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Deep rooting is an important trait in rice drought resistance. Genetic resources of deep-rooting varieties are valuable in breeding of water-saving and drought-resistant rice. In the present study, 234 BC 2 F 7 backcross introgression lines were derived from a cross of Dongye 80 (an accession of Dongxiang wild rice as the donor parent) and R974 (an indica restorer line as the recurrent parent). A genetic linkage map containing 1 977 bin markers was constructed by ddRADSeq for QTL analysis. Thirty-one QTLs for four root traits (the number of deep roots, the number of shallow roots, the total number of deep roots and the ratio of deep roots) were assessed on six rice chromosomes in two environments (2020 Shanghai and 2021 Hainan). Two of the QTLs, qDR5.1 and qTR5.2 , were located on chromosome 5 in a 70-kb interval. They were detected in both environments. qDR5.1 explained 13.35% of the phenotypic variance in 2020 Shanghai and 12.01% of the phenotypic variance in 2021 Hainan. qTR5.2 accounted for 10.88% and 10.93% of the phenotypic variance, respectively. One QTL (qRDR2.2) for the ratio of deep roots was detected on chromosome 2 in a 210-kb interval and accounted for 6.72% of the phenotypic variance in 2020. The positive effects of these three QTLs were all from Dongxiang wild rice. Furthermore, nine and four putative candidate genes were identified in qRDR2.2 and qDR5.1 / qTR5.2 , respectively. These findings added to our knowledge of the genetic control of root traits in rice. In addition, this study will facilitate the future isolation of candidate genes of the deep-rooting trait and the utilization of Dongxiang wild rice in the improvement of rice drought resistance. [ABSTRACT FROM AUTHOR]

• Deep root structural and functional traits are poorly known in forest ecosystems. • Deep fine root traits are oriented towards the acquisition and transport of water. • Climatic factors affect root dynamics throughout deep soil profiles differently. • Deep roots have a crucial role in the global carbon, water and nutrient cycles. While the number of studies dealing with fine root dynamics in deep soils layers (depth > 1 m) has increased sharply recently, the phenology, the morphology, the anatomy and the role of deep fine roots are still poorly known in forest ecosystems. This review summarizes the current knowledge on fine root production, mortality and longevity in deep soil layers, mycorrhizal association with deep roots, and the role of deep fine roots on carbon, water and nutrient cycling in forest ecosystems. Plant species are known to be more deeply rooted in tropical ecosystems than in temperate and boreal ecosystems, but deep-rooted species are common in a wide range of climates. Deep fine roots are highly plastic in response to changes in environmental conditions and soil resources. Recent studies show that functional traits can be different for deep and shallow roots, with a possible functional specialization of deep fine roots to take up nutrients. With higher vessel diameter and larger tracheid, the anatomy of deep fine roots is also oriented toward water acquisition and transport by increasing the hydraulic conductivity. Deep fine roots can have a great impact on the biogeochemical cycles in many forests (in particular in tropical areas where highly weathered soils are commonly very deep), making it possible to take up water and nutrients over dry periods and contributing to store carbon in the soil. The biogeochemical models in forest ecosystems need to consider the specificity of deep root functioning to better predict carbon, water and nutrient cycling as well as net ecosystem productivity. [ABSTRACT FROM AUTHOR]

• Deep rooting in Eucalyptus plantations is a common phenomenon in tropical soils. • Studies about the influence of edaphoclimatic conditions on tree growth are rare. • Soil water, fine root distribution and behavior were studied in a chronosequence. • Soil evolution plays a major rule in rooting and other plant/stand performances. • Oxisols assured better stand performances than poorly developed Entisols. Brazilian roundwood industry is one of the most important and productive in the world, with Eucalyptus plantations alone representing 73% of the total planted forests. Deep rooting in these plantations represents a more common phenomena than generally expected. However, there is still a lack of information on environmental factors that drive root growth in deep soil layers, with particular emphasis on edaphoclimatic conditions, and related consequence in terms of soil water behavior. As a part of a larger project, this research aimed to investigate soil water and fine root system distribution in deep tropical soils under a commercial Eucalyptus plantation chronosequence. Along a 2800-km gradient (from south- to north-east Brazil), 14 experimental areas were planted with a "plastic" clone (E. urophylla) and investigated in terms of climatic conditions, soil and water features, and plant/stand development for an entire 6-years rotation period. Fine roots distribution were investigated in one site (in Brazil) till to 20 m deep at 3, 9, 24, 48, and 65 months after planting. Results showed a fast displacement of the root front down to 75, 325, 825, 1250, and 1575 cm at month 3, 9, 24, 48, and 65 after planting, respectively. Fine root densities (g cm−3) and proportional water capture exponentially decreased with soil depth. Deep fine roots showed a relativelly higher efficiency in acquiring water than the shallower, denser roots. The relationship between stand height vs root front depth followed an exponential trend, suggesting that these stands developed relatively faster in height rather than in depth during the first 48 months, with the opposite characterizing plantation afterwards. Regardless of stand age, E. urophylla trees rapidly explored a considerable volume of soil at a relatively limited carbon cost. Multivariate statistics showed that edaphoclimatic conditions play a major role in Eucalyptus plant/stand development. This study outlined the major role played by soil development. From poorly developed sandy Entisols, to medium developed Inceptisols, and to most developed fine textured Oxisols, both plant growth and stand productivity greatly improved accordingly. This study suggests that soil type, together with other environmental factors, are likely to influence both the development and behavior of Eucalyptus plantations for an extent greater than commonly anticipated. [ABSTRACT FROM AUTHOR]