Genotypic Difference Of Maize In Response To Phosphorus Deficiency And Al Toxicity And Effects Of Organic Acids On Phosphorus Availability In Soil

Phosphorus is often sparingly soluble in soils and consequently P deficiency in plants represents a major constraint to world agricultural production.High phosphate fertilizer inputs intensive crop areas have been the practice for several decades.Generally,the P was widely considered to be firmly fixed onto the soil particles,and it was largely unavailable to plants,which results in "P deficiency in heredity".Consequently much research has concentrated on the potential to manipulate plants either through conventional breeding of genetic engineering to enhance their capability to mobilize P in soil.Maize was an important grain and forage crop in the world,there were P-efficiency difference among different maize genotypes.Most of cultivated land in acid soil was in heavy P-deficiency,after screen more than 300 maize genotypes in seedling stage with soil culture,and identify some of them in full-life stage with pot culture experiment,we achieved some typical low-P tolerant and Acid-tolerant maize genotypes.In this study, obtained typical lines were selected to research their nutritional characters and physiological mechanism.Meanwhile,three types of low-P soils collected from Hubei province were tested to analyze their inorganic phosphorus fractions after incubated with added various organic acids and different phosphorus sources.The main results of this study were summarized as follows:1.Aluminum(Al) toxicity and phosphorus(P) deficiency often coexist in acid soils that severely limit crop growth and production,including maize.Understanding the physiological mechanisms relating to plant Al and P interactions should help facilitate the development of more Al-tolerant and/or P-efficient crops.In this study,both nutrient solution and soil experiments were conducted to study the effects of Al and P interactions on maize biology and nutrient characteristics.The results demonstrated that P deficiency and acid stress severely hinder the growing of maize.P deficiency had a negative influence on biological traits,especially on plant dry matter weight.Low-P tolerant maize genotypes,had longer roots and larger dry root weight than low-P sensitive maize genotype;and the plant heigh of low-P tolerant maize genotypes were less affected by the phosphorus defficiency than that of sensetive genotypes.Under low phosphorus condition, the ratio of root to shoot in all genotypes increased;uptaking and distribution of P,K,Ca, Mg,Fe,Zn between roots and shoots also changed.Under stress of aluminum condition, the root lengtht and relative dry weigh of Al-tolerant maize genotypes were less affected by the Al toxicity than those of Al-sensetive genotypes.2.Nutrient characteristics of seedling stage were studied for different maize genotypes.The efficiency of P uptake is the main contributor to low-P tolerance.And the P uptake amounts of P-tolerance lines M02,M08 and M11are significantly higher than P sensitive line M05 under low P stress.P deficiency has some influence on the uptake of N, P,K,Ca,Mg,Fe,Mn and Zn at seedling stage.P deficiency restrains the uptake of N and K for the maize.However,it affects less of P tolerant lines than that of P sensitive lines. The P tolerant lines show stronger abilities of Ca,Mg,Fe uptake and accumulation than P sensitive lines.P deficiency decreases concentration and accumulation of Zn in root and shoot of P sensitive lines but increases that of P tolerant lines.Under stress of aluminum condition,accumulation of P,K,Ca,Mg,Fe,Zn was seriously affected,the addition of P could alleviate the toxicities of acid and aluminum.There were genotypic differences in tolerance to low-P and acid stress among different lines.It was also found that there are some relation between low P tolerance and acid tolerance.M12 is sensitive line to both acid-aluminum stress and low P stress;The acid and aluminum tolerant lines M02 and M08 show the same tolerance to low P,whereas the low P tolerant line M01 has some tolerance to acid and aluminum stress,which are tolerant lines of both stress.3.The genotypic differences in response to K,Fe,Zn deficiency of maize with different phosphorus efficiency were investigated in nutrient solution under controlled conditions.K deficiency was significant effect on shoot growth and number of leaves. The genotypic differences existed in response to K deficiency,which decreased the dry weight of shoot in low-P tolerant genotypes more significantly than in low-P sensitive genotypes,and root/shoot ratio of low-P tolerant genotypes sharply droped.The K deficiency was also significant decreased P uptake in root,shoot and the root efficiency ratio,but increased P utilization efficiency,and P uptake in root in P sensitive genotypes more significantly than in low-P tolerant genotypes.Fe deficiency decreased the dry weight of shoot in low-P sensitive genotypes more significantly than in low-P tolerant genotypes.Compared with supplying Fe treatment (+Fe),in-Fe treatment,the P accumulation in shoot and root of low-P sensitive decreased significantly,but was not significant effect on that in low-P tolerant genotypes. The same response to Fe deficiency existed in chlorophyll content between P sensitive genotypes and P tolerant genotypes,the contents of different genotypes in chlorophyll decreased greatly respectively.Shoot of maize appears to be the causative factor of the different phosphorus efficiency genotypes.The genotypic differences existed in response to Zn deficiency,which decreased the content and uptake of Zn of seedling in low-P sensitive genotypes more significantly than in low-P tolerant genotypes.Compared with supplying Zn treatment,in-Zn treatment,the P content in shoot of low-P sensitive genotypes increased significantly than in root;but the P content in root of low-P tolerant genotypes decreased signifecantly than in shoot; the P utilization efficiency in shoot of low-P sensitive and in root of low-P tolerant genotypes decreased respectively.4.Low phosphate availability is one of the major limitations to crop production. Organic acids are a principal component of root exudates and have been hypothesized by many authors to be involved in the mobilization of nutrients within the rhizosphere. Mobilization of insoluble phosphates by root exudates plays an important role in improving P nutrition of crops.The effect of different phosphorus level on dynamic of available phophorus in soils had been studied.At the same time,two maize inbred lines were grown for 15 days in nutrient solution with different phosphorus treatment.The root exudates were collected and added into the three types of soil which had incubated for 95days.The results showed that the available phosphorus content quickly increased by application of different phsphate,and then constantly decreased by time,and were steady after 60 day;and the available phosphorus from acid soil is significant lower than alkali soil and neutral soil.The soil available phosphorus content was extracted by the root exudates of M02 collected under low phosphorus condition significant pronounced with the addition of insoluble phosphate to the deionized soil;and AlPO₄ mobilization by root exudates was significantly higher than Ca₃(PO₄)₂.5.Three types of soils collected from Hubei province were tested to analyze their inorganic phosphorus fractions and content of available P after incubated with added various organic acids and djfferent phosphorus sources.The results indicated that application of phosphorus sources increased content of available P in all soils.On soils of pH value 4.6 and 6.8 the fertilized phosphorus was transformed into Fe-P and Al-P mainly.However,on soil of pH value 8.3 the fertilized phosphorus significant increased content of Ca-P.The release of phosphorus by organic acids from soils is significant, especially Al-P in acid soil and neutral soil,Ca-P in Alkali soil.