Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Direct and indirect effects of elevated CO2 on transpiration from Quercus myrtifolia in a scrub-oak ecosystem (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Elevated atmospheric carbon dioxide (Ca) usually reduces stomatal conductance, but the effects on plant transpiration in the field are not well understood. Using constant-power sap flow gauges, we measured transpiration from Quercus myrtifolia Willd., the dominant species of the Florida scrub-oak ecosystem, which had been exposed in situ to elevated Ca (350 µmol mol−1 above ambient) in open-top chambers since May 1996. Elevated Ca reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively. Temporarily reversing the Ca treatments showed that at least part of the reduction in transpiration was an immediate, reversible response to elevated Ca. However, there was also an apparent indirect effect of Ca on transpiration: when transpiration in all plants was measured under common Ca, transpiration in elevated Ca-grown plants was lower than that in plants grown in normal ambient Ca. Results from measurements of stomatal conductance (gs), leaf area index (LAI), canopy light interception and correlation between light and gs indicated that the direct, reversible Ca effect on transpiration was due to changes in gs caused by Ca, and the indirect effect was caused mainly by greater self-shading resulting from enhanced LAI, not from stomatal acclimation. By reducing light penetration through the canopy, the enhanced self-shading at elevated Ca decreased stomatal conductance and transpiration of leaves at the middle and bottom of canopy. This self-shading mechanism is likely to be important in ecosystems where LAI increases in response to elevated Ca.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00557.x
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Net grassland carbon flux over a subambient to superambient CO2 gradient (2001)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 7 (2001), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Increasing atmospheric CO2 concentrations may have a profound effect on the structure and function of plant communities. A previously grazed, central Texas grassland was exposed to a 200-µmol mol−1 to 550 µmol mol−1 CO2 gradient from March to mid-December in 1998 and 1999 using two, 60-m long, polyethylene- covered chambers built directly onto the site. One chamber was operated at subambient CO2 concentrations (200–360 µmol mol−1 daytime) and the other was regulated at superambient concentrations (360–550 µmol mol−1). Continuous CO2 gradients were maintained in each chamber by photosynthesis during the day and respiration at night. Net ecosystem CO2 flux and end-of-year biomass were measured in each of 10, 5-m long sections in each chamber. Net CO2 fluxes were maximal in late May (c. day 150) in 1998 and in late August in 1999 (c. day 240). In both years, fluxes were near zero and similar in both chambers at the beginning and end of the growing season. Average daily CO2 flux in 1998 was 13 g CO2 m−2 day−1 in the subambient chamber and 20 g CO2 m−2 day−1 in the superambient chamber; comparable averages were 15 and 26 g CO2 m−2 day−1 in 1999. Flux was positively and linearly correlated with end-of-year above-ground biomass but flux was not linearly correlated with CO2 concentration; a finding likely to be explained by inherent differences in vegetation. Because C3 plants were the dominant functional group, we adjusted average daily flux in each section by dividing the flux by the average percentage C3 cover. Adjusted fluxes were better correlated with CO2 concentration, although scatter remained. Our results indicate that after accounting for vegetation differences, CO2 flux increased linearly with CO2 concentration. This trend was more evident at subambient than superambient CO2 concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00445.x
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    VALIDATION OF THE SWAT MODEL ON A LARGE RWER BASIN WITH POINT AND NONPOINT SOURCES (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 37 (2001), S. 0 
    Details
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The State of Texas has initiated the development of a Total Maximum Daily Load program in the Bosque River Watershed, where point and nonpoint sources of pollution are a concern. Soil Water Assessment Tool (SWAT) was validated for flow, sediment, and nutrients in the watershed to evaluate alternative management scenarios and estimate their effects in controlling pollution. This paper discusses the calibration and validation at two locations, Hico and Valley Mills, along the North Bosque River. Calibration for flow was performed from 1960 through 1998. Sediment and nutrient calibration was done from 1993 through 1997 at Hico and from 1996 through 1997 at Valley Mills. Model validation was performed for 1998. Time series plots and statistical measures were used to verify model predictions. Predicted values generally matched well with the observed values during calibration and validation (R2≥ 0.6 and Nash-Suttcliffe Efficiency ≥ 0.5, in most instances) except for some underprediction of nitrogen during calibration at both locations and sediment and organic nutrients during validation at Valley Mills. This study showed that SWAT was able to predict flow, sediment, and nutrients successfully and can be used to study the effects of alternative management scenarios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1752-1688.2001.tb03630.x
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Effects of soil type on soybean crop water use in weighing lysimeters (1990)
    Springer
    Irrigation science 11 (1990), S. 77-81 
    Details
    ISSN: 1432-1319
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Different soils are known to affect the amount and distribution of both available water and roots. Optimising irrigation water use, especially when shallow water-tables are present requires accurate knowledge of the root zone dynamics. This study was conducted to determine the effect of two soil types on root growth, soil water extraction patterns, and contributions of a water-table to crop evaporation (E). Two weighing lysimeters (L1 and L2) with undisturbed blocks of soil were used. The soil in L1 had higher hydraulic conductivity and lower bulk density than that in L2. Well watered conditions were maintained by irrigation for the first 110 days from sowing (DFS). Root length density (RLD) was calculated from observations made in clear acrylic tubes installed into the sides of the lysimeters. Volumetric soil water contents were measured with a neutron probe. A water-table (EC = 0.01 S m-1) was established 1 m below the soil surface 18 DFS. RLD values were greater in L1 than L2 at any depth. In L1, maximum RLD values (3 × 104 m m-3) were measured immediately above the water-table at physiological maturity (133 DFS). In L2, maximum RLD values (1.5 × 104 m m-3) were measured at 0.42 m on 120 DFS and few roots were present above the water-table. From 71 to 74 DFS, 55 and 64% of E was extracted from above 0.2 m for L1 and L2, respectively. In L2, extraction was essentially limited to the upper 0.4 m, while L1 extraction was to 0.8 m depth. Around 100 DFS the water-table contributed 29% (L1) and 7% (L2) of the water evaporated. This proportion increased rapidly as the upper soil layers dried following the last substantial irrigation 106 DFS. Over the whole season the water-table contributed 24% in L1 and 6.5% in L2 of total E.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188443
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Effects of soil type on soybean crop water use in weighing lysimeters (1990)
    Springer
    Irrigation science 11 (1990), S. 69-75 
    Details
    ISSN: 1432-1319
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Accurate estimation of crop evaporation from a range of soil types is fundamental to the continued improvement of irrigation management. In this experiment soybean crop evaporation was measured using two weighing lysimeters, one with an undisturbed block of Hanwood loam (L1), the other with undisturbed Mundiwa clay loam (L2). Although both soils have clay profiles the Hanwood loam was much more freely draining. A fresh water-table (EC = 0.01 S m-1) was maintained 1 m below the soil surface of each lysimeter after 18 days from sowing (DFS). The crop (var. Chaffey) was sown on 18 November 1985 both in and around the lysimeters and was harvested 136 days later. Early crop growth was slower in L2 but growth stages after 60 DFS were similar to L1. Estimated leaf area indices exceeded 3 about 51 and 56 DFS for L1 and L2 respectively and were both greater than 9 at 90 DFS. The crop was well watered until at least 110 DFS. However daily rates of evaporation (E) from L1 noticeably exceeded those of L2 beginning around 50 DFS and increased to 30% greater for the period 70 to 115 DFS. This difference was not due to incorrect calibration. Plant water status measurements were generally similar although covered leaf water potential and foliage temperature values indicated that plants on L1 were less well hydrated than on L2. The causes of the E difference are not known, but it was observed that plants in L2 were about 0.1 m shorter than the surrounding plants which were similar in stature to those in L1. It was speculated that this difference in height created a shelter effect which reduced the net radiant energy absorbed by the canopy at low sun angles and reduced the wind speed controlling the turbulent exchange of water vapour. This study highlights the lack of under-standing that exists about the effect that small discontinuities in crop height can have on the spatial variability of evaporation within crops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188442
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Spatial variability of water vapor turbulent transfer within the boundary layer (1992)
    Springer
    Boundary layer meteorology 61 (1992), S. 389-406 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Although the physics of evaporation within the inner region of the boundary layer is believed to be well understood, observations of mass-energy exchange processes have been hindered by the limitations of point sensors. A combination of point sensors and active remote sensing, namely, water-Raman Lidar measurements, offers new opportunities to study relatively large areas at temporal and spatial scales previously unattainable. Results from experiments over uniform canopies both confirm some traditional theories and challenge some of the underlying assumptions concerning the homogeneity of the surface-atmosphere interface and the use of point sensors to characterize large areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119099
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...