Effect of soil temperature on nutrient allocation and mycorrhizas in Scots pine seedlings

We studied the effect of soil temperature on nutrient allocation and mycorrhizal development in seedlings of Scots pine (Pinus sylvestris L.) during the first 9 weeks of the growing season. One-year-old seedlings were grown in Carex-peat from a drained and forested peatland at soil temperatures of 5, 9, 13 and 17 °C under controlled environmental conditions. Fourteen seedlings from each temperature treatment were harvested at intervals of three weeks and the current and previous year's parts of the roots, stems and needles were separated. Mineral nutrient and Al contents in all plant parts were determined and the tips and mycorrhizas of the new roots were counted. Microbial biomass C and N in the growth medium were determined at the end of the experiment. None of the elements studied, except Fe, were taken up from the soil by the seedlings during the first three weeks. Thereafter, the contents of all the elements increased at all soil temperatures except 5 °C. Element concentrations in needles, stems and roots increased with soil temperature. Higher soil temperature greatly increased the number of root tips and mycorrhizas, and the numbers of mycorrhizas increased more than did the length of new roots. Cenococcum geophilum was relatively more abundant at lower soil temperatures (5 and 9 °C) than at higher ones (13 and 17 °C). A trend was observed for decreased microbial biomass C and N in the peat soil at higher soil temperatures at the end of the experiment.     

Extreme temperatures and thermal tolerances for seedlings of desert succulents

Summary Extreme temperatures near the soil surface, which can reach 70°C at the main study site in the northwestern Sonoran Desert, markedly affect seedling survival. Computer simulations indicated that for the rather spherical barrel cactus Ferocactus acanthodes (Lem.) Britt. & Rose the maximum surface temperature decreased 8°C and the minimum temperature increased 3°C as the seedling height was increased from 1 mm up to 50 mm. Simulated changes in shortwave and longwave irradiation alone showed that shading could decrease the maximum temperature by about 5°C for the common desert agave, Agave deserti Engelm., and raise the minimum 1°C. Actual field measurements on seedlings of both species, where shading would affect local air temperatures and wind speeds in addition to irradiation, indicated that shading decreased the average maximum surface temperature by 11°C in the summer and raised the minimum temperature by 3°C in winter.Seedlings grown at day/iight air temperatures of 30°C/20°C tolerated low temperatures of about -7°C and high temperatures of about 56°C, as measured by the temperature where stain uptake by chlorenchyma cells was reduced 50%. Seedling tolerance to high temperatures increased slightly with age, and F. acanthodes was more tolerant than A. deserti. Even taking the acclimation of high temperature tolerance into account (2.7°C increase per 10°C increase in temperature), seedlings of A. deserti would not be expected to withstand the high temperatures at exposed sites, consistent with previous observations that these seedlings occur only in protected microhabitats. Based primarily on greater high temperature acclimation (4.3°C per 10°C), seedlings of F. acanthodes have a greater high temperature tolerance and can just barely survive in exposed sites. Wide ranges in photoperiod had little effect on the thermal sensitivities of either species. When drought increased the chlorenchyma osmotic pressure from about 0.5 MPa to 1.3 MPa, seedlings of both species became about 2°C less tolerant of high temperatures, which would be nonadaptive in a desert environment, and 2°C more tolerant of low temperatures, which also occurs for other species.In conclusion, seedlings of A. deserti and F. acanthodes could tolerate tissue temperatures over 60°C when acclimated to high temperatures and below -8°C when acclimated to low temperatures. However, the extreme environment adjacent to desert soil requires sheltered microhabitats to protect the plants from high temperature damage and also to protect them from low temperature damage at their upper elevational limits.     

Response of Douglas fir seedlings to phosphorus fertilization and influence of temperature on this response

Summary Effects of P fertilizers on growth of Douglas fir (Pseudotsuga menziesii var.menziesii (Mirb.) Franco.) seedlings were examined in pots and nursery beds. In pot experiments levels of P equivalent to 300 kg/ha were adequate for maximum growth over 14–18 weeks and resulted in available soil P levels of 80 ppm after 15 weeks' growth. Maximum growth in pots was obtained with shoot P concentrations of 0.18%–0.20%, with higher values at lower temperatures, but the optimum concentration for one-year old (1-0) nursery seedlings was 0.16% P. Growth of seedlings was greatly restricted at a soil temperature of 5°C and an air temperature of 12°C. At a soil temperature of 10°C and an air temperature of 14°C seedling P requirement was greater than at soil and air temperatures of 20°C.Comparison showed that monammonium phosphate was more effective than calcium superphosphate in stimulating growth in pots and nursery. Triple superphosphate was also effective in the nursery. Diammonium phosphate, potassium dihydrogen phosphate and phosphoric acid had no advantages as P sources in the nursery. Available P levels of 100–130 ppm, in the loamy sand and sandy loam nurseries studied, and needle P concentrations of 0.18%, when sampled in October, were associated with maximum growth of two-year old (2-0) seedlings.P fertilization decreased root/shoot ratio, but did not alter the allometric relationship of shoot to root. Improving P status from a low level increased root growth capacity in 2-0 seedlings and P fertilization of potted seedlings increased dry weight/height ratio. Uptakes per seed bed ha of 236 kg N, 31 kg P, 81 kg K and 73 kg Ca by 2-0 seedlings were comparable with, or greater than, uptake rates of agricultural crops. Recoveries of 6–11% of P from fertilizer were recorded in the nursery.     

Photosynthetic gas exchange and temperature-induced damage in seedlings of the tropical alpine species Argyroxiphium sandwicense

The capacity of Argyroxiphium sandwicense (silverword) seedlings to acclimate photosynthetic processes to different growing temperatures, as well as the tolerance of A. sandwicense to temperatures ranging from –15 to 60° C, were analyzed in a combination of field and laboratory studies. Altitudinal changes in temperature were also analyzed in order to explain the observed spatial distribution of A. sandwicense. A. sandwicense (Asteraceae) is a giant rosette plant that grows at high elevation on two Hawaiian volcanoes, where nocturnal subzero temperatures frequently occur. In addition, the soil temperatures at midday in the open alpine vegetation can exceed 60° C. In marked contrast to this large diurnal temperature variation, the seasonal variation in temperature is very small due to the tropical maritime location of the Hawaiian archipelago. Diurnal changes of soil and air temperature as well as photosynthetic photon flux density were measured on Haleakala volcano during four months. Seedlings were grown in the laboratory, from seeds collected in ten different A. sandwicense populations on Haleakala volcano, and maintained in growth chambers at 15/5, 25/15, and 30/25° C day/night temperatures. Irreversible tissue damage was determined by measuring electrolyte leakage of leaf samples. For seedlings maintained at each of the three different day/night temperatures, tissue damage occurred at –10° C due to freezing and at about 50° C due to high temperatures. Tissue damage occurred immediately after ice nucleation suggesting that A. sandwicense seedlings tend to avoid ice formation by permanent supercooling. Seedlings maintained at different day/night temperatures had similar maximum photosynthetic rates (5 mol m^–2 s^–1) and similar optimum temperatures for photosynthesis (about 16° C). Leaf dark respiration rates compared at identical temperatures, however, were substantially higher for seedlings maintained at low temperatures, but almost perfect homeostasis is observed when compared at their respective growing conditions. The lack of acclimation in terms of frost resistance and tolerance to high temperatures, as well as in terms of the optimum temperature for photosynthesis, may contribute to the restricted altitudinal range of A. sandwicense. The small seasonal temperature variations in the tropical environment where this species grows may have prevented the development of mechanisms for acclimation to longterm temperature changes.     

Effect of soil temperature and drought on peanut pod and stem temperatures relative to Aspergillus flavus invasion and aflatoxin contamination

Peanut stem and pod temperatures of plants growing in irrigated, drought, drought-heated soil, and drought-cooled soil treatments were determined near the end of the growing season. Mean soil temperatures of the treatments during this period were 21.5°, 25.5°, 30° and 20 °C, respectively. Peanut stem temperatures in all drought treatments reached a maximum of ca. 40 °C and for 6–7 h each day were as much as 10 °C warmer than irrigated peanut stems. Pod temperatures in drought-heated soil and drought treatments were ca. 34 °C and 30 °C, respectively, for several hours each day. As pod temperatures approached the optimum for A. flavus growth (ca. 35 °C), the proportion of kernels colonized and aflatoxin concentrations increased. Increased plant temperature without accompanying pod temperature increases (drought-cooled soil) resulted in colonization percentages and aflatoxin concentrations only slightly higher than those of the irrigated peanuts.     

Soil temperatures and inoculation techniques affect emergence and reisolation of Sclerotinia sclerotiorum from soybean

Emergence of Amsoy soybean (Glycine max) seed inoculated withSclerotinia sclerotiorum was significantly reduced below noninoculated seed at soil temperatures of 25°, 30°, and 35 °C, but not at 20 °C.S. sclerotiorum was readily reisolated from wound-inoculated stems of seedlings and nearly mature plants above the point of inoculation and below to the crown area, but not from roots. The fungus was recovered from stems but not roots of 15-day seedlings grown in sterile soil before infestation of the soil surface with a suspension of mycelium and sclerotia and assayed at 15 days after soil infestation. When compared to healthy, seeds, infected seeds withS. sclerotiorum were characterized by appearing flattened.Supported in part by the Illinois Agricultural Experiment Station; Regional Project S-72; and U.S. Agency for International Development, grant csd-1922.     

The influence of root-zone temperature on growth of Betula pendula Roth.

We have examined shoot and root growth and the concentration of carbohydrates in seedlings of a northern (67°N) and a southern (61°N) ecotype of Betula pendula Roth. cultivated at root-zone temperatures of 2, 6, 12 and 17°C. Three hydroponic experiments were conducted in controlled environments. We used three different pretreatments before seedlings were subjected to the experimental temperature treatments. Actively growing seedlings that were acclimated to the hydroponic solution for 3 weeks at a root temperature of 17°C, continued to grow at all the experimental temperatures, with an expected increase in growth from 2 to 17°C. However, if we started with ecodormant cold stored plants or used seedlings grown actively in perlite, no growth was observed at 2°C and only minor growth was found at 6°C. The highest root temperature always produced the best growth. The concentration of nonstructural carbohydrates was higher in seedlings grown at 2°C than at 17°C, and this is probably due to extensive incorporation of carbohydrates into cell walls and other structural elements at 17°C. We found no evidence for differences between the two ecotypes in root growth, in timing of bud burst, but shoot growth terminated in the northern ecotype in the first experiment because the natural photoperiod was below the critical value. Our study highlights the importance of post-transplantation stress (planting check) related to root growth, and that root threshold temperatures may change according to the way plants are pretreated.     

The range of micrometeorological diversity in the biological environment

The range of temperature and humidity conditions that can exist simultaneously at or near the ground surface on a bright summer day in a temperate climate are shown in a diagram. Cool and warm conditions are defined as having respectively a lower and a higher temperature than the air at a height of 1.50 m above the surface of the ground. Similarly, humid and dry conditions are defined by a lower and a higher saturation deficit (S.D.), respectively. Cool, humid conditions are found in the open shade where only diffuse solar radiation is received. In high reed vegetations on wet soil, temperatures can lie 8°C below that of the free atmosphere and humidity is close to the saturation point. Warm and humid conditions are found in thin vegetations on damp soil with a temperature excess of up to 10°C and a strongly reduced S.D. In dry grassland, air temperatures 1 cm above the ground are up to 20°C higher and S.D. up to 40 mm Hg higher than at a height of 1.50 m. On suitably oriented slopes covered with dark organic material, surface temperatures can reach 50°C above the air temperature.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Effect of planting date,ventilation and soil temperature on growth and nutrition of tomato in high tunnels

Growth rates and tissue nutrient concentrations were measured in tomato (Lycopersicon esculentum Mill) grown in unheated high tunnels in the spring in the northeast USA. Two weeks after transplant on 3 April, seedlings had low concentrations of Nitrogen, Magnesium and other nutrients, while later plantings on 17 April and 1 May had adequate nutrition. The low yield and small fruit of the 3 April planting, compared to the later plantings, was likely related to this nutrient stress soon after transplant. Air and soil temperatures were less than 10°C at planting on 3 April. Air and soil were warmed during the day to different extents in tunnels vented at different temperatures. Over all plantings and ventilation regimes, relative growth rates over the two weeks after transplant were correlated to average air temperature. However, there was little uptake of P, N and Mg, when soil was cooler than 12°C. Nutrient concentrations in the shoot became very low because shoot growth continued when soil temperature limited nutrient uptake.     

The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

Effects of day-to-day changes in root temperature on leaf conductance to water vapour and CO2 assimilation rates of Vigna unguiculata L. Walp.

Summary Leaf gas exchange of Vigna unguiculata was influenced by short-term (day-to-day) changes in soil temperature and the response depended upon the aerial environment. When aerial conditions were constant at 30° C leaf temperature, high air humidity and moderate quantum flux, CO₂ assimilation rate and leaf conductance increased with increases in soil temperature from 20 to 35° C, and this response was reversible. Decreases in CO₂ assimilation rate and leaf conductance were observed at root temperatures above 30° C when root temperatures were increased from 20° C to 40° C and when air humidity was decreased in steps during the day. In contrast, varying soil temperatures between 20 to 35° C had no influence on gas exchange when shoots were subjected to a wide range of temperatures during each day.The gain ratio A/E remained constant at different air humidities when root temperature was less than or equal to 30° C indicating optimal gas exchange regulation, but changed with humidity at higher root temperatures. Leaf conductance responded independently from leaf water potential which remained relatively constant during individual experiments.The results indicate that plant responses to high root temperatures may have relevance to plant performance in semi-arid environments. They also illustrate the importance of controlling soil temperatures when studying the responses of potted plants in controlled aerial environments.Dedicated to K.F. Springer     

Physiological ecology of Juniperus virginiana in oldfields

Juniperus virginiana plants grow faster than other associated tree species in abandoned fields. During the summer the needles of the species do not light saturate even at 1,750 E m^-2 s^-1, reach optimum photosynthesis at 20°C, and maintain maximum photosynthesis at-8 to-12 bar twig water potential. In the field, the plants experience pronounced daily changes in water potential. The magnitude of the changes becomes more pronounced later in the summer. Leaves of the mature plants have highest rate of photosynthesis, young trees intermediate, and seedlings lowest. In winter there is a slight shift in optimum temperature for photosynthesis and the plants photosynthesize at 0°C. The rates of photosynthesis are lower in winter than in summer. On sunny days with calm winds, mature individuals and seedlings maintain significantly higher temperatures than air temperature while intermediate plants do not. The latter exhibit a lower photosynthetic rate than both mature plants and seedlings. The trends of photosynthesis, in the 3 size classes, both in winter and summer, correspond to the chlorophyll content of their leaves. It is concluded that J. virginiana grows well in open field habitats because it is a sun-adapted, drought resistant species with a long growing season which includes winter. The species is excluded from mature forests because it is shade-intolerant.     

Temperature and seedling age affect susceptibility of perennial ryegrass seedlings to pathogenic fungi

Summary Effects of temperature and seedling age on survival of perennial ryegrass (Lolium perenne L.) seedlings grown on sand-wheat wholemeal cultures of different isolates ofFusarium spp. (9 isolates),Pythium spp. (9 isolates), andChaetomium spp. (1 isolate) are reported. Some isolates were virulent over the whole range of temperatures tested (7.5–27.5°C). The virulence of others depended on temperature. Most isolates were less virulent at intermediate temperatures (12.5–22.5°C) than at higher or lower temperatures. At 25°C ryegrass seedlings were susceptible to fungal attack for only a limited period after germination commenced. This period differed for different fungi, but for most isolates tested, seedlings were resistant after 2–3 days.     

Pollen selection for low temperature adaptation in tomato

Summary Pollen selection experiments were conducted in tomato to determine the effects of low temperature conditions during pollination on the rate of root elongation of the progeny. Pollen was harvested from an F₁ interspecific hybrid between a high altitude Lycopersicon hirsutum accession and the cultivated tomato L. esculentum. The pollen was applied to stigmas of malesterile L. esculentum plants maintained in growth chambers set at either 12°C/7°C or 24°C/18°C. BC₁ seeds from the low and normal temperature crosses were germinated and root elongation rate was measured at either 9°C or 24°C. At 9°C, the rate of root elongation for progeny of the low temperature crosses was higher than for progeny of crosses at normal temperatures; at 24°C the rate of root elongation was similar for the two crossing treatments. To compare the temperature responses of the two backcross populations we also calculated the relative inhibitory effect of low temperature on the rate of root elongation: the ratio between the rate of root elongation at 9°C to that at 24°C. Root elongation of seedlings from the low temperature crosses was less inhibited by the cold than root elongation for progeny of the normal temperature crosses. These results suggest a relationship between pollen selection at low temperatures and the expression of a sporophytic trait under the same environmental stress.     

The use of a temperature-profiled position transducer for the study of low-temperature growth in Gramineae

A device is described for measuring linear extension of grass leaves during controlled cooling and heating of the growing region. The instrument was employed to investigate the sensitivity to temperature of the expanding third and fourth leaves of Lolium temulentum L. seedlings. Using a stepped temperature profile it was established that there was no lag in the response of growth rate to rapid changes in temperature below 16°C. If cooling was continued to the point where growth ceased (1°C) but no further, then rates of growth on rewarming were enhanced over the chilling range and reverted to the original rate at 20°C. Cooling to successively lower subzero temperatures before rewarming abolished the hysteretic enhancement, progressively raised the temperature at which growth resumed and decreased the rate of extension until, at-5.3°C, no recovery occurred. The temperature sensitivity of growth, measured as Q₁₀, was essentially constant when cooling from 20°C to 5°C, with 5°C-grown leaf tissue exhibiting a higher mean Q₁₀ than tissue developed at 20°C. The possible physiological significance of these data is discussed.Abbreviations LVDT linear variable displacement transformer - Pe, Fx temperatures at which growth ceases during cooling and resumes during rewarming     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

Soil temperatures and inoculation techniques affect emergence and reisolation of sclerotinia Sclerotiorum from soybean

Emergence of Amsoy soybean (Glycine max) seed inoculated withSclerotinia sclerotiorum was significantly reduced below noninoculated seed at soil temperatures of 25, 30 and 35 °C, but not at 20 °C.S. sclerotiorum was readily·reisolated from wound-inoculated stems of seedlings and nearly mature plants above the point of inoculation below to the crown area, but not from roots. The fungus was recovered from stems but not roots of seedlings grown in sterile soil for 15 days before infestation of the soil surface with a suspension of mycelium and sclerotia and assayed at 15 days after soil infestation. When compared to healthy, seed infected withS. sclerotiorum were characterized by appearing flattened.Supported in part by the Illinois Agricultural Experiment Station; Regional Project S-72; and U.S. Agency for International Development, grant csd-1922.     

Use of chitin for controlling plant-parasitic nematodes

Cabbage plants were grown in soil amended with Clandosan (CLA) prepared from crustacean chitin (0.3% w/w). The plants were maintained in constant temperature tanks set to 15° or 30°C, in soils naturally infested with cyst nematodeHeterodera schachtii, or inoculated with the root-knot nematode,Meloidogyne javanica, respectively. At 30°C, after the first month following inoculation, CLA caused an increase in top fresh weight of plants but no reduction in nematode—induced root galling was recorded. However, when fresh plants were planted, CLA induced a large reduction in gall formation and caused an increase in top fresh weight of nematode-inoculated plants. At 15°C, CLA significantly affected the plants only after 60 days: an increase in top fresh weight and a reduction in the number of eggs per cyst were recorded. Ammonium was not detected in soil after 30 days, at 30°C, whereas at 15°C, CLA-treated soil contained twice as much ammonium as non-treated soil. After 60 days, ammonium was not detected at all. After 30 days nitrate concentrations in soil attained higher values at 30°C than at 15°C, whereas after 60 days high levels were detected only at 15°C. At 30°C, CLA induced an increase in the number of fungi, chitinolytic bacteria, and total amount of bacteria; at 15°C, such an increase was detected only with the chitinolytic microorganisms.Contribution from the Agricultural Research Organization (ARO), Bet Dagan, Israel No. 2196-E, 1987 series.     

Root nodulation and nitrogen accumulation and partitioning in legume crops as affected by soil solarization

Soil solarization is a preplanting technique used in hot climates to control weeds and soilborne pathogens consisting of mulching the soil surface with polyethylene sheets. The increase in temperature associated with solarized soil could affect nitrogen availability for grain legume crops through effects on nitrogen fixing soil microorganisms or other mechanisms. To examine the effects of solarization on natural root nodulation and nitrogen accumulation and partitioning in the plant, two solarization field experiments were carried out over two planting seasons, involving genotypes of both faba bean (Vicia faba) and chickpea (Cicer arietinum). The effect of sowing date was also studied in the first season. Solarization increased the maximum soil temperature by 9–10 °C in the first, and by 13–15 °C in the second season. At 5 cm below the solarized soil surface, a temperature of over 46 °C prevailed for 146 and 280 h over the two respective seasons, while this temperature was not attained in unmulched soil. Solarization delayed the initiation of nodulation and consistently reduced the nodule number per host plant, but generated an approximate doubling of mean nodule weight. The total nodule mass per plant was not affected by the treatment in the first season, but was reduced in the second season. Solarization significantly increased the concentrations of NO₃^– -N, Na⁺, Zn²⁺, Ca²⁺ and K⁺ in the soil extract, and the total nitrogen accumulated in the whole plant. This latter increase was due to both higher plant growth and a greater plant nitrogen concentration. The increased nitrogen level in the plant was not uniform with respect to plant component, varying from 57% in the roots to 198% in the pods and seeds. The plants grown in non-solarized soil accumulated about 31% of their total N content in the shoots of the parasitic weed Orobanche crenata. Solarization dramatically improved grain yield by 300–900% in both seasons and in all genotypes studied, due to increased N availability in soil, N accumulation in plants, improved plant growth, and complete control of the parasite weed O. crenata. On the basis of these beneficial effects, soil solarization, which avoids site contamination and is suited to organic farming, should be a good opportunity in Mediterranean areas where the level and stability of grain yields are low, and the infestation of O. crenata is high.     

Behavioural thermoregulation of the Andean toad (Bufo spinulosus) at high altitudes

Summary The body temperature of free-ranging Andean toadsBufo spinulosus was measured either directly or radiotelemetrically during two 15-day periods at 3200 m elevation in the Mantaro Valley, Central Perú. All toads attempted to maintain their diurnal sum of body temperature within a narrow range. Consequently thermoregulatory behaviour differed according to cloud cover and precipitation. If the sky was clear, toads emerged from their hiding place and exposed themselves to solar radiation during 3–5 h in the morning. Core temperature increased up to 15° C above the air temperature in shade and reached maximum values of about 32° C. At air temperatures (in sun) exceeding 29° C, toads maintained body temperatures below 32° C by evaporative cooling. Following heliothermic heating during the moring toads retreated to the shade, thereby decreasing body temperature below air temperature. Under overcast sky toads remained exposed during the whole day displaying body temperatures at or slightly above ambient levels. Quantitative models to predict the core temperature of toads under the different weather conditions demonstrated that the substrate temperature was the main energy source accounting for 64.6–77.9% of total variance whereas air temperature was of minor importance (1.5–4.4%). The unexplained variance was probably due to evaporative cooling. The volume of urine stored into the urinary bladder of toads varied diurnally; during basking in the morning hours most bladders contained large volumes of urine, whereas during the afternoon the bladders were mostly empty. The bladder contents probably serve as water reserves during basking when evaporative water loss was high. Toads preferred sites that provided shady hiding places as well as sun-exposed bare soil within a radius of 5 m. However, they frequently changed their centers of activity and moved to other sites in 20–70 m distance after periods of 2–5 days. The helio-and thigmothermic behaviour of the Andean toad permits the maintenance of high core temperature during morning which probably increases the digestion rate and accelerate growth. Evaporative cooling and preference of shady sites were employed to regulate body temperature below the morning levels in response to the constraints of water balance. Periodic changes between thigmothermic behaviour and locomotory activity during the night maintains body temperature above air temperature and prolongs the period of food uptake.Dedicated to Prof. Dr. H. Schneider on the occasion of his sixtieth birthday