Low Soil Temperatures Research Articles

Evaluation of Community Climate System Model soil temperatures using observations from Russia

Soil temperatures simulated by the fully coupled Community Climate System Model (CCSM) version 3.0 are evaluated using three gridded climatologies (1951–1980, 1961–1990, 1971–2000) based on data from more than 400 Russian sites. CCSM captures the annual phase of the soil temperature cycle well, but not the amplitude. It provides slightly too high (low) soil temperatures in winter (summer). Root mean square errors, on average, are less than 5 K. Simulated near-surface air temperatures agree well, on average, with near-surface air temperatures from reanalysis data. Errors in simulated atmospheric-temperature forcing correlate statistically significantly (95% or higher confidence level) with soil temperature errors, i.e. contribute to discrepancy in soil temperature simulation. Comparison to International Satellite Cloud Climatology project data shows that errors in simulated cloud fraction explain some soil and near-surface air temperature and precipitation discrepancies. Evaluation by means of Global Precipitation Climatology Centre data identifies inaccurately-simulated precipitation as a contributor to underestimating summer soil temperatures. Comparison to snow-depth observations shows that overestimating snow depth yields winter soil-temperature overestimation. Sensitivity studies show that uncertainty in mineral-soil composition notably, and differences between the vegetation in CCSM and nature marginally contribute to discrepancies between simulated and observed soil-temperature climatology.

The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia

Abstract. Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, Reco and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m−2 yr−1, which is composed of an Reco=+141 g C m−2 yr−1 and GPP=−232 g C m−2 yr−1. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14°C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (Rg<200 W m−2), whereas Reco depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO2e m−2 yr−1, so that the greenhouse gas balance was −64 g C-CO2e m−2 yr−1. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition.

POPs in Mountain Soils from the Alps and Andes: Suggestions for a ‘Precipitation Effect’ on Altitudinal Gradients

POPs are still a priority environmental problem, but can be used as a scientific tool for understanding the distribution phenomena. Both high mountains and polar areas are seen as priority zones for contamination studies. In this context, two altitudinal series of soil samples were analysed for several classes of Persistent Organic Pollutants (PCBs, DDTs, HCHs, HCB and chlordane). Two transects were carried out – one in the Peruvian Andes (Cordillera Blanca) and the other in the Italian Alps (Mount Legnone). In these two areas, POP composition and levels both gave different results, linked to regional emission history. The Italian samples were characterized by high levels of industrial type compounds, and by surprisingly high DDT contamination, due to a defined consistent local source in Northern Italy. The Peruvian samples, on the other hand, were characterized by generally low POP levels with relatively high DDT contamination. The concentration increase in line with elevation was evident only in the Italian transect, where higher precipitation intensities and an increasingly higher precipitation gradient in accordance with altitude was found present. Precipitations are considered a key factor for enhancing the condensation effect at high altitudes and for reducing summer revolatilisation, as they lower soil temperature. In the Italian altitudinal gradient, evidence of fractionation processes, with a shift of the PCB composition towards less chlorinated congeners, and a vegetation effect with a mean woodland/grassland enrichment factor between 2 and 4 were also observed.

Consequences of including adapted white clover in northern European grassland: transfer and deposition of nitrogen

The interspecific transfer of nitrogen (N) between white clover (Trifolium repens) and smooth meadow grass (Poa pratensis) in legume-based grasslands was assessed under North European field conditions using 15N individual plant leaf labelling. On average 50% of N in the grass was transferred from the white clover and about 6% of N in white clover was transferred from the grass. This corresponds to 2.5 and 0.3 g N m−2 being transferred over the growing season between the two species, respectively, and demonstrates that a significant part of the total N of the grass is coming through interspecific transfer. The majority of the 15N transferred was within a period of 20 days at relatively low soil temperatures. This implies that there is a need for a new focus on direct transfer pathways or exudation and transfer of organic N sources. Rhizodeposition in the top 10 cm of the soil was found to be 2.98 g N m−2 on average over the growing season for the grass and white clover mixture. Inclusion of adapted white clover varieties in the low-input grassland systems of northern Europe will lead to a substantial contribution of N.

The effect of roots and litter of Calamagrostis canadensis on root sucker regeneration of Populus tremuloides

Summary Marsh reed grass ( Calamagrostis canadensis (Michx.) Beauv.) is a common, highly competitive grass native to the boreal mixedwood forest. This grass increases in abundance after clear-cut logging but little is known about its effects on trembling aspen ( Populus tremuloides Michx.) sucker regeneration. The effects of Calamagrostis sod and its litter on aspen regeneration were studied in two separate greenhouse studies. Calamagrostis sod did not affect the initiation of suckers, but resulted in 30 per cent fewer suckers emerging above the soil that were smaller and had 40 per cent less leaf area. Calamagrostis litter had little effect on the initiation and number of emerged suckers; however, it delayed emergence by 10 days. The physical barrier by roots and litter of Calamagrostis reduced or delayed the expansion of suckers and therefore prolonged their dependence on root reserves. By the time the suckers reached the surface, they had to compete for light with Calamagrostis shoots that had emerged a week earlier. This, coupled with low soil temperatures associated with Calamagrostis in other experiments, will signifi cantly reduce the number and growth of suckers. Any reduction and delay in sucker emergence will decrease aspen regeneration and productivity since the growing season in the boreal forest region is short.

Effects of straw mulching on soil temperature, evaporation and yield of winter wheat: field experiments on the North China Plain

AbstractStraw mulching is an effective measure to conserve soil moisture. However, the existence of straw on the soil surface also affects soil temperature, which in turn influences crop growth, especially of winter crops. Five‐year field experiments (2000–2005) investigated the effects of straw mulching and straw mass on soil temperature, soil evaporation, crop growth and development, yield and water use efficiency (WUE) of winter wheat (Triticum aestivum L.) at Luancheng Station on the North China Plain. Soil is a moderately well‐drained loamy soil with a deep profile at the station. Two quantities of mulch were used: 3000 kg ha−1 [less mulching (LM)] and 6000 kg ha−1 [more mulching (MM)], representing half and all of the straw from the previous crop (maize). In the control (CK), the full quantity of mulch was ploughed into the top 20 cm of soil. The results showed that the existence of straw on the soil surface reduced the maximum, but increased the minimum diurnal soil temperature. When soil temperature was decreasing (from November to early February the next year), soil temperature (0–10 cm) under straw mulching was on average 0.3°C higher for LM and 0.58°C higher for MM than that without mulching (CK). During the period when soil temperature increased (from February to early April, the recovery and jointing stages of winter wheat), average daily soil temperature of 0–10 cm was 0.42°C lower for LM and 0.65°C lower for MM than that of CK. With the increase in leaf area index, the effect of mulching on soil temperature gradually disappeared. The lower soil temperature under mulch in spring delayed the development of winter wheat up to 7 days, which on average reduced the final grain yield by 5% for LM and 7% for MM compared with CK over the five seasons. Mulch reduced soil evaporation by 21% under LM and 40% under MM compared with CK, based on daily measuring of microlysimeters. However, because yield was reduced, the overall WUE was not improved by mulch.

The role of low soil temperature in the inhibition of growth and PSII function during dark chilling in soybean genotypes of contrasting tolerance

Dark chilling affects growth and yield of warm-climate crops such as soybean [Glycine max (L.) Merr.]. Several studies have investigated chilling-stress effects on photosynthesis and other aspects of metabolism, but none have compared effects of whole-plant chilling (WPC; shoots and roots) with that of aboveground chilling in legumes. This is important because low root temperatures might induce additional constraints, such as inhibition of N(2) fixation, thereby aggravating chilling-stress symptoms. Effects of dark chilling on PSII, shoot growth, leaf ureide content and photosynthetic capacity were studied in two soybean genotypes, Highveld Top (chilling tolerant) and PAN809 (chilling sensitive), in experiments comparing effects of WPC with that of shoot chilling (SC). Both treatments inhibited shoot growth in PAN809 but not Highveld Top. Also, WPC in PAN809 caused a decrease in leaf ureide content followed by severe chlorosis and alterations in O-J-I-P fluorescence-rise kinetics, distinct from SC. A noteworthy difference was the appearance of a Delta K peak in the O-J-I-P fluorescence rise in response to WPC. These genotypic and treatment differences also reflected in the degree of inhibition of CO(2) assimilation rates. The appearance of a Delta K peak, coupled with growth inhibition, reduced ureide content, chlorosis and lower CO(2) assimilation rates, provides mechanistic information about how WPC might have aggravated chilling-stress symptoms in PAN809. We introduce a model explaining how chilling soil temperatures might trigger N-limitation in sensitive genotypes and how characteristic changes in O-J-I-P fluorescence-rise kinetics are linked to changes in carbon and nitrogen metabolism.

Long-term soil tillage effects on selected physical and biological parameters

The lowest soil temperature values were found for no-tillage both on the surface and in each examined soil layer to 0.5 m depth. However, there were differences among the ploughed treatments only in the topsoil (0.1 m), below this layer similar soil temperature values were obtained. In our experience maize emergence and growing were strongly affected by soil temperature in the upper 0.1 m depth. Our results of pore size distribution indicated that changes in the total porosity occurred due to the changes in the macroporosity since the meso- and the microporosity were not affected by soil management. The lowest macroporosity was observed under no-tillage, but it can be assumed that the majority of these pores (>30 mm) belongs to biopores due to a higher abundance of earthworms improving the general physical and biological state of soil.

Detoxification of hydrogen peroxide maintains the water transport activity in figleaf gourd (Cucurbita ficifolia) root system exposed to low temperature

The figleaf gourd (Cucurbita ficifolia Bouché) root system has the ability to take up water and nutrients at low soil temperatures, and in the present paper, we attempt to reveal some of the molecular mechanisms behind this low‐temperature tolerance. Exposure of figleaf gourd root system to low temperature induced accumulation of H2O2 along the plasma membrane but not in the cytoplasm. H+‐ATPase (EC 3.6.1.35) activity of isolated root plasma membranes and root hydraulic conductivity (Lpr) were largely insensitive to externally applied H2O2. However, using bromocresol purple, it was shown that the acidification of the medium surrounding the root was strongly inhibited with low temperature‐ and H2O2‐treated roots. Addition of catalase (EC 1.11.1.6) to the root medium during low‐temperature exposure led to a recovery of H+‐efflux along the root surface and increased Lpr, demonstrating the importance of an H2O2 detoxification system in the root cells. Additional evidence for an increased Lpr was obtained by the Fenton reaction wherein a warming of the solution increased the activity of the detoxification system. All available evidence suggests that the ability of figleaf gourd root system to maintain a low level of H2O2 in the cytoplasm and to detoxify reactive oxygen species is related to the maintenance of water transport activity at low temperatures.

Avaliação de genótipos de milho para semeadura precoce sob influência de baixa temperatura

O milho (Zea mays L.) é uma planta de clima tropical que exige calor e umidade para produzir satisfatoriamente e proporcionar rendimentos compensadores. Diversos fatores podem comprometer a germinação das sementes e a emergência de plântulas no campo, merecendo destaque a semeadura em solos com baixas temperaturas. Em regiões que predominam condições de baixas temperaturas, seria importante o uso de sementes mais tolerantes a essa condição de estresse. Sementes de milho apresentam variabilidade genética para a germinação a baixas temperaturas. O objetivo deste trabalho foi classificar genótipos de milho quanto a tolerância das sementes à baixa temperatura de germinação, identificando àqueles com potencial para utilização em semeadura precoce. Avaliaram-se 16 genótipos provenientes do programa de melhoramento de milho da empresa KSP Sementes e Pesquisas Ltda., sendo 10 linhagens em diferentes estádios endogâmicos, seis populações de fecundação aberta e três híbridos simples comerciais, recomendados para semeadura precoce na Região Sul do Brasil. A avaliação da qualidade fisiológica das sementes foi feita pelos testes de germinação, primeira contagem de germinação, comprimento de plântula, biomassa seca, área foliar e radicular nas temperaturas de 25°C e 10°C. Foram realizadas análises eletroforéticas para os sistemas isoenzimáticos da fosfatase ácida, esterase e peroxidase. Os resultados permitiram classificar os genótipos quanto à tolerância das sementes à baixa temperatura, evidenciando que há variabilidade entre eles e potencialidades para serem usados em semeadura precoce na região sul do Brasil.

Soil temperature, growth and yield of maize (Zea mays L.) as affected by wheat straw mulch

Maize crop is grown mostly in tropical/subtropical environments where drought adversely affects its production. A field experiment was conducted on sandy loam soil for four years (1999 – 2002) to study the effect of wheat straw mulch (0 and 6 t ha−1) and planting methods (flat and channel) on maize sown on different dates. Maximum soil temperature without mulch ranged from 32.2 – 44.4°C in channel and 31.6 – 46.4°C in flat planting method. Mulching, however, lowered soil temperature by 0.8 – 7.0°C in channel and 0 – 9.8°C in flat planting. Mulching, on an average, improved leaf area index by 0.42, plant height by 14 cm, grain yield by 0.24 t ha−1 and biomass by 1.57 t ha−1, respectively. Mulching improved grain yield only in flat sowing. Interaction between sowing date and planting method was significant. Seasonal variation in biomass were significantly correlated (p = 0.05) with mean air temperature during 0 – 45 days after planting (DAP) (r = −0.95), pan evaporation during 0 – 15 DAP (r = 0.79) and negative correlation with rainfall in entire cropping season (r = −0.89), whereas biomass increase with mulch in different cropping seasons had negative relation (r = −0.74) with amount of rain during 0 – 15 DAP.

Impacts of Environmental Factors on Degradation of Cry 1 Ab Insecticidal Protein in Leaf-Blade Powders of Transgenic Bt Rice

The determination of the environmental fate of Bt insecticidal protein released by Bt rice plants in paddy soils is a key issue in its ecological risk assessment. In this study, the impacts of soil water content, pH. and temperature on the degradation of Cry1Ab protein expressed in the leaves of Bt rice KMD2 were studied in the laboratory. Three types of paddy soils were used, i.e., blue clayey paddy soil, pale paddy soil on quaternary red soil, and marine-fluvigenic yellow loamy paddy soil. Ground powders of KMD2 leaf blades were mixed with each type of soil, and degradation dynamics of Cry1Ab were measured using enzyme-linked immunosorbent assay (ELISA). The degradation rate of Cry1Ab was high at the early experimental stage, but slowed down steadily at middle and later stages, which could be described by exponential equations, with the half-life period of degradation determined as 1.8–4.0 d. The soil water content, pH. and temperature could affect the degradation of Cry1Ab, but the effects of soil pH and temperature were relatively greater. In general, Cry1Ab degradations were slower under lower soil pH and temperature conditions, especially for marine-fluvigenic yellow loamy paddy soil.

Differences in the Development of Lateral Roots among Several Cultivars in Japanese Radishes (Raphanus sativus L.) under Low Temperature Condition

Seeds of cv. T-340 were sown in the field on 10 March and 9 April 1997. The lateral root (LR) production was progressively intensified in early sown plot (ESP) instead of late (LSP). Plants in the ESP produced roots with small mean weights, diameter and length as compared with those in the LSP. Early-sown seedlings were subjected to low soil temperature conditions, below approximately 12°C during the first growth stage. In a second experiment, seeds of cvs. T-340 and T-396 were sown in 2 experimental plots: a control plot and a high soil temperature plot (HTP). The minimum soil temperatures in the control were often remained below 10°C for about 25 days after sowing, but the temperatures in the HTP kept above 15°C during the growth period. When grown under the control, larger number of thickened LRs was observed in roots of cv. T-340, but roots of cv. T-396 did not exhibit this disorder at any soil temperature plot. In both cvs., hinder root elongation was observed in the control as compared with the HTP. In a third experiment, varietal difference in the occurrence of LR in roots of cvs. Oshin, T-340, T-396 and Tenpou was compared. Although no correlation was observed between the different cvs. and root growth, active meristematic activity was observed in the pericycle region outside the protoxylem in roots of susceptible cvs. Oshin and T-340. Conversely, this meristematic activity remained low in roots of resilient cvs. T-396 and Tenpou. These observations led to the hypothesis that the obstruction of root elongation caused by low soil temperatures (below 12°C) during the first growth period often results in activation of the basal region of the LR meristem in susceptible cvs. prompting LR development. However, in resilient cvs., the LR seldom occur, even when root elongation is inhibited by low soil temperatures that normally decrease the meristematic activity of this region.

Soil Genesis and Mineral Transformation Across an Environmental Gradient on Andesitic Lahar

Soils derived from andesite are regionally important in the western USA, and expression of andic soil properties may be directly related to climate. The objective of this research was to quantify mineral transformation on andesitic lahar across an environmental gradient on the western slope of the Sierra Nevada of California. We hypothesized that the dominance of short‐range‐order (SRO) materials would increase with increasing elevation as precipitation increased and temperatures decreased. Seven pedons were sampled across an elevation gradient (150–2800 m) having large variations in mean annual soil temperature (3–17°C) and mean annual precipitation (45–150 cm). The soil mineral assemblage was characterized by x‐ray diffraction, selective dissolution, total elemental analysis, and microprobe analysis. Weathering and soil development displayed maxima in the zone just below the permanent winter snowline (∼1590 m), with a sharp decrease at higher elevations. Rainfall‐dominated soils at lower elevations had a clay fraction dominated by kaolin. In the snowfall‐dominated zone, SRO (allophane and imogolite) dominated the clay fraction, except for the soils in the cryic soil temperature regime, where interlayered 2:1 layer silicates dominated. The 2:1 mineral is probably inherited, based on the presence of a chlorite‐like mineral in the andesite parent material. With increasing elevation, soil development followed the order Mollisols → Alfisols → Ultisols → Andisols → Inceptisols. Weathering, mineralogical transformations and soil development are limited by water availability at low elevations, whereas low soil temperature is the major limitation at high elevations.

Fluxes and production of N2O, CO2 and CH4 in boreal agricultural soil during winter as affected by snow cover

Agricultural soils are important source of atmospheric nitrous oxide (N2O) and a considerable part of annual N2O release occurs during the cold season in the boreal region. According to recent studies N2O can be produced in soils at low temperatures, below 0°C. We studied if removal of the snowcover lowers soil temperatures and whether this would affect flux rates of N2O, carbon dioxide (CO2) and methane (CH4) from an agricultural soil in eastern Finland. Gas flux rates and concentrations in soil were measured from study plots with undisturbed snow cover and from plots with snow removed. This experiment simulates changes in the soil thermal conditions with less snowfall. Plots without snow had even 15°C lower temperature at the depth of 5 cm and they had higher N2O emissions during soil freezing and thawing. However, there were only minor changes in CH4 or CO2 flux rates after removal of snow over the cold season. N2O and CO2 accumulated in the soil during winter and were then released rapidly during thawing in spring. CH4 concentrations in the soil remained lower than the atmospheric levels during winter and subsequently increased to the ambient levels after thawing. Future climate scenarios suggest possible decline in snowfall in northern Europe resulting in lower soil temperatures. This could lead to higher N2O emissions from boreal agricultural soils.

Tillage and root heat stress in wheat in central Alberta

Heat stress occurs often in wheat on the Canadian Prairies especially during reproductive growth, which has markedly negative impacts on yield. As previous studies reported that wheat growth was affected more by heat stress in roots than in shoot, we suspected that the cooling effect of no-till (NT) on soil may reduce the risk of root heat stress and benefit the yield compared with conventional tillage (CT). Data were collected between 2000 and 2003 from a tillage study using a continuous wheat cropping system on a Thin Black Chernozemic clay loam in central Alberta. Consistently lower soil temperatures at 5 and 10 cm in NT than CT were observed in the whole growing season every year. At the grain growth stage, NT mitigated heat shock (>32°C at 5 cm) which occurred in 2001 and 2002 under CT and considerably reduced root heat stress index (HSI), calculated as accumulations of hourly soil temperatures greater than 20°C, every year compared with CT. By reducing root heat stress especially during the grain growth stage and slightly increasing pre-seeding soil moisture, no-till increased above-ground biomass (33–160%) and grain yield (18–147%) every year except 2003 when heat and water stress were relatively mild. Key words: Heat stress, soil temperature, no-till, conventional tillage, wheat, root

Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline

AbstractFrom 2001 to 2004 we experimentally warmed 40 large, naturally established, white spruce [Picea glauca(Moench) Voss] seedlings at alpine treeline in southwest Yukon, Canada, using passive open‐top chambers (OTCs) distributed equally between opposing north and south‐facing slopes. Our goal was to test the hypothesis that an increase in temperature consistent with global climate warming would elicit a positive growth response. OTCs increased growing season air temperatures by 1.8°C and annual growing degree‐days by one‐third. In response, warmed seedlings grew significantly taller and had higher photosynthetic rates compared with control seedlings. On the south aspect, soil temperatures averaged 1.0°C warmer and the snow‐free period was nearly 1 month longer. These seedlings grew longer branches and wider annual rings than seedlings on the north aspect, but had reduced Photosystem‐II efficiency and experienced higher winter needle mortality. The presence of OTCs tended to reduce winter dieback over the course of the experiment. These results indicate that climate warming will enhance vertical growth rates of young conifers, with implications for future changes to the structure and elevation of treeline contingent upon exposure‐related differences. Our results suggest that the growth of seedlings on north‐facing slopes is limited by low soil temperature in the presence of permafrost, while growth on south‐facing slopes appears limited by winter desiccation and cold‐induced photoinhibition.

Correlation between derived weather parameters and crop parameters as influenced by land configuration, herbicide and plant geometry under polyethylene film mulched groundnut (Arachis hypogaea L.)

Crop parameters, namely, dry matter production (DMP), mature pods/plant, pod yield and harvest index (HI) were recorded in a field experiment repeated in the autumn of 2001 and in the winter of 2001 – 2002 and in another set of experiments repeated in autumn 2002 and winter 2002 – 2003 to study the crop-weather relationship in polyethylene film mulched groundnut. The crop parameters were correlated with derived weather parameters, namely, Growing Degree Days (GDD), Heat Unit Efficiency (HUE), Relative Temperature Disparity (RTD), Relative Humidity Disparity (RHD) and with soil temperatures recorded at three depths (10, 20 and 30 cm). The correlations and regressions obtained in the first experiment revealed that soil temperatures in the 10 cm depth layer are ineffective to groundnut production in the autumn, while they are advantageous in winter. In the second experiment, a lower soil temperature up to 20 cm depth resulted favorable for autumn groundnut, while for the winter crop a better production is obtained with higher soil temperatures in the first 10 cm of depth. In the autumn 2001, except HI, all other crop parameters were positively correlated with weather parameters, while during winter 2002, on the contrary, all crop parameters were negatively influenced by GDD, RTD and RHD, and positively by HUE. In the second experiment, HI showed a significant positive correlation with HUE during winter 2002 – 2003, but it was negative in autumn 2002.

Permo-Pennsylvanian palaeotemperatures from Fe-Oxide and phyllosilicate δ18O values

The oxygen isotope composition of fossil roots that have been permineralized by hematite are presented from eight different stratigraphic levels spanning the Upper Pennsylvanian and Lower Permian strata of north-central Texas. Hematite δ 18O values range from − 0.4% to 3.7%. The most negative δ 18O values occur in the upper Pennsylvanian strata, and there is a progressive trend toward more positive δ 18O values upward through the lower Permian strata. This stratigraphic pattern is similar in magnitude and style to δ 18O values reported for penecontemporaneous authigenic palaeosol phyllosilicates and calcites, suggesting that all three minerals record similar paragenetic histories that are probably attributed to temporal palaeoenvironmental changes across the Late Pennsylvanian and Early Permian landscapes. Palaeotemperature estimates based on paired δ 18O values between penecontemporaneous hematite and phyllosilicate samples suggest these minerals co-precipitated at relatively low temperatures that are consistent with a supergene origin in a low-latitude soil-forming environment. Hematite–phyllosilicate δ 18O pairs indicate (1) relatively low soil temperatures (∼ 24 ± 3 °C) during deposition of the upper Pennsylvanian strata followed by (2) a considerable rise in soil temperatures (∼ 35–37 ± 3 °C) during deposition of the lowermost Permian strata. Significantly, δD and δ 18O values of contemporaneous phyllosilicates provide single mineral palaeotemperature estimates that are analytically indistinguishable from temperature estimates based on hematite–phyllosilicate oxygen isotope pairs. The results between the two temperature-proxy methods suggest that the inferred large temperature change across the Upper Pennsylvanian–Lower Permian boundary might be taken seriously. If real, such a significant climate change would have undoubtedly had far-reaching ecological effects within this region of Pangaea. Notably, there are important lithological and palaeobotanical changes, such as disappearance of coal and coal swamp floras, across the Upper Pennsylvanian–Early Permian boundary of north-central Texas that may be consistent with major climatic change toward warmer conditions.

Incubation temperature and phenotypic traits of Sceloporus undulatus: implications for the northern limits of distribution

Cold environmental temperature is detrimental to reproduction by oviparous squamate reptiles by prolonging incubation period, negatively affecting embryonic developmental processes, and by killing embryos in eggs directly. Because low soil temperature may prevent successful development of embryos in eggs in nests, the geographic distributions of oviparous species may be influenced by the thermal requirements of embryos. In the present study, we tested the hypothesis that low incubation temperature determines the northern distributional limit of the oviparous lizard Sceloporus undulatus. To compare the effects of incubation temperature on incubation length, egg and hatchling survival, and hatchling phenotypic traits, we incubated eggs of S. undulatus under temperature treatments that simulated the thermal environment that eggs would experience if located in nests within their geographic range at 37 degrees N and north of the species' present geographic range at latitudes of 44 and 42 degrees N. After hatching, snout-vent length (SVL), mass, tail length, body condition (SVL relative to mass), locomotor performance, and growth rate were measured for each hatchling. Hatchlings were released at a field site to evaluate growth and survival under natural conditions. Incubation at temperatures simulating those of nests at 44 degrees N prolonged incubation and resulted in hatchlings with shorter SVL relative to mass, shorter tails, shorter hind limb span, slower growth, and lower survival than hatchlings from eggs incubated at temperatures simulating those of nests at 37 and 42 degrees N. We also evaluated the association between environmental temperature and the northern distribution of S. undulatus. We predicted that the northernmost distributional limit of S. undulatus would be associated with locations that provide the minimum heat sum (approximately 495 degree-days) required to complete embryonic development. Based on air and soil temperatures, the predicted northern latitudinal limit of S. undulatus would lie at approximately 40.5-41.5 degrees N. Our predicted value closely corresponds to the observed latitudinal limit in the eastern United States of approximately 40 degrees N. Our results suggest that soil temperatures at northern latitudes are not warm enough for a sufficient length of time to permit successful incubation of S. undulatus embryos. These results are consistent with the hypothesis that incubation temperature is an important factor limiting the geographic distributions of oviparous reptile species at high latitudes and elevations.