A Dendrochemical Survey of Sugar Maple (Acer saccharum Marsh) in South-Central Ontario,Canada

A dendrochemical survey of sugar maple (Acer saccharum Marsh) was conducted insouth-central Ontario, which encompassed twenty-two sites in areas that both exceeded orwere below the published Critical Loads with respect to acid deposition. Areas thatexceeded the Critical Load were located remote from point emission sources, but were alsocharacterized by thin, nutrient-poor soils overlying the Precambrian Shield. ThepH_aq of surface soils (A-horizon) was lower at sites on the Precambrian Shield andwater-extractable concentrations of Ca decreased exponentially with decreasing soil pH. Significant polynomial relationships between soil pH and soil Ca and sugar maple growth,assessed as cumulative tree-ring growth between 1949 and 1998, explained 40% and 37% ofthe variation in sugar maple growth respectively, with lowest growth associated with lowsoil pH and low soil Ca. Furthermore, there was a significant linearrelationship between wood Ca concentrations (averaged between 1949 and 1998) and soil pHand concentrations of several trace elements in wood (Mn, Pb, Zn, Cd, Sr and Rb) were greater atlow soil pH. Poor sugar maple growth was associated with low wood Ca concentrations andhigh wood Al levels, which together accounted for 43% of the variation in sugar maplegrowth in a multiple regression model. None of the other wood chemistry variablescontributed significantly to the model. These data suggest that sugar maple grows poorlyon acidic soils with low Ca and high Al levels. Although such acidic podzols occurnaturally in some areas overlying the Precambrian Shield, if Ca losses due to aciddeposition and/or harvesting exceed inputs through weathering and deposition(i.e. exceed Critical Load), sugar maple growth may be adversely affected and ultimately lead toincreased incidence of sugar maple decline.     

Aluminum toxicity in forests exposed to acidic deposition: The ALBIOS results

The ALBIOS project was conducted to examine the influence of acidic deposition on aluminum transport and toxicity in forested ecosystems of eastern North America and northern Europe. Patterns of aluminum chemistry were evaluated in 14 representative watersheds exposed to different levels of sulfur deposition. Controlled studies with solution and soil culture methods were used to test interspecific differences in aluminum sensitivity for one indicator species (honeylocust - Gleditsia triacanthos L. ) and six commercial tree species (red spruce - Picea rubens Sarg., red oak - Quercus rubra L., sugar maple - Acer saccharum Marsh., American beech - Fagus grandifolia Ehrh., European beech - Fagus sylvatica, and loblolly pine - Pinus Taeda L. ). Overall, red spruce was the tree species whose growth was most sensitive to soluble aluminum, with significant biomass reductions occurring at Al concentrations of approximately 200–250 umol/L. Analyses of soil solutions from the field sites indicated that the conditions for aluminum toxicity for some species exist at some of the study areas. At these watersheds, aluminum toxicity could act as a contributing stress factor affecting forest growth.     

An Assessment of the Ca:Al Ratios of Selected Pennsylvania Forest Soils

The Ca:Al status of selected Pennsylvania forest soils was assessed based on data compiled from various soil chemistry evaluations done between 1991–94. A total of 116 horizons (76 mineral, 40 organic) from 39 different soil profiles representing 18 different soil series were evaluated. Ca and Al were determined by extraction with 0.01M SrCl₂. Non-linear regression analysis (logarithmic curve) showed a significant (p < 0.01) negative relationship between extractable Ca and Al across all horizons (R² = 0.64). An acid soil infertility and aluminum stress risk assessment was conducted using the method suggested by Cronan and Grigal (1995). None of the soil organic horizons were found to be at risk; however, nearly 42% of the AE/E horizons were classified at a 50% or greater risk of producing aluminum stress to trees. The B horizons had the highest risk levels, with 91.2% classified at a 50% or greater risk level. The Ca:Al ratios of most of the mineral soil horizons included in this evaluation were low enough to present considerable risk of aluminum stress to trees growing on the sites from which these soils were collected. The application of Ca:Al ratio as a diagnostic tool in declining and nondeclining sugar maple stands in northcentral Pennsylvania generally produced consistent results for soil and roots but not for organic soil horizons and foliage of declining sugar maples.     

Soil microbial biomass and nitrogen transformations among five tree species of the Catskill Mountains, New York, USA

We measured soil microbial biomass nitrogen (MBN), microbial uptake of ¹⁵N, potential net mineralization and net nitrification in the laboratory to determine the influence of tree species on nitrogen (N) transformations in soils of the Catskills Mountains, New York, USA. Organic horizon soils were taken from single species plots of beech (Fagus grandifolia), hemlock (Tsuga canadensis), red oak (Quercus rubra), sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis). ¹⁵NH₄Cl was added to the soils and N pools were sampled at 1, 3, 10 and 28 days to examine microbial uptake of ¹⁵N over time. Soil MBN was about 60% lower in red oak and sugar maple soils than in the other three species. Soil pools of NO₃⁻ and rates of net nitrification were significantly greater in soils associated with sugar maple than hemlock, red oak and yellow birch. With the exception of sugar maple soils, microbial recovery of ¹⁵N was significantly greater after 10 and 28 days compared to 60 min and 1 day following ¹⁵N tracer addition. Microbial ¹⁵N recovery declined significantly within sugar maple stands within the first 3 days of incubation. Soil carbon to nitrogen ratio (C:N) was lowest in sugar maple soils and highest in red oak soils. However, correlations between soil C:N and MBN or rates of net mineralization and nitrification were not significant. Soil moisture could account for 22% of the variation in MBN and 36% of the variation in net mineralization. Soil microbial transformations of N vary among tree species stands and may have consequences for forest N retention and loss.     

Remnant sugar maple (Acer saccharum subsp. skutchii) populations at their range edge: Characteristics,environmental constraints and conservation implications in tropical America

Relationships between environmental conditions and persistence of populations at edges of ranges should be useful for predicting consequences of climate change. We characterized environmental conditions of six disjunct sites in Mexico and Guatemala that contain all known relict populations of the most southern subspecies of sugar maple, cloud forest sugar maple (Acer saccharum subsp. skutchii). We also sampled abundance and basal area of all tree species, recording 164 species, 92 genera (61% tropical), and 54 families at these sites. Temperate genera decreased in number from north to south, but mixtures of temperate and tropical species were co-dominant with cloud forest sugar maple at all sites. For all species, basal area was 24–52 m² ha^?1 and density was 990–2986 trees/ha at the six sites. Cloud forest sugar maple comprised 7–43% of total basal area and 1–16% of total densities at each site. Populations of cloud forest sugar maple currently are vulnerable to environmental change. Anthropogenic disturbance is negatively affecting four populations, and regeneration is successfully occurring in only two sites. As a result, densities and basal area are much reduced compared to more northern temperate populations. NMS-ordination indicated that elevation and hurricane frequency are major environmental constraints related to abundance. Maple recruitment is associated with short hurricane return intervals that maintain higher elevation cloud forests in states conducive for regeneration. We establish the conservation status of cloud forest sugar maple at the southern end of its range relative to expected climate change and propose this subspecies be included in the IUCN-Red List.     

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Abstract

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.     

Effects of experimental acidification and alkalinization on soil and growth and health of Acer saccharum Marsh.

Experimental application of eight acidifying, neutral, or alkalizer compounds (range: –16 to 16 kmol ha^–1 of acid‐neutralizing capacity [ANC]) was realized in two northern hardwood stands having significantly different soil base saturation (BS) (a “poor” and a “rich” site) to assess responses of soil physico‐chemical properties, and nutrition, growth, and health of sugar maple (Acer saccharum Marsh.) trees in the short (3 y) and longer term (10 y). The treatments influenced the main indicators of acidity in the forest floor (soil exchangeable‐Ca saturation [S_Ca], BS, exchangeable‐acidity saturation [S_H+Al], and the S_Ca/S_H+Al ratio) at both sites, their values increasing (decreasing for S_H+Al) along the ANC treatment gradient in both the short and longer term, except for pH. Base saturation of the upper 15 cm of the mineral B horizons of soils was influenced at the two sites 10 y after treatment application. Although ANC treatments affected nutrient concentrations of tree foliage in the short term, their effect was no longer detectable after 10 y at the two sites. Growth, however, was strongly related to ANC treatments after 10 y, but only at the poor site. From 1990 to 2000, the basal‐area growth rate of trees at the poor site was (mean ± SE) –0.62 ± 0.28 cm² y^–2 tree^–1 for the most negative ANC treatment to +0.90 ± 0.20 cm² y^–2 tree^–1 for the most positive ANC treatment. A climatic‐stress episode occurring in 1995/96 appeared to accentuate the growth decline of trees subjected to the most negative ANC treatment at the poor site. The experimental results support the hypothesis that atmospheric acid deposition load can cause forest soil base‐cation depletion, acidification, and predispose sugar maple to health and growth decline in the longer term in base‐cation‐poor soils, and that the phenomenon may be reversible by adding alkalizers.     

Activities and results of the terrestrial effects program: Acid precipitation in ontario study (APIOS)

Studies on the terrestrial effects of acidic precipitation in Ontario involve determining the effects on .soils, crops, forests, lichens, mosses and biogeochemical systems. In the soils program, a baseline study was started in 1980 to establish a reliable and uniform data base for soils across the province, in order to identify future trends. Soil sensitivity criteria are being derived for mapping purposes. Starting in 1982, a complex, sophisticated mobile rain exclusion canopy system was constructed outdoors for controlled acid rain studies to determine the dose-response relationships of field crops. In response to numerous complaints a program was designed to determine the role that acidic precipitation is playing in the decline of sugar maple trees in Ontario. At 8 sites, tree conditions were noted, samples of foliage, bark, roots and soil were collected for chemical analysis, and increment cores and discs (from felled trees) were taken for radial growth patterns. Results from this study indicated that acidic precipitation was an additional stress to insect outbreaks and spring droughts. Intensive surveys have been conducted in selected areas in Ontario to identify the current viability and distribution of common denominator lichens and mosses. Biogeochemical studies are being conducted at four watersheds in Ontario. The different watersheds are located in progessively decreasing atmospheric deposition loadings from east to west across the province. The studies are attempting to document the role of contrasting terrestrial ecosystems in the process of lake acidification by atmospheric deposition.     

The Impact of Simulated Acid Rain and Fertilizer Application on a Mature Sugar Maple (Acer Saccharum Marsh.) Forstt in Central Ontario Canada

The effects of two year's addition of simulated acid precipitation, with and without added fertilizer, on mycorrhizae, litter decomposition and soil and tree chemistry in a sugar maple (Acer saccharum Marsh.) dominated forest were investigated. The forest floor beneath mature sugar maple trees was irrigated at monthly intervals between May and September with local lake water acidified to pH 3, pH 4 or untreated lakewater of pH 4.9. In addition, a commercial organic slow-release fertilizer (Maple Gro) was added to the soil prior to irrigation with pH 3 spray. Trees to which no experimental spray was applied were also included as controls. Eight trees were used for each of the five treatments. Application of the acid spray alone did not acidify surface soil nor cause visible symptoms of decline in trees. The pH of the soil solution and soil leachate was increased by addition of acidified lakewater. An increase in the concentration of sulphate (SO₄ ^2-), calcium (Ca), and magnesium (Mg) in soil leachate was only recorded in plots irrigated with water acidified to pH 3 + Maple Gro. The initial rate of litter decomposition tended to be higher following application of the acid sprays, although mycorrhizal infection of sugar maple roots was reduced in the pH 3 and pH 4 treatments. Concentrations of zinc (Zn), chromium (Cr) and nickel (Ni) were highest in wood formed during the period irrigated with water acidified to pH 3. Foliar nitrogen (N) concentrations tended to be higher in all irrigated treatments, although there were no differences between treatment in any of the other nutrients measured in foliage after two years of treatment. It is concluded that the application of simulated acid rain under field conditions results in a complex interaction of events which are not reproduced in pot trials and must be fully understood before the impact of acid rain on sugar maple forests can be evaluated.     

Nutrient relations and root mycorrhizal status of healthy and declining beech (Fagus sylvatica L.) in Southern Britain

Many studies have been carried out to investigate the wide scale problem of forest decline that is affecting vast numbers of trees throughout Europe and North American. Evidence of nutritional disturbances, both above- and below-ground, has been found for a variety of species. Furthermore, it has been suggested that differences in above-ground tree health are often reflected below ground, particularly in the root systems of declining trees. An investigation of root vitality, soil and leaf chemistry of healthy and unhealthy beech (Fagus sylvatica L.) was carried out at a number of sites in southern Britain, covering a range of different soil types. At each site, healthy and unhealthy trees growing in very close proximity were compared in order to avoid large scale environmental differences that might be expected when comparing stands of trees at different locations. Healthy trees were found to have significantly greater proportions of live mycorrhizal roots than their unhealthy neighbours at most of the sites investigated. In addition, significant differences in soil chemistry were found between trees in contrasting health, with healthy trees generally growing in soil containing higher concentrations of calcium, magnesium and potassium and lower aluminium/calcium ratios. Very few differences were found in leaf nutrient content, suggesting that soil chemistry is not yet limiting nutrient uptake. The importance of root system differences in the tolerance of unfavourable edaphic and climatic conditions is discussed with respect to tree health.     

Uptake of fluoride and aluminum by plants grown in contaminated soils

Soils collected from areas at different distances from an aluminum smelter were studied to determine the soluble and labile F and soluble Al contents and availabilities to selected plants. Red maple seedlings (Acer rubrum L.) and orchard grass (Dactylis glomerata L.) were grown in pots containing the soils and after 3 mo foliar tissues were sampled and analyzed for the two elements. The soluble and labile contents of soil F as predictors of foliar F were compared. Significant decreases in soluble and labile F and soluble Al in soils were found with increasing distance from the smelter. As F levels in the soils increased, the F in the foliage of both orchard grass and maple increased. As Al in the soil increased, Al in maple foliage increased. Overall, F concentrations in plant foliage were below those considered as background. The results imply that, at least in the soils studied, the soil F content is not an important source of F to plants and therefore to herbivores in the area. Labile F values in the soils were significantly greater than soluble F at all sites, but, contrary to previous studies, soluble F was a better predictor of foliar F than was labile F.     

Effects of forest vegetation on spatial variability of surface mineral soil pH,soluble aluminum and carbon

The purpose of this study was to examine spatial variability in forest soils at several levels including variability due to soil structure, to the presence of individual trees and to populations of different species of trees. Both classic statistical and geostatistical methods were used. Soil chemical properties measured include pH and Al and C in solution which was in equilibrium with the surface mineral soil. Results indicated that soil cores 1.8 cm in diameter were as effective as larger cores in incorporating variability in surface mineral soil pH. There was no spatial correlation in soil pH in samples separated by a distance of 20 to 360 cm. The presence of individual Norway spruce and red pine trees affected soil in their vicinity. Soil pH was depressed and soluble Al elevated. in soil near the base of the tree compared to soil 120 cm from the tree, independent of direction. In addition, in soil sampled at least 100 cm from the base of trees, pH was lower in Norway spruce compared to sugar maple plantations and soluble C was greater in red pine compared to Norway spruce plantations. It is concluded that in less than 50 yr the presence of individual trees and populations of different tree species can affect chemical properties of surface mineral soils. These effects should be considered in the design and interpretation of experiments.     

Growth trends and nutritional status of sugar maple stands on the appalachian plateau of Pennsylvania,U.S.A.

Growth of sugar maple trees and element concentrations of soil and foliage were investigated at 12 stands in north-central Pennsylvania and southern New York. The goal of this exploratory study was to evaluate growth trends since the 1950s and to determine whether element concentrations were within limits conducive for normal growth. Basal area growth of overstory maple trees increased at six sites, declined at five, and remained nearly constant at one. Overall, the growth of overstory sugar maple trees did not change appreciably since the late 1950s, but growth of subcanopy maples decreased markedly, probably because of intensified shading in these maturing stands. Concentrations of Al, Cu, Fe, K, Mg, N, P, and Zn in soil and maple foliage were within the range of values reported for other sugar maple stands in North America. Calcium concentrations appeared adequate for growth, although at some sites they were near the low end of the typical range. Basal area growth of the overstory maples was correlated to the concentrations of Ca, Al, and the Ca∶Al ratio of soil, whereas growth of the subcanopy maples was not. Growth of the overstory trees was also correlated to the Ca concentration of maple foliage, which in turn was correlated to pH, Ca, Al, and the Ca∶Al ratio of soil. Manganese concentrations in soil and foliage were comparatively high, but were not correlated to trends in growth. The results of this investigation do not indicate abnormal changes in growth of sugar maple since the late 1950s. They suggest, however, that Ca availability limits growth at some sites and indicate that Al concentrations in the soil may be inhibiting Ca uptake.     

Ecological-genetic investigations in environmentally stressed mature sugar maple (Acer saccharum marsh.) populations

In six mature, environmentally stressed sugar maple (Acer saccharum) populations totalling 350 trees, genetic structures were studied within stands. Genetic variation was electrophoretically analyzed for 12 enzyme systems. The populations revealed Hardy-Weinberg proportions for all 11 polymorphic loci. Observed and conditional heterozygosity were. 141 and 899, respectively. Analysis of fixation indices indicated a slight heterozygote deficiency compared to panmictic conditions. Population differentiation was weak (F _ST =.017). Between healthy and declining subpopulations no significant differences were detected in terms of allozyme variation. However in healthy trees, conditional heterozygosity (H _c) and relative genotypic multiplicity (M _rel) were higher in five out of six populations.     

Effects of edaphic factors on the tree stand diversity in a tropical forest of Sierra Madre del Sur, Mexico

Two sites with similar environmental parameters, except for the edaphic factor, were selected in the mountainous tropical forest of southern Mexico. Site 1 was established on an Alisol; site 2, on a Phaeozem. Representative soil profiles were examined on each of the sites, and topsoil was sampled on a regular grid pattern. The soil of site 2 was richer in organic matter and major nutrients and had a less acid reaction than the soil of site 1. The species diversity of the trees at site 2 (30 species) was higher than that at site 1 (17 species). The species compositions of the trees were different on the two soils: there were only six species in common for both sites. The coefficients of species similarity on the sites were low. We concluded that the presence of different soils within the same type of forest ecosystem increases its ??-diversity. The examination of edaphic preferences of the species showed that Alstonia longifolia and Thouinidium decandrum preferred rich soils, Inga punctata and Ocotea sinuata preferred poor soils, and Cupania dentata and Hamelia patens did not display preferences in the studied range of soil properties. Thus, the spatial variability of the soil properties affect the spatial pattern of tree species in the studied tropical forest ecosystems.     

Pedologic and geomorphic impacts of a tornado blowdown event in a mixed pine-hardwood forest

Biomechanical effects of trees on soils and surface processes may be extensive in forest environments. Two blowdown sites caused by a November 2005 tornado in the Ouachita National Forest, Arkansas allowed a case study examination of bioturbation associated with a specific forest blowdown event, as well as detailed examination of relationships between tree root systems, soils, and underlying bedrock. The sites occur within mixed shortleaf pine and hardwood forests. More than 95% of trees in the severe blowdown areas were either uprooted or suffered trunk break, with uprooting more common than breakage. Within the most heavily damaged areas all uprooted trees were pines, while all trees left standing were hardwoods. Root wads of uprooted trees had a mean surface area of about 3 m² and volume of about 2 m³, though individual sizes were quite variable. Nearly 4% of the ground surface area was affected by uprootings, with a soil volume equivalent to a disturbance of the entire surface area to a depth of 2.4 cm. Tree size (as measured by diameter at breast height) was significantly related to the area and volume of root wads (R² = 0.55, 0.71, respectively), with volume of uprooted soil varying as diameter to the ~ 3 power, suggesting that the timing of blowdown events relative to tree age or growth stage significantly influences the area of disturbance and the mass and volume of material involved. In 93% of cases the roots of the uprooted trees contacted or penetrated the underlying bedrock, and in all those cases bedrock was quarried by uprooting. Only 11% of the tree throws showed evidence of general lateral root turning at the soil–bedrock interface; in most cases roots penetrated bedrock along joints. The propensity for tree roots to penetrate bedrock joints, facilitate weathering, and excavate bedrock during uprooting supports the idea that tree roots play a predominant role in locally deepening soils.     

Spatial variation of soil enzyme activities and microbial functional diversity in temperate alley cropping systems

Spatially dependent patterns in microbial properties may exist in temperate alley cropping systems due to differences in litter quality and microclimate in areas under trees compared to those in the alleys. The effect of tree row location was evaluated for its impact on soil enzyme activities and Biolog substrate use patterns. Soils were sampled to a depth of 30 cm at the tree row and at the middle of the alley at two sites: a 21-year-old pecan (Carya illinoinensis)/bluegrass (Poa trivials) intercrop (Pecan site) and a 12-year-old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site). Sampling was done in fall 2001 and summer 2002. β-Glucosidase activities, Biolog patterns expressed as average well color (AWC), substrate richness, and Shannon diversity index, and total Kjeldahl nitrogen (TKN) were significantly higher (P<0.05) in the tree row than at the middle of the alley for surface soils at the Pecan site. Fluorescein diacetate (FDA) hydrolytic activity was also higher at the tree row for soils sampled in the fall, but did not differ significantly for soils sampled in the summer. At the Maple site, AWC and substrate richness were significantly higher at the tree row for soils sampled in 2001. Soil volumetric water content and temperature were generally lower in the tree row at the Maple site. The results of this study suggest that functionally different microbial populations may be present under pecan trees compared to cropped alleys which may promote disparities in nutrient availability necessitating differential long-term nutrient management in such alley cropping systems.     

Evaluation of black spruce (Picea mariana) as a bioindicator of aluminum contamination

The aim of this work is to evaluate black spruce (Picea mariana) as an indicator of environmental aluminum contamination. The territory studied extends to a radius of 100 km around the Alcan aluminum refinery in Jonquiere, Quebec, Canada. Samples of wood were taken from the trunks of trees at 26 sites at distances of 5, 10, 20, 30, 40, 50 and 100 km from the refinery. Five trees were sampled at each site. Each sample was cut into 25 pieces corresponding to 50 yr growth. These were analyzed for aluminum by neutron activation. Soil samples taken near the bases of the trees were also analyzed and significant variations in exchangeable aluminum were observed as a function of direction from the refinery and distance. The pH of organic and mineral horizons show no significant difference. Exchangeable aluminum increased with soil acidity. The most contaminated sites showed important correlations (r²=0.73) between exchangeable aluminum in soil and aluminum in bark. We observed greater aluminum concentrations in tree rings corresponding to the last 20 yr, especially at sites directly exposed to environmental contamination along prevailing winds. In conclusion, black spruce appears to be a better spatial than chronological indicator of aluminum contamination.     

Soil properties and tree growth at medieval ridge and furrow sites in Brandenburg,northeastern Germany

Background

Ridge and furrow (RIFU) systems and associated soils are a widespread legacy of medieval agriculture, are archives of historical land use, and might affect recent ecosystems. Open questions about RIFU formation and potential legacy effects still exist, especially related to physical soil properties.

Aims

Our aims were (1) to characterize the soil properties of RIFU soils and (2) to compare the drought sensitivity and the growth resistance in extremely dry years of trees growing on ridges and furrows, respectively.

Methods

We studied soil physical (bulk density, saturated soil hydraulic conductivity, and texture) and chemical (soil pH, soil organic matter, and nitrogen content) properties and the climate sensitivity of tree growth on RIFU systems for three study sites in Prignitz, Germany.

Results

RIFU systems showed a high spatial heterogeneity of soil stratigraphy due to ridge construction and increased accumulation of soil moisture and organic matter in furrows due to post-abandonment pedogenesis. Slight spatial differences in soil physical properties were found, with increased air capacity in ridge soils and higher available water contents in furrow soils. No differences in drought sensitivity were observed for trees growing on ridges and furrows, except for a wet site, where trees in furrows showed a higher sensitivity. Resistance in dry years tended to be similar or increase from furrows to ridges.

Conclusions

The results reflect a spatial differentiation of stratigraphy and post-abandonment pedogenesis on abandoned RIFU systems and suggest an adaption to different moisture conditions through RIFU construction. Differences in drought sensitivity of tree growth with relative land surface could only be detected for one of the three sites, where trees were found to be less drought sensitive on ridges.     

Litter quality effects on soil carbon and nitrogen dynamics in temperate alley cropping systems

Microcosm and litterbag experiments were conducted to determine the effects of litter quality, soil properties and microclimate differences on soil carbon (C) and nitrogen (N) mineralization in alley cropping systems. Bulk soils were collected from 0 to 20 cm depth at three sites: a 21-year old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (Pecan site) in north-central Missouri, a 12-year old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site) in northeastern Missouri and a restored prairie site (MDC site) in southwestern Missouri. Seven tree and crop litters with varying composition were collected, including pecan, silver maple, chestnut and walnut leaf litter (tree litter) and maize, soybean and bluegrass residues (crop litter). Aerobic microcosm incubations were maintained at 25 °C and a soil water potential of −47 kPa. Unamended MDC soil mineralized 24 and 18% more CO₂ than the Pecan and Maple soils, respectively. Soil amended with crop litter mineralized on average 32% more CO₂ than when amended with tree litter. Net N mineralization from soybean litter was 40 mg kg⁻¹, while all other litter immobilized N for various durations. A double pool and a single pool model best described C and N mineralization from amended soils, respectively. Cumulative CO₂ mineralized, labile C fraction (C₁) and potentially mineralizable C (C₀) were correlated to litter total N and lignin contents and to (lignin + polyphenol):N ratio. In the field, bluegrass litter decomposed and released N twice as fast as pecan leaf litter. Soybean, maize and silver maple litter released 84, 75 and 63% of initial N, respectively, 308 days after field placement, while no differences in mass loss was observed among the three litter materials. At the Maple site, mass and N remaining, 308 days after field placement was lower at the middle of the alley, corresponding to higher soil temperature and water content. No differences in mass loss and N release patterns were observed at the Pecan site. Microclimate and litter quality effects can lead to differences in nutrient availability in alley cropping systems.