Gongga Mountain Research Articles

The complete mitochondrial genome of a blue sheep (Pseudois nayaur szechuanensis) from Gongga mountains of Sichuan, China

The blue sheep (Pseudois nayaur) belongs to the subfamily Caprinae. Here, we report the complete mitochondrial genome of a blue sheep subspecies (Pseudois nayaur szechuanensis) from Gongga Mountains of Sichuan, China. The genome (GenBank accession number MH719216) has a length of 16,664 bp and exhibits the typical structure of mammalian mitochondrial genomes. Phylogenetically, the newly generated mitochondrial genome is nested within the genus Pseudois group and formed a strongly supported (100% bootstrap) sister lineage to the previously reported P. n. szechuanensis (GenBank accession number, KJ784494). These results provide more molecular data for the genetic diversity conservation of this rare species.

Characteristics of Air Pollutants and Greenhouse Gases at a Regional Background Station in Southwestern China

The characteristics of air pollutants and greenhouse gases at regional background sites are critical to assessing the impact of anthropogenic emissions on the atmospheric environment, ecosystems and climate change. However, observational studies are still scarce at such background sites. In this study, continuous hourly observations of air pollutants (O-3, CO, SO2, NOx, PM2.5 and PM10) and greenhouse gases (CO2, CH4 and N2O) were performed for one year (from January 1 to December 31, 2017) at the Gongga Mountain background station (GGS; 101 degrees 97'E, 29 degrees 55'N; elevation: 3541 m) in southwestern China. The concentrations and variations of these air pollutants and greenhouse gases were determined, and the effect of transboundary atmospheric transport on the air pollution at the study site was investigated. The results showed that the average annual concentrations (mixing ratios) of the O-3, CO, SO2, NO2, CO2, CH4, N2O, PM2.5 and PM10 were 74.7 +/- 22.0 mu g m(-3), 0.3 +/- 0.2 mg m(-3), 0.5 +/- 0.6 mu g m(-3), 1.7 +/- 1.3 mu g m(-3), 406.1 +/- 9.5 ppm, 1.941 +/- 0.071 ppm, 324.5 +/- 14.8 ppb, 6.5 +/- 6.2 mu g m(-3) and 10.6 +/- 11.2 mu g m(-3), respectively. The concentrations (mixing ratios) of the abovementioned substances at the GGS are comparable to those at other background sites in China and around the world. The slight differences among concentrations at different sites may be mainly attributable to the impacts of anthropogenic emissions near the background sites and meteorological conditions. High values of O-3 were observed in spring and summer, while SO2 and PM2.5 showed higher concentrations in summer than in autumn. Relatively high CO, NO2 and PM10 values were mostly observed in spring and winter. Relatively low CO2 concentrations were observed in summer due to the vigorous summertime photosynthesis of vegetation. The lowest concentrations for CH4 were recorded in summer, whereas the levels in the other three seasons were similar to each other; by contrast, the highest N2O concentrations were observed in summer due to enhanced microbial activity resulting from high ambient summer temperatures. A diurnal variation in O-3 was observed, with early morning minima and afternoon maxima. CO and NO2 displayed higher concentrations in the daytime than in the nighttime. A slight increase in both PM2.5 and PM10 concentrations was also recorded in the daytime. These patterns were closely related to scattered anthropogenic emissions and regional atmospheric transport. Nevertheless, CO2 exhibited lower concentrations in the daytime than in the nighttime, although CH4 showed no obvious diurnal variation. The N2O concentration peaked between 10:00 and 12:00 (local time), which can be ascribed to the enhancement of microbial activity due to the increased soil temperature. The results based on the relationship between the wind and the concentrations of air pollutants and greenhouse gases were almost consistent with those based on the potential contribution source function. It appears that O-3 and its precursors in parts of Inner Mongolia and Gansu, Ningxia, Sichuan, Chongqing and Hubei Provinces as well as adjacent areas of Hunan, Guizhou and Guangxi Provinces contributed to the increase in O-3 at the study site. The potential source areas for CO and SO2 were similar and mainly distributed in India and Pakistan and areas of Inner Mongolia and Gansu and Guizhou Provinces in China. Potential source areas for NO2, PM2.5 and PM10 were found in neighboring countries of South Asia in addition to domestic regions, including Inner Mongolia, Gansu Province and the Cheng-Yu economic region. Furthermore, parts of Yunnan Province (China) as well as India and Pakistan were potential source areas for CO2, CH4 and N2O.

Intraspecific Trait Variation and Phenotypic Plasticity Mediate Alpine Plant Species Response to Climate Change.

In a rapidly changing climate, alpine plants may persist by adapting to new conditions. However, the rate at which the climate is changing might exceed the rate of adaptation through evolutionary processes in long-lived plants. Persistence may depend on phenotypic plasticity in morphology and physiology. Here we investigated patterns of leaf trait variation including leaf area, leaf thickness, specific leaf area, leaf dry matter content, leaf nutrients (C, N, P) and isotopes (δ13C and δ15N) across an elevation gradient on Gongga Mountain, Sichuan Province, China. We quantified inter- and intra-specific trait variation and the plasticity in leaf traits of selected species to experimental warming and cooling by using a reciprocal transplantation approach. We found substantial phenotypic plasticity in most functional traits where δ15N, leaf area, and leaf P showed greatest plasticity. These traits did not correspond with traits with the largest amount of intraspecific variation. Plasticity in leaf functional traits tended to enable plant populations to shift their trait values toward the mean values of a transplanted plants’ destination community, but only if that population started with very different trait values. These results suggest that leaf trait plasticity is an important mechanism for enabling plants to persist within communities and to better tolerate changing environmental conditions under climate change.

Rebirth after death: forest succession dynamics in response to climate change on Gongga Mountain, Southwest China

Global climate change is having long-term impacts on the geographic distribution of forest species. However, the response of vertical belts of mountain forests to climate change is still little known. The vertical distribution of forest vegetation (vertical vegetation belt) on Gongga Mountain in Southwest China has been monitored for 30 years. The forest alternation of the vertical vegetation belt under different climate conditions was simulated by using a mathematical model GFSM (the Gongga Forest Succession Model). Three possible Intergovernmental Panel on Climate Change (IPCC) climate scenarios (increase of air temperature and precipitation by 1.8°C/5%, 2.8°C/10% and 3.4°C/15% for B1, A1B and A2 scenarios, respectively) were chosen to reflect lower, medium and higher changes of global climate. The vertical belts of mountainous vegetation will shift upward by approximately 300 m, 500 m and 600 m in the B1, A1B and A2 scenarios, respectively, according to the simulated results. Thus, the alpine tree-line will move to a higher altitude. The simulation also demonstrated that, in a changing climate, the shift in the vegetation community will be a slow and extended process characterized by two main phases. During the initial phase, trees of the forest community degrade or die, owing to an inability to adapt to a warmer climate. This results in modest environment for the introduction of opportunistic species, consequently, the vegetation with new dominant tree species becomes predominant in the space vacated by the dead trees at the expense of previously dominated original trees as the succession succeed and climate change advance. Hence, the global climate change would dramatically change forest communities and tree species in mountainous regions because that the new forest community can grow only through the death of the original tree. Results indicated that climate change will cause the change of distribution and composition of forest communities on Gongga Mountain, and this change may enhance as the intensity of climate change increases. As a result, the alternation of death and rebirth would finally result in intensive landscape changes, and may strongly affect the eco-environment of mountainous regions.

Differences in xylogenesis between dominant and suppressed trees.

Most dendroecological studies focus on dominant trees, but little is known about the growing season of trees belonging to different size classes and their sensitivity to biotic factors. The objective of this study was to compare the dynamics of xylem formation between dominant and suppressed trees of Abies fabri of similar age growing in the Gongga Mountains, southeastern Tibetan Plateau, and to identify the association between xylem growth and climate. The timing and duration of xylogenesis in histological sections were investigated weekly during the 2013-2015 growing seasons. Our investigation found that timing and duration of xylogenesis varied with canopy position and its associated tree size. Xylogenesis started 6-14 days earlier, and ended 5-11 days later in dominant trees than in suppressed trees, resulting in a significantly longer growing season. Dominant trees also exhibited higher temperature sensitivity of tracheid production rate than suppressed trees. The observed differences in xylogenesis among trees suggested that competition affects tree growth by reducing the growing period in suppressed trees. Representative climate-growth relationships should involve trees of all size classes when evaluating the effects of the environment on forest dynamics.

Spatial Downscaling of Gross Primary Productivity Using Topographic and Vegetation Heterogeneity Information: A Case Study in the Gongga Mountain Region of China

Due to the spatial heterogeneity of land surfaces, downscaling is an important issue in the development of carbon cycle models when evaluating the role of ecosystems in the global carbon cycle. In this study, a downscaling algorithm was developed to model gross primary productivity (GPP) at 500 m in a time series over rugged terrain, which considered the effects of spatial heterogeneity on carbon flux simulations. This work was carried out for a mountainous area with an altitude ranging from 2606 to 4744 m over the Gongga Mountain (Sichuan Province, China). In addition, the Moderate Resolution Imaging Spectroradiometer (MODIS) GPP product at 1 km served as the primary dataset for the downscaling algorithm, and the 500 m MODIS GPP product was used as the reference dataset to evaluate the downscaled GPP results. Moreover, in order to illustrate the advantages and benefits of the proposed downscaling method, the downscaled results in this work, along with ordinary kriging downscaled results, spline downscaled results and inverse distance weighted (IDW) downscaled results, were compared to the MODIS GPP at 500 m. The results showed that (1) the GPP difference between the 500 m MODIS GPP and the proposed downscaled GPP results was primarily in the range of [−1, 1], showing that both vegetation heterogeneity factors (i.e., LAI) and topographic factors (i.e., altitude, slope and aspect) were useful for GPP downscaling; (2) the proposed downscaled results (R2 = 0.89, RMSE = 1.03) had a stronger consistency with the 500 m MODIS GPP than those of the ordinary kriging downscaled results (R2 = 0.43, RMSE = 1.36), the spline downscaled results (R2 = 0.40, RMSE = 1.50) and the IDW downscaled results (R2 = 0.42, RMSE = 1.10) for all Julian days; and (3) the inconsistency between MODIS GPP at 500 m and 1 km increased with the increase in altitude and slope. The proposed downscaling algorithm could provide a reference when considering the effects of spatial heterogeneity on carbon flux simulations and retrieving other fine resolution ecological-physiology parameters (e.g., net primary productivity and evaporation) over topographically complex terrains.

Stair-Step Pattern of Soil Bacterial Diversity Mainly Driven by pH and Vegetation Types Along the Elevational Gradients of Gongga Mountain, China.

Ecological understandings of soil bacterial community succession and assembly mechanism along elevational gradients in mountains remain not well understood. Here, by employing the high-throughput sequencing technique, we systematically examined soil bacterial diversity patterns, the driving factors, and community assembly mechanisms along the elevational gradients of 1800–4100 m on Gongga Mountain in China. Soil bacterial diversity showed an extraordinary stair-step pattern along the elevational gradients. There was an abrupt decrease of bacterial diversity between 2600 and 2800 m, while no significant change at either lower (1800–2600 m) or higher (2800–4100 m) elevations, which coincided with the variation in soil pH. In addition, the community structure differed significantly between the lower and higher elevations, which could be primarily attributed to shifts in soil pH and vegetation types. Although there was no direct effect of MAP and MAT on bacterial community structure, our partial least squares path modeling analysis indicated that bacterial communities were indirectly influenced by climate via the effect on vegetation and the derived effect on soil properties. As for bacterial community assembly mechanisms, the null model analysis suggested that environmental filtering played an overwhelming role in the assembly of bacterial communities in this region. In addition, variation partition analysis indicated that, at lower elevations, environmental attributes explained much larger fraction of the β-deviation than spatial attributes, while spatial attributes increased their contributions at higher elevations. Our results highlight the importance of environmental filtering, as well as elevation-related spatial attributes in structuring soil bacterial communities in mountain ecosystems.

Barrier effects of remote high mountain on atmospheric metal transport in the eastern Tibetan Plateau

Anthropogenic metals adsorbed on suspended fine particles can be deposited on remote and inaccessible high mountains by long-range atmospheric transport. In this study, we investigated the cadmium (Cd) and lead (Pb) in the soils, mosses and rainfall of three transects on the Gongga Mountain, eastern Tibetan Plateau, to understand the mountain interception effects on their atmospheric transport. The concentrations of Cd and Pb in the soils and mosses displayed a pattern of eastern transect>northern transect>western transect. The distribution of Cd and Pb on the eastern transect increased from 2000 to 2900m a.s.l. (above sea level), decreased toward the timberline, and increased again with altitude; on the northern transect, it generally decreased with altitude whereas a distribution trend was not clearly observed on the western transect. The Cd and Pb concentrations in the rainfall of the eastern transect generally decreased with altitude, and they were higher inside forests than outside forests and temporally higher in the winter than the summer. The Pb isotopic ratios coupled with moss bio-monitoring distinguished anthropogenic sources of Cd and Pb on the eastern and northern transects, whereas bedrock weathering was the main source of Cd and Pb on the western transect. We proposed a conceptual model to delineate the effects of terrain, local climate and vegetation on the transport of atmospheric metals. Our results highlighted the high mountains in the eastern Tibetan Plateau as an effective natural barrier limiting atmospheric metal transport.

贡嘎山峨眉冷杉树干呼吸空间特征及其对温度的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 贡嘎山峨眉冷杉树干呼吸空间特征及其对温度的响应 DOI: 10.5846/stxb201705160912 作者: 作者单位: 中国科学院水利部成都山地灾害与环境研究所;中国科学院大学,中国科学院水利部成都山地灾害与环境研究所,中国科学院水利部成都山地灾害与环境研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划课题（2017YFC0505004）；中国科学院成都山地所"一三五重点培育项目"；国家自然科学基金项目（41471232） Spatial variations in the stem CO2 efflux rate of Abies fabri and the response to temperature in the Gongga Mountains Author: Affiliation: Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu,Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu,Institute of Mountain Hazards and Environment,Chinese Academy of Sciences,Chengdu Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用红外线气体分析仪-土壤呼吸气室水平测定法（HOSC）原位监测了贡嘎山东坡峨眉冷杉（Abies fabri）树干CO2释放速率（Es），分析了树干Es与树干温度（Tstem）的关系。贡嘎山峨眉冷杉树干Es和Tstem空间变化格局明显，不同测定高度树干温度为0.3m > 1.3m > 2.3m，以1.3m处Es最大；不同方向Es和Tstem均表现为南面>北面。生长季和非生长季的峨眉冷杉Es分别在0.51-0.99μmol m-2 s-1和0.14-0.22μmol m-2 s-1之间波动。峨眉冷杉树Es变化趋势和Tstem一致，二者具有显著的指数函数关系（P<0.01）。峨眉冷杉非生长季树干呼吸Q10显著高于生长季（P<0.01），其中生长季变幅在1.9-3.0之间，非生长季在4.6-6.8之间，暗示个体或群落水平树干CO2释放通量的估算应充分考虑树干Es空间特征和Q10变化。 Abstract:As an important component of carbon budgets and net ecosystem CO2 exchange in forest ecosystems, stem CO2 efflux rate (Es) plays a crucial role in the global carbon balance. Investigation of spatial variations and the response of Es to temperature, are essential for improving the accuracy of Es estimates at individual and community levels. In this study, the horizontally oriented soil chamber (HOSC) technique was applied to measure the CO2 released by stems. We measured Es in situ in the Abies fabri forest on Gongga Mountain using IRGA with a Li-6400-09 from September to December 2014. Our objectives were to examine the spatial variations in Es of A. fabri and to explore the response of Es to stem temperature (Tstem). Two representative trees in an immature A. fabri forest stand were selected. An opaque PVC collar (10.7cm inside diameter and 5cm high) was cut to match the approximate curvature of the stem with the other end being cut flat. Then the custom-built PVC collar was fastened to the south of the stem at a height of 0.3, 1.3 and 2.3m and to the north at a height of 1.3m, with 100% silicone sealant 24h before the measurement was made. Loose bark and moss were carefully removed from the stem surface curved by the PVC collar using a hairbrush without damaging the underlying cambium before installing the PVC collars. Measurements were made over three cycles at each sampling point, every 2h from 8:00 to 18:00 in the same day of every month. The A. fabri stem Es and Tstem showed an apparent spatial pattern. The Tstem at different heights ranked as follows:0.3 > 1.3 > 2.3m with maximum Es appearing at 1.3m. The Es and Tstem on the south face of the stem were higher than that on the north. The monthly averages Es of the growing season (September and October) and the non-growing season (November and December) was 0.51-0.99 and 0.14-0.22μmol m-2 s-1, respectively. The trend in A. fabri stem Es was consistent with Tstem with a significantly exponential relationship observed. The temperature coefficient (Q10) during the non-growing season (4.6-6.8) was much higher than that in the growing season (1.9-3.0). It was concluded that spatial variations of Es and Q10 should be considered when estimating individual and community stem Es. 参考文献 相似文献 引证文献

Evaluation study on ecosystem based on system dynamics: A case study of Gongga Mountain forest ecosystem

At present, Gongga Mountain forest ecosystem is facing the impacts of external pollution and human factors, and the development of Gongga Mountain forest ecosystem in the future is bound to be affected. System dynamics is a discipline which can solve the highly non-linear, high-order, multi-variable, multi-feedback, complex and time-varying large-scale system problems of society, economy, ecology and biology, requiring low data accuracy. Therefore, in this paper, firstly, a simulation of Gongga Mountain forest ecosystem was carried out using the system dynamics, and the validity of model was tested; secondly, according to the simulation results, it was pointed out that the total quantity of plants in Gongga Mountain forest ecosystem declined constantly, but the quantity of shrubs increased, and grassland area decreased constantly, so Gongga Mountain forest ecosystem was facing a rapid degradation trend; finally, suggestions were put forward for the protection and improvement of Gongga Mountain forest ecosystem according to the analysis results.

Air-drying changes the distribution of Hedley phosphorus pools in forest soils

Hedley labile phosphorus (P) pools in soil tend to be several times larger than annual forest requirements, even in highly weathered soils characterized by P limitation. The discrepancy between plant and soil P status could be partly attributable to the frequently adopted air-drying pretreatment that tends to increase soil P solubility. In this study, the effects of air-drying on the distribution of Hedley P fractions were examined using soils collected under 4 forest types at Gongga Mountain, southwestern China. The results showed that the microbial biomass P (Pmic) in the organic horizon decreased markedly after air-drying. The concentrations of Hedley labile P in the air-dried samples were 31%–73% more than those in the field-moist samples. Consequently, the air-drying-induced increments of Hedley labile P pools in the surface soil horizons were 0.8–3.8 times the annual plant P requirements. The organic horizon was more susceptible to the air-drying-induced increases in Hedley labile P than the mineral horizon, probably because of the stronger release of Pmic and disruption of soil organic matter. The quality of P, indexed by the ratio of Hedley labile P to slowly cycling P, shifted in favor of the Hedley labile fractions after air-drying, further revealing that air-drying changed the distribution of Hedley P pools in forest soils. These indicated that the effects of air-drying could not be ignored when interpreting the discrepancy between the P status of plants and the Hedley labile P pools in forest soils. To more efficiently evaluate the P status in forest soils via the Hedley fractionation procedure, the use of field-moist soils is recommended.

Rapid warming forces contrasting growth trends of subalpine fir (Abies fabri) at higher- and lower-elevations in the eastern Tibetan Plateau

Tree radial growth is expected to increase at higher elevations under climate warming, while lower elevation tree growth is expected to decline. However, numerous studies have found tree radial growth responds consistently to climate along elevational gradients. Here, we sampled five plots across the subalpine Abies fabri forest belt on Gongga Mountain in the eastern Tibetan Plateau to determine tree radial growth trends and responses to climate. Three commonly used detrending methods all consistently showed that tree radial growth at high elevation (>3100m) increased, while tree growth declined at the lower elevations (2700m–2900m) over the last three decades. Increasing late-growing season temperature positively (p<0.05) correlated to tree radial growth at higher elevations, but the sign of this relationship reversed to become negative at lower elevations. Moving-window correlation analyses indicated the difference between high and low elevations response to temperature variation increased strongly with warming. Placing our result into the global context, 62% of 39 published studies found that trees along elevation gradients respond divergently to warming, and that these are located in warmer and wetter regions of the Earth. Notably, 28% of studies found non-significant responses to temperature at both high and low elevations. Our findings in the subalpine mountain forest in the eastern Tibetan Plateau were consistent with the majority of published datasets, and imply increasing temperature benefit for tree populations at higher elevation, while warming dampens growth at lower elevations.

Seasonal and spatial distribution of trace metals in alpine soils of Eastern Tibetan Plateau, China

The distribution of trace metals in remote alpine region is an effective way to understand the impacts of regional human activity and vegetation on the alpine ecosystem. In this study, the concentrations of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in the soils of Gongga Mountain, Eastern Tibetan Plateau, were investigated to reveal their seasonal and spatial distribution and enrichment state, and to decipher the effects of atmospheric deposition and vegetation on their distributions among five vegetation zones. The results showed that the concentrations of Cd, Pb, and Zn were higher in the O horizon than in other horizons despite the seasonal changes, whereas Cu was enriched in the C horizon. The enrichment states of the metals studied in the soils decreased in the order of Cd > Pb > Zn > Cu. Cd and Pb were mainly sourced from atmospheric deposition; Zn was from both atmospheric deposition and parent materials, whereas Cu was mainly from parent materials. Seasonally, the trace metals were generally higher in May and December but lower in September, implying the impact of vegetation on the distribution of trace metals under the plant uptake and the litter decomposition. Spatially, the higher enrichment of Cu, Pb, and Zn in the soils existed in the mixed broadleaf-coniferous forests and coniferous forests (approximately 3000 m above sea level). The results suggested that atmospheric deposition and biological processes are main factors controlling the seasonal and spatial distribution of trace metals in the soils of the remote alpine ecosystem.

Effects of phosphorus availability on later stages of primary succession in Gongga Mountain glacier retreat area

Intra- and interspecific competition and modifications in environmental characteristics are the main drivers of plant community dynamics, but few studies have investigated the combined effects of competition and phosphorus (P) availability on ecological succession. Seedlings of conifers Abies fabri and Picea brachytyla were collected from the late-stage Hailuogou glacier retreat area and grown under different P regimes (control and P fertilization) to investigate the impact of intra- and interspecific competition on photosynthetic capacity, resource (water, N and P) use efficiency and growth performance in two types of native soil. In the control treatment, there were no differences in the total biomass of A. fabri between the two competition patterns under either type of soil, whereas interspecific competition decreased the total biomass of P. brachytyla grown in the soil collected from A. fabri plots. However, under P fertilization, A. fabri individuals exposed to interspecific competition showed a stronger competitive ability, as their total biomass, absolute height growth rate, net photosynthetic rate, water use efficiency (δ13C) and leaf P content were significantly higher under interspecific competition compared to intraspecific competition. No differences in these traits were detected in P. brachytyla between the two competition patterns. The results indicated that P plays an important role in determining asymmetric competition patterns among Pinaceae species. The interactive effect of interspecific competition and P availability highlighted here could influence the community composition and dynamics of plants during late-stage primary succession in a glacier retreat area.

Reproductive investments driven by sex and altitude in sympatric Populus and Salix trees.

The sex ratios of co-existing Populus and Salix vary depending on altitude and species: 1:1 equlibrium sex ratios are observed at mid-altitude but skewed ones at high altitudes, where Populus shows male-biased and Salix female-biased sex ratios. However, the underlying ecological mechanisms are poorly known. Reproductive investments of Populus purdomii Rehd. and Salix magnifica Hemsl. were assessed at altitudes of 2000 and 2600 m in the Gongga Mountain by different metrics, including biomass, carbon (C), nitrogen (N) and phosphorus (P) concentrations and construction cost, and by estimating the payback time that combines energy gain and associated costs. Reproductive investment measured as C, N and P concentrations, and construction cost was higher in P. purdomii females at 2600 m. However, in S. magnifica, no difference was observed for biomass, C and N at 2600 m, but the investments for P and construction cost were even greater in males. The payback time showed no significant differences for the sexes at 2000 m, but it was shorter for P. purdomii males and S. magnifica females at 2600 m. We concluded that nutrient- and construction cost-based estimates of reproductive allocation can provide more informative insight into the cost of reproduction than does biomass, and together with the payback time they can supply an explanation for divergent sex ratios in Populus and Salix. Consequently, our results improve our understanding of the causes and consequences of sexual dimorphism in dioecious species.

Polar organic tracers in PM2.5 aerosols from an inland background area in Southwest China: Correlations between secondary organic aerosol tracers and source apportionment

PM2.5 aerosol samples were collected over 12 hr and 24 hr intervals in an inland background area, Gongga Mountain National Nature Reserve (hereafter shortened to Gongga), during the summer of 2011. Polar organic tracers, inorganic ions and meteorological data were measured. The purpose of this work was to investigate the variation patterns, formation and sources of the secondary organic aerosol tracers in the studied atmosphere. The average concentrations of isoprene oxidation products, α-pinene oxidation products, β-caryophyllinic acid, sugars, sugar alcohols and anhydrosugars were 88.6 ± 106.1, 3.6 ± 5.7, 0.13 ± 0.30, 13.6 ± 13.1, 31.9 ± 31.4 and 14.8 ± 10.7 ng/m3 respectively in all aerosol samples. The aged α-pinene second organic aerosol (SOA) tracers (i.e., 3-hydroxyglutraric acid (3HGA), 3-hydroxy-2,2-dimethylglutaric acid (HDMGA), 3-acetylpentandioic acid (APDA) and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA)) correlated significantly with each other in the 24 hr PM2.5 aerosol samples, indicating that OH· is the major factor controlling the formation of these α-pinene SOA tracers. Using the positive matrix factorization (PMF) model and the tracer-based source apportionment method, we calculated that isoprene oxidation products, α-pinene oxidation products, sesquiterpene oxidation products, biomass burning, fungi spores and anthropogenic SOA accounted for 21.9% ± 5.5%, 8.4% ± 2.1%, 3.0% ± 0.7%, 5.2% ± 5.3%, 5.0% ± 6.2% and 31.4% ± 7.8% of organic carbon respectively during the sampling period.

Bulk deposition of organic and inorganic nitrogen in southwest China from 2008 to 2013

China is regarded as one of the nitrogen deposition hotspots in the world. Measurements to-date have focused mainly on the North China Plain, ignoring the fact that atmospheric chemical and physical properties vary across the country and that there may be other hotspots regions that should be investigated. For this reason we have conducted a six year study, measuring the bulk deposition of reduced (NH4-N), oxidized (NO3-N), and dissolved organic nitrogen (DON) at three contrasting sites in the Sichuan province, southwest China. The study sites were a high altitude forest in the Gongga Mountains (GG), an agriculture dominated region in Yanting (YT) and an urban site in the mega city Chengdu (CD). The annual average bulk deposition fluxes of total dissolved nitrogen (TDN) were 7.4, 23.1 and 36.6 kg N ha−1 yr−1 at GG, YT and CD sites, respectively, during the study period 2008 to 2013. The contributions of NH4-N, NO3-N and DON to the TDN were in the range of 48.4–57.8%, 28.8–43.7%, and 8.0–15.6%, respectively. DON bulk deposition was mainly dominated by agricultural activities. TDN bulk deposition fluxes showed increasing trends at the agricultural and urban sites from 2008 to 2013, but there was little change at the remote forest (GG) site. While reduced N dominated bulk N deposition at all the three sites, its contribution showed a decreasing trend, suggesting a gradual increase in the importance of oxidized N. These results reveal the value of long term monitoring in detecting changes in the atmospheric chemical composition of this rapidly changing region, and their inclusion in the policy debate regarding which sources should be controlled in order to reduce the long term impacts of N deposition, especially for southwest China, where there are few measurements of N deposition.

Soil methanotrophic community structure and diversity in different vegetation types at elevation gradient of Gongga Mountain, Southwest China

Methane (CH4) is the second abundant greenhouse gas. Aerobic methane oxidations of topsoil in forest are identified as an important sink of atmosphere methane, playing critical roles in carbon cycle and global warming alleviation. Comparing the community structure and diversity of methane oxidizing bacteria (MOBs) in different vegetation ecosystems could provide new insights into the relationships between vegetation types and community of MOBs. In this study, we collected 92 soil samples from four types of vegetation along the elevation gradient of Gongga Mountain, and further assessed the community structure, diversity and potential drivers of MOBs across the four vegetation types using Miseq sequencing and bioinformatics methods. The result indicated that MOBs community compositions in evergreen and deciduous broad-leaved forest (EDBF) and coniferous and broad-leaved mixed forest (CBMF) was more similar, whereas in dark coniferous forest (DCF) and shrub meadow area (SMA) soils, MOB composition was more similar. In the four types of vegetation, α-diversities of MOBs in EDBF and CBMF were significantly higher than that in the other three vegetation types (P＜0.001), whereas β-diversities in soils of DCF and SMA were significantly higher than those in EDBF and CBMF (P＜0.001). Spearman analysis indicated that the relative abundance of different MOBs in four types of vegetation showed different responses to environmental change. Factors including soil total nitrogen, conductivity and soil temperature appeared to govern the variation of α-diversity across the four vegetation types. Partial Mantel test and redundancy ana-lysis (RDA) suggested that environmental parameters likely contributed more to diversity variations in soils from EDBF and CBMF, whereas diversity variations in soils from DCF and SAM might be driven by other potential environmental factors or mechanism. Precipitation appeared to drive the β-diversity variation between vegetation of EDBF and CBMF and vegetation of DCF and SAM. Our study suggested that the community structure and diversity variation of MOBs in different vegetation types might be governed by both soil properties and climate change.

Precipitation and air temperature control the variations of dissolved organic matter along an altitudinal forest gradient, Gongga Mountains, China.

Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) contribute significantly to C and N cycling in forest ecosystems. Little information is available on the variations in the DOC and DON concentrations and depositions in bulk and stand precipitation within forests along an altitudinal gradient. To determine the temporal variations in the DOC and DON concentrations and depositions in different forests and the spatial variations along the elevation gradient, the DOC and DON concentrations and depositions were measured in bulk precipitation, throughfall, and stemflow within three forest types, i.e., broadleaf forest (BLF), broadleaf-coniferous forest (BCF), and coniferous forest (CF), during the wet season (May to October) on Gongga Mountain, China, in 2015. The concentrations of bulk precipitation in BLF, BCF, and CF were 3.92, 4.04, and 2.65mgL-1, respectively, for DOC and were 0.38, 0.26, and 0.29mgL-1, respectively, for DON. BCF had the highest DOC deposition both in bulk precipitation (45.12kgha-1) and stand precipitation (98.52kgha-1), whereas the highest DON deposition was in BLF (3.62kgha-1 bulk precipitation and 4.11kgha-1 stand precipitation) during the study period. The meteorological conditions of precipitation and air temperature significantly influenced the dissolved organic matter (DOM) depositions along the elevation gradient. The leaf area index did not show any correlation with DOM depositions during the growing season.

Nitrogen-controlled intra- and interspecific competition between Populus purdomii and Salix rehderiana drive primary succession in the Gongga Mountain glacier retreat area.

In this study, intra- and interspecific competition were investigated in early successional Salix rehderiana Schneider and later-appearing Populus purdomii Rehder under non-fertilized (control) and nitrogen (N)-fertilized conditions in the Hailuogou glacier retreat area. Our aim was to discover whether N is a key factor in plant-plant competition and whether N drives the primary succession process in a glacier retreat area. We analyzed differences in responses to intra- and interspecific competition and N fertilization between P. purdomii and S. rehderiana, including parameters such as biomass accumulation, nutrient absorption, non-structural carbohydrates, photosynthetic capacity, hydrolysable amino acids and leaf ultrastructure. In the control treatments, S. rehderiana individuals subjected to interspecific competition benefited from the presence of P. purdomii plants, as indicated by higher levels of biomass accumulation, photosynthetic capacity, N absorption, amino acid contents and photosynthetic N-use efficiency. However, in the N-fertilized treatments, P. purdomii individuals exposed to interspecific competition benefited from the presence of S. rehderiana plants, as shown by a higher growth rate, enhanced carbon gain capacity, greater amino acid contents, and elevated water-use efficiency, whereas the growth of S. rehderiana was significantly reduced. Our results demonstrate that N plays a pivotal role in determining the asymmetric competition pattern among Salicaceae species during primary succession. We argue that the interactive effects of plant-plant competition and N availability are key mechanisms that drive primary succession in the Gongga Mountain glacier retreat area.