Strategies in the use of light energy by Genipa spruceana Steyerm seedlings subjected to flooding

In an attempt to elucidate strategies in the use of light energy by G. spruceana seedlings subjected to flooding, we investigated the capacity of light capture and use of light energy by G. spruceana in three growing conditions: 1- absence of flooding (SA), 2- partially flooded (PA) and 3- totally flooded (TA). Destructive and non-destructive measurements, such as specific leaf area, chloroplast pigment (chlorophyll and carotenoids) content and fluorescence analyses, were made at regular intervals over a period of 90 days. All parameters decreased in seedlings subjected to flooding. Plants of treatment TA dropped all of their leaves after 30 days of complete submergence. Chloroplast pigment content differed between treatments SA and TA after 30 days from the start of the experiment; whereas SA and PA plants only differed for this variable after 90 days. Plants subjected to flooding (PA and TA) exhibited high dissipation of photochemical de-excitation (DIo/ABS), indicating a limited efficiency of light energy use. This fact was proven by the performance index (PI ABS) only in analyses after 90 days, and no significant difference was verified for PI ABS among treatments up to 30 days. Therefore, considering that G. spruceana seedlings subjected to flooding reduced the chloroplast pigment content more quickly than PI ABS, we suggest that the light energetic flux in G. spruceana seedlings subjected to flooding, in the beginning, is more restricted to a decrease in the structures that captures light (reduction chlorophyll pigment content) than how the photosynthetic apparatus functions (alterations in photochemical efficiency of photosystem II).Na tentativa de elucidar estratégias de utilização da energia luminosa em plantas jovens de Genipa spruceana Steyerm submetidas ao alagamento, nós investigamos a capacidade de captura e uso de energia luminosa em G. spruceana sob três condições de crescimento1- ausência de alagamento (SA), 2- plantas parcialmente alagadas (PA) e 3- plantas totalmente alagadas (TA). Medidas de área foliar específica, teores de pigmentos cloroplastídicos e fluorescência da clorofila a foram feitas em intervalos regulares no período de 90 dias. Todos os parâmetros analisados diminuíram em condições de alagamento (PA e TA). Aos 30 dias, as plantas no tratamento TA sofreram abscisão foliar. Os teores dos pigmentos cloroplastídicos (clorofilas e carotenóides) entre os tratamentos SA e TA diferiram aos 30 dias. Ao passo que, somente foi possível verificar diferenças entre os tratamentos SA e PA aos 90 dias. As plantas submetidas ao alagamento (PA e TA) exibiram alta dissipação de energia de excitação (DIo/ABS) indicando limitada eficiência na utilização da energia luminosa. Este fato foi comprovado pelos resultados do índice de desempenho (PI ABS) somente ao fim do período experimental (90 dias). Mas, não foi verificado diferença para PI ABS entre os tratamentos aos 30 dias. Portanto, considerando que G. spruceana submetidas ao tratamento TA reduziram seus teores de clorofilas mais rapidamente do que decrescem seus PI ABS, sugere-se que o fluxo de energia luminosa em plântulas de G. spruceana sob alagamento total, no início, é mais restringido pelo decréscimo na estrutura de captura de luz (diminuição dos pigmentos cloroplastídicos) do que no funcionamento do aparato fotossintético (alterações na eficiência fotoquímica do fotossistema II)

Crescimento, partição de biomassa e fotossíntese em plantas jovens de Genipa spruceana submetidas ao alagamento

Genipa spruceana Steyerm (Rubiaceae) is a species often found in flooded environments in the central Amazonia. The objective of this study was elucidate possible adaptive strategies that enable this species to occupy environments under flooding, targeting the potential of the species for restoration of floodplains. In order to achieve these objectives growth traits, number of leaves, leaf expansion, biomass production, carbon assimilation and stomatal conductance were investigated in G. spruceana seedlings subjected to treatments: 1- Non flooded plants (control –SA), 2- partially flooded (PA) and 3- completely flooded (TA) up to 90 days. Flooded treatments (PA and TA) induced smaller increments in all variables of height and diameter growth when compared to the control treatment. With increase of flooding, biomass allocation to leaves decreased until complete leaf abscission in TA, while increased in the stem. In PA treatment was observed reduction in C assimilation rates of 58% and 64% after 60 and 90 days, respectively, and 96% after 60 days in TA treatment. However, in the end of the experiment all treatments presented 100% of survival. Our results indicate that the loss of leaves and gain of the stem biomass can be protective strategy to alleviate the harmful effects of the flooding. On the other hand, the maxim survival rates suggest that G. spruceana exhibit high potential for establishment in frequently flooded areas

Flooding of tropical forests in central Amazonia: what do the effects on the photosynthetic apparatus of trees tell us about species suitability for reforestation in extreme environments created by hydroelectric dams?

Brazil plans to construct many new hydroelectric dams in the Amazon region. The new conditions of flooding promoted by reservoirs can alter photosynthetic processes, and the study of physiological responses of trees can be used for selected suitable species to reforest these altered areas. The present study analyzed changes in pigment content and photosynthetic performance in flood-tolerant and flood-intolerant species that are common in the floodplains along the Uatumã River and on islands in the reservoir of the Balbina Hydroelectric Dam. Their photosynthetic responses were tested using chloroplast pigment content and chlorophyll a fluorescence. Flooding caused a significant reduction in pigment content in all of the three flood-intolerant species and in one of the seven flood-tolerant species studied. Flood-tolerant species were unaffected and neither a change in their chlorophyll contents nor a decrease in the efficiency of energy use in the photosynthetic process was observed. From chlorophyll a fluorescence transients (OJIP transients) was calculated the performance index (PIABS), a parameter derived from the OJIP transient by means of the JIP-test (translation of original fluorescence measurements into biophysical expressions quantifying the stepwise flow of energy through photosystem II). This parameter was a very sensitive indicator of the physiological status of trees under field and was shown to be a particularly sensitive indicator of stress tolerance in flood-intolerant species during inundation, whereas flood-tolerant species had only minor reductions in their photosynthetic performance. We suggest that tree species selection for reforestation around reservoirs can benefit from species-specific measurements of photosynthetic response using the JIP-test. © 2015, Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków

Germinative behaviour of ten tree species in white-water floodplain forests in central Amazonia

Amazonian floodplain forests (known as várzea) are classified into high or low várzea depending on the spatial position on the plains. This topographic feature exposes the terrain over different time periods of inundation, causing a major limiting factor for tree seedling establishment. We hypothesize that, strategically, most of the seeds produced by trees in low várzea forests germinate faster and in synchrony (temporally concentrated germination), and that their seedlings tend to have cotyledons without reserve or foliaceous cotyledons (PEF). By contrast, seeds produced by high-várzea specialist trees exhibit slower and temporally scattered germination, and their seedlings tend to have reserve storage cotyledons (CHR). Generalist species may show no clear pattern or may be related to high-várzea species. To test this hypothesis, diaspores of 10 tree species were collected: five of low-várzea specialist trees, three of high-várzea specialist trees and two of generalist species. Seedling emergence and morphology were monitored daily in a nursery for a period of 150 days of being subjected to non-flooded (sown directly in várzea soil) and flooded conditions (15 days in water before sowing in the same soil). The seedling emergence of low-várzea species showed an increase of 37% in germinability whereas high-várzea and generalist species exhibited a decrease of 38% and 35% of germinability, respectively. Foliaceous cotyledons were preferentially found in seedlings of low-várzea species, and storage cotyledons were more common in those of high-várzea species, indicating how cotyledon morphology may determine the amount and use of resources available to a seedling during the first stages of establishment and growth. Conservation plans aiming for the maintenance of ecosystem services must consider these strategies. © 2017, Institute of Botany, Academy of Sciences of the Czech Republic

Indirect effects of habitat loss via habitat fragmentation: A cross-taxa analysis of forest-dependent species

Recent studies suggest that habitat amount is the main determinant of species richness, whereas habitat fragmentation has weak and mostly positive effects. Here, we challenge these ideas using a multi-taxa database including 2230 estimates of forest-dependent species richness from 1097 sampling sites across the Brazilian Atlantic Forest biodiversity hotspot. We used a structural equation modeling approach, accounting not only for direct effects of habitat loss, but also for its indirect effects (via habitat fragmentation), on the richness of forest-dependent species. We reveal that in addition to the effects of habitat loss, habitat fragmentation has negative impacts on animal species richness at intermediate (30–60%) levels of habitat amount, and on richness of plants at high (>60%) levels of habitat amount, both of which are mediated by edge effects. Based on these results, we argue that dismissing habitat fragmentation as a powerful force driving species extinction in tropical forest landscapes is premature and unsafe