To test whether the altitudinal distribution of trees is determined by a carbon shortage or an insufficient sugar fraction (sugar:starch ratio) in treeline trees, we studied the status of nonstructural carbohydrates (NSC) and their components (total soluble sugars and starch) in Abies fabri (Mast.) Craib and Picea balfouriana var. hirtella Rehd. et Wils. trees along three elevational gradients, ranging from lower elevations to the alpine treeline, on the eastern edge of the Tibetan Plateau. For comparison, we investigated a low-altitude species (Tsuga yunnanensis (Franch.) Pritz.) which served as a warm-climate reference because it is distributed in closed montane forests below 3100 m a.s.l. in the study area. The carbon status of T. yunnanensis responded to altitude differently from that of the treeline species. At the species level, total NSC was not consistently more abundant in treeline trees than in trees of the same species growing at lower elevations. Thus there was no consistent evidence for carbon limitation of growth in treeline trees. For the three treeline species studied (P. balfouriana and A. fabri in the Kang-Ding Valley and A. fabri in the Mo-Xi Valley), winter NSC concentrations in treeline trees were significantly lower than in lower-elevation trees of the same species, suggesting that, in winter, carbon is limited in treeline trees. However, in no case was there total overwinter depletion of NSC or its components in treeline trees. Treeline and low-altitude species had similar sugar:starch ratios of about three at their upper-elevational limits in April. We conclude that survival and growth of trees at the elevational or latitudinal climate limit depend not only on NSC concentration in perennial tissues, but also on the maintenance of an overwintering sugar:starch ratio greater than three.

No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source-sink ratio of carbon; or (3) a sufficient C-N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were speciesspecific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source-sink relationship.

No abstract

Many studies have tried to explain the physiological mechanisms of the alpine treeline phenomenon, but the debate on the alpine treeline formation remains controversial due to opposite results from different studies. The present study explored the carbon-physiology of an alpine shrub species ( Quercus aquifolioides ) grown at its upper elevational limit compared to lower elevations, to test whether the elevational limit of alpine shrubs (<3 m in height) are determined by carbon limitation or growth limitation. We studied the seasonal variations in non-structural carbohydrate (NSC) and its pool size in Q. aquifolioides grown at 3000 m, 3500 m, and at its elevational limit of 3950 m above sea level (a.s.l.) on Zheduo Mt., SW China. The tissue NSC concentrations along the elevational gradient varied significantly with season, reflecting the season-dependent carbon balance. The NSC levels in tissues were lowest at the beginning of the growing season, indicating that plants used the winter reserve storage for re-growth in the early spring. During the growing season, plants grown at the elevational limit did not show lower NSC concentrations compared to plants at lower elevations, but during the winter season, storage tissues, especially roots, had significantly lower NSC concentrations in plants at the elevational limit compared to lower elevations. The present results suggest the significance of winter reserve in storage tissues, which may determine the winter survival and early-spring re-growth of Q. aquifolioides shrubs at high elevation, leading to the formation of the uppermost distribution limit. This result is consistent with a recent hypothesis for the alpine treeline formation.

Caused by Verticillium spp. pathogens, verticillium wilt is a common detrimental disease damaging yield production of many important crops. Isolation of verticillium wilt resistance genes and their transgenic application is a fundamental way to control this disease. Here we report the cloning and sequence characterization of a potential Verticillium dahliae Kleb. resistance gene (Ve) from Solanum lycopersicoides Dun. (designated as SlVe1). The nucleotide sequence of SlVe1 is 3400 bp with an ORF of 3156 bp encoding a protein precursor of 1051 amino acids (aa). Unlike tomato Ve1, SlVe1 had a short leader sequence of 22 bp. Multiple polyadenylation sites were detected, which may result from alternative cleavages directed by the common polyadenylation signal AATAAA, and nucleotide sequences of the cleavage sites for polyadenylation conform to PyPyA. Sharing high homologies to tomato verticillium wilt disease resistance genes Ve1 and Ve2, SlVe1 encoded a cell-surface glycoprotein with receptor-mediated endocytosis-like signal. The leucine rich (16.51%) putative SlVe1 protein had a calculated molecular weight of 116.97 kDa with an isoelectric point of 5.22. It possessed a hydrophobic N-terminal signal peptide of 23 aa and 28 predicted significant leucine-rich repeats (LRRs) containing 29 potential N-glycosylation sites (18 being significant). A membrane-associated hydrophobic domain resided within the C-terminal, flanked by a neutral/acidic aa rich domain and a neutral/basic aa rich domain. Forty-four predicted phosphorylation sites (28 for S, 5 for T and 11 for Y) distributed in SlVe1, and an endocytosis signal EKWLLW resided in the neutral/basic aa rich C-terminal domain. As compared with Ve1, several clues of variations have been detected in SlVe1 and their possible implications are discussed.