Effects of silicate application on rice growth, yield and quality under nighttime warming in southern China.

The main feature of climate warming is that nighttime warming is higher than the daytime warming. Nighttime warming reduced single rice production in southern China, while silicate application increased rice yield and stress resistance. It is still unclear regarding the effects of silicate application on growth, yield, and especially quality in rice under nighttime warming. We performed a field simulation experiment to investigate the effects of silicate application on tiller number, biomass, yield and quality of rice. Warming was set at two levels, ambient temperature (control, CK) and nighttime warming (NW). The open passive nighttime warming method was used, with rice canopy being covered with aluminum foil reflective film at night (19:00-6:00) to simulate nighttime warming. Silicate fertilizer (steel slag) was applied at two levels, i.e., Si0(0 kg SiO2·hm-2) and Si1(200 kg SiO2·hm-2). The results showed that, compared with the control (ambient temperature), average temperature at nighttime on rice canopy and at 5 cm soil layer increased by 0.51-0.58 ℃ and 0.28-0.41 ℃ during rice growing season, respectively. Nighttime warming decreased tiller number and chlorophyll content by 2.5%-15.9% and 0.2%-7.7%, respectively. In contrast, silicate application increased tiller number and chlorophyll content by 1.7%-16.2% and 1.6%-16.6%, respectively. Under nighttime warming, silicate application increased dry weight of shoot, total dry weight of the whole plant, and yield at grain filling-maturity stage by 64.1%, 55.3%, and 7.1%, respectively. Under nighttime warming, silicate application significantly increased milled rice rate, head rice rate, and total starch content by 2.3%, 2.5%, and 41.8%, respectively. Nighttime warming reduced rice yield by decreasing the number of effective panicles, seed setting rate, and 1000-grain weight, but increasing empty grains. Silicate application increased rice yield by increasing the number of effective panicles, filled grains per panicle, seed setting rate and 1000-grain weight, but reducing empty grains. In conclusion, silicate application could effectively alleviate the suppressive effects of nighttime warming on growth, yield, and quality of single rice in Southern China.

[Effects of solar radiation on CH4 emission in paddy field]. / 太阳辐射对稻田甲烷排放的影响.

Decrease in solar radiation is one of the main components of climate change. Studies aimed at examining the effects of decreased solar radiation on CH4 emission and estimation of CH4 emission based on hyperspectral data in paddy fields are still scarce. A field simulation experiment was conducted to investigate the effects of shading intensity on CH4 emission in a paddy field and rice canopy hyperspectral properties. CH4 emission flux was estimated with rice canopy hyperspectral data. The shading intensities were set at three levels, i.e. control (CK, no shading), light shading (S1, 60% of shading rate), and heavy shading (S2, 84% of shading rate). The results showed that shading significantly reduced CH4 emission. However, CH4 emission under heavy shading (S2) was higher than that under light shading (S1). The reflectance of the near-infrared spectrum on rice canopy from the jointing stage to grain filling stage was in the sequence of CK>S2>S1. The spectral reflectance on rice canopy was significantly and positively correlated with CH4 flux in the near-infrared band (699-1349 nm), with a correlation coefficient of 0.64 (P<0.01). The six vegetation indices were significantly correlated with CH4 flux. The correlation coefficient between Ratio Vegetation Index (RVI) and CH4 flux was the largest, with R2=0.84 (P<0.01). The stepwise regression model with RVI, Normalized Difference Vegetation Index (NDVI), and 507 nm original reflectance (Ρ507) parameters was the best one (fitting model R2=0.86, prediction model R2=0.85) for estimating CH4 emission.

Effects of silicon application on diurnal variations of physiological properties of rice leaves of plants at the heading stage under elevated UV-B radiation.

We investigated the effects of silicon (Si) application on diurnal variations of photosynthetic and transpiration physiological parameters in potted rice (Oryza sativa L. cv Nanjing 45) at the heading stage. The plants were subjected to two UV-B radiation levels, i.e., reference UV-B (A, ambient, 12.0 kJ m(-2) day(-1)) and elevated UV-B radiation (E, a 20% higher dose of UV-B than the reference, 14.4 kJ m(-2) day(-1)), and four Si application levels, i.e., Si0 (no silicon supplementation, 0 kg SiO2 ha(-1)), Si1 (sodium silicate, 100 kg SiO2 ha(-1)), Si2 (sodium silicate, 200 kg SiO2 ha(-1)), and Si3 (slag silicon fertilizer, 200 kg SiO2 ha(-1)). Compared with the reference, elevated UV-B radiation decreased the diurnal mean values of the net photosynthetic rate (Pn), intercellular carbon dioxide (CO2) concentration (Ci), transpiration rate (Tr), stomatal conductivity (Gs), and water use efficiency (WUE) by 11.3, 5.5, 10.4, 20.3, and 6.3%, respectively, in plants not supplemented with silicon (Si0), and decreased the above parameters by 3.8-5.5, 0.7-4.8, 4.0-8.7, 7.4-20.2, and 0.7-5.9%, respectively, in plants treated with silicon (Si1, Si2, and Si3), indicating that silicon application mitigates the negative effects of elevated UV-B radiation. Under elevated UV-B radiation, silicon application (Si1, Si2, and Si3) increased the diurnal mean values of Pn, Ci, Gs, and WUE by 16.9-28.0, 3.5-14.3, 16.8-38.7, and 29.0-51.2%, respectively, but decreased Tr by 1.9-10.8%, compared with plants not treated with silicon (E+Si0), indicating that silicon application mitigates the negative effects of elevated UV-B radiation by significantly increasing the P n, C i, G s, and WUE and decreasing the T r of rice. Evident differences existed in mitigating the depressive effects of elevated UV-B radiation on diurnal variations of physiological parameters among different silicon application treatments, exhibiting as Si3>Si2>Si1>Si0. In addition to recycling steel industrial wastes, the application of slag silicon fertilizer mitigates the negative effects of elevated UV-B radiation on photosynthesis and transpiration in rice.

[Effects of silicon supply on rice growth and methane emission from paddy soil under elevated UV-B radiation].

A pot experiment was conducted to investigate the effects of silicon supply on rice growth and methane (CH4) emission in paddy field under elevated UV-B radiation. The experiment was designed with two UV-B radiation levels, i.e. ambient UV-B (ambient, A) and elevated UV-B radiation (elevated by 20%, E) ; with four silicon supply levels, i.e., Si0 (control, without silicon), Si2 (as sodium silicate, 100 kg SiO2 . hm-2), Si2 (as sodium silicate, 200 kg SiO2 hm-2) and Si3 (as slag fertilizer, 200 kg SiO2 . hm-2). The results indicated that, silicon supply obviously alleviated the depressive effect of elevated UV-B radiation on rice growth, and increased the tiller numbers, chlorophyll content, and shoot and root dry masses. Silicon supply promoted rice growth, which increased with the silicon supply level (sodium silicate). Slag fertilizer was better than*sodium silicate in promoting rice growth. CH4 flux and accumulated CH4emission were obviously increased by elevated UV-B radiation, but significantly decreased by silicon application. CH4 emission was reduced with increasing the silicon supply level. Under the same silicon supply level, slag fertilizer was better than sodium silicate in inhibiting CH4 flux and accumulated CH4 emission. This research suggested that fertilizing slag in rice production was helpful not only in utilizing industrial wastes, but also in significantly mitigating CH4 emissions in rice paddy under elevated UV-B radiation.

[Effects of silicon supply on diurnal variations of physiological properties at rice heading stage under elevated UV-B radiation].

A pot experiment was conducted to investigate the effects of silicon (Si) supply on diurnal variations of photosynthesis and transpiration-related physiological parameters at rice heading stage under elevated UV-B radiation. The experiment was designed with two UV-B radiation levels, i.e. ambient UV-B. (ambient, A) and elevated UV-B (elevated by 20%, E), and four Si supply levels, i.e. Sio (control, 0 kg SiO2 . hm-2), Si, (sodium silicate, 100 kg SiO2 . hm-2), Si2 (sodium silicate, 200 kg SiO2 . hm2), Si3 (slag fertilizer, 200 kg SiO2 . hm-2). The results showed that, compared with ambient UV-B radiation, elevated UV-B radiation decreased the net photosynthesis rate (Pn) , intercellular CO2 concentration (Ci), transpiration rate (Tr), stomatal conductivity (gs) and water use efficiency (WUE) by 11.3%, 5.5%, 10.4%, 20.3% and 6.3%, respectively, in the treatment without Si supply (Si, level), and decreased the above parameters by 3.8%-5.5%, 0.7%-4.8%, 4.0%-8.7%, 7.4%-20.2% and 0.7%-5.9% in the treatments with Si supply (Si1, Si2 and Si3 levels) , respectively. Namely, elevated UV-B radiation decreased the photosynthesis and transpiration-related physiological parameters, but silicon supply could obviously mitigate the depressive effects of elevated UV-B radiation. Under elevated UV-B radiation, compared with control (Si0 level), silicon supply increased Pn, Ci, gs and WUE by 16.9%-28.0%, 3.5%-14.3%, 16.8% - 38.7% and 29.0% - 51.2%, respectively, but decreased Tr by 1.9% - 10.8% in the treatments with Si supply (Si1 , Si2 and Si3 levels). That is, silicon supply could mitigate the depressive effects of elevated UV-B radiation through significantly increasingnP., CigsgK and WUE, but decreasing T,. However, the difference existed in ameliorating the depressive effects of elevated UV-B radiation on diurnal variations of physiological parameters among the treatments of silicon supply, with the sequence of Si3>Si2>1i >Si0. This study suggested that fertilizing slag was helpful not only in recycling industrial wastes, but also in effectively mitigating the depressive effects of elevated UV-B radiation on photosynthesis and transpiration in rice production.

Soil CO2 flux in relation to dissolved organic carbon, soil temperature and moisture in a subtropical arable soil of China.

Soil CO2 emission from an arable soil was measured by closed chamber method to quantify year-round soil flux and to develop an equation to predict flux using soil temperature, dissolved organic carbon(DOC) and soil moisture content. Soil CO2 flux, soil temperature, DOC and soil moisture content were determined on selected days during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil, the Chinese Academy of Sciences, in a subtropical region of China. Soil CO2 fluxes were generally higher in summer and autumn than in winter and spring, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The estimation was 2.23 kgCO2/(m2 x a) for average annual soil CO2 flux. Regressed separately, the reasons for soil flux variability were 86.6% from soil temperature, 58.8% from DOC, and 26.3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained approximately 85.2% of the flux variance, however by stepwise regression, soil temperature was the dominant affecting soil flux. Based on the exponential equation developed from soil temperature, the predicted annual flux was 2.49 kgCO2/(m2 x a), and essentially equal to the measured one. It is suggested the exponential relationship between soil flux and soil temperature could be used for accurately predicting soil CO2 flux from arable soil in subtropical regions of China.