Lianas are a diverse group of plants that are mainly distributed in the tropics and play an important role in the forests dynamics. The semideciduous seasonal forests, a phytophysiognomy characterized by a high abundance of lianas, have marked seasonality, presenting a dry and another rainy season. Because they are commonly found in the borders or in clearings of forest fragments, it is suggested that the lianas are heilophytes, but there are still few studies on its ecophysiology. Due to the fact that they are of great importance in the context of the fragmentation of the cerrado biome, the understanding of the physiology of the lianas is necessary. The present study aimed to characterize the photosynthetic activity, as well as characterize some leaf morphological attributes, in two species of lianas of a semidecidual seasonal forest fragment in the Uberlândia-MG region, during different periods of the dry season, one at the beginning, and another at the peak of the season. The species chosen were Banisteriopsis argyrophylla and Fridericia florida. For this, leaf gas exchanges, chlorophyll fluorescence and water potential of xylem (Ψw) were measured during April, June and August 2018. In addition, it was measured the leaf area (LA), the specific leaf area (SLA) and the relative water content (RWC) in July and December 2018, representing the dry and the rainy season, respectively. At the end of the dry season, when compared
to the beginning of the dry season, there was a clear reduction in stomatal conductance.
The lower opening of the stomatal pore resulted in reductions in CO2 net assimilation
(A) and transpiration (E) of the two species. Water use efficiency values remained
relatively stable even at the end of the dry season when Ψw and relative humidity (RH)
were lower. The potential quantum yield (Fv/Fm) pointed to a dynamic photoinhibition,
since the two species presented a depression of the Fv/Fm ratio close to midday with
recovery at the end of the day. The effective quantum yield (ΔF/Fm’) indicated that the
two species followed the tendency to adjust to the prevailing conditions. The difference
in seasonality was also evidenced by the leaf attributes. The values of leaf area (LA),
specific leaf area (SLA) and relative water content (RWC) were significantly higher in
the rainy season, when compared to the dry season. The Falker chlorophyll index
indicated a significant difference only in chlorophyll a in B. argyrophylla, which
presented a slightly lower value in the dry season when compared to rainy season. The
data obtained suggest that the lianas studied have mechanisms of protection against
damage in photosystem II (PS II) and tolerance to water scarcity, once they showed
recovery of the photoinhibition, and maintained relatively high net CO2 rates even at the
end of the dry season resulting in water use efficiency (A/E) stability.