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1

Digitale Medien

Nitrogen deposition and atmospheric CO2 interactions on fine root dynamics in temperate forests: a theoretical model analysis (2002)

Rasse, Daniel P.

Oxford, UK : Blackwell Science Ltd

Global change biology 8 (2002), S. 0

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ISSN: 1365-2486

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Energietechnik , Geographie

Notizen: Fine root turnover is a critical component of below-ground forest ecology, which regulates nutrient dynamics, forest net primary productivity, carbon input to soils, and soil respiration. Understanding fine root responses to changing environmental conditions is critical for predicting the productivity and carbon sequestration potential of forest ecosystems during the 21st century. The first objective of this study is to demonstrate that a mechanistic model can realistically simulate spatial and temporal fine root demography in temperate forests on the basis of two hypotheses: (1) absorption of mineral N (N) stimulates the production of new roots, and (2) fine root longevity decreases with increasing N availability. Based on this model, my second objective is to predict fine root responses to changing atmospheric CO2 levels and N deposition rates. To meet these objectives, an extensive description of the N cycle and the new fine root module were implemented in the ASPECTS model. In agreement with a wide body of literature information, the new model predicted: (1) a preferential colonisation by fine roots of the uppermost soil layer, and (2) a flush of fine root growth in the spring. The simulations indicate that fine root biomass will increase in response to elevated CO2 under the double effect of (1) an increase in root longevity due to increased N stress, and (2) larger amounts of assimilates available to the growth of plant tissue due to increased photosynthesis. Although the simulated total fine root biomass increased under both increasing N deposition rates and atmospheric CO2 concentrations, the model predicts that the distribution of fine roots among soil layers will be altered. This suggests that experimental studies must consider the full depth of the root system in order to accurately assess effects of environmental changes on fine root dynamics. The model also suggests that fine root longevity is a plastic parameter, which varied from less than 1 year to more than 3 years depending on forcing values of N deposition rates and atmospheric CO2 concentrations. Finally, the model indicates that the increase in net ecosystem exchange (NEE) and soil respiration in temperate forests under elevated CO2 will be proportional to the amount of available N, with little to no response in low N conditions and up to +28% for both NEE and soil respiration under the highest deposition rate (7.0 g N m−2 y−1).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00481.x

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2

Digitale Medien

Seventeen years of elevated CO2 exposure in a Chesapeake Bay Wetland: sustained but contrasting responses of plant growth and CO2 uptake (2005)

Rasse, Daniel P. ; Peresta, Gary ; Drake, Bert G.

Oxford, UK : Blackwell Science Ltd

Global change biology 11 (2005), S. 0

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ISSN: 1365-2486

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Energietechnik , Geographie

Notizen: Increased atmospheric CO2 concentration (Ca) produces a short-term stimulation of photosynthesis and plant growth across terrestrial ecosystems. However, the long-term response remains uncertain and is thought to depend on environmental constraints. In the longest experiment on natural ecosystem response to elevated Ca, we measured the shoot-density, biomass and net CO2 exchange (NEE) responses to elevated Ca from 1987 to 2003 in a Scirpus olneyi wetland sedge community of the Chesapeake Bay, MD, USA. Measurements were conducted in five replicated open-top chambers per CO2 treatment (ambient and elevated). In addition, unchambered control plots were monitored for shoot density. Responses of daytime NEE, Scirpus plant biomass and shoot density to elevated Ca were positive for any single year of the 17-year period of study. Daytime NEE stimulation by elevated Ca rapidly dropped from 80% at the onset of the experiment to a long-term stimulation average of about 35%. Shoot-density stimulation by elevated Ca increased linearly with duration of exposure (r2=0.89), exceeding 120% after 17 years. Although of lesser magnitude, the shoot biomass response to elevated Ca was similar to that of the shoot density. Daytime NEE response to elevated Ca was not explained by the duration of exposure, but negatively correlated with salinity of the marsh, indicating that this elevated-Ca response was decreased by water-related stress. By contrast, circumstantial evidence suggested that salinity stress increased the stimulation of shoot density by elevated Ca, which highlights the complexity of the interaction between water-related stresses and plant community responses to elevated Ca. Notwithstanding the effects of salinity stress, we believe that the most important finding of the present research is that a species response to elevated Ca can continually increase when this species is under stress and declining in its natural environment. This is particularly important because climate changes associated with elevated Ca are likely to increase environmental stresses on numerous species and modify their present distribution. Our results point to an increased resilience to change under elevated Ca when plants are exposed to adverse environmental conditions.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-2486.2005.00913.x

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Digitale Medien

Simulating Inbred-Maize Yields with CERES-IM (2000)

Rasse, Daniel P. ; Ritchie, Joe T. ; Wilhelm, Wallace W. ; [weitere]

Springer

Semigroup forum 92 (2000), S. 672-678

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ISSN: 1432-2137

Quelle: Springer Online Journal Archives 1860-2000

Thema: Mathematik

Notizen: Zea mays L.), cannot be applied directly to seed-producing inbred maize because of specific field operations and physiological traits of inbred maize plants. We developed CERES-IM, a modified version of CERES-Maize 3.0 that accommodates these inbred-specific operations and traits, using a set of phenological measurements conducted in Nebraska (NE), and further tested this model with a set of field data from Michigan (MI). Detasseling (i.e., removal of the tassels from the female plants) was conducted prior to silking. Male rows were removed approximately 10 d following 75% silking. The thermal time from emergence to the end of the juvenile phase (P1) and the potential number of kernels per plant (G2) were assessed from field data, and were the only two coefficients allowed to vary according to the inbred line. Rate of leaf appearance of the inbreds was accurately simulated using a measured phyllochron interval of 54 degree-days (°Cd). Simulation of detasseling and male-row removal improved grain yield simulation for inbreds. For a set of 35 inbred-site-year simulations, the model simulated grain yield with satisfactory accuracy RMSE = 429 kg ha−1. Average grain yields were 4556 and 4721 kg ha−1 for the measured and simulated values, respectively. CERES-IM simulations suggest that the effect of male-row removal on grain yield is extremely sensitive to the precise date at which this operation is conducted. This would explain the inconsistent effect of male-row removal on female grain yields reported in the literature.

Materialart: Digitale Medien

URL: http://dx.doi.org/

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Digitale Medien

Modifications of Soil Nitrogen Pools in Response to Alfalfa Root Systems and Shoot Mulch (1999)

Rasse, Daniel P. ; Smucker, Alvin J.M. ; Schabenberger, Oliver

Springer

Semigroup forum 91 (1999), S. 471-477

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ISSN: 1432-2137

Quelle: Springer Online Journal Archives 1860-2000

Thema: Mathematik

Notizen: Medicago sativa L.) shoots and roots generate large amounts of NO3-N available to the next crop but also susceptible to deep leaching. This study was aimed at determining the specific contributions of above- and belowground alfalfa biomass to soil N pools. Dynamics of soil and plant N pools were studied in a Kalamazoo loam soil (fine-loamy, mixed, mesic Typic Hapludalfs) over a 2-yr period under bare fallow (BF), bare fallow to which alfalfa shoot mulch was applied (BFSM), living alfalfa plants with shoots removed after harvest (A), and living alfalfa with shoot mulch remaining on the soil surface after harvest (ASM). Organic N pools were monitored in alfalfa plant parts, soil-incorporated debris, and soil organic matter to depths of 150 cm. Inorganic N pools were monitored by suction lysimeters, soil extraction, and evaluation of soil denitrification rates. Living alfalfa stands kept soil inorganic N at very low levels, whether shoot mulch was applied or not. Soluble inorganic N concentrations decreased earlier in the fall in the upper horizons of bare fallow soils receiving alfalfa shoot mulch, suggesting enhanced leaching from bare soil under alfalfa mulch. Alfalfa crown and roots contained an average of 115 kg N-1 after 2 yr of treatment. In conclusion, alfalfa shoot mulch contributed little to sustained increased in soil N pools, while crowns and roots contributed larger quantities to the soil N pool.

Materialart: Digitale Medien

URL: http://dx.doi.org/

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5

Digitale Medien

Root recolonization of previous root channels in corn and alfalfa rotations (1998)

Rasse, Daniel P. ; Smucker, Alvin J.M.

Springer

Plant and soil 204 (1998), S. 203-212

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ISSN: 1573-5036

Schlagwort(e): alfalfa roots ; corn roots ; field lysimeters ; minirhizotrons ; root-induced macropores (RIMs) ; root recolonization

Quelle: Springer Online Journal Archives 1860-2000

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Abstract Distribution of root systems through soils and recolonization of root channels by successive crops are fundamental, though difficult to study, processes of soil ecology. This article reports a minirhizotron (MR) study of corn and alfalfa root systems throughout the soil profile of Kalamazoo loam (fine-loamy, mixed, mesic Typic Hapludalf) monolith lysimeters for a three-year succession of corn, alfalfa and corn. Multiple-date comparisons within and between years were conducted to estimate total root densities in each soil horizon. Root recolonization was assessed by comparing every video frame of paired minirhizotrons, from recordings conducted one growing season apart. Distributions of corn root systems were modified by tillage practices. In 1994, root populations of corn in the Bt1 horizon peaked 75–90 days after planting (DAP). Numbers of corn roots per m2 in the Bt1 horizon were consistently higher for no-tillage (NT) than for conventional tillage (CT) lysimeters, in 1994 and 1996. Distribution of alfalfa roots within the soil profile was not significantly modified by tillage. However, alfalfa root decomposition rates responded to conventional and no-tillage practices and were specific for each soil horizon. Corn root systems growing in soils previously cropped with alfalfa presented similar patterns of root distribution by horizons as that of the previous alfalfa crop. Successive corn root systems did not display similar distribution patterns throughout the soil profile from one growing season to the next. Proportions of roots of the current crop recolonizing root induced macropores (RIMs) of the previous crop averaged 18% for corn after corn, 22% for alfalfa after corn and 41% for corn after alfalfa, across Bt horizons and tillage treatments. In conclusion, distribution of corn root systems appeared to be modified by tillage practices and root recolonization of RIMs was controlled by the preceding crop.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1004343122448

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6

Digitale Medien

Alfalfa Root and Shoot Mulching Effects on Soil Hydraulic Properties and Aggregation (2000)

Rasse, Daniel P. ; Smucker, Alvin J.M. ; Santos, Djail

Springer

Soil Science Society of America journal 64 (2000), S. 725-731

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ISSN: 1435-0661

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Medicago sativa L.) stands have been reported to improve soil physical properties, little is known about the specific influences of above- and belowground alfalfa components on soil physical properties. A 2-yr study was conducted to investigate alfalfa root and shoot mulch modifications of soil physical properties and water movement in the root zone of a Kalamazoo loam soil (fine-loamy, mixed, mesic Typic Hapludalf) in southwest Michigan. Four treatments were considered: bare fallow (BF), bare fallow with alfalfa shoot mulch (BFSM), alfalfa with shoots removed and roots remaining (AR), and alfalfa with alfalfa shoot mulch (ASM). Volumetric soil water contents were measured by time domain reflectometry (TDR). Development of fine roots was monitored by minirhizotron technology. Alfalfa root systems increased saturated hydraulic conductivity (K sat) by 57%, total and macroporosities by 1.7 and 1.8%, respectively, and water recharge rate of the soil profile by as much as 5.4% per day. These effects of alfalfa roots on soil porosity were mainly attributed to increased amplitudes of wetting and drying cycles and high rates of root turnover in the Ap horizon. K sat was significantly correlated with macroporosity (r = 0.90, P ≤ 0.01). Mean weight diameter (MWD) of aggregates from bare fallow soils was 20% higher when alfalfa shoot mulch was applied. Our results suggest that aggregate stability was more affected by C sources from shoot mulch and root turnover than by factors specific to root activities such as physical enmeshment of aggregates and increased soil wetting and drying cycles.

Materialart: Digitale Medien

URL: http://dx.doi.org/

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