Plant-plant interactions, environmental gradients and plant diversity: A global synthesis of community-level studies

Previous syntheses on the effects of environmental conditions on the outcome of plant-plant interactions summarize results from pairwise studies. However, the upscaling to the community-level of such studies is problematic because of the existence of multiple species assemblages and species-specific responses to both the environmental conditions and the presence of neighbors. We conducted the first global synthesis of community-level studies from harsh environments, which included data from 71 alpine and 137 dryland communities to: (i) test how important are facilitative interactions as a driver of community structure, (ii) evaluate whether we can predict the frequency of positive plant-plant interactions across differing environmental conditions and habitats, and (iii) assess whether thresholds in the response of plant-plant interactions to environmental gradients exists between ``moderate'' and ``extreme'' environments. We also used those community-level studies performed across gradients of at least three points to evaluate how the average environmental conditions, the length of the gradient studied, and the number of points sampled across such gradient affect the form and strength of the facilitation-environmental conditions relationship. Over 25% of the species present were more spatially associated to nurse plants than expected by chance in both alpine and chyland areas, illustrating the high importance of positive plant-plant interactions for the maintenance of plant diversity in these environments. Facilitative interactions were more frequent, and more related to environmental conditions, in alpine than in dryland areas, perhaps because drylands are generally characterized by a larger variety of environmental stress factors and plant functional traits. The frequency of facilitative interactions in alpine communities peaked at 1000 mm of annual rainfall, and globally decreased with elevation. The frequency of positive interactions in dtyland communities decreased globally with water scarcity or temperature annual range. Positive facilitation-drought stress relationships are more likely in shorter regional gradients, but these relationships are obscured in regions with a greater species turnover or with complex environmental gradients. By showing the different climatic drivers and behaviors of plant-plant interactions in dryland and alpine areas, our results will improve predictions regarding the effect of facilitation on the assembly of plant communities and their response to changes in environmental conditions.

Only Neochordoplasty Achieves Physiological Trans-valvular Pressure Gradients After Repair Of Acute Posterior Leaflet Prolapse In Porcine Mitral Valves

Objective: Minimizing resection and preserving leaflet tissue has been previously shown to be beneficial for mitral valve function and leaflet kinematics after repair of acute posterior leaflet prolapse in porcine valves. We examined the effects of different additional methods of mitral valve repair (neochordoplasty, ring annuloplasty, edge-to-edge repair and triangular resection) on hemodynamics at different heart rates in an experimental model. Methods: Severe acute P2 prolapse was created in eight porcine mitral valves by resecting the posterior marginal chordae. Valve hemodynamics was quantified under pulsatile conditions in an in vitro heart simulator before and after surgical manipulation. Mitral regurgitation was corrected using four different methods of repair on the same valve: neochordoplasty with expanded polytetrafluoroethylene sutures alone and together with ring annuloplasty, edge-to-edge repair and triangular resection, both with non-restrictive annuloplasty. Residual mitral valve leak, trans-valvular pressure gradients, flow and cardiac output were measured at 60 and 80 beats/min. A validated statistical linear mixed model was used to analyze the effect of treatment. The p values were calculated using a two-sided Wald test. Results: Only neochordoplasty with expanded polytetrafluoroethylene sutures but without ring annuloplasty achieved similar hemodynamics compared to those of the native mitral valve (p range 0.071-0.901). Trans-valvular diastolic pressure gradients were within a physiologic range but significantly higher than those of the native valve following neochordoplasty with ring annuloplasty (p=0.000), triangular resection (p=0.000) and edge-to-edge repair (p=0.000). Neochordoplasty alone was significantly better in terms of hemodynamic than neochordoplasty with a ring annuloplasty (p=0.000). These values were stable regardless of heart rate or ring size. Conclusions: Neochordoplasty without ring annuloplasty is the only repair technique able to achieve almost native physiological hemodynamics after correction of leaflet prolapse in a porcine experimental model of acute chordal rupture.

Can urethrolysis resolve outlet obstruction related symptoms after Burch colposuspension for stress urinary incontinence?

OBJECTIVE Bladder outlet obstruction may occur after any incontinence surgery and may present as OAB, hesitancy and or the feeling of incomplete emptying. Aim of this study was to analyze the clinical and urodynamical outcome after urethrolysis in patients presenting with various clinical symptoms after Burch colposuspension for stress urinary incontinence. STUDY DESIGN Between January 2005 and December 2014, all patients who presented with symptoms and with bladder outlet obstruction were included. All patients had undergone Burch or Cowan colposuspension for stress urinary incontinence previously. Primary endpoint was the visual analogue scale (VAS) as measurement of patient perceived disease impact. Secondary endpoints were the various domains of the King's Health Questionnaire, urodynamic parameters as detrusor pressure at maximum flow, residual urine and sonographic bladder wall thickness before and six months after intervention. RESULTS Seventy-two female patients were included in this study whereof 42 suffered from urgency and urge incontinence, 20 from hesitancy and/or slow stream, seven from residual urine of more than 100ml and three from a combination of urgency and residual urine. VAS improved significantly (p<0.0001). Quality of life as determined by the King's Health Questionnaire improved for the domains general health, role limitations, emotions, physical limitations, personal limitations and incontinence impact significantly. Micturition pressure dropped significantly from 43cmH2O (95% CI 19-59cmH2O) to 18cmH2O (95% CI 16-23.5 H2O). Residual urine changed from 110ml (range 20-380ml) to 32ml (20-115ml). Bladder wall thickness decreased from 7mm (95% CI 6.235-7.152) to 5mm (95% CI 5.037-5.607; p<0.01). CONCLUSION Urethrolysis may resolve patients' symptoms and lower micturition pressure but irritative symptoms may persist.