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1.
在林地分别喷加0、50、100和150kgNhm^-2a^-1,研究鼎湖山马尾松林、马尾松荷木混交林和季风常绿阔叶林乔木层植物胸径生长(年增长率)对增施氮的响应。结果表明,不喷加N,马尾松林、混交林和阔叶林胸径年增长率分别为4.84%、4.09%和2.99%;外加氮对植物胸径生长的影响因森林类型和植物种而异。马尾松林和混交林,低氮处理(喷加50kgNhm^-2a^-1)没有对胸径生长产生明显影响,中氮处理(喷加100kgNhm^-2a^-1)则分别增加了77、8%和105.6%。外加氮处理均使阔叶林胸径年增长率下降,低氮、中氮和高氮处理(喷加150kgNhm^-2a^-1)分别比对照(不喷N)低36.8%、28.5%和41.0%。这表明外加氮处理促进马尾松生长,但抑制大多数阔叶树种生长。  相似文献
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Non-neutral patterns of species abundance in grassland communities   总被引:6,自引:0,他引:6  
Although the distribution of plant species abundance in a Minnesota grassland was consistent with neutral theory, niche but not neutral mechanisms were supported by the ability of species traits to predict species abundances in three experimental grassland communities. In particular, data from 27 species grown in monoculture showed that species differed in a trait, R *, which is the level to which each species reduced the concentration of soil nitrate, the limiting soil nutrient and which is predicted to be inversely associated with competitive ability for nitrogen (N). In these N-limited habitats, species abundance ranks correlated with their predicted competitive ranks: low R * species, on average dominated. These correlations were significantly different than expected for neutral theory, which assumes the exchangeability of species traits. Additionally, we found that changes in relative abundance after environmental change (N-addition or disturbance) were not neutral but also were significantly associated with R *.  相似文献
4.
 该文比较了羊草草原群落中包括建群种和优势种在内的6种植物,羊草(Leymus chinensis)、西伯利亚羽茅(Achnatherum sibiricum)、大 针茅(Stipa grandis)、 冰草(Agropyron cristatum)、糙隐子草(Cleistogenes squarrosa)和黄囊苔草(Carex korshinskyi)的比叶 面积(Specific leaf area, SLA)、叶片含氮量和叶绿素含量等叶片功能特性( Leaf functional trait)对氮素添加的响应,旨在探讨草原生态 系统中,不同物种对氮素可利用性改变的响应和适应对策。结果表明:随着氮素添加量的增加,物种对光资源的竞争增强,不同物种在光资源 的竞争策略和竞争力间存在着显著的差异。羊草通过提高SLA、单位质量叶片的叶绿素含量和含氮量,使单位面积叶片含氮量和叶绿素含量均呈 线性提高,进而增强了其对光的竞争力。西伯利亚羽茅主要通过提高SLA增加光合总面积,来增强自身的光竞争力。冰草在SLA和单位质量叶片 的叶绿素和氮含量均有一定的可塑性,但对光的竞争力明显弱于羊草和西伯利亚羽茅。大针茅和黄囊苔草对SLA的调节能力较低,加之大针茅 SLA较低,而黄囊苔草处于群落的下层,这两种植物的光竞争力较弱。糙隐子草具有较高的SLA,对单位质量叶片叶绿素和氮含量的调节能力相 对较强,其光竞争力高于黄囊苔草。同时,糙隐子草叶片叶绿素a与叶绿素b的比值沿氮素添加梯度显著降低,进一步证实氮素添加改变了群落 的光环境。  相似文献
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The ability of Salix aquatica Smith, S. fragilis L. and S. viminalis L. to absorb nitrogen at varied growth rates was investigated in nutrient solutions. The effects of five nitrogen addition rates on growth rates, nitrogen contents of the plants, nitrogen concentration of the media, and dry matter distribution between roots, stems and leaves, were studied.
These clones are highly efficient in absorbing nitrogen at low concentrations in the root medium, independent of growth rate. Strong linear regressions were found between any two of the three factors: relative rate of nitrogen supply (RN), nitrogen content (plant), and relative growth rate (R). Dry matter production per unit nitrogen taken up and unit time (N-productivity) and per unit nitrogen taken up independent of time (N-efficiency) was closely correlated to the nitrogen status of the plant. Root development was favoured in the sub-optimum treatments, and leaf development in the optimum treatments. With regard to their ability to absorb nitrogen, these Salix clones appear satisfactory for efficient short rotation energy forestry.  相似文献
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Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very high long-term ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/broadleaf forest in subtropical southern China. All three forests have previously been shown to have high nitrate (NO3) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results showed that under ambient deposition (35–50 kg N ha−1 y−1 as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5–16.9 kg N ha−1 y−1). DON leaching increased 35–162% following 2.5 years of experimental input of 50–150 kg N ha−1 y−1. The fertilizer-driven increase of DON leaching comprised 4–17% of the added N. A concurrent increase in DOC loss was observed only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for 23–38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had the highest DON loss under ambient conditions. DON leaching was highly correlated with NO3 leaching in all three forests. We hypothesize that abiotic incorporation of excess NO3 (through chemically reactive NO2) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the consistent and large DON loss in the N-saturated subtropical forests of southern China. Dr. YT Fang performed research, analyzed data, and wrote the paper; Prof. WX Zhu participated in the initial experimental design, analyzed data, and took part in writing the paper; Prof. P Gundersen conceived the study and took part in writing; Prof. JM Mo and Prof. GY Zhou conceived study; Prof. M Yoh analyzed part of the data and contributed to the development of DON model.  相似文献
7.
氮素添加对内蒙古羊草草原净氮矿化的影响   总被引:4,自引:0,他引:4       下载免费PDF全文
 为了更好地了解天然草原氮素矿化对全球氮沉降背景和草原施肥管理模式的响应, 从2000年起对内蒙古典型草原羊草(Leymus chinensis)群落开展了长期的氮素添加实验, 分别设置对照(N0), 添加5 g NH4NO3·m–2 (N1.75)、30 g NH4NO3·m–2(N10.5)和80 g NH4NO3·m–2 (N28) 4个氮素添加梯度。2002年, 从相邻的同时进行施肥的两个生态系统类型, 即1979年围封的样地A和1999年围封的样地B进行土壤取样, 在最佳温度(25 ℃)和最适土壤湿度(即60%田间持水量)下进行5周的室内培养, 并用阶段性淋溶方法研究了氮素添加对土壤氮矿化动态的影响。在A和B两个样地内, 氮素添加都显著改变了土壤的累积氮矿化量。最高氮素处理N28对应于最低的累积氮矿化量, 而低氮素处理N1.75使得累积氮矿化量达到最高。在N0和N1.75处理中, 硝态氮的含量高于铵态氮; 在N28处理中, 却表现出相反的趋势。氮素添加显著降低了土壤的pH值, 但累积氮矿化量与土壤pH值、有机碳和全氮均没有显著的相关性。大多数氮素添加处理水平在样地A具有比样地B更高的土壤累积氮矿化量。  相似文献
8.
 生长在供给NO-3 N、NH+4 N和NH4NO3 N氮源下的荫香(Cinnamomum burmanni)幼树暴露在增高空气NH3浓度下30 d。利用气体交换测定和氮分析研究了植株的光合作用、氮利用和氮在光合过程一些组分中的分配,根据Farquhar-von Caemmerer模式得出相关光合参数。结果表明在增高空气NH3下生长于NO-3 N的植株Rubisco最大羧化速率(Vcmax)和最大光合电子传递速率(Jmax)较正常空气下的高,但生长于NH+4 N和NH4NO3 N的植株则较正常空气下的低。无论生长于何种形式氮下的植株,在空气NH3增高下以单位叶面积为基准的叶氮含量(Na)显著增高(p<0.05)。在增高空气NH3下,生长于NO-3 N下的植株,其类囊体氮量(NT)、Rubisco氮(NR)和结合于光合电子传递链的氮(NE)的含量较正常空气下的增高(p<0.05);而生长于NH+4 N和NH4NO3 N下的植株则较正常空气下的低。表明在空气NH3增高下生长于NO-3 N的植株能有效地利用氮合成光合过程必要的组份,而生长于NH+4 N和NH4NO-3 N的植株氮在NT、NR和NE的分配受到部分限制。在空气NH3增高下生长于NO-3 N和NH4NO3 N的植株,其以单位干重为基准的有机氮量较正常空气下的高,但生长于NH+4 N的植株则较正常空气下的低,此外在空气NH3增高下生长于NO-3 N的植株的可溶性蛋白氮较正常空气下增高,而生长在NH+4 N的植株亦见降低。结果表明空气NH3增高可能有利于NO-3 N下生长的荫香植株利用空气中的氮,促进叶片光合速率提高,而空气NH3增高能抑制NH+4 N或NH4NO3 N下生长的荫香植株光合作用和氮的利用和再分配。  相似文献
9.
施氮对几种草地植物生物量及其分配的影响   总被引:3,自引:0,他引:3       下载免费PDF全文
祁瑜  黄永梅  王艳  赵杰  张景慧 《生态学报》2011,31(18):5121-5129
为了研究施氮对不同草地植物生物量及其分配的影响,以及温带草地生态系统碳交换过程对氮素的响应,在内蒙古太仆寺旗农田-草地生态系统野外站,以4种草地植物:紫花苜蓿(Medicago sativa L.)、高丹草(Sorghum bicolor L.) 、羊草(Leymus chinensis T.)和小叶锦鸡儿(Caragana microphylia L.)为材料,进行了3种氮素水平 的盆栽控制实验。研究结果表明:施氮显著促进了4种植物地上生物量的积累,紫花苜蓿在中氮水平地上生物量最大,较对照增加了24.8%,高丹草、羊草、小叶锦鸡儿在高氮水平地上生物量最大,分别较对照增加了45.6%、39.3%和72.2%。4种植物在中氮水平地下生物量最大,而细根(直径≤2mm)生物量随施氮量的增加显著减少。羊草根茎生物量及其分配比例随施氮量的增加而增大。施氮显著降低了4种植物的根冠比,紫花苜蓿的根冠比在中氮水平时最小,为1.62,高丹草、羊草、小叶锦鸡儿的根冠比在高氮水平时最小,分别为0.57、1.02和0.41。随施氮量的增加,植物地下部分特别是细根的分配比例显著降低,地上部分分配比例显著增加。不同植物对施氮水平的响应不同,相比豆科植物,施氮显著促进禾本科植物生物量积累,并使其生物量分配格局发生显著改变。  相似文献
10.
青藏高原正经历着明显的温暖化过程,由此引起的土壤温度的升高促进了土壤中微生物的活性,同时青藏高原东缘地区大气氮沉降十分明显,并呈逐年增加的趋势,这些环境变化均促使土壤中可利用营养元素增加,因此深入了解青藏高原高寒草甸植物生物量对可利用营养元素增加的响应,是准确预测未来全球变化背景下青藏高原高寒草甸碳循环过程的重要基础。该研究基于在青藏高原高寒草甸连续4年(2009–2012年)氮、磷添加后对不同功能群植物地上生物量、群落地上和地下生物量的测定,探讨高寒草甸生态系统碳输入对氮、磷添加的响应。结果表明:(1)氮、磷添加均极显著增加了禾草的地上绝对生物量及其在群落总生物量中所占的比例,同时均显著降低了杂类草在群落总生物量中的比例,此外磷添加极显著降低了莎草地上绝对生物量及其在群落总生物量中所占的比例。(2)氮、磷添加均显著促进了青藏高原高寒草甸的地上生物量增加,分别增加了24%和52%。(3)氮添加对高寒草甸地下生物量无显著影响,而磷添加后地下生物量有增加的趋势。(4)氮添加对高寒草甸植物总生物量无显著影响,而磷添加后植物总生物量显著增加。研究表明,氮、磷添加可缓解青藏高原高寒草甸植物生长的营养限制,促进植物地上部分的生长,然而高寒草甸植物的生长极有可能更受土壤中可利用磷含量的限制。  相似文献
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