Influence of temperature and salinity on germination of eelgrass (Zostera marina L.) seeds

Seagrass restoration as part of ocean ecosystem protection has been launched for many years all over the world, but intensive research on this subject in China has just begun in recent years. Seed broadcasting has been widely accepted as the most potentially useful method for seagrass restoration over large areas. We examined the influence of key environmental factors on seed germination to help promote eelgrass bed restoration. Under anoxic conditions, the influence of temperature and salinity on the germination rate of eelgrass (Zostera marina L.) seeds was examined at different combinations of four temperatures (4, 9, 14, and 24°C) and nine salinities (5 to 45, increment of 5). The effect of significant interaction of temperature and salinity on germination rate was observed (ANOVA) (P<0.001). The highest germination rate (83.3 ± 3.5)% was reached in 8 weeks at 14°C and salinity 5. Higher temperature significantly increased the germination rate at salinity 5 (P<0.001) during the whole observation period except for 24°C, while lower salinity significantly increased the germination rate at 14°C (P<0.001). Although significant interaction was found between temperature and salinity (P<0.001), the influence of salinity was stronger than that of temperature for the germination of eelgrass seeds. These results provide useful information for the propagation of artificial seedlings for seagrass restoration in China.     

Effects of feeding and stocking density on digestion of cultured Atlantic salmon Salmo salar L.

The combined effects of feeding rate （0.8%, 1.0%, and 1.2% initial body weight/day）, feeding frequency （two, three, and four times/day） and stocking density （10, 15, and 20 kg/m3） in recirculating aquaculture systems （RAS） on growth performance, digestion and waste generation of Atlantic salmon （Salmo salar L.） were investigated in an 8-week orthogonal experiment （L9（3）3） with a constant daily water renewal at 7.50% of total volume. No mortality occurred during the experimental period. Feed conversion ratio （FCR） varied from 0.90 to 1.13 and specific growth rate （SGR） ranged from 0.48% to 0.69%/day. SGR, thermal growth coefficient （TGC） and FCR were not significantly （P〉0.05） affected by the three factors, while net protein utilization （NPU） was significantly （P〈0.05） affected. Apparent digestibility coefficients （ADC） of dry matter in the present study were in the range 66.12%-73.55%. ADC in protein, lipid and energy were statistically different among all treatments and in the range of 90.07%-93.67%, 81.54%-89.15%, and 67.55%-71.87%, respectively. The proportion of mean total ammonia nitrogen excreted ranged from 1.37% to 1.64% of feed nitrogen at steady state, and the concentration of nitrogenous and phosphorus compounds were differently correlated to the three factors. The results will provide valuable reference data for culture management decisions in the Atlantic salmon farming industry.     

Unpalatable weed Stellera chamaejasme L. provides biotic refuge for neighboring species and conserves plant diversity in overgrazing alpine meadows on the Tibetan Plateau in China

Steller chamaejasme L. (S. chamaejasme for short) is one of the most noxious unpalatable weeds in China, which has been frequently reported its negative interaction (i.e. competition and allelopathy) with other herbaceous species in grasslands. This study compared species diversity, biomass and sexual reproduction of herbaceous plants in meadows with S. chamaejasme and in open meadows without S. chamaejasme in overgrazing meadows on the Tibetan Plateau in China to determine whether positive facilitation exist between S. chamaejasme and other herbaceous species under livestock’s overgrazing. The results showed that there are more herbaceous species in meadows with S. chamaejasme than those in open meadows (35s and 30s, respectively). Diversity index and above-ground biomass were also significantly higher in meadows with S. chamaejasme. There were 39% (11/28) of all species with sexual reproduction found in meadows with S. chamaejasme, which was 7 times more than those in open meadows. Our study showed that S. chamaejasme could provide biotic refuge for neighboring plants and preserve plant diversity from livestock’s overgrazing in alpine meadows on the Tibetan Plateau. It also suggested that inter-specific facilitation between S. chamaejasme and other herbaceous species may play a key role in overgrazing alpine meadows.