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In this research the relative importance of leaf area and microclimatic factors in determining water use of tree lines was
examined in sub-humid Western Kenya. Measurements of tree water-use by a heat-balance technique, leaf area, bulk air saturation
deficit, daily radiation, and soil water content were done in an experiment with tree lines within crop fields. The tree species
were Eucalyptus grandis W. Hill ex Maiden, Grevillea robusta A. Cunn. and Cedrella serrata Royle, grown to produce poles on a phosphorus-fixing Oxisol/Ferralsol with (+P) or without (−P) phosphorus application. Doubling
the leaf area of Cedrella and Grevillea doubled water use in a leaf area (LA) range of 1–11 m2 per tree. The response of Eucalyptus water use (W) to increases in leaf area was slightly less marked, with W = LAn, n<1. Transpiration rate per unit leaf area (Tr) was the other important determinant of water use, being affected by both tree
species and phosphorus fertilization. A doubling of the saturation deficit (SD) halved the water use of all trees except for
Cedrella +P, in which water use increased. A direct effect of soil water content on water use was only found in Grevillea -P,
with a small increase (60%) as available water increased from 1.4 to 8.9% above wilting point (32%). This low direct response
to soil water content is probably due to the extensive tree-root systems and the deep clayey soils supplying sufficient water
to meet the evaporative demand. Indirect responses to soil water content via decreases in leaf area occurred in the dry season.
The results showed that water use of tree lines was more determined by leaf area and transpiration rate per unit leaf area
than by micro meteorological factors. The linear response of tree water use to leaf area, over a wide range leaf areas, is
a specific characteristic of tree line configurations and distinguished them from forest stands. In tree lines light interception
and canopy conductance increase with leaf area much more than a similar leaf area increase would have caused in a closed forest
canopy. 相似文献
4.
Derero Abayneh Coe Richard Muthuri Catherine Hadgu Kiros M. Sinclair Fergus 《Agroforestry Systems》2021,95(7):1309-1326
Agroforestry Systems - Increasing tree cover and managing trees better on farms in Ethiopia supports livelihoods and the environment but most tree-planting schemes promote only a few species. This... 相似文献
5.
- The amplitude, duration, frequency, and predictability of runoff and inundation of aquatic habitats are key hydrological characteristics linked to aquatic ecosystem functioning and biodiversity, but they are seldom integrated into analyses of Amazon floodplain ecology. Remote sensing approaches, measurements and modelling of floodplain hydrology provide a basis for this integration.
- Effective legislation to protect floodplains and other wetlands depends on operational definitions that require application of hydrological data.
- Extent and changes of flooded areas are linked to fish diversity and to presence and growth of flooded forests and floating plants.
- Dam construction reduces river system connectivity and modifies the flood pulse, with major negative implications for floodplain ecosystems adapted to and dependent on a natural flood regime.
- Trends and variability in climate plus deforestation are altering the Amazon's hydrological cycle, causing changes in discharge and flooded area with concomitant ecological impacts.
6.
Coe WR 《Science (New York, N.Y.)》1945,102(2649):344-346
7.
Models predict that food-web structure is regulated by both consumers and resources, and the strength of this control is dependent on trophic position and food-web length. To test these hypotheses, a meta-analysis was conducted of 11 fish (consumer)-by-nutrient (resource) factorial plankton community experiments. As predicted, zooplankton biomass was under strong consumer control but was weakly stimulated by nutrient additions; phytoplankton biomass was under strong resource control with moderate control by fish. However, the phytoplankton and zooplankton responses to nutrient additions did not follow theoretical predictions based on the number of trophic levels in the food web. 相似文献
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TF. JUBB P. BRIGHTLING J. MALMO† MT. LARCOMBE GA. ANDERSON SJ. HIDES‡ 《Australian veterinary journal》1989,66(10):334-336
Anoestrous dairy cows in seasonally calving herds in the Macalister Irrigation District of Gippsland, Victoria were treated at the start of the mating period with a progesterone releasing intravaginal device (CIDR). The CIDR was inserted for 7 days and 400 IU of PMSG was injected intramuscularly at removal. There was no clinically useful difference among cows receiving the CIDR, a placebo and untreated cows in the interval from treatment to either first oestrus or conception, the conception rate to first service or percent pregnant by the end of mating. Analyses of data from 2-year-old cows, older cattle, cows calved at least 45 days or cows calved at least 55 days and cows treated 3 weeks after the start of mating did not show improved reproductive performance following treatment with the CIDR. 相似文献
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