Browsing by Author "Ellsworth, David S"

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    Fire Affects Ecophysiology and Community Dynamics of Central Wisconsin Oak Forest Regeneration
    (1990) Reich, Peter B; Abrams, Marc D; Ellsworth, David S; Kruger, Eric L; Tabone, Tom J
    In order to understand better the ecophysiological differences among competing species that might influence competitive interactions after, or in the absence of, fire, we examined the response to fire of four sympatric woody species found in intermediatesized gaps in a 30-yr-old mixed-oak forest in central Wisconsin. Selected blocks in the forest were burned in April 1987 by a low-intensity controlled surface fire. The fire had significant effects during the following growing season on community structure, foliar nutrient concentrations, and photosynthesis. Acer rubrum seedling density declined by 70% following the fire, while percent cover increased several-fold in Rubus allegheniensis. In general, leaf concentrations of N, P, and K were increased by the fire in all species, although the relative enhancement decreased as the growing season progressed. Daily maximum photosynthetic rates were 30-50% higher in burned than unburned sites for Prunus serotina, Quercus ellipsoidalis, and R. allegheniensis, but did not differ between treatments for A. rubrum. Mean sunlit photosynthetic rates and leaf conductances were stimulated by the burn for all species, with the greatest enhancement in photosynthesis measured in Q. ellipsoidalis. Leaf gas exchange in R. allegheniensis was most sensitive to declining leaf water potential and elevated vapor pressure gradient, with Q. ellipsoidalis the least sensitive. Fire had no discernable effect on water status of these plants during a year of relatively high rainfall. In comparison with other species, A. rubrum seedlings responded negatively after fire-both in terms of survival/reproduction (decline in the number of individuals) and relative leaf physiological performance. Fire enhanced the abundance of R. allegheniensis and the potential photosynthetic performance of R. allegheniensis, P. serotina, and particularly Q. ellipsoidalis. We conclude that post-fire stimulation of net photosynthesis and conductance was largely the result of enhanced leaf N concentrations in these species.
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    From tropics to tundra: global convergence in plant functioning
    (National Academy of Sciences, 1997) Reich, Peter B; Walters, Michael B; Ellsworth, David S
    Methylation of cytosines in the dinucleotide CpG has been shown to suppress transcription of a number of tissue-specific genes, yet the precise mechanism is not fully understood. The vertebrate globin genes were among the first examples in which an inverse correlation was shown between CpG methylation and transcription. We studied the methylation pattern of the 235-bp ρ-globin gene promoter in genomic DNA from primary chicken erythroid cells using the sodium bisulfite conversion technique and found all CpGs in the promoter to be methylated in erythroid cells from adult chickens in which the ρ-globin gene is silent but unmethylated in 5-day (primitive) embryonic red cells in which the gene is transcribed. To elucidate further the mechanism of methylation-induced silencing, an expression construct consisting of 235 bp of 5′ promoter sequence of the ρ-globin gene along with a strong 5′ erythroid enhancer driving a chloramphenicol acetyltransferase reporter gene, ρ-CAT, was transfected into primary avian erythroid cells derived from 5-day embryos. Methylation of just the 235-bp ρ-globin gene promoter fragment at every CpG resulted in a 20- to 30-fold inhibition of transcription, and this effect was not overridden by the presence of potent erythroid-specific enhancers. The ability of the 235-bp ρ-globin gene promoter to bind to a DNA Methyl Cytosine binding Protein Complex (MeCPC) was tested in electrophoretic mobility shift assays utilizing primary avian erythroid cell nuclear extract. The results were that fully methylated but not unmethylated 235-bp ρ-globin gene promoter fragment could compete efficiently for MeCPC binding. These results are a direct demonstration that site-specific methylation of a globin gene promoter at the exact CpGs that are methylated in vivo can silence transcription in homologous primary erythroid cells. Further, these data implicate binding of MeCPC to the promoter in the mechanism of silencing.
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    Generality of leaf traits relationships: a test across six biomes
    (Ecological Society of America, 1999) Reich, Peter B; Ellsworth, David S; Walters, Michael B; Vose, James M; Gresham, Charles; Volin, John C; Bowman, William D
    Convergence in interspecific leaf trait relationships across diverse taxonomic groups and biomes would have important evolutionary and ecological implications. Such convergence has been hypothesized to result from trade-offs that limit the combination of plant traits for any species. Here we address this issue by testing for biome differences in the slope and intercept of interspecific relationships among leaf traits: longevity, net photosynthetic capacity (Amax), leaf diffusive conductance (Gs), specific leaf area (SLA), and nitrogen (N) status, for more than 100 species in six distinct biomes of the Americas. The six biomes were: alpine tundra–subalpine forest ecotone, cold temperate forest–prairie ecotone, montane cool temperate forest, desert shrubland, subtropical forest, and tropical rain forest. Despite large differences in climate and evolutionary history, in all biomes mass-based leaf N (Nmass), SLA, Gs, and Amax were positively related to one another and decreased with increasing leaf life span. The relationships between pairs of leaf traits exhibited similar slopes among biomes, suggesting a predictable set of scaling relationships among key leaf morphological, chemical, and metabolic traits that are replicated globally among terrestrial ecosystems regardless of biome or vegetation type. However, the intercept (i.e., the overall elevation of regression lines) of relationships between pairs of leaf traits usually differed among biomes. With increasing aridity across sites, species had greater Amax for a given level of Gs and lower SLA for any given leaf life span. Using principal components analysis, most variation among species was explained by an axis related to mass-based leaf traits (Amax, N, and SLA) while a second axis reflected climate, Gs, and other area-based leaf traits.
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    Nitrogen limitation constrains sustainability of ecosystem response to CO2
    (Nature Publishing Group, 2006) Reich, Peter B; Hobbie, Sarah E; Lee, Tali; Ellsworth, David S; West, Jason B; Tilman, David; Knops, Johannes M H; Naeem, Shahid; Trost, Jared
    Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming. However, it is unknown whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen (N) availability constrains greater plant growth in a CO2-enriched world1, 2, 3, 4, 5, 6, 7, 8, 9. Here we show, after a six-year field study of perennial grassland species grown under ambient and elevated levels of CO2 and N, that low availability of N progressively suppresses the positive response of plant biomass to elevated CO2. Initially, the stimulation of total plant biomass by elevated CO2 was no greater at enriched than at ambient N supply. After four to six years, however, elevated CO2 stimulated plant biomass much less under ambient than enriched N supply. This response was consistent with the temporally divergent effects of elevated CO2 on soil and plant N dynamics at differing levels of N supply. Our results indicate that variability in availability of soil N and deposition of atmospheric N are both likely to influence the response of plant biomass accumulation to elevated atmospheric CO2. Given that limitations to productivity resulting from the insufficient availability of N are widespread in both unmanaged and managed vegetation5, 7, 8, 9, soil N supply is probably an important constraint on global terrestrial responses to elevated CO2.
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    Species and functional group diversity independently influence biomass accumulation and its response to CO2 and N
    (National Academy of Sciences, 2004) Reich, Peter B; Tilman, David; Naeem, Shahid; Ellsworth, David S; Knops, Johannes; Craine, Joseph; Wedin, David; Trost, Jared
    The characteristics of plant assemblages influence ecosystem processes such as biomass accumulation and modulate terrestrial responses to global change factors such as elevated atmospheric CO2 and N deposition, but covariation between species richness (S) and functional group richness (F) among assemblages obscures the specific role of each in these ecosystem responses. In a 4-year study of grassland species grown under ambient and elevated CO2 and N in Minnesota, we experimentally varied plant S and F to assess their independent effects. We show here that at all CO2 and N levels, biomass increased with S, even with F constant at 1 or 4 groups. Likewise, with S at 4, biomass increased as F varied continuously from 1 to 4. The S and F effects were not dependent upon specific species or functional groups or combinations and resulted from complementarity. Biomass increases in response to CO2 and N, moreover, varied with time but were generally larger with increasing S (with F constant) and with increasing F (with S constant). These results indicate that S and F independently influence biomass accumulation and its response to elevated CO2 and N.
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    Why are non-photosynthetic tissues generally 13C enriched compared with leaves in C3 plants? Review and synthesis of current hypotheses
    (CSIRO, 2009) Cernusak, Lucas A; Tcherkez, Guillaume; Keitel, Claudia; Cornwell, William K; Santiago, Louis S; Knohl, Alexander; Barbour, Margaret M; Williams, David G; Reich, Peter B; Ellsworth, David S; Dawson, Todd E; Griffiths, Howard G; Farquhar, Graham D; Wright, Ian J
    Non-photosynthetic, or heterotrophic, tissues in C3 plants tend to be enriched in 13C compared with the leaves that supply them with photosynthate. This isotopic pattern has been observed for woody stems, roots, seeds and fruits, emerging leaves, and parasitic plants incapable of net CO2 fixation. Unlike in C3 plants, roots of herbaceous C4 plants are generally not 13C-enriched compared with leaves. We review six hypotheses aimed at explaining this isotopic pattern in C3 plants: (1) variation in biochemical composition of heterotrophic tissues compared with leaves; (2) seasonal separation of growth of leaves and heterotrophic tissues, with corresponding variation in photosynthetic discrimination against 13C; (3) differential use of day v. night sucrose between leaves and sink tissues, with day sucrose being relatively 13C-depleted and night sucrose 13C-enriched; (4) isotopic fractionation during dark respiration; (5) carbon fixation by PEP carboxylase; and (6) developmental variation in photosynthetic discrimination against 13C during leaf expansion. Although hypotheses (1) and (2) may contribute to the general pattern, they cannot explain all observations. Some evidence exists in support of hypotheses (3) through to (6), although for hypothesis (6) it is largely circumstantial. Hypothesis (3) provides a promising avenue for future research. Direct tests of these hypotheses should be carried out to provide insight into the mechanisms causing within-plant variation in carbon isotope composition.