土壤易矿化有机态氮和微生物态氮作为土壤氮素生物有效性指标的评价

通过盆栽试验研究了土壤易矿化有机态氮和土壤微生物态氮与土壤净矿化氮及植物吸氮量之间的关系。结果表明,种植前土壤易矿化有机态氮和土壤微生物态氮以及种植前后土壤易矿化有机态氮的变化量均与土壤氮素净矿化量和植物吸氮量之间存在显著的相关性。在盆栽试验条件下,土壤易矿化有机态氮和种植前土壤微生物态氮能够较好地反映土壤氮素的矿化和供应能力,可以作为土壤氮素的生物有效性指标。     

土壤微生物量氮含量、矿化特性及其供氮作用

论述了土壤中微生物体氮的含量及其影响因素,土壤微生物量氮的矿化特性及其与土壤矿化氮间的关系,土壤微生物量氮含量与土壤供氮指标间的关系等。提出研究不同生态系统中土壤微生物量氮的含量及其变化规律,不同耕作栽培措施对土壤微生物量氮含量的影响。土壤微生物量在土壤氮素保持和释放中的作用,土壤微生物量氮的转化率与其供氮量间的关系;土壤微生物量氮与作物氮素吸收间的关系等,是土壤微生物量氮方面应重点研究的问题。     

氮输入对东北土壤碳蓄积氮素利用效率的影响

由于人类活动影响,通过沉降和施肥方式进入生态系统的活性氮显著增加,其对土壤有机碳库产生重要影响。氮素利用效率(NUE)作为深入理解陆地生态系统碳氮耦合关系的重要参数,对NUE时空规律的研究不仅可以评估目前氮输入对陆地生态系统碳汇增加的贡献,同时也有助于预测未来氮输入情况下陆地生态系统的碳平衡。利用生态系统过程模型——CEVSA2模型的模拟结果,分析了东北地区氮输入情况下,土壤碳的氮素利用效率(SNUE)的时空变化规律及其影响因素,结果表明:(1)1961—2010年,氮输入的显著增加促进了土壤碳的蓄积,但SNUE显著下降;(2)森林的平均SNUE最高,农田最低;灌丛的下降速率最大,森林的SNUE变化趋势最不显著;(3)三江平原和长白山地区以及大小兴安岭的部分地区SNUE最大,其次是辽河平原、松嫩平原地区;内蒙古高原、呼伦贝尔高原地区以及大、小兴安岭的部分地区SNUE出现负值,说明在这些地区,外援氮输入抑制了土壤碳的蓄积;(4)氮输入的空间分异和不同生态系统响应氮输入的差异共同决定了SNUE及其变化的空间格局。该研究结果可为进一步分析不同区域氮促汇潜力和预测未来氮输入情景下的区域碳平衡提供参考。     

土壤微生物生物量氮及其在氮素循环中作用

简述了土壤微生物生物量氮的含量及其影响因素,阐述了其在土壤氮素循环中的重要作用,着重讨论了其与可矿化氮、矿质氮、有机氮和固定态铵之间的关系,指出土壤微生物生物量氮与供氮因子间的关系在氮素循环研究中有非常重要的作用,可为调控土壤氮素的供应状况,减少氮素损失,提高氮肥利用率提供科学依据,并提出了需要深入研究的问题。     

武夷山不同海拔高度土壤有机碳矿化速率的比较

应用土壤培养法,比较分析了武夷山不同海拔高度土壤在25℃和60%田间饱和含水量条件下培养110 d有机碳矿化速率和矿化率的差异.结果表明:不同海拔高度土壤有机碳矿化速率随海拔高度的升高而加快,高山草甸(0.08 g CO2-C·kg-1·d-1)分别比亚高山矮林、针叶林、常绿阔叶林快14.3%、60.0%和166.7%,差异主要存在于0～10 cm.土壤碳矿化率以针叶林最高(16.6%),分别比亚高山矮林、常绿阔叶林、高山草甸高37.0%、67.6%和79.1%.土壤有机碳矿化速率和矿化率均随土层加深而递减,递减的幅度在不同海拔高度土壤间存在显著差异(P＜0.05).研究结果揭示,土壤碳矿化速率和矿化比率随着海拔高度的变化而产生显著的变化.     

草地生态系统中土壤氮素矿化影响因素的研究进展

氮素是各种植物生长和发育所需的大量营养元素之一,也是牧草从土壤吸收最多的矿质元素．土壤中的氮大部分以有机态形式存在,而植物可以直接吸收利用的是无机态氮．这些有机态氮在土壤动物和微生物的作用下。由难以被植物直接吸收利用的有机态转化为可被植物直接吸收利用的无机态的过程就是土壤氮的矿化．氮素矿化受多种因子的影响,这些因子可以归结为生物因子和非生物因子．生物因子包括：土壤动物、土壤微生物和植物种类．土壤动物可以促进土壤有机质的矿化;土壤微生物种类、结构及功能与氮的分解、矿化有密切的关系;不同的植物种类对土壤氮素的矿化作用是不相同的,一般来说。有豆科植物生长的土壤比其它种类土氮素矿化的作用大．非生物因素一般可以分为环境因子和人类活动干扰．环境因子中土壤温度和含水量对土壤氮素矿化的影响是国内外众多科学家研究的方向．尽管如此,在此方面的研究还没有取得一致意见,仍然需要进行这方面的研究,而在其他诸如：不同的土壤质地与土壤类型方面,研究报道的结论也很不一致,草地生态系统中人类活动对土壤氮素矿化的影响主要包括,不同强度的放牧,割草以及施肥、火烧强度等．非生物因子对氮素矿化的影响非常直接和明显,尤其是人类活动．本文综述了近年来影响草地生态系统土壤氮素矿化有关因素的一些进展．     

沙地不同树种人工林土壤氮素矿化过程及其有效性

土壤氮素（N）转化是生态系统重要的生态过程之一,可作为生态恢复评价的重要指标。以位于科尔沁沙地东南缘的章古台地区草地、30年生的樟子松（Pinus sylvestris vat．mongolica）、赤松（P.densiflora）和杨树（Populus simonii）人工林为对象。采用PVC顶盖埋管法和离子交换树脂袋法研究了土壤N矿化特征及其有效性。结果表明,生长季内土壤N净矿化量表现为草地（8.06μg／g）和赤松林（9．06μg／g）低于樟子松林（18．36μg／g）和杨树林（17．88μg／g）（P〈0．05）;树脂吸附的无机N表现为草地（283．50μg／g dry resin）和杨树林（297.00μg／g dry resin）最低,樟子松林（440．10μg／g dry resin）居中,而赤松林（835．65μg/g dry resin）最高（P〈0．05）。综合分析林地土壤理化特性、矿化特征和N有效性,表明樟子松、赤松和小叶杨均可作为固沙造林选择树种,其表现为赤松〉樟子松〉小叶杨。认为深入开展生态系统N平衡研究有利于更好地评价固沙林的功能。     

毛竹扩张对常绿阔叶林土壤氮素矿化及有效性的影响

采用时空替代法和PVC顶盖原位培养法,分析了江西大岗山毛竹扩张形成的竹-阔混交林与邻近常绿阔叶林土壤中的无机氮含量、氮矿化速率和吸收速率等指标.结果表明:两种林分土壤总无机氮含量时空变化趋势相同;竹-阔混交林年均矿化速率低于常绿阔叶林,前者以氨化作用为主,后者氨化作用与硝化作用相当,但生长季硝化作用明显占优势.两林分全年都以吸收NH4+-N为主,但生长季常绿阔叶林对NO3--N的吸收明显占优势.说明毛竹向常绿阔叶林扩张会增强土壤氮素氨化作用、减弱硝化作用和总矿化作用,同时也会增加对NH4+-N的吸收,减少对NO3--N和总无机氮的吸收.     

秸秆在土壤内分解初期氮素矿化与固持的模拟测定

利用模拟软件Modelmaker对3种作物秸秆在土壤内分解初期氮素循环转化过程进行了模拟,取得了土壤铵态氮、硝态氮、微生物氮及其¹⁵N丰度等个变量模拟值和测定值的良好一致性.模型模拟对氮转化速率测定的结果表明,土壤微生物主要固持铵态氮,对硝态氮固持非常微弱.氮矿化主要发生于作物秸秆,腐殖质氮的矿化极其微弱.一级动力学方程对秸秆氮素矿化过程的描述优于零级动力学方程.微生物固持氮的再矿化过程落后于氮固持过程,假定再矿化不发生或认为再矿化与固持化同时进行可导致氮矿化与固持速率测定的严重误差.忽略氮硝化过程和挥发损失将导致氮矿化和固持速率的测定值偏低.净固持或净矿化的产生不仅与秸秆碳氮比有关,而且与秸秆在土壤内分解时间有关.     

赣中亚热带森林转换对土壤氮素矿化及有效性的影响

采用原位培养法和时空替代法,对江西中部亚热带常绿阔叶林、天然马尾松林、人工杉木林、人工马褂木林的土壤氮素矿化速率及其有效性进行了比较研究,以探讨森林转换对土壤氮素矿化作用的影响。结果表明：转换前后各森林土壤无机氮库（NH4 -N、NO3--N）及氮素矿化速率(氨化速率、硝化速率)均呈现明显的季节动态,NH4 -N库冬春较大,NO3--N库夏秋较大,氨化速率与硝化速率均以夏秋强烈。森林转换改变了土壤氮素矿化格局,常绿阔叶林转变成马尾松林、杉木林、马褂木林后,土壤年均氨化速率分别降低了110.67%、100.76%、96.20%,而硝化速率提高了54.92%、24.19%、 24.46%;马尾松林年均总净矿化速率与常绿阔叶林相近,杉木林、马褂木林分别降低了24.68%、26.01%;另外,除常绿阔叶林外,马尾松林、杉木林、马褂木林的土壤氮素矿化量都小于植被吸收量。这些研究结果说明亚热带地区常绿阔叶林转换成其它次生林会增加氮素流失的危险性,氮素缺乏会成为这些森林生长的限制因子。     

Effect of cultivation on the mineralization of nitrogen in soil

Summary The effect of cultivation (ploughing followed by rotavation) on the mineralization of soil nitrogen was measured at 2 sites on a silt loam soil. Both sites had a predominantly arable cropping history but one had been under grass for the previous 2 years and the other had carried wheat. Mineralization of N was slightly faster in cultivated soil but the difference was only significant at the site previously under grass. At this site cultivated soil contained 7 kg ha^–1 more mineral N than uncultivated soil 2 weeks after treatment, and 9 kg ha^–1 after 6 weeks. The corresponding figures for the site that had grown wheat were 4 and 6 kg N ha^–1.     

土壤氮素循环模型及其模拟研究进展

N既是植物必需的营养元素,又是造成环境污染的重要元素.正确模拟土壤中N循环已经成为科学家共同关注的热点问题.简述了土壤N循环的基本过程,重点介绍了13种土壤N循环模型和6个土壤N循环过程的模拟,并讨论了模拟中存在的参数化问题.     

Modelling the change in soil organic C and N and the mineralization of N from soil in response to applications of slurry manure

A computer simulation model of the turnover of organic matter in soil was adapted to simulate the change in soil organic C and N contents of soil during several years following annual additions of farm slurry to maize fields. The model proved successful in estimating the build-up of both C and N in soil and the leaching of N to ground-water in response to applications of slurry ranging from 50 to 300 tons per hectare per year. The model was then used to estimate the build-up of organic matter in soil under crops of fodder maize that were grown using the excess of manure produced during the last 20 years in the Netherlands. The build-up of organic matter from these applications was estimated to lead to about 70 kg extra nitrogen mineralized ha^-1 yr^-1. As a result of legislation manure applications have decreased and are expected to decrease further in the immediate future. Calculations suggest that after 10 years of manure applied at rates no longer exceeding the amount needed to replace the phosphorus removed by crops, the extra mineralization of N will still be between 45 and 60 kg ha^-1 yr^-1. If manure applications cease altogether then the extra mineralization will be about 25–30 kg N ha^-1 yr^-1.     

不同氮输入对湿地草甸沼泽土N_2O排放和有机碳矿化的影响

通过室内培养实验,研究了不同氮输入梯度下(N0:0mg·g-1,N1:0.1mg·g-1,N2:0.2mg·g-1,N3:0.5mg·g-1)湿地草甸沼泽土N2O排放和有机碳矿化特征,并分析了土壤微生物量碳、氮变化规律。整个培养期(23d)内,N0、N1、N2和N3处理N2O排放总量分别为91.12、133.02、147.75和303.45μg.kg-1,随氮输入量增大而增大,表明氮输入对N2O排放产生促进作用;氮输入处理的有机碳矿化速率在整个培养期除最后培养阶段外均低于对照,表明氮输入对有机碳矿化有一定的抑制作用;各氮输入处理土壤微生物量碳降低,与对照差异显著(P0.05),但各处理间差异未达到显著水平,土壤微生物量氮随氮输入量增大呈线性增加,各处理间差异显著(P0.05),表明氮输入影响土壤微生物结构和组成,具体影响机理须进一步探讨。     

Controls on inorganic N species transformations and potential leaching in freely drained sub-soils of heavily N-impacted acid grassland

In N-polluted, minimally managed soils, recent research has shown that ammonium-N, as well as nitrate-N, may move down through soil profiles. There is a need, therefore, to reassess what controls N species transformations below the rooting depth in such soils. The changes with depth down to 1 m in extractable ammonium-N and nitrate-N concentrations have been studied for two heavily N-impacted acid grassland soils near York, UK, for fresh soils and for soils incubated after either deionised water (d.w.) or ammonium-N spiking. Although in close proximity, the profiles showed marked differences in their relationships of ammonium- and nitrate-N to soil pH, C%, N% and C:N ratio. One profile was slightly more acidic at the surface, which seems to have changed the distribution of organic matter throughout the soil profile. Trends in ammonium production with depth were clearer when ammonium-N concentrations were recalculated on the basis of ammonium-N per unit mass of soil organic C. This then allowed a consistent trend with soil pH to be discerned for both profiles. Ammonium-N spiking showed that ammonium substrate availability was limiting potential net nitrification rate at 20–60 cm depth for both profiles. Potential mineral-N production was considerable at depth, which would facilitate transport of N to surface waters and/or groundwaters.     

增氮对青藏高原东缘典型高寒草甸土壤有机碳组成的影响

土壤有机碳动态是陆地生态系统碳平衡研究的关键环节,有关青藏高原高寒草甸土壤有机碳组成对大气氮沉降增加的响应研究至今尚未开展。基于中国科学院海北生态站的大气氮沉降模拟控制实验平台,于2010年5月、7月和9月中旬分别测定不同施氮处理下0—10cm、10—20cm、20—30cm土壤中粗颗粒态有机碳(CPOC)、细颗粒态有机碳(FPOC)和矿质结合有机碳(MOC)含量,研究不同施氮类型(NH4Cl,(NH4)2SO4和KNO3)和施氮水平(0、10、20、40 kgN.hm-.2a-1)对土壤POC和MOC含量以及POC/MOC比值的影响。结果表明:青藏高原高寒草甸土壤POC积聚在土壤表层,占总土壤有机碳(SOC)含量的64%以上,稳定性较差。施氮水平显著改变了土壤CPOC、FPOC和MOC含量,而施氮类型的影响不显著。不同月份土壤POC和MOC含量对增氮的响应不同,反映了SOC组分对增氮响应的时间异质性。在生长季中期,施氮倾向于增加表层土壤POC含量,而在生长季初期和末期恰好相反。土壤MOC对增氮的响应不敏感。另外,施氮显著降低生长季初期表层土壤POC/MOC比例,SOC稳定性增加。表明,青藏高原高寒草甸土壤有机碳活性组分较高,未来大气氮沉降增加短期内即可降低活性有机碳含量,相应地改变了其组成和稳定性。     

土壤水分和氮添加对华北平原高产农田有机碳矿化的影响

通过105 d的恒温(25℃)控湿室内培养方法,探讨了华北平原高产粮田土壤有机碳矿化特征以及水分和有机、无机氮输入对其影响。试验设4个肥料添加水平和4个水分梯度,分别为对照(S0)、仅添加无机氮(尿素)(S1)、无机氮和有机氮(鸡粪)配施(S2)以及仅添加有机氮(S3)和25%(田间持水量;M0)、50%(M1)、75%(M2)和100%(M3)共16个处理,每处理3次重复。结果表明,各处理有机碳矿化速率均在培养后1 d达第1高峰,之后直线下降,培养7 d时下降幅度达57.2%—75.0%,培养20—30 d时出现第2高峰。有机碳累积矿化量有208.8—1161 mg/kg,主要集中在前30 d,可占整个培养期的59.1%—69.9%,105 d的净矿化率为0.07%—2.01%。根据双指数方程模拟结果,研究了土壤潜在矿化碳库(C1+C2),其中活性碳库(C1)和惰性碳库(C2)分别为53.0—135.1 mg/kg和156.9—1069 mg/kg,潜在矿化率为1.75%—9.66%。土壤含水量显著影响有机碳矿化,且与潜在矿化碳库呈二次函数关系(P0.05)。田间持水量25%—100%范围内,随着土壤含水量的升高,有机碳矿化速率呈增加趋势,但增幅降低,其中M2(田间持水量75%)的有机碳净矿化率最高。有机碳矿化量与土壤微生物碳和矿质氮含量呈线性正相关(P0.05),保持氮水平(200 kg N/hm2)相同,有机氮(鸡粪)和无机氮(尿素)均显著促进土壤有机碳矿化,但两者间差异不显著(P0.05),且有机氮和无机氮对有机碳矿化的影响均与土壤含水量有显著交互作用(P0.05)。     

Effect of mild drying on the mineralization of soil nitrogen

Summary Drying soil to –100 kPa increased the subsequent mineralization of nitrogen under optimal moisture conditions. The effect was greater when the soils were dried to –1500 Pa. Mineralization was greater after four cycles of wetting and drying than after one. Depending on the drying conditions, the amount of nitrogen mineralized after drying to –1500 Pa was between 6.8 and 18.2% of that mineralized after chloroform fumigation. After drying the soils the average ratio of CO₂-C respired to min N was 21.1–22.3 depending on the drying conditions, whereas after chloroform treatment and autoclaving the ratio was 6.0 and 9.9 respectively. The effect of drying on nitrogen mineralization is attributed to two causes: the death and subsequent lysis of a small proportion of the soil organisms, and to the desorption of organic substances with a wide C/N ratio.Because of the stimulation of even mild drying conditions, marked differences in mineralization rates of soil nitrogen between cropping seasons must be expected.     

Effects of roots and litter on mineralization processes in forest soil

Summary Leaf litter breakdown and fine root production, including exudation, are two major influences upon carbon and nitrogen mineralization rates in forest soil. Sieving and root removal experiments were used to examine their effects. Although carbon mineralization rates declined in smaller particle size fractions of forest litter, this trend largely disappeared when results were calculated on an ash-free basis. Nitrogen mineralization by contrast, was greatest in smaller fractions.Much of the variation in carbon mineralization rates appeared to be associated with fine roots. A rapid initial exponential decay phase noted in laboratory respiration studies was probably associated with disappearance of available carbon in the form of root exudates and/or the microorganisms dependent on them. Clear cutting caused a marked reduction in the size of available carbon pools, reflecting decreased root exudation and rhizosphere activity. A model of mineralization is proposed which represents the available and humified carbon pools.Deceased