双季稻不同生育期净同化速率对大气CO2浓度和温度升高的响应

大气CO₂浓度和温度升高对水稻干物质积累的影响因不同栽培区域和不同稻作类型而异。目前,我国双季稻轮作系统干物质生产力对温度、CO₂浓度升高和二者交互作用的响应特征尚不明确。本研究以早稻‘两优287’和晚稻‘湘丰优9号’为供试材料,在湖北省荆州市利用开顶式气室(OTC)进行连续3年的大田原位模拟试验,设置大田(UC)、对照(CK,OTC控制大气温度和CO₂浓度)、增温2 ℃(ET)、CO₂浓度增加60 μmol·mol^-1(EC)、增温2 ℃+CO₂浓度增加60 μmol·mol^-1(ETEC)5个处理,研究温度和CO₂浓度升高对早稻和晚稻地上部生物量、叶面积和净同化速率的影响。结果表明: CO₂浓度和/或温度升高对早稻和晚稻移栽-拔节阶段净同化速率影响不显著,提高了拔节-齐穗阶段净同化速率,但降低了齐穗-成熟阶段净同化速率(除早稻对高CO₂浓度表现为正响应外)。CO₂浓度和/或温度升高促进了各生育期叶面积的增长,以ETEC处理叶面积指数最高(除成熟期外)。在齐穗期,温度和CO₂浓度升高协同促进了地上部干物质积累,ETEC处理早稻和晚稻地上部生物量比CK高10.3%～39.8%和23.6%～34.4%;在早稻成熟期,增温在一定程度上抵消了增加CO₂浓度对地上部干物质积累的促进作用,ETEC比EC地上部生物量降低3.2%～14.1%;而晚稻成熟期,增温和增加CO₂浓度表现为正向的交互作用,可进一步提高地上部生物量。回归分析表明,温度和CO₂浓度升高在双季稻营养生长阶段对植株净同化能力以正向作用为主,在生殖生长阶段增温表现为负向作用。由于生长特性、生育期跨度和温度资源配置的差异,CO₂浓度和温度升高可能提高我国双季稻轮作系统干物质生产力。

Responses of net assimilation rate to elevated atmospheric CO2and temperature at different growth stages in a double rice cropping system

Effects of elevated atmospheric CO₂ concentration and temperature on rice dry matter accumulation vary in planting regions and cropping systems. It remains unclear how dry matter productivity responds to factorial combination of elevated CO₂ and temperature in the double rice cropping system of China. Field experiments were conducted using open-top chambers (OTC) to simulate different scenarios of elevated CO₂ and/or temperature for three rotations of double rice in Jingzhou, Hubei Province. Liangyou 287 and Xiangfengyou 9 were used as rice cultivar for early rice and late rice, respectively. There were five treatments: UC, paddy field without OTC covering; CK, OTC with the similar temperature and CO₂ concentration to field environment; ET, OTC with 2 ℃ temperature elevation; EC, OTC with 60 μmol·mol^-1 CO₂ elevation; ETEC, OTC with simu-ltaneous 2 ℃ temperature elevation and 60 μmol·mol^-1 CO₂ elevation. We measured aboveground biomass, leaf area index (LAI) and net assimilation rate (NAR) of dry matter under different treatments. Our results showed that elevated CO₂ and/or temperature had no significant effects on NAR from transplanting to jointing, increased NAR from jointing to heading, but decreased NAR from heading to maturity (except for EC treatment in early rice). Elevated CO₂ and/or temperature promoted leaf area development at all growth stages, with ETEC showing the highest increase in LAI except at maturity. Warming and CO₂ enrichment jointly promoted dry matter accumulation at heading, with ETEC increasing aboveground biomass by 10.3%-39.8% and 23.6%-34.4% compared with CK in early rice and late rice, respectively. At maturity of early rice, elevated temperature partly offset the positive effects of elevated CO₂ on aboveground biomass, as shown by a reduction of 3.2%-14.1% under ETEC compared with EC. Contrarily at maturity of late rice, co-elevation of CO₂ and temperature further increased aboveground biomass, showing a synergistic interaction. Results from regression analysis showed that warming and CO₂ enrichment had positive effects on NAR at vegetative stages of double rice, while warming showed negative effects on NAR at reproductive stages. Considering the dissimilarities in growth characteristics, growing periods and ambient temperature, elevated CO₂ and temperature might increase dry matter production in the Chinese double rice cropping system.