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1.
Ribosomal (r)RNA and rDNA have been golden molecular markers in microbial ecology. However, it remains poorly understood how ribotype copy number (CN)‐based characteristics are linked with diversity, abundance, and activity of protist populations and communities observed at organismal levels. Here, we applied a single‐cell approach to quantify ribotype CNs in two ciliate species reared at different temperatures. We found that in actively growing cells, the per‐cell rDNA and rRNA CNs scaled with cell volume (CV) to 0.44 and 0.58 powers, respectively. The modeled rDNA and rRNA concentrations thus appear to be much higher in smaller than in larger cells. The observed rRNA:rDNA ratio scaled with CV0.14. The maximum growth rate could be well predicted by a combination of per‐cell ribotype CN and temperature. Our empirical data and modeling on single‐cell ribotype scaling are in agreement with both the metabolic theory of ecology and the growth rate hypothesis, providing a quantitative framework for linking cellular rDNA and rRNA CNs with body size, growth (activity), and biomass stoichiometry. This study also demonstrates that the expression rate of rRNA genes is constrained by cell size, and favors biomass rather than abundance‐based interpretation of quantitative ribotype data in population and community ecology of protists.  相似文献   
2.
CLN025 is one of the smallest fast-folding proteins. Until now it has not been reported that CLN025 can autonomously fold to its native conformation in a classical, all-atom, and isothermal–isobaric molecular dynamics (MD) simulation. This article reports the autonomous and repeated folding of CLN025 from a fully extended backbone conformation to its native conformation in explicit solvent in multiple 500-ns MD simulations at 277 K and 1 atm with the first folding event occurring as early as 66.1 ns. These simulations were accomplished by using AMBER forcefield derivatives with atomic masses reduced by 10-fold on Apple Mac Pros. By contrast, no folding event was observed when the simulations were repeated using the original AMBER forcefields of FF12SB and FF14SB. The results demonstrate that low-mass MD simulation is a simple and generic technique to enhance configurational sampling. This technique may propel autonomous folding of a wide range of miniature proteins in classical, all-atom, and isothermal–isobaric MD simulations performed on commodity computers—an important step forward in quantitative biology.  相似文献   
3.
Habitat destruction is driving biodiversity loss in remaining ecosystems, and ecosystem functioning and services often directly depend on biodiversity. Thus, biodiversity loss is likely creating an ecosystem service debt: a gradual loss of biodiversity‐dependent benefits that people obtain from remaining fragments of natural ecosystems. Here, we develop an approach for quantifying ecosystem service debts, and illustrate its use to estimate how one anthropogenic driver, habitat destruction, could indirectly diminish one ecosystem service, carbon storage, by creating an extinction debt. We estimate that c. 2–21 Pg C could be gradually emitted globally in remaining ecosystem fragments because of plant species loss caused by nearby habitat destruction. The wide range for this estimate reflects substantial uncertainties in how many plant species will be lost, how much species loss will impact ecosystem functioning and whether plant species loss will decrease soil carbon. Our exploratory analysis suggests that biodiversity‐dependent ecosystem service debts can be globally substantial, even when locally small, if they occur diffusely across vast areas of remaining ecosystems. There is substantial value in conserving not only the quantity (area), but also the quality (biodiversity) of natural ecosystems for the sustainable provision of ecosystem services.  相似文献   
4.
《Chirality》2017,29(10):610-615
A novel, green possibility of the further purification of the diastereomeric salt of 4‐chloromandelic acid and 1‐phenylethane‐1‐amine was developed. Gas antisolvent method using supercritical carbon dioxide was applied for the first time to precipitate the diastereomeric salts with increased purity followed by the supercritical fluid extraction of the dissolved diastereomers. The RR ‐salt can be purified to >99%, while fractionation‐based purification of the SR ‐salt is limited to ~80%. The limiting initial diastereomeric excess correlates strongly with the atmospheric melting eutectic composition of the same salts, which suggests that despite the fast precipitation, the diastereomeric excess of the solid product is not kinetically determined. The efficiency of the diastereomeric enrichment is in the same range as that of the atmospheric reference experiments; however, technological advantages provided by the antisolvent precipitation method such as fast processing and dry product obtained suggest that this novel procedure is a promising alternative to the atmospheric methods.  相似文献   
5.
刘莹  李鹏  沈冰  冯朝红  刘琦  张祎 《生态学报》2017,37(9):3055-3064
本研究以黄土高原乡土草种白羊草(Bothriochloa ischaemum(L.)Keng.)为研究对象,采用盆栽控制实验,比较白羊草在3个水分处理(CK80%FC、MS60%FC和SS 40%FC)下的生物量积累和分配模式、瞬时水分利用效率(WUE)、不同部位(新叶、老叶、茎、细根、粗根)的稳定碳同位素组成(δ~(13)C)和碳同位素分辨率(Δ~(13)C)及其相互关系,以及干旱胁迫下影响水分利用效率的主导环境因子。结果表明:1)重度干旱胁迫显著降低植物整体生物量,显著增加根冠比和细根生物量比例;2)随着干旱胁迫加剧,白羊草各器官的δ~(13)C均呈上升趋势,Δ~(13)C呈减小趋势,SS处理不同器官δ~(13)C和Δ~(13)C没有显著差异,CK和MS处理的各器官δ~(13)C均值表现分别为细根粗根老叶新叶茎、细根新叶老叶粗根茎,CK和MS处理Δ~(13)C的值总体呈根叶茎。3)新叶的δ~(13)CNL和Δ~(13)CNL与WUE的相关系数均最大,说明利用稳定碳同位素方法测定白羊草水分利用效率具有可行性。4)不同水分处理的WUE的主导影响因子不同,CK、MS、SS水分处理WUE分别受到叶面温度、大气水汽压亏缺和空气温度的影响最大。为采用稳定碳同位素方法指示白羊草水分利用效率可行性及阐明植物的胁迫响应机制提供理论依据。  相似文献   
6.
以贵州西南部喀斯特山区35年生和14年生花椒林为研究对象,并以未退耕旱地为对照,研究表层土壤(0~20 cm)水稳性团聚体分布及有机碳矿化特征,探讨土壤有机碳周转对不同花椒种植年限的响应。结果表明:随团聚体粒径的降低,两种年龄花椒林土壤水稳性团聚体含量呈现先增加后减少的倒"V"形分布,土壤水稳性团聚体分布主要出现在5~2、2~1和1~0.5 mm 3个粒级中;与旱地相比,花椒种植明显增加了全土和团聚体中有机碳和活性有机碳含量,并以14年生花椒林较高,而35年生花椒林存在较明显的衰减;随花椒种植年限的增加,土壤有机碳矿化累积量呈递减趋势,但土壤有机碳周转半衰期以14年生花椒林较长,显著高于旱地和35年生花椒林,表明14年生花椒林土壤有机碳更易累积,表现出较好的土壤碳固存能力;喀斯特山区种植花椒后,土壤有机碳存在"汇-源"的转换过程,因此花椒种植应注重长期维护管理,防止土壤质量的衰退。  相似文献   
7.
为分析比较不同浓度石灰氮对连作黄瓜田土壤环境的作用效果,通过2年温室定位试验,在黄瓜秸秆还田的基础上以不施石灰氮为对照(CK),研究施用\[高浓度石灰氮1350 kg·hm-2(CaCN2 90)、中浓度石灰氮900 kg·hm-2(CaCN2 60)、低浓度石灰氮450 kg·hm-2(CaCN2 30)\]对连作黄瓜土壤微生物生物量碳(SMBC)、微生物生物量氮(SMBN)及酶活性的影响.结果表明:与其他处理相比,CaCN2 90显著降低苗期0~10 cm 土层SMBC,但增加了初瓜期后0~20 cm土层SMBC.施用石灰氮处理均显著提高了末瓜期0~20 cm土层SMBC及盛瓜期至末瓜期0~10 cm土层SMBN,但第1年(2012年)不同石灰氮用量间无明显规律,第2年(2013年)盛瓜期后SMBN随着石灰氮施用浓度的增加而升高.施用石灰氮有利于秸秆的腐熟,提高土壤有机质含量,且石灰氮浓度越高越有利于秸秆的腐熟.相比对照,施用石灰氮能有效提升土壤脲酶、过氧化氢酶和多酚氧化酶活性,其中脲酶活性随石灰氮浓度的增加升高,而多酚氧化酶活性随石灰氮浓度的增加而降低,CaCN2 60可有效提高过氧化氢酶活性.相关分析表明:土壤有机质、脲酶及过氧化氢酶活性与SMBC、SMBN呈极显著正相关,多酚氧化酶活性与SMBC、SMBN呈显著负相关.表明黄瓜秸秆还田后施用石灰氮900 kg·hm-2能够改善温室黄瓜连作田土壤环境,有效减缓温室黄瓜连作障碍.  相似文献   
8.
Climate extremes, such as drought, may have immediate and potentially prolonged effects on carbon cycling. Grasslands store approximately one‐third of all terrestrial carbon and may become carbon sources during droughts. However, the magnitude and duration of drought‐induced disruptions to the carbon cycle, as well as the mechanisms responsible, remain poorly understood. Over the next century, global climate models predict an increase in two types of drought: chronic but subtle ‘press‐droughts’, and shorter term but extreme ‘pulse‐droughts’. Much of our current understanding of the ecological impacts of drought comes from experimental rainfall manipulations. These studies have been highly valuable, but are often short term and rarely quantify carbon feedbacks. To address this knowledge gap, we used the Community Land Model 4.0 to examine the individual and interactive effects of pulse‐ and press‐droughts on carbon cycling in a mesic grassland of the US Great Plains. A series of modeling experiments were imposed by varying drought magnitude (precipitation amount) and interannual pattern (press‐ vs. pulse‐droughts) to examine the effects on carbon storage and cycling at annual to century timescales. We present three main findings. First, a single‐year pulse‐drought had immediate and prolonged effects on carbon storage due to differential sensitivities of ecosystem respiration and gross primary production. Second, short‐term pulse‐droughts caused greater carbon loss than chronic press‐droughts when total precipitation reductions over a 20‐year period were equivalent. Third, combining pulse‐ and press‐droughts had intermediate effects on carbon loss compared to the independent drought types, except at high drought levels. Overall, these results suggest that interannual drought pattern may be as important for carbon dynamics as drought magnitude and that extreme droughts may have long‐lasting carbon feedbacks in grassland ecosystems.  相似文献   
9.
北京城市绿地表层土壤碳氮分布特征   总被引:12,自引:4,他引:8  
罗上华  毛齐正  马克明  邬建国 《生态学报》2014,34(20):6011-6019
在北京中心城区及周边郊区(覆盖六环路范围),采集不同类型绿地表层(0—20cm)土壤样品490份,测定了土壤有机碳、无机碳、全碳和全氮含量,探讨了城市土壤碳氮分布特征。结果表明:城市不同类型绿地土壤中碳含量差异明显,行道树土壤的有机碳、无机碳和全碳含量均显著高于其他类型绿地,而其它类型土壤有机碳含量差异不显著;居住绿地、道路绿地、单位绿地和公园绿地土壤无机碳含量显著高于生产绿地、防护绿地;城市土壤有机碳、无机碳和全碳含量与距离城市中心距离呈显著的负相关关系;与郊区土壤相比,城区绿地土壤有机碳、无机碳含量有富集的趋势,且无机碳增加更加明显;与郊区农业土壤相比,城市绿地土壤中有机碳有明显地增加趋势,说明北京的城市化在一定程度上有利于土壤碳库的累积。不同类型绿地土壤全氮含量差异不显著,城郊之间全氮含量也无显著差异,土壤全氮质量分数和碳氮比有逐渐减小的趋势,城市化对土壤氮的影响需要进一步研究。  相似文献   
10.
以中国科学院新疆巴音布鲁克草原生态站为依托,于2010年5月—2011年10月利用静态箱-气相色谱法对短期禁牧(2005年围封)、长期禁牧(1984年围封)和自由放牧(冬季放牧)3种草地的CO2、CH4、N2O气体通量进行了野外连续试验研究。结果表明:新疆天山高寒草原对CO2,CH4和N2O通量表现出明显的季节排放特点。在植物的生长季(5—10月),新疆天山高寒短期禁牧、长期禁牧和自由放牧草原的CO2通量平均值分别为:(89.8±49.3)、(52.8±28.7)、(57.0±30.7)mg·m-2·h-1,CH4通量平均值分别为:(-66.3±21.3)、(-104.5±32.8)、(-103.0±39.0)μg·m-2·h-1,N2O通量平均值分别为:(21.2±11.8)、(13.6±6.9)、(13.2±6.2)μg·m-2·h-1;短期禁牧草原与长期禁牧和自由放牧草原CH4平均通量具有显著性差异(P0.05),但CO2和N2O差异不显著(P0.05)。在植物的非生长季(11月—翌年4月),新疆天山高寒短期禁牧、长期禁牧以及自由放牧草原的3种温室气体的通量较低且差异均不显著。  相似文献   
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