No abstract

To understand how light intensity influences plant morphology and photosynthesis in the forage crop alfalfa (Medicago sativa L. cv. Zhongmu 1), we investigated changes in leaf angle orientation, chlorophyll fluorescence, parameters of photosynthesis and expression of genes related to enzymes involved in photosynthesis, the Calvin cycle and carbon metabolism in alfalfa seedlings exposed to five light intensities (100, 200, 300, 400 and 500 μmol m−2 s−1) under hydroponic conditions. Seedlings grown under low light intensities had significantly increased plant height, leaf hyponasty, specific leaf area, photosynthetic pigments, leaf nitrogen content and maximal PSII quantum yield, but the increased light-capturing capacity generated a carbon resource cost (e.g., decreased carbohydrates and biomass accumulation). Increased light intensity significantly improved leaf orientation toward the sun and upregulated the genes for Calvin cycle enzymes, thereby increasing photosynthetic capacity. Furthermore, high light (400 and 500 μmol m−2 s−1) significantly enhanced carbohydrate accumulation, accompanied by gene upregulation and increased activity of sucrose and starch-synthesis-related enzymes and those involved in carbon metabolism. Together, these results advance our understanding of morphological and physiological regulation in shade avoidance in alfalfa, which would guide the identification of suitable spatial planting patterns in the agricultural system.

No abstract

This research explored the relationship between a single count of radicle emergence (RE) and mean germination time (MGT) with seed vigour for Chinese milk vetch (Astragalus sinicus) (CMV), a globally important legume used as a forage, green manure, and rotation crop. Fourteen seed lots of CMV were used to determine standard germination (SG), RE and MGT in the laboratory. Field experiments were conducted at two sites to measure the emergence performance including field emergence (FE), seedling dry weight (SDW) and simplified vigour index (SVI). The SG ranged from 89.0 to 95.5% and was not significantly correlated with field performance at either of two sites. However, both a single count of RE at 20 hours and MGT were highly predictive of FE, SDW and SVI at both sites (R2 ranged from 0.612 to 0.897 for RE; 0.604 to 0.870 for MGT). The RE was positively related to field performance while MGT was negatively related. The seed lots with lower RE at 20 hours had lower FE and higher MGT. Overall, both RE at 20 hours and MGT are suitable indices for the vigour evaluation of CMV. However, a single count of RE is more accurate, quick and convenient.

Chenopodium album L. is a troublesome annual species in various cropping systems, and a sound knowledge of the ecological response of C. album germination to environmental factors would suggest suitable management strategies for inhibiting its spread. Preliminary laboratory-based research was conducted to investigate germination and emergence requirements of C. album under various environmental conditions (e.g., photoperiods, constant temperature, salinity, moisture, soil pH, burial depth, and oat crop residue). Results showed C. album seeds were found to be photoblastic, with only 13% germination in darkness. The maximum germination (94%) of C. album occurred at an optimal temperature of 25°C, and the depressive effect of other temperatures on germination was more severe at lower rather than higher temperatures. Seed germination was suitably tolerant of salinity and osmotic potential, with germination observed at 200 mM NaCl (37.0%) and -0.8 MPa (20%), respectively. Germination was relatively uniform (88–92%) at pH levels ranging from 4 to 10. The maximum germination of C. album was observed on the soil surface, with no or rare emergence of seeds at a burial depth of 2 cm or under 7000 kg ha-1 oat straw cover, respectively. Information provided by this study will help to develop more sustainable and effective integrated weed management strategies for the control of C. album, including (i) a shallow-tillage procedures to bury weed seeds in conventional-tillage systems and (ii) oat residue retention or coverage on the soil surface in no-tillage systems.