Restingas & Facilitation

Growth, survival, and phenotypic plasticity of seedlings from Brazilian coastal sandy plains (Restingas) in response to experimental gradients of light and water availability

Fieldwork at the Restinga of Massambaba (RJ, Brazil) - Photo credit: I.Matos

Sunset at the Restinga of Massambaba (RJ, Brazil) - Photo credit: I. S. Matos.

In patchy coastal habitats (Restingas) plant recruitment is hampered by multiple stressful factors. Sheltered conditions beneath nurse plants can enhance seedlings’ performance through increased moisture or inhibit seedlings' growth due to light suppression. The net outcome between facilitation and competition interactions between nurse plants and seedlings may vary among species (depending on their ability to cope with limiting resources), as well as across seasons (due to seasonality on stress levels).

My Master's dissertation aimed to evaluate the growth, survival, phenotypic plasticity, and biotic interactions of coastal dune seedlings in response to light and water availability that simulate environmental conditions beneath and away from nurse plant canopies. My master was divided into the following four chapters:

CHAPTER 1

Microclimatic amelioration inside vegetation patches as a mechanism of facilitation in a Semiarid Sandy Coastal Plain in Brazil

Measurement of microclimatic conditions inside and outside the vegetation patches of the Restinga of Massambaba (RJ, Brazil) - Photo credit: I. S. Matos.

In this first chapter, we measured a series of microclimatic conditions (sunlight, air temperature, air humidity, soil temperature, and soil moisture) inside and outside nurse plants' canopy over four seasons to evaluate: (1) whether nurse plants improve environmental conditions beneath their canopy (i.e. reduced sunlight exposure, increased humidity, increased soil water availability), and (2) if microclimatic improvements are consistent across the seasons or they show seasonal variation. We observed that (1) soil and air temperatures easily reached potentially lethal values outside the nurse plants canopies. Constrastingly, inside the vegetation patches, conditions were shaded, cooler, wetter and presumably more favourable for seedling establishment; (2) the amelioration on both above- and below-ground microclimatic conditions occured along the four seasons. Therefore, the facilitative mechanism (positive interaction) between nurse plants and seedlings can occur throught the year, resulting in the patchy spatial organization of the Restinga vegetation.

CHAPTER 2

Restinga seedlings’ performance in response to light and water limitations: trade-off between increased survival and reduced growth

Greenhouse at the Rio de Janeiro Botanical Garden were the shade and drought experiments were conducted - Photo credit: I. S. Matos.

I design and conducted a series of greenhouse experiments to investigate if the net outcome between facilitation and competition among nurse plants and beneficiary seedlings would vary across species as a function of their combined tolerance to shade and drought. I evaluated the survival and growth responses of eight seedling species (check out the 8 studied species at the end of this webpage!) under distinct light (2, 10 and 80% of light) and water conditions (high versus low soil water availability), which simulate the microclimatic gradient found from inside to outside vegetation patches in the Restingas. Shaded conditions beneath nurse plants (i.e. inside vegetation patches) enhanced seedlings' survival, but reduced their growth rates. Three patterns of seedling response to ligth and water availability were observed: (1) obligatory beneficiary seedlings do not survive under high light and have their regeneration niches restricted to inside the vegetation patches; (2) facultative beneficiary species may or may not be favored by the presence of the nurse plant depending on the level of water availability; and (3) neutral species can establish both inside or outside the vegetation patches.

CHAPTER 3

Functional traits linked to facilitative responses of seedlings from a Semiarid Sandy Coastal Plain vegetation in Brazil

Scheme of seedling spatial distribution inside and outside Restinga vegetation patches. Nurse plant (black), obligatory beneficiary species (green: Clusia hilariana, Erythroxylum ovalifolium, Garcinia brasiliensis, Maytenus obtusifolia, Ormosia arborea) and non-obligatory beneficiary species (orange: Allagoptera arenaria, Eugenia selloi, Neomitranthes obscura).

I also measured morphological traits linked to biomass production and allocation (such as, specific leaf area, leaf dry matter content, root:shoot ratio) and performed a principal component analysis to investigate the different plant functional strategies in response to microclimatic changes provided by nurse plants. I found that obligatory beneficiary species are characterized by an opportunistic strategy, exhibiting lower seed mass, higher relative growth rates and higher efficiency in allocating biomass on structures for water absorption and light-capturing; while non-obligatory beneficiary species showed traits linked to a conservative resource-use strategy ( larger seeds, lower relative growth rates and lower specific leaf area), that could sustain seedling persistence under more stressful conditions found outside the vegetation patches. Therefore, I concluded that morphological traits of seedlings can be used to predict the net effect of plant-plant interactions, providing important insights into the factors that regulate the structure and the natural regeneration of Restinga communities.

CHAPTER 4

Morphological phenotypic plasticity and integration of seedlings from a coastal vegetation in response to light and water

Greenhouse experiment with seedlings of Maytenus obtusifolia (Celastraceae) from the Restinga of Massambaba (RJ, Brazil) - Photo credit: I.Matos

I measured the degree of morphological traits plasticity and integration in response to light and water conditions. I found that neither plasticity nor integration were important to differentiate obligatory from non-obligatory seedling species. Both functinal types can exhibit either low or high values of plasticity and integration for their traits. Thus, our results did not support the hypotehsis that a high degree of integration could constrain plastic response of seedlings to light and water.

GENERAL CONCLUSIONS

Interspecific differences on seedlings’ performance have implications on natural regeneration of coastal communities, altering the balance between plant-plant interactions and the spatial distribution of species.

8 SEEDLING SPECIES FROM THE RESTINGA OF MASSAMBABA

Seeds and seedlings (60 days) of 8 species from the Restinga of Massambaba (RJ, Brazil): A. Allagoptera arenaria (Arecaceae); B. Clusia hilariana (Clusiaceae); C. Erythroxylum ovalifolium (Erythroxylaceae); D. Eugenia selloi (Myrtaceae); E. Garcinia brasiliensis (Clusiaceae); F. Maytenus obtusifolia (Celastraceae); G. Neomitranthes obscura (Myrtaceae); H. Ormosia arborea (Fabaceae) - Photo credit: I. S. Matos.

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