Climate change has caused advances in spring phases of many plant species. Theoretically, however, strong warming in winter could slow the fulfillment of chilling requirements, which may delay spring phenology. This phenomenon should be particularly pronounced in regions that are experiencing rapid temperature increases and are characterized by highly temperature-responsive vegetation. To test this hypothesis, we used the Normalized Difference Vegetation Index ratio method to determine the beginning, end, and length of the growing season of meadow and steppe vegetation of the Tibetan Plateau in Western China between 1982 and 2006. We then correlated observed phenological dates with monthly temperatures for the entire period on record. For both vegetation types, spring phenology initially advanced, but started retreating in the mid-1990s in spite of continued warming. Together with an advancing end of the growing season for steppe vegetation, this led to a shortening of the growing period. Partial least-squares regression indicated that temperatures in both winter and spring had strong effects on spring phenology. Although warm springs led to an advance of the growing season, warm conditions in winter caused a delay of the spring phases. This delay appeared to be related to later fulfillment of chilling requirements. Because most plants from temperate and cold climates experience a period of dormancy in winter, it seems likely that similar effects occur in other environments. Continued warming may strengthen this effect and attenuate or even reverse the advancing trend in spring phenology that has dominated climate-change responses of plants thus far. C limate change has influenced the timing of developmental stages of most plants of the temperate and cold regions (1-9). Many studies have provided evidence that increasing temperatures have led to progressive advances in spring phases. In a study that compared more than 125,000 observational time series of plant and animal phenology between 1971 and 2000, Menzel et al. found that 78% of species showed advanced phenology (significant advances for 22% of all time series) (3). An analysis of observations of the first flowering date of 385 plant species in England by Fitter and Fitter, showed three quarters of species flowering earlier in the decade between 1991 and 2000 than in the previous four decades (10). A recent comprehensive meta-analysis of several studies on phenology trends (5) supports the impression that most species show advanced spring phenology. However, all these studies contain a sizeable proportion of species that do not conform to this pattern. Twenty-two percent of species in Menzel et al.'s study (3) and 24% of species in Fitter and Fitter's article (10) showed trends toward later spring phenology. In both studies, this delay was significant for 3% of species. Because temperatures clearly increased over time in both studies, the spectrum of spring phenology trends suggests that plant responses to warming are not linear and differ among species.Th...

The capacity to fix nitrogen is widely distributed in phyla of Bacteria and Archaea but has long been considered to be absent from the Pseudomonas genus. We report here the complete genome sequencing of nitrogen-fixing root-associated Pseudomonas stutzeri A1501. The genome consists of a single circular chromosome with 4,567,418 bp. Comparative genomics revealed that, among 4,146 protein-encoding genes, 1,977 have orthologs in each of the five other Pseudomonas representative species sequenced to date. The genome contains genes involved in broad utilization of carbon sources, nitrogen fixation, denitrification, degradation of aromatic compounds, biosynthesis of polyhydroxybutyrate, multiple pathways of protection against environmental stress, and other functions that presumably give A1501 an advantage in root colonization. Genetic information on synthesis, maturation, and functioning of nitrogenase is clustered in a 49-kb island, suggesting that this property was acquired by lateral gene transfer. New genes required for the nitrogen fixation process have been identified within the nif island. The genome sequence offers the genetic basis for further study of the evolution of the nitrogen fixation property and identification of rhizosphere competence traits required in the interaction with host plants; moreover, it opens up new perspectives for wider application of root-associated diazotrophs in sustainable agriculture.genome sequencing ͉ root-associated diazotroph