[Environmental Effects of Algae Bloom Cluster: Impact on the Floating Plant Water Hyacinth Photosynthesis].

It is an efficient and effective ecological restoration method by using the adaptability, large biomass of aquatic plants to purify the polluted water at present. However, there is a lack of systematic research on the impact on the physiological ecology of aquatic plants and its environmental effects of algae blooms cluster in summer. The aim of this paper is to reveal the mechanism of macrophytes demise in a shallow ecosystem by studying the influence on photosynthesis of water hyacinth caused by the cynaobacterial blooms gathered, and also to provide the theoretical basis for full effects of purification function of macrophytes to reduce the negative effects on the aquatic plants after algae blooms gathered during the higher temperature (not lower 25 degrees C) through simulating experiments. Results showed the dissolved oxygen quickly consumed in root zone of aquatic plants after algae blooms gathered and showed a lack of oxygen (DO < 0.2 mg x L(-1)); and the ORP was lower than -100 mV after 1 d, and it declined to -200 mV at the end of the experiment, and pH declined 0. 7unit compared with that of control group ( CK). There were lots of nutrients releasing to the water after the algae cell died and the NH4+ -N concentration was 102 times higher than that of the control group root zone. And the macrophytes photosynthesis reduced quickly and the plant body damaged with the intimidation of higher NH4+ -N concentration (average content was 45.6 mg x L(-1)) and hypoxia after algae cell decomposed. The average net photosynthesis rate, leaf transpiration rate were 0.6 times, 0.55 times of the control group, and they reduced to 3.96 micromol x (m2 x s)(-1), 1.38 mmol x (m2 x s)(-1), respectively. At the end of the experiment, they were 22.0 micromol x (m2 x s)(-1) and 7.61 mmol x (m2 x s)(-1) for the control group. Results also showed the algae bloom together had the irreversible damage to the aquatic plants. So in the practice of ecological restoration, it should avoid the harm to the plant after the algae bloom cells gathered and decomposed so as to play the purification function of the plant in the ecological rehabilitation project.

[Effects of nitrogen application rates on apparent soil nitrogen surplus of late sowing wheat with straw returning in rice-wheat rotation].

Field experiments were conducted to study the effects of varying rates of nitrogen application on soil mineral nitrogen content, amount of nitrogen released from the straw, and grain yield of late sowing wheat with straw returning. The result showed that a high nitrogen fertilizer application rate enhanced the mineral nitrogen content in the soil layer of 0 to 50 cm, and also in the lower soil layers when using N at 270 and 360 kg · hm(-2) with the advance of growth stages. The amount of nitrogen released form the straw increased as the nitrogen application rate increased; the lowest appeared from overwintering to jointing, and the highest from jointing to maturity. During the whole growing season, apparent nitrogen surplus occurred when the nitrogen application rate was higher than 180 kg · hm(-2). The N surplus before jointing was significantly higher than that from jointing to maturity. Grain yield reached the highest at a nitrogen application rate of 270 kg · hm(-2), and a higher application rate obviously decreased the nitrogen use efficiency. It could be concluded that applying nitrogen at 270 kg · him(-2) could improve the grain yield of late sowing wheat with straw returning with the optimal ecological benefit.