Four dominant psammophyte species are air‐seeded in attempts to revegetate the Mu Us sandy land in Inner Mongolia, but seedling emergence is low. This study sought to clarify the behaviour of seedling emergence under different water supply and sand burial regimes to improve the technology of air seeding. Seeds were buried in sand at depths of 0, 0.5, 1, 1.5, 2, 3 and 5 cm and supplied one time with 2.5, 5, 7.5, 10, 15, 20, 30 or 40 mm of water or with 2.5 mm once every 3 days for 30 days. Our study showed that a 0.5‐cm burial depth and under 10‐ to 20‐mm single‐watering regimes resulted in highest seedling emergence percentage and rate of these four species. All emerged seedlings of Caragana korshinskii, Hedysarum laeve and Artemisia ordosica died under 2.5, 5 and 7.5 mm of watering, respectively, but seedling mortality was <50% when the single‐watering regime was >10 mm. In the field, germination of the four species increased from the top of the dune to the middle of the leeward side and then to the bottom. Based on precipitation pattern in the Mu Us sandy land, our study indicates that 0.5‐cm burial depth and a single‐watering regime of >7.5 mm is the threshold condition for seedling emergence.
Three experiments are reported, two of which involved cotyledon excision, to elucidate seedling developmental strategy of a North China rangeland legume, Medicago falcata. Early loss of cotyledons was fatal, with data indicating a possible hormonal-type signal from cotyledons to initiate first leaf expansion. Cotyledons made a substantive photosynthetic contribution for some 28 days from imbibition, but high seedling relative growth rates were not observed until after first leaf expansion. On removal of both cotyledons at 7 days, seedlings responded with an increase in shoot:root dry weight ratio; on removal of one cotyledon only at this time a transitory shift of allocation from shoot to root was observed until normal ontogeny was restored. Removal of one or both cotyledons at 14 days delayed seedling development but did not change seedling ontogeny. This study was part of a series of experiments to better understand the autecology of M. falcata.
A field study compared the seedling emergence and structure of five forage legumes (Trifolium repens L., Medicago falcata L., Melilotus suaveolens Ledeb, Medicago sativa L. and Lespedeza davurica Schindler) at five planting depths (1, 2, 4, 6 and 8 cm) and two light levels (full light and shade) on the 21st day after planting. As expected, increaseing depth lowered and slowed seedling emergence. Maximum emergence occurred at 1 and 2 cm depths for all five forage legumes irrespective of light levels; then decreased as the burial depth increased. Improved seedling emergence was also observed under shade compared to full light. Increased sowing depth diminished seedling size by reducing the plant height, biomass, leaf number and size of all five forage legumes. All the morphological traits and seedling biomass were reduced under shade condition except seedling height and cotyledon size. The optimal planting depth for all the forage legumes in this study was 1 to 2 cm. M. falcata, M. suaveolens and M. sativa had high percentage of emergence and better growth from deeper depth or under shade condition.
A kind of metastable β type Ti-30Nb-13Zr-0.5Fe (wt.%) alloy for biomedical application was newly designed and developed. In order to exam the phase transformation during aging and its effects on the mechanical properties, the alloy was β solubilized and aged at 350°C-550°C for 4 hours. The microstructures were observed by OM and TEM, and the phase structures were identified by XRD. The tensile tests were performed with various aged microstructures. The results show that a lot of ω phase precipitates during aging at 350°C, leading to the increase of strength and elastic modulus and drastic decrease of plasticity. Aging at 450°C, dot α phase uniformly precipitates from metastable β phase. The good combination of high strength 、high plasticity and low elastic modulus was obtained under this aging condition. With increasing aging temperature and aging time α precipitations coarsen and precipitation free zones (PFZ) along prior β grain boundaries form, which are the main reasons to lower the strength and plasticity.
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