Carbon and nitrogen dynamics in erythrina poeppigiana (Leguminosae: Phaseoleae) trees managed by periodic prunings / Pekka Nygren

Academic dissertation Agriculture and Forestry University of Helsinki, Department of Forest Ecology 1995

Incluye bibliografía

Multipurpose woody legumes are commonly used in tropical agroforestry systems, in which ther are generally managed by periodic prunings. In the present study, a functional analysis of the carbon and nitrogen dynamics in five genotypes of the Neotropical agroforestry tree species Erythrina poeppigiana (Walpers) O.F. Cook (Leguminosae: Phaseoleae) was carried out in order to gain understanding of the factors regulating the resprouting and growth of the species between the prunings. The study was carried out in humid tropical field conditions on trees pruned twice a year. The maximum leaf CO2 assimilation rate was 17.9-20.5 æmol.m-2.s-1, depending on genotype. A simulation model based on canopy development, penetration of photon flux to canopy and leaf CO2 exchange was used to compute the whole canopy CO2 exchange. According to the simulations, the canopy intercepted 26-36% of the potential photon exposure. The molar ratio of the whole canopy C assimilation to intercepted photon flux was 1.03-1.63%. The production of harvestable biomass (foliage and branches) was 2.79-6.19 kg per tree per pruning, which was equivalent to 32-45% of the total C assimilation between two prunings. Following a complete pruning, the major proportion of C was allocated to the growing foliage. The trees partially depended on the reserve carbohydrates even at 15 week after pruning. This indicates that the reserve C pool is large but, on the other hand, its replenishment rate is low. All the nodules disappeared after the pruning, and renodulation was initiated ca. 10 weeks after pruning. Subsequently, nodulation was abundant, and seemed to be regulated by the N requirements of the foliage. eng

The N concentration of mature leaves was 44.7-53.8 mg.g-1. The potential N supply to the soil was 135-268 g per tree per pruning interval. Pruning residues formed 70-80% of the total N supply. The abundant production of N rich foliage makes E. poeppigiana a suitable species for green manure systems and forage production. It should no be pruned more frequently than every four months, because the initiation of nodulation and replenishment of reserve C pool are slow processes. The genotypic variation in productivity was most probably caused by the differences in the size of the reserve C pool and canopy structure. eng