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Rice (Oryza sativa) growth is always threatened by heat as well as cold stress, when it is exposed to natural environment. Heat growing degree hours (HGDH) and cold growing degree hours (CGDH1 and CGDH2) were firstly proposed to quantify heat and cold stress occurred during different growing stages. Information diffusion method was effectively used to fit the distribution and estimate probability of single stress at each station, with an advantage of no limitation in data series. In terms of single stress, highest probability was seen in HGDH, followed by CGDH1 and CGDH2. Seven copula functions, i.e., normal and t, Gumbel-Hougaard, Clayton, Frank, Joe, and Ali-Mikhail-Haq, were applied to fit the distribution of multi-stress with significant dependence, and simple calculation based on single stress was used to quantify the probability for multi-stress with independence. In these copulas, t was the most chosen one in the fitting of HGDH-CGDH1, HGDH-CGDH2, CGDH1-CGDH2, and HGDH-CGDH1-CGDH2, selected by the statistic of Akaike information criterion. Regarding bi-stress, higher joint probability was in HGDH-CGDH1, relative to HGDH-CGDH2 and CGDH1-CGDH2. As expected, the co-occurrence probability of tri-stress was lower than that of bi-stress in the magnitude and spatial extent, while joint probability of tri-stress was larger. Given the condition of occurrence of HGDH or CGDH1, the joint probability of HGDH-CGDH1 was higher than other pairs of bi-stress and tri-stress. It was special that higher joint probability of CGDH1-CGDH2 was detected under the condition of CGDH2 relative to CGDH1. Joint probability of tri-stress was lower under the condition of HGDH-CGDH1, in comparison with HGDH-CGDH2 and CGDH1-CGDH2. Hazards of single stress and multi-stress were expressed by the integration of intensity of stress index and corresponding probability. Most consistent conclusions agreed that central Fujian, Zhejiang, and northeastern Jiangxi were exposed to higher hazard, derived from not only single stress but also multi-stress. These results can be helpful in provision of information regarding prevention and adaptation strategies for rice cultivation as a response to extreme temperature stress. [ABSTRACT FROM AUTHOR]

• Rice heat – lead characteristics of hot weather processes/events has been explored. • Particular phenological period severely hit by rice heat was investigated. • Hot weather event-based evaluation of rice heat was constructed. • Spatial-temporal characteristics of rice heat risk was identified in Jiangxi province. Frequent occurrences of extreme hot weather create severe rice heat disasters. Precisely assess rice heat risk based on the identification of the particular period severely hit by hot weather events is of great merit to improve public planning to minimize the deleterious impact of rice heat. In this study, maximum temperature, disaster and phenophase data on rice in Jiangxi province (typical planting area for double early rice in South China) were integrated to represent the historical heat of early double-cropping rice, facilitating the identification of particular period severely hit by historical rice heat and construction of hot weather event-based evaluation level of rice heat. Afterwards, a rice heat index (RHI) were constructed and calculated based on hot weather events and the exact rice growth stage (days before/after flowering, DF). The results showed that (1) Heat disasters occur approximately 15 d before flowering and the DF −5 to 0 was determined to have the highest possibility of rice heat, followed by the DF −10 to −5, with 29.41 and 22.06% of heat disasters starting in each period, respectively. (2) The probability of moderate and light heat damage was more than 80% when 3–5 d of hot weather occurred in the DF −5 to 5, while the probability of moderate and severe heat damage increased to 100% when >5 d of hot weather occurred in this period. More than 80% of >8 d rice heat started in DF −15 to 0, with severe rice heat accounting for approximately 90% in such a period. (3) Severe, moderate and light rice heat for 3–5 d was identified at DF −6 to 3, 4–5 and 6–9, respectively. Similarly, severe, moderate and light rice heat lasting for 6–8 d and >8 d started at DF −6 to 1, 2–5, 6–18 and −7 to −5, −4 to 4, 5–14, respectively. (4) A high RHI was mainly found in the middle and northeastern part of the study area from 1981 to 2015, with the RHI in most stations being greater than 0.25. Increasing trends of a high RHI occurred in the same areas of the RHI belt. Most stations in such areas exhibited slopes >0.15/10a. The results can provide technical and theoretical support for targeted rice heat assessment, and it can also universally applied in relative researches on rice heat. [ABSTRACT FROM AUTHOR]

The influences of long-term static interaction between flotation reagents and minerals on mineral surface properties and their flotation behaviors were investigated in this work. Single mineral results showed that when the static interaction time between flotation reagents and minerals increased from 0 to 8 days, there were no significant differences in the recovery of fluorite (ranging from 77.50% to 74.50%), while the recovery of calcite dramatically decreased from 97.17% to 41.13%. The collector adsorption results indicated that after the long-term static interaction between the collector and minerals, adsorption and desorption of collector on the minerals occurred, and the adsorption amount of collector on fluorite and calcite varied from 0.396 mg/g to 0.421 mg/g, and from 0.444 mg/g to 0.404 mg/g, respectively. The contact angles of fluorite and calcite decreased from 134.3° and 105.0° for 0 days to 109.7° and 52.5° for 8 days, respectively, which demonstrated that the fluorite had a higher hydrophobicity than that of calcite after 8 days of static interaction between the minerals and collector. The Fourier transform infrared spectroscopy (FTIR) analysis showed that there were chemisorptions between the collector and the surfaces of the fluorite and calcite. Meanwhile, the X-ray photoelectron spectroscopy (XPS) results further elucidated that the amount of C=O from the oleic acid (OA) molecule for calcite treated for 8 days was less than for that treated for 0 days. In addition, the flotation results of the tailings from Jiangxi containing fluorite and calcite, indicated that the grade and recovery of fluorite increased from 87.18% and 40.99% for 0 days to 93.00% and 46.01% for 8 days, respectively, indicating that the separation of fluorite from calcite could be achieved via increasing the long-term static interaction between the flotation reagents and minerals. [ABSTRACT FROM AUTHOR]