A world-wide study of high altitude treeline temperatures

Aim At a coarse scale, the treelines of the world's mountains seem to follow a common isotherm, but the evidence for this has been indirect so far. Here we aim at underpinning this with facts. Location We present the results of a data‐logging campaign at 46 treeline sites between 68° N and 42° S. Methods We measured root‐zone temperatures with an hourly resolution over 1–3 years per site between 1996 and 2003. Results Disregarding taxon‐, landuse‐ or fire‐driven tree limits, high altitude climatic treelines are associated with a seasonal mean ground temperature of 6.7 °C (±0.8 SD; 2.2 K amplitude of means for different climatic zones), a surprisingly narrow range. Temperatures are higher (7–8 °C) in the temperate and Mediterranean zone treelines, and are lower in equatorial treelines (5–6 °C) and in the subarctic and boreal zone (6–7 °C). While air temperatures are higher than soil temperatures in warm periods, and are lower than soil temperatures in cold periods, daily means of air and soil temperature are almost the same at 6–7 °C, a physics driven coincidence with the global mean temperature at treeline. The length of the growing season, thermal extremes or thermal sums have no predictive value for treeline altitude on a global scale. Some Mediterranean (Fagus spp.) and temperate South Hemisphere treelines (Nothofagus spp.) and the native treeline in Hawaii (Metrosideros) are located at substantially higher isotherms and represent genus‐specific boundaries rather than boundaries of the life‐form tree. In seasonal climates, ground temperatures in winter (absolute minima) reflect local snow pack and seem uncritical. Main conclusions The data support the hypothesis of a common thermal threshold for forest growth at high elevation, but also reflect a moderate region and substantial taxonomic influence.     

Relationship between temperature and cauliflower (<Emphasis Type="Italic">Brassica oleracea</Emphasis> L. <Emphasis Type="Italic">var. botrytis</Emphasis>) growth and development after curd initiation

Two experiments were conducted to assess the response of cauliflower (Brassica oleracea L. var. botrytis) cv. “Nautilus” F1 hybrid to different constant temperatures after curd initiation by keeping the plants in six different temperature-controlled glasshouse compartments with heating set point temperatures of 6, 10, 14, 18, 22, and 26 °C (±4 °C) at the School of Plant Sciences, The University of Reading, UK during winter 1998–1999 and summer 1999. Many of the growth parameters increased with increasing mean growing temperature up to an optimum temperature and then declined with further increases in temperature. Therefore, cauliflower’s growth and development after curd initiation could be resolved into linear or curvilinear function of effective temperatures calculated with optimum temperatures between 19 and 23 °C. It is suggested that future warmer climates will be beneficial for winter cauliflower production rather than summer cauliflower production.     

The influence of various temperature regimes on the abundance dynamics and thermal tolerance of cladoceran Ceriodaphnia quadrangula (O.F. Müller, 1785)

Experimental studies on the abundance dynamics and thermal tolerance of cladoceran Ceriodaphnia quadrangula (O.F. Müller, 1785) as they depend on the value and action pattern of a thermal factor, as well as field observations and mathematical calculations were carried out. Based upon the results of these studies, the values of the temperature zone of normal vital functions (17.0–25.0°C) and of the zones of temperature “static” optimum (21.4–25.0°C) were determined for C. quadrangula. It was shown using experimental populations of C. quadrangula as an example that it is necessary not only to keep the range of the factor optimal values within the tolerance scale (i.e., the static optimum) but also to maintain the optimal parameters of dynamic factor changes (or “dynamic optimum”) in order to form optimal conditions for their growth and development. For C. quadrangula this dynamic temperature optimum is 24.0 ± 1.1°C, with non-periodical (graded) warming to 24.7–25.3°C over five to eight days.     

Upper limits of temperature for growth inChlorella (Chlorophyceae)

The upper limit of temperature for growth is a species-specific character in the genusChlorella. The limits of 14Chlorella species range from 26–30°C (C. saccharophila) to 38–42°C (C. sorokiniana), withC. fusca var.vacuolata (34°C) andC. kessleri (34–36°C) assuming an intermediate position. Thus, there is no wide gap in the temperature limits between the normal (“low-temperature”) species ofChlorella and the “high-temperature” species,C. sorokiniana.     

Heat resistance of allograft tissue

Lyophilized allograft musculoskeletal tissue is generally intended to be stored at “ambient” or “room” temperature, and usually is kept in climate controlled indoor storage areas. However, there is a question of what temperature extremes tissue may see, especially during transportation, in that these extremes may exceed even the limits of “ambient” conditions. Temperatures may become quite hot, but only for a few hours and only during daytime. Damage from high temperatures, if it occurs, is expected to be evident by damage to the collagen component of bone, soft tissue, and demineralized bone, as well as to the growth factors contained in demineralized bone. If damage is significant, then temperature monitoring requirements for lyophilized allograft tissue might be necessary. To answer this question, a literature review was carried out to look at the short-term temperature resistance of collagen and demineralized bone. Both collagen and the growth factors in demineralized bone show remarkable short term tolerance to elevated temperatures in the dry state, and it was concluded that temperature excursions of 50°C or less, lasting for a few days or less, would not cause any significant deterioration. This means that temperature monitoring also should not be required.     

Heliorestis daurensis, gen. nov. sp. nov., an alkaliphilic rod-to-coiled-shaped phototrophic heliobacterium from a Siberian soda lake

A novel alkaliphilic heliobacterium was isolated from microbial mats of a low-salt alkaline Siberian soda lake. Cells of the new organism were tightly coiled when grown in coculture with a rod-shaped bacterium, but grew as short filaments when finally obtained in pure culture. The new phototroph, designated strain BT-H1, produced bacteriochlorophyll g and a neurosporene-like pigment, and lacked internal photosynthetic membranes. Similar to other heliobacteria, strain BT-H1 grew photoheterotrophically on a limited range of organic compounds including acetate and pyruvate. Sulfide was oxidized to elemental sulfur and polysulfides under photoheterotrophic conditions; however, photoautotrophic growth was not observed. Cultures of strain BT-H1 were alkaliphilic, growing optimally at pH 9, and unlike other heliobacteria, they grew optimally at a temperature of 25 °C rather than at 40 °C or above. Analysis of the 16S rRNA gene sequence of the new organism showed that it groups within the heliobacterial clade. However, its branching order was phylogenetically basal to all previously investigated species of heliobacteria. The G+C content of the DNA of strain BT-H1 (44.9 mol%) was also quite distinct from that of other heliobacteria. This unique assemblage of properties implicates strain BT-H1 as a new genus and species of the heliobacteria, Heliorestis daurensis, named for its unusual morphology (“restis” is Latin for “rope”) and for the Daur Steppe in Russia in which these soda lakes are located. Received: 15 March 1999 / Accepted: 25 June 1999     

A study of the macro-environment at BenCat in southern Vietnam

Based on the meteorological data over a period of 4 years (1980–3), the macro-environment of BenCat Farm situated in the southern part of Vietnam (27 m above mean sea-level, 11° N and 106° E) was categorized as a “monsoon tropical climate”, due to heavy rainfall (annual mean 2028.96 mm) and about 32% wet days (annual mean 116.52 days) together with high air temperature (annual mean daily temperature 28.58, max. 32.33 and min 24.85° C). April was the hottest (monthly mean >35°C) and January the coldest month (monthly mean <22° C) of the year. The maximum number of wet days were during September and October (mean 18 days.month), whereas the minimum number of wet days were during January and February (mean <1 day/month). The months of December and January at Ben-Cat buffalo farm were categorized as the “comfortable (moderate-Dry) period” as the mean daily temperature was <27° C, while the remaining 10 months of the Calender year (February–November) were categorized as the “hot period” (mean daily temperature >27° C). On the basis of rainfall and the number of wet days, the hot period was further subdivided into a “hot-dry period” (February–April, mean of 1.67 wet days/month and mean rainfall 19.43 mm/month) and a “hot-humid period” (May–November, mean of 15.57 wet days/month and mean rainfall 276.28 mm/month).     

Temperature dependent UV-Vis spectral changes in hydrogen-and deuterium-bonded photosynthetic reaction centers of Rhodobacter sphaeroides

The UV-Vis absorption spectra of detergent-isolated hydrogen-and deuterium-bonded reaction centers (RCs) from Rhodobacter sphaeroides PUC 705Ba were examined as a function of temperature between 20 and 55 °C. The enthalpy and entropy of denaturation for the specimens was determined, revealing that their process of thermal denaturation is significantly different. Deuterium-bonded RCs are most stable at 37 °C, rather than at room temperature, and undergo a “cold denaturation” as the temperature is lowered to room temperature. At room temperature the addition of 1,3,5-heptanetriol brought the deuterium-bonded RC back to its more stable configuration. Hence the hydrogen bonding interactions in the RC do influence its conformation and this is reflected in the microenvironment of its associated pigments.     

Final thermal preference in parthenogenetic females of Daphnia magna straus (Crustacea: Cladocera) acclimated to various temperatures

The final thermal preference FTP) range in parthenogenetic females of cladoceran Daphnia magna was assessed by “acute” and “chronic” methods. The first method included 4-month acclimation to different temperatures in the range of 14.2 ± 0.7 to 27.1 ± 0.3°C; the “chronic” method was characterized by long-term acclimation to +20°C. Two ranges of FTP were found for D. magna, 13.3–15.4°C and 20.2–26.2°C. The thermal preference of daphnids and the temperature of acclimation were correspondingly linearly. The range of FTP was independent of the season. The searching activity of D. magna rose in April, when the FTP range increased, and the FTP was less pronounced.     

Evidence of threshold temperatures for xylogenesis in conifers at high altitudes

Temperature is the most important factor affecting growth at high altitudes. As trees use much of the allocated carbon gained from photosynthesis to produce branches and stems, information on the timing and dynamics of secondary wood growth is crucial to assessing temperature thresholds for xylogenesis. We have carried out histological analyses to determine cambial activity and xylem cell differentiation in conifers growing at the treeline on the eastern Alps in two sites during 2002–2004 with the aim of linking the growth process with temperature and, consequently, of defining thresholds for xylogenesis. Cambial activity occurred from May to July–August and cell differentiation from May–June to September–October. The earliest start of radial enlargement was observed in stone pine in mid-May, while Norway spruce was the last species to begin tracheid differentiation. The duration of wood formation varied from 90 to 137 days, depending on year and site, with no difference between species. Longer durations were observed in trees on the south-facing site because of the earlier onset and later ending of cell production and differentiation. The threshold temperatures at which xylogenesis had a 0.5 probability of being active were calculated by logistic regressions. Xylogenesis was active when the mean daily air temperature was 5.6–8.5°C and mean stem temperature was 7.2–9°C. The similar thresholds among all trees suggested the existence of thermal limits in wood formation that correspond with temperatures of 6–8°C that are supposed to limit growth at the treeline. Different soil temperature thresholds between sites indicated that soil temperature may not be the main factor limiting xylogenesis. This study represents the first attempt to define a threshold through comparative assessment of xylem growth and tissue temperatures in stem meristems at high altitudes.