【作者】 李仁洪；

【导师】 胡庭兴；

【作者基本信息】 四川农业大学 ， 森林培育学， 2009， 硕士

【摘要】 随着全球经济的高速发展及人口增长、化石燃料消费的增加,大气氮沉降成比例增加。目前,中国已成为继欧洲、美国之后的全球第三大N沉降集中区。在欧美地区已开展了大量关于氮沉降对温带森林生态系统结构和功能的影响的研究。然而国内在这方面的研究还处在起步阶段。慈竹（Neosinocalamus affinis）作为退耕还林的主要竹种之一,在长江中上游生态屏障建设及地区经济发展中,具有重要的生态、经济和社会效益。因此,在氮沉降全球化的背景下,对华西雨屏区慈竹林进行模拟氮沉降研究,可以填补这一地区关于竹林生态系统对氮沉降响应特征和机制研究的空白,为华西雨屏区乃至亚热带地区关于竹林生态系统对氮沉降响应的研究提供理论基础,为该地区慈竹林可持续经营提供参考。在不考虑大气N沉降的情况下,通过原位进行了对照(CK:0kg·hm^-2·a^-1)、低氮(LN:50kg·hm^-2·a^-1)、中氮(MN:150kg·hm^-2·a^-1)和高氮(HN:300kg·hm^-2·a^-1)处理,研究了华西雨屏区慈竹林不同组分凋落物分解、养分释放特征及其对模拟N沉降的响应。研究结果表明:（1）在不同凋落物组分分解中,叶分解速率最快,其次是箨,枝最慢,分解15个月时,叶、箨、枝的物质残留率分别为26.38%、46.18%和54.54%,叶分解显著高于箨和枝（P＜0.001）,箨分解显著高于枝（P＜0.001）;叶在凋落后第1～2月和7～10月分解速率较大,而箨和枝则在第5～8月分解较快;凋落叶分解95%需要2.573a,分别比箨和枝分解95%所需时间短1.686a和3.319a。凋落叶分解15个月时,各N沉降处理间分解率差异不显著;凋落箨分解95%需要2.679～4.259a,分解率最高的为MN,最低的为CK;凋落枝经过15个月的分解,各处理分解率大小顺序为MN＞HN＞LN＞CK,MN与LN间差异达显著水平（P＜0.05）。总的来看,N沉降对三种凋落物分解均有明显促进作用,对凋落箨促进作用最强,但随着N沉降浓度的增加和时间的延长,其促进作用减缓。（2）经过12个月的分解,凋落叶各养分元素释放速率的大小顺序为:Mg＞P＞C＞Ca＞K＞N;凋落箨为:C＞Mg＞Ca＞K＞P＞N;凋落枝为:C＞Mg＞P＞K＞N＞Ca。凋落叶各养分元素释放速率均高于凋落箨和凋落枝;凋落箨C、Ca、Mg元素释放速率大于凋落枝,而凋落枝N、P、K元素释放速率大于凋落箨。凋落叶、箨、枝在分解过程中,C元素均呈释放状态:凋落叶N浓度变化动态为下降-上升-下降,而凋落箨、凋落枝N浓度一直单调上升,凋落叶N元素释放模式为淋溶-富集-释放,凋落箨、枝为富集-释放;凋落叶P元素总体上呈释放态势,凋落箨先少量释放,再大量富集,而凋落枝在前期平稳释放,后期少量富集;凋落叶和凋落枝K元素表现为在分解初期富集,随后释放,而凋落箨则恰好相反;凋落叶Ca元素总体上呈释放态势,凋落箨先富集后释放,而凋落枝却一直处于富集状态;Mg元素在凋落叶、凋落箨、凋落枝的分解过程中一直处于释放状态。（3）在凋落叶分解过程中,N沉降促进了C、N、P、K、Ca、Mg元素的释放,且MN处理促进作用最强。在凋落箨分解过程中,N沉降促进了C、K、Ca、Mg元素的释放,且MN处理促进作用最强;N、P元素在富集过程中,N沉降抑制N、P元素的富集,在N、P释放阶段,N沉降促进其释放。在凋落枝分解过程中,LN抑制C元素的释放,MN、HN促进其释放;N沉降有利于N元素的富集,随着N浓度的增加富集量增加;N沉降对P元素的影响表现为,分解前4个月有利于P元素的释放,随后起抑制作用;LN处理抑制了K元素的释放,MN、HN促进其释放;N沉降在分解前4个月有利于Ca元素的富集,随后促进其释放;Mg元素的释放对N处理的响应为,随着N浓度的增加,促进其释放作用增强。（4）在凋落叶分解过程中,分解前2个月N处理降低了凋落叶C/N比,2个月后提高其C/N比;在凋落箨分解中,N沉降提高了C/N比,随着N处理浓度的增加,C/N比有下降的趋势;在凋落枝分解中,N沉降降低了C/N比,MN处理下降程度最大。更多还原

【Abstract】 With global economic rapid development and population growth,fossil fuel consumption,atmospheric nitrogen deposition increased proportionally.Now,China has become one of the most seriously deposited nitrogen regions,followed by Europe and America.In Europe and North America,Ecologists have done lots of studies on impacts of nitrogen deposition on structure and function of forest ecosystems,but these researches mainly concentrated on temperate forests;China in this field is still in initial stage.Neosinocalamus affinis,which is deemed as one of the most important species of bamboo in the project of returning land for farming to forestry,has positive effects on ecological construction and economic development along the upper and middle reaches of the Yangtze River.Therefore,under the background of N deposition increased remarkably in many regions,study on decomposition traits,nutrient release of litters and their responses to simulate nitrogen in Neosinocalamus affinis stands in Rainy Area of West China were conducted as reference and theory to the management and supervision of sub-tropical bamboo eco-system.The further study on mechanism of the bamboo eco-system response to nitrogen deposition was conducted to provide reference for influence of nitrogen deposition and protection of plantation in similar areas and basic data for the degraded bamboo’s regeneration and renewal.The study was conducted in Neosinocalamus affinis stands in Rainy Area of West China.Nitrogen addition experiments were initiated within the stands in Dec 2007.Four treatments（three repeats） were installed,i.e.,null N level（CK）,low N level(LN,50 kg.hm^-2.a^-1),moderate level(MN,150 kg.hm^-2.a^-1) and high level(HN,300 kg.hm^-2.a^-1). All plots（3m×3m） and treatments were laid out randomly,Ammonium nitrate（NH₄NO₃） solution was sprayed on floor of these plots during decomposition process twice a month and began in Dec 2007.Litter decomposition was determined by using closed litter bags in the plots.These bags were polyvinyl screen（1mm in the top and bottom） of approximately 25cm×25cm in dimension.Each bag was filled with about 0.01kg,air-dried mass,of leaf and sheath litters,while 0.02kg twig mass was put into each bag.In Dec 1^st 2007,these litter bags were evenly distributed among 3 plots selected randomly.Two leaf litter bags were collected from each plot at about decomposing 2,4,6,8,10,12,15 months after the start of the experiment,while these sheath and twig bags were fetched at about decomposing 4, 8,12,15 months.The results showed that:（1） The leaf,sheath and twig litter had different decomposition rates.The highest one was leaf litter and the lowest one was twig litter.After decomposing for 15 months,the remained litter mass rate in leaf,Sheath and twig litter were 26.38%,46.18%,54.54%respectively,and the differences were significant（P＜0.001）. Leaf litter had a faster decomposition speed during the first 2 months and from the 7^th month to the 10^th month,while the decomposing rate of sheath and twig was faster than other stages from the 5^th month to the 8^th month.It would take 2.573 years to decompose 95%of leaf litter mass,which were 1.686 years and 3.319 years shorter than sheath and twig.15 months later of leaf decomposition,difference of different N deposition treatments were not significant.It might take 2.679～4.259 years to decompose 95%of sheath litter,the longest in CK and the shortest in MN.After decomposing for 15 months, the order of decomposing rate of twig litter was MN＞HN＞LN＞CK,and significant difference existed between MN and LN.On the whole,the effect of N deposition on the three component litter decomposition was positive,but this effect could be slowed down with the increase of deposited N concentration and time extension. （2） During 12 months decomposition,the six nutrient elements could be arranged with respect to nutrient release rate in this sequence:Mg＞P＞C＞Ca＞K＞N in leaf, C＞Mg＞Ca＞K＞P＞N in sheath,C＞Mg＞P＞K＞N＞Ca in twig.All nutrient release rates in leaf litter were higher than those in sheath and twig litters.The nutrient release rates of C,Ca,Mg in sheath litter were faster than that in twig litter,and N,P,K were on the contrary.In the decomposition process of three litter components,changes on C content featured a pattern of nutrient release.The dynamics of N concentration in the decomposed leaf litter featured decrease-increase-decrease,while N concentration in sheath and twig increased all the time.P content in the decomposed leaf litter appeared a decreasing trend,and the sheath released P content a little,accumulated a lot later, whereas P released slowly in the early stage and accumulated a little in twig litter. Changes on K content in leaf and twig litter had a pattern of nutrient accumulation in the first stage and release later on,and sheath was on the contray.Ca content had a decreasing trend in the decomposed leaf litter,accumulation and releasing in sheath,and consistent accumulation in twig.Mg contents of three litter components remained releasing in the decomposition process.（3） During the decomposing process of leaf litter,N-addition treatments stimulated C,K,Ca,Mg release.N,P release rates were inhibited by N treatments in the first 2 months and accelerated from the 3^rd decomposing month.C,Ca,Mg release rates of N treatments were higher than that of CK in the decomposition process of sheath,with the highest one in MN.The response of K release rate to N deposition showed positive effect,and the order of the release rates was LN＞MN＞HN＞CK.As for N,P elements,N treatments showed inhibitory effects in the accumulating stage and appeared positive effects in the releasing process.In the decomposing course of twig litter,LN inhibited C element release,while C released faster in MN,HN than CK.With the increase of deposited N concentration,the N contents in N treatments were increased regularly,all of which were more than CK.N deposition was beneficial of P release during the first 4 months,and inhibited P release from the 5^th month to the 12^th month.The amount of Ca element in N treatments was increased before decomposing 4 months,and then N deposition stimulated Ca release.As for Mg,the positive effect could be strengthened with the increase of deposited N concentration.（4） C/N ratios were decreased by N deposition in the leaf decomposed process of first 2 months,and then were increased.In the decomposing process of sheath litter,the four treatments could be arranged with respect to C/N ratio in this sequence: CK＞LN＞MN＞HN.C/N ratios in N treatments were decreased during twig decomposition,with the lowest one in MN.更多还原