It has long been observed that leaf nitrogen concentrations decline with depth in closed canopies in a number of plant communities. This phenomenon is generally believed to be related to a changing radiation environment and it has been suggested by some researchers that plants allocate nitrogen in order to optimize total whole canopy photosynthesis. Although optimization theory has been successfully utilized to describe a variety of physiological and ecological phenomena, it has some shortcomings that are subject to criticism (e.g., time constraints, oversimplifications, lack of insights, etc.). In this paper we present an alternative to the optimization theory of plant canopy nitrogen distribution, which we term coordination theory. We hypothesize that plants allocate nitrogen to maintain a balance between two processes, each of which is dependent on leaf nitrogen content and each of which potentially limits photosynthesis. These two processes are defined as W, the Rubiscolimited rate of carboxylation, and W, the electron transport-limited rate of carboxylation. We suggest that plants allocate nitrogen differentially to, leaves in different canopy layers in such a way that W and W remain roughly balanced. In this scheme, the driving force for the allocation of nitrogen within a canopy is the difference between the leaf nitrogen content that is required to bring W and W into balance and the current nitrogen content. We show that the daily carbon assimilation of a canopy with a nitrogen distribution resulting from this internal coordination of W and W is very similar to that obtained using optimization theory.

Due to its excellent biological and mechanical properties, silk fibroin has been intensively explored for tissue engineering and regenerative medicine applications. However, lack of translational evidence has hampered its clinical application for tissue repair. Here a silk fibroin film is developed and its translational potential is investigated for skin repair by performing comprehensive preclinical and clinical studies to fully evaluate its safety and effectiveness. The silk fibroin film fabricated using all green chemistry approaches demonstrates remarkable characteristics, including transmittance, fluid handling capacity, moisture vapor permeability, waterproofness, bacterial barrier properties, and biocompatibility. In vivo rabbit full-thickness skin defect study shows that the silk fibroin film effectively reduces the average wound healing time with better skin regeneration compared with the commercial wound dressings. Subsequent assessment in porcine model confirms its long-term safety and effectiveness for full-thickness skin defects. Finally, a randomized single-blind parallel controlled clinical trial with 71 patients shows that the silk fibroin film significantly reduces the time to wound healing and incidence of adverse events compared to commercial dressing. Therefore, the study provides systematic preclinical and clinical evidence that the silk fibroin film promotes wound healing thereby establishing a foundation towards its application for skin repair and regeneration in the clinic.

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ECMO provides a good temporary cardiopulmonary support in patients with postcardiotomy shock. The preoperative risk factors of failure to withdraw ECMO are poor left-ventricular ejection fraction, systolic blood pressure <90 mmHg and refractory severe metabolic acidosis. The peri-ECMO predictors of mortality include low serum albumin level, low platelet count, low oxygen pressure of the venous tube of the ECMO and poor cardiac systolic function.