Response Of Poa Pratensis To Exogenous Calcium Addition Under Salt Stress

Kentucky bluegrass?Poa pratensis L.?is one of the most world-widely used and of great development potential cold-season turf grass in turf and landscape construction in China.The exogenous addition of calcium to enhance the salt tolerance of Kentucky bluegrass in grassland is particularly important for the construction,maintenance and improvement of the quality of lawns and the modifying saline-alkali lands.In this study,14 commercial Kentucky bluegrass varieties were used as the tested objectives,and the experimental scheme shows as follows:1)TP germination method adapted through putting seeds in petri dishes,salt tolerance of Kentucky bluegrass in seedling stage under five kinds of NaCl with different concentration ingredient?0,0.3%,0.6%,0.9%and 1.2%?,respectively.Germination related indexes,root system indexes and comprehensive indexes)were determined to evaluating and screening different varieties with stronger salt tolerance and those sensitive to saline;2)Hydroponics method with 1/2 Hoagland calcium-free nutrient solution was adopted to explore the root system indexes?root length,root surface area,and root volume,etc.?and calcium absorption characteristics?kinetic parameter equation and calcium absorption rate?in early seedling stage for varieties with different salt-tolerance screened previously.Then the appropriate calcium ion concentration will be determined through the above-mentioned trials;3)Potted plants in PVC pipes grown in glasshouse was combined,the effects of additional calcium1.0mmol/L,5.0 mmol/L and 10 mmol/L CaCl₂ with 0 as control on the growth and physiological response in Kentucky bluegrass were researched under 0.6%NaCl concentration.More salt tolerant Kentucky blue grass strains to saline-alkaline soil and the most suitable calcium chloride concentration extra applied under salt stress were attempted screened.The research contents and achievements of this dissertation are as follows:?1?Salt tolerance related indexes of Kentucky bluegrass decreased in a great margin under 0.6%NaCl,of which was considered as the suitable concentration for salt tolerance identification for Kentucky bluegrass at seedling stage.Salt tolerance of Kentucky bluegrass is closely related to its germination rate,vigor index,total root length,average stem diameter,seedling height,root length,seedling fresh biomass and ratio of shoot to root.According to the principal component analysis,the weights of the three principal components are 0.616,0.216,and 0.168,and the cumulative contribution rate of the salt tolerance coefficient of all indexes was 84.263%.The salt tolerance of 14 Kentucky bluegrass varieties was evaluated by membership function methods,the results showed that the stronger salt tolerance Kentucky bluegrass varieties were:'Blue Swan','Merit',meanwhile,the poorer salt tolerance were'Blue chip','Leopard'and'Blue moon'.?2?Calcium ions absorption characteristics of different Kentucky bluegrass varieties under different salt-tolerant conditions conformed to the enzyme kinetic model.The absorption rate for calcium ions was higher in the strong salt-tolerant'Merit'than that in the salt-sensitive cultivar of'Golden Leopard';The Ca²⁺absorption rate in'Merit'and'Leopard'increased with the increase calcium level rising,and reached to its maximum value at 10 mmol/L CaCl₂,which were 1.22?mol·dm^-2·h^-1and 0.87?mol·dm^-2·h^-1,respectively.The absorption rate for calcium ion of Kentucky bluegrass increases firstly and then decreases with the increase of time and reaching a peak at 36 h.The root length,root surface area,and root volume of'Merit'and'Leopard'are mainly distributed in the root diameter ranges of 0.5 to 1.0 mm,1.5 to2.0 mm,and 1.5 to 2.0 mm.Under 0.6%NaCl condition,extra application of 2.5mmol/L exogenous calcium significantly increased the leaf surface area and its length,the total length and surface area of roots and its number.Application of 5.0 mmol/L exogenous calcium leaf length/width,individual stem thickness,total root length,root surface area and average shoot diameter,and number of roots significantly increased in the'Leopard'compared to control.?3?Under 0.6%NaCl stress with additional application of 2.5 mmol/L of exogenous calcium chloride,the relative moisture content,proline content,soluble sugar concentration in leaves,and root vigor in'Merit'significantly increased,and while electrolytic permeability and malondialdehyde Content in vivo significantly reduced;extra application of 5.0 mmol/L of exogenous calcium,the relative water content,cumulative proline content,soluble sugar content and root vigor increase significantly in the'Leopard',meanwhile reduced its electrolytic permeability and malondialdehyde contents remarkably.Under NaCl stress,the K⁺and Ca²⁺contents and the K⁺/Na⁺and Ca²⁺/Na⁺ratios in Kentucky bluegrass in different salt-tolerant types were reduced,and help to increasing Na⁺contents.The ratio of Ca²⁺/Na⁺in roots was greater than that in the stems.Appropriate application of exogenous calcium chloride can increase the uptake of K⁺and Ca²⁺by Kentucky bluegrass;under the extra addition of 2.5 mmol/L CaCl₂,the absorption rate for K⁺and Ca²⁺in'Merit'increased highest,and under 5.0 mmol/L CaCl₂,K⁺and Ca²⁺absorption area in the'Golden Leopard'increased to maximum value.