RÉSUMÉ
Taking Deyeuxia angustifolia as the research object, a representative plant of wetland in Sanjiang Plain, we analyzed the variations of individual size and biomass among the habitats of swamp wetlands, swampy meadows, typical meadows and miscellaneous grass meadows, and the relationship between reproductive components and plant biomass. We explored the effects of water level on individual biomass and reproductive allocation of D. angustifolia in different types of wetlands. The results showed that plant biomass, height and the characteristics of sexual reproduction significantly decreased with the increases of water level. The reproductive thresholds of D. angustifolia in miscellaneous grass meadow, typical meadow, swampy meadow, and swamp wetland were 0.245, 0.149, 0.148 and 0.157 g, respectively. There was a significantly negative correlation between plant size and reproductive allocation in three habitats except swampy meadow. Compared with individual size, soil water content had a stronger effect on reproductive allocation of D. angustifolia. The different investment between individual size and reproductive allocation in different habitats was the basic condition that contributes to the good ecological adaptability of D. angustifolia.
Sujet(s)
Eau , Zones humides , Chine , Écosystème , Poaceae , ReproductionRÉSUMÉ
OBJECTIVE: The purpose of this study was to select the optimal monochromatic level for gemstone spectral imaging (GSI) to minimize both the image noise and beam-hardening artifacts (BHAs) in nonenhanced cranial computed tomography (CT). MATERIALS AND METHODS: One hundred subjects scanned with GSI mode on Discovery CT750HD were enrolled. Six sets of CT images were obtained from a single GSI acquisition: conventional 140 kilovolt (peak) (kV[p]) polychromatic images and 5 sets of monochromatic images (80, 75, 70, 65, and 60 kiloelectron volts [keV]). The background noise in the corona and the BHA in 4 different anatomic regions (medulla oblongata, cerebellar, pons, and the inferior part of frontal lobes) were measured and compared between the polychromatic and monochromatic images. Beam-hardening artifact is defined as the square root of the squared noise difference between the region of interest and background. RESULTS: The background noise with the monochromatic sets reduced by -36%, -11%, 11%, 10%, and -14%, respectively, compared to the polychromatic image. For BHA, the reductions were 73%, 91%, 92%, and 80%; 53%, 75%, 65%, and 41.%; 27%, 59%, 44%, and 26%; 7%, 46%, 25%, and 20%; and -14%, 33%, 6%, and 19% for the 4 regions of interest. Both the 70 and 65 keV sets had positive background noise reduction (P = 0.285) and BHA reduction with 70 keV were statistically higher (P < 0.05). CONCLUSION: In the nonenhanced cranial CT with GSI, the optimal monochromatic level was determined at 70 keV to provide both image noise reduction (11%) and BHA reduction compared to the conventional polychromatic images.
