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。     

荒漠草原不同放牧强度背景下添加氮水对凋落物分解的影响

凋落物分解是连接生态系统地上、地下过程的重要环节,决定了生态系统养分循环速率,但到目前为止对凋落物分解在荒漠草地生态系统受放牧以及外源资源补给影响的研究较少。本研究通过对不同放牧强度(对照、轻牧、中牧和重牧)短花针茅草原群落进行添加氮素(10.0 g N m~(-2) a~(-1))和增水(108 mm/a)处理,探讨群落水平凋落物分解速率的变化。研究结果显示,过去不同强度放牧历史对群落凋落物分解影响极显著(P0.0001)。凋落物前期分解(135 d)过程中,凋落物初始C∶N比与凋落物分解速率常数呈显著负相关关系,表明凋落物可降解性在凋落物前期分解中起主要作用。轻度放牧影响下凋落物分解速度最快,这与该条件下凋落物C∶N比显著低于其他放牧强度下的有关,说明适度放牧不仅有利于群落维持,也在一定程度上有利于生态系统养分循环。当凋落物分解更长时间(870 d)后,对照区凋落物分解速率显著低于放牧处理样地,但凋落物初始C∶N比对凋落物分解速率没有显著影响。进一步分析显示,不同放牧强度背景下长期凋落物分解速率与分解环境的土壤微生物多样性成正相关关系,与群落盖度呈极显著(P0.001)负相关关系。添加氮素显著(P0.05)降低凋落物分解速度,但对凋落物氮含量无显著影响。生长季加水未影响凋落物质量及凋落物分解速度。研究结果表明,凋落物前期分解受凋落物质量影响,但较长时间凋落物分解则与分解过程中接受到的太阳辐射量有关。     

我国中东部不同气候带成熟林凋落物生产和分解及其与环境因子的关系

在大尺度气候梯度上研究森林凋落物生产分解与气候因子的关系,对于了解森林生态系统碳循环有着重要的作用.在寒温带的黑龙江呼中、温带的吉林长白山、暖温带的北京东灵山、北亚热带的湖北神农架、中亚热带的四川都江堰和浙江古田山,选择典型地带性成熟林,设置72个样地.观测和研究各地点森林凋落物的产量、凋落动态和分解速率,分析三者与环境因子之间的关系,结果表明:不同气候带森林生态系统凋落物年产量为亚热带森林＞暖温带森林＞温带森林＞寒温带森林.随纬度的增加,凋落物产量逐渐减少,凋落物产量与森林类型极显著相关,与年均温显著相关,而与年均降水关系不显著.凋落物生产动态表现为亚热带地区3个类型森林生态系统为双峰型,暖温带、温带、寒温带3个类型森林生态系统为单峰型.凋落物分解速率k表现出了与凋落物产量相似的变化趋势,即随着纬度的增加,分解速率k值逐渐降低,分解速率与年均温极显著相关,与年均降水显著相关.     

放牧对内蒙古典型草原大针茅凋落物中土壤动物组成及其分解功能的影响

放牧是影响草地生态系统中土壤动物组成和凋落物分解的重要因素.2010—2012年,选择内蒙古锡林郭勒盟白音锡勒牧场境内的禁牧草地、放牧草地和沙地为研究样地,以凋落物袋法研究了大针茅凋落物分解过程中主要理化特性以及其中土壤动物群落的变化特征.共采集到土壤动物67056头52类,隶属于5门8纲,其中螨类23科,昆虫19科.大针茅凋落物的初始有机质含量为92.5%,分解780 d后分别降至40.0%(禁牧草地)和41.3%(放牧草地),差异不显著;凋落物残留率分别降低至50.0%(禁牧草地)和23.0%(放牧草地),差异显著.放牧影响下,大针茅残留凋落物中土壤动物多度显著降低.将大针茅凋落物置入沙地环境,有机质分解速率无显著变化,但凋落物残留率显著降低,螨类群落组成发生显著变化.在内蒙古典型草原环境下,放牧显著改变了植物凋落物中的土壤动物群落组成和多度,但凋落物中有机质分解速率未发生显著变化;半干旱地区土壤动物的凋落物分解功能较为微弱.     

放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。     

围封对退化高寒草甸土壤微生物群落多样性及土壤化学计量特征的影响

围封对植被处于近自然恢复状态的退化草地有一定的修复作用,开展轻度退化草地围封过程中生物与非生物因素的协同互作研究是完整地认识草地生态系统结构和功能的基础.本试验对围栏封育10年的轻度退化草地的土壤化学计量特征进行了研究,同时采用高通量基因测序技术并结合Biolog-Eco方法,调查了土壤微生物多样性和功能的变化.结果表明:轻度退化草地实施围封后,土壤铵态氮含量显著升高,全钾含量显著降低,土壤有机碳、全氮、全磷、硝态氮、速效磷和速效钾则无明显变化.高寒草甸土壤微生物碳和氮在轻度退化和围栏封育草地间差异不显著;围栏封育后草地土壤微生物碳氮比显著高于轻度退化草地.随培养时间的延长,高寒草甸不同土层土壤微生物碳代谢强度均显著升高,土壤微生物碳代谢指数在轻度退化和围栏封育草地间差异不显著.高寒草甸土壤细菌OTUs显著高于真菌,轻度退化与围栏封育草地土壤微生物相似度为27.0%～32.7%.围封后,土壤真菌子囊菌门、接合菌门和球壶菌门相对丰富度显著升高,担子菌门显著降低,土壤细菌酸杆菌门显著低于轻度退化草地.土壤真菌和细菌群落组成在不同土层间差异较大,在轻度退化和围栏封育草地间仅有表层土壤真菌群落组成表现出较大差异.土壤细菌多样性受土壤全氮和速效钾影响较大,真菌多样性受地上生物量影响较大.土壤微生物对碳源利用能力主要受土壤速效钾影响.综上,长期围封禁牧对轻度退化草地土壤养分和土壤微生物无明显影响,且会造成牧草资源浪费,适度放牧可以保持草地资源的可持续利用.     

放牧对呼伦贝尔草地植物和土壤生态化学计量学特征的影响

放牧通过畜体采食、践踏和排泄物归还影响草地群落组成、植物形态和土壤养分,植物通过改变养分利用策略适应环境变化。通过分析呼伦贝尔草原放牧和围封样地中的群落植物和土壤的碳氮磷养分及化学计量比,探讨放牧对生态系统化学计量学特征和养分循环速率的影响机制。结果如下:(1)群落尺度上,放牧和围封草地植物叶片C、N和P的含量没有显著差异;但是在种群尺度上,放牧草地植物叶片N含量显著高于围封草地;(2)放牧草地土壤全C、全N、有机C、速效P含量,低于围封草地,硝态N含量高于围封草地;土壤全P和铵态N指标没有显著差异;(3)放牧草地植物C∶N比显著低于围封草地,植物残体分解速率较快,提高了生态系统养分循环速率。     

~(13)C脉冲标记揭示放牧对高寒草甸同化碳分配的影响

放牧是人类对草地进行利用的重要方式之一,放牧影响草地生态系统的结构和功能,改变植物光合碳(C)分配,进而改变土壤有机碳的储存。青藏高原的高寒草甸是世界上海拔最高的草地生态系统,寒冷季节长等独特的环境特点使其具有高的土壤有机碳含量。为了揭示长期轻度放牧对植物光合碳分配及植物光合碳在各库之间运移的影响,基于在青藏高原矮嵩草草甸开展的长期冬季轻度放牧和围栏封育实验,利用~(13)C示踪方法揭示了放牧对光合碳在植物地上、地下组织的分配以及光合碳在植物、土壤各碳库中的运移和滞留。研究结果发现,在~(13)C标记之后第30天,冬季轻度放牧样地的植物地上部分内~(13)C约占开始时~(13)C含量的32%,根和土壤中的~(13)C约占22%,植物地上部分呼吸中的~(13)C量约占30%。在放牧和围封这两个不同处理中,土壤中光合碳的滞留以及光合碳随土壤呼吸释放的速率存在显著差异。长期冬季轻度放牧促使植物将更多的光合碳输入到根和土壤碳库中。与围栏封育处理相比较,放牧处理下的~(13)C从植物地上部分输入到地下的速率较快,通过土壤呼吸释放的速率也快,而植物地上部分和植物地上部分呼吸中~(13)C的量较低。另外,高寒矮嵩草草甸土壤C储量在冬季轻度放牧和围栏封育处理下没有显著差异。我们的研究表明,尽管冬季轻度放牧改变了植物光合碳分配在地上和地下碳库中的分配,但是没有显著影响土壤碳库储量。     

13C脉冲标记揭示放牧对高寒草甸同化碳分配的影响

放牧是人类对草地进行利用的重要方式之一, 放牧影响草地生态系统的结构和功能, 改变植物光合碳(C)分配, 进而改变土壤有机碳的储存。青藏高原的高寒草甸是世界上海拔最高的草地生态系统, 寒冷季节长等独特的环境特点使其具有高的土壤有机碳含量。为了揭示长期轻度放牧对植物光合碳分配及植物光合碳在各库之间运移的影响, 基于在青藏高原矮嵩草草甸开展的长期冬季轻度放牧和围栏封育实验, 利用 ¹³C示踪方法揭示了放牧对光合碳在植物地上、地下组织的分配以及光合碳在植物、土壤各碳库中的运移和滞留。研究结果发现, 在 ¹³C标记之后第30天, 冬季轻度放牧样地的植物地上部分内 ¹³C约占开始时 ¹³C含量的32%, 根和土壤中的 ¹³C约占22%, 植物地上部分呼吸中的 ¹³C量约占30%。在放牧和围封这两个不同处理中, 土壤中光合碳的滞留以及光合碳随土壤呼吸释放的速率存在显著差异。长期冬季轻度放牧促使植物将更多的光合碳输入到根和土壤碳库中。与围栏封育处理相比较, 放牧处理下的 ¹³C从植物地上部分输入到地下的速率较快, 通过土壤呼吸释放的速率也快, 而植物地上部分和植物地上部分呼吸中 ¹³C的量较低。另外, 高寒矮嵩草草甸土壤C储量在冬季轻度放牧和围栏封育处理下没有显著差异。我们的研究表明, 尽管冬季轻度放牧改变了植物光合碳分配在地上和地下碳库中的分配, 但是没有显著影响土壤碳库储量。     

Effects of grazing intensity and grazing exclusion on litter decomposition in the temperate steppe of Nei Mongol,China

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R² = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R² = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R² = 0.263, p < 0.01), C:N (R² = 0.349, p < 0.01) and cellulose content (R² = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.     

刈割、围封、放牧三种利用方式下草原生态系统的多功能性与植物物种多样性之间的关系

随着全球变化对生物多样性的影响不断加剧, 生物多样性与生态系统功能之间相互关系(BEF)的研究显得极为重要。过去的20多年, BEF的研究大多集中在对物种多样性与单一或少数生态系统功能之间关系的探讨, 但生态系统最为重要的价值是同时维持多种服务和功能的能力, 基于此, 该文首次在国内引入近年来不断完善的生态系统多功能性(multifunctionality)的概念, 并对目前主流的评价方法进行了改进, 从而对内蒙古三种利用方式(刈割、围封、放牧)下的草地群落进行了多功能性评价, 并探讨了多功能性与物种多样性之间的关系。结果显示本研究改进的方法和目前主流方法评价得出的多功能性指数在样方和样地尺度上都有很高的相关性(R² = 0.6956, p < 0.0001; R² = 0.9231, p < 0.0001), 表明该文作者改进后的方法是可靠的。重度放牧的草地群落物种多样性水平最低, 绝大多数土壤功能指标较差, 表现出退化特征; 7年的围封和刈割群落均有较高的物种多样性水平和改善的土壤功能指标; 三者的多功能性指数为刈割(0.2178) >围封(0.0704) >放牧(-0.8031)。植被样方主要沿水肥梯度分布; 多样性指数中, 均匀度指数(Pielou index)和丰富度指数(Margelf index)对多功能性的影响作用最大, 均为样方尺度(R² = 0.1871, p < 0.0001; R² = 0.1601, p < 0.0001)小于样地尺度(R² = 0.5921, p = 0.0093; R² = 0.7499, p = 0.0007), 有尺度依赖性; 多功能性在样方和样地尺度上均与物种均匀度呈线性正相关关系, 而与物种丰富度呈单峰曲线关系。该文研究结果表明, 相对于重度放牧和围封, 刈割更有利于维持该地区生态系统的多功能性; 物种丰富度适中且物种分布均匀的生态系统可能有更好的多功能性。     

Relationship between ecosystem multifuntionality and species diversity in grassland ecosystems under land-use types of clipping,enclosure and grazing

Aims Over the past twenty years, most biodiversity and ecosystem functioning (BEF) research has focused on the effects of species diversity on single or just a few ecosystem functions. However, ecosystems are primarily valued for their ability to maintain multiple functions and services simultaneously (i.e. multifunctionality here- after). This paper first introduced the constantly perfected concept of “multifunctionality”, and then tried to make some modifications to the current mainstream quantitative method in order to evaluate the multifunctionality of grassland communities with the management of clipping, enclosure and grazing in Inner Mongolia, investigating the relationship between the multifunctionality and species diversity. Methods In free grazing grassland, four sites were set and each site was divided into two parts to conduct enclosure and clipping management respectively. After seven years, 15 quadrats (1 m × 1 m) were established for each type of management in each site (total 60 quadrats for each type) using the regular arrangement method; as a control, we also established 20 quadrats (two sites) in grazing grassland. For each quadrat, we carried out plants census and collected soil mixture sample, measuring 16 soil variables, and then calculated the biodiversity indices and multifunctionality index (M-index) by means of factor analysis. Important findings The results showed that M-indexes by the two evaluation methods were strongly correlated at both quadrat and site scale, suggesting that our modified method was reliable. Over-grazed communities had the lowest biodiversity indices and their most soil indicators were also low, showing obvious degradation features. Enclosure and clipping communities (seven years) had higher biodiversity and better soil indicators. The rank of M-indexes was clipping community (0.2178) > enclosure community (0.0704) > grazing community (-0.8031). The vegetation was distributed mainly along the gradients of water and fertility. Among the biodiversity indices, evenness (Pielou) index and richness (Margelf) index were most strongly correlated with multifunctionality, and their explanatory power (R²) for M-index were higher at site scale (R² = 0.5921, p = 0.0093; R² = 0.7499, p = 0.0007) than at quadrat scale (R² = 0.1871, p < 0.0001; R² = 0.1601, p < 0.0001), indicating study scale played an important role in the determinants of multifunctionality. At both quadrat and site scales, M-indexes is a linear positive function with species evenness and a hump-shaped function of species richness. Therefore, in contrast to enclosure, clipping was more conducive to maintain the ecosystem multifunctionality in this region, and the ecosystem with moderate specie richness, where these species are evenly distributed might have better multifunctionality.     

Effect of p53 genotype on gene expression profiles in murine liver

The tumor suppressor protein p53 is a key regulatory element in the cell and is regarded as the “guardian of the genome”. Much of the present knowledge of p53 function has come from studies of transgenic mice in which the p53 gene has undergone a targeted deletion. In order to provide additional insight into the impact on the cellular regulatory networks associated with the loss of this gene, microarray technology was utilized to assess gene expression in tissues from both the p53^−/− and p53^+/− mice. Six male mice from each genotype (p53^+/+, p53^+/−, and p53^−/−) were humanely killed and the tissues processed for microarray analysis. The initial studies have been performed in the liver for which the Dunnett test revealed 1406 genes to be differentially expressed between p53^+/+ and p53^+/− or between p53^+/+ and p53^−/− at the level of p ≤ 0.05. Both genes with increased expression and decreased expression were identified in p53^+/− and in p53^−/− mice. Most notable in the gene list derived from the p53^+/− mice was the significant reduction in p53 mRNA. In the p53^−/− mice, not only was there reduced expression of the p53 genes on the array, but genes associated with DNA repair, apoptosis, and cell proliferation were differentially expressed, as expected. However, altered expression was noted for many genes in the Cdc42-GTPase pathways that influence cell proliferation. This may indicate that alternate pathways are brought into play in the unperturbed liver when loss or reduction in p53 levels occurs.     

凋落物输入变化和氮添加对半干旱草原群落生产力及功能群组成的影响

不同的草原利用方式(围封、放牧和割草等)随着大气氮沉降的不断加剧, 改变了凋落物输入量。凋落物作为连接地上-地下碳循环过程的关键环节, 对草原生态系统生产力和碳循环过程影响显著。氮是草原生产力的主要限制因子, 凋落物输入量的变化对草原生态系统结构和功能的影响仍缺乏长期实验证据支持。该研究在内蒙古半干旱典型草原建立一个凋落物输入变化和氮添加控制实验平台, 通过连续6年对群落生产力和功能群组成的监测, 研究了凋落物添加与去除和氮添加对半干旱草原群落生产力和功能群组成的影响。研究发现: 1)凋落物输入量增加和氮添加均显著提高了群落生产力, 在对照和氮添加处理下, 凋落物去除处理导致生产力分别降低了8.4%和7.6%, 而凋落物添加处理使生产力分别提高了10.7%和6.3%; 2)不同植物功能群对凋落物输入变化和氮添加的响应存在差异, 导致群落功能群结构发生变化。随着凋落物输入量增加和氮添加, 群落优势功能群多年生禾草(包括多年生丛生禾草和多年生根茎禾草)的生物量显著提高, 对群落生产力的贡献增加, 在群落中的优势地位增强; 而另一优势功能群多年生杂类草生物量对凋落物和氮添加处理均无显著响应, 进而导致在氮添加处理下其对群落生物量的贡献比例显著降低; 3)凋落物输入主要改善土壤水分状况, 而氮添加则主要通过提高土壤养分含量, 促进群落生产力, 并通过影响主要功能群生物量, 导致群落结构发生变化。以上结果表明, 适当的草原管理方式如围封禁牧和降低放牧强度等都能通过增加凋落物的输入来提高草原生产力, 维持生态系统稳定性。而适量的氮等养分添加管理也有助于提高草原生产力, 促进其恢复。     

Effect of altered litter input and nitrogen addition on ecosystem aboveground primary productivity and plant functional group composition in a semiarid grassland

不同的草原利用方式(围封、放牧和割草等)随着大气氮沉降的不断加剧, 改变了凋落物输入量。凋落物作为连接地上-地下碳循环过程的关键环节, 对草原生态系统生产力和碳循环过程影响显著。氮是草原生产力的主要限制因子, 凋落物输入量的变化对草原生态系统结构和功能的影响仍缺乏长期实验证据支持。该研究在内蒙古半干旱典型草原建立一个凋落物输入变化和氮添加控制实验平台, 通过连续6年对群落生产力和功能群组成的监测, 研究了凋落物添加与去除和氮添加对半干旱草原群落生产力和功能群组成的影响。研究发现: 1)凋落物输入量增加和氮添加均显著提高了群落生产力, 在对照和氮添加处理下, 凋落物去除处理导致生产力分别降低了8.4%和7.6%, 而凋落物添加处理使生产力分别提高了10.7%和6.3%; 2)不同植物功能群对凋落物输入变化和氮添加的响应存在差异, 导致群落功能群结构发生变化。随着凋落物输入量增加和氮添加, 群落优势功能群多年生禾草(包括多年生丛生禾草和多年生根茎禾草)的生物量显著提高, 对群落生产力的贡献增加, 在群落中的优势地位增强; 而另一优势功能群多年生杂类草生物量对凋落物和氮添加处理均无显著响应, 进而导致在氮添加处理下其对群落生物量的贡献比例显著降低; 3)凋落物输入主要改善土壤水分状况, 而氮添加则主要通过提高土壤养分含量, 促进群落生产力, 并通过影响主要功能群生物量, 导致群落结构发生变化。以上结果表明, 适当的草原管理方式如围封禁牧和降低放牧强度等都能通过增加凋落物的输入来提高草原生产力, 维持生态系统稳定性。而适量的氮等养分添加管理也有助于提高草原生产力, 促进其恢复。     

Effects of nitrogen addition on soil respiration of Rhododendron simsii shrubland in the subtropical mountainous areas of China

Aims As the second largest C flux between the atmosphere and terrestrial ecosystems, soil respiration plays a vital role in regulating atmosphere CO₂ concentration. Therefore, understanding the response of soil respiration to the increasing nitrogen deposition is urgently needed for prediction of future climate change. However, it is still unclear how nitrogen deposition influences soil respiration of shrubland in subtropical China. Our objectives were to explore the effects of different levels of nitrogen fertilization on soil respiration, root biomass increment, and litter biomass, and to analyze the relationships between soil respiration and soil temperature and moisture.
Methods From January 2013 to September 2014, we conducted a short-term simulated nitrogen deposition experiment in the Rhododendron simsii shrubland of Dawei Mountain, located in Hunan Province, southern China. Four levels of nitrogen addition treatments (each level with three replicates) were established: control (CK, no nitrogen addition), low nitrogen addition (LN, 2 g·m^-2·a^-1), medium nitrogen addition (MN, 5 g·m^-2·a^-1) and high nitrogen addition (HN, 10 g·m^-2·a^-1). Soil respiration was measured by LI-8100 soil CO₂ efflux system. At the same time, we measured root biomass increment and litter biomass in each plot.
Important findings Soil respiration exhibited a strong seasonal pattern, with the highest rates found in summer and the lowest rates in winter. Annual accumulative soil respiration rate in the CK, LN, MN and HN was (2.37 ± 0.39), (2.79 ± 0.42), (2.26 ± 0.38) and (2.30 ± 0.36) kg CO₂·m^-2, respectively. Annual mean soil respiration rate in the CK, LN, MN and HN was (1.71 ± 0.28), (2.01 ± 0.30), (1.63 ± 0.27) and (1.66 ± 0.26) μmol CO₂·m^-2·s^-1, respectively, and it was 17.25% higher in the LN treatment compared with CK (p = 0.06). The root biomass increment was increased by LN, MN, and HN treatments by 18.36%, 36.49% and 61.63%, respectively, compared to CK. The litter biomass was increased by LN, MN, and HN treatments by 35.87%, 22.17% and 15.35%, respectively, compared with CK. Soil respiration exhibited a significant exponential relationship with soil temperature (p < 0.01, R² is 0.77 to 0.82) and a significant linear relationship with soil moisture at the depth of 5 cm (p < 0.05, R² is 0.10 to 0.15). The temperature sensitivity (Q₁₀) value of CK, LN, MN and HN plots was 3.96, 3.60, 3.71 and 3.51, respectively. These results suggested that nitrogen addition promoted plant growth and decreased the temperature sensitivity of soil respiration. The increase of root biomass under N addition may be an important reason for the change of soil respiration in the study area.     

半干旱草地不同植物枯落物分解对放牧和封育的响应

为探究放牧和封育对半干旱草地植物枯落物分解的影响,选取赖草、牛枝子及其混合物为研究对象,调查了不同网孔分解袋中宁夏半干旱草地植物枯落物分解特征及对放牧和封育的响应规律。结果表明：（1）放牧样地250目网孔中,枯落物质量残留率表现为牛枝子显著高于赖草和混合物（P<0.05）,而在放牧样地30目网孔、封育样地2种网孔中,枯落物质量残留率均表现为3种枯落物间无显著差异。（2）250目网孔中,放牧和封育样地枯落物分解衰减常数均表现为混合物显著高于牛枝子,而赖草居中;并且,牛枝子枯落物分解衰减常数表现为封育样地显著高于放牧样地。30目网孔中,放牧和封育样地枯落物分解衰减常数均表现为赖草、混合物显著高于牛枝子（P<0.05）;并且,牛枝子枯落物分解衰减常数表现为封育样地显著高于放牧样地（P<0.05）。（3）在放牧样地,仅牛枝子枯落物R_m表现为30目显著低于250目网孔（P<0.05）,k表现为30目显著高于250目网孔（P<0.05）;土壤动物对枯落物分解的贡献率表现为混合物显著低于牛枝子,赖草居中（P<0.05）。而在封育样地,仅牛枝子枯落物k表现为30目显著高于250目网孔（P<0.05）;土壤动物对枯落物分解的贡献率表现为混合物和牛枝子均显著高于赖草,且混合枯落物的土壤动物贡献率表现为封育样地显著高于放牧样地（P<0.05）。（4）枯落物残留率与其初始N、P、木质素/N、C/P呈显著相关性（P<0.05）;枯落物分解衰减常数与其初始N、P、木质素、N/P、C/P和木质素/P间均呈显著相关性（P<0.05）。研究表明,植物种类组成显著影响枯落物的残留率和分解衰减常数。放牧与封育管理通过影响网孔中土壤动物分布来调控半干旱区草地植物枯落物的分解,而且封育管理更有利于促进土壤动物对低质量枯落物（牛枝子）的分解。