【作者】 吴雪仙；

【导师】 陈林武； 宫洲波；

【作者基本信息】 四川农业大学 ， 森林培育学， 2007， 硕士

【摘要】 氮是植物生长所必需的主要营养元素，它是植物的蛋白质、核酸、叶绿素等物质的组成成分。氮循环的研究，对森林生态系统具有重要意义。本研究对嘉陵江上游低山暴雨区湿地松林、刺槐林、湿地松与刺槐混交林三种不同植被类型进行系统研究，探讨了不同植被类型凋落物的年凋落量及其养分归还量、凋落物的分解速率、凋落物现存量及养分含量、降水中氮的输入和输出、土壤养分的季节动态变化，旨在为提高林地生产力及可持续发展提供理论依据。研究结果表明：(1)湿地松林、刺槐林、湿地松与刺槐混交林的年凋落物量分别为4942.60kg／hm~2、3609.60kg／hm~2、4689.20kg／hm~2，其大小顺序为湿地松林＞混交林＞刺槐林。三种植被类型凋落物各组分量，湿地松林和混交林以叶的凋落量最大，其次是杂物；刺槐林以杂物最大，落叶占其次。湿地松凋落物总量、叶和杂物在全年出现三个凋落高峰，刺槐林和混交林凋落物总量和杂物全年也是出现三个高峰，叶两个高峰期；枝和果的凋落主要集中在夏季。(2)湿地松林、刺槐林、湿地松与刺槐混交林凋落物N的年归还量分别为：31.06kg／hm~2，38.96kg／hm~2，40.05kg／hm~2，大小顺序为：混交林＞刺槐林＞湿地松林。凋落物各组分N的归还量大小，湿地松林为叶＞杂物＞枝＞果；刺槐林和混交林为杂物＞叶＞果＞枝。(3)湿地松林、刺槐林、湿地松与刺槐混交林凋落物现存量的年平均值分别为：5902.98kg／hm~2、5186.75kg／hm~2、6361.87kg／hm~2，其大小顺序为混交林＞湿地松林＞刺槐林。三种植被类型未分解层N的年平均含量的大小顺序为刺槐林＞混交林＞湿地松林，半分解层N的年平均含量大小顺序为混交林＞刺槐林＞湿地松林。(4)湿地松林、刺槐林、湿地松与刺槐混交林N元素的年淋溶归还量分别为：13.09kg／hm~2，13.10kg／hm~2，14.14kg／hm~2，淋溶归还量的大小与林分的郁闭度和冠层厚度大小有关；三种植被类型林冠雨的归还量分别为：12.649kg／hm~2、12.550kg／hm~2、13.291kg／hm~2，树干径流的归还量分别为：1.18kg／hm~2，1.35kg／hm~2，1.84kg／hm~2，表明在降水归还途径中，主要是林冠雨的归还。湿地松林、刺槐林、湿地松与刺槐混交林地表径流的氮输出量分别为：0.55kg／hm~2、0.55kg／hm~2、1.27kg／hm~2，混交林的氮输出量比较大可能与林下凋落物的现存量较少有关。(5)三种植被类型各组分N含量的变化范围在0.758～14.989g／kg，各组分的N含量大小顺序，湿地松林为叶＞根＞皮＞枝＞干；刺槐林为叶＞果＞根＞皮＞枝＞干；混交林的湿地松为叶＞根＞枝＞皮＞干；混交林的刺槐：果＞叶＞皮＞根＞枝＞干；湿地松纯林与混交林的湿地松相比，混交林的枝、叶、根均大于纯林，干和皮的N含量是纯林大于混交林；混交林中刺槐枝、干、皮、果的N含量均比刺槐纯林高，而叶、根的N含量是纯林高于混交林。湿地松林、刺槐林、湿地松与刺槐混交林N的总积累量分别为136.432kg／hm~2、210.403kg／hm~2、169.661kg／hm~2，以刺槐纯林N积累量最大，其次是混交林。(6)三种植被类型凋落物的分解在第一季度分解比较缓慢，第二、三季度失重率明显，第四季度时分解减慢。凋落物在分解过程中三种植被类型各组分N浓度的变化趋势表现为：枝：淋溶—富集—释放；叶的变化趋势有所不同，湿地松林表现为净富集，混交林中的湿地松和刺槐及纯林中的刺槐表现为淋溶—富集—释放；果的浓度变化也表现为淋溶—富集—释放。(7)三种植被类型土壤中氮素的含量除土壤铵态氮外，其余的均是刺槐林＞混交林＞湿地松林，铵态氮含量的大小顺序为：刺槐林＞湿地松林＞混交林。各氮素在一年中的变化趋势不相同，有机质和全氮的变化趋势相同，先升高后降低，然后再升高，最后又降低；铵态氮的变化趋势表现为降——升——降；硝态氮的变化趋势为：从2005．12—2006．6月基本保稳定，尔后开始下降，9月降到最低值；水解氮的变化趋势表现为先升后降。(8)生态系统养分循环的特点可以通过吸收系数、利用系数及循环系数来表征，湿地松林、刺槐林、湿地松与刺槐混交林N元素的年吸收量分别为37.561kg／hm~2、48.976kg／hm~2、48.127kg／hm~2，刺槐纯林的年吸收量最大，湿地纯林的吸收量最小；三种植被类型年存留量的大小顺序为：刺槐林＞混交林＞湿地松林；归还量的大小顺序为：混交林＞刺槐林＞湿地松林。三种植被类型N元素的吸收系数、利用系数、循环系数的大小顺序均是混交林＞湿地松林＞刺槐林，说明混交林对N元素的贮存能力和循环速率最大。(9)三种植被类型的N输入量均大于输出量，系统处于良好的养分积累状态，土壤中养分的输入量也大于输出量，说明植被不需要外源补给，也能保持持续稳定的发展。三种植被系统N的净积累量的大小顺序为：湿地松林、刺槐林＞混交林，土壤中N净积累量的大小顺序为：湿地松林＞混交林＞刺槐林。更多还原

【Abstract】 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.更多还原