【作者】 左应梅；

【导师】 杨重法；

【作者基本信息】 海南大学 ， 作物栽培学与耕作学， 2010， 博士

【摘要】 木薯是三大薯类之一,主要栽培在热带和亚热带地区。由于木薯生长期常常有干旱、台风等自然灾害的发生,因此木薯生产受环境因素的影响较大。另外,与稻麦等作物相比木薯尚缺乏系统的栽培理论和栽培技术,特别是光合特性、逆境生理等基础研究较少。光合作用是物质生产的基础,研究木薯的光合特性及其与环境的关系不仅对于丰富木薯的栽培理论和逆境生理理论、发掘木薯生产潜力具有重要意义,同时还能为木薯的品种布局、适应性栽培和稳产高产提供理论依据和技术参数。为此,本研究以不同的土壤水分和光环境下培育的木薯为材料,从生理生态角度探讨了木薯的光合特性及其对环境因子的响应,主要研究结果如下：1.通过分析,在诸多环境因子中,土壤相对含水量(SRWC)、光合有效辐射(PAR)、空气相对湿度(RH)对气孔导度(Gs)的影响较大。RH与Gs之间呈极强的正相关关系,说明RH对Gs的影响受其它因子影响较小；PAR、SRWC与Gs之间虽然呈显著的正相关关系,但是它们对Gs的影响程度随SRWC的变化而变化,当SRWC较低时,SRWC是影响Gs的主导因子,而当SRWC较高时,PAR是影响Gs的主导因子；SRWC、PAR、RH与Gs的关系可用指数模型表达。该模型拟合精度高,不仅可以通过SRWC、PAR、RH等3个环境因子对Gs进行定量描述,同时模型参数b2指示干旱胁迫临界值,为深入研究木薯品种的耐旱特性及耐旱机理提供了数量依据。由模型可知,华南8号(SC8)适宜SRWC的低限临界值为51.9%。2.5个木薯品种的最大净光合速率(Pmax)、表观量子效率(AQY)、光饱和点(LSP)和C02羧化效率(CE)、C02饱和点(CSP)对土壤水分的变化具有明显的阈值响应。光合特性的主要参数在55%SRWC-75%SRWC变化幅度较小,在35%SRWC-55%SRWC范围出现明显的增大或减小趋势。根据SRWC对光合效率的影响程度,初步认为在5个参试品种中,华南10号(SC10)、华南8号(SC8)、华南5号(SC5)的抗旱能力强于华南9号(SC9)和华南205号(SC205)。SC10、SC8、SC5的抗旱能力相对较强的主要原因：Pmax、AQY降幅相对较小；气孔导度的降幅相对较小,同时非气孔因素对光合作用制约相对较小；叶绿素a(Chla)、叶绿素b(Chlb)、叶绿素a、b和(Chl(a+b))、类胡萝卜素(Car)、叶绿素a与叶绿素b比值、类胡萝卜素与叶绿素比值对土壤水分的变化相对敏感,在干旱条件下上升幅度大；磷酸烯醇式丙酮酸羧化酶(PEPCase)与1,5-二磷酸核酮糖羧化酶(RuBPCase)比值随着SRWC的减少而增大,即C4途径的表达增强。3.随着遮光程度的增加,5个木薯品种的Pmax、LCP和LSP均下降,不同品种间AQY的变化则不同；Pmax-C02和CE呈下降趋势；SC9、SC8、SC205的C02补偿点(CCP)、CO2饱和点(CSP)呈升高趋势,SC10的CCP、CSP呈降-升-降的趋势,SC5的CCP、CSP呈降-升的趋势。通过比较遮光55%和85%条件下各品种的光合效率,初步认为SC10、SC5、SC8的耐荫性优于SC9、SC205。SC10、SC8、SC5耐荫性相对较强的主要原因在于其在遮光条件下气孔导度的降幅较小,AQY的增加幅度大。在诸多影响Pmax的因子中,LSP、AQY、胞间CO2浓度(Ci)、LCP与Pmax关系密切,因此,初步认为LSP、AQY、Ci、LCP等因子可作为木薯耐荫性的评价指标。4.本研究利用净光合速率(Pn)、Gs、大气CP2浓度(Ca)和胞间CO2浓度(Ci)间的关系表达式ci=Ca-Pn/Gs,分析了不同土壤水分和光照条件下,影响木薯光合作用的主要因素。发现,不同土壤水分条件下,在一定光照范围内,木薯光合作用主要受气孔限制,光照强度的影响较小；超出此范围后,其受光照强度的影响较大,出现由气孔限制向非气孔限制转变的PAR临界值,本试验条件下,该临界值约为600μmol·m-2.s-1。而其限制作用的大小则与土壤水分密切相关,品种间存在差异。在不同光照条件下,影响木薯光合作用的主要因素也存在发生转变的PAR临界值,即当光照强度在某一范围值时,光合作用主要受气孔限制,当光照强度超过该范围后,光合原料(C02)的供求达到动态平衡,光合作用受气孔因素和非气孔因素的影响均较小,且该临界值因品种及其遮光程度的不同而不尽相同。5.土壤干旱对PEPCase活性的诱导作用品种间存在差异,干旱胁迫使SC10、SC8、SC5的PEPCase/RuBPCase比值升高,,SC9和SC205的PEPCase/RuBPCase比值下降。且当土壤干旱超过一定程度后,PEPCase/RuBPCase比值由开始的升高出现下降趋势。不同土壤水分条件下,各品种的Chla/b比值的变化范围为：2.812-3.347；不同土壤水分和光照条件下CO2补偿点的变化范围分别为57.5～92.2μmol·mol-1和69.5～104.6μmol·mol-1；短时间大气CO2浓度增加均使光合速率提高超过10%。木薯的这些变化特性均与C3植物类似。更多还原

【Abstract】 Cassava is one of the three potato categories, mainly cultivated in tropical and sub-tropical regions. Because during the course of growth and development of cassava often have droughts, typhoons and other natural disasters, so will have a greater impact on cassava production by environmental factors. Moreover, cassava is still a lack of systematic cultivation of theories and techniques to compare with the crops of rice and wheat, in particular the basic research of photosynthesis, stress physiology is less. Photosynthesis is the basis of material production, photosynthetic characteristics of cassava and its relationship to the environment not only for the rich theories of cassava cultivation and stress physiological and important for exploring the potential production capabilities of cassava, and while provide theoretical basis and technical parameters for the varieties layout, adaptability cultivation and high yield and stable. Therefore, this study used the cassava which cultivated under different moisture and light as a test materials, and investigated photosynthetic characteristics of cassava and its response to environmental factors from the ecophysiology point of view. The main results were as follows:1. Through the analysis of many environmental factors, we found that soil relativ water content (SRWC), photosynthetically active radiation (PAR) and air humidty (RH)had a great influence on stomatal conductance. RH with constant strong positive correlation with Gs was the principal environmental factors working quite independently. Although SRWC and PAR had significant positive correlation with Gs, yet their impact magnitude would vary with the change of SRWC. This was because when the SRWC was low, the SRWC became the dominant factor affecting Gs, while the SRWC was high, the PAR was the dominant factor. The relationship between the Gs and SRWC, PAR, and RH could be expressed as exponential exponential model. And this model has high accuracy, not only could be described Gs quantitatively by three environmental factors of SRWC, PAR and RH, but also the b2 of the model’s parameter indicated that the critical value of drought stress, and it provided the data basis to go on investigating the characteristics and mechanism of drought tolerance among cassava varieties. Using the constructed model, we found that the lower limit threshold of appropriate SRWC for cassava variety SC8 was 51.9%.2. The results showed that the maximum photosynthetic rate (Pmax), apparent quantum yield (AQY), light saturation point (LSP), carboxylation efficiency (CE) and CO2 saturation point (CSP), had evidently threshold responsed to the variations of soil moisture. The main parameters of photosynthesis with a little change under the range from 55% SRWC to 75%SRWC, but with significant increase or decrease trends under the range from 35%SRWC to55%SRWC. According to the impact of SRWC on photosynthetic efficiency, we preliminarily viewed that the drought tolerance cassava varieties of SC10, SC5 and SC8 was better than SC9 and SC205, mainly due to the small decline of Pmax and AQY relatively; the small decline of stomatal conductance relatively, while the small limition of non-stomatal factor on photosynthesis relatively; chlorophylla(Chla), chlorophyllb(Chlb), chlorophyll(a+b)(Chl(a+b)), carotenoid(Car), Chla/b and Car/Chl were relatively sensitive to the changes of soil moisture and rose more steeply under drought conditions. The ratio of phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase increased with the decreasing SRWC, that was the C4 pathway to increase expression.3. With the increase of shading level, Pmax, LCP and LSP decreased, while the AQY was different in varieties. The trend was generally decreased of Pmax-co2 and CE in all varieties and increased of CO2 compensation point(CCP), CO2 saturation point(CSP) in SC9, SC8, SC205; the trend was down-up-down of the CCP, CSP in SC10, and down-up in SC5. By comparing the photosynthetic efficiency of shading55% and 85%, we preliminarily viewed that the shade tolerance of SC10, SC5 and SC8 was better than SC9 and SC205, mainly due to their stomatal conductance showed a smaller decline, and the increase large of AQY. The LSP, AQY, intercellular CO2 concentration (Ci), LCP were closed to Pmax in all the factors that influence the Pmax. Therefore, the LSP, AQY, Ci, LCP were preliminarily considered as evaluation indicators for shade tolerance of cassava.4. The study used the expression of relationship among net photosynthetic rate (Pn), Gs, atmosphere CO2 concentration (Ca)and Ci, that is Ci=Ca - Pn/Gs to analyse the main factor affecting on photosynthesis of cassava under different moisture and light conditions. We found that the main affect factor on photosynthesis of cassava closely related to the light intensity. In a certain light intensity range, photosynthesis was mainly affected by stomatal limit rather than PAR. Out of this range, photosynthesis was obviously affected by PAR, and the critical turning point of PAR was observed with the change from stomatal limit to non-stomatal limit. In this experiments, the critical turning point of PAR was 600μmol·m-2·s-1. And its action degree closely related to the soil moisture, also there was difference in varieties. Under different light conditions, the main factors affect the photosynthesis of cassava also shift the PAR threshold, that was, when the light intensity in a range of value, photosynthesis was mainly affected by stomatal limit, when the light intensity out of the range, photosynthetic materials (CO2) to achieve dynamic balance of supply and demand, photosynthesis was affected by stomatal and non-stomatal factors were small, and the threshold level was different due to varieties and their differences in shading. 5. The induction of drought on PEPCase activity was different among varieties. The ratio of PEPCase and RuBPCase of SC10, SC8 and SC5 increased, while the SC9 and SC205’s decreased under drought conditions. Although the ratio of PEPCase and RuBPCase from initial increase to decrease when the drought exceeded a certain degree. The variation range of the ratio of chlorophylla and chlorophyllb was 2.812～3.347 under different soil moisture. Under different soil moisture and light conditions the variation range of CO2 compensation point was 57.5～92.2μmol·mol-1,69.5～104.6μmol·mol-1, respectively. The photosynthetic rate was increased more than 10% by short time increase CO2 concentration. These changes of cassava were similar to the C3 plants.更多还原