Study On Biological Nitrogen Fixation Of Red Paddy Soil In Nanping And Quanzhou,Fujian

Biological nitrogen fixation(BNF)plays an important role in nitrogen cycle system.Therefore,in order to investigate the nitrogen fixation of typical paddy soil in Fujian province and its effect factors,two paddy soils were selected as the different research objects,soil(A)from Pucheng County in Nanping and soil(B)from Yongchun County in Quanzhou.The field in-situ growth chamber and outdoor nature incubation with rice plant growth were carried out.Combined with 15N2 labeling technique and acetylene reduction method(ARA),the study was carried out on studying the nitrogen fixation amount,soil nitrogen-fixing nitrogenase activity and factors influencing them.The results showed that:The paddy soil from different location and planting conditions would affect the nitrogen fixation.Under the conditions of rice planting,there was no significant difference in biological nitrogen fixation between soil A and soil B.Soil A has stronger nitrogen-fixing ability than soil B.However,the BNF in unplanted soil was far below than that of planting soil,and planting rice could equiped the soil with stronger nitrogen fixation ability.The higher NH4+-N content consisted,the more amount of ethylene produced.The decrease of inorganic nitrogen in soil with rice planting didn’t increase the ethylene production rate,but a significant positive relationship between ethylene production rate and soil soluble organic carbon was observed.The high available phosphorus content in B soil did not increase the ethylene production rate.The results of 15N2 labeling showed that the 15N abundance of root and soil of layer 0-1 cm was higher than that in the aboveground part of rice and soil below layer 1cm.The 15N abundance of samples under 15N2 labeling condition was higher than the natural abundance of samples.However,the fixed nitrogen content was high in aboveground plant and soil below layer 1 cm because of the large dry mass of them,and the fixing amount of nitrogen in soil was more than that in plant.The effect of gradient molybdenum(Mo)and phosphorus(P)nutrient addition on nitrogen fixation in paddy soil was not more and better,and the effects of nutrients coexist on the nitrogenase activity were different.Paddy soil with high concentration of Mo(100×Mo)and low concentration of P(10×P)were more conducive to nitrogenase activity.Higher P content(100×P)would inhibit the nitrogen fixation rate.The addition of Mo allone could improve the activity of soil nitrogenase activity.The higher the Mo concentration was.the stronger nitrogenase activity was.Whereas,when both Mo and P were added,the activity of nitrogenase appeared to be restricted.And the higher concentration of P added,the weaker nitrogenase activity occurred.The addition of carbon(C)could improve the ability of biological nitrogen fixation,especially in the soil without both Mo and P.High concentration of iron(Fe)enhanced the nitrogen fixation in soil.The addition of ammonoium nitrogen(NH4+-N)did not inhibit soil nitrogen fixation.but it was more beneficial to the biological nitrogen fixation in soil with high Mo contentUnder different nutrient addition with rice planting conditions,soil with carbon addition and their interaction accelerated the ethylene production rate.The incubation with rice increased the ability of photosynthetic nitrogen fixation.Nitrogen-fixing microbes absorbed nutrient elements from soil,which promoted the biological nitrogen fixation better.Addition of carbon at the booting stage of rice would accelerate the stimulation of Mo effect,and the nitrogen fixation rate would reach the peak value.The effect of nutrient elements on nitrogen fixation changed with different rice growth stage.Under normal illumination,the plant stomatal opening with photosynthesis enhancement,might increase photosynthetic nitrogen fixation capacity.The nutrient element were mainly absorbed by the root and transported to the plant organization and accumulated at the root,therefore,therefore,15N abundance in root was very high.However,shading condition caused stomatal closure and blocked the transport of organic matter.Thus,nutrients exchange between organizations was abated,as well as biological nitrogen fixation.The ability of heterotrophic nitrogen fixation was increased under waterlogging conditions.The free movement of microorganisms in the water layer made the thickness of the water layer less affected the soil nitrogen fixation microorganisms.Whether stormatal switch on or off seemed have different effect on nitrogen fixation in all parts of plants,but there was no significant difference in whole plant.The 15N abundance of leaves and stems were low in the normal illumination.It is also not obvious that the thickness of water layer had influence on soil biological nitrogen fixation.