RESUMO

Golden genotype of papaya (Carica papaya), named for its yellowish leaves, produces fruits very much appreciated by consumers worldwide. However, its growth and yield are considerably lower than those of other genotypes, such as 'Sunrise Solo', which has intensely green leaves. We undertook an investigation with the goal of evaluating key physiological traits that can affect biomass accumulation of both Golden and Sunrise Solo genotypes. Papaya seeds from two different genotypes with contrasting leaf colour 'Sunrise Solo' and Golden were grown in greenhouse conditions. Plant growth (plant height, leaf number, stem diameter, leaf area, plant dry weight), leaf gas exchanges, leaf carbon balance, RuBisCO oxygenation and carboxylation rates, nitrogen, as well as chlorophyll concentrations and fluorescence variables were assessed. Although no significant differences were observed for photosynthetic rates between genotypes, the accumulation of small differences in photosynthesis, day after day, over a long period, might contribute to some extend to a higher C-budget in Sunrise Solo, higher leaf area and, thus, to higher productivity. Additionally, we consider that physiological processes other than photosynthesis and leaf respiration can be as well involved in lower growth and yield of Golden. One of these aspects could be related to the higher rates of photorespiration observed in Sunrise Solo, which could improve the rate of N assimilation into organic compounds, such as amino acids, thus contributing to the higher biomass production in Sunrise Solo relative to Golden. Further experiments to evaluate the effects of N metabolism on physiology and growth of Golden are required as it has the potential to limit its yield.

RESUMO

Se evaluó el proceso de bioestimulación por nutrientes utilizando fertilizantes inorgánicos compuestos (FIC) N:P:K 28:12:7 y sales inorgánicas simples (SIS) NH4NO3 y K2HPO4 en suelos contaminados con hidrocarburos utilizando respirometría. El suelo fue contaminado con lodos aceitosos a una concentración 40.000 mgTPH/kgps. Para cuantificar el consumo de oxígeno se utilizaron dos respirómetros de medición manométrica HACH® 2173b y OXITOP® PF600 durante ensayos de 13 días (n=3). Se evaluaron dos tratamientos (FIC y SIS) y tres controles (abiótico, sustrato de referencia y sin nutrientes). Se analizaron parámetros físico-químicos (pH, nutrientes y TPH) y microbiológicos (heterótrofos y degradadores) al inicio y al final de cada ensayo. SIS y el control sin nutrientes presentaron las mayores tasas de respiración, en el equipo HACH se obtuvieron valores de 802,28 y 850,72 mgO2kgps-1d-1 respectivamente, y en OXITOP fueron de 936,65 y 502,05 mgO2kgps-1d-1, respectivamente, indicando que los nutrientes de SIS estimularon el metabolismo microbiano. Por otro lado, FIC presentó los recuentos y tasas de respiración más bajas (188,18 y 139,87 mgO2kgps-1d-1 en HACH y OXITOP, respectivamente), esto pudo estar relacionado a un efecto inhibitorio generado por la acumulación de amoniaco, limitando el crecimiento de la población degradadora.

The biostimulation process was evaluated in a hydrocarbon contaminated soil by respirometry after amendment with inorganic compound fertilizer (ICF) (N:P:K 28:12:7) and simple inorganic salts (SIS) (NH4NO3 and K2HPO4). The soil was contaminated with oily sludge (40,000 mgTPH/kgdw). The oxygen uptake was measured using two respirometers (HACH® 2173b and OXITOP® PF600) during thirteen days (n=3). Two treatments (ICF and SIS) and three controls (abiotic, reference substance and without nutrients) were evaluated during the study. Physicochemical (pH, nutrients, and TPH) and microbiological analysis (heterotrophic and hydrocarbon-utilizing microorganisms) were obtained at the beginning and at the end of each assay. Higher respiration rates were recorded in SIS and without nutrient control. Results were 802.28 and 850.72-1d-1,mgO2kgps-1d-1 in HACH, while in OXITOP were 936.65 and 502.05 mgO2kgps respectively. These data indicate that amendment of nutrients stimulated microbial metabolism. ICF had lower respiration rates (188.18 and 139.87 mgO2kgps-1d-1 in HACH and OXITOP, respectively) as well as counts, this could be attributed to ammonia toxicity.