An alpine treeline in a carbon dioxide-rich world: synthesis of a nine-year free-air carbon dioxide enrichment study

We evaluated the impacts of elevated CO2 in a treeline ecosystem in the Swiss Alps in a 9-year free-air CO2 enrichment (FACE) study. We present new data and synthesize plant and soil results from the entire experimental period. Light-saturated photosynthesis (A max) of ca. 35-year-old Larix decidua and Pinus uncinata was stimulated by elevated CO2 throughout the experiment. Slight down-regulation of photosynthesis in Pinus was consistent with starch accumulation in needle tissue. Above-ground growth responses differed between tree species, with a 33% mean annual stimulation in Larix but no response in Pinus. Species-specific CO2 responses also occurred for abundant dwarf shrub species in the understorey, where Vaccinium myrtillus showed a sustained shoot growth enhancement (+11%) that was not apparent for Vaccinium gaultherioides or Empetrum hermaphroditum. Below ground, CO2 enrichment did not stimulate fine root or mycorrhizal mycelium growth, but increased CO2 effluxes from the soil (+24%) indicated that enhanced C assimilation was partially offset by greater respiratory losses. The dissolved organic C (DOC) concentration in soil solutions was consistently higher under elevated CO2 (+14%), suggesting accelerated soil organic matter turnover. CO2 enrichment hardly affected the C-N balance in plants and soil, with unaltered soil total or mineral N concentrations and little impact on plant leaf N concentration or the stable N isotope ratio. Sustained differences in plant species growth responses suggest future shifts in species composition with atmospheric change. Consistently increased C fixation, soil respiration and DOC production over 9years of CO2 enrichment provide clear evidence for accelerated C cycling with no apparent consequences on the N cycle in this treeline ecosyste

Assembly and Function of a Bioengineered Human Liver for Transplantation Generated Solely from Induced Pluripotent Stem Cells

The availability of an autologous transplantable auxiliary liver would dramatically affect the treatment of liver disease. Assembly and function in vivo of a bioengineered human liver derived from induced pluripotent stem cells (iPSCs) has not been previously described. By improving methods for liver decellularization, recellularization, and differentiation of different liver cellular lineages of human iPSCs in an organ-like environment, we generated functional engineered human mini livers and performed transplantation in a rat model. Whereas previous studies recellularized liver scaffolds largely with rodent hepatocytes, we repopulated not only the parenchyma with human iPSC-hepatocytes but also the vascular system with human iPS-endothelial cells, and the bile duct network with human iPSC-biliary epithelial cells. The regenerated human iPSC-derived mini liver containing multiple cell types was tested in vivo and remained functional for 4 days after auxiliary liver transplantation in immunocompromised, engineered (IL2rg−/−) rats.Fil: Takeishi, Kazuki. University of Pittsburgh; Estados UnidosFil: Collin de I'Hortet, Alexandra. University of Pittsburgh; Estados UnidosFil: Wang, Yang. University of Pittsburgh; Estados UnidosFil: Handa, Kan. University of Pittsburgh; Estados UnidosFil: Guzman Lepe, Jorge. University of Pittsburgh; Estados UnidosFil: Matsubara, Kentaro. University of Pittsburgh; Estados UnidosFil: Morita, Kazutoyo. University of Pittsburgh; Estados UnidosFil: Jang, Sae. University of Pittsburgh; Estados UnidosFil: Haep, Nils. University of Pittsburgh; Estados UnidosFil: Florentino, Rodrigo M.. University of Pittsburgh; Estados UnidosFil: Yuan, Fangchao. University of Pittsburgh; Estados UnidosFil: Fukumitsu, Ken. University of Pittsburgh; Estados UnidosFil: Tobita, Kimimasa. University of Pittsburgh; Estados UnidosFil: Sun, Wendell. University of Pittsburgh; Estados UnidosFil: Franks, Jonathan. University of Pittsburgh; Estados UnidosFil: Delgado, Evan R.. University of Pittsburgh; Estados UnidosFil: Shapiro, Erik M.. University of Pittsburgh; Estados UnidosFil: Fraunhoffer Navarro, Nicolas Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Centro de Estudios Farmacológicos y Botánicos. Universidad de Buenos Aires. Facultad de Medicina. Centro de Estudios Farmacológicos y Botánicos; ArgentinaFil: Duncan, Andrew W.. University of Pittsburgh; Estados UnidosFil: Yagi, Hiroshi. University of Pittsburgh; Estados UnidosFil: Mashimo, Tomoji. University of Pittsburgh; Estados UnidosFil: Fox, Ira J.. University of Pittsburgh; Estados UnidosFil: Soto Gutierrez, Alejandro. University of Pittsburgh; Estados Unido

Tree and ecosystem responses to four years of in situ CO2 enrichment at the Swiss treeline

Following four years of CO2 enrichment (2001-2004) of trees and their understory dwarf heath, and a one-time tree defoliation treatment in the spring of the second year at the Swiss treeline FACE site on Stillberg (Davos, Switzerland), this dissertation summarizes responses from both the above- and below-ground components of this treeline ecosystem. At the tree physiological level (Handa et al. 2005, chapter 2), we found that elevated CO2 enhanced photosynthesis in both Larix decidua and Pinus uncinata by ca. 40% and led to increased nonstructural carbohydrate concentrations in the needles of both species, but to no significant decrease in stomatal conductance. There was no evidence for photosynthetic downregulation in either of the conifer species. Irrespective of CO2 concentration, defoliation in both species stimulated photosynthesis (Larix, +7 %; Pinus +52%) and increased stomatal conductance (Larix, +42%; Pinus, +108%) in remaining current-year needles in the treatment year and reduced leaf nitrogen concentration (-11% in Larix only) in the year following defoliation. These results are by and large consistent with what has been observed in multiple other CO2 enrichment experiments to date (Ceulemans et al. 1999, Norby et al. 1999, Nowak et al. 2004, Zotz et al. 2005) and the strong physiological effects on the trees from the carbon source removal treatment highlight how an extreme disturbance can impact the tree’s carbon budget. Despite the c. 40% stimulation of photosynthesis in response to CO2 enrichment, this did not translate into carbon that is purely available for growth regardless of whether one looks at the shoot or stem increment growth records for either of the studied tree species. In response to elevated CO2, we observed a consistent positive growth response in Larix evident both in the annual shoot increment record (c. +20-30%; Handa et al. 2005, chapters 2&3) and the stem increment record (+41%; when cumulatively integrated over four years and measured relative to four years of pre-treatment measurements; Handa et al. 2006, chapter 3). The increase in radial stem wood growth was the result of more latewood production, in particular, the formation of larger tracheids, rather than a greater number of cells. In contrast, both of these lines of evidence (shoot and stem increment record) showed no positive growth response of Pinus trees, with the exception of the very first year of shoot increment data (Hättenschwiler et al. 2002, chapter 5). Our studies underline, yet again, how CO2 effects on plants show strong species specificity (Loehle 1995), and how any meaningful study attempting to address ecosystem responses, must consider all its key players and account for species diversity (Körner et al. 2005). Defoliation led to a pronounced decrease in annual ring width of both species, marked in particular by less latewood production in the treatment as well as subsequent year, underlining again the importance of how a biotic interaction within the system might completely modify ecosystem responses in a changing global environment (Zvereva & Kozlov 2006). Plants are frequently observed to increase carbon allocation to below-ground sinks and particularly, to accelerate fine root turnover in response to elevated CO2 concentration. Our study shows that in this natural system, no change in response to elevated CO2 exposure occurred. There was no difference in total root standing crop after four years, in new root production measured over three years and also no effect on root decomposition measured over 26 months (Handa et al. 2008, chapter 4). The lack of positive growth response below-ground contrasts with the sustained four year aboveground growth response of Larix decidua, but is in line with the lack of positive aboveground growth response of the later successional Pinus uncinata trees and that of some of the understory dwarf shrubs (Zumbrunn 2004). Multiple studies have reported positive root growth responses to elevated CO2 concentrations, although very few have been conducted in the field, have exceeded a study duration >1 year or have used mature trees (Norby & Jackson 2000, Tingey et al. 2000). Root quality measurements indicated that elevated CO2 significantly increased starch concentration, but there was no change in N concentration or in dehydrogenase activity. Other studies have also shown higher starch concentration (Janssens et al. 1998), but also lower N content in roots under elevated CO2 (Janssens et al. 1998, Pregitzer et al. 2000, Wan et al. 2004). However, this result is certainly not ubiquitous (Tingey et al. 2003, King et al. 2005). Finally, our stable isotope data indicate that only ca. 30% of the new carbon was incorporated into new roots indicating a rather slow root turnover in this system

Springtail community structure is influenced by functional traits but not biogeographic origin of leaf litter in soils of novel forest ecosystems

With ongoing global change, shifts in the ranges of non-native species and resulting novel communities can modify biotic interactions and ecosystem processes. We hypothesized that traits and not biogeographic origin of novel plant communities will determine community structure of organisms that depend on plants for habitat or as a food resource. We tested the functional redundancy of novel tree communities by verifying if six pairs of congeneric European and North American tree species bearing similar leaf litter traits resulted in similar ecological filters influencing the assembly of springtail (Collembola) communities at two sites. Litter biogeographic origin (native versus non-native) did not influence springtail community structure, but litter genus, which generally reflected trait differences, did. Our empirical evidence suggests that a functional trait approach may be indeed as relevant as, and complementary to, studying biogeographic origin to understand the ecological consequences of non-native tree species in soils of novel forest ecosystems

The importance of litter traits and decomposers for litter decomposition: a comparison of aquatic and terrestrial ecosystems within and across biomes

1. Plant leaf litter comprises the major common source of energy and nutrients in forested soil and freshwater ecosystems world-wide. However, despite the similarity of physical and biochemical processes, generalizations across aquatic and terrestrial ecosystems regarding litter decomposition drivers remain elusive. 2. We re-analysed data from a published field decomposition experiment conducted in two ecosystems (forest floors and streams) across five biomes (from the tropics to subarctic) with increasing decomposer community complexity (microbes, microbes and mesofauna, microbes and meso- and macrofauna). 3. Using a wide litter quality gradient (15 litter combinations), we aimed to disentangle the roles of decomposer community complexity from that of leaf litter traits (18 traits encompassing four broad trait categories: nutrients, C quality, physical structure and stoichiometry) on litter C and N loss. Comparisons of decomposition drivers between ecosystems were evaluated across and within biomes. 4. Differences in environmental conditions (e.g. climate, soil/water fertility) and litter nutrients – with a particular focus on Mg and Ca – across biomes were the major drivers of litter C loss in both ecosystems, but decomposer complexity also played a prominent role in streams. Within biomes, we observed consistent effects of litter nutrients and stoichiometry on litter C and N loss between ecosystems, but the effects of decomposer complexity differed between streams and forest floors in the temperate, Mediterranean and tropical biomes. 5. Our results highlight that, beyond the litter traits commonly identified as controlling decomposition (e.g. C, N and lignin), micronutrients (e.g. Mg and Ca) can also play an important, and globally consistent, role in both aquatic and terrestrial ecosystems. In addition, in forest streams the complexity of decomposer communities had similar importance as litter traits for predicting litter C and N turnover across all five biomes. 6. The identification of common drivers in our large-scale ecosystem comparison suggests a basis to develop common models across aquatic and terrestrial ecosystems for C and N dynamics during decomposition. Future modelling efforts should account for the global similarities (litter micronutrient effects) and biome-level differences (contingent decomposer effects) found between ecosystems.This study was funded by the ‘BioCycle’ research project (part of the ESF EUROCORES programme EuroDIVERSITY). BioCycle was endorsed by DIVERSITAS as contributing towards current scientific research priorities in biodiversity science. PGP was funded by the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n°DECOMFORECO-2011-299214.Peer reviewe

Forest Tent Caterpillar Outbreaks Drive Change in Ant Communities in Boreal Forests

Insect outbreaks are major drivers of natural disturbances in forest ecosystems. Outbreaks can have both direct and indirect effects on the composition of soil arthropod communities through canopy opening, nutrient addition and predator-prey interactions. In this study, we aimed to understand the effects of forest tent caterpillar (Malacosoma disstria; FTC) outbreaks through cascading effects on ant communities in both temperate and boreal forests in Canada. Pitfall traps and Berlese funnels were used to compare the ant communities, as well as the surrounding arthropod communities, between control and outbreak sites in boreal and temperate forests (in Quebec, Canada). Using the Sørensen dissimilarity index, we determined the alpha and beta diversity of the ant community. Other arthropods collected in the traps were counted to evaluate the richness and abundance of potential prey for the ants and other potential predators of the FTC. We used an indicator species analysis to examine the species associated with sites defoliated by the outbreak. In the boreal forest, we found that FTC outbreaks caused decreases in species richness and increases in the evenness of ant communities in defoliated sites. In the boreal forest sites, species composition varied significantly between control and outbreak sites. This pattern was driven in part by the presence of other predators. A similar, but weaker pattern was observed in the temperate forest. We saw no changes in the beta diversity in the boreal forest, but did see a significant decrease in the temperate forest between the outbreak sites and the control sites. Ant species in the boreal forest tended to exhibit a more marked preference for either control or previously defoliated sites than species in the temperate forest. Our study showed that disturbances such as insect outbreaks can drive changes in the ant community. While we saw small effects of outbreaks, manipulation experiments using resource addition could help us validate the mechanisms behind these relationships

Data from: Decomposition of leaf litter mixtures across biomes: The role of litter identity, diversity and soil fauna

1. At broad spatial scales, the factors regulating litter decomposition remain ambiguous, with the understanding of these factors largely based on studies investigating site-specific single litter species, whereas studies using multi litter species mixtures across sites are rare. 2. We exposed in microcosms containing single species and all possible mixtures of four leaf litter species differing widely in initial chemical and physical characteristics from a temperate forest to the climatic conditions of four different forests across the northern hemisphere for one year. 3. Calcium, magnesium and condensed tannins predicted litter mass loss of single litter species and mixtures across forest types and biomes, regardless of species richness and microarthropod presence. However, relative mixture effects differed among forest types and varied with the access to the litter by microarthropods. Access to the microcosms by microarthropods modified the decomposition of individual litter species within mixtures, which differed among forest types independent of litter species richness and composition of litter mixtures. However, soil microarthropods generally only little affected litter decomposition. 4. Synthesis. We conclude that litter identity is the dominant driver of decomposition across different forest types and the non-additive litter mixture effects vary among biomes despite identical leaf litter chemistry. These results suggest that across large spatial scales the environmental context of decomposing litter mixtures, including microarthropod communities, determine the decomposition of litter mixtures besides strong litter trait based effects

Decomposition of leaf litter mixtures across biomes : The role of litter identity, diversity and soil fauna

At broad spatial scales, the factors regulating litter decomposition remain ambiguous, with the understanding of these factors largely based on studies investigating site-specific single litter species, whereas studies using multi litter species mixtures across sites are rare. We exposed in microcosms containing single species and all possible mixtures of four leaf litter species differing widely in initial chemical and physical characteristics from a temperate forest to the climatic conditions of four different forests across the Northern Hemisphere for 1 year. Calcium, magnesium and condensed tannins predicted litter mass loss of single litter species and mixtures across forest types and biomes, regardless of species richness and microarthropod presence. However, relative mixture effects differed among forest types and varied with the access to the litter by microarthropods. Access to the microcosms by microarthropods modified the decomposition of individual litter species within mixtures, which differed among forest types independent of litter species richness and composition of litter mixtures. However, soil microarthropods generally only little affected litter decomposition. Synthesis. We conclude that litter identity is the dominant driver of decomposition across different forest types and the non-additive litter mixture effects vary among biomes despite identical leaf litter chemistry. These results suggest that across large spatial scales the environmental context of decomposing litter mixtures, including microarthropod communities, determine the decomposition of litter mixtures besides strong litter trait-based effects