缺钾油菜叶片光合速率下降的主导因子及其机理

【目的】钾是油菜(Brassica napus L.)生长发育所必需的矿质元素,缺钾胁迫可导致油菜叶片光合功能的衰退,最终影响籽粒产量。本文通过比较田间条件下蕾薹期油菜叶片(长柄叶、 短柄叶和无柄叶)对缺钾胁迫的反应,探讨缺钾导致叶片光合速率下降的主导因子及其作用机理,为合理施用钾肥提高油菜产量提供理论依据。【方法】采用大田试验,研究不施钾(-K)和施钾(+K)条件下华油杂9号和中双9号单株重,蕾薹期不同类型叶片单叶重、 叶面积、 K含量和叶绿素含量。利用Li-6400 XT便携式光合测定系统测定各类叶片的光合速率(Pn)和气孔导度(gs)等气体交换参数,以及PSⅡ最大光化学量子效率(Fv/Fm)和实际光化学量子效率(PSⅡ)等叶绿素荧光参数。并利用胞间CO2浓度(Ci)和气孔限制值(Ls)的变化,分析叶片光合作用的限制因子。【结果】1) 缺钾胁迫使成熟期华油杂9号和中双9号籽粒产量分别下降13.9%和27.2%。2)缺钾显著抑制了蕾薹期中双9号的生长,单株重下降了12.4%; 长柄叶的干重比正常供钾处理降低了19.2%,而对华油杂9号无影响。3) 缺钾主要影响蕾薹期长柄叶的光合生理特性,对短柄叶和无柄叶无影响。缺钾条件下,油菜长柄叶钾含量和叶绿素含量明显降低,其Pn也显著低于正常供钾处理。但缺钾对不同品种Pn的限制原因并不同,缺钾胁迫导致华油杂9号Ci显著降低,Ls增加了16.6%,即气孔因素是华油杂9号Pn下降的主要原因; 而中双9号Ci显著增加,Ls却下降了14.0%,Pn的下降是由非气孔因素引起的。4) 缺钾胁迫下中双9号长柄叶的Fv/Fm、 PSⅡ、 qP和ETR均显著降低,说明PSⅡ反应中心受损,NPQ显著上升,间接表明缺钾条件下中双9号Pn下降的原因与非气孔因素有关; 而华油杂9号各荧光参数均未受缺钾胁迫的影响。油菜收获期籽粒产量与各叶片钾素含量以及长柄叶气体交换和叶绿素荧光参数关系密切。【结论】缺钾胁迫导致蕾薹期油菜长柄叶光合功能加速衰退,影响收获期籽粒产量。中双9号长柄叶光合性能受缺钾胁迫的影响大于华油杂9号,这与品种自身对缺钾胁迫的耐受能力有关。

Main factors and mechanism leading to the decrease of photosynthetic efficiency of oilseed rape exposure to potassium deficiency

Objectives] Potassium (K) is essential for oilseed rape (Brassica napus L. ), insufficient supply will decline the leaf photosynthetic capacity, as well as seed yield. The present study was conducted to compare the response of different leaves ( namely long-stalk leaf, short-stalk leaf and no-stalk leaf) to K deficiency at stem elongation stage under field conditions. Additionally, we attempted to find out the dominant limitations and reveal the underlying mechanisms due to K deficiency which restrained the leaf photosynthesis, and to provide theoretical basis for the reasonable application of potash fertilizer on the purpose of improving seed yield. Methods] A field experiment with no K supply (- K) and normal K supply ( + K) was conducted using two rapeseed cultivars (Huayouza No. 9 and Zhongshuang No. 9). The plant dry matter biomass, leaf dry matter content, leaf area, leaf K concentration and chlorophyll content were concurrently determined. The leaf gas exchange parameters, including net photosynthesis (Pn ) and stomatal conductance (gs ), and leaf chlorophyll fluorescence parameters, including maximum quantum yield of PSⅡ(Fv / Fm) and effective quantum efficiency of PSⅡ (ΦPSⅡ), the changes of Ci and stomatal limitations (Ls ) were detected. Results]1) Potassium deficiency leaded to a significant reduction of seed yield, in Huayouza No. 9 the decrease was 13. 9% and in Zhongshuang No. 9 was 27. 2% . 2) The growth of Zhongshuang No. 9 was significantly suppressed under insufficient potassium supply, with 12. 4% and 19. 2%decreases of plant dry matter content and leaf dry matter content in long-stalk leaf, respectively, while those in Huayouza No. 9 were unaffected. 3 ) Potassium deficiency mainly affected the photosynthetic physiological characteristics of long-stalk leaf, but not on those of short and no-stalk leaves. Under K deficient, the K content, chlorophyll content and Pn of long-stalk leaf were sharply declined. The dominant factors involved in Pn decline were different between the two cultivars. Potassium deficiency led to sharply decline of Ci but 16. 6% increase in Ls in Huayouza No. 9, indicating that Pn was primarily affected by stomatal limitations. Conversely, K deficiency led to the dramatic increase in Ci and 14. 0% of decrease in Ls in Zhongshuang No. 9, which suggested that Pn was primarily limited by non-stomatal limitations. 4) Moreover, K deficiency caused sharp decline in the leaf Fv / Fm,ΦPSⅡ, qP and ETR of Zhongshuang No. 9, but not in those of Huayouza No. 9, indicating that the PSⅡreaction center was suffered of damage. Meanwhile, the obvious increment of NPQ hinted that non-stomatal limitations induced the decline of Pn . Conclusions] The decline of photosynthetic efficiency in the long-stalk leaf of rapseed is exacerbated under K deficiency, which resultes in the decrease of seed yield. The Zhongshuang No. 9 was more sensitive to K-starvation than Huayouza No. 9, which is associated with its tolerance to K deficiency.