Effects Of Potassium Fertilize On Storage Root Yield And Physiological Mechanism Of Sweetpotato Under Drought Stress

The experiment was carried out in 2014 in the agronomy experimental station and State Key Laboratory of Crop Biology of Shandong Agricultural University,Taian,China.Sweet potato cultivar?Taizhong NO.6? was used as tested crop and potassium sulphate?K₂SO₄? as K fertilizer,the water treatments included normal water supply?W1,soil with water content of 60?70%? and drought stress?W0,soil with water content of 30?40%?.The K fertilizer treatments included K0?K₂O content 0 g/m²?,K1?K₂O content 12.0 g/m²?,K2?K₂O content24.0 g/m²? and K3?K₂O content 36.0 g/m²?.The effects of different potassium rate on the stem and leaf growth,storage root yield formation and physiological mechanism were analyzed,which revealed the effect of potassium fertilize on improving the drought resistance and storage root yield of drought land,in order to provide theoretical basis for drought resistance and high yield cultivation of sweet potato.The main result showed that:1 The suitable potassium application of sweetpotato under drought stressDrought stress inhibited the stem and leaf growth and the storage root thickening,decreased dry matter accumulation of plant and storage root and starch formation of storage root,and reduced the storage root yield.Under drought stress,the stem length,branch number per plant,stem width and leaf area index tuber number and storage root yield were maximum on K2 or K1,the increasing velocity of storage root,dry matter of plant and storage root,starch content and accumulation increased firstly,K1 was maximum,K2 increased little and K3 decreased remarkably as potassium application increasing,the difference between K2 and K1 was non-significant;Under well-watered condition,the above mentioned indexes were maximum on K2,K2 increased little as potassium application increasing,the difference between K3 and K2 was non-significant.In the experiment condition,the suitable potassium application of sweetpotato under drought stress was 12g/m²,and the suitable potassium application of sweetpotato under drought stress was 24g/m².2 Potassium application improved leaf photosynthetic performance of sweetpotatoDrought stress decreased leaf relative water content?RWC?and chlorophyll content,reduced leaf Pn.Under both water conditions,potassium application increased leaf RWC and chlorophyll content,improved leaf Pn,which effect of potassium application were more remarkable under drought stress.There were significant differences between the two water conditions.Under drought stress,potassium application reduced leaf Gs of sweetpotato,and stomatal resistance increased.Tr and Ci decreased,the water transpiration decreased,and WUE increased.But the results were opposite under well-watered condition.Under drought stress,potassium application improved ?_PS?,Fv/Fm and q_P,and decreased NPQ,which relieved the hurt on photosynthetic apparatus of chloroplast and ovygen-evolving complex of PS?of drought stress.The researches illustrated that the effect of potassium fertilize was not only the nutrient function,and the more important was that potassium enhanced the drought resisting ability by means of adjusting stomatal resistance,reducing water loss and improving Pn.3 The physiological mechanism of improving drought resistance of sweetpotato by potassium fertilize under drought stressThe leaf proline,leaf and storage root soluble sugar and soluble protein content increased remarkably under drought stress.Application of potassium could increase leaf proline,leaf and storage root soluble sugar and soluble protein content,and improve potassium distribution to overground part,which enhanced the drought resistance ability of the sweetpotato plant.The difference of proline and soluble sugar content after potassium application were significant,which illustrated that proline and soluble sugar was the osmotic adjustment substance playing the leading role for improving osmotic adjustment ability of sweetpotato.Under well-watered condition,potassium application increased leaf and storage root soluble sugar and soluble protein content significantly,and leaf proline content changed non-significantly.Under drought stress,the leaf and storage ABA content during each stage were higher than that under well-watered condition remarkably.Under both water conditions,there was significant difference on the effect of potassium application on ABA content,which was the primary cause of significant difference of photosynthetic parameter?Gs,Ci,Tr,WUE?.Application of potassium increased ABA content as important signal conditioning substance remarkably under drought stress,which adjusted stomatal closing,stomatal conductance decreasing,transpiration rate reducing,water use efficiency increasing and enhanced drought resisting of sweetpotato.Under well-watered condition,application of potassium improved the synthesis of IAA?ZR and GA,and inhibited ABA produce,which made ABA content decreasing,stomatal aperture magnifying,and assimilating more CO₂,and finally improved Pn.The research showed that,the approaches of improving drought resistance of sweetpotato mainly with potassium application concluded two sides:firstly,under drought stress,application of potassium could improved osmotic adjustment substance content to lower Tr,reduce transpiration,increase WUE,and enhanced photosynthetic performance.4 The effect of potassium fertilize on antioxidant protection ability of sweetpotato under drought stressThe leaf MDA and H₂O₂ content increased under drought stress,and the membrane peroxidation aggravated.Application of potassium reduced the leaf MDA and H₂O₂ content remarkably.Under drought stress,the minimum of leaf MDA and H₂O₂ content was K2,and K3 increased.Under well-watered condition,the minimum of leaf MDA and H₂O₂ content was K3.Under drought stress,the leaf SOD?POD?CAT?APX?GR?MDHAR enzyme gene expression and enzymatic activity during each stage were higher than that under well-watered condition.Under both water conditions,there was significant difference on the effect of potassium application on each antioxidant enzymes activity.Under drought stress,after application of potassium the leaf SOD?POD?CAT?APX?GR?MDHAR gene expression levels decreased,and enzymes activity reduced,K2 was the lowest.The cause might be application of potassium improved plant growth trait to decrease H₂O₂ content,which induced antioxidant enzyme gene expression levels decreasing by H₂O₂ as signal molecule,and enzymes activity reduced.Under well-watered condition,each antioxidant enzymes gene levels increased remarkably with potassium application,and the maximum was K2.