Responses to Drought in Seedlings of European Larch (Larix decidua Mill.) from Several Carpathian Provenances

Abstract

European larch (Larix decidua Mill.) has been reported either as more tolerant or as more sensitive to drought than conifers with perennial leaves. Previous studies have revealed that Carpathian populations of European larch display a high genetic variability. A comparative study of the responses of these populations to drought stress at the seedling stage might allow the identification of drought tolerant genotypes and reliable drought stress biomarkers, which could be eventually used for the early detection of drought effects in larch, not only under control greenhouse conditions, but also in their natural stands. Growth responses were analyzed in larch seedlings from six Romanian Carpathian populations, submitted to one month of mild drought stress under controlled conditions. Levels of photosynthetic pigments (chlorophylls a and b, and carotenoids), osmolytes (proline and total soluble sugars), monovalent cations (Na+ and K+), and malondialdehyde (MDA) and non-enzymatic antioxidants (total phenolics and flavonoids) were compared with control treatments and between populations. Growth and the pattern of the biochemical responses were very similar in the six populations. Drought stress lead to stem length decrease in all population, whereas reduction of fresh weight of needles was significant only in one population (BVVC), and reduction of water content of needles in two populations (BVVC and GuHo). The optimal biochemical traits for an early detection of drought symptoms in this species is the increase—in most populations—of total soluble sugars, MDA, and total phenolic compounds, whereas K+ reduction was significant in all populations. Photosynthetic pigments remained unchanged, except for the Anin population where they were reduced under stress. Multivariate principal component and hierarchical clustering analyses confirmed the impact of drought in the growth and physiology of European larch, and revealed that the humidity of the substrate was positively correlated with the growth parameters and the levels of K+ in needles, and negatively correlated with the levels of MDA, total soluble sugars, total phenolic compounds, and flavonoids in needles.

Responses to Water Deficit and Salt Stress in Silver Fir (Abies alba Mill.) Seedlings

“…On the contrary, in A. alba, salt stress caused the accumulation of relatively high concentrations of Na + and Cl − (and also Ca 2+ ) in roots and needles, in parallel to the increasing NaCl concentration in the irrigation water. This behaviour has also been reported for other coniferous species [18,65,69]. What should be highlighted is that, for each NaCl concentration, the levels of all tested ions were substantially higher in the needles than in the roots, indicating the presence of active systems for their transport to the aerial parts of the plants.…”

“…Photosynthetic pigments can be included in these putative stress markers, as inhibition of photosynthesis is also a common effect of stress [60][61][62], and is accompanied by a reduction of chlorophyll contents, by inhibition of its synthesis combined with activation of its degradation [63]. Previous studies on plants of different conifer species exposed to salt or drought treatments have also reported a decrease in chlorophylls a and b and, in some cases, in total carotenoids [59,64,65]. Following this general trend, in the present study, water and salt stress caused a significant reduction of chlorophylls a and b contents in silver fir needles.…”

Toward the Genetic Improvement of Drought Tolerance in Conifers: An Integrated Approach

“…This is understandable, but it means that many ecologically important taxa, such as Cupressaceae, should receive more attention, as they could provide valuable information, being remarkably drought-tolerant [46]. Efforts have been made to integrate different approaches to better understand conifer adaptations to water stress [49,66,133,135,145,164]; most of the studies, especially those looking at gene expression, were performed on seedlings or young ramets [142,144,145,150,223]. This, although important to understanding the molecular mechanisms involved in plant responses to drought, does not necessarily reflect the behavior of an adult tree when subjected to the same conditions.…”

“…In Larix decidua, six Carpathian populations were submitted to a month of mild DS under controlled conditions. Several biochemical parameters were measured, looking for the optimal biochemical markers for an early detection of drought symptoms [135]. A lot of attention has been given in the last decade to NSC dynamics, specifically to understanding whether a dehydration-induced carbohydrate limitation (source limitation) or a direct effect of low water availability (sink limitation) is responsible for reducing plant growth under DS [66,75,136].…”

Moderate and severe water stress effects on morphological and biochemical traits in a set of pepino (Solanum muricatum) cultivars

“…Soluble sugars are also functional osmolytes in many different plant species (e.g., Gil et al, 2013;Al Hassan et al, 2016;Plesa et al, 2019). It is, however, unlikely that these compounds play any relevant role in pepino responses to drought, as no significant changes in TSS levels were detected in the water-stressed plants, as compared with the controls.…”