Eucalyptus spp. and Populus spp. coping with salinity stress: an approach on growth, physiological and molecular features in the context of short rotation coppice (SRC)

Abstract

A holistic approach, molecular and eco-physiological, has provided a better understanding of the response of eucalyptus and poplar genotypes to salt stress. Different tolerance mechanisms with varying degrees of effectiveness as well as differences in the response of genes linked to xylem differentiation have been identified. We studied the behavior of four eucalyptus genotypes (Eucalyptus camaldulensis Dehnh: ‘169’; E. grandis Hill ex Maiden × E. urophylla S.T. Blake: ‘5E’; Eucalyptus globulus Labill: ‘Anselmo’ and ‘Odiel’) and four poplar genotypes (Populus alba L.: ‘PO 10-10-20’ and ‘J 1-3-18’, P. tremula L. × P. alba: ‘7171-B4’ and P. × canadensis Moench.: ‘Oudenberg’) in relation to their response to saline conditions and their capacity to grow in short rotation for biomass production. For this purpose, plants were grown under greenhouse conditions and subjected to two different saline concentrations of NaCl, one moderate (50 mM) and one severe (125 mM), as well as a control treatment. Growth, as well as several functional, morphological and biochemical parameters were considered. We also performed an expression analysis of genes that encode enzymes and transcription factors involved in wood formation. The four eucalyptus genotypes showed a very high survival rate under both moderate and severe salt treatments, as did both white poplar genotypes (‘PO 10-10-20’ and ‘J 1-3-18’). All of them displayed a tolerant behavior toward salinity stress. In contrast, the poplar hybrids (‘7171-B4’ and ‘Oudenberg’) exhibited medium-tolerance or sensitive behavior. Possible tolerance mechanisms based on stomatal control, water use efficiency, capacity of dilute toxic ions through decreasing the specific leaf area and higher root/aerial biomass ratios were detected. These mechanisms were deemed to have varying degrees of effectiveness. A molecular approach identified changes in the expression of genes linked to xylem differentiation, the more tolerant genotypes being those with fewer modifications. These findings could contribute towards enabling the cultivation of fast-growing species in short rotation on marginal land affected by salinity for the production of lignocellulosic biomass. The response variability detected could lead to advances in breeding for tolerance to this type of stress.