Ecophysiological processes and wood anatomy related to growth and drought resistance in genotypes of Eucalyptus grandis

TESÓN, N.1, MONTEOLIVA, S.2, LICATA, J. A1 AND FERNÁNDEZ, M. E

Bahia

Conferencia; IUFRO 2011 Conference. Improvement and Culture of Eucalyptus; 2011

The main objective of this study is to identify ecophysiological processes and wood functional characteristics of four different clones of Eucalyptus grandis that would explain their growth differences under normal and water stress situations. This abstract examines preliminary results and outline our in progress research projects. The study was performed on a 14 year-old E.grandis clonal productivity trial located in Concordia, Entre Ríos, Argentina (Lat: 31°22’ S, Long: 58° 07’ W Alt: 43 m. Four clones named: 2, 4, B and K were selected from the Tree Breeding Program of INTA (Instituto Nacional de Tecnología Agropecuaria) with a variable range of growth rates and contrasting values in wood density: high and low. diameter breast height, sap flow density, leaf water potential (predawn and midday), specific leaf area, osmotic adjustment, and weekly measurements of soil water content were measured. In addition, wood anatomy was characterized through morphometric measurements of sapwood samples from nine trees per clone  at 1.3 m height. The clones evaluated showed different response patterns to drought stress that could be explained by the measured physiological and anatomical variables. Clone 2 growth, one of the high wood density clones, was the most negatively affected (both in absolute growth rate and relative to previous mean growth rate) during the severe drought period. However, the other high wood density clone (clone K) was the one with the best performance during the drought period. This differential growth rate was related to water use during the drought period, where the clone K showed the highest and clone 2 the lowest transpiration rates. The better performance by the clone K could also be explained by the significantly higher osmotic adjustment capacity than the other clones. during the period after drought, all the clones increased their water use and growth rates (Table 1). However, during the post drought period transpiration rates differed among clones in correspondence with their wood density, suggesting that the high density clones (K and 2) recovered from the drought stress faster than the low density clones (B and 4). The transpiration response sensitivity to evaporative demand, also showed a higher sensitivity of high density than low density clones. This could imply a loss of either leaf area or hydraulic conductivity in the low density clones, which would require a longer period to recover to a previous drought condition. High wood density clones showed a greater fiber walls thickness than low density clones. Clone B, the clone with the highest mean growth rate and poor performance after drought had the thinnest fiber walls, the highest percentage of vasicentric tracheids, the vessels with the largest lumen diameter, and the lowest midday leaf water potential during the drought period (-3.3 +/- 0.23 MPa vs. -2.9 +/- 0.3 MPa in other clones).This suggests that a lower stomatal control of water potential maybe leading to cavitation under severe drought. When calculated the theoretical wood specific hydraulic conductivity (ks) of wood, clone B had the highest ks (Table 1). Therefore, there could be a tradeoff between conductivity and resistance to cavitation in this clone, implying a high growth rate when resources are available, but a fast shutdown when they are not, plus a slower recovery than non cavitated trees. On the other hand, this tradeoff does not appear to occur for clone K, which presented a small reduction in growth rate during the drought period, and at the same time a high growth rate after the drought. It is possible that wood and leaf anatomy and physiology could explain this behavior. Clone K had high density wood, but also high ks due to large vessel diameters. Additionally, its leaves showed a high osmotic adjustment, and low specific leaf area. Specific leaf area was also lower in both clones with higher wood density (SLA: 80 and 124 mm2 g-1), suggesting a functional relationship between wood and foliar anatomy which deserves to be more explored. Some of the wood anatomical variables, such as vessel diameter and frequency, showed a significant block effect, implying a high plasticity of these features that determine the wood’s capacity to conduct water. More measurements are needed to understand which specific conditions of the sites created this response. The results presented above are still preliminary. However, given the response differences found among clones, we expect that anatomical and ecophysiological measurements will help to understand the differential responses to environmental conditions of Eucalyptus grandis and will consequently become useful tools to aid in the selection of breeding material.