Effects Of Split-root Salt Treatments On Yield And Root Responses In Maize

The experiment was carried out in the Maize Technological Innovation Center in the Yellow River Basin and the Huaihe River Basin and in the States Key Laboratory of Crop Biology from2010to2011. This study used the technology line of integration of pot experiment in the field and physiological and biochemical experiments indoor. We studied the effects of split-root salt treatments on maize (ZD958and DH9) under several concentrations of NaCl. The contents of study included yield, grain quality, phytosynthesic performance, osmotic adjustment, antioxidative system, soil enzymes, root morphology and physilogical characteristics. The results summaries were as follows:1Effects of split-root salt treatements on yield, grain quality in maizeBiomass and grain yield had similar changing rule with salt treatments:At the lowest salt concentration (W1or N1), it enhanced these yields. When it came to higher NaCl concentrations, biomass and yield decreased significantly. When NaCl concentration reached to102mM, the growth of maize had been seriously inhibited and dry matter accumulation was very low, and plant could not flowering, even to death.Excision partial root significantly increased maize yield and growth when irrigated with tap water or34mM NaCl solution. When irrigated with moderate NaCl solutiion, the yield of maize with partial root pruned was not different from whole-root maize or lower than that. And high NaCl treatments had no yield. Excision partial root siginificantly improved the protein contents of maize grain when irrigated with tap water or lower concentration NaCl solution.Unequal salt stress siginificantly improved maize growth than equal salt stress, and got higher yield than the control. The contents of seed starch were increased in unequal salt treatments, and the contents of protein and fat were changed with the cultivar and the salt solution.2Effects of split-root salt treatments on phytosynthetic characteristics in maizeExcision partial roots significantly affected phytosynthesic characteristics in maize, specifically as follows:When irrigated with tap water or lower concentration of NaCl solution, excision partial root increased chlorophyll contents, improved the net photosynthetic rate, somatal conductivity, transpirition rate, ΦPSⅡ, qP and increased dry matter accumulation in maize postanthesis; when irrigated with moderate and high NaCl solution, the photosynthetic performance of maize with partial root pruned was inhibited; chlorophyll contents and leaf area both decreased, photosynthetic rate, transpiration rate, stomatal conductivity reduced, dry matter weights had little difference or slightly smaller than whole-root maize.Unequal salt treatments significantly increased chlorophyll contents, photosynthetic rate, transpiration rate, stomatal conductivity,ΦPSⅡ, qP, and intercelluar CO2concentration, while NPQ were decreased. After big flare phase, leaf area significantly higher than control and dry matter accumulation were more.3Effects of split-root salt treatments on osmotic adjustment and antioxidative system of maize3.1Effects of split-root salt treatments on osmotic adjustment of maizewhen irrigated with tap water or low NaCl solution, WP, contents of K+, Ca2+, proline, soluble sugar, ascorbic acid of leave in maize with partial root pruned significantly increased than the control; and Na+and Cl-contents in leave significantly lower than the control. So excision partial root induced the ability of osmotic adjustment in maize when irrigated with tap water and low NaCl solution. Cultivar DH9has the more osmotic adjustment ability than ZD958.Unequal salt treatments improved water uptake and the concentration of K+, Ca2+, GB, and Pro, which induced shoot and roots growth. Inorganic ions were the main contributors in unequal salt treatments for the long-term tolerance to the salt stress, and K+and Ca2+were the primary inorganic ions, which were very important in osmotic adjustment, especially maintaining the high K/Na and Ca/Na ratios. Organics played a relatively minor role in osmotic adjustment, whereas in those GB and Pro played larger roles, followed by SS.3.2Effects of split-root salt treatments on antioxidant system of maizeMDA contents in maize with partial root pruned were lower than whole-root maize when irrigated with low NaCl solution, and were undifferent when irrigated with tap water. When it came to moderate and high NaCl, the contents of MDA in pruned-root maize were significantly higher than the control. After big flare stage, SOD and POD activity of pruned-root maize leaves significantly higher than whole-root maize when irrigated with tap water and low NaCl solution. APX and GPX activity presents different rules at different stages. MDA contents in unequal salt treatments maize leaves were all lower than control at three stages, only at milk-ripe stage, MDA contents of U1and U2in ZD958slightly larger than the control.Three enzymes which responsible for the removal H2O2play different role at different stages:at big flare stage, POD and APX played the main role in unequal salt treatments, at anthesis stage, POD, GPX and APX together played the role; at milk-ripe, APX activity was lower than control, POD and GPX played the main role.4Effects of split-root salt treatments on rhizosphere soil of physiological and biochemical indictors of maize4.1Effects of split-root salt treatments on rhizosphere soil conductivity and ion accumulation in maizeExcept for tap water, at different stages, soil conductivity, contents of Na+and Cl-in pruned-root maize irrigated with three different salt concentration were significantly higher than control. In unequal salt treatments, the soil conductivity of root part irrigated with tap water were increased with the increase of the salt concentration that irrigating the other root part. This reflected a translocation of mineral elements from one root part to the other. Because irrigated with different concentration salt solution, Na+and Cl-contents in the two root parts were different. Except for high salt solution, Na+contents in two soil parts were little different.4.2Effects of split-root salt treatments on soil enzymes activities in maizeThe rule of soil urease activity was little different in two maize cultivars:at jionting and big flare stage, urease activity of ZD958rhizosphere soil were lower than the control, and after anthesis, the condition was the reverse; at jionting stage, urease activity of DH9rhizosphere soil were lower than the control, but after big flare stage, the condition was the reverse. With salt solution increased, soil catalase activity firstly increased and then decreased. The soil catalase activity change of two cultivars presents the same trend:at jionting stage, catalase activity in pruned-root maize rhizosphere soil was lower than the control, after big flare stage, the condition was the reverse. After anthesis, sucrase activity of pruned-root rhizosphere soil was higher than control. And the change rule of two cultivars was the same.Urease activity in two soil parts irrigated with different salt solution were significantly different, and the differnet was more when salt concentration was biggest in two soil parts. The urease activity of soil irrgated with tap water was significantly higher than the other soil part irrigated with salt solution. The change rule of sucrase and catalse activity was the same as urease activity. 5Responses of root to split-root salt treatments in maize5.1Responses of root to pruned-root salt treatments in maizeThe roots of pruned-root maize appeared compenstory growth, the root number, root area, root tips, root volume, whole root length, root activities and antioxidative enzymes activities increased, maize biomass and yield induced, grain quality improved, Na+and Cl-contents in plants decreased, photosynthesis performance improved, and the tolerance of NaCl also impoved when maize irrigated with tap water and low salt concentration solution.5.2Responses of root to unequal salt treatments in maizeUnequal salt treatments induced growth of maize root:root volume, root number, root tips, root area, root length and root activities increased, root antioxidative enzymes activities improved, MDA contents decreased, the salt damage in cell of root hair zone were less than the control. So unequal salt treatments alleviated high salt stress, induced maize growth and got higher yield.