The limits to tree height

Trees grow tall where resources are abundant, stresses are minor, and competition for light places a premium on height growth. The height to which trees can grow and the biophysical determinants of maximum height are poorly understood. Some models predict heights of up to 120 m in the absence of mechanical damage, but there are historical accounts of taller trees. Current hypotheses of height limitation focus on increasing water transport constraints in taller trees and the resulting reductions in leaf photosynthesis. We studied redwoods (Sequoia sempervirens), including the tallest known tree on Earth (112.7 m), in wet temperate forests of northern California. Our regression analyses of height gradients in leaf functional characteristics estimate a maximum tree height of 122-130 m barring mechanical damage, similar to the tallest recorded trees of the past. As trees grow taller, increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth, even with ample soil moisture.     

Fisheries: mislabelling of a depleted reef fish

Any fish species that appears to be readily available in the marketplace will create an impression among the public that there is a plentiful supply of that fish in the sea, but this may belie the true state of the fisheries' stock. Here we use molecular genetic analysis to show that some three-quarters of the fish sold in the United States as 'red snapper'--the US Food and Drug Administration's legally designated common name for Lutjanus campechanus--belong to another species. Mislabelling to this extent not only defrauds consumers but could also adversely affect estimates of stock size if it influences the reporting of catch data that are used in fisheries management.     

Long-lasting sensitization to a given colour after visual search

Visual attention enables an observer to select specific visual information for processing. In an ambiguous motion task in which a coloured grating can be perceived as moving in either of two opposite directions depending on the relative salience of two colours in the display, attending to one of the colours influences the direction in which the grating appears to move. Here, we use this secondary effect of attention in a motion task to measure the effect of attending to a specific colour in a search task. Observers performed a search task in which they searched for a target letter in a 4 x 4 coloured matrix. Each of the 16 squares within a matrix was assigned one of four colours, and observers knew that the target letter would appear on only one of these colours throughout the experiment. Observers performed the ambiguous motion task before and after the search task. Attending to a particular colour for a brief period in the search task profoundly influenced the perceived direction of motion. This effect lasted for up to one month and in some cases had to be reversed by practising searches for the complementary colour, indicating a much longer-persisting effect of attention than has been observed previously.     

A functional variant of lymphoid tyrosine phosphatase is associated with type I diabetes

We report that a single-nucleotide polymorphism (SNP) in the gene (PTPN22) encoding the lymphoid protein tyrosine phosphatase (LYP), a suppressor of T-cell activation, is associated with type 1 diabetes mellitus (T1D). The variants encoded by the two alleles, 1858C and 1858T, differ in a crucial amino acid residue involved in association of LYP with the negative regulatory kinase Csk. Unlike the variant encoded by the more common allele 1858C, the variant associated with T1D does not bind Csk.     

欧洲联盟步入新世纪时所面临的问题

欧洲一体化运动兴起以来，欧洲联盟面临一第列严重的问题，其中台刀约的修订，欧共体成员国扩大而引起的矛盾，与高生活水平同时存在的高失业率等。由此说明，欧盟的组织结构已不适应新形势的需要，需对其进行彻底“检修”。