| About 30% of the areas in guizhou province are typical karst ecologically fragile areas,and the problem of seasonal drought is prominent.To understand and study the response mechanism of plants under drought stress is of great significance for the selection of pioneer and suitable plants for ecological restoration in karst ecologically fragile areas,promoting plant growth and safeguarding ecological environment.In this paper,based on the seedlings of paper mulberry as the experimental material,guizhou yellow soil and lime soil two main types of soil for growing medium,using pot experiment,the acquisition research normal water,low drought stress,moderate drought stress and severe drought stress under four kinds of processing plant seedlings roots,leaf root morphology,physiological and biochemical indexes,and rhizosphere soil nutrient,rootexudate,enzyme activity and microbial population change,clear paper mulberry under different soil and drought stress response mechanism.The main research conclusions are as follows:(1)With the increase of drought stress,the root length of paper mulberry seedlings in yellow soil generally tends to decrease,and the lower root length of each treatment group is lower than that of the control group;The average root diameter,root surface area and root volume generally tend to decrease,but under severe stress,the three increase slightly,but are still lower than the control group.The dry weight of root biomass tends to decrease in general.In limestonesoil,root length tends to decrease in general,slightly increases under moderate stress,but is lower than that of the control group.Root volume decreased with the deepening of drought.The average root diameter,root surface area and root biomass dry weight increased under mild,severe and severe stress respectively,but were all smaller than those of the control group.In the two soils,Broussonetia papyrifera seedling roots are more responsive to different drought conditions in yellow soil.(2)With the increase of drought stress,the content changes of malondialdehyde,superoxide dismutase,peroxidase and chlorophyll in paper mulberry seedling leaves in yellow soil and limestone soil are consistent.In the two soil types,MDA content increased with the increase of drought degree.Superoxide dismutase and peroxidase increased with the increase of drought degree.Chlorophyll content decreased with the increase of stress.(3)oxalic acid,tartaric acid,citric acid,acetic acid,lactic acid,malic acid,maleic acid and succinic acid were detected in rhizosphere soil of paper mulberry seedlings under different drought conditions.Succinic acid,lactic acid,malic acid and citric acid have the highest content.The total amount of root organic acids in yellow soil increased with the increase of drought stress,oxalic acid,tartaric acid,malic acid and lactic acid increased with the increase of stress,while maleic acid,succinic acid,citric acid and acetic acid decreased with the increase of stress.In limestone soil,the content of organic acids increased first and then decreased and then increased with the increase of stress degree,among which tartaric acid,malic acid,acetic acid,succinic acid,citric acid and maleic acid increased with the increase of stress degree,while the remaining two organic acids lactic acid and oxalic acid both increased first and then decreased and then increased with the increase of stress degree.Furthermore,the results of principal component analysis of organic acid further confirmed the characteristics of organic acid secretion in paper mulberry tree seedlings under different drought conditions(4)under different drought conditions of the two kinds of soil,the soil nutrients were also different.The variation trend of organic matter and alkali-hydrolyzed nitrogen content in yellow soil was consistent,and it decreased first,then increased and then decreased with the increase of drought stress degree.The change trend of organic carbon was decreasing first and then increasing.The contents of organic matter and organic carbon in different drought conditions were as follows: moderate drought > normal water > severe drought > mild drought;The change trend of alkali-hydrolyzed nitrogen was decreasing first and then increasing.The content of available phosphorus and available potassium increased first and then decreased.The order of alkali-hydrolyzed nitrogen content was: moderate > severe > normal water > mild drought;The contents of available phosphorus and available potassium were ranked as moderate drought > severe drought > mild > normal water.The results showed that moderate to severe water stress affected the uptake of alkali-hydrolyzed nitrogen,available phosphorus and available potassium by plant roots in yellow soil.The change trend of organic matter,organic carbon,alkali-hydrolyzed nitrogen and available potassium in limestone soil is the same,and the trend of decrease first and then increase.The contents of organic matter,organic carbon and alkali-hydrolyzed nitrogen under different drought conditions were ranked as severe stress > normal water > moderate stress >low stress.Alkali-hydrolyzed nitrogen and available phosphorus were first decreased and then increased.Under different drought conditions,the available phosphorus content was ranked as follows: moderate stress of normal water > moderate stress > severe stress > low stress;The content of available potassium increased with the increase of drought stress.The results showed that moderate to severe water stress affected the absorption of available potassium,alkali-hydrolyzed nitrogen and organic matter by the roots of limestone paper mulberry seedlings.(5)two kinds of different soil types under different drought conditions,the seedlings of paper mulberry rhizosphere soil amylase,protease,phosphatase activity have the same change trend,as the drought degree increasing enzyme activity,three enzymes under two different soil types in the content are as follows: under the severe drought content is high,moderate,mild content times,normal water lowest.Urease showed different changes with the other three enzymes.Urease activity in yellow soil and limestone soil decreased first and then increased with the increase of drought degree.In yellow soil,urease activity was ranked as: normal water > mild drought >severe drought > moderate drought.In limestone soil,urease activity was ranked as normal water > severe drought > moderate drought > mild drought.The correlation analysis of soil nutrients and soil enzyme activity showed that amylase was positively correlated with phosphatase,phosphatase with available phosphorus,urease with organic matter,urease with available potassium in rhizosphere soil of Formosa seedlings under different degrees of drought stress in yellow soil.There was a significant positive correlation between organic matter and alkali-hydrolyzed nitrogen,organic matter and available potassium,organic matter and organic carbon,alkali-hydrolyzed nitrogen and available potassium,and available potassium and organic carbon.The correlation between other analysis indexes was not significant.Under different degrees of drought stress in limestone soil,amylase was positively correlated with available potassium,phosphatase with available potassium,organic matter was positively correlated with organic carbon,and other indexes were not significantly correlated.(6)Different drought stresses have different effects on the diversity of rhizosphere soil microbial structure.In yellow soil,the number of bacteria in rhizosphere soil decreased under light and moderate drought stress;but increased under severe drought.Moderate stress increased the number of fungi,while moderate and severe drought reduced the number of fungi.The number of actinomycetes decreased with the increase of stress.In limestone soil,moderate drought stress increased the number of bacteria for a short time,but severe drought reduced the number of bacteria.The number of fungi decreased with the increase of drought stress.However,the number of actinomycetes increased with the increase of drought stress.No consistent change rule was found in the two soil types.Pearson correlation analysis showed that there was a significant correlation between organic acids in roots,enzyme activity in rhizosphere soil and total amount of microorganisms at different drought levels. |
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