Photosynthetic response of umbu trees to vapor pressure deficit

Abstract

The objective of this work was to evaluate the photosynthetic response to vapor pressure deficit (VPD) in umbu (Spondias tuberosa) tree accessions. The experiment was carried out in a completely randomized design in a 5×7×2 factorial arrangement (five umbu accessions – BRS-68, EPAMIG-05, BGU-61, BGU-75, and BGU-50 –, seven evaluation times, and two reading times – at 8 a.m. and 2 p.m.) in split-split plots in time. Leaf temperature increased with air temperature. The variation of stomatal conductance and transpiration with the VPD was not significant. Net photosynthesis rate, carboxylation efficiency, and instantaneous water-use efficiency decreased with increasing VPD in all accessions, except in BRS-68, whose rates remained positive.

Gas exchange in umbu tree accessions

“…This condition contributed to higher VPD in the afternoon and increased transpiration rates, which is related to the plant's heat exchange mechanism to reduce thermal stress, even with a reduction in stomatal conductance (Arantes et al, 2016;Coelho et al, 2021). There may be no correlation between stomatal conductance and transpiration with VPD in umbu trees (Donato et al, 2022).…”

“…Conversely, the highest WUE and A/C i rates were recorded on 12/23/2020 and 04/27/2021, justified by the occurrence of rainfall in the period prior to the day of evaluation, 18.13 mm on 12/20/2020 and 88.5 mm between 04/19 and 23/04/2021. Rain events improved water availability in soil and contributed to a milder atmosphere with lower VPD because both WUE and A/C i vary inversely with VPD for the umbu accessions (Donato et al, 2022).…”

“…Assessing gas exchanges allows characterizing genotypes through physiological responses to local conditions (Donato et al, 2022), establishing genotypic variation and guiding the choice of accessions that are more adapted to site-specific conditions. The effect of the interaction between gas exchange and environmental variations can instantly correlate with productivity and 2 p.m. Gas exchange rates were measured from the rainy season to the beginning of the dry season (December to May) on leaves in the middle third of the canopy, between the 3rd and 5th fully expanded leaf pair, using an infrared gas analyzer (IRGA) model Lcpro + ® Portable Photosynthesis System (ADC BioScientific Limited, UK), under ambient temperature and irradiance, air flow of 200 ml min -1 and, radiation shield facing the sun (Donato et al, 2022). The readings were incident leaf radiation -Q leaf (μmol photons m -2 s -1 ), leaf temperature -T leaf (ºC), internal CO 2 concentration -C i (μmol CO 2 mol -1 ), stomatal conductance -g s (mol H 2 O m -2 s -1 ), transpiration -E (mmol H 2 O m -2 s -1 ), net photosynthesis -A (μmol CO 2 m -2 s -1 ); instantaneous water use efficiency -WUE (μmol at the beginning and at the end of the rainy season;…”