The objective of this study was to examine some mechanisms of bottomland hardwood afforestation and their impacts on above- and belowground carbon sequestration. Six combinations of bottomland hardwood species and two levels each of fertilizer and herbicide were applied in a completely randomized design on two sites in the LMAV. Survival, ground line diameter and total height were monitored for two growing seasons. Soil carbon and nitrogen to a depth of one meter, herbaceous biomass, and tree biomass were sampled in the first and second years of establishment. Species mixes, fertilizer, and herbicide application significantly affected survival, growth, above- and belowground tree biomass carbon after two years of establishment. Survival was generally average, while growth for most species mixes was below expectation. Species mixes E (green ash/oak mix) and F (NRCS species mix) had the highest tree vegetation carbon both above- and belowground. Soil carbon and nitrogen were not significantly affected by any treatments.

No description available.

Nutrient availability and herbivory can regulate primary production in ecosystems, but little is known about how, or whether, they may interact with one another. Here I investigate how nitrogen availability and insect herbivory interact to alter above- and belowground plant community biomass in an old-field ecosystem. In 2004, 36 experimental plots were established in which soil nitrogen (N) availability (at three levels) was manipulated and insect abundance (at two levels) in a completely randomized plot design. In 2009, after six years of treatment, I measured aboveground biomass and assessed root production at peak growth. Overall, I found a significant effect of soil N availability on both above- and belowground plant biomass while insects affected only aboveground biomass of subdominant plant species and coarse root production; there were no statistical interactions between N availability and insect herbivory for any response variable. Specifically, responses of aboveground and belowground community biomass to nutrients were driven by reductions in soil N, but not additions, indicating that soil N may not be primarily limiting production in this ecosystem. Insect herbivory altered the aboveground biomass of the subdominant plant species and altered allocation patterns to coarse root production belowground. Overall, the results of six years of nutrient amendments and insect removals suggest strong bottom-up influences on total plant community productivity.

Nutrient availability and herbivory can regulate primary production in ecosystems, but little is known about how, or whether, they may interact with one another. Here I investigate how nitrogen availability and insect herbivory interact to alter above- and belowground plant community biomass in an old-field ecosystem. In 2004, 36 experimental plots were established in which soil nitrogen (N) availability (at three levels) was manipulated and insect abundance (at two levels) in a completely randomized plot design. In 2009, after six years of treatment, I measured aboveground biomass and assessed root production at peak growth. Overall, I found a significant effect of soil N availability on both above- and belowground plant biomass while insects affected only aboveground biomass of subdominant plant species and coarse root production; there were no statistical interactions between N availability and insect herbivory for any response variable. Specifically, responses of aboveground and belowground community biomass to nutrients were driven by reductions in soil N, but not additions, indicating that soil N may not be primarily limiting production in this ecosystem. Insect herbivory altered the aboveground biomass of the subdominant plant species and altered allocation patterns to coarse root production belowground. Overall, the results of six years of nutrient amendments and insect removals suggest strong bottom-up influences on total plant community productivity.

Forests play an important role in mitigating climate change by removing carbon dioxide (CO2) from the atmosphere via photosynthesis and storing it in plant tissues and soil organic matter (SOM). Plant roots are a major conduit for transporting recently fixed CO2 belowground, where carbon (C) remains in SOM or returns to the atmosphere via respiration of soil microbes. Compared to aboveground plant processes related to the C cycle, there is little understanding of how belowground plant-C allocation to roots, symbiotic root fungi and secretions into the soil influence the gain or loss of C from the soil. Further, the uncertainty in the timing and amount of root growth that occurs in forests is a barrier to understanding how root activity responds to global change and feeds back to the C cycle. Therefore, the objective of my research is to quantify the timing and magnitude of C allocation to roots and soil via data compilation, field studies and modeling across broad spatial scales. Using data compilation at the global scale, I show that root and shoot phenology are often asynchronous and that evergreen trees commonly have later root growth compared to deciduous trees using meta-analysis across four biomes. At the plot scale, field studies in a mid-latitude forest demonstrate that deciduous stands allocate more C belowground earlier in the growing season compared to a conifer stand. The difference in phenology between stands can be attributed to the timing of root growth. At the root scale, zymographic analysis demonstrates that microbial extracellular enzyme activity is concentrated near the surface of roots and that the rhizosphere can extend well beyond 2 mm from the root surface. Finally, I developed a new model of microbial physiology and extracellular enzyme activity to assess how climate change may affect plant - microbe interactions and soil organic matter decomposition. I show that increases in temperature and the quantity of C inputs substantially alter decomposition. Collectively, these results demonstrate the importance of belowground allocation to the C cycle of terrestrial ecosystems.

No description available.

Soils contain the largest terrestrial pool of carbon (C), but the magnitude and distribution of the soil C sink may be sensitive to climate change. My dissertation aims to identify key processes that mediate patterns of belowground carbon storage across the globe and quantify the effect of environmental perturbations associated with global change on existing soil carbon stocks in peatland ecosystems. Using meta-analysis, I show that the relationship between plant growth, C allocation, and soil nutrient availability varies on a global scale and high-latitude ecosystems allocate >60% of fixed C to belowground structures. As high latitude ecosystems are warming faster than the global mean, the future of this belowground C store is potentially sensitive to climate change. In high latitude ecosystems in particular, I further show that belowground warming increases the rate of peatland carbon dioxide (CO2) and methane (CH4) losses, although CH4 emissions are more sensitive to warming than CO2 emissions, which is likely to shift the nature of greenhouse gas emissions and increase the importance of CH4 as a radiative forcing agent in the near-term. I also use a natural peatland water table gradient to identify the effect of water table reduction on peatland C and N cycling and find that microbial community shifts in C and N demand may attenuate production of C-degrading enzymes and C mineralization in the presence of plant roots and in areas with low water tables. Together, my dissertation work highlights the important role of belowground plant and microbial processes in high latitude ecosystems, and identifies the potential influence of factors associated with global change on belowground C and nutrient cycling.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Biomassa de raízes em sistemas florestais dispersos nas matrizes de savana da Amazônia é pobremente estudada e indiretamente calculada dentro do Inventário Nacional sobre fontes e reservatórios de carbono do Brasil. O objetivo do estudo foi estimar a biomassa de raízes em ilhas de mata dispersas na savana de Roraima levando em consideração o efeito da dimensão destes fragmentos florestais, distribuição espacial (borda e interior) e das variáveis edáficas como fontes de variação da biomassa. A amostragem foi desenvolvida em 12 ilhas de mata distintas por categorias de dimensão (pequenas ≤ 10 ha, médias = 1020 ha, grandes = 20-60 ha) e pela borda e interior do fragmento. Tradagens de solo (1 m de profundidade) foram realizadas de forma equidistante ao longo de transectos estabelecidos no sentido norte sul em cada ilha. Todas as raízes com diâmetro ≥ 2 mm foram triadas manualmente a intervalos de 10 cm no perfil vertical do solo e transformadas em massa por unidade de área. Foram realizadas análises químicas e físicas do solo a cada intervalo de 10 cm. A análise dos dados foi realizada através de ANOVA, teste t e regressão linear. A biomassa de raízes não diferiu em relação a dimensão dos fragmentos (38,8 22,4 Mg ha-1 de média geral). No entanto, a média das bordas (37,6 19,6 Mg ha-1) foi distinta do interior (23,3 24,4 Mg ha-1), independente da dimensão das ilhas, sugerindo ser afetada por diferenças florísticas e estruturais entre a borda e o interior. Apenas 50% da variação da biomassa de raízes ao longo do perfil vertical (0-1 m) foram explicados pelas variáveis edáficas devido à uniformidade química e física dos solos amostrados. A maior concentração de raízes foi registrada entre 0-30 cm (finas = 32,8%, médias = 55,9% e grossas = 11,3%), não sendo observadas diferenças entre as dimensões dos fragmentos neste intervalo de profundidade. O valor médio da razão root:shoot nas ilhas amostradas foi de 0,40 0,28 no perfil de 0 a 1 m de profundidade A conclusão do estudo é que biomassa de raízes em fragmentos florestais dispersos na savana de Roraima não é afetada pela dimensão dos fragmentos, mas é distinta entre borda e interior das ilhas, podendo ser explicada pelas diferenças na estrutura e composição florística entre borda e interior. / Root biomass in forest ecosystems scattered in Amazonian savanna matrix is poorly studied and indirectly calculated within the National Inventory of carbon sources and reservoirs in Brazil. The goal of the study is to estimate root biomass in forest islands dispersed in Roraima savanna taking into account the size effect of these forest fragments, spatial distribution (edge and interior) and edaphic variables as biomass sources of variation. Sampling was conducted in 12 different forest islands by size categories (small ≤10 ha, medium = 10-20 ha, large = 20-60 ha) and the edge and the forest interior. Soil samples (1 m deep) were performed at equal distances along transects established in the north - south direction on each forest island. All root diameter ≥ 2 mm were manually screened at intervals of 10 cm in the soil vertical column and converted in mass per unit area. Chemical and physical soil analyzes were made in each10 cm interval. Data analysis was performed using ANOVA, t test and linear regression. The average root biomass did not differ in the size of fragments, resulting in 38.8 22.4 t ha-1 as the overall mean for all fragments. However the edge mean (37.6 19.6 t ha-1) was distinct from the interior (23.3 24.4 t ha-1), regardless of the size of the islands, suggesting that it is affected by floristic and structural distinctions between the edge and the interior. Only 50% of the variation in root biomass along the vertical profile (0-1 m) were explained by the soil characteristics due to chemical and physical uniformity of the sampled soils. The highest concentration of roots was recorded between 0-30 cm (fine = 32.8%, medium = 55.9% and coarse = 11.3%), with no differences between the sizes of the fragments in this depth range. The ratio root: shoot in the sampled forest islands was 0.40 0.28 (0-1 m deep). The conclusion is that root biomass in forest fragments dispersed in Roraima savannah is not affected by the size of the fragments, but is distinct between edge and interior of the islands, which can be partially explained by differences in the structure and floristic composition between edge and interior.

The root systems of five tree species (Populus deltoides × nigra clone DN-177, Juglans nigra, Quercus rubra, Picea abies, and Thuja occidentalis) are described following non-intrusive imaging using ground penetrating radar (GPR). This research aimed to 1) assess the utility of GPR for in situ root studies and 2) employ GPR to estimate tree root biomass and distribution in an agroforestry system in southern Ontario, Canada. The mean coarse root biomass estimated from GPR analysis was 54.1 ± 8.7 kg tree-1 (± S.E.; n=12), within 1 % of the mean coarse root biomass measured from matched excavations. The vertical distribution of detected roots varied among species, with T. occidentalis and P. abies roots concentrated in the top 20 cm and J. nigra and Q. rubra roots distinctly deeper. I evaluate these root systems based on their C storage potential and complementary root stratification with adjacent crops.

The root systems of five tree species (Populus deltoides × nigra clone DN-177, Juglans nigra, Quercus rubra, Picea abies, and Thuja occidentalis) are described following non-intrusive imaging using ground penetrating radar (GPR). This research aimed to 1) assess the utility of GPR for in situ root studies and 2) employ GPR to estimate tree root biomass and distribution in an agroforestry system in southern Ontario, Canada. The mean coarse root biomass estimated from GPR analysis was 54.1 ± 8.7 kg tree-1 (± S.E.; n=12), within 1 % of the mean coarse root biomass measured from matched excavations. The vertical distribution of detected roots varied among species, with T. occidentalis and P. abies roots concentrated in the top 20 cm and J. nigra and Q. rubra roots distinctly deeper. I evaluate these root systems based on their C storage potential and complementary root stratification with adjacent crops.