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At least 73 records · Page 4Linked to original sources
PubMed2007

Water source partitioning among trees growing on shallow karst soils in a seasonally dry tropical climate.

The sources of water used by woody vegetation growing on karst soils in seasonally dry tropical regions are little known. In northern Yucatan (Mexico), trees withstand 4-6 months of annual drought in spite of the small water storage capacity of the shallow karst soil. We hypothesized that adult evergreen trees in Yucatan tap the aquifer for a reliable supply of water during the prolonged dry season. The naturally occurring concentration gradients in oxygen and hydrogen stable isotopes in soil, bedrock, groundwater and plant stem water were used to determine the sources of water used by native evergreen and drought-deciduous tree species. While the trees studied grew over a permanent water table (9-20 m depth), pit excavation showed that roots were largely restricted to the upper 2 m of the soil/bedrock profile. At the peak of the dry season, the delta(18)O signatures of potential water sources for the vegetation ranged from 4.1 +/- 1.1 per thousand in topsoil to -4.3 +/- 0.1 per thousand in groundwater. The delta(18)O values of tree stem water ranged from -2.8 +/- 0.3 per thousand in Talisia olivaeformis to 0.8 +/- 1 per thousand in Ficus cotinifolia, demonstrating vertical partitioning of soil/bedrock water among tree species. Stem water delta(18)O values were significantly different from that of groundwater for all the tree species investigated. Stem water samples plotted to the right of the meteoric water line, indicating utilization of water sources subject to evaporative isotopic enrichment. Foliar delta(13)C in adult trees varied widely among species, ranging from -25.3 +/- 0.3 per thousand in Enterolobium cyclocarpum to -28.7 +/- 0.4 per thousand in T. olivaeformis. Contrary to initial expectations, data indicate that native trees growing on shallow karst soils in northern Yucatan use little or no groundwater and depend mostly on water stored within the upper 2-3 m of the soil/bedrock profile. Water storage in subsurface soil-filled cavities and in the porous limestone bedrock is apparently sufficient to sustain adult evergreen trees throughout the pronounced dry season.

Carbon Isotopes↗
PubMed1992

Use of two types of estradiol-releasing skin patches for menopausal patients in a tropical climate.

As part of a program to evaluate nonoral routes for delivery of estrogen replacement therapy at the National University Hospital, Singapore, we assessed two different 50 micrograms estradiol patches. The first study (patch A) was terminated because of a high rate of skin reactions. Tests of the components of this patch identified the alcohol carrier as the cause of these reactions when combined with an occlusive membrane in the tropical Singapore climate. A subsequent clinical trial with 21 female subjects was undertaken with a different 50 micrograms estradiol patch (patch B). Twenty patients completed the 6-month study. Patch B was as effective as patch A, caused fewer skin reactions, and adhered better.

Administration, Cutaneous↗
PubMed1991

[Nasal mucosa in tropical climate].

Morphological and functional results of the factors influencing the nasal mucous membranes of 150 persons living in a tropical zone are presented. In particular, an increased rate of hyperplastic mucosa was found in comparison with a group of 850 subjects from central Germany. The macroscopic results correlated with exfoliative cytological examination. On the other hand, the rates of moderate and severe hyposmia (9.3%) as well as moderate and extreme nasal obstruction (34%) were lower.

Adult↗