Plasticidade fenotípica de quatro espécies arbóreas na alocação de biomassa e de características funcionais foliares em resposta a diferentes condições ambientais
Resumo
Forest degradation is characterized by the loss of biomass production, resilience, and resistance of
the ecosystem. The level of degradation of these ecosystems varies greatly between degraded areas,
generating a great variability in environmental conditions, which compromises the predictability
regarding the survival and growth speed of plants reintroduced in forest restoration projects. Several
plant species have a wide geographic distribution and can occur in places with different
environmental conditions above and below the ground. The morphological and physiological
characteristics of plants, which are related to resource use and conservation, may vary with different
abiotic conditions and resource availability. This study experimentally evaluated the effect of soil
fertility and light availability under nursery and field conditions on the allocation of biomass
between aerial parts (leaves and branches), root parts (thick and thin roots) and six functional
characteristics of plants: leaf area, specific leaf area, leaf dry matter content, leaf thickness, root
mass fraction and relative growth rate, after the first four months of planting. We selected four tree
species commonly used in forest restoration, namely Colubrina glandulosa Perkins (Rhamnaceae),
Hymenaea courbaril L. (Fabaceae), Myroxylon peruiferum L. f. e Pterogyne nitens Tul. (as três,
Fabaceae). In the nursery, we evaluated the effect of fertilization at three levels: the addition of low
or high amounts of mineral nutrients (NPK), composed of nitrogen (N), phosphorus (P) and
potassium (K), and the addition of organic matter to the soil. All fertilization treatments were
carried out in full sun and in 75% shading conditions to evaluate the effect of light in conjunction
with the effect of fertilization. We also evaluated the response of these plants when introduced in
the field, in a deforested area adjacent to a fragment of remaining riparian forest, but with high
fertility. The addition of NPK mineral fertilizer in the soil of the bags resulted in higher values of P
and K, but not of N, the addition of organic matter resulted in higher values of cation exchange
capacity, saturation of pH and N bases in the soil. In all species, plants reached higher biomass in
the nursery under high light intensity (full sun) and lower biomass in the field. In general, plants
tended to allocate more biomass to leaves and less to fine roots when grown in full sun. The
functional characteristics of the plants of the four species responded similarly to different conditions
of light, nutrient availability and the field. Light availability strongly influenced the functional
attributes of all species, with plants grown in shade showing higher values of specific leaf area and
lower values of leaf dry matter content and leaf thickness, thus producing softer and thinner leaves.
In the field, plants tended to produce smaller leaves, which may have been a response to water
stress. Our results showed that within the same species, plants are able to adjust to low light
conditions, forming leaves that are more efficient in light interception, characteristics associated
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with a more acquisitive strategy, within the foliar economy spectrum model, and when grown in full
sun, the plants tended to produce harder and thicker leaves, and therefore longer lasting, which is
characteristic of more conservative strategies. The type of fertilization had a little or neglectable
effect on the biomass production and the functional attributes of the plants. Plants in the field
tended developing leaves with a smaller area, probably as a strategy to reduce the effects of water
stress due to the long drought that occurred throughout the time of the experiment. This study
demonstrated that all species are quite plastic and that they responded similarly to the availability of
light and water, but that the variation in functional attributes in response to environmental
conditions was not enough to compensate for the extremes of water and light deficit. Therefore, the
functional attributes may reflect the different conditions of resource availability above and below
the ground in degraded areas, and the study of the phenotypic plasticity of plants may help to
understand the trajectories of plant communities, through greater predictability of biomass
production and management strategies in forest restoration projects.
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