The Influence Of Different Nitrogen, Phosphorus And Potassium Level On The Growth Of Sweet Sorghum Under Salt Stress

In pot experiment, seedlings of sweet sorghum [Jitianza 2 （hybrid）] were supplied withdifferent nitrogen levels (0.1 mmol·L^-1, 2 mmol·L^-1, 5 mmol·L^-1, 10 mmol·L^-1), phosphoruslevels(0.1 mmol·L^-1, 0.2 mmol·L^-1, 0.6 mmol·L^-1, 1 mmol·L^-1) and potassium levels(0.1mmol·L^-1, 3 mmol·L^-1, 6 mmol·L^-1, 9 mmol·L^-1) to study their growth under salt stress （0.6%NaCl） in order to confirm appropriate nitrogen, phosphorus and potassium level in salt stress,and to provide theoretical foundation for reasonable application of fertilizer in production. Theexperimental results were as follows:1 The effect of different nitrogen levels on the growth of sweet sorghum in salt stressUnder different nitrogen concentrations, the growth of sweet sorghum was all inhibited by0.6% NaCl. Yet with the increase of nitrogen level, sweet sorghum grew better, wherein, it wasthe best when the nitrogen level reached 5mmol·L^-1. With the increase of nitrogen concentration,the net photosynthetic rate of sweet sorghum （Pn）, transpiration rate （Tr）, stomatal conductance（Gs）, the maximum photochemical efficiency （PHI（Po））, driving force with absorption of lightenergy as basis （D.F.）, number of reaction center on unit leaf area （RC/CSm）, the size of PQbank measured by acceptor of PSâ…¡reaction center（Sm）,actual photochemical efficiency（ΦPSII） and photochemical quenching rate（qP） all took on an upward trend, and basically theeffect was the best when the nitrogen level was 5mmol·L^-1, while no evident promting effectwhen in 10 mmol·L^-1nitrogen treatment and it even had counteractive effect on some indicators;while heat dissipation on unit leaf area（DIo/CSm）, closure level of activated reaction center （Vj）,leaf MDA content and leaf relative conductivity take on a downward trend and the value was thelowest at 5 mmol·L^-1, while it increased on the contrary at 10 mmol·L^-1nitrogen level;intercellular CO2concentration （Ci） decreased gradually and becams the smallest at 10mmol·L^-1.In the treatment under the same salinity, with the increase of nitrogen level, the Na⁺content in root and shoot was the lowest at 5 mmol·L^-1nitrogen level; in none-salt treatment, with theincrease of nitrogen concentration, the K⁺content in shoot under 5 mmol·L^-1nitrogen level wasthe highest, while the K⁺content in root was the lowest; in 0.6% NaCl treatment, with theincrease of nitrogen level, the K⁺content in shoot increased significantly, on the contrary, the K⁺content in root decreased significantly, and it took the most advantages when in 5 mmol·L^-1and10 mmol·L^-1nitrogen treatments. It indicated that the increase of nitrogen concentration canmaintain large quantities of Na⁺to gather around the root meanwhile promote transportation ofK⁺from the root to the shoot. Based on the indices we gathered, the appropriate nitrogen levelfor the growth of sweet sorghum in salt stress is 5 mmol·L^-1.2 The effect of different phosphorus levels on the growth of sweet sorghum in salt stressWith the increase of phosphorus level, seedlings of sweet sorghum grew better and better,and best when the phosphorus level reached 1 mmol·L^-1; in the same salinity, with the increaseof phosphorus concentration, Pn, Tr, Gs, PHI（Po）, D.F, RC/CSm, Sm,ΦPSII and qP all took onan upward trend, and the effect was the best when the phosphorus level was 1 mmol·L^-1; whileDIo/CSm, Vj, leaf MDA content and leaf relative conductivity take on a downward trend and thevalue was the lowest when phosphorus level was 1mmol·L^-1; Ci decreased gradually and itbecame the smallest when the phosphorus level reached1 mmol·L^-1.As a whole, the Na⁺content in root was higher than that in shoot; while the K⁺content inroot was higher than that in shoot in none-salt treatment but a little bit less in the root than in theshoot in 0.6% NaCl treatment. Under 0.6% NaCl treatment, The Na⁺contents under allphosphorus levels were all significantly higher than those under 0% NaCl, both in the root and inthe shoot, while the K⁺content in both root and shoot were lower than those under 0% NaCl. In0.6% NaCl treatment, the Na⁺content in shoot in 0.2 mmol·L^-1, 0.6 mmol·L^-1and 1 mmol·L^-1phosphorus treatment is significantly lower than that in 0.1 mmol·L^-1phosphorus level treatment,while the change of Na⁺in root was not obvious. It proved that the increase of phosphorus levelwas beneficial to sweet sorghum to prevent the transportation of Na⁺to the shoot. Under thesame salinity treatment, the K⁺content in root and shoot had no significant difference in 0.2mmol·L^-1, 0.6 mmol·L^-1and 1 mmol·L^-1phosphorus treatments, which proved that the increaseof phosphorus level has little effect on sweet sorghum’s absorption of K⁺. Considering the resultswe determined, the appropriate phosphorus level for the growth of sweet sorghum in salt stress was 1 mmol·L^-1.3 The effect of different potassium levels on the growth of sweet sorghum in salt stressWith the increase of potassium level, the growth of sweet sorghum became better and bettergradually, and best when the potassium level reached 6 mmol·L^-1and 9 mmol·L^-1,and there wasno obvious difference between 6 mmol·L^-1and 9 mmol·L^-1. In the same salinity, with theincrease of potassium concentration, Pn, Tr, Gs, PHI（Po）, D.F, RC/CSm, Sm,ΦPSII and qP alltook on an upward trend, and basically it was the best when the potassium level was 6mmol·L^-1and 9 mmol·L^-1; Sm under salt stress was the highest in 6 mmol·L^-1potassium level;while DIo/CSm, Vj, leaf MDA content and leaf relative conductivity took on a downward trendand the value was the lowest when potassium level was 6 mmol·L^-1and 9 mmol·L^-1; DIo/CSm insalt stress was the lowest in 6 mmol·L^-1potassium level.Under different salinity treatment, the Na⁺content in root was higher than that in the shoot;while the K⁺content in root was higher than that in shoot in 0% NaCl treatment, and just theopposite in 0.6% NaCl treatment except in 0.1 mmol·L^-1potassium treatment; with the increaseof potassium level, the Na⁺content in shoot first increased and then decreased, and the lowestvalue appeared at 6 mmol·L^-1and 9 mmol·L^-1potassium level. Furthermore, the Na⁺content inroot at 6 mmol·L^-1and 9 mmol·L^-1potassium level was significantly higher than that in otherpotassium levels; meanwhile, in 0% and 0.6% NaCl treatments, with the increase of potassiumlevel, the K⁺contents in both root and shoot increased; the K⁺content in shoot was the highestwhen in 6 mmol·L^-1and 9 mmol·L^-1potassium treatment and there was no obvious differencebetween them; In 0% NaCl treatment, the K⁺content in the root under 9 mmol·L^-1potassiumwas the highest, while in 0.6% NaCl treatment, the value is 3 mmol·L^-1potassium and no furtherincrease was found with the increase of potassium level; it indicated that the increase ofpotassium application can increase sweet sorghum’s absorption of potassium so as to absorb lessNa⁺. Based on results we measured, the appropriate potassium level for the growth of sweetsorghum in salt stress is 6 mmol·L^-1.