Coarse Roots Research Articles

Functional diversity buffers biomass production across variable rainfall conditions through different processes above‐ versus below‐ground

Abstract Understanding precipitation controls on functional diversity is important in predicting how change in rainfall patterns will alter plant productivity in the future. Trait‐based approaches can provide predictive knowledge about how certain species will behave and interact with the community. However, how functional diversity relates to above‐ and below‐ground biomass production in variable rainfall conditions remains unclear. Here, we tested the role of mass ratio and niche complementarity hypotheses in shaping above‐ and below‐ground biomass–functional diversity relationships in seasonal drought. We implemented a fully crossed experiment that manipulated drought timing (fall dry, spring dry, consistent dry and ambient rainfall) and community composition (grass‐dominated, forb‐dominated and mixed grass–forb) in a California annual grassland. Plant communities with mixed functional groups showed higher above‐ and below‐ground biomass than either the grass‐ or forb‐dominant communities. We found divergent functional diversity–biomass relationships for above‐ and below‐ground biomass. Above‐ground biomass decreased with community weighted means (CWMs) of specific leaf area (SLA) and height, supporting the mass ratio hypothesis, which posits that dominant species with specific traits drive biomass production of the community. Below‐ground biomass showed no evidence of either mass ratio hypothesis or niche complementarity. While biomass was largely unaffected by the timing of drought in one season, we found community‐wide functional trait shifts in response to rainfall treatments. Above‐ground traits shifted to higher SLA in consistent dry compared to ambient. Below‐ground traits shifted to longer, finer and denser roots in fall and consistent dry, and shorter and coarser roots in spring dry. Functional diversity buffered biomass production by enabling shifts in above‐ and below‐ground functional traits across variable rainfall conditions. Read the free Plain Language Summary for this article on the Journal blog.

The Comparative Root System Architecture of Declining and Non-Declining Trees in Two Apple Orchards in New York.

Rapid apple decline is a phenomenon characterized by a weakening of young apple trees in high density orchards, often followed by their quick collapse. The nature of this phenomenon remains unclear. In this work, we investigated the root system architecture (RSA) of declining and non-declining apple trees in two orchards in New York State. High-density orchard A consisted of 4-year-old 'Honeycrisp' on 'Malling 9 Nic29', and conventional orchard B consisted of 8-year-old 'Fuji' on 'Budagovsky 9'. In both orchards, a negative correlation (-0.4--0.6) was observed between RSA traits and decline symptoms, suggesting that declining trees have weaker root systems. Scion trunk diameter at the graft union, total root length, and the length of fine and coarse roots were significantly (p < 0.05) reduced in declining trees in both orchards. Additionally, internal trunk necrosis at, above, and below the graft union was observed in declining trees in orchard A but not in orchard B. Finally, latent viruses were not associated with decline, as their occurrence was documented in declining and non-declining trees in orchard A, but not in orchard B. Together, these results showed weakened root systems of declining trees, suggesting that these trees may experience deficiencies in water and nutrient uptake, although distinct RSA and trunk health traits between the two orchards were noticeable.

Effects of Tree Competition on Biomass Allocation of Stump and Coarse Roots of Larix olgensis of Different Site Classes

Site class is a quantitative indicator used to evaluate site quality. It reflects site conditions, mainly climate, the suitability of soil for tree species and soil fertility. Despite the economic and ecological importance of tree competition and site class in sustainable forest management, there has been little research on its impact on the stump and coarse root biomass allocation within plantations. The stump and coarse roots were divided into five components ((stump disc (SD), stump knot (SK), coarse roots (&gt;10 cm in diameter) (CR1), medium coarse roots (5–10 cm) (CR2) and fine coarse roots (2–5 cm) (CR3)), and the biomass of each component was obtained via the weighing method. It was found that the biomass of SD, CR1, CR2 and CR3 was mainly affected by competition (p ≤ 0.01). In the three site classes, the biomass of CR3 increased significantly with the increase in the competition index (CI) (p &lt; 0.01); the biomass of CR1 decreased gradually. In site V, the biomass of SK, sapwood and heartwood increased significantly with the increase in CI. The results show that competition affects the allocation of stump and coarse root biomass mainly by changing the coarse root biomass. The development of stump knots is greatly influenced by site class. This study provides a reference for solving the competition mechanism underlying larch wood forest development, which will in turn promote more effective utilization of larch wood forests. This study also provides a scientific basis for accurately estimating the belowground biomass and carbon storage of artificial plantation forests.

Estimation of Coarse Root System Diameter Based on Ground-Penetrating Radar Forward Modeling

Root diameter is an important indicator of plant growth and development to a large extent. However, the field monitoring of these parameters is severely limited by the lack of appropriate methods, and some traditional methods may harm the plant and its growing environment. Ground-penetrating radar (GPR) is a new nondestructive detection method for underground root systems. A new method for the estimation of the diameter of coarse roots using GPR with 900 MHz frequency was proposed in this paper. First, a simulation model was established to simulate the root system under natural conditions, and the root diameter estimation model based on the scanning results of GPR was obtained. Secondly, by studying the influence of soil and root relative permittivity on the diameter estimation model, a method was found to devise a coarse root diameter estimation model under different soil and root conditions of relative permittivity. Thirdly, the applicability of the diameter estimation model to roots with different growth orientations was tested by simulating roots with different growth orientations. Finally, the practical applicability of the estimation method was verified by field experiments. The results suggest that the root diameter estimation model can be constructed by extracting the pixel distance (∆p) of waveform parameters from the 900 MHz scanning results. This method can be used to estimate the diameter of coarse roots with diameters of no less than 2 cm and a relative permittivity greater than 5, and to estimate the diameter of roots in any orientation and soil environment effectively. At the same time, the application in the field experiment also resulted in a good estimation effect. This method provides a new opportunity to achieve more reliable root diameter estimation in complex situations. The estimation of coarse root diameter provides an experimental basis and data support for the healthy growth of trees, and also provides some information for the study of coarse root ecology.

Decomposition and Nutrient Release from Larix olgensis Stumps and Coarse Roots in Northeast China 33-Year Chronosequence Study

Stumps and coarse roots form an important C pool and nutrient pool in a Larix olgensis (Larix olgensis Henry) plantation ecosystem, and their decomposition processes would affect nutrient cycling dynamics of the overall Larix olgensis plantation. We studied the decomposition and release of nutrients from stumps and coarse roots that were cleared 0, 6, 16, 26 and 33 years ago in Northeast China. The stumps and coarse roots were divided into stump discs (SD), stump knots (SK), coarse roots (&gt;10 cm in diameter) (CR1), medium-coarse roots (5–10 cm in diameter) (CR2) and fine-coarse roots (2–5 cm in diameter) (CR3). During the entire 33-year study period, SK, CR1, CR2 and CR3 lost 87.37%, 96.24%, 75.76% and 91.98% of their initial mass, respectively. The average annual decomposition rate (k) was 0.068 for SD, 0.052 for SK, 0.092 for CR1, 0.068 for CR2 and 0.066 for CR3. After 33 years of decomposition, CR3 lost 5% of its initial C, CR2 lost 2%, and SK accumulated 1%, indicating slow C release. The N residues in SK, CR1, CR2 and CR3 were 186%, 109%, 158% and 170%, respectively. Coarse roots released P significantly faster than SD and SK, with 13% of the initial P released in CR1. SD and SK release cellulose, hemicellulose and lignin faster than coarse roots. The results show that Larix olgensis stumps and coarse roots could contribute to soil fertility recovery and serve as a long-term nutrient reservoir for forest vegetation.

Soil versus atmospheric drought: A test case of plant functional trait responses.

Climate change alters mean global surface temperatures, precipitation regimes, and atmospheric moisture. Resultant drought affects the composition and diversity of terrestrial ecosystems worldwide. To date, there have been no assessments of the combined impacts of reduced precipitation and atmospheric drying on functional trait distributions of any species in an outdoor experiment. Here, we examined whether soil and atmospheric drought affected the functional traits of a focal grass species (Poa secunda) growing in monoculture and eight-species grass communities in outdoor mesocosms. We focused on specific leaf area (SLA), leaf area, stomatal density, root:shoot ratio, and fine root:coarse root ratio responses. Leaf area and overall growth were reduced with soil drying. Root:shoot ratio only increased for P. secunda growing in monoculture under combined atmospheric and soil drought. Plant energy allocation strategy (measured using principal components) differed when P. secunda was grown in combined soil and atmospheric drought conditions compared with soil drought alone. Given a lack of outdoor manipulations of this kind, our results emphasize the importance of atmospheric drying on functional trait responses more broadly. We suggest that drought methods focused purely on soil water inputs may be imprecisely predicting drought effects on other terrestrial organisms as well (other plants, arthropods, and higher trophic levels).

Root and branch hydraulic functioning and trait coordination across organs in drought-deciduous and evergreen tree species of a subtropical highland forest.

Vessel traits are key in understanding trees' hydraulic efficiency, and related characteristics like growth performance and drought tolerance. While most plant hydraulic studies have focused on aboveground organs, our understanding of root hydraulic functioning and trait coordination across organs remains limited. Furthermore, studies from seasonally dry (sub-)tropical ecosystems and mountain forests are virtually lacking and uncertainties remain regarding potentially different hydraulic strategies of plants differing in leaf habit. Here, we compared wood anatomical traits and specific hydraulic conductivities between coarse roots and small branches of five drought-deciduous and eight evergreen angiosperm tree species in a seasonally dry subtropical Afromontane forest in Ethiopia. We hypothesized that largest vessels and highest hydraulic conductivities are found in roots, with greater vessel tapering between roots and equally-sized branches in evergreen angiosperms due to their drought-tolerating strategy. We further hypothesized that the hydraulic efficiencies of root and branches cannot be predicted from wood density, but that wood densities across organs are generally related. Root-to-branch ratios of conduit diameters varied between 0.8 and 2.8, indicating considerable differences in tapering from coarse roots to small branches. While deciduous trees showed larger branch xylem vessels compared to evergreen angiosperms, root-to-branch ratios were highly variable within both leaf habit types, and evergreen species did not show a more pronounced degree of tapering. Empirically determined hydraulic conductivity and corresponding root-to-branch ratios were similar between both leaf habit types. Wood density of angiosperm roots was negatively related to hydraulic efficiency and vessel dimensions; weaker relationships were found in branches. Wood density of small branches was neither related to stem nor coarse root wood densities. We conclude that in seasonally dry subtropical forests, similar-sized coarse roots hold larger xylem vessels than small branches, but the degree of tapering from roots to branches is highly variable. Our results indicate that leaf habit does not necessarily influence the relationship between coarse root and branch hydraulic traits. However, larger conduits in branches and a low carbon investment in less dense wood may be a prerequisite for high growth rates of drought-deciduous trees during their shortened growing season. The correlation of stem and root wood densities with root hydraulic traits but not branch wood points toward large trade-offs in branch xylem towards mechanical properties.

Ectomycorrhizal diversity, taxon-specific traits and root N uptake in temperate beech forests.

Roots of forest trees are colonized by a diverse spectrum of ectomycorrhizal (EM) fungal species differing in their nitrogen (N) acquisition abilities. Here, we hypothesized that root N gain is the result of EM fungal diversity or related to taxon-specific traits for N uptake. To test our hypotheses, we traced 15 N enrichment in fine roots, coarse roots and taxon-specific ectomycorrhizas in temperate beech forests in two regions and three seasons, feeding 1 mM NH4 NO3 labelled with either 15 NH4 + or 15 NO3 - . We morphotyped > 45 000 vital root tips and identified 51 of 53 detected EM species by sequencing. EM root tips exhibited strong, fungal taxon-specific variation in 15 N enrichment with higher NH4 + than NO3 - enrichment. The translocation of N into the upper parts of the root system increased with increasing EM fungal diversity. Across the growth season, influential EM species predicting root N gain were not identified, probably due to high temporal dynamics of the species composition of EM assemblages. Our results support that root N acquisition is related to EM fungal community-level traits and highlight the importance of EM diversity for tree N nutrition.

Storage of persistent organic matter in temperate gypsum soils –Relevance of the parent material and vegetation cover

By storing large amounts of terrestrial carbon (C), soils prevent it from being released into the atmosphere as carbon dioxide, the main greenhouse gas. We examined soils derived from gypsum and limestone, assuming the former had a special ability to accumulate and stabilise soil organic matter (SOM) under temperate climatic conditions when compared to limestone-derived soil. We compared the benefit of gypsum or limestone as a parent material and the effect of vegetation cover on the quantity and quality of SOM. Properties of the soil humus horizons were determined, including texture, available potassium (K) and phosphorus (P), pH, amount of gypsum and calcite, enzyme activity, and vegetation cover (biomass, K, P, sodium, calcium (Ca), and amount of lignin in the plant upper parts, coarse roots and fine roots). The structure and composition of humic acids (HAs), as indicators of SOM quality, were also studied. Stocks of organic carbon accumulated in 0–20 cm depth were much higher in gypsum soils (9.72 and 10.09 kg/m2) than in limestone soils (5.02 and 6.36 kg/m2). We found that the SOM in the gypsum soils was more mature, and contained more aromatic HAs, than in the limestone soils. Also, the gypsum soils had higher enzyme activity and a greater mass of vegetation cover, the fine roots providing higher amounts of lignin than the limestone soils. The factors that shaped the soil properties were identified and the interaction between the parent material and the vegetation cover and its effect on SOM storage was determined, indicating the importance of fine-root composition (lignin, Ca, K) and enzyme activity on C accumulation. Gypsum as a parent material favoured SOM accumulation through its physical stabilization, by providing active Ca cations to protect the SOM together with silt and clay, and its biochemical stabilization, through high enzyme activity and the quantity and quality of the biomass. Our results show that gypsum soils are important as a response to global warming through their ability to preserve SOM over the long term.

Non-structural carbohydrates contributed to cold tolerance and regeneration of Medicago sativa L.

Soil water content only affected regeneration time, whereas the NSC content was related to the success of alfalfa regeneration. Non-structural carbohydrates (NSCs) are important factors influencing the overwintering and regeneration of alfalfa. In this study, we analyzed eight in-situ samplings at three depths of coarse roots (crown, 20 and 40cm depths) during the overwintering period and assessed the dynamic change and allocation of root NSCs under three irrigation frequencies (irrigation once every second day/4days/8days). Primary results showed that: (i) before cold acclimation, irrigation once every second day was beneficial to the accumulation of soluble sugars and starch in crown tissues, which would be maintained until the following spring and accelerate the regeneration time of alfalfa; (ii) during the overwintering process, the soluble sugars and starch contents in the crown were significantly higher than those in deeper roots, and there was an asynchronous effect caused by the change in soluble sugars and starch among roots at three depths; and (iii) the change trend of soluble sugar and starch contents was consistent with that of semi-lethal temperature, and there was a significant negativecorrelation between the content of soluble sugar (R2 = 0.8046) and starch (R2 = 0.6332) and the semi-lethal temperature. This study demonstrated that NSCs are the key driver of cold tolerance and regeneration under the three irrigation frequencies evaluated. Our results provide further insight into the allocation of NSCs in winter. This improved understanding of the mechanism of overwintering will allow for improved water management of alfalfa in high latitude areas.

Can fertilization and stand uniformity affect the growth and biomass production in a Pinus taeda plantation in southern Brazil

Silvicultural activities employed during stand development are used to manage the distribution of site resources (light, water and nutrients) to the trees within the stand. Because heterogeneity within forest plantations has been shown to increase the number of dominated trees and decrease stand productivity, the establishment of efficient and productive plantations should presumably include nutrient regimes which ensure readily available nutrients and tree-to-tree homogeneity. The study aimed to evaluate how fertilization and uniformity can affect growth and biomass production in a Pinus taeda plantation in southern Brazil. Clones of loblolly pine (Pinus taeda L; Arborgen GE34) were subjected to two factors: (i) uniformity (U) or heterogeneity (H) of planting; and (ii) fertilization (F) or no fertilization (W) to the plants. Trees were evaluated up to 11.2 years of age. Individual survival (%), diameter at breast height (DBH), total height (H), dominant height (Hdom), basal area (G), stem volume (Vol), mean annual increment (MAI), leaf area index (LAI), uniformity index (PV50), needles, branches, bark, trunk, thick roots, and total biomass were measured. Trees grown under uniform and fertilized conditions showed the highest values of the variable’s uniformity index (PV50 index); growth (height, DBH, and LAI), productivity(MAI and stem volume), and biomass (stembark, stemwood, branches, coarse roots, and total) compared to trees grown under heterogeneous and unfertilized conditions. Our results show that the productivity of fast growing, genetically identical trees can be improved with silvicultural activities which promote uniformity and improve nutrient availability.

Micropropagated walnut dependency on phosphate fertilization and arbuscular mycorrhiza for growth, nutrition and quality differ between rootstocks both after acclimatization and post-acclimatization

The English walnut (Juglans regia L.) is the main species cultivated for the production of edible nuts. In vitro micropropagation of walnut explants, necessary for mass propagation of high-quality walnut rootstocks, needs an ex vitro acclimatization phase followed by a post-acclimatization growth in greenhouse when plantlets become photoautotrophic. However, poor survival and slow growth rates are common difficulties encountered in nurseries when establishing micropropagated walnut saplings. Walnut exhibits dependency on symbiotic soil-borne arbuscular mycorrhizal fungi for better soil nutrient acquisition and development due to a coarse root architecture that limits soil inorganic phosphate (Pi) uptake. In the context of rootstock production, the objective of this study was to investigate for the first time the effect of the arbuscular mycorrhizal fungus Rhizophagus irregularis on the growth, quality, and Pi nutrition of seven in vitro grown walnut rootstocks of economic interest (RG2, RG6, R17, RX1, VLACH, VX211, and WIP3). For this purpose, inoculation was performed before both acclimatization and post-acclimatization of rootstocks under two contrasting Pi fertilization regimes. Two months after inoculation, we analysed mycorrhizal growth, phosphate and quality responses in the four conditions tested by measuring plant height, root length, root surface, branch number, collar, biomass dry weight, Pi content, and quality (Dickson's index). The results indicated that Pi fertilization impacted root colonization parameters only in a few cases. Irrespective of root colonization parameters and developmental stages, mycorrhizal growth depression after inoculation with R. irregularis was generally observed with increasing Pi availability in the substrate. Principal component analysis showed that mycorrhizal dependency, growth and quality responses were positively correlated to each other under the lowest Pi fertilization regime tested, both at the acclimatization and post-acclimatization stages. We also found that mycorrhizal benefits in terms of growth, quality and Pi nutrition, were rootstock-dependent, indicating that walnut dependency for Pi nutrition varies between cultivars.

Hydrological responses to early-peak rainfall in unsaturated rooted soils

Vegetation has been commonly used in sponge city to remediate problems related to rainstorm events. Unlike uniform rainfall which has been widely studied, effects of early-peak rainfall on hydrological responses in vegetated soils are unclear. Besides, there is a lack of quantitative method of accurately measuring wetting front (WF). This study aims to propose a new WF tracing method, and explore the hydrological responses to early-peak rainfall in unsaturated soils vegetated with dwarf mondo grass. During soil column tests, WF position, matric suction, volumetric water content, surface ponding and overflow drainage were measured. The new WF tracing method works reasonably well for all cases. As compared to uniform rainfalls, early-peak rainfalls caused (1) earlier onsets of ponding (by 20 minutes for vegetation case and by 5 minutes for bare soil) and overflow (by 52 minutes for vegetation case and by 37 minutes for bare soil), (2) greater overflow velocity (by 28% for vegetation case and by 41% for bare soil), and (3) slightly more total overflow amount. Vegetation delayed the ponding/overflow generations, and decreased total overflow drainage, due to enhanced infiltration of surface soil. At 5 cm depth, high-density mixture of fine and coarse roots caused an increase in the saturated water content (θs) and a reduction in the residual water content (θr), because of root-induced changes in soil structure. At 10 cm depth, low-density fine roots caused reductions in both θs and θr, and increased air-entry value, as roots occupy the pores.

Influence of Paulownia fortunei (Seem.) Hemsl. roots on preferential flow in the red soil hilly region

Preferential water flow in soil significantly affects runoff, water infiltration, storage, groundwater environment, and soil stability. Plant roots positively affect preferential flow development. This study explored the relationship between the root system of <i>Paulownia fortunei</i> (Seem.) Hemsl. and preferential flow using dyeing tracer test and image analysis techniques. A typical red soil hilly region on the outskirts of Guilin City (Guangxi, China) was selected as the study area. A Bright Blue solution was used to visualize the pathways followed by the infiltrated water in simulated rainfall experiments, and Image Analyzer of Plants was used to analyze the root length, surface area, and volume. The results revealed significant differences in the root surface area density of coarse roots (RSAD-CR) and length index of preferential flow (LI) among soil profiles at various distances from the tree trunk. The root volume density of coarse (RVD-CR) and total roots (RVD-TR), the root length density of coarse roots (RLD-CR), and RSAD-CR were significantly correlated with the characteristics of dyeing morphology. Conversely, the root length density and root surface area density of fine (RLD-FR and RSAD-FR, respectively) and total roots (RLD-TR and RSAD-TR, respectively), and the root volume density of fine roots (RVD-FR) were not significantly correlated with the characteristic parameters of dyeing morphology. The root systems of <i>P. fortunei</i> were critical for enhancing soil water infiltration and developing preferential flow in red soil hilly regions. Coarse roots had a greater impact on the development of preferential flow than fine roots, and root volume had a greater influence on preferential flow development than root length and root surface area. This study contributes to a better understanding of the hydrological cycle at the plant-soil interface in red soil hilly regions.

Chromosome groups 5, 6 and 7 harbor major quantitative trait loci controlling root traits in bread wheat (Triticum aestivum L.).

Identifying genomic regions for root traits in bread wheat can help breeders develop climate-resilient and high-yielding wheat varieties with desirable root traits. This study used the recombinant inbred line (RIL) population of Synthetic W7984 × Opata M85 to identify quantitative trait loci (QTL) for different root traits such as rooting depth (RD), root dry mass (RM), total root length (RL), root diameter (Rdia) and root surface areas (RSA1 for coarse roots and RSA2 for fine roots) under controlled conditions in a semi-hydroponic system. We detected 14 QTL for eight root traits on nine wheat chromosomes; we discovered three QTL each for RD and RSA1, two QTL each for RM and RSA2, and one QTL each for RL, Rdia, specific root length and nodal root number per plant. The detected QTL were concentrated on chromosome groups 5, 6 and 7. The QTL for shallow RD (Q.rd.uwa.7BL: Xbarc50) and high RM (Q.rm.uwa.6AS: Xgwm334) were validated in two independent F2 populations of Synthetic W7984 × Chara and Opata M85 × Cascade, respectively. Genotypes containing negative alleles for Q.rd.uwa.7BL had 52% shallower RD than other Synthetic W7984 × Chara population lines. Genotypes with the positive alleles for Q.rm.uwa.6AS had 31.58% higher RM than other Opata M85 × Cascade population lines. Further, we identified 21 putative candidate genes for RD (Q.rd.uwa.7BL) and 13 for RM (Q.rm.uwa.6AS); TraesCS6A01G020400, TraesCS6A01G024400 and TraesCS6A01G021000 identified from Q.rm.uwa.6AS, and TraesCS7B01G404000, TraesCS7B01G254900 and TraesCS7B01G446200 identified from Q.rd.uwa.7BL encoded important proteins for root traits. We found germin-like protein encoding genes in both Q.rd.uwa.7BL and Q.rm.uwa.6AS regions. These genes may play an important role in RM and RD improvement. The identified QTL, especially the validated QTL and putative candidate genes are valuable genetic resources for future root trait improvement in wheat.

Upside down and the game of C allocation.

Non-structural carbohydrates (NSCs) represent the primary carbon (C) reserves and play a crucial role for plant functioning and resilience. Indeed, these compounds are involved in the regulation between C supply and demand, and in the maintenance of hydraulic efficiency. NSCs are stored in parenchyma of woody organs, which is recognized as a proxy for reserve storage capacity of tree. Notwithstanding the importance of NSCs for tree physiology, their long-term regulation and trade-offs against growth were not deeply investigated. This work evaluated the long-term dynamics of mature tree reserves in stem and root, proxied by parenchyma features, and focusing on the trade off and interplay between the resources allocation in radial growth and reserves in stem and coarse root. In a Mediterranean beech forest, NSCs content, stem and root wood anatomy analysis, and eddy covariance data, were combined. The parenchyma fraction (RAP) of beech root and stem was different, due to differences in axial parenchyma (AP) and narrow ray parenchyma (nRP) fractions. However, these parenchyma components and radial growth showed synchronous inter-annual dynamics between the two organs. In beech stem, positive correlations were found among soluble sugars content and nRP, and among starch content and the AP. Positive correlations were found among Net Ecosystem Exchange (NEE) and AP of both organs. In contrast, NEE was negatively correlated to radial growth of root and stem. Our results suggest a different contribution of stem and roots to reserves storage, and a putative partitioning in the functional roles of parenchyma components. Moreover, a long-term trade-off of C allocation between growth and reserve pool was evidenced. Indeed, in case of C source reduction, trees preferentially allocate C towards reserves pool. Conversely, in high productive years, growth represents the major C sink.

Belowground Biomass and Root:Shoot Ratios of Three Willow Cultivars at Two Sites

Belowground biomass is an important but less studied component of energy crop systems that is essential in understanding the greenhouse gas benefits of these systems. In this study, a complete above- and belowground biomass inventory (foliage, stems, stools, coarse and fine roots) was performed on three cultivars of short-rotation willow biomass crops at two sites. Mixed models were used to analyze the proportion of biomass allocated to each component and the ratios between different components. The root:shoot (R:S) ratio, defined here as the stable unharvested biomass (stool and coarse roots) divided by the shoot biomass, averaged 0.63 (SE: +0.04). Though the portion of the plant where the willows distributed their belowground biomass varied, the R:S ratio was not significantly different across sites (p = 0.8970), cultivars (p = 0.2834), nor in the site × cultivar interaction (p = 0.8481). These results may be associated with the consistently good growth across sites and limited differences in site conditions. However, the R:S ratios were affected by the overall productivity of the stand (p = 0.0978), with higher producing stands having moderately lower ratios. This information on biomass allocation between components is essential for understanding and estimating the carbon balance of these systems and breeding and selection programs.

Allometric equations for the estimation of above- and below-ground biomass for Larix sibirica Ledeb. in Northern Mongolia

The accurate estimation of tree above-ground (AGB) and below-ground (BGB) biomass components and their root/shoot ratio play key roles in stand and country-level forest biomass and carbon stock estimation. Nevertheless, site-specific and appropriate biomass equations and root/shoot ratio are hardly available for natural larch (Larix sibirica Ledeb.) forests in Mongolia. The present study aimed (1) to develop allometric equations to estimate the above- and below-ground biomass of L. sibirica trees, and (2) to estimate the root/shoot ratio applicable for estimating the root biomass based on above-ground biomass of natural larch forests in northern Mongolia. A total of 40 trees with DBH ranging from 6.8 to 40.8 cm were sampled for tree biomass analyses. For each biomass component, we calculated the proportion of biomass allocated to different components, and also tested four allometric equations based on diameter at breast height (DBH) and height (H) as independent variables. Our results, based on measurements of oven-dried biomass, revealed that stem biomass on average accounted for 44.5% and followed by branch (28.6%) and root (19.9%) biomass, respectively. Stem and branch biomass proportions were gradually increased with increasing DBH, while a contrary trend was observed for needles. The root/shoot ratio averaged 0.25. A comparison of the allocation of root biomass by diameter fractions showed an ever-growing trend of coarse roots with an increase in stem diameter, which often exceeded more than 50% of the total root biomass. However, biomass equations, which include both DBH and H were more precise than equations that are solely based only on DBH. Consequently, among the proposed allometric regression models for estimating the AGB and BGB, the equation y = aD b H c was selected as the best-fitted equation for estimating each biomass component in Siberian larch forests. These allometric equations are available to be used for the estimation of natural larch forest biomass and carbon stocks in the Khentii Mountains of Mongolia, where extreme continental climate conditions dominate.

Effect of soil quality and planting material on the root architecture and the root anchorage of young hybrid poplar plantations on waste rock slopes

ABSTRACT On mine waste rock slopes, trees with inadequate root development could be prone to uprooting. The anchorage of trees is mainly determined by the architecture of the root systems that drive their mechanical interactions with the soil. The objective of this study was to evaluate the effects of soil quality and of different planting materials on the architecture and resistance to shear stress of root systems of hybrid poplars four years after they were initially planted. The study was conducted in an open-pit-gold mine. A hybrid poplar plantation was established in 2013 on 33% soil-covered waste rock slopes, using a randomised complete block design, that is, 3 replicated blocks × 3 planting materials × 2 soil qualities. The stability of the hybrid poplars (resistance to uprooting) was evaluated using lateral traction tests. Complete excavations were performed to characterise their coarse root (>4 mm) architecture. Results showed no significant differences between treatments in terms of the maximum resistance force to uprooting, which varied between 7142 and 8989 N. After four growing seasons, no significant effects due to soil quality or planting material were observed in the number of lateral roots, mean root diameter, root biomass, aboveground biomass, and shoot/root ratio.

Effect of planting density on root biomass and distribution, and soil organic carbon stock of Acacia decurrens stands in Northwestern Ethiopia

Background:The expandingAcacia decurrenswoodlots in Northwestern Ethiopia is recognized for carbon storageviaroot biomass and soil organic carbon (SOC) enhancement but its planting densities have varied considerably. This study evaluated the effect of planting density on the root biomass, SOC stock, and vertical distributions in the stands.Methods:Five planting densities (0.5 m x 0.5 m, 0.75 m x 0.75 m, 1 m x 1 m, 1.25 m x 1.25 m, and 1.5 m x 1.5 m) were replicated four times with randomized complete block design. Soil core (6.67 cm diameter) and pit (900 cm2area) methods were used to collect fine and coarse root samples within 0–50 cm soil depth (having five soil layers in 10 cm intervals), respectively. Fine root biomass samples were classified as live and dead (necromass) and further as tree and herbaceous root. All root biomass samples were washed, oven-dried, weighed, and standardized into gram per meter square (g m-2) for root biomass comparisons for each planting density and soil depth, then summed up for 0–50 cm depth as a total root biomass. The vertical distributions of fine and coarse root biomass at each depth were expressed as a percentage (in decimal) of the total root biomass (0–50 cm).Conclusions:Planting density had significant effects on root biomass, SOC stock, and root distributions (P &lt; 0.05) but inconsistent for the percentage of SOC stock at all soil layers except at 40-50 cm. PlantingA. decurrenswith high density is recommended to increase root biomass, SOC, and percentage of roots in deep soil layers. Further study is suggested for the effects of stand age on root biomass dynamics and SOC stock with large scale.