We determined controls on litter decomposition and nutrient release for the widespread native tree Metrosideros polymorpha in 11 sites arrayed on gradients of elevation, precipitation, and substrate age on Hawaiian lava flows. The effects of site characteristics were evaluated using three common substrates (Metrosideros leaf litter from one of the sites, wood dowels, and filter paper) decomposed in each of the sites, and the inherent decomposability of tissue (substrate quality) was evaluated using Metrosideros leaf litter from each of the sites decomposed in a common site. Site characteristics were responsible for most of the variation in rates of decomposition in the range of sites and substrates examined. Common substrates decomposed much more rapidly in warm, low elevation sites; apparent Q10 values, calculated on the basis of variation in mean annual temperature with elevation on individual lava flows, ranged from 4 to 11. Litter decomposed slowly in the dry sites, but leaf litter produced in the dry sites decomposed more than twice as rapidly as litter from wet sites when both were measured in the same site. The higher substrate quality of litter from dry sites could be due to trade—offs among nutrient—use efficiency, water—use efficiency, and carbon gain by water—limited Metrosideros. We used these results to test a revision of the CENTURY soil organic matter model that had been designed to simulate the decomposition of surface litter. Simulations accurately matched the pattern but underestimated the magnitude of among—site differences in the decomposition of common substrates in a range of sites. Analyses of both field and simulation results suggested that the decomposition of Metrosideros leaf litter could be limited by nitrogen availability.

We determined the consequences of systematic changes in nutrient availability during long—term soil development by measuring foliar nutrient concentrations. Sun leaves of the dominant tree Metrosideros polymorpha and of eight other species were sampled in Hawaiian rain forests developed on substrates that were 0.3 ° 103, 2.1 ° 103, 5 ° 103, 20 ° 103, 150 ° 103, 1400 ° 103, and 4100 x 103 yr old. Elevation, annual precipitation, parent material, and dominant species were nearly constant along this gradient. Foliar N and P concentrations in Metrosideros were lowest in the youngest site (0.72% and 0.052% for N and P, respectively), increased to a maximum on 20 ° 103 and 150 ° 103—yr—old substrates (1.45% and 0.108%), and then declined close to the initial concentrations in the oldest site (0.86% and 0.061%); N:P ratios in foliage varied relatively little across the sites. Most other species followed a similar pattern of variation. On a per unit leaf area basis, foliar N and P contents in Metrosideros also peaked on intermediate—aged substrates. Foliar nutrient concentrations in Metrosideros sun leaves were determined across a parallel but wetter substrate age gradient. The pattern of variation was similar on both gradients, but the magnitude of variation was smaller on the wetter sequence of sites. Overall, the pattern of variation in foliar nutrients with substrate age is consistent with conceptual models for the dynamics of soil nutrient availability during long—term soil development, and with measurements of soil properties along this sequence.

The accumulation of total carbon, nitrogen, and phosphorus in soils, available soil nutrients, and foliar nutrients in the native dominant Metrosideros polymorpha were determined across a wide elevational range on 9 lava flows on Mauna Loa, Hawai'i. The flows included a young (<140 y) and an old (>2800 y) áá (rough surface texture) and pāhoehoe (smooth) flow on the wet east and dry northwest side of the mountain. Soil element pools and nutrient availability increased with flow age independent of climate. The dry sites accumulated organic matter and nutrients more slowly than comparable wet sites, but relative nutrient availability to plants (as indicated by soil assays and foliar nutrients) was greater in the dry sites. Accumulation of soil organic matter and nutrients occurred most rapidly in lowerelevation sites on the young flows, but the largest accumulations occurred at higher elevations on old flows. The range of sites sampled represents a complete and largely independent matrix of major factors governing ecosystem structure and function.

Background Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence.Methods ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362.

Cystic adventitial disease (CAD) is a rare vascular disorder, predominantly seen in young healthy men with minimal cardiovascular risk factors. Cystic adventitial disease can affect both arteries and veins. Patients with arterial CAD present with sudden onset or rapidly progressing claudication symptoms, and those with venous CAD present with limb swelling or very rarely deep vein thrombosis. Diagnosis is confirmed with the aid of imaging techniques such as ultrasonography, computed tomography, or magnetic resonance scan. Surgical resection or evacuation of the lesion is usually the preferred approach, with only mixed results reported for percutaneous endovascular techniques.