Acclimation Patterns Research Articles

Effect of Heat Exposure on Percentage of Dead Sperm and Pyriform Cell in Male New Zealand White (NZW) Rabbit

Experiment has been done on the effect of heat exposure on the percentage of dead sperm and pyriform cell in male NZW rabbit. The bucks were exposed to 34°C for 8 hours on either 1 or 5 days. It was found that scrotal temperature (ScT) increased very rapidly during the first hour of exposure by 4°C in group 1 (1x8h). In group 2 (5x8h of exposure) ScT differed significantly between days (P < 0.05). The bigest response was on day 1 (36.6°C) and followed a progressive reduction, day by day, in an apparent acclimation pattern. At different times of exposure, ScT was observed to rise rapidly during the first hour (by 14 percent or 4.4°C). In the 1x8h treatment dead sperm achieved a maximum level of 14.5 ± 4.7 percent in the first week after hotroom treatment. In week 2, the percentage dead sperm started to decline. When rabbits were exposed to 5x8h, this group was more severely affected than the 1x8h. In week 1, the percentage dead sperm in the 5x8h group was 2.1 fold greater than in the 1x8h group (31.0 vs 14.5 percent). Recovery in the 5x8h group took longer than in the 1x8h group, and the percentage dead sperm finally returned to normal levels only after 7 weeks, compared to 5 weeks after 1x8h treatment.Between weeks, the incidence of pyriforms did differ significantly (P < 0.05). In the 1x8h treatment, the percentage pyriforms increased in the first week after hotroom exposure by 3.8 percent. In week 2, the percentage pyriform started to decline and continued to do so gradually until week 6. In the 5x8h treatment, the number of pyriforms was higher than it was in 1x8h treatment. In week 1, for example, the percentage pyriform was 16 percent higher than in 1x8h treatment group. Hence, the mean pyriform cell count was 1.6 times higher in the 5x8h compared to the 1x8h group.

Acclimation of Fine Root Systems to Soil Warming: Comparison of an Experimental Setup and a Natural Soil Temperature Gradient

Global warming is predicted to impact high-latitude and high-altitude forests severely, jeopardizing their overall functioning and carbon storage, both of which depend on the warming response of tree fine root systems. This paper investigates the effect of soil warming on the biomass, morphology and colonizing ectomycorrhizal community of spruce fine and absorptive fine roots. We compare the responses of spruce roots growing at a man-made long-term soil warming (+ 4°C) experiment to results obtained from a geothermal soil temperature gradient (+ 1 to + 14°C) extending to the forest die-off edge, to shed light on the generalizability of the warming response and reveal any thresholds in acclimation ability. Trees in warmer soils formed longer and less-branched absorptive roots with higher specific root length and area, and lower root tissue density in both spruce stands, irrespective of warming method and location. Soil warming at the experimental warming site also supported the occurrence of a more varied EcM community and an increase in the abundance of Tomentella spp., indicating a shift in nutrient foraging. Fine and absorptive fine root biomass decreased toward warmer soil, with a sharp reduction occurring between + 4 and + 6°C from the ambient and leading to the collapse of the fine root system at the geothermal gradient. At the experimental warming site, the applied + 4°C warming had no effect on fine and absorptive fine root biomass. The similar fine root responses at the two warming sites suggest that the observations possibly reflect general acclimation patterns in spruce forests to global warming.

Unraveling the Photoprotective Response of Lichenized and Free-Living Green Algae (Trebouxiophyceae, Chlorophyta) to Photochilling Stress.

Lichens and free-living terrestrial algae are widespread across many habitats and develop successfully in ecosystems where a cold winter limits survival. With the goal of comparing photoprotective responses in free-living and lichenized algae, the physiological responses to chilling and photochilling conditions were studied in three lichens and their isolated algal photobionts together as well as in a fourth free-living algal species. We specifically addressed the following questions: (i) Are there general patterns of acclimation in green algae under chilling and photochilling stresses? (ii) Do free-living algae exhibit a similar pattern of responses as their lichenized counterparts? (iii) Are these responses influenced by the selection pressure of environmental conditions or by the phylogenetic position of each species? To answer these questions, photosynthetic fluorescence measurements as well as pigment and low molecular weight carbohydrate pool analyses were performed under controlled laboratory conditions. In general, photochemical efficiency in all free-living algae decreased with increasing duration of the stress, while the majority of lichens maintained an unchanged photochemical activity. Nevertheless, these patterns cannot be generalized because the alga Trebouxia arboricola and the lichen Ramalina pollinaria (associated with Trebouxia photobionts) both showed a similar decrease in photochemical efficiency. In contrast, in the couple Elliptochloris bilobata-Baeomyces rufus, only the algal partner exhibited a broad physiological performance under stress. This study also highlights the importance of the xanthophyll cycle in response to the studied lichens and algae to photochilling stress, while the accumulation of sugars was not related to cold acclimation, except in the alga E. bilobata. The differences in response patterns detected among species can be mainly explained by their geographic origin, although the phylogenetic position should also be considered, especially in some species.

Cold Hardiness of Vitis vinifera Roots

Grapevine buds have identifiable patterns of cold acclimation and deacclimation, but it is not known whether roots also follow these patterns. A better understanding of root cold hardiness thresholds and/or acclimation patterns would enable mitigation strategies to be developed to reduce the likelihood of root damage. This study had two major objectives: 1) to improve protocols for electrolyte leakage and then quantitatively compare the results to differential thermal analysis; and 2) to quantify whether Vitis vinifera roots acclimate to preconditioning temperatures. Existing protocols were optimized and root cold hardiness was evaluated on own-rooted Vitis vinifera Merlot and Chardonnay. To determine whether grapevine roots acclimate to their environment, three preconditioning regimes were applied: ambient air temperature during active vine growth; 12°C for one week during dormancy; and 0°C for one week during dormancy. Following preconditioning, root samples were collected and exposed to fixed temperatures of −2.0, −4.0, −6.0, or −8.0°C, and electrolyte leakage, the standard indicator of root cold damage, was measured. The incidence of low temperature exotherms from differential thermal analysis was used as a potential alternative to identify temperatures that cause tissue damage. Overall, Chardonnay and Merlot roots did not have dynamic cold acclimation patterns like grapevine buds. There was little variation in maximum cold hardiness (

Seasonal changes in morpho-functional aspects of two Anemonia sulcata (Pennant, 1777) wild populations

Marine benthic organisms can be used as indicators of the quality of environmental status and as monitoring tools to detect natural or anthropogenic perturbations. In temperate waters, metabolic and biochemical responses may be governed by physiological changes driven by seasonal factors. Gathering baseline information on the mechanisms underlying seasonal acclimation patterns is therefore a critical step towards the understanding of the physiological responses of biological indicators. In poikilothermic metazoans, the production of regulatory metabolic enzymes can be used as tools for deciphering the acclimation potential. The aim of this study was to characterize the natural seasonal variability in biometric traits and enzymatic biomarkers over a 12-month period in the sea anemone, Anemonia sulcata (Anthozoa, Cnidaria), from two areas with different environmental and anthropic impacts. Seasonality and site factors affected enzymatic kinetics at tentacle levels, while seasonality, site and biometrical characteristics modulated the same enzymes in the body column of A. sulcata. The results showed a decrease in enzymatic activity in summer and an increased synthesis of enzymes in the late fall and winter months. The interaction between biometric features and temperature appeared significant for mesolittoral sea anemones but not for infralittoral specimens. This study showed seasonal patterns of variations of biochemical responses in A. sulcata, suggesting that this species, an abundant member of shallow rocky bottom communities in temperate European seas, may represent a sensitive bio-indicator organism worth considering for further ecological studies on climate change as well as for environmental monitoring programs.

Optimal Regulation of the Balance between Productivity and Overwintering of Perennial Grasses in a Warmer Climate

Seasonal growth patterns of perennial plants are linked to patterns of acclimation and de-acclimation to seasonal stresses. The timing of cold acclimation (development of freezing resistance) and leaf growth cessation in autumn, and the timing of de-acclimation and leaf regrowth in spring, is regulated by seasonal cues in the environment, mainly temperature and light factors. Warming will lead to new combinations of these cues in autumn and spring. Extended thermal growing seasons offer a possibility for obtaining increased yields of perennial grasses at high latitudes. Increased productivity in the autumn may not be possible in all high latitude regions due to the need for light during cold acclimation and the need for accumulating a carbohydrate storage prior to winter. There is more potential for increased yields in spring due to the availability of light, but higher probability of freezing events in earlier springs would necessitate a delay of de-acclimation, or an ability to rapidly re-acclimate. In order to optimize the balance between productivity and overwintering in the future, the regulation of growth and acclimation processes may have to be modified. Here, the current knowledge on the coordinated regulation of growth and freezing resistance in perennial grasses is reviewed.

Acclimation to light and avoidance of photoinhibition in Typha latifolia is associated with high photosynthetic capacity and xanthophyll pigment content.

Tall monocots with long, linear leaves have lower canopy light attenuation than plants with horizontal leaves, yet little is known about their light acclimation and sun-shade responses. The genus Typha, common in nutrient-rich wetlands, is highly productive with dense canopies of such leaves. The objective of this study was therefore to investigate photosynthetic acclimation and pigment content in linear leaves of Typha latifolia L. in response to light availability. This was done in a growth experiment with two light intensities and in the field. In the laboratory, T. latifolia exhibited typical morphological, anatomical and gas exchange sun-shade responses. Net photosynthesis rates in high light were very high for a C3 plant (>40µmol CO2 m-2s-1) in both laboratory and field studies, and this was associated with stomatal conductances that were correspondingly high (maximum values >1.0mol H2O m-2s-1). The size of the xanthophyll (violaxanthin, antheraxanthin and zeaxanthin; VAZ) pool was also among the top 0.5% of all species. In the field, T. latifolia was able to maintain high net photosynthetic rates (26-41µmol CO2 m-2s-1) throughout its canopy and could avoid photoinhibition through high investment in the VAZ pool (0.7-1.3µmolg-1 DW total VAZ pigments). This pattern of acclimation is likely to be adaptive, explaining why this species is so successful and dominant in high-light, high-nutrient wetland environments.

Seasonal variations of the photosynthetic activity and pigment concentrations in different reproductive phases of Gigartina skottsbergii (Rhodophyta, Gigartinales) in the Magellan region, sub-Antarctic Chile

Seasonal environmental changes may significantly influence macroalgal diversity and biomass. Cryptogam species richness increases towards the poles, especially in sub-Antarctic environments. Yet, subpolar seaweed biodiversity and ecophysiology remain understudied even though it is essential for the management and sustainability of endemic species of significant economic interest (e.g., Gigartina skottsbergii). We evaluate the seasonality and ecophysiology of the different life phases of the rhodophyte G. skottsbergii by analyzing variation in fluorescence yield and photosynthetic pigment composition. There were significant seasonal differences in maximum relative electron transport rate (rETRmax) between gametophyte and tetrasporophyte phase, and between reproductive and vegetative specimens. Photosynthetic efficiency (α) was not significantly different between reproductive states of G. skottsbergii. We found significant differences in mean concentrations of allophycocyanin (APC), phycocyanin (PC), and chlorophyll a (Chl a) between gametophyte and tetrasporophyte phases. Results obtained provide new insight into seasonal acclimation patterns of an ecologically important species, which can be used for the design of appropriate management and cultivation strategies of G. skottsbergii towards the restoration of natural populations in fragile, subpolar regions where some of the last, relatively undisturbed communities of G. skottsbergii still remain.

Diversity of the nitrogen starvation responses in subarctic Desmodesmus sp. (Chlorophyceae) strains isolated from symbioses with invertebrates.

We report on common and strain-specific responses to nitrogen (N) starvation recorded in four closely related symbiotic Desmodesmus strains from taxonomically very distant animals (hydroids, a sponge and a polychaete) dwelling in the White Sea. A number of common for the studied strains and free-living microalgae as well as some specific patterns of acclimation to the N starvation were documented. The common responses included a slowdown of cell division, a reduction of photosynthetic apparatus and a vast expansion of storage subcompartments of the cell. Although these responses were qualitatively similar to those known in free-living chlorophytes, in the studied strains they occurred in a strain-specific manner. The specific N-starvation responses comprised formation of chloroplast envelope membrane twirls, thinning of the appressed thylakoid membranes and a loss of the luminal depositions and channeling of the fixed carbon to cell wall polysaccharide layer. Desmodesmus sp. from a hydroid featured a unique, among the studied strains, capability of 'emergency' degradation of Rubisco, apparently to salvage the N contained in this protein. The obtained results are discussed in view of the remarkable physiological plasticity of the symbiotic Desmodesmus spp. and their survival under the harsh conditions of the subarctic sea habitat.

Mitochondrial physiology and reactive oxygen species production are altered by hypoxia acclimation in killifish (Fundulus heteroclitus).

Many fish encounter hypoxia in their native environment, but the role of mitochondrial physiology in hypoxia acclimation and hypoxia tolerance is poorly understood. We investigated the effects of hypoxia acclimation on mitochondrial respiration, O2kinetics, emission of reactive oxygen species (ROS), and antioxidant capacity in the estuarine killifish ( ITALIC! Fundulus heteroclitus). Killifish were acclimated to normoxia, constant hypoxia (5 kPa O2) or intermittent diel cycles of nocturnal hypoxia (12 h:12 h normoxia:hypoxia) for 28-33 days and mitochondria were isolated from liver. Neither pattern of hypoxia acclimation affected the respiratory capacities for oxidative phosphorylation or electron transport, leak respiration, coupling control or phosphorylation efficiency. Hypoxia acclimation also had no effect on mitochondrial O2kinetics, but ITALIC! P50(the O2tension at which hypoxia inhibits respiration by 50%) was lower in the leak state than during maximal respiration, and killifish mitochondria endured anoxia-reoxygenation without any impact on mitochondrial respiration. However, both patterns of hypoxia acclimation reduced the rate of ROS emission from mitochondria when compared at a common O2tension. Hypoxia acclimation also increased the levels of protein carbonyls and the activities of superoxide dismutase and catalase in liver tissue (the latter only occurred in constant hypoxia). Our results suggest that hypoxia acclimation is associated with changes in mitochondrial physiology that decrease ROS production and may help improve hypoxia tolerance.

COLD ACCLIMATION PATTERNS OF ACTINIDIA ARGUTE CULTIVARS IN A TEMPERATE CLIMATE ZONE

The kiwi berry, Actinidia arguta Planch is gaining importance in temperate Europe. Warm transient intervals during the winter season can initiate cold deacclimation and bud break of woody plants. Most A. arguta cultivars are characterised by an early bud burst which may result in horticultural limitations due to a high sensitivity to spring frost of these young shoots/inflorescences. The evolution of bud dormancy was observed in two Actinidia arguta 'Weiki' and 'Geneva' cultivars. From September through mid-October the final 30-day shooting percentage (FS) was low. Between mid-October and mid-December a steep rise in FS indicates that bud endodormancy was broken. 'Weiki' appears to have a lesser need for cold exposure in order to release it from dormancy. The seasonal pattern of cold acclimation and deacclimation was determined for both cultivars using the electrolyte leakage test. Maximal cold tolerance was achieved in midwinter. In early spring cold tolerance of the buds declined again. 'Geneva' was more cold tolerant than 'Weiki'.

Is the OJIP Test a Reliable Indicator of Winter Hardiness and Freezing Tolerance of Common Wheat and Triticale under Variable Winter Environments?

OJIP analysis, which explores changes in photosystem II (PSII) photochemical performance, has been used as a measure of plant susceptibility to stress. However, in the case of freezing tolerance and winter hardiness, which are highly environmentally variable, the use of this method can give ambiguous results depending on the species as well as the sampling year and time. To clarify this issue, we performed chlorophyll fluorescence measurements over three subsequent winters (2010/11, 2011/12 and 2012/13) on 220 accessions of common winter wheat and 139 accessions of winter triticale. After freezing, leaves were collected from cold-acclimated plants in the laboratory and field-grown plants. Observations of field survival in seven locations across Poland and measurements of freezing tolerance of the studied plants were also recorded. Our results confirm that the OJIP test is a reliable indicator of winter hardiness and freezing tolerance of common wheat and triticale under unstable winter environments. Regardless of species, the testing conditions giving the most reliable results were identical, and the reliability of the test could be easily checked by analysis of some relationships between OJIP-test parameters. We also found that triticale is more winter hardy and freezing tolerant than wheat. In addition, the two species were characterized by different patterns of photosynthetic apparatus acclimation to cold.

General patterns of acclimation of leaf respiration to elevated temperatures across biomes and plant types

Respiration is instrumental for survival and growth of plants, but increasing costs of maintenance processes with warming have the potential to change the balance between photosynthetic carbon uptake and respiratory carbon release from leaves. Climate warming may cause substantial increases of leaf respiratory carbon fluxes, which would further impact the carbon balance of terrestrial vegetation. However, downregulation of respiratory physiology via thermal acclimation may mitigate this impact. We have conducted a meta-analysis with data collected from 43 independent studies to assess quantitatively the thermal acclimation capacity of leaf dark respiration to warming of terrestrial plant species from across the globe. In total, 282 temperature contrasts were included in the meta-analysis, representing 103 species of forbs, graminoids, shrubs, trees and lianas native to arctic, boreal, temperate and tropical ecosystems. Acclimation to warming was found to decrease respiration at a set temperature in the majority of the observations, regardless of the biome of origin and growth form, but respiration was not completely homeostatic across temperatures in the majority of cases. Leaves that developed at a new temperature had a greater capacity for acclimation than those transferred to a new temperature. We conclude that leaf respiration of most terrestrial plants can acclimate to gradual warming, potentially reducing the magnitude of the positive feedback between climate and the carbon cycle in a warming world. More empirical data are, however, needed to improve our understanding of interspecific variation in thermal acclimation capacity, and to better predict patterns in respiratory carbon fluxes both within and across biomes in the face of ongoing global warming.

Effects of temperature and body size on the physiological energetics of the stalked sea squirt Styela clava

An assessment of the patterns of thermal acclimation of physiological processes of the stalked sea squirt Styela clava is needed to further understand growth patterns associated with large seasonal fluctuations in ambient temperature. The effects of different exposure temperatures on physiological processes of S. clava were measured at 5, 10, 15, 20, and 25°C. The impact of temperature on energy balance at a whole organism level was then assessed by scope for growth (SFG) and net growth efficiency (K2) measures. Physiological rates of S. clava were well correlated with its dry tissue weight (DW). Positive allometry with DW indicated that all physiological rates investigated were generally higher in the larger individuals regardless of temperature. Some allometric equations (e.g., feces production rate vs. DW and respiration rate vs. DW) exhibited identical estimates of exponents, enabling accurate comparisons of the rates across temperatures. In contrast, disparities across temperatures of the values for the weight exponent were detected in other allometric equations, revealing that thermal effects on these rates have different degrees for large and small individuals. The SFG value in S. clava of different sizes was similar at lower temperatures (5–10°C), peaking at 15°C. The SFG was positive with a relatively constant K2 in this temperature range. This positive energy balance reflects the reduction in metabolic costs at lower temperatures. In contrast, increased metabolic costs at higher temperatures (20–25°C) resulted in lowered SFG and K2 values, indicating that the feeding rate did not increase as greatly in compensation for the increased metabolic costs at higher temperatures. The lowered absorption at 25°C (compared with 20°C) resulted in negative SFG and K2 values. Finally, our results confirm that the absence of compensatory adjustment to warmer conditions leads to energetic disruption at a whole organism level at such temperatures.

Asymmetric thermal acclimation responses allow sheepshead minnow Cyprinodon variegatus to cope with rapidly changing temperatures.

Thermal acclimation responses in sheepshead minnow Cyprinodon variegatus were quantified by transfer and reciprocal transfer of fish between 11.1° and 18.2°C, between 18.2° and 25.7°C, or between 25.7° and 32.8°C. Changes in thermal acclimation status were assessed by posttransfer time series determinations of thermal tolerance (i.e., critical thermal minima and maxima). In general, heat tolerance gain and loss were complete in 20 and 25 d, respectively. Cold tolerance gain was achieved ca. 24 d posttransfer, but attrition was complete after only 12-13 d. Heat tolerance was gained asymmetrically, with fish acquiring approximately one-half of their accruable tolerance at the lowest transfer temperature. Likewise, the majority of cold tolerance accruement occurred during the warmest temperature transfer. Relatively uniform losses of heat and cold tolerance were seen in reciprocal transfers. Acclimation patterns were related to initial acclimation temperature, final acclimation temperature, and acclimation time and could be accurately modeled by multiple linear regression. The results suggest that sheepshead minnow accrue a majority of their high- or low-temperature tolerance early in the acclimation process well before potential damaging temperatures are likely to occur. This novel pattern of asymmetric heat and cold tolerance acquisition in sheepshead minnow may be a key adaptation for surviving rapid and unpredictable water temperature changes commonly encountered in their natural environment.

Fruit Ripening Has Little Influence on Grapevine Cold Acclimation

This four-year study tested whether the physiological demand of fruit ripening may interfere with grapevine cold acclimation in autumn or with midwinter hardiness. Three harvest time treatments were established in a mature vineyard of own-rooted Cabernet Sauvignon vines: clusters were removed after fruit set, at veraison, or after the first fall frost. Average yield of the late harvested vines varied from 4.2 to 5.1 kg/vine (7.5 to 9.2 t/ha) among years, and soluble solids varied from 23.4 to 25.6 Brix. The presence of fruit during ripening delayed leaf senescence, measured as chlorophyll decline. The fruit also tended to delay the senescence-associated decrease in photosynthesis. All vines showed typical patterns of autumn cold acclimation, midwinter hardiness, and spring deacclimation. Cold hardiness of buds, cane phloem, and cane xylem varied during winter depending on prevailing temperature, and during the coldest winter reached levels of −27°C for 50% bud damage and −28°C for the onset of xylem injury. Early fruit removal had no effect on cane nonstructural carbohydrates and, with few exceptions, failed to enhance cold hardiness. Depending on the year, early fruit removal improved bud hardiness on 5 to 15% and xylem hardiness on 8 to 38% of all measurement dates. On those dates, the early harvested vines tended to be 1 to 2°C hardier than the late harvested vines, irrespective of the time of crop removal. No trend was found for phloem hardiness. These results indicate that cropping, at least within commercially acceptable limits in regions with sufficiently long or warm growing seasons, rarely impacts cold acclimation and maximum hardiness. Grapevines appear to adjust seasonal leaf physiology to meet their carbon demand for both fruit ripening and cold acclimation.

Fall Acclimation and the Lift/Store Pathway: Effect on Reforestation

This review compares fall acclimation patterns and lift/store practices for Pseudotsuga menziesii var. menziesii, Picea glauca (Moench) Voss x P. engelmannii Parry ex engelm and Pinus taeda L. seedlings. Spruce seedlings achieve budset and an endodormant state in late summer, coastal Douglas-fir in early fall, while loblolly pine achieves a less endodormant state with a limited amount of mitotic activity. Natural chilling during the fall reduces days to budbreak (DBB) and increases freezing tolerance, with northern species achieving greater freezing tolerance. Although root growth potential (RGP) in some years may increase from early fall to mid-winter, this trend does not always occur. Chilling hours and/or freezing tolerance status is used to initiate storage of Douglas-fir and spruce seedlings but there is no proven attribute to make the lifting decision for loblolly pine. When properly hardened, all species can be cooler stored to meet lift/store requirements of a few months, though fall lifted interior spruce seedlings are typically freezer stored for up to six months. Lengthy storage can cause declines in DBB, freezing tolerance, RGP, and carbohydrate reserves. Douglas-fir and interior spruce seedlings require an appropriate length of fall acclimation, typically including chilling, to develop a level of hardiness for lengthy storage and high survival after outplanting. Loblolly pine seedlings benefit from chilling, though non-chilled, hardened seedlings may exhibit high survival after four weeks of cooler storage. Each species has a unique fall acclimation pattern making it difficult to define universal culture practices across all regional forest regeneration programs.

Vulnerability and acclimation to increased UVB radiation in three intertidal macroalgae of different morpho-functional groups

The vulnerability and acclimation to increased UVB radiation in three macroalgae of different morpho-functional groups collected in the Mediterranean coastal waters were evaluated. The algae were submitted for 7 days to increased (PAB+) and decreased (PAB−) UVB radiation. The thickness and morphology influenced the response to increased UVB radiation, being Cystoseira tamariscifolia the less vulnerable algae followed by Ellisolandia elongata. The highest resistance to increased UVB radiation in C. tamariscifolia was related to the accumulation of polyphenols and high antioxidant activity, whereas E. elongata was due to its high reflectance. Finally, Ulva rigida suffered the highest photoinhibition under PAB+ culture. The latest species presented 10 times lower polyphenol content and antioxidant activity than C. tamariscifolia. The three species showed different acclimation patterns to the changes of UVB radiation related to the morphology, photosynthetic activity, accumulation of photoprotectors and antioxidant activities. The ecological implications of the UVB variations on macroalgae are discussed.

Characterization of tobermolite as a bed material for selective growth of methanotrophs in biofiltration

Tobermolite was characterized as a bed material for methanotrophic biofiltration. A lab-scale biofilter packed with tobermolite was operated for different operation times under identical conditions. The three different runs showed similar acclimation patterns of methane oxidation, with methane removal efficiency increasing rapidly for the first few days and peaking within three weeks, after which the efficiency remained stable. The mean methane removal capacities ranged from 766gm−3d−1 to 974gm−3d−1 after acclimation. Pyrosequencing indicated that the methanotrophic proportion (methanotroph/bacteria) increased to 71–94% within three weeks. Type I methanotrophs Methylocaldum and Methylosarcina were dominant during the initial growth period, then Methylocaldum alone dominated the methanotrophic community. A community comparison showed that total bacterial and methanotrophic communities were temporally stable after the initial growth period. Quantitative PCR showed that methanotrophic density increased during the first 3–4 weeks, then remained stable over 120 days. Tobermolite can provide a special habitat for the selective growth of methanotrophs, resulting in rapid acclimation. Tobermolite also allows the microbial community and methanotrophic density to remain stable, resulting in stable methane biofiltration.

Photosynthetic responses and acclimation of two castor bean cultivars to repeated drying–wetting cycles

To investigate the responses of castor bean to repeated drying–wetting cycles (RDWC), morpho-physiological parameters of two cultivars (Jiaxiang 2 and Hangbi 8) were determined by a pot experiment under well-watered control and RDWC. RDWC inhibited plant growth and leaf development, decreased water loss rate (WLR), and enhanced leaf mass per area (LMA) and chlorophyll content as indicated by spectral reflectance indices for both cultivars. Photosynthesis was inhibited by progressive drought stress but quickly recovered after rewatering for each cycle. Both cultivars exhibit a similar pattern of acclimation to RDWC: (1) higher LMA and lower WLR, (2) increased photosynthetic capacity under drought stress with increasing cycle numbers, (3) quick recovery and over-compensation for photosynthesis after rewatering, and (4) increased chlorophyll content. Jiaxiang 2 shows a high capacity for water preservation under drought stress and an over-compensation for photosynthesis after rewatering compared with Hangbi 8.