Temperate Typical Steppe Research Articles

Estimating Grassland Carbon Stocks in Hulunber China, Using Landsat8 Oli Imagery and Regression Kriging.

Accurately estimating grassland carbon stocks is important in assessing grassland productivity and the global carbon balance. This study used the regression kriging (RK) method to estimate grassland carbon stocks in Northeast China based on Landsat8 operational land imager (OLI) images and five remote sensing variables. The normalized difference vegetation index (NDVI), the wide dynamic range vegetation index (WDRVI), the chlorophyll index (CI), Band6 and Band7 were used to build the RK models separately and to explore their capabilities for modeling spatial distributions of grassland carbon stocks. To explore the different model performances for typical grassland and meadow grassland, the models were validated separately using the typical steppe, meadow steppe or all-steppe ground measurements based on leave-one-out crossvalidation (LOOCV). When the results were validated against typical steppe samples, the Band6 model showed the best performance (coefficient of determination (R2) = 0.46, mean average error (MAE) = 8.47%, and root mean square error (RMSE) = 10.34 gC/m2) via the linear regression (LR) method, while for the RK method, the NDVI model showed the best performance (R2 = 0.63, MAE = 7.04 gC/m2, and RMSE = 8.51 gC/m2), which were much higher than the values of the best LR model. When the results were validated against the meadow steppe samples, the CI model achieved the best estimation accuracy, and the accuracy of the RK method (R2 = 0.72, MAE = 8.09 gC/m2, and RMSE = 9.89 gC/m2) was higher than that of the LR method (R2 = 0.70, MAE = 8.99 gC/m2, and RMSE = 10.69 gC/m2). Upon combining the results of the most accurate models of the typical steppe and meadow steppe, the RK method reaches the highest model accuracy of R2 = 0.69, MAE = 7.40 gC/m2, and RMSE = 9.01 gC/m2, while the LR method reaches the highest model accuracy of R2 = 0.53, MAE = 9.20 gC/m2, and RMSE = 11.10 gC/m2. The results showed an improved performance of the RK method compared to the LR method, and the improvement in the accuracy of the model is mainly attributed to the enhancement of the estimation accuracy of the typical steppe. In the study region, the carbon stocks showed an increasing trend from west to east, the total amount of grassland carbon stock was 79.77 × 104 Mg C, and the mean carbon stock density was 47.44 gC/m2. The density decreased in the order of temperate meadow steppe, lowland meadow steppe, temperate typical steppe, and sandy steppe. The methodology proposed in this study is particularly beneficial for carbon stock estimates at the regional scale, especially for countries such as China with many grassland types.

Floristic features and vegetation classification of the Hulun Buir Steppe in North China: Geography and climate-driven steppe diversification

This study aims to present a comprehensive description of the plant communities of the Hulun Buir Steppe based on floristically complete vegetation records as a baseline reference for future ecological and palaeoecological studies. We identify the main vegetation types in the Hulun Buir Steppe, provide their formal definitions and describe their species composition, habitat affinities and distributions. Floristic features (including floristic composition, life form and plant water ecotypes, floristic geographical elements) were also assessed. We recorded a total of 765 vascular plant taxa belonging to 68 families and 327 genera. The Hulun Buir Steppe indicates typical temperate steppe vegetation where the most frequent life form is hemicryptophytes with the maximum number of species. The most frequent water ecotype of Hulun Buir Steppe is typical-mesophytes. And the most frequent geographical element is the East Paleo-Arctic element. According to China vegetation classification system (China-VCS), the classification of 371 relevés resulted in assignment into 31 formations (Form.) grouped into threeVegetation-types and eleven Vegetation-subtypes. Hulun Buir Steppe vegetation classifications were described for the first time based on complete floristic data and community survey data. Our conclusions show that among the 765 vascular plant taxa, the main plant group among all vascular plants in terms of species numbers comprises dicotyledons, followed by monocotyledons and pteridophyta, with gymnosperms demonstrating the lowest numbers. The life forms are dominated by hemicryptophytes, the water ecological type is dominated by typical-mesophytes, and the floristic geographical element is dominated by the East Palaeo-Arctic element. Plant community types are diverse and can be conceptualized as meadow steppe, typical steppe and desert steppe. The vegetation types of the Hulun Buir Steppe are mainly affected by geographic variables and climatic factors: the geographic variables are mainly affected by the change in precipitation caused by the longitude gradient, while the climatic factors are mainly affected by the East Asian winter monsoon caused by the Siberian High and the East Asian Summer Monsoon caused by the Western Pacific Subtropical High. In addition, the surface runoff caused by forest snowmelt and seasonal rainfall, as well as the distance from the Greater Khingan Mountains, also affect the distribution of the Hulun Buir Steppe vegetation.

Response of plant functional traits of Leymus chinensis to extreme drought in Inner Mongolia grasslands

Understanding the effects of climate change, in particular, climate extremes on plant functional traits can provide a mechanistic basis for predicting how plant communities may be altered in the future. Here, we focused on a dominant species in Inner-Mongolia typical temperate steppe, Leymus chinensis (Trin.) Tzvei, to examine the responses of plant functional traits to experimentally imposed extreme drought at three sites along an aridity gradient. When comparing the driest (high aridity) to the wettest sites (low aridity), plant height, leaf dry matter content and δ13C (water use efficiency) were increased at the intermediate and low aridity sites, whereas specific leaf area and leaf nitrogen content were reduced at the high-aridity site. When extreme drought (~ 66% reduction in the growing season precipitation) was experimentally imposed at all sites, plant height decreased and δ13C of L. chinensis increased at the intermediate and low aridity sites. The extreme drought of 66% precipitation reduction also increased leaf dry matter content in high- and low-aridity sites. Compared to the control (ambient precipitation), extreme drought increased the strength of the positive association between plant height and δ13C, as well as the negative associations of specific leaf area with plant height and leaf dry matter content. Thus, extreme drought altered key functional traits of the dominant grass of Inner Mongolia steppe, particularly at the low-aridity site where the drought decreased plant size and increased water use efficiency and affected relationships between these traits.

Patterns of soil respiration and its temperature sensitivity in grassland ecosystems across China

Abstract. Soil respiration (Rs), a key process in the terrestrial carbon cycle, is very sensitive to climate change. In this study, we synthesized 54 measurements of annual Rs and 171 estimates of Q10 value (the temperature sensitivity of soil respiration) in grasslands across China. We quantitatively analyzed their spatial patterns and controlling factors in five grassland types, including temperate typical steppe, temperate meadow steppe, temperate desert steppe, alpine grassland, and warm, tropical grassland. Results showed that the mean (±SE) annual Rs was 582.0±57.9 g C m−2 yr−1 across Chinese grasslands. Annual Rs significantly differed among grassland types, and was positively correlated with mean annual temperature, mean annual precipitation, soil temperature, soil moisture, soil organic carbon content, and aboveground biomass, but negatively correlated with soil pH (p<0.05). Among these factors, mean annual precipitation was the primary factor controlling the variation of annual Rs among grassland types. Based on the overall data across Chinese grasslands, the Q10 values ranged from 1.03 to 8.13, with a mean (±SE) of 2.60±0.08. Moreover, the Q10 values varied largely within and among grassland types and soil temperature measurement depths. Among grassland types, the highest Q10 derived by soil temperature at a depth of 5 cm occurred in alpine grasslands. In addition, the seasonal variation of soil respiration in Chinese grasslands generally cannot be explained well by soil temperature using the van't Hoff equation. Overall, our findings suggest that the combined factors of soil temperature and moisture would better predict soil respiration in arid and semi-arid regions, highlight the importance of precipitation in controlling soil respiration in grasslands, and imply that alpine grasslands in China might release more carbon dioxide to the atmosphere under climate warming.

Characteristics of soil organic carbon and total nitrogen under various grassland types along a transect in a mountain-basin system in Xinjiang, China

Soil organic carbon (SOC) and soil total nitrogen (STN) in arid regions are important components of global C and the N cycles, and their response to climate change will have important implications for both ecosystem processes and global climate feedbacks. Grassland ecosystems of Funyun County in the southern foot of the Altay Mountains are characterized by complex topography, suggesting large variability in the spatial distribution of SOC and STN. However, there has been little investigation of SOC and STN on grasslands in arid regions with a mountain-basin structure. Therefore, we investigated the characteristics of SOC and STN in different grassland types in a mountain-basin system at the southern foot of the Altai Mountains, north of the Junggar Basin in China, and explored their potential influencing factors and relationships with meteorological factors and soil properties. We found that the concentrations and storages of SOC and STN varied significantly with grassland type, and showed a decreasing trend along a decreasing elevation gradient in alpine meadow, mountain meadow, temperate typical steppe, temperate steppe desert, and temperate steppe desert. In addition, the SOC and STN concentrations decreased with depth, except in the temperate desert steppe. According to Pearson's correlation values and redundancy analysis, the mean annual precipitation, soil moisture content and soil available N concentration were significantly positively correlated with the SOC and STN concentrations. In contrast, the mean annual temperature, pH, and soil bulk density were significantly and negatively correlated with the SOC and STN concentrations. The mean annual precipitation and mean annual temperature were the primary factors related to the SOC and STN concentrations. The distributions of the SOC and STN concentrations were highly regulated by the elevation-induced differences in meteorological factors. Mean annual precipitation and mean annual temperature together explained 97.85% and 98.38% of the overall variations in the SOC and STN concentrations, respectively, at soil depth of 0–40 cm, with precipitation making the greatest contribution. Our results provide a basis for estimating and predicting SOC and STN concentrations in grasslands in arid regions with a mountain-basin structure.

Effects of grazing exclusion on the grassland ecosystems of mountain meadows and temperate typical steppe in a mountain-basin system in Central Asia's arid regions, China

Grazing exclusion has been proposed as a method of restoring degraded grassland ecosystems. However, its effectiveness remains poorly understood in mountain-basin grasslands in arid regions. Thus, we investigated the plant community characteristics, C and N storage levels, and soil organic carbon and total nitrogen concentrations and storage within the upper 0–40 cm soil layer in a grazed grassland (GG) and a fenced grassland (FG) with grazing exclusion in mountain meadow (MM) and temperate typical steppe (TTS) habitats in a mountain-basin ecosystem in an arid region of Central China, which are both vital grassland resources for livestock grazing and ecological conservation. In MM, our investigation revealed that grazing exclusion was beneficial to the productivity, coverage, height, diversity, and C and N storage of aboveground plants. However, grazing exclusion was not an effective option for soil C and N sequestration. In TTS, grazing exclusion effectively improved the plant productivity, coverage, height, plant and soil C and N sequestration, although it was not beneficial for maintaining plant diversity. Our findings suggest that reduced or rotational grazing may be a better choice than grazing exclusion in MM. In addition, considering the trade-off between biomass productivity and species diversity in TTS, short-term grazing exclusion should be considered. Additionally, grazing exclusion should be combined with other appropriate measures rather than operating on a standalone basis.

植被退化对温带典型草原根系-土壤系统碳氮分配的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 植被退化对温带典型草原根系-土壤系统碳氮分配的影响 DOI: 10.5846/stxb201612312725 作者: 作者单位: 内蒙古大学生态与环境学院,内蒙古大学生态与环境学院,内蒙古大学生态与环境学院,内蒙古大学生态与环境学院,内蒙古大学生态与环境学院,内蒙古大学生态与环境学院,内蒙古大学生态与环境学院,内蒙古大学生态与环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金青年基金项目（31400391）；国家自然科学基金地区科学基金项目（31560146）；内蒙古自治区自然科学基金项目（2016MS0330）；第57批中国博士后科学基金面上项目（2015M571289）；内蒙古自治区自然科学基金项目（2017BS0311） Effects of vegetation degradation on carbon and nitrogen distribution of roots-soil system in temperate typical steppe Author: Affiliation: College of ecology and environment,Inner Mongolia University,College of ecology and environment,Inner Mongolia University;China,,,,, Fund Project: The Inner Mongolia Autonomous Region Natural Science Foundation;The fifty-seventh batch of Chinese postdoctoral science fund 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以3种不同退化程度的温带典型草原（大针茅轻度退化、中度退化和重度退化）为研究对象，研究植被退化对温带典型草原土壤及根系碳氮含量及储量的影响。结果显示：（1）植被退化对地下根系碳含量影响不显著（P > 0.05），而对地下根系氮含量的影响显著（P < 0.05），中度退化样地根系氮含量显著高于轻度退化和重度退化样地（P < 0.05）。（2）植被退化对根系碳氮储量影响显著（P < 0.05），根系碳氮储量随着土层深度增加而减少，总根系碳氮储量随退化程度加剧而降低。（3）土壤有机碳、总碳和总氮含量及储量均受退化程度和采样深度的影响显著（P < 0.05），其含量随着土壤深度的增加而显著减少，随退化程度加剧而显著降低（P < 0.05）。（4）土壤是根系-土壤系统碳氮储存的最主要场所，储量占比90%以上。虽然土壤碳氮储量均存在表层聚集现象，但表层储量所占比例在各样地间差异显著（P < 0.05）。 Abstract:The objective of this article was to determine the influence of vegetation degradation on carbon and nitrogen storage in root-soil systems. We studied three typical temperate steppes with different levels of degradation in Inner Mongolia, including three different degraded temperate grasslands (Stipa grandis light degradation, moderate degradation, and severe degradation). The effects of vegetation degradation on soil carbon and nitrogen content in typical temperate steppe root-soil systems were studied. The results showed that:(1) the effect of vegetation degradation on carbon concentration of underground roots was not significant (P > 0.05), but the effect on the nitrogen concentration of underground roots was significant (P < 0.05). The nitrogen concentration of roots in the moderately degraded plot was significantly higher than in the light degradation and severe degradation plots. (2) the effects of vegetation degradation on carbon and nitrogen storage of root systems was significant (P < 0.05). Carbon and nitrogen reserves decreased with increasing levels of degradation. Carbon and nitrogen storage of roots in three study plots decreased as depth increased. (3) there were significant differences in soil organic carbon and nitrogen between different sampling plots (P < 0.05). With the increase in soil depth, the content of soil organic carbon and nitrogen decreased. The carbon and nitrogen storage of soil decreased as degradation increased. (4) Soil is the main carbon and nitrogen pool in root-soil systems. About 90% of carbon and nitrogen were stored in soil. In soil systems, carbon and nitrogen were stored mainly in the top soil layer. The effect of vegetation degradation on the proportion of carbon and nitrogen content in the top soil layer, however, was not significant (P < 0.05). 参考文献 相似文献 引证文献

Responses of gross primary productivity to different sizes of precipitation events in a temperate grassland ecosystem in Inner Mongolia, China

Changes in the sizes of precipitation events in the context of global climate change may have profound impacts on ecosystem productivity in arid and semiarid grasslands. However, we still have little knowledge about to what extent grassland productivity will respond to an individual precipitation event. In this study, we quantified the duration, the maximum, and the time-integrated amount of the response of daily gross primary productivity (GPP) to an individual precipitation event and their variations with different sizes of precipitation events in a typical temperate steppe in Inner Mongolia, China. Results showed that the duration of GPP-response (τ R) and the maximum absolute GPP-response (GPPmax) increased linearly with the sizes of precipitation events (P es), driving a corresponding increase in time-integrated amount of the GPP-response (GPPtotal) because variations of GPPtotal were largely explained by τ R and GPPmax. The relative contributions of these two parameters to GPPtotal were strongly P es-dependent. The GPPmax contributed more to the variations of GPPtotal when P es was relatively small (<20 mm), whereas τ R was the main driver to the variations of GPPtotal when P es was relatively large. In addition, a threshold size of at least 5 mm of precipitation was required to induce a GPP-response for the temperate steppe in this study. Our work has important implications for the modeling community to obtain an advanced understanding of productivity-response of grassland ecosystems to altered precipitation regimes.

Response of N2O emission to water and nitrogen addition in temperate typical steppe soil in Inner Mongolia, China

The Chinese steppe is undergoing a drastic increase in nitrogen (N) deposition, and the precipitation in this region is predicted to increase. However, the response of soil N2O emissions to the coupling changes of precipitation and N deposition in grassland ecosystem has been seldom discussed. A manipulative field experiment was conducted to investigate the individual and interactive effects of precipitation increase and N deposition on soil N2O efflux in semi-arid temperate grassland in Inner Mongolia during the growing seasons of 2010 and 2011.The treatments included four N addition levels [20gNm−2y−1 (N20), 10gNm−2y−1 (N10), 5gNm−2y−1 (N5), and a zero-N control (CK)] and two water application levels [natural precipitation for dry (D) and 15% increase of long-term mean annual precipitation for wet (W) treatments]. Results indicated that N and water addition both significantly increased soil N2O effluxes (P<0.01). The maximum N2O emissions were observed within 2–3 days after N addition to all treatments, and the N2O effluxes in W treatments were generally higher than in D treatments for the same N input level. For the treatments without N inputs, the N2O emission peak of WCK was 9.8% higher than DCK in 2010. The effect of water addition on N2O emission was more evident when more N fertilizer was applied. For the high N input treatments, the maximum N2O emission of WN20 treatment was 222.6% higher than DN20 in 2010. The changes in N and water availabilities accounted for 91.3% (2010) and 75.6% (2011) of the N2O cumulative efflux variation among different treatments (P<0.01). The N2O effluxes were significantly affected by the interactive effect between N and water in 2010 and 2011 (P<0.05). Significant interannual variability in the cumulative N2O emissions was observed, the cumulative N2O emissions in 2011 were significantly lower than those in 2010 even though the summer of 2011 experienced higher rainfall (P<0.01). Temperature also significantly influenced soil N2O emission apart from the effects of water and N. The temperature change accounted for 41.3% (W) to 47.2% (D) of the temporal variations in N2O emission during the relatively dry 2010. The combined changes in soil moisture, NH4+-N, and temperature accounted for 43.1% (D) to 54.5% (W) of the temporal variations in N2O emission in the relatively wet year of 2011.

Six-year fertilization modifies the biodiversity of arbuscular mycorrhizal fungi in a temperate steppe in Inner Mongolia

Arbuscular mycorrhizal fungi (AMF) play key roles in supporting ecosystem sustainability, stability and function, but little is known about how fertilization practices affect AMF abundance and community composition in the grassland ecosystems. In the present study, a field trial was established to examine the effects of 6 years of nitrogen (N) and phosphorus (P) fertilization on the community structure of AMF both in soils and plant roots in a typical temperate steppe in Inner Mongolia, northern China. The AMF small-subunit (SSU) rRNA genes were subjected to PCR, cloning, sequencing, and phylogenetic analyses. A total of 1554 sequenced SSU rRNA clones, including 919 clones from the soil and 635 clones from the roots, were analyzed. The 31 AMF sequence types belonging to Glomeromycota were identified: 17 to Glomus group A and 14 to Glomus group B. The experimental results indicated that N fertilization significantly altered the AMF communities in both soils and mixed roots but had no obvious influence on AMF abundance. However, P fertilization showed no significant influence on the AMF community structure, but induced a significant decrease in mycorrhizal colonization rate, arbuscule colonization and hyphal length density. Furthermore, N and P application showed significant interactions in affecting AMF species compositions in soils but not in roots. Generally the AMF diversity in the soil was higher than that in the roots. The study suggested that N fertilization predominantly altered AMF species composition, while P fertilization influenced AMF abundance in this steppe.

Estimation of chlorophyll content in the typical steppe vegetation of Inner Mongolia, China, using various red-edge position extraction techniques

The red-edge position (REP) was extracted from reflectance spectral data at canopy and leaf scale using six different methods in the temperate typical steppe of Inner Mongolia with relatively high species richness. The results suggested that the REPs varied with the extraction methods, sampling sites, plant species, and estimation scales. At the canopy scale, chlorophyll content (CC) was estimated with the linear extrapolation method, and the polynomial fitting technique had coefficients of determination (R 2 >0.4 ). The chlorophyll estimates at Leymus chinensis- and Stipa grandis-dominated sites were slightly better than those from the large sampling sites with multiple dominant plant species. At the leaf scale, the linear extrapolation method and the polynomial fitting technique presented high coefficients of determination (R 2 >0.6 ). CC estimated at L. chinensis-dominated sites was substantially higher than at S. grandis-dominated sites as well as the large sampling site. The results using the maximum first-derivative method and Lagrangian interpolation techniques revealed a discontinuity, whereas the REPs, as extracted by the linear interpolation method, were shifted toward longer wavelengths. The linear interpolation and inverted Gaussian method were easily saturated. The results obtained with the polynomial fitting technique and the linear extrapolation method had higher sensitivity and accuracy for estimation of CC.

Response of soil N2O emissions to precipitation pulses under different nitrogen availabilities in a semiarid temperate steppe of Inner Mongolia, China

Short-term nitrous oxide (N2O) pulse emissions caused by precipitation account for a considerable portion of the annual N2O emissions and are greatly influenced by soil nitrogen (N) dynamics. However, in Chinese semiarid temperate steppes, the response of N2O emissions to the coupling changes of precipitation and soil N availability is not yet fully understood. In this study, we conducted two 7-day field experiments in a semiarid temperate typical steppe of Inner Mongolia, China, to investigate the N2O emission pulses resulting from artificial precipitation events (approximately equivalent to 10.0 mm rainfall) under four N addition levels (0, 5, 10, and 20 g N/(m2·a)) using the static opaque chamber technique. The results show that the simulated rainfall during the dry period in 2010 caused greater short-term emission bursts than that during the relatively rainy observation period in 2011 (P<0.05). No significant increase was observed for either the N2O peak effluxes or the weekly cumulative emissions (P>0.05) with single water addition. The peak values of N2O efflux increased with the increasing N input. Only the treatments with water and medium (WN10) or high N addition (WN20) significantly increased the cumulative N2O emissions (P<0.01) in both experimental periods. Under drought condition, the variations in soil N2O effluxes were positively correlated with the soil NH4-N concentrations in the three N input treatments (WN5, WN10, and WN20). Besides, the soil moisture and temperature also greatly influenced the N2O pulse emissions, particularly the N2O pulse under the relatively rainy soil condition or in the treatments without N addition (ZN and ZWN). The responses of the plant metabolism to the varying precipitation distribution and the length of drought period prior to rainfall could greatly affect the soil N dynamics and N2O emission pulses in semiarid grasslands.

Evaluation of six methods to predict grassland net primary productivity along an altitudinal gradient in the Alxa Rangeland, Western Inner Mongolia, China

AbstractAccurately estimating grassland net primary productivity (NPP) plays an important role in the study of global carbon budgeting. The six different methods (Miami Model, Schuur Model, Chikugo Model, Beijing Model, Synthetic Model and Classification Indices‐based Model) were compared in terms of their performance in predicting grassland NPP with NPP derived from field‐observed data at eight study sites along an altitudinal gradient in the Helan Mountain range and the surrounding desert in the Alxa Rangeland, Western Inner Mongolia, China. One hundred and twenty plot‐based NPP sets from the eight study sites were used, which were obtained from 2003 to 2005, within areas classified as alpine meadow, cold temperate‐humid montane meadow, cool temperate‐subhumid meadow steppe, cool temperate‐semiarid temperate typical steppe and cool temperate‐arid temperate zonal semi‐desert according to the Integrated Orderly Classification System of Grassland (IOCSG). The relative high model efficiency in predicting grassland NPP using the Classification Indices‐based Model and Chikugo Model indicates that these models outperform others. On the basis of input data requirements and the number of free parameters involved in each model, the Classification Indices‐based Model was found to be the best choice for the given grassland classes. The results presented in this study were not only specific to this region, but more importantly, were specific to the given grassland classes according to the IOCSG approach, which can be scaled up from plots to estimate landscape‐scale effects.

Responses of ammonia-oxidizing bacteria and archaea to nitrogen fertilization and precipitation increment in a typical temperate steppe in Inner Mongolia

As the first and rate-limiting step of nitrification, ammonia oxidation can be realized either by ammonia-oxidizing bacteria (AOB) or archaea (AOA). However, the key factors driving the abundance, community structure and activity of ammonia oxidizers are still unclear, and the relative importance of AOA and AOB in ammonia oxidation is unresolved. In the present study, we examined the effects of long-term (6 years) nitrogen (N) addition and simulated precipitation increment on the abundance and community composition of AOA and AOB based on a field trial in a typical temperate steppe of northern China. We used combined approaches of quantitative PCR, terminal-restriction fragment length polymorphism (T-RFLP) and clone library analyses of amoA genes. The study objective was to determine (1) AOA and AOB diversity and activity in response to N addition and increased precipitation and (2) the relative contributions of AOA and AOB to soil ammonia oxidation in the typical temperate steppe. The results showed that the potential nitrification rate (PNR) increased with N addition, but decreased with increased precipitation. Both N addition and increased precipitation significantly increased AOB but not AOA abundance, and a significant correlation was only observed between PNR and AOB amoA gene copies. The T-RFLP analysis showed that both N and precipitation were key factors in shaping the composition of AOB, while AOA were only marginally influenced. Phylogenetic analysis indicated that all AOA clones fell within the soil and sediment lineage while all AOB clones fell within the Nitrosospira. The study suggested that AOA and AOB had distinct physiological characteristics and ecological niches. AOB were shown to be more sensitive to N and precipitation than AOA, and the ammonia oxidation process was therefore supposed to be mainly driven by AOB in this temperate steppe.

Integrated diurnal soil respiration model during growing season of a typical temperate steppe: Effects of temperature, soil water content and biomass production

Soil respiration was measured with the enclosed chamber method in an ungrazed Leymus chinensis steppe during the growing seasons of 2001 and 2002. Soil respiration rate ( R S) was significantly influenced by air temperature ( T) at the diurnal scale, and could be described by Van't Hoff's equation ( R S = R 10 exp( β( T − 10))). At the seasonal scale, the normalized soil respiration rate at 10 °C ( R 10) was mainly controlled by soil water content ( R 2 = 0.717, P < 0.001), while the sensitivity of soil respiration to temperature ( Q 10) was partially affected by absolute growth rate ( R 2 = 0.482, P = 0.004). Thus, soil respiration could be described as R S = (20.015 W − 84.085) (0.103AGR + 1.786) ( T−10)/10 during the growing seasons, integrating soil water content ( W) and absolute growth rate (AGR) into the temperature-dependent soil respiration equation. It was validated by the observed soil respiration rates in this study ( R 2 = 0.890, P < 0.001) and observations from near-field experiment ( R 2 = 0.687, P = 0.011). It implied that accurately evaluating annual soil respiration should include the effects of plant biomass production and other abiotic factors besides air temperature.

Improvement, Comparison, and Application of Field Measurement Methods for Grassland Vegetation Fractional Coverage

: As one of the important vegetation parameters, vegetation fractional coverage (VFC) is more difficult to measure accurately among a good many parameters of plant communities. The temperate typical steppe in the north of China was chosen for investigation in the present study and a digital camera was used to measure herb community coverage in the field, adopting methods of ocular estimation, gridding measurement, visual interpretation, supervised classification, and information extraction of color spatial transformation to calculate the VFC of images captured by the digital camera. In addition VFC calculated by various methods was analyzed and compared VFC, enabling us to propose an effective method for measuring VFC using a digital camera. The results of the present study indicate that: (i) as two common useful and effective methods of measuring VFC with a digital camera, not only does the error of estimated values of visual estimation and supervised classification vary considerably, but the degree of automatization is very low and depends, to a great extent, on the manipulator; (ii) although the method of visual interpretation may assure the precision of the calculated VFC and enable the precision of results obtained using other methods to be determined, as far as large quantities of data are concerned, this method has the disadvantages of wasting time and energy, and the applications of this method are limited; (iii) the precision and stability of VFC calculated using the grid and node method are superior to those of visual estimation and supervised classification and inferior to those of visual interpretation, but, as for visual interpretation and supervised classification, gridding measurements are difficult to apply in practice because they are not time efficient; and (iv) in terms of the precision of calculation of the VFC, an information-extracting model based on an intensity, hue, saturation (IHS) color space-multi-component series segmentation strategy is superior to methods of ocular estimation, gridding measurement, and supervised classification. In terms of practical efficiency, the information-extracting model is superior to visual interpretation, supervised classification, and gridding measurement. It has been proven that estimating the VFC of the north temperate typical steppe using this model is feasible. This is very fundamental research work in grassland ecology. (Managing editor: Ya-Qin HAN)

Importance of clonal plants and plant species diversity in the Northeast China Transect

In plant communities, the internal (genet‐level) control mechanisms on a spatio‐temporal scale of clonal plants impose strong constraints on spatial pattern as well as on competitive relations and, thus, species coexistence. Therefore, the presence of clonal species within a plant community affects spatio‐temporal dynamics and plant species diversity. We examined the distribution of plants with different clonal growth forms in the Northeast China Transect (NECT) and correlated plant species diversity with the importance of clonal plants, and the importance of phalanx and guerilla clonal plants. Phalanx clonal plants were more abundant in western communities where the altitude was higher and both the soil nitrogen contents and precipitation were relatively low. Whereas guerilla clonal plants were more abundant in the middle of the NECT where the precipitation, mean annual temperature and photosynthetically active radiation were relatively high. In the relatively productive temperate typical steppe, plant species diversity was negatively correlated with the importance of phalanx clonal plants and positively correlated with the importance of guerilla clonal plants. In relatively unproductive temperate desert steppe, plant species diversity was positively correlated with the importance of both phalanx and guerilla clonal plants.