Convergence in phosphorus constraints to photosynthesis in forests around the world.

Tropical forests take up more carbon (C) from the atmosphere per annum by photosynthesis than any other type of vegetation. Phosphorus (P) limitations to C uptake are paramount for tropical and subtropical forests around the globe. Yet the generality of photosynthesis-P relationships underlying these limitations are in question, and hence are not represented well in terrestrial biosphere models. Here we demonstrate the dependence of photosynthesis and underlying processes on both leaf N and P concentrations. The regulation of photosynthetic capacity by P was similar across four continents. Implementing P constraints in the ORCHIDEE-CNP model, gross photosynthesis was reduced by 36% across the tropics and subtropics relative to traditional N constraints and unlimiting leaf P. Our results provide a quantitative relationship for the P dependence for photosynthesis for the front-end of global terrestrial C models that is consistent with canopy leaf measurements.

Chemical composition of desert willow (Salix psammophila) grown in the Kubuqi Desert, Inner Mongolia, China: bark extracts associated with environmental adaptability.

Bark of desert willow (Salix psammophila, Spsa) grown in Inner Mongolia was successively extracted with n-hexane, diethyl ether, acetone, methanol, and hot water to examine chemical components associated with its environmental adaptability to desert conditions. The yield of n-hexane extract (5.0% based on dry bark), mainly composed of wax, was higher than those of acetone and methanol extracts (3.7% and 4.2%, respectively), whereas the yields of n-hexane extract (1.4%) from willow bark grown in humid areas were much lower than those of acetone (17.4% and 19.9%) and methanol (12.5% and 14.0%) extracts. Unlike other willow bark samples, Spsa bark contained a certain amount of sugar alcohols. In particular, we identified arabinitol (0.21%), which has not previously been reported as a major component of extracts of willow bark. The high content of wax and sugar alcohol would be associated with the ability of Spsa to survive in desert conditions. Accumulation of wax on the outer bark surface would reduce water loss, while sugar alcohols might improve freezing tolerance.