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.

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.

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No description available.

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 forest product industry is keenly interested in extending the normal planting season, as well as in the comparative field performance of standard nursery bare-root seedlings and containerized rooted cuttings. The effect of seasonal planting dates on survival, above and belowground biomass allocation, water relations, gas exchange attributes and foliar carbon isotope composition (δ13C) of two stock types of slash pine (Pinus elliottii Engelm.) were examined. Slash pine bare-root seedlings (BRS) and containerized rooted cuttings (CRC) were hand planted in September, November, January, March and April in three consecutive planting seasons (2000-2001, 2001-2002 and 2002-2003) on three sites with silt loam topsoils in southwestern Louisiana. First-year mean survival of CRC across all planting dates and sites was consistently high at 96 to 98%, whereas BRS survival was significantly (P < 0.0001) lower at 59 to 81% and highly variable among study sites and dates through three planting seasons. Generally, there was a negative relationship between soil moisture at the time of planting and first-year survival of BRS planted September through March in 2001-2002 and 2002-2003 planting seasons, whereas the opposite was observed only for BRS planted in April 2002 and 2003. Survival of CRC was affected very little by the variation in soil moisture. Containerized rooted cuttings had higher early above and belowground biomass, and height and diameter than did BRS. However, three years after planting the size differences between stock types disappeared or became negligible. Early size differences among trees planted September through March also decreased after three years, although September trees were tallest. Growth of the April-planted trees was poor compared to trees planted in other months. Late-planted April trees had higher δ13C values, and higher water-use efficiency in the first growing season compared to earlier planted trees. Differences in δ13C values among the planting dates disappeared in the second growing season. Net photosynthesis rates did not differ considerably between stock types or among planting dates in the second and third growing seasons. This study indicates that it is possible to extend the planting season to as early as September and as late as March by using CRC.

The forest product industry is keenly interested in extending the normal planting season, as well as in the comparative field performance of standard nursery bare-root seedlings and containerized rooted cuttings. The effect of seasonal planting dates on survival, above and belowground biomass allocation, water relations, gas exchange attributes and foliar carbon isotope composition (&#948;13C) of two stock types of slash pine (Pinus elliottii Engelm.) were examined. Slash pine bare-root seedlings (BRS) and containerized rooted cuttings (CRC) were hand planted in September, November, January, March and April in three consecutive planting seasons (2000-2001, 2001-2002 and 2002-2003) on three sites with silt loam topsoils in southwestern Louisiana. First-year mean survival of CRC across all planting dates and sites was consistently high at 96 to 98%, whereas BRS survival was significantly (P < 0.0001) lower at 59 to 81% and highly variable among study sites and dates through three planting seasons. Generally, there was a negative relationship between soil moisture at the time of planting and first-year survival of BRS planted September through March in 2001-2002 and 2002-2003 planting seasons, whereas the opposite was observed only for BRS planted in April 2002 and 2003. Survival of CRC was affected very little by the variation in soil moisture. Containerized rooted cuttings had higher early above and belowground biomass, and height and diameter than did BRS. However, three years after planting the size differences between stock types disappeared or became negligible. Early size differences among trees planted September through March also decreased after three years, although September trees were tallest. Growth of the April-planted trees was poor compared to trees planted in other months. Late-planted April trees had higher &#948;13C values, and higher water-use efficiency in the first growing season compared to earlier planted trees. Differences in &#948;13C values among the planting dates disappeared in the second growing season. Net photosynthesis rates did not differ considerably between stock types or among planting dates in the second and third growing seasons. This study indicates that it is possible to extend the planting season to as early as September and as late as March by using CRC.

Nutrients are usually patchily distributed in natural soils. Plants are often able to respond to nutrient heterogeneity in artificial conditions by active plastic changes of root system morphology. The occurrence or magnitude of a foraging response can be altered by the presence of competition. However, it is unclear to what extent root foraging takes place in the field. I conducted a field experiment in order to determine the effect of an artificial nutrient patch on fine belowground biomass of (a) an established community and (b) model plants. The study array consisted of a grid of 30×30 cm plots with model plants located in the centre. Half of the plots contained the artificial patch located 5.5 cm from the model plant. Fertilizer patch treatment did not increase mean plot fine underground biomass. Instead, fine underground biomass was higher in places of greater soil moisture estimated from mean plot EIVs. Neither total model plant root biomass nor proportion of roots in the enriched quarter increased in the fertilizer treatment. Competition was probably higher in fertilized than in control plots judging by a 2-fold increase in death rate of model plants. However, greater proportion of model plants flowered in the treatment plots. Possible causes include a plastic response to the patch as well...