干旱胁迫下平邑甜茶对外源硅处理的生理响应特性

A study on the physiological responses of Malus hupenensis to exogenous silicon treatment under drought stress

【目的】探究外源硅(Si)对干旱胁迫下苹果砧木生理特性的影响。【方法】采用盆栽控水方法,设置正常水分(对照)和干旱胁迫外加5种浓度硅处理(Na2Si O3·9H2O),即0(T1)、1.25 mmol·L^-1(T2)、2.5 mmol·L^-1(T3)、3.75 mmol·L^-1(T4)、5.0 mmol·L^-1(T5),测定各处理的叶绿素含量、光合特性、荧光参数及抗氧化酶活性,并利用主成分分析对其进行综合评价。【结果】平邑甜茶叶片的胞间CO2浓度(Ci)、丙二醛(MDA)和脯氨酸(Pro)含量随干旱胁迫时间的延长逐渐增加,净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、最大荧光(Fm)、最大光能转化率(Fv/Fm)、光合电子传递速率(ETR)以及叶绿素相对含量(SPAD)则呈下降趋势,而初始荧光(F0)和超氧化物歧化酶(SOD)活性随胁迫时间的延长分别呈先降后升和先升后降的趋势。相比对照,外源硅处理后叶片各指标的变化幅度均有减小,且存在明显的浓度效应。其中,T4(3.75 mmol·L^-1)处理下SPAD、Pn、Gs、Fv/Fm、ETR及SOD降幅最小,显著高于T1,MDA升幅最小,且显著低于T1及CK;Pro升幅最大,显著高于T1。12个指标相关性分析结果表明,Pn与SPAD、Gs、Tr、Fv/Fm、F0、Fm、ETR、Pro及SOD呈正相关,与Ci和MDA呈负相关。对此12个指标进行主成分分析,提取特征值>1的3个主成分,其特征值分别为8.366、2.370和1.060。第一、二、三主成分方差贡献率分别为69.719%、19.754%和8.834%,累计方差贡献率达到98.307%,符合分析要求。综合分析表明,干旱胁迫下不同浓度外源硅对平邑甜茶生理特性的影响排名依次为:T4>T3>T5>T2>T1。【结论】3.75 mmol·L^-1的硅酸钠能更好地改善平邑甜茶的光合能力、提高抗氧化酶活性、增加生物膜的稳定性,进而达到缓解干旱胁迫的目的。

【Objective】Mauls domestica Mill.is the most important deciduous fruit tree in the world,which is well adapted to the climate of the loess plateau in Northwest China with sufficient sunlight and great diurnal temperature difference.The northwestern region is the best ecological area for apple cultivation,but there are many adverse environmental factors,such as drought,have caused huge losses in agricultural production,and seriously threaten the sustainable development of the apple industry.It is of great significance to select suitable treatments to control the size of trees canopy,enhance resistance to diseases and abiostresses.Many studies have shown that spraying with SA,ABA or SE promotes the growth of apple seedlings under drought stress,improves the structure of trees and the photosynthetic characteristics of leaves,which can effectively alleviate the damage of drought stress on plants.With seedlings of Malus hupenensis seedlings at 8 leaf ages as the experimental material,the effects of exogenous silicon(Si)on the physiological characteristics of apple rootstock under drought stress were studied by spraying sodium silicate at different concentrations.【Methods】When the seedlings of M.hupenensis grew to 4-leaf age,they were moved into pots with the same size and the same weight of nutrient soil.Intact and uniform M.hupenensis with 8 true leaves were selected for the drought stress experiment.The soil moisture was controlled by weighing method,and the severity of drought stress increased with elongated drought.At the same time,Na2Si O3·9H2O solutions of 0,1.25,2.5,3.75 and 5mmol·L^-1were sprayed.When the field capacity was 50%and normal water(CK)soil maintained 75%of the field capacity,spraying was stopped.Treatments including normal irrigation(CK),drought stress(T1),drought stress+1.25 mmol·L^-1Na2Si O3·9H2O(T2),drought stress+2.5 mmol·L^-1Na2Si O3·9H2O(T3),drought stress+3.75 mmol·L^-1Na2Si O3·9H2O(T4),drought stress+5.0 mmol·L^-1Na2Si O3·9H2O(T5)were set for the experiment,which lasted for 20 days.The effects of these treatments on photosynthetic characteristic indices[such as net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)and intercellular CO2concentration(Ci)],chlorophyll fluorescence parameters[such as Initial fluorescence(F0),maximum fluorescence(Fm),the maximum light conversion rate of PSII(Fv/Fm)and photosynthetic electron transfer rate(ETR)],chlorophyll content(SPAD),proline content(Pro),superoxide dismutase(SOD),malondialdehyde(MDA)were determined every five days from the day of treatment.Finally,multiple indicators were analyzed using the correlation analysis method and principal component analysis.【Results】With the prolongation of drought stress,Ci,MDA and Pro increased,while Pn,Gs,Tr,Fm,Fv/Fm,ETR and SPAD showed a decreased trend.Besides,as the drought stress extended,Fo first decreased and then increased,while the activity of SOD increased first and then decreased.With the silicon treatments,the declines or increases in the above leaf indexes were significantly lower than that CK,and there was an obvious concentration effect.Under T4(3.75 mmol·L^-1),the SPAD,Pn,Gs,Fv/Fm,ETR and SOD demonstrated minimum drop and were significantly higher than under T1,while MDA in T4 had the smallest increase and was significantly lower than in T1 and CK,while Pro had the largest increase and was significantly higher than that in T1.The correlation analysis of the 12 indexes displayed that Pnwas positively correlated with SPAD,Gs,Tr,Fv/Fm,F0,Fm,ETR,Pro and SOD,but negatively correlated with Ciand MDA.Principal component analysis was performed on these 12 indicators,and three principal components with feature value>1 were extracted,whose eigenvalues were 8.366,2.370 and 1.060,respectively.The variance contribution rates of the first,second and third principal components were 69.719%,19.754%and 8.834%,respectively,and the cumulative variance contribution rate reached 98.307%,which met the analysis requirements.The comprehensive analysis showed that the effects of exogenous silicon treatments on the physiological characteristics of M.hupenensis were in the order of T4>T3>T5>T2>T1.【Conclusion】Exogenous silicon could alleviate drought stress by regulating osmotic substances,eliminating reactive oxygen species,activating antioxidant enzymes,and improving heat dissipation with improved light protection.The treatment of 3.75 mmol·L^-1sodium silicate could alleviate the drought stress by improving the photosynthetic capacity,antioxidant enzyme activity and the stability of the membrane.