C4作物FACE(free-air CO2 enrichment)研究进展

持续迅速上升的大气二氧化碳浓度([CO₂])是全球变暖最大的驱动因子,但其作为光合作用底物直接增加了作物的生产力。相比C₃作物,人们对未来高浓度CO₂情形下C₄作物的响应规律认识较少。与封闭或半封闭气室研究相比,FACE(free-air CO₂ enrichment)试验在空气自由流动的大田条件下对作物表现进行研究,它提供了对未来作物生长环境的真实模拟,因此提供了评估CO₂肥料效应以及揭示植物响应机制的最好机会。作为人类重要的粮食和饲料来源,高粱和玉米是最重要的C₄作物。在简介美国玉米和高粱FACE系统的基础上,综述了FACE情形下高浓度CO₂(模拟本世纪中叶大气CO₂浓度,即550 μmol/mol)对两大作物生理、生长和产量以及土壤特性等方面的影响,同时比较了与气室研究结果的异同点。(1)FACE使干旱条件下两作物光合作用显著增强,但湿润条件下没有影响;FACE条件下高粱出现光合适应现象,而玉米没有;(2)FACE使两作物气孔导度大幅下降,导致叶温升高、蒸腾速率下降、蒸发蒸腾总量减少或没有变化、叶片总水势和水分利用效率增加或没有变化;(3)FACE对两作物物候期和化学组分影响很少;(4)FACE使干旱条件下两作物生长和产量略有增加,但湿润条件下没有影响;(5)FACE使高粱田土壤丛枝状菌根真菌的长度和易提取胶状物质浓度显著增加,导致水稳性土壤团聚体增加;FACE对高粱田N₂O或含氮气体(N₂O+N₂)的排放没有影响;(6)高浓度CO₂对两作物气孔导度的影响FACE试验明显大于气室试验,而对生长和产量的影响呈相反趋势。阐明CO₂与基因型、土壤湿度和大气温度间的互作效应及其机制是下一轮C₄作物FACE研究优先考虑的方向,技术的不断进步已为利用大型FACE系统来研究这些互作效应提供了可能。     

开放式空气二氧化碳浓度增高对小麦物质生产与分配的影响

2001—2003年,利用农田开放式空气CO₂浓度增高 (FACE) 技术平台,以冬小麦宁麦9号为供试材料,研究开放式条件下CO₂浓度增高对小麦整个生育期干物质生产与分配的影响.结果表明：与对照相比,FACE处理使小麦播种-越冬始期的干物质生产量略有增加（10.8%),使越冬始期-拔节期、拔节期-孕穗期、孕穗期-抽穗期显著增加,分别增加了31.6%、40.5%、27.2%,使抽穗期-成熟期略有减少(-5.5%),使成熟期生物产量显著增加(13.6%);FACE处理对小麦播种-越冬始期的平均叶面积系数(LAI)和净同化率(NAR)均无显著影响,但使越冬始期-抽穗期LAI显著增加,NAR稍有增加,使抽穗期-抽穗后20 d NAR显著下降;FACE处理使不同生育时期叶片占全株质量的比例下降,而使茎鞘占全株质量的比例增加;FACE小麦抽穗期和成熟期茎鞘可溶性糖和淀粉含量及总量均明显增加.     

大气O3浓度升高和模拟N沉降对黄豆光合、生物量和非结构性碳水化合物积累及分配的影响

为探究全球气候变化带来的大气臭氧(O₃)浓度升高和氮(N沉降)对黄豆气体交换、生物量和非结构性碳水化合物(NSCs)积累及分配的影响, 利用开顶式气室(OTC)设置了2个O₃浓度(AA, 正常大气; AAO60, 正常大气+60 μg/m³O₃)和2个施N梯度(对照;施N)并开展了相关实验。研究结果表明： (1) N沉降处理后叶片净光合速率(Pn)和气孔导度(Gs)显著提高了96.21%和83.77%, 但是对黄豆各部位生物量的促进作用没有达到显著水平。N沉降处理后根系溶性糖和非结构性磷水化合物(NSCs)的比例显著下降了42.17%和38.95%, 而叶片淀粉分配比增加了41.55%, 豆粒和茎的可溶性糖含量分别提高了59.41%和95.29%。(2) O₃浓度升高处理后叶片Gs增加了94.89%, Pn降低了2.34%。叶片、茎、根和豆粒的生物量在O₃处理后分别显著降低了38.14%、56.25%、66.67%和25.49%。豆粒的可溶性糖和淀粉含量和总NSCs分别显著下降了21.94%和49.65%和30.55%。O₃浓度升高后根系中淀粉总量的比例的增加了56.21%。(3) O₃和N沉降处理二者共同处理在叶片净光合速率、蒸腾速率、豆粒、茎、根系NSCs组分均具有显著交互作用, 主要表现为拮抗作用。综上, 中度N沉降提高了叶片光合作用, 增加了对地上部分NSCs的分配而降低了对地下根系的分配;O₃浓度升高抑制了黄豆生长和NSCs积累, 但是相对增加了根系中淀粉总量的比例;N沉降一定程度上能够缓解O₃对光合和NSCs造成的损害, 但未见对生物量下降存在类似效应。     

开放式空气二氧化碳浓度增高对小麦产量形成的影响

利用农田开放式空气CO₂浓度增高(FACE)系统平台,以弱筋小麦宁麦9号为供试品种,研究大气CO₂浓度增高和不同施氮水平对小麦生育期、株高、产量和产量构成因素的影响.结果表明：FACE处理的小麦播种至抽穗期、抽穗至成熟期及全生育期天数分别比对照缩短1.3、1.3和2.6 d,但均未达到显著水平;FACE处理的小麦穗长、穗下第1和第2节间长度显著变长,成熟期株高显著增加,比对照增加4.0%;低、中、高氮条件下,FACE处理小麦的籽粒产量分别比对照提高15.2%、21.4%和35.4%,平均增产24.6%,均达极显著水平;FACE处理小麦的单位面积穗数极显著增加,比对照增加17.8%,使穗粒数和粒重显著增加,分别比对照增加了2.9%和4.8%.FACE处理使小麦显著增产主要是由于单位面积穗数显著增加,而单位面积穗数的增加主要是由于小麦的分蘖能力明显增强所致.     

胞外ATP对AlCl3诱导的细胞死亡过程中胞内H2O2和Ca2+水平的影响及其生理机制分析

该实验以烟草悬浮细胞 BY 2 为材料,在烟草悬浮细胞中分别加入0.05、0.10、0.15、0.20 mmol·L^-1AlCl₃,以等体积去离子水处理的悬浮细胞液为对照,并依据前述实验结果选择0.15 mmol·L^-1 AlCl₃,分别添加5 mmol·L^-1 DMTU(H₂O₂ 抑制剂)、20 μmol·L^-1CaCl₂、15 μmol·L^-1 LaCl₃(Ca²⁺通道抑制剂)和50 μmol·L^-1 ATP设计多项处理,分析胞外ATP(eATP)对铝离子(Al³⁺)胁迫引起的植物细胞死亡及其胞内H₂O₂、Ca²⁺的影响,以揭示Al³⁺胁迫下植物调节细胞死亡的可能机制,进一步扩展对eATP功能的认知。结果显示：(1)随着 AlCl₃ 胁迫浓度的提高,细胞死亡水平和胞内H₂O₂水平上升,而胞内Ca²⁺和eATP水平则逐渐降低。(2)外援施加H₂O₂抑制剂 DMTU(二甲基硫脲)和Ca²⁺能够有效缓解AlCl₃诱导的细胞死亡水平的上升;而Ca²⁺通道抑制剂LaCl₃(三氯化镧)则加剧了AlCl₃胁迫下的细胞死亡。(3)在AlCl₃胁迫下对细胞添加外源ATP,能够缓解AlCl₃胁迫下胞内H₂O₂水平上升和Ca²⁺水平下降的同时,并显著降低AlCl₃胁迫导致的细胞死亡。研究表明, Al³⁺以剂量依赖的模式提升细胞死亡和细胞内H₂O₂的水平并降低胞内Ca²⁺和eATP水平,AlCl₃诱导的细胞死亡受到H₂O₂和Ca²⁺水平变化的调节,eATP可以通过调节H₂O₂与Ca²⁺水平缓解AlCl₃诱导的细胞死亡。推测Al³⁺胁迫可能通过抑制钙离子通道而破坏了细胞内H₂O₂和Ca²⁺之间的协同关系,外源ATP对Al³⁺诱导H₂O₂上升的缓解作用可能是由于其提升了细胞的抗氧化能力。     

高浓度臭氧胁迫两种园林观赏草的逆境生理特征比较

以两种常见园林观赏草：白穗狼尾草（Pennisetum alopecuroides ‘White’）和拂子茅（Calamagrostis epigeios）作为试验材料,利用开顶箱（OTCs）模拟法,研究了不同高浓度臭氧（O₃,EO）：80 nmol/mol（EO-80）、120 nmol/mol（EO-120）和160 nmol/mol（EO-160）下两种观赏草叶片逆境生理特征的变化规律。结果表明：（1）短期（7 d）内随O₃浓度增加,白穗狼尾草叶绿素和类胡萝卜素含量较对照呈下降趋势,拂子茅较对照无显著变化。（2）在EO-120、EO-160下处理7 d时,两种观赏草叶片的净光合速率（P_n）和气孔导度（g_s）较对照显著下降,且白穗狼尾草下降的幅度均大于拂子茅。（3）不同高浓度O₃胁迫下,两种观赏草叶片丙二醛（MDA）含量较对照均有所升高,其中在EO-160下处理21 d时白穗狼尾草和拂子茅叶片MDA含量分别增加30.2%（P<0.05）和13.5%（P>0.05）,表明在EO-160浓度胁迫下白穗狼尾草受到的膜脂过氧化伤害大于拂子茅。（4）在EO-120和EO-160下处理21 d时,白穗狼尾草叶片可溶性蛋白含量较对照分别显著下降24.2%和43.1%,而拂子茅较对照分别下降19.0%和22.9%（P<0.05）。（5）与对照组相比,高浓度O₃下两种观赏草叶片的过氧化物酶（POD）活性随胁迫时间延长呈下降趋势,超氧化物歧化酶（SOD）活性呈先升后降。（6）综合以上生理特征比较及主成成分分析表明,佛子茅比白穗狼尾草更耐O₃,前者在O₃高污染地区可能会有更高的应用价值。     

过氧化氢对培养心肌细胞损伤作用的研究

氧化应激时产生大量的自由基,造成心肌细胞的损伤.过氧化氢(H₂O₂)是有机体氧化代谢产物,同时是一种活性氧.应用不同浓度的H₂O₂,分别于不同作用时间,动态观察其对心肌细胞的损伤作用.从实验结果看到,低浓度的H₂O₂（＜0.1 mmol/L）作用2 h,使心肌细胞产生早期的生物化学的改变,如MDA产生堆积和细胞周期时相改变（G1期细胞增加,G2期细胞减少）,此时心肌酶基本无泄漏,心肌细胞的死亡率很低,HE形态学观察基本无改变;随着H₂O₂浓度的增加（1～5 mmol/L）和作用时间的延长,进一步诱导细胞损伤加剧,LDH释放和MDA积累明显升高,细胞死亡率也明显增加,已具有统计学意义.同时可观察到其病理形态学的坏死性改变;当10 mmol/L H₂O₂作用时,细胞大量死亡,形态学可见细胞极度收缩、脱落,形成大面积的细胞脱失区.因此,H₂O₂作为一种活性氧自由基,依其浓度和作用时间不同可造成不同程度的心肌细胞的损伤.辣根过氧化物酶作为一种自由基清除剂,可明显减少H₂O₂活性氧自由基对心肌细胞的损伤作用.     

细胞氧化损伤时8-羟基鸟嘌呤的测定

利用H₂O₂易通过细胞膜而到达核这一特点,初步探讨了不同浓度H₂O₂对HL-60细胞DNA的氧化损伤程度.发现H₂O₂浓度在0.4 mmol/L以上时,作用8～24 h可以用气相色谱/火焰离子检测器(GC/FID)检测到氧化损伤标志产物——8-羟基鸟嘌呤(8-oh-G),并观测到在0.4～0.8 mmol/L H₂O₂作用一定时间时,8-羟基鸟嘌呤含量随H₂O₂浓度升高而升高.     

外源H2O2对盐碱胁迫下苹果矮化砧木幼苗生理特性的影响

以2年生苹果矮化砧木M9 T337为试材,采用盆栽试验法,设置浇灌清水(CK)和盐碱胁迫(0.1 mol/L NaCl+NaHCO₃溶液)+ 喷施5种浓度的H₂O₂ ［0(T₁)、0.2 mmol/L(T₂)、0.4 mmol/L(T₃)、0.6 mmol/L(T₄)、0.8 mmol/L(T₅)］ 处理,测定各处理叶片叶绿素含量、光合气体交换参数、渗透调节物质含量、抗氧化酶活性和细胞膜透性,并利用相关性与主成分分析进行综合评价,以探讨外源过氧化氢(H₂O₂)增强其盐碱耐性的生理机制。结果表明：(1)随着盐碱胁迫(T₁)的时间延长,M9 T337幼苗叶片叶绿素a(Chl a)含量、叶绿素b (Chl b)含量、叶绿素总量(Chl t)、净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)、可溶性蛋白(SP)含量均呈逐渐下降趋势;胞间CO₂浓度(C_i)、可溶性总糖(TSS)含量、脯氨酸(Pro)含量、过氧化氢酶(CAT)活性、抗坏血酸过氧化物酶(APX)活性、相对电导率(REC)、丙二醛(MDA)含量均呈上升趋势;超氧化物歧化酶(SOD)活性、过氧化物酶(POD)活性均呈先升后降趋势。(2)与CK相比,盐碱胁迫+外源H₂O₂(T₂- T₅)处理后M9 T337幼苗叶片各指标均呈现不同幅度变化,且存在明显浓度效应,并以T₃(0.4 mmol/L H₂O₂)处理叶片的Chl a、Chl b、Chl t、SP和G_s降幅最小,C_i、REC、MDA升幅最小,TSS、Pro、APX升幅最大。(3)M9 T337幼苗叶片P_n与T_r、G_s、Chl a、Chl b、Chl t、SP、SOD、POD呈显著正相关,与C_i、MDA、CAT、APX、REC呈显著负相关。(4)综合评价表明,各处理对M9 T337幼苗叶片生理特性的效应依次为：CK>T₃>T₄>T₂>T₅>T₁。研究发现,叶面喷施适宜浓度H₂O₂可有效改善盐碱胁迫下M9 T337幼苗光合能力,显著提高抗氧化酶活性和渗透调节物质的含量,降低细胞膜透性,从而达到缓解盐碱胁迫的作用,并以0.4 mmol/L H₂O₂处理效果最佳。     

深圳市大气污染时空分布及其与景观格局的关系

气溶胶和臭氧是我国大部分地区的两种主要大气污染物,对城市生态环境和人类身体健康影响严重。以深圳市为研究区,利用大气监测站点提供的监测数据和普通kriging空间插值法,从年、季、月尺度上开展近5年（2015-2019）深圳全市PM_2.5和臭氧的时空分布研究,通过皮尔逊分析和显著性检验从月尺度上分析土地覆盖类型及其景观格局对大气污染的影响。结果表明：（1）近5年内深圳市PM_2.5浓度总体呈现下降趋势,臭氧浓度则先降后升,二者季节性和月度差异显著。（2）PM_2.5和臭氧在年、季、月尺度上空间差异明显,全市PM_2.5浓度整体为西北高、东南低;臭氧浓度西北、东南较高,其余区域相对较低。（3）植被占比的增多对PM_2.5浓度有明显的抑制和调控作用,植被斑块间距离越近,对PM_2.5浓度的调控作用越明显;水体占比的增高会导致臭氧浓度增高和变化幅度增大。研究结果可为城市大气污染防治和景观格局规划管理提供参考。     

不同秧苗素质和移栽密度条件下臭氧胁迫对水稻光合作用、物质生产和产量的影响

近地层臭氧浓度升高使水稻生长受抑进而使产量下降,但这种影响是否因不同栽培条件而异尚不清楚。2011年依托先进的稻田臭氧FACE(Free Air gas Concentration Enrichment)技术平台,以汕优63为供试材料,臭氧设置大气臭氧浓度(Ambient)和高臭氧浓度(比Ambient高50%),秧苗素质设置弱苗(移栽时无分蘖)和壮苗(移栽时带两个分蘖),移栽密度设置低密度(16穴/m2)、中密度(24穴/m2)和高密度(32穴/m2),研究不同秧苗素质和移栽密度条件下臭氧胁迫对水稻生长和产量的影响。结果表明:高浓度臭氧使水稻结实期叶片SPAD值、净光合速率、气孔导度和蒸腾速率明显下降,但胞间CO2浓度和叶温无显著变化。高浓度臭氧对水稻拔节前物质生产量没有影响,但使拔节至抽穗期、抽穗至成熟期物质生产量平均分别降低13%和29%,进而使成熟期生物产量和籽粒产量均显著下降。方差分析表明,臭氧与秧苗素质间没有互作效应,但臭氧与移栽密度的互作对最终产量的影响达显著水平。以上结果表明,臭氧胁迫使水稻生长后期光合受阻,导致物质生产和产量显著下降;适当增加移栽密度可能会减少臭氧胁迫下水稻产量的损失。     

Season-long elevation of ozone concentration to projected 2050 levels under fully open-air conditions substantially decreases the growth and production of soybean

Mean surface ozone concentration is predicted to increase 23% by 2050. Previous chamber studies of crops report large yield losses caused by elevation of tropospheric ozone, and have been the basis for projecting economic loss. This is the first study with a food crop (soybean, Glycine max) using free-air gas concentration enrichment (FACE) technology for ozone fumigation. A 23% increase in ozone concentration from an average daytime ambient 56 p.p.b. to a treatment 69 p.p.b. over two growing seasons decreased seed yield by 20%. Total above-ground net primary production decreased by 17% without altering dry mass allocation among shoot organs, except seed. Fewer live leaves and decreased photosynthesis in late grain filling appear to drive the ozone-induced losses in production and yield. These results validate previous chamber studies suggesting that soybean yields will decrease under increasing ozone exposure. In fact, these results suggest that when treated under open-air conditions yield losses may be even greater than the large losses already reported in earlier chamber studies. Yield losses with elevated ozone were greater in the second year following a severe hailstorm, suggesting that losses caused by ozone might be exacerbated by extreme climatic events.     

不同密度下臭氧胁迫对Ⅱ优084水稻光合作用和物质生产的影响—FACE研究

依托中国稻田臭氧FACE(free air ozone concentration enrichment)技术平台,以超级稻Ⅱ优084为供试材料,臭氧设置当前大气臭氧浓度和高臭氧浓度(比前者高50%),移栽密度设置低密度(16穴·m^-2)、中密度(24穴·m^-2)和高密度(32穴·m^-2),研究不同移栽密度条件下近地层臭氧浓度升高对水稻光合作用、物质生产以及茎鞘非结构性碳水化合物浓度和含量的影响.结果表明: 臭氧浓度升高使水稻移栽后63 d、77 d和86 d剑叶SPAD值分别下降6%、11%和13%,均达显著或极显著水平.臭氧胁迫下结实期叶片净光合速率、气孔导度和蒸腾速率的降幅亦随时间推移而明显增加.高臭氧浓度使水稻抽穗至成熟期的物质生产量平均下降46%,从而使最终生物产量下降25%,均达显著水平.臭氧浓度升高使水稻拔节后茎鞘可溶性糖和淀粉的浓度和含量均显著降低,但使抽穗前茎鞘贮藏同化物的转运率大幅增加.方差分析表明,臭氧与密度间的互作对水稻所有测定参数均无显著影响.综上,近地层臭氧浓度升高使超级稻Ⅱ优084生育中后期的光合和生长均明显受抑,但这种抑制作用不受移栽密度的影响.
     

Differential ozone sensitivity of rice cultivars as indicated by visible injury and grain yield

Surface ozone pollution may cause reductions in rice ( Oryza sativa L.) yield. Ozone sensitivity in rice cultivars is often evaluated based on visible leaf injury at an early growth stage. However, it is not clear whether reduction in grain yield is related to visible injury. Therefore, visible damage and grain yield reduction were examined in Japanese and Asian rice cultivars exposed to ozone. In experiment 1, 3-week-old rice seedlings were exposed to ozone (min.: 20 nl·l⁻¹, max.:120 nl·l⁻¹) for 12 h in open-top chambers (OTCs). Visible leaf injury was quantified according to a leaf bronzing score. In experiment 2, rice plants were exposed to ozone in OTCs throughout the cropping season until grain harvest. Daily mean ozone concentrations were maintained at 2, 23, 28, 42, and 57 nl·l⁻¹ with a regular diurnal pattern of exposure. After harvest, grain yield was determined. Based on visible injury to the uppermost fully expanded leaf, the indica cultivar 'Kasalath' was most tolerant, and the japonica cultivar 'Kirara 397' was most sensitive to ozone. However, grain yields for both 'Kasalath' and 'Kirara 397' were significantly decreased after ozone exposure. The indica cultivar 'Jothi' suffered severe injury after ozone exposure but had no reduction in grain yield. Therefore, ozone sensitivity of rice cultivars evaluated by visible injury did not coincide with that evaluated by the reductions in grain yield. These results suggest that mechanisms that induce acute leaf injury do not relate to chronic ozone toxicity that reduces yield.     

臭氧胁迫对稻穗不同部位糙米直链淀粉含量和RVA谱特征值的影响

近地层臭氧浓度升高使水稻产量下降,但臭氧胁迫对稻米品质的影响及其强弱势粒差异尚不清楚.本研究以8个不同类型水稻品种为供试材料,利用自然光气体熏蒸平台,设置对照(9 nL·L^-1)和高浓度臭氧(约100 nL·L^-1)处理,研究臭氧胁迫对稻穗不同部位糙米直链淀粉含量和RVA谱特征值的影响.结果表明: 与对照相比,臭氧处理使糙米直链淀粉含量、最高粘度、热浆粘度、崩解值和冷胶粘度分别下降5.9%、7.6%、5.9%、11.6%、2.9%,消减值和糊化温度分别增加24.9%和1.0%,均达显著水平.稻米直链淀粉含量和所有RVA特征参数的品种间差异均达极显著水平.稻穗不同部位稻米直链淀粉含量、最高粘度、热浆粘度、崩解值、冷胶粘度从大到小依次为强势粒>中势粒>弱势粒,消减值则表现相反.绝大多数情形下,臭氧与年度或臭氧与品种间的互作对稻米直链淀粉含量和RVA谱的影响达显著水平;尽管稻米RVA特征值对臭氧胁迫的响应多表现为稻穗上部略小于中部和下部,但臭氧与部位间的互作均未达显著水平.表明中等强度的臭氧胁迫使水稻食味品质明显变劣,变劣的程度因生长季和供试品种而异,籽粒着生位置受臭氧胁迫的影响较弱.     

Negative effects of tropospheric ozone on the feed value of rice straw are mitigated by an ozone tolerance QTL

High surface ozone concentrations are recognized as an emerging threat to food security in Asia. This study aimed at determining the effects of ozone on the nutritive quality of rice straw, a by‐product of rice grain production and a major feed resource for ruminant livestock. Further, the question was addressed whether negative effects of ozone can be mitigated through molecular breeding. Rice plants from three different genotypes were exposed to four different ozone treatments in fumigation chambers from transplanting to maturity. These genotypes were (i) IR64, one of the most wide spread indica varieties in the world, (ii) Nipponbare, a typical japonica variety, and (iii) SL41, an ozone tolerant breeding line that carried chromosomal inserts at the ozone tolerance QTL OzT9 in the genetic background of Nipponbare. The treatments consisted of (i) charcoal filtered air, (ii) simulated ambient ozone concentration, (iii) 2 × ambient ozone concentration, and (iv) 2.5 × ambient ozone concentration. The effects of ozone on the chemical composition of straw were clearly dependent of the ozone level, and were significant even at ambient ozone concentration. Increases in crude ash, lignin and phenolics concentration adversely affected the digestibility as demonstrated in incubation experiments simulating rumen digestion in vitro. Negative ozone effects included reductions in the rate and extent of gas production due to inhibition of microbial fermentation, reduced formation of short chain fatty acids (SCFA), and a decrease in the true organic matter digestibility. The ozone tolerant genotype SL41 was less responsive to ozone than its more susceptible recurrent parent Nipponbare in terms of lignin and phenolics formation, organic matter digestibility and SCFA production. These data demonstrate that the feed quality of rice straw is affected by ozone even at ambient concentration, and that these negative effects are mitigated by the ozone tolerance QTL OzT9.     

Ozone exposure during growth affects the feeding value of rice shoots

Rising tropospheric ozone concentrations have been observed in many Asian countries in recent years. Ozone pollution reduces the yield of agricultural crops but may also affect crop quality. This study aimed at estimating the effect of ozone exposure on feeding quality of rice shoots for ruminant herbivores. Rice plants from two genotypes differing in ozone tolerance were exposed to ozone at a concentration of 120 nl/l for 18 days, and feeding value was determined by chemical analyses and in vitro incubation in rumen fluid. Rice biomass was reduced by an average of 24% in the ozone treatment as compared to the control. Moreover, ozone exposure affected various feed quality parameters. Crude protein content was lower in ozone treated plants (P<0.05). Potential gas production during the in vitro incubation for 96 h also dropped (P<0.01) due to ozone treatment, indicating reduced digestibility of the plant materials. This was explained with an increase in the antinutritive components lignin (P<0.05) and phenolics (P<0.001) due to ozone exposure. An ozone tolerant genotype exhibited a more pronounced increase in phenolics, suggesting that this may constitute a stress defense mechanism. Our results suggest that ozone may affect the feeding value of cereal straws and calls for further research in this direction.     

近地层臭氧浓度升高对杂交稻颖花形成的影响

依托全球唯一的稻田开放式空气中臭氧浓度增高系统平台,以汕优63和两优培九为供试材料,设置大气背景臭氧浓度和高臭氧浓度（比大气背景臭氧浓度高50%）两个浓度水平,研究FACE条件下高O₃浓度对杂交稻颖花形成的影响.结果表明：高O₃浓度使汕优63和两优培九每穗颖花数分别减少28朵和34朵,下降幅度分别为15%和13%.从稻穗构成看,高O₃浓度胁迫下杂交稻每穗颖花数减少主要与每穗2次枝梗颖花数明显减少有关,对每穗1次枝梗颖花数的影响较小,因此高O₃浓度胁迫下水稻每穗1次枝梗颖花数占全穗的比率增加,每穗2次枝梗颖花数占全穗的比率降低.从颖花形成看,高O₃浓度胁迫下杂交稻每穗颖花数下降主要是颖花（特别是2次颖花）的分化受到抑制所致,而颖花的退化数不增反降.上述结果表明,采取相应措施削弱高O₃浓度胁迫对颖花分化的抑制作用可能是近地层高O₃浓度条件下减少杂交稻产量损失的关键.     

The impact of atmospheric CO2 concentration enrichment on rice quality – A research review

Global atmospheric carbon dioxide concentration ([CO₂]) is increasing rapidly. The Intergovernmental Panel on Climate Change estimated that atmospheric [CO₂] has risen from approximately 280 μmol mol^?1 in pre-industrial times to approximately 381 μmol mol^?1 at present and will reach 550 μmol mol^?1 by 2050. In the absence of strict emission controls, atmospheric [CO₂] is likely to reach 730–1020 μmol mol^?1 by 2100. Rising atmospheric [CO₂] is the primary driver of global warming, but as the principal substrate for photosynthesis it also directly affects the yield and quality of crops. Food quality is receiving much more attentions recently, however, compared with grain yield, our understanding in the response of grain quality to elevated [CO₂] is very limited. Rice (Oryza sativa L.) is one of the most important crops in the world and the first staple food in Asia, providing nutrition to a large proportion of the world’s population. Elevated [CO₂] leads to numerous physiological changes in rice crops, such as changes in the photosynthesis and assimilate translocation, nutrient uptake and translocation, water relation, and altered gene expression and enzyme activity. These altered processes are very likely to affect the chemical and physical characteristics of rice grains. In this review, we first describe main characteristics of rice grain quality, and then summarize findings in literature related to the impact of elevated [CO₂] on grain quality falling into four categories: processing quality, appearance, cooking and eating quality, and nutritional quality, as well as the possible mechanisms responsible for the observed impacts. Elevated [CO₂] caused serious deterioration of processing suitability, in particular, head rice percentage was significantly decreased. In most cases, elevated [CO₂] increased chalkiness of rice grains. The evaluation of physicochemical characteristics together with starch Rapid Visco Analyser (RVA) properties indicated no change or small changes in cooking and eating quality under elevated [CO₂], and these changes could not be detected by sensory taste panel evaluation. Elevated [CO₂] significantly decreased nitrogen or protein concentration in rice grains, while in most cases other macro- and micro-nutrients showed no change or decrease in concentration. In addition, the responses of rice quality to elevated [CO₂] might be modified by varieties, applied fertilizer rates or gas fumigation methodologies. The available information in the literature indicates a clear tendency of quality deterioration and thus lower commercial value for rice grains grown under a projected high CO₂ environment. Understanding the factors causing quality deterioration in rice and the related biological mechanisms might be the utmost important scientific theme in future research. Here we also discuss the necessity of formulating adaptation strategies for rice production in future atmospheric environments, nevertheless, the increase in yield, the improvement in quality and stress resistance of rice should be combined and integrated into the adaptation approaches. Compared with enclosure studies, the field experiments using Free-Air CO₂ Enrichment (FACE) system provide sufficient experimental space and the most realistic mimic of a future high CO₂ atmosphere, and give scientists perhaps the best opportunity to achieve multiple goals.     

Quantitative trait locus analyses of ozone-induced grain yield reduction in rice

Reduction of grain yield (total seed weight) by ozone in rice (Oryza sativa L.) is believed to be caused by ozone-induced reduction of photosynthetic activity followed by growth inhibition. Here, japonica rice cultivar Sasanishiki and indica rice cultivar Habataki showed different responses to ozone. When exposed to ozone, the leaves of Habataki exhibited no critical damage, whereas those of Sasanishiki developed lesions. Conversely, ozone exposure reduced total seed weight by 19% in Habataki, but not significantly in Sasanishiki. Chronic ozone exposure also significantly decreased culm length, number of primary rachis branch, and number of spikelets per panicle in Habataki. QTL analysis in Sasanishiki/Habataki chromosome segment substitution lines identified a single locus associated with the yield loss caused by ozone on chromosome 6 of Habataki close to marker RM3430 (107.6 cM). A QTL for reduction of primary rachis branch number and total spikelet number was found in the same position. These results indicate that a QTL on chromosome 6 has an important role in ozone-induced yield loss, and is also involved in primary rachis branch formation and total spikelet number in ozone-exposed rice.