Hilton Thadeu Zarate do Couto

Modelos volumétricos para a Floresta Nacional do Tapirapé-Aquirí, Serra dos Carajás (PA)

Accurate volume estimate is a crucial variable for effective forest management in the tropics. In this study, we investigated volumetric models for Tapirape-Aquiri National Forest in Carajas, PA, Brazil, based on 55 cubed trees by obtaining dbh, stem commercial height, and solid stem volume. A total of 8 double- and 4 single-entry models were tested for minimum dbh at 14 cm. Statistical procedures, such as coefficient of determination (R2), distribution of residuals, and standard error of estimate, were used to evaluate the accuracy of the estimates. Among simple-entry models, Husch logarithmic model showed the best fit to the data (R2 = 0.9105), whereas Schumacher & Hall logarithmic model showed the best performance among double-entry models (R2 = 0.9942). One previously published regression model, developed for Tapajos National Forest, and a taper function with a form factor of 0.70 were also cross-validated against the trees of this study. These two models subestimated the true volume. This study therefore highlights the importance of developing local volumetric models in order to obtain accurate estimates.

Synergistic effects of seed disperser and predator loss on recruitment success and long-term consequences for carbon stocks in tropical rainforests

The extinction of large frugivores has consequences for the recruitment of large-seeded plants with potential lasting effects on carbon storage in tropical rainforests. However, previous studies relating frugivore defaunation to changes in carbon storage ignore potential compensation by redundant frugivores and the effects of seed predators on plant recruitment. Based on empirical data of the recruitment success of a large-seeded hardwood tree species (Cryptocarya mandioccana, Lauraceae) across a defaunation gradient of seed dispersers and predators, we show that defaunation increases both seed dispersal limitation and seed predation. Depending on the level of seed predator loss, plant recruitment is reduced by 70.7–94.9% as a result of the loss of seed dispersers. The loss of large seed predators increases the net seed mortality by 7–30% due to the increased abundance of small granivorous rodents. The loss of large seed dispersers can be buffered by the compensatory effects of smaller frugivores in seed removal, but it is not sufficient to prevent a decrease in plant recruitment. We show that the conservation of both seed predators and dispersers is necessary for the recruitment of large-seeded plants. Since these plants contribute substantially to carbon stocks, defaunation can jeopardize the maintenance of tropical forest carbon storage.

Analysis of Phosphorus Use Efficiency Traits in Coffea Genotypes Reveals Coffea arabica and Coffea canephora Have Contrasting Phosphorus Uptake and Utilization Efficiencies

Background and Aims: Phosphate (Pi) is one of the most limiting nutrients for agricultural production in Brazilian soils due to low soil Pi concentrations and rapid fixation of fertilizer Pi by adsorption to oxidic minerals and/or precipitation by iron and aluminum ions. The objectives of this study were to quantify phosphorus (P) uptake and use efficiency in cultivars of the species Coffea arabica L. and Coffea canephora L., and group them in terms of efficiency and response to Pi availability. Methods: Plants of 21 cultivars of C. arabica and four cultivars of C. canephora were grown under contrasting soil Pi availabilities. Biomass accumulation, tissue P concentration and accumulation and efficiency indices for P use were measured. Key Results: Coffee plant growth was significantly reduced under low Pi availability, and P concentration was higher in cultivars of C. canephora. The young leaves accumulated more P than any other tissue. The cultivars of C. canephora had a higher root/shoot ratio and were significantly more efficient in P uptake, while the cultivars of C. arabica were more efficient in P utilization. Agronomic P use efficiency varied among coffee cultivars and E16 Shoa, E22 Sidamo, Iêmen and Acaiá cultivars were classified as the most efficient and responsive to Pi supply. A positive correlation between P uptake efficiency and root to shoot ratio was observed across all cultivars at low Pi supply. These data identify Coffea genotypes better adapted to low soil Pi availabilities, and the traits that contribute to improved P uptake and use efficiency. These data could be used to select current genotypes with improved P uptake or utilization efficiencies for use on soils with low Pi availability and also provide potential breeding material and targets for breeding new cultivars better adapted to the low Pi status of Brazilian soils. This could ultimately reduce the use of Pi fertilizers in tropical soils, and contribute to more sustainable coffee production.

Regulated deficit irrigation benefits the production of container-grown citrus nursery trees

Key messageWithholding irrigation at − 15 to − 25xa0kPa water potential significantly saved water with minimal changes in plant growth, water relations, and percentage of shippable citrus trees on drought-tolerant and -sensitive rootstocks.AbstractWe evaluated the impacts of regulated deficit irrigation (RDI) on plant growth, water relations, and biochemical variables of Valencia sweet orange nursery trees grafted on drought-tolerant Rangpur lime (RL) and drought-sensitive Swingle citrumelo (SC) rootstocks in pots. Irrigation was withheld to potting mix water potential of −u200915 (mild RDI) and −u200925xa0kPa (moderate RDI), with daily irrigation as control, in three graft growth periods (20–60, 61–120, and 20–120 days after grafting, DAG). Plant growth was reduced by moderate RDI, albeit RL induced more vigor than SC. SC induced higher CO2 assimilation rates and water use efficiency (WUE), regardless of the irrigation regime, and only trees grafted on RL decreased WUE under moderate RDI. Most leaf nutrient concentrations were increased with RDI intensity, while K levels were decreased by moderate RDI. Starch reserves were drastically decreased, while reducing sugars were increased by RDI in all plant organs, most notably in the leaves; roots represented the main source of carbohydrates for both rootstocks under water deficit. Starch concentration promptly recovered in all organs after restoring irrigation. Leaf proline concentration was 20 times higher at RDI, but decreased by 50% just 1xa0day after rehydration. Mild-to-moderate RDI resulted in water savings of 54–80%, but a 0–40% reduction in the percentage of shippable trees at 120 DAG; the biological responses were mainly related to the RDI duration. The production of container-grown citrus nursery trees in greenhouses could greatly benefit from the use of RDI, without major negative effects on tree quality.