Aboveground Responses Research Articles

The Effects of Thinning on Fine Root Distribution and Litterfall in a Pinus koraiensis Plantation

The purpose of this study was to investigate the effects of thinning on fine root biomass and vertical distribution. and litterfall amount in a 50 year old Pinus koraiensis plantation in Chuncheon, Kangwon Province. Fine root (< 2 mm in diameter) biomass (<TEX>$367\;g/m^2$</TEX>) in the site 'OC_75', thinning once in 1975, was 68% of those in the site 'CON', no thinning after planting, and in the site 'TC_00', thinning twice in 1975 and 2000. There were no significant differences of dead roots among treatments. Diameter <TEX>$0{\sim}1\;mm$</TEX> roots were vertically decreased only in the TC_00 site. The litterfall was very similar between OC_75 (<TEX>$5.2\;Mg\;ha^{-1}\;yr^{-1}$</TEX>) and TC_00 (<TEX>$4.7\;Mg\;ha^{-1}\;yr^{-1}$</TEX>), but the composition of litterfall was different: The proportion of leaves and branches was 80% and 13% in OC_75 and 56% and 36% in TC_00, respectively. Reduction of P. koraiensis density by thinning decreased leaf litter as well as fine roots of P. koraiensis, but increased fine roots production by neighboring understory plants offset the reduction of fine roots of P. koraiensis. We suggest that belowground as well as aboveground responses, including both over- and understory vegetation, should be considered to measure the responses of trees in thinned forest ecosystems.

Biomass and morphology of fine roots in temperate broad-leaved forests differing in tree species diversity: is there evidence of below-ground overyielding?

Biodiversity effects on ecosystem functioning in forests have only recently attracted increasing attention. The vast majority of studies in forests have focused on above-ground responses to differences in tree species diversity, while systematic analyses of the effects of biodiversity on root systems are virtually non-existent. By investigating the fine root systems in 12 temperate deciduous forest stands in Central Europe, we tested the hypotheses that (1) stand fine root biomass increases with tree diversity, and (2) ‘below-ground overyielding’ of species-rich stands in terms of fine root biomass is the consequence of spatial niche segregation of the roots of different species. The selected stands represent a gradient in tree species diversity on similar bedrock from almost pure beech forests to medium-diverse forests built by beech, ash, and lime, and highly-diverse stands dominated by beech, ash, lime, maple, and hornbeam. We investigated fine root biomass and necromass at 24 profiles per stand and analyzed species differences in fine root morphology by microscopic analysis. Fine root biomass ranged from 440 to 480 g m−2 in the species-poor to species-rich stands, with 63–77% being concentrated in the upper 20 cm of the soil. In contradiction to our two hypotheses, the differences in tree species diversity affected neither stand fine root biomass nor vertical root distribution patterns. Fine root morphology showed marked distinctions between species, but these root morphological differences did not lead to significant differences in fine root surface area or root tip number on a stand area basis. Moreover, differences in species composition of the stands did not alter fine root morphology of the species. We conclude that ‘below-ground overyielding’ in terms of fine root biomass does not occur in the species-rich stands, which is most likely caused by the absence of significant spatial segregation of the root systems of these late-successional species.

Below and aboveground responses to lupines and litter mulch in a California grassland restored with native bunchgrasses

Goals of ecosystem restoration in California grasslands include the reestablishment of plant communities with a high proportion of native species, and simultaneously improve soil nutrient cycling. Addition of annual lupines and a litter mulch layer were hypothesized to be factors that would promote the growth of the native perennial bunchgrass, Nassella pulchra, in a restored California grassland. To test this hypothesis, field mesocosms were installed, each encircling a Nassella plant, at a perennial grassland restoration site in Carmel Valley, California. Two sets of treatments were imposed: (1) seeding of the annual N-fixing legume, Lupinus bicolor; and (2) exchanging the grassland litter for a thicker mulch layer of C 4 grass litter (C/N = 99). Stable isotope analysis allowed the tracking of fates of N fixed by the legume and the C 4-litter derived C. Treatments continued for 28 months, from December 2002 to April 2005, when most of the destructive measurements were taken. In 2005, neither treatment had significantly increased the biomass of the annuals or the perennial bunchgrass, and there was little effect on total soil C and N. Lupinus decreased the δ 15N content, but did not affect the biomass, N and P content of the litter, which was largely composed of annual plants from the previous year. Lupinus resulted in higher soil microbial biomass carbon (SMB-C), and distinct effects on soil microbial communities, especially soil fungi, as measured by phospholipid fatty acid analysis (PLFA) and ergosterol. The high C/N litter mulch tended to increase biomass of Nassella, despite its lower P concentration, and it reduced SMB-C, presumably due to lower decomposition rates compared to the ambient litter. Using a high C/N litter mulch thus is ambiguous for grassland restoration. Repeated increases of legumes over a longer time frame may potentially increase soil fertility and soil C pools in California grasslands, but this study suggests that native perennial grasses may be slow to benefit.

Differences in Belowground Heterogeneity Within a Restoration of a Dewatered Reservoir in Southwestern Wisconsin

Abstract Integrating belowground properties into ecological restoration is critical for understanding aboveground response. We investigated a recently dewatered basin in southwestern Wisconsin to test hypotheses related to the magnitude, heterogeneity, and spatial dependence of physicochemical properties between sediments and buried soils. A spatial grid was established in a 2.4‐ha basin to sample 7 physical and 13 chemical properties. Sediment depth (Sd) averaged 43 cm (std dev = 15) across the study area. The mean bulk density (BD) of the buried soils (1.41 g/cm3) was significantly greater than the sediments (0.97 g/cm3), which corresponded with a significantly higher soil moisture content (SMC) and hydraulic conductivity (Ks) of the sediments. Relative to one another, buried soils had significantly higher concentrations of Bray P, Cu, and Mn, whereas sediments had higher concentrations of Bray K, K, total phosphorus, Na, S, Al, and Ca and thus had a higher pH; Fe and B concentrations were similar between the sediments and the buried soil. Sediments were consistently less spatially heterogeneous than the buried soils. Using geostatistics, sediment BD and SMC displayed both small‐scale spatial structures and large‐scale trends, whereas Sd and the buried soil SMC displayed only small‐scale variability. Distance from the former dam was positively related to nine physicochemical properties and negatively related to only S, SMC, and the percentage of clay; no trends were found in the buried soils. These results demonstrate that damming, inundation, and dewatering due to dam removal yielded a spatially distinct and homogenized substrate relative to the soils that were buried.

Contrasting below- and aboveground responses of two deciduous trees to patchy nitrate availability

We investigated how patchy nitrate availability influences growth and functioning of plant roots and generates, through vascular constraints on long-distance transport, aboveground heterogeneity in plant growth and chemistry. We examined two broadleaf tree species, Acer rubrum L. and Betula papyrifera Marsh. Plants were grown either in a split-root setup where a single root received full nutrient supply and the rest of the root system received all nutrients except nitrogen (patchy treatment), or in a single pot with full nutrient supply (homogeneous treatment). In both species, fine roots proliferated in the nitrogen patch, but B. papyrifera produced twice as much fine root biomass in response to patchy nitrate availability as did A. rubrum. There was no difference between treatments in nitrogen uptake rate in either species. In general, specific water uptake was higher in A. rubrum than in B. papyrifera, especially in the nitrogen-rich side pot. When nitrate availability was patchy, nitrate reductase activity in roots and leaves was unaffected in either species. In A. rubrum, but not in B. papyrifera, patchy nitrate supply resulted in aboveground heterogeneity, with leaves above the N-fertilized roots being larger and having a higher relative chlorophyll concentration than those inserted in the opposite quater of the stem.

Light availability influences root carbohydrates, and potentially vigor, in white oak advance regeneration

Oaks ( Quercus spp.) are experiencing recurring regeneration failures associated with pervasive mid- and under-story strata of shade tolerant species in intact, undisturbed forests. Where oak regeneration occurs, inadequate vertical height and depleted root carbohydrate stores impede the ability of regenerating oaks to respond when light does become available. A variety of silvicultural techniques have been developed to increase the penetration of diffuse light, enhancing the light environment on the forest floor, and thereby increasing the likelihood of regenerating oaks to successfully respond to increased light transmittance. We measured shoot and root characteristics, and root soluble non-structural carbohydrate concentrations of white oak ( Q. alba L.) advance regeneration exposed to enhanced light intensities associated with a mid-story removal and a clearcut, and compared white oak regeneration vigor to untreated controls. Root diameter and soluble non-structural carbohydrates increased with increasing light availability. Our data suggest that white oak responds to increases in light transmittance by building below-ground biomass and carbohydrates in the root system prior to an above-ground response. Our study shows that white oak regeneration vigor increases with only modest increases in light. In the absence of other pressures, enhancing the light environment to the forest floor should contribute to successful regeneration of this species.

Aboveground Responses of Cool-Season Lawn Species to Nitrogen Rates and Application Timings

Lawns are the largest managed turf acreage in the USA. This large acreage of fertilized turf has generated public concern regarding nitrogen (N) fertilizer misuse. This 2-yr field study evaluated the effects of eight N programs that varied by N amount, 0 to 196 kg N ha−1 yr−1, and seasonal application timing on the aboveground plant responses of three cool-season lawn species: Kentucky bluegrass (Poa pratensis L.; KBG), perennial ryegrass (Lolium perenne L.; PRG), and turf-type tall fescue (Festuca arundinacea Schreb.; TTTF). Significant cumulative species dry matter yield differences were measured for the study, with 9426, 7750, and 7011 kg ha−1 for TTTF, KBG, and PRG, respectively. Kentucky bluegrass generally possessed the greenest canopy when averaged across all N programs, followed by TTTF and PRG. Annual turfgrass quality (TQ) was highest and most seasonally consistent for TTTF, followed by KBG and PRG. Although, KBG overall TQ was lower than TTTF, primarily due to slow spring green-up, KBG was superior to TTTF on many ratings during active growth. Perennial ryegrass produced the lowest TQ compared with TTTF and KBG. This was due to summer disease in both years and substantial turf cover losses, 24 to 81% in 2005. If the goal in lawn management is to maximize turfgrass response with the fewest N inputs, the species that met this goal was TTTF, which provided acceptable TQ and color, and had less disease at relatively low, 73 to 123 kg ha−1 yr−1, N levels.

Partial Root Drying Effects on Biomass Production in Brassica napus and the Significance of Root Responses

Partial root drying (PRD) has been shown to stimulate stomatal-closure response and improve water-use efficiency and thus biomass production and grain yield under water deficiency. While most studies focus on above-ground responses to PRD, we examined how root responses contributed to effects of partial root drying. In particular, in two experiments with oilseed rape (Brassica napus L.) we investigated whether roots were able to forage for patchily distributed water, and how this affected plant growth compared with uniform watering and alternate watering (in which different parts of the roots receive water alternately). The first pot experiment was carried out in the greenhouse and the second outside under a rain-shelter in which also the watering amount was varied. The results indicate that B. napus roots were able to forage for fixed water patches by selective root placement. In the first experiment with small plants, root foraging was equally effective as enhanced water-use efficiency under alternate watering. Both treatments resulted in about 10% higher shoot biomass compared with uniform watering. Alternate watering generally outperformed uniform watering in the second experiment, but the success depended on the time of harvest and the water supply level. Measurements indicated that only the alternate watering regime effectively reduced stomatal conductance, but lead to a higher shoot biomass only under more severe (50%) rather than under milder water deficiency (70% of a well watered control). Water deficiency strongly reduced leaf initiation rates and leaf sizes in B. napus, but for a given level of water supply the supply pattern (uniform control, fixed patchy or alternate watering) hardly influenced these growth parameters. Although also in the second experiment, the plants selectively placed their roots in the wet parts of the pot, root foraging was not as effective as in the first experiment. Possible reasons for these discrepancies are discussed as well as their implications for the application of PRD effects for crop growth.

Importance of soil moisture and its interaction with competition and clipping for two montane meadow grasses

Meadow classification studies have demonstrated the importance of water table fluctuation patterns in determining plant community composition in the western United States. However, a mechanism causing an overall increase in Poa pratensis ssp. pratensis populations and local declines in Deschampsia cespitosa populations in western montane meadows over the past century has not been defined. In order to better understand plant species interactions in these often highly grazed systems, we observed aboveground responses of Poa and Deschampsia to changes in species composition, soil moisture gradients, and clipping in the field. As well, we conducted a factorial greenhouse experiment, varying plant density, water availability, and clipping. While Poa is adapted to dry meadows and Deschampsia to wet meadows, their ranges overlap in wet conditions where soil moisture averages 50% in the early growing season. Deschampsia appears to be excluded from dry meadows where Poa is prevalent and soil moisture is closer to 30% water content in the early growing season. Our greenhouse experiment revealed that Deschampsia’s competitive ability decreases, while Poa’s increases, at soil moistures of 19%. However in more mesic conditions (50% soil moisture), each species aboveground biomass, tillering, and inflorescence weight was adherent to soil moisture conditions, and species interactions were less important. Our early growing season clipping treatments significantly reduced biomass of both grasses, but did not appear to favor one species over the other. This work points to the importance of soil water content in determining the performance of each plant species and the level of species interactions in montane meadows.

Aboveground growth responses of understory Abies lasiocarpa saplings to different release cuts

A white birch (Betula papyrifera Marsh.) overstory of a 30+ year old stand was thinned or completely removed, releasing an advance regeneration of subalpine fir (Abies lasiocarpa (Hook.) Nutt.). The overstory was clear-cut (T0), thinned to 600 (T600) or to 1200 (T1200) stems/ha, or left uncut (control). Three years after release, understory responses were best demonstrated by decreasing specific leaf area with increasing release level and by changes to height and radial growth increments. Clear-cutting the overstory stalled the height growth in fir for two seasons and radial growth at the tree base for one season. Compared with the control, the 3-year height increment was proportionally greatest in intermediate trees of T600, and this treatment produced the overall best response in height growth. Complete birch removal produced the best radial growth response despite the initial growth check. However, no release treatment significantly affected the whole tree variables (aboveground biomass, height, diameter at breast height (DBH), live crown ratio) within the studied time frame. Shoot silhouette ratios were lowest in the completely released understory trees, while they were similar to those of the controls in all partial-release treatments. Tree sturdiness (height/DBH ratio) was 80–90 in most treatments except T0, where it declined to below 80. Despite this improvement, large trees in T0 have been damaged by wind and snow.

The dose-response relationship between No. 2 fuel oil and the growth of the salt marsh grass, Spartina alterniflora

The effect of No. 2 fuel oil on the biomass production of the salt marsh plant, Spartina alterniflora, was studied in a greenhouse dose-response experiment. S. alterniflora were transplanted into soil with 10 dosage levels of No. 2 fuel oil ranging from 0 to 456 mg g −1 dry soil. Three months after transplantation, values for plant biomass, stem density, and shoot height decreased significantly with increasing fuel oil level in a dose-response fashion. Evapo-transpiration rates were correlated with the total biomass response. Relative to the control, a significant decrease in total (above- plus below-ground) plant biomass was observed at concentrations above 57 mg g −1 dry soil. Within the 3-month experimental period, detrimental effects on below-ground biomass accumulation and bioluminescence of the marine bacterium Viberio fisheri in the Microtox Solid Phase Test were observed at oil concentrations >29 mg g −1 dry soil, suggesting that biological effects of oil within the sediment matrix may be more pronounced than on above-ground biomass, requiring a dosage ⩾228 mg g −1 dry soil to elicit a significant detrimental effect. Hence, measurements of oil effects with biological end-points based solely on above-ground responses may underestimate the potential impacts of petroleum hydrocarbon spills, especially when the oil has penetrated the soil. While S. alterniflora was proved to be relatively tolerant to the No. 2 fuel oil spills, its effectiveness in phytoremediation operations may be limited at fuel oil levels 228 mg g −1 dry soil, as both plant growth and microbial activity may be constrained.

Effects of grazing intensity on growth, reproduction, and abundance of three palatable forbs in Kansas tallgrass prairie

The effects of different intensities of cattle grazing on theaboveground growth, reproduction, and abundances of three palatable forbs werestudied in native tallgrass prairie. Populations of Asterericoides, Ruellia humilis, andAmorpha canescens were sampled at peak flowering duringthe1993–1995 growing seasons in four annually-burned sites varying incattle stocking density [ungrazed, low, moderate, high]. The threeforbs exhibited reduced shoot growth and/or reproduction under moderate toheavy grazing, and in no case did grazing increase any measure of plantperformance. Ruellia showed reduced shoot height andbiomass, percentage of stems flowering, and reproductive biomass in response tograzing. Aster showed decreases in shoot biomass andheightwith grazing. Amorpha showed no change in shoot orreproductive biomass, but a decrease in percent of flowering stems and inreproductive allocation with grazing. Patterns in the percentage of stemsgrazedindicated generally high but variable palatability among these species. Bycontrast, the three species showed inconsistent population response to grazing.Abundance (frequency) of all three species indicated no short-term changebetween years in response to grazing intensity. Responses of these speciesdiffer considerably from those of most other perennial tallgrass prairie forbsthat are unpalatable, unconsumed, and increase in performance (e.g. size,abundance) due to release from competition from the dominant grasses underungulate grazing. The results demonstrate that immediate aboveground growth andreproductive responses of established adults to grazing are not good predictorsof grazer effects on population abundances in tallgrass prairie.

Restoring riparian meadows currently dominated by Artemisa using alternative state concepts – above-ground vegetation response

Livestock overgrazing and stream incision in the western USA often result in encroachment and dominance of Artemisia tridentata ssp. tridentata (Big sagebrush) in ripar- ian areas that formerly supported meadows. To define the alternative states and thresholds for these ecosystems, we conducted a restoration experiment that included sites with high, intermediate or low water tables. We used a paired-plot approach in which one plot on each site was burned and seeded with native grasses and forbs typical of naturally occurring dry meadow and Artemisia/Leymus cinereus ecological types, while adjacent unburned plots served as controls. Sites with high and intermediate water tables had greater initial abun- dances of perennial grasses typical of dry meadows, such as Leymus triticoides and Poa secunda ssp. juncifolia, and these species increased after the burn. In contrast, sites with low water tables were dominated by annual forbs such as Chenopo- dium album and Descurainia pinnata after the burn. Biomass increased progressively from 1997 to 1999 on burned plots, while controls showed little change. Burning effects were microsite specific, with former Artemisia microsites exhibit- ing lower biomass than interspaces initially, but similar or higher biomass by the third year. Establishment of seeded species was low and species composition was determined largely by pre-burn vegetation. Artemisia dominated sites with high water tables appear to represent an alternative state of the dry meadow ecological type, while sites with low water table sites have crossed an abiotic threshold governed by water tables and represent a new ecological type. Burning is an effective tool for restoring relatively high water table sites, but low water table sites will require burning and seeding with species adapted to more xeric conditions.

Weed Aboveground and Seedbank Community Responses to Agricultural Management Systems

Weed Aboveground and Seedbank Community Responses to Agricultural Management Systems

Photosynthesis and biomass under elevated CO2 in a semi-natural grassland - a six-years' field study

In a six years' field study (1995-2000) we have studied the effects of elevated CO2 on photosynthesis, above- and below-ground production and root dynamics in a species-rich semi-natural grassland with a long history of grazing in Central Sweden (59° 48'N, 17° 38'E, 10 m a.s.l.). We used open-top chambers with ambient (A, ca 350 µmol/mol) and elevated (E, ca 700 µmol/mol) CO2 treatments, and a control treatment consisting of rings without mounted chambers. Elevated CO2 was supplied to treatment E continuously during the field season (April-October/November). During each field season, elevated CO2 stimulated light-saturated leaf-level photosynthesis of Taraxacum vulgare and Plantago media. Although photosynthesis showed a significant decrease during each growing season, the CO2 effect (treatment E/A) was rather constant. We found no trend in photosynthesis or the effect of CO2 hereon over the years, but during the dry and extremely dry summers of 1996 and 1999, respectively, the CO2 effect on leaf-level photosynthesis was significantly larger than during rainy summers. Elevated CO2 stimulated above-ground production (standing crop in early August) in 1995-1997, but not in 1998-2000. Root production (measured with minirhizotrons and ingrowth-bags) was stimulated during each growing season. The lack of above-ground production response during the latter years may be explained by unusual weather circumstances (1998 and 2000 being extremely wet and overcast with only few sunny days, and 1999 being extremely dry). However, increasing nutrient limitation might also be involved.

Evaluating the Progress of Restored Cordgrass (Spartina foliosa) Marshes: Belowground Biomass and Tissue Nitrogen

We report the first data on belowground tissue mass and nitrogen (N) concentration forSpartina foliosa in southern California, assessing one natural and two constructed marshes on San Diego Bay. Biomass at the natural marsh was low compared to that of otherSpartina spp., but higher than values reported forS. foliosa in northern California. In sandy constructed marshes planted 5 and 10 years before this study,S. foliosa had lower belowground tissue N, lower N crop (%N×biomass), and shallower roots than in the adjacent natural marsh. We took advantage of a 2-yr, large-scale fertilization project being performed in the older constructed marsh and examined biomass and N storage after N additions. Although there was a trend toward N accumulation with fertilization, N crop remained at approximately 50% of natural marsh levels, unlike the large aboveground responses to N addition in our previous studies. Lower belowground reserves help to explain poor aerial growth in the created marshes and suggest the need for finer sediments (with greater potential for holding and supplying nutrients) to sustain (S. foliosa. While fine sediments are beginning to accumulate on the surface of the created marshes, vertical accretion is more likely to shift the plant community toward other species than to enhanceS. foliosa growth. We suggest salvaging and importing fine, organic marsh sediments or providing organic amendments to establish proper substrate conditions. Overexcavating and allowing fine sediments to accumulate remains an option, although the time scale is unpredictable due to the stochasticity of accretion events.

Aboveground modular component responses to intraspecific competition within density-stressed black spruce stands

A broad range of measures of aboveground growth were used to assess whether competition occurs by processes of resource depletion or resource preemption within monospecific, even-aged, density-stressed, and spatially heterogeneous black spruce (Picea mariana (Mill.) BSP) stands. The assessments proceeded by evaluating the relationships between relative growth and partitioning indices of individual subject trees and directional-specific indices of cumulative competition. Significant directional-specific asymmetrical relationships between subject trees and their local competitors were found, indicating the occurrence of competition by resource preemption. All measures of growth, however, did not respond to directional-specific competition to the same degree. Larger responses, characterizing the response of black spruce trees to increasing competition from their larger neighbours, involved decreased branch production and changes in foliar morphology. Such adaptive, plastic responses in phenotype, combined with lesser responses of foliage production and nutrient concentrations, suggest a strategy used by black spruce to compete within density-stressed populations situated on nutrient-limiting sites: decreased allocation of resources to nonphotosynthetic components, maintenance of the photosynthetic apparatus through adjustments in foliage morphology, and nutrient conservation through foliage retention.

Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti.

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root∶shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.

Ectomycorrhizal fungi in the NITREX site at Gårdsjön, Sweden; below and above-ground responses to experimentally-changed nitrogen inputs 1990–1995

Changes in the ectomycorrhizal fungus flora were studied in connection with nitrogen addition and removal experiments in a Norway spruce forest at Gårdsjön, W Sweden during a 5-year period. The above-ground ectomycorrhizal fruit body production was recorded from permanent transect plots, and the below-ground mycorrhizal fine-roots density and morphotype differentiation were studied from soil core samples from the surface root layer. The experiments were performed by adding N-enriched and N-free water, respectively, by means of sprinkling systems. Ammonium nitrate (about 35 kg N ha −1 yr −1) was added to catchment G2 NITREX, whereas at adjacent catchment G1 ROOF ambient N deposition was removed by means of a roof. The addition of N led to a rapid and substantial decrease in species diversity and fruit body production of most species in the NITREX catchment, representing one of very few biological responses to the treatments at Gårdsjön. Stress-intolerant groups such as the initially-dominant genus Cortinarius were almost absent after 5 yr of N addition. Only one dominant species ( Cantharellus tubaeformis) increased fruit body production after treatment. In the nitrogen removal (G1 ROOF) experiment, the fruit body production increased strongly the first years, but then declined. No response in the below-ground mycorrhiza and fine-root density and diversity was found. All fine roots had developed ectomycorrhiza. The difference in response above ground and below ground indicates that: (1) the fruit-body producing macrofungi play a minor role below ground, and that (2) there is probably a considerable time-lag in the mycorrhizal fine-root versus fruit body production response to enhanced N levels.

Aboveground modular component responses to intraspecific competition within density-stressed black spruce stands

Aboveground modular component responses to intraspecific competition within density-stressed black spruce stands