Freeze-thaw Events Research Articles

Characterization and differentiation of key odor-active compounds of ‘Beibinghong’ icewine and dry wine by gas chromatography-olfactometry and aroma reconstitution

Freezing-thawing events contribute to the unique aroma profile of icewines. Differences in key odor-active volatile compounds between ‘Beibinghong’ (Vitis amurensis × V. vinifera) icewines and dry wines were investigated by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Acceptable agreement between the olfactometric and quantitative results was obtained. ‘Beibinghong’ icewine was characterized by high concentrations of volatile phenols, lactones, (E)-β-damascenone, and phenylacetaldehyde, which were associated with on-vine freezing-thawing events in grape. Low concentrations of higher alcohol acetates and ethyl esters of fatty acids were attributed to hyperosmotic stress during fermentation. The overall aroma of icewine could be mimicked by reconstitution containing 44 identified volatiles. Partial least squares regression analysis demonstrated that the concentrations of these volatile compounds determined the distinct sensory profiles of icewines, which have higher intensities of honey/sweet, smoky, caramel, dried fruit, apricot/peach, and floral aromas, and lower intensities of fresh fruity and herbaceous notes in comparison with dry wines.

Diamidoamine Salt as the Admixture for Concrete Increasing the Resistance to the Freeze-Thaw Cycle

Concrete freeze-thaw resistance, along with compressive strength, is one of its basic features, which have a significant impact on the durability of structures of buildings and engineering structures. Numerous studies presented in domestic and foreign literature showed that there is a relationship between the concrete mix’s composition and the extent of frost damage. The frost durability of concrete depends on many factors. Therefore, cyclic changes of air temperature in winter conditions (over 100 freeze-thaw event cycles per year are estimated in Poland) must be taken into consideration as soon as in the phase of designing a concrete mix and structural elements. Proper designing of the concrete mix, optimal selecting of proportions and kinds of components, applying of appropriate kinds of additives and admixtures as well as proper maintenance of concrete can protect the investor against serious financial consequences. The paper discussed the influence of sub-zero temperatures effect on cement concretes properties. The requirements that are imposed on designers in terms of concretes resistance to frosts cyclic effect by the currently applicable standards were presented. The paper also presents the results of an original research programme showing the effectiveness of diamidoamine salt as an admixture for concretes that increases their resistance to the freeze-thaw cycle. Within the preliminary tests, the influence of the diamidoamine salt on early and 28-day compressive strength was marked. The air content in fresh concrete, absorbability and water permeability were also specified. The freeze-thaw resistance of concretes with the addition of the diamidoamine salt after 50 freeze-thaw cycles was determined. The conducted preliminary laboratory tests showed that applying the diamidoamine salt causes the decrease in compressive strength. This decrease is proportional to the admixture content. The applied admixture significantly decreases the absorbability, improves waterproofness and freeze-thaw resistance of the concrete.

Seasonal changes in the occurrence of embolisms among broad-leaved trees in a temperate region

Sap freeze–thaw events are a main determinant of the distribution of broad-leaved woody plants in cool regions but the effect in other climates remains unknown. We used cryoscanning electron microscopy to examine the differences in plant growth patterns based on seasonal variation in xylem water distribution in four broad-leaved species (one ring-porous and three diffuse-porous species) in a temperate region of Japan. Leaf fall was detected in November for the ring-porous species Maackia amurensis Rupr. et Maxim., although embolisms were detected in large earlywood vessels in January of the following year. The percentage of embolisms in latewood vessels varied significantly between years. By contrast, xylem embolisms in diffuse-porous species (deciduous and evergreen) were barely detectable during winter. In one evergreen species, embolisms and refilling were detected in some vessels during the growing season. Based on the variation in the number of freeze–thaw events among years in Asian monsoon forests, we infer that M. amurensis obtained no benefit from extending leaf phenology because of the occurrence of vessel embolisms in winter. On the other hand, the leaf phenologies of deciduous and evergreen diffuse-porous species were less constrained by winter embolisms. Maackia amurensis persists in cool temperate regions by limiting the photosynthetic period.

A proxy-year analysis shows reduced soil temperatures with climate warming in boreal forest

Scientists unequivocally agree that winter air temperature (TA) in northern high latitudes will increase sharply with anthropogenic climate change, and that such increases are already pervasive. However, contrasting hypotheses and results exist regarding the magnitude and even direction of changes in winter soil temperature (TS). Here we use field and satellite data to examine the ‘cold soil in a warm world’ hypothesis for the first time in the boreal forest using a proxy year approach. In a proxy warm year with a mean annual temperature similar to that predicted for ~2080, average winter TS was reduced relative to the baseline year by 0.43 to 1.22 °C in open to forested sites. Similarly, average minimum and maximum winter TS declined, and the number of freeze-thaw events increased in the proxy warm year, corresponding to a reduction in the number of snow-covered days relative to the baseline year. Our findings indicate that early soil freezing as a result of delayed snowfall and reduced snow insulation from cold winter air are the main drivers of reduced winter active-layer TS (at ~2-cm depth) under warming conditions in boreal forest, and we also show that these drivers interact strongly with forest stand structure.

Modification of the composition of dissolved nitrogen forms, nitrogen transformation processes, and diversity of bacterial communities by freeze–thaw events in temperate soils

Freeze–thaw (FT) events can influence the soil nitrogen (N) availability, although their effect on the diversity of bacterial communities during these processes remains uncertain. To test our hypothesis that close relationships exist between dissolved N pools (including NO3−, NH4+, NO3− + NH4+, and dissolved organic N [DON]), N transformation processes (including N mineralization, N immobilization, nitrification, and denitrification), and bacterial communities in response to FT events, we varied the temperature amplitude of these events by using freezing temperatures of -15 °C, −9 °C, and −3 °C and thawing temperatures of 2 °C and 5 °C in microcosms incubated in a temperate agricultural soil. All the pools of total dissolved inorganic N (DIN: i.e., NO3− + NH4+) decreased in concentration as the amplitude of freezing and thawing temperatures increased, whereas the opposite trend was observed for dissolved organic N (DON). Changes in the concentration of all the dissolved N forms examined were highly linearly correlated with N transformation processes. Partial correlation networks highlighted the transformation between the dissolved N forms during N mineralization and the direct immobilization of either NH4+ or DON by microorganisms in response to FT events. In addition, the total dissolved N content was primarily driven by the DON pool, thus suggesting a primary role for protease activity in response to FT. The Mental and Procrustean tests indicated that the N pools examined and the transformation processes were significantly correlated with bacterial community diversity. This linkage could be significantly weakened by warmer freezing temperatures, in which the orders Cytophagales and Sphingobacteriales may play an important role.

Effect of Freeze-Thaw on a Midtemperate Soil Bacterial Community and the Correlation Network of Its Members.

Freeze-thaw (FT) events can influence soil functions. However, the overall impact of FTs on soil bacterial communities, especially in temperate regions, remains unclear. In this study, soil samples were collected from a midtemperate region in the northeast of China, and three incubation tests were then designed with varied FT amplitudes (i.e., at a freezing temperature of −15, −9, and −3°C, respectively), frequencies of FT cycles (i.e., under one, six, and 15 FT cycles, respectively) and soil water content (SWC) values (i.e., at 10 and 30% SWC, respectively). High-throughput sequencing of 16S rRNA gene amplicons was performed and the functional profile was further predicted based on these data, in addition to examinations of bulk microbial properties. Data analyses suggested that, first of all, the FT amplitude significantly influenced the bulk microbial properties and bacterial community (composition and function); certain taxa showed a nonlinear response to the three amplitudes. Next, compared to a single FTC, multiple FT cycles had only minor effects on the bacterial functional capabilities, although the bulk microbial properties changed significantly after multiple FT cycles. In addition, the bacterial response to FTs was influenced by the SWC, characterized by the significantly different bacterial community structures (composition and function) and the opposite trends of enzyme activities. Finally, RDA plots and a correlation network assembled data from all soil samples across the three tests and suggested that bacterial response trajectories changed because some species were influenced mainly by other species (i.e., biotic environment) during FT processes.

Differential arthropod responses to warming are altering the structure of Arctic communities.

The Arctic is experiencing some of the fastest rates of warming on the planet. Although many studies have documented responses to such warming by individual species, the idiosyncratic nature of these findings has prevented us from extrapolating them to community-level predictions. Here, we leverage the availability of a long-term dataset from Zackenberg, Greenland (593 700 specimens collected between 1996 and 2014), to investigate how climate parameters influence the abundance of different arthropod groups and overall community composition. We find that variation in mean seasonal temperatures, winter duration and winter freeze–thaw events is correlated with taxon-specific and habitat-dependent changes in arthropod abundances. In addition, we find that arthropod communities have exhibited compositional changes consistent with the expected effects of recent shifts towards warmer active seasons and fewer freeze–thaw events in NE Greenland. Changes in community composition are up to five times more extreme in drier than wet habitats, with herbivores and parasitoids generally increasing in abundance, while the opposite is true for surface detritivores. These results suggest that species interactions and food web dynamics are changing in the Arctic, with potential implications for key ecosystem processes such as decomposition, nutrient cycling and primary productivity.

Changes in the mineral element compositions of soil colloidal matter caused by a controlled freeze-thaw event

This study investigated the effects of a controlled freeze-thaw event on the mineral element compositions of colloidal matter in soil interstitial water. The experiment was designed to decouple the freeze-thaw effect from the warming effect by conducting sequential treatments. The temperate soil samples were incubated in a refrigerator at 2°C for four weeks and compared with those frozen at −20°C in the second week and thawed at 2°C for the following two weeks; this was done in order to study the freeze-thaw effect while minimizing the influence caused by warming. The soil samples incubated at 25°C in the fourth week after two weeks of the freeze-thaw treatment were compared with the freeze-thaw treatment group to investigate the warming effect. The laser-induced breakdown spectroscopy (LIBS) technique was used to analyze the relative elemental concentrations in the soil colloidal matter (SCM), which was collected on nylon membrane filters. The six predominant mineral elements were classified into two groups based on their distinct trends in response to the treatment conditions. The type 1 element (Si, Mg, Al) contents were decreased both by the warming condition and by the freeze-thaw treatment, whereas the type 2 element (Fe, Ca, Ba) contents were decreased by the freeze-thaw treatment but increased by the warming condition. Only type 1 elements showed positive correlations with the amount of organic carbon. From the results of the elemental compositions in SCM, the effects of a freeze-thaw event can be contradictory depending on the thawing temperatures.

Nitrous oxide emissions following seasonal freeze-thaw events from arable soils in Northeast China

Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide (N2O) emissions in cold regions. However, the mechanisms of soil N2O emission during the freeze-thaw cycling in the field remain unclear. We evaluated N2O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China, and the structural equation model (SEM) was used to determine which factors affected N2O production during non-growing season. Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period, but simultaneously increased the gaseous N2O-N losses at the annual time scale under field condition. The N2O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha−1 for the paddy and maize fields, respectively, and contributed to 66 and 18% of the annual total. The highest emission rates (199.2–257.4 µg m−2 h−1) were observed during soil thawing for both fields, but we did not observe an emission peak during soil freezing in early winter. Although the pulses of N2O emission in spring were short-lived (18 d), it resulted in approximately 80% of the non-growing season N2O-N loss. The N2O burst during the spring thawing was triggered by the combined impact of high soil moisture, flush available nitrogen and carbon, and rapid recovery of microbial biomass. SEM analysis indicated that the soil moisture, available substrates including NH4+ and dissolved organic carbon (DOC), and microbial biomass nitrogen (MBN) explained 32, 36, 16 and 51% of the N2O flux variation, respectively, during the non-growing season. Our results suggested that N2O emission during the spring thawing make a vital contribution of the annual nitrogen budget, and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.

Aeolian Erosion Processes in Humid Subtropical Ultisols in Southeastern United States

Aeolian Erosion Processes in Humid Subtropical Ultisols in Southeastern United States Jamie L. Kincheloe, Dr. Arpita Nandi, Dr. Ingrid Luffman Abstract Many aeolian erosion studies have been performed in arid and semi-arid environments, while few have been performed in humid subtropical environments. Since the primary erosional factor in humid environments is precipitation, aeolian erosion is often not accounted for. This study focuses on the role of wind and wind-driven rain erosion in humid subtropical environments on an east Tennessee hill slope, USA. Three years of wind data were aggregated to weekly soil erosion measurement periods using five wind and precipitation parameters: average wind speed, peak gust, average wind direction, high wind direction, and maximum precipitation intensity. Predictive statistical regression models were generated for aeolian erosion in gully interfluves and sidewalls. Principal Components Analysis was used to develop two independent factors for wind speed and direction. Ordinary Least Square regression models for erosion on interfluves and sidewalls using the two factors and wind-driven precipitation interaction variables explained 5.9% and 15%, respectively, of variability in erosion data. A comparison of erosion on lee and stoss sidewalls indicated no significant differences in the three-year lumped dataset, but differences at the weekly time scale were significant during winter months, likely related to freeze thaw events. Full Text: PDF DOI: 10.15640/jges.v6n1a3

Effects of Repeated Freezing and Thawing and High Temperature Aging on the Solidification and Stabilization of Arsenic Contaminated Soil

The impact of solidification and stabilization effects on arsenic (As) contaminated soil before and after repeated freezing and thawing or high temperature aging was investigated by tests of unconfined compressive strength (UCS), permeability, leaching concentration and fractionation. The microstructure appearance of the soil was observed using SEM. The results show that the UCS of solidified soil decreases and its permeability increases after repeated freezing and thawing or high temperature aging. In stabilized soil, the unstable species of As increase and the leaching concentration of As rises accordingly after both treatments. The concentration of unstable species of As increased accordingly by 19.81% and 25.1%, and the leaching concentration rose from 115.5 μg·L-1 to 151.5 μg·L-1 and 164.5 μg·L-1 respectively after 300 freeze-thaw treatments or under 10 h of high temperature aging under 80℃. In general, the influence of the effects increases with more freeze-thaw events and higher temperature aging of longer duration. More damage and fragmentation was observed after both treatments.

Climate–growth relationship for different directions of Pinus pumila radial growth at the treeline of northern Daxing’an Mountains, China

Pinus pumila radial growth in differing radii directions’ response to climatic factors is inconsistent. The effects of freeze–thaw events on growth differ between spring and autumn. Pinus pumila is a crucial shrub species of sub-alpine treelines in northeast Daxing’an Mountains, China, but the growth–climate relationship for this eccentric shrub is not well understood. A total of 15 disks near the trunk base of individual Pinus pumila were collected at the treeline of Xiaobai Mountain, China. We investigated the growth–climate relationships in four reaction directions (A and B: left and right perpendicular radii; C: opposite radius to compression wood; D: compression wood radius). Results indicated that the shrub-ring width at the D direction was the widest (0.70 ± 0.14 mm/a) of the four directions, while the opposite direction (C) is narrowest (0.43 ± 0.07 mm/a). Water availability in June was the major limiting factor for P. pumila growth in the A and B directions. However, the radial growth in the C direction was mainly affected by mean and maximum temperatures in June, and growth in the D direction positively correlated with mean temperature in the current February and the previous October and minimum temperature in the previous November. In addition, the radial growth at all four directions negatively correlated with the sunshine hours in June of the current year, which could be related to the increase of soil drought and respiration caused by higher temperatures. Radial growth at the A, B, and C directions negatively correlated with the freeze–thaw magnitude and frequency in May, which may cause the frost damage in shrub leaves and roots. Our findings suggested that the eccentric shrub growth at the perpendicular radii may not contain the best climate signals, while the growth at the compression wood direction seems to be of normal use in dendroclimatology.

More fishers and fewer martens due to cumulative effects of forest management and climate change as evidenced from local knowledge

BackgroundMonitoring of fur-bearing species populations is relatively rare due to their low densities. In addition to catch data, trappers’ experience provides information on the ecology and status of the harvested species. Fisher (Pekania pennanti) and American marten (Martes americana) are mustelids that are sensitive to forest management and therefore considered to be ecological indicators of forest health. Fisher populations have increased in eastern North America since the early 2000s and this could have resulted in a northeastern extension of the species’ range and increased overlap with marten’s range. Moreover, habitats of both species are subject to natural and anthropogenic disturbances. The objective of this study was to document the knowledge held by local trappers in the northern area of sympatry between fisher and marten to identify factors that could explain variation in populations of the two species and interactions between them.MethodForty-one semi-directed interviews with Indigenous and non-Indigenous trappers in the Abitibi-Témiscamingue region of western Quebec (Canada), at the northern limit of the overlapping ranges of the two mustelid species.ResultsTrappers highlighted the lack of exclusivity of marten and fisher to coniferous forests, although marten is more closely associated with them than is fisher. Fisher apparently also takes advantage of open environments, including agroforestry systems. Moreover, climate change increases the frequency of freeze-thaw events that cause the formation of an ice crust on the snow surface, which favors fisher movements.ConclusionThe fisher was identified as a competitor and even a predator of the marten. Furthermore, the fisher is less affected than the marten by forest management, and it also seems to benefit from climate change to a greater extent.

Coupled land surface–subsurface hydrogeophysical inverse modeling to estimate soil organic carbon content and explore associated hydrological and thermal dynamics in the Arctic tundra

Abstract. Quantitative characterization of soil organic carbon (OC) content is essential due to its significant impacts on surface–subsurface hydrological–thermal processes and microbial decomposition of OC, which both in turn are important for predicting carbon–climate feedbacks. While such quantification is particularly important in the vulnerable organic-rich Arctic region, it is challenging to achieve due to the general limitations of conventional core sampling and analysis methods, and to the extremely dynamic nature of hydrological–thermal processes associated with annual freeze–thaw events. In this study, we develop and test an inversion scheme that can flexibly use single or multiple datasets – including soil liquid water content, temperature and electrical resistivity tomography (ERT) data – to estimate the vertical distribution of OC content. Our approach relies on the fact that OC content strongly influences soil hydrological–thermal parameters and, therefore, indirectly controls the spatiotemporal dynamics of soil liquid water content, temperature and their correlated electrical resistivity. We employ the Community Land Model to simulate nonisothermal surface–subsurface hydrological dynamics from the bedrock to the top of canopy, with consideration of land surface processes (e.g., solar radiation balance, evapotranspiration, snow accumulation and melting) and ice–liquid water phase transitions. For inversion, we combine a deterministic and an adaptive Markov chain Monte Carlo (MCMC) optimization algorithm to estimate a posteriori distributions of desired model parameters. For hydrological–thermal-to-geophysical variable transformation, the simulated subsurface temperature, liquid water content and ice content are explicitly linked to soil electrical resistivity via petrophysical and geophysical models. We validate the developed scheme using different numerical experiments and evaluate the influence of measurement errors and benefit of joint inversion on the estimation of OC and other parameters. We also quantify the propagation of uncertainty from the estimated parameters to prediction of hydrological–thermal responses. We find that, compared to inversion of single dataset (temperature, liquid water content or apparent resistivity), joint inversion of these datasets significantly reduces parameter uncertainty. We find that the joint inversion approach is able to estimate OC and sand content within the shallow active layer (top 0.3 m of soil) with high reliability. Due to the small variations of temperature and moisture within the shallow permafrost (here at about 0.6 m depth), the approach is unable to estimate OC with confidence. However, if the soil porosity is functionally related to the OC and mineral content, which is often observed in organic-rich Arctic soil, the uncertainty of OC estimate at this depth remarkably decreases. Our study documents the value of the new surface–subsurface, deterministic–stochastic inversion approach, as well as the benefit of including multiple types of data to estimate OC and associated hydrological–thermal dynamics.

Assessing the thermal dissipation sap flux density method for monitoring cold season water transport in seasonally snow-covered forests.

Productivity of conifers in seasonally snow-covered forests is high before and during snowmelt when environmental conditions are optimal for photosynthesis. Climate change is altering the timing of spring in many locations, and changes in the date of transition from winter dormancy can have large impacts on annual productivity. Sap flow methods provide a promising approach to monitor tree activity during the cold season and the winter-spring and fall-winter transitions. Although sap flow techniques have been widely used, cold season results are generally not reported. Here we examine the feasibility of using the Granier thermal dissipation (TD) sap flux density method to monitor transpiration and dormancy of evergreen conifers during the cold season. We conducted a laboratory experiment which demonstrated that the TD method reliably detects xylem water transport (when it occurs) both at near freezing temperature and at low flow rate, and that the sensors can withstand repeated freeze-thaw events. However, the dependence between sensor output and water transport rate in these experiments differed from the established TD relation. In field experiments, sensors installed in two Abies forests lasted through two winters and a summer with low failure. The baseline (no-flow) sensor output varied considerably with temperature during the cold season, and a new baseline algorithm was developed to accommodate this variation. The Abies forests differed in elevation (2070 and 2620 m), and there was a clear difference in timing of initiation and cessation of transpiration between them. We conclude that the TD method can be reliably used to examine water transport during cold periods with associated low flow conditions.

Evaluating the Effects of Open Shelters on Limestone Deterioration at Archaeological Sites in Different Climatic Locations

ABSTRACTOpen shelters have been proposed as suitable preservation strategies for a variety of heritage sites. However, no concerted attempt has yet been made to analyze their performance in a range of climatic conditions. This study aims to quantify limestone deterioration outside and inside the shelters at two archaeological sites, Hagar Qim (Malta) and the Bishop’s Palace (England), to obtain information on their impact. A simple methodology based on exposure trials and non-destructive tests was used. Globigerina limestone blocks were exposed at both sites from July 2013 to July 2014. Changes in appearance, weight, hardness, color, and moisture content of the blocks in addition to temperature and the likelihood of NaCl crystallization and freeze-thaw events were assessed over the year. This research shows that while deterioration rate is reduced as microclimatic conditions are moderated, open shelters do not completely prevent limestone deterioration at either site, especially in relation to salt weathering.

Earlier snowmelt accompanied by warmer soil temperatures in mid-latitude aspen forest and subalpine meadow: Implications for soil carbon

An advance in snowmelt timing in seasonally snow covered ecosystems has a wide range of potential impacts on plant and soil processes. Plants may respond to earlier melt through changes in phenology and altered allocation of resources to growth and reproduction, and earlier snowmelt may impact active pools of soil C such as microbial biomass and dissolved organic C (DOC). In subalpine aspen forests and open meadows in the Wasatch Plateau of the western Rocky Mountains, we manipulated snowmelt timing by adding dust to the snow surface. We obtained a treatment-induced snow-free interval of 6 to 22 days (3% to 11% reduction in snow-covered days). We observed the growth of early and mid-season herbaceous species, measuring above ground biomass, flower and seed counts, and seed mass. We also monitored microbial biomass, DOC, and soil respiration in the days and weeks following snowmelt. We observed generally warmer soil temperatures in the early snowmelt plots compared to controls. However, we found no difference in microbial biomass C or DOC following snowmelt and we found no legacy effect in growing season soil respiration as a result of earlier snowmelt. After three years of repeated treatments, total soil organic C remained unchanged between treatment and control plots. Although earlier snowmelt is likely to have a variety of impacts on subalpine ecosystems, we found no change in plant biomass or reproductive allocation and we found that carbon pools and fluxes were not perturbed by earlier snowmelt. A common expectation is that earlier snowmelt will lead to more frequent freeze-thaw cycles in soils, and studies have shown that freeze-thaw events can have significant but temporary impacts on soil C efflux. This study indicates that subalpine plants and soils may be at least partially buffered from some of the anticipated effects of earlier snowmelt. One direction of continuing research may be to identify adaptive buffers in subalpine ecosystems, an understanding of which may be useful in anticipating and responding to future climate change.

Globally important nitrous oxide emissions from croplands induced by freeze–thaw cycles

Large fluxes of nitrous oxide occur when frozen soils thaw. Field measurements and mathematical models suggest that freeze–thaw events are responsible for 17 to 28% of nitrous oxide emitted from agricultural soils globally.

Past freeze–thaw events on Pinus seeds increase seedling herbivory

AbstractSeed and seedling survival are key components of plant population persistence. Although freeze–thaw events are experienced by many dispersed seeds in temperate ecosystems, it is unclear whether freeze–thaw stresses experienced by seeds can alter seedling susceptibility to herbivores during the growing season. We evaluated how freezing stress (temperature at −6°C for 6 h) experienced by seeds of two conifer species (Pinus resinosa and Pinus strobus) affects seedling herbivory by a generalist herbivore (Spodoptera exigua). For both Pinus species, herbivores consumed twofold more seedling biomass from freeze–thaw‐treated plants than seedlings from the constant temperature treatment. Herbivores grew ~66% faster when feeding on freeze–thaw P. resinosa seedlings relative to controls, but herbivore growth rate did not differ between treatments for P. strobus. Our results show that the thermal environment experienced by a seed can have subsequent effects on plant–herbivore interactions, suggesting that (1) early ontogenetic stress could be a cryptic, yet unappreciated, determinant of future herbivory and (2) increasingly frequent cold events, such as those projected under winter climate change, may amplify seedling herbivory and reduce recruitment in managed and natural conifer forests.

Altered soil carbon and nitrogen cycles due to the freeze-thaw effect: A meta-analysis

Global climate change may result in changes in snow cover, which may enhance freeze-thaw phenomena in mid and high latitude and high elevation ecosystems, especially in the northern hemisphere, in the future. As a common non-biological stress, the freeze-thaw process can substantially alter soil carbon and nitrogen cycles. However, a comprehensive understanding of nutrient pools and dynamics in response to freeze-thaw cycles is not available. Here, we evaluated the effect sizes of the responses of 18 variables related to soil carbon and nitrogen cycles to the freeze-thaw effect from 46 papers. Seventeen studies that reported field observations and 28 studies that reported results from laboratory experiments were included, as well as one paper that used both methods to explore freeze-thaw processes. We used a random-effects model to examine whether soil origins, effect phases (including initial and long-term effects), methods and soil horizons affect the magnitudes of the responses to freeze-thaw events. The soil sources include forest, shrubland, grassland/meadow, cropland, tundra and wetland. We used meta-regression to explore possible relationships among effect sizes with freezing temperature, soil pH, soil C/N ratios and other factors. Our results suggest that the freeze-thaw process causes microbial N and the microbial C/N ratio to decrease by 12.2% and 8.5%, respectively. Soil solution dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are enhanced by 27.5% and 37.3%, respectively. The freeze-thaw effect increases the concentrations of NH4+, NO3− and dissolved inorganic nitrogen (DIN) by 84.1%, 29.6% and 35.4%, respectively. N2O emissions are also increased by 95.0% in freeze-thaw treatments. Laboratory measurements resulted in contrasting responses in terms of mineralization, nitrification and respiration. Freeze-thaw events promote turnover of fine roots but have no effect on the long-term aboveground biomass of grassland and heath. The results of this meta-analysis help to achieve a better understanding of the overall effects of freeze-thaw events on soil carbon and nitrogen cycles and their modulation across different environments.