Small-scale species richness and its spatial variation in an alpine meadow on the Qinghai-Tibet Plateau

We investigated how the high small-scale species richness of an alpine meadow on the Qinghai-Tibet Plateau, China, is maintained. This area is characterized by strong wind and severe cold during long winters. In winter, most livestock is grazed on dead leaves in small pastures near farmers' residences, whereas in the short summer, livestock is grazed in mountainous areas far from farmers' residences. The number of plant species and the aboveground biomass were surveyed for three adjacent pastures differing in grazing management: a late-winter grazing pasture grazed moderately from 1 February to 30 April, an early-winter grazing pasture grazed lightly from 20 September to late October, and a whole-year grazing pasture grazed intensively throughout the entire year. In each pasture, we harvested the aboveground biomass from 80 or 100 quadrats of 0.01 m(2) along a transect and classified the contents by species. We observed 15.5-19.7 species per 0.01 m(2), which is high richness per 0.01 m(2) on a worldwide scale. The species richness in the two winter grazing pastures was higher than that in the whole-year grazing pasture. The spatial variation in species richness and species composition in the two winter grazing pastures in which species richness was high was greater than that in the whole-year grazing pasture in which species richness was lower. Most of the leaves that are preserved on the winter grazing pastures during summer are blown away by strong winds during winter, and the remaining leaves are completely exhausted in winter by livestock grazing. A pasture with a high richess is accompanied by a high spatial variation in species richness and species composition. There is a high possibility that the characteristic of spatial variation is also caused by traditional grazing practices in this area.

Genetic variation in the endangered Anisodus tanguticus (Solanaceae), an alpine perennial endemic to the Qinghai-Tibetan Plateau

We used random amplified polymorphic DNA markers (RAPDs) to assess genetic variation between- and within-populations of Anisodus tanguticus (Solanaceae), an endangered perennial endemic to the Qinghai-Tibetan Plateau with important medicinal value. We recorded a total of 92 amplified bands, using 12 RAPD primers, 76 of which (P = 82.61%) were polymorphic, and calculated values of H-t and H-sp of 0.3015 and 0.4459, respectively, suggesting a remarkably high rate of genetic variation at the species level. The average within-population diversity also appeared to be high, with P, H-e and H-pop values of 55.11%, 0.1948 and 0.2918, respectively. Analyses of molecular variance (AMOVA) showed that among- and between-population genetic variation accounted for 67.02% and 32.98% of the total genetic variation, respectively. In addition, Nei's coefficient of differentiation (G(ST)) was found to be high (0.35), confirming the relatively high level of genetic differentiation among the populations. These differentiation coefficients are higher than mean corresponding coefficients for outbreeding species, but lower than reported coefficients for some rare species from this region. The genetic structure of A. tanguticus has probably been shaped by its breeding attributes, biogeographic history and human impact due to collection for medicinal purposes. The observed genetic variations suggest that as many populations as possible should be considered in any planned in situ or ex situ conservation programs for this species.

Seasonal and interannual variation in water vapor and energy exchange over a typical steppe in Inner Mongolia, China

In this study, we conducted eddy covariance (EC) measurements of water vapor exchange over a typical steppe in a semi-arid area of the Inner Mongolia Plateau, China. Measurement sites were located within a 25-year-old enclosure with a relatively low leaf area index (similar to 1. 5 m(2) m(-2)) and dominated by Leymus chinensis. Energy balance closure was (H + LE) = 17.09 + 0.69 x (Rn - G) (W/m(2); r(2) = 0.95, n = 6596). Precipitation during the two growing seasons of the study period was similar to the long-term average. The peak evapotranspiration in 2004 was 4 mm d(-1), and 3.5 mm d(-1) in 2003. The maximum latent heat flux was higher than the sensible heat flux, and the sensible heat flux dominated the energy budget at midday during the entire growing season in 2003; latent heat flux was the main consumption component for net radiation during the 2004 growing season. During periods of frozen soil in 2003 and 2004, the sensible heat flux was the primary consumption component for net radiation. The soil heat flux component was similar in 2003 and 2004. The decoupling coefficient (between 0.5 and 0.1) indicates that evapotranspiration was strongly controlled by saturation water vapor pressure deficit (VPD) in this grassland. The results of this research suggest that energy exchange and evapotranspiration were controlled by the phenology of the vegetation and soil water content. In addition, the amount and frequency of rainfall significantly affect energy exchange and evapotranspiration upon the Inner Mongolia plateau. (c) 2007 Published by Elsevier B.V.

Genetic variation and phylogeographic history of Picea likiangensis revealed by RAPD markers

Repeated cycles of retreat and recolonization during the Quaternary ice ages are thought to have greatly influenced current species distributions and their genetic diversity. It remains unclear how this climatic oscillation has affected the distribution of genetic diversity between populations of wind-pollinated conifers in the Qinghai-Tibetan region. In this study, we investigated the within-species genetic diversity and phylogenetic relationships of Picea likiangensis, a dominant forest species in this region using polymorphic DNA (RAPD) markers. Our results suggest that this species has high overall genetic diversity, with 85.42% of loci being polymorphic and an average expected heterozygosity (H (E)) of 0.239. However, there were relatively low levels of polymorphism at population levels and the differences between populations were not significant, with percentages of polymorphic bands (PPB) ranging from 46.88 to 69.76%, Nei's gene diversity (H (E)) from 0.179 to 0.289 and Shannon's indices (Hpop) from 0.267 to 0.421. In accordance with our proposed hypothesis, a high level of genetic differentiation among populations was detected based on Nei's genetic diversity (G (ST) = 0.256) and AMOVA analysis (Phi (st) = 0.236). Gene flow between populations was found to be limited (Nm = 1.4532) and far lower than reported for other conifer species with wide distribution ranges from other regions. No clusters corresponding to three morphological varieties found in the south, north and west, respectively, were detected in either UPGMA or PCO analyses. Our results suggest that this species may have had different refugia during the glacial stages in the southern region and that the northern variety may have multiple origins from these different refugia.

Patterns of genetic variation in Swertia przewalskii, an endangered endemic species of the Qinghai-Tibet Plateau

Swertia przewalskii Pissjauk. (Gentianaceae) is a critically endangered and endemic plant of the Qinghai-Tibet Plateau in China. RAPD and ISSR analyses were carried out on a total of 63 individuals to assess the extent of genetic variation in the remaining three populations. Percentage of polymorphic bands was 94% (156 bands) for RAPD and 96% (222 bands) for ISSR. A pairwise distance measure calculated from the RAPD and ISSR data was used as input for analysis of molecular variance (AMOVA). AMOVA indicated that a high proportion of the total genetic variation (52% for RAPD and 56% for ISSR) was found among populations; pairwise Phi(ST) comparisons showed that the three populations examined were significantly different (p < 0.001). Significant genetic differentiation was found based on different measures (AMOVA and Hickory theta(B)) in S. przewalskii (0.52 on RAPD and 0.56 on ISSR; 0.46 on RAPD and 0.45 on ISSR). The differentiation of the populations corresponded to low average gene flow (0.28 based on RAPD and 0.31 based on ISSR), whereas genetic distance-based clustering and coalescent-based assignment analyses revealed significant genetic isolation among populations. Our results indicate that genetic diversity is independent of population size. We conclude that although sexual reproduction and gene flow between populations of S. przewalskii are very limited, they have preserved high levels of genetic diversity. The main factors responsible for the high level of difference among populations are the isolation and recent fragmentation under human disturbance.

Mitochondrial cytochrome b sequence variation and phylogenetics of the highly specialized schizothoracine fishes (Teleostei : Cyprinidae) in the Qinghai-Tibet Plateau

The complete 1140 bp mitochondial cytochrome b sequences were obtained from 39 individuals representing five species of all four genera of highly specialized schizothoracine fishes distributed in the Qinghai-Tibet plateau. Sequence variation of the cytochrome b gene was surveyed among the 39 individuals as well as three primitive schizothoracines and one outgroup. Phylogenetic analysis suggested that the group assignment based on 1140 bp of the cytochrome b sequence is obviously; different from previous assignments, and the highly specialized schizothoracine fishes (Schizopygopsis pylzovi, Gymnocypris przewalskii, G. eckloni, Chuanchia lablosa, and Platypharodon extremus) form a monophyletic group that is sister to the clade formed by the primitive schizothoracine fishes (Schizothorax prenanti, S. pseudaksaiensis, and S. argentatus). The haplotypes of Schizopygopsis pylzovi and G. przewalskii were paraphyletic based on cytochrome b data, which most likely reflected incomplete sorting of mitochondrial DNA lineages. The diploid chromosome numbers of Schizofhoracinae were considered in phylogenetic analysis and provided a clear pattern of relationships. Molecular dating estimated for highly specialized schizothoracine fishes suggested that the highly specialized schizothoracine fishes diverged in the late Miocene Pliocene to Pleistocene (4.5x10(4)-4.05x10(6) Years BP). The relationship between the cladogenesis of highly specialized schizothoracine fishes and geographical events of the Qinghai-Tibet plateau is discussed.

Geographic variation in the leaf essential oils of Juniperus sabina L. and J-sablina var. arenaria (E.H. Wilson) Farjon

The composition of the leaf oils from seven populations of J. sabina L., one population of Juniperus sabina var. arenaria (E. H. Wilson) Farjon were examined for their geographic variation. In addition, the leaf oils of J. chinensis L. and J. davurica Pall. were compared to J. sabina. Juniperus sabina var. arenarla, the sand loving juniper, oil was found to be very similar to that of J. davurica, Mongolia, and J. sabina, on sand dunes in Mongolia. This suggests that J. sabina var. arenaria might be conspecific with J. davurica. Farjon's move (2001) of J. sabina var. arenaria out of J. chinensis is supported. Considerable differentiation was found in populations of J. sabina from the Iberian peninsula. Cedrol, citronellol, safrole, trans-sabinyl acetate, terpinen-4-ol and beta-thujone were found to be polymorphic in several populations.

Diurnal, seasonal and annual variation in net ecosystem CO2 exchange of an alpine shrubland on Qinghai-Tibetan plateau

Thus far, grassland ecosystem research has mainly been focused on low-lying grassland areas, whereas research on high-altitude grassland areas, especially on the carbon budget of remote areas like the Qinghai-Tibetan plateau is insufficient. To address this issue, flux of CO2 were measured over an alpine shrubland ecosystem (37 degrees 36'N, 101 degrees 18'E; 325 above sea level [a. s. l.]) on the Qinghai-Tibetan Plateau, China, for 2 years (2003 and 2004) with the eddy covariance method. The vegetation is dominated by formation Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. To interpret the biotic and abiotic factors that modulate CO2 flux over the course of a year we decomposed net ecosystem CO2 exchange (NEE) into its constituent components, and ecosystem respiration (R-eco). Results showed that seasonal trends of annual total biomass and NEE followed closely the change in leaf area index. Integrated NEE were -58.5 and -75.5 g C m(-2), respectively, for the 2003 and 2004 years. Carbon uptake was mainly attributed from June, July, August, and September of the growing season. In July, NEE reached seasonal peaks of similar magnitude (4-5 g C m(-2) day(-1)) each of the 2 years. Also, the integrated night-time NEE reached comparable peak values (1.5-2 g C m(-2) day(-1)) in the 2 years of study. Despite the large difference in time between carbon uptake and release (carbon uptake time < release time), the alpine shrubland was carbon sink. This is probably because the ecosystem respiration at our site was confined significantly by low temperature and small biomass and large day/night temperature difference and usually soil moisture was not limiting factor for carbon uptake. In general, R-eco was an exponential function of soil temperature, but with season-dependent values of Q(10). The temperature-dependent respiration model failed immediately after rain events, when large pulses of R-eco were observed. Thus, for this alpine shrubland in Qinghai-Tibetan plateau, the timing of rain events had more impact than the total amount of precipitation on ecosystem R-eco and NEE.

Effect of spatial variation on areal evapotranspiration simulation in Haibei, Tibet plateau, China

Quantification of areal evapotranspiration from remote sensing data requires the determination of surface energy balance components with support of field observations. Much attention should be given to spatial resolution sensitivity to the physics of surface heterogeneity. Using the Priestley-Taylor model, we generated evapotranspiration maps at several spatial resolutions for a heterogeneous area at Haibei, and validated the evapotranspiration maps with the flux tower data. The results suggested that the mean values for all evapotranspiration maps were quite similar but their standard deviations decreased with the coarsening of spatial resolution. When the resolution transcended about 480 m, the standard deviations drastically decreased, indicating a loss of spatial structure information of the original resolution evapotranspiration map. The absolute values of relative errors of the points for evapotranspiration maps showed a fluctuant trend as spatial resolution of input parameter data layers coarsening, and the absolute value of relative errors reached minimum when pixel size of map matched up to measuring scale of eddy covariance system. Finally, based on the analyses of the semi-variogram of the original resolution evapotranspiration map and the shapes of spatial autocorrelation indices of Moran and Geary for evapotranspiration maps at different resolutions, an appropriate resolution was suggested for the areal evapotranspiration simulation in this study area.

Phylogeography of the Qinghai-Tibetan Plateau endemic Juniperus przewalskii (Cupressaceae) inferred from chloroplast DNA sequence variation

The vegetation of the northeast Qinghai-Tibetan Plateau is dominated by alpine meadow and desert-steppe with sparse forests scattered within it. To obtain a better understanding of the phylogeography of one constituent species of the forests in this region, we examined chloroplast trnT-trnF and trnS-trnG sequence variation within Juniperus przewalskii, a key endemic tree species. Sequence data were obtained from 392 trees in 20 populations covering the entire distribution range of the species. Six cpDNA haplotypes were identified. Significant population subdivision was detected (G(ST) = 0.772, N-ST = 0.834), suggesting low levels of recurrent gene flow among populations and significant phylogeographic structure (N-ST > G(ST), P < 0.05). Eight of the nine disjunct populations surveyed on the high-elevation northeast plateau were fixed for a single haplotype (A), while the remaining, more westerly population, contained the same haplotype at high frequency together with two low frequency haplotypes (C and F). In contrast, most populations that occurred at lower altitudes at the plateau edge were fixed or nearly fixed for one of two haplotypes, A or E. However, two plateau edge populations had haplotype compositions different from the rest. In one, four haplotypes (A, B, D and E) were present at approximately equivalent frequencies, which might reflect a larger refugium in the area of this population during the last glacial period. Phylogenetic analysis indicated that the most widely distributed haplotype A is not ancestral to other haplotypes. The contrasting phylogeographic structures of the haplotype-rich plateau edge area and the almost haplotype-uniform plateau platform region indicate that the plateau platform was recolonized by J. przewalskii during the most recent postglacial period. This is supported by the findings of a nested clade analysis, which inferred that postglacial range expansion from the plateau edge followed by recent fragmentation is largely responsible for the present-day spatial distribution of cpDNA haplotypes within the species.

Variation of active constituents of an important Tibet folk medicine Swertia mussotii Franch. (Gentianaceae) between artificially cultivated and naturally distributed

Concentrations of seven phytochemical constituents (swertiamarin, mangiferin, swertisin, oleanolic acid, 1,5,8-trihydroxy-3methoxyxanthone, 1,8-dihydroxy-3,7-dimethoxyxanthone and 1,8-dihydroxy-3,5-dimethoxyxanthone) of "ZangYinChen" (Swertia mussotii, a herb used in Tibetan folk medicine) were determined and compared in plants collected from naturally distributed high-altitude populations and counterparts that had been artificially cultivated at low altitudes. Levels of mangiferin, the most abundant active compound in this herb, were significantly lower in cultivated samples and showed a negative correlation with altitude. The other constituents were neither positively nor negatively correlated with cultivation at low altitude. Concentrations of all of the constituents varied substantially with growth stage and were highest at the bud stage in the cultivars, but there were no distinct differences between flowering and fruiting stages in this respect. (c) 2005 Elsevier Ireland Ltd. All rights reserved.

Genetic variation within and among populations of Rhodiola alsia (Crassulaceae) native to the Tibetan Plateau as detected by ISSR markers

Genetic variation of 10 Rhodiola alsia ( Crassulaceae) populations from the Qinghai - Tibet Plateau of China was investigated using intersimple sequence repeat (ISSR) markers. R. alsia is an endemic species of the Qinghai - Tibet Plateau. Of the 100 primers screened, 13 were highly polymorphic. Using these primers, 140 discernible DNA fragments were generated with 112 (80%) being polymorphic, indicating pronounced genetic variation at the species level. Also there were high levels of polymorphism at the population level with the percentage of polymorphic bands (PPB) ranging from 63.4 to 88.6%. Analysis of molecular variance (AMOVA) showed that the genetic variation was mainly found among populations (70.3%) and variance within populations was 29.7%. The main factors responsible for the high level of differentiation among populations are probably the isolation from other populations and clonal propagation of this species. Occasional sexual reproduction might occur in order to maintain high levels of variation within populations. Environmental conditions could also influence population genetic structure as they occur in severe habitats. The strong genetic differentiation among populations in our study indicates that the conservation of genetic variability in R. alsia requires maintenance of as many populations as possible.

RAPD profiling in detecting genetic variation in endemic Coelonema (Brassicaceae) of Qinghai-Tibet Plateau of China

Random amplified polymorphic DNA ( RAPD) markers were used to measure genetic diversity of Coelonema draboides ( Brassicaceae), a genus endemic to the Qilian Mountains of the Qinghai-Tibet Plateau. We sampled 90 individuals in 30 populations of Coelonema draboides from Datong and Huzhu counties of Qinghai Province in P. R. China. A total of 186 amplified bands were scored from the 14 RAPD primers, with a mean of 13.3 amplified bands per primer, and 87% ( 161 bands) polymorphic bands (PPB) was found. Analysis of molecular variance (AMOVA) shows that a large proportion of genetic variation (84.2%) resides among individuals within populations, while only 15.8% resides among populations. The species shows higher genetic diversity between individuals than other endemic and endangered plants. The RAPDs provide a useful tool for assessing genetic diversity of rare, endemic species and for resolving relationships among populations. The results show that the genetic diversity of this species is high, possibly allowing it to adapt more easily to environmental variations. The main factor responsible for the high level of differentiation within populations and the low level of diversity among populations is probably the outcrossing and long-lived nature of this species. Some long-distance dispersal, even among far separated populations, is also a crucial determinant for the pattern of genetic variation in the species. This distributive pattern of genetic variation of C. draboides populations provides important baseline data for conservation and collection strategies for the species. It is suggested that only populations in different habitats should be studied and protected, not all populations, so as to retain as much genetic diversity as possible.

Short-term variation of CO2 flux in relation to environmental controls in an alpine meadow on the Qinghai-Tibetan Plateau

[1] The alpine meadow ecosystem on the Qinghai-Tibetan Plateau may play a significant role in the regional carbon cycle. To assess the CO2 flux and its relationship to environmental controls in the ecosystem, eddy covariance of CO2, H2O, and energy fluxes was measured with an open-path system in an alpine meadow on the plateau at an elevation of 3,250 m. Net ecosystem CO2 influx (Fc) averaged 8.8 g m(-2) day(-1) during the period from August 9 to 31, 2001, with a maximum of 15.9 g m(-2) day(-1) and a minimum of 2.3 g m(-2) day(-1). Daytime Fc averaged 16.7 g m(-2) day(-1) and ranged from 10.4 g m(-2) day(-1) to 21.7 g m(-2) day(-1) during the study period. For the same photosynthetic photon flux density (PPFD), gross CO2 uptake (Gc) was significantly higher on cloudy days than on clear days. However, mean daily Gc was higher on clear days than on cloudy days. With high PPFD, Fc decreased as air temperature increased from 10degreesC to 23degreesC. The greater the difference between daytime and nighttime air temperatures, the more the sink was strengthened. Daytime average water use efficiency of the ecosystem (WUEe) was 8.7 mg (CO2)(g H2O)(-1); WUEe values ranged from 5.8 to 15.3 mg (CO2)(g H2O)(-1). WUEe increased with the decrease in vapor pressure deficit. Daily albedo averaged 0.20, ranging from 0.19 to 0.22 during the study period, and was negatively correlated with daily Fc. Our measurements provided some of the first evidence on CO2 exchange for a temperate alpine meadow ecosystem on the Qinghai-Tibetan Plateau, which is necessary for assessing the carbon budget and carbon cycle processes for temperate grassland ecosystems.

Variation in mitochondrial DNA and phylogeny of six species of pikas (Ochotona)

Phylogenetic relationships of six species of Ochotona were investigated using mitochondrial DNA (mtDNA) restriction-site analysis. The phylogenetic tree constructed using PAUP was based on 62 phylogenetically informative sites with O. erythrotis designated as an outgroup. Two clades were evident. One contained O. curzoniae, O. huangensis, and O. thibetana. in the second, O. daurica was a sister taxon of O. cansus. The five species appear to come from different maternal lineages. The branching structure of the tree and sequence divergence confirm that huangensis and cansus are distinct species, and that mol-osa is a synonym of O. cansus rather than O. thibetana. Divergence time, estimated from genetic distances, indicates that the ancestors of the two maternal lineages diverged ca. 6.5 x 10(6) years ago. O. curzoniae diverged from O. huangensis, and O. daurica diverged from O. cansus, at about the same time (ca. 3.4 x 10(6) years ago). These data suggest a period of rapid radiation of the genus Ochotona in China, perhaps during the late Pliocene. These calculations correspond roughly to tectonic events and environmental changes in China throughout this period, and appear to be substantiated by the fossil record.