Ascorbic acid prolongs the viability and stability of isolated perfused lungs: A mechanistic study using 31P and hyperpolarized 13C nuclear magnetic resonance

Ex vivo lung perfusion (EVLP) has recently shown promise as a means of more accurately gauging the health of lung grafts and improving graft performance post-transplant. However, reperfusion of ischemic lung promotes the depletion of high-energy compounds and a progressive loss of normal mitochondrial function, and it remains unclear how and to what extent the EVLP approach contributes to this metabolic decline. Although ascorbate has been used to mitigate the effects of ischemia–reperfusion injury, the nature of its effects during EVLP are also not clear. To address these uncertainties, this study monitored the energy status of lungs during EVLP and after the administration of ascorbate using ³¹P and hyperpolarized ¹³C NMR (nuclear magnetic resonance). Our experiments demonstrated that the oxidative phosphorylation capacity and pyruvate dehydrogenase flux of lungs decline during ex vivo perfusion. The addition of ascorbate to the perfusate prolonged lung viability by 80% and increased the hyperpolarized ¹³C bicarbonate signal by a factor of 2.7. The effect of ascorbate is apparently due not to its antioxidant quality but rather to its ability to energize cellular respiration given that it increased the lung’s energy charge significantly, whereas other antioxidants (glutathione and α-lipoic acid) did not alter energy metabolism. During ascorbate administration, inhibition of mitochondrial complex I with rotenone depressed energy charge and shifted the metabolic state of the lung toward glycolysis; reenergizing the electron transport chain with TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) recovered metabolic activity. This indicates that ascorbate slows the decline of the ex vivo perfused lung’s mitochondrial activity through an independent interaction with the electron transport chain complexes.     

Predator and detritivore niche width helps to explain biocomplexity of experimental detritus-based food webs in four aquatic and terrestrial ecosystems

In the study of food webs, the existence and explanation of recurring patterns, such as the scale invariance of linkage density, predator–prey ratios and mean chain length, constitute long-standing issues. Our study focused on litter-associated food webs and explored the influence of detritivore and predator niche width (as δ¹³C range) on web topological structure. To compare patterns within and between aquatic and terrestrial ecosystems and take account of intra-habitat variability, we constructed 42 macroinvertebrate patch-scale webs in four different habitats (lake, lagoon, beech forest and cornfield), using an experimental approach with litterbags. The results suggest that although web differences exist between ecosystems, patterns are more similar within than between aquatic and terrestrial web types. In accordance with optimal foraging theory, we found that the niche width of predators and prey increased with the number of predators and prey taxa as a proportion of total taxa in the community. The tendency was more marked in terrestrial ecosystems and can be explained by a lower per capita food level than in aquatic ecosystems, particularly evident for predators. In accordance with these results, the number of links increased with the number of species but with a significantly sharper regression slope for terrestrial ecosystems. As a consequence, linkage density, which was found to be directly correlated to niche width, increased with the total number of species in terrestrial webs, whereas it did not change significantly in aquatic ones, where connectance scaled negatively with the total number of species. In both types of ecosystem, web robustness to rare species removal increased with connectance and the niche width of predators. In conclusion, although limited to litter-associated macroinvertebrate assemblages, this study highlights structural differences and similarities between aquatic and terrestrial detrital webs, providing field evidence of the central role of niche width in determining the structure of detritus-based food webs and posing foraging optimisation constraints as a general mechanistic explanation of food web complexity differences within and between ecosystem types.     

Phytomass change in natural phytocenosis as an indicator of technogenic pollution of soils with heavy metals

This study considered the possibility of using plant community phytomass for the assessment of soil pollution with heavy metals (HM) from industrial wastes. The three-year-long field experiment was run under the regional natural meadow vegetation; the polymetallic galvanic slime was used as an industrial waste contaminant. It is shown that soil contamination primarily causes decrease of phytomass in the growing phytocenosis. The vegetation experiments determined nonlinear dependence of cultivated and wild plant biomass on the level of soil contamination; it is described by the equations of logistic and Gaussian regression. In the absence of permanent contaminants, the soil is self-cleaned over time. It reproduces phytomass mainly due to the productivity increase of the most pollution-tolerant species in the remaining phytocenosis. This phenomenon is defined as environmental hysteresis. Soil pollution by industrial waste leads to the loss of plant biodiversity. The research shows that the study of the HM impact on ecosystems is expedient given the consideration of the “soil–phytocenosis–pollutant” complex in the “dose–response” aspect. The reaction of phytocenosis on HM showing decline in phytomass leads to serious limitations in the choice of accumulating plants, because the adsorbed HM are rejected through phytomass.     

江西省森林净初级生产力动态变化特征及其驱动因子分析

亚热带森林生态系统具有巨大的固碳潜力。净初级生产力(NPP)在碳循环过程中具有重要的作用, 受到气候变化、大气成分、森林扰动的强度和频度、林龄等因子的综合影响, 然而目前上述各因子对亚热带森林NPP变化的贡献尚不明确, 需要鉴别森林NPP时空变化的主要驱动因子, 以准确认识亚热带森林生态系统碳循环。该文综合气象数据、年最大叶面积指数(LAI)、参考年NPP (BEPS模型模拟)、林龄、森林类型、土地覆盖、数字高程模型(DEM)、土壤质地、CO₂浓度、氮沉降等多源数据, 利用InTEC模型(Integrated Terrestrial Ecosystem Carbon-budget Model)研究亚热带典型地区江西省森林生态系统1901-2010年NPP时空动态变化特征, 通过模拟情景设计, 着重讨论1970-2010年气候变化、林龄、CO₂浓度和氮沉降对森林NPP动态变化的影响。研究结果如下: (1) InTEC模型能较好地模拟研究区NPP的时空变化; (2)江西省森林NPP 1901-2010年为(47.7 ± 4.2) Tg C·a^-1 (平均值±标准偏差), 其中20世纪70年代、80年代、90年代分别为50.7、48.8、45.4 Tg C·a^-1, 2000-2009年平均为55.2 Tg C·a^-1; 随着森林干扰后的恢复再生长, 江西省森林NPP显著上升, 2000-2009年NPP增加的森林面积占森林总面积的60%; (3) 1970-2010年, 仅考虑森林干扰因子和仅考虑非干扰因子(气候、氮沉降、CO₂浓度)情景下NPP分别为43.1和53.9 Tg C·a^-1, 比综合考虑干扰因子和非干扰因子作用下的NPP分别低估7.3 Tg C·a^-1 (低估的NPP与综合考虑干扰因子和非干扰因子作用下NPP的比值为14.5%,下同)和高估3.6 Tg C·a^-1 (7.1%); 气候因子导致平均NPP减少2.0 Tg C·a^-1 (4.7%), 氮沉降导致平均NPP增加4.5 Tg C·a^-1 (10.4%), CO₂浓度变化及耦合效应(氮沉降+ CO₂浓度变化)分别导致平均NPP增加4.4 Tg C·a^-1 (10.3%)和9.4 Tg C·a^-1 (21.8%)。     

Litter type and soil minerals control temperate forest soil carbon response to climate change

Temperate forest soil organic carbon (C) represents a significant pool of terrestrial C that may be released to the atmosphere as CO₂ with predicted changes in climate. To address potential feedbacks between climate change and terrestrial C turnover, we quantified forest soil C response to litter type and temperature change as a function of soil parent material. We collected soils from three conifer forests dominated by ponderosa pine (PP; Pinus ponderosa Laws.); white fir [WF; Abies concolor (Gord. and Glend.) Lindl.]; and red fir (RF; Abies magnifica A. Murr.) from each of three parent materials, granite (GR), basalt (BS), and andesite (AN) in the Sierra Nevada of California. Field soils were incubated at their mean annual soil temperature (MAST), with addition of native ¹³C‐labeled litter to characterize soil C mineralization under native climate conditions. Further, we incubated WF soils at PP MAST with ¹³C‐labeled PP litter, and RF soils at WF MAST with ¹³C‐labeled WF litter to simulate a migration of MAST and litter type, and associated change in litter quality, up‐elevation in response to predicted climate warming. Results indicated that total CO₂ and percent of CO₂ derived from soil C varied significantly by parent material, following the pattern of GR>BS>AN. Regression analyses indicated interactive control of C mineralization by litter type and soil minerals. Soils with high short‐range‐order (SRO) mineral content exhibited little response to varying litter type, whereas PP litter enriched in acid‐soluble components promoted a substantial increase of extant soil C mineralization in soils of low SRO mineral content. Climate change conditions increased soil C mineralization greater than 200% in WF forest soils. In contrast, little to no change in soil C mineralization was noted for the RF forest soils, suggesting an ecosystem‐specific climate change response. The climate change response varied by parent material, where AN soils exhibited minimal change and GR and BS soils mineralized substantially greater soil C. This study corroborates the varied response in soil C mineralization by parent material and highlights how the soil mineral assemblage and litter type may interact to control conifer forest soil C response to climate change.     

Expanding forests and changing growth forms of Siberian larch at the Polar Urals treeline during the 20th century

The ongoing climatic changes potentially affect plant growth and the functioning of temperature‐limited high‐altitude and high‐latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest–tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright‐growing trees are <80 years old. Because thousands of more than 500‐year‐old subfossil trees occur in the same area but tree remnants of the 15–19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree‐free tundra during the last century by about 20–60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi‐stem tree clusters, 90% of the trees emerging after 1950 were single‐stemmed. Tree‐ring analysis of horizontal and vertical stems of multi‐stemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5–20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above‐ and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40–75 t ha^?1 and a carbon accumulation of approximately 20–40 g C m^?2 yr^?1 during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 °C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals.     

Why is the South Orkney Island shelf (the world's first high seas marine protected area) a carbon immobilization hotspot?

The Southern Ocean archipelago, the South Orkney Islands (SOI), became the world's first entirely high seas marine protected area (MPA) in 2010. The SOI continental shelf (~44 000 km²), was less than half covered by grounded ice sheet during glaciations, is biologically rich and a key area of both sea surface warming and sea‐ice losses. Little was known of the carbon cycle there, but recent work showed it was a very important site of carbon immobilization (net annual carbon accumulation) by benthos, one of the few demonstrable negative feedbacks to climate change. Carbon immobilization by SOI bryozoans was higher, per species, unit area and ice‐free day, than anywhere‐else polar. Here, we investigate why carbon immobilization has been so high at SOI, and whether this is due to high density, longevity or high annual production in six study species of bryozoans (benthic suspension feeders). We compared benthic carbon immobilization across major regions around West Antarctica with sea‐ice and primary production, from remotely sensed and directly sampled sources. Lowest carbon immobilization was at the northernmost study regions (South Georgia) and southernmost Amundsen Sea. However, data standardized for age and density showed that only SOI was anomalous (high). High immobilization at SOI was due to very high annual production of bryozoans (rather than high densities or longevity), which were 2x, 3x and 5x higher than on the Bellingshausen, South Georgia and Amundsen shelves, respectively. We found that carbon immobilization correlated to the duration (but not peak or integrated biomass) of phytoplankton blooms, both in directly sampled, local scale data and across regions using remote‐sensed data. The long bloom at SOI seems to drive considerable carbon immobilization, but sea‐ice losses across West Antarctica mean that significant carbon sinks and negative feedbacks to climate change could also develop in the Bellingshausen and Amundsen seas.     

Cheatgrass is favored by warming but not CO2 enrichment in a semi‐arid grassland

Elevated CO₂ and warming may alter terrestrial ecosystems by promoting invasive plants with strong community and ecosystem impacts. Invasive plant responses to elevated CO₂ and warming are difficult to predict, however, because of the many mechanisms involved, including modification of phenology, physiology, and cycling of nitrogen and water. Understanding the relative and interactive importance of these processes requires multifactor experiments under realistic field conditions. Here, we test how free‐air CO₂ enrichment (to 600 ppmv) and infrared warming (+1.5 °C day/3 °C night) influence a functionally and phenologically distinct invasive plant in semi‐arid mixed‐grass prairie. Bromus tectorum (cheatgrass), a fast‐growing Eurasian winter annual grass, increases fire frequency and reduces biological diversity across millions of hectares in western North America. Across 2 years, we found that warming more than tripled B. tectorum biomass and seed production, due to a combination of increased recruitment and increased growth. These results were observed with and without competition from native species, under wet and dry conditions (corresponding with tenfold differences in B. tectorum biomass), and despite the fact that warming reduced soil water. In contrast, elevated CO₂ had little effect on B. tectorum invasion or soil water, while reducing soil and plant nitrogen (N). We conclude that (1) warming may expand B. tectorum's phenological niche, allowing it to more successfully colonize the extensive, invasion‐resistant northern mixed‐grass prairie, and (2) in ecosystems where elevated CO₂ decreases N availability, CO₂ may have limited effects on B. tectorum and other nitrophilic invasive species.     

1 alpha, 25-Dihydroxyvitamin D3 directly induces fusion of alveolar macrophages by a mechanism involving RNA and protein synthesis, but not DNA synthesis

The results of our present study indicate that 1 alpha, 25-dihydroxyvitamin D3[1 alpha, 25(OH)2D3] directly induces fusion of mouse alveolar macrophages without any participation of T-lymphocytes by a mechanism involving RNA and protein synthesis but not DNA synthesis. We have reported that 1 alpha, 25(OH)2D3 induces fusion of alveolar macrophages by a direct mechanism and by a spleen cell-mediated indirect mechanism [(1983) Proc. Natl. Acad. Sci. USA 80, 5583-5587]. Alveolar macrophages pretreated with or without anti-Thy 1.2 antibody and complement fused similarly when they were incubated with 1 alpha, 25(OH)2D3. The vitamin suppressed DNA synthesis, but it significantly enhanced RNA and protein synthesis. The 1 alpha, 25(OH)2D3-induced fusion was blocked by adding actinomycin D or cycloheximide, but not by hydroxyurea.