Carbon isotope compositions (δ(13) C) of leaf, wood and holocellulose differ among genotypes of poplar and between previous land uses in a short-rotation biomass plantation.

The efficiency of water use to produce biomass is a key trait in designing sustainable bioenergy-devoted systems. We characterized variations in the carbon isotope composition (δ(13) C) of leaves, current year wood and holocellulose (as proxies for water use efficiency, WUE) among six poplar genotypes in a short-rotation plantation. Values of δ(13) Cwood and δ(13) Cholocellulose were tightly and positively correlated, but the offset varied significantly among genotypes (0.79-1.01‰). Leaf phenology was strongly correlated with δ(13) C, and genotypes with a longer growing season showed a higher WUE. In contrast, traits related to growth and carbon uptake were poorly linked to δ(13) C. Trees growing on former pasture with higher N-availability displayed higher δ(13) C as compared with trees growing on former cropland. The positive relationships between δ(13) Cleaf and leaf N suggested that spatial variations in WUE over the plantation were mainly driven by an N-related effect on photosynthetic capacities. The very coherent genotype ranking obtained with δ(13) C in the different tree compartments has some practical outreach. Because WUE remains largely uncoupled from growth in poplar plantations, there is potential to identify genotypes with satisfactory growth and higher WUE.

Seasonal variations in photosynthesis, intrinsic water-use efficiency and stable isotope composition of poplar leaves in a short-rotation plantation.

Photosynthetic carbon assimilation and transpirational water loss play an important role in the yield and the carbon sequestration potential of bioenergy-devoted cultures of fast-growing trees. For six poplar (Populus) genotypes in a short-rotation plantation, we observed significant seasonal and genotypic variation in photosynthetic parameters, intrinsic water-use efficiency (WUEi) and leaf stable isotope composition (δ13C and δ18O). The poplars maintained high photosynthetic rates (between 17.8 and 26.9 µmol m(-2) s(-1) depending on genotypes) until late in the season, in line with their fast-growth habit. Seasonal fluctuations were mainly explained by variations in soil water availability and by stomatal limitation upon photosynthesis. Stomatal rather than biochemical limitation was confirmed by the constant intrinsic photosynthetic capacity (Vcmax) during the growing season, closely related to leaf nitrogen (N) content. Intrinsic water-use efficiency scaled negatively with carbon isotope discrimination (Δ13Cbl) and positively with the ratio between mesophyll diffusion conductance (gm) and stomatal conductance. The WUEi-Δ13Cbl relationship was partly influenced by gm. There was a trade-off between WUEi and photosynthetic N-use efficiency, but only when soil water availability was limiting. Our results suggest that seasonal fluctuations in relation to soil water availability should be accounted for in future modelling studies assessing the carbon sequestration potential and the water-use efficiency of woody energy crops.

Environmental controls on ozone fluxes in a poplar plantation in Western Europe.

Tropospheric O3 is a strong oxidant that may affect vegetation and human health. Here we report on the O3 fluxes from a poplar plantation in Belgium during one year. Surprisingly, the winter and autumn O3 fluxes were of similar magnitude to ones observed during most of the peak vegetation development. Largest O3 uptakes were recorded at the beginning of the growing season in correspondence to a minimum stomatal uptake. Wind speed was the most important control and explained 44% of the variability in the nighttime O3 fluxes, suggesting that turbulent mixing and the mechanical destruction of O3 played a substantial role in the O3 fluxes. The stomatal O3 uptake accounted for a seasonal average of 59% of the total O3 uptake. Multiple regression and partial correlation analyses showed that net ecosystem exchange was not affected by the stomatal O3 uptake.

Randomized clinical trial of mesh fixation with "double crown" versus "sutures and tackers" in laparoscopic ventral hernia repair.

BACKGROUND: Although laparoscopic intra-peritoneal mesh repair (LVHR) is a well-established treatment option to repair ventral and incisional hernias, no consensus in the literature can be found on the best method of fixation of the mesh to the abdominal wall. METHODS: Between December 2004 and July 2008, 76 patients undergoing a LVHR were randomized between mesh fixation using a double row of spiral tackers (DC) (n = 33) and mesh fixation with transfascial sutures combined with one row of spiral tackers (S&T) (n = 43), in the WoW trial (with or without sutures). Patients were clinically examined and evaluated using a visual analog scale for pain (VAS) in rest and after coughing 4 h post-operatively, after 4 weeks and 3 months after surgery. Primary endpoint of the study was abdominal wall pain, defined as a VAS score of at least 1.0 cm, at 3 months post-operative. Quality of life was quantified with the SF-36 questionnaire preoperatively and after 3 months. Secondary endpoint was the recurrence rate at 24-month follow-up. RESULTS: The DC and S&T group were comparable in age, gender, ASA score, BMI, indication, hernia, and mesh variables. The DC group had a significant shorter operating time compared with the S&T group (74 vs 96 min; p = 0.014) and a significant lower mean VAS score 4 h post-operatively (in rest; p = 0.028/coughing; p = 0.013). At 3 months, there were significant more patients in the S&T group with VAS score ≥1.0 cm (31.4 vs 8.3 %; p = 0.036). Clinical follow-up at 24 months was obtained in 63 patients (82.9 %). The recurrence rate at 24 months was 7.9 % overall (5/63). There were more recurrences in the S&T group (4/36) than in the DC group (1/27), but this difference was not significant (11.1 vs 3.7 %; p = 0.381). CONCLUSION: We found that double-crown fixation of intra-peritoneal mesh during laparoscopic ventral hernia repair was quicker, was less painful immediately post-operative and after 3 months, and did not increase the recurrence rate at 24 months. In hernias at a distance from the bony borders of the abdomen, transfascial sutures can be omitted if a double crown of tackers is placed.

Perioperative outcomes of revisional laparoscopic gastric bypass after failed adjustable gastric banding and after vertical banded gastroplasty: experience with 107 cases and subgroup analysis.

BACKGROUND: A growing number of revision procedures are to be expected in bariatric surgery after failed restrictive procedures such as failed adjustable gastric banding (AGB) or vertical banded gastroplasty (VBG). Conversion to revisional laparoscopic Roux-en-Y gastric bypass (ReLRYGBP) has been advocated as the procedure of choice. METHODS: The results of ReLRYGBP were reviewed in a retrospective chart review. A subgroup analysis compared perioperative results after VBG and after AGB. A second subgroup analysis compared perioperative results of ReLRYGBP immediately after AGB removal and after a delay as a two-step procedure. RESULTS: Between 2003 and 2009, ReLRYGBP was performed for 107 patients. Of these 107 operations, 21 were performed after failed VBG and 86 after failed AGB. The mean body mass index (BMI) was 42 kg/m(2). The causes of failure were mainly insufficient weight loss or reflux disease-related symptoms. During a median follow-up period of 44 months, there was no mortality, and morbidity was 34 %, including late complications. Major early complications occurred in 11 % of the cases (n = 12). Conversions and major early complications occurred significantly more frequently after VBG than after AGB (p < 0.05). In 59 % of the cases (n = 50), ReLRYGBP was performed as a single-stage procedure immediately after removal of AGB and in 41 % of the cases (n = 36) as a delayed two-step procedure. The outcomes did not differ significantly (p > 0.5). CONCLUSIONS: The perioperative outcomes of ReLRYGBP are worse after VBG than after AGB. The ReLRYGBP operation can be performed safely as a one-step procedure after AGB removal.

Fine root biomass and turnover of two fast-growing poplar genotypes in a short-rotation coppice culture.

BACKGROUND AND AIMS: The quantification of root dynamics remains a major challenge in ecological research because root sampling is laborious and prone to error due to unavoidable disturbance of the delicate soil-root interface. The objective of the present study was to quantify the distribution of the biomass and turnover of roots of poplars (Populus) and associated understory vegetation during the second growing season of a high-density short rotation coppice culture. METHODS: Roots were manually picked from soil samples collected with a soil core from narrow (75 cm apart) and wide rows (150 cm apart) of the double-row planting system from two genetically contrasting poplar genotypes. Several methods of estimating root production and turnover were compared. RESULTS: Poplar fine root biomass was higher in the narrow rows than in the wide rows. In spite of genetic differences in above-ground biomass, annual fine root productivity was similar for both genotypes (ca. 44 g DM m-2 year-1). Weed root biomass was equally distributed over the ground surface, and root productivity was more than two times higher compared to poplar fine roots (ca. 109 g DM m-2 year-1). CONCLUSIONS: Early in SRC plantation development, weeds result in significant root competition to the crop tree poplars, but may confer certain ecosystem services such as carbon input to soil and retention of available soil N until the trees fully occupy the site.

Soil CO2 efflux in a bioenergy plantation with fast-growing Populus trees - influence of former land use, inter-row spacing and genotype.

AIMS: In this study we quantified the annual soil CO2 efflux (annual SCE) of a short rotation coppice plantation in its establishment phase. We aimed to examine the effect of former (agricultural) land use type, inter-row spacing and genotype. METHODS: Annual SCE was quantified during the second growth year of the establishment rotation in a large scale poplar plantation in Flanders. Automated chambers were distributed over the two former land use types, the two different inter-row spacings and under two poplar genotypes. Additional measurements of C, N, P, K, Mg, Ca and Na concentrations of the soil, pH, bulk density, fine root biomass, microbial biomass C, soil mineralization rate, distance to trees and tree diameters were performed at the end of the second growth year. RESULTS: Total carbon loss from soil CO2 efflux was valued at 589 g m-2 yr-1. Annual SCE was higher in former pasture as compared to cropland, higher in the narrow than in the wider inter-row spacings, but no effect of genotype was found. CONCLUSIONS: Spatial differences in site characteristics are of great importance for understanding the effect of ecosystem management and land use change on soil respiration processes and need to be taken into account in modeling efforts of the carbon balance.

Importance of crown architecture for leaf area index of different Populus genotypes in a high-density plantation.

Crown architecture is an important determinant of biomass production and yield of any bio-energy plantation since it determines leaf area display and hence light interception. Four Populus genotypes-of different species and hybrids and with contrasting productivity and leaf area-were examined in terms of their branch characteristics in relation to crown architecture during the first and second growing seasons after plantation establishment. The trees were planted at high density (8000 ha(-1)) on two different former land use types, cropland and pasture. We documented significant differences in branch architecture among the genotypes and for the first year among the former land use types. Land use effects only affected factors not related to canopy closure and wood production, and decreased after the first growing season. This suggested that both former land use types were equally suited for the establishment success of a poplar bio-energy plantation. Tree height and branch dimensions-branch diameter and branch length-were the most important determinants of wood production and maximum leaf area index. Despite the secondary importance of the number of sylleptic branches, these branches contributed significantly to the total leaf area in three out of the four studied genotypes. This indicated that enhanced syllepsis accelerates leaf area development and hence carbon assimilation, especially in the early stages of a high-density plantation with poplar.

Insights into ozone deposition patterns from decade-long ozone flux measurements over a mixed temperate forest.

Long-term fluxes of ozone (O(3)) were measured over a mixed temperate forest using the aerodynamic gradient method. The long-term average O(3) flux (F) was -366 ng m(-2) s(-1) for the period 2000-2010, corresponding to an average O(3) concentration of 48 µg m(-3) and a deposition velocity v(d) of 9 mm s(-1). Average nocturnal ozone deposition amounted to -190 ng m(-2) s(-1), which was about one third of the daytime flux. Also during the winter period substantial O(3) deposition was measured. In addition, total O(3) fluxes were found to differ significantly among canopy wetness categories. During the day, highest deposition fluxes were generally measured for a dry canopy, whereas a rain-wetted canopy constituted the best sink at night. Flux partitioning calculations revealed that the stomatal flux (F(s)) contributed 20% to the total F but the F(s)/F fraction was subject to seasonal and diurnal changes. The annual concentration-based index AOT40 (accumulated dose over a threshold of 40 ppb) and the Phytotoxic Ozone Dose (POD(1) or accumulated stomatal flux above a threshold of 1 nmol m(-2) s(-1)) were related in a curvilinear way. The O(3) deposition was found to be largely controlled by non-stomatal sinks, whose strength was enhanced by high friction velocities (u(*)), optimizing the mechanical mixing of O(3) into the canopy and the trunk space. The long-term geometrical mean of the non-stomatal resistance (R(ns)) was 136 s m(-1) but lower R(ns) values were encountered during the winter half-year due to higher u(*). The R(ns) was also subject to a marked diurnal variability, with low R(ns) in the morning hours, when turbulence took off. We speculate that non-stomatal deposition was largely driven by scavenging of ozone by biogenic volatile organic compounds (BVOCs) and especially NO emitted from the crown or the forest floor.

A comparison of two stomatal conductance models for ozone flux modelling using data from two Brassica species.

In this study we tested and compared a multiplicative stomatal model and a coupled semi-empirical stomatal-photosynthesis model in their ability to predict stomatal conductance to ozone (gst) using leaf-level data from oilseed rape (Brassica napus L.) and broccoli (Brassica oleracea L. var. italica Plenck). For oilseed rape, the multiplicative model and the coupled model were able to explain 72% and 73% of the observed gst variance, respectively. For broccoli, the models were able to explain 53% and 51% of the observed gst variance, respectively. These results support the coupled semi-empirical stomatal-photosynthesis model as a valid alternative to the multiplicative stomatal model for O3 flux modelling, in terms of predictive performance.

Soil [N] modulates soil C cycling in CO2-fumigated tree stands: a meta-analysis.

Under elevated atmospheric CO(2) concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO(2) effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that: (1) elevated atmospheric CO(2) stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO(2) induces a C allocation shift towards below-ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO(2). Soil N concentration strongly interacted with CO(2) fumigation: the effect of elevated CO(2) on fine root biomass and -production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO(2) are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.

Enhanced ozone strongly reduces carbon sink strength of adult beech (Fagus sylvatica)--resume from the free-air fumigation study at Kranzberg Forest.

Ground-level ozone (O(3)) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O(3)-fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest (Germany). A novel canopy O(3) exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O(3) levels. Elevated O(3) significantly weakened the C sink strength of the tree-soil system as evidenced by lowered photosynthesis and 44% reduction in whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O(3) responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O(3) can substantially mitigate the C sequestration of forests in view of climate change.

Response and potential of agroforestry crops under global change.

The use of agroforestry crops is a promising tool for reducing atmospheric carbon dioxide concentration through fossil fuel substitution. In particular, plantations characterised by high yields such as short rotation forestry (SRF) are becoming popular worldwide for biomass production and their role acknowledged in the Kyoto Protocol. While their contribution to climate change mitigation is being investigated, the impact of climate change itself on growth and productivity of these plantations needs particular attention, since their management might need to be modified accordingly. Besides the benefits deriving from the establishment of millions of hectares of these plantations, there is a risk of increased release into the atmosphere of volatile organic compounds (VOC) emitted in large amounts by most of the species commonly used. These hydrocarbons are known to play a crucial role in tropospheric ozone formation. This might represent a negative feedback, especially in regions already characterized by elevated ozone level.

Multicentric observational cohort study evaluating a composite mesh with incorporated oxidized regenerated cellulose in laparoscopic ventral hernia repair.

BACKGROUND: A variety of newly developed mesh products have recently become available to use inside the peritoneal cavity. This analysis reports the first clinical data evaluating the experience with the use of Proceed mesh in laparoscopic ventral hernia repair. PATIENTS AND METHODS: During a 6-month period, 114 adult patients underwent a laparoscopic ventral hernia repair using an intra-abdominal placement of a Proceed mesh. The operative procedure was stratified for all centers. Perioperatively, different parameters were evaluated considering the conversion rate to open procedure, complications such as seroma and hematoma, bowel lesions, urinary retention, acute, and chronic pain, mesh infection, and recurrences. RESULTS: The mean age of the patients was 45 years (range 19-84 years). There were no conversions to open repair and no mortality. Complications included 12 seromas/hematomas (four aspirated), chronic discomfort in two patients, and urinary retention in one patient. There have been four recurrences (3.5%), occurring 3, 4, 4, and 15 months after surgery, respectively. The mean follow-up period was 27 months (range 12-38 months). There have been no documented infections of the mesh. CONCLUSIONS: This multicentric study documents a favorable experience using large-pore mesh in laparoscopic ventral hernia repair. There were no major complications related to the mesh. Technical advantages considering mesh handling and long-term advantages considering chronic pain might be of interest with the use of this lightweight mesh for minimally invasive ventral hernia repair.

Bidirectional ammonia exchange above a mixed coniferous forest.

Two canopy compensation point models were used to study the bidirectional exchange of ammonia over a mixed coniferous forest subjected to high nitrogen deposition. The models were tested for 16 time series, average fluxes of which ranged between -270 and +1 ng m(-2)s(-1). The static model consisted of a bidirectional stomatal flux and a unidirectional cuticular flux component. The dynamic model also allowed for desorption of ammonia from the leaf surface and took into account ammonia fluxes from precedent periods. The apoplastic ammonium/hydrogen ion ratio (Gamma), which was derived to estimate the stomatal compensation point (chi(s)), amounted to 3300 in spring and 1375 during the summer/autumn. Empirical descriptions for cuticular resistances (R(w)) in the static model, developed as a function of micrometeorological conditions and codeposition effects, failed to reproduce the measured fluxes. A better match with measurements was obtained using the dynamic model, which succeeded in simulating net-emission during the daytime.

Plasticity in hydraulic architecture of Scots pine across Eurasia.

Widespread tree species must show physiological and structural plasticity to deal with contrasting water balance conditions. To investigate these plasticity mechanisms, a meta-analysis of Pinus sylvestris L. sap flow and its response to environmental variables was conducted using datasets from across its whole geographical range. For each site, a Jarvis-type, multiplicative model was used to fit the relationship between sap flow and photosynthetically active radiation, vapour pressure deficit (D) and soil moisture deficit (SMD); and a logarithmic function was used to characterize the response of stomatal conductance (G(s)) to D. The fitted parameters of those models were regressed against climatic variables to study the acclimation of Scots pine to dry/warm conditions. The absolute value of sap flow and its sensitivity to D and SMD increased with the average summer evaporative demand. However, relative sensitivity of G(s) to D (m/G (s,ref), where m is the slope and G(s,ref) is reference G(s) at D = 1 kPa) did not increase with evaporative demand across populations, and transpiration per unit leaf area at a given D increased accordingly in drier/warmer climates. This physiological plasticity was linked to the previously reported climate- and size-related structural acclimation of leaf to sapwood area ratios. G (s,ref), and its absolute sensitivity to D(m), tended to decrease with age/height of the trees as previously reported for other pine species. It is unclear why Scots pines have higher transpiration rates at drier/warmer sites, at the expense of lower water-use efficiency. In any case, our results suggest that these structural adjustments may not be enough to prevent lower xylem tensions at the driest sites.