Crescimento de mudas de mangue sob diferentes níveis de sombreamento na península de Ajuruteua, Bragança, Pará / Growth of mangrove seedlings under different levels of shading at the Peninsula of Ajuruteua, Bragança, Pará

The purpose of this study was to evaluate the influence of different levels of shading on the development of seedlings of three mangrove species (Avicennia germinans (L.) Stearn., Rhizophora mangle L. and Laguncularia racemosa (L.) Gaertn. f.). The experiment was conducted at the community of Tamatateua, Ajuruteua peninsula, Bragança, PA, Brazil. For seedling production, the propagules and seeds of the mangrove species were planted in polyethylene bags (17 x 27 cm), filled with a typical mangrove substrate. The seedlings of the three species were grown under full sun (0), 30% and 60% shading, in a completely randomized design, a 3 x 3 factorial (three species and three shading levels), with eight seedlings per replication. After nine months under shading, plant samples were taken. The variables evaluated were: the shoot/height ratio, stem diameter, shoot dry matter, stem mass, root dry matter, total dry mass matter and morphological indices. Growth of seedlings of R. mangle occurred at all light levels. Seedlings of A. germinans grew faster at full sun and at 30% shading. Whereas, seedlings of L. racemosa were able to grow at 30 and 60% shading, but they also grew faster at full sunlight.

O objetivo do estudo foi avaliar a influência de diferentes níveis de sombreamento sobre o desenvolvimento de mudas das espécies arbóreas de mangue Avicennia germinans (L.) Stearn., Rhizophora mangle L. e Laguncularia racemosa (L.) Gaertn. f. O experimento foi conduzido na comunidade de Tamatateua, na península de Ajuruteua, município de Bragança. Para a produção das mudas, os propágulos das espécies arbóreas de mangue foram semeados em embalagens de polietileno (17 x 27 cm), preenchidas com substrato típico de manguezal. As mudas das três espécies foram testadas a pleno sol, 30% e 60% de sombreamento em delineamento experimental inteiramente casualizado em esquema fatorial (3 x 3) x 3 (3 espécies arbóreas e 3 níveis de sombreamento). Após as plantas atingirem a idade de nove meses, retiraram-se amostras de oito mudas por repetição de cada tratamento. As variáveis avaliadas foram: altura da parte aérea, diâmetro do coleto, massa da parte aérea, massa seca do caule, matéria seca das raízes e matéria seca total e índices morfológicos. O crescimento das mudas de R. mangle ocorreu em todos os níveis de luminosidade. As mudas de A. germinans apresentaram maior crescimento a pleno sol e a 30% de sombreamento. Já as mudas de L. racemosa foram tolerantes a 30% e 60% de sombra, mas se desenvolveram melhor a pleno sol.

Respuesta de la regeneración natural en manglares del Golfo de Urabá (Colombia) a la variabilidad ambiental y climática intra-anual / Natural regeneration response in mangroves of the Gulf of Urabá (Colombia) to the environmental and intra-annual climate variability

The natural regeneration process allows the mangrove forests remain over time. Both, biological and physical factors can affect the establishment and early stages along the development of trees. This study examined the response of natural regeneration of mangroves in the Turbo River delta and El Uno bay (Urabá Gulf, Colombia) to intra-annual environmental variability. We quantified mortality, survival and recruitment of seedlings of three mangrove species, seasonally during one year, in 72 semi-perma-nent sub-plots of 1m². In the sub-plots, the total height and the diameter at the base of the stem of all mangrove seedlings with basal diameter less than 2.5cm were measured. Damage by herbivores was also recorded to each seedling. While Laguncularia racemosa recorded the highest rates of mortality, Rhizophora mangle showed the highest survival rate during the study period, although Avicennia germinans dominated the natural regeneration. Through a Redundancy Analysis these processes were associated to environmental variables such as: Direct Site Factor-DSF (sunlight), sediments input rate, herbivory, distances from mangroves to the river, to inner lakes, and to the coastline. These variables explained 43% of the natural regeneration variation; sedimentation rate was the most important variable, while light was very representative for the R. mangle survival. Based on historical records of precipitation, Turbo River flow rate and associated sediment loads, it was established that during the highest precipitation peak, the survival of all species decreases and during the dry season, when the conditions of flooding and sediments input were lower, it was improved. The results indicated that the sediments input rates and sunlight play an important role in the survival of natural regeneration of evaluated mangrove species.

En los bosques de mangle, tanto factores biológicos como físicos, afectan el establecimiento y los estados tempranos de desarrollo de los árboles y determinan la distribución espacial de las especies. Se evaluó la respuesta de la regeneración natural de los manglares del delta del río Turbo y la bahía El Uno a la variabilidad ambiental y climática intra-anual. Se cuantificaron la mortalidad, la sobrevivencia y el reclutamiento de las plántulas de tres especies, estacionalmente durante un año. Avicennia germinans dominó la regeneración natural, Rhizophora mangle presentó la mayor la supervivencia y Laguncularia racemosa la mayor mortalidad. Estos procesos se asociaron principalmente con el aporte de sedimentos aluviales, la disponibilidad de luz, la herbivoría, la distancia al río, a las lagunas internas y a la línea de costa, las cuales explicaron el 43% de la variación en la regeneración. La sedimentación fue la variable más importante para el reclutamiento de A. germinans, mientras la luz fue muy representativa para la supervivencia de R. mangle. Con base en registros históricos de precipitación, caudales y carga de sedimentos, se estableció que en la época con mayor precipitación se presenta un descenso en la supervivencia, y en la época seca se favorece el balance entre el reclutamiento y la mortalidad. Los resultados indicaron que la precipitación, el aporte de sedimentos y la luz desempeñan un papel importante en el proceso de la regeneración de las especies evaluadas.

Differential leaf gas exchange responses to salinity and drought in the mangrove tree Avicecennia germinans (Avicenniaceae)

Leaf gas exchange was assessed in Avicennia germinans L. grown under different NaCl concentrations (0-40 per thousand), after salt-relief, and then during drought. Stomatal conductance (gs) and net photosynthetic rate (Pn) decreased with increasing NaCl concentration, and intrinsic water use efficiency (Pn / gs) increased. Under desalinization Pn / gs declined. Thus, gs did not change in plants grown at low NaCl concentration (10 per thousand), but increased up to 30-32% at higher NaCl concentration (20-40 per thousand). However, Pn was only slightly enhanced (10-15%). Under drought, Pn decreased by as much as 46% in plants grown at low NaCl concentration (10 per thousand) and by 22% at high NaCl concentration (40 per thousand). Thus, Pn / gs decreased and water use efficiency was lower during drought compared to estimates prior to salt-relief.

Se estudió el intercambio de gases en las hojas de Avicennia germinans L. en varias concentraciones de NaCl (0-40‰), después de la desalinización y durante la desecación. La conductancia de los estomas (gs) y la tasa de fotosíntesis (Pn) decrecieron con el incremento en la concentración de NaCl, y se incrementó la eficiencia en el uso intrínseco de agua (Pn / gs). Bajo desalinización Pn / gs declinó. Así, gs no cambia en el crecimiento de las plantas a bajas concentraciones de NaCl (10‰), pero se incrementó hasta 30-32% a las concentraciones de NaCl más altas (20 - 40‰). Sin embargo, Pn aumentó ligeramente (10-15%). En desecación Pn fue reducido hasta un 46% a bajas concentaciones (10‰) de NaCl, y a un 22% a altas concentraciones (40‰) de NaCl. Así, Pn / gs decrecieron y la eficiencia en el uso de agua fue menor durante desecación en comparación con los evalolres stimados previos a la desalinización.