Nutritional status and stress tolerance index in effective selection of poplar clones

The assessment of poplar clone productivity, with the goal of selection of elite genotypes for diverse ecological conditions, is the main pillar of tree breeding. The significance of GEI (genotype x environment interaction) in the volume stock production is the consequence of differences among genotypes on different sites or the changes in the relative ranking of genotypes [1]. Biotope- related stress is mostly linked to the low availability of elementary plant requirements, such as water and nutrients. There are three main factors that determine a success in poplar production: well aerated soil, favourable water supply and adequate mineral nutrition [2]. In the last decade the problems in management of poplar plantations and cultures (low increment, dieback of trees, difficult reforestation) in eastern Slavonia are becoming more common. As these are concurrent with the significant changes in the regime of floods and groundwater table, it is logical to assume that these phenomena are related. The stress caused by drought is characterized by loss of water, reduced water potential and leaf turgor loss with stomatal closure, which leads to a halt photosynthesis, disruption of metabolism and ultimately to the death of plants [3]. The growth and development of fast-growing trees such as poplars is dependent on the significant water consumption – for poplar plantations about 500 mm for a vegetation season [4], significantly more than the autochtonous forest vegetation. The understanding of morphological-anatomical and physiological changes caused by the lack of water can be used as a tool in tree breeding selection [5]. Optimum nutrition of fast-growing trees – given the adequate climatic conditions, water supply and soils free from toxic substances – is the most important prerequisite for high and lasting yields [6]. One of the most important goals of poplar selection is finding the genotypes that can produce high volume stock with a lower nutrient consumption. While for cultivation on most productive and optimal sites the genotypes with high demand for nutrients and water are most interesting, but selection of genotypes with smaller requirements will benefit the efficiency of poplar cultures on less productive sites [2]. The selection of poplar genotypes with a high adaptation value (high stress tolerance and potential production) in various stand conditions is the main goal of selection of poplar clones in eastern Slavonia. The reasons of recent poor performance of poplar clones in eastern Slavonia cannot be attributed to only one factor, but to various interactions of water availability and nutrients to plants that are specific for different siites. To better determine the causes for low increment, tree dieback and problematic reforestation of poplar cultures in eastern Slavonia this research should be directed towards a more detaild determination of water availability to the roots of a larger number of poplar clones in comparison with their nutritional status, preferably through several vegetational seasons, so as to encompass the dynamics of floods, soil water table and the influence of meteorological parameters. Since 'M1' and 'S 1-8' genotypes have modest yields both in high- and low-stress environments, future research should be based on a larger number of poplar clones.