干湿交替灌溉改善稻田根际氧环境进而促进氮素转化和水稻氮素吸收

【目的】阐明不同水氮管理模式下水稻根际内外氧环境变化特征及其对土壤碳氮转化和水稻氮吸收利用的影响,以期从稻田“根际氧环境”调控角度揭示适宜水氮耦合促进水稻生长和提高氮素利用效率的内在机制。【方法】在长期定位试验基础上,采用根箱模拟培养以及Unisense微电极系统和15N同位素示踪相结合的研究方法,以常规粳稻日本晴和常规籼稻扬稻6号为供试材料,试验设常规淹灌(conventional flood irrigation,CF)、干湿交替(alternate wet and dry irrigation,AWD)两种灌溉模式,以及无氮(0 g/kg,N_(0))、中氮(0.8 g/kg,N_(0.8))、高氮(1.2 g/kg,N_(1.2))3个施氮水平。对比分析了不同水氮耦合下水稻根际内外氧环境、可溶性有机碳、微生物量碳氮和碳氮转化相关酶活性,并分析了水稻生长和氮吸收利用的关系。【结果】(1)与CF相比,AWD显著增加了水稻根际内外溶氧量和氧化还原电位,扬稻6号根际土壤的增加量高于日本晴;(2)与N0相比,在N_(0.8)、N_(1.2)水平下,AWD显著增加了两个水稻品种根际微生物量碳氮和可溶性有机碳含量,增加了水稻根际碳氮代谢相关酶活性(脲酶、蔗糖酶、过氧化氢酶和N-乙酰-β-D-葡萄糖苷酶);(3)与N_(0)相比,在N_(0.8)、N_(1.2)水平下,AWD显著增加了水稻根际硝化速率和提取态总氮、硝态氮和游离氨基酸含量,但降低了其铵态氮含量;同时,增加了2个水稻品种根系铵态氮吸收速率、干物质重和氮素利用指数,且上述各指标扬稻6号均显著高于日本晴;(4)相关性分析结果表明,水稻生物量和氮素利用指数与根际土壤硝化速率、微生物量碳氮、可溶性碳氮有效性和根系铵态氮/硝态氮吸收速率均呈显著正相关。【结论】AWD管理可通过提高溶解氧含量和氧化还原电位,创造良好的根际环境,进而提高根际可溶性有机碳、微生物量碳氮和碳氮代谢相关酶活性,增强根际硝化速率及根系铵态氮和硝态氮吸收速率,提高水稻干物质累积和氮素利用效率。

氨基酸水溶肥施用模式对水稻氮素吸收和转运的影响

采用大田小区试验研究了不同时期喷施氨基酸水溶肥对水稻产量、氮素吸收和转运的影响。结果表明,氨基酸水溶肥浸种以及分蘖期、破口前5~7 d和抽穗期喷施氨基酸水溶肥处理(T3),秧苗期、破口前5~7 d和抽穗期喷施氨基酸水溶肥处理(T5),氨基酸水溶肥浸种以及秧苗期、分蘖期、破口前5~7 d和抽穗期喷施氨基酸水溶肥处理(T6)水稻产量较高,分别达8355 kg/hm^2、8259 kg/hm^2和8313 kg/hm^2,较常规施肥处理(T1)显著增产7.2%、6.0%和6.7%。这可能与上述时期喷施氨基酸水溶肥能提高水稻千粒质量有关。与T1处理相比,各水溶肥施用组合均能显著增加齐穗期叶片、成熟期穗氮含量和分蘖盛期至齐穗期茎鞘氮素累积速率;T3、T5、T6处理显著增加齐穗期至成熟期叶片氮素转运量及氮素转运率,并提高水稻氮素回收利用率。水稻产量与抽穗前营养器官(茎鞘、叶片)氮素累积量、抽穗后叶片向穗的氮素转运量呈显著正相关关系。总之,通过施用氨基酸水溶肥增加水稻营养器官氮素积累量以及叶片氮素向穗转运,有利于提高水稻产量和氮素利用率,其中以秧苗期、破口前5~7 d和抽穗期喷施3次氨基酸水溶肥(T5处理)效果较好。

褪黑素和茉莉酸甲酯基质育秧对水稻耐低温胁迫的调控作用

早稻育秧过程中易遭受低温冷害,引起水稻减产。因此,有必要研制耐低温的水稻育秧基质来保障早稻生产。本研究以我们实验室自己研制的发酵基质作为研究对象,外源添加褪黑素和茉莉酸甲酯后,分别在水稻萌发阶段和水稻生长7 d后进行为期3 d的低温处理,然后测定水稻的萌发状况、理化性质和基因表达,从而明确2种不同激素对早稻秧苗耐低温胁迫的调控机制。结果表明,褪黑素和茉莉酸甲酯均显著提高水稻在低温条件下的发芽率和发芽势;两者均能提高水稻在低温条件下的生长,包括提高株高、根长、根条数、干物重、叶龄和养分含量。在低温条件下,褪黑素和茉莉酸甲酯均能通过调节水稻体内抗氧化系统酶的活性和降低水稻体内过氧化氢与丙二醛含量来缓解低温胁迫导致的脂质过氧化损伤。褪黑素和茉莉酸甲酯均能提高低温条件下水稻体内的脯氨酸含量和叶绿素含量,降低脱落酸的含量,而茉莉酸甲酯则单独提高了水稻体内GA_(3)的含量。褪黑素和茉莉酸甲酯对水稻耐冷基因存在不同的调控作用,在低温条件下,两者均显著上调OsCDPK7和OsLti6b,显著下调OsWRKY45基因的表达,褪黑素单独上调OsFer1基因的表达,茉莉酸甲酯单独上调OsTrx23基因的表达。以上结果表明,褪黑素和茉莉酸甲酯均能通过调控水稻体内抗氧化系统酶活、渗透物质含量、叶绿素含量、植物激素含量和耐冷基因表达提高水稻耐低温胁迫能力。

Effects of salt stress on rice growth, development characteristics, and the regulating ways： A review

Rice （Oryza safiva L.） is highly susceptible to the rhizosphere salinity than other cereals. High sensitivity has been ob- served, mainly at vegetative and reproductive stages in rice. It is the duty of plant physiologists to comprehend the growth, development, and physiological processes of rice plants under stress. This paper includes the overview of rice growth and developmental processes influenced by salt stress and the regulation pathways involved in these processes. It also includes the promising salt tolerance strategies, i.e., genetic modification techniques, agronomic practices to improve rice growth, yield; and role of phytohormones and their management, especially inhibition of ethylene biosynthesis by using inhibitors 1-methylcyclopropene （1-MCP）. Rice cultivation may be a first choice for improvement of salt tolerance through plant growth regulators and improved cultivation techniques. This study will significantly improve the understanding toward low rice grain yield and poor rice resistance under salt stress and will also stream scientific knowledge for effective utilization of salt affected soils by using different regulating ways.

Effects of Aerated Irrigation on Leaf Senescence at Late Growth Stage and Grain Yield of Rice

With the japonica inbred cultivar Xiushui 09, indica hybrid combinations Guodao 6 and Liangyoupeijiu as materials, field experiments were conducted in 2007 and 2008 to study the effects of aerated irrigation on leaf senescence at late growth stage and grain yield of rice. The dissolved oxygen concentration of aerated water evidently increased and decreased at a slow rate. The soil oxidation-reduction potential under aerated irrigation treatment was significantly higher than that of the CK, contributing to significant increases in effective panicles, seed setting rate and grain yield. In addition, the aerated irrigation improved root function, increased superoxide dismutase activity and decreased malondialdehyde content in flag leaves at post-flowering, which delayed leaf senescence process, prolonged leaf functional activity and led to enhanced grain filling.

Male Parent Plays More Important Role in Heat Tolerance in Three-Line Hybrid Rice

Ten F1 combinations with their male and female parents were employed to evaluate their heat tolerance during the flowering and early grain filling stages. The rice plants were subjected to heat stress（39 °C–43 °C） for 1–15 d during flowering. Based on the heat stress index, heat tolerance was only observed in the F1 combinations H2（K22A × R207）, H3（Bobai A × R207） and H4（Bobai A × Minghui 63）, whereas the others received above 0.5000 of heat stress index. Both parents of the tolerant combination（heat-tolerant × heat-tolerant） possessed heat tolerance, whereas the susceptible combinations were crossed by heat-tolerant（sterile lines） × heat-susceptible（restorer lines）, heat-susceptible × heat-tolerant, or heat-susceptible × heat-susceptible parents. This result indicated that heat tolerance in rice was controlled by recessive genes. Thus, both parents should possess high temperature tolerance to develop heat-tolerant F1 combinations. Furthermore, the heat stress index of F1 combinations was significantly correlated with the heat stress index of restorer lines but not with the heat stress index of maintainer lines. This result suggested that male parents play a more important role in heat-tolerant combinations than female parents. Therefore, the heat susceptibility of the hybrid rice in China is mainly due to the wide application of low-heat-tolerant restorer lines with high yield in three-line hybrid rice breeding.

Increased ammonification,nitrogenase,soil respiration and microbial biomass N in the rhizosphere of rice plants inoculated with rhizobacteria

Azospirillum brasilense and Pseudomonas fluorescens are well-known plant growth promoting rhizobacteria.However,the effects of A.brasilense and P.fluorescens on the N cycles in the paddy field and rice plant growth are little known.This study investigated whether and how A.brasilense and P.fluorescens contribute to the N transformations and N supply capacities in the rhizosphere,and clarified the effects of A.brasilense and P.fluorescens on the N application rate in rice cultivation.Inoculations with A.brasilense and P.fluorescens coupled with N application rate trials were conducted in the paddy field in 2016 and 2017.The inoculations of rice seedlings included four treatments:sterile saline solution(M_(0)),A.brasilense(M_(b)),P.fluorescens(M_(p)),and co-inoculation with a mixture of A.brasilense and P.fluorescens(M_(bp)).The N application rate included four levels:0 kg N ha^(–1)(N_(0)),90 kg N ha^(–1)(N_(90)),180 kg N ha^(–1)(N_(180)),and 270 kg N ha^(–1)(N_(270)).The results indicated that the M_(bp) and M_(p) treatments significantly enhanced the ammonification activities in the rhizosphere compared with the M_(0) treatment,especially for higher N applications,while the Mbp and M_(b) treatments greatly enhanced the nitrogenase activities in the rhizosphere compared with the M_(0) treatments,especially for lower N applications.Azospirillum brasilense and P.fluorescens did not participate in the nitrification processes or the denitrification processes in the soil.The soil respiration rate and microbial biomass N were greatly affected by the interactions between the rhizobacteria inoculations and the N fertilizer applications.In the M_(bp) treatment,N supply capacities and rice grain yields showed no significant differences among the N_(90),N_(180),and N_(270) applications.The N application rate in the study region can be reduced to 90 kg N ha^(–1) for rice seedlings co-inoculated with a mixture of A.brasilense and P.fluorescens.