Mean Annual Soil Temperature Research Articles

Effects of bryophyte and lichen cover on permafrost soil temperature at large scale

Abstract. Bryophyte and lichen cover on the forest floor at high latitudes exerts an insulating effect on the ground. In this way, the cover decreases mean annual soil temperature and can protect permafrost soil. Climate change, however, may change bryophyte and lichen cover, with effects on the permafrost state and related carbon balance. It is, therefore, crucial to predict how the bryophyte and lichen cover will react to environmental change at the global scale. To date, current global land surface models contain only empirical representations of the bryophyte and lichen cover, which makes it impractical to predict the future state and function of bryophytes and lichens. For this reason, we integrate a process-based model of bryophyte and lichen growth into the global land surface model JSBACH (Jena Scheme for Biosphere–Atmosphere Coupling in Hamburg). The model simulates bryophyte and lichen cover on upland sites. Wetlands are not included. We take into account the dynamic nature of the thermal properties of the bryophyte and lichen cover and their relation to environmental factors. Subsequently, we compare simulations with and without bryophyte and lichen cover to quantify the insulating effect of the organisms on the soil. We find an average cooling effect of the bryophyte and lichen cover of 2.7 K on temperature in the topsoil for the region north of 50° N under the current climate. Locally, a cooling of up to 5.7 K may be reached. Moreover, we show that using a simple, empirical representation of the bryophyte and lichen cover without dynamic properties only results in an average cooling of around 0.5 K. This suggests that (a) bryophytes and lichens have a significant impact on soil temperature in high-latitude ecosystems and (b) a process-based description of their thermal properties is necessary for a realistic representation of the cooling effect. The advanced land surface scheme, including a dynamic bryophyte and lichen model, will be the basis for an improved future projection of land–atmosphere heat and carbon exchange.

Thermal impacts of engineering activities and vegetation layer on permafrost in different alpine ecosystems of the Qinghai–Tibet Plateau, China

Abstract. Climate warming and engineering activities have various impacts on the thermal regime of permafrost in alpine ecosystems of the Qinghai–Tibet Plateau. Using recent observations of permafrost thermal regimes along the Qinghai–Tibet highway and railway, the changes of such regimes beneath embankments constructed in alpine meadows and steppes are studied. The results show that alpine meadows on the Qinghai–Tibet Plateau can have a controlling role among engineering construction effects on permafrost beneath embankments. As before railway construction, the artificial permafrost table (APT) beneath embankments is not only affected by climate change and engineering activities but is also controlled by alpine ecosystems. However, the change rate of APT is not dependent on ecosystem type, which is predominantly affected by climate change and engineering activities. Instead, the rate is mainly related to cooling effects of railway ballast and heat absorption effects of asphalt pavement. No large difference between alpine and steppe can be identified regarding the variation of soil temperature beneath embankments, but this difference is readily identified in the variation of mean annual soil temperature with depth. The vegetation layer in alpine meadows has an insulation role among engineering activity effects on permafrost beneath embankments, but this insulation gradually disappears because the layer decays and compresses over time. On the whole, this layer is advantageous for alleviating permafrost temperature rise in the short term, but its effect gradually weakens in the long term.

Impact of climate change on soil thermal and moisture regimes in Serbia: An analysis with data from regional climate simulations under SRES-A1B

We considered temporal and spatial variations to the thermal and moisture regimes of the most common RSGs (Reference Soil Groups) in Serbia under the A1B scenario for the 2021–2050 and 2071–2100 periods, with respect to the 1961–1990 period. We utilized dynamically downscaled global climate simulations from the ECHAM5 model using the coupled regional climate model EBU-POM (Eta Belgrade University-Princeton Ocean Model). We analysed the soil temperature and moisture time series using simple statistics and a Kolmogorov complexity (KC) analysis. The corresponding metrics were calculated for 150 sites. In the future, warmer and drier regimes can be expected for all RSGs in Serbia. The calculated soil temperature and moisture variations include increases in the mean annual soil temperature (up to 3.8°C) and decreases in the mean annual soil moisture (up to 11.3%). Based on the KC values, the soils in Serbia are classified with respect to climate change impacts as (1) less sensitive (Vertisols, Umbrisols and Dystric Cambisols) or (2) more sensitive (Chernozems, Eutric Cambisols and Planosols).

Appraisal of branched glycerol dialkyl glycerol tetraether-based indices for North China

The distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) are quite promising for quantitative reconstruction of temperature and pH in paleoclimate studies. Recently, the separate quantification of the 5- and 6-methyl brGDGTs allowed establishment of new indices that may provide more accurate temperature and pH estimates than traditional brGDGT indices. Here, we systematically investigated the applicability of various brGDGT indices in an independent set of 148 soils from the temperate northern area of China. The results support the idea that the new brGDGT indices are more applicable than the traditional ones, with regional calibrations showing more accurate mean annual air temperature (MAAT) and pH estimates than the global calibrations. Previous studies noted that variation in soil temperature might differ from variation in air temperature. The mismatch may cause scatter in the brGDGT-MAAT calibrations, as soil bacteria producing brGDGTs should respond more directly to soil temperature variation. We therefore monitored year round, in-situ soil temperature variation for 20 selected soils from this large region. Each temperature proxy correlated better with the in-situ soil mean annual temperature (MAT) than with the meteorological MAAT. Further comparison of correlations between seasonal soil temperature and brGDGT indices showed that the latter related best to growing season temperature (tentatively defined as the mean temperature of spring, summer and autumn) and most weakly to winter temperature, pointing to a seasonal preference for brGDGT production. Hence, the offset between soil MAT and MAAT and the seasonal production of brGDGTs are both likely responsible for part of the scatter and bias in the brGDGT-MAAT calibrations for temperate regions. Additionally, we propose two supplementary indices to the recently proposed multiple linear regression index and Index 1, for tracing soil temperature variation for the region of North China. The 4 indices could yield regional temperature calibrations with R2>0.90 and root mean square error (RMSE)<1.6°C vs. the growing season soil temperature. Our study also implies that, on a global scale, the calibrations between brGDGT temperature proxies and in-situ soil temperature may provide more reliable temperature estimates in paleoclimate studies, so in-situ soil temperature measurements of globally distributed soils are required for the development of improved temperature calibrations using soil brGDGTs.

Soil Temperature Variability in Complex Terrain Measured Using Fiber‐Optic Distributed Temperature Sensing

Core Ideas Soil temperature variability within land surface units is low, with a SD of &lt;1.5°C. Land surface effects are greater than a 911‐m elevation change. Fiber‐optic DTS provides a unique look at soil temperature variability. Soil temperature (Ts) exerts critical controls on hydrologic and biogeochemical processes, but the magnitude and nature of Ts variability in a landscape setting are rarely documented. Fiber‐optic distributed temperature sensing (DTS) systems potentially measure Ts at high density across a large extent. A fiber‐optic cable 771 m long was installed at a depth of 10 cm in contrasting landscape units (LUs) defined by vegetative cover at Upper Sheep Creek in the Reynolds Creek Experimental Watershed (RCEW) and Critical Zone Observatory in Idaho. The purpose was to evaluate the applicability of DTS in remote settings and to characterize Ts variability in complex terrain. Measurement accuracy was similar to other field instruments (±0.4°C), and Ts changes of approximately 0.05°C at a monitoring spatial scale of 1 m were resolved with occasional calibration and an ambient temperature range of 50°C. Differences in solar inputs among LUs were strongly modified by surface conditions. During spatially continuous snow cover, Ts was practically homogeneous across LUs. In the absence of snow cover, daily average Ts was highly variable among LUs due to variations in vegetative cover, with a standard deviation (SD) greater than 5°C, and relatively uniform (SD &lt; 1.5°C) within LUs. Mean annual soil temperature differences among LUs of 5.2°C was greater than those of 4.4°C associated with a 910‐m elevation difference within the RCEW. In this environment, effective Ts simulation requires representation of relatively small‐scale (&lt;20 m) LUs due to the deterministic spatial variability of Ts.

Distribution of tetraether lipids in agricultural soils – differentiation between paddy and upland management

Abstract. Rice paddies constitute almost a fifth of global cropland and provide more than half of the world's population with staple food. At the same time, they are a major source of methane and therewith significantly contribute to the current warming of Earth's atmosphere. Despite their apparent importance in the cycling of carbon and other elements, however, the microorganisms thriving in rice paddies are insufficiently characterized with respect to their biomolecules. Hardly any information exists on human-induced alteration of biomolecules from natural microbial communities in paddy soils through varying management types (affecting, e.g., soil or water redox conditions, cultivated plants). Here, we determined the influence of different land use types on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs), which serve as molecular indicators for microbial community structures, in rice paddy (periodically flooded) and adjacent upland (non-flooded) soils and, for further comparison, forest, bushland and marsh soils. To differentiate local effects on GDGT distribution patterns, we collected soil samples in locations from tropical (Indonesia, Vietnam and Philippines) and subtropical (China and Italy) sites. We found that differences in the distribution of isoprenoid GDGTs (iGDGTs) as well as of branched GDGTs (brGDGTs) are predominantly controlled by management type and only secondarily by climatic exposition. In general, upland soil had higher crenarchaeol contents than paddy soil, which by contrast was more enriched in GDGT-0. The GDGT-0 ∕ crenarchaeol ratio, indicating the enhanced presence of methanogenic archaea, was 3–27 times higher in paddy soils compared to other soils and increased with the number of rice cultivation cycles per year. The index of tetraethers consisting of 86 carbons (TEX86) values were 1.3 times higher in upland, bushland and forest soils than in paddy soils, potentially due to differences in soil temperature. In all soils brGDGT predominated over iGDGTs with the relative abundance of brGDGTs increasing from subtropical to tropical soils. Higher branched vs. isoprenoid tetraether (BIT) values in paddy soils compared to upland soils together with higher BIT values in soils from subtropical climates indicated effects on the amounts of brGDGT induced by differences in management as well as climate. In acidic soils cyclization ratio of branched tetraethers (CBT) values correlated well with soil pH. In neutral to alkaline soils, however, no correlation but an offset in CBT between paddy and upland managed soils was detected. This is interpreted as indicating soil moisture exerting an additional control on the CBT in these soils. Lower modified methylation index of branched tetraether (MBT′) values and temperatures calculated from this (TMC) in paddy soils compared to upland soils are attributed to a management-induced (e.g. enhanced soil moisture via flooding) effect on mean annual soil temperature (MST).

Variations in soil carbonate formation and seasonal bias over &gt;4 km of relief in the western Andes (30°S) revealed by clumped isotope thermometry

Abstract Carbonate clumped isotope thermometry provides a new method for investigating long-standing questions regarding seasonal biases in soil carbonate formation and the relationship between soil carbonate formation temperatures recorded by clumped isotopes ( T ( Δ 47 ) ) and surface temperatures. We address these questions by comparing C, O, and clumped isotope data from Holocene soil carbonates to meteorological and in situ soil monitoring data along a 170 km transect with >4 km of relief in Chile (30°S). This arid transect experiences a winter wet season, and a >20 °C range in mean annual air temperature. We test the hypothesis that, regardless of soil moisture conditions, soil carbonates from arid regions record warm season biases and form in isotopic equilibrium with soil water and soil CO2. Below 3200 m, precipitation falls as rain and soil carbonate T ( Δ 47 ) values at depths >40 cm resemble summer soil temperatures. Above 3200 m, precipitation falls as snow and T ( Δ 47 ) values resemble mean annual soil temperatures. Soil carbonates from the highest site yield anomalous δ 18 O , δ 13 C , and T ( Δ 47 ) values indicative of kinetic isotope effects consistent with cryogenic carbonate formation. Our findings (1) demonstrate that soil carbonate T ( Δ 47 ) values from shallow ( 40 cm; (3) highlight the role of the soil moisture regime in modulating the timing of soil carbonate formation, which affects the resulting carbonate T ( Δ 47 ) values; and (4) show that soil carbonates from high elevation or high latitude sites may form under non-equilibrium conditions. These findings underscore the importance of understanding past soil moisture conditions when attempting to reconstruct paleotemperatures using carbonate clumped isotope thermometry.

Change of climate conditions in the forest area of South Yakutia

A statistical analysis of meteorological parameters which influence the intensity of exogenous processes in the forest area of South Yakutia has been performed. The indicated increase in mean annual air and soil temperature rates occurred non-uniformly. Annual precipitation increase was due to precipitation rates in cold or transitional seasons; increase in snow cover depth and decrease in diurnal air temperature range was observed in cold season.

Methane-cycling microorganisms in soils of a high-alpine altitudinal gradient.

Methanogens and methanotrophs play unique roles as producers and consumers of the greenhouse gas methane (CH4) in soils, respectively. Here, we aimed to reveal whether and to which extent methane-cyclers occur in high-alpine soils, and to assess their spatial distribution along an altitudinal gradient (2700-3500 m) in the Austrian Alps at sites located within the alpine (2700-2900 m), the alpine-nival (3000-3100 m) and the nival belts (3200-3500 m). Methanococcales and Methanocella spp. were most abundant among all quantified methanogenic guilds, whereas Methanosarcinales were not detected in the studied soil. The detected methanogens seem to be capable of persisting despite a highly oxic low-temperature environment. Methanogenic and methanotrophic activities and abundances of methanotrophs, Methanococcales and Methanocella spp. declined with altitude. Methanogenic and methanotrophic abundances were best explained by mean annual soil temperature and dissolved organic carbon, respectively. Alpine belt soils harbored significantly more methane-cyclers than those of the nival belt, indicating some influence of plant cover. Our results show that methanogens are capable of persisting in high-alpine cold soils and might help to understand future changes of these environments caused by climate warming.

Underground urban heat island below Moscow city

Long-term measurements of the soil temperature on different depths in Moscow and its suburbs have been collected since the end of the XIX century. At Moscow University this parameter has been measured simultaneously at two locations since 1954: one below the usual natural cover and one below a special naked area. Following the air warming, in the last 116years the soil temperature increased in Moscow by 1.8–1.9°C (at 160cm depth). During the last half a century the temperature increased much faster at the University below the naked area (+0.04°C/year) than below the natural cover (meaning the snow cover in winter and grass and sod cover during other seasons): +0.02°C/year.The spatial distribution of the soil temperature in Moscow region has been discussed using the simultaneous data of ground meteorological network. Mean annual values of the surface temperature (0cm) and soil temperature at eight depths from 20 to 320cm have been analyzed. Mean annual soil temperature in the city center is higher by up to 1.0–1.2°C than at the city periphery and by up to 1.6–1.7°C than in Moscow region rural zone (at the depths of 120 and 160cm). At smaller depths these differences are a bit less but still statistically significant. Thus, an underground urban heat island exists at any depth. The evident cause of this phenomenon is human activity which has resulted in a lot of factors. A special index has been suggested for estimation of the average intensity of the underground urban heat island. According this index, the mean difference of the soil temperatures can amount to +0.6…+0.8°C if we compare the city with the rural zone and from +0.4 to +0.6°C if we compare only urban periphery (without city center) with the rural zone. Another discovery was that the underground heat island evidently extends below the depth of 320cm. The annual dynamic of the difference between urban and rural soil temperatures reaches its maximum in winter (+0.9…+1.2°C depending on the depth) due to strong urban heating and drops to its minimum in summer (−0.5…+0.4°C at different depths).

Changes of Soil Thermal Regimes in the Heihe River Basin Over Western China

Investigation of the changes in soil thermal regimes is essential to the understanding of ecohydrological processes, resource development, and climate change. We use soil temperatures from 12 meteorological stations of the China Meteorological Administration in the Heihe River Basin to estimate soil seasonal freeze depth, the onset and end dates of soil freeze, and the duration of soil freeze. Based on the characteristics of the soil temperature in the seasonal freezing layer, the freeze/thaw processes of this layer were divided into four stages: the winter freezing stage, spring thawing stage, summer warming stage, and autumn cooling stage. Spring, summer, autumn, and winter ground surface temperatures in the basin exhibit significant increasing trends in 1972–2006, of 0.65 °C decade-1, 0.73 °C decade-1, 0.48 °C decade-1, and 0.44 °C decade-1, respectively. Mean annual soil temperature at 0.0–0.20 m depths reveals an increasing trend of 0.58–0.63 °C decade-1 in 1972–2006. The onset date of soil freeze, the end date of soil freeze, and the duration of soil freeze in 1972–2006 exhibit a statistically significant trend of +2 days decade-1, -4 days decade-1, and -6 days decade-1, respectively. The maximum thickness of the seasonally frozen ground for 1960–2007 reveals a statistically significant trend of -4.0 cm decade-1 and a net change of -19.2 cm for the 48-year period. These are all related to the increase in spring, summer, autumn, and winter air temperature and the mean annual air temperature in the basin, a possible result of global warming.

Irregular precipitation events in control of seasonal variations in CO2 exchange in a cold desert-shrub ecosystem in northwest China

Net ecosystem productivity (NEP) of a cold desert-shrub ecosystem was continuously monitored during 2012 and 2013 using the eddy covariance method. The aim was to examine the influence of irregular precipitation in control of seasonal variations in NEP at multiple timescales. The ecosystem was a weak annual carbon sink. Difference in NEP between 2012 and 2013 (2013, having higher NEP) was caused by a suppression in gross ecosystem productivity (GEP; 55 g C m−2) compared to ecosystem respiration (ER; 33 g C m−2) in 2012, as a result of (i) fewer frequent and low-intensity rainy days and more carbon-source days in summer, (ii) lower annual mean air and soil temperature, and (iii) lower daily mean photosynthetically active radiation. Daily GEP and ER both decreased during dry periods, with GEP decreasing more than ER, causing NEP to decrease. Persistent and high available soil water associated with frequent and low-intensity precipitation during DOY 207 to 224 was central to maintaining carbon-sink strength in 2013, resulting in a noticeable increase in daily NEP from 0.3 g C m−2 to 1.2 g C m−2. Frequent and low-intensity precipitation was responsible for maintaining plant growth, while sporadic and high-intensity precipitation decreased NEP.

The variations in soil microbial communities, enzyme activities and their relationships with soil organic matter decomposition along the northern slope of Changbai Mountain

We present a comprehensive analysis of the changes in the structure and functioning of the soil microbial communities, as well as their driving factors along the northern slope of Changbai Mountain by analyzing soil phospholipid fatty acids (PLFAs) profiles and enzymatic activities. The four vertical zones of vegetation selected in this study were as follows: (1) mixed coniferous and broad-leaved forest (MCB) located below 1100m (site A and B); (2) dark-coniferous spruce-fir forest (DCF) located between 1100–1700m (site C); (3) Ermans birch forest (EB) located between 1700 and 2000m (site D); and (4) alpine tundra (AT) located above 2000m (sites E and F). The results showed that the total viable microbial PLFAs varied with altitude, with the highest value detected in the EB (site D) (76.8nmolg−1). The fungal/bacterial (F/B) and the Gram positive/Gram negative (G+/G−) ratios increased with elevation. The lower values of F/B obtained in the MCB (site A) and in DCF (site C) for G+/G－. The soil microbial community structure observed in the MCB (sites A and B) was different from that observed in the other four sites, with lower fungal biomass. The soil microbial activities such as β-glucosidase (βG), N-acetylglucosaminidase (NAG), acid phosphatase (AP) and leucine aminopeptidase (LAP) in the MCB (sites A and B) were significantly higher than those documented in the other four sites. The substantial differences in the soil microbial community composition were significantly correlated with the mean annual temperature (MAT), the mean annual precipitation (MAP) and soil temperature, silt and clay fraction, total phosphorus, nitrate nitrogen. However, the variations in soil enzyme activities were significantly correlated with soil nutrients. The MAP and nitrate nitrogen were the significant predictors of the variance in the soil microbial community and enzyme activity, respectively. The soil organic matter (SOM) decomposition rate showed a significant positive relationship with the total microbial, bacterial, actinomycetes PLFAs and the soil enzyme activities. Our results suggest that studies incorporating the microbial community structure and soil enzyme activity with the SOM decomposition may enhance our understanding of the mechanisms of biogeochemical processes.

Spatial Prediction of Soil Temperature in China

Temperature affects many soil biochemical and geochemical processes. The growth of plants, seed germination, circulations of carbon and nitrogen are all significantly influenced by soil temperature, thus it is important to estimate the spatial pattern of soil temperature. This paper shows the results of spatial patterns of mean annual soil temperature interpolated from the measurements of 698 meteorological stations in China. Four geostatistical methods, ordinary kriging (OK), regression kriging with mean annual air temperature (RK-1), regression kriging with latitude, longitude and elevation (RK-2) and regression kriging with multi-auxiliary predictors (RK-3), were compared. Ordinary kriging (OK) directly interpolated the mean annual soil temperature data extracted from meteorological stations to obtain the spatial patterns of the mean annual soil temperature. For the three regression kriging methods, intensive auxiliary variables (mean annual air temperature, elevation, latitude and longitude), which were correlated with mean annual soil temperature, were used to increase the accuracy of estimation. The results suggested that RK-3 preformed best, followed by RK-1 and RK-2. The intensive data of auxiliary variables used in the regression kriging significantly improved the accuracy of interpolation results.

Elevational patterns of Polylepis tree height (Rosaceae) in the high Andes of Peru: role of human impact and climatic conditions.

We studied tree height in stands of high-Andean Polylepis forests in two cordilleras near Cuzco (Peru) with respect to variations in human impact and climatic conditions, and compared air and soil temperatures between qualitatively defined dry and humid slopes. We studied 46 forest plots of 100 m2 of five Polylepis species at 3560–4680 m. We measured diameter at breast height (dbh) and tree height in the stands (1229 trees in total), as well as air and soil temperatures in a subset of plots. The data was analyzed combining plots of given species from different sites at the same elevation (±100 m). There was no elevational decrease of mean maximum tree height across the entire data set. On humid slopes, tree height decreased continuously with elevation, whereas on dry slopes it peaked at middle elevations. With mean maximum tree heights of 9 m at 4530 m on the humid slopes and of 13 m at 4650 m on the dry slopes, we here document the tallest high-elevation forests found so far worldwide. These highest stands grow under cold mean growing season air temperatures (3.6 and 3.8°C on humid vs. dry slopes) and mean growing season soil temperatures (5.1 vs. 4.6°C). Mean annual air and soil temperature both decreased with elevation. Dry slopes had higher mean and maximum growing season air temperatures than humid slopes. Mean annual soil temperatures did not significantly differ and mean annual air temperatures only slightly differed between slopes. However, maximum air temperatures differed on average by 6.6 K between dry and humid slopes. This suggests that the differences in tree height between the two slopes are most likely due to differences in solar radiation as reflected by maximum air temperatures. Our study furthermore provides evidence that alpine Polylepis treelines grow under lower temperature conditions than global high-elevation treelines on average, suggesting that Polylepis species may have evolved special physiological adaptations to low temperatures.

금산장기생태조사지 낙엽활엽수림내 토양이산화탄소 방출량의 연변동

산림생태계 토양 호흡량은 지구탄소순환에 중요한 역할을 한다. 본 연구는 금산 장기생태 연구 조사지 낙엽활엽수림을 대상으로 4년 동안 토양 이산화탄소 방출량의 연 변동을 조사하였다. 금산 장기생태 연구 조사지 월별 토양 이산화탄소 방출량은 토양온도 변화와 밀접한 관계가 있었으며 토양수분함량과는 뚜렷한 경향을 보이지 않았다(P > 0.05). 동절기(1월과 2월, 2007년의 경우 1월부터 3월)를 제외한 평균 토양 이산화탄소 방출량은 2008년 0.32 g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX>, 2009년 0.40g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX>, 2007년 0.41g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX>, 2010년 0.54 g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX> 순이었으며, 2008년의 연 평균토양온도는 <TEX>$12.0^{\circ}C$</TEX>로 다른 연도의 토양 온도 <TEX>$13.0-13.5^{\circ}C$</TEX>에 비해 유의적으로(P<0.05) 낮았다. 토양 이산화탄소 방출량과 토양 20cm 깊이의 토양온도는 지수함수 관계가 있었으며 (<TEX>$R^2$</TEX> = 0.31-0.75, P < 0.05), 토양수분함량은 토양 이산화탄소 방출량과 유의적인 관계가 없었다(P > 0.05). 본 연구 결과에 따르면 금산장기생태연구 조사지 토양 이산화탄소 방출량의 연 변동은 토양수분보다는 토양온도 변화와 관계가 있었다. Soil respiration in forest ecosystems play an important role in global carbon cycle. This study was carried out to determine the annual variation of soil <TEX>$CO_2$</TEX> efflux for 4 years in a broadleaved deciduous forest of the Geumsan (Mt.) Long-Term Ecological Research (GLTER) site in Southern Korea. The soil <TEX>$CO_2$</TEX> efflux in the GLTER site showed annual variations with the fluctuations of annual mean soil temperature, but not with those of soil water content. The annual mean soil <TEX>$CO_2$</TEX> efflux except for winter season was 0.32 g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX> for 2008, 0.40 g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX> for 2009, 0.41 g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX> for 2007, and 0.54 g <TEX>$CO_2\;m^{-2}h^{-1}$</TEX> for 2010. The lowest soil <TEX>$CO_2$</TEX> effluxin 2008 was associated with the lowest soil temperature (<TEX>$2.0^{\circ}C$</TEX>) in comparison with those of other years (<TEX>$13.0-13.5^{\circ}C$</TEX>). The exponential relationships between monthly soil <TEX>$CO_2$</TEX> efflux and the corresponding soil temperature at the soil depth of 20 cm were significant (<TEX>$R^2$</TEX> = 0.31-0.75, P < 0.05). The results indicate that the annual variation of soil <TEX>$CO_2$</TEX> efflux was attributed to the variations of soil temperature rather than soil water content in the GLTER site.

Effects of vegetation height and density on soil temperature variations

Reduction in vegetation cover caused by human activities has a great impact on soil temperature. It is important to assess how soil temperature responds to reduction of vegetation height and density. In this paper we first report the trends of mean annual soil surface and air temperatures recorded at the meteorological stations near the Ecological Research Station for Grassland Farming (ERSGF) from 1961 to 2007, then we setup an experiment using reed (Phragmites australis) stalks with different heights and densities to simulate effects of different vegetation height and density on soil and air temperatures. The warming rates of the mean annual soil and air temperatures were 0.043 and 0.041°C a−1, respectively. Changes of soil temperature were characterized by both increased mean annual maximum and minimum soil temperatures. At the experimental site, mean daily temperature, mean daily maximum soil and air temperatures increased significantly. In contrast, mean daily minimum soil temperature increased significantly while mean daily minimum air temperature decreased significantly as the height and density of reed stalks reduced during the experimental period. Mean diurnal soil temperature ranges were smaller than mean diurnal air temperature ranges. These results highlight that the importance of vegetation cover on soil and air temperatures.

Impacts of Soil Climate on Desert Scrubs Distribution in the Mojave Desert

Based on the mean annual soil temperature collected with the Pallmann method and data on evaporation, precipitation, and the perennial plant species in 75 monitoring sites in the Mojave Desert from 1982 to 2000, we investigated the interrelationships of soil temperature and aridity on the distribution of several dominant desert scrubs in the Mojave Desert. It showed that the creosote bush-white bursage communities populated in the areas with lower elevation (<1,200 m) and higher soil temperature (>20°C). The sagebrush communities were found in wetter areas with higher elevation (>1,500 m) and lower soil temperature (<18°C). The blackbrush communities occupied areas between the creosote bush-white bursage communities and sagebrush communities. The distribution of yucca species is similarly affected by the soil temperature and aridity. Climate change is expected to significantly alter the distribution patterns of vegetation in Mojave Desert.

Hot or not? Impact of seasonally variable soil carbonate formation on paleotemperature and O-isotope records from clumped isotope thermometry

Quantifying the timing and temperature of soil carbonate formation is important for interpreting isotopic records of Earth-surface temperature and soil water composition from paleosols. Pedogenic carbonates typically have been assumed to form at mean annual temperature, but recent work suggests warm-season bias in carbonate formation could impact the interpretation of δ18O values and carbonate formation temperatures for paleosol carbonates. We investigate the relationship between seasonally variable soil temperatures and carbonate formation temperatures estimated using clumped isotope thermometry (T(Δ47)). Holocene soil carbonates were collected along the eastern flank of the Andes (33°S) over 2km of relief and a nearly 15°C range of mean annual air temperature (MAAT). This area receives both westerly, winter season precipitation and easterly, summer season precipitation, leading to a reversal of soil moisture regimes that occurs at ∼2km elevation. In instrumented pits sampled to 1m depth, we do not observe systematic variation in T(Δ47) with depth or with elevation-dependent MAAT. Average T(Δ47) values for soil carbonates collected above 2km elevation reflect summer soil temperatures. In contrast, T(Δ47) values below ∼2km track mean annual soil temperature. These results may reflect the dominance of summer precipitation below ∼2km, which likely delays soil drying and carbonate growth until fall. This seasonal variability in carbonate formation greatly impacts carbonate formation temperature, with important implications for estimating soil water δ18O values. Calculating soil water δ18O values using T(Δ47) produces a soil water δ18O lapse rate of −4.6‰/km, remarkably similar to that of modern surface waters (−4.8‰/km), and significantly improving on previous soil water estimates assuming MAAT for carbonate formation temperatures. Although seasonal bias can prevent the straightforward translation of soil carbonate T(Δ47) into meaningful surface air temperatures, direct constraints on temperature from clumped isotopes can both provide a window into soil processes and aid in the interpretation of conventional stable isotopic data to reconstruct surface conditions in the past.

A new fractional snow‐covered area parameterization for the Community Land Model and its effect on the surface energy balance

One function of the Community Land Model (CLM4) is the determination of surface albedo in the Community Earth System Model (CESM1). Because the typical spatial scales of CESM1 simulations are large compared to the scales of variability of surface properties such as snow cover and vegetation, unresolved surface heterogeneity is parameterized. Fractional snow‐covered area, or snow‐covered fraction (SCF), within a CLM4 grid cell is parameterized as a function of grid cell mean snow depth and snow density. This parameterization is based on an analysis of monthly averaged SCF and snow depth that showed a seasonal shift in the snow depth–SCF relationship. In this paper, we show that this shift is an artifact of the monthly sampling and that the current parameterization does not reflect the relationship observed between snow depth and SCF at the daily time scale. We demonstrate that the snow depth analysis used in the original study exhibits a bias toward early melt when compared to satellite‐observed SCF. This bias results in a tendency to overestimate SCF as a function of snow depth. Using a more consistent, higher spatial and temporal resolution snow depth analysis reveals a clear hysteresis between snow accumulation and melt seasons. Here, a new SCF parameterization based on snow water equivalent is developed to capture the observed seasonal snow depth–SCF evolution. The effects of the new SCF parameterization on the surface energy budget are described. In CLM4, surface energy fluxes are calculated assuming a uniform snow cover. To more realistically simulate environments having patchy snow cover, we modify the model by computing the surface fluxes separately for snow‐free and snow‐covered fractions of a grid cell. In this configuration, the form of the parameterized snow depth–SCF relationship is shown to greatly affect the surface energy budget. The direct exposure of the snow‐free surfaces to the atmosphere leads to greater heat loss from the ground during autumn and greater heat gain during spring. The net effect is to reduce annual mean soil temperatures by up to 3°C in snow‐affected regions.