相似文献   

19.
The influence of soil temperature on nutrient accumulation in aerial portions of sorghum plants was evaluated in a greenhouse experiment. Plants were grown in 20‐liter containers at cooled and ambient soil temperatures of 20 and 25C, respectively, and were harvested at the 8‐ and 12‐leaf stages of development for yield and nutrient analysis.

At the 8‐leaf stage, sorghum plants subjected to 25C were significantly higher in concentration of N, P, K, Mg, and Cu, but were significantly lower in Ca. Soil temperature did not significantly affect concentration of Zn, Fe, and Mn. At the 12‐leaf stage, sorghum plants grown in the warm soil temperature treatment were lower in concentration of N, K, Ca, Mg, Zn, Fe, Mn, and Cu than plants grown in the cooled‐soil treatment. Phosphorus showed a negative response to increased temperature.

It was concluded that further research relating element uptake and translocation to temperature is needed. Element accumulation in the roots, stems, leaves, and floral and seed portions of the plant should be included. In addition, the interaction between plant age and element concentration should be studied more thoroughly. Both this study and the published literature indicate that this interaction is significant for many of the elements.  相似文献   


20.
Abstract

On air‐drying, the ATP contents of two moist soils fell to about one quarter of their original values. When a freshly‐sampled soil (field temperature 5.5°C) was stored moist (43% water holding capacity) for 7 days at 25°C the ATP content increased from 4.54 to 7.84 μg ATP g‐1 soil. Storage at 10°C caused a smaller increase; to 5.39 μg g‐1 soil. Microbial biomass C also increased on storage but the relative increase was less than that of ATP. Thus the biomass C/ATP ratio fell from 234 in the freshly sampled soil to 168 in the soil stored moist for 7 days at 25°C. The ATP content declined to less than half its starting value if storage was under waterlogged conditions.

The ATP method for determining microbial biomass in soil depends on the use of a constant factor (5.85 mg ATP g‐1 biomass C) for converting ATP content to biomass C. This factor came from work on soils that had been stored moist at 25°C for several days before biomass C and ATP measurements were made: it is only applicable to soils that have been stored in this way.  相似文献   

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