不同生育时期遮阴对大豆叶片光合和叶绿素荧光特性的影响

【目的】研究在不同生育时期遮阴处理下,不同大豆品种植株叶片叶面积、比叶重、叶绿素含量、光合参数、叶绿素荧光参数和产量构成因素的变化规律,为中国南方丘陵和山区大面积推广的玉米大豆间套作种植技术提供理论依据。【方法】采用透光率50%的遮阳网对生育期和生育时期总天数不同的3个参试大豆品种桂夏2号、南豆12和C103进行遮阴,设置4个处理,分别为不遮阴(CK)、出苗至盛花期遮阴(VER2)、出苗至鼓粒期遮阴(VER5)和盛花期至完熟期遮阴(R2R8),测定叶面积、比叶重、叶绿素含量、光合参数、荧光参数和产量构成因素。【结果】VER2处理下大豆品种叶面积、叶绿素(a+b)含量和表观量子效率分别比对照高15.50%、12.95%和74.13%,比叶重、光补偿点和最大光合速率分别比对照低15.78%、26.16%和26.52%,R2R8处理下大豆品种叶面积、叶绿素(a+b)和表观量子效率平均分别比对照高0.3%、10.53%和28.07%,比叶重、光补偿点和最大光合速率平均分别比对照低10.15%、20.34%和12.13%;盛花期复光PSⅡ最大量子产量平均比对照低3.01%,非光化学荧光淬灭系数平均比对照高26.80%,鼓粒期复光PSⅡ最大量子产量平均比对照低8.47%,非光化学荧光淬灭系数平均比对照高40.79%;VER2、VER5和R2R8处理下,桂夏2号单株粒重分别比对照低40.84%、48.67%和59.16%,百粒重分别比对照低23.69%、39.31%和26.39%,南豆12单株粒重分别比对照低46.67%、54.16%和21.19%,百粒重分别比对照低3.91%、19.93%和26.14%,C103单株粒重分别比对照低69.8%、74.85%和73.89%,百粒重分别比对照低68.8%、69.55%和71.64%。【结论】出苗至盛花期遮阴对参试大豆品种叶片光合及叶绿素荧光特性的影响大于盛花期至完熟期遮阴,大豆植株遮阴后在盛花期复光,叶片光合能力有一定程度的恢复,在鼓粒期复光,则表现为受到强光胁迫,因此,从减小遮阴对大豆叶片光合作用不良影响的角度考虑,在中国南方丘陵和山区玉米大豆间作优于玉米大豆套作,在玉米大豆套作模式下选择品种、播期及种植技术时,应确保大豆在盛花期前恢复光照,避免遮阴超过大豆鼓粒期。前期遮阴和后期遮阴对大豆产量的影响大小因大豆品种而异,但遮阴时间越长对大豆产量构成影响越大。

Effect of Shading on Soybean Leaf Photosynthesis and Chlorophyll Fluorescence Characteristics at Different Growth Stages

【Objective】The present work studied the effect of shading on photosynthesis and chlorophyll fluorescence characteristics, including leaf area, lamina mass per unit area, chlorophyll content, yield characters, photosynthetic and fluorescence parameters of three soybean cultivars at different growth stages, in order to support the development of maize-soybean intercropping and relay-intercropping systems in hilly and mountainous area of southern China.【Method】Three cultivars named Guixia 2, Nandou 12 and C103, whose period and total days for growth were different with each other, were studied. Soybean plants were shaded by shading nets with 50% transmittance during growth stages of emergence to full-bloom (VER2), emergence to pod-fill (VER5), and full-bloom to full-ripe (R2R8), respectively. Plants grown under natural light were used as control (CK). Leaf area, lamina mass per unit area, chlorophyll content, photosynthetic and fluorescence parameters, as well as yield characters were measured and analyzed. 【Result】 Compared to the control (CK), leaf area, chlorophyll (a+b) content and apparent quanta efficiency at the VER2 stage increased by 15.5%, 13.0% and 74.1%, respectively; lamina mass per unit area, light compensation point and maximum photosynthetic rate were decreased by 15.8%, 26.2% and 26.5%, respectively, compared to CK. Leaf area, chlorophyll (a+b) content and apparent quanta efficiency increased by 0.3%, 10.5% and 28.1%, respectively at the R2R8 stage; while lamina mass per unit area, light compensation point and maximum photosynthetic rate decreased by 10.2%, 20.3% and 12.1%, respectively, compared to CK. When soybean plants were re-illuminated at full bloom stage, maximal quantum yield of PSII was decreased by 3.0% and non-photochemical quenching was increased by 26.8%, compared to CK. When plants were re-illuminated at pod-fill stage, maximal quantum yield of PSII was decreased by 8.5% and non-photochemical quenching was increased by 40.8%, compared to CK. In addition, at VER2, VER5 and R2R8 stages for Guixia 2, yields per plant decreased by 40.8%, 48.7% and 59.2%, and 100-seed weight decreased by 23.7%, 39.3% and 26.4%, respectively, compared to CK. For Nandou 12 at these stages, yields per plant decreased by 46.7%, 54.2% and 21.2%, and 100-seed weight were decreased by 3.9%, 19.9% and 26.1%, respectively, compared to CK. For C103, yields per plant decreased by 69.8%, 74.9% and 73.9%, and 100-seed weight decreased compared to CK by 68.8%, 69.6% and 71.6%, respectively.【Conclusion】Shading to the VER2 stage had a greater impact than for R2R8 on the photosynthesis and chlorophyll fluorescence characteristics of soybean. Photosynthetic capacity of soybean leaves made some recovery from shading when re-illuminated at R2. However, high-light stress was observed for plants re-illuminated at R5. Therefore, we suggest that maize-soybean intercropping to be a more advantageous system than relay-intercropping in hilly and mountainous area of southern China, with the perspective of minimizing the negative effects of shading on soybean photosynthesis. We also suggest, it is necessary to re-illuminate the soybean plants before full-bloom stage, in order to avoid an excessively long shading duration, when making decisions about on cultivar use, sowing time, and planting technology. The effect of shading period can influence yield of soybean. Moreover, the longer the shading duration last, the more the expected yield loss.