Effect of temperature on nitrogen transformation in Hawaiian soils

Summary In a field experiment soil samples buried at the warmer temperature regime nitrified added ammonium faster than soils buried at the cooler temperature regime. Nitrification occurred more rapidly under both regimes in a soil which had developed in a warm climatic zone than in two other soils developed under cooler conditions.The rate of nitrification of added ammonium in soils incubated at 5, 15, 25 and 40°C in the laboratory increased with increase in the temperature up to 25°C in three out of four soils. In the fourth soil nitrification was as active at 40°C as at 25°C. The temperature range for appreciable nitrification to occur in a soil was related to the environmental conditions where the soil was formed.Mineralization of organic nitrogen occurred to a greater extent at 40°C than at three lower incubating temperatures of 5, 15, and 25°C. Rapid and active mineralization was associated with high organic matter and C/N ratio in soils     

Phosphorylation of the tubulin-binding protein, stathmin, by Cdk5 and MAP kinases in the brain

Regulation of cytoskeletal dynamics is essential to neuronal plasticity during development and adulthood. Dysregulation of these mechanisms may contribute to neuropsychiatric and neurodegenerative diseases. The neuronal protein kinase, cyclin-dependent kinase 5 (Cdk5), is involved in multiple aspects of neuronal function, including regulation of cytoskeleton. A neuroproteomic search identified the tubulin-binding protein, stathmin, as a novel Cdk5 substrate. Stathmin was phosphorylated by Cdk5 in vitro at Ser25 and Ser38, previously identified as mitogen-activated protein kinase (MAPK) and p38 MAPKdelta sites. Cdk5 predominantly phosphorylated Ser38, while MAPK and p38 MAPKdelta predominantly phosphorylated Ser25. Stathmin was phosphorylated at both sites in mouse brain, with higher levels in cortex and striatum. Cdk5 knockout mice exhibited decreased phospho-Ser38 levels. During development, phospho-Ser25 and -Ser38 levels peaked at post-natal day 7, followed by reduction in total stathmin. Inhibition of protein phosphatases in striatal slices caused an increase in phospho-Ser25 and a decrease in total stathmin. Interestingly, the prefrontal cortex of schizophrenic patients had increased phospho-Ser25 levels. In contrast, total and phospho-Ser25 stoichiometries were decreased in the hippocampus of Alzheimer's patients. Thus, microtubule regulatory mechanisms involving the phosphorylation of stathmin may contribute to developmental synaptic pruning and structural plasticity, and may be involved in neuropsychiatric and neurodegenerative disorders.     

Relationship between photosynthetic phosphorus‐use efficiency and foliar phosphorus fractions in tropical tree species

How plants develop adaptive strategies to efficiently use nutrients on infertile soils is an important topic in plant ecology. It has been suggested that, with decreasing phosphorus (P) availability, plants increase photosynthetic P‐use efficiency (PPUE) (i.e., the ratio of instantaneous photosynthetic carbon assimilation rate per unit foliar P). However, the mechanism to increase PPUE remains unclear. In this study, we tested whether high PPUE is explained by an optimized allocation of P in cells among P‐containing biochemical compounds (i.e., foliar P fractions). We investigated the relationships among mass‐based photosynthetic carbon assimilation rate (A_mass), PPUE, total foliar P concentration, and foliar P fractions in 10 tree species in two tropical montane rain forests with differing soil P availability (five species on sedimentary soils and five species on P‐poorer ultrabasic serpentine soils) on Mount Kinabalu, Borneo. We chemically fractionated foliar P into the following four fractions: metabolic P, lipid P, nucleic acid P, and residual P. A_mass was positively correlated with the concentrations of total foliar P and of metabolic P across 10 tree species. Mean A_mass and mean concentrations of total foliar P and of each foliar P fraction were lower on the P‐poorer ultrabasic serpentine soils than on the sedimentary soils. There was a negative relationship between the proportion of metabolic P per total P and the proportion of lipid P per total P. PPUE was positively correlated with the ratio of metabolic P to lipid P. High PPUE is explained by the net effect of a relatively greater investment of P into P‐containing metabolites and a relatively lesser investment into phospholipids in addition to generally reduced concentrations of all P fractions. We conclude that plants optimize the allocation of P among foliar P fractions for maintaining their productivity and growth and for reducing demand for P as their adaptation to P‐poor soils.     

MRI Characterization of Paranodal Junction Failure and Related Spinal Cord Changes in Mice

The paranodal junction is a specialized axon-glia contact zone that is important for normal neuronal activity and behavioral locomotor function in the central nervous system (CNS). Histological examination has been the only method for detecting pathological paranodal junction conditions. Recently, diffusion tensor MRI (DTI) has been used to detect microstructural changes in various CNS diseases. This study was conducted to determine whether MRI and DTI could detect structural changes in the paranodal junctions of the spinal cord in cerebroside sulfotransferase knock-out (CST-KO) mice. Here, we showed that high-resolution MRI and DTI characteristics can reflect paranodal junction failure in CST-KO mice. We found significantly lower T1 times and significantly higher T2 times in the spinal cord MRIs of CST-KO mice as compared to wild-type (WT) mice. Spinal cord DTI showed significantly lower axial diffusivity and significantly higher radial diffusivity in CST-KO mice as compared to WT mice. In contrast, the histological differences in the paranodal junctions of WT and CST-KO mice were so subtle that electron microscopy or immunohistological analyses were necessary to detect them. We also measured gait disturbance in the CST-KO mice, and determined the conduction latency by electrophysiology. These findings demonstrate the potential of using MRI and DTI to evaluate white matter disorders that involve paranodal junction failure.     

Root-exudate flux variations among four co-existing canopy species in a temperate forest,Japan

Plants allocate carbon to root exudates to mine nitrogen (N) from soil organic matter (SOM). Little is known about how the root-exudation rate varies among co-existing woody species. We conducted an in situ experiment in a warm temperate forest on two dominant species, Quercus serrata and Ilex pedunculosa, and two of their congeneric species, Quercus glauca and Ilex macropoda, respectively. We hypothesized that the root-exudation rate varies among these species because of their distinct functional traits and N demands. Root-exudation rates were measured using a non-soil culture method during the growing season from June 2013 to May 2014. We also measured foliar N concentrations and the activities of N-degrading enzymes in the rhizosphere soils. The annual demand for N was calculated from the growth rate and allometric equations for biomass. The root-exudation rates of Q. serrata and I. macropoda were consistently greater than those of their congeneric evergreen species on root-length, root-weight, and individual-tree bases. The variations of the annual N demand of these species mirrored this pattern. Within a species, root-exudation rates correlated positively to leaf N contents, suggesting a physiological linkage between photosynthetic capacities and belowground carbon allocation. Root-exudation rates also correlated positively to the activities of polyphenol oxidase, an enzyme that decomposes N from recalcitrant SOM. Our results suggest that the variations of the root-exudation among co-existing species relate to their functional traits and demand for N.     

Soil Phosphorus Fractionation and Phosphorus-Use Efficiency of a Bornean Tropical Montane Rain Forest During Soil Aging With Podozolization

We compared phosphorus (P) dynamics and plant productivity in two montane tropical rain forests (Mount Kinabalu, Borneo) that derived from similar parent materials (largely sedimentary rocks) and had similar climates but differed in terms of soil age. The younger site originated from Quaternary colluvial deposits, whereas the older site had Tertiary-age material. The older site had a distinctive spodic horizon, reduced levels of labile inorganic soil P, higher concentrations of recalcitrant organic soil P, and lower rates of net soil N mineralization. P fertilization led to soil nitrogen (N) immobilization in the P-deficient soil, indicating that soil N mineralization was limited by P at the P-deficient older site. Mean foliar nutrient concentration (on both a weight and an area basis) was similar at the two sites for all elements except P, which was lower at the older site. Aboveground net primary production (ANPP) was lower at the older site than at the younger one; this difference could be explained by the reduced availability of P and N (as down-regulated by P) at the older site. The relatively ample allocation of P and N to leaves, despite the reduced availability at the P-deficient old site, was attributable to its high resorption efficiency. High resorption resulted in lower concentrations of elements in leaf litter—that is, less decomposable low-quality litter. On the other hand, the concentration of leaf litter lignin was considerably lower at the older site; this appeared to be a de facto adaptive mechanism to avoid retarding litter decomposition.     

Silicon cycled by tropical forest trees: effects of species,elevation and parent material on Mount Kinabalu,Malaysia

Plant and Soil - We aimed to compare uptake and litter flux of silicon (Si) across tropical tree species and sites on Mt. Kinabalu, Borneo. Si flux components were measured at eight plots in...     

Engineering functional two- and three-dimensional liver systems in vivo using hepatic tissue sheets

Hepatic tissue engineering using primary hepatocytes has been considered a valuable new therapeutic modality for several classes of liver diseases. Recent progress in the development of clinically feasible liver tissue engineering approaches, however, has been hampered mainly by insufficient cell-to-cell contact of the engrafted hepatocytes. We developed a method to engineer a uniformly continuous sheet of hepatic tissue using isolated primary hepatocytes cultured on temperature-responsive surfaces. Sheets of hepatic tissue transplanted into the subcutaneous space resulted in efficient engraftment to the surrounding cells, with the formation of two-dimensional hepatic tissues that stably persisted for longer than 200 d. The engineered hepatic tissues also showed several characteristics of liver-specific functionality. Additionally, when the hepatic tissue sheets were layered in vivo, three-dimensional miniature liver systems having persistent survivability could be also engineered. This technology for liver tissue engineering is simple, minimally invasive and free of potentially immunogenic biodegradable scaffolds.     

Interactive influences of climate and parent material on soil microbial community structure in Bornean tropical forest ecosystems

Climate and parent material strongly control vegetation structure and function, yet their control over the belowground microbial community is poorly understood. We assessed variation in microbial lipid profiles in undisturbed forest soils (organic and surface mineral horizons) along an altitudinal gradient (700, 1,700, and 2,700 m a.s.l. mean annual temperature of 12–24°C) on two contrasting parent materials (acidic metasedimentary vs. ultrabasic igneous rock) in Mt. Kinabalu, Borneo. Soil organic carbon and nitrogen concentrations were generally higher at higher altitudes and, within a site, at upper soil horizons. Soil pH ranged from 3.9 to 5.3, with higher values for the ultrabasic soils especially at higher altitudes. The major shifts in microbial community structure observed were the decline in the ratio of fungal to bacterial lipid markers both with increasing soil depth and decreasing altitude. The positive correlation between this ratio with soil C and N concentrations suggested a strong substrate control in accord with the literature from mid to high-latitude ecosystems. Principal component analysis using seven groups of signature lipids suggested a significant altitude by parent material interaction—the significant difference in microbial community structure between the two rock types found at 2,700-m sites developed on weakly weathered soils diminished with decreasing altitude towards 700-m sites where soils were strongly weathered. These results are consistent with the hypothesis that parent material effect on soil microbial community (either directly via soil geochemistry or indirectly via floristic composition) is stronger at an earlier stage of ecosystem development.