Grassland plays an important role in the global carbon cycle and climate regulation. However, there are still large uncertainties in grassland carbon pool and also its role in global carbon cycle due to the lack of me...Grassland plays an important role in the global carbon cycle and climate regulation. However, there are still large uncertainties in grassland carbon pool and also its role in global carbon cycle due to the lack of measured grassland biomass at regional scale or global scale with a unified survey method, particular for below-ground biomass. The present study, based on a total of 44 grassland sampling plots with 220 quadrats across Ningxia, investigated the characteristics of above-ground biomass （AGB）, below-ground biomass （BGB）, litter biomass （LB）, total biomass （TB） and root：shoot ratios （R：S） for six predominantly grassland types, and their relationships with climatic factors. AGB, BGB, LB and TB varied markedly across different grassland types, the median value ranging from 28.2-692.6 g m-2 for AGB, 130.4-2 036.6 g m-： for BGB, 9.2-82.3 g m2 for LB, and 168.0-2 681.3 g m-： for TB. R：S showed less variation with median values from 3.2 to 5.3 （excluding marshy meadow）. The different grassland types showed similar patterns of biomass allocation, with more than 70% BGB for all types. There is evidence of strong positive effects associated with mean annual precipitation （MAP） and negative effects associated with mean annual temperature （MAT） on AGB, BGB, and LB, although both factors have the opposite effect on R：S.展开更多
Coherent beam combining(CBC)is recently used to generate high power vortex beams which are strongly required in specific applications.In this paper,based on the extended Huygens-Fresnel principle,the exact theoretical...Coherent beam combining(CBC)is recently used to generate high power vortex beams which are strongly required in specific applications.In this paper,based on the extended Huygens-Fresnel principle,the exact theoretical forms for the intensity distribution of CBC Bessel-Gaussian beams(BGBs)in turbulent ocean are derived.To show the superiority of CBC BGBs in turbulent channels,the comparison in the intensity evolution of CBC BGBs with ideal BGBs is performed.It is found that the beam spreading of CBC BGBs is smaller than that of ideal BGBs under the same oceanic turbulence conditions.Moreover,the effect of the beam parameters and channel parameters on the quality of CBC BGBs is also analyzed.The results show that the oceanic turbulence with a higher rate of dissipation of kinetic energy per unit mass of fluid,lower dissipation rate of the mean-squared temperature,or smaller ratio of temperature and salinity contributions to the refractive index spectrum has smaller impact on CBC BGBs.Moreover,the increasing number of the beamlets,the increasing waist width of each beamlet,and the decreasing radius of the beam distribution cause the optical energy to be more concentrated,and thus leading to a longer non-diffraction propagation distance.展开更多
Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for abovegrou...Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for aboveground biomass (AGB), belowground biomass (BGB) is poorly reported at the re- gional scales. The present study, based on a total of 113 sampling sites in temperate grassland of the Inner Mongolia, investigated regional distribution patterns of AGB, BGB, vertical distribution of roots, and their relationships with environmental factors. AGB and BGB increased from the southwest to the northeast of the study region. The largest biomass occurred in meadow steppe, with mean AGB and BGB of 196.7 and 1385.2 g/m2, respectively; while the lowest biomass occurred in desert steppe, with an AGB of 56.6 g/m2 and a BGB of 301.0 g/m2. In addition, about 47% of root biomass was distributed in the top 10 cm soil. Further statistical analysis indicated that precipitation was the primary determinant factor in shaping these distribution patterns. Vertical distribution of roots was significantly affected by precipitation, while the effects of soil texture and grassland types were weak.展开更多
基金supported by the Strategic-Leader Sci-Tech Projects of Chinese Academy of Sciences(XDA05050403)the Important Direction Project of Innovation of Chinese Academy of Sciences(CAS)(KSCX1-YW-12)
文摘Grassland plays an important role in the global carbon cycle and climate regulation. However, there are still large uncertainties in grassland carbon pool and also its role in global carbon cycle due to the lack of measured grassland biomass at regional scale or global scale with a unified survey method, particular for below-ground biomass. The present study, based on a total of 44 grassland sampling plots with 220 quadrats across Ningxia, investigated the characteristics of above-ground biomass （AGB）, below-ground biomass （BGB）, litter biomass （LB）, total biomass （TB） and root：shoot ratios （R：S） for six predominantly grassland types, and their relationships with climatic factors. AGB, BGB, LB and TB varied markedly across different grassland types, the median value ranging from 28.2-692.6 g m-2 for AGB, 130.4-2 036.6 g m-： for BGB, 9.2-82.3 g m2 for LB, and 168.0-2 681.3 g m-： for TB. R：S showed less variation with median values from 3.2 to 5.3 （excluding marshy meadow）. The different grassland types showed similar patterns of biomass allocation, with more than 70% BGB for all types. There is evidence of strong positive effects associated with mean annual precipitation （MAP） and negative effects associated with mean annual temperature （MAT） on AGB, BGB, and LB, although both factors have the opposite effect on R：S.
基金This work was supported by the National Natural Science Foundation of China(NSFC)(Nos.61505155 and 61571367The Fundamental Research Funds for the Central Universities(Nos.JB160110 and XJS16051)The 111 Project of China(No.B08038).
文摘Coherent beam combining(CBC)is recently used to generate high power vortex beams which are strongly required in specific applications.In this paper,based on the extended Huygens-Fresnel principle,the exact theoretical forms for the intensity distribution of CBC Bessel-Gaussian beams(BGBs)in turbulent ocean are derived.To show the superiority of CBC BGBs in turbulent channels,the comparison in the intensity evolution of CBC BGBs with ideal BGBs is performed.It is found that the beam spreading of CBC BGBs is smaller than that of ideal BGBs under the same oceanic turbulence conditions.Moreover,the effect of the beam parameters and channel parameters on the quality of CBC BGBs is also analyzed.The results show that the oceanic turbulence with a higher rate of dissipation of kinetic energy per unit mass of fluid,lower dissipation rate of the mean-squared temperature,or smaller ratio of temperature and salinity contributions to the refractive index spectrum has smaller impact on CBC BGBs.Moreover,the increasing number of the beamlets,the increasing waist width of each beamlet,and the decreasing radius of the beam distribution cause the optical energy to be more concentrated,and thus leading to a longer non-diffraction propagation distance.
基金Supported by the National Natural Science Fundation of China (Grant Nos. 90211016, 40021101 and 30700090)
文摘Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for aboveground biomass (AGB), belowground biomass (BGB) is poorly reported at the re- gional scales. The present study, based on a total of 113 sampling sites in temperate grassland of the Inner Mongolia, investigated regional distribution patterns of AGB, BGB, vertical distribution of roots, and their relationships with environmental factors. AGB and BGB increased from the southwest to the northeast of the study region. The largest biomass occurred in meadow steppe, with mean AGB and BGB of 196.7 and 1385.2 g/m2, respectively; while the lowest biomass occurred in desert steppe, with an AGB of 56.6 g/m2 and a BGB of 301.0 g/m2. In addition, about 47% of root biomass was distributed in the top 10 cm soil. Further statistical analysis indicated that precipitation was the primary determinant factor in shaping these distribution patterns. Vertical distribution of roots was significantly affected by precipitation, while the effects of soil texture and grassland types were weak.
