荒漠地区地表藻类的生态功能

 藻类在地球上的分布极为广泛,即使在降水量少、温差大、辐射强的荒漠地区也存在。在荒漠地区,植被的生长受到限制,藻类则在漫长的进化过程中形成了一套对极端环境的适应机制,被认为是荒漠表层土中的主要生产者。在干旱的荒漠地区,藻类能够利用土壤表层暂时可用的水分快速生长,与真菌等异养微生物、土壤粒子相互作用,在土壤表层形成几毫米厚土壤有机复合体即土壤生物结皮。土壤结皮能够在植被稀疏分布地区的土壤表层形成一个连续的光合层,在一些干旱区域这些光合层的分布甚至能够达到70%。藻类的存在促进了生物结皮的形成及演替,并且通过生物结皮自身的生理和代谢方式改变周围的微环境,增加荒漠生态系统的稳定性。     

丙酮酸铁氧化还原蛋白酶对蓝藻光合生长速率影响的仿真分析

光合生物通过光合作用,可将光能转化为储存在生物体内部的生物质能,生物质能的生成速率受光合生长速率的影响.研究影响光合生长速率的因素,有利于提高生物质能的生成速率.蓝藻是最早进行光合作用和释氧的原核生物,具有遗传背景简单、固碳效率高等特点.丙酮酸铁氧化还原蛋白酶(PFOR)是丙酮酸固碳代谢的关键酶,在丙酮酸异化过程中起着重要作用.首先根据蓝藻的代谢网络,模拟敲除其中的酶PFOR,并利用通量平衡分析、通量可变性分析和多目标优化方法研究基因敲除后的代谢网络.通过研究分析,推测出酶PFOR对蓝藻光合生长速率的影响.     

安徽省怀远灵璧地区表层土壤碳储量研究

利用安徽省多目标区域地球化学调查(怀远-灵璧地区)数据,计算怀远-灵璧地区土壤全碳、有机碳、无机碳储量,按照不同的土壤类型、成土母质以及土地利用方式等,分析研究区表层土壤全碳、无机碳、有机碳储量及其分布分配特征.结果表明,表层土壤平均全碳储量为3 866.13t·km-2,有机碳平均碳储量为2 528.22t·km-2,无机碳平均碳储量为1 337.91t·km-2.与第二次土壤普查结果对比发现,区内土壤有机碳储量增加了0.77 Mt,累计速率2.9%.从平均碳储量分布特征看,全碳、无机碳在河流冲积物母质、潮土中储量最高,有机碳在酸性盐类风化物母质、水稻土、林地中储量最高.     

北方农牧交错带草地土壤微生物量碳空间格局及驱动因素

为探究我国北方农牧交错带草地表层(0~10 cm)和次表层(10~20 cm)土壤微生物量碳的空间格局及其环境驱动力, 选择蒙辽平原、京北坝上、阴山北麓和宁陕黄土高原4个区域总计456个土壤样品(两个土层, 57个样点, 每个样点4个样方)进行调查。结果表明, 表层与次表层土壤微生物量碳的空间格局具有一致性, 均随纬度增加而增加, 随经度和海拔增加无显著变化。随着草地退化程度加剧, 次表层土壤微生物量碳的降低幅度小于表层土壤。两层土壤 pH 值的差异随草地退化程度的加剧而缩小, 表层与次表层土壤微生物量碳的差异受土壤pH值调控, 两个土层的pH值差异越小, 微生物量碳的差异越小。气候、植被和土壤因素均会影响微生物量碳的空间变异, 其中土壤因素为区域尺度微生物量碳的主要驱动力, 表层土壤微生物量碳的主要影响因素为土壤总碳, 次表层土壤微生物量碳受土壤总氮的影响最大。在气候变化和人类活动影响加剧的背景下, 研究结果对预测区域尺度土壤微生物的响应规律及退化草地生态功能的维持和修复有重要意义。     

毛乌素沙地南缘沙区不同类型地表水分特征曲线测定与分析

为探明不同类型地表(裸沙、浅灰色藻类结皮、黑褐色藻类结皮和藓类结皮)的持水性能,采用砂性漏斗法对毛乌素沙地南缘沙区不同类型地表表层[(0~5)cm]土壤水分特征曲线进行了测定;并用v-G模型进行拟合。结果表明:1不同类型地表持水性能有差异,持水性能由弱到强依次是裸沙、浅灰色藻类结皮、黑褐色藻类结皮和藓类结皮,不同类型生物结皮样地持水性能分别是裸沙的1.3、1.7和2倍,不同类型生物结皮的持水性随结皮的发育呈增加的趋势;2不同类型地表土壤水分特征曲线呈"S"型分布,不同类型地表吸湿过程较脱湿过程具有显著的滞后性;3用v-G模型对测定结果进行拟合,拟合系数均小于0.009,拟合度高,表明该模型适用于此地区土壤,可用于模拟水分特征曲线;研究结果有助于全面了解生物结皮的水文效应,为受损系统的生态修复过程具有现实意义。     

新疆古尔班通古特沙漠生物结皮在沙丘尺度的生态与环境解释

研究表明，古尔班通古特沙漠广泛发育着种类丰富的地衣、苔藓和藻类生物结皮，其形成、类型和分布状况与所处沙丘部位的环境条件密切相关，在沙丘顶部的流动或半流动沙面上，以微生物种类为主，沙丘两坡的上部至中部主要为藻类结皮，沙丘的中、下部为地衣结皮，苔藓结皮主要分布在沙丘下部及丘间地带．从沙丘上部、中部至沙丘下部及丘间，生物结皮的厚度及发育程度呈增强态势，并且与不同植物群落类型的分布形成显明对照．生物结皮在沙丘不同部位的发育特点和分异是不同类型生物结皮对区域环境条件综合适应的一种生态表现和自然选择，与沙丘不同地貌部位的土壤理化性状、地表基质稳定性等生态条件有着密切的关系．     

光生物反应器和跑道式循环生物反应器对荒漠藻类生物量和多糖产量的影响

采用光生物反应器和跑道式循环生物反应器对荒漠藻类进行规模化培养,对比研究了两种规模化培养系统对荒漠藻类生物量和多糖产量的影响,探讨了温度、酸碱度、生长周期以及氮、磷含量对荒漠藻类生长和多糖积累的作用.结果表明,在光生物反应器和跑道式循环生物反应器两种培养系统中,藻类的生长呈现出不同的变化趋势,而藻多糖含量则呈现相同的波动性变化趋势,并且藻类生物量和多糖分泌受培养条件的影响并不同步.此外,在两种规模化培养模式中,温度、酸碱度、营养盐以及生长周期等都对荒漠藻类的生长和多糖产量产生重要影响.     

沙漠土壤的守护者——苔藓植物

正沙漠的土壤结皮层中有一类重要的植物——苔藓。它们用特殊繁殖方式适应不同的沙漠环境,对沙漠土壤结皮层的维持和稳定具有重要作用,成为沙漠土壤的守护者。沙漠区经常有风沙,风可把沙子刮到空中,最小的沙尘被吹离地面最高,落到地面也最慢,当最小的黏粒落在地面后就可形成一层质地细腻的结皮层,同时掩埋在结皮层内的藻类、菌类、地衣和苔藓组成生物土壤结皮层。沙漠生物土     

科尔沁沙地生物结皮藻类的组成及生物量的变化规律

科尔沁沙地生物结皮中蓝藻和绿藻共有23种,其中蓝藻15种占总种数的65.22%,绿藻8种,占总种数的34.78%.在不同类型的样地中,生物结皮藻类组成及分布也不同,流动沙丘表层的种类组成最少,固定沙丘藻结皮层的种类组成最多.这种现象表明,随着沙丘的固定,生物结皮的进一步发育,藻类的种类也随之增多.固定沙丘藻结皮叶绿素a含量明显高于半固定沙丘藻结皮叶绿素a的含量,并且在春季和冬季固定沙丘藻结皮叶绿素a含量极显著高于半固定沙丘藻结皮叶绿素a的含量(P＜0.01),对于同种类型沙丘藻结皮藻类生物量在不同季节的变化则表现出夏、秋季藻结皮藻类生物量显著高于春、冬季(P＜0.05).藻结皮不同季节藻类生物量含量与当地季节降雨量和温度呈明显的正相关,因此科尔沁沙地降雨量与温度是影响藻类生物量的重要生态因子.     

1977-2017年三江源区植被固碳量及影响因素评估

近年气候变化和人类活动对三江源生态环境产生了深刻的影响,植被固碳量是反应生态环境的重要指标. 根据1977-2017 年的气候资料,利用Thornthwaite Memorial 模型分析了三江源地区植被固碳量变化,并探讨了气候因子和人类活动对其的影响. 结果表明,研究期间的植被平均固碳量为1 130.3 g·m-2·a-1,总体上呈从东南向西北逐渐减少的态势,降水量是影响固碳量的主要因子,且存在超前性,3-7 月的降水量对固碳量的影响最大;研究期间的固碳量呈波动性增加趋势,主要是由于降水量的增加所导致. 另外,21 世纪后三江源实施的生态保护措施和政策对该区固碳量增加产生了一定的作用.     

Net carbon dioxide losses of northern ecosystems in response to autumn warming

The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring, with spring and autumn temperatures over northern latitudes having risen by about 1.1 degrees C and 0.8 degrees C, respectively, over the past two decades. A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity. These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future. Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn-to-winter carbon dioxide build-up, suggesting a shorter net carbon uptake period. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We use a process-based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In contrast, warming increases photosynthesis more than respiration in spring. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC degrees C(-1), offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested.     

Winter forest soil respiration controlled by climate and microbial community composition

Most terrestrial carbon sequestration at mid-latitudes in the Northern Hemisphere occurs in seasonal, montane forest ecosystems. Winter respiratory carbon dioxide losses from these ecosystems are high, and over half of the carbon assimilated by photosynthesis in the summer can be lost the following winter. The amount of winter carbon dioxide loss is potentially susceptible to changes in the depth of the snowpack; a shallower snowpack has less insulation potential, causing colder soil temperatures and potentially lower soil respiration rates. Recent climate analyses have shown widespread declines in the winter snowpack of mountain ecosystems in the western USA and Europe that are coupled to positive temperature anomalies. Here we study the effect of changes in snow cover on soil carbon cycling within the context of natural climate variation. We use a six-year record of net ecosystem carbon dioxide exchange in a subalpine forest to show that years with a reduced winter snowpack are accompanied by significantly lower rates of soil respiration. Furthermore, we show that the cause of the high sensitivity of soil respiration rate to changes in snow depth is a unique soil microbial community that exhibits exponential growth and high rates of substrate utilization at the cold temperatures that exist beneath the snow. Our observations suggest that a warmer climate may change soil carbon sequestration rates in forest ecosystems owing to changes in the depth of the insulating snow cover.     

A possible nitrogen crisis for Archaean life due to reduced nitrogen fixation by lightning.

Nitrogen is an essential element for life and is often the limiting nutrient for terrestrial ecosystems. As most nitrogen is locked in the kinetically stable form, N2, in the Earth's atmosphere, processes that can fix N2 into biologically available forms-such as nitrate and ammonia-control the supply of nitrogen for organisms. On the early Earth, nitrogen is thought to have been fixed abiotically, as nitric oxide formed during lightning discharge. The advent of biological nitrogen fixation suggests that at some point the demand for fixed nitrogen exceeded the supply from abiotic sources, but the timing and causes of the onset of biological nitrogen fixation remain unclear. Here we report an experimental simulation of nitrogen fixation by lightning over a range of Hadean (4.5-3.8 Gyr ago) and Archaean (3.8-2.5 Gyr ago) atmospheric compositions, from predominantly carbon dioxide to predominantly dinitrogen (but always without oxygen). We infer that, as atmospheric CO2 decreased over the Archaean period, the production of nitric oxide from lightning discharge decreased by two orders of magnitude until about 2.2 Gyr. After this time, the rise in oxygen (or methane) concentrations probably initiated other abiotic sources of nitrogen. Although the temporary reduction in nitric oxide production may have lasted for only 100 Myr or less, this was potentially long enough to cause an ecological crisis that triggered the development of biological nitrogen fixation.     

我国北方温带草地土壤微生物群落组成及其环境影响因素

选择我国北方温带草原中的草甸草原、典型草原、荒漠草原3种类型共13个样点进行调查,对土壤微生物磷脂脂肪酸(phospholipid fatty acids,PLFAs)进行测定。对土壤微生物群落进行无量度多维标定排序(nonmetric multidimensional scaling,NMDS),排序后的样点空间异质性显示3种草原类型微生物群落结构差异明显。结合10种环境因素,对土壤微生物群落组成进行冗余分析,解释率达到79.87%。研究结果表明:土壤含水量、土壤总碳和土壤总氮影响草甸草原土壤微生物群落组成;典型草原土壤微生物群落组成主要受到土壤轻组碳和土壤轻组氮的调节;影响荒漠草原土壤微生物群落组成的因素为年均温和土壤p H值。     

Variable effects of nitrogen additions on the stability and turnover of soil carbon

Soils contain the largest near-surface reservoir of terrestrial carbon and so knowledge of the factors controlling soil carbon storage and turnover is essential for understanding the changing global carbon cycle. The influence of climate on decomposition of soil carbon has been well documented, but there remains considerable uncertainty in the potential response of soil carbon dynamics to the rapid global increase in reactive nitrogen (coming largely from agricultural fertilizers and fossil fuel combustion). Here, using 14C, 13C and compound-specific analyses of soil carbon from long-term nitrogen fertilization plots, we show that nitrogen additions significantly accelerate decomposition of light soil carbon fractions (with decadal turnover times) while further stabilizing soil carbon compounds in heavier, mineral-associated fractions (with multidecadal to century lifetimes). Despite these changes in the dynamics of different soil pools, we observed no significant changes in bulk soil carbon, highlighting a limitation inherent to the still widely used single-pool approach to investigating soil carbon responses to changing environmental conditions. It remains to be seen if the effects observed here-caused by relatively high, short-term fertilizer additions-are similar to those arising from lower, long-term additions of nitrogen to natural ecosystems from atmospheric deposition, but our results suggest nonetheless that current models of terrestrial carbon cycling do not contain the mechanisms needed to capture the complex relationship between nitrogen availability and soil carbon storage.     

Prolonged suppression of ecosystem carbon dioxide uptake after an anomalously warm year

Terrestrial ecosystems control carbon dioxide fluxes to and from the atmosphere through photosynthesis and respiration, a balance between net primary productivity and heterotrophic respiration, that determines whether an ecosystem is sequestering carbon or releasing it to the atmosphere. Global and site-specific data sets have demonstrated that climate and climate variability influence biogeochemical processes that determine net ecosystem carbon dioxide exchange (NEE) at multiple timescales. Experimental data necessary to quantify impacts of a single climate variable, such as temperature anomalies, on NEE and carbon sequestration of ecosystems at interannual timescales have been lacking. This derives from an inability of field studies to avoid the confounding effects of natural intra-annual and interannual variability in temperature and precipitation. Here we present results from a four-year study using replicate 12,000-kg intact tallgrass prairie monoliths located in four 184-m(3) enclosed lysimeters. We exposed 6 of 12 monoliths to an anomalously warm year in the second year of the study and continuously quantified rates of ecosystem processes, including NEE. We find that warming decreases NEE in both the extreme year and the following year by inducing drought that suppresses net primary productivity in the extreme year and by stimulating heterotrophic respiration of soil biota in the subsequent year. Our data indicate that two years are required for NEE in the previously warmed experimental ecosystems to recover to levels measured in the control ecosystems. This time lag caused net ecosystem carbon sequestration in previously warmed ecosystems to be decreased threefold over the study period, compared with control ecosystems. Our findings suggest that more frequent anomalously warm years, a possible consequence of increasing anthropogenic carbon dioxide levels, may lead to a sustained decrease in carbon dioxide uptake by terrestrial ecosystems.     

Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization

Global warming is predicted to be most pronounced at high latitudes, and observational evidence over the past 25 years suggests that this warming is already under way. One-third of the global soil carbon pool is stored in northern latitudes, so there is considerable interest in understanding how the carbon balance of northern ecosystems will respond to climate warming. Observations of controls over plant productivity in tundra and boreal ecosystems have been used to build a conceptual model of response to warming, where warmer soils and increased decomposition of plant litter increase nutrient availability, which, in turn, stimulates plant production and increases ecosystem carbon storage. Here we present the results of a long-term fertilization experiment in Alaskan tundra, in which increased nutrient availability caused a net ecosystem loss of almost 2,000 grams of carbon per square meter over 20 years. We found that annual aboveground plant production doubled during the experiment. Losses of carbon and nitrogen from deep soil layers, however, were substantial and more than offset the increased carbon and nitrogen storage in plant biomass and litter. Our study suggests that projected release of soil nutrients associated with high-latitude warming may further amplify carbon release from soils, causing a net loss of ecosystem carbon and a positive feedback to climate warming.     

Biodiversity improves water quality through niche partitioning

Excessive nutrient loading of water bodies is a leading cause of water pollution worldwide, and controlling nutrient levels in watersheds is a primary objective of most environmental policy. Over the past two decades, much research has shown that ecosystems with more species are more efficient at removing nutrients from soil and water than are ecosystems with fewer species. This has led some to suggest that conservation of biodiversity might be a useful tool for managing nutrient uptake and storage, but this suggestion has been controversial, in part because the specific biological mechanisms by which species diversity influences nutrient uptake have not been identified. Here I use a model system of stream biofilms to show that niche partitioning among species of algae can increase the uptake and storage of nitrate, a nutrient pollutant of global concern. I manipulated the number of species of algae growing in the biofilms of 150 stream mesocosms that had been set up to mimic the variety of flow habitats and disturbance regimes that are typical of natural streams. Nitrogen uptake rates, as measured by using (15)N-labelled nitrate, increased linearly with species richness and were driven by niche differences among species. As different forms of algae came to dominate each unique habitat in a stream, the more diverse communities achieved a higher biomass and greater (15)N uptake. When these niche opportunities were experimentally removed by making all of the habitats in a stream uniform, diversity did not influence nitrogen uptake, and biofilms collapsed to a single dominant species. These results provide direct evidence that communities with more species take greater advantage of the niche opportunities in an environment, and this allows diverse systems to capture a greater proportion of biologically available resources such as nitrogen. One implication is that biodiversity may help to buffer natural ecosystems against the ecological impacts of nutrient pollution.     

洪湖湿地野菰群落储碳、固碳功能研究

通过实地调研与实验室测定相结合的方法,研究洪湖湿地野菰（Zizania latifolia）的现存生物量和初级生产力,测算其碳储量、固碳能力,探讨其固碳潜力.结果得出：洪湖湿地野菰地上现存生物量平均0.75kg.m-2（0.52～0.96kg.m-2）,现存碳储量平均0.33kg.m-2（0.23～0.42kg.m-2）;地下部分的生物现存量平均为1.47kg.m-2,其碳储量平均为0.65kg.m-2,均约为地上2倍,因此野菰碳储量主要在地下部分;洪湖湿地野菰地上部分净初级生产力平均合计达0.75kg.m-2.a-1,加上地下部分,平均为1.2kg.m-2.a-1,固碳能力为0.53kg.m-2.a-1,高于全国陆地植被平均固碳能力和全球植被平均固碳能力.与中国不同生态系统的固碳能力相比,由于洪湖湿地野菰种群郁闭度较高,其平均固碳能力强于城市、河流等生态系统,明显高于其他湖泊生态系统.     

森林生态系统的固碳功能和碳储量研究进展

森林是陆地生态系统的重要组成部分,充分发挥森林的固碳能力关系到能否降低大气CO2浓度和抑制全球变暖趋势.本文在回顾森林固碳作用和碳储量研究进展的基础上,对未来研究提出粗浅看法:探知全球森林生态系统的碳储量和碳通量是调控碳循环过程的必要环节和最大难题之一,样地清查、遥感分析和模型模拟等方法的综合运用将是解决这一问题的根本途径;森林生态系统的固碳和生物多样性保护等生态功能与采伐森林资源不存在绝对对立关系,以演替理论指导森林管理有利于发挥森林生态系统的固碳作用和生物多样性保护功能,同时能够实现对森林资源的适度经济利用;应重视和加强对中高纬度森林枯落物碳库的研究.