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تاريخ موجز للبكتيريا : اللعبة الأزلية بين الإنسان والبكتيريا
يشرح كتاب \"تاريخ موجز للبكتيريا : اللعبة الأزلية بين الإنسان والبكتيريا\" كيف تسبب البكتيريا الأمراض، وكيف يطلق الجهاز المناعي البشري آليات دفاع فعالة في الوقت المناسب ضد العدوى البكتيرية، والسبب وراء الأهمية البالغة لاكتشاف وتطبيق البنسلين والستربتوميسين، وكيف ابتكر العلماء أدوية للتغلب على البكتيريا، أيضا إمكانية تفوق هذه البكتيريا على الأدوية الحديثة.
Book
Meta-analysis shows positive effects of plant diversity on microbial biomass and respiration
Soil microorganisms are key to biological diversity and many ecosystem processes in terrestrial ecosystems. Despite the current alarming loss of plant diversity, it is unclear how plant species diversity affects soil microorganisms. By conducting a global meta-analysis with paired observations of plant mixtures and monocultures from 106 studies, we show that microbial biomass, bacterial biomass, fungal biomass, fungi:bacteria ratio, and microbial respiration increase, while Gram-positive to Gram-negative bacteria ratio decrease in response to plant mixtures. The increases in microbial biomass and respiration are more pronounced in older and more diverse mixtures. The effects of plant mixtures on all microbial attributes are consistent across ecosystem types including natural forests, planted forests, planted grasslands, croplands, and planted containers. Our study underlines strong relationships between plant diversity and soil microorganisms across global terrestrial ecosystems and suggests the importance of plant diversity in maintaining belowground ecosystem functioning.
The effect of plant biodiversity on microbial function has been tested in limited studies and is likely to be context-dependent. In this meta-analysis of 106 prior studies comparing plant monocultures to mixtures, the authors find that plant diversity increases microbial biomass and respiration rates, an effect moderated by stand age.
Journal Article
Plant mixture balances terrestrial ecosystem C:N:P stoichiometry
Plant and soil C:N:P ratios are of critical importance to productivity, food-web dynamics, and nutrient cycling in terrestrial ecosystems worldwide. Plant diversity continues to decline globally; however, its influence on terrestrial C:N:P ratios remains uncertain. By conducting a global meta-analysis of 2049 paired observations in plant species mixtures and monocultures from 169 sites, we show that, on average across all observations, the C:N:P ratios of plants, soils, soil microbial biomass and enzymes did not respond to species mixture nor to the species richness in mixtures. However, the mixture effect on soil microbial biomass C:N changed from positive to negative, and those on soil enzyme C:N and C:P shifted from negative to positive with increasing functional diversity in mixtures. Importantly, species mixture increased the C:N, C:P, N:P ratios of plants and soils when background soil C:N, C:P, and N:P were low, but decreased them when the respective background ratios were high. Our results demonstrate that plant mixtures can balance terrestrial plant and soil C:N:P ratios dependent on background soil C:N:P. Our findings highlight that plant diversity conservation does not only increase plant productivity, but also optimizes ecosystem stoichiometry for the diversity and productivity of today’s and future vegetation.
Plant and soil C:N:P ratios are critical to ecosystem functioning, but it remains uncertain how plant diversity affects terrestrial C:N:P. In this meta-analysis of 169 studies, the authors find that plant mixtures can balance plant and soil C:N:P ratios according to background soil C:N:P.
Journal Article
Individual size inequality links forest diversity and above‐ground biomass
Despite the mounting evidence for positive diversity–productivity relationships found in controlled experiments, diversity effects on productivity in natural systems remain hotly debated. Understanding the multivariate links between diversity and productivity in natural systems, in particular natural forests that host the majority of terrestrial biodiversity and provide essential services for humanity, remains a critical challenge for ecologists. We analysed data from 448 plots of varying tree species diversity, stand ages and local nutrient availability in Canada's boreal forest (52°30′–55°24′ N latitude and 102°36′–108° W longitude). We used structural equation models to link multivariate relationships between above‐ground biomass, tree species diversity, stand age and soil nutrient availability. Above‐ground biomass increased with diversity indirectly via increasing tree size inequality, increased with stand age and was higher on sites of medium soil nutrient regime directly as well as indirectly via increased tree size inequality. Synthesis. Our results demonstrate positive diversity effects on above‐ground biomass in natural forests of diverse forest ages and soil resource availability. Furthermore, we show that tree size inequality acts as a mechanism for the positive diversity effects on above‐ground biomass and as a mechanism in regulating above‐ground biomass and species diversity simultaneously via interactions among individuals in natural forests.
Journal Article
مختارات من المسرح الصيني الحديث
تكمن أهمية كتاب \"مختارات من المسرح الصيني الحديث\" (الصادر ضمن سلسلة \"آفاق عالمية\"، الهيئة المصرية العامة لقصور الثقافة في القاهرة)، في أنه يسلط الضوء على جانب مهم في الثقافة الصينية التي لا يعرف القارئ العربي عنها كثيرا، يضم الكتاب ثمانية نصوص مسرحية وهي المسافر، ليلة اصطياد النمر، زهرة التانج دي، اخفض سوطك، بعد الثمالة، الظلم، الأعود، موقف الباص، لستة كتاب صينيين، تولى فريق من المترجمات المصريات نقلها إلى العربية، تحت إشراف المترجم والأكاديمي محسن فرجاني، وقد لاحظ فرجاني أن أي محاولة لترجمة نص درامي صيني حديث، ستجد نفسها مطالبة، تقريبا، بالرجوع المستمر إلى الأوبرا الكلاسيكية، تاريخا وفنا وتقنيات وأدوات ووسائل فنية، وحضورا جماهيريا، وطاقات تواصل، ورموزا ودلالات، مثلما ستكون مصغية بتقدير بالغ إلى أهمية عملية التنوع الخصب في المواد الدرامية وطرق التعبير عنها، كما لاحظ فرجاني أن الحركة المسرحية الصينية الحديثة وصفت بغلبة عنصر الأيديولوجيا السياسية عليها لدرجة أنها أصبحت بديلا من الشخصية الفنية الأصيلة للدراما بوصفها شكلا تمثيليا ذا صبغة فنية جمالية بحتة وأن وظيفتها كوسيلة للإمتاع قد تراجعت وراء مهام التوجيه الأيديولوجي، وهو وصف يرى فرجاني أنه يبدو إلى حد ما صادق التقدير معقول النظر بيد أنه يغفل درجة التعقيد التي تصبغ العلاقة بين السياسة والفن المسرحي الصيني على صعيد تطوره ويتجاهل المنظور المناسب لتقدير خصوصية هذه العلاقة.
BOOK
Negative effects of fertilization on plant nutrient resorption
Plants in infertile habitats are thought to have a high rate of nutrient resorption to enable them reuse nutrients more efficiently than those in fertile habitats. However, there is still much debate on how plant nutrient resorption responds to nutrient availability. Here we used a meta-analysis from a global data set of 9703 observations at 306 sites from 508 published articles to examine the effects of nitrogen (N) and phosphorus (P) fertilization on plant foliar N and P concentrations and resorption efficiency. We found that N fertilization enhanced N concentration in green leaves by 27% and P fertilization enhanced green-leaf P by 73% on average. The N and P concentrations in senesced leaves also increased with respective nutrient fertilization. Resorption efficiencies (percentage of nutrient recovered from senescing leaves) of both N and P declined in response to respective nutrient fertilization. Combined N and P fertilization also had negative effects on both N and P resorption efficiencies. Whether nutrient resorption efficiency differs among plant growth types and among ecosystems, however, remains uncertain due to the limited sample sizes when analyzed by plant growth types or ecosystem types. Our analysis indicates that fertilization decreases plant nutrient resorption and the view that nutrient resorption is a critical nutrient conservation strategy for plants in nutrient-poor environments cannot be abandoned. The response values to fertilization presented in our analysis can help improve biogeochemical models.
Journal Article
Global negative effects of nitrogen deposition on soil microbes
Soil microbes comprise a large portion of the genetic diversity on Earth and influence a large number of important ecosystem processes. Increasing atmospheric nitrogen (N) deposition represents a major global change driver; however, it is still debated whether the impacts of N deposition on soil microbial biomass and respiration are ecosystem-type dependent. Moreover, the extent of N deposition impacts on microbial composition remains unclear. Here we conduct a global meta-analysis using 1408 paired observations from 151 studies to evaluate the responses of soil microbial biomass, composition, and function to N addition. We show that nitrogen addition reduced total microbial biomass, bacterial biomass, fungal biomass, biomass carbon, and microbial respiration. Importantly, these negative effects increased with N application rate and experimental duration. Nitrogen addition reduced the fungi to bacteria ratio and the relative abundances of arbuscular mycorrhizal fungi and gram-negative bacteria and increased gram-positive bacteria. Our structural equation modeling showed that the negative effects of N application on soil microbial abundance and composition led to reduced microbial respiration. The effects of N addition were consistent across global terrestrial ecosystems. Our results suggest that atmospheric N deposition negatively affects soil microbial growth, composition, and function across all terrestrial ecosystems, with more pronounced effects with increasing N deposition rate and duration.
Journal Article
Role of environmental factors in shaping the soil microbiome
The soil microbiome comprises one of the most important and complex components of all terrestrial ecosystems as it harbors millions of microbes including bacteria, fungi, archaea, viruses, and protozoa. Together, these microbes and environmental factors contribute to shaping the soil microbiome, both spatially and temporally. Recent advances in genomic and metagenomic analyses have enabled a more comprehensive elucidation of the soil microbiome. However, most studies have described major modulators such as fungi and bacteria while overlooking other soil microbes. This review encompasses all known microbes that may exist in a particular soil microbiome by describing their occurrence, abundance, diversity, distribution, communication, and functions. Finally, we examined the role of several abiotic factors involved in the shaping of the soil microbiome.
Journal Article