Impact of early and late winter icing events on sub-arctic dwarf shrubs

Polar regions are predicted to undergo large increases in winter temperature and an increased frequency of freeze-thaw cycles, which can cause ice layers in the snow pack and ice encasement of vegetation. Early or late winter timing of ice encasement could, however, modify the extent of damage caused to plants. To determine impacts of the date of ice encasement, a novel field experiment was established in sub-arctic Sweden, with icing events simulated in January and March 2008 and 2009. In the subsequent summers, reproduction, phenology, growth and mortality, as well as physiological indicators of leaf damage were measured in the three dominant dwarf shrubs: Vaccinium uliginosum, Vaccinium vitis-idaea and Empetrum nigrum. It was hypothesised that January icing would be more damaging compared to March icing due to the longer duration of ice encasement. Following 2 years of icing, E. nigrum berry production was 83% lower in January-iced plots compared to controls, and V. vitis-idaea electrolyte leakage was increased by 69%. Conversely, electrolyte leakage of E. nigrum was 25% lower and leaf emergence of V. vitis-idaea commenced 11 days earlier in March-iced plots compared to control plots in 2009. There was no effect of icing on any of the other parameters measured, indicating that overall these study species have moderate to high tolerance to ice encasement. Even much longer exposure under the January icing treatment does not clearly increase damage.

Comparison of weight loss achieved after laparoscopic adjustable gastric banding between Afro-Caribbean, Caucasian and South Asian adult female patients in a London bariatric centre

INTRODUCTION

It has been shown that following laparoscopic adjustable gastric banding (LAGB) procedures, Afro-Caribbeans achieve poorer weight loss compared with Caucasians. The reasons for this are multifactorial. However, studies have been based on mainly female patients from the US and none to date have been from the UK. Furthermore, South Asians have not previously been compared. The aim of this study was to compare excess weight loss percentage (%EWL) outcomes up to five years following LAGB in Afro-Caribbean, Caucasian and South Asian females in a London-based teaching hospital.

METHODS

An analysis was carried out of prospectively collected data of female patients aged ≥16 years of Afro-Caribbean, Caucasian or South Asian origin who underwent LAGB between October 2000 and December 2011. Data included demographics, co-morbidities and anthropometrics.

RESULTS

Overall, 596 females underwent LAGB; 316 Caucasians (53.0%), 64 Afro-Caribbeans (10.8%) and 27 South Asians (4.5%) formed the majority of those who disclosed ethnicities. Age and initial body mass index (BMI) were comparable between Afro-Caribbeans and Caucasians (mean BMI: 47.3kg/m²[standard deviation [SD]: 7.5kg/m², range: 37.0-78.3kg/m²] vs 45.8kg/m²[SD: 7.1kg/m², range: 24.7-79.8kg/m²], p=0.225). A non-significant trend suggested less %EWL in Afro-Caribbeans than in Caucasians at 6 months, and at 1, 2, 3, 4 and 5 years (21.4% vs 24.4%, p=0.26; 27.4% vs 31.3%, p=0.27; 33.0% vs 36.8%, p=0.15; 39.0% vs 45.8%, p=0.14; 34.2% vs 45.3%, p=0.16; 37.1% vs 47.6%, p=0.67). South Asians and Caucasians had a similar age and preoperative BMI (mean BMI: 43.6kg/m² [range: 32.5-59.1kg/m²] vs 45.8kg/m² [range: 24.7-79.8kg/m²], p=0.08). The %EWL was greatest at three and four years among South Asians although numbers were small (n=4 and n=3 respectively).

CONCLUSIONS

A non-significant trend suggests poorer weight loss outcomes in Afro-Caribbeans compared with Caucasians in our cohort. Discussion of realistic weight loss outcomes as well as enhanced follow-up and dietary modifications are required for Afro-Caribbean patients. Low numbers prevent definitive conclusions regarding South Asians. Multicentre studies across England are required to better define any differences between ethnicities.

Impacts of long-term enhanced UV-B radiation on bryophytes in two sub-Arctic heathland sites of contrasting water availability

BACKGROUND AND AIMS

Anthropogenic depletion of stratospheric ozone in Arctic latitudes has resulted in an increase of ultraviolet-B radiation (UV-B) reaching the biosphere. UV-B exposure is known to reduce above-ground biomass and plant height, to increase DNA damage and cause accumulation of UV-absorbing compounds in polar plants. However, many studies on Arctic mosses tended to be inconclusive. The importance of different water availability in influencing UV-B impacts on lower plants in the Arctic has been poorly explored and might partially explain the observed wide variation of responses, given the importance of water in controlling bryophyte physiology. This study aimed to assess the long-term responses of three common sub-Arctic bryophytes to enhanced UV-B radiation (+UV-B) and to elucidate the influence of water supply on those responses.

METHODS

Responses of three sub-Arctic bryophytes (the mosses Hylocomium splendens and Polytrichum commune and the liverwort Barbilophozia lycopodioides) to +UV-B for 15 and 13 years were studied in two field experiments using lamps for UV-B enhancement with identical design and located in neighbouring areas with contrasting water availability (naturally mesic and drier sites). Responses evaluated included bryophyte abundance, growth, sporophyte production and sclerophylly; cellular protection by accumulation of UV-absorbing compounds, β-carotene, xanthophylls and development of non-photochemical quenching (NPQ); and impacts on photosynthesis performance by maximum quantum yield (F(v) /F(m)) and electron transport rate (ETR) through photosystem II (PSII) and chlorophyll concentrations.

RESULTS

Responses were species specific: H. splendens responded most to +UV-B, with reduction in both annual growth (-22 %) and sporophyte production (-44 %), together with increased β-carotene, violaxanthin, total chlorophyll and NPQ, and decreased zeaxanthin and de-epoxidation of the xanthophyll cycle pool (DES). Barbilophozia lycopodioides responded less to +UV-B, showing increased β-carotene and sclerophylly and decreased UV-absorbing compounds. Polytrichum commune only showed small morphogenetic changes. No effect of UV-B on bryophyte cover was observed. Water availability had profound effects on bryophyte ecophysiology, and plants showed, in general, lower growth and ETR, together with a higher photoprotection in the drier site. Water availability also influenced bryophyte responses to +UV-B and, in particular, responses were less detectable in the drier site.

CONCLUSIONS

Impacts of UV-B exposure on Arctic bryophytes were significant, in contrast to modest or absent UV-B effects measured in previous studies. The impacts were more easily detectable in species with high plasticity such as H. splendens and less obvious, or more subtle, under drier conditions. Species biology and water supply greatly influences the impact of UV-B on at least some Arctic bryophytes and could contribute to the wide variation of responses observed previously.

Contrasting strategies for UV-B screening in sub-Arctic dwarf shrubs

The content and distribution of UV-absorbing phenolic compounds was investigated in leaves of three species of Vaccinium co-existing at a site in north Sweden. Vaccinium myrtillus L., Vaccinium vitis-idaea L., and Vaccinium uliginosum L. exhibit markedly different strategies, in terms of localization and content of leaf phenolics and in their responses to UV-B enhancement. Plants were exposed to either ambient radiation or to enhancement of UV-B corresponding to 15% (clear sky) depletion of stratospheric ozone for approximately 10 years prior to commencement of this study. Vaccinium myrtillus contained the highest concentration of methanol-extractable UV-B-absorbing compounds, which was elevated in plants exposed to enhanced UV-B. Fluorescence and confocal laser scanning microscopy showed that these compounds were distributed throughout the leaf, and were particularly concentrated in chlorophyll-containing cells. In V. vitis-idaea, most phenolic compounds were cell wall-bound and concentrated in the walls of the epidermis; this pool increased in response to UV-B enhancement. It is suggested that these two plants represent extreme forms of two divergent strategies for UV-B screening, the different responses possibly being related to leaf longevity in the two species. The response of V. uliginosum was intermediate between the other two, with high concentrations of cell wall-bound phenolics in the epidermis but with this pool decreasing, and the methanol-soluble pool tending to increase, after exposure to enhanced UV-B. One explanation for this response is that this plant is deciduous, like V. myrtillus, but has leaves that are structurally similar to those of V. vitis-idaea.