植被恢复对红壤侵蚀区土壤氮组分的影响

为了解植被恢复过程中土壤不同氮组分变化规律,以福建省长汀县典型红壤侵蚀区为研究对象,利用时空互代法,选取5个典型植被恢复阶段样地(裸地、恢复10、20、30年马尾松人工林和天然林)。土壤样品采集后,测定不同土壤氮组分,并探讨了其与土壤养分的关系。结果表明:(1)土壤全氮和有机氮组分(微生物量氮、溶解性有机氮、颗粒有机氮和粘粒有机氮)均为天然林>马尾松恢复20年人工林>裸地。天然林土壤铵态氮含量显著高于其他恢复阶段样地,植被恢复10年后硝态氮含量显著升高;(2)天然林土壤微生物量氮和粘粒有机氮与全氮的比例分别是裸地的5.37倍和2.81倍,并且其两种矿质氮(铵态氮和硝态氮)与全氮的比例也分别是裸地的3.23倍和5.67倍。(3)土壤全氮、有机氮组分和矿质氮与土壤其他养分(全碳、全磷、有机质、碱解氮、速效磷和速效钾)呈显著正相关,说明植被恢复过程中,土壤肥力也逐渐改善。     

长期施肥对红壤旱地团聚体特性及不同组分钾素分配的影响

基于祁阳红壤旱地长期施肥定位试验,选取CK(不施肥)、NP(氮磷肥配施)、N P K(氮磷钾肥配施)、N P K M(氮磷钾肥和猪粪配施)和N P K S(氮磷钾肥和秸秆半量还田)处理,于试验26年(2016年)玉米收获后采集不同施肥处理原状土壤(全土),分析土壤团聚体组分中全钾、非交换性钾和交换性钾含量变化,并进一步探讨土壤团聚体组分钾对全土钾的贡献率及其与作物吸钾量的相关关系。结果表明:(1)在所有处理中,NPKM处理下2 mm、1~2 mm和0.5~1 m m的团聚体组分比例最高,但0.0 5 3~0.2 5 m m和0.0 5 3 m m的团聚体组分比例则显著低于其他处理,而NPKS处理下2 mm、1~2 mm和0.5~1 mm的团聚体组分比例则无显著增加。(2)与NPK处理相比,NPKM处理各团聚体组分中非交换性钾和交换性含量分别增加24.37%~49.04%和82.02%~176.3%,且NPKM处理下较大的团聚体组分(0.5 mm)中全钾、交换性钾和非交换性钾对全土全钾、交换性钾和非交换性钾的贡献率显著增加(增幅分别为6.25%~31.97%、5.72%~43.16%和6.33%~41.98%),而在较小粒级团聚体组分(0.25 mm)中则呈下降趋势(降幅分别为14.37%~21.44%、17.04%~33.66%和34.40%~43.84%)。(3)NPKS处理各团聚体组分的非交换性钾和交换性钾含量以及各团聚体组分钾对全土钾的贡献率均与NPK处理无显著差异。(4)线性回归分析表明,当0.25 mm团聚体组分钾对全土钾的贡献率增加1%时,作物吸钾量相应增加9.92~11.89 kg hm-2。长期化肥配施猪粪可显著改善红壤旱地的团聚体组分,进而提高团聚体组分钾对全土钾的贡献能力,促进作物对钾素的吸收。     

水氮调控对设施土壤有机氮组分、全氮和矿质氮的影响

为探讨水氮调控对设施土壤有机氮组分、全氮和矿质氮的影响,通过膜下滴灌设施番茄田间定位试验,采用灌水下限(W_1、W_2、W_3)和施氮量(N_1、N_2、N_3)的两因素三水平随机区组设计,研究水氮调控对休耕期0—30cm土层土壤有机氮组分、全氮和矿质氮的影响。结果表明,不同水氮调控下,设施土壤有机氮主要是以酸解态氮为主,总体表现酸解态氮大于非酸解态氮含量。土壤有机氮组分在酸解态氮和非酸解态氮中分配比例差异明显。土壤有机氮各组分含量及占全氮比例的大小顺序为氨基酸氮/氨态氮未知氮氨基糖氮。除氨基糖氮,其余酸解态氮各组分和酸解总氮含量及其占全氮比例均随着土层深度的增加而降低,不同土层含量差异显著(P0.05)。土壤全氮、矿质氮和总有机氮含量随土层深度的增加也呈降低趋势,且含量差异达到极显著水平(P0.01)。除氨基糖氮,全氮与其他有机氮各组分、酸解总氮间均达到极显著正相关(P0.01);矿质氮仅与酸解氨态氮及酸解总氮的影响达到极显著(P0.01)和显著正相关(P0.05)。灌水下限、施氮量及水氮交互对设施土壤全氮、矿质氮和总有机氮及有机氮组分影响均达到极显著水平(P0.01)。因此,设施土壤氮素含量的变化与水氮管理模式紧密相关。氨态氮和氨基酸氮是设施土壤中最主要的有机氮形态,是土壤活性氮中的主要组分,亦是土壤供氮潜力的表征。考虑土壤供氮潜力,灌水下限35kPa、施氮量300kg/hm~2为该设施生产下最优的水氮管理措施。     

长期定位施肥对旱作农田土壤全氮及其组分的影响

基于田间定位试验,研究了长期施肥对旱作冬小麦农田土壤全氮及其组分的影响,试验设4个处理(对照不施肥CK、氮磷配施NP、化肥与有机肥配施NPM以及长期休闲地BL),测定了0—15,15—30,0—30cm土壤全氮、微生物量氮、潜在矿化氮和颗粒有机氮含量。结果表明,长期持续施肥30a后,在0—30cm土层,NPM处理土壤全氮、微生物量氮、潜在矿化氮分别较CK提高了35.0%,27.0%和48.9%(P0.05),且这种增加作用在15—30cm更明显,土壤全氮增幅达到41.3%(P0.05),但颗粒有机氮差异并不显著;此外,NPM处理微生物量氮、颗粒有机氮含量较NP处理分别提高了35.2%,307.5%(P0.05),而NP处理与CK仅潜在矿化氮差异显著。与种植作物相比,长期休闲降低了土壤全氮、微生物量氮、潜在矿化氮和颗粒有机氮含量,差异分别为15.0%,1.8%,31.3%和33.6%,但均未达到显著水平。相关性分析表明,土壤全氮、潜在矿化氮、微生物量氮和颗粒有机氮两两之间存在着显著的正相关关系。总的来说,长期持续施入有机肥能够有效地增加旱作农田土壤全氮,同时增加其组分含量,有助于维持土壤健康,保持其供氮能力。     

Evidence of Current Soil Acidification in Spruce Stands in the Vosges Mountains,North-Eastern France

To demonstrate directly soil acidification under spruce stands in the Strengbach catchment, soils from two adjacent stands aged 40 and 90 years were sampled intensively in 1990 and resampled in 1996. Soils already were very acid in 1990. Between 1990 and 1996, soils had experienced a significant decrease in exchangeable Ca2+ and Mg2+ at all depths at the two sites except in the 0-10 cm layer, for which base saturation remained constant. Losses of Ca2+ calculated from a budget study at the same sites and from the comparison of exchangeable stores were similar. In contrast, the loss of Mg2+ from the exchange complex was higher than that computed from the field budget. Various reasons, including most probably uncertainties linked to the extremely low levels of Mg in the ecosystem, may explain this discrepancy. Since 1987, a general decrease of the (Ca2+ + Mg2+)/Al3+ ratio in soil solution was observed at both sites. These results are consistent with present day acidification of soils poor in weatherable minerals under spruce stands in the Vosges Mountains.     

模拟氮沉降对温带不同森林类型土壤氮矿化速率的影响

通过室内模拟不同氮形态(NH4+-N、NO3--N、NH4+-N+NO3--N)沉降实验,研究不同氮形态沉降对温带不同森林类型(椴树红松混交林、白桦天然次生林、红松人工林和落叶松人工林)土壤氮矿化速率的影响。结果表明:在整个培养期间,与对照相比,经过氮沉降土壤净氨化速率、净硝化速率及净矿化速率都呈现出增长趋势,而其增加的程度又取决于森林类型、土层、氮处理类型和处理时间。不同林型土壤净氨化速率、净硝化速率及净矿化速率受氮沉降影响不同,混交林对氮沉降的响应要弱于阔叶林,高于针叶人工纯林;土壤A层比土壤B层对氮沉降敏感;以铵态氮形态沉降时对铵态氮含量、净氨化速率影响较大,以硝态氮形态沉降时对硝态氮含量、净硝化速率影响较大,混合形态的氮沉降要比单种形态的氮沉降使土壤净氨化速率、净硝化速率及净矿化速率增加幅度更高;氮沉降时间越长,土壤净氨化速率、净硝化速率及净矿化速率与对照差距越大,说明氮沉降对土壤的影响存在累加效应。     

Dissolved Organic Nitrogen Concentrations and Ratios of Dissolved Organic Carbon to Dissolved Organic Nitrogen in Throughfall and Soil Waters in Norway Spruce and Scots Pine Forest Stands Throughout Norway

Dissolved organic nitrogen (DON) plays an important ecological role in forest ecosystems, and its concentration is related to that of dissolved organic carbon (DOC). We investigated DON concentrations and ratios of DOC to DON in throughfall and soil waters in 16 Norway spruce and two Scots pine forest stands sampled at weekly intervals between 1996 and 2006. The stands are all included in the ICP Forests Level II monitoring program and are located throughout Norway. DON concentrations were significantly and positively related to DOC concentrations in throughfall (r ²?=?0.72, p?<?0.0001) and soil water at 5, 15, and 40 cm (r ²?=?0.86, 0.32, and 0.84 and p?<?0.0001, 0.04, and <0.0001, respectively). At most sites, the annual median DOC/DON ratio in throughfall ranged from 20.3 to 55.5, which is lower than values in soil water, which ranged from 24.5 to 81.3, gradually decreasing with soil depth. DON concentrations varied seasonally in throughfall at many plots and in soil water at 5-cm depth at one plot only, with higher values in the growing season, but there was no noticeable seasonality at greater depth. The ratios of DOC/DON in soil water were significantly positively related to the C/N ratio in soil at the same depth. Above-ground litter input was the main factor having a significant, negative relationship to DOC/DON in soil water at all depths studied. This might reflect the effect of site conditions on both DOC/DON ratios and litter quantity.     

红河谷不同林分土壤养分状况研究

为了掌握秦岭红河谷森林公园不同林分的土壤养分状况,采用野外调查、土样采集及化学分析相结合的方法,对秦岭红河谷南坡优势树种槲栎、橿子栎、鹅耳栎、辽东栎林下土壤养分状况进行了分析比较。结果表明:鹅耳栎可以显著提高林下土壤有机质的积累量,0—20cm土层有机质含量高达97.45g/kg;橿子栎林下土壤碱解氮含量最高,20—30cm土层碱解氮含量为204.92mg/kg;鹅耳栎林对提高速效磷和速效钾含量有积极的作用;槲栎林的保肥效果、缓冲性能较其他林种好。随土层加深,各种养分含量逐渐降低。     

长期不同施肥对红壤碳氮储量的影响

利用20年长期肥料定位实验,研究了不同施肥条件下土壤全氮在0~20 cm、20~40 m、40~60 cm层次中分布特征。结果表明,不同施肥处理土壤全氮含量、C/N比值均以0~20 cm土壤层次中最高,随着土壤层次加深而出现下降。长期不同施肥处理后土壤全氮储量高低趋势为:有机肥料区组>化学肥料平衡施用区组>化学肥料不平衡施用区组,有机肥料和有机无机肥料配合施用效果最为显著。长期不同施肥,土壤碳氮比(C/N)无显著差异,长期施用有机肥料,土壤有机碳和土壤全氮数量同步上升,土壤C/N比值保持稳定。有机肥料与化学肥料配合施用能够提高土壤碳氮库容,是维持土壤肥力的最优施肥方式。     

耕作方式对土壤不同粒径团聚体氮素矿化的影响

研究了常规耕作和垄作免耕两种耕作方式下紫色水稻土不同粒径团聚体中氮的矿化过程。结果表明,不同粒径团聚体氮素矿化强度具有显著差异:潜在矿化势(Np)的最高值均出现在2.0～0.25 mm大团聚体中,最低值在>2.0 mm的宏团聚体中;2.0～0.25 mm团聚体的潜在矿化速率(Vp)和实际矿化速率(Va)比其他团聚体高1.2～1.6倍。常规耕作和垄作免耕两种耕作方式下不同团聚体的净矿化率随时间的变化趋势相同;垄作免耕显著增加了氮素的净矿化量,以原土为例:垄作免耕处理Np比常规耕作处理高33.9%,Vp和Va分别比常规耕作处理高85.2%和52.0%。虽然垄作免耕可以显著促进土壤中氮素的矿化作用,但是耕作方式对不同粒径团聚体内的氮矿化动力学过程并无显著影响,表明耕作方式对不同大小团聚体中可矿化氮和微生物的分布影响较小。     

不同生物炭对安徽宣城旱地红壤氮矿化的影响

采用连续间隙淋洗培养法,研究了竹炭、烟草秸秆炭及棉花秸秆炭对安徽宣城旱地红壤氮素矿化作用的影响。结果表明:3种生物炭均可提高土壤p H,但p H增长幅度与生物炭用量相关,最高可增加2个单位;不同用量的生物炭添加都会导致土壤氮素硝化速率及矿化速率的降低,竹炭、烟草秸秆炭及棉花秸秆炭分别使硝化速率最大降幅达49.2%、72.3%与69.2%,矿化速率最大降幅达33.7%、61.9%与61.1%。因此,生物炭实际施用需作谨慎的评估,优化其使用方法。     

尿素与有机肥配施对棕红壤氮素转化的影响

为了解析尿素配施有机肥对土壤氮库活动的影响,通过室内恒温培养试验研究尿素(225kg N·hm~(-2))分别与低量(30 t·hm~(-2))、中量(60 t·hm~(-2))及高量(120、150 t·hm~(-2))有机肥配施条件下棕红壤有机氮库、无机氮库的动态变化。结果表明,配施有机肥土壤的有机氮含量较单施尿素增加16.3%~85.6%。中、高量配施显著提高土壤氮素矿化速率(p0.05),加剧无机氮转化强度,与单施尿素相比,无机氮最大矿化量增加52.9~246.0 mg·kg~(-1),有效矿化持续时间延长5 d,转化量增大2.3倍~8.7倍;配施有机肥提高土壤氨化强度,加快铵态氮(NH_4~+-N)转化速率。与单施尿素相比,配施有机肥处理NH_4~+-N含量峰值增加2.6~42.6 mg·kg~(-1),平均氨化速率提高7.8 mg·kg~(-1)·d~(-1),转化速率增加1.4倍~8.8倍。一定量配施有机肥(30~120 t·hm~(-2))对土壤的硝化过程无显著影响,但过高量配施有机肥(150 t·hm~(-2)),强化土壤硝化作用,硝化速率较单施尿素提高4.2倍,引起土壤硝态氮(NO-3-N)大量累积。氮素表观平衡结果表明,中、高量配施有机肥显著增加培养体系氮素表观损失,60、90和120 t·hm~(-2)处理氮素损失量分别较单施尿素增加2.2倍、2.8倍和2.3倍,占总输入氮的27.5%~34.5%,其中,NH_4~+-N转化损失是体系氮表观损失的主要途径。本研究结果为棕红壤合理培肥提供了理论依据。     

培肥措施对复垦土壤轻重组有机碳氮的影响

为揭示复垦土壤轻重组分有机碳氮随复垦年限和培肥措施变化的特征,采用密度分组方法研究了不施肥(CK)、单施化肥(CF)、单施有机肥(M)、有机无机配施(MCF)和生物有机肥与化肥配施(MCFB)5种培肥措施下复垦4,8年土壤轻重组分碳氮含量及碳氮比变化规律。结果表明:复垦土壤总有机碳氮与轻重组有机碳氮含量变化趋势总体均表现为随复垦年限的增加而显著提高。经过8年复垦,不同处理间,单施有机肥对总有机碳(TOC)、总有机氮(TON)、轻组有机碳(LFOC)、重组有机碳(HFOC)与轻组有机氮(LFON)、重组有机氮(HFON)的提高效果总体优于其他处理,与生土相比,增加幅度分别为148.10%,68.09%,163.68%,129.51%,35.00%,92.59%。土壤轻组组分C/N重组组分C/N,土壤轻组组分C/N总体表现为随复垦年限增加而提高,以单施化肥最高,达25.48;重组C/N表现为随复垦年限增加而降低,以单施化肥最低,为6.44。施肥对土壤碳氮库管理指数影响显著,各施肥处理均以生物有机肥与化肥配施处理效果最好。综合来看,在等量养分投入的情况下,单施有机肥更有利于采煤塌陷区复垦土壤总有机碳氮库及轻重组有机碳的积累,单施化肥更大程度促进了轻组组分有机碳和重组组分有机氮的提升幅度。     

不同氮素添加对不同土地利用方式黑土氮素转化特征的影响

以吉林省典型黑土区的玉米、果树、森林、水稻和菜地土壤为研究对象,采用室内培养法研究氮素在不同土地利用方式黑土中的形态转化特征。结果表明:施加氮肥使不同土地利用方式黑土的铵态氮和硝态氮含量均有不同程度的提高,其中铵态氮含量差异不显著,硝态氮含量差异显著。对于施加尿素的处理而言,S2(129.82 mg/kg)和C2(138.01 mg/kg)硝态氮含量显著高于G2(111.89 mg/kg)和D2(105.35 mg/kg),且Y2(126.92 mg/kg)显著高于D2。对于施加磷酸二铵的处理而言,各土壤硝态氮含量由大到小的顺序为C3(160.23 mg/kg)>Y3(150.00 mg/kg)>S3(140.12 mg/kg)>G3(133.45 mg/kg)>D3(126.70 mg/kg),且C3和Y3显著高于G3和D3。土壤净矿化速率和净硝化速率分别与土壤C/N,土壤微生物量碳、土壤微生物量氮呈显著负相关。整个培养期间,Y、G、C和D土壤平均NMR由大到小的顺序均为处理2>处理3>CK处理,S土壤平均NMR由大到小的顺序为处理3>处理2>CK处理。Y、G和D土壤平均NR由大到小的顺序均为处理2>处理3>CK处理,S和C土壤平均NR由大到小的顺序为处理3>处理2>CK处理。土壤理化性质对黑土氮素转化特征有重要影响。     

Potential of Chemically Labile Fractions to Measure Mineralizable Soil Nitrogen

Nitrogen (N) in the soil is largely organic and is available to crops only after it is mineralized to inorganic N by microbial or enzyme action. To develop a soil test for guiding N applications, a method to predict the relative amount of organic N that will mineralize in a growing season is necessary. Several chemical analysis methods proposed in the literature to measure mineralizable N were examined for chemical interference, measurement precision, response to procedure modifications, and ability to distinguish differences among soils. The chemical analyses examined involved various acid or alkaline hydrolysis, with the resulting inorganic ammonium N measured by steam distillation and manual or automated diffusion. A gelatinous precipitate in the filtered and neutralized 6 M hydrochloric acid (HCl) hydrolysis solution interfered with magnesium oxide (MgO) diffusion traditionally used to measure inorganic ammonium N. Removing the precipitate appeared to circumvent the interference. The precipitate did not appear to interfere with the sodium hydroxide (NaOH) diffusion. The 6 M HCl hydrolysis extracted 34 to 103% of clay‐fixed ammonium in the soils. Steam distillation was shown to be an acceptable alternative to diffusion for measuring NaOH‐labile N. The vigor of NaOH measurement conditions caused differences in results, showing that precise and reproducible conditions are necessary. Several methods were closely correlated (r² > 0.62) with N mineralized during aerobic incubations and could be considered for further evaluation for soil N testing. This study showed that modifications are required to several proposed analytical methods to improve their potential to estimate mineralizable N for fetilizer or other amendment recommendations for crop production     

磷高效转基因水稻OsPT4对红壤无机磷组成的影响

本研究以磷高效转基因水稻OsPT4为材料,以非转基因亲本日本晴(Nipp)和磷高效突变体水稻PHO2为对照,设施磷和不施磷2个处理,利用根盒试验研究磷高效转基因水稻OsPT4的种植对根际及非根际土壤无机磷组成的影响。结果表明:(1)Os PT4和PHO2的植株干重和磷含量均显著高于Nipp,而土壤全磷和无机磷总量均低于Nipp;(2)Os PT4和PHO2水稻根际和非根际土壤无机磷组分含量均表现为O-PFe-PAl-PCa-P;(3)施磷处理时,Os PT4和PHO2的根际土壤O-P、Ca-P含量显著低于Nipp,其非根际土壤Al-P、Fe-P和O-P含量也显著低于Nipp。不施磷处理时,Os PT4和PHO2的根际土壤Fe-P含量和非根际土壤Fe-P、O-P含量均显著低于Nipp,其根际土壤Ca-P含量显著高于Nipp。说明在供磷条件下,磷高效转基因水稻对A1-P、O-P和Ca-P的吸收活化能力较强,而缺磷条件下,磷高效转基因水稻可促进其根系对Fe-P的吸收利用。     

无机改良剂对皖南植烟红壤氮矿化的影响

以皖南植烟旱地红壤为研究对象,通过模拟试验分析了无机改良剂(T20、G20、硅藻土)对土壤氮矿化及硝化作用的影响。试验采用室内恒温间歇淋洗好气培养法(Stanford法),研究无机改良剂添加量处理(1%,2%,5%和10%)对皖南植烟红壤氮矿化的影响。结果表明,3种改良剂均可提高土壤淋洗液pH,pH增加幅度与改良剂添加量显著相关,T20、G20与硅藻土的土壤淋洗液pH增加幅度最大可提高0.30,0.50,0.43个单位;利用一级动力学方程N_t=N_0(1-e~(-kt))拟合土壤氮矿化过程,不同处理的相关系数R~2为0.970 9~0.998 0,相关性均达到极显著水平;39个供试土壤样品的有机氮矿化势N0为14.86~177.1mg/kg,平均50.53mg/kg。不同处理的N0均与改良剂添加量显著正相关,对照N0为14.86mg/kg,添加10%硅藻土、T20与G20处理的N0分别为104.1,177.1,26.01 mg/kg,是对照处理的7,11.9,1.75倍。39个土壤样品的供氮指数N0×k为0.66~6.39mg/(kg·d),平均为2.19mg/(kg·d);添加1%,2%的硅藻土处理及添加1%,5%,10%的G20处理的综合指数N0×k均显著高于对照处理。不同处理的土壤硝化累积量随时间变化符合Logistic的"S"形生长曲线,其决定系数R2为0.953 3~0.996 2,达到极显著水平。硅藻土、G20与T20处理的最大氮矿化促进率分别可达27.46%,94.76%,0.63%,而最大硝化促进率分别可达82.83%,136.4%,40.44%;氮矿化促进作用与无机改良剂添加量呈显著正相关。通过对3种改良剂的氮矿化与硝化作用比较,G20较硅藻土与T20在促进氮矿化与硝化方面具有比较优势。可见,合理增加无机改良剂,可以促进土壤有机氮的矿化以及硝化作用的进行,增强皖南旱地植烟土壤氮素的有效利用。     

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Abstract

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.     

施肥对黑土密度分组中碳、氮的影响

以中国科学院海伦农业生态实验站的长期定位施肥土壤为基础,研究长期施肥对黑土密度分组中碳和氮的影响。结果表明:氮肥能够增加土壤有机碳和全氮含量,但不如NPKOM效果明显。土壤中各组分有机碳含量的变化趋势为重组>游离态轻组>闭蓄态轻组,三者之间差异达极显著水平(p<0.01),重组有机碳的含量最大值为23.72 g/kg,而闭蓄态轻组有机碳的平均值仅为0.69 g/kg;全氮的含量的变化呈重组最大,且极显著大于闭蓄态轻组和游离态轻组,后两者之间无明显差异。不同组分中有机碳浓度和全氮浓度的变化规律一致,为游离态轻组>闭蓄态轻组>重组,且游离态轻组明显大于其它两个组分。NPKOM处理的闭蓄态轻组和重组组分中的有机碳浓度和全氮浓度大于其它施肥处理。碳氮比的变化趋势为游离态轻组>闭蓄态轻组>土壤>重组,重组和土壤中,NPKOM处理的碳氮比最低,CK处理的碳氮比最大,可见有机肥的施用加快了土壤碳的周转速度。     

Nitrogen Saturation and Soil N Availability in a High-Elevation Spruce and Fir Forest

A field study was conducted during the summer of 1995 to gain abetter understanding of the causes of nitrate (NO₃-N)leaching and ongoing changes in soil nitrogen (N) availabilityin high-elevation (1524–2000 m) spruce (Picea rubens) andfir (Abies fraseri) forests of the Great Smoky MountainsNational Park, Tennessee and North Carolina, U.S.A. Indicatorsof soil N availability (total soil N concentrations,extractable NH₄-N, extractable NO₃-N, and C/N ratios)were measured in Oa and A horizons at 33 study plots. Dynamicmeasures included potential net soil N mineralization determinedin 12-week aerobic laboratory incubations at 22 °C.Potential net nitrification in the A horizon was correlated (r =+0.83, P < 0.001) with total soil N concentrations. Mostmeasures of soil N availability did not exhibit significanttrends with elevation, but there were topographic differences.Potential net soil N mineralization and net nitrification in theA horizon were higher in coves than on ridges. Relative amountsof particulate and organomineral soil organic matter influencedpotential net N mineralization and nitrification in the Ahorizon. Calculations indicate that soil N availability andNO₃-N leaching in high-elevation spruce and fir forests ofthe Great Smoky Mountains National Park will increase inresponse to regional warming.