遮阴对大豆幼苗光合和荧光特性的影响

为了探寻不同遮阴条件下大豆幼苗叶片的光合响应机理及寻求适度的遮阴比例,本试验模拟田间玉/豆套作,以强耐阴“南豆12号”和弱耐阴“桂夏3号”2个大豆品种为材料,在不遮阴、半侧遮阴(30%,50%,70%)和全遮阴(50%)5个不同遮阴方式下,测定了不同生育期遮阴和复光后大豆幼苗叶片色素含量、光合速率和叶绿素荧光参数的变化。结果表明,随着遮阴程度增加,大豆幼苗叶片的色素含量和初始荧光强度(F₀)增加,叶绿素a/b值变小;光合速率(P_n)、最大光化学效率(F_v/F_m)、PSⅡ实际光化学效率(Φ_PSⅡ)和光化学淬灭系数(qP)呈先升后降趋势,非光化学淬灭系数(NPQ)则呈先降后升的趋势。遮阴胁迫对2个大豆品种幼苗第四复叶期的影响最为显著。2个品种间比较,“南豆12号”和“桂夏3号”在弱遮阴下都能通过改变色素组分比例、促进光合电子传递等途径提高光能潜力的利用来适应弱光环境。在强遮阴胁迫下,“南豆12号”的PSⅡ反应中心抗胁迫能力更强,“桂夏3号”则不能及时耗散过剩光能,导致光合机构受到破坏。

Effect of shading on photosynthetic and chlorophyll fluorescence characteristics of soybean

This study investigated the photosynthetic response of soybean seedlings under different shading conditions. Simulating the field maize/soybean relay-cropping pattern, two soybean cultivars, “Nandou 12” and “Guixia 3”,were utilized to analyze changes in the pigment content, photosynthetic rate and chlorophyll fluorescence parameters at different growth stages under shading and during light recovery stages. Five shading treatments were set; no shading, 30% partial shading, 50% partial shading, 70% partial shading and 50% full shading. Shading increased the pigment content and original fluorescence intensity while the chlorophyll a/b ratio decreased. Photosynthetic rate, maximal photochemical efficiency, photochemical efficiency and photochemical quenching initially increased and then decreased, while non-photochemical quenching initially decreased before increasing. The soybean seedlings grew strongly under 50% partial shading but growth was poor under 50% full shading. Shading had a marked effect on seedlings at the four-trifoliolate leaf stage; when shaded, seedlings accommodated the weak light environment by changing the pigment composition or promoting photosynthetic electron transport. “Nandou 12” showed better shade tolerance and higher photo chemical efficiency than “Guixia 3”. “Guixia 3” was unable to dissipate excess light energy under light recovery resulting in severe damage to the photosynthetic system.