Fluxes of carbon dioxide and water vapor above paddy fields

An experiment was conducted to investigate the influence of stage of growth at harvest on fermentative characteristics of Digitaria eriantha subsp. eriantha silage. The treatment included three different growth stages (early vegetative, boot stage and full-bloom stage). The materials were ensiled either directly (unwilted) or after wilting for a period of 5–6 h prior to the ensiling. Samples of silage were taken from three bottles at 0, 7, 21 and 120 d for analysis of fermentative characteristics. Within the directly cut silage, stage of harvesting had no effect on pH on day 7, but on days 21 and 120 there were differences. Lower pH was recorded consistently for the boot stage silage. Within the prior-wilted groups, lower pH was recorded on day 7 for the boot growth stage while the difference between the growth stages in terms of pH was not significant on day 21. Within the directly cut silage, lactic acid concentration was consistently higher for the boot stage as compared to the early or full-bloom stage. Similarly, within the prior-wilted group, silages harvested at the boot growth stage resulted in higher lactic acid concentration on days 7 and 21, but on day 120 lactic acid concentration was higher for the early vegetative stage. In directly cut silages, harvesting at the boot growth stage resulted in a higher acetic acid concentration than that of the early vegetative growth stage or the full-bloom growth stage. For wilted silage, however, lower acetic acid concentration was recorded for the boot stage silage. In directly cut silage, the total nitrogen (N) concentration of boot-stage silage on day 120 was higher compared to the rest, but within the wilted silage the N value for boot-stage silage was not significantly different compared to the early vegetative stage. At day 120 the ammonianitrogen concentration increased for the early vegetative growth stage and full-bloom growth stage, while it was either reduced or remained similar for the boot-stage harvest when compared to the control. Under the current set of experiments, harvesting at the boot growth stage seems beneficial as the silage is lower in pH, higher in lactic acid concentration and able to retain most of the nitrogen in the silage for later use by the target animal.

Nitrogen (N) is the most limiting nutrient for coffee production in Colombia. An adequate supply is especially important during the vegetative period of growth, since any deficiency during this short period is known to have lasting effects on subsequent coffee bean production. Urea fertilizer is commonly applied on the soil surface since steep slopes hamper incorporation into soil, a practice which increases the risk of N volatilization. Little information is available on N recovery during early growth stages under different fertilizer application practices. The aim of this study was therefore to provide a comparison of 15N uptake during the early vegetative growth stage under surface-applied and incorporation practices at two contrasting locations. The highest proportion of plant N derived from fertilizer (Ndff) occurred 60 days following application at the site with greater precipitation and soil organic matter, where surface application also increased the Ndff in roots and stems after 120 days. Although fertilizer N supplied approximately 20–29% of total plant N after 4 months, this fertilizer-derived N corresponded on average to only 5% of the total application, indicating that very little fertilizer (relative to how much is applied) reaches plants during this time. Apart from the difference in Ndff observed at the wetter site, there was no effect of application method on dry weight and macronutrient content in different plant components, root to shoot ratio, and leaf 13C content. However, site effects were registered for most of these measurements, with the exception of total nutrient uptake. Similarly to Ndff trends, lower root/shoot ratio and higher concentrations of N, K, and Mg in aboveground biomass were found in the site with higher rainfall and soil organic matter, likely resulting from higher soil water and N availability. These findings provide new information useful as a direction for further research looking toward increasing NUE during the vegetative stage in Colombian coffee crops.

Continuous and direct measurements of ecosystem carbon dioxide and water vapour fluxes can improve our ability to close regional and global carbon and hydrological budgets. On this behalf, an international and multidisciplinary group of scientists (micrometeorologists, ecophysiologists and biogeochemists) assembled at La Thuile, Italy to convene a workshop on ‘Strategies for Monitoring and Modelling CO2 and Water Vapour Fluxes over Terrestrial Ecosystems’. Over the course of the week talks and discussions focused on: (i) the results from recent field studies on the annual cycle of carbon dioxide and water vapour fluxes over terrestrial ecosystems; (ii) the problems and pitfalls associated with making long‐term flux measurements; (iii) alternative methods for assessing ecosystem carbon dioxide and water vapour fluxes; (iv) how direct and continuous carbon dioxide and water vapour flux measurements could be used by the ecological and biogeochemical modelling communities; and (v) if, how and where to proceed with establishing a network of long‐term flux measurement sites. This report discusses the purpose of the meeting and summarizes the conclusions drawn from the discussions by the attending scientists.There was a consensus that recent advances in instrumentation and software make possible long‐term measurements of carbon dioxide and water vapour fluxes over terrestrial ecosystems. At this writing, eight research teams have conducted long‐term carbon dioxide and water vapour flux experiments and more long‐term studies are anticipated. The participants advocated an experimental design that would make long‐term flux measurement valuable to a wider community of modelers, biogeochemists and ecologists. A network of carbon dioxide and water vapour flux measurement stations should include ancillary measurements of meteorological, ecological and biological variables. To assess spatial representativeness of the long term and tower‐based flux measurements, periodic aircraft‐based flux experiments and satellite‐based assessments of land cover were recommended. Occasional cuvette‐based measurements of leaf‐level carbon dioxide and water vapour fluxes were endorsed to provide information on the biological control of surface fluxes. They can also provide data to parameterize ecophysiological models. Flask sampling of stable carbon isotopes was advocated to extend the flux measurements to the global scale.

Accurate estimation of the canopy chlorophyll content (CCC) plays a key role in quantitative remote sensing. Maize (Zea mays L.) is a high-stalk crop with a large leaf area and deep canopy. It has a non-uniform vertical distribution of the leaf chlorophyll content (LCC), which limits remote sensing of CCC. Therefore, it is crucial to understand the vertical heterogeneity of LCC and leaf reflectance spectra to improve the accuracy of CCC monitoring. In this study, CCC, LCC, and leaf spectral reflectance were measured during two consecutive field growing seasons under five nitrogen treatments. The vertical LCC profile showed an asymmetric ‘bell-shaped’ curve structure and was affected by nitrogen application. The leaf reflectance also varied greatly between spatio–temporal conditions, which could indicate the influence of vertical heterogeneity. In the early growth stage, the spectral differences between leaf positions were mainly concentrated in the red-edge (RE) and near-infrared (NIR) regions, whereas differences were concentrated in the visible region during the mid-late filling stage. LCC had a strong linear correlation with vegetation indices (VIs), such as the modified red-edge ratio (mRER, R2 = 0.87), but the VI–chlorophyll models showed significant inversion errors throughout the growth season, especially at the early vegetative growth stage and the late filling stage (rRMSE values ranged from 36% to 87.4%). The vertical distribution of LCC had a strong correlation with the total chlorophyll in canopy, and sensitive leaf positions were identified with a multiple stepwise regression (MSR) model. The LCC of leaf positions L6 in the vegetative stage (R2-adj = 0.9) and L11 + L14 in the reproductive stage (R2-adj = 0.93) could be used to evaluate the canopy chlorophyll status (L12 represents the ear leaf). With a strong relationship between leaf spectral reflectance and LCC, CCC can be estimated directly by leaf spectral reflectance (mRER, rRMSE = 8.97%). Therefore, the spatio–temporal variations of LCC and leaf spectral reflectance were analyzed, and a higher accuracy CCC estimation approach that can avoid the effects of the leaf area was proposed.

In several maize (Zea mays L.) growing regions, sudden, shortterm decreases in temperature may occur when plants are in early vegetative growth stages. Limited research has been reported, however, on the effects of short periods of cold stress during early vegetative stages on subsequent growth and development. Consequently, we studied responses of inbreds A619, B14A, B37, and FR4A to 3/8, 5/10, and 7/12 C night/day temperatures administered for 72 hours at three vegetative growth stages in a growth chamber. Distinct genotypic responses to temperature stress were observed. Seedling growth of B14A was reduced by about 50% by 3/8 and 5/10 C temperatures compared to control plants under constant 10/16 C night/day temperatures. The 3/8 C treatment caused a significant increase in heat units required for B14A to reach the pollen shedding stage of development. These traits were not affected by cold treatments for A619 and B37.A second experiment with B14A, B37, and their single cross hybrid (B14A ✕ B37) was performed with a 72‐hour, 3/8 C temperature treatment imposed at the third‐leaf stage. Treated plants of inbred B14A produced significantly less shoot, root, and total plant dry weight/heat unit than did control plants grown constantly at 10/16 C night/day temperatures. Inbred B37 was not affected by temperature treatments, and the B14A ✕ B37 single cross exhibited a dominant phenotype for tolerance to cold stress. We concluded that maize response to short‐term temperature stress is under genetic control.

Azorhizobium caulinodans was directly inoculated onto rice plants in three short-term pot trials. Addition of increasing amounts of sucrose (23, 46, 92 kg ha–1) did not influence the N economy of the A. caulinodans-rice association during the early vegetative growth stage. A. caulinodans inoculation alone and in combination with the highest amount of sucrose had a significantly positive effect on the N balance, with small but significant N gains in the system. Application of 60 kg urea-N ha–1 had a negative impact on the N economy of the inoculated treatments. N losses increased and the amount of atmospheric N2 fixed and incorporated decreased significantly as compared to the amounts under the 20 kg urea-N ha–1 regime. However, N losses were low – a maximum of 8% – at the early vegetative growth stage under the conditions of the experiments. C limitation does not seem to be a limiting factor for the incorporation of fixed N2 in this bacteria-plant association. Biological N2 fixation caused by A. caulinodans inoculation was responsible for 14% of the plant N at the vegetative growth stage and under low N conditions.

Chloris gayana is a warm-season grass, often cultivated in areas where soil salinity is a major constraint for forage production. Five cultivars (2 unselected populations and 3 synthetic varieties) were evaluated through agronomic traits as well as Inter Simple Sequence Repeats (ISSRs) and Sequence-related Amplified Polymorphism (SRAP) molecular markers. The consensus between both agronomic and molecular data sets was high (>99%) suggesting that both systems provided similar estimates of genetic relationships. The analysis revealed that synthetic varieties, Finecut, Topcut and Santana, were the most genetically different cultivars, whereas the unselected populations, Pioneer and Katambora, were closely related. Responses to salinity stress during germination and early vegetative growth stages were evaluated in only the synthetic varieties. The results showed that Finecut and Santana were able to germinate in the same proportion as controls even at concentrations of 200 mM NaCl. Under hydroponic conditions, Santana attained approximately 20% higher total dry weight than the other 2 varieties and the longest roots. Finecut presented the highest root dry weight. These results suggested that Santana and Finecut showed high salinity tolerance at germination and early vegetative growth stages, both crucial phases when seeking a successful pasture establishment, particularly in saline environments. Further studies in the field are needed to determine if these hydroponic results are reproduced under field conditions.

Soybean cultivars are sensitive to flooding stress and their seed yields are substantially reduced in response to the stress. This study was conducted to investigate the genetic basis of flooding tolerance at an early vegetative growth stage. Sixty recombinant inbred lines derived from a cross between a relatively tolerant cv. ‘Misuzudaizu’ and a sensitive cv. ‘Moshidou Gong 503’ were grown in pots in a vinyl plastic greenhouse in 2002 and 2003. At the two‐leaf stage, half of the pots were waterlogged by water placed in plastic containers and adjusted to 5 cm above the soil surface. After 3 weeks of treatment, the pots were returned to the greenhouse and grown until maturity. Flooding tolerance was evaluated by dividing the seed weight of the treated plants by that of the control plants. Quantitative trait loci (QTL) analysis using 360 genetic markers revealed three QTLs for flooding tolerance, ft1 to ft3 in 2002. The ft1 (molecular linkage group C2) was reproducible and an additional four QTLs, ft4 to ft7, were found in 2003. The ft1 had a high LOD score in both years (15.41 and 7.57) and accounted for 49.2% and 30.5% of the total variance, respectively. A large QTL for days to flowering was consistently observed across treatments and years at a similar position to ft1. Comparing the relative location with markers, the maturity gene probably corresponds to E1. Late maturity may have conferred a longer growth period for recovery from flooding stress.

At the early vegetative growth stage, mungbean are mostly affected by drought, and it is also one of the most promising stages that can be used to screen for drought stress tolerance traits in multiple varieties. Therefore, this study utilized polyethylene glycol (PEG-6000) to induce drought stress towards selection of drought tolerance mungbean varieties in their early vegetative growth stage using both hydroponics and soil based systems. In this study, leaf wilting index and responses of biochemical molecules were used as the basic factors to determine the effect of PEG-induced drought stress among the mungbean varieties. Prior to the imposition of drought stress, germination potentials of the varieties were evaluated and all had germination = 60%. Except for Tvr29 and Tvr44, hydroponic system revealed that = 80% of the varieties had = 1 of their leaves significantly (P = 0.05) wilted. The highest LWI were recorded for Tvr49 and Tvr79. Re-evaluation of Tvr29, Tvr44, Tvr49 and Tvr79 using soil, shows that Tvr29 and TVr44 resisted drought stress. The hydrogen peroxide, superoxide radical and malondialdehyde contents decreased in TVr29 and Tvr44, and increased in Tvr49 and Tvr79 in comparison to the control. Tvr29 and Tvr44 had high proline content than Tvr49 and Tvr79. Based on LWI and biochemical molecules, this study revealed that Tvr29 and Tvr44 should be utilized where water deficit is a challenge to mungbean globally.

Seasonal variation in toxic steroidal alkaloids of foothill death camas (Zigadenus paniculatus)

Salinity is a principal environmental severe stress that significantly threatens crop production, including soybeans. It considerably affects various plant growth and physiological traits at different soybean growth stages, especially in coastal areas. However, the high soil pH in these regions presents a challenge. In this study, we screened two soybean varieties using an easy and rapid, and inexpensive screening technique. This study aimed to select soybean tolerance salinity stress in the early vegetative growth stage under hydroponic culture. The study was meticulously done with a randomized complete block design comprising two factors (varieties and NaCl) with three replications. Two soybean varieties, i.e., ‘Gepak Kuning and Dering 1’, were tested at three NaCl levels, i.e., 0, 60, and 120 mM. The results showed that each type of plant behaved differently to each stress level. The stress of 60 mM revealed that the Dering 1 variety was tolerant, whereas the Gepak Kuning variety was only somewhat tolerant. In conclusion, the Gepak Kuning variety was tolerant to 60 mM salinity stress, while the Dering 1 variety showed 60 mM and 120 mM salinity tolerance. These results will help select the most tolerant varieties to develop salinity-tolerant varieties in the future.

The photochemical reflectance index from directional cornfield reflectances: Observations and simulations

Relationship of area-averaged carbon dioxide and water vapour fluxes to atmospheric variables

Fluxes of carbon dioxide, water vapor, and heat were measured above crop canopy using the eddy covariance method during the 2008 maize growing season, over an agricultural field within an oasis located in the middle reaches of Heihe River basin, northwest China. The values for friction velocity, the Monin–Obukhov stability parameter, and energy balance closure indicated that the eddy covariance system at this study site provided reliable flux estimates. Results from measurements showed that the mean sensible heat flux was 70 W m−2 with a maximum value of 164 W m−2 (May) and a minimum value of 45 W m−2 (July) during the maize growing season. In contrast, the mean latent heat was 278 W m−2 with a maximum value of 383 W m−2 (July) and minimum of 101 W m−2 (May). The mean downward soil heat flux was 55 W m−2 with a maximum value of 127 W m−2 (May) and minimum of 49 W m−2 (July). The magnitude of mean daytime net CO2 uptake was −11.50 μmol m−2 s−1 with a maximum value of −28.32 μmol m−2 s−1 (18 and 19 July) and a minimum values of −0.32 μmol m−2 s−1 (18 and 19 May). Correlation was observed between daytime half-hourly carbon dioxide flux and canopy conductance. In addition, the relationship between carbon dioxide flux and photosynthetically active radiation for selected days during different stages of maize growing season indicated the carbon dioxide flux uptake by the canopy was controlled by actual photosynthetic activity related to the variation of green leaf area index for the different growing stages.

ABSTRACTForests in the south‐eastern United States experienced a prolonged dry spell and above‐normal temperatures during the 1995 growing season. During this episode, nearly continuous, eddy covariance measurements of carbon dioxide and water vapour fluxes were acquired over a temperate, hardwood forest. These data are used to examine how environmental factors and accumulating soil moisture deficits affected the diurnal pattern and magnitude of canopy‐scale carbon dioxide and water vapour fluxes. The field data are also used to test an integrative leaf‐to‐canopy scaling model (CANOAK), which uses micrometeorological and physiological theory, to calculate mass and energy fluxes. When soil moisture was ample in the spring, peak rates of net ecosystem CO2 exchange (NF) occurred around midday and exceeded 20 μmol m−2 s−1. Rates of NK were near optimal when air temperature ranged between 22 and 25°C. The accumulation of soil moisture deficits and a co‐occurrence of high temperatures caused peak rates of daytime carbon dioxide uptake to occur earlier in the morning. High air temperatures and soil moisture deficits were also correlated with a dramatic reduction in the magnitude of NE. On average, the magnitude of NE decreased from 20 to 7 μmol m−2 s−1 as air temperature increased from 24 to 30°C and the soil dried. The CANAOK model yielded accurate estimates of canopy‐scale carbon dioxide and water vapour fluxes when the forest had an ample supply of soil moisture. During the drought and heat spell, a cumulative drought index was needed to adjust the proportionality constant of the stomatal conductance model to yield accurate estimates of canopy CO2 exchange. The adoption of the drought index also enabled the CANOAK model to give improved estimates of evaporation until midday. On the other hand, the scheme failed to yield accurate estimates of evaporation during the afternoon.