Quantitative aspects of heterogeneity in soil organic matter dynamics in a cool-temperate Japanese beech forest: a radiocarbon-based approach

Soil is the largest carbon reservoir in terrestrial ecosystems; it stores twice as much carbon as the atmosphere. It is well documented that global warming can lead to accelerated microbial decomposition of soil organic carbon (SOC) and enhance the release of CO₂ from the soil to the atmosphere; however, the magnitude and timing of this effect remain highly uncertain due to a lack of quantitative data concerning the heterogeneity of SOC biodegradability. Therefore, we sought to identify SOC pools with respect to their specific mean residence times (MRTs), to use those SOC pools to partition soil respiration sources, and to estimate the potential response of the pools to warming. We collected surface soil and litter samples from a cool-temperate deciduous forest in Japan, chemically separated the samples into SOC fractions, estimated their MRTs based on radiocarbon (¹⁴C) isotope measurements, and used the data to construct a model representing the soil as a complex of six SOC pools with different MRT ranges. We estimate that a minor, fast-cycling SOC pool with an MRT of less than 10 years (corresponding to the O horizon and recognizable plant leaf fragments in the A1 horizon) is responsible for 73% of annual heterotrophic respiration and 44% of total soil respiration. However, the predicted response of these pools to warming demonstrates that the rate of SOC loss from the fast-cycling SOC pool diminishes quickly (within several decades) because of limited substrate availability. In contrast, warming will continue to accelerate SOC loss from slow-cycling pools with MRTs of 20–200 years over the next century. Although using a ¹⁴C-based approach has drawbacks, these estimates provide quantitative insights into the potential importance of slow-cycling SOC dynamics for the prediction of positive feedback to climate change.     

Discovery of lipoprotein lipase pI isoforms and contributions to their characterization

Lipoprotein lipase (LPL) plays a pivotal role in lipid metabolism and is implicated in several pathophysiological conditions. A large number of LPL studies have been performed in rat, although the amount of information derived from direct study of the protein in this species is limited. Here we attempted to examine possible modifications of LPL using proteomic tools. By combining high-resolution two-dimensional gel electrophoresis and Western blot with biological mass spectrometry we demonstrate the coexistence of multiple LPL pI isoforms in rat heart. We studied the origin of this pI heterogeneity by: (1) comparison with the 2D pattern of LPL from post-heparin rat plasma (as a source of mature LPL); (2) protein dephosphorylation; (3) protein deglycosylation; and (4) partial sequencing of LPL isoforms. The results reveal that LPL pI heterogeneity does not correspond to different stages of intracellular maturation or protein phosphorylation. It can be partially explained by glycosylation, although other post-translational modifications must also be involved. We also report the first partial sequence to be obtained from direct study of rat LPL protein. These findings should be the basis for further research aimed at identifying the molecular differences between LPL isoforms and exploring their potential functional implications.     

Environmental factors determining invasibility of urban waters for exotic macroinvertebrates

Aim Urbanization usually leads to biotic homogenization with a decrease in native species and increase in exotic species. We investigated whether local environmental factors in urban water bodies, such as water quality, habitat structure and biotic interactions, influenced the invasion of these systems by exotic macroinvertebrate species. Location Urban surface water systems in lowlands of the Rhine‐Meuse delta. Methods Presence and abundance of native and exotic macroinvertebrate species were compared between different urban water types and related to environmental variables with multivariate analysis and spearman’s correlations. Moreover, co‐existence of related native and exotic species was studied. Results In total nine exotic species were found in the following taxa: Tricladida (1), Crustacea (5), Bivalvia (1) and Gastropoda (2). Taxonomically related native and exotic crustacean species did not seem to be influenced by competition in nutrient‐rich urban waters; most species showed high abundances. Nevertheless, two exotic crustacean species were much more abundant in waters where other crustacean species were absent, possibly filling empty niches. Native species richness and abundance was positively related to environmental heterogeneity in the form of submerged vegetation. The occurrence and abundance of most exotic species were positively related to several eutrophication indicators, such as nitrate, sludge layer and lemnid vegetation. Main conclusions Exotic species in urban waters were mostly detritivorous or omnivorous and therefore dependent on leaf breakdown. In nutrient‐rich water systems, where food availability was high, exotic crustacean species co‐existed with native crustacean species, while in nutrient‐poor, richly vegetated systems, native Asellidae dominated exotic Asellidae. In the turbid water bodies with very little vegetation, native species richness was low and two exotic crustacean species were relatively abundant in these water systems. Invasibility of urban water systems could be reduced by stimulating the development of submerged and nymphaeid vegetation and decreasing nutrient levels.     

Investigation of the age-at-onset heterogeneity in type 1 diabetes through mathematical modeling

The heterogeneity between young- and adult-onset type 1 diabetes (T1D) is well known, but not well understood. We approach this question through mathematical formulation and analysis of the dynamic interactions between the immune cells and the pancreatic islet beta-cells that lead to the beta-cell destruction. Utilizing the perturbation expansion method we investigate the dynamic stability of our system under fast and slow beta-cell turnover limits. We find that if autoimmunity is initiated when the turnover is slow (adult age), a stable steady state can exist with reduced number of beta-cells, where the beta-cell regeneration balances the ongoing autoimmune destruction. This implies that a slow disease process is possible. In contrast, if autoimmunity occurs when the beta-cell turnover is rapid (young age), such a stable state will never be attained and the destruction will progress unabated, leading to an acute disease onset. The major findings of our model are consistent with clinical observations, and it offers an explanation for the dynamic and phenotypic heterogeneity between young- and adult-onset T1D. More importantly, the model analyses point out that pathways regulating beta-cell turnover can be new targets to interfere with the disease process of T1D.     

适应性策略：人类致病真菌新生隐球菌的“杀手锏”

绝大多数引发人体系统感染的致病真菌来自于环境,这些环境来源的真菌往往是条件致病菌,其毒力衍生于它们独特的生境适应策略。新生隐球菌是进化最为成功的环境真菌之一,在自然界中的分布极为广泛。而作为人类致病菌,新生隐球菌能够引发致命的隐球菌病和真菌脑膜炎,据统计全球每年由于隐球菌病死亡的人数超过60万人。近几年的研究表明,新生隐球菌的环境适应策略对其条件致病性至关重要。细胞-细胞交流、细胞形态转换和细胞异质性等重要环境适应行为在协调新生隐球菌的致病性方面都扮演了重要的角色。文章从致病菌-自然栖居环境-人类宿主三方的关系解析了新生隐球菌环境适应策略影响毒力的机制及相关进化动机,并对其潜在的研究前景和临床应用提出了一些思考。     

Establishment and maintenance of adaptive genetic divergence under migration, selection, and drift

There is a long tradition in population genetics of exploring the maintenance of variation under migration-selection balance using deterministic models that assume infinite population size. With finite population size, stochastic dynamics can greatly reduce the potential for the maintenance of polymorphism, but this has yet to be explored in detail. Here, classical two-patch models are extended to predict: (1) the probability of a locally beneficial mutation rising in frequency in the patch where it is favored and (2) the critical threshold migration rate above which the maintenance of polymorphism is much less likely. Individual-based simulations show that these approximations provide accurate predictions across a wide range of parameter space.     

长白山低山区森林土壤有机碳及养分空间异质性

以吉林延边汪清林业局金仓林场境内森林土壤为对象,采用多元线性回归方法和地统计学回归克里格方法,研究了土壤有机碳及养分的垂直分布规律,预测了其空间分布,并对预测结果进行插值.结果表明: 0～60 cm深度土壤有机碳密度为(16.14±4.58) kg·m^-2.随土壤深度增加,土壤有机碳含量、有机碳密度以及土壤全N、全P、全K、有效P及速效K含量都呈减小趋势,其中不同土层间土壤有机碳含量、有机碳密度差异显著(P<0.01).0～60 cm土层土壤有机碳含量和碳密度的拟合方程中,地形因子中高程和坡向余弦值是最优的拟合因子,方程的决定系数分别为0.34和0.39(P<0.01).0～20和0～60 cm土层的半方差函数模型分别为高斯模型和指数模型,利用回归克里格插值方法得到土壤有机碳的空间分布图.与普通克里格法相比,回归克里格法的空间预测精度改进了18%～58%.利用回归克里格插值方法预测了土壤全N的空间分布特征.