Contrasting changes in above- and below-ground biomass allocation across treeline ecotones in southeast Tibet

Under conditions of a warmer climate, the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems. However, the above- and below-ground live biomass allocations among different vegetation types within the treeline ecotones are not well investigated. To determine the altitudinal patterns of above-/below-ground carbon allocation, we measured the root biomass and estimated the above-ground biomass (AGB) in a subalpine forest, treeline forest, alpine shrub, and alpine grassland along two elevational transects towards the alpine tundra in southeast Tibet. The AGB strongly declined with increasing elevation, which was associated with a decrease in the leaf area index and a consequent reduction in carbon gain. The fine root biomass (FRB) increased significantly more in the alpine shrub and grassland than in the treeline forest, whereas the coarse root biomass changed little with increasing altitudes, which led to a stable below-ground biomass (BGB) value across altitudes. Warm and infertile soil conditions might explain the large amount of FRB in alpine shrub and grassland. Consequently, the root to shoot biomass ratio increased sharply with altitude, which suggested a remarkable shift of biomass allocation to root systems near the alpine tundra. Our findings demonstrate contrasting changes in AGB and BGB allocations across treeline ecotones, which should be considered when estimating carbon dynamics with shifting treelines.     

C:N:P stoichiometry of perennial herbs' organs in the alpine steppe of the northern Tibetan Plateau

The patterns of C:N:P stoichiometry across ecosystems are important in understanding biogeochemical processes. The stoichiometry of nutrients at the leaf and root level have been reported previously, but relationships of other plant organs, such as stems and the reproductive organs, remain unclear. We collected 228 samples of leaves, roots, stems and reproductive organs from 11 common plant species at 25 sites on the Tibetan Plateau to explore the relationships of C:N:P stoichiometry both within and across plant organs. The average C concentrations in the roots, leaves, stems and reproductive organs were 427.32, 410.51, 421.11 and 416.72 mg g~(-1), respectively. The shoot tissues(leaves, stems and reproductive organs) had significantly higher N and P concentrations than the roots. The N and P concentrations had a significant positive correlation within the same organ. The nutrient concentrations(N and P) and nutrient ratios(C:N, C:P and N:P) were significantly correlated across all pairwise organ combinations. Our data suggest that alpine perennial herbs share similar evolutionary histories and have constrained patterns of covariation for C concentrations, with differential patterns for N and P stoichiometry across organs. Our data also indicate that covarying sets of nutrient traits are consistent across environments and biogeographical regions and demonstrate convergent evolution in plant nutritional characteristics in extreme alpine environments.     

Degradation induces changes in the soil C:N:P stoichiometry of alpine steppe on the Tibetan Plateau

Due to the Tibetan Plateau's unique high altitude and low temperature climate conditions,the region's alpine steppe ecosystem is highly fragile and is suffering from severe degradation under the stress of increasing population,overgrazing,and climate change.The soil stoichiometry,a crucial part of ecological stoichiometry,provides a fundamental approach for understanding ecosystem processes by examining the relative proportions and balance of the three elements.Understanding the impact of degradation on the soil stoichiometry is vital for conservation and management in the alpine steppe on the Tibetan Plateau.This study aims to examine the response of soil stoichiometry to degradation and explore the underlying biotic and abiotic mechanisms in the alpine steppe.We conducted a field survey in a sequent degraded alpine steppe with seven levels inNorthern Tibet.The plant species,aboveground biomass,and physical and chemical soil properties such as the moisture content,temperature,pH,compactness,total carbon(C),total nitrogen(N),and total phosphorus(P)were measured and recorded.The results showed that the contents of soil C/N,C/P,and N/P consistently decreased along intensifying degradation gradients.Using regression analysis and a structural equation model(SEM),we found that the C/N,C/P,and N/P ratios were positively affected by the soil compactness,soil moisture content and species richness of graminoids but negatively affected by soil pH and the proportion of aboveground biomass of forbs.The soil temperature had a negative effect on the C/N ratio but showed positive effect on the C/P and N/P ratios.The current study shows that degradation-induced changes in abiotic and biotic conditions such as soil warming and drying,which accelerated the soil organic carbon mineralization,as well as the increase in the proportion of forbs,whichwere difficult to decompose and input less organic carbon into soil,resulted in the decreases in soil C/N,C/P,and N/P contents to a great extent.Our results provide a sound basis for sustainable conservation and management of the alpine steppe.     

Impacts of warming on root biomass allocation in alpine steppe on the north Tibetan Plateau

Biomass is an important component of global carbon cycling and is vulnerable to climate change. Previous studies have mainly focused on the responses of aboveground biomass and phenology to warming, while studies of root architecture and of root biomass allocation between coarse and fine roots have been scarcely reported in grassland ecosystems. We conducted an open-top-chamber warming experiment to investigate the effect of potential warming on root biomass and root allocation in alpine steppe on the north Tibetan Plateau. The results showed that Stipa purpurea had significantly higher total root length, root surface area and tips than Carex moocroftii. However,there were no differences in total root volume, mean diameter and forks for the two species. Warming significantly increased total root biomass(27.60%), root biomass at 0–10 cm depth(27.84%) and coarse root biomass(diameter 0.20 mm, 57.68%) in the growing season(August). However, warming had no significant influence on root biomass in the non-growing season(April). Root biomass showed clear seasonalvariations: total root biomass, root biomass at 0–10 cm depth and coarse root biomass significantly increased in the growing season. The increase in total root biomass was due to the enhancement of root biomass at 0–10 cm depth, to which the increase of coarse root biomass made a great contribution. This research is of significance for understanding biomass allocation, carbon cycling and biological adaptability in alpine grassland ecosystems under future climate change.     

Temporal stability of aboveground net primary production in northern Tibet alpine steppe in response to nitrogen addition

The mechanism that sustains the temporal stability of aboveground net primary production(ANPP) respond to nitrogen deposition is still controversial. Consequently, we investigated the mechanism of temporal stability of ANPP through the effect of N addition on diversity, species asynchrony and portfolio effects in northern Tibet alpine steppe over a period of three years. Our results showed that the community temporal stability did not significantly correlate with the species richness and Shannon–Wiener diversity. Species asynchrony and stability was also not significantly affected by N addition(p 0.05). Furthermore, there was no significant relationship between species asynchrony and temporal stability. Although the value of portfolio effects(z)(z = 1.304, 95% confidence intervals:1.029–1.597) was more than 1, the portfolio effects was not a primary driver of temporal stability due to the biodiversity being unaffected. The above results suggested that the richness, species asynchrony and portfolio effect could not support for mechanism of stability at the alpine steppe. From the results of path analysis, species temporal stability positively supports the community temporal stability in the alpine steppe ecosystem. According to the character of environment and vegetation of alpine steppe at North Tibet, we inferred that dominance species stability is more important than species richness for the community temporal stability.     

THE N／P RATIO IN THE NORTHERN SOUTH YELLOW SEA IN AUTUMN

Study of horizontal and vertical distributions of the N/P(nitrogen versus phosphate)atom ratio in the northem South Yellow Sea showed that the ratio varied greatly in upper waters of the in-vestigated area and was always much greater than the theoretical Redfield ratio of 16:1 found below the thermocline zone.It was in general higher near the coast and lower in the central part.With increasing depth,the ratio became smaller and smaller.This distribution pattem is attributed to :1)the anthropo-genic influence of the surface N and P which makes the N/P ratio differ from the normal value;2)the easy adsorption of P on particles hinders P trasport to the central part;3)below the thermocline zone,the N and P mainly come from the remineralization of the sedimented phytoplankton residues which have almost the theoretical Redfield value and;4)the existence of the Yellow Sea Bottom Cold Water which inhibits the vertical exchange of the water.     

MOLAR RATIOS OF C, N, P OF PARTICULATE MATTER AND THEIR VERTICAL FLUXES IN THE YELLOW SEA

The vertical fluxes and molar ratios of carbon, nitrogen and phosphorus of suspended particulate matter in the Yellow Sea were studied based on the analysis of suspended particulate matter,sediments and sinking particles obtained by use of moored sediment traps. The POC ： PON ratios indicate that most of the particulate organic matter in the Yellow Sea water column comes from marine life rather than the continent. The vertical fluxes of SPM, POC, PON and POP in the Yellow Sea are much higher than those in other seas over the world, and present a typical pattern in shallow epicontinental seas. The estimated residence time of the bioactive elements showed that the speed of the biogeochemical process of materials in the Yellow Sea is much shorter than that in the open ocean as there was high primary productivity in this region.     

Variation in carbon,nitrogen and phosphorus partitioning between above- and belowground biomass along a precipitation gradient at Tibetan Plateau

Precipitation is a potential factor that significantly affects plant nutrient pools by influencing biomass sizes and nutrient concentrations. However, few studies have explicitly dissected carbon(C), nitrogen(N) and phosphorus(P) pools between above- and belowground biomass at the community level along a precipitation gradient. We conducted a transect(approx. 1300 km long) study of Stipa purpurea community in alpine steppe on the Tibet Plateau of China to test the variation of N pool of aboveground biomass/N pool of belowground biomass(AB/BB N) and P pool of aboveground biomass/P pool of belowground biomass(AB/BB P) along a precipitation gradient. The proportion of aboveground biomass decreased significantly from mesic to drier sites. Along the belt transect, the plant N concentration was relatively stable; thus, AB/BB N increased with moisture due to the major influences by above- and belowground biomass allocation. However, P concentration of aboveground biomass decreased significantly with increasing precipitation and AB/BB P did not vary with aridity because of the offset effect of the P concentration and biomass allocation. Precipitation gradients do decouple the N and P pool of a S. purpurea community along a precipitation gradient in alpine steppe. The decreasing of N:P in aboveground biomass in drier regions may indicate much stronger N limitation in more arid area.     

Community composition,abundance and biomass of zooplankton in Zhangzi Island waters,Northern Yellow Sea

Samples were collected monthly from the sea area around Zhangzi Island,northern Yellow Sea,from July 2009 to June 2010.Vertical net towing was used to examine spatial and temporal variability in zooplankton abundance and biomass.Overall,C alanus sinicus and Saggita crassa were the dominant species found during the study period,while the amphipod T hemisto gracilipes was dominant in winter and spring.Vast numbers of the ctenophore species of the genus Beroe were found in October and November.It was not possible to count them,but they constituted a large portion of the total zooplankton biomass.Zooplankton species diversity was highest in October,and species evenness was highest in April.Zooplankton abundance(non-jellyfi sh)and biomass were highest in June and lowest in August,with annual averages of 131.3 ind./m3and 217.5 mg/m3,respectively.Water temperature may be responsible for the variations in zooplankton abundance and biomass.B eroe biomass was negatively correlated with other zooplankton abundance.Longterm investigations will be carried out to learn more about the infl uence of the environment on zooplankton assemblages.     

Aboveground biomass of the alpine shrub ecosystems in Three-River Source Region of the Tibetan Plateau

Though aboveground biomass (AGB) has an important contribution to the global carbon cycle, the information about storage and climatic effects of AGB is scare in Three-River Source Region (TRSR) shrub ecosystems. This study investigated AGB storage and its climatic controls in the TRSR alpine shrub ecosystems using data collected from 23 sites on the Tibetan Plateau from 2011 to 2013. We estimated the AGB storage (both shrub layer biomass and grass layer biomass) in the alpine shrubs as 37.49 Tg, with an average density of 1447.31 g m^-2. Biomass was primarily accumulated in the shrub layer, which accounted for 92% of AGB, while the grass layer accounted for only 8%. AGB significantly increased with the mean annual temperature (P < 0.05). The effects of the mean annual precipitation on AGB were not significant. These results suggest that temperature, rather than precipitation, has significantly effects on of aboveground vegetation growth in the TRSR alpine shrub ecosystems. The actual and potential increase in AGB density was different due to global warming varies among different regions of the TRSR. We conclude that long-term monitoring of dynamic changes is necessary to improve the accuracy estimations of potential AGB carbon sequestration across the TRSR alpine shrub ecosystems.     

Scaling of soil carbon,nitrogen, phosphorus and C:N:P ratio patterns in peatlands of China

Inspired by the importance of Redfield-type C:N:P ratios in global soils,we looked for analogous patterns in peatlands and aimed at deciphering the potential affecting factors.By analyzing a suite of peatlands soil data(n = 1031),mean soil organic carbon(SOC),total nitrogen(TN) and total phosphorous(TP) contents were 50.51%,1.45% and 0.13%,respectively,while average C:N,C:P and N:P ratios were 26.72,1186.00 and 46.58,respectively.C:N ratios showed smaller variations across different vegetation coverage and had less spatial heterogeneity than C:P and N:P ratios.No consistent C:N:P ratio,though with a general value of 1245:47:1,was found for entire peatland soils in China.The Northeast China,Tibet,Zoigê Plateau and parts of Xinjiang had high soil SOC,TN,TP,and C:P ratio.Qinghai,parts of the lower reaches of the Yangtze River,and the coast zones have low TP and N:P ratio.Significant differences for SOC,TN,TP,C:N,C:P and N:P ratios were observed across groups categorized by predominant vegetation.Moisture,temperature and precipitation all closely related to SOC,TN,TP and their pairwise ratios.The hydrothermal coefficient(RH),defined as annual average precipitation divided by temperature,positively and significantly related to C:N,C:P and N:P ratios,implying that ongoing climate change may prejudice peatlands as carbon sinks during the past 50 years in China.     

Effects of grazing exclusion on plant productivity and soil carbon,nitrogen storage in alpine meadows in northern Tibet,China

Grazing exclusion is widely adopted in restoring degraded alpine grasslands on the Qinghai-Tibetan Plateau. However, its effectiveness remains poorly understood. In this study, we investigated the effects of grazing exclusion on plant productivity, species diversity and soil organic carbon （SOC） and soil total nitrogen （STN） storage along a transect spanning from east to west of alpine meadows in northern Tibet, China. After six years of grazing exclusion, plant cover, aboveground biomass （AGB）, belowground biomass （BGB）, SOC and STN were increased, but species diversity indices declined. The enhancement of AGB and SOC caused by grazing exclusion was correlated positively with mean annual precipitation （MAP）. Grazing exclusion led to remarkable biomass increase of sedge species, especially Kobresia pygmaea, whereas decrease of biomass in forbs and no obvious change in grass, leguminous and noxious species. Root biomass was concentrated in the near surface layer （10 cm） after grazing exclusion. The effects of grazing exclusion on SOC storage were confined to shallow soil layer in sites with lower MAP. It is indicated that grazing exclusion is an effective measure to increase forage production and enhance soil carbon sequestration in the studied region. The effect is more efficient in sites with higher precipitation. However, the results revealed a tradeoff between vegetation restoration and ecological biodiversity. Therefore, carbon pools recover more quickly than plant biodiversity in the alpine meadows. We suggest that grazing exclusion should be combined with other measures to reconcile grassland restoration and biodiversitv conservation.     

Variation of alkaline phosphatase activity in sediments of shrimp culture ponds and its relationship with the contents of C,N and P

1Introduction Activities of extracellular enzymes can serve as theindicators of organic matter content.Enzyme assayinghas been used in the analyses of dissolved organic ma-terials in aquatic environments(Chrost,1991),massloss of plant litter in terrestrial systems(Sinsabaughet al.,1992;Sinsabaugh et al.,1994),processing ofpaniculate and dissolved organic carbon(POC,DOC)in streams(Sinsabaugh and Findlay,1995;Findlayet al.,1998),and processing of particulate organicmatter(POM)in wetlands(J…     

Response of biomass spatial pattern of alpine vegetation to climate change in permafrost region of the Qinghai-Tibet Plateau,China

Alpine ecosystems in permafrost region are extremely sensitive to climate changes.To determine spatial pattern variations in alpine meadow and alpine steppe biomass dynamics in the permafrost region of the Qinghai-Tibet Plateau,China,calibrated with historical datasets of above-ground biomass production within the permafrost region's two main ecosystems,an ecosystem-biomass model was developed by employing empirical spatialdistribution models of the study region's precipitation,air temperature and soil temperature.This model was then successfully used to simulate the spatio-temporal variations in annual alpine ecosystem biomass production under climate change.For a 0.44°C decade-1 rise in air temperature,the model predicted that the biomasses of alpine meadow and alpine steppe remained roughly the same if annual precipitation increased by 8 mm per decade-1,but the biomasses were decreased by 2.7% and 2.4%,respectively if precipitation was constant.For a 2.2°C decade-1 rise in air temperature coupled with a 12 mm decade-1 rise in precipitation,the model predicted that the biomass of alpine meadow was unchanged or slightly increased,while that of alpine steppe was increased by 5.2%.However,in the absence of any rise in precipitation,the model predicted 6.8% and 4.6% declines in alpine meadow and alpine steppe biomasses,respectively.The response of alpine steppe biomass to the rising air temperatures and precipitation was significantly lesser and greater,respectively than that of alpine meadow biomass.A better understanding of the difference in alpine ecosystem biomass production under climate change is greatly significant with respect to the influence of climate change on the carbon and water cycles in the permafrost regions of the Qinghai-Tibet Plateau.     

Soil Erosion and Vegetation Succession in Alpine Kobresia Steppe Meadow Caused by Plateau Pika A Case Study of Nagqu County, Tibet

This paper evaluated the impacts of mounds created by the plateau pika (Ochotona curzoniae) on the vege- tation composition, structure, and species diversity of an alpine Kobresia steppe meadow in Nagqu County, Tibet Autonomous Region, China. Based on mound height or the depth of erosion pit, we defined five stages of erosion and compared the floristic features of communities at these stages with those in undisturbed sites. In the study area, the mounds and pits covered up to 7% of the total area. Lancea tibetica, Lamiophlomis rotata, and Potentilla bifurca were the dominant species in erosion pits, and Kobresia pygmaea, the dominant species in undisturbed sites, became a com- panion species in eroded areas. In the process of erosion, the original vegetation was covered by soil ejected by the pika, then the mounds were gradually eroded by wind and rain, and finally erosion pits formed. The vegetation coverage in- creased with increasing erosion stages but remained significantly lower than that in undisturbed sites. Improved coverage eventually reduced soil erosion, and pit depth eventually stabilized at around 20cm. Aboveground biomass increased with increasing erosion stage, but the proportion of low-quality forage reached more than 94%. The richness index and Shannon-Wiener index increased significantly with increasing erosion stage, but the richness index in mound and pit areas was significantly lower than that in undisturbed sites.     

Protist Interactions and Seasonal Dynamics in the Coast of Yantai,Northern Yellow Sea of China as Revealed by Metabarcoding

Facilitated by the high-throughput sequencing(HTS) technique, the importance of protists to aquatic systems has been widely acknowledged in the last decade. However, information of protistan biotic interactions and seasonal dynamics is much less known in the coast ecosystem with intensive anthropic disturbance. In this study, year-round changes of protist community composition and diversity in the coastal water of Yantai, a city along the northern Yellow Sea in China, were investigated using HTS for the V4 region of 18 S rDNA. The interactions among protist groups were also analyzed using the co-occurrence network. Data analyses showed that Alveolata, Chlorophyta, and Stramenopiles are the most dominant phytoplanktonic protists in the investigated coastal area. The community composition displayed strong seasonal variation. The abundant families Dino-Group-I-Clade-1 and Ulotrichales_X had higher proportions in spring and summer, while Bathycoccaceae exhibited higher ratios in autumn and winter. Alpha diversities(Shannon and Simpson) were the highest in autumn and the lowest in spring(ANOVA test, P 0.05). Nutrients(SiO_4~(2-), PO_4~(3-)), total organic carbon(TOC), and pH seemed to drive the variation of alpha diversity, while temperature, PO_4~(3-) and TON were the most significant factors influencing the whole protist community. Co-variance network analyses reveal frequent co-occurrence events among ciliates, chlorophytes and dinoflagellate, suggesting biotic interactions have been induced by predation, parasitism and mixotrophy.     

Trait complementarity between fine roots of Stipa purpurea and their associated arbuscular mycorrhizal fungi along a precipitation gradient in Tibetan alpine steppe

Development of fine roots and formation of symbiosis with arbuscular mycorrhizal(AM) fungi represent two strategies for plants to acquire nutrient and water from soil. Here, we elucidated how fine root development and symbolized mycorrhizal fungi with Stipa purpurea responded to the precipitation change in Tibetan alpine steppe ecosystem across a precipitation gradient from 50 mm to 400 mm. As precipitation increased, the proportion of thinner fine roots(diameter 0.4 mm) in total roots increased significantly; while the mycorrhizal colonization percentage, either associated with thinner or thicker roots, decreased. This phenomenon indicated that fine root development and symbolized mycorrhizal fungi are likely alternative, and plant preferred to develop fine root rather than build a symbiotic relationship with mycorrhizal fungi in more benign niches with higher precipitation. Also, root diameter was negatively correlated with specific root length(SRL), but positively correlated with AM fungal colonization percentage, indicating thicker-root species rely more on mycorrhizal fungi in alpine steppe. The complementarity between fine root and mycorrhizal fungi of S. purpurea is mediated by precipitation in Tibetan alpine steppe.     

藏北安多县抱布德铅多金属矿床地质特征及找矿方向

抱布德铅多金属矿产于硅质岩、灰岩中,围岩主要为灰岩、少量泥岩,蚀变普遍,构造发育。通过野外地质工作,结合已有资料,从区域地质特征及构造演化成矿方面对抱布德铅多金属矿床进行分析,初步分析矿床与区域构造运动、广泛发育的NW向断裂、三叠纪地层有关,矿区断裂构造、硅质岩为以后探矿的重点区域。     

Co-occurrence patterns of above-ground and below-ground mite communities in farmland of Sanjiang Plain,Northeast China

One of the fundamental questions in community ecology is whether communities are random or formed by deterministic mechanisms. Although many efforts have been made to verify non-randomness in community structure, little is known with regard to co-occurrence patterns in above-ground and below-ground communities. In this paper, we used a null model to test non-randomness in the structure of the above-ground and below-ground mite communities in farmland of the Sanjiang Plain, Northeast China. Then, we used four tests for non-randomness to recognize species pairs that would be demonstrated as significantly aggregated or segregated co-occurrences of the above-ground and below-ground mite communities. The pattern of the above-ground mite commu- nity was significantly non-random in October, suggesting species segregation and hence interspecific competition. Additionally, species co-occurrence patterns did not differ from randomness in the above-ground mite community in August or in below-ground mite com- munities in August and October. Only one significant species pair was detected in the above-ground mite community in August, while no significant species pairs were recognized in the above-ground mite community in October or in the below-ground mite communities in August and October. The results indicate that non-randomness and significant species pairs may not be the general rule in the above-ground and below-ground mite communities in farmland of the Sanjiang Plain at the fine scale.     

Biomass allocation patterns of alpine grassland species and functional groups along a precipitation gradient on the Northern Tibetan Plateau

Variations in the fractions of biomass allocated to functional components are widely considered as plant responses to resource availability for grassland plants. Observations indicated shoots isometrically relates to roots at the community level but allometrically at the species level in Tibetan alpine grasslands. These differences may result from the specific complementarity of functional groups between functional components, such as leaf, root, stem and reproductive organ. To test the component complementary responses to regional moisture variation, we conducted a multi-site transect survey to measure plant individual size and component biomass fractions of common species belonging to the functional groups： forbs, grasses, legumes and sedges on the Northern Tibetan Plateau in peak growing season in 2010. Along the mean annual precipitation （MAP） gradient, we sampled 7o species, in which 2o are in alpine meadows, 20 in alpine steppes, 15 in alpine desert-steppes and 15 in alpine deserts, respectively. Our results showed that the size of alpine plants is small with individual biomass mostly lower than 1.0 g. Plants keep relative conservative component individual responses moisture functional fractions across alpine grasslands at the level. However, the complementary between functional components to variations specifically differ among groups. These results indicate that functional group diversity may be an effective tool for scaling biomass allocation patterns from individual up to community level. Therefore, it is necessary andvaluable to perform intensive and systematic studies on identification and differentiation the influences of compositional changes in functional groups on ecosystem primary services and processes.