Herbivores limit the population size of big-leaf mahogany trees in an Amazonian forest

The Janzen–Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host-specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps – canopy-disturbed areas that enhance seedling growth into saplings – over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen–Connell effects in a spatially explicit individual-based population model, the caterpillar's impact was critical to limiting Swietenia's adult tree density, with a > 10-fold reduction estimated at 300 years. Our research demonstrates the crucial but oft-ignored linkage between Janzen–Connell effects on offspring and population-level consequences for a long-lived, potentially dominant tree species.

Caracterización del crecimiento de plantines de Brassica rapa var. pekinensis en contenedores.

Brassica rapa var. pekinensis, hakusay, es una hortaliza cuya producción puede iniciarse a partir de transplantes o siembra directa. El objetivo de este trabajo fue caracterizar el crecimiento de plantines de esta hortaliza en contenedores, previo al transplante, a través de variables morfogenéticas y de crecimiento. La biomasa total (PST), el peso seco aéreo (PSA) y el peso seco de raíces (PSR) mostraron una tendencia creciente, particular en cada caso. El área foliar (AF) se incrementó hasta estabilizarse días antes del transplante, momento en el cual se observó el efecto limitante del contenedor. Las variables morfogenéticas: razón de área foliar (RAF) y área foliar específica (AFE) descendieron hasta alcanzar valores casi constantes la semana previa al transplante. Las variables de crecimiento: índice de crecimiento relativo de la planta (ICRP) e índice de crecimiento relativo foliar (ICRF) descendieron, el primero con valores superiores hasta el día 31, hecho que se refleja a través de Gamma (Gf); la tasa absoluta de crecimiento (TAC) se incrementó hasta el día 31 del período y después cayó abruptamente; la tasa de asimilación neta (TAN) creció hasta el día 31 posterior a la siembra para luego caer al final del período. El productor podría decidir el momento del transplante como aquel definido por la detención de la expansión foliar.

Relación de la calidad fisiológica de semillas de maíz con pH y conductividad eléctrica.

En semillas de diferentes cultivares de maíz provenientes de 12 lotes adquiridos en distintos años se estudió la relación entre la conductividad eléctrica y el pH del agua de remojo y la germinación y crecimiento de plántulas en invernadero, utilizando semillas sin tratar y semillas sometidas a la cámara de envejecimiento acelerado (72 h a 45 ± 1°C y 100% de humedad relativa). Se empleó un diseño de bloques completos al azar con cuatro repeticiones, se realizó el análisis de varianza y las diferencias entre cultivares se detectaron mediante la prueba de la mínima diferencia significativa. Los lotes mostraron a los 16 días de evaluación altos porcentajes de germinación en semillas no tratadas y se evidenció el efecto desfavorable sobre la germinación previo envejecimiento de las semillas. La altura de la planta, el peso seco del vástago y de las raíces mostraron diferencias significativas entre los lotes estudiados. La conductividad eléctrica se relacionó con los porcentajes de germinación de semillas sometidas a envejecimiento. Los lotes de semillas con altos valores de altura de planta y peso seco de vástago y de raíces presentaron bajos valores de conductividad eléctrica, por lo tanto, esta prueba podría ser indicativa del comportamiento de semillas de maíz en condiciones de invernadero. La prueba de pH no arrojó relación directa con la emergencia y el vigor de las semillas.

Fertilización nitrogenada en plantines de pimiento (Capsicum annuum L.) cultivados en sustratos con diferentes proporciones de materiales compostados : efecto sobre los parámetros de calidad del plantín

La etapa inicial en el crecimiento de los plantines constituye el momento más crítico en su producción. Los materiales compostados pueden resultar beneficiosos por el aporte de nutrientes y la mejora en la condición física del medio de crecimiento. Para evaluar el efecto de sustratos preparados con y sin materiales compostados [Testigo (60% turba de Sphagnum+40% perlita); Mezcla I (45% turba de Sphagnum+30% perlita+25% material compostado); Mezcla II (30% turba de Sphagnum+20% perlita+50% material compostado) y un sustrato Comercial (turba de Sphagnum+40% compost+perlita+vermiculita], sobre la nutrición inicial de plantines de pimiento (Capsicum annuum L.), se realizó un ensayo fertilizando con 0, 150 y 300 mg N L-1. Se determinaron altura, diámetro del tallo y pesos frescos y secos de hoja, tallo y raíz. Se calculó relación vástago/raíz y hoja/tallo en fresco y seco, y porcentual de materia seca. El diseño experimental fue completamente aleatorizado con cuatro repeticiones. Los materiales compostados mejoraron la calidad de los plantines, los cuales no fueron afectados cuando se aplicó N a los sustratos con compost, y sólo se observaron leves mejoras en el crecimiento de los plantines al fertilizar los sustratos carentes de compost, debido a su escasa retención hídrica y elevada lixiviación de N.

The relevance of seed size in modulating leaf physiology and early plant performance in two tree species

he size of seeds and the microsite of seed dispersal may affect the early establishment of seedlings through different physiological processes. Here, we examined the effects of seed size and light availability on seedling growth and survival, and whether such effects were mediated by water use efficiency. Acorns of Quercus petraea and the more drought-tolerant Quercus pyrenaica were sowed within and around a tree canopy gap in a sub-Mediterranean forest stand. We monitored seedling emergence and measured predawn leaf water potential (Ψpd), leaf nitrogen per unit area (Na), leaf mass per area, leaf carbon isotope composition (δ13C) and plant growth at the end of the first summer. Survival was measured on the next year. Path analysis revealed a consistent pattern in both species of higher δ13C as Ψpd decreased and higher δ13C as seedlings emerged later in the season, indicating an increase in 13C as the growing season is shorter and drier. There was a direct positive effect of seed size on δ13C in Q. petraea that was absent in Q. pyrenaica. Leaf δ13C had no effect on growth but the probability of surviving until the second year was higher for those seedlings of Q. pyrenaica that had lower δ13C on the first year. In conclusion, leaf δ13C is affected by seed size, seedling emergence time and the availability of light and water, however, leaf δ13C is irrelevant for first year growth, which is directly dependent on the amount of seed reserves.

Softening-up mannan-rich cell walls

The softening and degradation of the cell wall (CW), often mannan enriched, is involved in several processes during development of higher plants, such as meristematic growth, fruit ripening, programmed cell death, and endosperm rupture upon germination. Mannans are also the predominant hemicellulosic CW polymers in many genera of green algae. The endosperm CWs of dry seeds often contain mannan polymers, sometimes in the form of galactomannans (Gal-mannans). The endo-beta-mannanases (MANs) that catalyse the random hydrolysis of the beta-linkage in the mannan backbone are one of the main hydrolytic enzymes involved in the loosening and remodelling of CWs. In germinating seeds, the softening of the endosperm seed CWs facilitates the emergence of the elongating radicle. Hydrolysis and mobilization of endosperm Gal-mannans by MANs also provides a source of nutrients for early seedling growth, since Gal-mannan, besides its structural role, serves as a storage polysaccharide. Therefore, the role of mannans and of their hydrolytic enzymes is decisive in the life cycle of seeds. This review updates and discusses the significance of mannans and MANs in seeds and explores the increasing biotechnological potential of MAN enzymes.

A postgermination developmental arrest checkpoint is mediated by abscisic acid and requires the ABI5 transcription factor in Arabidopsis

Seed dormancy is a trait of considerable adaptive significance because it maximizes seedling survival by preventing premature germination under unfavorable conditions. Understanding how seeds break dormancy and initiate growth is also of great agricultural and biotechnological interest. Abscisic acid (ABA) plays primary regulatory roles in the initiation and maintenance of seed dormancy. Here we report that the basic leucine zipper transcription factor ABI5 confers an enhanced response to exogenous ABA during germination, and seedling establishment, as well as subsequent vegetative growth. These responses correlate with total ABI5 levels. We show that ABI5 expression defines a narrow developmental window following germination, during which plants monitor the environmental osmotic status before initiating vegetative growth. ABI5 is necessary to maintain germinated embryos in a quiescent state thereby protecting plants from drought. As expected for a key player in ABA-triggered processes, ABI5 protein accumulation, phosphorylation, stability, and activity are highly regulated by ABA during germination and early seedling growth.

Arabidopsis mutant analysis and gene regulation define a nonredundant role for glutamate dehydrogenase in nitrogen assimilation.

Glutamate dehydrogenase (GDH) is ubiquitous to all organisms, yet its role in higher plants remains enigmatic. To better understand the role of GDH in plant nitrogen metabolism, we have characterized an Arabidopsis mutant (gdh1-1) defective in one of two GDH gene products and have studied GDH1 gene expression. GDH1 mRNA accumulates to highest levels in dark-adapted or sucrose-starved plants, and light or sucrose treatment each repress GDH1 mRNA accumulation. These results suggest that the GDH1 gene product functions in the direction of glutamate catabolism under carbon-limiting conditions. Low levels of GDH1 mRNA present in leaves of light-grown plants can be induced by exogenously supplied ammonia. Under such conditions of carbon and ammonia excess, GDH1 may function in the direction of glutamate biosynthesis. The Arabidopsis gdh-deficient mutant allele gdh1-1 cosegregates with the GDH1 gene and behaves as a recessive mutation. The gdh1-1 mutant displays a conditional phenotype in that seedling growth is specifically retarded on media containing exogenously supplied inorganic nitrogen. These results suggest that GDH1 plays a nonredundant role in ammonia assimilation under conditions of inorganic nitrogen excess. This notion is further supported by the fact that the levels of mRNA for GDH1 and chloroplastic glutamine synthetase (GS2) are reciprocally regulated by light.

Community attributes determine facilitation potential in a semi-arid steppe

Studies on positive plant–plant relations have traditionally focused on pair-wise interactions. Conversely, the interaction with other co-occurring species has scarcely been addressed, despite the fact that the entire community may affect plant performance. We used woody vegetation patches as models to evaluate community facilitation in semi-arid steppes. We characterized biotic and physical attributes of 53 woody patches (patch size, litter accumulation, canopy density, vegetation cover, species number and identity, and phylogenetic distance), and soil fertility (organic C and total N), and evaluated their relative importance for the performance of seedlings of Pistacia lentiscus, a keystone woody species in western Mediterranean steppes. Seedlings were planted underneath the patches, and on their northern and southern edges. Woody patches positively affected seedling survival but not seedling growth. Soil fertility was higher underneath the patches than elsewhere. Physical and biotic attributes of woody patches affected seedling survival, but these effects depended on microsite conditions. The composition of the community of small shrubs and perennial grasses growing underneath the patches controlled seedling performance. An increase in Stipa tenacissima and a decrease in Brachypodium retusum increased the probability of survival. The cover of these species and other small shrubs, litter depth and community phylogenetic distance, were also related to seedling survival. Seedlings planted on the northern edge of the patches were mostly affected by attributes of the biotic community. These traits were of lesser importance in seedlings planted underneath and in the southern edge of patches, suggesting that constraints to seedling establishment differed within the patches. Our study highlights the importance of taking into consideration community attributes over pair-wise interactions when evaluating the outcome of ecological interactions in multi-specific communities, as they have profound implications in the composition, function and management of semi-arid steppes.

Effectiveness of Low-Cost Planting Techniques for Improving Water Availability to Olea europaea Seedlings in Degraded Drylands

Reforestation projects in semiarid lands often yield poor results. Water scarcity, poor soil fertility, and structure strongly limit the survival and growth of planted seedlings in these areas. At two experimental semiarid sites, we evaluated a variety of low-cost planting techniques in order to increase water availability to plants. Treatments included various combinations of traditional planting holes; water-harvesting microcatchments; stone or plastic mulches; small waterproof sheets to increase water harvesting; dry wells; buried clay pots; and deep irrigation. Some of these treatments were also combined with addition of composted biosolids. Waterproof sheets significantly enhanced water harvesting (43%) and soil moisture in the planting hole (40%), especially for low-intensity rainfall events. Treatment effects on the survival and growth of Olea europaea seedlings varied between experimental sites. At the most water-limited site, clay pots, and dry wells improved seedling survival, while no treatment enhanced seedling growth. At the least water-stressed site, the application of composted sludge significantly improved seedling growth. We conclude that nutrient-mediated stress is subordinate to water stress in arid and semiarid environments, and we suggest modifications on the microsite scale to address these limiting conditions in Mediterranean drylands.

Woody Debris in the Mangrove Forests of South Florida

Woody debris is abundant in hurricane-impacted forests. With a major hurricane affecting South Florida mangroves approximately every 20 yr, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential. Here, we report on line-intercept woody debris surveys conducted in mangrove wetlands of South Florida 9–10 yr after the passage of Hurricane Andrew. The total volume of woody debris for all sites combined was estimated at 67 m3/ha and varied from 13 to 181 m3/ha depending upon differences in forest height, proximity to the storm, and maximum estimated wind velocities. Large volumes of woody debris were found in the eyewall region of the hurricane, with a volume of 132 m3/ha and a projected woody debris biomass of approximately 36 t/ha. Approximately half of the woody debris biomass averaged across all sites was associated as small twigs and branches (fine woody debris), since coarse woody debris >7.5 cm felled during Hurricane Andrew was fairly well decomposed. Much of the small debris is likely to be associated with post-hurricane forest dynamics. Hurricanes are responsible for large amounts of damage to mangrove ecosystems, and components of associated downed wood may provide a relative index of disturbance for mangrove forests. Here, we suggest that a fine:coarse woody debris ratio ≤0.5 is suggestive of a recent disturbance in mangrove wetlands, although additional research is needed to corroborate such findings.

Biometria de frutos e sementes, crescimento e produção de mudas de Campomanesia adamantium Blume e Campomanesia pubescens O. Berg

Campomanesia adamantium and Campomanesia pubescens are morphologically similar, occur in the same regions of the Cerrado, are difficult to differentiate and exhibit naturally slow growth and development. The objectives of this study were to analyze fruit and seed biometric data, emergence capacity and seedling growth characteristics. Fruit from both species was collected and used to measure biometric data of the fruit and seeds and to set up two emergence and two seedling growth experiments. C. adamantium fruit is round and has wider, pale yellow seeds while C. pubescens fruit is ellipsoidal to pyriform with yellow gold seeds. C. adamantium’s greater fresh fruit mass and biometric variability favors selection of promising material for commercialization. Seed drying reduced the speed and rate of seedling emergence of C. adamantium, but had no effect on C. pubescens. Leaf number, height, shoot dry weight and the ratio of shoot dry weight to root dry weight were greater in C. adamantium than in the slower growing C. pubescens. Increases in substrate volume favor seedling development. Slow-release fertilizer application at 1g per 115 cm3 substrate increased leaf formation, plant height and shoot dry weight of seedlings of both species and lateral budding in C. adamantium. Until 120 days after transplant, lateral budding was not observed in C. pubescens seedlings. For all traits evaluated in this experiment, C. adamantium seedling growth was greater than that of C. pubescens.

Potencial fisiológico de sementes de soja enriquecidas com molibdênio no armazenamento e sua influência na atividade de enzimas do metabolismo do nitrogênio

Molybdenum is one of the essential micronutrients for soybeans, acting directly on nitrogen metabolism as enzyme cofactor of nitrogenase. Usually, this nutrient is supplied to the plants through seed treatment or foliar application. The aim of this study was to evaluate the molybdenum effects by foliar in the physiological potential of soybean seeds and verify its interference in the enzyme activities involved in nitrogen metabolism. Soybean seeds of BMX Turbo cultivar were used, produced in Erechim, RS, harvest 2013, from plants treated with the following Mo concentrations: 0; 25; 50 and 75 g ha-1, supplied through two commercial products (Biomol and Molybdate) and stored during 0 and 6 months in uncontrolled conditions. The first experiment was conducted in Seedtes Seed Analysis Laboratory in Pato Branco, PR. The used design was completely randomized in a factorial analysis 4 x 2 x 2 with four replications each. The physiological potential of the seeds was evaluated by the germination test, seedling growth, accelerated aging and emergence on the soil. The second experiment was conducted in a greenhouse, where the seeds derived from treatments with different concentrations of Mo: 0; 25; 50 and 75 g ha-1 supplied through two commercial products (Biomol and Molybdate) were grown in vases. The used design was completely randomized in a factorial analysis 4 x 2 with four replications. Evaluations were performed when the plants reached the R1 phenological stage concerning the nodulation, dry matter of root and shoot of the plants and the determination of the activity of the enzymes glutamine synthetase and glutamate synthetase and the content of total soluble proteins. The data were submitted to variance analysis and when significant they were assessed by Tukey’s test for comparison of products and seed storage and with regression study to the concentrations at 5% probability. Analyses were performed using SISVAR statistical software. The soybean seed storage under uncontrolled conditions affected the seed vigour produced with Mo, regardless of the commercial product used during production. The application of Mo through foliar positively influences the production of soya beans which presented increasing responses in the germination and vigour with the application of Mo above 25 g ha-1 . The enrichment of Mo through foliar did not affect the nodulation of plants of the next generation, however, the use of Mo above 25 g ha-1 provided an increase in the activity of enzymes involved in nitrogen metabolism as well as on the total protein content.

Regeneration in felling gaps after logging in Acre state, Western Amazon.

Regeneration of tree species in felling gaps were studied during the first two years following harvesting in a tropical forest in Acre state, Brazil. Felling gaps averaged 340 m2 in size, while canopy openings averaged 17%. Seedling mortality in adjacent undisturbed forest was 4.6% yr', and 59.6% yr·1 and 100% yr' in the crown and trunk zones respectively, two years after logging. Recruitment of new seedlings inthe undisturbed forest understorey averaged 462 plants ha' yr', two years after gap creation. Inthe crown zones of the gaps, recruitment of seedlings averaged 1350 ha' yr', and in the trunk zones 1392 ha' yr'. The entire seedling community in trunk zones after logging was composed of new recruits. lhere was a tendency for seedling growth rates to increase from the natural forest (0,21cm yr-1) to the crown zone (0.40cm yr'), Before gap creation, species richness and diversity and seedling density were quite similar. After gap creation a sharp decrease could be verified in the gap.zones, however the differences between gap and undisturbed forest decreased rapidly in the second year after gap creation. lhe regeneration of commercial species was not affected by gap creation apart from the increase in growth rates.