Research On Physiological Mechanism Of Ammonium And Nitrate Response Difference Between Phyllostachys Edulis And Castanopsis Fargesii Franch Seedlings

Phyllostachys edulis and Castanopsis fargesii Franch are common plants in subtropical regions of China.In recent years,P.edulis have rapidly expanded to surrounding evergreen broad-leaved forests and coniferous and broad-leaved mixed forests,and the niche of C.fargesii has been gradually replaced by P.edulis.Previous studies have shown that P.edulis expansion causes changes in the N cycle and N mineralization processes of the soil,soil after expansion is dominated by ammoniating,the content of available phosphorus and available potassium was significantly reduced,and both P.edulis and C.fargesii prefer ammonium nitrogen.In order to further explore the nutrition control strategies of habitat for the expansion of P.edulis,in the controlled environment,this paper studied different factors between the seedlings of P.edulis and C.fargesii,which include the relationship between response of different N forms and K,the differences in the absorption capacity of NH₄⁺/NO3-,and activities of N-metabolizing enzyme such as NR,Ni R,GS/GOGAT and GDH,and N-inducible ability.This study aims to understand the growth mechanism of response to ammonium and nitrate,and the physiological mechanism of the difference between ammonium and nitrate of P.edulis and C.fargesii seedlings,the results are as follows:?1?P.edulis and C.fargesii had some differences in the treatment of different N and K levels.The main factors influencing the growth indexes of P.edulis and C.fargesii were N forms and N concentrations.Both P.edulis and C.fargesii were tree species that prefer NH₄⁺,and NH₄⁺ concentrations of 8 m M is better than 32 m M,NH₄⁺ poisoning is caused by high NH₄⁺ concentration,high NO3-concentration leads to death of C.fargesii seedlings.P.edulis has stronger ability of absorbing NH₄⁺ and higher soil NO3-resistant ability than C.fargesii,and K+ has weak effect on the growth of two tree species.The K+ concentration of promotes growth was low??0.5 m M for P.edulis,0 m M and 3 m M for C.fargesii?.?2?NH₄⁺/NO3-ion flux in root tips of P.edulis and C.fargesii were measured by Non-invasive micro-test technique,the results confirmed that both P.edulis and C.fargesii absorbed NH₄⁺ preferentially,the absorption areas of two tree spieces were both concentrated in the apical meristem.There was a maximum inflow value,which was located at a distance of 300 ?m from the root tip.But P.edulis has greater NH₄⁺ uptake.At the same time,it was found that NH₄⁺ and NO3-were also exfluxed in both tree species.?3?P.edulis and C.fargesii trees were fed with 8 m M N of different forms,and 15 N isotope labeling method was used to study the differences of N absorption,utilization and distribution in the two tree species.The results showed that whether in a single N source or a 50:50 mixed N source with the same N concentration,the absorption of NH₄⁺ by P.edulis was greater than that of NO3-,and the NH₄⁺ treatment was more conducive to N accumulation in P.edulis plants,and the N content in each part of the body were leaf>stem>root.The absorption of NH₄⁺ by C.fargesii was also greater than that of NO3-,but in the 50:50 mixed N source,the presence of NH₄⁺ will inhibit the absorption of NO3-,and the treatment of ammonium nitrogen mixed nitrogen source and ammonium nitrogen is more favorable to C.fargesii,and the N content in each part of the body were root>leaf>stem.The nitrogen uptake of P.edulis showed a significant positive correlation with the root architecture,but there was no significant correlation between the 15 N net absorption and the root architecture of C.fargesii.?4?The five N-metabolizing enzyme activities in P.edulis and C.fargesii were quite different.The main factors influencing enzyme activity are N forms and parts.The activities of NR in two species were higher in NO3-nutrient leaves,Ni R activity in P.edulis and C.fargesii were higher in NO3-nutrient leaves and NH₄⁺ nutrient roots.All of GS,GOGAT,and GDH activities in NH₄⁺ nutrition roots were higher in P.edulis,while that were higher in NH₄⁺ nutrient stems of C.fargesii.The activity of Ni R,GOGAT,and GDH of P.edulis was higher than that of C.fargesii,among which,the difference of activity of Ni R and GDH reached extremely significant level;the activities of NR and GS were both lower than that of C.fargesii,but there was no significant difference among the two species.In summary,the study provides physiological basis for the ammonium properties of two species from the aspects of NH₄⁺/NO3-absorption,accumulation and distribution in vivo and metabolic enzyme activity.The research results not only provide the theoretical basis for the expansion of P.edulis,but also provide a theoretical reference for the appropriate application of nitrogen fertilizer for the corresponding tree species,and at the same time,lay a certain foundation for further research on the molecular physiological mechanism of N nutrient differences in P.edulis and C.fargesii.