Cycling of soil carbon in a Japanese red pine forest II. Changes occurring in the first year after a clear-felling

Cycling of soil carbon in the first year after a clear-felling was compared with that before the felling in a Japanese red pine forest in Hiroshima Prefecture, west Japan. The daily mean temperature at the soil surface in summer was increased after the felling in comparison to that before felling, and the water content of both the A₀ layer and the surface mineral soil was decreased due to the loss of the forest canopy. The rate of weight loss of the A₀ layer was reduced after felling. However, accumulation of the A₀ layer rapidly decreased because of the lack of litter supply to the forest floor. Low soil respiration after felling was mainly caused by the cessation of root respiration. Analysis of annual soil carbon cycling was then conducted using a compartment model. The relative decomposition rate of the A₀ layer decreased whereas that of humus and dead roots in mineral soil increased to some extent after felling. The accumulation of carbon in mineral soil, however, increased slightly due to the supply of humus from roots killed by the felling.     

Periodic carbon flushing to roots of Quercus rubra saplings affects soil respiration and rhizosphere microbial biomass

Patterns of root/shoot carbon allocation within plants have been studied at length. The extent, however, to which patterns of carbon allocation from shoots to roots affect the timing and quantity of organic carbon release from roots to soil is not known. We employed a novel approach to study how natural short-term variation in the allocation of carbon to roots may affect rhizosphere soil biology. Taking advantage of the semi-determinate phenology of young northern red oak (Quercus rubra L.), we examined how pulsed delivery of carbon from shoots to roots affected dynamics of soil respiration as well as microbial biomass and net nitrogen mineralization in the rhizosphere. Young Q. rubra exhibit (1) clear switches in the amount of carbon allocated below-ground that are non-destructively detected simply by observing pulsed shoot growth above-ground, and (2) multiple switches in internal carbon allocation during a single growing season, ensuring our ability to detect short-term effects of plant carbon allocation on rhizosphere biology separate from longer-term seasonal effects. In both potted oaks and oaks rooted in soil, soil respiration varied inversely with shoot flush stage through several oak shoot flushes. In addition, upon destructive harvest of potted oaks, microbial biomass in the rhizosphere of saplings with actively flushing shoots was lower than microbial biomass in the rhizosphere of saplings with shoots that were not flushing. Given that plants have evolved with their roots in contact with soil microbes, known species-specific carbon allocation patterns within plants may provide insight into interactions among roots, symbionts, and free-living microbes in the dynamic soil arena.     

Ecophysiological responses of Japanese forest tree species to ozone, simulated acid rain and soil acidification

In this review, I summarized the results obtained from experimental studies on the ecophysiological responses of Japanese forest tree species to O₃, simulated acid rain and soil acidification. Based on the studies conducted in Japan, exposure to ambient levels of O₃ below 100 nl·l⁻¹ (ppb) for several months is sufficient to inhibit dry matter production and net photosynthesis of sensitive Japanese forest tree species such as Siebold's beech and Japanese zelkova. On the other hand, exposure to simulated acid rain with a pH of 4.0 or above for several months cannot induce any adverse effects on dry matter production and physiological functions of Japanese forest tree species. However, when the pH of simulated rain or fog is lowered below 4.0, negative effects appear on dry matter production and physiological functions such as transpiration in several sensitive Japanese forest tree species such as Japanese fir and Nikko fir. Based on limited information, it may be concluded that (1) Al dissolved into soil solution is the most important limiting factor for dry matter production, physiological functions and nutrient status of Japanese forest tree species grown in acidic soil, (2) the (Ca+Mg+K)/Al molar ratio in soil solution is a useful indicator to evaluate and predict the effects of soil acidification due to acid deposition on whole-plant dry matter production of Japanese forest tree species at the present time and in the future, and (3) Japanese coniferous tree species such as Japanese cedar and red pine are relatively sensitive to a reduction in (Ca+Mg+K)/Al molar ratio in soil solution compared with European forest tree species such as Norway spruce.     

模拟氮沉降对中亚热带杉木幼树根系生物量的影响

植物根系是全球陆地生态系统碳储量的重要组成部分,在全球生态系统碳循环中起着重要作用,日益加剧的氮沉降会影响根系生物量在空间和不同径级的分配,进而影响森林生态系统的生产力和土壤养分循环。以杉木幼树为研究对象,通过野外氮沉降模拟实验,研究氮沉降四年后对不同土层、不同径级根系生物量的影响。结果发现：（1）低氮和高氮处理总细根生物量较对照均无显著差异（P > 0.05）,高氮处理粗根生物量及总根系生物量较对照分别增加45%和40%（P < 0.05）;（2）与对照相比,施氮处理显著增加20-40 cm与40-60 cm土层细根和粗根生物量,且在低氮处理下,20-40 cm土层细根、粗根在总土层细根与粗根生物量的占比显著提高。（3）与对照相比,高氮处理显著增加了2-5 mm、5-10 mm及10-20 mm径级的根系生物量,低氮处理显著增加2-5 mm、5-10 mm径级根系生物量,且显著降低20-50 mm径级根系生物量。综上所述表明：氮沉降后杉木幼树通过增加较粗径级根系来增加对养分及水分的输送,同时通过增加深层根系生物量及其比例的策略来维持杉木幼树的快速生长;而根系生物量的增加,在一定程度上会增加根系碳源的输入,影响土壤碳循环过程。     

Root distribution in an Amazonian seasonal forest as derived from δ13C profiles

Carbon isotope ratios of the main stem in trees, saplings, and seedlings were correlated with their main stem diameter in an Amazonian seasonal forest. This correlation became the basis of using carbon isotope ratios of roots from various levels of the soil profile in order to determine root distribution from emergent, canopy and subcanopy trees, saplings and herbaceous understorey plants. It was observed that the distribution of roots in the soil profile is horizontally and vertically heterogeneous. Pockets of roots from saplings or herbaceous understorey plants were found as deep as 4 m and pockets of roots from emergent trees were found as shallow as 1 m depth.     

Contribution of root respiration to total soil respiration in a Japanese cedar (Cryptomeria japonica D. Don) artificial forest

Soil respiration was measured for 2 years in an artificial gap and in an undisturbed area in a Japanese cedar (Cryptomeria japonica D. Don) forest to estimate the contribution of root respiration to total soil respiration. Measurement plots were set up at the center of the gap, the edge of the gap, the edge of the surrounding stand and within the stand. Using a small gap (2.5 m × 2.5 m) enabled us to maintain the same soil temperature and soil moisture as found in the stand. Seasonal fluctuations in soil respiration, increasing in summer and decreasing in winter, corresponded to changes in the soil surface temperature. Soil respiration in the gap site did not differ significantly from those in the stand in the first year of gap formation. However, in the second year, the minimum CO₂ flux was observed at the center of the gap and the maximum at the edge of the surrounding stand. Assuming that the differences between soil respiration in the center of the gap and that in the stand were equal to the root respiration, the root respiration rate was calculated from the relationship between the root respiration rates (Rr) and the soil surface temperature (Ts) by Ln(Rr) = 0.07Ts + 3.48. The average contribution of root respiration to total soil respiration, as estimated from the soil surface temperature in the stand by using the above equation, was 49%. After taking root decomposition into consideration, the contribution of root respiration to soil respiration increased from 49 to 57%.     

Autotrophic and heterotrophic soil respiration in a Norway spruce forest: estimating the root decomposition and soil moisture effects in a trenching experiment

The two components of soil respiration, autotrophic respiration (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic respiration (from decomposers), was separated in a root trenching experiment in a Norway spruce forest. In June 2003, cylinders (29.7 cm diameter) were inserted to 50 cm soil depth and respiration was measured both outside (control) and inside the trenched areas. The potential problems associated with the trenching treatment, increased decomposition of roots and ectomycorrhizal mycelia and changed soil moisture conditions, were handled by empirical modelling. The model was calibrated with respiration, moisture and temperature data of 2004 from the trenched plots as a training set. We estimate that over the first 5 months after the trenching, 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root and mycelia decomposition. Autotrophic and heterotrophic respiration contributed to about 50% each of total soil respiration in the control plots averaged over the two growing seasons. We show that the potential problems with the trenching, decomposing roots and mycelia and soil moisture effects, can be handled by a modelling approach, which is an alternative to the sequential root harvesting technique.     

跨地带土壤置换实验研究

以温带针阔混交林暗棕壤地带内的白浆土、草甸土、泥炭土为原料,以长白山自然保护区内的寒温带山地棕色针叶林土为置换对象,完成了仿自然原型的土壤合成,进行了跨地带的土壤置换与植被生长实验研究。结果表明:①山地棕色针叶林土的腐殖质层厚度、酸度和速效氮含量为植被生长的限制性因子;②合成土壤理化指标必须以原生土壤限制因子拐点(值)指标为确定依据,作为合成土壤的关键性指标;③在长白山采用泥炭土与草甸土各占1/4,白浆土占1/2进行混合,土层厚度40cm,并使用石灰进行调酸达到中性后,植被恢复效果最好、造价最低。     

Respiration of wood ant nest material affected by material and forest stand characteristics

We studied differences in respiration of materials from different parts of wood ant nest (top, bottom, and rim) and from the nest surroundings (humus layer and mineral soil). Samples were taken from 8 wood ant (Formica aquilonia) nests in each of the two types of forest (birch and pine) in eastern Finland. The differences were related to material and forest stand characteristics (i.e., moisture, pH, carbon content, and C:N ratio). As a result, the highest respiration per g DW was measured at the top of ant nests in the birch forest. However, respiration did not significantly differ between the parts of ant nests in the pine forest. Respiration of the humus layers in both forest stands was on average higher, whereas respiration of the mineral soils in both forest stands was lower in comparison with respiration of the nest materials. The respiration per g C did not show any significant differences between different parts of nests and surrounding soil. The most important factors influencing respiration of the materials appeared to be moisture, carbon content, and pH. In conclusion, respiration of wood ant nest material is affected by the specific material and forest stand characteristics.     

Root respiration and its importance for the carbon balance of beech saplings (Fagus sylvatica L.) in a montane beech forest

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Solling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5–9.8 nmol CO₂ gDW^–1 s^–1 at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p<0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p<0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO₂ gDW^–1 s^–1 were reached in the middle of July. Due to low light intensities in the under storey, daily net CO₂ assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO₂ assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.     

Plant species control and soil faunal involvement in the processes of above‐ and below‐ground litter decomposition

Among the factors determining litter decomposition rates, the role of soil fauna as decomposers still remains unclear, especially for how they are involved in decomposing below‐ground root litter compared to their relatively‐known contributions to decomposing above‐ground leaf litter. We conducted a litterbag experiment using two sizes of meshes and pursued the leaf and root decomposition of six major tree species in a Japanese temperate forest over 411‐days to test the interactive effects of soil mesofauna and litter quality addressed based on two features (litter types and species) on the process. Moreover, given a possible correlation between litter traits of the leaves and roots, we examined whether soil mesofauna alters the relationship between leaf and root decomposition across species. We found that the effects of plant species identity was stronger than that of soil mesofauna for determining the litter mass loss rate and the microbial respiration rate in both above‐ground and below‐ground decomposition. In addition, we found a significant positive correlation between leaf and root litter decomposition processes, regardless of the involvement soil mesofauna. On the other hand, the presence of soil mesofauna increased microbial respiration rates in the early stage of leaf decomposition; however, soil mesofauna did not affect root microbial respiration rates during the experiment. Such differential involvement of mesofauna in the leaf and root litter decomposition may drive the general patterns of faster and slower decomposition of plant leaves and roots in the soil, respectively.     

Response of Soil Respiration to Acid Rain in Forests of Different Maturity in Southern China

The response of soil respiration to acid rain in forests, especially in forests of different maturity, is poorly understood in southern China despite the fact that acid rain has become a serious environmental threat in this region in recent years. Here, we investigated this issue in three subtropical forests of different maturity [i.e. a young pine forest (PF), a transitional mixed conifer and broadleaf forest (MF) and an old-growth broadleaved forest (BF)] in southern China. Soil respiration was measured over two years under four simulated acid rain (SAR) treatments (CK, the local lake water, pH 4.5; T1, water pH 4.0; T2, water pH 3.5; and T3, water pH 3.0). Results indicated that SAR did not significantly affect soil respiration in the PF, whereas it significantly reduced soil respiration in the MF and the BF. The depressed effects on both forests occurred mostly in the warm-wet seasons and were correlated with a decrease in soil microbial activity and in fine root biomass caused by soil acidification under SAR. The sensitivity of the response of soil respiration to SAR showed an increasing trend with the progressive maturity of the three forests, which may result from their differences in acid buffering ability in soil and in litter layer. These results indicated that the depressed effect of acid rain on soil respiration in southern China may be more pronounced in the future in light of the projected change in forest maturity. However, due to the nature of this field study with chronosequence design and the related pseudoreplication for forest types, this inference should be read with caution. Further studies are needed to draw rigorous conclusions regarding the response differences among forests of different maturity using replicated forest types.     

Effects of Pinus sylvestris root growth and mycorrhizosphere development on bacterial carbon source utilization and hydrocarbon oxidation in forest and petroleum-contaminated soils

The hypothesis that Pinus sylvestris L. root and mycorrhizosphere development positively influences bacterial community-linked carbon source utilization, and drives a concomitant reduction in mineral oil levels in a petroleum hydrocarbon- (PHC-) contaminated soil was confirmed in a forest ecosystem-based phytoremediation simulation. Seedlings were grown for 9 months in large petri dish microcosms containing either forest humus or humus amended with cores of PHC-contaminated soil. Except for increased root biomass in the humus/PHC treatment, there were no other significant treatment-related differences in plant growth and needle C and N status. Total cell and culturable bacterial (CFU) densities significantly increased in both rhizospheres and mycorrhizospheres that actively developed in the humus and PHC-contaminated soil. Mycorrhizospheres (mycorrhizas and extramatrical mycelium) supported the highest numbers of bacteria. Multivariate analyses of bacterial community carbon source utilization profiles (Biolog GN microplate) from different rhizosphere, mycorrhizosphere, and bulk soil compartments, involving principal component and correspondence analysis, highlighted three main niche-related groupings. The respective clusters identified contained bacterial communities from (i) unplanted bulk soils, (ii) planted bulk PHC and rhizospheres in PHC-contaminated soils, and (iii) planted bulk humus and rhizosphere/mycorrhizosphere-influenced humus, and mycorrhizosphere-influenced PHC contaminated soil. Correspondence analysis allowed further identification of amino acid preferences and increased carboxylic/organic acid preferences in rhizosphere and mycorrhizosphere compartments. Decreased levels of mineral oil (non-polar hydrocarbons) were detected in the PHC-contaminated soil colonized by pine roots and mycorrhizal fungi. These data further support our view that mycorrhizosphere development and function plays a central role in controlling associated bacterial communities and their degradative activities in lignin-rich forest humus and PHC-contaminated soils.     

Root respiration rate before and just after clear-felling in a mature,deciduous, broad-leaved forest

Soil respiration was measured throughout the year (June 1992 to May 1993) in a mature, deciduous, broad-leaved forest and an adjacent, clear-felled stand which was made in November 1991, in Hiroshima Prefecture, west Japan. The same soil temperature and soil moisture content as those in the forest stand were maintained in two frame boxes covered with sheets of white netting in the clear-felled stand to observe soil respiration. A herbicide was applied to the cut end of all stumps in one of the two frame boxes in order to kill the root system. There was no significant difference in the aboveground biomass and soil environmental conditions between the forest and the frame boxes in the clear-felled stands. The difference in soil respiration rate between the forest and the frame box, in which the root system was killed by the herbicide, was considered to be due largely to the contribution of root respiration. Taking into consideration CO₂ evolution due to the decomposition of roots killed and the change in A₀ layer respiration rate after clear-felling, the proportion of root respiration to the total soil respiration before clear-felling was estimated to be 51% annually, which coincides closely with those values estimated previously in mature forests by other methods. The difference in the soil respiration rate between the two frame boxes (one with killed roots and the other with undisturbed roots) suggested that the annual root respiration rate just after clear-felling dropped to about two-thirds (70%) of that before clear-felling.     

Moso bamboo and Japanese cedar seedlings differently affected soil N2O emissions

毛竹和日本柳杉幼苗对土壤氧化亚氮排放的影响及微生物机制 毛竹(Phyllostachys edulis)向日本柳杉(Cryptomeria japonica)林的扩张现象越发普遍,其扩张对大 气重要温室气体氧化亚氮(N₂O)排放的影响也引起了更多的关注,而其微生物机制尚不明确。本研究通过添加微生物抑制剂链霉素和扑海因分别抑制细菌和真菌活性,连续观测土壤N₂O排放速率以及相关土壤养分和植物生物量。研究结果表明：(i)毛竹土壤N₂O的排放速率显著高于日本柳杉;与对照相比,细菌抑制剂、真菌抑制剂及其交互作用均对N₂O排放速率具有显著抑制效应,但三者之间无显著差异;(ii)毛竹生物量显著高于日本柳杉;(iii)日本柳杉土壤有机质、全氮和铵态氮显著高于毛竹土壤,日本柳杉土壤pH和全磷显著低于毛竹土壤。真菌抑制剂降低了土壤有机质含量,细菌抑制剂降低了土壤硝态氮含量。真菌抑制剂与物种在影响土壤pH、全磷和铵态氮方面具有显著交互作用。细菌抑制剂与物种在影响土壤全氮方面有显著交互作用。综上所述,毛竹和日本柳杉在生长过程中土壤N₂O排放速率不同,毛竹幼苗土壤N₂O排放及生物量均高于日本柳杉。细菌抑制剂和真菌抑制剂对N₂O的排放速率均具有一定抑制作用。因而,在全球气候变化背景下,应进一步深入了解森林生态系统物种组成和变化对N₂O排放的影响,以有效评估毛竹扩张等导致的生物多样性变化对全球N₂O排放的贡献。     

Citrus root responses to localized drying soil: A new approach to studying mycorrhizal effects on the roots of mature trees

Because fine roots tend to be concentrated at the soil surface, exposure to dry surface soil can have a large influence on patterns of root growth, death and respiration. We studied the effects of arbuscular mycorrhizas (AM) formation on specific root length (SRL), respiration and mortality of fine roots of bearing red grapefruit (Citrus paradisi Macf.) trees on Volkamer lemon (C. volkameriana Tan. & Pasq.) rootstock exposed to drying soil. For each tree, the fine roots were removed from two woody lateral roots, the roots were surface sterilized and then each woody root was placed in a separate pair of vertically divided and independently irrigated soil compartments. The two split-pot systems were filled with sterilized soil and one was inoculated with arbuscular mycorrhizal fungi (Glomus etunicatum/G. intraradices). New fine lateral roots that emerged from the woody laterals were permitted to grow inside the pots over a 10-month period. Irrigation was then removed from the top compartment for a 15-week period. At the end of the study, roots inoculated with AM fungi exhibited about 20% incidence of AM formation, whereas the uninoculated roots were completely void of AM fungi. Arbuscular mycorrhizal roots exhibited lower SRL, lower root/soil respiration and about 10% lower fine root mortality than nonmycorrhizal roots after 15 weeks of exposure to dry surface soil. This study demonstrates the feasibility of examining mycorrhizal effects on the fine roots of adult trees in the field using simple inexpensive methods.     

Partitioning of belowground C in young sugar maple forest

Background and aims

Trees allocate a high proportion of assimilated carbon belowground, but the partitioning of that C among ecosystem components is poorly understood thereby limiting our ability to predict responses of forest C dynamics to global change drivers.

Methods

We labeled sugar maple saplings in natural forest with a pulse of photosynthetic ¹³C in late summer and traced the pulse over the following 3 years. We quantified the fate of belowground carbon by measuring ¹³C enrichment of roots, rhizosphere soil, soil respiration, soil aggregates and microbial biomass.

Results

The pulse of ¹³C contributed strongly to root and rhizosphere respiration for over a year, and respiration comprised about 75 % of total belowground C allocation (TBCA) in the first year. We estimate that rhizosphere carbon flux (RCF) during the dormant season comprises at least 6 % of TBCA. After 3 years, 3.8 % of the C allocated belowground was recovered in soil organic matter, mostly in water-stable aggregates.

Conclusions

A pulse of carbon allocated belowground in temperate forest supplies root respiration, root growth and RCF throughout the following year and a small proportion becomes stabilized in soil aggregates.     

Fertilization effects on fineroot biomass, rhizosphere microbes and respiratory fluxes in hardwood forest soils

Fertilizer-induced reductions in CO(2) flux from soil ((F)CO(2)) in forests have previously been attributed to decreased carbon allocation to roots, and decreased decomposition as a result of nitrogen suppression of fungal activity. Here, we present evidence that decreased microbial respiration in the rhizosphere may also contribute to (F)CO(2) reductions in fertilized forest soils. Fertilization reduced (F)CO(2) by 16-19% in 65-yr-old plantations of northern red oak (Quercus rubra) and sugar maple (Acer saccharum), and in a natural 85-yr-old yellow birch (Betula allegheniensis) stand. In oak plots, fertilization had no effects on fine root biomass but reduced mycorrhizal colonization by 18% and microbial respiration by 43%. In maple plots, fertilization reduced root biomass, mycorrhizal colonization and microbial respiration by 22, 16 and 46%, respectively. In birch plots, fertilization reduced microbial respiration by 36%, but had variable effects on root biomass and mycorrhizal colonization. In plots of all three species, fertilization effects on microbial respiration were greater in rhizosphere than in bulk soil, possibly as a result of decreased rhizosphere carbon flux from these species in fertile soils. Because rhizosphere processes may influence nutrient availability and carbon storage in forest ecosystems, future research is needed to better quantify rhizo-microbial contributions to (F)CO(2).     

Below-ground respiratory responses of sugar maple and red maple saplings to atmospheric CO2 enrichment and elevated air temperature

The research described in this paper represents a part of a much broader research project with the general objective of describing the effects of elevated [CO2] and temperature on tree growth, physiological processes, and ecosystem-level processes. The specific objective of this research was to examine the below-ground respiratory responses of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) seedlings to elevated atmospheric [CO2] and temperature. Red maple and sugar maple seedlings were planted in the ground in each of 12 open-top chambers and exposed from 1994 through 1997 to ambient air or air enriched with 30 Pa CO2,< in combination with ambient or elevated (+4 °C) air temperatures. Carbon dioxide efflux was measured around the base of the seedlings and from root-exclusion zones at intervals during 1995 and 1996 and early 1997. The CO2 efflux rates averaged 0.4 μmol CO2 m-2 s-1 in the root-exclusion zones and 0.75 μmol CO2 m-2 s-1 around the base of the seedlings. Mineral soil respiration in root-exclusion zones averaged 12% higher in the high temperature treatments than at ambient temperature, but was not affected by CO2 treatments. The fraction of total efflux attributable to root + rhizosphere respiration ranged from 14 to 61% in measurements made around red maple plants, and from 35 to 62% around sugar maple plants. Root respiration rates ranged from 0 to 0.94 μmol CO2 s-1 m-2 of soil surface in red maple and from 0 to 1.02 in sugar maple. In both 1995 and 1996 root respiration rates of red maple were highest in high-CO2 treatments and lowest in high temperature treatments. Specific red maple root respiration rates of excised roots from near the soil surface in 1996 were also highest under CO2 enrichment and lowest in high temperature treatments. In sugar maple the highest rates of CO2 efflux were from around the base of plants exposed to both high temperature and high-CO2, even though specific respiration rates were< lowest for this species under the high temperature and CO2 enrichment regime. In both species, patterns of response to treatments were similar in root respiration and root mass, indicating that the root respiration responses were due in part to differences in root mass. The results underscore the need for separating the processes occurring in the roots from those in the forest floor and mineral soil in order to increase our understanding of the effects of global climate change on carbon sequestration and cycling in the below-ground systems of forests.     

The role of soil conditions in fine root ecomorphology in Norway spruce (Picea abies (L.) Karst.)

The present study is an attempt to investigate the pattern of morphological variability of the short roots of Norway spruce (Picea abies (L.) Karst.) growing in different soils. Five root parameters – diameter, length and dry weight of the root tip, root density (dry weight per water-saturated volume) and specific root area (absorbing area of dry weight unit) were studied with respect to 11 soil characteristics using CANOCO RDA analysis. The investigation was conducted in seven study areas in Estonia differing in site quality class and soil type. Ten root samples per study area were collected randomly from the forest floor and from the 20 cm soil surface layer. Eleven soil parameters were included in the study: humus content, specific soil surface area, field capacity, soil bulk density, pH (KCl and H₂O dilution's), N and Ca concentrations, Ca/Al and C/N ratios, and the decomposition rate of fine roots (<2 mm dia.). Root morphological characteristics most strongly related to the measured soil characteristics in the different sites were specific root area, root density and diameter of the short roots, the means varying from 29 to 42 m² kg⁻¹, from 310 to 540 kg m⁻³ and from 0.26 to 0.32 mm, respectively; root density being most sensitive. The most favourable site and soil types resulting in fine roots with morphological characteristics for optimizing nutrient uptake (e.g. low short root density and high specific root area) were Umbric Luvisol (Oxalis), Dystric Gleysol (Oxalis) and Gleyic Luvisol (Hepatica). These soil types correspond to highly productive natural forest stands of Norway spruce in Estonia. All measured soil variables explained 28% of total variance of the root characteristics. The most important variables related to root morphology were the humus content, field capacity and specific soil surface area. This revised version was published online in June 2006 with corrections to the Cover Date.