放牧对天山北坡山地草原生态系统土壤δ<sup>15</sup>N的影响

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张青青, 安沙舟, 于辉, 吐尔逊娜依#cod#x000b7;热依木, 张沛, 张玲卫, 禹朴家. 放牧对天山北坡山地草原生态系统土壤δ¹⁵N的影响 . 草业科学, 2016,33(7):1260-1266
Zhang Qing-qing, An Sha-zhou, Yu Hui, Tuerxunnayi Reyimu, Zhang Pei, Zhang Ling-wei, Yu Pu-jia. Impact of grazing on soil δ¹⁵N of mountainous grassland ecosystems over the northern Tianshan Mountains, China . Pratacultural Science,2016,33(7): 1260-1266 复制到剪切板

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《草业科学》编辑部

放牧对天山北坡山地草原生态系统土壤δ¹⁵N的影响

张青青¹, 安沙舟¹, 于辉¹, 吐尔逊娜依·热依木¹, 张沛², 张玲卫¹, 禹朴家³

1.新疆农业大学草业与环境科学学院,新疆乌鲁木齐 830052

2.中国科学院新疆生态与地理研究所,新疆乌鲁木齐 830011

3.中国科学院东北地理与农业生态研究所,吉林长春 130102

通讯作者:安沙舟(1956-),男,陕西富平人,教授,博士,主要从事草地资源与生态的研究。E-mail:xjasz@126.com

第一作者:张青青(1983-),女,新疆和静人,副教授,博士,主要从事干旱区生态恢复与保护的研究。E-mail:greener2010@sina.com

收稿日期: 2016-04-01

基金: 新疆农业大学校前期资助课题(XJAU201218); 国家自然科学基金青年基金项目(41101534)

摘要

测定了天山北坡山地草原优势植物种针茅( Stipa capillata)、羊茅( Festuca ovina)、短柱苔草( Carex turkestanica)、博乐绢蒿( Seriphidium borotalense)根际0-10 cm土壤和非根际10-20、20-30 cm土层土壤稳定性N同位素和全氮含量,通过对比放牧和围封草地优势植物根际土壤δ¹⁵N的变化,分析不同利用方式对不同植物根际土壤和不同土层深度土壤δ¹⁵N的影响。结果表明,天山北坡山地草原生态系统土壤δ¹⁵N值在2.25‰~16.03‰变化,放牧显著降低了表层0-10 cm土壤δ¹⁵N值;放牧草地0-30 cm土壤δ¹⁵N值(7.14‰±0.67‰)整体上比围封(6.95‰±0.34‰)增加了2.8%,但差异不显著( P>0.05)。放牧和围封条件下天山北坡山地草原土壤δ¹⁵N值均随着土层深度的加深而显著增加( P<0.05),且土壤δ¹⁵N值与土壤全氮含量呈显著的负相关( P<0.05)。放牧对天山北坡山地草原不同植物种根际土壤δ¹⁵N的影响程度不同,放牧草地的针茅和羊茅0-30 cm土壤δ¹⁵N分别比围封草地的高17%和53%,但放牧降低了短柱苔草和博乐绢蒿0-30 cm土壤δ¹⁵N,且对短柱苔草的降低作用显著。

关键词: 放牧; 围封; 土壤δ15N; 山地草原生态系统

中图分类号:S812.29 文献标志码:A 文章编号:1001-0629(2016)7-1260-07 doi: 10.11829/j.issn.1001-0629.2015-0487

Impact of grazing on soil δ¹⁵N of mountainous grassland ecosystems over the northern Tianshan Mountains, China

Zhang Qing-qing¹, An Sha-zhou¹, Yu Hui¹, Tuerxunnayi Reyimu¹, Zhang Pei², Zhang Ling-wei¹, Yu Pu-jia³

1.College of Grassland and Environment Sciences, Xinjiang Agricultural University, Urumqi 830052, China

2.Xinjiang Institute of Ecology and Geography, Chinese Academy of Science, Urumqi 830011, China

3.Northeast Institute of Geography and Agroecology, Chinese Academy of Science, Changchun 130102, China

Corresponding author: An Sha-zhou E-mail:xjasz@126.com

Abstract

The total N and δ¹⁵N of rhizosphere soil 0-10 and 10-20, 20-30 cm of Stipa capillata, Festuca ovina, Carex turkestanica and Seriphidium borotalense in the mountainous grassland ecosystems over the northern Tianshan Mountains were measured. δ¹⁵N of dominant plants' rhizosphere soil in grazing and fencing grassland was compared to reveal the impacts of different usage patterns on δ¹⁵N of rhizosphere soil in different plants and different soil layer. The results indicated that the range of soil δ¹⁵N of mountainous grassland ecosystems over the northern Tianshan Mountains were from 2.25‰ to 16.03‰. Grazing significantly decreased δ¹⁵N in 0-10 cm soil. The δ¹⁵N in 0-30 cm soil of grazing grassland (7.14‰±0.67‰) increased by 2.8% than that of fencing grassland (6.95‰±0.34‰) although there was no significant difference between them. The δ¹⁵N in soil significantly increased with the increasing of soil depth in both grazing and fencing grassland and it had significantly negative correlation with soil total N. The impacts of grazing on δ¹⁵N in rhizosphere soil of different plants were different. The δ¹⁵N in the 0-30 cm rhizosphere soils of Stipa capillata and Festuca ovina in the grazing grassland were 17% and 53% higher than that in fenced grassland respectively. However, the δ¹⁵N in the 0-30 cm rhizosphere soils of Carex turkestanica and Seriphidium borotalense were lower than that in fenced grassland. The measurement of δ¹⁵N supported an aggregative indicator of N cyclic process in a typical area for the ecosystem and showed that grazing changed the N cycle of grassland ecosystem.

Keyword: grazing; fencing; δ15N of soil; mountainous grassland ecosystem

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物质循环是生态系统的基本功能, 氮(N)是物质的基本组成元素。地球表面氮素的生物地球化学循环过程及其环境效应是当前全球变化中区域尺度上研究的重要内容, 国内外许多核心项目也都把氮素循环作为主要研究内容。氮是植物生长发育最重要的元素之一, 在自然生态系统中, 大部分的氮只有首先被矿化才能被生物所利用。草地生态系统可利用氮素的供应与草地生态系统的生产力有直接相关性, 在很大程度上是第一性生产力的重要限制因子^[1]。植物和土壤中¹⁵N自然丰度(δ ¹⁵N)是探明生态系统N循环与评价生态系统氮效应的一个重要指标, δ ¹⁵N在N的输入、转化和输出过程中由于同位素的分馏而引起δ ¹⁵N值的差异^[2]。例如, 动物的践踏、啃食和富N粪尿的增加等都会直接或间接影响土壤的N循环, 从而会不同程度地造成δ ¹⁵N值的变化。而放牧是草地生态系统最主要的土地利用方式之一, 对草原生态系统N循环过程的改变起着重要的作用, 为理解生态系统中的N循环提供有用的信息^{[3, 4, 5, 6]}。近年来, 国内外进行了大量针对草地生态系统中氮素循环的研究^{[6, 7, 8, 9]}, 包括草地生态系统氮素循环的通量和过程的系统研究^{[10, 11]}以及氮肥草地生态系统结构与功能的调控机理方面的研究^{[12, 13]}等, 而且也已经有不少学者开展了放牧对草地生态系统N素分配的影响^{[10, 14, 15]}。从全球范围来看, 影响δ ¹⁵N格局的因素主要有气候、时间、地形和土地利用等^{[16, 17, 18, 19]}。而在区域范围内, 土壤δ ¹⁵N值主要受土壤N输入(包括牲畜粪尿、氮沉降和生物固氮)、输出、转化中的分馏作用以及植物的生长生理等一系列生物地球化学循环的影响^{[2, 20]}。

新疆作为我国五大牧区之一, 天然草地分布区域广, 总面积5.725 88× 10⁷ hm², 占全国草地总面积的14.6%^{[21, 22]}。由于受人类利用方式和自然因素的影响, 草地生态系统的承载力常常被忽略, 使该区大部分天然草地长期处于不同程度的过度放牧状态, 导致草地生态系统退化。草地生态系统服务功能的降低常常是由于其自身的退化所引起的, N素循环也常常由于生态系统处于开放状态而造成N素流失, 从而使生态系统结构和功能的耦合机制失调。种类成分(如不同功能型植物之间的替代)以及植物生长特性的变化进一步造成N素循环过程的变化。因此, 有必要选取典型草原生态系统通过成对比较放牧和围封条件下山地草原优势植物种根际土壤δ ¹⁵N的变化, 分析不同草地利用方式对不同植物根际土壤δ ¹⁵N的影响是否存在差异, 分析放牧对草原生态系统N循环过程的影响, 为提高草地生产力、合理并持续利用草地资源提供理论依据。

1 研究区概况

研究区位于天山北坡乌鲁木齐县甘沟乡的山地草原生态系统(43° 33'56″ N, 87° 13'10″ E), 海拔1 524 m, 位于亚欧大陆腹地, 远离海洋, 显著的大陆性气候, 其特点是冬季寒冷漫长, 夏季炎热, 气温年、日较差大, 春秋季气温变化剧烈, 光照充足, 热量丰富, 年降水量200~550 mm。

试验样地选择自由放牧和围封保护的山地草原为研究对象。研究区地带性土壤为淡栗钙土, 土壤含水量为4.99%~7.95%, pH为8.05~8.52, 有机质11.823~23.061 g· kg^-1, 全氮0.563~1.298 g· kg^-1, 全磷0.690~0.802 g· kg^-1。草地建群植物有针茅(Stipa capillata)、羊茅(Festuca ovina)、短柱苔草(Carex turkestanica)、博乐绢蒿(Seriphidium borotalense), 且所选择样地无固氮植物出现。采样区于20世纪90年代建立围栏, 分别进行自由放牧和围栏封育恢复试验。试验前后, 自由放牧和围栏封育区没有添加化肥, 土壤性质也没有显著差异。自由放牧样地和围栏封育样地相邻, 放牧在每年的5-6月和9-11月进行。

表1 放牧与围栏样地土壤理化性质 Table 1 Physical and chemical properties of the soil in grazing and fencing plot

样地 Plot	土层深度 Soil depth/ cm	土壤含水量 Soil moisture/ %	pH	有机质 Organic matter/ g· kg^-1	全氮 Total N/ g· kg^-1	全磷 Total P/ g· kg^-1	铵态氮 N $\begin{matrix} {H_{4}}^{+} \end{matrix}$ -N/ mg· kg^-1	硝态氮 N $\begin{matrix} {O_{3}}^{-} \end{matrix}$ -N/ mg· kg^-1
围栏 Fencing	0-10	4.99	8.14	17.481	0.711	0.802	1.812 5	1.075
	10-20	6.14	8.52	16.753	0.621	0.723	0.697 5	1.575
	20-30	7.95	8.05	15.349	0.773	0.714	0.522 5	1.275
放牧 Grazing	0-10	3.38	8.15	23.061	1.298	0.747	1.352 5	2.425
	10-20	5.95	8.25	16.226	0.889	0.721	0.852 5	1.525
	20-30	5.98	8.46	11.823	0.563	0.690	1.407 5	1.425

表1 放牧与围栏样地土壤理化性质 Table 1 Physical and chemical properties of the soil in grazing and fencing plot

2 研究方法

2.1 土壤样品的采集

在一处地势较为平坦的区域, 选取3个样地, 每个样地4个1 m× 1 m的样方, 于2013年8月24日, 用土钻分别取每个样方中针茅、羊茅、短柱苔草、博乐绢蒿4种植物根际0-10 cm土壤和非根际10-20、20-30 cm土层土壤, 每种植物根际周围土壤取3钻混合, 作为一个重复。将其放入封口袋后带回实验室。在实验室内自然风干后, 研磨, 再过孔径0.18 mm的土壤筛, 然后取筛好的土壤样品5 g放在封口袋中保存, 作为土壤稳定性N同位素待测样品^{[8, 10]}。另外, 将4种植物根际周围的土壤分别取少量混合, 与土壤稳定性N同位素样品一样分层处理, 作为土壤全氮的待测样品。

2.2 土壤样品稳定性氮同位素的测定

将适量过筛处理后的土壤稳定性N同位素样品(取样量根据样品的氮含量而定)装入专用的金属锡舟中, 然后在配有自动进样装置的EA1112HT-MAT253高温裂解元素分析仪和稳定性同位素质谱仪(Thermo Scientific, USA)上进行测试, 标样连续测试精度小于0.3‰ ^{[8, 10]}。EA反应炉温度为960 ℃, GC柱温为50 ℃, 载体流速为85 mL· min^-1。测得的δ ¹⁵N值是一个相对比例, 用公示表达为:

δ ¹⁵N=(R_sample/R_standard-1)× 1 000‰ .

其中:R_sample、R_standard分别表示样品和标准物(空气)之间¹⁵N/¹⁴N的比值。

2.3 数据分析

用SPSS 13.0软件进行单因素方差分析(One-way ANOVA)和最小显著差异法(LSD)比较检验放牧与围封、不同土层深度、不同植物之间土壤δ ¹⁵N值的差异程度, 用Pearson相关系数分析土壤δ ¹⁵N值和土壤全氮含量的相关关系。

3 结果与分析

3.1 放牧与围封条件下不同深度土壤氮同位素含量的变化

天山北坡山地草原生态系统, 土壤δ ¹⁵N值的变化范围在2.25‰ ~16.03‰ , 围封样地土壤δ ¹⁵N值是(6.95‰ ± 0.34‰ ), 放牧样地土壤δ ¹⁵N值是(7.14‰ ± 0.67‰ ), 放牧后0-30 cm土壤δ ¹⁵N值整体上比围封增加了2.8%, 但无显著差异(P> 0.05)。

放牧对不同深度土壤δ ¹⁵N的影响有所差异(图1)。无论是放牧样地还是围封样地, 天山北坡山地草原生态系统土壤δ ¹⁵N值随着土层深度的增加而不断增加。放牧后, 10-20和20-30 cm土壤δ ¹⁵N均比围封样地土壤δ ¹⁵N值有所增加, 均增加15%, 但差异不显著(P> 0.05)。而0-10cm土壤δ ¹⁵N值在放牧后有所降低, 比围封样地土壤δ ¹⁵N值低32%, 且差异显著(F=6.946, P< 0.05)。

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	图1 山地草原生态系统不同深度土壤δ ¹⁵N的变化注:不同小写字母表示同一土层不同处理间差异显著(P< 0.05)。Fig. 1 Soil δ ¹⁵N of different soil layer in mountainous grassland ecosystems Note: Different lower case letters in the same soil layer indicate significant difference between fencing and grazing at 0.05 level.

3.2 放牧与围封条件下不同植物根际土壤氮同位素含量的变化

放牧对不同植物种根际土壤δ ¹⁵N的影响程度不同(图2)。围封样地, 针茅和羊茅根际0-30 cm深度土壤δ ¹⁵N值分别为8.19‰ 和6.22‰ , 比放牧样地土壤δ ¹⁵N值增加了17%和53%, 且针茅根际0-30 cm深度土壤δ ¹⁵N值在放牧和围封样地差异显著(F=16.607, P< 0.05), 羊茅差异极显著(F=28.506, P< 0.01)。而短柱苔草和博乐绢蒿根际0-30 cm土壤δ ¹⁵N值在围封样地分别为6.47‰ 和6.91‰ , 放牧后样地0-30 cm土壤δ ¹⁵N值均相比围封样地有所降低(图2), 分别降低了28%和30%, 且短柱苔草根际0-30 cm深度土壤δ ¹⁵N值在放牧和围封样地差异极显著(F=27.930, P< 0.01), 博乐绢蒿差异不显著(P> 0.05)。

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图2 不同植物不同土层根际土壤δ ¹⁵N的变化
注:不同大、小写字母分别表示同一土层不同处理间差异极显著(P< 0.01)和显著(P< 0.05)。Fig.2 Soil δ ¹⁵N of different plant rhizosphere(different soil layer)
Note: Different capital and lower case letters in the same soil layer indicate significant difference between fencing and grazing at 0.01 and 0.05 level, respectively.

3.3 不同植物根际和不同深度土壤氮同位素含量的变化

从放牧与围封对不同植物种根际不同深度土壤δ ¹⁵N的影响来看(图2), 短柱苔草和博乐绢蒿根际0-10 cm土壤和非根际10-20、20-30 cm土壤的δ ¹⁵N值在放牧条件下均比围封有所降低, 其中短柱苔草根际0-10 cm土壤的δ ¹⁵N值在放牧条件比围封降低了43%, 差异显著(F=8.447, P< 0.05), 博乐绢蒿根际0-10 cm和非根际10-20 cm土壤的δ ¹⁵N值在放牧条件下比围封分别降低了46%和38%, 差异显著(分别为F=14.627, P< 0.05; F=15.554, P< 0.05), 其余深度的土壤δ ¹⁵N值在放牧和围栏条件下差异不显著(P> 0.05)。针茅和羊茅根际0-10 cm土壤的δ ¹⁵N值在放牧条件下均比围封有所降低, 分别降低19%和14%, 但差异不显著; 而羊茅非根际10-20和20-30 cm土壤的δ ¹⁵N值在放牧条件下比围封有所增加, 增加幅度分别为75%和74%, 差异显著(分别为F=32.584, P< 0.01; F=12.908, P< 0.05); 针茅非根际10-20和20-30 cm土壤的δ ¹⁵N值在放牧条件下比围封有所增加, 增加幅度分别为48%和16%, 但10-20 cm土壤的δ ¹⁵N值在放牧和围封条件下差异不显著, 20-30 cm差异显著(F=8.505, P< 0.05)。

3.4 土壤稳定性氮同位素与氮含量的关系

把所有放牧与围封条件下不同植物根际不同深度的土壤δ ¹⁵N值放在一起考虑, 土壤δ ¹⁵N值与全氮值的Pearson相关系数为-0.633, 存在显著的相关关系(R²=0.400 1, P< 0.01)。无论在放牧还是围封条件下, 随着土壤全氮含量的增加土壤δ ¹⁵N值均表现为先降低后增加, 且放牧条件下的多项式拟合(y=16.597x²-31.476x+17.543, R²=0.771 2)比围封条件下的多项式(y=23.508x²-34.06x+17.764, R²=0.394 5)拟合程度高(图3)。

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	图3 土壤全氮含量与土壤δ ¹⁵N的相关关系Fig.3 Relationship between soil total nitrogen content and soil δ ¹⁵N

4 讨论

放牧是草地生态系统最主要的土地利用方式之一, 对草原生态系统N循环过程的改变起着重要的调节作用。放牧提高土壤的净氮矿化速率, 促进淋溶、挥发和反硝化等过程, 增加贫化¹⁵N的流失, 形成一个开放的氮系统, 从而引起土壤δ ¹⁵N值的增加^{[16, 23, 24]}。但也有研究表明, 长期的放牧导致氮循环速率降低, 土壤的δ ¹⁵N值也随之降低^{[25, 26]}。本研究表明, 天山北坡山地草原生态系统0-30 cm土壤δ ¹⁵N值在放牧条件下整体上比在围封条件下有所增加, 而表层0-10 cm土壤δ ¹⁵N值在放牧条件下比围栏降低了32%, 且差异显著(F=6.946, P< 0.05)。本研究所选择的天山北坡山地草原生态系统的放牧样地, 仅有极少量的牲畜粪尿, 有研究表明, 较少的或呈斑块化分布的排泄物对生态系统土壤δ ¹⁵N值的作用相对较小^[27]。且选择的放牧样地与围封样地是相邻样地, 因此氮沉降所造成的差别也可以忽略不计。由于所选择的样地没有固氮植物出现, 因此生物固氮的影响也可以忽略不计。另外, 仅表层0-10 cm土壤δ ¹⁵N值在放牧条件下比围封降低, 而10-20和20-30 cm土壤δ ¹⁵N值在放牧条件下比围封有所增加(图1)。且不管是在放牧条件下还是围封条件下, 土壤δ ¹⁵N值均随着土层深度的加深而显著增加, 这与国内外的许多研究^{[28, 29]}结果相一致。在围封条件下, 10-20 cm土壤δ ¹⁵N值比0-10 cm增加了24%, 20-30 cm土壤δ ¹⁵N值比0-10 cm增加了62%, 而在放牧条件下, 10-20 cm土壤δ ¹⁵N值比0-10 cm增加了110%, 20-30 cm土壤δ ¹⁵N值比0-10 cm增加了172%, 土壤δ ¹⁵N值随着土层深度的加深而增加的速度比在围封条件下快。综上可知, 放牧对草原生态系统N循环过程的改变有着重要的调节作用, 降低土壤δ ¹⁵N值。

短柱苔草根际0-10 cm土壤、博乐绢蒿根际0-10 cm和非根际10-20 cm土壤的δ ¹⁵N值在放牧条件下均比围封有所降低, 且差异显著。针茅和羊茅根际0-10 cm土壤的δ ¹⁵N值在放牧条件下也比围封有所降低, 但差异不显著。不同植物会不同程度地影响土壤δ ¹⁵N值的变化, 但从总体上来看, 不同植物根际的表层0-10 cm土壤, 均在放牧条件比围封有所降低, 也就是说放牧对不同植物根际土壤表层0-10 cm土壤δ ¹⁵N值的降低作用是一致的。干旱区土壤水分含量有限, 土壤微生物活动相对较弱, 因此, 土壤中的N主要来自植物残体的贡献。本研究结果与¹⁵N贫化的凋落物输入导致表层土壤较低的¹⁵N含量的结果也恰好相符。另外, 放牧与围栏条件下, 土壤全氮含量均在表层0-10 cm土壤中最高(放牧条件下土壤全氮量为1.298 g· kg^-1; 围栏条件下, 土壤全氮量为0.711 g· kg^-1), 而相应的放牧与围栏条件下0-10 cm土壤δ ¹⁵N是各个土层最低的, 分别为5.36‰ 和5.40‰ , 这恰好与土壤δ ¹⁵N值和全氮值存在显著的负相关关系相一致, 土壤全氮含量越高, 土壤δ ¹⁵N值越低。这与吴田乡和黄建辉^[26]的观点一致, 认为放牧后0-10 cm土壤δ ¹⁵N值的显著降低可能与长期放牧有关, 长期放牧引起N循环速率减小, 从而使土壤δ ¹⁵N值降低。

5 结论

本研究以山地草原生态系统为研究对象, 通过对比放牧和围封条件下山地草原4种优势植物种土壤δ ¹⁵N的变化, 分析不同利用方式对不同植物土壤δ ¹⁵N的影响, 探讨草原生态系统土壤δ ¹⁵N值在放牧与围栏条件存在差异的原因, 得到以下结论:天山北坡山地草原生态系统土壤δ ¹⁵N值在2.25‰ ~16.03‰ 变化, 放牧显著降低了表层0-10 cm土壤δ ¹⁵N值, 0-30 cm土壤δ ¹⁵N值(7.14‰ )整体上比围封(6.95‰ )增加了2.8%, 但差异不显著, 不管在放牧还是围栏条件下, 土壤δ ¹⁵N值均随着土层深度的加深而显著增加, 且土壤δ ¹⁵N值与土壤全氮量显著负相关。放牧对不同植物种根际土壤δ ¹⁵N的影响程度不同, 放牧后, 针茅和羊茅根际0-30 cm土壤δ ¹⁵N值分别比围封增加17%和53%, 但放牧降低了短柱苔草和博乐绢蒿0-30 cm土壤δ ¹⁵N值, 且对短柱苔草的降低作用显著。δ ¹⁵N值的测定为生态系统提供了一个区域范围内氮循环过程的综合指标, 反映出放牧改变了草原生态系统的N循环速率。

The authors have declared that no competing interests exist.

参考文献

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2003

0.0

... 草地生态系统可利用氮素的供应与草地生态系统的生产力有直接相关性,在很大程度上是第一性生产力的重要限制因子^[1] ...

1994

0.0

... ¹⁵N值的差异^[2] ...

... ¹⁵N值主要受土壤N输入(包括牲畜粪尿、氮沉降和生物固氮)、输出、转化中的分馏作用以及植物的生长生理等一系列生物地球化学循环的影响^[2,20] ...

1997

0.0

... 而放牧是草地生态系统最主要的土地利用方式之一,对草原生态系统N循环过程的改变起着重要的作用,为理解生态系统中的N循环提供有用的信息^[3,4,5,6] ...

2001

0.0

2006

0.0

2007

0.0

... 近年来,国内外进行了大量针对草地生态系统中氮素循环的研究^[6,7,8,9],包括草地生态系统氮素循环的通量和过程的系统研究^[10,11]以及氮肥草地生态系统结构与功能的调控机理方面的研究^[12,13]等,而且也已经有不少学者开展了放牧对草地生态系统N素分配的影响^[10,14,15] ...

2010

0.0

2011

0.0

... 18 mm的土壤筛,然后取筛好的土壤样品5 g放在封口袋中保存,作为土壤稳定性N同位素待测样品^[8,10] ...

... ^[8,10] ...

2015

0.0

斯贵才, 袁艳丽, 王建, 王光鹏, 雷天柱, 张更新. 围封对当雄县高寒草原土壤微生物和酶活性的影响. 草业科学, 2015, 32(1): 1-10.

Si G

, Yuan Y

, Wang

, Wang G

, Lei T

, Zhang G

Effects of fencing on microbial communities and soil enzyme activities in Damxung alpine grassland .

Pratacultural Science, 2015, 32(1): 1-10. (in Chinese)

The deterioration of soil ecosystem and soil degradation related to overgrazing were serious and cannot be restored in short period. In order to determine the impacts of fencing on the soil enzyme activities and soil microbial communities in Damxung steppe, the activities of β-glucosidase, invertase, phenol oxidase, peroxidase, L-asparaginase, protease, urease and alkaline phosphatase were investigated, as well as the biomass of bacteria, fungi, actinomycete, gram-positive bacteria and gram-negative bacteria. Water soluble organic carbon (WSOC) and water soluble organic nitrogen (WSON) in soils with all fencing treatments were significantly higher ( P ＜0.05) than that in grazing soils. There were significant variations of soil moisture and pH between grazing and fencing 6 years. Invertase and L-asparaginase activities significantly increased with the fencing year extended. The biomass of bacteria, actinomycete and gram-positive bacteria in soil with 6 years fencing were significantly higher ( P ＜0.05) than that in soil. All of these results suggested that fencing changed not only soil physicochemical properties, but also soil enzyme activities and microbial communities. The further pearson correlation analysis showed that WSOC, WSON and moisture had significantly positive correlation with soil enzyme activities and soil microbial communities which suggested that all of tested factors could be good indicators for grassland degradation and restoration. All of these results showed that fencing helped improving soil organic matter to promote growth of microorganism and recovery of alpine grassland ecosystem.

1.Gansu Provincial Key Laboratory of Petroleum; Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China; 2.Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China; 3.Graduate University of Chinese Academy of Sciences, Beijing 100049, China

过度放牧会严重破坏土壤生态系统,造成土壤退化,土壤一旦退化,即使很长年限也难以恢复。本研究通过围栏禁牧(1、4、6年)对青藏高原当雄县高寒草原退化草地进行修复,分析围封时间对高寒草原土壤理化性质、土壤微生物和酶活性的影响,以期阐明围封对高寒退化草地修复的影响。结果表明,与放牧土壤相比,围封1、4和6年的草地土壤水溶性有机碳和水溶性有机氮含量显著提高( P ＜0.05),围封6年的土壤含水量显著增加,pH值显著降低;围封显著改变了土壤蔗糖酶和L-天冬酰胺酶活性,土壤蔗糖酶和L-天冬酰胺酶活性均随着围封年限的延长有增加的趋势;围封6年土壤细菌、放线菌和革兰氏阳性细菌含量相比放牧显著升高。因此,围封不仅会引起土壤物理化学性质的变化,而且土壤酶活性与土壤微生物群落结构都会发生相应改变。Pearson相关性分析表明,水溶性有机碳、水溶性有机氮、土壤水均与土壤酶活性和微生物类群生物量显著或极显著( P ＜0.01)相关,因此这些指标可以指示退化草地修复状况。围栏禁牧有利于提高土壤易降解有机质含量,从而促进微生物生长,加速营养物质循环,促进高寒草原生态系统的恢复。

2004

0.0

潘庆民, 白永飞, 韩兴国, 杨景成. 内蒙古典型草原羊草群落氮素去向的示踪研究. 植物生态学报, 2004, 28(5): 665-671.

Pan Q

, Bai Y

, Han X

, Yang J

Study on the fate of labeled nitrogen applied to a Leymus chinensis community of typical steppe in Inner Mongolia grassland .

Chinese Journal of Plant Ecology, 2004, 28(5): 665-671. (in Chinese)

An important grassland ecosystem management strategy is the application of nitrogen fertilizer; however, the fate of applied nitrogen is highly correlated with risks and benefits associated with the fertilization of grasslands. The fate of nitrogen tracers applied to a typical Inner Mongolia steppe ecosystem has not been studied previously. We examined the fate of 15N-labelled fertilizer in a Leymus chinensis site at the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. The results showed that after one growing season an average of 31.61% (range from 25.33% to 38.65%) of the applied 15N was recovered in the plant pool. 15N recovered by aboveground and belowground organs significantly increased with increasing nitrogen rates suggesting that nitrogen fertilizer significantly affected the recovery of 15N by plants. About 2.92% (range from 2.58% to 3.16%) of the applied 15N was recovered in the litter, with the percent 15N in the belowground litter significantly higher than in the aboveground litter pool. About 36.16% of the labelled nitrogen was retained in the soil pool, mostly in the 0-40 cm soil layer. 15N retained by the soil increased significantly with increases in the nitrogen application rate. The loss of 15N was about 21.77%-43.38% of the labelled nitrogen. Risk/benefit analysis showed that, under the climatic and soil conditions prevailing during this experiment, fertilizer application rates of 5.25 g N•m-2 and 28 g N•m-2 were associated with high risk/benefit ratios, whereas the 17.5 g N•m-2 fertilizer treatment achieved the lowest risk/benefit ratio among the nitrogen rate treatments. These results provide a reference for future grassland ecosystem management strategies.

Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China

在中国科学院内蒙古草原生态系统定位研究站的羊草样地，采用15N同位素示踪技术研究了羊草（Leymus chinensis）群落标记氮素的去向。结果表明：在我国典型草原羊草群落，植物对标记氮素的回收率为31.61%，氮素添加显著影响植物对标记氮素的回收，随着氮素添加量的增加，地上和地下植物器官对标记氮素的回收量均显著提高。标记氮素被凋落物的回收率为2.92%，地下凋落物的回收率显著高于地上凋落物。标记氮素的土壤存留率为36.16%，主要分布在地表0～40 cm的土层范围内；各土层存留的标记氮素量均随着氮素添加量的增加而显著提高。标记氮素的当季损失率为21.77%～43.38%。风险/收益比分析表明，在该试验条件下，添加5.25 g N•m-2与28 g N•m-2的处理风险大于收益，添加17.5 g N•m-2的处理风险最低，收益最高，在草原生态系统的管理中可供参考。

... 18 mm的土壤筛,然后取筛好的土壤样品5 g放在封口袋中保存,作为土壤稳定性N同位素待测样品^[8,10] ...

... ^[8,10] ...

2004

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2005

0.0

潘庆民, 白永飞, 韩兴国, 杨景成. 氮素对内蒙古典型草原羊草种群的影响. 植物生态学报, 2005, 29(2): 311-317.

Pan Q

, Bai Y

, Han X

, Yang J

Effects of nitrogen additions on a Leymus chinensis population in typical steppe of Inner Mongolia.

Chinese Journal of Plant Ecology, 2005, 29(2): 311-317. (in Chinese)

Leymus chinensis, a rhizomatous graminoid, is a dominant species in the grasslands of northern China. The characteristics of L. chinensis populations have been well documented in many research papers. Because of overgrazing, grasslands of northern China have become degraded since the 1980s. As a result, the density and biomass of L. chinensis populations have decreased significantly. Fertilization is a common technique for management of pastures in many countries; however, it is not widely used in the grasslands of China. Nitrogen is an important driver of community succession in grassland ecosystems, but the response of L. chinensis populations to nitrogen additions in typical steppe, a semiarid area of northern China, remains unclear. We conducted a sequential nitrogen addition experiment in a lightly degraded grassland plot that was fenced in 1999. Nitrogen (NH4NO3) was applied on July 5 for two years at application rates of: 0, 1.75, 5.25, 10.5, 17.5, and 28 g N·m-2,respectively. There were 9 replicate 5 m×5 m plots of each of the six treatments with each plot spaced 1 m apart. A completely randomized design was used for this experiment. Before the experiment, soil samples were collected and dry bulk density, pH, soil nitrogen and soil carbon were analyzed. After two years of nitrogen fertilization, we measured the density, height, aboveground biomass and belowground biomass of L. chinensis in each plot. The results showed that L. chinensis population characteristics were highly responsive to nitrogen additions. With an increase in nitrogen application rates, the density, height, aboveground biomass, belowground biomass and total biomass of L. chinensis increased significantly whereas the ratio of aboveground biomass/belowground biomass decreased. The allocation of biomass among plant parts was significantly affected by nitrogen additions: the proportion of biomass allocated to rhizomes decreased remarkably with increasing nitrogen rates whereas that allocated to leaves and roots increased significantly. The relative biomass and relative density of L. chinensis also increased with increasing nitrogen additions. In summary, adding nitrogen to lightly degraded grassland not only increased the density and biomass of L. chinensis population but changed the resource partitioning among plant parts as well.

(Inner Mongolia Grassland Ecosystem Research Station, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China)

为了研究氮素对内蒙古典型草原植物种群的影响，在中国科学院内蒙古草原生态系统定位研究站，实施了长期的氮素添加试验。就两年来不同梯度氮素处理对羊草(Leymus chinensis)种群的影响进行了分析。结果表明，氮素对羊草种群具有显著的调节效应，随着氮素梯度的增加，羊草种群密度、种群高度、地上生物量、地下生物量、总生物量均显著增加，羊草种群地下生物量／地上生物量比值逐渐降低。氮素对羊草种群构件的生物量分配有显著影响，随着氮素梯度的增加，羊草种群生物量向根茎的分配比例显著降低，向叶片和根系的分配比例显著提高。羊草种群的相对密度和相对生物量也随着氮素梯度的增加而显著提高。

2014

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2014

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邓建明, 姚步青, 周华坤, 赵新全, 魏晴, 陈哲, 王文颖. 水氮添加条件下高寒草甸主要植物种氮素吸收分配的同位素示踪研究. 植物生态学报, 2014, 38(2): 116-124.

Deng J

, Yao B

, Zhou H

, Zhao X

, Wei

, Chen

, Wang W

Nitrogen uptake and allocation characteristics of alpine meadow main species under water and nitrogen additions based on ¹⁵N isotope.

Chinese Journal of Plant Ecology, 2014, 38(2): 116-124. (in Chinese)

Aims Resource-use differentiation among species, which can reduce species competition for the same resources, is the main mechanism to maintain species diversity. Changes in soil temperature and moisture conditions, in the context of global change, may affect nitrogen (N) nutrition of plants of alpine meadow ecosystems. Our objective is to compare the characteristics of N uptake and resource allocation of dominant species of alpine meadow with changes in soil N and water. Methods An alpine meadow was treated with N and water addition for three years using the method of 15 N isotope injection. We determined the growth responses of dominant species to the N and water additions, as well as the features of N uptake capacity, N allocation and root to shoot ratio. Important findings The species showed significantly different responses to the N and water treatments, with respect to functional traits of species in N absorption capacity, root N content and root to shoot ratio. There was no significant relationship between N absorption capacity and root N content, whereas N absorption capacity was negatively correlated with root to shoot ratio across all plant species. These results indicated there was ecological niche differentiation in N uptake and a trade-off between the N absorption capacity and resource allocation strategies among species.

1 Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining 810001, China; 2 School of Life Science, Lanzhou University, Lanzhou 730000, China; 3 Department of Life and Geography Sciences, Qinghai Normal University, Xining 81008, China; 4 University of Chinese Academy of Sciences, Beijing 100049, China

资源利用方式的分化可以减小物种间对相同资源的竞争, 是群落物种多样性维持的主要机制。在全球变化背景下, 土壤温度和水分条件的变化可能影响高寒草甸生态系统植物的氮素(N)营养。该实验在经N、水处理3年的高寒草甸开展, 通过 15 NH 4 15 NO 3 的 15 N稳定性同位素注射, 比较高寒草甸主要植物种对N、水处理的响应方式, 以及N吸收能力、分配和根冠比特点, 研究其营养吸收和资源分配方式的分化。结果发现不同植物种对N、水处理响应差异显著, N吸收能力、根N含量和根冠比等功能性状种间差异显著; 回归分析发现植物种N吸收能力和根N含量之间的关系不显著, 和根冠比之间呈显著线性负相关。说明高寒草甸生态系统不同植物种间N吸收具有生态位分化, 并且存在N营养吸收能力和资源分配策略的权衡。

2014

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宋智芳, 安沙舟, 孙宗玖. 放牧地伊犁绢蒿营养元素分配特点. 草业科学, 2014, 31(1): 132-138.

Song Z

, An S

, Sun Z

Characteristics of nutrition allocation of Seriphidium transiliense under grazing condition.

Pratacultural Science, 2014, 31(1): 132-138. (in Chinese)

In order to understand resources allocation pattern of Seriphidium transiliense under grazing condition, the content and storage allocation of carbon, nitrogen, phosphorus and potassium of roots, stems, leaves and flowers (or seeds) were measured. The results showed that the phosphorus content of roots, the nitrogen, phosphorus, potassium and carbon content of flowers or seeds decreased under grazing condition and the other nutrition content changed complicatedly without regular pattern. It proved that grazing contribute to potassium and carbon accumulation allocation of S.transiliense . The rates of potassium and carbon accumulation allocation in roots increased by 3.16%～12.79% and 2.12%～12.74%, respectively. The rates of potassium accumulation allocation decreased in stems, leaves and flowers (seeds) by 1.67%～14.13%, 1.49%～2.89% and 0.33%～0.41%, respectively. The rates of the carbon reserve allocation decreased in stems, leaves and flowers (seeds) by 6.45%～11.37%, 0.77%～4.18% and 0.01%～0.09%, respectively. During vegetative period and flowering stage, the nitrogen accumulation allocation of S.transiliense in root increased by 11.91%～18.45% and that in leaves and flowers (seeds) decreased by 8%～14.58% and 1.78%～4.76%, respectively. The phosphorus accumulation allocation had no relationship with grazing.

College of Grassland and Environment Science, Xinjiang Agricultural University, Key Laboratory of Grassland Resources and Ecology of Xinjiang, Urumqi 830052, China

以蒿类荒漠草地上的建群种伊犁绢蒿( Seriphidium transiliense )为对象, 研究其根、茎、叶、花/种子中的氮、磷、钾、有机碳含量及其贮量分配对放牧干扰的响应。结果表明, 放牧导致伊犁绢蒿根中的磷含量减少, 花/种子中的氮、磷、钾以及有机碳含量减少, 而放牧对其他构件中营养元素的影响不一致。从分配格局来看, 放牧后根中的钾、有机碳的分配增加, 分别为3.16%~12.79%、2.12%~12.74%;茎、叶和花中钾和碳元素分配减小, 钾元素分别减少1.67%~14.13%、1.49%~2.89%和0.33%~0.41%, 碳元素分别减少6.45%~11.37%、0.77%~4.18%和0.01%~0.09%。在营养期和开花期放牧后, 伊犁绢蒿根中氮分配增加, 增加11.91%~18.45%;茎和叶中氮分配减小, 分别为8.00%~14.58%、1.78%~4.76%, 磷分配规律性不明显。

1999

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... ¹⁵N格局的因素主要有气候、时间、地形和土地利用等^{[16,17,18,19]} ...

... ¹⁵N值的增加^[16,23,24] ...

2003

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... ¹⁵N格局的因素主要有气候、时间、地形和土地利用等^{[16,17,18,19]} ...

2004

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... ¹⁵N格局的因素主要有气候、时间、地形和土地利用等^{[16,17,18,19]} ...

2008

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刘卫国, 王政. 黄土高原现代植物-土壤氮同位素组成及对环境变化的响应. 科学通报, 2008, 53(23): 2917-2924.

Liu W

, Wang

Reponses of N isotope of modern plant-soil form to the environmental change in Loess Plateau.

Chinese Science Bulletin, 2008, 53(23): 2917-2924. (in Chinese)

由于土壤氮同位素组成被认为是气候环境变化和自然生态系统氮循环过程的可能指示, 开展全球不同区域、不同生态系统氮同位素组成的研究将有助于对这个可能性的认识. 对中国黄土高原中西部不同环境条件下的现代植物和相应的土壤氮同位素进行了调查, 氮同位素组成变化范围分别为: 植物根: -5.1‰ ~ 1.9‰; 植物残体: -6.6‰ ~ 2.9‰; 土壤: -1.2‰ ~ 5.8‰. 结果表明: (1) 土壤与植物有相近的变化趋势, 但土壤的氮同位素组成较植物根的氮同位素要偏正, 其Δ δ 15 N值变化范围为: 0.3‰ ~ 7.2‰, 平均值为: 4.1‰, 表明植物分解过程氮同位素存在分馏; (2) 该地区现代生态系统的氮同位素对降水和温度变化有明显的响应, 沿西北到东南方向, 年平均降水每增加100 mm可能导致土壤氮同位素组成偏负约1.31‰, 随温度的增加, 土壤氮同位素也趋向偏负; (3) 在降水和温度共同增加的影响下, 植物根系、植物残体和土壤的氮同位素偏负, 这个现象可能归因于降水是该地区植物-土壤氮同位素变化的主要控制因素. 尽管目前对植物-土壤氮同位素组成变化与降水和温度关系的机制尚不清楚, 但初步的研究结果表明土壤的氮同位素组成可能为黄土高原环境变化示踪提供指示.

... ¹⁵N格局的因素主要有气候、时间、地形和土地利用等^{[16,17,18,19]} ...

2007

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1993

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... 6%^[21,22] ...

1992

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... 6%^[21,22] ...

1997

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... ¹⁵N值的增加^[16,23,24] ...

1994

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... ¹⁵N值的增加^[16,23,24] ...

2007

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... ¹⁵N值也随之降低^[25,26] ...

2010

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吴田乡, 黄建辉. 放牧对内蒙古典型草原生态系统植物及土壤δ¹⁵N的影响. 植物生态学报, 2010, 34(2): 160-169.

Wu T

, Huang J

Effects of grazing on the δ¹⁵N values of foliage and soil in a typical ecosystem in Inner Mongolia, China.

Chinese Journal of Plant Ecology, 2010, 34(2): 160-169. (in Chinese)

Aims Stable N isotope signature ( δ 15 N) in both plant and soil is potentially an important parameter to evaluate N cycling in grassland ecosystems. Grazing is a dominant land use in northern China grasslands and might have greatly changed N cycling. Our objective was to determine the 15N signature of leaves and soils in grazed and fenced plots of a typical steppe to investigate how δ 15 N values in an ecosystem are affected by grazing. Methods We collected foliar and soil samples in a nearly 20 years fenced plot and an adjacent freely grazed plot. The foliar samples came from eight dominant species, including three perennial legumes ( Caragana microphylla , Astragalus galactites and Melilotoides ruthenica ), two grasses ( Leymus chinensis and Stipa grandis ), two forbs ( Heteropappus altaicus and Potentilla acaulis ) and a semi-shrub ( Kochia prostrata ). We also sampled 0–10 and 10–20 cm rhizosphere soils of C. microphylla and K. prostrata . Nitrogen isotope ratios were determined with a Thermal Finnigan MAT Delta plus XP isotope-ratio mass spectrometer (IRMS). Important findings Although the δ 15 N value of leaves of different plant species varied greatly, the observed pattern of variability is consistent in both grazed and fenced plots, i.e., semi-shrub > forbs and grasses > legumes. Long-term grazing reduced foliar δ 15 N values of forbs, semi-shrub and S. grandis significantly while changing little or even increasing that of potential biological N fixers (legumes and L. chinensis ). As the only arbuscular mycorrhizae non-infected plant species, K. prostrata is enriched in 15 N (with δ 15 N values of 4.34‰ ± 0.35‰ and 2.04‰ ± 0.20‰ in fenced and grazed plots, respectively) compared with the depletion of other species. Mycorrhizal association may be considered to play an important role in plant nutrient transfer in those N-limited grassland ecosystems. In contrast to results of previous studies, soil δ 15 N values decreased significantly with grazing.

1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; and 2Graduate University of Chinese Academy of Sciences, Beijing 100049, China

植物和土壤中的 15 N自然丰度值( δ 15 N)是评价生态系统N循环的一个重要指标, 而放牧是草原生态系统的主要土地利用方式, 对草原生态系统的N循环过程的改变起着重要作用。该研究测定了内蒙古锡林河流域放牧和围封条件下草原群落主要优势植物和土壤的 δ 15 N值, 探讨放牧对草原N循环的影响。研究中所测定的8种植物叶片 δ 15 N变化很大(–4.04‰–4.34‰), 但与植物功能型有一定的相关性。放牧显著降低了大针茅( Stipa grandis )、杂类草和小半灌木木地肤( Kochia prostrata )的 δ 15 N值。具有潜在共生固氮能力的豆科植物 δ 15 N偏低负值(–4.04‰ – –1.90‰), 但在放牧和围封条件下无显著差异; 而被认为具有联合固氮能力的羊草( Leymus chinensis ), 放牧后 δ 15 N显著增加, 一定程度上表明了豆科植物和羊草生物固氮能力的存在。所有植物中, 除无菌根侵染的木地肤外, 其他有丛枝菌根真菌侵染记录的物种 δ 15 N值较低, 通常接近0或为负值, 说明在N限制的内蒙古草原, 菌根转运N可能也是一种重要的N源途径。放牧显著降低了0–20 cm土壤 δ 15 N值, 这也与过去的研究结果不同。 δ 15 N的测定为生态系统提供了一个整合时空N循环过程的综合指标, 反映出放牧改变了草原生态系统的N循环。

... ¹⁵N值也随之降低^[25,26] ...

... 这与吴田乡和黄建辉^[26]的观点一致,认为放牧后0-10 cm土壤#cod#x003b4 ...

1993

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... ¹⁵N值的作用相对较小^[27] ...

2006

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... ¹⁵N值均随着土层深度的加深而显著增加,这与国内外的许多研究^[28,29]结果相一致 ...

1989

0.0

... ¹⁵N值均随着土层深度的加深而显著增加,这与国内外的许多研究^[28,29]结果相一致 ...