不同退化沙地土壤碳的矿化潜力

通过实验室土壤培养试验 ,研究了科尔沁退化沙质草地不同生境 (流动沙地 ,半固定沙地 ,固定沙地和丘间低地 )下土壤碳的矿化潜力及不同凋落物在沙地土壤中的分解。经 33d的室内培养 ,不同生境土壤 CO2 - C的释放有极显著的差异 ,与生境植被盖度 ,凋落物积累 ,土壤沙化程度 ,土壤有机碳和全氮含量的分布有显著相关。流动沙地土壤有极低的土壤有机碳和氮的含量及其微弱的土壤微生物呼吸 ,表明土地沙漠化不仅导致土壤有机碳库衰竭 ,也使土壤微生物活性丧失。在有机质含量很低的流动沙地和半固定沙地土壤中 ,含氮量高的小叶锦鸡儿 (Caragana microphylla)凋落物比含氮量低、C/N比高的差巴嘎蒿(Artemisia halodendron)和 1年生植物凋落物有较快的分解。在沙漠化的演变中 ,土壤的粗粒化 ,有机物质和养分及微生物活性的丧失制约着凋落物在土壤中的矿化潜力。灌木的存在使更多的有机物质和养分积聚在灌丛下 ,形成灌丛肥岛 ,因而显著贡献于碳的固存。     

海南岛中部丘陵地区植被恢复过程中凋落物动态及土壤碳氮含量变化

为探究海南岛中部丘陵地区植被恢复过程中凋落物分解动态和土壤碳氮含量变化,采用时空互代法,在琼中湾岭地区同时具有经自然恢复的草丛、灌丛、次生林和人工恢复的马占相思林4种植物群落的两个山坡采用凋落物袋法进行凋落物交互分解实验。结果表明:4类型凋落物在同一样地中分解时,灌丛凋落物肖梵天花分解速率最高;同一种类凋落物在4个样地中分解时,在灌丛样地的分解率较高,而在3个自然植被样地中,分解速率为灌丛>草丛>次生林,显示随着植物群落进展演替的进程,凋落物分解速率呈现先增加后降低的趋势;马占相思凋落物和在马占相思林样地分解凋落物的分解率均低于次生林。土壤碳氮含量变化不显著,但有随植被恢复进程而增加的趋势。     

草地利用方式对土壤呼吸和凋落物分解的影响

草地利用方式影响植被群落结构和土壤微环境, 制约草地生态系统碳循环。该文通过测定温带草原在放牧、割草、围封3种利用方式下湿润年(2012年)和干旱年(2011年)的凋落物产量、质量及其分解速率和土壤碳通量, 分析了草地利用方式对土壤呼吸和凋落物的影响, 探讨了凋落物对土壤呼吸的贡献机制。结果表明: 在干旱年份, 放牧样地土壤呼吸最大, 分别达到割草和围封样地的1.5倍和1.29倍; 在湿润年份, 割草样地土壤呼吸最大, 为309 g C∙m^-2∙a^-1, 明显高于放牧样地和围封样地。不论干旱年还是湿润年, 围封样地凋落物产量都大于放牧样地和割草样地。3种利用方式下湿润年土壤呼吸和凋落物分解均比干旱年增强。因此, 水分是温带草原植物生长和生态系统碳循环的主要限制因子, 草地利用方式则显著影响凋落物生产和分解。进一步分析表明, 经过两年的分解, 同一样地内凋落物质量C:N下降, N含量和木质素:N升高, 土壤呼吸与凋落物产量、凋落物分解速率以及木质素:N正相关, 而与凋落物C:N负相关。     

Effects of grassland-use on soil respiration and litter decomposition

 草地利用方式影响植被群落结构和土壤微环境, 制约草地生态系统碳循环。该文通过测定温带草原在放牧、割草、围封3种利用方式下湿润年(2012年)和干旱年(2011年)的凋落物产量、质量及其分解速率和土壤碳通量, 分析了草地利用方式对土壤呼吸和凋落物的影响, 探讨了凋落物对土壤呼吸的贡献机制。结果表明: 在干旱年份, 放牧样地土壤呼吸最大, 分别达到割草和围封样地的1.5倍和1.29倍; 在湿润年份, 割草样地土壤呼吸最大, 为309 g C·m^–2·a^–1, 明显高于放牧样地和围封样地。不论干旱年还是湿润年, 围封样地凋落物产量都大于放牧样地和割草样地。3种利用方式下湿润年土壤呼吸和凋落物分解均比干旱年增强。因此, 水分是温带草原植物生长和生态系统碳循环的主要限制因子, 草地利用方式则显著影响凋落物生产和分解。进一步分析表明, 经过两年的分解, 同一样地内凋落物质量C:N下降, N含量和木质素:N升高, 土壤呼吸与凋落物产量、凋落物分解速率以及木质素:N正相关, 而与凋落物C:N负相关。     

内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响

放牧和围封通过影响植物群落结构和土壤微环境来调控草地生态系统的碳循环。该研究在内蒙古温带草原设置轻度放牧后围封、轻度放牧、重度放牧后围封、重度放牧4种样地, 通过测定干旱年(2011年)和湿润年(2012年)地上、地下凋落物产量、质量及其分解速率和土壤养分含量, 分析不同放牧强度对凋落物形成和分解的影响, 以及围栏封育对生态系统恢复的作用。结果表明: 重度放牧地上凋落物产量和分解速率均高于轻度放牧。干旱年轻度放牧样地地下凋落物产量和分解速率高于重度放牧, 湿润年相反。短期围封显著提高了凋落物产量, 轻度放牧样地围封后地上凋落物分解速率和养分循环加快, 而重度放牧样地围封后地上凋落物分解减慢。因此, 与重度放牧相比, 轻度放牧草地的恢复更适合采用围栏封育措施; 而重度放牧草地的恢复可能还需辅以必要的人工措施。降水显著促进地上、地下凋落物形成和分解。地下凋落物的生产和分解受降水年际波动影响较大, 重度放牧草地对降水变化的敏感度比轻度放牧草地高。地上凋落物分解速率与凋落物N含量显著正相关, 与土壤全N显著负相关, 与地上凋落物C:N和木质素:N相关性不大; 地下凋落物分解速率与凋落物C、C:N和纤维素含量显著负相关。该研究结果将为不同放牧强度的草地生态系统恢复和碳循环研究提供理论依据。     

库布齐沙漠不同人工固沙灌木林土壤微生物量与土壤养分特征

在库布齐沙漠东段选取人工油蒿+杨柴半灌木混交林、人工柠条锦鸡儿灌木林和人工沙柳灌木林3种人工固沙灌木林为对象,以流动沙地为对照,研究了不同人工固沙灌木林土壤微生物生物量碳和氮、土壤微生物数量、土壤养分变化特征及其相互间的关系,并运用综合指数法对不同人工固沙灌木林的土壤恢复效果进行评价.结果表明: 与流动沙地相比,3种人工固沙灌木林土壤有机质、全氮、全磷、速效氮、速效磷含量均有不同程度的提高,表现为油蒿+杨柴林地＞柠条锦鸡儿林地＞沙柳林地,且均随土层加深而依次降低;3种人工固沙灌木林土壤微生物数量、微生物生物量碳和氮均较流动沙地有不同程度的提高,油蒿+杨柴林地土壤微生物生物量碳氮和细菌相对数量高于柠条锦鸡儿林地和沙柳林地,而真菌与放线菌相对数量则表现为柠条锦鸡儿林地＞沙柳林地＞油蒿+杨柴林地;影响3种人工固沙灌木林土壤细菌相对数量、微生物生物量碳和氮的因素是土壤有机质、全氮、全磷、速效氮、速效磷含量及C/N,而放线菌、真菌相对数量主要受土壤全磷、速效氮和速效磷含量的影响;不同人工固沙灌木林土壤质量排序为:油蒿+杨柴林地＞柠条锦鸡儿林地＞沙柳林地＞流动沙地,表明不同人工固沙灌木林的建植均能提高沙漠土壤质量,其中营造油蒿+杨柴半灌木混交林对提高土壤综合质量效果最好.     

广西大青山杉木人工林碳氮磷生态化学计量特征

为研究杉木人工林生态系统植物、凋落物和土壤碳(C)、氮(N)、磷(P)生态化学计量特征的差异和相互关系,以广西大青山杉木密度试验林为研究对象,测定了5种初植密度下杉木人工林针叶、草本、凋落物和土壤的C、N、P含量及其比值。结果表明:针叶的C、N、P含量最高,凋落物次之,土壤最低。C∶N、C∶P表现为凋落物针叶草本土壤,N∶P表现为凋落物草本针叶土壤。其中针叶的N∶P均值为16.69,凋落物C∶N显著高于N发生释放的C∶N的临界值(30)。杉木人工林针叶和草本N、C∶N呈显著负相关关系,针叶和土壤的C∶N、N∶P,草本和凋落物P含量、C∶P均呈显著正相关关系,体现了杉木生态系统内的C、N、P在针叶、草本、凋落物和土壤之间相互转化和循环。南亚热带杉木人工林植物生长受P限制,凋落物分解慢,土壤有机质的矿化作用慢,养分循环能力低,因此在人工林抚育管理中,应保护林下植被,适当施肥,提高土壤肥力,维持杉木林长期生产力。     

冬小麦生境中土壤养分对凋落物碳氮释放的影响

土壤养分影响植物生长, 进而影响凋落物质量和产量; 凋落物质量和产量影响凋落物分解过程。基于一个生长实验和一个相同环境分解实验, 研究了冬小麦(Triticum aestivum)生境中养分可利用性对凋落物碳(C)和氮(N)释放的影响。结果显示: (1)冬小麦凋落物产量、叶/根C:N比、C释放量和N释放量随土壤养分梯度呈单调变化; (2)土壤养分影响叶凋落物丢失率而不影响根凋落物丢失率; (3)初始叶/根C:N比与其C、N释放量之间存在负相关关系; (4)分解过程降低叶C:N比和根C:N比。结果表明: 生境中土壤养分的提高可加速凋落物C、N归还, 这反过来可能促进冬小麦生长, 因此这种效应是正反馈; 初始C:N比可预测凋落物C、N释放量。     

模拟N沉降下不同林龄马尾松林凋落叶分解-土壤C、N化学计量特征

模拟N沉降对森林生态系统的影响是当今全球变化生态学研究的一个热点问题,土壤碳库对N沉降比较敏感,N沉降增加了凋落叶分解过程中外源N含量,间接影响凋落叶分解的化学过程并改变凋落叶分解速率,因此,研究模拟N沉降下凋落叶分解-土壤C-N关系对预测森林C吸存有重要意义。利用原位分解袋法研究了模拟N沉降下三峡库区不同林龄马尾松林(Pinus massoniana)凋落叶分解过程中凋落叶-土壤C、N化学计量响应及其关系;N沉降水平分对照(CK,0 g m~(-2)a~(-1))、低氮(LN,5 g m~(-2)a~(-1))、中氮(MN,10 g m~(-2)a~(-1))和高氮(HN,15 g m~(-2)a~(-1))。结果表明:分解540 d后,N沉降促进20年生和30年生马尾松林凋落叶分解,46年生马尾松林中仅低氮处理促进凋落叶分解,4种处理均是30年生分解最快,说明同一树种起始N含量低的凋落叶对N沉降呈正响应,N沉降处理促进起始N含量低的凋落叶分解,起始N含量高的凋落叶分解过程中易达到"N饱和"。N沉降抑制20年生和46年生凋落叶C释放(低于对照0.62%—6.69%),促进30年生C释放(高于对照0.28%—5.55%);30年生和46年生林分N固持量均高于对照(高于对照0.15%—21.34%),20年生则低于对照(5.70%—13.87%),说明模拟N沉降处理促进起始C含量低的凋落叶C释放和起始N含量低的凋落叶N固持。N沉降处理下仅30年生马尾松林土壤有机碳较对照增加,且土壤有机质与凋落叶C、N和分解速率呈正相关,与凋落叶C/N比呈显著负相关;土壤总氮与凋落叶分解速率、凋落叶N含量呈正相关,土壤有机碳/总氮比与凋落叶C、N含量呈正相关;对照处理中凋落叶分解指标对土壤养分影响顺序是分解速率凋落物C含量凋落物C/N比凋落物N含量,低、中、高氮处理中则是凋落物C含量分解速率凋落物N含量凋落物C/N比。研究表明低土壤养分含量马尾松林对N沉降呈正响应,N沉降促进低土壤养分马尾松林凋落叶分解并提高土壤肥力;凋落叶质量和土壤养分含量低的生态系统土壤C对N沉降响应更显著。     

土壤动物对川西高山/亚高山森林凋落物分解的贡献

采用凋落物分解袋法,研究了土壤动物对川西高山/亚高山森林代表性植物康定柳、方枝柏、红桦和岷江冷杉凋落物在分解第一年(2011年11月-2012年10月)不同关键时期质量损失的贡献.结果表明: 在凋落物第一年的分解过程中, 不同物种凋落物的分解速率大小依次为康定柳＞红桦＞岷江冷杉＞方枝柏,且均为生长季节大于冻融季节.土壤动物对凋落物分解的贡献率(P_fau)为方枝柏(26.7%)＞岷江冷杉(18.8%)＞红桦(15.7%)＞康定柳(13.2%),其中康定柳和方枝柏的P_fau在生长季节大于冻融季节,而红桦和岷江冷杉的P_fau为冻融季节大于生长季节.冻融季节土壤动物的作用与凋落物初始C、P和N/P显著相关,而生长季节则与N、C/N、木质素、木质素/纤维素显著相关.     

喀斯特森林植被自然恢复过程中土壤可矿化碳库特征

2011年9月,采用空间代替时间方法,研究了茂兰自然保护区喀斯特森林自然恢复过程中土壤可矿化碳库的特征.结果表明: 研究期间,喀斯特森林自然恢复过程中不同深度土壤的总有机碳含量、可矿化碳含量和矿化速率随土层加深而减少,随恢复的进程而增加;累积矿化排放量及其速率随恢复的进程增加,其速率随培养时间延长而减小;矿化率随恢复的进程增加,而随土层加深的变化不明显;qCO₂值随恢复的进程和土层加深而递减;土壤可矿化碳与凋落物现存量及其分解质量损失率分别呈负相关(r=-0.796)和正相关(r=0.924);土壤生境由早期干扰强烈转向中后期日趋稳定,土壤的固碳能力由早期差、潜力大转向中后期强、潜力小.     

胶州湾滨海湿地凋落物分解对土壤有机碳矿化的影响

通过室内培养试验和三维荧光光谱技术(3D-EEMs),开展了胶州湾滨海湿地碱蓬、芦苇和互花米草的分解对土壤有机碳矿化的影响研究。结果表明,凋落物的添加提高了土壤有机碳矿化速率和累积矿化量,具体表现为碱蓬互花米草芦苇空白对照;乘幂曲线模型能较好地描述有机碳矿化速率和累积矿化量的变化趋势。光谱分析表明,分解过程中类蛋白荧光强度始终大于类腐殖酸荧光强度;利用荧光区域积分进行定量分析表明,不同处理下类蛋白质物质占比最高,类腐殖质物质次之;荧光参数表明,土壤有机碳的芳香化程度在培养期间先升高后降低。凋落物分解通过增加土壤中的营养物质,提高了土壤中微生物活性,从而改变了土壤有机碳的结构和化学组分,且凋落物的植被特征决定了其对土壤有机碳矿化影响程度的大小。     

植被类型与坡位对喀斯特土壤氮转化速率的影响

土壤氮素转化对于植物氮素营养具有重要作用,尤其是对于受氮素限制的喀斯特退化生态系统。选取植被恢复过程中4种典型喀斯特植被类型(草丛、灌丛、次生林、原生林)和3个坡位(上、中、下坡位)表层土壤(0—15cm)为对象,利用室内培养的方法,研究不同植被类型和坡位下土壤氮素养分与氮转化速率(氮净矿化率、净硝化率和净氨化率)的特征及其影响因素。结果表明,植被类型对土壤硝态氮含量、无机氮含量、氮净矿化率、净硝化率和净氨化率均有显著影响(P0.01),即随着植被的正向演替(草丛—灌丛—次生林—原生林),土壤硝态氮含量、无机氮含量、土壤氮净矿化速率和净硝化速率整体上呈增加趋势,而坡位以及坡位与植被类型的交互作用对上述土壤氮素指标无显著影响(P0.05)。冗余分析结果表明凋落物氮含量、凋落物C∶N比和硝态氮含量对土壤氮转化速率有显著影响,其中凋落物氮含量是影响土壤氮转化速率的主要因子(F=35.634,P=0.002)。可见,尽管坡位影响喀斯特水土再分配过程,但植被类型决定的凋落物质量(如凋落物氮含量等)对喀斯特土壤氮素转化速率的作用更为重要。因此,在喀斯特退化生态系统植被恢复初期,应注重植被群落的优化配置(如引入豆科植物)和土壤质量的改善(如降低土壤C∶N),促进土壤氮素转化及氮素的有效供给。     

Carbon mineralization in the southern Sonoran Desert

We measured carbon mineralization in four different desert habitats (Arroyos, Hillsides, Canopies-Plains and Open-Plains) and the separate effect of litter addition from annual and perennial plants on soil microbial respiration using two laboratory soil incubation experiments. The differences in total aboveground phytomass among habitats correlates with soil nutrient content, soil particulate organic matter (POM) and consequently, C mineralization. The Arroyos habitat with the highest perennial plant phytomass and litter production, had the highest soil nutrient content, soil POM and C mineralization. Litter from annual plants had twice the P concentration than litter from the perennials, but only half the N concentration. Soil microbial respiration was higher with annual plant litter than with perennial plant litter in the Hillsides and Canopies-Plains, suggesting that microbial activity in both habitats was improved by litter with a higher C quality. In contrast, in the poorest habitat, the Open-Plains, the better response to the addition of perennial plant litter suggests that microbial activity may have been constrained by N input.     

Vegetation Leachate During Arctic Thaw Enhances Soil Microbial Phosphorus

Leachate from litter and vegetation penetrates permafrost surface soils during thaw before being exported to aquatic systems. We know this leachate is critical to ecosystem function downstream and hypothesized that thaw leachate inputs would also drive terrestrial microbial activity and nutrient uptake. However, we recognized two potential endpoint scenarios: vegetation leachate is an important source of C for microbes in thawing soil; or vegetation leachate is irrelevant next to the large background C, N, and P pools in thaw soil solution. We assessed these potential outcomes by making vegetation leachate from frozen vegetation and litter in four Arctic ecosystems that have a variety of litter quality and soil C, N, and P contents; one of these ecosystems included a disturbance recovery chronosequence that allowed us to test our second hypothesis that thaw leachate response would be enhanced in disturbed ecosystems. We added water or vegetation leachate to intact, frozen, winter soil cores and incubated the cores through thaw. We measured soil respiration throughout, and soil solution and microbial biomass C, N, and P pools and gross N mineralization immediately after a thaw incubation (?10 to 2°C) lasting 6 days. Vegetation leachate varied strongly by ecosystem in C, N, and P quantity and stoichiometry. Regardless, all vegetated ecosystems responded to leachate additions at thaw with an increase in the microbial biomass phosphate flush and an increase in soil solution carbon and nitrogen, implying a selective microbial uptake of phosphate from plant and litter leachate at thaw. This response to leachate additions was absent in recently disturbed, exposed mineral soil but otherwise did not differ between disturbed and undisturbed ecosystems. The selective uptake of P by microbes implies either thaw microbial P limitation or thaw microbial P uptake opportunism, and that spring thaw is an important time for P retention in several Arctic ecosystems.     

Use of biochemical indices in the mediterranean environment: comparison among soils under different forest vegetation.

In the present study, soil biomass activity, organic carbon storage, and turnover times were compared in adjacent mediterranean biotopes with different forest vegetation, to analyze the effects of litter diversity and soil management protocols on microbial decomposition rates. Samples of forest soil from four vegetation types were collected at depths of 0-20 and 20-40 cm in the 'Tenuta Presidenziale di Castelporziano' Reserve on the Tyrrhenian coast, near Rome (Italy). The samples were incubated under standard laboratory conditions (-33 kPa water tension, and 30 degrees C), in order to compare the microbial activity independently of temperature and humidity. The CO2-C accumulation curves over a 28-d incubation period showed substantially different kinetics between the samples; in particular, soils with above-ground diversity were characterised by high mineralization activity when compared with those sampled under monospecific vegetation. For all the sites, statistically significant linear correlation was observed between nitrogen concentration and potentially mineralizable carbon (r = 0.97), and microbial biomass carbon (Cmic) to total organic carbon (Corg) ratio and the microbial metabolic quotient q(CO2) (r = -0.96). The q(CO2), indicator of the stability of ecosystems, was enhanced by plant diversity, while the Cmic:Corg ratio was reduced.     

凋落物中水溶性有机物和残渣对亚热带森林土壤氮素转化的影响

设置60%和90%WHC两种土壤水分条件,并添加凋落物过滤液、剩余残渣和丙氨酸,进行为期36 d的室内培养(25 ℃),研究了凋落物中水溶性有机物和残渣对土壤氮素转化的影响.结果表明: 在60%和90%WHC条件下,丙氨酸在土壤中迅速矿化,该处理的土壤铵态氮(NH₄⁺-N)含量分别比对照显著提高5.4%～44.7%和16.1%～41.3%,净氮矿化和氨化速率在培养前期也高于对照,而凋落物过滤液和残渣添加处理则降低了土壤NH₄⁺-N含量,且残渣的降幅大于过滤液.试验期间,土壤硝态氮(NO₃^--N)含量呈直线增长趋势,培养结束时60%WHC条件下NO₃^--N含量显著高于90%WHC.土壤水分含量增多不利于土壤有机质的矿化;90%WHC条件下可溶性有机碳(SOC)含量明显低于60%WHC,而土壤氧化亚氮(N₂O)排放量比60%WHC提高1.5～63.0倍,且在60%WHC条件下凋落物残渣添加处理显著促进了土壤N₂O的排放.凋落物在分解过程中的可溶性物质和剩余物对土壤氮的影响存在差异,且这种差异随分解而发生动态变化.     

不同来源可溶性有机物对亚热带森林土壤CO2排放的影响

采用室内培养法, 比较分析了亚热带地区杉木(Cunninghamia lanceolata)和米槠(Castanopsis carlesii)鲜叶及凋落叶浸提得到的可溶性有机物(dissolved organic matter, DOM)组成和化学性质差异对土壤CO₂排放的影响。结果表明: 添加不同来源的DOM后, 土壤CO₂瞬时排放速率在培养第1天内均显著高于对照(添加去离子水) (p < 0.05), 分别比对照增加了91.5% (添加杉木鲜叶DOM)、12.8% (添加米槠鲜叶DOM)、61.0% (添加杉木凋落叶DOM)和113.3% (添加米槠凋落叶DOM), 但培养5天后, 分别下降到对照的24.1%、8.3%、14.6%和13.2%, 随后逐渐趋于平稳。单次添加外源DOM到土壤中, 引起土壤CO₂排放速率增加的强度较大, 但持续时间短暂。培养31天时, 添加不同来源的DOM均对土壤CO₂累积排放量具有显著影响(p < 0.05), 而在培养59天时, 添加杉木鲜叶和凋落叶DOM的土壤CO₂累积排放量均显著高于添加米槠鲜叶和凋落叶DOM的土壤CO₂累积排放量, 但添加相同树种鲜叶与凋落叶DOM的土壤CO₂累积排放量之间差异不显著。培养结束后, 添加杉木鲜叶DOM和杉木凋落叶DOM后增加的土壤碳排放量, 分别是外源添加可溶性有机碳量的1.76倍和2.56倍, 而添加米槠鲜叶DOM和米槠凋落叶DOM后增加的土壤碳排放量只占外源添加可溶性有机碳量的22.5%和50.0%, 表明单次添加不同来源的DOM对土壤总有机碳库的影响是不一致的。     

Effects of understory removal, N fertilization, and litter layer removal on soil N cycling in a 13-year-old white spruce plantation infested with Canada bluejoint grass

Canada bluejoint grass [Calamagrostis canadensis (Michx.) Beauv., referred to as bluejoint below] is a competitive understory species widely distributed in the boreal region in North America and builds up a thick litter layer that alters the soil surface microclimate in heavily infested sites. This study examined the effects of understory removal, N fertilization, and litter layer removal on litter decomposition, soil microbial biomass N (MBN), and net N mineralization and nitrification rates in LFH (the sum of organic horizons of litter, partially decomposed litter and humus on the soil surface) and mineral soil (0–10 cm) in a 13-year-old white spruce [Picea glauca (Moench.) Voss] plantation infested with bluejoint in Alberta, Canada. Removal of the understory vegetation and the litter layer together significantly increased soil temperature at 10 cm below the mineral soil surface by 1.7 and 1.3°C in summer 2003 and 2004, respectively, resulting in increased net N mineralization (by 1.09 and 0.14 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004) and net nitrification rates (by 0.10 and 0.20 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004). When the understory vegetation was intact, nitrification might have been limited by NH₄ ⁺ availability due to competition for N from bluejoint and other understory species. Litter layer removal increased litter decomposition rate (percentage mass loss per month) from 2.6 to 3.0% after 15 months of incubation. Nitrogen fertilization did not show consistent effects on soil MBN, but increased net N mineralization and nitrification rates as well as available N concentrations in the soil. Clearly, understory removal combined with N fertilization was most effective in increasing rates of litter decomposition, net N mineralization and nitrification, and soil N availability. The management of understory vegetation dominated by bluejoint in the boreal region should consider the strong effects of understory competition and the accumulated litter layer on soil N cycling and the implications for forest management.