Fine-root biomass and dynamics of six tropical tree species

Estimations of fine-root storage and dynamics have been lacking in most ecological studies in tropical forests, deterring proper quantification of productivity in this biome. My thesis addresses this issue by exploring fine-root biomass and growth rates for five native species (Hyeronima alchorneoides, Pentaclethra macroloba, Virola koschnyi, Vochysia ferruginea and Vochysia guatemalensis) and one exotic (Pinus tecunumanii), grown as single-dominated, 16-year-old plantations in Costa Rica. The main objectives in my study were (1) to describe fine-root systems, in terms of size and vertical distribution, fine-root growth rates and fine-root carbon and nitrogen content and (2) to compare fine-root carbon dynamics, with other carbon fluxes in the plantations. Fine-root systems were shallow, with\u3e 75% of the total fine-root biomass situated in the uppermost 30 cm of the soil for all the species. Species showed differences in biomass only in the upper 15 cm layer, ranging from 182 g m⁻² in Pinus tecunumanii to 433 g m⁻² in Hyeronima alchorneoides plots, on average. Fine-root growth ranged from 304 to 1308 g C m⁻² yr⁻¹, which are moderate to high rates in comparison with growth rates reported in the tropics. In contrast with the global relationships between N concentration and longevity in leaves, fine-root lifespan was not correlated with root nitrogen concentration and growth rates were positively correlated with root C:N ratio. Results did not support the hypothesis that fine root longevity is related to root nitrogen concentration among species. Species also differed in allocation patterns. Hyeronima alchorneoides and Vochysia guatemalensis had similar aboveground litter and fine root production, whereas Pinus tecunumanii produced substantially more aboveground litter than fine roots. Mean total detritus production was higher in Hyeronima and V. guatemalensis plots than in Virola and Pinus plots. Soil-CO₂ emissions ranged from 1610 to 2365 g C m⁻² yr⁻¹ among species. Soil-CO₂ emissions were marginally correlated with fine-root ingrowth (P = 0.06) but not with fine litterfall (P = 0.26), suggesting that fine-root detritus production is an important factor explaining soil-CO₂ emissions. Rhizosphere respiration was similar among species and contributed 52% of the total soil-CO₂ flux estimated on average. Similarities in belowground carbon allocation and rhizosphere respiration indicated that tropical tree species have similar metabolic activity belowground despite the substantial variation in root production

Initial nitrogen enrichment conditions determines variations in nitrogen substrate utilization by heterotrophic bacterial isolates

Background The nitrogen (N) cycle consists of complex microbe-mediated transformations driven by a variety of factors, including diversity and concentrations of N compounds. In this study, we examined taxonomic diversity and N substrate utilization by heterotrophic bacteria isolated from streams under complex and simple N-enrichment conditions. Results Diversity estimates differed among isolates from the enrichments, but no significant composition were detected. Substrate utilization and substrate range of bacterial assemblages differed within and among enrichments types, and not simply between simple and complex N-enrichments. Conclusions N substrate use patterns differed between isolates from some complex and simple N-enrichments while others were unexpectedly similar. Taxonomic composition of isolates did not differ among enrichments and was unrelated to N use suggesting strong functional redundancy. Ultimately, our results imply that the available N pool influences physiology and selects for bacteria with various abilities that are unrelated to their taxonomic affiliation. Electronic supplementary material The online version of this article (doi:10.1186/s12866-017-0993-7) contains supplementary material, which is available to authorized users

Nonlinearity of root trait relationships and the root economics spectrum

The root economics spectrum (RES), a common hypothesis postulating a tradeoff between resource acquisition and conservation traits, is being challenged by conflicting relationships between root diameter, tissue density (RTD) and root nitrogen concentration (RN). Here, we analyze a global trait dataset of absorptive roots for over 800 plant species. For woody species (but not for non-woody species), we find nonlinear relationships between root diameter and RTD and RN, which stem from the allometric relationship between stele and cortical tissues. These nonlinear relationships explain how sampling bias from different ends of the nonlinear curves can result in conflicting trait relationships. Further, the shape of the relationships varies depending on evolutionary context and mycorrhizal affiliation. Importantly, the observed nonlinear trait relationships do not support the RES predictions. Allometry-based nonlinearity of root trait relationships improves our understanding of the ecology, physiology and evolution of absorptive roots

Nodulation capacity in legume forest species (Fabaceae) according to their phylogeny and morphological characteristics

Gran parte del éxito de las plantas leguminosas (Familia Fabaceae) en los diferentes ecosistemas de Costa Rica podría deberse a su capacidad de establecer relaciones simbióticas con microorganismos de la familia Rhizobiaceae y al nitrógeno fijado que estas bacterias les pueden proveer. En este trabajo, evaluamos la presencia de nódulos, tejido donde se realiza la fijación de nitrógeno, en 24 especies forestales de leguminosas pertenecientes a cuatro subfamilias de Fabaceae y se anotaron varias características morfológicas de las raíces. Se detectó la presencia de nódulos en 14 de las 24 especies (58.3 %), sin embargo, hubo grandes diferencias entre las subfamilias. En las dos subfamilias consideradas las más basales (Detarioideae y Cercidoideae) no se detectaron nódulos. En la subfamilia Caesalpinioideae, se reportaron nódulos en el 58.3% de las especies, restringidas mayoritariamente al clado Mimosoideae. En la familia Papilionoideae, considerada la más derivada, se observó la presencia de nódulos en el 87.5 % de las especies evaluadas. La mayoría de especies con nódulos presentaron una coloración clara en sus raíces y las especies sin nódulos una coloración más oscura, con algunas excepciones. Estas tendencias están relacionadas con la historia filogenética de las subfamilias y los orígenes de la nodulación. Sin embargo, también podrían responder a diferentes mecanismos de infección e incluso podrían relacionarse con características fisiológicas de las plantas, como la producción de compuestos secundarios inhibitorios de la nodulación. De esta forma, este estudio establece un primer paso para entender mejor las interacciones entre los microorganismos fijadores de nitrógeno con sus hospederos.A large part of the success of legume plants (Fabaceae) in the different ecosystems of Costa Rica could be due to their ability to establish symbiotic relationships with microorganisms of the Rhizobiaceae family and to the fixed nitrogen that these bacteria can provide them. In this work, we evaluated the presence of nodules, the tissue where nitrogen fixation is carried out, in 24 forest species of legumes belonging to four subfamilies of Fabaceae, and several morphological characteristics of the roots were determined. The presence of nodules was detected in 14 of the 24 species (58.3 %); however, there were large differences between the subfamilies. In the two subfamilies considered the most basal (Detarioideae and Cercidoideae), no nodules were detected. In the Caesalpinioideae subfamily, nodules were reported in 58.3 % of the species, mostly restricted to the clade Mimosoideae. In the Papilionoideae family, considered the most derived, the presence of nodules was observed in 87.5 % of the evaluated species. Most species with nodules had a light coloration on their roots, and species without nodules had a darker coloration, with some exceptions. These trends are related to the phylogenetic history of the subfamilies and the origins of nodulation. However, they could also respond to different infection mechanisms and could even be related to physiological characteristics of plants, such as the production of secondary inhibitory compounds of the nodulation. In this way, this study constitutes. the first step to understand better the interactions between nitrogen-fixing microorganisms with their hosts.Universidad de Costa Rica/[111-B9-204]/UCR/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Toward a Coordinated Understanding of Hydro-Biogeochemical Root Functions in Tropical Forests for Application in Vegetation Models

Tropical forest root characteristics and resource acquisition strategies are underrepresented in vegetation and global models, hampering the prediction of forest–climate feedbacks for these carbon-rich ecosystems. Lowland tropical forests often have globally unique combinations of high taxonomic and functional biodiversity, rainfall seasonality, and strongly weathered infertile soils, giving rise to distinct patterns in root traits and functions compared with higher latitude ecosystems. We provide a roadmap for integrating recent advances in our understanding of tropical forest belowground function into vegetation models, focusing on water and nutrient acquisition. We offer comparisons of recent advances in empirical and model understanding of root characteristics that represent important functional processes in tropical forests. We focus on: (1) fine-root strategies for soil resource exploration, (2) coupling and trade-offs in fine-root water vs nutrient acquisition, and (3) aboveground–belowground linkages in plant resource acquisition and use. We suggest avenues for representing these extremely diverse plant communities in computationally manageable and ecologically meaningful groups in models for linked aboveground–belowground hydro-nutrient functions. Tropical forests are undergoing warming, shifting rainfall regimes, and exacerbation of soil nutrient scarcity caused by elevated atmospheric CO2. The accurate model representation of tropical forest functions is crucial for understanding the interactions of this biome with the climate

Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia

• Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. • We used a large‐scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low‐fertility soils in Central Amazonia after one year of fertilisation. • Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. • Here we show that rock‐derived nutrients determine root functioning in low‐fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicate that even slow‐growing tropical rainforests can respond rapidly to changes in resource availability

Termite sensitivity to temperature affects global wood decay rates.

Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate change effects on wood carbon pools. Using data from 133 sites spanning six continents, we found that termite wood discovery and consumption were highly sensitive to temperature (with decay increasing >6.8 times per 10°C increase in temperature)-even more so than microbes. Termite decay effects were greatest in tropical seasonal forests, tropical savannas, and subtropical deserts. With tropicalization (i.e., warming shifts to tropical climates), termite wood decay will likely increase as termites access more of Earth's surface

Impacto de la extracción de madera en la estructura florística y la regeneración de un bosque de cativo (Prioria copaifera Griseb.) en la Costa Caribe de Costa Rica

Tesis (magister scientiae en biología)--Universidad de Costa Rica. Sistema de Estudios de Posgrado, 2003.UCR::Vicerrectoría de Investigación::Sistema de Estudios de Posgrado::Ciencias Básicas::Maestría Académica en Biologí

Impactos de la extracción en la estructura y la dinámica de plántulas en un bosque tropical dominado por Prioria copaifera (Fabaceae), (Talamanca, Costa Rica)

The factors that determine the existence of tropical forests dominated by a single species (monodominated forests) have been the subject of debate for a long time. It has been hypothesized that the low frequency of disturbances in monodominated forests and the tolerance to shade of the monodominant species are two important factors explaining the prolonged dominance of a single species. We determined the role of these two factors by examining the effects of logging activities on the floristic composition and seedling dynamics in a Prioria copaifera dominated forest in Southeastern Costa Rica. We determined the floristic composition for trees ≥2.5cm DBH and the associated recruitment, survival and mortality of tree canopy seedlings in two sites logged two (L-02) and 12 years (L-12) prior to sampling and an unlogged forest (ULF). Our results showed that L-02 stands had lower species richness (25 species) than the L-12 and ULF stands (49 and 46 species, respectively). As expected, we found significant logging effects on the canopy structure of the altered forests, particularly when comparing the L-02 and the ULF stands. Seedling density was higher in ULF (0.96 seedlings/m2) than in the L-02and L-12 stands (0.322 and 0.466 seedlings/m2, respectively). However, seedling mortality was higher in the ULF stands (54%) than in the L-02 (26%) and L-12 (15%) stands. P. macroloba in L-02 was the only species with abundant regeneration under P. copaifera in L-02 stand, where it accounted for 35% of the seedlings. Despite the reduction in seedling abundance observed after logging, P. copaifera seems to maintain large seedling populations in these forests, suggesting that this species maintains its dominance after logging disturbances. Our findings challenge the hypothesis that the regeneration of monodominant species is not likely to occur under heavily disturbed canopy conditions.La determinación de los factores responsables de la existencia de bosques tropicales dominados por una sola especie (bosques monodominados) ha sido motivo de debate por largo tiempo. Se ha propuesto que la baja frecuencia de alteraciones en esos bosques y la tolerancia a la sombra de las plántulas de la especie monodominante son dos de los factores que contribuyen a explicar la prolongada dominancia de una sola especie en estos bosques. Se estudió el rol de estos dos factores evaluando el efecto de la extracción de madera sobre la composición florística y la supervivencia y crecimiento de plántulas en un bosque dominado por Prioria copaifera en la región sureste de Costa Rica. Para ello se determinó la composición florística de los árboles con un diámetro a la altura de pecho (DAP) ≥2.5cm y el reclutamiento, supervivencia y mortalidad de las plántulas de especies arbóreas en sitios donde se extrajo madera dos (L-02) y doce años (L-12) antes de este estudio y un sitio del que nunca se ha extraído madera (ULF). Nuestros resultados muestran que los bosques L-02 tienen una riqueza de especies menor (25 especies) que los bosques L-12 y ULF (49 y 46 especies, respectivamente). Como era de esperar, la extracción de madera tuvo efectos significativos en la estructura del dosel del bosque, particularmente al comparar los bosques L-02 y ULF. La densidad de plántulas fue mayor en bosques ULF (0.96 plántulas/m2) que en L-02 y L-12 (0.322 and 0.466 plántulas/m2, respectivamente). Sin embargo, la mortalidad de plántulas fue mayor en ULF (54%) que en L-02 (26%) y L-12 (15%). Pentachletra macroloba fue la única especie que mostró abundante regeneración bajo P. copaifera en parcelas L-02, representando el 35% las plántulas encontradas. A pesar de la reducción de la abundancia de plántulas observada después de la extracción de madera, P. copaifera parece capaz de mantener grandes poblaciones de plántulas en estos bosques. Estos resultados sugieren que P. copaifera puede mantener su dominancia después de las alteraciones causadas por la extracción de madera. Nuestros resultados no apoyan la hipótesis de que la regeneración de las especies monodominates es menos probable cuando el dosel del bosque sufre fuertes alteraciones

Logging impacts on forest structure and seedling dynamics in a Prioria copaifera (Fabaceae) dominated tropical rain forest (Talamanca, Costa Rica)

The factors that determine the existence of tropical forests dominated by a single species (monodominated forests) have been the subject of debate for a long time. It has been hypothesized that the low frequency of disturbances in monodominated forests and the tolerance to shade of the monodominant species are two important factors explaining the prolonged dominance of a single species. We determined the role of these two factors by examining the effects of logging activities on the floristic composition and seedling dynamics in a Prioria copaifera dominated forest in Southeastern Costa Rica. We determined the floristic composition for trees ≥2.5cm DBH and the associated recruitment, survival and mortality of tree canopy seedlings in two sites logged two (L-02) and 12 years (L-12) prior to sampling and an unlogged forest (ULF). Our results showed that L-02 stands had lower species richness (25 species) than the L-12 and ULF stands (49 and 46 species, respectively). As expected, we found significant logging effects on the canopy structure of the altered forests, particularly when comparing the L-02 and the ULF stands. Seedling density was higher in ULF (0.96 seedlings/m²) than in the L-02and L-12 stands (0.322 and 0.466 seedlings/m², respectively). However, seedling mortality was higher in the ULF stands (54%) than in the L-02 (26%) and L-12 (15%) stands. P. macroloba in L-02 was the only species with abundant regeneration under P. copaifera in L-02 stand, where it accounted for 35% of the seedlings. Despite the reduction in seedling abundance observed after logging, P. copaifera seems to maintain large seedling populations in these forests, suggesting that this species maintains its dominance after logging disturbances. Our findings challenge the hypothesis that the regeneration of monodominant species is not likely to occur under heavily disturbed canopy conditions. Rev. Biol. Trop. 62 (1): 347-357. Epub 2014 March 01