Study On Nitrogen Cycle Of Different Vegetation Types In Low-mountainn And Rainstorm Section Of Upper Reaches Of JiaLing River

The nitrogen is the main nutritive element that plants need for growth, it is thematerial component on plant's protein, nucleic acid, chlorophyll.The reseach ofnitrogen cycle, has the vital significance to the forest ecosystem. This research had beencarried out in the low mountain storm rainfall area three different vegetation types toJialing River upstream. Studied year falling quantity of the litter and its the nutrientreturns quantity, litter decomposition rate, storage of litter and in the nutrient content,the precipitation the nitrogen input and the output, the soil nutrient season dynamicchange.the result showed:(1)The annual litter production of three vegetation types of pinus elliottill, robiniapseudoacaciaand mixed forest were 4942.60kg/hm²,3609.60kg/hm²,4689.20kg/hm².the sequence of litter production was pinus elliottill＞mixed forest＞robiniapseudoacacia.the components of litter production of the three vegetation types was:litter production of leaf was the largest in pinus elliottill and mixed forest, Be sundrysecondly; robinia pseudoacacia withers and falls with the sundry measuring amaximum, the fallen leaf takes up a secondary, pinus elliottill withers and falls thingall quantity, leaf and sundry three wither and fall in appearing yearly peak.there werethree peaks of litter total, leaf and sundry of pinus elliottill in the whole year. The littertotal production and sundry of robinia pseudoacacia and mixed frost have three peaksin the whole year, but the leaf has only two peaks, branches and fruit fell main insummer.(2)the annual nitrogen return of pinus elliottill, robinia pseudoacacia and mixed frostwere 31.06kg/hm², 38.96kg/hm², 40.05kg/hm².the sequence of nitrogen return wasmixed frost＞robinia pseudoacacia＞pinus elliottill.the sequence of nitrogen return ofthe component were:pinus elliottill was leaf＞sundry＞branch＞fruit, robiniapseudoacacia and mixed frost were sundry＞leaf＞fruit＞branch.(3)annual average Biomass of litter of the pinus elliottill, robinia pseudoacacia andmixed frost were 5902.98kg/hm²,5186.75kg/hm²,6361.87kg/hm²,the sequence of thethree vegetation types was mixed frost＞pinus elliottill＞robinia pseudoacaci.the sequence of nitrogen content in undecomposted litter was robinia pseudoacacia＞mixed frost＞pinus elliottill. The sequence of the nitrogen content in halfundecomposted litter was mixed frost＞robinia pseudoacacia＞pinus elliottill.(4)annual leaching return amount of the nitrogen element were13.09kg/hm²,13.10kg/hm²,14.14kg/hm² in pinus elliottill, robinia pseudoacacia andmixed frost. The size of leaching return amount have to do with the size of crowndensity and canopy height, the return amount of canopy rain was12.649kg/hm²,12.550kg/hm²,13.291kg/hm²,the return amount of stem flow was1.18kg/hm²,1.35kg/hm²,1.84kg/hm²,this showed return of canopy rain was main meansin return. Nitrogen output of surface runoff was 0.55kg/hm²,0.55kg/hm²,1.27kg/hm² inpinus elliottill, robinia pseudoacacia and mixed frost. Nitrogen output of mixed frostwas larger relation with Biomass of litter.(5)range of nitrogen content of component of the three vegetation was 0.758～14.989g/kg.the sequence of nitrogen content in component was:pinus elliottill was leaf＞root＞bark＞branch＞trunk, robinia pseudoacacia was leaf＞fruit＞root＞bark＞branch＞trunk, pinus elliottill in mixed frost was leaf＞root＞branch＞bark＞trunk,robinia pseudoacacia in mixed frost was fruit＞leaf＞bark＞root＞branch＞trunk.pinus elliottill compare with mixed frost, nitrogen content of the branch, leaf and rootin mixed frost larger pinus elliottill, trunk and bark be opposite to them; nitrogencontent of the branch, trunk, bark and fruit were mixed frost larger robiniapseudoacacia, leaf and root was robinia pseudoacacia larger mixed frost, accumulationof nitrogen in pinus elliottill, robinia pseudoacacia and mixed frost were136.432kg/hm²,210.403kg/hm², 169.661kg/hm², Maximal being robinia pseudoacacia,Be secondly mixed frost.(6)Decomposition of litters for three vegetation types was slow in one quarter,weightlessness rate was obvious in two and three quarters. Decomposition of litters wasslow in four quarter. In decomposition process of litters, nitrogen content changers ofdifferent component showed:branch was leaching——accumulation---release, changerstendency of leaf was different, pinus elliottill showed net accumulation, robiniapseudoacacia and mixed frost showed leaching——accumulation---release, fruit changers tendency was too leaching accumulation—release.(7)nitrogen content of soil for three vegetation types were robinia pseudoacacia＞mixed frost＞pinus elliottill except NH4⁺-N. the sequence of NH4⁺-N content wasrobinia pseudoacacia＞pinus elliottill＞mixed frost. different nitrogen element changetendency was different in a year. Change tendency of organic and total nitrogen weresame, showed rise-drop-rise-drop, NH4⁺-N showed drop-rise-drop, NO₃-N showed drop,hydrolysable N showed rise-drop.(8) Characteristic of nutrient cycles can indication by absorb a modulus, Operating ratioand Circulation modulus in ecosystem. annual absorb amount of nitrogen element forthree vegetation types were 37.561kg/hm², 48.976kg/hm², 48.127kg/hm². robiniapseudoacacia annual absorb amount was the largest, pinus elliottill was the least. Thesequence of annual accumulation for three vegetation were robinia pseudoacacia＞mixed frost＞pinus elliottill. The sequence of return amount was mixed frost＞robiniapseudoacacia＞pinus elliottill. The sequence of absorb a modulus, Operating ratio andCirculation modulus of nitrogen element for three vegetation were mixed frost＞pinuselliottill＞robinia pseudoacacia, this indicate that Store up an ability and Circulationrate of the mixed frost to nitrogen was the largest.(9)nitrogen input more than nitrogen output in three vegetation types, System is in finenutrient accumulation state. nitrogen input larger output in soil, indicate that thevegetation not need supplied with the external source can keep sustained stabledevelopment. The sequence of nitrogen accumulation for three vegetation system waspinus elliottill and robinia pseudoacacia more than mixed frost tile sequence of netaccumulation of nitrogen in soil was pinus elliottill＞mixed frost＞robiniapseudoacacia.