The role of canopy structural complexity in wood net primary production of a maturing northern deciduous forest

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117132/1/ecy20119291818.pd

Growth and nitrogen accretion of dinitrogen-fixing Alnus glutinosa (L.) Gaertn. under elevated carbon dioxide

Short-term studies of tree growth at elevated CO 2 suggest that forest productivity may increase as atmospheric CO 2 concentrations rise, although low soil N availability may limit the magnitude of this response. There have been few studies of growth and N 2 fixation by symbiotic N 2 -fixing woody species under elevated CO 2 and the N inputs these plants could provide to forest ecosystems in the future. We investigated the effect of twice ambient CO 2 on growth, tissue N accretion, and N 2 fixation of nodulated Alnus glutinosa (L.) Gaertn. grown under low soil N conditions for 160 d. Root, nodule, stem, and leaf dry weight (DW) and N accretion increased significantly in response to elevated CO 2 . Whole-plant biomass and N accretion increased 54% and 40%, respectively. Delta- 15 N analysis of leaf tissue indicated that plants from both treatments derived similar proportions of their total N from symbiotic fixation suggesting that elevated CO 2 grown plants fixed approximately 40% more N than did ambient CO 2 grown plants. Leaves from both CO 2 treatments showed similar relative declines in leaf N content prior to autumnal leaf abscission, but total N in leaf litter increased 24% in elevated compared to ambient CO 2 grown plants. These results suggest that with rising atmospheric CO 2 N 2 -fixing woody species will accumulate greater amounts of biomass N through N 2 fixation and may enhance soil N levels by increased litter N inputs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43880/1/11258_2004_Article_127613.pd

Observations of stem water storage in trees of opposing hydraulic strategies

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116368/1/ecs2201569165.pd

Sustained carbon uptake and storage following moderate disturbance in a Great Lakes forest

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117030/1/eap20132351202.pd

Contrasting strategies of hydraulic control in two codominant temperate tree species

Biophysical controls on plant water status exist at the leaf, stem, and root levels. Therefore, we pose that hydraulic strategy is a combination of traits governing water use at each of these three levels. We studied sap flux, stem water storage, stomatal conductance, photosynthesis, and growth of red oaks (Quercus rubra) and red maples (Acer rubrum). These species differ in stomatal hydraulic strategy and xylem architecture and may root at different depths. Stable isotope analysis of xylem water was used to identify root water uptake depth. Oaks were shown to access a deeper water source than maples. During non‐limiting soil moisture conditions, transpiration was greater in maples than in oaks. However, during a soil dry down, transpiration and stem water storage decreased by more than 80% and 28% in maples but only by 31% and 1% in oaks. We suggest that the preferential use of deep water by red oaks allows the species to continue transpiration and growth during soil water limitations. In this case, deeper roots may provide a buffer against drought‐induced mortality. Using 14 years of growth data, we show that maple growth correlates with mean annual soil moisture at 30 cm but oak growth does not. The observed responses of oak and maple to drought were not able to be explained by leaf and xylem physiology alone. We employed the Finite‐difference Ecosystem‐scale Tree Crown Hydrodynamics model version 2 plant hydrodynamics model to demonstrate the influence of root, stem, and leaf controls on tree‐level transpiration. We conclude that all three levels of hydraulic traits are required to define hydraulic strategy.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136732/1/eco1815_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136732/2/eco1815.pd

Response of soil biota to elevated atmospheric CO 2 in poplar model systems

We tested the hypotheses that increased belowground allocation of carbon by hybrid poplar saplings grown under elevated atmospheric CO 2 would increase mass or turnover of soil biota in bulk but not in rhizosphere soil. Hybrid poplar saplings ( Populus × euramericana cv. Eugenei) were grown for 5 months in open-bottom root boxes at the University of Michigan Biological Station in northern, lower Michigan. The experimental design was a randomized-block design with factorial combinations of high or low soil N and ambient (34 Pa) or elevated (69 Pa) CO 2 in five blocks. Rhizosphere microbial biomass carbon was 1.7 times greater in high-than in low-N soil, and did not respond to elevated CO 2 . The density of protozoa did not respond to soil N but increased marginally ( P  < 0.06) under elevated CO 2 . Only in high-N soil did arbuscular mycorrhizal fungi and microarthropods respond to CO 2 . In high-N soil, arbuscular mycorrhizal root mass was twice as great, and extramatrical hyphae were 11% longer in elevated than in ambient CO 2 treatments. Microarthropod density and activity were determined in situ using minirhizotrons. Microarthropod density did not change in response to elevated CO 2 , but in high-N soil, microarthropods were more strongly associated with fine roots under elevated than ambient treatments. Overall, in contrast to the hypotheses, the strongest response to elevated atmospheric CO 2 was in the rhizosphere where (1) unchanged microbial biomass and greater numbers of protozoa ( P  < 0.06) suggested faster bacterial turnover, (2) arbuscular mycorrhizal root length increased, and (3) the number of microarthropods observed on fine roots rose.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42279/1/442-113-2-247_81130247.pd

Characterization of MCF mammary epithelial cells overexpressing the Arylhydrocarbon receptor (AhR)

<p>Abstract</p> <p>Background</p> <p>Recent reports indicate the existence of breast cancer cells expressing very high levels of the Arylhydrocarbon receptor (AhR), a ubiquitous intracellular receptor best known for mediating toxic action of dioxin and related pollutants. Positive correlation between the degree of AhR overexpression and states of increasing transformation of mammary epithelial cells appears to occur in the absence of any exogenous AhR ligands. These observations have raised many questions such as why and how AhR is overexpressed in breast cancer and its physiological roles in the progression to advanced carcinogenic transformation. To address those questions, we hypothesized that AhR overexpression occurs in cells experiencing deficiencies in normally required estrogen receptor (ER) signaling, and the basic role of AhR in such cases is to guide the affected cells to develop orchestrated cellular changes aimed at substituting the normal functions of ER. At the same time, the AhR serves as the mediator of the cell survival program in the absence of ER signaling.</p> <p>Methods</p> <p>We subjected two lines of Michigan Cancer Foundation (MCF) mammary epithelial cells to 3 different types ER interacting agents for a number of passages and followed the changes in the expression of AhR mRNA. The resulting sublines were analyzed for phenotypical changes and unique molecular characteristics.</p> <p>Results</p> <p>MCF10AT1 cells continuously exposed to 17-beta-estradiol (E2) developed sub-lines that show AhR overexpression with the characteristic phenotype of increased proliferation, and distinct resistance to apoptosis. When these chemically selected cell lines were treated with a specific AhR antagonist, 3-methoxy-4-nitroflavone (MNF), both of the above abnormal cellular characteristics disappeared, indicating the pivotal role of AhR in expressing those cellular phenotypes. The most prominent molecular characteristics of these AhR overexpressing MCF cells were found to be overexpression of ErbB2 and COX-2. Furthermore, we could demonstrate that suppression of AhR functions through anti-AhR siRNA or MNF causes the recovery of ERalpha functions.</p> <p>Conclusion</p> <p>One of the main causes for AhR overexpression in these MCF breast cancer cells appears to be the loss of ERalpha functions. This phenomenon is likely to be based on the mutually antagonistic relationship between ER and AhR.</p

Towards an online-coupled chemistry-climate model: evaluation of trace gases and aerosols in COSMO-ART

Peer reviewe

Effects of selected food phytochemicals in reducing the toxic actions of TCDD and p,p′-DDT in U937 macrophages

To assess the effectiveness of selected food phytochemicals in reducing the toxic effects of the environmental toxicants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and p,p′-DDT (DDT), we tested the potencies of auraptene, nobiletin, zerumbone, and (±)-13-hydroxy-10-oxo-trans-11-octadecenoic acid (13-HOA) in reversing the inflammatory action of these toxicants in U937 human macrophages. Using quantitative RT–PCR as the initial screening assay, we identified antagonistic actions of zerumbone and auraptene against the action of TCDD and DDT in up-regulating the mRNA expressions of COX-2 and VEGF. The functional significance of the inhibitory action of zerumbone on COX-2 expression was confirmed by demonstrating its suppression of TCDD-induced activation of COX-2 gene expression in mouse MMDD1 cells. We tested auraptene on DDT-induced reactive oxygen species (ROS) formation in U937 macrophages and found that auraptene is a powerful agent antagonizing this action of DDT. To confirm the significance of these actions of zerumbone and auraptene at the cellular level, we assessed their influence on TCDD-induced apoptosis resistance in intact U937 macrophages and found that they are capable of reversing this action of TCDD. In conclusion, zerumbone and auraptene were identified to be the most effective agents in protecting U937 macrophages from developing these cell toxic effects of TCDD and DDT