Seasonal phenology of the heterotrophic dinoflagellate Noctiluca scintillans(Macartney) in Jiaozhou Bay and adjacent coastal Yellow Sea,China

Seasonal variations in numerical abundance, cell diameter and population carbon biomass of the heterotrophic dinoflagellate Noctiluca scintillans were studied for 10 years from 2004 to 2013 in Jiaozhou Bay and adjacent coastal Yellow Sea, China, and their ecological functions were evaluated. In both areas, N. scintillans occurred throughout the year and demonstrated an essentially similar seasonality; the cell abundance increased rapidly from the winter minimum to an annual peak in late spring and early summer, and decreased gradually toward the autumn-winter minimum. The peak abundance differed by years, and there was no consistent trend in long-term numerical variations. The cell diameter also showed a seasonal fluctuation, being larger in spring and early summer than the other seasons. Estimated carbon biomass of N. scintillans population reached to a peak as high as 90.3 mg C/m~3, and occasionally exceed over phytoplankton and copepod biomass. Our results demonstrate that N. scintillans in northwestern Yellow Sea displays the seasonal phenology almost identical to the populations in other temperate regions, and play important trophic roles as a heterotroph to interact with sympatric phytoplankton and copepods.     

Characteristics of Phytoplankton Community Structure During and After a Bloom of the Dinoflagellate Scrippsiella trochoidea by HPLC Pigment Analysis

A bloom of the dinoflagellate Scrippsiella trochoidea was detected for the first time in inner Tolo Harbor,Hong Kong in 2 000. Water samples were collected at eight stations along a transect passing through a red tide patch for microscopic analysis of phytoplankton composition and high-performance liquid chromatography(HPLC) analysis of phytoplankton pigments. During the bloom,the density of dinoflagellates was 1.1×106 cells L-1 within the patch and 8.6×105 cells L-1 outside the patch where the phytoplankto...     

Allelopathic effects of mixotrophic dinoflagellate Akashiwo sanguinea on co-occurring phytoplankton: the significance of nutritional ecology

Blooms of Akashiwo sanguinea frequently break out around the world, causing huge economic losses to the aquaculture industry and seriously damaging coastal ecosystems. However, the formation mechanisms of A. sanguinea blooms remain unclear. We investigated the allelopathic effects of A. sanguinea on multiple phytoplankton species, explored the mode of allelochemicals action and the way of nutrient factors regulation of the allelopathic activity. Results show that strains of A. sanguinea could inhibit the growth of co-occurring phytoplankton including Scrippsiella trochoidea, Phaeocystis globosa, and Rhodomonas salina, but inhibition of Prorocentrum micans was not obvious. The inhibition rates on phytoplankton were positively correlated with the cell densities of A. sanguinea. The highest inhibition rate of 94% on R. salina was for A. sanguinea CCMA256 culture of 2 000 cells/mL at 72 h. We observed that cells of S. trochoidea, Ph. g lobosa, and R. sali na were lysed when co-cultured with A. sanguinea, with the shortest time for S. trochoidea. Additionally, the growth rates of A. sanguinea were promoted by coculturing with S. trochoidea, Ph. globosa, and R. salina. Four components of A. sanguinea culture were all able to inhibit growth of R. salina:the strongest inhibitory effect was found in the sonicated culture, followed by whole-cell culture, filtrates of sonicated culture, and filtrate culture. The crude extract of A. sanguinea culture also lysed cells of R. salina, and the inhibition rates on R. salina increased with the increasing dose of crude extract. It was shown that both nutrient enrichment and nitrogen:phosphorus ratio imbalance enhanced remarkably the allelopathic activity of A. sanguinea. The highest inhibition rate on R. salina of 70% occurred in A. sanguinea JX13 treatment at 2 000 cells/mL under high nutrient condition in 48 h. In JX14 treatment at 2 000 cells/mL for N:P of 10:1, the inhibition rate increased by 1.7 times of that for N:P of 20:1. In addition, the allelopathy of A. sanguinea could not only be a competitive strategy but also a nutrition strategy, playing an important role in formation and/or maintenance of blooms of the mixotrophic dinoflagellate A. sanguinea.     

EFFECT OF NITROGEN AND PHOSPHORUS ON THE GROWTH OF A RED TIDE DINOFLAGELLATE SCRIPPSIELLA TROCHOIDEA (STEIN) LOEBLICH III

INTRODUCTIONRedtidecanadverselyaffectcoastalfisheriesbycausingthedeathofculturedfishandshrimporproducingtoxinsthatcanbeaccumulatedthroughfoodchains (Anderson ,1 989) .Phytoplanktonisoftenthemaincomponentofmanyredtides.AlongthecoastofJiaozhouBay ,P .R .China,theredtideismainlyformedbyadinoflagellate ,Scrippdiellatrochoidea ,duringsummer (JulytoSep tember)andthecelldensitycanreach 9.98× 1 0 7cells ml (Zou ,unpublisheddata) .Manyresearcherssuggestedthatredtideofphytoplanktonmightresultf…     

Estimating areal carbon fixation of intertidal macroalgal community based on composition dynamics and laboratory measurements

The community dynamics and potential carbon ?xation of intertidal macroalgae were investigated monthly from April 2014 to April 2015 in the northwest coast of Yellow Sea. Seasonal variations in biomass and carbon ?xation were presented and showed close relationship with community structure.The carbon ?xation rate ranged from 0.48±0.13 mg C/(g FW ·d) to 4.35±0.12 mg C/(g FW ·d). Sargassum thunbergii, Chondrus ocellatus and Ulva intestinalis were three most in?uential species which contributed27%, 21.9% and 18.5% variation of carbon ?xation rate, respectively. Standing carbon stocks ranged from7.52 g C/m~2 to 41.31 g C/m~2, and estimated carbon stocks varied from 11.77 g C/m 2 to 96.49 g C/m~2. The larger dif ference between estimated and standing carbon stocks implied that more ?xed carbon was exported from the community in summer and autumn than in winter. This study suggested that intertidal macroalgal community could provide a potential function in carbon ?xation of coastal ecosystem.     

Spatial-temporal variation of phytoplankton community structure in Jiaozhou Bay,China

To better understand the spatial-temporal variation in phytoplankton community structure and its controlling factors in Jiaozhou Bay,Qingdao,North China,four seasonal sampling were carried out in 2017.The phytoplankton community structure and various environmental parameters were examined.The phytoplankton community in the bay was composed of mainly diatoms and dinoflagellates,and several other species of Chrysophyta were also observed.Diatoms were the most dominant phytoplankton group throughout the year,except in spring and winter,when Noctiluca scintillans was co-dominant.High Si/N ratios in summer and fall reflect the high dominance of diatoms in the two seasons.Temporally,the phytoplankton cell abundance peaked in summer,due mainly to the high temperatures and nutrient concentrations in summer.Spatially,the phytoplankton cell abundance was higher in the northern part of the bay than in the other parts of the bay in four seasons.The diatom cell abundances show significant positive correlations with the nutrient concentrations,while the dinoflagellate cell abundances show no correlation or a negative correlation with the nutrient concentrations but a significant positive correlation with the stratification index.This discrepancy was mainly due to the different survival strategies between diatoms and dinoflagellates.The Shannon-Wiener diversity index(H')values in the bay ranged from 0.08 to 4.18,which fell in the range reported in historical studies.The distribution pattern of H' values was quite different from that of chlorophyll a,indicating that the phytoplankton community structure might have high biomass with a low diversity index.Compared with historical studies,we believe that the dominant phytoplankton species have been changed in recent years due mainly to the changing environment in the Jiaozhou Bay in recent 30 years.     

Effects of modified clay on cysts of <Emphasis Type="Italic">Scrippsiella trochoidea</Emphasis> for harmful algal bloom control

We present results on the effect of modified clay on cyst formation of Scrippsiella trochoidea in harmful algal bloom （HAB）. Modified clay （in concentration of 0, 0.1, 0.5, and 1.0 g/L） were added to cultures, and observations were made on cysts of S. trochoidea under controlled laboratory conditions. Results indicate that the removal rate of algal cells reached 97.7% at the clay concentration of 1.0 g/L. The cyst formation rate increased from 4.6% to 24.6% when the concentration of clay was increased from 0 to 1.0 g/L. Two cyst metamorphs were observed： spinal calcareous cysts and smooth noncalcareous ones. The proportion of the spinal cysts decreased from 76.9% to 24.1% when clay concentration increased from 0 to 1.0 g/L. In addition, modified clay affected cyst germination. The germination rate decreased with the increases in the clay concentrations. Non-calcareous cysts had a lower germination rate with a longer germination time. We conclude that modified clay could depress algal cell multiplication and promote formation of temporal cysts of S. trochoidea, which may help in controlling HAB outbreaks.     

Effects of modified clay on cysts of Scrippsiella trochoidea for harmful algal bloom control

We present results on the effect of modified clay on cyst formation of Scrippsiella trochoidea in harmful algal bloom(HAB).Modified clay(in concentration of 0,0.1,0.5,and 1.0 g/L) were added to cultures,and observations were made on cysts of 5.trochoidea under controlled laboratory conditions.Results indicate that the removal rate of algal cells reached 97.7%at the clay concentration of 1.0 g/L.The cyst formation rate increased from 4.6%to 24.6%when the concentration of clay was increased from 0to 1.0 g/L.Two cyst metamorphs were observed:spinal calcareous cysts and smooth noncalcareous ones.The proportion of the spinal cysts decreased from 76.9%to 24.1%when clay concentration increased from0 to 1.0 g/L.In addition,modified clay affected cyst germination.The germination rate decreased with the increases in the clay concentrations.Non-calcareous cysts had a lower germination rate with a longer germination time.We conclude that modified clay could depress algal cell multiplication and promote formation of temporal cysts of 5.trochoidea,which may help in controlling HAB outbreaks.     

Acute Toxicities of Potassium Permanganate, Formalin, and Lugol's Iodine Solution to a Marine Ciliate,Pleuronema coronatum ( Ciliophora, Scuticociliatida)

Acute toxicities of potassium permanganate, formalin, and Lugol's iodine solution to a commonly occurred ma-rine ciliate Pleuronema coronatum (Ciliophora, Scuticociliatida) were measured. Linear regression analysis of the resultshighlighted the close relationships between doses of the medicines and mortalities of the organisms, thus providing a capabili-ty to predict toxicity effects from the dose. Toxic effects of the medicines on the ciliates were described in the present paper,and the median lethal concentrations (LC50 values) were given. Results of measurements indicated that 2 h-LC50 and 12 h-LC50 values of formalin on P. coronatum were 59.00 × 10-6 and 43.57 × 10 6, while those of Lugol's solutions were 90.13 and67.84 × 10 6 respectively. The tolerance of P. coronatum to formalin is apparently lower than that to Lugol' s iodine solutionand potassium permanganate is a suitable medicine to kill ciliates in short time.     

NEW OBSERVATIONS ON THE MEIOTIC PROCESS IN THE MARINE DINOFLAGELLATE NOCTILUCA SCINTILLANS (NOCTILUCALES, DINOPHYCEAE)

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Carbon dynamics in woody biomass of forest ecosystem in China with forest management practices under future climate change and rising CO2 concentration

It is critical to study how different forest management practices affect forest carbon sequestration under global climate change regime. Previous researches focused on the stand-level forest carbon sequestration with rare investigation of forest carbon stocks influ- enced by forest management practices and climate change at regional scale. In this study, a general integrative approach was used to simulate spatial and temporal variations of woody biomass and harvested biomass of forest in China during the 21st century under dif- ferent scenarios of climate and CO2 concentration changes and management tasks by coupling Integrated Terrestrial Ecosystem Carbon budget （InTEC） model with Global Forest Model （G4M）. The results showed that forest management practices have more predominant effects on forest stem stocking biomass than climate and CO2 concentration change. Meanwhile, the concurrent future changes in cli- mate and CO2 concentration will enhance the amounts of stem stocking biomass in forests of China by 12%-23% during 2001-2100 relative to that with climate change only. The task for maximizing stem stocking biomass will dramatically enhance the stem stocking biomass from 2001~100, while the task for maximum average increment will result in an increment of stem stocking biomass before 2050 then decline. The difference of woody biomass responding to forest management tasks was owing to the current age structure of forests in China. Meanwhile, the sensitivity of long-term woody biomass to management practices for different forest types （coniferous forest, mixed forest and deciduous forest） under changing climate and CO2 concentration was also analyzed. In addition, longer rotation length under future climate change and rising CO2 concentration scenario will dramatically increase the woody biomass of China during 2001~100. Therefore, our estimation indicated that taking the role of forest management in the carbon cycle into the consideration at regional or national level is very important to project the forest carbon sequestration under future climate change and rising atmospheric CO2 concentration.     

Interspecific Competition Between Levanderina fissa(Dinophyceae) and the Other Three Microalgal Species in Co-Cultures

Growth interactions between the dinoflagellate Levanderina fissa(=Gyrodinium instriatum) and the other three algal bloom species Skeletonema costatum(Bacillariophyceae), Prorocentrum micans(Dinophyceae), and Chattonella marina(Raphidophyceae) were studied using bi-or tri-algal co-cultures under laboratory conditions. The Lotka-Volterra model was applied to estimate the interspecific competition between them. Results showed that the growth of L. fissa was significantly suppressed in both bi-algal and tri-algal cultures, and the maximum cell densities in co-cultures were only between 21% and 69% of that in mono-culture. L. fissa outcompeted P. micans; however, its effects on S. costatum and C. marina were generally less than the effects of their intraspecific competitions based on the competition coefficients. Contrarily, the inhibitory effects of S. costatum and C. marina on L. fissa were much greater. S. costatum outcompeted the other three species in all co-cultures, and its competition coefficients on the other species were more than 10000 times higher than the opposite. The growth of C. marina was suppressed by S. costatum; however, it outcompeted L. fissa and P. micans. The growth of P. micans was most strongly inhibited in co-cultures, and the maximum cell densities in co-cultures were less than 15% of that in mono-species culture. The results suggested that L. fissa had few advantages in the interspecific competition. The adaptation to low salinity and the utilization of organic phosphorus might be the important reasons for L. fissa to take the competitive predominance in brackish estuarine environments.     

森林碳蓄积量估算方法及其应用分析

近些年来,森林锐减、土地退化、环境污染、生物多样性丧失,特别是人类活动产生的C0₂浓度急剧上升和由此导致的温室效应等是目前人类面临最严峻的全球环境变化问题,所以全球碳循环问题日益成为全球变化与地球科学研究领域的前沿与热点问题,其中陆地生态系统碳循环又是全球碳循环中最复杂、受人类活动影响最大的部分。而森林生物量占整个陆地生态系统生物量的90%,因此,为了正确评估森林在全球碳平衡中的作用,了解森林生态系统在碳循环中的作用,森林的碳动态研究正日益成为人们关注的重点。本文总结了估算森林固碳量的几种方法--样地清查法、模型模拟法和遥感估算法,分析了它们的特点及应用等有关问题。     

Crown fuel characteristics and carbon emission from Japanese red pine stands burned by crown fire in Mt. Palgong, South Korea

Carbon emissions from forest fires are considered an important factor of ecosystem carbon balance and global climate change. Carbon emissions from Japanese red pine stands (Pinus densiflora S. et Z.) burned by crown fire were estimated at Mt. Palgong in Daegu Metropolitan City, and crown fuel characteristics, including crown bulk density, crown base height, and fuel moisture content of Japanese red pine, were analyzed. Total biomass combusted was calculated by subtracting the biomass of burned stands from that of unburned stands exhibiting similar stand structures and site environments. Ten trees in the unburned area and five trees in the burned area were cut by using direct harvesting techniques to estimate crown layer biomass. All biomass sampled was oven-dried and weighed. The dry weight ratios of stems, branches, and needles were 70%, 21%, and 9%, respectively. The available fuel load susceptible to combustion during the crown fire spread was equivalent to 55% of the crown layer biomass. The crown bulk density was 0.24 kg/ m 3 on average. The estimated amount of CO 2 was 23,454 kg CO 2 /ha for the crown layer. These results will be useful for calculating the amount of CO 2 emitted from forest fires and for developing a forest carbon model in P. densiflora forests.     

Identification of dissolved and particulate carbonyl compounds produced by marine harmful algal bloom species

Carbonyl compounds,especially polyunsaturated aldehydes(PUAs),are increasingly reported as teratogenic to grazers and deleterious to phytoplankton.While PUAs have been considered to be mainly produced by diatoms after cell wounding,little is known about whether microalgae other than diatoms,particularly harmful algal bloom(HAB)-forming species,produce carbonyl compounds.In this study,we analyzed the carbonyl compounds from eight common HAB-forming species(Akashiwo sanguinea,Karenia mikimotoi,Karlodinium veneficum,Margalefidinium polykrikoides,Prorocentrum donghaiense,P.minimum,Scrippsiella trochoidea,and Heterosig,ma akashiwo)using gas chromatography-mass spectrometry in full scan and selected ion monitoring(SIM)modes.Our results show a ubiquitous presence of carbonyl colmpounds in both dissolved and particulate forms in all species we examined.In the full scan mode,133 chromatographic peaks were detected from 51 samples altogether.Both the varieties of carbonyl compounds and their quantities were algal species dependent,although most of the carbonyl compounds could not be fully identified according to the mass spectral database only due to the unavailability of enough standards for all analytes.Aided with nine standards in SIM mode,we further identified and quantified all nine aldehydes(2-methyl-2-pentenal,trans-2-nonenal,cis-6-nonenal,2,6-dimethyl-5-heptenal,trans-2-hexenal,trans-2-decenal,2,4-heptadienal,trans-trans-2,4-octadienal,and trans-trans-2,4-decadienal).Four of these nine aldehydes were detected in particulate form,which confirmed that trans-2-nonenal could be produced by K.mikimotoi,Karl.veneficum,P.donghaiense,P.minimum,S.trochoidea,and H.akashiwo,2,4-heptadienal and trans-trans-2,4-decadienal by A.sanguinea,M.polykrikoides,and S.trochoidea,and trans,trans-2,4-octadienal by S.trochoidea,respectively.We proved that some dinoflagellate and raphidophyte species could contribute to the pool of carbonyl compounds including PUAs in a marine ecosystem.Some carbonyl compounds,particularly those in high cell quota and/or dissolved concentration,may be related to fishkilling or allelopathy which needs further identification and quantification.     

Solid sand particle addition can enhance the production of resting cysts in dinoflagellates

Resting cysts are an important part of the life cycle for many harmful algal bloom-forming dinoflagellates, and play vital roles in the recurrence and geographical spread of harmful algal blooms. Numerous factors have been suggested to regulate the formation of resting cysts, although only a few have been proven to be significant. Cyst formation can be induced by adverse environmental conditions such as drastic changes in temperature, light, salinity, and nutrient levels, and by biological interactions. In this study, we evaluated the ability of an artificial factor(fine sand particles) to enhance the formation of resting cysts. Fine sand particles were added to cultures of dinoflagellates that are known to produce cysts. The addition of fine sand particles significantly increased both the production rate and final yield of cysts in cultures of S crippsiella trochoidea, Biecheleria brevisulcata, and Levanderina fissa(= Gymnodinium fissum, Gyrodinium instriatum, Gyr odinium uncatenum). The largest increase in the final yield(107-fold) of cysts as a result of sand addition was in S. trochoidea. However, addition of fine sand particles did not induce cyst formation, or barely af fected cyst formation, in A kashiwo san guinea, Cochlodinium polykrikoides and Pheopolykrikos hartmannii, which are also known to be cyst-producing species. We speculated that addition of sand significantly increased the chances of cell collision, which triggered cyst formation. However, further research is required to test this idea. Importantly, our findings indicate that the addition of fine sand particles is a useful method to obtain a large quantity of cysts in a short time for laboratory studies or tests; for example, if a cyst viability test is being used to assess the eff ectiveness of ships' ballast water treatment.     

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.     

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.     

Effects of culture conditions on growth and docosahexaenoic acid production from Schizochytrium limacinum

The effects of temperature, initial pH, salinity of culture medium, and carbon and nitrogen sources on growth and docosahexaenoic acid （C22：6 n-3, DHA） production from Schizochytrium limacinum OUC88 were investigated in the present study. The results revealed that the optimal temperature, initial pH and salinity level of the medium for DHA production were 23 ℃, 7.0 and 18, respectively. Glucose was proved the best carbon source for the growth and DHA production from S. limacinum. Among the nitrogen sources tested, soybean cake hydrolysate, a cheap by-product, was found to be effective for the accumulation of DHA in S. limacinum cells. In addition, increasing the concentration of carbon sources in the medium caused a significant increase in cell biomass; however, accumulation of DHA in cells was mainly stimulated by the ratio of C/N in the medium. Under the optimal culture conditions, the maximum DHA yield achieved in flasks was 4.08 g L^-1 after 5 d of cultivation     

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.