Effects of slash retention and wood ash addition on fine root biomass and production and fungal mycelium in a Norway spruce stand in SW Sweden

In the study reported here we examined the short-term effects (1–3 years) of slash retention (SR) and the long-term effects (13–15 years) of wood-ash application (A) on fine roots and mycorrhizae in a 40-year-old Norway spruce forest in southwest Sweden. Soil cores were used to obtain estimates of the biomass (g m⁻²) of roots in three diameter classes (<0.5, 0.5–1 and 1–2 mm), root length density (RLD), specific root length (SRL) and mycorrhizal root tip density (RTD). Fine root (<1 mm) length production and mortality, and mycelium production, were estimated using minirhizotron and mesh bag techniques, respectively. Compared with the control plots (C), the biomass of fine roots in diameter classes <0.5 mm and 0.5–1 mm was significantly higher in A plots, but lower in SR plots. In addition, RLD was significantly lower in the humus layer of SR plots than in the humus layers of C and A plots, but not in the other layers. None of the treatments affected the SRL. In all soil layers, the SR treatment resulted in significant reductions in the number of ectomycorrhizal root tips, and the mycelia production of fungi in mesh bags, relative to the C treatment, but the C and A treatments induced no significant changes in these variables. Fine root length production in the C, A and SR plots amounted to 94, 87 and 70 mm tube⁻¹ during the 2003 growing season, respectively. Fine root mortality in treated plots did not change over the course of the study. We suggest that leaving logging residues on fertile sites may result in nitrogen mineralisation, which may in turn induce reductions in root biomass, and both root and mycelium production, and consequently affect nutrient uptake and the accumulation of organic carbon in soil derived from roots and mycorrhizae.     

Interspecific competition impacts on the morphology and distribution of fine roots in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.)

Morphology and vertical distribution patterns of spruce and beech live fine roots (diameter ≤2 mm) were studied using a soil core method in three comparable mature stands in the Solling: (1) pure beech, (2) pure spruce and (3) mixed spruce–beech. This study was aimed at determining the effects of interspecific competition on fine root structure and spatial fine root distribution of both species. A vertical stratification of beech and spruce fine root systems was found in the mixed stand due to a shift in beech fine roots from upper to lower soil layers. Moreover, compared to pure beech, a significantly higher specific root length (SRL, P<0.05) and specific surface area (SSA, P<0.05) were found for beech admixed with spruce (pure beech/mixed beech SRL 16.1–23.4 m g⁻¹, SSA 286–367 cm² g⁻¹). Both indicate a flexible ‘foraging’ strategy of beech tending to increase soil exploitation and space sequestration efficiency in soil layers less occupied by competitors. Spruce, in contrast, followed a more conservative strategy keeping the shallow vertical rooting and the root morphology quite constant in both pure and mixed stands (pure spruce/mixed spruce SRL 9.6/7.7 m g⁻¹, P>0.10; SSA 225/212 cm² g⁻¹, P>0.10). Symmetric competition belowground between mixed beech and spruce was observed since live fine roots of both species were under-represented compared to pure stand. However, the higher space sequestration efficiency suggests a higher competitive ability of beech belowground.     

Rooting patterns and fine root biomass of Pinus pinaster assessed by trench wall and core methods

Variability of fine root (diameter < 2 mm) distribution was investigated in four 55 to 56-year-old Maritime pine (Pinus pinaster) stands using a combination of trench wall observations and destructive sampling. Our objectives were to assess patterns of fine root distribution, to estimate tree fine root biomass and to explore interactions with understorey vegetation in a gradient of relevant site conditions. Results showed that root density decreased with soil depth in all stands, and variability appeared to be highest in litter and subsoil layers especially where compacted soil layers occurred. Roots were clustered in patches in the top 0–50 cm of the soil or were present as root channels at greater depths. Cluster number, cluster size and number of root channels were comparable in all four stands. Overall fine root biomass at depths of 0–120 cm ranged from 2.7 to 7.2 Mg ha⁻¹ and was highest for the two driest stands. The use of trench wall records made it possible to reduce the variability of these estimates. Understorey species represented as much as 90% of the total number of fine roots in the upper layers, and the understorey formed a considerable proportion of the total ecosystem biomass, suggesting that understorey species are likely competitors for nutrients in this ecosystem. Further studies should focus on the interaction of the understorey and pine roots and the ecological significance of clustered roots and nutrient distributions.     

Life cycles of individual roots in fine root system of Chamaecyparis obtusa Sieb. et Zucc.

Recent studies have remarked on differences in the life cycles of individual fine roots. However, the dynamics of individual roots with different life cycles, such as ephemeral and perennial, during root system development are still unknown. We examined individual roots during fine root system development in a mature stand of Chamaecyparis obtusa Sieb. et Zucc. (Cupressaceae) using the sequential ingrowth core method and an anatomical method. The visual classification, i.e., orange, red, brown, intact dead, and fragmented dead, of fine roots corresponded well with the anatomical classification. Orange and red roots contained passage cells, and brown roots contained cork cambium. The proportions of protoxylem groups differed among visual classes. Brown secondary roots were mainly triarch (43%) and tetrarch (40%) and rarely diarch (12%), whereas fragmented dead roots, which constituted more than 95% of the dead roots, were mainly diarch (67%). These results imply that triarch and tetrarch roots tend to form secondary roots, whereas diarch roots tend to become dead roots without secondary growth. Using the numbers of root tips and clusters, root system development could be classified into three stages: colonization, branching within the root system, and maintenance. During the colonization stage, mainly triarch and tetrarch roots, which tend to be secondary growth, invaded ingrowth cores. During the branching stage, primarily diarch roots, which tend to be ephemeral, emerged. Fine root system development involved the recruitment of different individual roots during the life cycle depending on the growth stage.     

Estimating the production and mortality of fine roots in a Japanese cedar (Cryptomeria japonica D. Don) plantation using a minirhizotron technique

Fine roots are a key component of forested ecosystems, but available information is still limited. This study examined the production and mortality of fine roots less than 1 mm in diameter in a Japanese cedar (Cryptomeria japonica D. Don) plantation located on the Kanto Plain in central Japan. We used a minirhizotron technique in combination with soil coring, and collected data for 1 year (May 2002–May 2003). Fine root production and mortality were determined from changes in the lengths of individual fine roots on minirhizotron tubes. Both fine root production and mortality rates were greater in the upper soil than in lower soil levels. Both rates were seasonal, with higher values in summer than in winter; this trend was more pronounced in upper soil levels. These results suggest that environmental conditions, such as temperature or soil properties, affect the production and mortality rates of fine roots. Fine root production and mortality occurred simultaneously, and their rates were similar, which may have led to unclear seasonal changes in fine root standing crop estimates. Soil coring indicated that the fine root biomass of this stand was about 120 g m⁻², of which 40% was from Japanese cedar. The estimated rates of dry matter production and mortality of total fine roots, including understory plants, were both approximately 300 g m⁻² year⁻¹.     

Sap flow of birch and Norway spruce during the European heat and drought in summer 2003

In this study the hydrological regime of Norway spruce (Picea abies) and birch (Betula pendula) growing on heavy soils in the south east of Austria was analysed. Results from the year 2003 characterised by an extremely hot and dry summer are presented in this paper. Due to the extreme weather conditions the soil water content in August 2003 was very low (0.10–0.25 m³ m⁻³) in the topsoil (0–50 cm) with no explicit difference between both tree species.     

林分密度对侧柏人工林细根形态的影响

以徐州林场50年生侧柏人工林为研究对象,采用挖掘法获取土壤根系样品,探究林分密度对侧柏人工林不同根序细根形态的影响。结果表明:细根的直径和根长随着根序上升而显著增大,而比根长则随着根序的上升而显著减小。低林分密度(1 679株/hm2)与中林分密度(2 250株/hm2)相比显著减小了表层土壤1、2级细根的平均直径和平均根长,亚表层土壤3级细根的根长,显著增大了亚表层土壤2级细根的平均比根长;高林分密度(3074株/hm2)比中林分密度显著增大了2级根的平均比根长。与高林分密度相比,低林分密度显著减小了表层土壤1、2级细根的平均直径,增大了亚表层土壤5级细根的平均直径。     

Heterogeneity of individual roots within the fine root architecture: causal links between physiological and ecosystem functions

This review covers the heterogeneity in functions within the fine root architecture in order to clarify the multiple functions of fine roots. Many fine root characteristics, such as anatomy, physiology, morphology, and their consequences for the ecosystem, differ among root ages and ontogenetic branching hierarchies. Individual root age can be characterized by tissue development, with the main tissues developing from primary to secondary tissues. The physiological characteristics of individual roots, such as absorptivity and respiration rates, decrease with increasing branching order, mainly because of aging and tissue development. The C/N ratio and lignin and suberin contents also increase with branching order because of root aging. Morphological characteristics, such as diameter and specific root length, differ among root orders because of both aging and ontogenetic differences. The mortality of individual roots differs among branching orders and root diameters. The life cycles of roots in the fine root architecture, that is, ephemeral and perennial, indicate ontogenetic differences in functions and demographic traits, similar to those for leaves and branches in shoots. In addition, differences in individual root life cycles may affect the root chemical composition, in turn, affecting the decomposition rate. Future studies should seek to identify heterorhizic units in mortality related to anatomical, physiological, and morphological differences for various species. The decomposition processes of each mortality unit within the fine root architecture are also important in understanding the link between physiological and ecosystem functions.     

Daily stem water deficit of Norway spruce and European beech in intra- and interspecific neighborhood under heavy drought

High-resolution measurements of stem radius variations provide information about the tree water status with changing climate conditions by swelling and shrinking due to the reduction of xylem water potential and to the exceedance of leaf transpiration over root water uptake. The aim of this study was to analyze daily stem radius variations of Norway spruce and European beech in intra- and interspecific neighborhood. The experimental plots are part of a rainfall exclusion experiment. These variations are species-specific, i.e. spruces have a higher phloem thickness and higher amplitudes during a day than beeches. The amplitudes were significantly higher at the rainfall exclusion plots, but the amplitudes of spruces decreased above 27°C with increasing drought due to reduced transpiration rates and exhausted soil water reserves. The shrinking amplitude was observed for spruces in intraspecific neighborhood from a soil volumetric water content of 0.21?m³?m^?3. In interspecific neighborhood, a shrinking amplitude for spruces could not be observed and revealed a lesser tree water deficit than in intraspecific neighborhood. Beeches showed minor differences with a higher tree water deficit in interspecific neighborhood. Consequently, stem radius variations give insights into a tree's water supply, which could help to understand changes in tree growth.     

Relationship between seedbed properties and the emergence of spruce germinants in recently cut Norway spruce selection stands in Southern Finland

The purpose of this study was to examine the effects of type and amount of ground vegetation and substrate on the germination and early survival of Norway spruce (Picea abies (L.) Karst) seedlings in uneven-aged stands on mineral soils in Southern Finland. The study was conducted on two permanent plots representing average site quality for spruce stands in the area. A gradient in selection cut intensity and residual stand density was imposed across each of the two permanent plots. Regeneration and vegetation surveys were repeated annually on a grid of unmanipulated microplots and on a set of soil treatment microplots. The results indicated that the number of spruce germinants per unit area was positively correlated with herb cover but negatively correlated with total plant cover. Germinant density was also related to vegetation-free seedbed conditions, high overstory competition index and presence of larger spruce seedlings. Regeneration microsites dominated by moss or with plants with a relatively high light demand were associated with low germinant numbers. Bare humus layer and decayed stumps seemed to promote germinant emergence. Exposure of mineral soil resulted in germination rates that were 4.3–6.9 times higher than in undisturbed conditions during the first growing season.     

Effects of repeated urea doses on soil chemistry and nutrient pools in a Norway spruce stand

Pools of macro-nutrients in soil and vegetation were studied in an old fertilization experiment with a large previous input of N. Different doses of N, in the form of urea, had been added four times during a 20-year period. In total, between 480 and 2400 kg N ha⁻¹ had been given. The experiment was established in a relatively productive Norway spruce stand and the expectation was that the large N input would cause an accelerated leaching of N, especially nitrate, accompanied by soil acidification and losses of several nutrients. The aim was to test for possible residual effects. Thirteen years after the last N addition, samples from the aboveground part of trees, field layer, S-layer, humus layer and mineral soil (0–10 cm) were analyzed for concentrations of most major nutrients. Nutrient pools were calculated. In the humus layer, the concentration of N increased and the C/N-ratio decreased with increasing N dose. The calculated recovery of added N in soil including ground vegetation was complete for the lowest N dose, while it was 25–50% for higher doses. The amount of N retained was unaffected by the N dose. The amount of extractable P in the upper part of the mineral soil was negatively correlated with N dose, as was also the concentration of total P in the S-layer. Neither soil pH, nor concentrations or amounts of Ca, Mg and K were affected by the previous fertilization. The calculated total soil-plant pool was only influenced by N dose in the case of P, which was 20% lower at the highest N dose compared with unfertilized conditions. Despite the large extra N input, the nutritional changes in plants and soil of the actual study site seemed surprisingly small.     

Estimation of the fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using minirhizotrons

We estimated fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using a min-irhizotron technique. Since data obtained from minirhizo-trons are limited to the length and diameter of fine roots observed on minirhizotron tubes, data conversion is necessary to determine the fine root biomass per unit soil volume or unit stand area. We first examined the regression between diameter squared and weight per unit length of fine roots in soil core samples, and calculated the fine root biomass on minirhizotron tubes from their length and diameter. Then we determined conversion factors based on the ratio of the fine root biomass in soil core samples to that on minirhizotron tubes. We examined calculation methods, using a single conversion factor for total fine root biomass in the soil for depths of 0–40cm (Cal1), or using four conversion factors for fine roots in the soil at 10-cm intervals (Cal2). Cal1 overestimated fine root biomass in the lower soil or underestimated that in the upper soil, while fine root biomass calculated using Cal2 better matched that in soil core samples. These results suggest that minirhizotron data should be converted separately for different soil depths to better estimate fine root biomass.     

Effects of soil temperature on shoot and root growth and nutrient uptake of 5-year-old Norway spruce seedlings

Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 degrees C during the first (GS I) and third growing seasons (GS III), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 degrees C during the second growing season (GS II). In GS II, shoot diameter growth was lowest in the 21 degrees C treatment and root growth was lowest in the 9 degrees C treatment. In GS III, shoot height and root length growth improved in seedlings that had been kept at 9 degrees C during GS II, indicating compensatory growth in response to increased soil temperature. The temporary decrease in soil temperature had no long-lasting significant effect on seedling biomass or total nutrient uptake. At the end of GS III, fine roots of seedlings exposed to a soil temperature of 21 degrees C in GS II were distributed more evenly between the organic and mineral soil layers than roots of seedlings in the other treatments. During GS II and GS III, root growth started earlier than shoot growth, decreased during the rapid shoot elongation phase and increased again as shoot growth decreased.     

Vertical distribution of the ectomycorrhizal community in the top soil of Norway spruce stands

The vertical distribution of the ectomycorrhizal (ECM) community was studied in four old high-mountain Norway spruce (Picea abies [L.] Karst.) stands in northern Italy. The aim was to verify if the variability in the community structure could be explained by characteristics of the organic and mineral soil horizons. The community structure was evaluated in terms of both fungal species and their ability to explore soil (exploration types). From the 128 humus profiles sampled over the two study periods, 31 ECM species were recorded. The study demonstrated that the number of both non-vital tips and vital non-mycorrhized tips decreases with soil depth, from organic to mineral horizons, while the number of ectomycorrhizal tips mainly increases with soil depth. A preference was found of some ECM species and exploration types for specific organic or mineral soil layers and their features, especially moisture and available nitrogen. These results can help in understanding how the functional role of the single consortia and the ecological features determining this “adaptive diversity” in ectomycorrhizal communities could be of major importance to assess the resilience in forest soil ecosystems.     

Manganese in tree rings of Norway spruce as an indicator for soil chemical changes in the past

Element concentrations in tree rings can be used to monitor changes in environmental quality. With regard to the detection of incipient soil acidification, the manganese concentration in soils and plants is a significant marker for the switch of acid buffering in soils mainly with the exchange of base cations or with the dissolution of aluminium oxides. This is a site-specific non-linear event, indicating the onset of Al³⁺ dominance in the soil solution, were damages to vegetation due to acid stress become possible. This turning point is also a marker for the attainment of pH 4.2 in soils, the critical threshold used for critical load calculations. On a plot of the German environmental monitoring in forests the element concentrations in tree rings of 60-year-old spruces reveal a distinct decline in the Mn concentration, beginning in the late 1960s ending in the late 1970s. With this information it was possible to assume a base saturation in the soil of about 15–20% in the late 1960s, and to model the development of the base saturation of the site. A decline from 17.5 to 6% within one decade could be related to the deposition. This is in accordance with the base saturation of 6.5%, measured in 1993 for this site, but also for adjacent spruce sites on the same geological substrate. The knowledge of the time span were this site-specific non-linear event occurred is essential for the reconstruction of the soil chemistry of a site. Moreover, it enables the assignment of observations like ‘forest damages’ to the onset of changes in environmental quality.     

Harvesting of logging residues affects diameter growth and pine weevil attacks on Norway spruce seedlings

Removal of logging residues causes significant nutrient losses from the harvesting site. Furthermore, collection of residues into piles could lead to small-scale differences in establishment conditions for seedlings. We studied the effects of stem-only (SOH) and aboveground whole-tree harvesting (WTH) on Norway spruce (Picea abies) seedling growth and pine weevil (Hylobius abietis) damage at two sites (SE and W Norway). We also compared two planting environments within the WTH plots (WTH-0: areas with no residues, WTH-1: areas where residue piles had been placed and removed before planting). In practice, one-third of the residues were left on site after WTH. After three growing seasons there were no differences for height or diameter increment between SOH and WTH (WTH-1 and WTH-0 combined) treatments. However, relative diameter increment was largest for WTH-1 seedlings and lowest for WTH-0 seedlings. Few seedlings sustained pine weevil attacks at the W Norway site, with no differences among treatments. At the SE Norway site, the percent of seedlings damaged by pine weevils and average debarked area were significantly higher after WTH (82% and 3.3?cm²) compared to SOH (62% and 1.7?cm²). We conclude that WTH may lead to spatial differences in establishment conditions.     

Effects of drought and canopy ozone exposure on antioxidants in fine roots of mature European beech (Fagus sylvatica)

We quantified ascorbate, glutathione and alpha-tocopherol in fine roots of mature Fagus sylvatica L. under free-air canopy ozone (O(3)) exposure (twice ambient O(3) concentration, 2x[O(3)]) during two growing seasons that differed in the extent of summer drought (exceptional drought year 2003, average year 2004). This design allowed us to test whether O(3) exposure or drought, or both, affected root antioxidants during the growing season. In both years, root ascorbate and alpha-tocopherol showed a similar relationship with volumetric soil water content (SWC): ascorbate concentrations on a root dry mass basis increased from about 6 to 12 micromol g(-1) when SWC dropped from 25 to 20%, and a-tocopherol increased from 100 to 150 nmol g(-1) at SWC values below 20%. Root glutathione showed no relationship with SWC or differences between the dry and the average year, but it was significantly and consistently diminished by 2x[O(3)]. Our results were inconclusive as to whether shoot-root translocation of glutathione or glutathione production in the roots was diminished. Phloem glutathione concentrations in the canopy remained constant, but reduced transport velocity in the phloem and, as a consequence, reduced mass flow of glutathione cannot be ruled out.     

Effects of experimental acidification,nitrogen addition and liming on ground vegetation in a mature stand of Norway spruce (Picea abies (L.) Karst.) in SE Sweden

During the period 1976–1991, a combined experiment of acidification, liming and nitrogen addition in a mature spruce stand was conducted at Farabol in south-east Sweden. The aim of this study was to investigate the effects of these treatments on the ground vegetation 0, 1, 5 and 15 years after experimental establishment. The treatment regimes were nitrogen (200 kg N ha⁻¹, repeated three times at 4–5-year intervals, totally 600 kg N ha⁻¹), sulphur powder (50 and 100 kg S ha⁻¹ a⁻¹, totally 600 and 1200 kg ha⁻¹), sulphur plus nitrogen (600+600 kg ha⁻¹) and limestone (500 kg ha⁻¹ a⁻¹, i.e. totally 6000 kg ha⁻¹). The results showed that nitrogen addition and liming promoted the abundance of the grass Deschampsia flexuosa, while acidification had a negative effect on D. flexuosa and herbs in the field layer. There was a negative reaction giving immediate damage to the bryophytes in connection with additions of nitrogen, sulphur powder and lime. The magnitude of damage and the capacity to recover varied among species as well as among treatments. The recovery from immediate damage after liming was much faster than after the treatments with sulphur powder and/or nitrogen. A negative interaction between sulphur powder and nitrogen was found for herbs and mosses where the combined effects were stronger than the effects of a single treatment alone. Acidification also had a negative effect on the total number of species. The results of this study showed that acidification and nitrogen deposition could negatively influence forest vegetation by changing the nutrient availability in the soils. Liming led to an improved growth of the forest ground vegetation and the flora changed towards a more nitrophilic species composition.     

Fertilization effects on mean stomatal conductance are mediated through changes in the hydraulic attributes of mature Norway spruce trees

Stomatal conductance was quantified with sap flux sensors and whole-tree chambers in mature Norway spruce (Picea abies (L.) Karst.) trees after 3 years of exposure to elevated CO(2) concentration ([CO(2)]) in a 13-year nutrient optimization experiment. The long-term nutrient optimization treatment increased tree height by 3.7 m (67%) and basal diameter by 8 cm (68%); the short-term elevated [CO(2)] exposure had no effect on tree size or allometry. Nighttime transpiration was estimated as approximately 7% of daily transpiration in unchambered trees; accounting for the effect of nighttime flux on the processing of sap flux signals increased estimated daily water uptake by approximately 30%. Crown averaged stomatal conductance (g(s)) was described by a Jarvis-type model. The addition of a stomatal response time constant (tau) and total capacitance of stored water (C(tot)) improved the fit of the model. Model estimates for C(tot) scaled with sapwood volume of the bole in fertilized trees. Hydraulic support-defined as a lumped variable of leaf-specific hydraulic conductivity and water potential gradient (K(l)DeltaPsi) -was estimated from height, sapwood-to-leaf area ratio (A(s):A(l)) and changes in tracheid dimensions. Hydraulic support explained 55% of the variation in g(s) at reference conditions for trees across nutrient and [CO(2)] treatments. Removal of approximately 50% of A(l) from three trees yielded results suggesting that stomatal compensation (i.e., an increase in g(s)) after pruning scales inversely with K(l)DeltaPsi, indicating that the higher the potential hydraulic support after pruning, the less complete the stomatal compensation for the increase in A(s):A(l).     

Effects of vitality fertilization on the growth of Heterobasidion annosum in Norway spruce roots

The effects of vitality fertilization on the growth of Heterobasidion annosum in roots of Norway spruce (Picea abies) were studied in a 53-year-old, naturally regenerated spruce stand in southern Finland. The fertilizer treatments were: (1), unfertilized control; (2), a compound fertilizer containing P, K, Ca, Mg, S, Cu, Zn and B; (3), as 2 with additional nitrogen; (4), as 3 with additional lime; and (5), a mixture composed on the basis of needle analysis, containing N, P, K and Cu. Three growing seasons after fertilization, four roots of eight trees in each treatment were inoculated with four different strains of H. annosum. Spread of the fungus from the inoculation point was determined after 12 months. Mean spread rates upwards in roots were 18.2, 25.6, 21.3, 26.0 and 29.8 cm/year in treatments 1, 2, 3, 4 and 5, respectively. These results suggest a tendency towards faster growth by H. annosum in fertilized trees. However, there was considerable variation in fungal growth at both the tree and root level and differences between treatments were not statistically significant.