| Cotton(Gossypium hirsutum L.)is a strong salt-tolerant crop species.However,there is little research on how root growth of cotton respond to phosphorus(P)supply,salinity level and colonization by arbuscular mycorrhizal fungi(AMF).The microcosm and field experiments were performed to study the responses of cotton cultivars released in different years(1950s,1970s,1980s and 2000s)to soil salinity,localized P application and the mycorrhizal colonization as importent objective improving the salinity resistance and yield of cotton by rhizosphere phosphorus regulation in this thesis.The effects of P application by drip irrigation on the fiber yield of the cotton were also investigated.Based on the above studies,the theoretical basis and technical support to improve P use efficiency and the yield of cotton were proposed.The main results were as followed:(1)The fine roots predominated in the cotton root systems,in terms of length.The root length of the diameter d<0.2 mm was more than 60%of the total root length,and the root length of the diameter d<0.4 mm was more than 90%of the total root length.Phosphorus supply intensity and salinity had significant effects on the cotton aboveground biomass,the cotton boll biomass,the plant height,the flowering time,the absorption of phosphorus(P),potassium(K),and sodium(Na)of cotton cultivar released in 1950s-2000s.Phosphorus supply intensity had no significant influences on root dry weight,root length,root average diameter,lateral root length and root length distributed in different soil layers.The effect of phosphorus application increased aboveground biomass,phosphorus uptake,and promoted root growth,and improved the plant phosphorus and potassium absorption and utilization.(2)Salt stress reduced the proportion of fine root length in total root length,but the effect of P application had little effect on fine root ratio.When 2 g·kg-1 NaCl was added,salt stress inhibited the fine roots(d?0.4 mm)and coarse roots(d>0.8 mm)of different varieties of cotton.Phosphorus application had significant influence on the fine roots(d?0.4 mm)distribution in the 0-20 cm soil layer of the early cotton varieties Xinluzao 1 and 2,but no significant effect was noted under salt stress.The sensitivity of different cotton varieties to P addition under different salt stress conditions was different.The effect of P application on Gossypium hirsum L.dry weight and P uptake of salt-tolerant variety SuK202 was significantly higher than that of Xinlu series.The cotton cultivars release in late years had relatively strong resistant ability to salt stress,but the sensitivity of them to P was week.(3)The P heterogeneity in the root layer in the vertical distance had significant influences on the aboveground growth of cotton,the growth and distribution of roots,and leaf and stem P uptake.Phosphorus supply in surface layer soil is more favorable for improving cotton growth.By simulating the P heterogeneity in three soil layers:0-16.7 cm(top soil layer),16.7-33.4 cm(middle soil layer)and 33.4-50 cm(subsoil layer),it was noted that increasing the P supply in top soil layer could stimulate root growth of cotton,aboveground biomass.The root length was mainly distributed in the 16.7-33.4 cm soil layer,and the salt stress transferred more root system distribution proportion to the surface layer of 0-16 cm soil.Increasing the phosphorus application in top soil(0-16.7 cm)had a significant effect on improving the salt tolerance of cotton and promoting cotton growth at the seedling stage and improving the biomass.This result showed that phosphorus supply in top soil plays a key role in taking up phosphorus for cotton at the seedling stage.Therefore,appropriate phosphorus-containing fertilizer supplement to seed contributes to the growth and development of cotton seedling in saline-alkali land.(4)Indigenous AMF communities significantly enhanced growth of cotton plant and root system in the seedling stage,whereas mycorrhizal effects were decreased by increasing salt concentration.Using vibration or holding static PVC pipe in-growth system method,the cotton plants with high infection(static PVC)and low infection(vibrating PVC)were obtained under salinization field conditions,and the indigenous AMF significantly increased growth,P concentration;proline concentration of the top tourth leaf and soluble sugar concentration in roots was significantly higher than that of cotton in the vibration treatment,respectively.The total leaf area,root biomass and K concentration in leaves were higher than that of vibration treatment,and Na concentration was lower than vibration treatment.The effect of indigenous AM fungi on cotton was higher than that of high salinity soil under low salinity conditions,so cotton production in saline-alkali land,developing the function of indigenous AM fungi can help cotton resistance to salt and increase production.(5)Field experiment results showed that cotton biomass and yield were not affected by P fertigation.Effect of potassium dihydrogen phosphate fertigation by drip irrigation with solution in the rhizosphere for cotton growth is studied,for cotton seedling and boll period respectively in low and extreme salinity soil.Results show that potassium dihydrogen phosphate fertigation have no significant effect on cotton growth and fiber yield(respectively supply one time in seedling and boll period).The main conclusions were as follows:root length of cotton was mainly rooted in fine roots,and percentage of fine roots with diameter less than 0.4 mm is the largest,90%.About 85%of the root length of cotton was distributed in soil layer with depth 0-40 cm soil layer.Phosphorus application could promote the development of fine roots in 0-20 cm soil layers.The major proportion of fine roots and the residues of coarse roots were significantly inhibited by salt stress;however,phosphorus facilitated the cotton seedlings salt tolerance with the exception of roots.Increasing P supply concentration in surface layer soil played an important role in facilitating cotton salt resistance in field experiment.The indigenous AM fungal community played a significant role in promoting cotton resistance to salt stress. |
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