【作者】 林伟；

【导师】 马红亮；

【作者基本信息】 福建师范大学 ， 生态学， 2016， 硕士

【摘要】 土壤氮库包括土壤有机氮和无机氮等重要组分,其成分复杂,土壤氮被认为是以不同形态和功能的氮在参与土壤氮矿化和转化。很多研究采用不同提取方法研究某一组分在氮素循环中的作用及影响,而对各组分间相互关系研究不够清楚。本文以福建建瓯市万木林自然保护区浙江桂天然林、罗浮栲天然林和杉木人工林为对象,进行野外模拟氮沉降试验,设置3个氮添加水平,对照(CK,0 kgN·hm-2·a-1)、低氮(LN,75 kgN·hm-2·a-1)和高氮(HN,150 kg N·hm-2·a-1)和2个凋落物处理(去除凋落物和保留凋落物),采用不同浸提剂(蒸馏水、0.5 mol·L-1 K2SO4、2.5和13mol·L-1 H2SO4等)序列浸提土壤氮素,定量分析土壤浸提氮组分,研究氮添加对亚热带土壤浸提氮含量的影响。通过室内培养法,添加不同氮形态(蛋白质、氨基酸、无机氮),测定土壤水溶性氮、交换性氮和氧化亚氮的释放量,以探究外源氮添加对土壤不同氮形态的响应,结果表明:(1)浸提有机氮和总氮在罗浮栲天然林土壤最高,浙江桂天然林最低,其中用水和K2SO4浸提的氮在阔叶林显著高于针叶林;虽然无机氮同样是阔叶林高于针叶林,但用水和K2SO4浸提的NH4+-N总和在各林分间差异不大,且罗浮栲天然林水溶性最高,交换性最低,而水浸提的NO3--N在浙江桂天然林最高,罗浮栲天然林最低。保留凋落物处理促进各林分土壤惰性氮转化而使其降低,增加LP Ⅰ-N、LPⅡ-N和EON(exctrable organic nitrogen)。因此,罗浮栲林有最大的氮活性、转化速率和利用率,保留凋落物对其有促进作用,林分间差异可能与凋落物长期输入的质量和数量有关。相关结果分析显示,不同浸提有机氮与微生物生物量氮呈显著正相关,这表明用不同浸提剂浸提土壤获得的浸提有机氮是土壤微生物的氮来源之一,但它们对土壤微生物的有效程度不同。(2)氮添加对亚热带不同森林土壤水溶性和交换性有机氮含量存在不同程度的影响。其中,氮添加降低罗浮栲交换性EON,也使得去除凋落物的杉木人工林水溶性有机氮显著降低,但保留凋落物的却增加。氮沉降使得去除凋落物的杉木人工林水溶性有机氮显著降低,而保留凋落物的却增加,同时促进了杉木人工林中水浸提的NH4+-N、NO3--N含量,说明微生物利用低分子化合物迅速的转化为无机氮;与对照相比,高氮处理可使杉木人工林土壤LP Ⅰ-N(活性有机氮库Ⅰ)增幅为78.6%;氮添加使得土壤SMB-N(土壤微生物生物量氮)增加0%～103.6%;在氮添加处理下,除杉木人工林土壤SMB-N/LP Ⅰ-N是随着氮添加水平的增加而降低外,微生物对其他林分土壤活性有机氮的利用均表现为随着氮添加量的增加而增加。结果表明,氮添加对阔叶林和针叶林土壤活性和惰性有机碳氮组分的影响存在差异,但差异不显著,这与它们归还土壤的凋落物性质差异有关,并且凋落物的分解差异也可能是影响土壤不同氮组分变化的原因。(3)有机氮添加促进水溶性NH4+-N增加,CK+Casein>CK+AA,且CK+Casein处理以最高值维持时间长达48天,而水溶性NO3--N则随培养时间持续升高,这与实验后期交换性NH4+-N降低有关,同时,培养后土壤惰性氮含量低于培养前的,可能是转化为LP Ⅰ-N,从而促使早期EON增加,后期大量EON矿化,补充NH4+-N以占据更多的交换位点,降低交换性硝态氮含量。土壤N20-N释放在1周左右达到最大,其释放量为CK+Casein>CK+AA>CK+N>CK,与土壤几种氮形态转化密切相关。结果表明,无机氮和氨基酸态氮能在短时间内对土壤氮素转化产生一定影响,而且蛋白质类氮的影响更大且更长久。另外,来源于凋落物中的有机氮对土壤氮循环的影响和作用细节应给以更多关注。更多还原

【Abstract】 Nitrogen plays an important role in chemical,physical,and biological processes in soil,it consists of organic and inorganic complicated fractions.Soil N is found that many differing forms and function participated in soil N mineralization and transformation.Most of these researches are focused on the N cycle of soil nitrogen fraction using different extaction method,the contribution of each of extractable nitrogen fraction to N mineralisation,and their mutual interaction,have not been quantified simultaneously.At the same time,To investigate the effects of nitrogen addition on the forest extractable nitro gen,the experiment was carried out in subtropical broad-leaved forest species(Cinnamomum chekiangense and Castanopsis fabri)and conifer forest(Cunninghamia lanceolata)with three nitrogen level applied as NH4NO3:control(0 kg·hm-2·a-1),low nitrogen(75 kg hm-2·a-1),high nitrogen(150 kg hm-2·a-1)and two litter treatments(removal of litter layer and retention of litter layer).To assess effects of increasing deposition on N cycling,we quantified the size of soil extractable organic N,and can study to the effects of nitrogen addition on soil extractable N.Then,indoor culture experiments were carried out with addition of three different nitrogen forms(protein,amino,inorganic nitrogen)incubation under 60%Water-holding capacity,to quantify the size of soil water and salt extraction nitrogen,and the N2O-N emission to exolore soil nitrogen pools on the response of the different nitrogen forms addition.The results showed as follows:(1)Soil extraction organic nitrogen and total nitrogen contents were higher at the Castanopsis fabri,the smaller content at Cinnamomum chekiangense.Exctrable nitrogen using distilled water and 0.5 mol·L-1K2SO4 in subtropical broad-leaved forest species was higher than conifer forest,as well as inorganic nitrogen contents.The different forest types did not have significant efferets on soil NH4+-N with distilled water and 0.5 mol·L-1 K2SO4.Therefore,soil NH4+-N of the Castanopsis fabri with distilled water was higher,but soil NH4+-N of the Castanopsis fabri with 0.5 mol-L-1K2SO4 were lowest.Soil NO3--N contents were higher in Cinnamomum chekiangense,the Castanopsis fabri was lowest Retention of litter layer could promote soil recalcitrant nitrogen transformation,also enhanced LPI-N,LPII-N and exctrable organic nitrogen contents.Hence,differences in the different forest types of extractable organic might be attributed to the quality and quantity of organic matter input,The result analysis showed that different extraction methods of organic nitrogen was significantly positively correlated with soil microbial biomass,it results that each soil extraction organic nitrogen represents source of soil microbial biomass nitrogen,but they had different efficiency.(2)To some degree,nitrogen addition has effects on exctratable organic nitrogen content of different forest types using distilled water,0.5 mol·L-1 K2SO4,2.5 mol·L-1H2SO4 and 13 mol·L-1H2SO4,nitrogen addition could reduce exctractable organic nitrogen of Castanopsis fabri using salt solution,and also reduce exctractable organic nitrogen of removal of litter layer treatment of Cunninghamia lanceolata using distilled water,while retention of litter layer treatment enhance.Meanwhile nitrogen deposition increased NH4+-N、NO3--N contents by water extraction,suggests that soil microbial biomass using low molecular compounds rapidly converted into inorganic nitrogen.The labile pool Ⅰ,Ⅱ and recalcitrant was evaluated following the two-step H2SO4 the hydrolysis method.Then the effects of N addition on labile and recalcitrant N fractions and soil microbial biomass N(SMB-N)were investigated,results that high nitrogen treatment increased soil labile nitrogen pool Ⅰ of Cunninghamia lanceolata by 78.6%compared with control,Nitrogen addition significantly increased SMB-Nfrom 0%to 103.6%compared with control;Except for SMB-N/LPI-N ratio of Cunninghamia lanceolata decreasing with nitrogen addition,the utilization of soil labile N in the other forests by microorganism increased with nitrogen addition.The results indicated that the differences of soil labile and recalcitrant organic nitrogen pools between broad-leaved and conifer forest were related to the quality of litter,and the differences in litter decomposition might provide some evidence for the change of soil carbon and nitrogen pools.(3)Organic nitrogen addition promoted NH4+-N content using distilled water,the order contents were by step of CK+Casein>CK+AA,even CK+Casein treatment maintain the highest content up to 48 days.While water-soluble NO3--N increases with culture time continue to rise,it was related to exctractable organic nitrogen by salt solution decrese at the later experiment Recalcitrant nitrogen content was decrease at the late experiment,it may translate into LPI-N,consequently increase extractable organic nitrogen content,and promote to translate into NH4+-N which occupied more exchange sites,the result leaded to decrease extractable NO3--N content.Different nitrogen forms have impact on the subtropical forest soil nitrogen and increase N2O-N flux,the soil N2O-N-emission rates were step by step of CK+Casein>CK+AA>CK+N>CK at one week,it closely related with soil nitrogen forms transformation The result shows that inorganic nitrogen and amino acid addition have influence on soil nitrogen transformation,and procein can influent more long.Moreover,we should pay close attention to organic nitrogen which comes from the litter influence on ecosystem N cycling.更多还原