Temperature sensitivities of extracellular enzyme Vmax and Km across thermal environments

The magnitude and direction of carbon cycle feedbacks under climate warming remain uncertain due to insufficient knowledge about the temperature sensitivities of soil microbial processes. Enzymatic rates could increase at higher temperatures, but this response could change over time if soil microbes adapt to warming. We used the Arrhenius relationship, biochemical transition state theory, and thermal physiology theory to predict the responses of extracellular enzyme V_max and K_m to temperature. Based on these concepts, we hypothesized that V_max and K_m would correlate positively with each other and show positive temperature sensitivities. For enzymes from warmer environments, we expected to find lower V_max, K_m, and K_m temperature sensitivity but higher V_max temperature sensitivity. We tested these hypotheses with isolates of the filamentous fungus Neurospora discreta collected from around the globe and with decomposing leaf litter from a warming experiment in Alaskan boreal forest. For Neurospora extracellular enzymes, V_max Q₁₀ ranged from 1.48 to 2.25, and K_m Q₁₀ ranged from 0.71 to 2.80. In agreement with theory, V_max and K_m were positively correlated for some enzymes, and V_max declined under experimental warming in Alaskan litter. However, the temperature sensitivities of V_max and K_m did not vary as expected with warming. We also found no relationship between temperature sensitivity of V_max or K_m and mean annual temperature of the isolation site for Neurospora strains. Declining V_max in the Alaskan warming treatment implies a short‐term negative feedback to climate change, but the Neurospora results suggest that climate‐driven changes in plant inputs and soil properties are important controls on enzyme kinetics in the long term. Our empirical data on enzyme V_max, K_m, and temperature sensitivities should be useful for parameterizing existing biogeochemical models, but they reveal a need to develop new theory on thermal adaptation mechanisms.     

我国三大城市群地区城市和农业用地地表热环境效应对比研究

以大中小城市协同发展为特征的城市群已成为我国城市化发展的主要形式,城市化和农业作为城市群地区最主要的土地利用活动,其气候效应是国际研究的热点。然而过去研究多关注大城市的热岛效应,对更为普遍的农业活动以及中小城市城市化的气候效应认识十分薄弱。基于MODIS地表温度数据,以自然林地为参照,提出了一种可逐像元估算土地利用地表热环境效应的新方法,进而对比分析了我国三大城市群地区（京津冀、长三角和珠三角）城市和农业用地地表热环境效应及其驱动因子差异。结果表明各城市群白天城市热岛效应明显,地级以上城市年平均热岛强度达3.2℃以上,但最强热岛均未发生在核心城市。夜晚热岛效应明显减弱,京津冀和长三角部分城市甚至出现冷岛效应。农业用地在白天亦表现出明显的增温效应,特别是在京津冀地区,而在夜晚除珠三角城市群外,降温效应明显,京津冀和长三角地区平均降温2.3℃和0.7℃。虽然城市用地平均增温强度大于农业用地,但农业用地因面积优势对区域温度变化起控制作用。白天城市和农业用地整体导致各城市群温度明显增加,京津冀增温最高（4.0℃）,夜晚二者导致长三角和京津冀地区平均温度降低。研究还发现各城市群城市和农业用地地表热环境效应时空异质性极大,主要受植被、地表反照率、气候背景和人口密度控制。本文对制定缓解气候变化的土地利用策略具有重要的指导意义。     

High predictability of direct competition between marine diatoms under different temperatures and nutrient states

The distribution of marine phytoplankton will shift alongside changes in marine environments, leading to altered species frequencies and community composition. An understanding of the response of mixed populations to abiotic changes is required to adequately predict how environmental change may affect the future composition of phytoplankton communities. This study investigated the growth and competitive ability of two marine diatoms, Phaeodactylum tricornutum and Thalassiosira pseudonana, along a temperature gradient (9–35°C) spanning the thermal niches of both species under both high‐nitrogen nutrient‐replete and low‐nitrogen nutrient‐limited conditions. Across this temperature gradient, the competitive outcome under both nutrient conditions at any assay temperature, and the critical temperature at which competitive advantage shifted from one species to the other, was well predicted by the temperature dependencies of the growth rates of the two species measured in monocultures. The temperature at which the competitive advantage switched from P. tricornutum to T. pseudonana increased from 18.8°C under replete conditions to 25.3°C under nutrient‐limited conditions. Thus, P. tricornutum was a better competitor over a wider temperature range in a low N environment. Being able to determine the competitive outcomes from physiological responses of single species to environmental changes has the potential to significantly improve the predictive power of phytoplankton spatial distribution and community composition models.     

Thermal stability of single‐domain antibodies estimated by molecular dynamics simulations

Single‐domain antibodies (sdAbs) function like regular antibodies, however, consist of only one domain. Because of their low molecular weight, sdAbs have advantages with respect to production and delivery to their targets and for applications such as antibody drugs and biosensors. Thus, sdAbs with high thermal stability are required. In this work, we chose seven sdAbs, which have a wide range of melting temperature (T_m) values and known structures. We applied molecular dynamics (MD) simulations to estimate their relative stability and compared them with the experimental data. High‐temperature MD simulations at 400 K and 500 K were executed with simulations at 300 K as a control. The fraction of native atomic contacts, Q, measured for the 400 K simulations showed a fairly good correlation with the T_m values. Interestingly, when the residues were classified by their hydrophobicity and size, the Q values of hydrophilic residues exhibited an even better correlation, suggesting that stabilization is correlated with favorable interactions of hydrophilic residues. Measuring the Q value on a per‐residue level enabled us to identify residues that contribute significantly to the instability and thus demonstrating how our analysis can be used in a mutant case study.     

Impacts of thermal mismatches on chytrid fungus Batrachochytrium dendrobatidis prevalence are moderated by life stage,body size,elevation and latitude

Global climate change is increasing the frequency of unpredictable weather conditions; however, it remains unclear how species‐level and geographic factors, including body size and latitude, moderate impacts of unusually warm or cool temperatures on disease. Because larger and lower‐latitude hosts generally have slower acclimation times than smaller and higher‐latitude hosts, we hypothesised that their disease susceptibility increases under ‘thermal mismatches’ or differences between baseline climate and the temperature during surveying for disease. Here, we examined how thermal mismatches interact with body size, life stage, habitat, latitude, elevation, phylogeny and International Union for Conservation of Nature (IUCN) conservation status to predict infection prevalence of the chytrid fungus Batrachochytrium dendrobatidis (Bd) in a global analysis of 32 291 amphibian hosts. As hypothesised, we found that the susceptibility of larger hosts and hosts from lower latitudes to Bd was influenced by thermal mismatches. Furthermore, hosts of conservation concern were more susceptible than others following thermal mismatches, suggesting that thermal mismatches might have contributed to recent amphibian declines.     

Adaptation to simultaneous warming and acidification carries a thermal tolerance cost in a marine copepod

The ocean is undergoing warming and acidification. Thermal tolerance is affected both by evolutionary adaptation and developmental plasticity. Yet, thermal tolerance in animals adapted to simultaneous warming and acidification is unknown. We experimentally evolved the ubiquitous copepod Acartia tonsa to future combined ocean warming and acidification conditions (OWA approx. 22°C, 2000 µatm CO₂) and then compared its thermal tolerance relative to ambient conditions (AM approx. 18°C, 400 µatm CO₂). The OWA and AM treatments were reciprocally transplanted after 65 generations to assess effects of developmental conditions on thermal tolerance and potential costs of adaptation. Treatments transplanted from OWA to AM conditions were assessed at the F1 and F9 generations following transplant. Adaptation to warming and acidification, paradoxically, reduces both thermal tolerance and phenotypic plasticity. These costs of adaptation to combined warming and acidification may limit future population resilience.     

红外成像技术在生命科学中的应用

红外成像技术是利用物体自身各部分对红外热辐射的差异把红外辐射图像转换为可视图像的技术.对红外成像技术历史进行了简单介绍,对远红外成像技术在生命科学包括医学、植物、动物及农业中的应用进行了综述,并对红外成像技术在生命科学中的应用作了展望.     

氮磷添加对栓皮栎不同地理种源幼苗温度耐性的影响

通过氮磷添加控制试验,对湖南城步(CB) 、湖北秭归(ZG)、河南内乡(NX)、河北临城(LC)和北京平谷(PG)5个种源的栓皮栎1年生幼苗的叶片温度耐性指标(耐寒性、耐热性及耐温范围)及相关生理指标(叶片养分浓度、非结构性碳水化合物及其组分和养分利用效率)进行测定,研究养分对植物种内不同地理种源的温度耐性影响.结果表明:不同种源的栓皮栎养分吸收与氮磷利用效率对氮磷添加存在显著差异但地理趋势不明显.PG在N、P及其二者复合添加的情况下均具有较高的氮磷利用效率,NX则在不同处理下磷利用效率均处于最低水平,CB在磷添加的情况下对磷的利用效率最高.与对照相比,养分(N、P或NP)添加能明显增加PG和LC的耐寒性,但N添加降低了NX的耐寒性.同时,养分添加在一定程度上增加了ZG、NX和LC的耐热性.耐温范围与耐寒性相反,表现为养分添加降低了PG和LC的温度耐受范围, 而增加了NX的温度耐受范围.偏相关分析表明,耐寒性与叶片可溶性糖浓度呈显著正相关;耐热性与叶片P呈显著负相关,与N/P呈显著正相关;叶片耐温范围与叶片物质浓度无显著相关性.因此,不同地理种源对养分利用程度及其效率可能与源生地土壤环境条件有关,表现出一定的局域适应特征,从而增加了温度耐性对养分响应的复杂程度.     

交配对广聚萤叶甲成虫耐饥与耐热能力的影响

昆虫交配是一个消耗能量的过程,因此交配后可能对其抗逆能力造成一定的影响。广聚萤叶甲是恶性杂草-豚草的专一性天敌,正常情况下,成虫耐饥饿和耐热能力较强。为明确交配对广聚萤叶甲成虫抗逆能力的影响,本研究观察在一次交配处理后,广聚萤叶甲在饥饿条件下或高温条件下继续存活时间。结果发现,在不提供食物的情况下,交配对雄虫的寿命影响不大,但雌虫的寿命(8.4 d±0.1 d)显著短于对照雌虫(10.8 d±0.1 d)。在高温状态下,无论取食与否,交配都会显著增加广聚萤叶甲雌雄成虫的耐热能力,尤其以雌虫表现更为明显(处理雌虫和对照雌虫存活时间分别为:取食(6.15 d±0.14 d,4.95 d±0.13 d)、不取食(5.55 d±0.13 d,4.81 d±0.11 d)。可见,交配降低广聚叶甲雌虫的饥饿能力,但成虫的耐热能力显著加强。