椪柑叶片硼毒害症状及光合生理响应研究

  【目的】  准确及时诊断硼毒害，了解硼毒害对叶片造成的生理影响，为硼毒害的有效防治提供理论依据。  【方法】  通过田间调查和叶片养分含量测定，明确福建省安溪县椪柑叶片黄化和脱落是由硼中毒引起的。分别采集不同程度硼毒害椪柑叶片，测定叶片光合作用速率、叶绿素荧光特性和细胞膜透性。  【结果】  在正常、中度黄化和重度黄化叶片中，钾、镁、锌含量均处于椪柑适宜范围内，而中度黄化和重度黄化叶片的硼含量比正常叶片分别提高了11.11和19.71倍，显示硼毒害是造成椪柑叶片黄化的原因。椪柑叶片硼毒害症状有两种表现形式:一是症状由叶尖沿主脉向下发展，叶肉和叶脉均褪绿黄化，黄化部位可见棕褐色的坏死斑点；二是症状由叶缘向主脉发展，主脉保持绿色，叶片呈不规则的黄、绿斑驳黄化。硼毒害椪柑叶片的光合色素含量、有效光化学效率 (Fv'/Fm')、电子传递效率 (ETR)、有效量子产额 (ΦPS II) 和光化学淬灭系数 (qP) 随症状的加重而下降，而非光化学淬灭系数 (NPQ)、过剩激发能 (E) 和天线热耗散 (D) 则随症状的加重而提高，引起光合作用速率、淀粉和可溶性糖含量下降，硼毒胁迫下椪柑叶片细胞膜透性明显提高。  【结论】  过量喷施硼肥所造成的硼毒害会导致椪柑叶片黄化、异常落叶，硼毒害使椪柑光合作用受抑、光合产物合成受阻，细胞膜受到伤害。柑橘生产上应重视含硼叶面肥的合理使用，以免造成硼中毒现象。有关椪柑硼毒害的防治措施还有待进一步研究。

Symposium of boron toxicity and photosynthesis response study in leaves of Ponkan (Citrus reticulata Blanco)

  【Objectives】  Precise diagnose of boron toxicity and the adverse impact on photosynthesis of leaf of Ponkan (Citrus reticulata Blanco) is necessary for the prevention and cure of the obstacle.  【Methods】  Field investigation and Ponkan leaf nutrition determination was carried out in a Ponkan orchard in Anxi County, Fujian Province, which indicated Ponkan leaves yellowing and abnormal dropping was caused by B toxicity. The leaf samples were collected in normal, moderate yellowing and severe yellowing leaves respectively, and the photosynthesis, chlorophyll fluorescence characteristics and cell membrane permeability were determined.  【Results】  The contents of K, Mg and Zn in normal, moderate yellowing and severe yellowing leaves all fell in the optimum range, while the B contents in moderate and severe yellowing leaves were 11.11 and 19.71 folds of that in normal leaves of Ponkan, indicating that the yellowing and abnormal dropping of leaves in the tested orchard were caused by B toxicity. There were two typical symptoms of boron toxicity in Ponkan leaves. One symptom was developed from leaf tip along midrib and yellow-bronze necrosis spots occurred on the yellowing area. The other one was developed from leaf edge along midrib and the green main veins surrounded by irregularly mottled yellow-green chlorosis. The content of photosynthetic pigments, the effective photochemical efficiency (Fv'/Fm'), electron transport efficiency (ETR), the effective quantum yield (ΦPS II) and photochemical quenching coefficient (qP) decreased with the aggravation of boron toxicity, whereas non-photochemical quenching coefficient (NPQ), excess excitation energy (E) and antenna heat dissipation (D) increased with the aggravation of B toxicity. Boron toxicity significantly decreased photosynthesis rate (Pn), starch and soluble sugar contents, whereas increased leaves cell membrane permeability.  【Conclusions】  Excessive foliar boron application could cause the boron toxicity of Ponkan. Boron toxicity will cause the yellowing and abnormal drop of Ponkan leaves and increase the cell membrane permeability, decrease the photosynthetic rate and block the assimilation of photosynthetic products seriously.