Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Resumen:

The anthropogenic deposition of nitrogen (N) and phosphorus (P) into terrestrial ecosystems has an influence on the leaf morphology and leaf properties of vegetation as well as on interactions within an ecosystem. In this context, the increased availability of nutrients has an impact on herbivory. In addition to the availability of nutrients, sea level has also been shown to influence these parameters. The shown work deals with the quantification of herbivory under the influence of N- and P-fertilization and differences in certain leaf parameters (leaf area, specific leaf area, leaf toughness, leaf nitrogen content and leaf area loss) between three altitudinal levels (1000 m, 2000 m, 3000 m). The study area was located in a tropical mountain rainforest in Southern Ecuador. In a nutrient manipulation experiment (NUMEX) 48 plots within the study areas were fertilized with either N, P or NP twice a year. Per plot 50 leaves were collected, examined for various parameters and then subjected to a nutrient analysis. The aim of this study was to figure out to what extent sea level influences the leaf morphology, nitrogen content and the leaf area loss of the vegetation within the control areas and to what extent fertilization with nitrogen, phosphorus or both elements changes these leaf properties. Finally, it was investigated whether possible changes in feeding rates resulted from an increased leaf nitrogen content. Sea level had a major influence on leaf strength, which increased with increasing height gradients, and on the specific leaf area and the mean leaf area, which decreased with increasing sea level. Many of the values differed significantly between the altitudinal levels. This suggests that not only the soil becomes nutrient-poorer with rising sea level, but also that the mineralisation of the few available nutrients is slower than at lower altitudes. The climatic environmental conditions, which become more extreme as the sea level rises, also explain the changes in the leaf parameters mentioned. Fertilisation instead did not have an influence as strong as sea level on the studied parameters. There were hardly any significant differences between the plots with different fertilisation. Since tropical forests are considered nutrient-limited, the addition of nitrogen led to the formation of large and soft leaves, which was expected. The correlations between leaf nitrogen content and SLA or leaf strength were positive and significant. Leaf area loss did not correlate with nitrogen content, which was unexpected. This can be attributed to the fact that plants show highly species-specific reactions to nutrient availability, which manifest themselves in very different plastic changes in growth and defence mechanisms against herbivore species. In this work a strong influence of the sea level on the leaf parameters could be determined. An increasing influence of fertilization on the feeding rate of herbivorous species was not found.

Resumen:

Global changes in nutrient deposition rates are likely to have profound effects on plant communities, particularly in the nutrient-limited systems of the tropics. We studied the effects of increased nutrient availability on the seedlings of six tree species in montane forests of southern Ecuador in situ. After five years of continued N, P, or N+P addition, naturally grown seedlings of each of the two most common species at each elevation (1000, 2000, and 3000 m asl) were harvested for analyses of leaf morphology, nutrient content, herbivory, and tissue biomass allocation. Most species showed increased foliar N and P concentrations after addition of each respective element. Leaf tissue N:P ratios of >20 in the control plants of all species suggest that P is more growth-limiting in these forests than N. Leaf morphological responses to nutrient addition were species and nutrient specific, with some species (Hedyosmum purparescens, Graffenrieda emarginata) exhibiting increased specific leaf area (SLA), and others (Graffenrieda harlingii) increased leaf area ratios (LAR). Pouteria torta (1000 m) had lower SLA and LAR after P addition. Increased herbivory was only evident in G. emarginata (after N and N+P addition). Only the species from 3000 m asl modified biomass allocation after nutrient addition. In general, N and N+P addition more strongly affected the species studied at the upper elevations, whereas P addition had a similar range of effects on the species at all elevations. We conclude that the responses of the studied tropical montane forest tree seedlings to chronic N and P addition are highly species-specific and that successful adaptation to increased nutrient availability will depend on species-specific morphological and physiological plasticity.

Resumen:

Uno de los aspectos importantes a considerarse en la producción eficiente de plántulas con fines de restauración es la calidad de semillas y su variabilidad. El objetivo de este estudio fue evaluar los parámetros de semillas de acuerdo con las reglas del “International Seed Testing Association” entre diferentes árboles madre o individuos de siete especies nativas (Cedrela montana, Morella pubescens, Inga acreana, Tabebuia chrysantha, Ocotea heterochroma, Oreocallis grandiflora y Myrcianthes rhopaloides) en dos bosques de montaña del sur del Ecuador. Estas especies fueron seleccionadas por la importancia ecológica, socioeconómica, y su gran potencial para la restauración. De un total de 35 árboles madre de todas las especies, se colectaron las semillas en sus respectivos periodos de fructificación, y en el laboratorio fueron analizados los siguientes parámetros: pureza, peso, contenido de humedad y germinación; adicionalmente se determinó el coeficiente de velocidad de germinación. Los resultados mostraron una similitud intraespecífica en cada especie para la mayoría de los parámetros; no obstante, el peso presentó alta variabilidad intraespecífica para todas las especies. El parámetro germinación obtuvo diferencias entre individuos para C. montana, T. chrysantha, O. heterochroma y M. rhopaloides. En cuanto a la velocidad de germinación, individuos de especies como O. grandiflora e I. acreana mostraron un alto coeficiente en contraste a los individuos de O. heterochroma y M. pubescens. La información generada en este estudio podría ser el primer paso en la formulación de pautas para la producción masiva de plántulas de especies nativas con fines de restauración.