松嫩退化草地芦苇不同叶位叶片营养元素代谢特征

对松嫩草地不同退化程度样地的芦苇(Phragmites australis)各叶位叶片的生长及营养元素代谢特征进行分析, 以探讨土壤盐碱化对芦苇叶片营养元素代谢的影响及其适应机制。结果表明: 松嫩草地土壤中Na ⁺含量、全盐含量、pH值是衡量土壤盐碱化程度的主要决定因子, 从典型草地到重度退化草地, 土壤盐碱化程度逐级加剧。芦苇具有一定程度的耐盐碱性, 植株高度和地上部分生物量随土壤盐分增加而降低。检测出10种营养元素: K、Na、Ca、Mg、Fe、Cu、Zn、Mn、P、B, 主成分分析结果显示全部样本均处于95%的置信区间内。方差分析结果表明, 芦苇不同叶位叶片对营养元素的富集能力有所差异。K、P含量随叶位降低而减少; 而Na、Ca、Mg呈现相反分布规律。Fe、Cu集中分布在功能叶和老叶中; Mn只大量聚集在老叶中; 而Zn集中分布在幼叶中。表明土壤盐碱化对老叶营养元素的影响大于幼叶, Na在老叶中的大量积累保护了幼叶免于或者减轻离子的毒害。功能叶和老叶中Ca、Mg、Fe、Cu的积累有利于保障芦苇正常的光合作用。盐碱胁迫下幼叶仍维持较高K、P含量, 这不仅为幼叶的生长提供所需营养, 同时提高了其抗逆性, 这可能是芦苇的生理响应策略。     

Upstream trophic structure modulates downstream community dynamics via resource subsidies

In many natural systems, the physical structure of the landscape dictates the flow of resources. Despite mounting evidence that communities’ dynamics can be indirectly coupled by reciprocal among ecosystem resource flows, our understanding of how directional resource flows might indirectly link biological communities is limited. We here propose that differences in community structure upstream should lead to different downstream dynamics, even in the absence of dispersal of organisms. We report an experimental test of the effect of upstream community structure on downstream community dynamics in a simplified but highly controlled setting, using protist microcosms. We implemented directional flows of resources, without dispersal, from a standard resource pool into upstream communities of contrasting interaction structure and then to further downstream communities of either one or two trophic levels. Our results demonstrate that different types of species interactions in upstream habitats may lead to different population sizes and levels of biomass in these upstream habitats. This, in turn, leads to varying levels of detritus transfer (dead biomass) to the downstream communities, thus influencing their population densities and trophic interactions in predictable ways. Our results suggest that the structure of species interactions in directionally structured ecosystems can be a key mediator of alterations to downstream habitats. Alterations to upstream habitats can thus cascade down to downstream communities, even without dispersal.     

Pattern and control of biomass allocation across global forest ecosystems

The underground part of a tree is an important carbon sink in forest ecosystems. Understanding biomass allocation between the below‐ and aboveground parts (root:shoot ratios) is necessary for estimation of the underground biomass and carbon pool. Nevertheless, large‐scale biomass allocation patterns and their control mechanisms are not well identified. In this study, a large database of global forests at the community level was compiled to investigate the root:shoot ratios and their responses to environmental factors. The results indicated that both the aboveground biomass (AGB) and belowground biomass (BGB) of the forests in China (medians 73.0 Mg/ha and 17.0 Mg/ha, respectively) were lower than those worldwide (medians 120.3 Mg/ha and 27.7 Mg/ha, respectively). The root:shoot ratios of the forests in China (median = 0.23), however, were not significantly different from other forests worldwide (median = 0.24). In general, the allocation of biomass between the belowground and aboveground parts was determined mainly by the inherent allometry of the plant but also by environmental factors. In this study, most correlations between root:shoot ratios and environmental factors (development parameter, climate, altitude, and soil) were weak but significant (p < .01). The allometric model agreed with the trends observed in this study and effectively estimated BGB based on AGB across the entire database.     

滨海深古菌的研究进展

深古菌(Bathyarchaeota),原名MCG(Miscellaneous Crenarchaeotal Group)古菌,是一类至今未被分离培养的古菌,普遍存在于海洋和陆地环境中。深古菌具有极高的种群多样性,目前已发现多达23个亚群。深古菌具有多种生理生化功能,能降解蛋白质、多聚碳水化合物、脂肪酸、芳香族化合物和甲基化合物等有机质,参与甲烷代谢循环,产乙酸,异化还原亚硝酸盐和硫酸盐,很可能是地球碳元素循环的重要驱动力之一。本文简要概述了深古菌的研究发展历史,阐述了深古菌的分子系统发育分析、分布和基于基因组的生理特征研究的最新进展,总结了滨海深古菌的研究现状,并对滨海深古菌研究的发展方向进行了分析和展望。     

Assessing the spatiotemporal dynamic of global grassland carbon use efficiency in response to climate change from 2000 to 2013

The carbon use efficiency (CUE) of grassland, a ratio of net primary production (NPP) to gross primary productivity (GPP), is an important index representing the capacity of plants to transfer carbon from the atmosphere to terrestrial biomass. In this study, we used the Moderate Resolution Imaging Spectroradiometer (MODIS) data to calculate the global grassland CUE, and explore the spatiotemporal dynamic of global grassland CUE from 2000 to 2013 to discuss the response to climate variations. The results showed that the average annual CUE of different grassland types follows an order of: open shrublands > non-woody grasslands > closed shrublands > woody savannas > savannas. The higher grassland CUE mainly occurred in the regions with cold and dry climate. By contrast, the regions with the lower grassland CUE were mostly in warm and wet environments. Moreover, the CUE exhibited a globally positive correlation with precipitation and a negative correlation with temperature. Therefore, the grassland CUE has considerable spatial variation associated with grassland type, geographical location and climate change.     

Disturbances catalyze the adaptation of forest ecosystems to changing climate conditions

The rates of anthropogenic climate change substantially exceed those at which forest ecosystems – dominated by immobile, long‐lived organisms – are able to adapt. The resulting maladaptation of forests has potentially detrimental effects on ecosystem functioning. Furthermore, as many forest‐dwelling species are highly dependent on the prevailing tree species, a delayed response of the latter to a changing climate can contribute to an extinction debt and mask climate‐induced biodiversity loss. However, climate change will likely also intensify forest disturbances. Here, we tested the hypothesis that disturbances foster the reorganization of ecosystems and catalyze the adaptation of forest composition to climate change. Our specific objectives were (i) to quantify the rate of autonomous forest adaptation to climate change, (ii) examine the role of disturbance in the adaptation process, and (iii) investigate spatial differences in climate‐induced species turnover in an unmanaged mountain forest landscape (Kalkalpen National Park, Austria). Simulations with a process‐based forest landscape model were performed for 36 unique combinations of climate and disturbance scenarios over 1000 years. We found that climate change strongly favored European beech and oak species (currently prevailing in mid‐ to low‐elevation areas), with novel species associations emerging on the landscape. Yet, it took between 357 and 706 years before the landscape attained a dynamic equilibrium with the climate system. Disturbances generally catalyzed adaptation and decreased the time needed to attain equilibrium by up to 211 years. However, while increasing disturbance frequency and severity accelerated adaptation, increasing disturbance size had the opposite effect. Spatial analyses suggest that particularly the lowest and highest elevation areas will be hotspots of future species change. We conclude that the growing maladaptation of forests to climate and the long lead times of autonomous adaptation need to be considered more explicitly in the ongoing efforts to safeguard biodiversity and ecosystem services provisioning.     

喀斯特森林植被自然恢复过程中土壤可矿化碳库特征

2011年9月,采用空间代替时间方法,研究了茂兰自然保护区喀斯特森林自然恢复过程中土壤可矿化碳库的特征.结果表明: 研究期间,喀斯特森林自然恢复过程中不同深度土壤的总有机碳含量、可矿化碳含量和矿化速率随土层加深而减少,随恢复的进程而增加;累积矿化排放量及其速率随恢复的进程增加,其速率随培养时间延长而减小;矿化率随恢复的进程增加,而随土层加深的变化不明显;qCO₂值随恢复的进程和土层加深而递减;土壤可矿化碳与凋落物现存量及其分解质量损失率分别呈负相关(r=-0.796)和正相关(r=0.924);土壤生境由早期干扰强烈转向中后期日趋稳定,土壤的固碳能力由早期差、潜力大转向中后期强、潜力小.     

放牧对内蒙古典型草原生态系统植物及土壤δ15N的影响

植物和土壤中的¹⁵N自然丰度值(δ¹⁵N)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δ¹⁵N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δ¹⁵N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δ¹⁵N值。具有潜在共生固氮能力的豆科植物δ¹⁵N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δ¹⁵N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δ¹⁵N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δ¹⁵N值, 这也与过去的研究结果不同。δ¹⁵N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。     

滇石林喀斯特植物群落不同演替阶段的溶痕生境中木本植物的更新特征

喀斯特生境与生物多样性的关系及其对人为干扰的响应是喀斯特地区生态恢复的重要内容。该文以云南石林为例对此进行研究。根据喀斯特溶痕与土壤、植物生长发育关系把石林的溶痕生境划分为溶蚀廊道、溶槽、裂隙溶沟、溶坑和溶蚀石堆等5种。依据石林的现有植被与演替特征, 选择了原生林、次生林、灌丛、灌草丛和石漠化草丛5种群落进行调查。在每一个样地中设置10个10 m × 10 m的样方, 采用记名计数样方法分片调查溶痕生境中的木本植物, 并区分更新层的萌生苗与实生苗; 采用Shannon-Wiener指数、Pielou指数、Simpson指数、Margalef指数进行生物多样性计算。调查结果显示: (1)溶痕生境的长度、宽度变化较大。溶痕生境结构比例随群落演替而变化, 其原因可能在于所处演替阶段和干扰程度的差异; (2) 在各种溶痕生境中, 随着群落的退化, 实生更新物种数与实生株数大致表现为递减, 在严重退化阶段部分溶痕生境中没有实生苗的分布, 而萌生更新的物种数则以灌丛为峰值向两极减少, 个体数变化较大。计算结果显示: 在各类溶痕生境(溶蚀石堆除外)中, 实生苗的多样性、丰富度、均匀度大致呈现随群落的退化而降低, 优势度增加; 萌生苗多样性、均匀度、丰富度除溶蚀廊道递减的趋势明显外, 其他类型变化较大。不同演替阶段植物更新策略不同。在喀斯特森林生态系统中, 随着群落的退化, 植物更新逐步趋向于营养繁殖, 其部分原因在于特殊的溶痕生境(除溶蚀廊道)能保存一些植物残体, 而这些残体在反复的干扰下不断萌出茎干(采用营养繁殖)以实现物种的持续生态位, 萌生茎干的成熟为生物多样性维持与生态恢复提供繁殖体来源。     

土地利用约束下中国东部南北样带生产力和植被分布对全球变化的响应

对现有的区域植被动态模拟模型进行了改进,使之包含了土地利用分布格局对植被和生态系统相关过程的影响.改进后的模型被用于研究中国东部南北样带(NSTEC)植被和净第一性生产力对未来气候变化的响应.模拟结果显示土地利用格局对未来气候条件下植被分布的变迁和生产力形成过程有非常显著的影响.与没有土地利用约束的情形相比较,土地利用作为限制条件缓减了植被类型之间的竞争,从而减少了模拟的样带区域内常绿阔叶林,但增加了模拟灌木和草地的分布.土地利用约束使得模拟得到的当前条件下的净第一性生产力更为接近实际情况,且未来气候条件下的生产力改变量更为可信.对未来CO2倍增条件下7个大气环流模型预测的气候情景的模拟结果表明:落叶阔叶林将显著增加,但针叶林、灌木和草原的分布将下降.未来气候条件下NSTEC样带的净第一性生产力总量将增加.预测样带北部的净第一性生产力的变化范围大于样带南部.温度变化比降水变化对样带的生产力具有更强的控制.