植物功能群去除对高寒草甸群落结构、多样性及生产力的影响

群落中物种的丧失在干扰下普遍存在,但对生态系统过程和功能的影响仍存在较大不确定性。选取青藏高原东缘典型高寒草甸为对象,开展优势植物功能群的梯度去除试验,以模拟长期过牧干扰下物种的损失。经过连续两个生长季的功能群去除,我们对群落的物种组成、结构、多样性和生物量等特征进行了分析,探讨了上述指标的响应过程和机制。研究结果表明：（1）功能群的去除降低了群落高度,增加了物种均匀度,并显著影响了禾草、杂草优势比以及功能群多样性和优势度;（2）同时,去除操作显著减小了凋落物量与禾草生物量,并显著影响了群落地上生物量;（3）进一步分析还发现,禾草、莎草和杂草功能群之间存在显著的竞争关系,群落生产力主要取决于禾草功能群并随物种均匀度的增大而显著减小。上述结果表明,禾草在高寒草甸群落中占据竞争优势地位,植物功能群的损失主要通过改变种间竞争关系、引起有机物质丢失影响群落过程和功能。     

黄龙山不同白桦林群落结构特征研究

在黄龙山林区以4种不同白桦林群落类型为研究对象,共设置20 m×20 m的样地15块,从林分特征、物种组成、物种多样性、灌木和草本生物量及乔木蓄积量等方面,对不同白桦林群落类型结构特征进行调查分析.结果显示：（1）群落B林（白桦＋茶条槭昆交）中白桦林分状况为最好,其次为群落A（油松＋白桦混交林）,群落D（自桦纯林）最差;（2）不同群落中植物种类分别为群落A（51种）＞群落B（49种）＞群落D（48种）＞群落C（38种）;（3）物种多样性指数为群落A＞群落B＞群落C＞群落D;（4）不同群落内草本和灌木总生物量排序为群落D（73.19t·hm^-2）＞群落B（65.07 t·hm^-2）＞群落C（59.93 t·hm^-2）＞群落A（44.82 t·hm^-2）,乔木蓄积量为群落A（123.50 m^3·hm^-2）＞群落D（69.50 m^3·hm^-2）＞群落B（53.25 m^3·hm^-2）＞群落C（50.25 m^3·hm^-2）.研究结果表明,黄龙山不同白桦林群落中混交林在生长状况、物种组成、物种多样性和生物量方面均优于纯白桦林.表明白桦混交林对保持黄龙山森林群落稳定性,提高林分质量,实现白桦林向松栎林的逐渐过渡有重要意义.     

Plant functional groups mediate effects of climate and soil factors on species richness and community biomass in grasslands of Mongolian Plateau

植物功能群在调控气候和土壤因子对蒙古高原草原群落物种丰富度和生物量影响中的作用 植物功能群组成主要受环境因素驱动,同时植物功能群组成也是影响草地生物多样性和生产力的主要因素之一。因此,理解植物功能群在调控环境因素对生态系统功能和生物多样性影响中可能发挥的作用至关重要。通过对蒙古高原草原65个样点的植物生物量和物种丰富度的调查,将157种多年生草本植物分为两种植物功能群(即禾草和杂类草)。通过随机森林模型和普通最小二乘回归,确定与植物功能群物种丰富度和地上生物量显著相关的环境因素(即干燥度、土壤总氮和pH),并利用结构方程模型探讨筛选出的环境因素与群落物种丰富度和生物量间的关系,以及植物功能群在驱动这种关系中发挥的作用。干燥度与禾草、杂类草以及整个群落的地上生物量和物种丰富度均呈显著的单峰关系。所有的物种丰富度和生物量指标均与土壤总氮和pH值显著相关。禾草在维持蒙古高原草原生态系统群落生物量中起着关键作用,并受气候因素的直接影响。而杂类草物种丰富度决定了群落总丰富度,并受到土壤因素直接的调控。因此,群落组成在调控环境因素对群落生物量和植物多样性的影响中起着关键作用。     

氮磷养分共同添加促进退化典型草原恢复的机制

土壤养分含量降低是我国草原退化的主要原因之一,养分添加是退化草原恢复的有效措施,但过量养分添加会导致物种多样性降低。为了探讨适宜的养分添加量以及养分添加促进退化草原恢复的机制,本研究选择内蒙古典型草原的退化群落,通过氮(N)磷(P)养分共同添加梯度试验,研究了退化典型草原在群落、功能群和物种3个组织水平上对养分添加的响应。结果表明: 在群落水平,养分添加显著促进了退化典型草原生物量,但没有降低物种多样性;群落生物量随养分添加水平表现为饱和曲线响应,在12.0 g N·m^-2、3.8 g P·m^-2水平趋于饱和;物种多样性在低养分添加水平(N<9.6 g·m^-2、P<3.0 g·m^-2)较对照显著增加,在其余养分添加水平未发生显著变化。在功能群水平,随着养分添加量的增加,多年生根茎禾草在群落中优势度增加,生物量和密度均显著提高;一年生植物生物量和密度在高养分水平添加下显著增加,多年生丛生禾草和杂类草无显著变化。在物种水平,6个物种对养分添加响应不同,羊草通过增加种群密度和个体大小显著增加了种群生物量;大针茅、冰草和糙隐子草种群生物量没有显著变化;星毛委陵菜和黄囊苔草分别因为降低个体大小和种群密度减少了种群生物量。养分添加作为草原恢复的措施,可以显著增加退化草原生物量和物种多样性,降低植物群落中退化指示种,增加多年生根茎禾草。     

高寒典型草原主要物种的株高和盖度预测种群和群落地上生物量

为快速、准确、无破坏地测定草原地上生物量,在祁连山高寒典型草原植物生长旺季,观测了冬季和春秋季放牧地60个样方内各物种的株高、盖度等生长指标。以冬季牧地紫花针茅（Stipa purpurea）、醉马草（Achnatherum inebrians）、赖草（Leymus secalinus）、扁穗冰草（Agropyron cristatum）、二裂委陵菜（Potentilla bifurca）、银灰旋花（Convolvulus ammannii）6个主要物种的株高、盖度、株高和盖度的乘积为自变量,分别预测同物种、其他物种和群落地上生物量。用春秋季牧场的数据验证模型的精确性和稳定性。结果表明：主要物种的生长指标可预测其自身、其他物种和群落地上生物量。对自身种群,株高和盖度乘积的复合因子预测效果最好;4种禾草对其他物种、二裂委陵菜对菊科植物种群,株高、盖度单因子预测效果优于复合因子;6个主要物种单独或2-6个种结合均可预测群落地上生物量,但是以6个物种株高和盖度的乘积同时预测时决定系数最大,可解释群落地上生物量89.5%的变异,为高寒典型草原群落地上生物量最优预测模型。     

高寒草甸植物物种丧失对草原毛虫的影响

植物多样性是调控食物网结构和生态系统功能最重要的生物因素, 植物多样性丧失深刻影响食草动物, 但由于小型食草动物种群数量波动明显、统计随机性较大等困难, 我们对植物多样性丧失如何影响小型食草动物依然知之甚少。基于在青藏高原高寒草甸设置的长期植物物种剔除试验, 本研究于2016-2020年7-8月连续调查了植物物种剔除各处理中草原毛虫(Gynaephora alpherakiif)的数量, 分析了植物物种及功能群丧失对草原毛虫的影响。结果表明, 虽然时空差异及统计随机性是影响草原毛虫数量变化的主要因素, 但植物物种剔除介导的群落差异对草原毛虫数量的影响依然显著: (1)在各观测时段, 优势种线叶嵩草(Kobresia capillifolia)的丧失导致群落中草原毛虫数量显著减少; 禾草类物种丧失也会减少草原毛虫数量, 但其影响仅在8月显著; (2)杂类草物种丧失通过增加群落中禾草物种多度, 可增加草原毛虫数量; 豆科物种丧失使莎草增多, 也会增加草原毛虫数量; (3)各植物功能群部分物种剔除并未显著影响草原毛虫数量。本研究证实了高寒草甸中草原毛虫数量会因优势植物嵩草和禾草的多度减少或禾草物种丧失而显著减少, 但群落总生物量、个体数和物种丰富度、豆科多度以及各功能群植物同比减少, 都对草原毛虫数量没有明显影响。这些结果说明在随机作用主导下, 植物群落中的特定功能群相对多度(而非物种多样性)变化深刻影响草原毛虫适合度, 进而影响生态系功能及服务; 未来生物多样性研究及草地虫害生物防控中应更多考虑统计随机性及植物功能多样性对小型食草动物的影响。     

黄河三角洲贝壳堤湿地优势灌木碳、氮、磷化学计量特征

为探讨黄河三角洲海岸带湿地不同水盐条件下植物叶片化学计量特征的季节动态及植物生长的限制性营养元素,以滨州贝壳堤岛与湿地国家级自然保护区内的柽柳、杠柳、酸枣3种优势灌木为研究对象,于2017-2018年的生长季（5-10月）每月定期采集叶片样品,测定叶片C、N、P含量。结果表明,生长季内3种灌木叶片C含量呈逐渐上升趋势;叶片N、P含量呈先下降后上升趋势,说明3种灌木采用防御性生活史策略适应盐生和干旱生境。3种灌木叶片C平均含量分别为（399.65±2.66）mg/g、（424.32±1.59）mg/g、（437.47±1.08）mg/g,低于全国（455.1 mg/g）及全球（461.6 mg/g）水平,呈现盐生生境下较低的植物碳储存能力。3种灌木叶片N和P平均含量分别为（30.14±0.26）mg/g和（1.81±0.03）mg/g、（23.18±0.38）mg/g和（2.06±0.04）mg/g、（27.36±0.49）mg/g和（2.01±0.03）mg/g,显著高于全国（N∶20.2 mg/g,P：1.46 mg/g）及全球（N∶19.3-20.1 mg/g,P：1.11-1.42 mg/g）水平。叶片C∶N∶P比呈先上升后下降的趋势,叶片P含量对C∶N∶P比变化具有主导作用。3种灌木叶片C∶N∶P质量比分别为246∶17∶1、224∶12∶1、237∶14∶1,说明柽柳的水盐胁迫适应能力高于杠柳和酸枣。从叶片N、P化学计量特征看,生长季内,柽柳生长一定程度上受土壤P限制,杠柳生长受到土壤N限制,酸枣生长则受土壤N、P共同限制,说明3种灌木的生物地球化学生态位发生了分化,避免了对同种资源的竞争,利于物种共生。     

宁夏东部风沙区荒漠草原植物群落物种多样性研究

通过野外植被调查,研究了宁夏东部风沙区荒漠草原植物群落组成与结构、物种多样性变化;采用典范对应分析（CCA）对植物群落分布与土壤性状关系进行了分析。结果表明：（1）风沙区荒漠草原物种较为单一,多集中在6~13种;不同群落类型间地上生物量和盖度差异显著;群落内竞争性较弱的物种减少,优势种具有较高的重要值。（2）群落间物种多样性差异显著,但变化趋势并不一致;物种多样性指数与丰富度指数、均匀度指数的相关系数分别为0.975 7和0.880 2,而与优势度指数相关系数为-0.519 8。（3）CCA结果表明,土壤含水率、有机质以及氮磷钾含量较高、容重小时,植物物种相对丰富;对群落分布影响较大的环境因子是土壤水分、容重和土壤有机质,相关系数分别为-0.742 8、0.683 8、0.532 9,物种和群落二者在CCA排序轴相关性较大的土壤因子较为一致。研究认为,宁夏东部风沙区荒漠草原植物优势种在群落中的地位明显,物种丰富度对植物多样性的影响大于均匀度,土壤水分是影响该区草原植物群落分布的决定性环境因子。     

土壤水分变化对黄土丘陵区撂荒群落共存种竞争的影响

群落共存种对限制性资源的竞争响应是群落组建、维持与演替的重要影响因素。以黄土丘陵区摞荒群落共存种为研究对象,研究不同水分条件下的竞争响应差异,以期揭示生境变化时群落演替的植物竞争机理。试验设土壤水分与混植密度两个处理,其中混植密度采用CDS （Community density series）法,含3个密度水平（衡水试验为3、12、21株/m²,变水试验为5、20、35株/m²）;土壤水分设衡水（高（75% FC）、中（60% FC）、低（45% FC）3个水平）与变水（由高水（75% FC）经50 d持续干旱至低水（45% FC））两种处理。根据共存种株高的阶段性生长与其在群落中的相对生物量等生长表现,在CDS法基础上扩展并测算了生长变化量、相对生物量和相对生长率等指标。据此,研究竞争效应和水分胁迫效应的相对影响,共存种相对竞争能力和竞争等级对土壤水分变化的响应,及高水期因竞争引起的个体大小不对称性与低水期死亡率的关系。结果表明：1）不同水分多种混植共存条件下,竞争效应对多数共存种在群落中的生长表现较水分胁迫效应影响更大;以相对生物量为指标的竞争的群落效应（4.30±0.49）较水分胁迫的群落效应（-23.56±20.38）大,且二者累加效应（4.76±0.4）大于二者单项效应之和（-19.26±20.48）,即竞争+水分胁迫对多种共存群落具有协同效应。2）当水分条件发生变化时,群落共存种的竞争等级并不完全相同（P > 0.05）,相应的会发生变化,且水分差别越大,共存种竞争等级的差别也越大;高水条件下群落共存种竞争所引起的群落效应最大（4.84±0.23）,部分支持最大生长率理论,即限制性资源水平越高,群落共存种竞争越激烈。3）变水试验中,10种群落共存种在高水期因竞争引起的个体大小差异与低水期的死亡率呈正相关关系（P=0.015,r²=0.801）,根据资源动态两阶段假说,说明试验条件下群落共存种竞争是群落组建的重要因素。     

极端干旱对草甸草原优势植物非结构性碳水化合物的影响

植物光合作用产生的非结构性碳水化合物(NSCs)水平可以反映植物和生态系统对环境变化的响应程度。近年来, 草原极端干旱事件的发生频率和持续时间增加趋势明显, 对生态系统结构和功能产生深远影响。该研究以内蒙古呼伦贝尔草甸草原为研究对象, 通过连续4年减少66%生长季降水量的控制实验来模拟极端干旱事件, 分析草原6种优势物种和植物功能群NSCs各组分对极端干旱的响应规律与机制。结果显示, 由于植物生物学、光合特性以及生理生态等特性的差异, 不同物种对干旱胁迫的响应具有明显差异。这表明草地植物NSCs组分及其利用策略对干旱胁迫的响应具有物种特异性, 从而导致其生物量的不同响应。将6种植物分为禾草和非禾草两类, 发现干旱显著增加了禾草的淀粉含量, 但对其可溶性糖含量无显著影响; 相反, 干旱显著增加了非禾草功能群的可溶性糖含量, 对其淀粉含量无显著影响, 表明不同功能群采取了不同的干旱应对策略。禾草选择将光合作用固定的能量进行储存以应对干旱胁迫, 其生物量对干旱响应不敏感; 而非禾草选择将能量以可溶性糖的形式直接供植物生长利用以及抵御干旱胁迫, 其生物量对干旱响应较为敏感。这一发现可为预测在全球气候变化背景下草甸草原生态系统结构与功能对极端干旱的响应提供科学参考。     

Caloric content of plant species and its role in a Leymus chinensis steppe community of Inner Mongolia, China

The caloric contents of 42 species and their composition in a Leymus chinensis steppe community of Inner Mongolia, China were determined and analyzed based on the field experiment for 11 years. The caloric content (x ± SD) of aboveground parts of plant species varied from (13156 ± 1141) J·g^?1 (ash contained) to (18141 ± 527) J·g^?1. The average caloric content of all species was (16899 ± 840) J·g^?1 and the inter-specific CV (coefficient of variation) was 4.9%. Of all the species, Caragana microphylla had the highest caloric content (18142 J·g^?1). Grasses had a higher average caloric content ((17425 ± 291) J·g^?1) than forbs ((16734 ± 844)J·g^?1). When the herbaceous species were classified into subgroups according to life-form and growth-form, the order of average caloric contents, from high to low, was: tall grasses ((17717 ± 92) J·g^?1) > legume ((17228 ± 433) J·g^?1) > short grasses ((17250 ± 218) J·g^?1) > remaining forbs ((16784 ± 529) J·g^?1) > subshrubs ((16719 ± 69) J·g^?1) > annuals and biennials ((15911 ± 1759) J·g^?1). There was a positive correlation (P < 0.05) between the caloric contents of 42 species and their relative biomass in the community. When all species were classified into 3 groups according to their composition in the community, the average caloric contents, weighed by the species relative biomass, followed the order: dominant (17740 J·g^?1) > companion (17244 J·g^?1) > incidental (16653 J·g^?1). The plants with high caloric contents were more competitive, which allowed them to gain a dominant status, whereas the competitive abilities of plants with low caloric contents were generally weak. The latter made up the companion or incidental species in a steppe community.     

Caloric content of plant species and its role in a Leymus chinensis steppe community of Inner Mongolia, China

The caloric contents of 42 species and their composition in a Leymus chinensis steppe community of Inner Mongolia, China were determined and analyzed based on the field experiment for 11 years. The caloric content (x ± SD) of aboveground parts of plant species varied from (13156 ± 1141) J·g^?1 (ash contained) to (18141 ± 527) J·g^?1. The average caloric content of all species was (16899 ± 840) J·g^?1 and the inter-specific CV (coefficient of variation) was 4.9%. Of all the species, Caragana microphylla had the highest caloric content (18142 J·g^?1). Grasses had a higher average caloric content ((17425 ± 291) J·g^?1) than forbs ((16734 ± 844)J·g^?1). When the herbaceous species were classified into subgroups according to life-form and growth-form, the order of average caloric contents, from high to low, was: tall grasses ((17717 ± 92) J·g^?1) > legume ((17228 ± 433) J·g^?1) > short grasses ((17250 ± 218) J·g^?1) > remaining forbs ((16784 ± 529) J·g^?1) > subshrubs ((16719 ± 69) J·g^?1) > annuals and biennials ((15911 ± 1759) J·g^?1). There was a positive correlation (P < 0.05) between the caloric contents of 42 species and their relative biomass in the community. When all species were classified into 3 groups according to their composition in the community, the average caloric contents, weighed by the species relative biomass, followed the order: dominant (17740 J·g^?1) > companion (17244 J·g^?1) > incidental (16653 J·g^?1). The plants with high caloric contents were more competitive, which allowed them to gain a dominant status, whereas the competitive abilities of plants with low caloric contents were generally weak. The latter made up the companion or incidental species in a steppe community.     

Exotic grasses and feces deposition by an exotic herbivore combine to reduce the relative abundance of native forbs

Increased resource availability can facilitate establishment of exotic plant species, especially when coincident with propagule supply. Following establishment, increased resource availability may also facilitate the spread of exotic plant species if it enhances their competitive abilities relative to native species. Exotic Canada geese (Branta canadensis) introduce both exotic grass seed and nutrients to an endangered plant community on the Gulf Islands of southwestern British Columbia, Canada. I used greenhouse experiments to assess the competitive advantage of the exotic grasses relative to native and exotic forbs in this community and to test the impacts of nutrient addition from goose feces on competitive outcomes. I grew experimental communities varying in their proportion of forbs versus exotic grasses, and added goose feces as a nutrient source. I found that both native and exotic forbs produced significantly more biomass in competition with conspecifics than in competition with the grasses, and that the proportional abundance of two out of three native forbs was lowest in the combined presence of exotic grasses and nutrient addition. In a second experiment, I found that in monoculture all species of forbs and grasses showed equal growth responses to nutrients. The exotic species did not convert additional nutrients into additional biomass at a higher rate, but did germinate earlier and grow larger than the native species regardless of nutrient availability. This suggests that the exotic species may have achieved their competitive advantage partly by pre-empting resources in community mixtures. Small and late-germinating native forbs may be particularly vulnerable to competitive suppression from exotic grasses and forbs and may be at an even greater disadvantage if their competitors are benefiting from early access to additional nutrients. In combination, the input of exotic propagules and additional nutrients by nesting geese may compromise efforts to maintain native community composition in this system.     

不同载畜率对荒漠草原群落结构和功能群生产力的影响

采用随机区组试验研究了内蒙古高原荒漠草原亚带短花针茅(S tip a brev if lora)草原群落不同载畜率对草原群落结构和功能群生产力的影响。结果表明:随着载畜率的增加,群落的植物种数逐渐减少,在每个载畜率水平下,冷蒿(A rtem isia f rig id a)占有绝对优势地位,优势度为35.66%~41.95%;群落的地上生物量随载畜率的增加而降低,各功能群地上生物量组成中,灌木类处于主体地位,分别占据了群落68%(CK)、77.40%(LG)、73.25%(M G)、76.91%(HG)的生物量;在植物生活型功能组成中,灌木类和杂类草、多年生丛生禾草和杂类草功能群,在生物量上具有生态互补效应(n iche com p lem en tary effect)。     

Priority effects produced by plant litter result in non-additive competitive effects

Litter may indirectly affect competitive interactions. It is not clear whether these changes are additive or non-additive indirect effects. Non-additivity could result from: (1) changes in biomass allocation patterns by competitors towards organs not directly involved in resource acquisition (e.g., longer hypocotyls); (2) changes in the proportion of different functional groups (e.g., grasses and forbs) that possess different competitive abilities; or (3) through priority effects caused by subtle changes in timing of emergence. We used a combination of field and glasshouse experiments in which Eucalyptus obliqua seedlings were grown either with or without leaf litter (grass litter/eucalypt litter), and with or without competitors. Eucalypt species growing in the field and in pots attained more biomass with litter than without when competitors were absent. Competition substantially decreased the biomass of eucalypt seedlings. Competitive intensity was heavily influenced by litter type and was most intense in the presence of grass litter. Litter produced a small change in patterns of biomass allocation in the competing herbaceous vegetation, and there was a slight (marginally non-significant) indication of a change in the proportion of grasses relative to forbs when litter was present. However, when the integral of competitor biomass over time was used to calculate competitive intensity, the combined effects of the experimental factors (litter and competition) became additive, suggesting that the effect of leaf litter on the timing of germination and establishment in the grasses and forbs, relative to that of Eucalyptus seedlings, was the principal mechanism by which leaf litter altered the interaction strength of the species studied.     

The roles of exotic grasses and forbs when restoring native species to highly invaded southern California annual grassland

Many semi-arid shrublands in the western US have experienced invasion by a suite of exotic grasses and forbs that have altered community structure and function. The effect of the exotic grasses in this area has been studied, but little is known about how exotic forbs influence the plant community. A 3-year experiment in southern California coastal sage scrub (CSS) now dominated by exotic grasses was done to investigate the influence of both exotic grasses (mainly Bromus spp.) and exotic forbs (mainly Erodium spp.) on a restoration seeding (9 species, including grasses, forbs, and shrubs). Experimental plots were weeded to remove one, both, or neither group of exotic species and seeded at a high rate with a mix of native species. Abundance of all species varied with precipitation levels, but seeded species established best when both groups of exotic species were removed. The removal of exotic grasses resulted in an increase in exotic and native forb cover, while removal of exotic forbs led to an increase in exotic grass cover and, at least in one year, a decrease in native forb cover. In former CSS now converted to exotic annual grassland, a competitive hierarchy between exotic grasses and forbs may prevent native forbs from more fully occupying the habitat when either group of exotics is removed. This apparent competitive hierarchy may interact with yearly variation in precipitation levels to limit restoration seedings of CSS/exotic grassland communities. Therefore, management of CSS and exotic grassland in southern California and similar areas must consider control of both exotic grasses and forbs when restoration is attempted.     

氮素添加对内蒙古退化草原生产力的短期影响

不合理的土地利用方式以及气候变化导致我国草原生态系统普遍退化, 主要表现在土壤养分降低、植被覆盖度减少、生产力下降。外源氮素添加是促进退化草原尽快恢复的一项重要措施, 尤其是对那些退化较为严重的草原。该研究选取内蒙古东乌珠穆沁旗不同退化程度(轻度、中度和重度)的草原群落, 于2014-2015年开展连续两年的氮素添加实验, 设置对照(不添加)、低水平(5.0 g N·m^-2·a^-1)、中水平(10.0 g N·m^-2·a^-1)和高水平(20.0 g N·m^-2·a^-1) 4种氮素添加处理, 探讨退化草原群落生产力在恢复过程中对不同水平氮素添加的响应。结果显示: (1)高、中水平氮素添加显著提高了轻度退化群落的地上生物量, 分别比对照增加了53.1%、51.6%, 氮素各水平添加对中度、重度群落地上生物量无显著影响; (2)高、中水平氮素添加显著提高了轻度退化群落中多年生根茎型禾草地上生物量, 分别比对照增加了45.1%、47.7%, 而多年生杂类草地上生物量分别比对照减少了37.4%、42.1%, 但中度和重度退化群落各功能群生物量的响应不显著; (3)三种水平氮素添加对轻、中、重度退化群落物种丰富度在试验期间均没有显著影响。研究结果表明氮素添加有助于提高轻度退化草原中多年生根茎型禾草的生物量, 进而提高群落的生物量, 但多年生杂类草会被逐渐替代, 导致生物量降低, 可见施氮对草原恢复的影响取决于草原退化 程度。     

Influence of nitrogen addition on the primary production in Nei Mongol degraded grassland

Aims Irrational utilization and global climate change have caused degradation of grassland ecosystems in northern China with low soil fertility, decreased vegetation coverage and productivity. Nitrogen addition has been suggested an effective way to enhance restoration of those degraded grasslands. In this study, we selected a typical steppe with three different degrading levels, including lightly, moderately and heavily degraded communities, in East Ujimqin, Nei Mongol. Our objectives of this study are to examine if and how nitrogen (N) addition can enhance restoration of those degraded grasslands Methods Treatments with four levels of N addition (0, 5.0, 10.0 and 20.0 g N·m^-2·a^-1) were conducted to each of the three degraded communities from 2014 to 2015. Nitrogen was applied as urea in June of both years. Aboveground biomass was collected at the species level in 1 m × 1 m plot in August each year, all species biomass was summed as net primary production, and biomass of plant functional groups was calculated by perennial rhizome grasses, perennial bunchgrasses, perennial forbs, shrubs and semi-shrubs, annuals and biennials.Important findings Our results showed that the high (20.0 g N·m^-2·a^-1) and medium level N addition (10.0 g N·m^-2·a^-1) significantly increased the aboveground biomass of the slightly degraded community by 53.1% and 51.6% compared with no N addition. N addition had no significant effects on the moderately and heavily degraded communities. N addition with high and medium levels increased aboveground biomass of perennial rhizome grasses by 45.1% and 47.7%, but decreased that of perennial forbs by 37.4% and 42.1% at the slightly degraded community. Our results indicated that N addition could increase the growth of perennial rhizome grasses, and the growth of perennial forbs was suppressed consequently. Our results suggest that even the application of N fertilizers can only be helpful to restoration of those slightly degraded grasslands. Besides, N addition had no significant effects on species richness in different degraded communities indicating the fact that the study may not last long enough. For the purpose of increasing aboveground biomass of degraded grassland, we should not only consider the type and quantity of fertilization, but also the attribute of the degraded communities. In addition, the response of degraded community in biomass may strongly be impacted by degrading level of studied grassland.     

Effects of a winter wildfire on plant community structure and forage quality in subalpine grassland of western Sichuan,China

火是继土壤、水分、温度之后, 塑造地表植被的主要力量。该文以2010年“12·5”冬草场火烧事件为背景, 通过对比川西亚高山草地火烧区域和未火烧区域火后第一年植被群落结构和牧草质量, 探讨亚高山草地植被对冬季火烧的响应机制。通过物种多样性分析、双向指示种分析(TWINSPAN)和干重等级法(dry-weight-rank)分析发现, 冬季火烧未改变植被的生物多样性、均匀度和物种丰富度, 却改变了植被群落结构的物种组成。冬季火烧导致一年生禾草、一年生杂草、灌木等3种生活型植物的数量和生物量增加; 多年生杂草数量减少, 生物量增加; 多年生禾草数量和生物量减少。冬季火烧也极大地减少了可食禾草的比例, 增加了各种杂草的生物量比例。此次火烧事件降低了细柄草(Capillipedium parviflorum)和早熟禾(Poa sp.)等可食禾草的竞争能力, 增加了一些杂草(如火绒草(Leontopodium leontopodioides)、白莲蒿(Artemisia sacrorum)、草玉梅(Anemone rivularis)等)在资源竞争中的相对优势, 最终表现为火后牧草的可食性下降。