Thawing Stage Research Articles

Early thawing after snow removal and no straw mulching accelerates organic carbon cycling in a paddy soil in Northeast China

Variations in soil organic carbon (SOC) have implications for atmospheric CO2 concentrations and the greenhouse effect. However, the effects of snow cover and straw mulching on the variations in SOC fractions across winter remain largely unknown. In this study, soil samples were collected during different stages of winter from an in situ experiment comprising three treatments: 1) snow removal with no straw mulching (Sn-SM-); 2) snow cover with no straw mulching (SC), and; 3) snow cover with straw mulching (SC + SM+). Results showed that labile organic carbon, semi-labile organic carbon, recalcitrant organic carbon (ROC), the light fraction of organic carbon (LFOC), and easily oxidized organic carbon (EOC) contents did not vary significantly (P > .05) during the unfrozen to hard frost stages. Compared to the unfrozen stage, microbial biomass carbon (MBC) contents decreased by 519.03 mg kg−1, 325.21 mg kg−1, and 244.09 mg kg−1 and dissolved organic carbon (DOC) contents increased by 473.36 mg kg−1, 348.10 mg kg−1, and 258.89 mg kg−1 at the hard frost stage in Sn-SM-, SC, and SC + SM + treatments, respectively. Throughout all thawing stages, > 61% and 59% of SOC and ROC accumulation, respectively in the three treatments were observed in thawing stage II, indicating that higher temperatures and microbial activities in thawing stage II accelerated the inputs of SOC and ROC. ROC accumulation accounted for >65% of the SOC accumulation and the proportions of ROC in SOC increased in the three treatments during the thawing stages. SC + SM + treatment maintained lower EOC contents during thawing stages than other treatments. The observation of lowest SOC and LFOC accumulation and contents in the SC + SM + treatment during thawing stages showed that SC + SM + experienced the least inputs of SOC in the soil.

Progressive stirred freeze-concentration of ethanol-water solutions

Progressive freeze-concentration is a technology to separate water from solutions by freezing. In the present investigation, ethanol-water solutions were freeze-concentrated by the progressive stirred technique. The freezing stage was carried out in a stirring vessel. Solute recovery by the fractionated thawing of ice was also studied. The effects of stirring speed (500, 1000, and 2000 rpm), initial concentration of the solution (3%, 5%, and 8% ethanol), and temperature of the thawing stage (0, 10, and 20 °C) on the solute yield and average distribution coefficient were determined using response surface analysis. The ethanol concentration was found to have increased by 1.3 and 2.1 times at the end of the freeze concentration process. It was found that the initial concentration had a significant effect on the distribution coefficient. In addition, the average yield was increased by 28% by fractionated thawing. Subsequently, a non-dimensional analysis of the distribution coefficient was developed to yield a model to predict the distribution coefficient as a function of the Reynolds number, the relationship between the average ice growth rate and the stirring speed, the agitator diameter, and the liquid fraction. This technique proved to be valid with respect to the concentration of ethanol-water solutions, with better yields being obtained at low initial concentrations. This model is the first of its kind to describe the ethanol-water interaction in agitated freeze-concentration systems.

Effects of snow cover plus straw mulching on microorganisms in paddy soil during winter

Soil microorganisms play key roles in the biogeochemical cycling of soil carbon and are sensitive to changes in the soil microclimate. A field experiment was conducted to investigate the effects of snow cover and straw mulching on microbial communities in paddy soils during winter, and four treatments were established: (i) snow removal with no straw mulching (Sn-SM-), (ii) snow cover with no straw mulching (SC), (iii) snow removal with straw mulching (SM), and (iv) snow cover with straw mulching (SC+SM+). The SC, SM, and, especially, SC+SM+ groups had more bacterial, gram-positive (G＋) bacterial, gram-negative (G－) bacterial, fungal, and total phospholipid fatty acids (PLFAs) than the Sn-SM- group from the freezing stage to the hard frost stage. The ratio of fungal/bacterial PLFAs first decreased, with the highest value in the SC+SM+ treatment, from the freezing to the hard frost stages and increased during the thawing stage, while the ratio of G＋/G－ PLFAs showed the opposite trend. The Sn-SM- treatment resulted in a rapid increase in microorganisms during the thawing stage. Our results demonstrated that the SC, SM, and, especially, SC+SM+ treatments reduced the losses of microbial biomass from the unfrozen stage to the hard frost stage and prevented an increase in microbial activity during the thawing stage in a paddy system.

Microbial network, phylogenetic diversity and community membership in the active layer across a permafrost thaw gradient

Biogenic production and release of methane (CH4 ) from thawing permafrost has the potential to be a strong source of radiative forcing. We investigated changes in the active layer microbial community of three sites representative of distinct permafrost thaw stages at a palsa mire in northern Sweden. The palsa site (intact permafrost and low radiative forcing signature) had a phylogenetically clustered community dominated by Acidobacteria and Proteobacteria. The bog (thawing permafrost and low radiative forcing signature) had lower alpha diversity and midrange phylogenetic clustering, characteristic of ecosystem disturbance affecting habitat filtering. Hydrogenotrophic methanogens and Acidobacteria dominated the bog shifting from palsa-like to fen-like at the waterline. The fen (no underlying permafrost, high radiative forcing signature) had the highest alpha, beta and phylogenetic diversity, was dominated by Proteobacteria and Euryarchaeota and was significantly enriched in methanogens. The Mire microbial network was modular with module cores consisting of clusters of Acidobacteria, Euryarchaeota or Xanthomonodales. Loss of underlying permafrost with associated hydrological shifts correlated to changes in microbial composition, alpha, beta and phylogenetic diversity associated with a higher radiative forcing signature. These results support the complex role of microbial interactions in mediating carbon budget changes and climate feedback in response to climate forcing.

The development of permafrost bacterial communities under submarine conditions

Submarine permafrost is more vulnerable to thawing than permafrost on land. Besides increased heat transfer from the ocean water, the penetration of salt lowers the freezing temperature and accelerates permafrost degradation. Microbial communities in thawing permafrost are expected to be stimulated by warming but how they develop under submarine conditions is completely unknown. We used the unique records of two submarine permafrost cores from the Laptev Sea on the East Siberian Arctic Shelf, inundated about 540 and 2500 years ago, to trace how bacterial communities develop depending on duration of the marine influence and pore water chemistry. Combined with geochemical analysis, we quantified total cell numbers and bacterial gene copies, and determined the community structure of bacteria using deep sequencing of the bacterial 16S rRNA gene. We show that submarine permafrost is an extreme habitat for microbial life deep below the seafloor with changing thermal and chemical conditions. Pore water chemistry revealed different pore water units reflecting the degree of marine influence and stages of permafrost thaw. Millennia after inundation by sea water, bacteria stratify into communities in permafrost, marine-affected permafrost, and seabed sediments. In contrast to pore water chemistry, the development of bacterial community structure, diversity and abundance in submarine permafrost appears site-specific, showing that both sedimentation and permafrost thaw histories strongly affect bacteria. Finally, highest microbial abundance was observed in the ice-bonded seawater unaffected but warmed permafrost of the longer inundated core, suggesting that permafrost bacterial communities exposed to submarine conditions start to proliferate millennia after warming.

Inhibition of Ice Recrystallization by Nylon-3 Polymers.

Nontoxic cryoprotectants are needed for storage of tissues and food preservation. Frozen tissue is particularly susceptible to damage caused by formation of large ice crystals during the thawing process. The current practice of using 5 wt % DMSO for cryopreservation does not produce 100% cell viability post-thaw, at least in part because of DMSO toxicity that is manifested during the freezing and thawing stages of the process. Recently, poly(vinyl alcohol) (PVA) has shown promise in inhibiting ice recrystallization, an activity that is critical for cryoprotection. Inspired by this discovery, we have evaluated nylon-3 polymers for ice recrystallization inhibition activity and for toxicity toward mammalian cells. A survey of homo- and heteropolymers, with side chains bearing variable functionality, has identified new nylon-3 materials that display excellent ice recrystallization inhibition activity and low toxicity.

Effect of reduced glutathione supplementation in semen extender on tyrosine phosphorylation and apoptosis like changes in frozen thawed Hariana bull spermatozoa

To provide new insights into the mechanisms through which reduced glutathione (GSH) is able to protect spermatozoa, we tested the hypothesis that cryocapacitation and apoptosis like changes can contribute to the negative effect of freezing and thawing on bull spermatozoa, and that GSH prevent this damage. Having known protective effects of GSH in terms of a potent antioxidant, we evaluated capacitation, tyrosine phosphorylation and apoptosis like changes in bull spermatozoa after freezing and thawing in egg yolk tris glycerol extender containing (0.5m M-GSH-T1 & 1mM GSH-T2) and without GSH serving as the control (C). Forty ejaculates were collected from four Hariana bulls and were pooled due to non significant variations among the bull ejaculates for the evaluation of sperm attributes. Capacitation like changes, tyrosine phosphorylation, localization of tyrosine phosphorylated proteins, apoptosis like changes in terms of mitochondrial transmembrane potential and DNA fragmentation after final dilution, 4h of equilibration at 4°C and 24h after freezing and thawing were evaluated. GSH supplementation at 0.5mM showed significant reduction in B- and AR- pattern spermatozoa during all stages of semen freezing and thawing. Immunoblot revealed six proteins which were tyrosine phosphorylated and protein of 30 and 75kDa (p30, p75) were the major tyrosine phosphorylted proteins. On further analysis, the p30 showed differential variation in intensity in all the three groups after freezing and thawing. Positive immune reactivity for tyrosine phosphorylated proteins was found in neck, middle piece and post-acrosomal regions of spermatozoa. Addition of 0.5mM GSH decreased percentage of spermatozoa showing fragmented DNA and increased the percentage of spermatozoa having high transmembrane mitochondrial potential (P<0.05). This study demonstrates that GSH favours survival of bull spermatozoa by interfering with apoptotic and cryocapacitation pathways, and thereby protects the spermatozoa from deleterious effects of cryopreservation. The findings of the study indicated that GSH at 0.5mM can be effectively used as an additive in bull semen extender for freezing and thawing.

Nonlinear CO2 flux response to 7years of experimentally induced permafrost thaw.

Rapid Arctic warming is expected to increase global greenhouse gas concentrations as permafrost thaw exposes immense stores of frozen carbon (C) to microbial decomposition. Permafrost thaw also stimulates plant growth, which could offset C loss. Using data from 7years of experimental Air and Soil warming in moist acidic tundra, we show that Soil warming had a much stronger effect on CO2 flux than Air warming. Soil warming caused rapid permafrost thaw and increased ecosystem respiration (Reco ), gross primary productivity (GPP), and net summer CO2 storage (NEE). Over 7years Reco , GPP, and NEE also increased in Control (i.e., ambient plots), but this change could be explained by slow thaw in Control areas. In the initial stages of thaw, Reco , GPP, and NEE increased linearly with thaw across all treatments, despite different rates of thaw. As thaw in Soil warming continued to increase linearly, ground surface subsidence created saturated microsites and suppressed Reco , GPP, and NEE. However Reco and GPP remained high in areas with large Eriophorum vaginatum biomass. In general NEE increased with thaw, but was more strongly correlated with plant biomass than thaw, indicating that higher Reco in deeply thawed areas during summer months was balanced by GPP. Summer CO2 flux across treatments fit a single quadratic relationship that captured the functional response of CO2 flux to thaw, water table depth, and plant biomass. These results demonstrate the importance of indirect thaw effects on CO2 flux: plant growth and water table dynamics. Nonsummer Reco models estimated that the area was an annual CO2 source during all years of observation. Nonsummer CO2 loss in warmer, more deeply thawed soils exceeded the increases in summer GPP, and thawed tundra was a net annual CO2 source.

Response of the soil hydrothermal process to difference underlying conditions in the Beiluhe permafrost region

The changes in hydrothermal dynamics under different underlying conditions are the important aspect of hydrological and ecological processes, and engineering stability in permafrost regions. This study monitored the temperature and moisture of soil at a depth range from 0 to 80 cm beneath the barren, alpine steppe, and alpine meadow at the Beiluhe Basin on the Qinghai–Tibet Plateau. The freezing and thawing process and hydrothermal dynamic changes were analyzed within the test range. In a year, the freezing and thawing process controlled the pattern of hydrothermal changes. The properties of ground surface affected the hydrothermal change process in various stages. In the freeze stages, moisture and the absolute value of ground temperature showed an exponential relationship. In the thawing stages, moisture may increase, decrease, or remain stable in different temperature ranges. This process is affected by precipitation, solar radiation, and so on. At a 0–30 cm depth range, moisture increased linearly with precipitation. At 0–20 cm depth range, precipitation had a significant effect on the ground temperature changes. With the same rainfall condition, the decline of ground temperature corresponds with solar radiation flux. Results confirmed that ground properties were important factors that control the soil moisture and temperature change in the permafrost region.

Cryopreservation of Indian Red Jungle Fowl (Gallus Gallus Murghi) Spermatozoa: A First Approach

The experiment was designed to show the capacity of Indian Red Jungle Fowl ( Gallus gallus murghi) sperm to be cryopreserved. The changes in characteristics of Indian Red Jungle Fowl spermatozoa during different phases of cryopreservation with the glycerol cryoprotectant and straw packaging were recorded. Semen from eight mature cocks were pooled, diluted at 37 °C in a Tselutin poultry extender, cooled to 4 °C in 2 h (0.275 min−1) and equilibrated for 10 min after the addition of 11% glycerol. Cooled semen was filled in 0.5 mL French straws, kept over liquid nitrogen vapour for 10 min and plunged into liquid nitrogen. Frozen semen was thawed at 37 °C for 30 s. Sperm motility, plasma membrane plasticity, livability, and acrosomal integrity were assessed at the stage of pre-dilution (37 °C), post-dilution, cooling, equilibration and freeze-thawing. The experiment was repeated five times. Sperm motility did not change at post-dilution and cooling and averaged 83.3±3.1%. However, motility declined ( P&lt;0.05) to 66.0±2.4% and 45.0±6.5% at post-equilibration and thawing stages, respectively. The sperm plasma membrane plasticity at the pre-dilution stage was 74.8±1.4% and decreased ( P&lt;0.05) to 62.3±1.7%, 51.7±1.7%, and 42.0±1.2% at the stages of post-dilution, cooling and freeze-thawing, respectively. A decline ( P &lt; 0.05) in acrosomal integrity was observed at post-cooling (83.8±2.4%), equilibration (80.8±0.8%) and thawing (73.8±2.4%). It is concluded that Indian Red Jungle sperm seem to adapt quite well to the freeze-thaw process that mainly alters the motility capacities and much less the acrosomal integrity. To our knowledge, this is the first ever report on cryopreservation of Indian Red Jungle Fowl spermatozoa.

Cryoelectrolysis-electrolytic processes in a frozen physiological saline medium.

BackgroundCryoelectrolysis is a new minimally invasive tissue ablation surgical technique that combines the ablation techniques of electrolytic ablation with cryosurgery. The goal of this study is to examine the hypothesis that electrolysis can take place in a frozen aqueous saline solution.MethodTo examine the hypothesis we performed a cryoelectrolytic ablation protocol in which electrolysis and cryosurgery are delivered simultaneously in a tissue simulant made of physiological saline gel with a pH dye. We measured current flow, voltage and extents of freezing and pH dye staining.ResultsUsing optical measurements and measurements of currents, we have shown that electrolysis can occur in frozen physiological saline, at high subzero freezing temperatures, above the eutectic temperature of the frozen salt solution. It was observed that electrolysis occurs when the tissue resides at high subzero temperatures during the freezing stage and essentially throughout the entire thawing stage. We also found that during thawing, the frozen lesion temperature raises rapidly to high subfreezing values and remains at those values throughout the thawing stage. Substantial electrolysis occurs during the thawing stage. Another interesting finding is that electro-osmotic flows affect the process of cryoelectrolysis at the anode and cathode, in different ways.DiscussionThe results showing that electrical current flow and electrolysis occur in frozen saline solutions imply a mechanism involving ionic movement in the fluid concentrated saline solution channels between ice crystals, at high subfreezing temperatures. Temperatures higher than the eutectic are required for the brine to be fluid. The particular pattern of temperature and electrical currents during the thawing stage of frozen tissue, can be explained by the large amounts of energy that must be removed at the outer edge of the frozen lesion because of the solid/liquid phase transformation on that interface.ConclusionElectrolysis can occur in a frozen domain at high subfreezing temperature, probably above the eutectic. It appears that the most effective period for delivering electrolytic currents in cryoelectrolysis is during the high subzero temperatures stage while freezing and immediately after cooling has stopped, throughout the thawing stage.

川西高寒生态系统不同海拔土壤动物对冬季凋落叶腐殖化过程的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 川西高寒生态系统不同海拔土壤动物对冬季凋落叶腐殖化过程的影响 DOI: 10.5846/stxb201510031996 作者: 作者单位: 四川农业大学,四川农业大学,四川农业大学,四川农业大学,四川农业大学,四川农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（31270498，31170423）；四川省杰出青年学术与技术带头人培育项目（2012JQ0008，2012JQ0059）；中国博士后科学基金特别资助项目（2012T50782）；高等学校博士学科点专项科研基金（20135103110002） Effects of soil fauna on winter litter humification along an altitudinal gradient in cold ecosystems in western Sichuan Author: Affiliation: Sichuan Agriculture University,Sichuan Agriculture University,Sichuan Agriculture University,,,Sichuan Agriculture University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:凋落叶在冬季的腐殖化过程是高寒生态系统土壤有机质形成和碳固定的重要阶段，并可能受到严酷冻结环境下仍具有一定活性的土壤动物的影响，但缺乏必要的关注。因此，以川西高山峡谷区海拔3000、3600、4000m的高寒森林和草甸典型凋落叶为研究对象，采用不同孔径大小的凋落物网袋去除土壤动物的方法，根据凋落叶的自然腐解过程，于2013年11月-2014年4月研究了不同冻融时期（冻结前期、深冻期、融化期）土壤动物对凋落叶腐殖化过程的作用。结果表明：通过对色调系数（ΔlogK）和光密度值（E4/E6）值的分析，在高寒生态系统中，冬季随着温度的降低土壤动物促进了凋落叶的腐殖化，而随着温度的升高土壤动物抑制了凋落叶的腐殖化。深冻期土壤动物对海拔3000m的森林凋落叶腐殖化过程具有显著促进作用；在冻结前期土壤动物对海拔3600m森林凋落叶腐殖化过程具有显著促进作用；而融化期土壤动物对海拔4000m的草甸凋落叶腐殖化过程具有显著的抑制作用；其他海拔和时期没有显著影响。冻结初期土壤动物对凋落叶的腐殖化速率的作用高于深冻期和融化期，腐殖化度在深冻期达到最大值。这些结果表明气候变化情景下冬季变暖可能导致土壤动物抑制凋落物腐殖化，减少凋落物向土壤有机质的转化。 Abstract:Foliar litter humification is one of the main mechanisms of carbon sequestration, and is essential in forming soil organic matter from foliar litter. Soil fauna is a type of decomposer that can influence litter humification. It was previously believed that soil fauna were dormant during the winter in cold biomes, and thus their activities were not considered to affect litter humification. However, recent studies have documented that some cold tolerant soil fauna remain active during the winter. However, little is known about the effects of soil fauna on litter humification during the winter in cold biomes. Therefore, a field experiment with different sizes of litterbags was conducted on three cold biomes along different altitudinal gradients in the eastern Tibet Plateau. Two species were selected to study litter decomposition at each of the three biomes:Betula albo-sinensis and Abies faxoniana in the subalpine forest at 3000 m, Sabina saltuaria and Salix paraplesia in the alpine forest at 3600m, and Ajania nubigena and Carex atrofusca in the alpine meadow at 4000 m. Litterbags were placed before the soil completely froze in November, 2013. Litterbags were sampled at the onset of three stages-freezing, deep freezing, and thawing-from 2013 to 2014. Tone coefficient (ΔlogK) and optical density value (E4/E6) were analyzed to determine the litter humification levels. The results showed that soil fauna promoted leaf litter humification as the temperature decreased, and suppressed leaf litter humification as the temperature increased during the winter in cold ecosystems. The effects of soil fauna on the process of leaf litter were regulated by altitude and litter species. The effect of soil fauna on leaf litter humification decreased as the altitude increased. Soil fauna increased litter humification at 3000m during the deep freezing stage and at 3600m at the onset of the freezing stage. However, soil fauna inhibited litter humification at 4000m during the thawing stage. Furthermore, soil fauna did not affect litter humification at other altitudes and sampling stages. The effects of soil fauna on litter humification rate at the onset of freezing stage were higher than those of the deep freezing stage and thawing stage, and humification rate peaked during the deep freezing stage. These results suggest that the activities of soil animals could promote humus formation from litter as the temperature decreases, indicating a possible increase in soil carbon sequestration. Together, these data provide a new understanding of soil organic matter formation and the carbon budget in cold ecosystems. 参考文献 相似文献 引证文献

Effect of different levels of egg-yolk on freezability of Jakhrana buck semen

The present study was designed to determine the effect of different levels of egg-yolk on freezability of Jakhrana buck semen. Six healthy Jakhrana bucks (BW=30 ± 2kg, age=12 ± 0.5 month) were used for semen collection. These bucks were maintained under semi-intensive system at Jakhrana Unit of C.I.R.G. Makhdoom, Mathura. A total of 48 ejaculates (6 bucks × 8 replicates) were collected twice a week using artificial vagina. Each ejaculate was divided into 4 groups (G1, G2, G3 and G4). The G1, G2, G3 and G4 were extended with Tris-egg yolk-citric acid- fructose-glycerol (TEYCFG) extenders containing 5, 10, 15 and 20% egg yolk level, respectively. Each ejaculate was evaluated for sperm motility, viability, abnormality, and hypo-osmotic swelling (HOS) response and acrosome integrity before and after freezing. At pre-freeze stage no significant (P&gt;0.05) difference in sperm motility and viability was found among all groups. Sperm abnormality was significantly (P&lt;0.05) higher in G4 as compared to other groups (G1, G2, G3). The HOS response and acrosomal integrity was significantly (P&lt;0.05) higher in G1, G2 and G3 as compared to G4. However, no significant (P&gt;0.05) difference was observed in HOS response and acrosomal integrity among G1, G2 and G3. At post thaw stage, sperm motility, viability and HOS response was significantly (P&lt;0.05) higher in G1 and G2 as compared to G3 and G4. Sperm abnormality was significantly (P&lt;0.05) lower in G2 as compared to other groups. The acrosomal integrity was significantly (P&lt;0.01) higher in G1 and G2 as compared to G3 and G4. It is concluded that 10% egg yolk in Tris based extender may be the best for successful cryopreservation of Jakhrana buck semen.

Ice morphology modification and solute recovery improvement by heating and annealing during block freeze-concentration of coffee extracts

Several treatments on ice blocks can be applied during block freeze-concentration to increase the solute recovery from the ice. In the present study, the changes in the ice block’s temperature and the application of annealing during the block freeze-concentration of aqueous coffee extracts were studied. The ice block was subjected to heating and annealing prior to the thawing stage. The effect of coolant temperature during ice block heating (T = −10 and −5 °C) and the application of annealing (+, −) on solute recovery and ice structure morphology was evaluated. The use of annealing during block freeze-concentration modified the ice crystal morphology and increased the solute recovery only when it is applied at the highest temperature. In general, the annealing process increased the size and circularity of the ice crystals, consequently improving the solute recovery. Thus, annealing can be used to increase the solute recovery during block freeze-concentration.

Elemental composition and optical properties reveal changes in dissolved organic matter along a permafrost thaw chronosequence in a subarctic peatland

The fate of carbon stored in permafrost-zone peatlands represents a significant uncertainty in global climate modeling. Given that the breakdown of dissolved organic matter (DOM) is often a major pathway for decomposition in peatlands, knowledge of DOM reactivity under different permafrost regimes is critical for determining future climate feedbacks. To explore the effects of permafrost thaw and resultant plant succession on DOM reactivity, we used a combination of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), UV/Vis absorbance, and excitation-emission matrix spectroscopy (EEMS) to examine the DOM elemental composition and optical properties of 27 pore water samples gathered from various sites along a permafrost thaw sequence in Stordalen Mire, a thawing subarctic peatland in northern Sweden. The presence of dense Sphagnum moss, a feature that is dominant in the intermediate thaw stages, appeared to be the main driver of variation in DOM elemental composition and optical properties at Stordalen. Specifically, DOM from sites with Sphagnum had greater aromaticity, higher average molecular weights, and greater O/C, consistent with a higher abundance of phenolic compounds that likely inhibit decomposition. These compounds are released by Sphagnum and may accumulate due to inhibition of phenol oxidase activity by the acidic pH at these sites. In contrast, sites without Sphagnum, specifically fully-thawed rich fens, had more saturated, more reduced compounds, which were high in N and S. Optical properties at rich fens indicated the presence of microbially-derived DOM, consistent with the higher decomposition rates previously measured at these sites. These results indicate that Sphagnum acts as an inhibitor of rapid decomposition and CH4 release in thawing subarctic peatlands, consistent with lower rates of CO2 and CH4 production previously observed at these sites. However, this inhibitory effect may disappear if Sphagnum-dominated bogs transition to more waterlogged rich fens that contain very little to no living Sphagnum. Release of this inhibition allows for higher levels of microbial activity and potentially greater CH4 release, as has been observed in these fen sites.

Effect of freeze–thaw cycles on carbon stocks of saline–alkali paddy soil

ABSTRACTThis study aims to provide basic data to support accurate estimation of carbon stocks and reveal the physicochemical factors that influence the carbon cycle in saline–alkali soils. Soil samples were collected during initial freezing, complete freezing, initial thawing and complete thawing stages. Levels of soil organic carbon (SOC), soil inorganic carbon (SIC), moisture, salinity, pH and available nitrogen were determined, and variations were observed during the freezing and thawing periods. Correlation analysis and regression analysis of carbon contents and physicochemical properties were performed. The results showed that freeze–thaw cycles have significant effects on carbon contents. The SOC content initially decreased in the freezing stage and then increased in the thawing stage. However, the SIC content initially increased in the freezing stage, decreased in the initial thawing stage and finally increased in the complete thawing stage. The migration and transformation of SOC and SIC were observed both temporally and spatially. SOC was positively correlated with available nitrogen, moisture and salinity and negatively correlated with pH; while SIC was negatively correlated with available nitrogen, moisture and salinity and positively correlated with pH. Among the factors evaluated, available nitrogen and salinity exerted the greatest effects on SOC and SIC contents, respectively.

A Simulation and Validation of CLM during Freeze-Thaw on the Tibetan Plateau

The applicability of a new soil hydraulic property of frozen soil scheme applied in Community Land Model 4.5 (CLM4.5), in conjunction with an impedance factor for the presence of soil ice, was validated through two offline numerical simulations conducted at Madoi (GS) and Zoige (ZS) on the Tibetan Plateau (TP). Sensitivity analysis was conducted via replacing the new soil hydraulic property scheme in CLM4.5 by the old one, using default CLM4.5 runs as reference. Results indicated that the new parameterization scheme ameliorated the surface dry biases at ZS but enlarged the wet biases which existed at GS site due to ignoring the gravel effect. The wetter surface condition in CLM4.5 also leads to a warmer surface soil temperature because of the greater heat capacity of liquid water. In addition, the combined impact of new soil hydraulic property schemes and the ice impedance function on the simulated soil moisture lead to the more reasonable simulation of the starting dates of freeze-thaw cycle, especially at the thawing stage. The improvements also lead to the more reasonable turbulent fluxes simulations. Meanwhile, the decreased snow cover fraction in CLM4.5 resulted in a lower albedo, which tended to increase net surface radiation compared to previous versions. Further optimizing is needed to take the gravel into account in the numerical description of thermal-hydrological interactions.

Enriching membrane cholesterol improves stability and cryosurvival of buffalo spermatozoa

Buffalo spermatozoa are comparatively more susceptible to freezing hazards than cattle spermatozoa. In recent times incubation of spermatozoa with cholesterol-loaded-cyclodextrins (CLC) has shown improvements in semen quality in several species. Therefore, this study was undertaken to evaluate the incubation level of CLC at which maximum benefit is derived for the buffalo spermatozoa. For the study, 120 million spermatozoa were incubated in 2, 3 and 4mg/mL of CLC (Gr II, III and IV, respectively) and cholesterol and phospholipids content, their ratio, flow cytometric evaluation of plasma membrane integrity (PMI), plasma membrane fluidity and extent of cryoinjury (Chlortetracycline, CTC assay) were compared with an untreated control (Gr I). Additionally the ability of cholesterol-loaded-spermatozoa to undergo induced acrosome reaction (IAR) using ionophore calcium (A23187) was evaluated in frozen–thaw samples. Data show a significant and linear increase (CV=0.88) in cholesterol content of spermatozoa in Gr II, III and IV and a significant decrease in phospholipids content at frozen–thaw stage in Gr IV than Gr III spermatozoa. The study revealed a significant improvement in PMI and significant reduction in plasma membrane fluidity and cryoinjury of CLC treated spermatozoa at progressive stages in three groups compared to control. Nevertheless, spermatozoa of Gr II, III and IV were significantly less responsive to ionophore calcium (A23187) than Gr I. This study shows for the first time that incubation of buffalo bull spermatozoa with CLC (3mg/120×106) prior to processing permits greater numbers of sperm to survive cryopreservation while allowing spermatozoa to capacitate and the acrosome to react to AR inducer ionophore calcium (A23187).

Effect of seasonal soil freeze–thaw cycles on bacterial diversity in the process of fine root decomposition at different critical periods

Abstract Soil microbial community plays a crucial role in fine roots decomposition in the forest ecosystem, and understanding the dynamics of soil microbial diversity in the fine roots will be helpful to reveal the mechanism of fine root decomposition at different critical periods. As yet, little is known about the dynamics of soil microbial diversity in the process of fine roots decomposition during the soil freeze–thaw season in the high-frigid forest ecosystem. In order to understand the effects of seasonal freeze–thaw cycles on bacterial diversity in the process of fine roots decomposition at different critical periods in cold winter, litterbags with spruce (Picea asperata), fir (Abies faxoniana) and birch (Betula albosinensis) fine roots were buried in the forest floor at altitudes of 3582 m, 3298 m, and 3023 m in different sites in the eastern Tibet Plateau on October 26, 2009. The litterbags were picked up and stored in ice box at the periods of onset of freezing (OF), deep freezing (DF), early thawing stage (ETS), middle thawing stage (MTS), late thawing stage (LTS), and early growing season (EGS) from freeze–thaw season to early growing season. DNA of bacterial in fine roots taken back was extracted immediately. Based on the PCR-DGGE technique, diverse bacterial communities in the studied fine roots were found in the whole process of fine roots decomposition. Bacterial diversity in fine roots were significantly higher at the periods of onset of freezing, middle thawing and late thawing, but significantly lower at the periods of in deep freezing and early thawing. Bacterial diversity in decomposing fine roots varied greatly with seasonal soil freeze–thaw process and tree species, but varied slightly with the studied altitudes. Regardless of tree species, higher similarity of bacterial community in fine roots was observed among different altitudes at the same period, while relatively lower similarity of bacterial community in fine roots was observed at different critical periods at the same altitude. However, the similarity of bacterial community in fine roots was always higher than 48% during the freeze–thaw season. Biodiversity indices of richness, Shannon–Wiener index, Simpson index and evenness of bacterial community were correlated significantly with average, maximum and minimum temperatures in soils during the freeze–thaw season, only except for the correlation between soil average temperature and Simpson index. The nitrogen concentration in fine roots was correlated significantly with Simpson index and evenness of bacterial community, but the phosphorus concentration was not significantly correlated with these bacterial indices. In conclusion, continuous soil freezing reduced the level of bacterial community diversity in fine roots, and the bacterial community diversity in fine roots at soil thawing period would recover the level at onset freezing period, regardless of the studied altitudes. The dynamics of bacterial community in fine roots conformed to the dynamics of root decomposition. Meanwhile, fine roots quality could also influence the level of bacterial community diversity.

Soil Fauna Affects Dissolved Carbon and Nitrogen in Foliar Litter in Alpine Forest and Alpine Meadow.

Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) are generally considered important active biogeochemical pools of total carbon and nitrogen. Many studies have documented the contributions of soil fauna to litter decomposition, but the effects of the soil fauna on labile substances (i.e., DOC and TDN) in litter during early decomposition are not completely clear. Therefore, a field litterbag experiment was carried out from 13th November 2013 to 23rd October 2014 in an alpine forest and an alpine meadow located on the eastern Tibetan Plateau. Litterbags with different mesh sizes were used to provide access to or prohibit the access of the soil fauna, and the concentrations of DOC and TDN in the foliar litter were measured during the winter (the onset of freezing, deep freezing and thawing stage) and the growing season (early and late). After one year of field incubation, the concentration of DOC in the litter significantly decreased, whereas the TDN concentration in the litter increased. Similar dynamic patterns were detected under the effects of the soil fauna on both DOC and TDN in the litter between the alpine forest and the alpine meadow. The soil fauna showed greater positive effects on decreasing DOC concentration in the litter in the winter than in the growing season. In contrast, the dynamics of TND in the litter were related to seasonal changes in environmental factors, rather than the soil fauna. In addition, the soil fauna promoted a decrease in litter DOC/TDN ratio in both the alpine forest and the alpine meadow throughout the first year of decomposition, except for in the late growing season. These results suggest that the soil fauna can promote decreases in DOC and TDN concentrations in litter, contributing to early litter decomposition in these cold biomes.