We analyzed the eddy covariance measurements of momentum, mass, and energy taken daily throughout five consecutive seasonal courses (i.e. 840 d after planting) of a pineapple [Ananas comosus (L.) Merr. cv. Red Spanish] field growing in the Orinoco lowlands. This field provides an opportunity for micrometeorological studies because of the flat and windy site; the seasonal weather including ENSO effects and the Crassulacean Acid Metabolism (CAM) physiology of the crop were additional attributes. Soil CO2 flux was quantified and added to the net ecosystem exchange in order to obtain the canopy flux (FC). The canopy CO2 flux partially followed the four phases of CAM sensu Osmond (1978). The daily pattern of gaseous exchange in pineapple showed a continuum spectrum in which a major proportion of CO2 uptake occurring during the daytime was common and in which the CAM expression was related to day and nocturnal CO2 uptake. However, the benefits of CO2 uptake at low water cost were constrained by the limited nocturnal CO2 uptake. Seasonal and ontogenetic changes affected the energy exchange as well as the partitioning of available energy into sensible (QH) and latent (QLE) heat. When the hourly net radiation (QRn) reached its maximum value, latent heat flux (QLE) to available energy throughout the vegetative and reproductive stages was 0.65, 0.05, 0.30, 0.11, and 0.33 for the 1997 wet season, 1997/98 dry season, 1998 wet season, 1998/99 dry season, and 1999 wet season, respectively. Throughout the growth period, we found the pivotal role of surface conductance (gs) in both QLE and FC. Furthermore, the canopy responded to environmental changes. During the wet seasons the gs was strongly influenced by humidity mole fraction deficit and was usually lower than aerodynamic conductance, whereas during the dry seasons, soil water deficit limited evapotranspiration and production rates. For the fully canopy cover, the hourly trend of marginal water cost of pineapple carbon gain in the dry seasons indicated that gs became sufficiently efficient to reduce the amount of water transported per unit of carbon gain. In the wet season, the coupling of CO2 uptake and stomatal conductance was more effective in maintaining a higher proportionality between QLE and gs. and J. San-José, R. Montes, N. Nikonova.
Lowering irradiance can delay the flower stalk, i.e., spike development, in order to schedule flowering time of Phalaenopsis; however, the effect on photosynthetic performance and spiking inhibition remains poorly understood. We compared light and shade treatments of Phalaenopsis aphrodite subsp. formosana in order to determine how limiting light affects day-night changes in the photosynthetic capacity of leaves and the carbon pool of leaves and stems resulting in delayed spiking. The low irradiance treatment [20 μmol(photon) m-2 s-1] for six weeks did not affect potential functions of photosynthetic apparatus estimated by chlorophyll a fluorescence analysis, but it significantly reduced the net CO2 uptake and O2 evolution rates, carbohydrate and organic acid concentrations, and amplitudes of CAM activity in new and fully expanded leaves of Phalaenopsis and delayed the spiking compared with the control kept at 150 μmol(photon) m-2 s-1. The shortened stem contained a remarkably high sucrose concentration, accounting for more than 80% of total soluble sugars for both treatments throughout the day. Moreover, the sucrose concentration was unaffected by the lowering of irradiance. The relationship between the sucrose content and spiking seemed to be loose; the major factor(s) for spiking in Phalaenopsis remained to be ascertained as the flower stalk bud is attached to the shortened stem., Y.-C. Liu, C.-H. Liu, Y.-C. Lin, C.-H. Lu, W.-H. Chen, H.-L. Wang., and Obsahuje seznam literatury
The article focuses on a list of options for using interpolations, often referred to as interpolation of higher types. The article pays attention to several representatives of control systems. The issue is also conceived in relation to the preparation of the NC program by CAD/CAM, where the data is prepared for control systems. The available functions of CAD/CAM systems are very diverse. The preparation of the NC program is also related to the issue of postprocessors and therefore they are mentioned in the article as well. Let this article be a basis for those who are interested in the creation of NC programs using non-standard interpolations and serve as an introduction to this issue. and Obsahuje seznam literatury
Leafless Duvalia velutina Lavranos (Apocynaceae) is an
arido-active stem succulent common in the arid region southwest of the Arabian Peninsula. This region is characterized by a short wet season with erratic rainfall and a long dry season with high temperature and high irradiance. We investigated the survival strategy of D. velutina by studying nurse association, gas exchange, and chlorophyll fluorescence. Results showed that D. velutina exhibited the strict nurse association with shade for protection against heat and high irradiance. Results also showed that D. velutina is an obligate CAM plant with ample physiotypic plasticity involving a shift to CAM-idling under prolonged drought. Chlorophyll fluorescence measurements revealed water stress-induced reduction of PSII activity occurring in concomitance with a marked rise of nonphotochemical quenching and chlorenchyma anthocyanin content. These results reflected photoprotective capacity involving nonradiative excess energy dissipation and antioxidative attributes. We concluded that the complex survival strategy of D. velutina in its natural arid habitat includes a multifaceted interplay of nurse association, physiotypic plasticity, and photoprotective mechanisms., Y. S. Masrahi, T. A. Al-Turki, O. H. Sayed., and Obsahuje seznam literatury