| Kentucky bluegrass(Poa pratensis L.)is a perennial cold season turf grass species with green leaf color having attractive leaf and plant shapes generally used for home lawns,golf courses and athletic fields.Temperatures at optimal range of 18 to 24 °C along with adequate amount of water and proper nutrient management it forms an attractive turf,nevertheless rapidly loses color,becomes thin,and goes dormant during period of prolonged water stress situations.In northern China arid and semi-arid regions,temperature often approach 38 °C or higher during summer months,water scarcity causes great amount of soil nitrogen losses,therefore drought stress and poor nutrient management are the two key limitations for growth and quality of Kentucky bluegrass.Hence,quick and efficient recuperation from drought stress may be amongst the key determinants of plant drought adjustment.Efficient nitrogen(N)nutrition has the capability to assuage water stress in crops by sustaining metabolic activities even at reduced tissue water potential.The present study was designed(1)to identify mechanisms between the morphogenesis and the plasticity of growth and development at the colonial strains level by studying the morphological plasticity,growth and development,and assimilation of nitrogen in Kentucky bluegrass colonial ramets under drought stress(2)to investigate antioxidant enzymes activities,nitrogen assimilation strength,transportation directions,and scope at the colonial strains level by studying the nitrogen assimilation and other nutrient transportation pattern affected by the environmental stress and adaptation and also to provide theory basis for developing and improving Kentucky bluegrass cultivars.Field as well as pot experiments were conducted in the Northeast Agricultural University Horticulture Experimental Station during growing seasons June to October of 2014 and 2015.In field experiment different water and nutritional conditions of soil(nutritional soil with full and less water;sand with full water and less water)after planting,forming one heterogeneous habitat(designated by(A)NS+NS-SS+SS-),and four treatments homogenous habitats(designated by(B)NS+NS+NS+NS+,(C)SS+SS+SS+SS+,(D)NS-NS-NS-NS-and(E)SS-SS-SS-SS-)each with four replications were examined.While in indoor experiments,nitrogen isotope labeled15NH4 Cl and K15NO3 was prepared to replace the KNO3 in the Hoaland solution with the concentration of 15NH4+ and 15NO3 of 30,15,and 1.5mM and their influences were studied on both roots and leaves of Kentucky bluegrass clonal ramets under drought stress.Most of the data were recorded at early stages of plants.The main results are as follows.(1)The research results revealed that drought stress exhibited significant reduction in nitrogen contents of both mother(22-72%)and first ramet(72-99%),maximum radius(40-91%),above and below ground mass(40-75%),number of ramets per plot(7-16%),leaf water contents(1-58%)and water potential(3-66%)but to increase the carbon contents(7-15%)and C:N ratio(36-64%)in both homogenous and heterogeneous plots.The observation under 1000 times the transmission electron microscopic study showed that drought stress shrink the vessel diameter,circumference and xylem area,but increased the sieve diameter,and phloem area of the leaf crosscutting structure of Kentucky bluegrass,first,second and third ramet leaf.Under the habitats of the same water supply and different substrate conditions,vessel diameter and circumference were smaller in nutrition soil,while the sieve diameter and xylem areas were increased.Nutrition soil assuaged the adverse effect of drought stress up to larger extent and NS+ and A(NS+)followed by NS-and A(NS-)were found the best than other treatments all plots of outdoor experiment.It can thus be concluded that nutritional soil with proper water management are significant for enhancing the Kentucky bluegrass performance under drought conditions and may be considered in formulating good feasible and cost-effective practices for the environmental circumstances related to those of this study.(2)The results of indoor experiments showed that applying nitrogen influenced the cell physiological matebolism of Kentucky bluegrass significantly during drought periods.Enhancing the amount of NH4 Cl and KNO3 reduced the adverse affects of drought.Nitrogenous nutrition reduced oxidative stress by elevating the activities of superoxide dismutase(SOD)(3-66%),peroxidase(POD)(0.5-39%),catalase(CAT)(2-38%)and proline(4-49%)contents of all the three clonal ramets leaves particularly under stress conditions.Nitrogen isotopes abundance(9-81%),nitrogen content(9-54%),relative water content(0.1-35%)and water potential(18-66%)were enhanced in both root and leaves of Kentucky bluegrass under control conditions.Nevertheless,application of 15NH4 Cl and K15NO3 at 30 mM had a positive influence up to some extent on these attributes under drought stress in the indoor experiment.Overall,our results suggested that nitrogen isotope contributed to drought tolerance in all the three clonal ramets of Kentucky bluegrass by maintaining better osmoprotectant and antioxidant defense system which helped the plants to eliminate reactive oxygen species(ROS).Nitrogen contributed to drought tolerance in all the three clonal ramets of Kentucky bluegrass by maintaining better osmoprotectant and antioxidant defense system which helped the plants to eliminate reactive oxygen species,and to enhance the integrity of cellular membranes and enabled the plant to sustain general metabolism during growth periods.In addition,manipulation of these nitrogen isotopes through genetic or biotechnological ways may consequence in the improvement of drought tolerance in grasses. |
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