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At least 1,747 records · Page 97Linked to original sources
USGS2012

Carbon stocks across a chronosequence of thinned and unmanaged red pine ( Pinus resinosa ) stands

Forests function as a major global C sink, and forest management strategies that maximize C stocks offer one possible means of mitigating the impacts of increasing anthropogenic CO 2 emissions. We studied the effects of thinning, a common management technique in many forest types, on age-related trends in C stocks using a chronosequence of thinned and unmanaged red pine ( Pinus resinosa ) stands ranging from 9 to 306 years old. Live tree C stocks increased with age to a maximum near the middle of the chronosequence in unmanaged stands, and increased across the entire chronosequence in thinned stands. C in live understory vegetation and C in the mineral soil each declined rapidly with age in young stands but changed relatively little in middle-aged to older stands regardless of management. Forest floor C stocks increased with age in unmanaged stands, but forest floor C decreased with age after the onset of thinning around age 40 in thinned stands. Deadwood C was highly variable, but decreased with age in thinned stands. Total ecosystem C increased with stand age until approaching an asymptote around age 150. The increase in total ecosystem C was paralleled by an age-related increase in total aboveground C, but relatively little change in total belowground C. Thinning had surprisingly little impact on total ecosystem C stocks, but it did modestly alter age-related trends in total ecosystem C allocation between aboveground and belowground pools. In addition to characterizing the subtle differences in C dynamics between thinned and unmanaged stands, these results suggest that C accrual in red pine stands continues well beyond the 60–100 year management rotations typical for this system. Management plans that incorporate longer rotations and thinning in some stands could play an important role in maximizing C stocks in red pine forests while meeting other objectives including timber extraction, biodiversity conservation, restoration, and fuel reduction goals.

Ecological Applications↗
USGS2004

Changes in plant functional groups, litter quality, and soil carbon and nitrogen mineralization with sheep grazing in an Inner Mongolian Grassland

This study reports on changes in plant functional group composition, litter quality, and soil C and N mineralization dynamics from a 9-year sheep grazing study in Inner Mongolia. Addressed are these questions: 1) How does increasing grazing intensity affect plant community composition? 2) How does increasing grazing intensity alter soil C and N mineralization dynamics? 3) Do changes in soil C and N mineralization dynamics relate to changes in plant community composition via inputs of the quality or quantity of litter? Grazing plots were set up near the Inner Mongolia Grassland Ecosystem Research Station (IMGERS) with 5 grazing intensities: 1.3, 2.7, 4.0, 5.3, and 6.7 sheep ha −1 ·yr −1 . Plant cover was lower with increasing grazing intensity, which was primarily due to a dramatic decline in grasses, Carex duriuscula , and Artemisia frigida . Changes in litter mass and percentage organic C resulted in lower total C in the litter layer at 4.0 and 5.3 sheep ha −1 ·yr −1 compared with 2.7 sheep ha −1 ·yr −1 . Total litter N was lower at 5.3 sheep ha −1 ·yr −1 compared with 2.7 sheep ha −1 ·yr −1 . Litter C:N ratios, an index of litter quality, were significantly lower at 4.0 sheep ha −1 ·yr −1 relative to 1.3 and 5.3 sheep ha −1 ·yr −1 . Cumulative C mineralized after 16 days decreased with increasing grazing intensity. In contrast, net N mineralization ( NH 4 NO − 3 ) after a 12-day incubation increased with increasing grazing intensity. Changes in C and N mineralization resulted in a narrowing of CO 2 -C:net N min ratios with increasing grazing intensity. Grazing explained 31% of the variability in the ratio of CO 2 -C:net N min . The ratio of CO 2 -C:net N min was positively correlated with litter mass. Furthermore, there was a positive correlation between litter mass and A. frigida cover. Results suggest that as grazing intensity increases, microbes become more C limited resulting in decreased microbial growth and demand for N.

Journal of Range Management↗
USGS2014

Productivity and carbon dioxide exchange of leguminous crops: estimates from flux tower measurements

Net CO 2 exchange data of legume crops at 17 flux tower sites in North America and three sites in Europe representing 29 site-years of measurements were partitioned into gross photosynthesis and ecosystem respiration by using the nonrectangular hyperbolic light-response function method. The analyses produced net CO 2 exchange data and new ecosystem-scale ecophysiological parameter estimates for legume crops determined at diurnal and weekly time steps. Dynamics and annual totals of gross photosynthesis, ecosystem respiration, and net ecosystem production were calculated by gap filling with multivariate nonlinear regression. Comparison with the data from grain crops obtained with the same method demonstrated that CO 2 exchange rates and ecophysiological parameters of legumes were lower than those of maize ( Zea mays L.) but higher than for wheat ( Triticum aestivum L.) crops. Year-round annual legume crops demonstrated a broad range of net ecosystem production, from sinks of 760 g CO 2 m –2 yr –1 to sources of –2100 g CO 2 m –2 yr –1 , with an average of –330 g CO 2 m –2 yr –1 , indicating overall moderate CO 2 –source activity related to a shorter period of photosynthetic uptake and metabolic costs of N 2 fixation. Perennial legumes (alfalfa, Medicago sativa L.) were strong sinks for atmospheric CO 2 , with an average net ecosystem production of 980 (range 550–1200) g CO 2 m –2 yr –1 .

Agronomy Journal↗
USGS1994

Adsorption and desorption of atrazine and deethylatrazine by low organic carbon geologic materials

The adsorption and desorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and a primary metabolite, deethylatrazine (2-amino-4-chloro-6-isopropylamino-s-triazine; DEA), by low organic C (≤ 3.3 g kg −1 ) materials were measured by batch-equilibrium techniques. The adsorbents were samples of glacial outwash sand, till, and stream sediments. The adsorption of both atrazine and DEA conformed to linear isotherms. The adsorption of atrazine by most of the adsorbents yielded apparent K oc values that were in excess of those based on surface agricultural soils. Adsorption correlated with only the pH of the sand-water suspensions. The desorption of atrazine was hysteretic under the conditions of the measurement. DEA had a lower affinity for the same adsorbents; the mean ratio of K d values of DEA to those of atrazine was 0.37 ± 0.20. DEA adsorption did not correlate with organic C, surface area, clay content of the adsorbents, or with the pH of the suspensions. DEA adsorption, unlike atrazine, tended to be reversible. There was a linear relationship between the adsorption constants of atrazine and those of DEA.

Journal of Environmental Quality↗
USGS2010

Soil organic carbon stocks in Alaska estimated with spatial and pedon data

Temperatures in high-latitude ecosystems are increasing faster than the average rate of global warming, which may lead to a positive feedback for climate change by increasing the respiration rates of soil organic C. If a positive feedback is confirmed, soil C will represent a source of greenhouse gases that is not currently considered in international protocols to regulate C emissions. We present new estimates of the stocks of soil organic C in Alaska, calculated by linking spatial and field data developed by the USDA NRCS. The spatial data are from the State Soil Geographic database (STATSGO), and the field and laboratory data are from the National Soil Characterization Database, also known as the pedon database. The new estimates range from 32 to 53 Pg of soil organic C for Alaska, formed by linking the spatial and field data using the attributes of Soil Taxonomy. For modelers, we recommend an estimation method based on taxonomic subgroups with interpolation for missing areas, which yields an estimate of 48 Pg. This is a substantial increase over a magnitude of 13 Pg estimated from only the STATSGO data as originally distributed in 1994, but the increase reflects different estimation methods and is not a measure of the change in C on the landscape. Pedon samples were collected between 1952 and 2002, so the results do not represent a single point in time. The linked databases provide an improved basis for modeling the impacts of climate change on net ecosystem exchange.

Soil Science Society of America Journal↗
USGS2014

Fifteen-year patterns of soil carbon and nitrogen following biomass harvesting

The substitution of forest-derived woody biofuels for fossil fuel energy has garnered increasing attention in recent years, but information regarding the mid- and long-term effects on soil productivity is limited. We investigated 15-yr temporal trends in forest floor and mineral soil (0–30 cm) C and N pools in response to organic matter removal treatments (OMR; stem-only harvest, SOH; whole-tree harvest, WTH; and whole-tree plus forest floor removal, FFR) at three edaphically distinct aspen ( Populus tremuloides Michx. and P. grandidentata Michx.) forests in the Great Lakes region. The OMR and temporal effects were generally site specific, and both were most evident in the forest floor and combined profile (mineral soil and forest floor) compared with the mineral soil alone. Forest floor and combined profile C and N pools were generally similar in the SOH and WTH treatments, suggesting that slash retention has little impact on soil C and N in this time frame. Temporal changes in C and N at one of the three sites were consistent with patterns documented following exotic earthworm invasion, but mineral soil pools at the other two sites were stable over time. Power analyses demonstrated that significant effects were more likely to be detected for temporal differences than the effects of OMR and in the combined profile than in the mineral soil. Our findings are consistent with previous work demonstrating that OMR effects on soil C and N pools are site specific and more apparent in the forest floor than the mineral soil.

Soil Science Society of America Journal↗