Abstracts on Global Climate Change

Apr 2005

Multi-scale observation and cross-scale mechanistic modeling on terrestrial ecosystem carbon cycle

Cao, MK Yu, GR Liu, JY Li, KR


To predict global climate change and to implement the Kyoto Protocol for stabilizing atmospheric greenhouse gases concentrations require quantifying spatio-temporal variations in the terrestrial carbon sink accurately. During the past decade multi-scale ecological experiment and observation networks have been established using various new technologies (e.g. controlled environmental facilities, eddy covariance techniques and quantitative remote sensing), and have obtained a large amount of data about terrestrial ecosystem carbon cycle. However, uncertainties in the magnitude and spatio-temporal variations of the terrestrial carbon sink and in understanding the underlying mechanisms have not been reduced significantly. One of the major reasons is that the observations and experiments were conducted at individual scales independently, but it is the interactions of factors and processes at different scales that determine the dynamics of the terrestrial carbon sink. Since experiments and observations are always conducted at specific scales, to understand cross-scale interactions requires mechanistic analysis that is best to be achieved by mechanistic modeling. However, mechanistic ecosystem models are mainly based on data from single-scale experiments and observations and hence have no capacity to simulate mechanistic cross-scale interconnection and interactions of ecosystem processes. New-generation mechanistic ecosystem models based on new ecological theoretical framework are needed to quantify the mechanisms from micro-level fast eco-physiological responses to macro-level slow acclimation in the pattern and structure in disturbed ecosystems. Multi-scale data-model fusion is a recently emerging approach to assimilate multi-scale observational data into mechanistic, dynamic modeling, in which the structure and parameters of mechanistic models for simulating cross-scale interactions are optimized using multi-scale observational data. The models are validated and evaluated at different spatial and temporal scales and real-time observational data are assimilated continuously into dynamic modeling for predicting and forecasting ecosystem changes realistically. In summary, a breakthrough in terrestrial carbon sink research requires using approaches of multi-scale observations and cross-scale modeling to understand and quantify interconnections and interactions among ecosystem processes at different scales and their controls over ecosystem carbon cycle.

timlambert:methods | /neutral/methods | 363

Leaf mineral nutrition of Arctic plants in response to warming and deeper snow in northern Alaska

Welker, JM Fahnestock, JT Sullivan, PF Chimner, RA

OIKOS 109:1 167-177

Articulating the consequences of global climate change on terrestrial ecosystem biogeochemistry is a critical component of Arctic system studies. Leaf mineral nutrition responses of tundra plants is an important measure of changes in organismic and ecosystem attributes because leaf nitrogen and carbon contents effect photosynthesis, primary production, carbon budgets, leaf litter, and soil organic matter decomposition as well as herbivore forage quality. In this study, we used a long term experiment where snow depth and summer temperatures were increased independently and together to articulate how a series of climate change scenarios would affect leaf N, leaf C, and leaf C: N for vegetation in dry and moist tussock tundra in northern Alaska, USA. Our findings were: 1) moist tundra vegetation is much more responsive to this suite of climate change scenarios than dry tundra with up to a 25% increase in leaf N; 2) life forms exhibit divergence in leaf C, N, and C:N with deciduous shrubs and graminoids having almost identical leaf N contents; 3) for some species, leaf mineral nutrition responses to these climate change scenarios are tundra type dependent (Betula), but for others (Vaccinium vitis-idaea), strong responses are exhibited regardless of tundra type; and 4) the seasonal patterns and magnitudes of leaf C and leaf N in deciduous and evergreen shrubs were responsive to conditions of deeper snow in winter. Leaf N is was generally higher immediately after emergence from the deep snow experimental treatments and leaf N was higher during the subsequent summer and fall, and the leaf C:N were lower, especially in deciduous shrubs. These findings indicate that coupled increases in snow depth and warmer summer temperatures will alter the magnitudes and patterns of leaf mineral nutrition and that the longterm consequences of these changes may feed-forward and affect ecosystem processes.

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Gaia’s breath - global methane exhalations

Kvenvolden, KA Rogers, BW


Methane (CH4) is the most abundant organic compound in the Earth’s atmosphere, where it acts as a greenhouse gas and thus has implications for global climate change. The current atmospheric CH4 budget, however, does not take into account geologically-sourced CH4 seepage. Geological sources of CH4 include natural macro- and micro-seeps, mud volcanoes, and other miscellaneous sources such as gas hydrates, magmatic volcanoes, geothermal regions, and mid-ocean ridges. Macro-seeps contribute similar to 25 Tg (teragrams) CH4/yr to the atmosphere, whereas, micro-seepage contributes perhaps 7 Tg CH4/yr. Mud volcanoes emit similar to 5 Tg CH4/yr, and miscellaneous sources emit similar to 8 Tg CH4/yr to the atmosphere. Thus, the total contribution to the atmosphere from geological sources is estimated to be 45 Tg CH4/yr, which is significant to the atmospheric organic carbon cycle and should be included in any global inventory of atmospheric CH4. We argue that the atmospheric CH4 global inventory of the Interplanetary Panel on Climate Change must be adjusted in order to incorporate geologically-sourced CH4 from naturally occurring seepage. Published by Elsevier Ltd.

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Denitrification and N2O emission from forested and cultivated alluvial clay soil

Ullah, S Breitenbeck, GA Faulkner, SP


Restored forested wetlands reduce N loads in surface discharge through plant uptake and denitrification. While removal of reactive N reduces impact on receiving waters, it is unclear whether enhanced denitrification also enhances emissions of the ‘greenhouse’ gas N2O, thus compromising the water-quality benefits of restoration. This Study compares denitrification rates and N2O:N-2 emission ratios from Sharkey clay soil in a mature bottomland forest to those from all adjacent cultivated site in the Lower Mississippi Alluvial Valley. Potential denitrification of forested soil was 2.4 times of cultivated soil. Using intact soil cores, denitrification rates of forested soil were 5.2, 6.6 and 2.0 times those of cultivated soil at 70, 85 and 100% water-filled pore space (WFPS), respectively. When NO3 was added, N2O emissions from forested soil were 2.2 times those of cultivated soil at 70% WFPS. At 85 and 100% WFPS, N2O emissions were not significantly different despite much greater denitrification rates in the forested soil because N2O:N-2 emission ratios declined more rapidly in forested soil as WFPS increased. These findings suggest that restoration of forested wetlands to reduce NO3 in surface discharge will not contribute significantly to the atmospheric burden of N2O.

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Coevolution and biogeography among Nematodirinae (Nematoda : Trichostrongylina) Lagomorpha and Artiodactyla (Mammalia): Exploring determinants of history and structure for the northern fauna across the Holarctic

Hoberg, EP


Nematodes of the subfamily Nematodirinae are characteristic components of a Holarctic fauna. The topology of a generic-level phylogenetic hypothesis, patterns of diversity. and geographic distributions for respective nematode taxa in conjunction with data for host occurrence are consistent with primary distributions determined across Beringia for species of Murielus, Rauschia, Nematodirus, and Nematodirella. Ancestral hosts are represented by Lagomorpha, with evidence for a minimum of 1 host-switching-event and subsequent radiation in the Artiodactyla. Diversification may reflect vicariance of respective faunas along with episodic or cyclical range expansion and isolation across Beringia during the late Tertiary and Quaternary. Secondarily, species of Nematodirus attained a distribution in the Neotropical region with minimal diversification of an endemic fauna represented by Nematodirus molini among tayassuids, Nematodirus lamae among camelids and Nematodirus urichi in cervids during the Pleistocene. Nematodirines are a core component of an Arctic-Boreal fauna of zooparasitic nematodes (defined by latitude and altitude) adapted to transmission in extreme environments characterized by seasonally low temperatures and varying degrees of desiccation. The history and distribution of this fauna is examined in the context of biotic and abiotic determinants for geographic colonization and host switching with an exploration of predicted responses of complex host-parasite systems to ecological perturbation under a regime of global climate change.

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Variation in leaf litter nutrients of a Costa Rican rain forest is related to precipitation

Wood, TE Lawrence, D Clark, DA


By assessing current leaf litter nutrient dynamics, we may be able to predict responses of nutrient cycling in tropical ecosystems to future environmental change. The goal of this study was to assess whether nutrient cycling is related to seasonal variation in rainfall in a wet tropical forest. We examined leaf litter of an old-growth tropical rain forest in N.E. Costa Rica over a 4-year period to explore seasonal and inter-annual changes in leaf litter nutrient concentrations, and to evaluate potential short- and long-term drivers of variation in litter nutrient concentration, particularly that of phosphorus (P) and nitrogen (N). We also examined the temporal dynamics of calcium, potassium, and magnesium in the leaf litter. Leaf litter [P] and %N changed significantly with time, both seasonally and inter-annually. Seasonal changes in leaf litter [P] were strongly positively correlated with rainfall from the previous 2 weeks; cations, however, were inversely related to this measure of current rainfall, while %N was not related to rainfall. We propose that the positive relationship between current rainfall and leaf litter [P] is due to a response by the vegetation to an increase in nutrient availability and uptake. In contrast, given the negative relationship between current rainfall and cation concentrations, leaching from live leaf tissue is a more likely driver of short-term changes in cations. Should global climate change include altered rainfall patterns in this biome, one class of ecosystem-level responses could be significant changes in P and cation cycling.

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Improved scheme for determining the thermal centroid of the oceanic warm pool using sea surface temperature data

Chen, G Fang, LX


During the past two decades, concern about the western Pacific Warm Pool (WP) has been growing following the recognition of its significant role in global climate change and its close association with El Nino-Southern Oscillation phenomena. A fundamental issue in WP related studies is to locate its centroid and track its trajectory. The method used by some previous researchers for estimating the WP position seems to oversimplify the problem to a purely geometric one. This, however, is found to be systematically biased in both zonal and meridional directions. A new scheme for determining the WP centroid, which takes into account the thermal structure of the surface water, is proposed, resulting in a significant improvement in precise tracking of the WP trajectory compared to previous results.

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Decomposition of soybean grown under elevated concentrations of CO2 and O-3

Booker, FL Prior, SA Torbert, HA Fiscus, EL Pursley, WA Hu, SJ


A critical global climate change issue is how increasing concentrations of atmospheric CO2 and ground-level O-3 will affect agricultural productivity. This includes effects on decomposition of residues left in the field and availability of mineral nutrients to subsequent crops. To address questions about decomposition processes, a 2-year experiment was conducted to determine the chemistry and decomposition rate of aboveground residues of soybean (Glycine max (L.) Merr.) grown under reciprocal combinations of low and high concentrations of CO2 and O-3 in open-top field chambers. The CO2 treatments were ambient (370 mu mol mol(-1)) and elevated (714 mu mol mol(-1)) levels (daytime 12 h averages). Ozone treatments were charcoal-filtered air (21 nmol mol(-1)) and nonfiltered air plus 1.5 times ambient O-3 (74 nmol mol(-1)) 12 h day(-1). Elevated CO2 increased aboveground postharvest residue production by 28-56% while elevated O-3 suppressed it by 15-46%. In combination, inhibitory effects of added O-3 on biomass production were largely negated by elevated CO2. Plant residue chemistry was generally unaffected by elevated CO2, except for an increase in leaf residue lignin concentration. Leaf residues from the elevated O-3 treatments had lower concentrations of nonstructural carbohydrates, but higher N, fiber, and lignin levels. Chemical composition of petiole, stem, and pod husk residues was only marginally affected by the elevated gas treatments. Treatment effects on plant biomass production, however, influenced the content of chemical constituents on an areal basis. Elevated CO2 increased the mass per square meter of nonstructural carbohydrates, phenolics, N, cellulose, and lignin by 24-46%. Elevated O-3 decreased the mass per square meter of these constituents by 30-48%, while elevated CO2 largely ameliorated the added O-3 effect. Carbon mineralization rates of component residues from the elevated gas treatments were not significantly different from the control. However, N immobilization increased in soils containing petiole and stem residues from the elevated CO2, O-3, and combined gas treatments. Mass loss of decomposing leaf residue from the added O-3 and combined gas treatments was 48% less than the control treatment after 20 weeks, while differences in decomposition of petiole, stem, and husk residues among treatments were minor. Decreased decomposition of leaf residues was correlated with lower starch and higher lignin levels. However, leaf residues only comprised about 20% of the total residue biomass assayed so treatment effects on mass loss of total aboveground residues were relatively small. The primary influence of elevated atmospheric CO2 and O-3 concentrations on decomposition processes is apt to arise from effects on residue mass input, which is increased by elevated CO2 and suppressed by O-3.

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