Study On N Accumulation And Physiological Characteristics Of Mining Ecotype Of Polygonum Hydropiper At Different N Treatment

The large quantity use of nitrogenous fertilizer and livestock manure emission in soils usually causes excessive N flow into water following runoff and leaching, thus raising water eutrophication process. Plant-assisted approaches are proven to be an efficient strategy for extracting excess nitrogen (N) from N-enriched water. Studying N accumulation characteristics of plant can provide a theoretical basis for its application. Previous study indicated that the mining ecotype (ME) of Polygonum hygropiper possessed greater removal capability of N from water than that of the non-mining ecotype (NME). In this study, pot experiments were carried out to investigate the effect of N application on N accumulation and distribution, enzymes activity of nitrogen assimilation, photosynthetic characteristics and root morphology of the ME, with the NME as control. The relationship between physiological characteristics and N accumulation was also elucidated in this study. The following is a summary of the results.(1) The biomass, N accumulation and N accumulation rate of the two ecotypes of P. hygropiper increased to the N level of 150 mg kg-1 with the increasing N application. The biomass of P. hygropiper increased with the growth periods, while the N content of P. hygropiper decreased. The maximum N accumulation and N accumulation rate of P. hygropiper were observed at the 12th week and 8th week, respectively. The N content, N accumulation and N accumulation rate of the ME was higher than those of the NME. The ME showed greater N accumulation capability than the NME. N distribution proportion in stems and leaves of P. hygropiper increased with the increasing N application, and accounted more than 85% of the whole plant. The N distribution proportion in leaves of the ME was 1.04?1.20 times greater than that of the NME. These results indicated that N mainly accumulated in the aboveground of P. hygropiper, and the N accumulation in the aboveground benefited from the N application. The great N accumulation of the ME was owing to the large N distribution proportion in leaves. In addition, structural nitrogen was the main N fractions in plant tissues. The proportions of structural nitrogen in roots, stems and leaves were 81.20%?88.81%,73.39%?81.12% and 79.49%?86.62%, respectively. The proportions of structural nitrogen in tissues of the ME were 1.03?1.22 times greater than those of the NME. The great proportions of structural nitrogen in plant represent great assimilation and reuse ability of N, which may be one of the reasons of the great N accumulation ability of the ME.(2) The maximum enzyme activities related to N metabolism in roots and leaves of P. hygropiper were noticed at the 8th week with the optimal N application of 150mg kg-1. The activity of nitrate reductase, glutamine synthetase and glutamate synthase in leaves of P. hygropiper were 1.94?2.57,1.97?2.33 and 1.41?1.81 times greater than those in roots. The nitrate reductase, glutamine synthetase and glutamate synthase activities in roots and leaves of the ME were 1.15?1.59,1.08?1.40 and 1.21-1.44 times significantly greater than those of the NME. All enzyme activities had significant positive correlations with the N accumulation increment among growth periods. The ME showed greater N assimilation ability than the NME, thus possessed greater N accumulation ability.(3) With the optimal N application of 150mg kg-1, the SPAD and net photosynthetic rate of P. hygropiper increased with the growth periods to the 8th week, and then there was a sharp decrease was observed in the 10th week. The SPAD of the ME and NME decreased by 16.22% and 22.15%. The net photosynthetic rate of the ME and NME decreased by 54.63% and 47.79%. The two ecotypes of P. hygropiper showed greater photosynthetic capacity in the 8th week. The net photosynthetic rate of P. hygropiper was dominantly influenced by stomatal limitations before the 10th week, beyond which the net photosynthetic rate of P. hygropiper was induced by non- stomatal limitations. The decrease of N content in plant may cause reduce of photosynthetic rate. The SPAD and net photosynthetic rate of the ME were 1.20?1.30 and 1.09?1.26 times significantly higher than those of the NME. SPAD showed a positive correlation with the N accumulation increment among growth periods. The ME showed greater photosynthetic ability than the NME, thus possessing greater N assimilation ability and N accumulation ability.(4) The parameters of root morphology and root activity increased with the increasing N application to 50mg L-1. Therefore,50mg L-1 was the optimal N application concentration for the root growth and development of P. hygropiper. The lateral root length of P. hygropiper accounted 70%?79% for the whole root length at different N applications, indicating that lateral roots played an important role in the root growth of P. hygropiper. The whole root morphology parameter, lateral root morphology parameter, root activity and N accumulation of the ME were significantly greater than those of the NME. There was no significant difference between the adventitious root morphology parameter of the two ecotypes. These results indicated that the difference of lateral root was the main reason for the difference of whole root growth of P. hygropiper. The ME possessed much more lateral root and higher root activity, thus providing better root system for N uptake than the NME.