Peatland ecosystems only cover 2-3 % of the Earth‟s surface but they represent significant carbon stores, holding approximately one third of the global soil carbon (C). The major peat forming genera Sphagnum appears to be highly sensitive to increased N availability. Many studies have shown decreased productivity of Sphagnum which could lead to a decrease in the amount of C stored, especially as many studies also show an increase in the decomposition rate with higher N deposition. However, the overall effects of N on CO2 fluxes of Sphagnum remain unclear. The present study aimed to look at the effects of increased N on Sphagnum productivity, decomposition and CO2 fluxes after long-term N additions (> 5 years) using a field experiment at Whim Moss in southern Scotland where N deposition has been manipulated employing a very realistic application coupled to rainfall since 2002. The experiment also has treatments with PK addition to test the effects of removing P and/or K-limitation. Measurements of plant tissue nutrient concentrations, visual assessments of Sphagnum viability, and pore water analysis were also carried out. Nitrogen additions increased tissue N, and decreased Sphagnum shoot extension and productivity. Simultaneous P and K additions alleviated the effects of N on tissue N concentrations and growth, although this was only significant for shoot extension. Visual assessments correlated well with tissue chemistry and productivity; the decline in health was associated with high %N and reduced productivity. Interestingly, in the present study increased N decreased the mass loss and again when PK was added with N decomposition rates were more similar to the control. With respect to the carbon balance of the site and the sustainability of peatlands the results suggest that the negative effect of N on C assimilation may be partially offset by the reduced decomposition rates. The CO2 measurements showed a large loss of C as CO2 from all the Sphagnum plots which was exacerbated by adding N especially when the air temperature increased. The positive temperature response of ecosystem respiration with N additions suggests that in high N deposition areas climate change and subsequent temperature rises will increase C losses from bogs.

Soil carbon dioxide efflux resulting from microbial and root respiration is a major component of the forest carbon cycle. We undertook this investigation to better understand the nature of soil carbon dioxide efflux of plantation loblolly pine, an important ecological and economical resource in the southeastern United States. Specifically, we hoped to learn how soil carbon dioxide efflux differs both spatially and temporally for four age classes of plantation loblolly pine on the Virginia piedmont. During a 12-month period, soil carbon dioxide efflux was repeatedly measured for four age classes of plantation loblolly pine using a dynamic, closed-chamber infrared gas analyzer. The age classes examined were 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands. Mean soil carbon dioxide efflux rates measured during the 12-month study were 1.72, 2.58, 2.84, and 2.90 micromole/sq m/s for 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands, respectively. Stand age had a significant effect on efflux rate during 10 of the 12 monthly sampling sessions. Additionally, mean efflux rates were consistently higher near the tree and a significant positional difference was detected during 8 of the 12 monthly sampling sessions. Mean soil carbon dioxide efflux rates, by position, for the 12-month study were 2.72 and 2.28 micromole/sq m/s for the near and away measurement positions, respectively. Based on monthly mean soil carbon dioxide efflux rates, annual carbon losses were estimated at 651, 976, 1074, and 1082 g C/sq m/yr for 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands, respectively. Regression analysis was used to examine the influence of soil and climatic factors on seasonal changes in soil carbon dioxide efflux. The most influential factors affecting soil carbon dioxide efflux during the 12-month study were soil temperature, soil moisture, stand age, and measurement position. We believe respiring roots significantly influence soil carbon dioxide efflux of plantation loblolly pine and account for differences observed between stands of different ages as well as spatial differences observed within a given stand. / Master of Science

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / High intensity of rains, associated with inadequate management in agricultural areas, have been caused loss of large volumes of soil by erosion, leading the sediments and nutrients to the hydric sources. The loss of sediments in hydrographic basins is a complex problem that requires studies to enable an understanding this dynamic, however, methods to describe and determine the dynamics of sediments without erosive process in river basins are still expensive and time consuming. One way used to evaluate and describe a dynamic of sediments is by isotope 137Cs, however, this method has a high cost to carry out analyzes, therefore, it is sought alternatives to know how sediment distribution on the slopes and/or hydrographic basins, using procedures that have lowest cost of analyses. One possibility is use the total C and 13C, because they have an uniform distribution in a soil profile and they are strongly associated with the soil mineral particles, being transferred and accumulated depending on how the sediment movement in the basin occurs. The present study evaluated a distribution of the C and 13C in two agricultural slopes with different cropping systems No-tillage (PD) and conventional tillage (PC) and the potential of total C and 13C to be used as alternatives for soil erosion inventory studies. For this, the results obtained by total C and 13C were compared with the results of the 137Cs, seeking to perceive the potential use of C and 13C as a supplier of qualitative information about sediment redistribution in agricultural slopes. In the profiles, layers were evaluated every 3 cm to a depth of 96 cm (or less if the profile it is less than that). The analysis of isotopic abundance of total C and 13C was done by mass spectrometry. The 137Cs were determined by spectrometry, without GeHP - Gamma spectrometry detectors using Germanic crystal. The data of total C and 13C do not show sediment redistribution in the PD, but, into the PC system is possible to perceive that there was intense movement of soil and C along slope. The 13C is efficient to demonstrate in what soil profiles happened the sediment redistribution along the slope, in areas that the vegetation has been replaced. Keywords: Conventional tillage; No-tillage; 137Cs; Soil Erosion; Carbon Loss. / Chuvas de alta intensidade, associadas ao manejo inadequado em áreas agrícolas, vêm causando perda de grandes volumes de solo por erosão, levando sedimentos e nutrientes para os corpos hídricos. A perda de sedimentos em bacias hidrográficas é uma problemática complexa que necessita de estudos para possibilitar o entendimento de sua dinâmica, porém, métodos que descrevam e determinem a dinâmica dos sedimentos no processo erosivo ainda são onerosos e demorados. Um dos principais métodos utilizado para avaliar e descrever a dinâmica de sedimentos é por meio do isótopo 137Cs, contudo, este método possui alto custo para realização das análises, portanto, buscam-se alternativas que possibilitem conhecer como ocorre a redistribuição de sedimentos em encostas e/ou bacias hidrográficas, utilizando procedimentos que possuam análises de menor custo. Uma possibilidade é o uso do C total e do 13C, pois possuem distribuição relativamente padrão no perfil do solo e estão fortemente associados com as partículas minerais do solo, sendo transferidos e acumulados dependendo de como ocorre a movimentação dos sedimentos na bacia. O presente estudo avaliou a distribuição do C e do 13C em duas encostas agrícolas com diferentes sistemas de cultivo, plantio direto (PD) e plantio convencional (PC) e o potencial do C total e do 13C serem utilizados como alternativas para estudos de inventario de erosão do solo. Para isso foi realizado a comparação dos resultados obtidos por meio do C e do 13C com o resultado do 137Cs, buscando perceber o potencial uso do C e do 13C como fornecedor de informações qualitativas acerca da redistribuição de sedimentos em encostas agrícolas. Nos perfis foram avaliadas camadas de 3 em 3 cm até a profundidade de 96 cm (ou menos se o perfil for menor que isso). A análise da abundância isotópica de C total e 13C no solo foi feita por espectrometria de massas. O 137Cs foi determinado por espectrometria, no equipamento GeHP - Gamma spectrometry detectors com uso de cristal germânico. Os dados de C total e 13C não evidenciaram redistribuição de sedimentos na encosta sob PD, já no PC foi possível perceber que houve intensa movimentação de solo e de C ao longo da encosta. O C total e o 13C são eficientes para demonstrar em quais perfis do solo houve a redistribuição de sedimentos ao longo da encosta, em áreas com substituição de vegetação.