Basin-wide variation in tree hydraulic safety margins predicts the carbon balance of Amazon forests

Tropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, [Formula: see text]50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3-5, little is known about how these vary across Earth's largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters [Formula: see text]50 and HSM50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both [Formula: see text]50 and HSM50 influence the biogeographical distribution of Amazon tree species. However, HSM50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50 are gaining more biomass than are low HSM50 forests. We propose that this may be associated with a growth-mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50 in the Amazon6,7, with strong implications for the Amazon carbon sink.

Comparison of Healon and Viscoat in cataract extraction and intraocular lens implantation

Sixty patients were randomly assigned to Healon (20 patients) or Viscoat (40 patients) treatment during extracapsular cataract extraction and intraocular lens implantation surgery. The 40 patients in the Viscoat group were randomly subdivided into two groups. In one group (20 patients), Viscoat was irrigated/aspirated from the eye at the close of surgery, while in the second group of 20 patients, Viscoat was left in the eye. In all Healon cases, the viscoelastic substance was removed from the eye at the end of the surgical procedure. Compared with Viscoat, Healon better facilitated the surgical procedure and appeared to be a more advantageous viscoelastic preparation. Viscoat, in many cases, caused rises in intraocular pressure in the immediate postoperative period when either removed or left in the eye at the close of surgery.

Three-dimensional structure of the murine muscle-tendon junction

At the muscle-tendon junction of skeletal muscle fibers the structural interface between muscle cell and connective tissue is amplified by tapering, by indentation, and by surface folding. The precise form taken by the surface folds has been unknown due to a lack of studies on the three-dimensional geometry of the muscle-tendon junction. Analysis of this region by scanning electron microscopy, using conventional preparative techniques, is uninformative because the muscle surface is covered by connective tissue. Removal of the connective tissue from individual murine muscle fibers by incubation of fixed fibers in hot HCl, followed in some instances by treatment with collagenase, permits SEM analysis of the uncovered fiber ends. The muscle fiber end is characterized by surface specializations in the form of anastamotic cylindrical folds. Transmission electron micrographs of cross sections and of serial longitudinal sections of muscle fiber ends confirm that the SEM observations are correct.