Sudden opening and slow changes in canopy coverage modulate acclimation, survival and growth of a shade-tolerant rainforest tree species

ANA PAULA MORETTI; OLGUIN, FLAVIA YESICA; GAUNA JUAN MARCELO; GRACIANO, CORINA

Journal of Forestry Research

Springer

Año: 2023

1007-662X

Disturbances at gap levels are one of the most important events for the regenerationand establishment of fast-growing intermediate species that initially established in theunderstory, but then require more light to grow and reach the upper strata. However,sudden changes in light could affect the survival and growth of plants established inthe understory that fail to acclimate to the new microenvironment. Sudden canopyremoval exposes plants to high light intensity and high evaporative demands thatstress shade-acclimated plants. On the other hand, the slow closure of gaps reducelight availability to young plants established when the incident irradiation was higher.The aim of this work was to evaluate the morphological and physiological acclimationof Cabralea canjerana (Vell) Mart. young plants to sudden and slow changes in canopycoverage. We carried out a pot experiment with plants exposed to a sudden opening ofthe natural canopy coverage (light shock) and another field experiment with plantsplanted in a natural coverage gradient in rainforest gaps. In the pot experiment, fewdays after the light shock, plants rapidly increased photosynthetic rate and decreasedleaf water potential. After two months, plants activated physiological responses at leaflevel and whole plant level to high light and water stresses, like increase stomatalconductance, stomatal index and reduction of leaf: fine roots ratio and chlorophyll. Afterseven months, plants increased hydraulic conductivity of petioles and the whole leafhydraulic conductance, and growth was much higher than plants that remained underthe canopy. In the field experiment, plants acclimated to all canopy coverageintensities, as environmental conditions were intermediate to those in the potexperiment. Seven years after planting, plant growth was maximal when trees wereplanted in open microenvironments within the gaps, even if the canopy closed during the first 20 months after planting. In conclusion, if the species is planted to enrich therainforest, the positions within the gaps with lower canopy coverage should be chosen,and gap closure will not affect plant growth. To manage C. canjerana naturalregeneration, the opening of gaps and removal of understory will increase plantsurvival and growth, without the risk that the stress caused by these sudden openingcould lead to the death of young plants. Finally, combining pot and field experiments isuseful to understand the autoecology of trees with particular ecological interest, and tobuild restoration practices with scientific knowledge.