Transpiration efficiency

The amount of growth occurring when rainfall is limited depends on the ratio of assimilation rate to transpiration rate. In a leaf the instantaneous transpiration efficiency, A E, is given approximately by... 

Genetic variation in discrimination and transpiration efficiency In the experiments decribed earlier on A and W in wheat, peanut, barley, tomato and cotton, there was a great deal of genetic variation which still fitted the relationship described by Equation 8. The range of A in one species is often about 2 to 4 x 10 (e.g. Hubick et al., 1986 with peanut, and similarly from surveys of wheat, cotton, barley and cowpea). 

Hubick, K.T. Farquhar, G.D. (1989). Genetic variation of transpiration efficiency among barley genotypes is negatively correlated with carbon isotope discrimination. Plant, Cell and Environment (in press). 

Thompson, A. J., J. Andrews et al. (2007). Overproduction of abscisic acid in tomato increases transpiration efficiency and root hydraulic conductivity and influences leaf expansion. Plant Physiol. 143(4) ... 

The solar radiation incident on a unit horizontal surface at the top of the atmosphere. It is sometimes referred to as solar irradiance. The latitudinal variation of insolation supplies the energy for the general circulation of the atmosphere. Insolation depends on the angle of incidence of the solar beam and on the solar constant, instantaneous transpiration efficiency... 

A measure of the amount of water used by plants per unit of plant material produced. The term can be applied at the leaf, whole-plant, and ecosystem levels. At the leaf level, it is more precisely referred to as the instantaneous transpiration efficiency, the C02 assimilation rate (photosynthesis) divided by the transpiration rate (the moles of C02 taken up divided by the moles of water lost through transpiration in a unit of time per unit leaf area). At the whole-plant level, it is more precisely referred to as the growth water-use efficiency, the units of dry matter... 

Consistent with conductance values, transpiration rates were much higher in Seaton Park under irrigation and closer to Clare ones under drought. Good agreement was presented between water economy indexes and photosynthetic parameters so transpiration efficiency and 1-Ce/Ca index values were always higher in Clare, both in water stressed and nonstressed plants at irradiation levels above and bellow 1000 pE m s (table 4). ... 

Rosenberg, N. J. (1981). The increasing CO2 concentration in the atmosphere and its implications on agricultural productivity. I. Effects on photosynthesis, transpiration and water use efficiency. Climat. Change 3,265-279. 

The effect of zearalenone on crop development may be connected to its influence on the status and functioning of the photosynthetic apparatus (Koscielniak et al. 2008). The after-effects of zearalenone on the growth of soybean and wheat plants, net photosynthesis and transpiration rates, stomatal conductance, photochemical efficiency of photosystem 2 and on final seeds yield were determined. Modifications in leaf area were more pronounced in soybean than in wheat, and this tendency increases in successive developmental phases. The net photosynthesis was stimulated during the juvenile phase and during that of the final one by about 13.6% (average) in soybean plants. Stimulation of transpiration was also observed after... 

Research on ABA has practical implications for Agriculture since water is a limiting factor for crop production in many areas of the world. On an experimental scale ABA and certain derivatives have been applied to crop plants as "antitranspir-ants (71, 72). In short-term experiments transpiration was considerably reduced without much effect on the rate of photosynthesis. Thus, applied ABA increased the water-use efficiency of plants. 

Evidence was obtained recently that pesticide vapors may enter the air by still another mechanism, involving plant circulation and water loss (57). Rice plants were found to efficiently transport root-zone applied systemic carbamate insecticides via xylem flow to the leaves, eventually to the leaf surface by the processes of guttation and/or stomatal transpiration, and finally to the air by surface volatilization. Results from a model chamber showed that 4.2, 5.8, and 5.7% of the residues of carbaryl, carbofuran, and aldicarb, respectively, present in rice plants after root soaking vaporized within 10 days after treatment. The major process was evaporation of surface residues deposited by guttation fluid. 

Pending further work on these new magnetic semiconductors, metallic ferromagnets are in principle, the most convenient spin polarized sources for spin device work. The obvious configuration of direct Ohmic contact between metal and semiconductor proved to have fundamental shortcomings. The conductivity mismatch between the two materials implies very indifferent spin injection efficiency [174, 175], However it transpires that this difficulty is surmountable [176] by placing a tunnel barrier between the... 

Leaf transpiration rates closely parallel photosynthetic rates over a range of light intensities (i.e., 400 to 1200 pmol m 2 sec 1) (Soja and Haunold, 1991). Water use efficiency, therefore, remains rather stable relative to photosynthesis until the light intensity drops below 300 pEm-2-sec 1. Here water use efficiency decreases sharply, with transpiration being higher relative to photosynthesis. 

A related quantity is the transpiration ratio, which is the reciprocal of the water-use efficiency and hence represents the water lost per CO2 fixed. 

By Equation 8.39, water-use efficiency (WUE) is proportional to photosynthesis/ transpiration, so... 

Under normal conditions of water availability, values for LAI in pastures of B. brizantha have been measured above 4.0. However with the establishment of a water deficit in the soil, these values decrease to below two or even lower in pastures of P. maximum (Roberts et al. 1996). A similar situation is found in abandoned pastures in eastern Amazonia, where a reduction of approximately 68% of green tissue has been observed in the dry season, while in an adjacent area of primary forest this reduction was only 16% (Nepstad et al. 1994). Primary forests, which have deep root systems and little seasonal variation in LAI, maintain stable subcanopy microclimatic conditions and transpirational flux, even during the dry season. Because of an evergreen forest canopy, the return of the rainy season has less impact on the microclimate near the soil in the forest than in the pastures, and the deep soil water stores are also more efficiently recharged in the forest. 

The transpiration of water to the atmosphere through biomass stomata is proportional to the vapor pressure difference between the atmosphere and the saturated vapor pressure inside the leaves. Transpiration is obviously affected by atmospheric temperature and humidity. The internal water is essential for biomass growth. The efficiency of utilizing this water (water-use efficiency, WUE) has been defined as the ratio of biomass accumulation to the water consumed, expressed as transpiration or total water input to the system. Analysis of the transpiration phenomenon and the possibilities for manipulation... 

Low humidity is a familiar problem to indoor gardeners. During the heating season, indoor humidity may only be 10 percent. Most tropical species require 40-60 percent humidity to thrive. The easiest way to increase humidity is to run a whole-house or portable humidifier. Not quite as efficient, but still worthwhile, is the practice of keeping a pan of water near a heat source. Grouping plants together also improves indoor humidity because leaf transpiration from a cluster of plants increases the air moisture in the immediate area. To further humidify a plant grouping, set plants on trays filled with l"of pebbles and A" of water. 

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