Root Necromass Research Articles

On the significance of belowground overyielding in temperate mixed forests: separating species identity and species diversity effects

Complementary soil exploration by the root systems of coexisting tree species has been hypothesised to result in a higher root biomass of mixed forests than of monocultures but the existing evidence for a belowground diversity effect in forests is scarce and not conclusive.In a species‐rich temperate broad‐leaved forest, we analysed the fine root biomass (roots ≤ 2 mm) and necromass in 100 plots differing in tree species diversity (one to three species) and species composition (all possible combinations of five species of the genera Acer, Carpinus, Fagus, Fraxinus and Tilia) which allowed us to separate possible species diversity and species identity effects on fine root biomass.We found no evidence of a positive diversity effect on standing fine root biomass and thus of overyielding in terms of root biomass. Root necromass decreased with increasing species diversity at marginal significance.Various lines of evidence indicate significant species identity effects on fine root biomass (10–20% higher fine root biomass in plots with presence of maple and beech than in plots with hornbeam; 100% higher fine root biomass in monospecific beech and ash plots than in hornbeam plots; differences significant). Ash fine roots tended to be over‐represented in the 2‐ and 3‐species mixed plots compared to monospecific ash plots pointing at apparent belowground competitive superiority of Fraxinus in this mixed forest.Our results indicate that belowground overyielding and spatial complementarity of root systems may be the exception rather than the rule in temperate mixed forests.

Comparison of the fine root dynamics of Populus euphratica forests in different habitats in the lower reaches of the Tarim River in Xinjiang, China, during the growing season

The fine root dynamics of Populus euphratica forests in the upper section (Yingsu) and lower section (Alagan) habitats of the lower reaches of the Tarim River, southern Xinjiang, China, were investigated and compared by a sequential soil coring method during the growing season of 2008. Soil organic carbon, total nitrogen, soil water content, fine root biomass, necromass, and production were significantly higher in Yingsu than in Alagan, suggesting better nutrient conditions for fine root growth in Yingsu than in Alagan. Fine root biomass, necromass, and production significantly increased from April until it peaked in August, and then it decreased. Fine root biomass, necromass, and production differed significantly among the soil layers, and their largest values appeared in the soil layer 40–80 cm deep. Mean turnover rates in the 0–120 cm soil layer were 1.60 and 1.52 year−1 in Yingsu and Alagan, respectively, and the fine root turnover rate did not differ significantly between the two habitats or among the soil layers. These results show that habitat change can significantly affect fine root biomass and the production of P. euphratica forests, leading to changes in plant primary production, nutrient cycling, and carbon sequestration in forest ecosystems in the lower reaches of the Tarim River.

Accumulation and biological cycling of heavy metal in four salt marsh species, from Tagus estuary (Portugal)

Pools of Zn, Cu, Cd and Co in leaf, stem and root tissues of Sarcocornia fruticosa, Sarcocornia perennis, Halimione portulacoides and Spartina maritima were analyzed on a bimonthly basis, in a Tagus estuary salt marsh. All the major concentrations were found in the root tissues, being the concentrations in the aboveground organs neglectable for sediment budget proposes, as seen by the low root-aboveground translocation. Metal annual accumulation, root turnovers and cycling coefficients were also assessed. S. maritima showed the higher root turnovers and cycling coefficients for most of the analyzed metals, making this a phytostabilizer specie. By contrast the low root turnover, cycling coefficient and low root necromass generation makes S. perennis the most suitable specie for phytoremediation processes. Although the high amounts of metal return to the sediments, due to root senescence, salt marshes can still be considered sinks of heavy metals, cycling heavy metals mostly between sediment and root.

Forest soil carbon cycle under elevated CO2 - a case of increased throughput?

Summary Forest soils account for a large part of the stable carbon pool held in terrestrial ecosystems. Future levels of atmospheric CO 2 are likely to increase C input into the soils through increased above- and below-ground production of forests. This increased input will result in greater sequestration of C only if the additional C enters stable pools. In this review, we compare current observations from four large-scale Free Air FACE Enrichment (FACE) experiments on forest ecosystems (EuroFACE, Aspen-FACE, Duke FACE and ORNL-FACE) and consider their predictive power for long-term C sequestration. At all sites, FACE increased fi ne root biomass, and in most cases higher fi ne root turnover resulted in higher C input into soil via root necromass. However, at all sites, soil CO 2 effl ux also increased in excess of the increased root necromass inputs. A mass balance calculation suggests that a large part of the stimulation of soil CO 2 effl ux may be due to increased root respiration. Given the duration of these experiments compared with the life cycle of a forest and the complexity of processes involved, it is not yet possible to predict whether elevated CO 2 will result in increased C storage in forest soil.

Tree fine root Ca/Al molar ratio – Indicator of Al and acidity stress

High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995;24:209 – 226). This article presents an overview of publications since 1995 where the reduced Ca/Al ratio in fine tree roots has been used as an indicator of stress for Al and/or soil acidity. The main aim of this review was to evaluate the use and the critical threshold of the fine root Ca/Al ratio as a potential indicator for Al toxicity stress to trees in acid soils. Based on the reviewed literature, the fine root Ca/Al molar ratio was strongly negatively related to Al stress in small tree seedlings in controlled environments, whereas the response was not clear under field conditions where other environmental factors interact. Fine root Ca/Al ranged from 0.03 to 17 in tree seedlings and from 0.1 to 18 in mature trees depending on experimental and site conditions, as well as the tolerance and uptake mechanisms of the different tree species. Fine root Ca/Al was positively related to the soil solution Ca/Al molar ratio. Fine root Ca/Al ratios were related positively to fine root length, growth, specific root length, and biomass, and negatively to root diameter, callose formation, respiration chain activity, starch concentration, and root necromass. A number of relationships have been also found between the fine root Ca/Al and above-ground seedling and/or mature tree growth and nutrient uptake. The critical thresholds for the Ca/Al fine root ratio of 0.2 suggested by Cronan and Grigal (1995) is estimated to represent 90% risk of inverse impact on root and above-ground tree growth. Values of Ca/Al molar ratio in the fine roots of mature trees were only rarely determined below the critical 0.2. The caveats for the use and the interpretation of Ca/Al ratio in fine roots have been addressed in detail. A protocol for root processing and elemental analysis to obtain reliable and comparable results of Ca and Al concentrations in roots is also provided. The article concludes with recommendations for a wider use of the Ca/Al ratio in roots as a bioindicator of Al toxicity to trees in acid soils.

Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands

Fine root systems may respond to soil chemical conditions, but contrasting results have been obtained from field studies in non-manipulated forests with distinct soil chemical properties. We investigated biomass, necromass, live/dead ratios, morphology and nutrient concentrations of fine roots (<2 mm) in four mature Norway spruce (Picea abies [L.] Karst.) stands of south-east Germany, encompassing variations in soil chemical properties and climate. All stands were established on acidic soils (pH (CaCl2) range 2.8–3.8 in the humus layer), two of the four stands had molar ratios in soil solution below 1 and one of the four stands had received a liming treatment 22 years before the study. Soil cores down to 40 cm mineral soil depth were taken in autumn and separated into four fractions: humus layer, 0–10 cm, 10–20 cm and 20–40 cm. We found no indications of negative effects of N availability on fine root properties despite large variations in inorganic N seepage fluxes (4–34 kg N ha−1 yr−1), suggesting that the variation in N deposition between 17 and 26 kg N ha−1 yr−1 does not affect the fine root system of Norway spruce. Fine root biomass was largest in the humus layer and increased with the amount of organic matter stored in the humus layer, indicating that the vertical pattern of fine roots is largely affected by the thickness of this horizon. Only two stands showed significant differences in fine root biomass of the mineral soil which can be explained by differences in soil chemical conditions. The stand with the lowest total biomass had the lowest Ca/Al ratio of 0.1 in seepage, however, Al, Ca, Mg and K concentrations of fine roots were not different among the stands. The Ca/Al ratio in seepage might be a less reliable stress parameter because another stand also had Ca/Al ratios in seepage far below the critical value of 1.0 without any signs of fine root damages. Large differences in the live/dead ratio were positively correlated with the Mn concentration of live fine roots from the mineral soil. This relationship was attributed to faster decay of dead fine roots because Mn is known as an essential element of lignin degrading enzymes. It is questionable if the live/dead ratio can be used as a vitality parameter of fine roots since both longevity of fine roots and decay of root litter may affect this parameter. Morphological properties were different in the humus layer of one stand that was limed in 1983, indicating that a single lime dose of 3–4 Mg ha−1 has a long-lasting effect on fine root architecture of Norway spruce. Almost no differences were found in morphological properties in the mineral soil among the stands, but vertical patterns were apparently different. Two stands with high base saturation in the subsoil showed a vertical decrease in specific root length and specific root tip density whereas the other two stands showed an opposite pattern or no effect. Our results suggest that proliferation of fine roots increased with decreasing base saturation in the subsoil of Norway spruce stands.

Patterns of Fine Root Mass and Distribution along a Disturbance Gradient in a Tropical Montane Forest, Central Sulawesi (Indonesia)

Large parts of the remaining tropical moist forests of South-east Asia are encroached at their margins by selective logging, rattan harvesting and the establishment of small agroforest plantations under the rainforest canopy. These slight to heavy disturbances affect aboveground forest structure by reducing wood biomass and canopy cover; however, they may also have a profound impact on the belowground compartment. In a lower montane moist forest of Central Sulawesi, we studied the profile totals of fine root biomass (FRBtot, roots <2 mm until 50 cm of soil depth) and of fine root necromass (FRNtot), the vertical distribution of fine root mass, and the fine root live/dead ratio by root coring in 12 forest stands that represented a gradient in forest use (or disturbance) intensity (forest use type A: undisturbed natural forest, B and C: slightly or moderately disturbed forests with selective timber extraction, D: heavily disturbed cacao agroforest systems under a remaining rainforest cover; each forest types being replicated three times). FRBtot decreased significantly from forest A to the disturbed B, C and D forests, and reached less than 60% of the FRBtot value of A in the agroforest systems D. A similar decrease with increasing disturbance intensity was found for FRNtot. Forest disturbance intensity had no significant influence on the vertical distribution of fine root biomass in the profiles. According to correlation and principal components analyses, fractional canopy cover was the most important factor influencing FRBtot and FRNtot, whereas diameter at breast height, stand basal area, stem density, soil pH and base saturation had only a minor or no influence on root mass. A reduction in canopy cover from 90% (forest type A) to 75% (types C and D) was associated with a reduction in FRBtot by about 45% which indicates that timber extraction leads not only to canopy gaps but to corresponding ‘root gaps’ in the soil as well. We conclude that forest encroachment that is widespread in large parts of South-east Asia’s remaining rainforests significantly reduces tree fine root biomass and associated carbon sequestration, even if it is conducted at moderate intensities only.

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.

Effects of elevated soil solution Al concentrations on fine roots in a middle-aged Norway spruce (Picea abies (L.) Karst.) stand

Aluminium (Al), mobilized by acidic deposition, has been claimed to be a major threat to forest vitality. Fine root mortality, decreased root growth and reduced nutrient uptake have been observed in controlled laboratory experiments where roots of tree seedlings were exposed to elevated concentrations of Al. Yet, evidence for Al-induced root damage from forest stands is scarcely reported. Nevertheless, Al dissolved in soil water has received a key role in the critical load concept for forests. Here, we present effects of artificially elevated concentrations of Al in the soil solution on fine roots in a middle-aged stand of Norway spruce (Picea abies (L.) Karst.). Although the inorganic Al concentrations about 200 µM and Ca:Al ratio about 0.7 that were established in the soil solution within this experiment have been associated with reduction of root growth and root mortality for spruce seedlings in hydroponic studies, no acute damage on fine roots was observed. Three years of treatment did not cause visual root damage, nor were effects on fine root necromass observed. Fine root necromass made up about 10% of fine root biomass for all treatments. However, significantly lower molar Ca:Al and Mg:Al ratios in living and dead fine roots were found in the plots where Al concentrations were highest and ratios of Ca to Al in the soil solution were lowest. The lack of response on fine root biomass suggests that forest stands tolerate higher Al levels than results from laboratory experiments indicate. We conclude that effect studies in the laboratory have limited value for field conditions. The key role of Al toxicity, expressed as the Ca/Al ratio, in critical load calculations for forests may have to be reconsidered.

Root turnover and root necromass accumulation of Norway spruce (Picea abies) are affected by soil acidity.

Fine root distribution and turnover were investigated in ca. 40-year-old pure Norway spruce (Picea abies Karst.) stands in Germany, growing on four sites that differed in soil acidity (Ebergötzen < Barbis < Fichtelgebirge = Harz). The density of fine root biomass and necromass in different soil horizons differed among the sites. At one of the most acidic sites (Harz), fine root density in the humus layer was more than twice that at the least acidic site (Ebergötzen). At the two most acidic sites, Fichtelgebirge and Harz, the ratio of biomass to necromass was significantly lower than at Ebergötzen and Barbis, particularly in the subsoil layer. In each stand, clear vertical gradients in fine root length density and root tip density were observed. Most of the roots and the root tips were in the humus layer and in the first mineral soil horizon (0-10 cm). There was a significantly different decrease in specific root length (cm gDM (-1)) and specific root tip density (root tips gDM (-1)) in the more acidified stands Fichtelgebirge and Harz compared with Ebergötzen and Barbis. Fine root production estimated by ingrowth cores and a net method was approximately twice as high in the more acidic stands Fichtelgebirge and Harz compared with Ebergötzen and Barbis. Rates of living fine root biomass turnover were higher at the Fichtelgebirge and Harz sites than at the Ebergötzen site. Rates of necromass turnover were similar at all sites. The results suggest that the accumulation of necromass was not due to a slower disappearance at the more acid sites, but to earlier root death. Roots contributed 46% to root + needle litter and 32% to root + total aboveground litter at the Harz site in 1997.

Root dynamics in bottomland hardwood forests of the Southeastern United States Coastal Plain

Effects of flooding on root dynamics appear nonlinear and therefore difficult to predict, leading to disparate and often contradictory reports of flooding impacts on production in bottomland hardwood forests. We explored root dynamics in two adjacent wetland habitats by comparing results obtained from several methods of estimating root processes. Also, we tested the influence of flooding on root dynamics of cherrybark, overcup, water and swamp chestnut oaks. Fine root biomass in the laurel oak habitat was greater ( α< 0.05) than in the swamp tupelo habitat (5.7 vs. 2.4 Mg ha −1 ), as was fine root necromass (2.4 vs. 1.3 Mg ha −1 ), productivity (2.3 vs. 0.3 Mg ha −1 yr −1 when the sum of significant increments method was used, 5.6 vs. 2.5 Mg ha −1 yr −1 when the maximum minus minimum method was used, and 1.2 vs. 1.0 Mg ha −1 yr −1 , when the root screen method was used), and turnover (40% and 12% per year). Mortality estimates were lower in the laurel oak habitat (1.3 and 1.2 Mg ha −1 yr −1 ) than in the swamp tupelo community (2.8 and 2.1 Mg ha −1 yr −1 ) when significant increment and maximum minus minimum methods were used, respectively. This apparent contradiction between estimates of production and mortality may be due to more rapid decomposition rates in the more aerated soil of the laurel oak than in the swamp tupelo forest type. Roots in the swamp tupelo habitat appeared to be longer-lived than in the laurel oak habitat. We concluded that there was greater investment in roots in the laurel oak habitat, where a shallow rooting zone and episodes of flooding and drought required drastic changes in root structure and physiology. In contrast, the swamp tupelo habitat had a deeper rooting zone and more consistently moist to flooded hydroperiod, allowing flood adapted roots to persist. The four oak species varied in their phenology of root production and response to flooding, from no difference among treatments for overcup oak to dramatic reductions in root growth during and after flooding for cherrybark oak. Flooding enhanced or at least did not negatively influence root growth in overcup oak, but seriously impacted root growth and survival of cherrybark oak and swamp chestnut oak. Different responses were attributed to the timing of root production: root growth began early for cherrybark oak so spring flooding severely affected this species. Growth in overcup oak began later and ended earlier than the other species tested, allowing the species a means of avoiding flood stress.

Fine root and nodule dynamics of Erythrina poeppigiana in an alley cropping system in Costa Rica

Fine root and nodule production and turnover in pruned 2- and 8-yr-old Erythrina poeppigiana (Walp.) O.F. Cook trees were estimated under humid tropical conditions by applying the compartment flow model (CFM) to fine root and nodule biomass and necromass measured in sequentially taken core samples. Shoot pruning intensities compared were complete pruning (i.e., complete removal of shoots) and partial pruning (i.e., retention of one branch on the pruned stump). The CFM provided reasonable estimates of nodule dynamics but did not apply to fine root data. Over a five-month observation period, nodule production in completely and partially pruned 2-yr-old trees was 58.2 and 115 g tree−1, respectively, and the corresponding values in 8-yr-old trees were 26.8 and 26.4 g tree−1. Senescent nodules and fine roots pass to soil organic matter via decomposition. Partially and completely pruned 2-yr-old trees added 95.4 and 50.4 g tree−1 decomposed nodules to soil, respectively. The respective value for 8-yr-old trees were 26.7 and 36.5g tree−1. Nodule and fine root turnover was compensated for by new production at 10–14 weeks after pruning. The retention of a branch on the pruned E. poeppigiana tree stump allows better fine root and nodule survival, and enhances tree biomass production.

Fine root biomass and production in Scots pine stands in relation to stand age.

We determined fine root biomass and production of 15-, 35- and 100-year-old Scots pine (Pinus sylvestris L.) stands during three growing seasons. Fine roots were sampled by the soil core method. Mean (+/- SE) annual fine root biomass of Scots pine in the 15-, 35- and 100-year-old stands was 220 +/- 25, 357 +/- 21 and 259 +/- 26 g m(-2), respectively. Fine root biomass of the understory vegetation was 159 +/- 54 g m(-2), 244 +/- 30 and 408 +/- 81 g m(-2), and fine root necromass was 500 +/- 112, 1,047 +/- 452 and 1,895 +/- 607 g m(-2) in the sapling, pole stage and mature stands, respectively. Both understory and Scots pine fine root production increased with stand age. Mean annual Scots pine fine root production was 165 +/- 131, 775 +/- 339 and 860 +/- 348 g m(-2) year(-1) in the sapling, pole stage and mature stand, respectively. The respective mean annual production of all fine roots (Scots pine and understory) was 181 +/- 129, 1,039 +/- 497 and 1,360 +/- 869 g m(-2) year(-1). The Scots pine and understory fine root biomass, necromass and production varied in relation to stand age, although the variation was not statistically significant.

Soil freezing alters fine root dynamics in a northern hardwood forest

The retention of nutrients within an ecosystem depends on temporal andspatial synchrony between nutrient availability and nutrient uptake, anddisruption of fine root processes can have dramatic impacts on nutrientretention within forest ecosystems. There is increasing evidence thatoverwinter climate can influence biogeochemical cycling belowground,perhaps by disrupting this synchrony. In this study, we experimentallyreduced snow accumulation in northern hardwood forest plots to examinethe effects of soil freezing on the dynamics of fine roots (< 1 mm diameter)measured using minirhizotrons. Snow removal treatment during therelatively mild winters of 1997–1998 and 1998–1999 induced mild freezingtemperatures (to −4 °C) lasting approximately three months atshallow soil depths (to −30 cm) in sugar maple and yellow birch stands.This treatment resulted in elevated overwinter fine root mortality in treatedcompared to reference plots of both species, and led to an earlier peak infine root production during the subsequent growing season. These shiftsin fine root dynamics increased fine root turnover but were not largeenough to significantly alter fine root biomass. No differences inmorality response were found between species. Laboratory tests on pottedtree seedlings exposed to controlled freezing regimes confirmed that mildfreezing temperatures (to −5 °C) were insufficient to directlyinjure winter-hardened fine roots of these species, suggesting that themarked response recorded in our forest plots was caused indirectly bymechanical damage to roots in frozen soil. Elevated fine root necromass intreated plots decomposed quickly, and may have contributed an excess fluxof about 0.5 g N/m2·yr, which is substantial relative tomeasurements of N fluxes from these plots. Our results suggest elevatedoverwinter mortality temporarily reduced fine root length in treatmentplots and reduced plant uptake, thereby disrupting the temporalsynchrony between nutrient availability and uptake and enhancing ratesof nitrification. Increased frequency of soil freezing events, as may occurwith global change, could alter fine root dynamics within the northernhardwood forest disrupting the normally tight coupling between nutrientmineralization and uptake.

Estimation of fine root mortality and growth from simple measurements: a method based on system dynamics

This study is a further development of a dynamic compartment-flow analysis, intended as an analytical tool for the empirical estimation of fine root growth, mortality and decomposition in forest soil. General properties of the dynamic system are utilised to interpret relatively simple measurements of standing biomass, necromass, and decomposition, in order to derive estimates of the process rates. The method is based on the finding that the ratio of fine root necromass to biomass is related to the specific rates of decomposition, mortality, and net growth. If the decomposition rate is measured and the net growth trend is determined from live root measurements, mortality and gross growth can be estimated using these relationships, provided certain regularity requirements are met. These requirements are explicated, such that the estimates can be easily assessed for reliability. To illustrate the use of the method, it was applied to the estimation of specific mortality rates in seven Scots pine stands of different ages and site types. A reanalysis of a previous sequential coring study yielded consistent results. The advantage of this method is that, unlike the standard analysis of sequential cores, it accounts for the possibility of simultaneous growth, mortality and decomposition. It is therefore applicable to situations with no apparent fluctuations or trend in the biomass and necromass levels. No minimum sampling interval is required; hence the method also allows for more extensive or prolonged studies.

Impacts of (NH4)2SO4 deposition on Norway spruce (Picea abies [L.] Karst) roots

The effects of enhanced (NH4)2SO4 (NS) deposition on Norway spruce (Picea abies [L.] Karst) fine root biomass, vitality and chemistry were investigated using root-free in-growth cores reproducing native organic and mineral soil horizons. The cores were covered and watered every 2 weeks with native throughfall or throughfall supplemented with NS to increase deposition by 75 kg ha-1 a-1 NH4+-N (86 kg ha-1 a-1 SO42--S). The in-growth cores were sampled after 19 months and assessed for root biomass, necromass, length, tip number, tip vitality and fine root chemistry. Root biomass and fine root aluminium (Al) concentration were negatively correlated, but NS deposition had no effect on root growth or root tip vitality. NS deposition caused increased fine root nitrogen (N) concentrations in the organic horizon and increased Calcium (Ca) concentrations in the mineral horizon. Fine root biomass was higher in the organic horizon, where fine root Al and potassium (K) concentrations were lower and Ca concentrations higher than in the mineral horizon. Results highlighted the importance of soil stratification on fine root growth and chemical composition.

The biology of mycorrhiza in the Ericaceae. XX. Plant and mycorrhizal necromass as nitrogenous substrates for the ericoid mycorrhizal fungus Hymenoscyphus ericae and its host

In the ‘F’ horizons of acid mor‐humus soils of heathland ecosystems, mycorrhizal roots of the dominant ericaceous species form a large fraction of the soil biomass. Rapid turnover of these roots provides the potential for recycling of substantial amounts of nitrogen contained in their fungal and plant components. Here, we first determine the amount of N in the biomass of ericoid roots growing in heathland and show it to constitute a large proportion of total soil N. In order to assess the accessibility of this N to ericaceous plants, experiments were then conducted using aseptically produced shoot and root necromass of Vaccinium macrocarpon Ait., the roots being grown with or without mycorrhizal colonization. These materials were provided as sole nitrogenous substrates in growth experiments using the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf &amp; Kernan in pure culture and V. macrocarpon in the mycorrhizal (M) or non‐mycorrhizal (NM) condition as test organisms. The experiments were designed to test the hypothesis that the N contained in these substrates can be mobilized by the mycorrhizal endophyte. The ability of the endophyte to utilize the substrates was determined by measuring fungal yields and by assessing the presence of its extra‐cellular protease and chitinase enzymes. Transfer of N to the host by the endophyte was determined through measurements of plant yield and tissue N contents. H. ericae produced a significantly greater yield on shoot and mycorrhizal root necromass than on non‐mycorrhizal root necromass. The extra‐cellular enzymes protease and chitinase were produced by the fungus when grown on the M root necromass. The fungus also transferred N to the host plant, up to 76% of N contained in the substrate being found in M plants whereas less than 5% was present in their NM counterparts.

Reaction of mycorrhizal and non-mycorrhizal Scots pine fine roots along a deposition gradient of air pollutants in eastern Germany

Based on an ecosystematic approach within the comprehensive SANA (Regeneration of the atmosphere above the new federal states) -project the influence of industrial air pollutants (SO2, NOx, alkaline fly ashes) on the vitality of mycorrhizae, mycorrhizal frequency, and on parameters of root growth such as root biomass and necromass and distribution of different root classes in the soil horizons was investigated. The studies were conducted in three comparable Scots pine ecosystems in eastern Germany which were exposed to different deposition loads of air pollutants during the time of the former German Democratic Republic. Site specific differences were obtained for all parameters investigated. The reference plot Neuglobsow (background deposition) revealed the highest number of vital mycorrhizae, highest mycorrhizal frequency, and largest biomass of finest roots in the humus layer. At the impact-sites Roesa and Taura (heavy and moderate deposition) located near Halle/Bitterfeld and Leipzig, the number of vital mycorrhizae was reduced and the life-span of mycorrhizae of reduced vitality was elongated. Finest root biomass and necromass of the humus layer were also lower at these plots as compared to Neuglobsow. At Neuglobsow a higher turnover of mycorrhizae and finest roots of the humus layer is assumed. The reduced growth of mycorrhizal and non-mycorrhizal finest roots at the two pollution impacted sites Roesa and Taura is seen as an adaptation mechanism of the root system to high nutrient inputs.