Effects Of Nitrogen Froms On Physiological And Root Morphology Of Tomato Seedlings Under Sub-low Temperature

In northern China, sub-low temperature is one of the major factors which severelyrestricts protected vegetables production. Therefore, studying the effects of different forms ofnitrogen fertilizer on the growth and psychological under sub-low temperature conditions isvery important in order to adopt proper application of ammonium nitrate for the optimumproduction of vegetables. In this experiment, the commonly grown tomato variety “Xinong2011” was taken as the experimental material and plants under normal temperature were takenas control treatment. A controlled hydroponic experiment was conducted to determine theeffects of five NO3--N/NH4+-N ratios treatments (100/0,75/25,50/50,25/75and0/100) onphysiological and root morphology of tomato seedlings under normal and sub-lowtemperature conditions. We studied the indicators for growth such as dry weight of root andshoot, root-shoot ratio and root activity in tomato seedling, the dynamic transformation ofsubstances of osmotic such as O2-�'production rate, MDA content, soluble protein contentand proline content adjustment in tomato seedling plant leaves SOD, POD, and CAT ofantioxidant enzyme activities in tomato seedling plant leaves, total root length, total surfacearea, total volume and average diameter of root morphology changes, the content ofchlorophyll, photosynthetic parameters and chlorophyll fluorescence parameters weredetermined in tomato seedling plant leaves, NR and GS of nitrogen metabolism enzymeactivities in tomato seedling plant leaves and roots. The main results are as follows:1.With sub-low temperature stress, dry biomass and root activity decreased significantly,while root-shoot ratio increased, and the tomato seedling plant growth was inhibited. With theincrease of the NO3--N/NH4+-N ratio, the dry biomass and root activity first increased andthen decreased, while root-shoot ratio first decreased and then increased no matter in normaland sub-low temperature. The dry biomass and root activity were the highest at theNO3--N/NH4+-N ratio of75/25, root-shoot ratio was the smallest at the NO3--N/NH4+-N ratioof50/50under normal temperature. The dry biomass and root activity were the highest at the NO3--N/NH4+-N ratio of50/50, root-shoot ratio was the smallest at the NO3--N/NH4+-N ratioof75/25under sub-low temperature. The dry biomass and root activity were the smallest androot-shoot ratio was highest when the NO3--N/NH4+-N ratio of0/100under both sub-low andnormal temperatures.2.As treatment time prolong, O2-·production rate, proline content, soluble protein content,the activities of SOD and POD first increased and then decreased, the content ofmalondialdehyde gradually increased, while the activity of CAT had shown a wavy change.Compared with normal temperature condition, sub-low temperature increased O2-·productionrate, the content of malondialdehyde and proline, the activity of SOD in tomato seedlingleaves, but they reduced the activities of CAT and POD, soluble protein content. Under bothsub-low and normal temperatures, the proportion of NO3--N/NH4+-N ratio of75/25wasfavorable to improve cold resistance to tomato seedling, the NO3--N/NH4+-N ratio of100/0was second, and then along with the increase of ammonium nitrogen proportion in thenutrition, the cold resistance weakened.3.Study indicates that total root length, total surface area, total volume and averagediameter of root morphology show a trend of increase with treatment time prolong. Comparedwith the normal temperature, tomato seedling root growth was inhibited, total root length,total surface area and total volume decreased, while average diameter increased under thecondition of sub-low temperature. With the decrease of the NO3--N/NH4+-N ratio, total rootlength, total surface area and total volume decreased, but the difference was not significantbetween NO3--N/NH4+-N ratio is100/0and75/25under normal temperature. With thedecrease of the NO3--N/NH4+-N ratio, total root length, total surface area and total volumefirst increased and then decreased, the indicates were the highest at NO3--N/NH4+-N ratio is75/25, while smallest at the NO3--N/NH4+-N ratio of0/100under sub-low temperature.4.The content of chlorophyll, Pn, Ci, Tr and Gs of photosynthetic parameters and Fv/Fm,ΦPS, qP, NPQ and ETR of chlorophyll fluorescence parameters decreased significantly, whileWUE, Ls and Fo increased under sub-low temperature. With the increase of theNO3--N/NH4+-N ratio, the trends of chorophyll content, photosynthetic parameters andchorophyll fluorescence parameters are basically the same under sub-low temperature andnormal temperature. These trends could be described with an approximate parabola curve, butthe maximum and the minimum of these indicators appears on the lower NO3--N/NH4+-Nratio under sub-low temperature. Under normal temperature, with the increase of theNO3--N/NH4+-N ratio, Pn, WUE, Fv/Fm, ΦPS, qP, NPQand ETR increased firstly thendecreased, these indicates were the highest at NO3--N/NH4+-N ratio is75/25, while smallest atthe NO3--N/NH4+-N ratio of0/100, and Gs, Ci and Tr decreased, while Ls increased. Under sub-low temperature, with the increase of the NO3--N/NH4+-N ratio, Pn, Ci, Tr, WUE, Gs,Fv/Fm, ΦPS, qP, NPQ and ETR increased firstly then decreased, Pn, WUE, ΦPS, qP, NPQand ETR were the highest at NO3--N/NH4+-N ratio is50/50, and Gs, Gs,Tr and Fv/Fm werethe highest at NO3--N/NH4+-N ratio is75/25.When NO3--N/NH4+-N ratio is0/100, Pn, Ci, Tr,Gs, Fv/Fm, ΦPS, qP, NPQ and ETR were smallest, while Ls and Fo were biggest.5.NR and GS of nitrogen metabolism activities in tomato seedling plant leaves and rootsdecreased significantly under sub-low temperature. Under normal temperature, NR activity inleaves and roots decreased, while GS activity first increased and then decreased with thedecrease of the NO3--N/NH4+-N ratio. GS activity in leaves and roots were the highest atNO3--N/NH4+-N ratio is50/50, while smallest at the NO3--N/NH4+-N ratio of100/0. Undersub-low temperature, both NR and GS activities in tomato seedling plant leaves and rootsincreased firstly then decreased with decrease of the NO3--N/NH4+-N ratio. The NR activity inleaves and roots were the highest at NO3--N/NH4+-N ratio is75/25, while smallest at theNO3--N/NH4+-N ratio of0/100. The GS activity in leaves was the highest at NO3--N/NH4+-Nratio is25/75, and highest at NO3--N/NH4+-N ratio is50/50in roots, while smallest at theNO3--N/NH4+-N ratio of100/0in both leaves and roots.