Root Growth Dynamics Research Articles

Global analysis of an exponential model of cell proliferation for estimation of cell cycle duration in the root apical meristem of angiosperms.

Information on cell cycle duration (T) in the root apical meristem (RAM) provides insight into root growth, development and evolution. We have previously proposed a simple method for evaluating T based on the dynamics of root growth (V), the number of cells in the RAM (Nm) and the length of fully elongated cells (l), which we named the rate-of-cell-production (RCP) method. Here, a global analysis was performed to confirm the reliability of this method in a range of angiosperm species and to assess the advantages of this approach. We measured V, Nm and l from live or fixed cleared primary roots of seedlings or adventitious roots of bulbs and used this information to estimate the average T values in 73 angiosperm species via the RCP method. The results were then compared with published data obtained using the classical but laborious and time-consuming 3H-thymidine method. In most species examined, the T values obtained by the RCP method were nearly identical to those obtained by the 3H-thymidine method. The global analysis demonstrated that the relationship between the variables V, Nm and l in roots in the steady state of growth is correctly described by the equation T = (ln2 Nm l)V-1. Thus, the RCP method enables cell cycle duration in the RAM to be rapidly and accurately determined. This method can be performed using live or fixed roots for each individual cell type. The simplicity of the approach suggests that it will be widely used in phenomics, evolutionary ecology and other plant biology studies.

Quantifying Soil Water and Root Dynamics Using a Coupled Hydrogeophysical Inversion

Core Ideas A novel coupled inversion algorithm estimated soil and root parameters. Electrical resistivity data were used to identify root and soil hydraulic properties. A unique root distribution was estimated despite input error and data density. This noninvasive technique can capture root dynamics in a variety of settings. Plot‐ to field‐scale root distribution data are relatively rare and difficult to measure with traditional methods. Nevertheless, these data are needed to accurately model root water uptake (RWU) processes within agronomic, hydrologic, and terrestrial biosphere models. New tools are needed to effectively observe root distributions and model dynamic root growth processes. In the past decade, geophysical tools have increasingly been used to study the vadose zone, and hydrogeophysical inversions have shown promise to noninvasively characterize water dynamics. In such an approach, the hydrology is modeled and hydrological data are inverted with the geophysical data, constraining the geophysical inversion results and decreasing uncertainty and the number of nonunique solutions. In this study, we developed and tested a coupled hydrogeophysical inversion approach that uses electrical resistivity data to estimate soil hydraulic, petrophysical, and root dynamic parameters. This builds on prior research that used either a coupled hydrogeophysical inversion to estimate soil hydraulic parameters only, or a hydrological inversion to estimate root distribution or root water uptake parameters. Our results indicate that under the conditions tested, this approach accurately captures root water dynamics and soil hydraulic parameters. This opens up opportunities to noninvasively image a variety of root distributions and soil systems, better understand the dynamics of RWU processes, and improve estimates of transpiration for systems models.

Initial recovery of compacted soil—planting and technical treatments decrease CO2 concentrations in soil and promote root growth

The combination of technical treatments and planting of alder trees in a compacted forest soil improves the circulation of air and water through the pore system. This leads to decreases in CO 2 concentrations and increases in root growth in the soil. Both are indicative of an initial recovery of soil structure. The compaction of forest soils, caused by forest machinery, has as a principal consequence: the destruction of soil structure and thus the reduction of the soil aeration status. Thus, the gas exchange between soil and atmosphere is reduced and the depth propagation of roots is limited, resulting in the shortage of water and nutrient supplies for trees. This research aimed at detecting the first stages of recovery of soil structure in a compacted forest soil, which was treated with a combination of techniques (i.e., planting tree species, mulching, addition of lime), which could presumably accelerate the regeneration of soil structure. The variation of CO2 concentrations and the dynamics of root growth were repeatedly measured. Linear mixed models were developed in order to test the effects of the treatments and the planting of trees on soil aeration, as well as to identify the influence of the different environmental effects on CO2 concentration in soil. The planting of root-active trees showed significant effects on decreases in CO2 concentrations. However, during the short-term observation, some negative effects occurred especially for the mulched sites. Nevertheless, all applied technical treatments promoted an improved soil aeration and a higher root growth compared to untreated sites which points to an initial enhanced recovery of soil structure. Pronounced seasonal and interannual variations of soil respiration were highly influenced by soil temperature and soil water content variations. An initial regeneration of soil structure is indicated by distinct changes of the soil aeration status. This regeneration is partially enhanced by the applied treatments. The quantitative potential of the regeneration techniques needs a longer observation period for mid- and long-term soil recoveries.

Root system architecture — budget experimental system for monitoring and analyses

AbstractQuantifications of root system architecture and growth dynamics became essential in sustainable agriculture, bio-engineering and underground ecology in general. Assessing of root architectural parameters is still challenging also owing to different methodological challenges and high-cost facilities required. The objective of this study was to design and examine a performance of a simple experimgal set-up for monitoring and analyses of root system architecture. The proposed system was examined with two cover crops – white mustard and sweet clover – grown in sand filled pots under controlled climate conditions for several weeks. Root systems of each crop were harvested in regular intervals of 2 to 3 weeks in 3 to 4 replicates. After careful washing, the intact root systems were photo captured in water filled cylinder in their quasi-natural position over entire rotation and then scanned using a flatbed professional scanner. The gained images (photos and scans) were analysed with AutoCAD and WinRhizo software for measuring of diverse root architectural parameters for modelling. The results showed that the selected experimental and methodical approaches were appropriate for monitoring and delivering data of good quality. Both, digital camera and scanner were regarded as essential complementary imaging tools for correct assessment of the root system architecture. To maximise the accuracy of the measurements, recommendation for improving the system were provided. Extracted root data are intended for parametrisation of root architectural models, but they also support researcher and experts in their efforts to improve crop uptake efficiency in sustainable agriculture and for bio-engineering purposes.

Root and aerial growth in early-maturing peach trees under two crop load treatments

The objectives of the paper were to study the pattern of root growth (measured by minirhizotrons) in relation to trunk, fruit and shoot growth and the effects of crop load on tree growth and yield in peach trees. Two crop load (commercial and low) treatments were applied in a mature early-maturing peach tree orchard growing in Mediterranean conditions. Root growth dynamics were measured using minirhizotrons during one growing season. Shoot, trunk and fruit growth were also measured. At harvest, all fruits were weighed, counted and sized. Roots grew throughout the year but at lower rates during the active fruit growth phase. Root growth was asynchronous with shoot growth, while root and trunk growth rates were highest after harvest, when the canopy was big enough to allocate the photo-assimilates to organs that would ensure the following season’s yield. Shoot and fruit growth was greater in the low crop load treatment and was accompanied by a non-significant increase in root growth. High level of fruit thinning decreased the current yield but the fruits were more marketable because of their greater size.

The Dynamics of Root Growth: A Geometric Model.

A new model for macroscopic root growth based on a dynamical Riemannian geometry is presented. Assuming that the thickness of the root is much less than its length, the model is restricted to growth in one dimension (1D). We treat 1D tissues as continuous, deformable, growing geometries for sizes larger than 1 mm. The dynamics of the growing root are described by a set of coupled tensor equations for the metric of the tissue and velocity field of material transport in non-Euclidean space. These coupled equations represent a novel feedback mechanism between growth and geometry. We compare 1D numerical simulations of these tissue growth equations to two measures of root growth. First, sectional growth along the simulated root shows an elongation zone common to many species of plant roots. Second, the relative elemental growth rate calculated in silico exhibits spatio-temporal dynamics recently characterized in high-resolution root growth studies but which thus far lack a biological hypothesis to explain them. In our model, these dynamics are a direct consequence of considering growth as both a geometric reaction-diffusion process and expansion due to a distributed source of new materials.

Nitrogen uptake, nitrate leaching and root development in winter‐grown wheat and fodder radish

AbstractEarly seeding of winter wheat (Triticum aestivum L.) has been proposed as a means to reduce N leaching as an alternative to growing cover crops like fodder radish (Raphanus sativus L.). The objective of this study was to quantify the effect of winter wheat, seeded early and normally, and of fodder radish on N dynamics and root growth. Field experiments were carried out on a humid temperate sandy loam soil. Aboveground biomass and soil inorganic N were determined in late autumn; N uptake and grain yield of winter wheat were measured at harvest. Nitrate leaching was estimated from soil water samples taken at 1 m depth. Root growth was measured late autumn using the core break and root washing methods. Winter wheat root growth dynamics were followed during the growing season using the minirhizotron method. The 2013–2014 results showed that early seeding of wheat improved autumn growth and N uptake and reduced N leaching during the winter compared with the normal seeding time. Early‐seeded wheat (WWearly) was, however, not as efficient as fodder radish at reducing N leaching. Proper establishment of WWearly was a prerequisite for benefiting from early seeding, as indicated by the 2012–2013 results. Early seeding improved root growth throughout the 2013–2014 growing season compared with normal seeding time, but had no significant effect on crop grain yield. Our results indicate the potential of using early seeding as a tool to limit drought susceptibility and increase nutrient uptake from the subsoil.

高寒草甸地下根系生长动态对积雪变化的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 高寒草甸地下根系生长动态对积雪变化的响应 DOI: 10.5846/stxb201605240995 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划资助项目（2013CBA01807）；国家自然科学基金项目（31370542）；中央高校基本科研业务专项资金项目（2014NZYTD01）；西南民族大学创新型科研项目（CX2016SZ073） Response of belowground root growth dynamics to snow cover change in alpine meadow Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:2013年11月至2014年8月在青藏高原东缘红原县高寒草甸通过人工堆积的方法，进行了积雪量野外控制试验。以自然降雪的积雪量为对照（CK），设置了S1、S2和S3（积雪量分别为自然对照的2倍、3倍和4倍）3个处理，运用微根窗法追踪研究了积雪量改变后高寒草甸植被根系生长动态，并测定了积雪变化对土壤温度的影响。结果表明：高寒草甸植被根系生长存在明显的季节性变化，随着时间的推移，根系表面积、根尖数量及现存量逐渐增加并在8-9月达到最大值；当冬季积雪量达到143.4 mm（S1），对根系生长最为有利（根系表面积、根尖数量、现存量及生产量最大），根系生长旺盛期（净生产速率较高）有所提前和延长，但随着积雪量进一步增加，积雪对根系生长的正效应逐渐降低，根系生长旺盛期逐渐推迟甚至消失；研究还发现，随着积雪量增加，0-10 cm土层土壤温度逐渐降低，相似的变化规律也出现在10-20 cm土层，但在时间上有所延迟；相关性分析表明，在不同土层中，根系生长与土壤温度均呈正相关。因此，积雪变化通过改变土壤温度影响高寒草甸植物根系的生长发育，最终可能会影响高寒草甸生态系统的碳分配与碳循环过程。 Abstract:Permanent or seasonal snow cover is widespread on the Tibetan Plateau. Seasonal snow cover, which is affected by global climate change, is dominant in the northwestern part of Sichuan Province, on the eastern edge of the Tibetan Plateau. The root system is sensitive to environmental change. The effects of seasonal snow accumulation and thawing on soil physicochemical properties and microorganisms change could influence the root system in alpine meadow. Understanding the environmental effect on the root system of alpine meadow is essential to better understand the response mechanisms of terrestrial ecosystems to global climate change. From November 2013 to August 2014, we conducted the field study on controlled snow cover gradients in an alpine meadow of northwestern Sichuan. Four snow cover gradients were established: natural snowpack (control), and snowpack manipulated to be 2-, 3-, and 4-folds that of control. The root growth dynamics of plant communities and their responses to snow cover gradients were continuously monitored using the Minirhizotron method. The effects of the snow cover gradients on soil temperature were also measured. The results showed that soil temperature decreased with increasing snowpack volume. The optimum root system growth was observed with the natural snowpack. The root growth period was lower in the doubled natural snowpack compared with other treatments at the beginning, but the final root growth of was faster than that of the control. Belowground root system growth was restricted in the tripled snowpack. Correlation analysis showed that the root growth was positively correlated with soil temperature. Our results indicate that the winter snowpack change directly impacts subsurface ice storage, which in turn affects hydrothermal regimes in the alpine meadow soil and thus root system growth. Belowground root systems may suffer damage when the melt water refreezes underground after infiltrating into the soil and undergoes subsequent freeze-thaw cycles. Overall, moderately increased snowfall is conducive to the growth of the belowground root system, but excessive snow inhibits the belowground root system. Therefore, change in winter snowpack could alter carbon distribution and the carbon cycle in alpine meadow ecosystem. 参考文献 相似文献 引证文献

A scanner-based rhizobox system enabling the quantification of root system development and response of <i>Brassica rapa</i> seedlings to external P availability

Rhizoboxes are soil-root compartments that may well provide the closest naturalistic conditions for studying root systems architectures (RSAs) in controlled environments. Rhizobox-based studies can however lead to mis-estimation of root traits due to poor recovery of roots and loss of fine root features during washing of roots. We used a novel scanner-based rhizobox system to evaluate: (i) RSA traits of Brassica rapa genotypes; (ii) the relationship between root traits recorded from rhizoboxes and those of harvested roots and (iii) genotypic variation of seedlings in response to external P ([P] ext) availability. Brassica rapa genotypes were grown in soil-filled rhizoboxes abutting flatbed scanners and were watered once with either deionised water or a solution of 600 μM KH2PO4 to approximately 80% field capacity on a weight basis. Shoot and root P concentrations ([P]shoot and [P]root) of the B. rapa lines grown on different [P]ext were quantified. Visible root length at the surface of rhizoboxes constituted 85% of the total root length recovered from harvested root samples. High P supply induced a strong increase in [P]shoot in all genotypes (P < 0.001) whereas low P supply generally led to greater partitioning to roots. Seed P concentration and tissue P concentration were correlated only at low [P]ext. Total root length was strongly correlated with tissue P content under both low [P]ext (r = 0.81, P < 0.05) and high [P]ext (r = 0.82, P < 0.05) conditions. The novel scanner-based rhizobox system used addresses the substantial limitations associated with current use of rhizoboxes to study root growth dynamics.

Root growth dynamics and fruit yield of melon (Cucumis melo L) genotypes at two locations with sandy loam and clay soils

In a two year minirhizotron study (2011 and 2012), the root growth, yield and fruit quality responses of six melon genotypes to two locations with different soil types were investigated. The field experiments were conducted in south Texas at two locations viz. Uvalde with clayey (hyperthermic aridic calciustolls) and Weslaco with sandy loam (hyperthermic typic calciustolls) type soils, with subsurface drip irrigated using black plastic mulch. Root length intensity (La, cmcm−2), marketable (MFY), total fruit yield (TFY; tha−1), fruit firmness (N) and soluble solids content (SSC; °Bx) of four TAMU inbreds and two commercial hybrids, Mission and Journey were measured. Root length intensity was lower in 2011 than in 2012, possibly due to the variations in climatic, and soil conditions, and minirhizotron tube artifacts. Sandy loam soil produced 77% higher La (1.6 vs. 0.9cmcm−2) as compared to clay soil. Under sandy loam soils, root growth distribution was deeper (40–70cm) while it was confined at the depth of drip tape (<30cm) in clay soils, which indicated that root growth distribution varies with soil type even under same irrigation system. Clay soils produced 40% and 24% higher MFY and TFY respectively as compared to sandy loam soils, most likely due to longer growing season at Uvalde. Texas A&M melon inbreds had similar La to most popular commercial cultivar Mission and higher La than Journey. These results reveal that under high input intensive production systems large root systems may not be required for high yielding potential, however under sandy loam soils cultivars vary in their root distribution patterns across soil depth. Further, the great rooting ability of TAMU breeding lines under different soil types and equivalent yield potential to commercial hybrids confirms their suitability as a potential parent for developing genetically improved and stable cultivars for a wide range of environments.

Root Development and Endosymbioses: DELLAs Lead the Orchestra.

DELLA proteins, acting as integrators of gibberellin (GA) action, are emerging as key regulators of root system architecture. Recent studies have revealed how they dictate the dynamics of root growth and are required for the establishment of root endosymbioses with rhizobial bacteria and mycorrhizal fungi. Like conductors, DELLAs can thereby harmonize root development depending on soil environments.

Construction of Minirhizotron Facilities for Investigating Root Zone Processes

Core Ideas Horizontal straight holes for rhizotube installation were bored by a homemade system. Dynamics of root growth and soil moisture could be described by rhizotron facilities. Soil moisture could be monitored by TDR and GPR approaches in rhizotron facilities. Minimally invasive monitoring of root development and soil states (soil moisture, temperature) in undisturbed soils during a crop growing cycle is a challenging task. Minirhizotron (MR) tubes offer the possibility to view root development in situ with time. Two MR facilities were constructed in two different soils, stony vs. silty, to monitor root growth, root zone processes, and their dependence on soil water availability. To obtain a representative image of the root distribution, 7‐m‐long tubes were installed horizontally at 10‐, 20‐, 40‐, 60‐, 80‐, and 120‐cm depths. A homemade system was developed to install MR tubes in the silty soil in horizontally drilled straight holes. For the stony soil, the soil rhizotubes were installed in an excavated and subsequently backfilled pit. In both facilities, three subplots were established with different water treatments: rain sheltered, rainfed, and irrigated. To monitor soil moisture, water potential, and soil temperature, time domain reflectometer probes, tensiometers, and matrix water potential sensors were installed. Soil water content profiles in space and time were obtained between two MR tubes using cross‐hole ground‐penetrating radar along the tubes at different depths. Results from the first growing season of winter wheat (Triticum aestivum L.) after installation demonstrate that differences in root development, soil water, and temperature dynamics can be observed among the different soil types and water treatments. When combined with additional measurements of crop development and transpiration, these data provide key information that is essential to validate and parameterize root development and water uptake models in soil–vegetation–atmosphere transfer models.

Root growth dynamics of olive (Olea europaea L.) affected by irrigation induced salinity

Irrigated olives are increasingly exposed to conditions of high salinity. Salt tolerance of olives is commonly attributed to ion exclusion. Our objective was to advance understanding of salt stress response of olive roots. Nine levels of root zone salinity originating from either irrigation water salinity or leaching level were applied to bearing olive cv. Barnea trees grown in large weighing-drainage lysimeters. Minirhizotrons were used to measure count, diameter, length and age (color) of roots while analysis of sampled roots and leaves quantified ion uptake and accumulation. Increased exposure to salinity caused reduction in number and length of roots and increased root turnover. The most drastic effects occurred at the first level of salt gradient. Concentration of Na+ and Cl− was 5–10 times greater in root compared to leaf tissue. The K+/Na+ ratio decreased tenfold as root zone salinity increased in both roots and leaves. Restricted ion transport from roots protected aerial tissue from ion toxicity, but at a high cost as root growth decreased and mortality rate increased. We suggest that the ionic component of salt stress is a prevailing force restricting root growth, life span and development in olives.

Root Architecture Diversity and Meristem Dynamics in Different Populations of Arabidopsis thaliana.

Arabidopsis thaliana has been an excellent model system for molecular genetic approaches to development and physiology. More recently, the potential of studying various accessions collected from diverse habitats has been started to exploit. Col-0 has been the best-studied accession but we now know that several traits show significant divergences among them. In this work, we focused in the root that has become a key system for development. We studied root architecture and growth dynamics of 12 Arabidopsis accessions. Our data reveal a wide variability in root architecture and root length among accessions. We also found variability in the root apical meristem (RAM), explained mainly by cell size at the RAM transition domain and possibly by peculiar forms of organization at the stem cell niche in some accessions. Contrary to Col-0 reports, in some accessions the RAM size not always explains the variations in the root length; indicating that elongated cell size could be more relevant in the determination of root length than the RAM size itself. This study contributes to investigations dealing with understanding the molecular and cellular basis of phenotypic variation, the role of plasticity on adaptation, and the developmental mechanisms that may restrict phenotypic variation in response to contrasting environmental conditions.

Plant root tortuosity: an indicator of root path formation in soil with different composition and density.

Background and Aims Root soil penetration and path optimization are fundamental for root development in soil. We describe the influence of soil strength on root elongation rate and diameter, response to gravity, and root-structure tortuosity, estimated by average curvature of primary maize roots.Methods Soils with different densities (1·5, 1·6, 1·7 g cm−3), particle sizes (sandy loam; coarse sand mixed with sandy loam) and layering (monolayer, bilayer) were used. In total, five treatments were performed: Mix_low with mixed sand low density (three pots, 12 plants), Mix_medium - mixed sand medium density (three pots, 12 plants), Mix_high - mixed sand high density (three pots, ten plants), Loam_low sandy loam soil low density (four pots, 16 plants), and Bilayer with top layer of sandy loam and bottom layer mixed sand both of low density (four pots, 16 plants). We used non-invasive three-dimensional magnetic resonance imaging to quantify effects of these treatments.Key Results Roots grew more slowly [root growth rate (mm h–1); decreased 50 %] with increased diameters [root diameter (mm); increased 15 %] in denser soils (1·7 vs. 1·5 g cm–3). Root response to gravity decreased 23 % with increased soil compaction, and tortuosity increased 10 % in mixed sand. Response to gravity increased 39 % and tortuosity decreased 3 % in sandy loam. After crossing a bilayered–soil interface, roots grew more slowly, similar to roots grown in soil with a bulk density of 1·64 g cm–3, whereas the actual experimental density was 1·48±0·02 g cm–3. Elongation rate and tortuosity were higher in Mix_low than in Loam_low.Conclusions The present study increases our existing knowledge of the influence of physical soil properties on root growth and presents new assays for studying root growth dynamics in non-transparent media. We found that root tortuosity is indicative of root path selection, because it could result from both mechanical deflection and active root growth in response to touch stimulation and mechanical impedance.

Microbial decomposition of 13C- labeled phytosiderophores in the rhizosphere of wheat: Mineralization dynamics and key microbial groups involved

Being low molecular weight carbon (LMW-C) compounds, phytosiderophores (PS) released by strategy II plants are highly susceptible to microbial decomposition. However, to date very little is known about the fate of PS in soil. Using in-house synthesized 13C4-2′-deoxymugineic acid (DMA), the main PS released by wheat, we investigated DMA mineralization dynamics, including microbial incorporation into phospholipid fatty acids (PLFA), in the wheat rhizosphere and bulk soil of two alkaline and one acidic soil. Half-lives of the intact DMA molecule (3–8 h) as well as of DMA-derived C-compounds (8–38 days) were in the same order of magnitude as those published for other LMW-C compounds like sugars, amino acids and organic acids. Combining mineralization with PLFA data showed that between 40 and 65% of the added DMA was either respired or incorporated into soil microbial biomass after 24 h, with the largest part of total incorporated DMA-13C being recovered in gram negative bacteria. Considering root growth dynamics and that PS are mainly exuded from root tips, the significantly slower mineralization of DMA in bulk soil is of high ecological importance to enhance the Fe scavenging efficiency of PS released into the soil.

Editorial note for the special issue “Dynamics and physiological processes of tree roots”

Plant roots are well known to have key roles in water and nutrient acquisition from soils. Recent studies using molecular techniques have facilitated our understanding of these physiological processes in tree roots (Mclean et al. 2011; Alber et al. 2012; Laur and Hacke 2013). On the other hand, a number of studies in the past decades have focused on tree roots as essential in carbon dynamics in terrestrial ecosystems, in which fine roots are a key component of below-ground carbon flux, whereas coarse roots function as a carbon reservoir (Brunner and Godbold 2007). In addition, recent studies have started to examine the effects of biodiversity on root dynamics or interactions between roots and other organisms, which are important topics to deepen our comprehensive understanding about ecosystem functions of tree roots (Brassard et al. 2013; Meier et al. 2013). Although studying roots that are hidden in the soil is often difficult, new techniques such as non-destructive imaging have been applied to better understand the dynamics of tree roots (Nakaji et al. 2008; Hirano et al. 2012). In September 2014, the ‘‘Sixth international symposium on physiological processes in roots of woody plants’’ was held at Nagoya University, Japan. In this symposium, current woody root studies were reported by 37 oral and 77 poster presentations. The topics discussed in the symposium were quite diverse including root growth dynamics, water and nutrient uptake, below-ground carbon allocation and biological interactions (e.g. symbiosis, biodiversity effects). This special issue ‘‘Dynamics and physiological processes of tree roots’’ was provided by 21 excellent papers, most of which were from the symposium in Nagoya. In the first part of this special issue, CO2 flux in roots and effects of elevated atmospheric CO2 on root dynamics were highlighted. Although a number of papers were published on root dynamics related to below-ground carbon flux in the past decades as mentioned above, there are still many uncertainties. Bloemen et al. (2016), in their review, showed that a substantial proportion of CO2 derived from root respiration remained in root systems and was transported through the transpiration stream. Although these findings were obtained from a limited number of species so far, this phenomenon could impact our current understanding of carbon dynamics in terrestrial ecosystems or CO2 metabolism in trees. Agathokleous et al. (2016) and Wang et al. (2016) reported results obtained by free-air-CO2 enrichment (FACE) experiments using deciduous broadleaved species (Betula and Quercus species) in Hokkaido, northern Japan. They examined the effects of elevated CO2 on the trees grown on two different types of the soil [fertile brown forest soil (BF) and immature volcanic ash soil (VA)]. Agathokleous et al. (2016) showed that elevated CO2 increased the growth of whole roots in nutrient poor VA soil, but not in fertile BF soil. Wang et al. (2016), on the other hand, reported that elevated CO2 decreased standing crop of fine roots and increased their life spans especially in the VA soil. The responses of tree roots to elevated CO2 varied with factors such as soil resource availability and periods of CO2 fumigation (Eissenstat et al. 2013; Pritchard et al. 2014). In their case, not only soil fertility, but also other factors such as soil porosity or growth stage of the trees may have affected the responses to CO2 fumigation. & Kyotaro Noguchi kyotaro@affrc.go.jp

The importance of a surface organic layer in simulating permafrost thermal and carbon dynamics

Abstract. Permafrost-affected soils contain twice as much carbon as currently exists in the atmosphere. Studies show that warming of the perennially frozen ground could initiate significant release of the frozen soil carbon into the atmosphere. Initializing the frozen permafrost carbon with the observed soil carbon distribution from the Northern Circumpolar Soil Carbon Database reduces the uncertainty associated with the modeling of the permafrost carbon feedback. To improve permafrost thermal and carbon dynamics we implemented a dynamic surface organic layer with vertical carbon redistribution, and introduced dynamic root growth controlled by active layer thickness, which improved soil carbon exchange between frozen and thawed pools. These changes increased the initial amount of simulated frozen carbon from 313 to 560 Gt C, consistent with observed frozen carbon stocks, and increased the spatial correlation of the simulated and observed distribution of frozen carbon from 0.12 to 0.63.

How to put plant root uptake into a soil water flow model: A documentation with complete computer code.

The need for improved crop water use efficiency calls for flexible modelingplatforms to implement new ideas in plant root uptake and its regulation mechanisms. Thispaper documents the details of modifying a soil infiltration and redistribution model to include(a) dynamic root growth, (b) non-uniform root distribution and water uptake, (c) the effect ofwater stress on plant water uptake, and (d) soil evaporation. The paper also demonstratesstrategies of using the modified model to simulate soil water dynamics and plant transpirationconsidering different sensitivity of plants to soil dryness and different mechanisms of rootwater uptake. In particular, the flexibility of simulating various degrees of compensateduptake (whereby plants tend to maintain potential transpiration under mild water stress)is emphasized. The paper also describes how to estimate unknown root distributionand rooting depth parameters by the use of a simulation-based searching method. Thefull documentation of the computer code will allow further applications and new development.

Contrasting synchrony in root and leaf phenology across multiple sub‐Arctic plant communities

Summary Roots account for &gt; 50% of net primary production in many ecosystems and are widely accepted as playing a fundamental role in ecosystem carbon and nutrient cycling. Despite this, the timing and controls of root production and the relationships between root and leaf phenology are still poorly understood in many plant communities, making it challenging to elucidate broad scale patterns and to predict ecosystem responses to a changing climate. Here, we investigate and compare the extent of synchrony of community‐level fine root and leaf production in 10 widespread sub‐Arctic plant communities, including deciduous forest, evergreen shrub, deciduous shrub and sedge‐dominated communities. We show that across contrasting plant communities, timing of leaf production does not vary substantially, but there are considerable differences in timing of root production between woody plant‐ and sedge‐dominated vegetation. In sedge communities, root production occurs early in the growing season, soon after the peak of leaf production, whereas in woody plant communities, leaf and root production are highly asynchronous, with the majority of root production occurring late in the growing season. Seasonal dynamics of root growth were not consistently correlated with soil temperature, suggesting that differences in timing of production relate to inherent differences between plant functional types. This raises important questions as to the drivers of root production, the functional reasons underlying these contrasting plant strategies, as well as the consequences for microbial communities and nutrient cycling of such contrasting timing of carbon inputs to soil. Synthesis. We demonstrate that major differences exist in the synchrony of temporal dynamics of leaf and root production between woody plant and sedge‐dominated sub‐Arctic vegetation. The substantially greater asynchrony in root and leaf production in woody plants compared with sedges suggests that vegetation change associated with climate warming will result in significant shifts in timing of carbon fluxes to soil, and highlights the need for separate leaf and root components in ecosystem carbon and nutrient cycle models.