Erel Ran, Yermiyahu Uri, Ben-Gal Alon, Dag Arnon, Shapira Or, Schwartz Amnon
Institute of Soil, Water and Environmental Sciences, Gilat Research Center, Agricultural Research Organization, Bet-Dagan, Israel; The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Institute of Soil, Water and Environmental Sciences, Gilat Research Center, Agricultural Research Organization, Bet-Dagan, Israel.
J Plant Physiol. 2015 Apr 1;177:1-10. doi: 10.1016/j.jplph.2015.01.005. Epub 2015 Jan 15.
Potassium (K) is an essential macronutrient shown to play a fundamental role in photosynthetic processes and may facilitate photoinhibition resistance. In some plant species, sodium (Na) can partially substitute for K. Although photosynthetic enhancement has been well established, the mechanisms by which K or Na affects photosynthesis are not fully understood. Olive (Olea europaea L.) trees were previously shown to benefit from Na nutrition when K is limiting. In order to study the effect of K and Na on photosynthetic performance, we measured gas exchange and chlorophyll fluorescence in young olive trees supplied with either K, Na or no fertilizer, and subjected to manipulated levels of CO2, O2 and radiation. Light and CO2 response curves indicate substantially superior photosynthetic capacity of K-sufficient trees, while Na substitution generated intermediate results. The enhanced performance of K, and to a lesser extent, Na-supplied trees was found to be related mainly to modification of non-stomatal limitation. This indicates that K deficiency promotes inhibition of enzymatic-photochemical processes. Results indicate lower chlorophyll content and altered Rubisco activity as probable causes of photosynthetic impairment. Potassium deficiency was found to diminish photoprotection mechanisms due to reduced photosynthetic and photorespiratory capacity. The lower CO2 and O2 assimilation rate in K-deficient trees caused elevated levels of exited energy. Consequently, non-photochemical quenching, an alternative energy dispersion pathway, was increased. Nonetheless, K-deficient trees were shown to suffer from photodamage to photosystem-II. Sodium replacement considerably diminished the negative effect of K deficiency on photoprotection mechanisms. The overall impact of K and Na nutrition plays down any indirect effect on stomatal limitation and rather demonstrates the centrality of these elements in photochemical processes of photosynthesis and photoprotection.
钾（K）是一种必需的大量营养素，在光合作用过程中发挥着重要作用，可能有助于提高抗光抑制能力。在一些植物物种中，钠（Na）可以部分替代钾。尽管光合作用增强已得到充分证实，但钾或钠影响光合作用的机制尚未完全了解。先前研究表明，当钾供应有限时，油橄榄（Olea europaea L.）树可从钠营养中受益。为了研究钾和钠对光合性能的影响，我们测量了供应钾、钠或不施肥的幼龄油橄榄树的气体交换和叶绿素荧光，并对二氧化碳、氧气和辐射水平进行了调控。光响应曲线和二氧化碳响应曲线表明，钾充足的树木光合能力明显更强，而钠替代则产生了中等结果。结果发现，钾供应充足以及在较小程度上钠供应充足的树木光合性能增强，主要与非气孔限制的改变有关。这表明钾缺乏会促进对酶促光化学过程的抑制。结果表明，叶绿素含量降低和 Rubisco 活性改变可能是光合作用受损的原因。由于光合和光呼吸能力降低，发现钾缺乏会削弱光保护机制。钾缺乏树木中较低的二氧化碳和氧气同化率导致激发能水平升高。因此，作为一种替代能量分散途径的非光化学猝灭增加。尽管如此，钾缺乏的树木被证明遭受了光系统 II 的光损伤。钠替代大大减轻了钾缺乏对光保护机制的负面影响。钾和钠营养的总体影响淡化了对气孔限制的任何间接影响，而是证明了这些元素在光合作用和光保护的光化学过程中的核心地位。
