Response of the annual biomass production of a typical steppe plant community to precipitation fluctuations

2014 ◽  
Vol 36 (6) ◽  
pp. 527 ◽  
Author(s):  
Zhen Wang ◽  
Qing Zhang ◽  
Xiaoping Xin ◽  
Yong Ding ◽  
Xiangyang Hou ◽  
...  
Keyword(s):  
Plant Community ◽  
Coefficient Of Variation ◽  
Positive Relationship ◽  
Net Primary Production ◽  
Northern China ◽  
Perennial Grasses ◽  
Annual Precipitation ◽  
Typical Steppe ◽  
Grassland Ecosystems ◽  
Annual Biomass

Understanding the relationship between the aboveground net primary production (ANPP) and annual precipitation in arid and semiarid grasslands is crucial for assessing the effects of climate change on grassland ecosystems. The temporal pattern of ANPP, based on long-term data on a semiarid ecosystem in Inner Mongolia, was investigated. The biomass of perennial grasses, perennial forbs and Stipa grandis P. Smirn., showed a positive relationship with annual precipitation. The amount of annual precipitation also changed the annual biomass of 13 other dominant species and consequently the ANPP. The coefficient of variation of the ANPP of the plant community was lower than the coefficient of variation of annual precipitation. Irrespective of the strong inter-annual variation in annual precipitation, the positive relationship found between ANPP and annual precipitation suggests the dependence of ANPP upon hydrological variations in typical steppe. Our findings highlight the importance of dominant perennial species and functional groups in mediating the responses of ANPP to annual precipitation in the typical steppe in northern China.

scholarly journals Remotely monitoring ecosystem respiration from various grasslands along a large-scale east-west transect across Northern China

2020 ◽  
Author(s):  
Xuguang Tang ◽  
Yanlian Zhou ◽  
Hengpeng Li ◽  
Li Yao ◽  
Zhi Ding ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Alpine Meadow ◽  
Ecosystem Respiration ◽  
Northern China ◽  
Climate Projections ◽  
Desert Steppe ◽  
Meadow Steppe ◽  
Typical Steppe ◽  
Environmental Controls ◽  
Grassland Ecosystems

Abstract Background: Grassland ecosystems play an important role in the terrestrial carbon cycles through carbon emission by ecosystem respiration (Re) and carbon uptake by plant photosynthesis (GPP). Surprisingly, given Re occupies a large component of annual carbon balance, rather less attention has been paid to developing the estimates of Re compared to GPP.Results: Based on 11 flux sites over the diverse grassland ecosystems in northern China, this study examined the amounts of carbon released by Re as well as the dominant environmental controls across temperate meadow steppe, typical steppe, desert steppe and alpine meadow, respectively. Multi-year mean Re revealed relatively less CO2 emitted by the desert steppe in comparison with other grassland ecosystems. Meanwhile, C emissions of all grasslands were mainly controlled by the growing period. Correlation analysis revealed that apart from air and soil temperature, soil water content exerted a strong effect on the variability in Re, which implied the great potential to derive Re using relevant remote sensing data. Then, these field-measured Re data were up-scaled to large areas using time-series MODIS information and remote sensing-based piecewise regression models. These semi-empirical models appeared to work well with a small margin of error (R2 and RMSE ranged from 0.45 to 0.88 and from 0.21 to 0.69 g C m-2 d-1, respectively). Conclusions: Generally, the piecewise models from the growth period and dormant season performed better than model developed directly from the entire year. Moreover, the biases between annual mean Re observations and the remotely-derived products were usually within 20%. Finally, the regional Re emissions across northern China's grasslands was approximately 100.66 Tg C in 2010, about 1/3 of carbon fixed from the MODIS GPP product. Specially, the desert steppe exhibited the highest ratio, followed by the temperate meadow steppe, typical steppe and alpine meadow. Therefore, this work provides a novel framework to accurately predict the spatio-temporal patterns of Re over large areas, which can greatly reduce the uncertainties in global carbon estimates and climate projections.

scholarly journals Remotely monitoring ecosystem respiration from various grasslands along a large-scale east-west transect across northern China

2020 ◽  
Author(s):  
Xuguang Tang ◽  
Yanlian Zhou ◽  
Hengpeng Li ◽  
Li Yao ◽  
Zhi Ding ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Alpine Meadow ◽  
Ecosystem Respiration ◽  
Northern China ◽  
Climate Projections ◽  
Desert Steppe ◽  
Meadow Steppe ◽  
Typical Steppe ◽  
Environmental Controls ◽  
Grassland Ecosystems

Abstract Background : Grassland ecosystems play an important role in the terrestrial carbon cycles through carbon emission by ecosystem respiration ( R e ) and carbon uptake by plant photosynthesis (GPP). Surprisingly, given R e occupies a large component of annual carbon balance, rather less attention has been paid to developing the estimates of R e compared to GPP. Results : Based on 11 flux sites over the diverse grassland ecosystems in northern China, this study examined the amounts of carbon released by R e as well as the dominant environmental controls across temperate meadow steppe, typical steppe, desert steppe and alpine meadow, respectively. Multi-year mean R e revealed relatively less CO 2 emitted by the desert steppe in comparison with other grassland ecosystems. Meanwhile, C emissions of all grasslands were mainly controlled by the growing period. Correlation analysis revealed that apart from air and soil temperature, soil water content exerted a strong effect on the variability in R e , which implied the great potential to derive R e using relevant remote sensing data. Then, these field-measured R e data were up-scaled to large areas using time-series MODIS information and remote sensing-based piecewise regression models. These semi-empirical models appeared to work well with a small margin of error ( R 2 and RMSE ranged from 0.45 to 0.88 and from 0.21 to 0.69 g C m -2 d -1 , respectively). Conclusions : Generally, the piecewise models from the growth period and dormant season performed better than model developed directly from the entire year. Moreover, the biases between annual mean R e observations and the remotely-derived products were usually within 20%. Finally, the regional R e emissions across northern China's grasslands was approximately 100.66 Tg C in 2010, about 1/3 of carbon fixed from the MODIS GPP product. Specially, the desert steppe exhibited the highest ratio, followed by the temperate meadow steppe, typical steppe and alpine meadow. Therefore, this work provides a novel framework to accurately predict the spatio-temporal patterns of R e over large areas, which can greatly reduce the uncertainties in global carbon estimates and climate projections.

Urinary melatonin, LH, oestradiol, progesterone excretion during the menstrual cycle or in women taking oral contraceptives

1987 ◽  
Vol 116 (1) ◽  
pp. 145-149 ◽  
Author(s):  
Jocelyne Brun ◽  
Bruno Claustrat ◽  
Michel David
Keyword(s):  
Oral Contraceptive ◽  
Menstrual Cycle ◽  
Urinary Excretion ◽  
Oral Contraceptives ◽  
Coefficient Of Variation ◽  
Luteal Phase ◽  
Positive Relationship ◽  
Follicular Phase ◽  
The Other ◽  
Normal Women

Abstract. Nocturnal urinary excretion of melatonin, LH, progesterone and oestradiol was measured by radioimmunoassay in nine normal women during a complete cycle. In addition, these hormonal excretions were studied in two women taking an oral contraceptive. A high within-subject coefficient of variation was observed for melatonin excretion in the two groups. In the nine normal cycling women, melatonin excretion was not decreased at the time of ovulation, but was significantly increased during the luteal phase compared with that of the follicular phase (P < 0.01). These data are consistent with a positive relationship between melatonin and progesterone during the luteal phase. In the two women under an oral contraceptive, melatonin excretion was found within the same range as for the other nine. The results are discussed in terms of pineal investigation in human.

Net Primary Production in the Shortgrass Steppe

2008 ◽  
Author(s):  
William K. Lauenroth ◽  
Daniel G. Milchunas
Keyword(s):  
Global Change ◽  
Primary Production ◽  
Net Primary Production ◽  
Regional Scale ◽  
Ecosystem Dynamics ◽  
Shortgrass Steppe ◽  
Annual Precipitation ◽  
Mean Annual Precipitation ◽  
Spatial And Temporal Patterns ◽  
Temporal And Spatial

Net primary production (NPP), the amount of carbon or energy fixed by green plants in excess of their respiratory needs, is the fundamental quantity upon which all heterotrophs and the ecosystem processes they are associated with depend. Understanding NPP is therefore a prerequisite to understanding ecosystem dynamics. Our objectives for this chapter are to describe the current state of our knowledge about the temporal and spatial patterns of NPP in the shortgrass steppe, to evaluate the important variables that control NPP, and to discuss the future of NPP in the shortgrass steppe given current hypotheses about global change. Most of the data available for NPP in the shortgrass steppe are for aboveground net primary production (ANPP), so most of our presentation will focus on ANPP and we will deal with belowground net primary production (BNPP) as a separate topic. Furthermore, our treatment of NPP in this chapter will ignore the effects of herbivory, which will be covered in detail in chapter 16. Our approach will be to start with a regional-scale view of ANPP in shortgrass ecosystems and work toward a site-scale view. We will begin by briefly placing ANPP in the shortgrass steppe in its larger context of the central North American grassland region. We will then describe the regional-scale patterns and controls on ANPP, and then move to the site-scale patterns and controls on ANPP. At the site scale, we will describe both temporal and spatial dynamics, and controls on ANPP as well as BNPP. We will then discuss relationships between spatial and temporal patterns in ANPP and end the chapter with a short, speculative section on how future global change may influence NPP in the shortgrass steppe. Temperate grasslands in central North America are found over a range of mean annual precipitation from 200 to 1200 mm.y–1 and mean annual temperatures from 0 to 20 oC (Lauenroth et al., 1999). The widely cited relationship between mean annual precipitation and average annual ANPP allows us to convert the precipitation gradient into a production gradient (Lauenroth, 1979; Lauenroth et al., 1999; Noy-Meir, 1973; Rutherford, 1980; Sala et al., 1988b).

scholarly journals Performance of Stock and Treasury Bills under Inflation and Floating: Evidence from Egypt

2018 ◽  
Vol 10 (6) ◽  
pp. 160
Author(s):  
Osama Wagdi ◽  
Yasmin Tarek ◽  
Nihad Edres
Keyword(s):  
Monetary Policy ◽  
Coefficient Of Variation ◽  
Positive Relationship ◽  
Inflation Rate ◽  
Common Stock ◽  
Treasury Bills ◽  
Average Return ◽  
Time Period ◽  
Strong Positive Relationship ◽  
The Impact

The aim of this study is comparing the performance of common stock & treasury bills, according to the central bank of Egypt and their monetary policy during the time period between “1994-2017”, using descriptive & inferential statistical methods. The Study concluded that there is a strong positive relationship between inflation rate & returns of Egyptian treasury bills, as the same relation as with floating Egyptian pound.in addition, the study found the impact of Inflation and Floating on the return of Egyptian T-bills, but don’t found this impact on the return of Egyptian common stock. Finally, the study founds the same average return but a different at variances of this return & the Coefficient of variation.

Comparison of CO2 Net Exchange between Different Plant Communities in Typical Steppe of Inner Mongolia Plateau

2012 ◽  
Vol 518-523 ◽  
pp. 1492-1495
Author(s):  
Jing Hui Hou ◽  
Yong Li Wang ◽  
Li Xin Wang ◽  
Hua Min Liu ◽  
Cheng Zhen Jia
Keyword(s):  
Plant Community ◽  
Plant Communities ◽  
Net Ecosystem Exchange ◽  
Eddy Covariance Method ◽  
Chamber Method ◽  
Typical Steppe ◽  
Dynamic Chamber ◽  
Free Grazing ◽  
Co2 Sink ◽  
Inner Mongolia Plateau

To measure the carbon exchange of two different plant communities in typical steppe, we used dynamic chamber method improved from static chamber method, and compared it with the regional eddy-covariance method. Results showed that: 1) Biomass of plant community with enclosed restoration was higher than that with free grazing; 2) After 6 years enclosed restoration, the plant community had become a CO2 sink though the region was still a CO2 source while the free grazing plant community had turned into a CO2 source in contrast with its regional CO2 sink, and 3) Net ecosystem exchange (NEE) of enclosed restoration plant community was significantly higher than that of typical steppe.

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