Characteristic And Mechanisms Of Root Respiration Of Fraxinus Mandushurica Rupr. To Soil Nitrogen

As an important part of forest soil respiration,total respiratory substrate that tree root respiration consumed around 50%of trees total products of photosynthesis in every year,and tree root respiration were the main ways of the forest ecosystem carbon cycle,in addition it's changes would be an important factor influencing the carbon balance of the whole land-ecosystem.In forest ecosystems,trees can maintain fine roots turnover while 40%～70%of the net photosynthesis product were consumed by trees itself.The net primary productions of underground part were 50%～80%of total net primary production. Therefore,the root respiration had important influence on the forest productivity.For exploring root respiration and its influencing factor,root function of different diameter of Fraxinus mandshurica,and analyzing regulation mechanism to root respiration about carbon and nitrogen metabolism,this paper systematically reaserch root respiration ofE mandshurica of the mixed forests of Moutain Changbai at different condition through combining research methods of field testing and laboratory analysis and from root respiration characteristic at different diameter and response to nitrogen supply.This paper has the following several aspects of the research results:(1) The root respiration rate of F.mandshurica had more apparent seasonal dynamic at different age class in Korean Pine forest of the Changbai mountain(P＜0.01),and the highest respiration rate observed in July and lowest rate in October.In trees growing season,root respiration was a single peak curve affected by temperature,and specific root respiration rate was decreased with increasing trees age but superficial area respiration rate had a reverse trend.Among different diameter,specific root respiration rate decreased with increasing root diameter but superficial area respiration rate had a reverse trend.The proportions of root maintain respiration was gradually improved with increasing root diameter and the proportion of root growth respiration was depressed.In natural conditions,root respiration rate of F.mandshurica was increased with increasing root N contents at different root diameter,but the relativity was decreased with increasing root diameter. Among different age,the relativity between root respiration and root N contents was inapparent.(2) In natural conditions,different diameter root respiration rate of F.mandshurica increased exponentially with air temperture and soil temperature of different depth,and the relativity between root respiration and soil temperature was decreased with deepening soil.The Q₁₀ of mature stand was higher than that of young stand;apparently root respiration of mature stand was more sensitive to temperature than young stand.In natural conditions,the Q₁₀ that temperature coefficient of root respiration from 2.21 to 2.33,and it was decreased with increasing root diameter,indicating that fine roots was more easily affected by soil temperature change than that of thick roots in wild wood of F.mandshurica.More soil water in a certain range would improve root respiration rate,but excessive water in soil would restrain root respiration rate.The root respiration rate increased linearly with soil N contents,the relativity was lower with increasing trees age,and was raise with increasing root diameter.(3) In cultivating conditions,seasonal variation regularities of root respiration rate of F.mandshurica seedling were consistent with air temperature,moreover highest respiration rate observed in July and lowest rate in October.During the growth season,specific root respiration rate ranged from 0.5732μmol·g^-1.s^-1(root＜2 mm in diameter) to 7.1861μmol·g^-1.s⁹-1)(root＜2 mm) and superficial area respiration rate were from 0.0132μmol·cm^-1.s^-1(root＜2 mm) to 0.6848μmol·cm^-1.s^-1(root＞5 mm). Specific root respiration rate decreased with increasing root diameter but superficial area respiration rate had a reverse trend.Air temperature rising influenced the response of root respiration to nitrogen fertility,and the influence was significant level(p＜0.05) between June and August.Root respiration rate increased exponentially with soil temperature at 10 cm(R²=0.779-0.981),with a Q10 of 2.37 to 4.64. Apparently,fine roots was more sensitive to temperature than thick roots.Nitrogen fertility influenced the Q10 of fine roots(p=0.0392＜p=0.05) but not that of thick roots(p＞0.05),thereby indicating that Q10 of fine roots was more easily affected by soil nitrogen concentration change than that of thick roots.(4) Root respiration rate of F.mandshurica seedling increased linearly with root N contents,the relativity was lower with increasing root diameter;indicate that the N concents of root tissue were major factor to root respiration.Root respiration rate increased also linearly with root nitrate nitrogen and root ammonium nitrogen contents,and the R² value bewteen root respiration and nitrate nitrogen was apparently higher than that bewteen root respiration and ammonium nitrogen.Root respiration apparetly increased logarithmic with root soluble protein contents.Root respiration rate apparetly increased linearly with the activity of key enzyme about nitrogen metabolism(NR and GS),and the relativity bewteen root respiration and the activity of NR was higher than that bewteen root respiration and the activity of GS.Root respiration rate increased binomial with root TNC(including soluble sugar and starch) contents.Root respiration rate apparetly increased linearly with root absorption area,and the relativity bewteen superficial area respiration rate and absorption area was higher than that of specific root respiration rate.