Efeito da limitação nutricional do solo no crescimento e herbivoria de plântulas na Amazônia Central

Abstract

The East-West nutritional gradient of the Amazon Basin, together with the seasonality of precipitation, availability of light and herbivory seem to shape the productivity in the Amazonian Forest. However, productivity models rarely consider the importance of seedlings and the nutritional limitation in Amazonian soils. Thus, the present study makes use of a large-scale in situ experiment to evaluate how the experimental addition of nutrients influences seedling growth and herbivory rates. We also aimed to investigate how the factors related to seasonality (especially precipitation) affect the growth of tree species at the Amazon Fertilization Experiment – (AFEX). The sampling design were designed in complete factorial, with four replicates (blocks) and eight plots of 50 x 50 m, one for control and the others with the addition of Nitrogen (N), Phosphorus (P) and Cations (K, Ca, Mg). For seedlings’data collection, 4 sub-plots of 1 x 1 meter per plot were established. All individuals with height ≥ 20 cm and diameter of the collection ≤ 1 cm were sampled. The number of total leaves per individual was counted and the 10 mature leaves closest to the apical bud were monitored for herbivory Herbivory (%) was estimated visually. The addition of nutrients did not promote growth, probably due to the low availability of light. The addition of N resulted in a significant increase in herbivory, probably because N is limiting the development of herbivores, so its addition improves their leaf palatability. The seasonality of rainfall was the factor that most influenced seedling growth and herbivory. Seedlings have a shallow root system and low water and nutrient storage capacity, making them susceptible to drought. Rainy months seem to boost herbivory due to the high abundance of herbivorous insects in this period. The greater number of leaves explained 50% of the growth for treatments with the addition of N. N increases the leaf area and photosynthetic rates, therefore, it may have promoted this positive relationship. As a highlight, our study proposes a secondary importance of nutrients, where low light and water seasonality seem to shape the productivity patterns of understory seedlings. Keywords: Seasonality, fertilization, plant-soil interaction, seedlings, herbivory