Elevated CO2 and plant nitrogen-use: is reduced tissue nitrogen concentration size-dependent?

Plants often respond to elevated atmospheric CO₂ levels with reduced tissue nitrogen concentrations relative to ambient CO₂-grown plants when comparisons are made at a common time. Another common response to enriched CO₂ atmospheres is an acceleration in plant growth rates. Because plant nitrogen concentrations are often highest in seedlings and subsequently decrease during growth, comparisons between ambient and elevated CO₂-grown plants made at a common time may not demonstrate CO₂-induced reductions in plant nitrogen concentration per se. Rather, this comparison may be highlighting differences in nitrogen concentration between bigger, more developed plants and smaller, less developed plants. In this study, we directly examined whether elevated CO₂ environments reduce plant nitrogen concentrations independent of changes in plant growth rates. We grew two annual plant species. Abutilon theophrasti (C₃ photosynthetic pathway) and Amaranthus retroflexus (C₄ photosynthetic pathway), from seed in glass-sided growth chambers with atmospheric CO₂ levels of 350 mol·mol^–1 or 700 mol·mol^–1 and with high or low fertilizer applications. Individual plants were harvested every 2 days starting 3 days after germination to determine plant biomass and nitrogen concentration. We found: 1. High CO₂-grown plants had reduced nitrogen concentrations and increased biomass relative to ambient CO₂-grown plants when compared at a common time; 2. Tissue nitrogen concentrations did not vary as a function of CO₂ level when plants were compared at a common size; and 3. The rate of biomass accumulation per rate of increase in plant nitrogen was unaffected by CO₂ availability, but was altered by nutrient availability. These results indicate that a CO₂-induced reduction in plant nitrogen concentration may not be due to physiological changes in plant nitrogen use efficiency, but is probably a size-dependent phenomenon resulting from accelerated plant growth.     

低温对氯化钠胁迫下蓝藻固氮活性的影响

低温加剧氯化钠对蓝藻固氮的抑制,营养液中氯化钠浓度增高时,抑制程度更甚.能源受限(暗处理和加抑制剂时的光合受抑,N_2和Ar的厌氧下呼吸代谢受阻)和氧下固氮酶受到伤害时,低温处理使氯化钠对蓝藻固氮的抑制进一步加剧.在能源和还原剂供应,合成固氨酶蛋白的物质基础(如CO_2和N_2的加合).光合作用正常进行的条件得到改善和保证,以及供应CO_2、外源蔗糖和氮氧加合时,低温加剧氯化钠对蓝藻固氮的抑制程度明显变小.     

低温对氯化钠胁迫下蓝藻固氮活性的影响

低温加剧氯化钠对蓝藻固氮的抑制,营养液中氯化钠浓度增高时,抑制程度更甚.能源受限(暗处理和加抑制剂时的光合受抑,N_2和Ar的厌氧下呼吸代谢受阻)和氧下固氮酶受到伤害时,低温处理使氯化钠对蓝藻固氮的抑制进一步加剧.在能源和还原剂供应,合成固氨酶蛋白的物质基础(如CO_2和N_2的加合).光合作用正常进行的条件得到改善和保证,以及供应CO_2、外源蔗糖和氮氧加合时,低温加剧氯化钠对蓝藻固氮的抑制程度明显变小.     

Acoustic communities in an environmental gradient from native to urban areas in Central Brazil

As urban areas expand due to increasing human populations, natural habitats are diminishing in quantity and quality. We conducted a study to examine the response of diurnal acoustic communities along a gradient of environments, ranging from native to dense urban areas. We hypothesized that acoustic indices would decline with urbanization, transitioning from natural and rural areas to urban environments. We conducted the research in and around Brasília, Central Brazil. We deployed 24 digital recorders in native, rural, low-density and high-density urban areas. We employed five commonly used acoustic indices (ADI, ACI, NDSI, H and BI) to characterize the acoustic communities and represent the existing biodiversity numerically. We initially compared the index values across different land use types using a non-parametric rank sum test. Subsequently, we selected eight landscape metrics and performed a principal component analysis to summarize the surrounding matrix at each sampling point. We then employed generalized linear models to determine if the acoustic indices exhibited the anticipated variations. The results indicated significant variations in all indices among the different land use types, indicating their responsiveness to distinct acoustic communities and environmental characteristics. ADI, H and NDSI exhibited declining values from native to urban areas, while ACI and BI displayed the opposite trend. These findings underscore the influence of landscape structure on acoustic indices. Consequently, we concluded that adopting appropriate landscape planning, mainly through integrating natural and urban areas, could help preserve biodiversity in tropical urban regions.     

声学指数在城市森林鸟类多样性评估中的应用

鸣声是鸟类之间进行沟通和传递信息的重要方式,这为通过声学监测评估鸟类多样性提供了独特的机会。利用声学指数快速评估生物多样性是一种新兴的调查方法,但城市森林中的复杂声环境可能会导致声学指数的指示结果出现偏差。为了解声学指数在城市森林中应用的可行性,本研究在北京市东郊森林公园设置了50个矩阵式调查样点,于2021年4–6月每月进行1次鸟类传统观测和同步鸣声采集,通过比较两种方法的结果来探究声学监测的有效性。采用Spearman相关分析和广义线性混合模型评估6个常用声学指数与鸟类丰富度和多度的关系,并衡量了每个指数的性能。结果表明:(1)本研究共记录到鸟类10目23科35种,通过声学监听识别的总物种数与传统鸟类观测相等,但具体鸟种存在差异;(2)不同月份间声学指数与鸟类丰富度和多度的相关性有明显差别,声学复杂度指数(ACI)和标准化声景差异指数(NDSI)优于其他指数,是评估鸟类多样性的关键变量;(3)声学指数对鸟类多度的预测能力(R²m=0.32,R2c=0.80)要高于丰富度(R²m=0.12,R2c=0.18)。声学指数为快速评估生物多样性提...     

模拟四季温度层积对南方红豆杉种子生理性状的影响

为了解濒危物种南方红豆杉(Taxus chinensis var. mairei)种子内含物含量受温度和湿度层积的影响,设置4个季节、2种湿度(16%和24%)基质层积处理,对种子的可溶性糖、淀粉、可溶性蛋白和脂肪等内含物质的变化进行研究。结果表明,不同层积处理下种子贮藏物质的含量有显著变化,春季层积9个月后,可溶性蛋白含量达到最高值;可溶性糖含量呈现降低-升高-降低的变化趋势;淀粉和脂肪含量均随层积逐渐减少。秋季层积9个月后,淀粉含量降至最低。相比于24%湿度,16%湿度的春季、秋季、冬季层积9个月后,脂肪含量均减少较多,说明16%湿度下种子代谢活动更强。春季和秋季的暖温更能促进种子代谢,促进种子形态后熟。夏季温度过高,导致种子生活力下降,夏季层积处理3个月后,种子已经发霉和腐烂。层积过程中,种子内含物在相关酶的作用下,降解为可溶性蛋白、可溶性糖等,为种子萌发提供物质与能量。种子层积时间、温度和湿度及交互作用可作为种子内含物的调控因子。     

Sectoriality and physiological organisation in herbaceous plants: an overview

The physiological organisation of plants is considered in relation to the carbon economy of plant parts. Although assimilate is partitioned according to the relative strength of sinks, in many species there is also a very close relationship between partitioning and shoot phyllotaxy, giving rise to sectorial patterns of allocation whereby only certain sinks are supported by any source leaf. Essentially these sinks are in the same orthostichy as the source leaf. This constraint of the vascular architecture on assimilate distribution to developing sinks such as leaves, flowers and fruits is not always absolute, as following the loss of their principal source leaves these sinks can in many cases be supplied with assimilate by other leaves via new inter-orthostichy pathways. The supply of assimilate to major sinks such as developing fruits becomes more and more localised with time so that a fruit in an axillary position becomes largely supported by its subtending leaf; the reproductive node—a metamer-can thus be regarded as a relatively autonomous unit of the plant (an IPU). Similary, once established after a developmental phase of assimilate import, tiller ramets and branches in unitary plants tend to become physiologically autonomous modules. However, the functional autonomy of tillers is reversed following defoliation or shading as they are then sustained by the import of assimilate, subject to its availability, from unaffected tillers. Consequently the plant becomes physiologically integrated by the flow of assimilate from one part to another. The mainly autonomous ramets of many stoloniferous and rhizomatous species display a similar pattern of physiological integration in response to source manipulation, but in some species the ramets appear to maintain their independent functioning as a normal feature of the carbon allocation within the clone. In other clonal species, as the clone develops and becomes more structurally complex, vascular constraints start to restrict the movement of resources, and the clone becomes composed of a number of semi-autonomous IPUs. In unitary plants branches appear to remain very physiologically isolated in terms of their carbon economy once they become established, irrespective of a range of source-sink manipulations.These different patterns of physiological integration and organisation are discussed in relation to different strategies of assimilate utilisation and conservation.     

湖南省冷水江市大嵊山大气污染与马尾松衰亡

 作者对湖南省冷水江市大嵊山大气污染与马尾松衰亡进行了研究,研究结果表明大气综合污染指数在3个研究点上分别为1.00(对照)、1.76和2.23。而以林分密度、林分非衰亡率、针叶长度、针叶干重、马尾松平均高、平均胸径等因子计算出的林分外貌综合得分从173.9下降到143.5和132.5。在一年四季,马尾松针叶中叶绿素含量也是清洁区显著高于污染区,而叶绿素a／b值则是污染区的高,峰值较正常的提前。马尾松在受到大气污染作用后,针叶中营养元素含量呈下降趋势,尤其是氮。根据树干解析发现大气污染对马尾松高生长和胸径生长都具有抑制作用,但并不表现出同步效应,对高生长的抑制有一个滞后现象,时间在2～3年。另外,大气污染对马尾松的结果影响很大,污染区的马尾松单株拥有球果数仅为清洁的25％,用灰色系统理论对马尾松材积与相关影响因子进行关联度分析发现,材积与综合污染指数的倒数有很好的关联性,关联度达到了0.773。     

Soil microbial diversity and the sustainability of agricultural soils

Many world ecosystems are in various states of decline evidenced by erosion, low productivity, and poor water quality caused by forest clearing, intensive agricultural production, and continued use of land resources for purposes that are not sustainable. The biological diversity of these systems is being altered. Little research has been conducted to quantify the beneficial relationships between microbial diversity, soil and plant quality, and ecosystem sustainability. Ecosystem functioning is governed largely by soil microbial dynamics. Differences in microbial properties and activities of soils have been reported but are restricted to general ecological enumeration methods or activity levels, which are limited in their ability to describe a particular ecosystem. Microbial populations and their responses to stresses have been traditionally studied at the process level, in terms of total numbers of microorganisms, biomass, respiration rates, and enzyme activities, with little attention being paid to responses at the community or the organismal levels. These process level measurements, although critical to understanding the ecosystem, may be insensitive to community level changes due to the redundancy of these functions. As microbial communities comprise complex interactions between diverse organisms, they should be studied as such, and not as a black box into which inputs are entered and outputs are received at measured rates. Microbial communities and their processes need to be examined in relation to not only the individuals that comprise the community, but the effect of perturbations or environmental stresses on those communities.     

Prevalence and upper limit of cardiac hypertrophy in professional cyclists

The term athlete's heart refers to an increased left ventricular mass. Few studies have assessed the prevalence and normal upper limit of cardiac hypertrophy in highly trained cyclists and this was the aim of this study. A group of 40 professional road cyclists [mean age 26 (SD 3) years] who had participated in European competitions for 3–10 years, were evaluated at the beginning of the 1992–93 season. Evaluation included a clinical history and physical examination, one and two-dimensional echocardiography, 12-lead resting electrocardiogram and a graded exercise test. Determination of the left ventricular mass index (LVMI) was performed using Devereux's formula with correction for the body surface area. Systolic and diastolic blood pressure were measured at rest and at peak exercise. Of the group 23 cyclists (58%) presented a LVMI greater than 130 g · m^–2, 21 cyclists presented a diastolic ventricular thickness equal to or greater than 13 mm, with a superior limit of 19 mm; 3 cyclists presented asymmetrical septum hypertrophy; and the relationship between posterior wall and left ventricular diastolic radius was equal to or greater than 0.45 in 14 cases (35%). Electrocardiographic abnormalities of ST-T segment were seen in only 1 subject. No correlation was found between the degree of ventricular hypertrophy and arterial blood pressure. We concluded that these professional cyclists showed a high prevalence of cardiac hypertrophy (58%). The distribution of this hypertrophy was concentric in 20/33 and asymmetric in 3/23 of the subjects with left ventricular hypertrophy. The electrocardiograms were normal in 98% of the subjects.