Flavio Moreno

Edaphic controls on ecosystem‐level carbon allocation in two contrasting Amazon forests

Studies of carbon allocation in forests provide essential information for understanding spatial and temporal differences in carbon cycling that can inform models and predict possible responses to changes in climate. Amazon forests play a particularly significant role in the global carbon balance, but there are still large uncertainties regarding abiotic controls on the rates of net primary production (NPP) and the allocation of photosynthetic products to different ecosystem components. We evaluated three different aspects of stand-level carbon allocation (biomass, NPP, and its partitioning) in two amazon forests on different soils (nutrient-rich clay soils versus nutrient-poor sandy soils) but otherwise growing under similar conditions. We found differences in carbon allocation patterns between these two forests, showing that the forest on clay soil had a higher aboveground and total biomass as well as a higher aboveground NPP than the sandy forest. However, differences between the two forest types in terms of total NPP were smaller, as a consequence of different patterns in the carbon allocation of aboveground and belowground components. The proportional allocation of NPP to new foliage was relatively similar between them. Our results of aboveground biomass increments and fine-root production suggest a possible trade-off between carbon allocation to fine roots versus aboveground compartments, as opposed to the most commonly assumed trade-off between total aboveground and belowground production. Despite these differences among forests in terms of carbon allocation, the leaf area index showed only small differences, suggesting that this index is more indicative of total NPP than its aboveground or belowground components.

Soil Organic Carbon Sequestration Under Different Tropical Cover Types in Colombia

Soils are important to the global carbon cycle because they store the largest pool of carbon of terrestrial ecosystems, part of which could be released to the atmosphere as a result of land use changes. This study assesses how soil organic carbon stocks differ as a function of soil depth and the tropical forest successional state. Soil shafts 4 m-deep were excavated in six primary forests (PF), six young secondary forests (SF, 6–12 year), and four pastures (PAS) plots located in a watershed of the Porce River in the Colombian Andes mountains. Soils were sampled from the four walls of each shaft using a progression of 14 depths between 0 and 4 m depth. Clay content, soil bulk density, and C content were determined at each depth. In order to understand the soil organic carbon (SOC) change in these cover types, we modeled the data using non- linear equations and found significant differences in carbon content (Mg C 100 Mg−1 soil; 1 Mg = 106 g) and carbon stocks (Mg ha−1) among cover types. The highest stocks of SOC to 4 m depth were found in soils of PF (227.9 Mg ha−1), followed by SF (192.5 Mg ha−1), and PAS (171.2 Mg ha−1). These results suggest that converting primary forests to degraded pastures over several decades leads to substantial losses of soil organic carbon. Development of secondary forests in the sites of abandoned pastures starts to recover soil carbon stocks at the early stages of forest development. Differences of soil organic carbon inventories between PF and PAS were only 11.5 Mg ha−1 in the first 30 cm but 56.8 Mg ha−1down to 4 m. These results strongly support the need to assess the effects of land use change on SOC by sampling along the whole soil profile. Monitoring the superficial layers alone could yield misleading conclusions.

Effect of dose and type of fertilizer on flowering and fruiting of vanilla plants

ABSTRACT Nutritional status affects the processes of flowering and fruiting of plants. This study was conducted to determine the effects of fertilizer application on flowering, fruiting, and leaf nutrient content of Vanilla planifolia (Jacks. ex Andr). Treatments consisted of the application of grade 10-20-20 nitrogen, phosphorus, and potassium (NPK) fertilizer to the substratum in annual doses of 20, 50, and 100 g/plant plus a monthly application of foliar fertilizer. Two more treatments were foliar fertilization and no fertilization (control). Treatments increased the number of inflorescences and flower buds per plant, as well as the number and weight of fruits per plant, and decreased the abortion of flowers and immature fruits. These effects depended on the type of fertilizer, the amount applied, and the time of evaluation. The best results were obtained with the 100 g/plant/year treatment with an annual production of 1.5 kg of fruits per plant in the second year. Unfertilized plants produced 0.55 kg/plant/year. Differences were also found in foliar content of N, P, K, and copper (Cu) between vegetative and reproductive branches. Application of fertilizer to the substratum appears to improve reproductive parameters of vanilla plants and the production of beans, while foliar fertilization alone was ineffective in increasing crop productivity. Nutrients also seem to translocate from mature leaves to fruit racemes.

Intra annual seed production and availability of two morphotypes of Brosimum rubescens taubert in forests of the Colombian Amazon

We assessed the reproductive phenology, production, and availability of seeds for two morphotypes of Brosimum rubescens Taub. (Moraceae), locally known as black palosangre (BP) and white palosangre (WP) during an annual cycle in a 20-ha mega plot located in a primary forest at the El Zafire Biological Station, in the Colombian Amazon. We found that 87% and 41% of potentially reproductive individuals of BP and WP respectively, was fertile and the production of reproductive structures was variable within and between morphotypes. The phenological pattern was seasonal in both morphotypes, characterized by flowering at the end of the dry season and fruiting at the start of the rainy season. BP produced and aborted large amounts of infructescences (approximately 21743), possibly as a response to satiate predators. Relative predation in terms of pre-dispersion of seeds was similar in both morphotypes, with a greater damage generated by a Scolytidae Curculionidae (Coleoptera) and to a lesser degree by frugivorous vertebrates. The number of mature fruits, total seeds, and removed seeds was similar for both morphotypes. Differences in the amount of reproductive structures and in the timing of phenophases between morphotypes decreased the competition and contributed to their coexistence. It seems that in undisturbed forests seed limitation could be more conditioning for WP, while other limitations after fruit and seed production could occur in BP.