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At least 235 records · Page 13Linked to original sources
PubMedDate not supplied

Offsetting changes in biomass allocation and photosynthesis in ponderosa pine (Pinus ponderosa) in response to climate change.

We examined the effect of climate on aboveground biomass allocation of ponderosa pine (Pinus ponderosa) by measuring trees in disjunct forest stands growing on the same substrate at high-elevation montane sites and low-elevation desert sites. Climatic differences between the sites were comparable to the difference between present and future climates of interior North America that is expected to result from a doubling of atmospheric CO(2) concentration. Relative to the montane populations, the desert populations allocated a greater proportion of biomass to sapwood (functional xylem) at the expense of foliage. The leaf/sapwood area ratio and percent of aboveground biomass in sapwood for trees of the same height were 0.201 m(2) cm(-2) and 58% for montane trees and 0.104 m(2) cm(-2) and 71% for desert trees. In a phytotron experiment, increases in net photosynthesis and net assimilation rate for seedlings grown under future conditions of high CO(2) and temperature were offset by a decrease in leaf area ratio. As was observed for large trees at different elevations, increased temperatures caused an increase in biomass allocation to stem in the phytotron seedlings. Thus, CO(2)- and temperature-driven shifts in biomass allocation negated the effect on growth of the CO(2)-driven increase in carbon assimilation rate. Our data from the controlled growth chamber and field experiments suggest that future climate conditions, including elevated atmospheric CO(2), may not stimulate growth and productivity of ponderosa pine.

Journal Article↗
PubMed2000

[Man in a hot climate--early studies of the Institute of Military Physiology].

In the 1950's many IDF soldiers were hospitalized for heat stroke--about 25% of whom died. Analyzing these cases revealed that commanders misinterpreted human ability to perform in the heat and ignored basic concepts of fluid and electrolyte balance and heat load. In the early 1960's a series of studies was conducted with regard to soldiers' performance in the heat. The first study (1959), which later became a classic, was conducted during a 21-day march from Eilat to Metula, crossing all climatic zones of Israel. The study was followed by other investigations which approached the issues of voluntary dehydration, fluid consumption vs sweat loss, salt additives, and the effect of heat load on performance. Based on these early studies, proper regulations were issued to field officers. Over the years, the lessons learned from these studies saved many lives. The number of cases of heat stroke and of other climate-related injuries was dramatically reduced, and performance was enhanced.

Acclimatization↗
PubMedDate not supplied

[Comparative statistics of cancers in Sahara (author's transl)].

Statistics of 204 cases of cancer observed in Saharian populations from 1969 to 1976 and a comparison with studies previously made in this area and statistics from other countries. Skin cancer have a special frequence which may be related to climatic and atmospheric environment.

Adolescent↗
PubMed2005

A late Eemian aridity pulse in central Europe during the last glacial inception.

Investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end, which has been a matter of much debate (see, for example, refs 1, 2). A recent ice core from Greenland demonstrates climate cooling from 122,000 years ago driven by orbitally controlled insolation, with glacial inception at 118,000 years ago. Here we present an annually resolved, layer-counted record of varve thickness, quartz grain size and pollen assemblages from a maar lake in the Eifel (Germany), which documents a late Eemian aridity pulse lasting 468 years with dust storms, aridity, bushfire and a decline of thermophilous trees at the time of glacial inception. We interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the North Atlantic drift, the ocean current that brings warm surface waters to the northern European region. The late Eemian aridity pulse occurred at a 65 degrees N July insolation of 416 W m(-2), close to today's value of 428 W m(-2) (ref. 9), and may therefore be relevant for the interpretation of present-day climate variability.

Atlantic Ocean↗
PubMed2004

Differences in ingestive balance of two populations of neotropical Thrichomys apereoides (Rodentia, Echimyidae).

Thrichomys apereoides is widely distributed in the Caatinga, a semi-arid region in Brazil, but is presumed to lack capabilities for water conservation. In the present study, we compared two populations of adult individuals living under different precipitation conditions (700 and 450 mm year(-1)). Animals from the less dry area were twice as heavy as those from the drier locality. Under ad libitum water regimen, there were differences between populations in relative food intake as well as in water intake and urine concentration, but not in normalized body mass water intake. Under short-term water deprivation, both populations presented similar body mass loss. Whereas individuals from the more arid locality maintained food consumption, urine volume and urine osmolality, Thrichomys from the less dry locality reduced food consumption and urine volume. The occurrence of anuria in 75% of animals from this population indicates that the limits of their ability to deal with water shortage had been reached. The morphological and physiological difference and the non-allometric similarities found between the two populations of T. apereoides fulfill the criteria for physiological adaptations to differences in annual rainfall. Our data challenge the hypothesis that the irregularity of annual rainfall in the Caatinga precludes the evolution of adaptations to this semi-arid climate.

Adaptation, Physiological↗
PubMed1977

Physiological responses of dogs on exposure to hot, arid conditions. Acid-base status.

Acid-base parameters were determined in chronically cannulated dogs exposed to ambient temperatures increasing from 25-47 degrees C (with relative humidity below 30%). pH increased from 7.409 +/- 0.004 (S.E.M.) to 7.538 +/- 0.017, PaCO2 decreased from 33.0 +/- 0.5 to 20.9 +/- 1.2 torr, and [HCO3-] decreased from 20.9 +/- 0.3 to 17.2 +/- 0.4 mEq/l. Minimal base excess change, together with a rapid return to normal parameters upon recooling to 25 degrees C, suggests that the stress is almost exclusively respiratory, with little metabolic involvement. Analysis of serial exposures shows no acclimatization effect in acid-base status. This suggests the possible existence of natural acclimation to heat in dogs maintained in a warm climate, permitting excellent tolerance of hot, arid conditions with limited acid-base disturbance.

Acclimatization↗
PubMed1992

Evaluating two different evaporative cooling management systems for dairy cows in a hot, dry climate.

Milk production, rectal temperature, live weight gain, reproductive performance, and weather data were obtained on 150 Holstein cows managed under two cooling systems on a large dairy farm in Saudi Arabia during the summer months. Cows were paired at the onset of the trial according to days postpartum, lactation number, and current milk production. Females were then allocated either to a system that forced air, precooled by evaporative cooling, over the cows or to a system that alternately showered a fine mist onto the surface of the cows and then forced air at ambient temperature over them. The cows receiving evaporative cooling and those with spray and fan cooling were on sand and on slatted concrete floor, respectively, during the periods of cooling. The onset of estrus was observed during the night when the cows preferred the unshaded corral. For the 120-d trial period, 84% (62 of 75) of the cows receiving evaporative cooling and 60% (44 of 75) of the cows receiving spray and fan cooling became pregnant. In the evaporative cooling system, the pregnancy rate per insemination was 35.2% (179 inseminations) versus 23.2% (194 inseminations) for spray and fan cooling. The mean postpartum interval to pregnancy was 117.6 d for the evaporative cooling cows and 146.7 d for spray and fan cooling cows. The evaporative cooling system, with its open shades and sand bedding, enhanced reproductive performance and milk production compared with that of cows cooled with a spray and fan system with slatted flooring in this hot climate.

Air Conditioning↗