Comparison of Fine Root Dynamics in Scots Pine and Pedunculate Oak in Sandy Soil

In this study, we investigated the relationship between the seasonality of vegetation cover and that of fine root processes in a man-made forest in northern Belgium. Due to their contrasting foliar development, we expected different seasonal patterns of fine root growth and standing biomass between Pedunculate oak (Quercus robur L.), and Scots pine (Pinus sylvestris L.). Biomass and necromass of fine and small roots were estimated by repeated core sampling in February, April, June, August and October 2003. Measurements showed that Pedunculate oaks maintained more live fine roots in winter than Scots pines. However, Scots pines produced more than twice as much fine roots in spring, such that in summer both species had similar root mass. Scots pine root production started before-, but declined during leaf unfolding. Pedunculate oak roots, in contrast, started elongating only after bud break. For both species, fine root production peaked in JuneJuly, but was more than offset by drought-induced mortality at the end of July and early August. Summer drought in 2003 was exceptionally long and intense, significantly reducing leaf area, killing most new roots, and inhibiting root decomposition, such that the obtained results cannot be typical for this forest.     

Does the age of fine root carbon indicate the age of fine roots in boreal forests?

To test the reliability of the radiocarbon method for determining root age, we analyzed fine roots (originating from the years 1985?C1993) from ingrowth cores with known maximum root age (1?C6?years old). For this purpose, three Scots pine (Pinus sylvestris L.) stands were selected from boreal forests in Finland. We analyzed root ¹⁴C age by the radiocarbon method and compared it with the above-mentioned known maximum fine root age. In general, ages determined by the two methods (root ¹⁴C age and ingrowth core root maximum age) were in agreement with each other for roots of small diameter (<0.5?mm). By contrast, in most of the samples of fine roots of larger diameter (1.5?C2?mm), the ¹⁴C age of root samples of 1987?C1989 exceeded the ingrowth core root maximum age by 1?C10?years. This shows that these roots had received a large amount of older stored carbon from unknown sources in addition to atmospheric CO₂ directly from photosynthesis. We conclude that the ¹⁴C signature of fine roots, especially those of larger diameter, may not always be indicative of root age, and that further studies are needed concerning the extent of possible root uptake of older carbon and its residence time in roots.     

Survival of black alder (Alnus glutinosa L.), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) seedlings in a reclaimed oil shale mining area

Early survival and growth of black alder, silver birch and Scots pine were investigated on reclaimed extremely stony and heterogeneous calcareous (pH 8) opencast oil shale mining areas (OOSMAs). Biomass allocation, production, leaf and root adaptations, and mineral nutrition in relation to tree species and soil heterogeneity were analysed. The adaptive strategies of tree species in first-year plantations on OOSMA were different. Scots pine allocated 1.5–2 times more biomass into leaves and fine roots than deciduous trees. The lower leaf/fine root biomass ratio was in proportion to the better survival (%) of seedlings, decreasing in the following order: black alder (93%) ≥ Scots pine (83%) > silver birch (64%). Deciduous trees improved mineral nutrition more by fine-root morphological adaptations than Scots pine; e.g. the mean specific root length (SRL, m g^?1) of short roots increased in the following order: Scots pine (62) < black alder (172) < silver birch (314). The effect of soil heterogeneity on growth and adaptations was minor. All studied species suffered from P and N, and deciduous species also from K deficiency. In the first year after planting, black alder was best adapted to the harsh conditions of the post-mining substrate. The approaches of this study can be used for other regions where wastelands require reclamation.     

TRAP: a modelling approach to below-ground carbon allocation in temperate forests

Tree root systems, which play a major role in below-ground carbon (C) dynamics, are one of the key research areas for estimating long-term C cycling in forest ecosystems. In addition to regulating major C fluxes in the present conditions, tree root systems potentially hold numerous controls over forest responses to a changing environment. The predominant contribution of tree root systems to below-ground C dynamics has been given little emphasis in forest models. We developed the TRAP model, i.e. Tree Root Allocation of Photosynthates, to predict the partitioning of photosynthates between the fine and coarse root systems of trees among series of soil layers. TRAP simulates root system responses to soil stress factors affecting root growth. Validation data were obtained from two Belgian experimental forests, one mostly composed of beech (Fagus sylvatica L.) and the other of Scots pine (Pinus sylvestris L.). TRAP accurately predicted (R = 0.88) night-time CO₂ fluxes from the beech forest for a 3-year period. Total fine root biomass of beech was predicted within 6% of measured values, and simulation of fine root distribution among soil layers was accurate. Our simulations suggest that increased soil resistance to root penetration due to reduced soil water content during summer droughts is the major mechanism affecting the distribution of root growth among soil layers of temperate Belgian forests. The simulated annual rate of C input to soil litter due to the fine root turnover of the Scots pine was 207 g C m^–2 yr^–1. The TRAP model predicts that fine root turnover is the single most important source of C to the temperate forest soils of Belgium.     

Plasticity in gas‐exchange physiology of mature Scots pine and European larch drive short‐ and long‐term adjustments to changes in water availability

Adjustment mechanisms of trees to changes in soil‐water availability over long periods are poorly understood, but crucial to improve estimates of forest development in a changing climate. We compared mature trees of Scots pine (Pinus sylvestris) and European larch (Larix decidua) growing along water‐permeable channels (irrigated) and under natural conditions (control) at three sites in inner‐Alpine dry valleys. At two sites, the irrigation had been stopped in the 1980s. We combined measurements of basal area increment (BAI), tree height and gas‐exchange physiology (Δ¹³C) for the period 1970–2009. At one site, the Δ¹³C of irrigated pine trees was higher than that of the control in all years, while at the other sites, it differed in pine and larch only in years with dry climatic conditions. During the first decade after the sudden change in water availability, the BAI and Δ¹³C of originally irrigated pine and larch trees decreased instantly, but subsequently reached higher levels than those of the control by 2009 (15 years afterwards). We found a high plasticity in the gas‐exchange physiology of pine and larch and site‐specific responses to changes in water availability. Our study highlights the ability of trees to adjust to new conditions, thus showing high resilience.     

A hydrological tracer study of water uptake depth in a Scots pine forest under two different water regimes

Little is known about the vertical distribution of water uptake by trees under different water supply regimes, the subject of this study, conducted in a Scots pine stand on sandy loam in northern Sweden. The objective was to determine the water uptake distribution in pines under two different water regimes, desiccation (no precipitation) and irrigation (2?mm day^?1 in July and 1?mm day^?1 in August), and to relate the uptake to water content, root and soil texture distributions. The natural ¹⁸O gradient in soil water was exploited, in combination with two added tracers, ²H at 10?cm and ³H at 20?cm depth. Extraction of xylem sap and water from the soil profile then enabled evaluation of relative water uptake from four different soil depths (humus layer, 0–10, 10–25 and 25–55?cm) in each of two 50-m² plots per treatment. In addition, water content, root biomass and soil texture were determined. There were differences in vertical water uptake distribution between treatments. In July, the pines at the irrigated and desiccated plots took up 50% and 30%, respectively, of their water from the upper layers, down to 25?cm depth. In August, the pines on the irrigated plots took up a greater proportion of their water from layers below 25?cm deep than they did in July. In a linear regression, the mean hydraulic conductivity for each mineral soil horizon explained a large part of the variation in relative water uptake. No systematic variation in the residual water uptake correlated to the root distribution. It was therefore concluded that the distribution of water uptake by the pines at Åheden was not a function of root density in the mineral soil, but was largely determined by the unsaturated hydraulic conductivity.     

Elevated atmospheric CO2 increases fine root production, respiration, rhizosphere respiration and soil CO2 efflux in Scots pine seedlings

In this study, we investigated the impact of elevated atmospheric CO₂ (ambient + 350 μmol mol^–1) on fine root production and respiration in Scots pine (Pinus sylvestris L.) seedlings. After six months exposure to elevated CO₂, root production measured by root in-growth bags, showed significant increases in mean total root length and biomass, which were more than 100% greater compared to the ambient treatment. This increased root length may have lead to a more intensive soil exploration. Chemical analysis of the roots showed that the roots in the elevated treatment accumulated more starch and had a lower C/N-ratio. Specific root respiration rates were significantly higher in the elevated treatment and this was probably attributed to increased nitrogen concentrations in the roots. Rhizospheric respiration and soil CO₂ efflux were also enhanced in the elevated treatment. These results clearly indicate that under elevated atmospheric CO₂ root production and development in Scots pine seedlings is altered and respiratory carbon losses through the root system are increased.     

Development of fine and coarse roots of Thuja occidentalis `Brabant' in non-irrigated and drip irrigated field plots

Aboveground dry mass, total root dry mass and root length density of the fine roots of Thuja occidentalis `Brabant' were determined under non- and drip-irrigated field conditions. Two-dimensional diffusion parameters for dynamic root growth were estimated based on dry mass production of the fine roots and the concept of the convective-diffusion model of cylindrical root growth and proliferation. Drip irrigation increased above-ground dry mass and the shoot:root ratio compared with no irrigation. Dry mass of the coarse roots increased as well due to drip irrigation. No effect on total or fine root dry mass was found. Drip irrigation increased root length densities in the top 0.1 m but not significantly. However, drip irrigation decreased root proliferation in depth by 27%, whereas proliferation in the horizontal direction was not altered. Measured root length densities were overestimated by 6–21% by the model (0.68 < R ² < 0.92).     

Clonal Variation in Morphology of Populus Root Systems Following Irrigation with Landfill Leachate or Water during 2 Years of Establishment

Increased municipal solid waste generation in North America has prompted the use of Populus for phytoremediation of waste waters including landfill leachate. Populus species and hybrids are ideal for such applications because of their high water usage rates, fast growth, and extensive root systems. Adventitious rooting (i.e., lateral rooting from primordia and basal rooting from callus) of Populus is important for phytotechnologies to ensure successful plantation establishment with genotypes that thrive when irrigated with highly variable or specific contaminants. We evaluated differences in root system morphology following establishment with high-salinity municipal solid waste landfill leachate or uncontaminated well water (control). Populus clones (NC13460, NC14018, NC14104, NC14106, DM115, DN5, NM2, and NM6) were irrigated during 2005 and 2006 in northern Wisconsin, USA and tested for differences in morphology of lateral and basal root types, as well as fine (0–2 mm diameter), small (2–5 mm), and coarse (>5 mm) roots. Across treatments and clones, trees averaged five roots per root type. Leachate-irrigated trees had 87% (lateral) and 105% (basal) as many roots as those irrigated with water. Leachate-irrigated trees had 96% as many fine roots as watering with irrigation water, whereas trees with leachate had 112% (small) and 88% (coarse) as many roots versus water. Despite root necrosis and regrowth in 23% of the trees, leachate irrigation did not negatively affect root diameter or dry mass. Given that adequate rooting is necessary for plantation establishment, leachate and similar waste waters are viable irrigation and fertilization sources of Populus crops used as feedstocks for biofuels, bioenergy, and bioproducts.     

Assessing fine-root biomass and production in a Scots pine stand – comparison of soil core and root ingrowth core methods

Soil core and root ingrowth core methods for assessing fine-root (< 2 mm) biomass and production were compared in a 38-year-old Scots pine (Pinus sylvestris L) stand in eastern Finland. 140 soil cores and 114 ingrowth cores were taken from two mineral soil layers (0–10 cm and 10–30 cm) during 1985–1988. Seasonal changes in root biomass (including both Scots pine and understorey roots) and necromass were used for calculating fine-root production. The Scots pine fine-root biomass averaged annually 143 g/m² and 217 g/m² in the upper mineral soil layer, and 118 g/m² and 66 g/m² in the lower layer of soil cores and ingrowth cores, respectively. The fine-root necromass averaged annually 601 g/m² and 311 g/m² in the upper mineral soil layer, and 196 g/m² and 159 g/m² in the lower layer of soil cores and ingrowth cores, respectively. The annual fine-root production in a Scots pine stand in the 30 cm thick mineral soil layer, varied between 370–1630 g/m² in soil cores and between 210 – 490 g/m² in ingrowth cores during three years. The annual production calculated for Scots pine fine roots, varied between 330–950 g/m² in soil cores and between 110 – 610 g/m² in ingrowth cores. The horizontal and vertical variation in fine-root biomass was smaller in soil cores than in ingrowth cores. Roots in soil cores were in the natural dynamic state, while the roots in the ingrowth cores were still expanding both horizontally and vertically. The annual production of fine-root biomass in the Scots pine stand was less in root ingrowth cores than in soil cores. During the third year, the fine-root biomass production of Scots pine, when calculated by the ingrowth core method, was similar to that calculated by the soil core method. Both techniques have sources of error. In this research the sampling interval in the soil core method was 6–8 weeks, and thus root growth and death between sampling dates could not be accurately estimated. In the ingrowth core method, fine roots were still growing into the mesh bags. In Finnish conditions, after more than three growing seasons, roots in the ingrowth cores can be compared with those in the surrounding soil. The soil core method can be used for studying both the annual and seasonal biomass variations. For estimation of production, sampling should be done at short intervals. The ingrowth core method is more suitable for estimating the potential of annual fine-root production between different site types.     

Root biomass changes after drainage and fertilization of a low-shrub pine bog

The stump and root systems of Scots pine (Pinus sylvestris) and field-layer vegetation were sampled before (1984) and three growing seasons after drainage and fertilization (1987) of a low-shrub pine bog. Average below-ground biomass of the field layer was 548 gDW m^–2 in 1984, with no significant treatment effects during experimentation. The stump-plus-root biomass of the pine stands was 1464 gDW m^–2 in the virgin state, and had increased to 1854 gDW m^–2 three years after the NPK-fertilizer treatment. The distribution over fractions also changed with this treatment. The fraction of fine roots ( < 1 mm) in stump-root biomass increased from 4% (56 gDW m^–2) to 11% (196 gDW m^–2), while the other compartments changed less. Total pine root length was 729 mm^–2 in 1984. Root length increased by 94% to 1380 mm^–2 on NPK-fertilized plots. Most of the fine pine roots were in the surface layer (0–10 cm), 79% in 1984 and 88% in 1987, and few pine roots were deeper than 20 cm. Maximum root length of fine pine roots ( < 1 mm) was estimated to be 2710 mm^–2 at about 800 gDW m^–2 (NPK treatment), and the corresponding maximum for small pine roots (=1–10 mm) was 227 mm^–2 at 809 gDW m^–2. Drainage stimulated net growth of fine roots, but this treatment also caused higher mortality rates of small roots. The fine roots responded to fertilization with higher net growth rate, and secondary growth of the large roots ( > 10 mm) was improved. The observed changes in root biomass and structure are explained as strategic adaptations to altered hydrological and nutritional circumstances in the root zone after drainage and fertilization.     

Morphology,biomass and nutrient status of fine roots of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis>) as influenced by seasonal fluctuations in soil moisture and soil solution chemistry

A field monitoring study was carried out to follow the changes of fine root morphology, biomass and nutrient status in relation to seasonal changes in soil solution chemistry and moisture regime in a mature Scots pine stand on acid soil. Seasonal and yearly fluctuations in soil moisture and soil solution chemistry have been observed. Changes in soil moisture accounted for some of the changes in the soil solution chemistry. The results showed that when natural acidification in the soil occurs with low pH (3.5–4.2) and high aluminium concentration in the soil solution (>3–10 mg l^–1), fine root longevity and distribution could be affected. However, fine root growth of Scots pine may not be negatively influenced by adverse soil chemical conditions if soil moisture is not a limiting factor for root growth. In contrast, dry soil conditions increase Scots pine susceptibility to soil acidification and this could significantly reduce fine root growth and increase root mortality. It is therefore important to study seasonal fluctuations of the environmental variables when investigating and modelling cause-effect relationships.     

Effects of irrigation on litterfall,fine root biomass and production in a semideciduous lowland forest in Panama

The effects of irrigation on fine root biomass, root production and litterfall were measured at the community level, in a semideciduous lowland forest in Panama. Biomass of roots less than 2 mm in dia. in the first 10 cm of the soil (measured with soil cores), was higher in irrigated (1.80 Mg ha^-1) than in non-irrigated plots (1.24 Mg ha^-1). During the dry season, productivity of roots (measured with ingrowth cylinders filled with root-free soil), was higher in irrigated (1.6 g m^-2 day^-1) than in control plots (0.3 g m^-2 day^-1). In control plots, root productivity was highly seasonal. Maximum root growth into the root-free soil, occurred during the transitions from dry to wet, and from wet to dry season, possibly as a response to water and/or nutrient pulses. Litterfall was not significantly different between irrigated (3.8 g m^-2 day^-1) and control plots (3.7 g m^-2 day^-1). The results of this study show that root-productivity is limited by the water supply during the dry season, and that water by itself, is not a limiting factor for community-level litter production. This revised version was published online in June 2006 with corrections to the Cover Date.     

Long-Term Effects of Liming on Health and Growth of a Masson Pine Stand Damaged by Soil Acidification in Chongqing,China

In the last decades, the Masson pine (Pinus massoniana) forests in Chongqing, southwest China, have increasingly declined. Soil acidification was believed to be an important cause. Liming is widely used as a measure to alleviate soil acidification and its damage to trees, but little is known about long-term effects of liming on the health and growth of declining Masson pine forests. Soil chemical properties, health condition (defoliation and discoloration), and growth were evaluated following application of limestone powder (0 (unlimed control), 1, 2, 3, and 4 t ha⁻¹) in an acidified and declining Masson pine stand at Tieshanping (TSP) of Chongqing. Eight years after liming, in the 0–20 cm and 20–40 cm mineral soil layers, soil pH values, exchangeable calcium (Ca) contents, and Ca/Al molar ratios increased, but exchangeable aluminum (Al) levels decreased, and as a result, length densities of living fine roots of Masson pine increased, with increasing dose. Mean crown defoliation of Masson pines (dominant, codominant and subdominant pines, according to Kraft classes 1–3) decreased with increasing dose, and it linearly decreased with length densities of living fine roots. However, Masson pines (Kraft classes 1–3) in all treatments showed no symptoms of discoloration. Mean current-year twig length, twig dry weight, needle number per twig, needle length per twig, and needle dry weight per twig increased with increasing dose. Over 8 years, mean height increment of Masson pines (Kraft classes 1–3) increased from 5.5 m in the control to 5.8, 6.9, 8.3, and 9.5 m in the 1, 2, 3, and 4 t ha⁻¹ lime treatments, and their mean DBH (diameter at breast height) increment increased from 3.1 to 3.2, 3.8, 4.9, and 6.2 cm, respectively. The values of all aboveground growth parameters linearly increased with length densities of living fine roots. Our results show that liming improved tree health and growth, and these effects increased with increasing dose.     

Laccaria bicolor S238N improves Scots pine mineral nutrition by increasing root nutrient uptake from soil minerals but does not increase mineral weathering

The role of ectomycorrhizal fungi on mineral nutrient mobilization and uptake is crucial for tree nutrition and growth in temperate forest ecosystems. By using a “mineral weathering budget” approach, this study aims to quantify the effect of the symbiosis with the ectomycorrhizal model strain Laccaria bicolor S238N on mineral weathering and tree nutrition, carrying out a column experiment with a quartz/biotite substrate. Each column was planted with one Scots pine (Pinus sylvestris L.) non-mycorrhizal or mycorrhizal with L. bicolor, with exception of the abiotic control treatment. The columns were continuously supplied with a nutrient-poor solution. A mineral weathering budget was calculated for K and Mg. The pine shoot growth was significantly increased (73%) when plants were mycorrhizal with L. bicolor. Whatever their mycorrhizal status, pines increased mineral weathering by factors 1.5 to 2.1. No difference between non-mycorrhizal and mycorrhizal pine treatments was revealed, however, mycorrhizal pines assimilated significantly more K and Mg. This suggests that in our experimental conditions, L. bicolor S238N improved shoot growth and K and Mg assimilation in Scots pine mainly by increasing the uptake of dissolved nutrients, linked to a better exploration and exploitation of the soil by the mycorrhizal roots.     

Recent 14C-labelled assimilate allocation to Scots pine seedling root and mycorrhizosphere compartments developed on reconstructed podzol humus,E- and B- mineral horizons

In northern boreal forests, podzolic soils prevail that comprise of a distinct upper organic humus/mor (O) horizon that is supported by underlying eluvial (E) and illuvial (B) mineral horizons. The dominant tree species, Scots pine (Pinus sylvestris L.), is known to be highly dependent on root symbiosis with ectomycorrhizal fungi that develop in constituent podzol horizons for growth in these nutrient limited soils. The aim of this microcosm-based study was a quantification of photosynthetically fixed ¹⁴C allocation, following standard pulse-feeding of 7-month-old Scots pine seedling shoots, to respective root and mycorrhizosphere compartments that developed in the reconstructed podzol (O, E and B) profile. Biomass of roots and mycorrhizas decreased with increasing soil depth but no soil origin, control forest vs. clear-cut area, related differences were observed. Similarly, no major soil origin- or podzol horizon-related differences in categorised ectomycorrhizal morphotypes and number of mycorrhizas, in relation to pooled root and mycorrhiza biomass, were detected. However, the total recovery of ¹⁴C-label was significantly higher in clear-cut soil microcosms compared to control counterparts. A significant finding was equivalent ¹⁴C-carbon allocation to roots and ectomycorrhizas in all three major, organic and mineral, podzol profile horizons studied. These carbon allocation data provide additional support for direct (or indirect) roles of roots and symbiotic mycorrhizal fungi in mineral weathering and biodegradation of organic ligands that are central for plant acquisition of growth limiting nutrients and the podzolization process in boreal forest ecosystems.     

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m^?2, and that of spruce and pine 297 g m^?2 and 277 g m^?2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.     

Short-term effects of manipulated increase in acid deposition on soil, soil solution chemistry and fine roots in Scots pine (Pinus sylvestris) stand on a podzol

A manipulated increase in acid deposition (15 kg S ha⁻¹), carried out for three months in a mature Scots pine (Pinus sylvestris) stand on a podzol, acidified the soil and raised dissolved Al at concentrations above the critical level of 5 mg l⁻¹ previously determined in a controlled experiment with Scots pine seedlings. The induced soil acidification reduced tree fine root density and biomass significantly in the top 15 cm of soil in the field. The results suggested that the reduction in fine root growth was a response not simply to high Al in solution but to the depletion of exchangeable Ca and Mg in the organic layer, K deficiency, the increase in NH₄:NO₃ ratio in solution and the high proton input to the soil by the acid manipulation. The results from this study could not justify the hypothesis of Al-induced root damage under field conditions, at least not in the short term. However, the study suggests that a short exposure to soil acidity may affect the fine root growth of mature Scots pine.     

Root dynamics of Carex stricta-dominated tussock meadows

Background and aims

The roots of tussock-forming plants contribute to the formation of microtopographic features in many ecosystems, but the dynamics of such roots are poorly understood. We examined the spatial heterogeneity of tussock fine root dynamics to investigate allocation patterns and the role of root productivity in the persistence of tussock structures.

Methods

We compared the spatial variability of fine root (<1 mm, 1–2 mm) density, biomass, % live, allocation, turnover rate (using bomb 14C), and productivity of four Carex stricta Lam.-dominated tussock meadows in the upper Midwest, USA (3 reference, 1 restored site).

Results

Relative to underlying microsites, tussocks were warm, dry, and high in root density, productivity, % live biomass, and turnover. Root productivity averaged 649 g?m^?2 yr^?1 (±208) in reference sites, comprised 57 % (±10) of total net production, and was concentrated in tussocks (70 %?±?4). Root turnover rate averaged 0.63 yr^?1 (±0.08), but tussocks had ~50 % faster root turnover than the underlying soil, and <1 mm roots turned over ~40 % faster than 1–2 mm roots.

Conclusions

Our detailed analysis of the spatial heterogeneity of tussock root dynamics suggests that high allocation and elevated turnover of tussock roots facilitates organic matter accumulation and tussock persistence over time.     

Variation of carbon age of fine roots in boreal forests determined from 14C measurements

Background and aims

The main objectives of this study were to determine how the carbon age of fine root cellulose varies between stands, tree species, root diameter and soil depth. In addition, we also compared the carbon age of fine roots from soil cores of this study with reported values from the roots of the same diameter classes of ingrowth cores on the same sites.

Methods

We used natural abundance of ¹⁴C to estimate root carbon age in four boreal Norway spruce and Scots pine stands in Finland and Estonia.

Results

Age of fine root carbon was older in 1.5–2 mm diameter fine roots than in fine roots with <0.5 mm diameter, and tended to be older in mineral soil than in organic soil. Fine root carbon was older in the less fertile Finnish spruce stands (11–12 years) than in the more fertile Estonian stand (3 and 8 years), implying that roots may live longer in less fertile soil. We further observed that on one of our sites carbon in live fine roots with the 1.5–2 mm diameter was of similar C age (7–12 years) than in the ingrowth core roots despite the reported root age in the ingrowth cores – being not older than 2 years.

Conclusions

From this result, we conclude that new live roots may in some cases use old carbon reserves for their cellulose formation. Future research should be oriented towards improving our understanding of possible internal redistribution and uptake of C in trees.