Molecular Soil Biology 2024, Vol.15, No.4, 172-182 http://bioscipublisher.com/index.php/msb 176 maintaining soil moisture levels and supporting plant growth during dry periods (David et al., 2013; Brunn et al., 2022) (Figure 2). This dual function of preventing soil erosion and conserving water underscores the ecological significance of tree root systems in sustaining healthy and resilient ecosystems. Figure 2 (a, b) Carbon (C) fluxes in Fagus sylvatica (a) and Picea abies (b) on control (left) and drought plots (right) after 5 yr of repeated summer drought. Numbers next to the arrows show C fluxes in g C m−2 plot surface area d−1 (net assimilation, stem respiration, root respiration and root exudation). Respiration fluxes are shown in gray. Numbers next to the roots give the fine-root exudation separated by soil depth increments (dark brown, 0-7 cm; brown, 7-30 cm; light brown, 30-50 cm). Total exudation of the entire rooting zone and the proportion of net-C assimilation allocated to total exudation (assimilation - stem respiration - root respiration; see the section on ‘Assessment of C fluxes and parameters for scaling to the rooting zone and the tree level’ and Supporting Information Methods S1) are given next to the brackets. Note that values for 30-50 cm soil depth were modeled from minirhizotron and soil water content data (see the section on ‘Exudation at the root system and tree level’). Bold numbers and asterisks indicate significant differences (P < 0.05) in scaled root respiration and proportion of net assimilation allocated to exudation between control and drought plots. Values are given as means with SEs for n = 3 plots per treatment. All data represent a 2 wk period in early summer (Adopted from Brunn et al., 2022) 6 Case Studies 6.1 Mediterranean tree species Mediterranean tree species have evolved unique root structures to adapt to the drought-prone climates characteristic of this region. For instance, the maritime pine (Pinus pinaster Ait.) exhibits constitutive drought tolerance mechanisms, with certain genotypes pre-adapted to cope with water stress by expressing stress-related genes even under non-stress conditions. This adaptation is crucial for their survival and performance during recurrent drought periods, which are expected to increase due to climate change (María et al., 2020). Additionally,
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