模拟N沉降对太岳山油松人工林和天然林草本群落的影响

由于人类活动氮沉降呈逐年增加的趋势,进而增加了陆地生态系统氮的输入,从而影响陆地生态系统多样性、物种组成和功能。为揭示氮沉降增加对油松林草本群落的影响,于2009年7月在太岳山油松人工林和天然林,设计4个施氮水平:对照(CK,0 kg N hm-2a-1),低氮(LN,50 kg N hm-2a-1),中氮(MN,100 kg N hm-2a-1)和高氮(HN,150 kg N hm-2a-1),研究草本群落的生物多样性、生物量以及草本元素含量对模拟N沉降的响应。研究结果表明:模拟N沉降未能显著影响人工林草本群落的生物多样性(P0.05),而中氮、高氮显著降低了天然林草本群落的生物多样性(P0.05);从Jaccard指数和Sorensen指数分析得出人工林不同氮水平之间草本群落差异性较小,而天然林不同氮水平之间草本群落差异性较大。模拟N沉降没有显著改变人工林草本群落生物量(P0.05),而高氮明显促进天然林草本群落生物量的增加(P0.05)。与对照相比,模拟N沉降提高了人工林和天然林羊胡子苔草叶根中的全N含量(P0.05),而降低了全Mg的含量(P0.05),并且根部元素含量变化与土壤养分含量变化较为一致。施氮提高了N/K、N/Ca、N/Mg(P0.05)的比值。说明油松林下草本群落对氮沉降的响应因林分土壤N饱和程度以及林地利用历史的不同而产生差异,其中天然林响应最为敏感。     

福建省马尾松和杉木针叶中7种营养元素含量特征

为了解福建省马尾松和杉木人工林养分需求特征,选取25个马尾松(Pinus massoniana)林和31个杉木(Cunninghamia lanceolata)林,测定了针叶中7种主要营养元素(C、N、P、S、K、Ca、Mg)含量。结果表明,马尾松针叶K、Ca、Mg含量显著低于杉木,分别是杉木的68%、14%、50%,表明杉木对矿质养分尤其Ca的需求远高于马尾松,提示马尾松比杉木更能适应矿质养分尤其Ca较贫瘠的立地。两树种针叶C、N、P、S含量及其化学计量比均表现出相似的内稳态特征,而Ca、Mg、K含量及其化学计量比的变异大,表明这3种矿质元素受立地条件的影响较大。两树种对N、P、K需求表现为协同正相关关系,N与Ca含量则为负相关关系,暗示持续N沉降或营林实践中长期施N肥可能抑制Ca的吸收。     

模拟氮沉降对杉木幼苗养分平衡的影响

为研究氮沉降对植物养分平衡的影响,对1a生杉木（Cunninghamia lanceolata（Lamb.）Hook.）幼苗进行了室内模拟试验。以NH4NO3作为外加氮源,设计了N0（0 g N m-2?a-1）、N1（6 g N m-2?a-1）、N2（12 g N m-2?a-1）、N3（24 g N m-2?a-1）和N4（48g N m-2?a-1）等5种氮沉降水平,每处理重复6次。通过1a的试验发现,杉木幼苗叶、茎、粗根和细根中的N、K、Mg含量随氮处理水平的增加而上升,但Ca在各器官中的含量则呈下降趋势;中低氮（N1,N2）对叶、茎和粗根中P的含量表现为促进作用,而高氮（N3,N4）则表现为抑制作用。幼苗各器官中的N与其他养分元素的比值随氮处理水平的增加而普遍升高,但粗根中的N/K、N/Mg则表现为下降。与对照（N0）相比,在N1、N2、N3、N4处理中,幼苗对外加氮素的表观利用率分别为60.7%、57.9%、43.3%和27.9%,随氮处理水平增加,利用率呈明显下降趋势。随着氮处理水平的增加,幼苗体内的氮分配到叶和细根中的比例增加,而分配到茎和粗根中的比例下降。因此,氮沉降明显增加了杉木幼苗各器官的氮含量,影响了幼苗的养分平衡。     

模拟氮沉降对典型阔叶红松林土壤有机碳和养分的影响

为探讨氮沉降对典型阔叶红松(Pinus koraiensis)林的影响,从2008年6月~2010年8月进行了人工模拟氮沉降实验,实验分为对照、低N、中N、高N4个处理,每个处理3个重复。所施氮肥为CO(NH2)2,以溶液的形式喷施,4个处理浓度分别为0、30、60、120 kg·hm-2·a-1。在氮沉降进行1年后,采集各处理0~20、20~40和40~60 cm的土壤样品,测定其土壤有机C、全N、碱解N和速效P、速效K。结果表明:相同处理下,有机C和全N含量随土层的加深均逐渐减少。总体上低、中N处理显著增加了土壤有机C、碱解N和速效K含量,中、高N处理显著降低了土壤速效P含量(P0.05),而对全N含量影响不显著(P0.05)。土壤有机C与土壤全N、碱解N、速效P、速效K之间存在极显著正相关关系(P0.001)。有机C和土壤养分对氮沉降的响应说明氮沉降在短期内可能影响阔叶红松林土壤碳库积累和土壤肥力水平。     

杉木人工林凋落物量对氮沉降增加的初期响应

通过野外模拟试验,研究了杉木人工林凋落物对氮沉降增加的初期响应。试验设计为4种处理,分别为N0(0kgN.hm-2.a-1,对照)、N1(60kgN.hm-2.a-1)、N2(120kgN.hm-2.a-1)、N3(240kgN.hm-2.a-1),3次重复。通过2年监测发现,对照样地的年凋落量为2427.51kg.hm-2,而经N1、N2、N3处理后,其年凋落物量分别为2238.10、2286.66和2599.50kg.hm-2。表明高氮(N3)处理显著增加了杉木林凋落物量(P<0.05),而中低氮处理(N1、N2)没有显著影响。各处理的总凋落物量表现出明显的季节动态,在2、5和7月出现3个比较明显的峰值。在凋落物的组成中,落叶占总凋落量的70.49%～73.67%,其次分别为落枝(19.38%～20.39%)、碎屑物(4.98%～7.70%)、落果(1.11%～2.16%)和树皮(0.29%～0.33%)。LSD多重比较显示,N3处理对落叶和落果产生显著影响,对其它组分的影响不明显。     

不同种源油松幼苗的光合色素和非结构性碳水化合物对模拟氮沉降的短期响应

以不同种源(内蒙NM、北京BJ和山西SX)的3年生油松幼苗为研究对象,研究不同种源油松幼苗的光合色素以及非结构性碳水化合物(NSC)对氮沉降增加的短期响应。实验中设置5个氮处理:CK(0 kg hm-2a-1)、N1(15 kg hm-2a-1)、N2(25 kg hm-2a-1)、N3(50 kg hm-2a-1)、N4(150 kg hm-2a-1)。研究结果表明:(1)不同生长季,3个种源油松幼苗的光合色素对氮沉降增加的响应存在差异,但是只有BJ种源油松幼苗的叶绿素含量在生长季中期受到了氮沉降增加的显著促进作用,并在N4水平下达到最大值。(2)氮沉降的增加促进了3个种源油松幼苗NSC的转移和消耗,在生长季初期和中期,随着氮沉降水平的升高,3个种源油松幼苗的可溶性糖(SS)含量、淀粉(ST)含量以及总非结构性碳水化物(TNC)含量呈不同程度的降低。生长季末期,3个种源油松幼苗的SS和TNC明显积累。N4水平抑制了NM种源油松幼苗SS和BJ种源油松幼苗ST的累积,促进了NM种源油松幼苗ST含量和BJ种源油松幼苗SS含量的提高。氮沉降的增加显著抑制了SX种源油松幼苗NSC的积累,延长了幼苗的生长期,推迟了幼苗进入休眠的时间。     

杉木光皮桦混交林效益的研究

对桂西北杉木光皮桦混交林和杉木纯林的对比研究表明,35年生杉桦混交林的立木蓄积量为441.087 m3*hm-2,比杉木纯林高3.6%。混交林枯枝落叶层现存量及其N,P,K,Ca,Mg等元素的质量浓度分别为13.18 t*hm-2,158.3,6.1,16.5,86.3和32.3 kg*hm-2,分别比杉木纯林高9.7%,76.7%,69.4%,96.4%,83.2%,17.0%。混交林地(0～100 cm)土壤容重为0.81～1.22 g*hm-3,比杉木纯林低1.0%～8.0%,而土壤孔隙度,通气度和持水量分别比杉木纯林高2.0%～3.9%。土壤有机质、全氮、水解氮、有效磷和速效钾分别比杉木纯林高5.5%～49.8%。     

模拟氮沉降条件下木荷幼苗光合特性、生物量与C、N、P分配格局

设置模拟氮沉降的控制试验,以NH4NO3作为外加氮源,设计CK(0kg N hm-2·a-1)、LN(50 kg N hm-2·a-1)、MN(100 kg N hm-2·a-1)、HN(150 kg N hm-2· a-1)4个处理,历时9个月,测定木荷(Schima superba)幼苗的光合特性、生物量和C、N、P含量及其分配格局对氮沉降的响应.结果表明:(1)木荷幼苗的最大净光合速率和光饱和点随着氮处理水平增加呈先增加后减小的特点,在中氮处理下极显著增加(P＜0.01).氮处理降低了幼苗的光补偿点和暗呼吸速率,光补偿点在低氮处理下显著降低(P＜0.05),暗呼吸速率在低中氮处理下极显著降低(P＜0.01),高氮处理下显著降低(P＜0.05).未见氮处理对表观量子效率产生显著影响.(2)氮处理促进了木荷的全株生物量以及各部分生物量的增长.随着氮处理水平的增加,叶重比呈升高的趋势,而根重比和根冠比呈降低的趋势,在高氮处理下叶重比的增加和根重比、根冠比的降低都达到了显著水平(P＜0.05).(3)氮沉降促进各器官N含量的增加,在高氮处理下根和茎中N含量极显著增加(P＜0.01),叶中N含量显著增加(P＜0.05).而各器官C含量随着氮沉降程度的增加呈先增加后降低的趋势,在中氮处理下根和茎中C含量极显著增加(P＜0.01),叶中C含量显著增加(P＜0.05).但各器官P含量变化趋势各不相同,随着氮的增加,根中P含量是呈先增加后降低的趋势,而茎和叶中P含量是呈降低的趋势.氮沉降一定程度上降低了木荷各器官的C/N比值而增加了N/P比值.     

氮沉降下杉木(Cunninghamia lanceolata)人工林凋落叶分解过程中C、N元素动态变化

在12年生的杉木(Cunninghamia lanceolata)人工林中开展模拟氮沉降试验,分N0(对照)、N1、N2、N3等4种处理,N沉降量依次为0、60、120、240 kg N hm-2 a-1,每处理重复3次.通过2 a的监测和分析发现,经N0、N1、N2、N3处理后,凋落物分解过程中C平均含量分别为46.47%、46.35%、46.79%、46.6%,各处理之间无显著差异,但均随着分解时间的增加呈下降趋势.氮沉降明显增加了凋落物中的N含量,且随着沉降水平的增加而增加.各处理凋落物C的分解系数依次为0.739、0.744、0.936、0.708,周转期为4.26 a、4.26 a、3.46 a、4.41 a;而N的分解系数分别为0.458、0.543、0.776、0.565,周转期为6.26 a、5.44 a、3.91 a、5.20 a.N1处理表现出促进N释放的作用,但对C释放影响不明显;N2处理促进了凋落物C、N元素的释放,而N3处理则表现出一定的抑制作用.氮沉降处理也明显降低了凋落物的C/N比,N1、N2、N3处理使C/N比分别比N0下降8.59%、14.20%和17.54%.     

杉木人工林凋落物生态化学计量与土壤有效养分对长期模拟氮沉降的响应

凋落物分解的快慢和养分释放的速度决定了生态系统中土壤有效养分的供应。探讨全球变化条件下森林生态系统凋落物与土壤养分的变化规律,有利于深入认识凋落物-土壤相互作用的养分调控因素,从而揭示生态系统C、N、P循环。通过模拟氮沉降增加试验,分4个水平处理,分别为0、60、120、240 kg N hm~(-2)a~(-1)。模拟氮沉降13年后,分析了杉木人工林凋落物中不同组分(落叶、落枝、落果)生态化学计量与土壤有效养分(有效氮、碱解氮、速效磷、速效钾)的关系。结果表明:氮沉降(N1、N2和N3)显著提高了落叶和落枝的N含量,平均增幅分别为35.27%和32.21%;高水平氮沉降(N3)处理显著降低了落叶和落枝的C/N,平均降幅分别为25.95%和22.32%,但N3增加了落枝和落果N/P,平均增幅分别为38.4%和31.7%;氮沉降对凋落物各组分的C、P和C/P均影响不显著。氮沉降处理显著增加了土壤NO_3~--N和NH_4~+-N含量,均表现为N3N2N1N0,其中NO_3~--N含量更容易受氮沉降处理的影响,表现为更大的增幅。N2显著增加0—20 cm土层的碱解氮含量,N1显著降低0—20 cm土层的速效钾,但氮沉降对速效磷含量没有影响。凋落物生态化学计量与土壤有效养分之间的Pearson相关和冗余分析(RDA)表明,凋落物生态化学计量与土壤有效养分之间关系紧密,凋落物P含量(蒙特卡罗检验,P=0.018)和C/P比值(P=0.037)对土壤有效养分影响显著。凋落物中C/N比值、C/P比值与土壤有效养分呈显著负相关,其比值越高越不利于土壤有效养分的累积。     

大气CO2浓度升高和N沉降对南亚热带主要乡土树种叶片元素含量的影响

大气CO₂浓度升高和N沉降以及二者之间的耦合作用对陆地森林生态系统的影响是当前国际生态学界关注的热点之一。该实验运用大型开顶箱(open-top chamber, OTC)研究: 1)高CO₂浓度(700 μmol×mol^-1) +高N沉降(100 kg N×hm^-2×a^-1) (CN); 2)高CO₂浓度(700 μmol×mol^-1)和背景N沉降(CC); 3)高N沉降(100 kg N×hm^-2×a^-1)和背景CO₂浓度(NN); 4)背景CO₂和背景N沉降(CK) 4种处理对南亚热带主要乡土树种木荷(Schima superba)、红锥(Castanopsis hystrix)、肖蒲桃(Acmena acuminatissima)、红鳞蒲桃(Syzygium hancei)、海南红豆(Ormosia pinnata)叶片元素含量的影响。研究结果表明, 大气CO₂浓度升高对5种乡土树种叶片元素含量有较大的影响, 除海南红豆叶片的Ca含量外, 其他树种的叶片元素含量在高CO₂浓度处理下都显著升高(p < 0.05); 而在N沉降处理下, 5个树种的叶片K和Ca含量都降低。大气CO₂浓度升高与N沉降处理对5种乡土树种植物叶片元素含量影响的交互作用不是很明显, 仅仅木荷和红鳞蒲桃的叶片Ca和Mn以及海南红豆的叶片Mn含量在大气CO₂浓度上升和N沉降交互处理下显著下降, 而肖蒲桃的叶片P含量在大气CO₂浓度上升和N沉降交互处理下显著上升。     

密云水库水源保护区板栗林主要养分元素生物循环研究

对密云水库北京集水区板栗林主要养分元素循环进行了研究。结果表明,22年生板栗林的生物量为38638kg·hm^-2;板栗林5种主要养分元素N、P、K、Ca、Mg贮存量为315．38kg·hm^-2,各器官中5种元素贮存量大小排序是干>枝>根>叶>花>果苞>果。板栗林生态系统乔木层每年从土壤中吸收的5种养分元素量为79．17kg·hm^-2,吸收量占0～30cm土层5种养分元素总量的0．15％,占0～30cm土层中5种元素有效养分量的1．95％。年吸收量中存留量为11．25kg·hm^-2,枯落物归还量为58．08kg·hm^-2。雨水及雨水淋溶输入到板栗林生态系统的养分元素量为38．63kg·hm^-2,果实输出量为9．84kg·hm^-2。雨水和雨水淋溶量与枯落物归还量之和大于吸收量,表明研究期间板栗林生态系统养分元素的收入略大于支出,5种元素的吸收系数排序为N>P>K>Ca>Mg,利用系数排序为K>N>Mg>P>Ca。循环系数排序为K>N>P>Mg>Ca。周转期排序是Ca>P>Mg>N>K。     

Dynamics of Nutrient Translocation in Stemwood across an Age Series of a Eucalyptus Hybrid

Despite the continuous nature of growth of eucalyptus hybridsin Congo, taper functions fitted to stem profiles of one clonethroughout stand development, combined with annual tree measurements,made it possible to locate accurately the position of annualrings in stems. Annual rings were identified on discs of woodsampled every 4 m in four trees cut from 1-, 2-, 3-, 4-, 5-,6- and 7-year-old stands. Chemical analysis, performed individuallyfor each ring per level and per tree sampled, made it possibleto quantify the changes in nutrient content of the rings duringstand development. Nutrient translocation in stemwood was thuscalculated in a stepwise manner between trees of two successiveages. The cumulated nutrient translocations in stemwood fromthe 1-year-old stage to the 6-year-old stage amounted to 18·5kg ha^-1N, 4·2 kg ha^-1P, 38·8 kg ha^-1K, 1·5kg ha^-1Ca and 3·2 kg ha^-1Mg. They represented 11, 18,121, 6, and 15% of the amounts of N, P, K, Ca and Mg accumulatedin stemwood, respectively, at the 7-year-old stage (loggingage). Negative translocations of N, P, Ca and Mg in stemwoodbetween 6 and 7 years might indicate an improvement in the nutritivestatus of the stand at the end of the rotation. Much translocationof K in stemwood suggests that this process might be involvedin the high use efficiency of this element. Copyright 2001 Annalsof Botany Company Translocation, stemwood, ring, nutrient, Eucalyptus, age series     

水氮配合对绿洲沙地农田玉米产量、土壤硝态氮和氮平衡的影响

在黑河中游边缘绿洲沙地农田研究了不同的水氮配合对玉米产量、土壤硝态氮在剖面中的累积和氮平衡的影响.结果表明,施氮处理较不施氮处理产量增加48.22%～108.6%,施氮量超过225 kg hm-2,玉米产量不再显著增加.受土壤结构影响土壤硝态氮在土壤中呈"W"型分布,即土壤硝态氮含量在0～20 cm、140～160 cm和260～300 cm土层均出现峰值,并随施氮量增加,峰值增高.在常规高灌溉量处理硝态氮含量峰值最高值出现在260～300 cm土层,节水25%灌溉处理硝态氮含量峰值最高值出现在土壤表层0～20 cm土层.在常规高灌溉量处理0～300 cm土层中200～300土层硝态氮累积量所占比例最高,介于27.56%～51.86%之间;节水25%灌溉处理在0～300 cm土层中100～200土层硝态氮累积量所占比例最高,介于32.94%～38.07%之间;表明低灌溉处理下土壤硝态氮在土壤浅层累积较多,而高灌溉处理使更多的硝态氮淋溶至土壤深层.与2006年相比,2007年不施氮处理0～200 cm土层土壤硝态氮含量和积累量均明显减少;而施氮处理变化很小,在低灌溉处理甚至表现出硝态氮含量和积累量增加,表明施氮是土壤硝态氮累积的主要来源,而灌溉则使硝态氮向土壤深层淋溶.0～200 cm 土层土壤硝态氮累积量平均介于27.66～116.68 kg hm-2、氮素表观损失量平均介于77.35～260.96 kg hm-2,和施氮量均呈线性相关,即随施氮量增加,土壤硝态氮累积量和氮素表观损失量均增加,相关系数R2介于0.79～0.99之间,相关均显著.随施氮量增加,玉米总吸氮量和氮收获指数增加,氮的农学利用率降低,而灌溉的影响较小.施氮量超过225 kg hm-2时,地上部植株氮肥吸收利用率和籽粒氮肥吸收利用率开始有降低趋势.所以,在沙地农田,节水10%～25%的灌溉水平和225 kg hm-2的施氮水平可以在避免水肥过量投入的基础上减少土壤有机氮淋溶对地下水造成的污染威胁.     

Internal Nutrient Translocation in Chestnut Tree Stemwood: III. Dynamics Across an Age Series of Castanea sativa (Miller)

Nutrient translocation in chestnut tree stemwood was calculatedfrom the distribution of nutrient content throughout the tissuelife-span. The dynamics of internal translocation were followedduring the crop rotation by means of an age series of five coppicedstands (2–19 years). N, P, K, Ca and Mg contents in treerings were estimated from the concentrations along a verticaland radial gradient and from the ring volume obtained usingstem ring analysis.Real nutrient translocation was calculatedstepwise between successive stages in the age series;apparenttranslocation was computed on a complete tree rotation by comparingthe initial content just after the ring was formed with themineral content in the oldest stand. There was a marked translocationof N, P, K and Ca when the rings were physiologically-activetissues. Real translocation of N, P and K (but not Ca) increasedwith stand age, obviously in parallel with the enlarged stemwoodbiomass reaching 23.2 and 20.6 kg ha^-1for K and N in the lastyears of rotation, nearly 5 kg ha^-1for Mg and about 3 kg ha^-1forCa and P. Potassium was the most mobile element since translocationreached 60% of the total amount immobilized in the stemwoodat the end of the rotation, whereas values for N, P and Mg wereapproximately 25% and 10% for calcium. Total apparent translocationreached respectively 39.2 and 32.4 kg ha^-1for K, N, approximately12 and 7 kg ha^-1for Mg and Ca and only 4.4 kg ha^-1for P. Totalapparent translocation as a percentage of total wood immobilizationwas 114% for K, 83% for Mg, 63% for P, but only 39% for N and24% for calcium. Translocation; nutrient content; stemwood; tree ring; coppice; age series; dynamics; chestnut tree; Castanea sativa Miller     

Tree growth and soil acidification in response to 30 years of experimental nitrogen loading on boreal forest

Relations among nitrogen load, soil acidification and forest growth have been evaluated based on short‐term (<15 years) experiments, or on surveys across gradients of N deposition that may also include variations in edaphic conditions and other pollutants, which confound the interpretation of effects of N per se. We report effects on trees and soils in a uniquely long‐term (30 years) experiment with annual N loading on an un‐polluted boreal forest. Ammonium nitrate was added to replicated (N=3) 0.09 ha plots at two doses, N1 and N2, 34 and 68 kg N ha^?1 yr^?1, respectively. A third treatment, N3, 108 kg N ha^?1 yr^?1, was terminated after 20 years, allowing assessment of recovery during 10 years. Tree growth initially responded positively to all N treatments, but the longer term response was highly rate dependent with no gain in N3, a gain of 50 m³ ha^?1 stemwood in N2 and a gain of 100 m³ ha^?1 stemwood in excess of the control (N0) in N1. High N treatments caused losses of up to 70% of exchangeable base cations (Ca²⁺, Mg²⁺, K⁺) in the mineral soil, along with decreases in pH and increases in exchangeable Al³⁺. In contrast, the organic mor‐layer (forest floor) in the N‐treated plots had similar amounts per hectare of exchangeable base cations as in the N0 treatment. Magnesium was even higher in the mor of N‐treated plots, providing evidence of up‐lift by the trees from the mineral soil. Tree growth did not correlate with the soil Ca/Al ratio (a suggested predictor of effects of soil acidity on tree growth). A boron deficiency occurred on N‐treated plots, but was corrected at an early stage. Extractable NH₄⁺ and NO₃^?were high in mor and mineral soils of on‐going N treatments, while NH₄+ was elevated in the mor only in N3 plots. Ten years after termination of N addition in the N3 treatment, the pH had increased significantly in the mineral soil; there were also tendencies of higher soil base status and concentrations of base cations in the foliage. Our data suggest the recovery of soil chemical properties, notably pH, may be quicker after removal of the N‐load than predicted. Our long‐term experiment demonstrated the fundamental importance of the rate of N application relative to the total amount of N applied, in particular with regard to tree growth and C sequestration. Hence, experiments adding high doses of N over short periods do not mimic the long‐term effects of N deposition at lower rates.     

模拟氮沉降对华西雨屏区苦竹林细根特性和土壤呼吸的影响

细根在森林生态系统地下碳循环过程中具有核心地位.2007年11月-2009年11月,对华西雨屏区苦竹人工林进行了模拟氮沉降试验.氮沉降水平分别为对照(CK,0 g N·m^-2·a^-1)、低氮(5 g N·m^-2·a^-1)、中氮(15 g N·m^-2·a^-1)和高氮(30 g N·m^-2·a^-1)处理,研究氮沉降对苦竹人工林细根和土壤根际呼吸的影响.结果表明：不同处理氮沉降下,<1 mm和1～2 mm细根特性差异较大,与< 1 mm细根相比,1～2 mm细根的木质素、磷和镁含量更高,而纤维素、钙含量更低;氮沉降显著增加了<2 mm细根生物量,对照、低氮、中氮和高氮处理的细根生物量分别为(533±89)、(630±140)、(632±168)和(820±161) g·m^-2,氮、钾、镁元素含量也明显增加;苦竹林各处理年均土壤呼吸速率分别为(5.85±0.43)、(6.48±0.71)、(6.84±0.57)和(7.62±0.55) t C·hm^-2·a^-1,氮沉降对土壤呼吸有明显的促进作用;苦竹林的年均土壤呼吸速率与<2 mm细根生物量和细根N含量呈极显著线性相关.氮沉降使细根生物量和代谢强度增加,并通过增加微生物活性促进了根际土壤呼吸.     

鼎湖山森林土壤渗透水酸度和无机氮含量对模拟氮沉降增加的早期响应

在林地分别喷加0、50、100和150kg N hm^-1a^-1,研究鼎湖山马尾松林、马尾松针阔混交林和季风常绿阔叶林中土壤20cm深渗透水酸度和无机氮含量在开始9个月的变化。结果表明,3种森林对照样方土壤渗透水pH值为3．82—4．24,外加氮处理使其平均降低了0．08—0．18。3个森林对照样方土壤渗透水无机氮平均含量分别为6．14、6．66和11．64mg L^-1,铵态氮占15．0％、11．9％和3．0％。外加氮处理使3种森林土壤渗透水铵态氮和硝态氮含量均有不同程度的提高,这表明外加氮处理不但增加了无机氮从森林土壤流失的潜力,而且使土壤进一步酸化。     

Nutrient Distribution Indicated Whole-Tree Harvesting as a Possible Factor Restricting the Sustainable Productivity of a Poplar Plantation System in China

We evaluated the biomass and contents of five major macronutrients (N, P, K, Ca and Mg) in 10-year-old poplar trees (Populus deltoids Bartr. cv. “Lux”), and determined their nutrient use efficiencies (NUEs) at Zhoushan Forestry Farm (32°20′ N, 119°40′ E), Jiangsu province, in eastern China. The above- and below-ground biomass of poplar trees was 161.7 t ha^-1, of which 53.3% was stemwood. The nutrient contents in the aboveground part were as follows: 415.1 kg N ha^-1, 29.7 kg P ha^-1, 352.0 kg K ha^-1, 1083.0 kg Ca ha^-1, and 89.8 kg Mg ha^-1. The highest nutrient contents were in stembark, followed by branches, roots, stemwood, and foliage. The NUEs of the aboveground parts of poplar for N, P, K, Ca and Mg were 0.313, 4.377, 0.369, 0.120, 1.448 t dry biomass kg^-1 nutrient, respectively, while those of stemwood were 1.294, 33.154, 1.253, 0.667, and 3.328 t dry biomass kg^-1, respectively. The cycling coefficients, defined as the percentage of annual nutrient return in annual nutrient uptake, of N, P, K, Ca and Mg for the aboveground part were 87, 95, 69, 92, and 84%, respectively. Based on the NUE and nutrient cycling characteristics, shifting from whole-tree harvesting to stemwood-only harvesting and appropriately extending the harvest rotation could prevent site deterioration and support sustainable productivity of poplar plantation systems.     

西藏色季拉山暗针叶林凋落物层化学性质研究

The storage and chemical properties of the forest litter in dark coniferous forest of Sejila Mountain were studied. The results showed that the existing storage was 5. 863t·hm^-2 and the annual litter fall was 0. 3205 t·hm^-2 It implied that the forest litter decomposed slowly and accumulated quickly, and the turnover of nutrient circles was slow. The contents of N, Ca, Na, and Mn nutrient elements in litter layer were in the order of un-decomposed layer (U layer) > semi-decomposed layer (S layer) > decomposed layer (D layer), those of K, Fe, and Mg were in the order of D layer > S layer > U layer, and P element content was in the order of U layer > D layer> S layer. The pool of elements was 78. 483 kg·hm^-2 N, 3. 843 kg·hm^-2P, 48. 205 kg·hm^-2 K, 23.115 kg·hm^-2 Ca, 13. 157 kg·hm^-2 Na, 30.554 kg·hm^-2 Fe, 2. 113 kg·hm^-2 Mn and 27. 513 kg·hm^-2 Mg. The turnover of forest litter was the total of nutrient release accumulation. K, Fe, and Mg were enriched, and N,Ca, Na, Mn, and P were released with the turnover rate in the order of N > Ca > Na > Mn >P.