Species-area relationship within and across functional groups at alpine grasslands on the northern Tibetan Plateau,China

The species-area relationship(SAR) is one of the most fundamental concepts in community ecology and is helpful for biodiversity conservation.However,few studies have systematically addressed this topic for different alpine grassland types on the Tibetan Plateau,China.We explored whether the plant composition of different functional groups affects the manner in which species richness increases with increasing area at scales ≤ 1.0 m~2.We also compared species richness(S) within and across forbs,legumes,sedges and grasses,with sampling subplot area(A) increasing from 0.0625 m~2 to 1.0 m~2 between alpine meadow and steppe communities.We applied a logarithmic function(S = b_0 + b_1 ln A) to determine the slope and intercept of SAR curves within and across functional groups.The results showed that the logarithmic relationship holds true between species richness and sampling area at these small scales.Both the intercept and slope of the logarithmic forbs-area curves are significantly higher than those for the three other functional groups(P 0.05).Forb accounts for about 91.9 % of the variation in the intercept and 75.0% of the variation in the slope of the SAR curve when allfunctional groups' data were pooled together.Our results indicated that the different SAR patterns should be linked with species dispersal capabilities,environmental filtering,and life form composition within alpine grassland communities.Further studies on the relationship between species diversity and ecosystem functions should specify the differential responses of different functional groups to variations in climate and anthropogenic disturbances.     

Crop residue incorporation and nitrogen fertilizer effects on greenhouse gas emissions from a subtropical rice system in Southwest China

Crop residue incorporation has been widely accepted as a way to increase soil carbon (C) sequestration and sustain soil fertility in agroecosystems. However, effect of crop residue incorporation on greenhouse gas (GHG) emissions in rice paddy soils remains uncertain. A field experiment was conducted to quantify emissions of CH₄ and N₂O and soil heterotrophic respiration (R_H) from a paddy rice field under five different crop residue treatments (i.e., 150 kg N ha^-1 of synthetic N fertilizer application only [NF], 150 kg N ha^-1 of synthetic N fertilizer plus 5.3 Mg ha^-1 wheat residue [NF-WR1], 150 kg N ha^-1 of synthetic N fertilizer plus 10.6 Mg ha^-1 wheat residue [NF-WR2], 75 kg N ha^-1 of synthetic N fertilizer plus 10.6 Mg ha^-1 wheat residue [50%NF-WR2] and 150 kg N ha^-1 of synthetic N fertilizer plus 21.2 Mg ha^-1 wheat residue [NF-WR3]) in southwest China. Our results showed that crop residue incorporation treatments (NF-WR1, NF-WR2, 50%NF-WR2, NF-WR3) significantly increased CH₄ emissions by at least 60%, but N₂O emissions were not enhanced and even suppressed by 25% in the NF-WR3 treatment as compared to the NF treatment. Soil R_H emissions were comparable among experimental treatments, while crop residue incorporation treatments significantly increased soil carbon sequestrations relative to the NF treatment. Overall, CH₄ emissions dominated total global warming potentials (GWP) across all experimental treatments. The average yieldscaled GWPs for the NF and NF-WR1 treatments were significantly lower than for the NF-WR2, 50%NFWR2 and NF-WR3 treatments. Given the comparable yield-scaled GWPs between the NF and NF-WR1 treatments, the NF-WR1 treatment could gain net carbon sequestration as compared with the NF treatment with net soil carbon loss. Our findings suggest that the NF-WR1 treatment should be an effective option to sustain rice production while mitigating GHG emissions from the rice field in China.     

Alterations to biological soil crusts with alpine meadow retrogressive succession affect seeds germination of three plant species

Biological soil crusts (BSCs) are the important components of alpine meadow ecosystems. The extent and morphology of BSCs vary greatly with alpine meadow retrogressive succession due to grazing pressure. There is significant interest in impacts of crust composition on plant seed germination, especially in (semi-) arid environments. However, little is known about the influences of BSCs, and their associations with alpine meadow succession, on germination of typical alpine meadow vascular plant species. In a full factorial common-garden experiment, we studied effects of: (1) crust type, (2) seed position, and (3) surface texture on seed germination. We chose three typical alpine meadow plant species (i.e. Poa pratensis, Tibetia himalaica and Potentillen nivea), which belonged to different functional groups (graminoids, legumes, and forbs) and play important roles in all alpine meadow succession stages. Crust type and seed position influenced seed germination, and the inhibitory effects of BSCs depended on the crust type and seed species tested. The major factors influencing seed germination were BSC type, seed position, soil texture, and the interactions between BSC type and seed position; species and seed position; species and surface texture; and species, crust type, and surface texture. Cyanobacteria crust significantly inhibited germination of all seeds. Seed position also had a significant effect on seed germination (p < 0.001). Fewer seedlings germinated on the surface than below the surface, this was especially true for P. nivea. seeds within cyanobacteria and lichen crusts. Only germination rates of T. himalaica on the soil surface were significantly correlated with plant occurrence frequency within the alpine meadow community. The poor correlation for the other two species is possibly that they are perennials. Our results clearly demonstrated that BSCs can be biological filters during seed germination, depending on the BSC succession stage. Through their influences on seed germination, BSCs can strongly influence community assemblages throughout alpine meadow retrogressive succession.     

Spatio-temporal Variation of Soil Respiration and Its Driving Factors in Semi-arid Regions of North China

Soil respiration (SR) is the second-largest flux in ecosystem carbon cycling. Due to the large spatio-temporal variability of environmental factors, SR varied among different vegetation types, thereby impeding accurate estimation of CO₂ emissions via SR. However, studies on spatio-temporal variation of SR are still scarce for semi-arid regions of North China. In this study, we conducted 12-month SR measurements in six land-use types, including two secondary forests (Populus tomentosa (PT) and Robinia pseudoacacia (RP)), three artificial plantations (Armeniaca sibirica (AS), Punica granatum (PG) and Ziziphus jujuba (ZJ)) and one natural grassland (GR), to quantify spatio-temporal variation of SR and distinguish its controlling factors. Results indicated that SR exhibited distinct seasonal patterns for the six sites. Soil respiration peaked in August 2012 and bottomed in April 2013. The temporal coefficient of variation (CV) of SR for the six sites ranged from 76.98% to 94.08%, while the spatial CV of SR ranged from 20.28% to 72.97% across the 12-month measurement. Soil temperature and soil moisture were the major controlling factors of temporal variation of SR in the six sites, while spatial variation in SR was mainly caused by the differences in soil total nitrogen (STN), soil organic carbon (SOC), net photosynthesis rate, and fine root biomass. Our results show that the annual average SR and Q₁₀ (temperature sensitivity of soil respiration) values tended to decrease from secondary forests and grassland to plantations, indicating that the conversion of natural ecosystems to man-made ecosystems may reduce CO₂ emissions and SR temperature sensitivity. Due to the high spatio-temporal variation of SR in our study area, care should be taken when converting secondary forests and grassland to plantations from the point view of accurately quantifying CO₂ emissions via SR at regional scales.     

Effect of barley straw biochar application on greenhouse gas emissions from upland soil for Chinese cabbage cultivation in short-term laboratory experiments

Chinese cabbage was cultivated in upland soil with the addition of biochar in order to investigate the potential for reduction of greenhouse gas emissions. Barley straw biochar (BSB) was introduced in a Wagner pot (1/5000a) in amounts of 0 (BSB0, control), 100 (BSB100), 300 (BSB300), and 500 (BSB500) kg 10a^-1. After the addition of BSB into the upland soil, carbon dioxide (CO₂) emission increased while methane (CH₄) and nitrous oxide (N₂O) emissions decreased. The highest CO₂ flux was measured for the BSB500 sample, (84.6 g m^-2) followed by BSB300, BSB100, and BSB0 in decreasing order. Relative to those of control, the total CH₄ flux and N₂O flux for the BSB500 treatment were lower by 31.6% and 26.1%, respectively. The global warming potential (GWP) of the treatment without biochar was 281.4 g CO₂ m^-2 and those for treatments with biochar were in the range from 194.1 to 224.9 g CO₂ m^-2. Therefore, introducing BSB into upland soil to cultivate Chinese cabbages can reduce the global warming potential.     

Unusual hydrocarbon waxes detected in <Emphasis Type="Italic">Salix oritrepha</Emphasis> leaf from Nianbaoyeze Mountains,eastern Qinghai-Tibetan Plateau

Plant biomarkers, such as hydrocarbon waxes, are frequently found in various sediments and could be adopted as paleovegetation and paleoclimate indicators. Nevertheless, scarce researches have focused on leaf waxes in higher plants of alpine region. Herein, hydrocarbon leaf wax components of Salix oritrepha, which flourish in Nianbaoyeze Mountains in eastern Tibetan Plateau were fully discussed. The n-alkane distribution in leaves ranges from n-C₂₁ to n-C₂₉ with maxima at n-C₂₅, which were entirely different with Salix taxa displayed in previous surveys in non-alpine regions. The unusual even carbon nalkenes from n-C_22:1 to n-C_30:1, which were thought to appear only in aquatic organisms, were firstly reported in an alpine plant. Additionally, iso-(2-methyl) alkanes, ranging from i-C₂₃ to i-C₂₉ with maxima at i-C₂₅, which have been commonly reported in microorganisms, were also identified in an alpine plant for the first time. Unusual hydrocarbon distribution detected in Salix oritrepha leaf from Nianbaoyeze Mountains is most likely due to the extreme environment in such alpine region.     

Effects of Anthropogenic Disturbance on Sediment Organic Carbon Mineralization Under Different Water Conditions in Coastal Wetland of a Subtropical Estuary

The changes in soil organic carbon(C) mineralization as affected by anthropogenic disturbance directly determine the role of soils as C source or sink in the global C budget. The objectives of this study were to investigate the effects of anthropogenic disturbance(aquaculture pond, pollutant discharge and agricultural activity) on soil organic C mineralization under different water conditions in the Minjiang River estuary wetland, Southeast China. The results showed that the organic C mineralization in the wetland soils was significantly affected by human disturbance and water conditions(P 0.001), and the interaction between human disturbance activities and water conditions was also significant(P 0.01). The C mineralization rate and the cumulative mineralized carbon dioxide-carbon(CO_2-C)(at the 49th day) ranked from highest to lowest as follows: Phragmites australis wetland soil aquaculture pond sediment soil near the discharge outlet rice paddy soil. This indicated that human disturbance inhibited the mineralization of C in soils of the Minjiang River estuary wetland, and the inhibition increased with the intensity of human disturbance. The data for cumulative mineralized CO_2-C showed a good fit(R~2 0.91) to the first-order kinetic model C_t = C_0(1 – exp(–kt)). The kinetic parameters C_0, k and C_0 k were significantly affected by human disturbance and water conditions. In addition, the total amount of mineralized C(in 49 d) was positively related to C_0, C_0 k and electrical conductivity of soils. These findings indicated that anthropogenic disturbance suppressed the organic C mineralization potential in subtropical coastal wetland soils, and changes of water pattern as affected by human activities in the future would have a strong influence on C cycling in the subtropical estuarine wetlands.     

Degradation significantly decreased the ecosystem multifunctionality of three alpine grasslands: evidences from a large-scale survey on the Qinghai-Tibetan Plateau

Owing to the joint effects of ecosystem fragility,anthropogenic disturbance and climate change,alpine grasslands(alpine meadow,alpine steppe and alpine desert)have experienced serious degradation during the past several decades.Grasslands degradation has severely affected the delivery of ecosystem multifunctionality(EMF)and services,and then threatens the livelihood of local herdsmen and ecological security of China.However,we still lack comprehensive insights about the effects of degradation and climatic factors on EMF of alpine grasslands,especially for alpine desert ecosystem.Therefore,we applied a large-scale field investigation to answer this question.Our results suggested grassland degradation significantly decreased the belowground ecosystem multifunctionality(BEMF)and EMF of alpine grasslands and aboveground ecosystem multifunctionality(AEMF)of alpine meadow,while did not reduce the AEMF of alpine steppe and desert.Except for the insignificant difference between degraded steppe and degraded desert in AEMF,the alpine meadow showed the highest AEMF,BEMF and EMF,alpine steppe ranked the second and alpine desert was the lowest.AEMF,BEMF and EMF of health alpine grasslands were strongly affected by mean annual precipitation(MAP)(19%-51%)and mean annual temperature(MAT)(9%-36%),while those of degraded meadow and degraded desert were not impacted by precipitation and temperature.AEMF and BEMF showed a synergistic relationship in healthy alpine grasslands(12%-28%),but not in degraded grasslands.Our findings emphasized the urgency of implementing the feasible ecological restoration project to mitigate the negative influences of grassland degradation on EMF of alpine ecosystems.     

Distribution and quantitative zonation of unloading cracks at a proposed large hydropower station dam Site

Rock mass unloading is an important rock engineering problem because unloading may impact the stability of a rock mass slope. Based on hydroelectric engineering principles, this study focuses on the classification of unloading zones to reflect the rock mass structure characteristics. Geological background and slope structure of the study region were considered to investigate the distribution and deformation of the unloading process. Quantitative indices were classified according to the formation mechanisms and the geological exhibition of unloading zones. The P-wave velocity (V _P ), the ratio of the wave velocity (K _V , the ratio of the test P-wave velocity along the adit depth to the P-wave velocity of intact rock), the sum of joint openings every 2 meters (S _t ), and the density of open joints (D _t ) were calculated as quantitative indices for the rock mass unloading zone. The characteristics of the unloading zone of rock mass slopes at the dam site were successfully determined. The method of combining qualitative data with quantitative indices was found to be effective for the classification of slope unloading zones.     

Diurnal variation of soil CO<Subscript>2</Subscript> efflux and its optimal measuring time-window of temperate meadow steppes in western Songnen Plain,China

In order to study the diurnal variation of soil CO_2 efflux from temperate meadow steppes in Northeast China, and determine the best time for observation, a field experiment was conducted with a LI-6400 soil CO_2 flux system under five typical plant communities(Suaeda glauca(Sg), Chloris virgata(Cv), Puccinellia distans(Pd), Leymus chinensis(Lc) and Phragmites australis(Pa)) and an alkali-spot land(As) at the meadow steppe of western Songnen Plain. The results showed that the diurnal variation of soil CO_2 efflux exhibited a single peak curve in the growing season. Diurnal maximum soil respiration(Rs) often appeared between 11:00 and 13:00, while the minimum occurred at 21:00–23:00 or before dawn. Air temperature near the soil surface(Ta) and soil temperature at 10 cm depth(T10) exerted dominant control on the diurnal variations of soil respiration. The time-windows 7:00–9:00 could be used as the optimal measuring time to represent the daily mean soil CO_2 efflux at the Cv, Pd, Lc and Pa sites. The daily mean soil CO_2 efflux was close to the soil CO_2 efflux from 15:00 to 17:00 and the mean of 2 individual soil CO_2 efflux from 15:00 to 19:00 at the As and Sg sites, respectively. During nocturnal hours, negative soil CO_2 fluxes(CO_2 downwards into the soil) were frequently observed at the As and Sg sites, the magnitude of the negative CO_2 fluxes were 0.10–1.55 μmol/(m~2·s) and 0.10–0.69 μmol/(m~2·s)at the two sites. The results implied that alkaline soils could absorb CO_2 under natural condition, which might have significant implications to the global carbon budget accounting.     

Contribution of aboveground litter to soil respiration in <Emphasis Type="Italic">Populus davidiana</Emphasis> Dode plantations at different stand ages

Soil respiration from decomposing aboveground litter is a major component of the terrestrial carbon cycle. However, variations in the contribution of aboveground litter to the total soil respiration for stands of varying ages are poorly understood. To assess soil respiration induced by aboveground litter, treatments of litter and no litter were applied to 5-, 10-, and 20-year-old stands of Populus davidiana Dode in the sandstorm source area of Beijing-Tianjin, China. Optimal nonlinear equations were applied to model the combined effects of soil temperature and soil water content on soil respiration. Results showed that the monthly average contribution of aboveground litter to total soil respiration were 18.46% ± 4.63%, 16.64% ± 9.31%, and 22.37% ± 8.17% for 5-, 10-, and 20-year-old stands, respectively. The relatively high contribution in 5- and 20-year-old stands could be attributed to easily decomposition products and high accumulated litter, respectively. Also, it fluctuated monthly for all stand ages due to substrate availability caused by phenology and environmental factors. Litter removal significantly decreased soil respiration and soil water content for all stand ages (p < 0.05) but not soil temperature (p > 0.05). Variations of soil respiration could be explained by soil temperature at 5-cm depth using an exponential equation and by soil water content at 10-cm depth using a quadratic equation, whereas soil respiration was better modeled using the combined parameters of soil temperature and soil water content than with either soil temperature or soil water content alone. Temperature sensitivity (Q ₁₀) increased with stand age in both the litter and the no litter treatments. Considering the effects of aboveground litter, this study provides insights for predicting future soil carbon fluxes and for accurately assessing soil carbon budgets.     

Study on the Liquefaction Properties of Silt at Yellow River Delta

The seabed of the Yellow River Delta is formed by the rapid deposition of sediments from the Yellow River. Recent researches have shown that the geological hazards in the Yellow River Delta are mainly related to the liquefaction of silty seabed under cyclic loading. In this paper, based on the theory of Stokes Viscous Principle, a self-design dragging ball apparatus was used to study the fluid characteristics of liquefied and post-liquefied silt more thoroughly. Wave flume and shaking table were used to apply wave loads and vibration loads. The pore pressure, earth pressure, and moving parameters of the dragging ball were recorded during tests. The effect of cyclic loads and excess pore pressure ratio on viscosity of silty soil is discussed. The constitutive model of flow characteristics of liquefied silt is also established. The results indicate that the apparent viscosity of silty soil is much higher than sand. Cyclic loads accelerated the process of silt liquefaction, resulting in the decrease in apparent viscosity. The excess pore pressure ratio (r_u) has effect on silt liquefaction. When the soil had not reached the completely liquefied state (r_u < 1), the apparent viscosity decreased with the increase of excess pore pressure ratio; when the soil had reached the completely liquefied state (r_u = 1), the shear stress decreased with the increase of strain rate. It was determined that silty soil characterized by shear thinning can be viewed as a type of non-Newtonian fluid. The equation of the shear stress and shear strain rates was established by fitting the test data.     

Determining critical support discharge of a riverhead and river network analysis: Case studies of Lhasa River and Nyangqu River

A riverhead is the demarcation point of continuous water channel and seasonal channel, which is characterized by a critical flow that can support a continuous water body. In this study, the critical support discharge(CSD) is defined as the critical steady flows required to form the origin of a stream. The CSD is used as the criterion to determine the beginning of the riverhead, which can be controlled by hydro-climate factors(e.g., annual precipitation, annual evaporation, or minimum stream flow in arid season). The CSD has a close correlation with the critical support/source area(CSA) that largely affects the density of the river network and the division of sub-watersheds. In general, river density may vary with regional meteorological and hydrological conditions that have to be considered in the analysis. In this paper, a new model referring to the relationship of CSA and CSD is proposed, which is based on the physical mechanism for the origin of riverheads. The feasibility of the model was verified using two watersheds(Duilongqu Basin of the Lhasa River and Beishuiqu Basin of the Nyangqu River) in Tibet Autonomous Region to calculate the CSA and extract river networks. A series of CSAs based on different CSDs in derived equation were tested by comparing the extracted river networks with the reference network obtained from a digitized map of river network at large scales. Comparison results of river networks derived from digital elevation model with real ones indicate that the CSD(equal to criterion of flow quantity(Q_c)) are 0.0028 m~3/s in Duilongqu and 0.0085 m~3/s in Beishuiqu. Results show that the Q_c can vary with hydro-climate conditions. The Q_c is high in humid region and low in arid region, and the optimal Q_c of 0.0085 m~3/s in Beishuiqu Basin(humid region) is higher than 0.0028 m~3/s in Duilongqu Basin(semi-arid region). The suggested method provides a new application approach that can be used to determine the Q_c of a riverhead in complex geographical regions, which can also reflect the effect of hydro-climate change on rivers supply in different regions.     

Effects of <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> YC459 and soil types on seed germination and seedling growth in rock slope restoration

We carried out experiments with various concentrations of Trichoderma harzianum YC459 in different soil types (forest soil, mixed soil, merchantable soil, and leaf mold soil) to evaluate its effect on seed germination and seedling establishment of four species (Festuca arundinacea Schreb., Dianthus barbatus var. asiaticus Nakai, Lespedeza cyrtobotrya Miq., and Parthenocissus tricuspidata Planch) for rock slope restoration. We also investigated the use of drilled slanted holes on the rock slopes for seedling establishment. The results showed that T. harzianum concentration had significant effects on seed germination, seedling growth, and seedling survival for all the species with different soil types. Seed germination and survival rates peaked at 5% T. harzianum concentration with leaf mold soil and decreased as T. harzianum concentration increased from 5% to 10%. Seedling survival rates of all four species were generally lowest at 0% T. harzianum concentration in all soil types. The height of F. arundinacea and L. cyrtobotrya peaked at 5% T. harzianum concentration whereas that of D. barbatus and P. tricuspidata peaked at 10% T. harzianum concentration. We concluded that 5% T. harzianum concentration with leaf mold soil is appropriate for seed germination and seedling survival rates of most species, thus enhancing seedling establishment. Practical application of the findings of this study will contribute in the vegetation restoration of steep rocks in mountain environments     

Estimating the properties of weathered bedrock and pilerock interaction from the geological strength index

The effect of variable rock mass properties on pile-rock interaction poses a great challenge to the design of stabilizing piles and numerical analysis of pile-rock interaction. The paper presents a novel method to estimate the properties of weathered bedrock, which can be applied to routine design of landslide-stabilizing piles for collivial landslides. The Ercengyan landslide located in the Three Gorges Reservoir, China, is the area of interest for this study. A geological investigation and triaxial tests were conducted to estimate the basic parameters, including Geological Strength Index(GSI), uniaxial compressive strength σ_(ci) and Hoek-Brown constant m_i of intact bedrock in the study area. Hoek-Brown criterion was used to estimate mechanical properties of the weathered rock, including elastic modulus E_m, cohesion c, friction angle Φ, and normal ultimate lateral resistance p_(max). A parametric study was performed to evaluate the effect of parameterizations of GSI, σ_(ci) and m_i on the bedrock properties and p-y curves. The estimated rock mass properties were used with PLAXIS 2D software to simulate pile-rock interaction. Effect of GSI on stress at the pile-rock interface and in the rock, pile bending moment, pile shear force, and p-y curve were analysed.     

An evaluation on using soil aggregate stability as the indicator of interrill erodibility

Aggregate stability is a very important predictor of soil structure and strength,which influences soil erodibility.Several aggregate stability indices were selected for estimating interrill erodibility of four soil types with contrasting properties from temperate and subtropical regions of China.This study was conducted to investigate how closely the soil interrill erodibility factor in the Water Erosion Prediction Project(WEPP) model relates to soil aggregate stability.The mass fractal dimension(FD),geometric mean diameter(GMD),mean weight diameter(MWD),and aggregate stability index(ASI) of soil aggregates were calculated.A rainfall simulator with a drainable flume(3.0 m long × 1.0 m wide × 0.5 m deep) was used at four slope gradients(5°,10°,15° and 20°),and four rainfall intensities(0.6,1.1,1.7 and 2.5 mm/min).Results indicated that the interrill erodibility(Ki) values were significantly correlated to the indices of ASI,MWD,GMD,and FD computed from the aggregate wet-sieve data.The Ki had a strong positive correlation with FD,as well as a strong negative correlation with ASI,GMD,and MWD.Soils with a higher aggregate stability and lower fractal dimension have smaller Ki values.Stable soils were characterized by a high percentage of large aggregates and the erodible soils by a high percentage of smaller aggregates.The correlation coefficients of Ki with ASI and GMD were greater than those with FDand MWD,implying that both the ASI and GMD may be better alternative parameters for empirically predicting the soil Ki factor.ASI and GMD are more reasonable in interrill soil erodibility estimation,compared with Ki calculation in original WEPP model equation.Results demonstrate the validation of soil aggregation characterization as an appropriate indicator of soil susceptibility to erosion in contrasting soil types in China.     

Effects of rainfall regime and its character indices on soil loss at loessial hillslope with ephemeral gully

Understanding the relationship between hillslope soil loss with ephemeral gully and rainfall regime is important for soil loss prediction and erosion control. Based on 12-year field observation data, this paper quantified the rainfall regime impacts on soil loss at loessial hillslope with ephemeral gully. According to three rainfall parameters including precipitation (P), rainfall duration (t), and maximum 30-minute rainfall intensity (I ₃₀), 115 rainfall events were classified by using K-mean clustering method and Discriminant Analysis. The results showed that 115 rainfall events could be divided into three rainfall regimes. Rainfall Regime 1 (RR1) had large I ₃₀ values with low precipitation and short duration, while the three rainfall parameters of Rainfall Regime 3 (RR3) were inversely different compared with those of RR1; for Rainfall Regime 2 (RR2), the precipitation, duration and I ₃₀ values were all between those of RR1 and RR3. Compared with RR2 and RR3, RR1 was the dominant rainfall regime for causing soil loss at the loessial hillslope with ephemeral gully, especially for causing extreme soil loss events. PI ₃₀ (Product of P and I ₃₀) was selected as the key index of rainfall characteristics to fit soil loss equations. Two sets of linear regression equations between soil loss and PI ₃₀ with and without rainfall regime classification were fitted. Compared with the equation without rainfall regime classification, the cross validation results of the equations with rainfall regime classification was satisfactory. These results indicated that rainfall regime classification could not only depict rainfall characteristics precisely, but also improve soil loss equation prediction accuracy at loessial hillslope with ephemeral gully.     

Soil nutrients in relation to vertical roots distribution in the riparian zone of Three Gorges Reservoir,China

Since the impoundment of the Three Gorges Reservoir (TGR), the riparian zone has been subjected to numerous environmental changes. This study was conducted to recognize the distribution of grass roots and its impacts on soil nutrients in the water level fluctuation zone of TGR. Roots of four predominant herbaceous plants in the study area, specifically, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, and their corresponding relation with soil nutrient contents were investigated. Root surface area density was determined with WinRHIZO, and the relationships of root distribution with soil depths and soil nutrient contents were studied. The results indicates that most roots are distributed in the top soil layer of 0–10 cm. Estimated root surface area density for the selected grass species ranges from 0.16 to 13.44 cm2/cm3, and decreases exponentially with an increase in soil depth. Soil organic matter and total nitrogen contents are significantly lower on bare control area than the corresponding values on the grasslands. Total nutrient contents on grasslands of C. dactylon and H. compressa are higher than those of other grass areas. Root length density and root surface area density are significantly correlated with soil organic matter and total nitrogen content for the four grasslands. The present results suggests that plant roots have significant effects on the distribution of soil nutrients in soil profiles in the riparian zone along the TGR. Nevertheless, additional investigations are needed to reveal the specific interactions between plant roots distribution, soil nutrients and water level fluctuations.     

Leaf stable carbon isotope composition in <Emphasis Type="Italic">Picea schrenkiana</Emphasis> var. <Emphasis Type="Italic">tianschanica</Emphasis> in relation to leaf physiological and morphological characteristics along an altitudinal gradient

To understand the effects of leaf physiological and morphological characteristics on δ ¹³C of alpine trees, we examined leaf δ ¹³C value, LA, SD, LNC, LPC, LKC, Chla+b, LDMC, LMA and N_area in one-year-old needles of Picea schrenkiana var. tianschanica at ten points along an altitudinal gradient from 1420 m to 2300 m a.s.l. on the northern slopes of the Tianshan Mountains in northwest China. Our results indicated that all the leaf traits differed significantly among sampling sites along the altitudinal gradient (P<0.001). LA, SD, LPC, LKC increased linearly with increasing elevation, whereas leaf δ ¹³C, LNC, Chla+b, LDMC, LMA and N_area varied non-linearly with changes in altitude. Stepwise multiple regression analyses showed that four controlled physiological and morphological characteristics influenced the variation of δ ¹³C. Among these four controlled factors, LKC was the most profound physiological factor that affected δ ¹³C values, LA was the secondary morphological factor, SD was the third morphological factor, LNC was the last physiological factor. This suggested that leaf δ ¹³C was directly controlled by physiological and morphological adjustments with changing environmental conditions due to the elevation.     

Distribution of soil carbon in different grassland types of the Qinghai-Tibetan Plateau

Accurate estimate of soil carbon storage is essential to reveal the role of soil in global carbon cycle. However, there is large uncertainty on the estimation of soil organic carbon (SOC) storage in grassland among previous studies, and the study on soil inorganic carbon (SIC) is still lack. We surveyed 153 sites during plant peak growing season and estimated SOC and SIC for temperate desert, temperate steppe, alpine steppe, steppe meadow, alpine meadow and swamp, which covered main grassland in the Qinghai Plateau during 2011 to 2012. The results showed that the vertical and spatial distributions of SOC and SIC varied by grassland types. The SOC amount mainly decreased from southeast to northwest, whereas the SIC amount increased from southeast to northwest. The magnitude of SOC amount in the top 50 cm across grassland types ranked by: swamp > alpine meadow > steppe meadow > temperate steppe > alpine steppe > temperate desert, while the SIC amount showed an opposite order. There was a great deal of variation in proportion of SOC and SIC among different grassland types (from 55.17 to 94.59 for SOC and 5.14 to 44.83 for SIC). The total SOC and SIC storage was 5.78 Pg and 1.37 Pg, respectively, in the top 50 cm of soil in Qinghai Province. The mixed linear model revealed that grassland types was the predominant factor in spatial variations of SOC amount while grassland types and soil pH accounted for those of SIC amount. Our results suggested that the community shift of alpine meadow towards alpine grassland induced by climate warming would decrease carbon sequestration capacity by 6.0 kg C m².