Fine-root carbon and nitrogen concentration of European beech (Fagus sylvatica L.) in Italy Prealps: possible implications of coppice conversion to high forest

Exogenous gibberellic acid shortening after-ripening process and promoting seed germination in a medicinal plant Panax notoginseng

BACKGROUND

Panax notoginseng (Burk) F.H. Chen is an essential plant in the family of Araliaceae. Its seeds are classified as a type of morphophysiological dormancy (MPD), and are characterized by recalcitrance during the after-ripening process. However, it is not clear about the molecular mechanism on the after-ripening in recalcitrant seeds.

RESULTS

In this study, exogenous supply of gibberellic acid (GA₃) with different concentrations shortened after-ripening process and promoted the germination of P. notoginseng seeds. Among the identified plant hormone metabolites, exogenous GA₃ results in an increased level of endogenous hormone GA₃ through permeation. A total of 2971 and 9827 differentially expressed genes (DEGs) were identified in response to 50 mg L^-1 GA₃ (LG) and 500 mg L^-1 GA₃ (HG) treatment, respectively, and the plant hormone signal and related metabolic pathways regulated by GA₃ was significantly enriched. Weighted gene co-expression network analysis (WGCNA) revealed that GA₃ treatment enhances GA biosynthesis and accumulation, while inhibiting the gene expression related to ABA signal transduction. This effect was associated with higher expression of crucial seed embryo development and cell wall loosening genes, Leafy Contyledon1 (LEC1), Late Embryogenesis Abundant (LEA), expansins (EXP) and Pectinesterase (PME).

CONCLUSIONS

Exogenous GA₃ application promotes germination and shorts the after-ripening process of P. notoginseng seeds by increasing GA₃ contents through permeation. Furthermore, the altered ratio of GA and ABA contributes to the development of the embryo, breaks the mechanical constraints of the seed coat and promotes the protrusion of the radicle in recalcitrant P. notoginseng seeds. These findings improve our knowledge of the contribution of GA to regulating the dormancy of MPD seeds during the after-ripening process, and provide new theoretical guidance for the application of recalcitrant seeds in agricultural production and storage.

New insights into the cortex-to-stele ratio show it to effectively indicate inter- and intraspecific function in the absorptive roots of temperate trees

The cortex-to-stele ratio (CSR), as it increases from thin- to thick-root species in angiosperms, is theorised to effectively reflect a compensation for the 'lag' of absorption behind transportation. But it is still not known if this compensatory effect exists in gymnosperm species or governs root structure and function within species. Here, anatomical, morphological, and tissue chemical traits of absorptive roots were measured in three temperate angiosperm and three gymnosperm species. Differences in the CSR and the above functional traits, as well as their intraspecific associations, were analyzed and then compared between angiosperms and gymnosperms. At the intraspecific level, the CSR decreased with increasing root order for all species. The expected functional indication of the CSR was consistent with decreases in specific root length (SRL) and N concentration and increases in the C to N ratio (C:N ratio) and the number of and total cross-sectional area of conduits with increasing root order, demonstrating that the CSR indicates the strength of absorption and transportation at the intraspecific level, but intraspecific changes are due to root development rather than the compensatory effect. These trends resulted in significant intraspecific associations between the CSR and SRL (R ² = 0.36 ~ 0.80), N concentration (R ² = 0.48 ~ 0.93), the C:N ratio (R ² = 0.47 ~ 0.91), and the number of (R ² = 0.21 ~ 0.78) and total cross-sectional area (R ² = 0.29 ~ 0.72) of conduits in each species (p< 0.05). The overall mean CSR of absorptive roots in angiosperms was four times greater than in gymnosperms, and in angiosperms, the CSR was significantly higher in thick- than in thin-rooted species, whereas in gymnosperms, the interspecific differences were not significant (p > 0.05). This suggests that the compensation for the lag of absorption via cortex thickness regulation was stronger in three angiosperm species than in three gymnosperm species. In addition, there was poor concordance between angiosperms and gymnosperms in the relationships between CSRs and anatomical, morphological, and tissue chemical traits. However, these gymnosperm species show a more stable intraspecific functional association compared to three angiosperm species. In general, absorptive root CSRs could manifest complex strategies in resource acquisition for trees at both intra- and interspecific levels.

Response of the fine root morphological and chemical traits of Tamarix chinensis to water and salt changes in coastal wetlands of the Yellow River Delta

To explore the adaptation of the fine root morphology and chemical characteristics of Tamarix chinensis to water-salt heterogeneity in the groundwater-soil system of a coastal wetland zone, T. chinensis forests at different groundwater levels (high: GW1 0.54 m and GW2 0.83 m; medium: GW3 1.18 m; low: GW4 1.62 m and GW5 2.04 m) in the coastal wetland of the Yellow River Delta were researched, and the fine roots of T. chinensis standard trees were excavated. The fine roots were classified by the Pregitzer method, and the morphology, nutrients, and nonstructural carbohydrate characteristics of each order were determined. The results showed that the groundwater level had a significant indigenous effect on the soil water and salt conditions and affected the fine roots of T. chinensis. At high groundwater levels, the specific root length and specific surface area of fine roots were small, the root tissue density was high, the fine root growth rate was slow, the nutrient use efficiency was higher than at low groundwater levels, and the absorption of water increased with increasing specific surface area. With decreasing groundwater level, the N content and C/N ratio of fine roots first decreased and then increased, and the soluble sugar, starch, and nonstructural carbohydrate content of fine roots first increased and then decreased. At high and low groundwater levels, the metabolism of fine roots of T. chinensis was enhanced, and their adaptability to high salt content and low water content soil environments improved. The first- and second-order fine roots of T. chinensis were mainly responsible for water and nutrient absorption, while the higher-order (from the third to fifth orders) fine roots were primarily responsible for the transportation and storage of carbohydrates. The fine root morphology, nutrients, nonstructural carbohydrate characteristics, and other aspects of the water and salt environment heterogeneity cooperated in a synergistic response and trade-off adjustment.

Adaptation of the Root System to the Environment

The plant fine roots system (i [...]

Gap Size in Hyrcanian Forest Affects the Lignin and N Concentrations of the Oriental Beech (Fagus orientalis Lipsky) Fine Roots but Does Not Change Their Morphological Traits in the Medium Term

Research Highlights: Fine roots play an important role in plant growth as well as in carbon (C) and nutrient cycling in terrestrial ecosystems. Gaining a wider knowledge of their dynamics under forest gap opening would improve our understanding of soil carbon input and below-ground carbon stock accumulation. Single-tree selection is increasingly recognized as an alternative regime of selection cutting sustaining biodiversity and carbon stock, along with timber production, among ecosystem functions. However, the fine root response in terms of morphological and chemical composition to the resulting harvest-created gaps remains unclear. Background and Objectives: This paper investigates the effect in the medium term (i.e., 6 years after logging) of differently sized harvest-created gaps on fine root dynamics and chemical composition. Materials and Methods: A total of 15 differently sized gaps (86.05–350.7 m2) and the adjacent 20 m distant closed canopies (control) were selected in a temperate Fagus orientalis forest (Hyrcanian region, Iran). Eight soil cores were collected at the cardinal points of the gap edge, including four facing the gap area—the same at the adjacent intact forest. Results: For the selected edge trees, the different size of gaps, the core position, and the tree orientation did not affect the investigated morphological traits, except for the slightly higher specific root length (SRL) for the larger fine root fraction (1–2 mm) in the side facing the gap area. Differently, the investigated chemical traits such as N concentration and cellulose:lignin ratio significantly increased with increasing gap size, the opposite for C:N ratio and lignin. Moreover, N concentration and C:N significantly decreased and increased with the fine root diameter, respectively. Conclusions: This work highlighted that, in the medium term and within the adopted size range, artificial gap opening derived from single-tree selection practice affected the chemistry rather than the biomass and morphology of gap-facing fine roots of edge trees. The medium term of six years after gap creation might have been long enough for the recovery of the fine root standing biomass to the pre-harvest condition, particularly near the stem of edge trees. A clear size threshold did not come out; nevertheless, 300 m2 may be considered a possible cut-off determining a marked change in the responses of fine roots.

Fine-Root Traits Reveal Contrasting Ecological Strategies in European Beech and Norway Spruce During Extreme Drought

Trees adjust multiple structural and functional organ-specific characteristics, "traits", to cope with diverse soil conditions. Studies on traits are widely used to uncover ecological species adaptability to varying environments. However, fine-root traits are rarely studied for methodological reasons. We analyzed the adaptability of the fine-root systems of European beech and Norway spruce to extreme drought within species-specific tree groups at Kranzberger Forst (Germany), focusing on the seasonality of morphological, physiological, and biochemical key traits in view of carbon (C) and nitrogen dynamics. We hypothesized that fine roots of both species adjust to seasonal drought: with beech representing a "fast" (i.e. with fast C turnover), and spruce a "slow" (i.e. with long-term C retention) ecological strategy. We identified three functional fine-root categories, based on root function (absorptive or transport fine roots), and mycorrhizal status of the absorptive fine-roots (mycorrhizal or non-mycorrhizal). Solely the non-mycorrhizal absorptive roots adjusted in a species-specific manner supporting fine-root ecological strategy hypothesis. During drought, beech produced thin ephemeral (absorptive non-mycorrhizal) fine roots with high specific fine-root area and high respiratory activity, representing fast C turnover and enabling effective resource exploitation. These adjustments reflect a "fast" ecological strategy. Conversely, spruce absorptive fine roots did not respond to the soil moisture deficit by growth but instead increased root suberization. Drastically lowered respiratory activity of this functional category facilitated C retention and structural persistence during drought, indicating a "slow" ecological strategy in spruce. Absorptive mycorrhizal fine roots maintained respiration throughout the drought event in both tree species, but in spruce this was the only fine-root category with high respiration. This suggests, that spruce relies heavily on mycorrhizal associations as a method of drought resistance. Accumulation of non-structural carbohydrates and high C concentrations were observed in the transport fine roots of both species, indicating drought-induced osmotic protection of these roots. Thus, functional classification enabled us to determine that fine-root branches of each species are not tied to one sole ecological strategy. The suggested approach helps to better understand the complex interplay between structure and function belowground.

Improving models of fine root carbon stocks and fluxes in European forests

Fine roots and above-ground litterfall play a pivotal role in carbon dynamics in forests. Nonetheless, direct estimation of stocks of fine roots remains methodologically challenging. Models are thus widely used to estimate these stocks and help elucidate drivers of fine root growth and turnover, at a range of scales.We updated a database of fine root biomass, necromass and production derived from 454 plots across European forests. We then compared fine root biomass and production to estimates obtained from 19 different models. Typical input variables used for the models included climate, net primary production, foliage and above-ground biomass, leaf area index (LAI), latitude and/or land cover type. We tested whether performance could be improved by fitting new multiple regression models, and explored effects of species composition and sampling method on estimated fine root biomass.Average fine root biomass was 332 g/m2, and necromass 379 g/m2, for European forests where the average fine root production was 250 g m-2 year-1. Carbon fraction in fine roots averaged 48.4%, and was 1.5% greater in broadleaved species than conifers.Available models were poor predictors of fine root biomass and production. The best performing models assumed proportionality between above- and below-ground compartments, and used remotely sensed LAI or foliage biomass as key inputs. Model performance was improved by use of multiple regressions, which revealed consistently greater biomass and production in stands dominated by broadleaved species as well as in mixed stands even after accounting for climatic differences. Synthesis. We assessed the potential of existing models to estimate fine root biomass and production in European forests. We show that recalibration reduces by about 40% errors in estimates currently produced by the best available models, and increases three-fold explained variation. Our results underline the quantitative significance of fine roots (live and dead) to the global carbon cycle.

Formation of Annual Ring Eccentricity in Coarse Roots within the Root Cage of Pinus ponderosa Growing on Slopes

The coarse roots of Pinus ponderosa included in the cage are the ones most involved in tree stability. This study explored the variations in traits, such as volume, cross-sectional area, and radius length of cage roots, and used those data to develop a mathematical model to better understand the type of forces occurring for each shallow lateral root segment belonging to different quadrants of the three-dimensional (3D) root system architecture. The pattern and intensity of these forces were modelled along the root segment from the branching point to the cage edge. Data of root cage volume in the upper 30 cm of soil showed a higher value in the downslope and windward quadrant while, at a deeper soil depth (>30 cm), we found higher values in both upslope and leeward quadrants. The analysis of radius length and the cross-sectional area of the shallow lateral roots revealed the presence of a considerable degree of eccentricity of the annual rings at the branching point and at the cage edge. This eccentricity is due to the formation of compression wood, and the eccentricity changes from the top portion at the branching point to the bottom portion at the cage edge, which we hypothesize may be a response to the variation in mechanical forces occurring in the various zones of the cage. This hypothesis is supported by a mathematical model that shows how the pattern and intensity of different types of mechanical forces are present within the various quadrants of the same root system from the taproot to the cage edge.

Estimating the effect of abandoning coppice management on carbon sequestration by oak forests in Turkey with a modeling approach

A significant area of the oak forests in Turkey has been historically managed by short-rotation coppicing for wood production. Coppice management was almost abandoned in Turkey in 2006 and so investigating its impact on forest carbon (C) sequestration has become an important issue. Therefore, we investigated the net effect of this change in management on C sequestration by oak forests in Turkey using field measurement data and a forest C model (Forest Biomass and Dead organic matter Carbon (FBDC) model). The FBDC model estimated the annual forest C dynamics and considered the effect of the substitution of wood for fossil fuels under two management scenarios over a 100-year period: (1) abandoning coppice (no management) and (2) continuing coppice (20-year-interval harvest). The field measurement data were used to parameterize the FBDC model to the study sites and to verify the simulated C stocks. Continuing coppice management constrained an increase in the C stocks (116.0-140.3 Mg C ha^-1) and showed a mean annual C sequestration of 0.6 Mg C ha^-1 yr^-1 if wood was substituted for fossil fuels. In contrast, abandoning coppicing practices increased the level of forest C stocks (128.1-236.2 Mg C ha^-1), enhancing the mean annual C sequestration to 1.1 Mg C ha^-1 yr^-1. Accordingly, the abandonment of coppice management increased the mean annual C sequestration by 0.5 Mg C ha^-1 yr^-1 in the long-term. However, sensitivity analysis showed a possibility of a larger difference in C sequestration between the two scenarios due to a decrease in the stand productivity by repeated coppices and a high likelihood of a lower substitution effect. The verification supported the scientific reliability of the simulation results. Our study can provide a scientific basis for enhancing C sequestration in coppice forests.

Fine Root Dynamics in Three Forest Types with Different Origins in a Subalpine Region of the Eastern Qinghai-Tibetan Plateau

Fine roots play a crucial role in plant survival potential and biogeochemical cycles of forest ecosystems. Subalpine areas of the Eastern Qinghai-Tibetan Plateau have experienced different forest re-establishment methods after clear-cutting primary forest. However, little is known about fine root dynamics of these forests originating from artificial, natural and their combined processes. Here, we determined fine root traits (biomass, production and turnover rate) of three subalpine forest types, i.e., Picea asperata Mast. plantation forest (artificial planting, PF), natural secondary forest (natural without assisted regeneration, NF) and P. asperata broadleaved mixed forest (natural regeneration after artificial planting, MF) composed of planted P. asperata and naturally regenerated native broadleaved species. At the soil depth of 0–30 cm, fine root biomass was the highest in PF and fine root production was the highest in NF, and both were the lowest in MF. Fine root dynamics of the three forest types tended to decrease with soil depth, with larger variations in PF. Fine root biomass and production were the highest in PF in 0–10 cm soil layer but were not significantly different among forest types in the lower soil layers. There were positive correlations between these parameters and aboveground biomass across forest types in soil layer of 0–10 cm, but not in the lower soil layers. Fine root turnover rate was generally higher in mixed forests than in monocultures at all soil depths. In conclusion, the natural regeneration procedure after clear-cutting in the subalpine region of western Sichuan seems to be superior from the perspective of fine root dynamics.

Poplar woody taproot under bending stress: the asymmetric response of the convex and concave sides

Background and Aims Progress has been made in understanding the physiological and molecular basis of root response to mechanical stress, especially in the model plant Arabidopsis thaliana, in which bending causes the initiation of lateral root primordia toward the convex side of the bent root. In the case of woody roots, it has been reported that mechanical stress induces an asymmetric distribution of lateral roots and reaction wood formation, but the mechanisms underlying these responses are largely unknown. In the present work, the hypothesis was tested that bending could determine an asymmetric response in the two sides of the main root axis as cells are stretched on the convex side and compressed on the concave side. Methods Woody taproots of 20 seedlings were bent to an angle of 90° using a steel net. Changes in the anatomy, lignin and phytohormone content and proteome expression in the two sides of the bent root were analysed; anatomical changes, including dissimilarities and similarities to those found in poplar bent woody stem, were also considered. Key Results Compression forces at the concave side of poplar root induced the formation of reaction wood which presented a high lignin content and was associated with the induction of cambium cell activity. Auxin seemed to be the main hormone triggering lignin deposition and cell wall strengthening in the concave sides. Abscisic acid appeared to function in the water stress response induced by xylem structures and/or osmotic alterations in the compression sides, whereas gibberellins may control cell elongation and gravitropisms. Conclusions Poplar root reaction wood showed characteristics different from those produced in bent stem. Besides providing biomechanical functions, a bent root ensures water uptake and transport in the deforming condition induced by tension and compression forces by two different strategies: an increase in xylem thickness in the compressed side, and lateral root formation in the tension side.

Acclimation of fine root respiration to soil warming involves starch deposition in very fine and fine roots: a case study in Fagus sylvatica saplings

Root activities in terms of respiration and non-structural carbohydrates (NSC) storage and mobilization have been suggested as major physiological roles in fine root lifespan. As more frequent heat waves and drought periods within the next decades are expected, to what extent does thermal acclimation in fine roots represent a mechanism to cope with such upcoming climatic conditions? In this study, the possible changes in very fine (diameter < 0.5 mm) and fine (0.5-1 mm) root morphology and physiology in terms of respiration rate and NSC [soluble sugars (SS) and starch] concentrations, were investigated on 2-year-old Fagus sylvatica saplings subjected to a simulated long-lasting heat wave event and to co-occurring soil drying. For both very fine and fine roots, soil temperature (ST) resulted inversely correlated with specific root length, respiration rates and SSs concentration, but directly correlated with root mass, root tissue density and starch concentration. In particular, starch concentration increased under 28 °C for successively decreasing under 21 °C ST. These findings showed that thermal acclimation in very fine and fine roots due to 24 days exposure to high ST (∼ 28 °C), induced starch accumulation. Such 'carbon-savings strategy' should bear the maintenance costs associated to the recovery process in case of restored favorable environmental conditions, such as those occurring at the end of a heat wave event. Drought condition seems to affect the fine root vitality much more under moderate than high temperature condition, making the temporary exposure to high ST less threatening to root vitality than expected.