Dynamics of water-use efficiency and status in promising Hevea brasiliensis genotypes: implications for clonal selection

Photosynthesis-Related Responses of Colombian Elite Hevea brasiliensis Genotypes under Different Environmental Variations: Implications for New Germplasm Selection in the Amazon

“…In the rainy period, the stomatal conductance was high in most genotypes, allowing a greater fixation of CO 2 that translated into a maximum use of soil water for transpiration, which was expressed by a lower WUE, results that coincide with that reported by Blum et al [44], but contradict other studies that have indicated greater photosynthesis in the dry period of the Amazon region [13,45,46]. This reflects contrasting photosynthetic responses at the intra-specific level of H. brasiliensis, in which some genotypes require greater water availability to maintain high photosynthetic rates; others are more efficient at using water to maintain these rates, and others are affected in terms of their efficiencies, photosynthesis and water status under drought conditions [11,19,20]. In this study, in both environments (semi-humid warm and humid warm), the dry period and range between 9:00 and 12:00 h saw 60-70% of the genotypes with minimal reductions (<30%) in photosynthetic rates while others (30-40%) had moderate increases in photosynthesis (>20%).…”

“…Similarly, increases in VPD and AT that directly affect the photosynthetic rate by reducing the supply of CO 2 to rubisco as a result of a decrease in g s and Ci in the dry period [41,42], are more evident in young plants than adults since they do not have a sufficient volume of roots that would facilitate better use of the water available in deep levels of the soil [43]. However, in this study, the young individuals (two years old) of the Colombian genotypes had more efficient use of water and avoided important reductions in the leaf water potential during the dry period between 9:00 and 12:00 h, as compared with some 9-year-old introduced genotypes evaluated in the same environments, which had reductions in Ψ L above 50% [20], and decreases in the photosynthetic rate, between 30 and 40% [13] as compared to Colombian genotypes.…”

“…Thus, various physiological traits related to the photosynthetic performance of H. brasiliensis, such as the photosynthetic rate, water use efficiency, girth growth, latex yield, and biomass production are influenced by the interaction of the genotype with environmental variations that allow the species to adapt or acclimate to limiting or stressful conditions [13,19,20,25,27,28].…”

“…The limitations evidenced in the gas exchange parameters during the dry period, which were associated with an increase in VPD, reflect the need to conserve water as a strategy to survive droughts [20,21], which, in this study at the time of highest photosynthetic efficiency (9:00 h), caused reductions between 45 and 47% in photosynthetic rates in some genotypes such as ECC 25 and ECC 60 and reductions between 31 and 35% in leaf water potentials in others such as IAN 873 and ECC 64, with respect to the rainy period (Figures 2 and 3).…”

“…Various studies carried out in the Colombian Amazon have sought to identify new introduced genotypes with desirable characters that are adaptable to different conditions and environments in the growth phase [13,20] and in the early production phase [21]. One of the greatest opportunities for the genetic improvement of H. brasiliensis lies in the regional elite germplasm [22].…”