Soil Microclimatic Conditions Research Articles

Bryophytes dominate plant regulation of soil microclimate in alpine grasslands

Soil temperature and moisture are important regulators of a broad range of biotic and abiotic processes in terrestrial ecosystems. Vegetation can, in turn, play a role in regulating soil microclimate, which creates potential for powerful and interactive feedbacks from soil and vegetation on the atmosphere. Although the regulatory effect of vegetation on soil microclimatic conditions has been quite extensively and empirically assessed, most studies have determined the net effect of intact woody vegetation versus bare ground. However, for other plant functional groups we lack a clear understanding of their role and any climate‐context dependency in controlling microclimatic conditions.We investigated the role of three major plant functional groups – graminoids, forbs and bryophytes – in regulating soil microclimate in semi‐natural alpine grasslands. Using a fully factorial above‐ground biomass removal experiment, we assessed the role of these plant functional groups in regulating soil temperature amplitude, soil moisture, and number of freezing days. The experiment was replicated across orthogonal temperature and precipitation gradients in Norway to assess whether the effects of functional group abundance varied with climate.The effect of plant biomass on soil microclimate varied among functional groups across the climatic gradients. Bryophytes reduced growing season soil temperature, whereas graminoids and forbs did not (0.5ºC compared to 0ºC), and with a stronger effect in colder climates at higher elevations and on days with high solar radiation. Bryophyte biomass further reduced the number of soil freezing days at boreal and sub‐alpine sites. Finally, graminoid biomass partly explained variation in soil moisture: soils dried more under graminoids at drier sites.Our findings highlight that functional group identity plays a key role in regulating soil microclimate in alpine grasslands across seasons. The strong effect of bryophytes on soil temperature points to their importance in the plant community for a variety of ecosystem functions, some of which may be indirectly vulnerable to future warming via biomass reductions of bryophytes.

Daily Variation on Soil Moisture and Temperature on Three Restinga Plant Formations

Restinga forests and open scrubby formations establish on sandy well-drained soils alongside the Brazilian coastline. Restinga plants are exposed to extreme conditions and vegetation types are mainly structured by species access to groundwater. But to date, no systematic evaluations have been done in order to characterize soil microclimatic conditions and understand how they are associated with variations in climatic drivers. We evaluated hourly soil moisture and temperature along 84 days at Restinga Seasonal Dry Forest (SDF), sparse (Open Clusia Scrubs—OCS), and dense (Open Ericacea Scrubs—OES) tickets at Restinga de Jurubatiba National Park, at Rio de Janeiro state (Brazil). Due to distinctions on physical structure and access to groundwater between plant formations, we expected higher daily soil moisture and lower daily moisture and temperature variations on forests than on open vegetated areas. Daily soil moisture was higher, respectively, on SDF, OES, and OCS, whereas soil moisture and temperature variability presented the opposite trend (SDF < OES < OCS), supporting our hypotheses. Daily soil temperature dynamics are quite well predicted by solar radiation incidence patterns, whereas daily soil moisture is mainly regulated by precipitation at OCS, an interaction of precipitation and temperature at OES and delayed effects of precipitation at SDF. Our results corroborate our expectations that forests are more effective in buffering both air temperature and precipitation effects on soil conditions than open vegetated areas. They also indicate that soil moisture and temperature conditions are important aspects differentiating Restinga vegetation types.

Karst Dolines Support Highly Diversified Soil Collembola Communities—Possible Refugia in a Warming Climate?

Karst dolines, as geomorphologically diverse natural landforms, usually exhibit more or less steep microclimatic gradients that provide a mosaic of diverse microhabitat conditions, resulting in a high diversity of soil biota with numerous rare endemic and/or relict species occupying these habitats. In this study, we investigated the spatial patterns of Collembola abundance, species richness, community structure and distribution of functional groups at topographically and microclimatically different sites across three open (unforested) karst dolines in a north-south direction in the Slovak Karst, Slovakia. We also assessed the refugial capacity of dolines for collembolan communities. The Friedman ANOVA test confirmed the significant differences in soil mean temperatures between the sites of all the dolines selected. The diverse soil microclimatic conditions within the dolines supported higher Collembola diversity (species numbers, diversity indices) compared with sites on the karst plateau and showed a potential to facilitate the persistence of some species that are absent or very rare in the surrounding landscape. In dolines with circular morphology and comparable size, the topography and soil microclimate had a stronger effect on community composition and structure than soil organic carbon. Shallow solution dolines provided microhabitats for various functional groups of soil Collembola in relation to the microclimatic character of the individual sites. It was observed that such landforms can also function as microclimatic refugia for cold-adapted species through the accumulation of colder air and the buffering of the local microclimate against the ambient mesoclimate, thus underlying the necessity of adequate attention in terms of the conservation of the karst natural phenomena.

Seasonal dynamics of soil and microbial respiration in the banj oak and chir pine forest of the central Himalaya, India

This research investigates seasonal changes of root respiration (Rroot), total soil respiration (Rtotal) and microbial respiration (Rmicrobial) in three central Himalayan forest types: banj oak (BO), chir pine (CP) and banj oak regenerated (BOR). The trenching method is used to separate Rroot from Rtotal. Soil physicochemical and biological properties were compared among the forest type and seasons using one-way ANOVA. Results indicated the significant (p < 0.05) influence of forest type and season on Rtotal, Rroot and Rmicrobial. BO forest had significantly (p < 0.05) higher Rtotal than the CP forest. This was attributed to lower bulk density (BD), pH and high soil moisture, soil organic carbon (SOC), total nitrogen (TN) and microbial biomass carbon (MBC) in the BO forest. Higher soil moisture, SOC, TN and MBC in BO reflects higher microbial metabolic activity than the CP, with low soil moisture and nutrient content. The Rroot/Rtotal ratio ranged from 35 to 62 % for BO, 12 to 58 % for CP and 14 to 45 % for BOR, indicating that Rroot was an important contributor to Rtotal. The contribution of Rroot was at a maximum in the rainy season (53 %) and a minimum in the winter season (11 %), indicating the synergistic effect of optimum soil micro-climatic conditions and soil nutrient content to Rroot. In an exponential regression analysis, soil temperature better explained Rtotal (r2 = 0.81–0.82, p < 0.001). In comparison to Rmicrobial (r2 = 0.58–0.85, p < 0.001), Rroot is better explained by soil moisture (r2 = 0.59–0.88, p < 0.001) in a linear regression model. Present findings suggest that the positive effect of temperature, moisture and litter nitrogen on Rtotal are majorly regulated by forest types, which potentially increases the understanding of climate change and nutrient dynamic processes on a global scale.

Microclimate and habitat heterogeneity as important drivers of soil Collembola in a karst collapse doline in the temperate zone

AbstractChanges in well‐delimited Collembola communities along a steep microclimatic gradient at the entrance of Silická ľadnica Ice Cave, Slovakia, were investigated after 10 years (2007, 2017). We focused on the occurrence of psychrophilic and endemic species occupying this unique karst collapse doline and their response to climatic singularities in the given years as well as the increasing trend in regional air temperature. The soil temperature means at sites across the doline slope corresponded with climatic trends in the periods 2006–2007 and 2016–2017. Significantly lower average soil temperatures but significantly higher mean abundances, species richness, and diversity indices of the collembolan communities were recorded at sites during the second study period, which was characterized by more favorable soil microclimatic conditions (temperature and moisture content) compared to the first period. The dominance structure and community composition of the studied assemblages appeared to be relatively constant after 10 years, indicating stable collembolan communities, especially at cold sites at the bottom of the doline. Redundancy ordination analysis documented a clear delimitation of the communities in relation to the soil temperature, pH, and C:N ratio in both periods. Long‐term (30‐year) regional climatic data showed an increasing trend of annual air temperature means and precipitation. However, an increase in the number and abundance of xerothermophilous species and a decline in psychrophilic species (mostly endemic) along the gradient as a potential response of the increasing regional temperature were not observed, suggesting the high resilience of these communities. Microclimate and habitat heterogeneity are probably major drivers of soil Collembola communities along the steep microclimatic gradient of a karst collapse doline, which was observed by the repeated sampling after 10 years. Karst dolines as potentially important local sources of ɑ‐diversity will likely become increasingly indispensable refugia for local biodiversity under ongoing global warming, thus deserving reliable conservation.

Effects of mound building Lasius flavus on organic carbon and nutrient fluxes in soils of temperate grassland ecosystems

Ants that build long-lasting mounds and move large amounts of mineral soil may influence the composition and fluxes of soil solutions, and thus soil nutrient cycling. However, studies quantifying such effects are scarce. In central Europe, the yellow meadow ant (Lasius flavus) is a common species that changes the character of extensively managed grasslands by its mound building activity.In total, sixteen mound-control pairs were selected within four plots on two grassland sites in Thuringia, Central Germany and monitored from 2013 to 2016. On each plot, bulk precipitation and soil solutions were collected via two open funnel samplers and eight suction plates to determine input and loss fluxes of dissolved organic carbon (DOC), nitrogen (DN), and base cations under L. flavus mounds and control locations. Effects of L. flavus mounds on soil microclimatic conditions were also investigated.In comparison to the controls, L. flavus mounds were characterised by slightly lower soil temperatures and always lower soil moisture. The main driver of lower fluxes of DOC and DN from mounds was related to the reduced seepage water flux under mounds compared to the adjacent grassland. Lasius flavus activity increased potassium (K) concentrations and fluxes in soil solutions from mounds in comparison to the controls, independent from plot-specific soil and seepage water flux variability. Increased concentrations of calcium (Ca) and magnesium (Mg) were measured in the soil solutions of the mounds but were generally not associated with higher Ca or Mg fluxes. In conclusion, L. flavus present unique micro-sites within grassland ecosystems by creating mounds that may function as ecosystem control points for the cycling of certain elements, such as K.

Larval Movement of Spotted Wing Drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae)

Laboratory experiments were conducted to determine larval movement of the spotted wing drosophila (Drosophila suzukii Matsumura). Movement of larvae outside of the wild blueberry fruit (Vaccinium angustifolium Aiton) can occur after exhausting fruit food resources pri- or to completion of development or just prior to pupation. We found that when provided a choice larvae select moist compared to dry environments both in plastic arenas providing only filter paper for shelter and in a soil filled petri dishes. Movement was usually limited to less than 7.5 cm in the soil from a release point. An exponential decay model suggests that only 0.1% of a larval population will move as far as 17.5 cm. Results of our study suggest that while larvae move readily, they have minimal ability to avoid localized xeric soil micro-climatic conditions through movement. However, they will select less stressful moist soil environments.

Ant communities andSolidagoplant invasion: Environmental properties and food sources

AbstractThe invasion ofSolidagois one of the main threats to the biodiversity of natural meadows, leading to changes in animal and plant communities, as well as soil features. We compared effects of soil microclimatic conditions (temperature and moisture) and the availability of potential protein sources (dry mass of epigean invertebrates) on ants between meadows invaded bySolidago altissimaandS. canadensisand those uninvaded. Our results showed that the ant communities were different between the uninvaded and invaded meadows, with reduction of ant abundance and species richness in the latter.Myrmicaspp. were abundant in the uninvaded meadows, whereasLasius nigerwas the dominant species in the invaded ones. We found that the lower moisture negatively influenced the abundance ofMyrmicaspecies in theSolidago‐invaded meadows. Moreover, the epigean invertebrate dry mass, as an estimation of the availability of protein sources, varied between the two types of meadows, with a higher abundance in the uninvaded ones. The abundance ofMyrmicaants with narrower ecological requirements showed a positive correlation with the invertebrate biomass in the invaded meadows. In contrast, the abundance ofL. nigerwith broad ecological requirements was negatively correlated with the invertebrate biomass in the invaded meadows, possibly as a strategy to reduce interspecific competition. Our study showed that the invasion ofSolidagoplants caused changes in the abundance and species composition of ant communities through modification in microhabitat conditions, that is, decreasing soil moisture, reducing biomass and changing distribution of prey invertebrates.

Boreal coniferous forest density leads to significant variations in soil physical and geochemical properties

Abstract. At the northernmost extent of the managed forest in Quebec, Canada, the boreal forest is currently undergoing an ecological transition between two forest ecosystems. Open lichen woodlands (LW) are spreading southward at the expense of more productive closed-canopy black spruce–moss forests (MF). The objective of this study was to investigate whether soil properties could distinguish MF from LW in the transition zone where both ecosystem types coexist. This study brings out clear evidence that differences in vegetation cover can lead to significant variations in soil physical and geochemical properties.Here, we showed that soil carbon, exchangeable cations, and iron and aluminium crystallinity vary between boreal closed-canopy forests and open lichen woodlands, likely attributed to variations in soil microclimatic conditions. All the soils studied were typical podzolic soil profiles evolved from glacial till deposits that shared a similar texture of the C layer. However, soil humus and the B layer varied in thickness and chemistry between the two forest ecosystems at the pedon scale. Multivariate analyses of variance were used to evaluate how soil properties could help distinguish the two types at the site scale. MF humus (FH horizons horizons composing the O layer) showed significantly higher concentrations of organic carbon and nitrogen and of the main exchangeable base cations (Ca, Mg) than LW soils. The B horizon of LW sites held higher concentrations of total Al and Fe oxides and particularly greater concentrations of inorganic amorphous Fe oxides than MF mineral soils, while showing a thinner B layer. Overall, our results show that MF store three times more organic carbon in their soils (B+FH horizons, roots apart) than LW. We suggest that variations in soil properties between MF and LW are linked to a cascade of events involving the impacts of natural disturbances such as wildfires on forest regeneration that determines the vegetation structure (stand density) and composition (ground cover type) and their subsequent consequences on soil environmental parameters (moisture, radiation rate, redox conditions, etc.). Our data underline significant differences in soil biogeochemistry under different forest ecosystems and reveal the importance of interactions in the soil–vegetation–climate system for the determination of soil composition.

Variations in snow depth modify N-related soil microbial abundances and functioning during winter in subalpine grassland

In alpine and arctic ecosystems, the snowpack has been shown to insulate soils from the winter climatic harshness. Ongoing climate change modifies snowpack quantity and quality, but the consequences of these changes on the soil functioning remain largely unknown. We benefited from a subalpine landscape of the French Alps where, 700 years ago, agricultural practices led to the formation of terraces. Subsequently, on each terrace, snow thickness patterns significantly differed between the bank and the front areas inducing strong divergence in their soil microclimatic conditions. Using this framework, we measured abundances and activities of nitrifiers and denitrifiers, together with a set of environmental variables, on three grassland terraces between December and May to test the following hypotheses: (i) soil N-related microbial abundances and activities are sensitive to soil microclimatic variations and differ along the terrace snow depth gradient during winter, (ii) a thicker snowpack favors higher abundances and activities, and (iii) the driving forces for nitrification and denitrification abundances and activities vary along the snow depth gradient. Our results showed significantly and changing N-related microbial activities and abundances during winter despite partly frozen soils, and suggested the selection and/or adaptation of psychrophilic microbial communities. Moreover, activities as well as abundances of nitrifiers and denitrifiers were significantly higher under a weak or absent snowpack during winter, and mostly related to soil water content and soil surface temperature according to our models. We suggest that strongly variable soil abiotic conditions at the front stations enabled the release of nutrients from soil organic and inorganic compounds favoring psychrophilic bacterial abundances and activities. Contrastingly, a thicker and permanent snowpack maintained circum-zero soil temperatures during winter which limited the microbial community's turnover and release of organic and inorganic N. This created N-limited conditions and N-competition between microbial populations resulting in lower abundances and activities. Overall, changes in the snowpack depth strongly affect the soil microbial functioning of subalpine grasslands with potential consequences on nutrient dynamic and other trophic levels.

Earthworm density, casting activities and its impact on canopy soil nutrient profile under different aboveground vegetations

Efforts were made to assess the earthworm’s density and their casting activity under different surface plant stands (Citrus reticulata, Rosa indica, Citrus + Rosa, Tabernaemontana divaricata, Dalbergia sissoo, and Cynodon dactylon) at few natural and planted sites of a semiarid part of Rajasthan, India. The role of earthworm community in nutrient dynamics of different layers of canopy soils was also measured during this study. Results suggested a direct impact of aboveground vegetation cover on soil microclimatic conditions and earthworm density. The maximum earthworm population density and casts production was under mixed plantation, i.e., Citrus + Rosa (119.2 ind. m−2 and 2,127.27 gm m2, respectively), while T. divaricata supported the minimum earthworm density and casting activities. The population density and total casts production was in the order: C. reticulata + R. indica > R. indica > D. sissoo > C. dactylon > C. reticulata > T. divaricata. Earthworm casts and canopy soils (0–10 and 10–20 cm depth) under different plant stand were analyzed for organic C, total N, available P, and exchangeable cations (K+, Ca2+ and Mg2+). Earthworm casts collected under Citrus + Rosa showed the maximum level of organic C, total N, available P, and exchangeable cations (K+ and Mg2+). It is concluded that resource input by standing plant community directly affects the canopy soil quality and, thereby nutrient level in earthworm casts. This study suggested that aboveground vegetation pattern plays an important role to improve the nutrient level of canopy soils and belowground earthworm activities.

Holocene vegetation characteristics of the southern Loess Plateau in the Weihe River valley in China

The Loess Plateau has a varied topography that creates a mosaic of hydrological and soil microclimatic conditions, and the study of its vegetation characteristics has been controversial. Two loess–palaeosol sequences of Xindian and Beizhuangcun were selected at different topographic units in the Weihe River valley to reconstruct the vegetation history for the Holocene period using high-resolution pollen analysis. Herb plants typically dominated the Xindian region during the Holocene, and sparse-wood grasslands became prominent around 8200–7700 years BP and 5500–4700 years BP. Forest-grassland covered the area between 7700 and 5500 years BP. Sparse-wood grassland dominated the Beizhuangcun region for most of the Holocene. This region contained mixed coniferous and broad-leaved forest dominated by Pinus between 6800 and 5300 years BP. Around 40% of the arboreal pollen indicates that the forest was relatively open with some grasses and shrubs. Therefore, the sparse-wood grasslands and grasslands were the dominant vegetation types in the Weihe River valley, which has the best hydrothermal conditions on the southern margin of the Loess Plateau. The forest in the Weihe valley only became extensively developed in the Holocene Optimum. Topographic units, terrain composition and loess thickness are the important factors controlling the development of this arboreal vegetation, along with temperature and precipitation.

The effect of tillage systems and mulching on soil microclimate, growth and yield of yellow yam (Dioscorea cayenensis) in Midwestern Nigeria

Yellow yam (Dioscorea cayenensis) is one of the major varieties of yam produced in Midwestern Nigeria mainly by traditional farmers. Most of these traditional farmers employ zero tillage system and mulching after planting. But, is this the best practice for optimising yield? This paper examines the effect of tillage systems and mulching on soil microclimatic conditions, growth and yield of yellow yam. To generate the needed data, the physiological approach was employed. An experimental farm that measured 35 x 47 m was established at Agbor, Delta State, Nigeria, for two planting seasons 1997/98 and 1998/99. The microclimatic parameters monitored include air and soil temperatures and relative humidity while the physiological parameters measured were emergence, growth rate, leaf area accumulation and yield. Time series, multiple correlations, chi-square, ANOVA, least square range test and stepwise regression analysis were the statistical tools employed in analysing the data. The results showed that soil moisture at 0-15 cm depth was significantly higher in zero tillage (40 g/g), followed by ridge (30 g/g) and mound (24 g/g) but the reverse was the case with soil temperature where mound tillage (34.2°C) had the highest temperature followed by ridge (31.4°C) and zero (29.5°C). Mulching also significantly influenced the soil microclimatic condition. While soil moisture enhanced yam emergence, soil temperatures favoured the growth, leaf area accumulation and yield. Mound tillage significantly gave the highest yam tuber yield (12.0 t/ha-1), followed by ridge (8.8 t/ha-1) and zero (5.0 t/ha-1). Partially mulched treatment significantly produced the highest yam tubers (10.3 t/ha-1), followed by the unmulched (8.1 t/ha-1) and mulched (7.4 t/ha-1) treatments. The best practice recommended for the production of ware yams is mound tillage that is partially mulched. This recommended practice yielded more than the local practice by 44.6%. Key words: Tillage systems, yellow yam, Midwestern Nigeria, soil microclimate, mulching, yam yield.

The effect of tillage systems and mulching on soil microclimate, growth and yield of yellow yam ( Dioscorea cayenensis ) in Midwestern Nigeria

Yellow yam (Dioscorea cayenensis) is one of the major varieties of yam produced in Midwestern Nigeria mainly by traditional farmers. Most of these traditional farmers employ zero tillage system and mulching after planting. But, is this the best practice for optimising yield? This paper examines the effect of tillage systems and mulching on soil microclimatic conditions, growth and yield of yellow yam. To generate the needed data, the physiological approach was employed. An experimental farm that measured 35 x 47 m was established at Agbor, Delta State, Nigeria, for two planting seasons 1997/98 and 1998/99. The microclimatic parameters monitored include air and soil temperatures and relative humidity while the physiological parameters measured were emergence, growth rate, leaf area accumulation and yield. Time series, multiple correlations, chi-square, ANOVA, least square range test and stepwise regression analysis were the statistical tools employed in analysing the data. The results showed that soil moisture at 0-15 cm depth was significantly higher in zero tillage (40 g/g), followed by ridge (30 g/g) and mound (24 g/g) but the reverse was the case with soil temperature where mound tillage (34.2°C) had the highest temperature followed by ridge (31.4°C) and zero (29.5°C). Mulching also significantly influenced the soil microclimatic condition. While soil moisture enhanced yam emergence, soil temperatures favoured the growth, leaf area accumulation and yield. Mound tillage significantly gave the highest yam tuber yield (12.0 t/ha-1), followed by ridge (8.8 t/ha-1) and zero (5.0 t/ha-1). Partially mulched treatment significantly produced the highest yam tubers (10.3 t/ha-1), followed by the unmulched (8.1 t/ha-1) and mulched (7.4 t/ha-1) treatments. The best practice recommended for the production of ware yams is mound tillage that is partially mulched. This recommended practice yielded more than the local practice by 44.6%.

The microbial communities of aspen and spruce forest floors are resistant to changes in litter inputs and microclimate

Previous studies have shown that forest floors from stands dominated by trembling aspen (ASPEN; Populus tremuloides Michx.) tend to support a greater microbial biomass with a different microbial community structure than forest floors from stands dominated by white spruce (SPRUCE; Picea glauca (Moench) Voss). A reciprocal transfer experiment, in concert with coarse and fine mesh bags that allowed or excluded fine root in-growth, was used to examine how the composition of these forest floor microbial communities respond to changes in belowground inputs from fine roots, aboveground inputs (e.g. from litter and through-fall) and soil microclimatic conditions over 1 year. Neither the microbial biomass nor the microbial community structure (assessed using phospholipid fatty acid analyses and substrate-induced respiration techniques) of forest floors of ASPEN or SPRUCE origin were altered by reciprocal transfer to SPRUCE or ASPEN stands, with or without fine root inputs. Despite the lack of changes in microbial community structure, the stand type during incubation had a strong effect on forest floor moisture content and concentrations of nitrate, while mesh size had a significant effect on forest floor pH and the abundance of mesofauna. Thus, changes in microbial community structure did not co-occur with changes in other characteristics of these forest floors. The resistance of the forest floor microbial communities to change may be a function of the high C contents of these soils. Further treatment effects may have been detected if the study had been extended beyond 1 year. Reciprocal transfer studies using coarse and fine mesh bags allow transferred soils to respond to fluctuations in microclimate, organic inputs and soil biota and, therefore, hold considerable promise for studies examining the influence of disturbances on soil properties.

Evaluation of Synthetic Mulches on the Establishment and Growth of Cottonwood

ABSTRACT Soil microclimatic conditions created by various weed-control mulches and the resulting survival, diameter, and height growth of cottonwood seedlings were studied in central Kansas. The treatments compared the effects of six synthetic plastic mulches often used in horticultural practices with the effects of cultivation or a herbicide. One-year-old seedlings were planted with either clear plastic, blue and yellow waste plastics, black or gray/black polyethylene, or polypropylene fabric weed barrier; cultivation; or herbicide weed-control treatment. After five years, sapling survival was more than 85% for all mulch types except the clear plastic (82% survival). Differences among weed-control treatments were significant for survival, height, stem diameter, and biomass. Sapling growth was best with sulfometron methyl herbicide, slightly less for cultivation, and nearly the same for all other materials for weed control. Stem temperature had no relationship to first year height growth. Soil temperature and moisture had a slight relationship to second year height. Use of herbicides or cultivation was clearly less expensive than synthetic mulch for weed control.

Microtopography and Plant-Cover Controls on Nitrogen Dynamics in Hummock Tundra Ecosystems in Siberia

Earth hummocks constitute the most common surface structures of Arctic regions. In hummock tundra ecosystems, small mounds of earth alternate with depressions, the so-called interhummock areas. This study aimed at elucidating how differences in microtopography and associated variations in abiotic and biotic factors control biogeochemical cycles in hummock tundra soils. We assessed N pools and N transformation rates in hummocks and interhummock areas in the southern tundra subzone and along a soil-moisture gradient in the typical tundra subzone of the Taymyr Peninsula, Siberia, Russia. On a regional scale, N pools and transformation rates were positively related to latitude and therefore to temperature. Generally, wetter or waterlogged soil conditions tended to decrease gross mineralization rates and soil microbial N at least in interhummock areas. In contrast, at small spatial scales, soil microclimatic conditions were not the main determinant of the observed nitrogen cycling pattern. We found higher N pools and N gross mineralization rates at interhummock areas (wetter and cooler) compared to the hummocks (warmer and drier). The observed differences in N cycling between microsites of hummock tundra may be the consequence of different plant-cover and variable substrate inputs resulting from differences in microrelief.

Production and structural characterization of the exopolysaccharide of the Antarctic fungus Phoma herbarum CCFEE 5080

The filamentous fungus Phoma herbarum CCFEE 5080 isolated from continental Antarctica soil was tested for exopolysaccharide (EPS) production. The fungus grew and produced EPS (up to13.6 g/l) on a variety of carbon sources among which sorbitol was best, particularly at the concentration of 60 g/l. EPS production was maximum when the nitrogen source was NaNO 3 (3 g/l) and the incubation temperature was 28 °C. The polysaccharide was purified by repeated precipitation in ethanol and gel filtration and characterized as a homopolymer of glucose having a molecular weight of 7.412×10 6; structural analysis indicated the presence of β-1,3 and β-1,6 linkages only. After repeated freezing and thawing of the fungal biomass in the presence of EPS, the mycelial growth was much higher than that observed after freezing in the absence of EPS and the difference increased with the number of freeze–thaw cycles. It is hypothesized that the adaptation of P. herbarum CCFEE 5080 to the Antarctic soil microclimatic conditions, characterized by low temperature, high thermal fluctuations and repeated freeze–thaw cycles, might be related to the EPS production ability.

Soil Surface Carbon Dioxide Fluxes Induced by Spring, Summer, and Fall Moldboard Plowing in a Sandy Loam

Soil tillage is believed to influence soil organic matter decomposition. We hypothesized that the short-term impacts of tillage on soil surface CO2 emissions would vary following spring, summer, and fall moldboard plowing of a sandy loam (loamy, mixed, frigid Umbric Dystrochrept). At all dates, plowing increased CO2 emissions by 7 to 20 µmol m-2s-1 during the first hours following tillage due to degassing of soil CO2. The effects of tillage following this initial burst varied with date of plowing. Fall incorporation of fresh maize residues increased CO2 losses by 173 kg C ha-1 during a period of 4 d compared with a non-tilled control, until halted by a sudden drop of 6°C in soil temperature with the onset of winter. In contrast, the cumulative CO2 fluxes following spring plowing of fall-applied residues were 186 kg C ha-1 lower than on a non-tilled control. This effect of spring plowing on CO2 fluxes lasted for 2 wk, during which soil temperatures in the plow layer were below 10°C. Summer plowing increased CO2 emissions by as much as 2 µmol m-2s-1 for a period of 65 d, resulting in cumulative soil C losses of 685 kg C ha-1 compared with the undisturbed control. Variations in tillage-induced CO2 emissions between dates were attributed to differences in soil microclimatic conditions following plowing events. The study of the impact of tillage on soil organic matter decomposition should consider the time of year when the soil is tilled.

Simulating Near-surface Soil Temperature and Water on Sagebrush Rangelands: A Comparison of Models

The objective of this study was to determine if uncalibrated soil water and temperature models, varying in complexity and data requirements, could simulate spatial and temporal variations in near-surface soil microclimatic conditions. The SWRRB, Opus, and SHAW models were compared on their ability to address small scale spatial and temporal variations in near-surface (0-5 cm) soil microclimatic conditions on rangelands. The models were used to simulate soil temperature and water at various depths at two locations: One under a sagebrush plant and the other in the interspace between plants within a sagebrush-grass plant community. Uncalibrated simulations were run for one year where the models all performed well at simulating annual sinusoidal patterns in soil temperature at the 1-cm depth under sagebrush and interspace locations. The models performed best during the fall and spring and poorest during the winter. SHAW simulated both the spatial variability between and the day-to-day temporal variations within each location more accurately than did the other two models. All three models had difficulties simulating soil water at the 1-cm depth throughout the year. SHAW and Opus performed quite well at simulating soil water at the 30-cm depth under sagebrush, but SHAW performed better in the interspace at the same depth.