Polymer hydrolysis in a cold climate

In this review we discuss the activity of an ecologically significant group of psychrophilic bacteria, which are involved in the hydrolysis of plant cell wall polymers. Until now these organisms have been largely overlooked, despite the key role they play in releasing organic carbon fixed by primary producers in permanently cold environments such as Antarctica. This review details a specific group of plant cell wall polymer-degrading enzymes known as β-glycanases. Studies on "cold" enzymes in general are in their infancy, but it has been shown that many exhibit structural and functional modifications that enable them to function at low temperature. β-Glycanases in particular are intriguing because their substrates (cellulose and xylan) are very refractile, which may indicate that their "cold" modifications are pronounced. In addition, mesophilic β-glycanases have been extensively studied and the current state of our knowledge is reviewed. This body of information can be exploited to enable meaningful comparative studies between mesophilic and psychrophilic β-glycanases. The aim of such investigations is to obtain a deeper insight into those structural and functional modifications that enable these enzymes to function at low temperature and to examine the evolutionary relationship between mesophilic and psychrophilic β-glycanases. Received: December 21, 1998 / Accepted: February 3, 1999     

Superior wood for violins--wood decay fungi as a substitute for cold climate

Violins produced by Antonio Stradivari during the late 17th and early 18th centuries are reputed to have superior tonal qualities. Dendrochronological studies show that Stradivari used Norway spruce that had grown mostly during the Maunder Minimum, a period of reduced solar activity when relatively low temperatures caused trees to lay down wood with narrow annual rings, resulting in a high modulus of elasticity and low density. The main objective was to determine whether wood can be processed using selected decay fungi so that it becomes acoustically similar to the wood of trees that have grown in a cold climate (i.e. reduced density and unchanged modulus of elasticity). This was investigated by incubating resonance wood specimens of Norway spruce (Picea abies) and sycamore (Acer pseudoplatanus) with fungal species that can reduce wood density, but lack the ability to degrade the compound middle lamellae, at least in the earlier stages of decay. Microscopic assessment of the incubated specimens and measurement of five physical properties (density, modulus of elasticity, speed of sound, radiation ratio, and the damping factor) using resonance frequency revealed that in the wood of both species there was a reduction in density, accompanied by relatively little change in the speed of sound. Thus, radiation ratio was increased from 'poor' to 'good', on a par with 'superior' resonance wood grown in a cold climate.     

Plants and climate change: complexities and surprises

Background Anthropogenic climate change (ACC) will influence all aspects of plant biology over coming decades. Many changes in wild species have already been well-documented as a result of increased atmospheric CO₂ concentrations, warming climate and changing precipitation regimes. A wealth of available data has allowed the use of meta-analyses to examine plant–climate interactions on more sophisticated levels than before. These analyses have revealed major differences in plant response among groups, e.g. with respect to functional traits, taxonomy, life-history and provenance. Interestingly, these meta-analyses have also exposed unexpected mismatches between theory, experimental, and observational studies.Scope We reviewed the literature on species’ responses to ACC, finding ∼42 % of 4000 species studied globally are plants (primarily terrestrial). We review impacts on phenology, distributions, ecophysiology, regeneration biology, plant–plant and plant–herbivore interactions, and the roles of plasticity and evolution. We focused on apparent deviations from expectation, and highlighted cases where more sophisticated analyses revealed that unexpected changes were, in fact, responses to ACC.Conclusions We found that conventionally expected responses are generally well-understood, and that it is the aberrant responses that are now yielding greater insight into current and possible future impacts of ACC. We argue that inconclusive, unexpected, or counter-intuitive results should be embraced in order to understand apparent disconnects between theory, prediction, and observation. We highlight prime examples from the collection of papers in this Special Issue, as well as general literature. We found use of plant functional groupings/traits had mixed success, but that some underutilized approaches, such as Grime''s C/S/R strategies, when incorporated, have improved understanding of observed responses. Despite inherent difficulties, we highlight the need for ecologists to conduct community-level experiments in systems that replicate multiple aspects of ACC. Specifically, we call for development of coordinating experiments across networks of field sites, both natural and man-made.     

Simulation of phytomass productivity based on the optimum temperature for plant growth in a cold climate

During long-term monitoring (more than 20 years) of the hydrologic regime at 20 mountainous sites in the Czech Republic (altitude 600–1400 m a.s.l.; vegetation season April-September; mean air temperature 8–10°C; mean total precipitation 400–700 mm; mean duration of sunshine 1100–1300 hours; mean potential transpiration 200–250 mm) it was found that plant temperature does not rise above about 25°C when plants transpire. According to the ecological optimality theory, the phytocenosis that is able to survive unfavourable conditions and produce the biggest amount of phytomass will prevail at sites occurring in long-term stable natural conditions. Simulation of phytomass productivity based on the optimum temperature for plant growth showed that plants with an optimum leaf temperature of about 25°C can survive the unfavourable conditions and produce the largest amount of phytomass at the site studied in the long-term.     

Impacts of long-term snow climate change on a high-elevation cold desert shrubland, California, USA

Ecological responses to 50-year old manipulations of snow depth and melt timing were assessed using snow fences arrayed across 50 km of a shrub–conifer landscape mosaic in eastern California, USA. We compared how increased, decreased, and ambient snow depth affected patterns of vegetation community composition, fire fuel accumulation, and annual tree ring growth. We also tested the effect of snow depth on soil carbon storage based on total C content under the two co-dominant shrub species (Artemisia tridentata and Purshia tridentata) in comparison with open, intershrub sites. Increased snow depth reduced the cover of the N-fixing shrub P. tridentata but not the water-redistributing shrub A. tridentata. Annual ring growth was greater on +snow plots and lower on ?snow plots for the conifer Pinus jeffreyi but not for Pinus contorta. Graminoid cover and aboveground biomass indicated higher fire fuel accumulation where snow depth was increased. Dead shrub stem biomass was greater regardless of whether snow depth was increased or decreased. Results demonstrate community shifts, altered tree growth, feedbacks on carbon storage, and altered fire fuel accumulation as a result of changes in snow depth and melt timing for this high-elevation, snow-dominated ecotone under future climate scenarios that envision increased or decreased snow depth.     

Mesostructure and activity of photosynthetic apparatus for three crassulacean species grown in cold climate

A comparative study of leaf anatomy and morphology and of CO₂ exchange was conducted with Rhodiola rosea L., Hylotelephium triphyllum (Haw.) Holub., and Sedum acre L. as representative Crassulacean species occurring in the northeast European Russia. The leaf mesophyll in R. rosea was clearly differentiated into the palisade and spongy tissues, whereas the mesophyll of stonecrops (H. triphyllum and S. acre) was composed of round-shaped cells. The leaves of S. acre featured the largest volume of mesophyll cells and possessed water-retaining cells located around conducting bundles. The chloroplast volume in S. acre (50 μm³) was three times smaller and the number of chloroplasts per cell (170 cell^?1) was three times higher than in R. rosea and H. triphyllum (50–55 cell^?1). The content of chlorophylls (5–7 mg/g dry wt) and carotenoids (1.5–2.0 mg/g dry wt) in R. rosea leaves was 2–3 times higher than in leaves of stonecrops. The rate of CO₂ net uptake in Crassulacean species depended on mesostructure and correlated with the content of pigments and soluble carbohydrates. The photosynthetic rate in R. rosea under optimal irradiance and temperature attained the value of 40 mg/(g dry wt), which is 3 and 8 times higher than in H. triphyllum and S. acre, respectively. The temperature optimum for photosynthesis of R. rosea was observed at 8–18°C, while the optimum for stonecrops was shifted towards higher temperatures by 3–5°C. At chilling temperatures (5–7°C), the leaves of R. rosea retained 50% of their maximal photosynthetic rate, while photosynthetic rates in H. triphyllum and S. acre leaves lowered to 25–30% of the maximal rate. The increase in temperature to 25–30°C led to depression of CO₂ net uptake in leaves of Crassulacean species. In R. rosea and H. triphyllum, the rate of photosynthetic electron flow was depressed at high irradiances and temperatures that were supraoptimal for net photosynthesis. It is concluded that the photosynthetic apparatus of Crassulacean species is well adapted to moderate and chilling temperatures, which adjusts the plant metabolism to “life strategies” under conditions of cold climate.     

气候变化背景下贵州省倒春寒灾害时空演变特征

基于1959-2007年贵州省19个气象台站的逐日平均气温资料,结合倒春寒强度指数指标和灾害等级划分标准,从倒春寒发生频率、站次比、年代际变化、气候突变、周期变化等方面,分析了贵州省倒春寒的时空演变特征.结果表明:1959--2007年,研究区无倒春寒发生的频率最大,其次为重级以上倒春寒,中级和轻级倒春寒的发生频率接近;在全球变暖背景下,研究期间贵州省发生中级倒春寒的站次比变化最明显,其气候倾向率达1.4%·(10a)-1,而无倒春寒、轻级和重级以上倒春寒的站次比则略微减少;贵州省倒春寒强度在20世纪90年代最强,20世纪80年代次强,2000-2007年最弱,20世纪70年代次弱,20世纪60年代居中;研究期间贵州省西部和西北部高海拔地区、中部和北部地区的倒春寒强度呈增强趋势,而东部、南部地区的倒春寒强度呈略微降低的趋势;贵州省西部、西北部、中部和北部地区的倒春寒强度在1975年发生由低值向高值的突变;贵州省倒春寒存在明显的周期波动特征,年际周期以2～4年为主,年代际周期以13～15年和27～29年为主.     

Winter climate change,plant traits and nutrient and carbon cycling in cold biomes

It is essential that scientists be able to predict how strong climate warming, including profound changes to winter climate, will affect the ecosystem services of alpine, arctic and boreal areas, and how these services are driven by vegetation–soil feedbacks. One fruitful avenue for studying such changing feedbacks is through plant functional traits, as an understanding of these traits may help us to understand and synthesise (1) responses of vegetation (through ‘response traits’ and ‘specific response functions’ of each species) to winter climate and (2) the effects of changing vegetation composition (through ‘effect traits’ and ‘specific effect functions’ of each species) on soil functions. It is the relative correspondence of variation in response and effect traits that will provide useful data on the impacts of winter climate change on carbon and nutrient cycling processes. Here we discuss several examples of how the trait-based, response–effect framework can help scientists to better understand the effects of winter warming on key ecosystem functions in cold biomes. These examples support the view that measuring species for their response and effect traits, and how these traits are linked across species through correspondence of variation in specific response and effects functions, may be a useful approach for teasing out the contribution of changing vegetation composition to winter warming effects on ecosystem functions. This approach will be particularly useful when linked with ecosystem-level measurements of vegetation and process responses to winter warming along natural gradients, over medium time scales in given sites or in response to experimental climate manipulations.     

Heating up relations between cold fish: competition modifies responses to climate change

Most predictions about species responses to climate change ignore species interactions. Helland and colleagues (2011) test whether this assumption is valid by evaluating whether ice cover affects competition between brown trout [Salmo trutta (L.)] and Arctic charr [Salvelinus alpines (L.)]. They show that increasing ice cover correlates with lower trout biomass when Arctic charr co-occur, but not in charr's absence. In experiments, charr grew better in the cold, dark environments that typify ice-covered lakes. Decreasing ice cover with warmer winters could mean more trout and fewer charr. More generally, their results provide an excellent example, suggesting that species interactions can strongly modify responses to climate change.     

Impacts of organic and inorganic fertilizers on nitrification in a cold climate soil are linked to the bacterial ammonia oxidizer community

The microbiology underpinning soil nitrogen cycling in northeast China remains poorly understood. These agricultural systems are typified by widely contrasting temperature, ranging from −40 to 38°C. In a long-term site in this region, the impacts of mineral and organic fertilizer amendments on potential nitrification rate (PNR) were determined. PNR was found to be suppressed by long-term mineral fertilizer treatment but enhanced by manure treatment. The abundance and structure of ammonia-oxidizing bacterial (AOB) and archaeal (AOA) communities were assessed using quantitative polymerase chain reaction and denaturing gradient gel electrophoresis techniques. The abundance of AOA was reduced by all fertilizer treatments, while the opposite response was measured for AOB, leading to a six- to 60-fold reduction in AOA/AOB ratio. The community structure of AOA exhibited little variation across fertilization treatments, whereas the structure of the AOB community was highly responsive. PNR was correlated with community structure of AOB rather than that of AOA. Variation in the community structure of AOB was linked to soil pH, total carbon, and nitrogen contents induced by different long-term fertilization regimes. The results suggest that manure amendment establishes conditions which select for an AOB community type which recovers mineral fertilizer-suppressed soil nitrification.