Calcium weathering in forested soils and the effect of different tree species

Soil weathering can be an important mechanism to neutralize acidity inforest soils. Tree species may differ in their effect on or response to soilweathering. We used soil mineral data and the natural strontium isotope ratio⁸⁷Sr/⁸⁶Sr as a tracer to identify the effect of treespecies on the Ca weathering rate. The tree species studied were sugar maple(Acer saccharum), hemlock (TsugaCanadensis), American beech (Fagusgrandifolia),red maple (Acer rubrum), white ash (FraxinusAmericana) and red oak (Quercus rubra) growingin a forest in northwestern Connecticut, USA. Three replicated sites dominatedby one of the six tree species were selected. At sugar maple and hemlock sitesthe dominant mineral concentrations were determined at three soil depths. Ateach site soil, soil water and stem wood of the dominant tree species weresampled and analyzed for the ⁸⁷Sr/⁸⁶Sr ratio, total SrandCa content. Atmospheric deposition was collected and analyzed for the sameconstituents. Optical analysis showed that biotite and plagioclaseconcentrations were lower in the soil beneath hemlock than beneath sugar mapleand suggested species effects on mineral weathering in the upper 10cm of the mineral soil. These results could not be confirmed withdata obtained by the Sr isotope study. Within the sensitivity of the Sr isotopemethod, we could not detect tree species effects on Ca weathering andcalculatedCa weathering rates were low at all sites (< 60mgm^–2yr^–1). Wefound a positive correlation between Ca weathering and the total Caconcentration in the surface soil. These results indicate that the absolutedifferences in Ca weathering rate between tree species in these acidic surfacesoils are small and are more controlled by the soil parent material(plagioclasecontent) than by tree species.     

Base-cation Cycling by Individual Tree Species in Old-growth Forests of Upper Michigan,USA

The influence of individual tree species on base-cation (Ca, Mg, K, Na) distribution and cycling was examined in sugar maple (Acer saccharum Marsh.), basswood (Tilia americana L.), and hemlock (Tsuga canadensis L.) in old-growth northern hardwood – hemlock forests on a sandy, mixed, frigid, Typic Haplorthod over two growing seasons in northwestern Michigan. Base cations in biomass, forest floor, and mineral soil (0–15 cm and 15–40 cm) pools were estimated for five replicated trees of each species; measured fluxes included bulk precipitation, throughfall, stemflow, litterfall, forest-floor leachate, mineralization + weathering, shallow-soil leachate, and deep-soil leachate. The three species differed in where base cations had accumulated within the single-tree ecosystems. Within these three single-tree ecosystems, the greatest quantity of base cations in woody biomass was found in sugar maple, whereas hemlock and basswood displayed the greatest amount in the upper 40 cm of mineral soil. Base-cation pools were ranked: sugar maple > basswood, hemlock in woody biomass; sugar maple, basswood > hemlock in foliage; hemlock > sugar maple, basswood in the forest floor, and basswood > sugar maple, hemlock in the mineral soil. Base-cation fluxes in throughfall, stemflow, the forest-floor leachate, and the deep-soil leachate (2000 only) were ranked: basswood > sugar maple > hemlock. Our measurements suggest that species-related differences in nutrient cycling are sufficient to produce significant differences in base-cation contents of the soil over short time intervals (<65 years). Moreover, these species-mediated differences may be important controls over the spatial pattern and edaphic processes of northern hardwood-hemlock ecosystems in the upper Great Lakes region.     

Coupled Nitrogen and Calcium Cycles in Forests of the Oregon Coast Range

Nitrogen (N) is a critical limiting nutrient that regulates plant productivity and the cycling of other essential elements in forests. We measured foliar and soil nutrients in 22 young Douglas-fir stands in the Oregon Coast Range to examine patterns of nutrient availability across a gradient of N-poor to N-rich soils. N in surface mineral soil ranged from 0.15 to 1.05% N, and was positively related to a doubling of foliar N across sites. Foliar N in half of the sites exceeded 1.4% N, which is considered above the threshold of N-limitation in coastal Oregon Douglas-fir. Available nitrate increased five-fold across this gradient, whereas exchangeable magnesium (Mg) and calcium (Ca) in soils declined, suggesting that nitrate leaching influences base cation availability more than soil parent material across our sites. Natural abundance strontium isotopes (⁸⁷Sr/⁸⁶Sr) of a single site indicated that 97% of available base cations can originate from atmospheric inputs of marine aerosols, with negligible contributions from weathering. Low annual inputs of Ca relative to Douglas-fir growth requirements may explain why foliar Ca concentrations are highly sensitive to variations in soil Ca across our sites. Natural abundance calcium isotopes (δ⁴⁴Ca) in exchangeable and acid leachable pools of surface soil measured at a single site showed 1 per mil depletion relative to deep soil, suggesting strong Ca recycling to meet tree demands. Overall, the biogeochemical response of these Douglas-fir forests to gradients in soil N is similar to changes associated with chronic N deposition in more polluted temperate regions, and raises the possibility that Ca may be deficient on excessively N-rich sites. We conclude that wide gradients in soil N can drive non-linear changes in base-cation biogeochemistry, particularly as forests cross a threshold from N-limitation to N-saturation. The most acute changes may occur in forests where base cations are derived principally from atmospheric inputs.     

Nitrogen enrichment regulates calcium sources in forests

Nitrogen (N) is a key nutrient that shapes cycles of other essential elements in forests, including calcium (Ca). When N availability exceeds ecosystem demands, excess N can stimulate Ca leaching and deplete Ca from soils. Over the long term, these processes may alter the proportion of available Ca that is derived from atmospheric deposition vs. bedrock weathering, which has fundamental consequences for ecosystem properties and nutrient supply. We evaluated how landscape variation in soil N, reflecting long‐term legacies of biological N fixation, influenced plant and soil Ca availability and ecosystem Ca sources across 22 temperate forests in Oregon. We also examined interactions between soil N and bedrock Ca using soil N gradients on contrasting basaltic vs. sedimentary bedrock that differed 17‐fold in underlying Ca content. We found that low‐N forests on Ca‐rich basaltic bedrock relied strongly on Ca from weathering, but that soil N enrichment depleted readily weatherable mineral Ca and shifted forest reliance toward atmospheric Ca. Forests on Ca‐poor sedimentary bedrock relied more consistently on atmospheric Ca across all levels of soil N enrichment. The broad importance of atmospheric Ca was unexpected given active regional uplift and erosion that are thought to rejuvenate weathering supply of soil minerals. Despite different Ca sources to forests on basaltic vs. sedimentary bedrock, we observed consistent declines in plant and soil Ca availability with increasing N, regardless of the Ca content of underlying bedrock. Thus, traditional measures of Ca availability in foliage and soil exchangeable pools may poorly reflect long‐term Ca sources that sustain soil fertility. We conclude that long‐term soil N enrichment can deplete available Ca and cause forests to rely increasingly on Ca from atmospheric deposition, which may limit ecosystem Ca supply in an increasingly N‐rich world.     

Differential effects of sugar maple, red oak, and hemlock tannins on carbon and nitrogen cycling in temperate forest soils

Tannins are abundant secondary chemicals in leaf litter that are hypothesized to slow the rate of soil-N cycling by binding protein into recalcitrant polyphenol–protein complexes (PPCs). We studied the effects of tannins purified from sugar maple, red oak, and eastern hemlock leaf litter on microbial activity and N cycling in soils from northern hardwood–conifer forests of the northeastern US. To create ecologically relevant conditions, we applied tannins to soil at a concentration (up to 2 mg g⁻¹ soil) typical of mineral soil horizons. Sugar maple tannins increased microbial respiration significantly more than red oak or hemlock tannins. The addition of sugar maple tannins also decreased gross N mineralization by 130% and, depending upon the rate of application, decreased net rates of N mineralization by 50–290%. At low concentrations, the decrease in mineralization appeared to be driven by greater microbial-N immobilization, while at higher concentrations the decrease in mineralization was consistent with the formation of recalcitrant PPCs. Low concentrations of red oak and hemlock tannins stimulated microbial respiration only slightly, and did not significantly affect fluxes of inorganic N in the soil. When applied to soils containing elevated levels of protein, red oak and hemlock tannins decreased N mineralization without affecting rates of microbial respiration, suggesting that PPC formation decreased substrate availability for microbial immobilization. Our results indicate that tannins from all three species form recalcitrant PPCs, but that the degree of PPC formation and its attendant effect on soil-N cycling depends on tannin concentration and the pool size of available protein in the soil.     

Differences in the success of sugar maple and red maple seedlings on acid soils are influenced by nutrient dynamics and light environment

Variation in tolerance to nutrient limitations may contribute to the differential success of sugar maple ( Acer saccharum Marsh.) and red maple ( Acer rubrum L.) on acid soils. The objectives of this study were to examine these relationships as influenced by light environment and test whether sensitivity to nutrient stress is mediated by oxidative stress. First-year sugar maple and red seedlings were grown on forest soil cores contrasting in nutrient availability under high or low light intensity. Foliar nutrition, photosynthesis, growth and antioxidant enzyme activity were assessed. Photosynthesis and growth of sugar maple were significantly lower on nutrient-poor soils and were correlated with leaf nutrient status with Ca and P having the strongest influence. For red maple, only chlorophyll content showed sensitivity to the nutrient-poor soils. High light exacerbated the negative effects of nutrient imbalances on photosynthesis and growth in sugar maple. Antioxidant enzyme activity in sugar maple was highest in seedlings growing on nutrient-poor soils and was inversely correlated with photosynthesis, Ca, P, and Mg concentrations. These results suggest that: (1) sugar maple is more sensitive to nutrient stresses associated with low pH soils than red maple; (2) high light increases sugar maple sensitivity to nutrient stress; (3) the negative effects of nutrient imbalances on sugar maple may be mediated by oxidative stress.     

Effect of soil K, Ca and Mg saturation and endomycorrhization on growth and nutrient uptake of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.     

Use of foliar Ca/Sr discrimination and <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and ⁸⁷Sr/⁸⁶Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the ⁸⁷Sr/⁸⁶Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios to trace Ca sources to plants.     

Foliar and wood chemistry of sugar maple along a gradient of soil acidity and stand health

The decline of sugar maple (Acer saccharum Marsh.) in forest of north-eastern North America is an important environmental issue. In this study, relationships between, soil, wood and foliar chemistry were assessed for 17 stands distributed within a large area of the Quebec sugar maple forest and that were growing on soils with a strong gradient of acidity and base saturation. There were many significant relationships between variables describing the acid-base status of the top-B soil (Ca and Mg concentrations, exchangeable acidity and base saturation) and Ca and Mn concentrations and Ca/Mn and Mg/Mn in tree tissues. Manganese was the element that showed the strongest inverse non-linear relationships with top-B soil base saturation with variance explanation of 71 and 65%, for wood and foliage, respectively. The 17 sites were divided in two groups according to their level of decline. The declining stands had significantly higher wood Mn and Mg concentrations and lower Ca/Mn ratios and significantly higher foliar Mn and lower Ca and Al concentrations. It was impossible to determine if these differences were a cause or a symptom of sugar maple health. However, the increase in Mn concentrations in tree tissues with increasing soil acidity, as well as the higher Mn concentrations in declining as compared to healthy stands suggest that Mn, as well as low Ca availability, could be an important contributing factor in the sugar maple decline.     

Calcium and temperature effects on seedling exudation and root rot infection of common bean on an acid sandy soil

Soil born fungi such as Phytium ultimum, Fusarium ssp., and Rhizoctonia solani (Kühn) severely restrict stand establishment of common bean (Phaseolus vulgaris L.) on acid soils of the Tropics. Calcium application is known to alleviate fungal infection in many legumes but the causes are still unclear. To investigate environmental factors and physiological mechanisms involved, growth chamber experiments were conducted with an acid sandy soil from Mexico. Treatments were soil liming at a rate of 0.67 g Ca(OH)₂ kg^-1, gypsum application at 0.49 g CaSO₄ 2H₂O kg^-1 soil placed around the seed, and an untreated control. Beans were grown under three temperature regimes with constant night and one constant day vs. two sinusoidal day temperatures. To examine patterns of seed and seedling exudation at regular intervals leachates of germinating seeds were collected on filter paper soaked with equilibrium solutions from soils of the three treatments. The severity of root rot in the control treatment was highest when plants were stressed by temperature extremes. At a sinusoidal day temperature peaking at 40°C soil liming and gypsum application to the seed increased the number of healthy seedlings similarly by over 60%. However, only liming which effectively eliminated growth constraints by low pH and high aluminum concentrations led to an increase in hypocotyl elongation by 22% and in total root length by 8%. Both calcium amendments increased the calcium and potassium contents in the hypocotyl tissue. From seeds exposed to the equilibrium solution of unlimed soil with pH 3.7, 1 mM Ca, and 0.6 mM Al considerable amounts of amino acids and carbohydrates were leached. In contrast, exposure to the equilibrium solution from limed soil with pH 4.3, 3 mM Ca, and negligible concentrations of Al led to a net uptake of amino acids and decreased leaching of carbohydrates. Exposure to the equilibrium solution of the gypsum treatment with pH 3.6, 20 mM Ca, and 1.2 mM Al resulted in a somewhat smaller net uptake of amino acids compared to liming. During germination pH around the seeds steeply increased in the untreated control but significantly less with both amendments. The results indicate that pH and the Ca/Al ratio in the soil solution around bean seeds determine their pattern of exudation and solute uptake. For bean germination and early growth on acid soils locally placed application of small amounts of gypsum as seed pelleting seems as effective as soil liming in reducing the incidence of root rot. The results indicate that this may be accomplished by decreasing the amount of leachates available for fungal development.     

Base cation biogeochemistry and weathering under oak and pine: a controlled long-term experiment

Large earthen-walled lysimeters at the San Dimas Experimental Forest in southern California present a unique opportunity to assess vegetation effects on biogeochemical processes and cation release by weathering in controlled soil-vegetation systems where archived samples of soil parent material are available for comparison. The lysimeters were filled in 1937 with homogenized fine sandy loam derived on site from the weathering of diorite, and planted in 1946 with scrub oak (Quercus dumosa) and Coulter pine (Pinus coulteri). Changes in base cation contents were measured in above-ground biomass, and total and exchangeable soil pools to a depth of 1 meter. All cations in the non-exchangeable soil pool decreased relative to the initial fill material, indicating release by weathering. Sodium and K were depleted from both exchangeable and non-exchangeable pools of the soils. Plant uptake of Na was minimal, whereas K storage in vegetation exceeded the loss from the exchangeable soil pool. In both soil-vegetation systems, but especially for oak, there was an increase in exchangeable Ca and Mg. For all base cations, storage in above-ground biomass was greater for oak, whereas losses by weathering from the non-exchangeable soil pool were greater under pine. Strong evidence supports biocycling as a controlling mechanism resulting in greater Ca and Mg release by weathering under pine. In addition, decreases in non-exchangeable Ca and Mg were strongly correlated to decrease in Si under oak, whereas no correlation was observed under pine. We conclude that weathering reactions or stoichiometry differed between vegetation types.Corresponding author     

The biogeochemistry of calcium at Hubbard Brook

A synthesis of the biogeochemistry of Ca was done during 1963–1992in reference and human-manipulated forest ecosystems of the Hubbard BrookExperimental Forest (HBEF), NH. Results showed that there has been a markeddecline in concentration and input of Ca in bulk precipitation, an overalldecline in concentration and output of Ca in stream water, and markeddepletion of Ca in soils of the HBEF since 1963. The decline in streamwaterCa was related strongly to a decline in SO +NO in stream water during the period. The soildepletion of Ca was the result of leaching due to inputs of acid rain duringthe past 50 yr or so, to decreasing atmospheric inputs of Ca, and tochanging amounts of net storage of Ca in biomass. As a result of thedepletion of Ca, forest ecosystems at HBEF are much more sensitive tocontinuing inputs of strong acids in atmospheric deposition than expectedbased on long-term patterns of sulfur biogeochemistry. The Ca concentrationand input in bulk precipitation ranged from a low of 1.0 µmol/and 15 mol/ha-yr in 1986–87 to a high of 8.0 µmol/ and 77mol/ha-yr in 1964–65, with a long-term mean of 2.74 µmol/during 1963–92. Average total atmospheric deposition was 61 and 29mol/ha-yr in 1964–69 and 1987–92, respectively. Dry depositionis difficult to measure, but was estimated to be about 20% of totalinput in atmospheric deposition. Streamwater concentration reached a low of21 µmol/ in 1991–92 and a high of 41 µmol/ in1969–70, but outputs of Ca were lowest in 1964–65 (121mol/ha-yr) and peaked in 1973–74 (475 mol/ha-yr). Gross outputs of Cain stream water were positively and significantly related to streamflow, butthe slope of this relation changed with time as Ca was depleted from thesoil, and as the inputs of sulfate declined in both atmospheric depositionand stream water. Gross outputs of Ca in stream water consistently exceededinputs in bulk precipitation. No seasonal pattern was observed for eitherbulk precipitation or streamwater concentrations of Ca. Net soil releasevaried from 390 to 230 mol/ha-yr during 1964–69 and 1987–92,respectively. Of this amount, weathering release of Ca, based on plagioclasecomposition of the soil, was estimated at about 50 mol/ha-yr. Net biomassstorage of Ca decreased from 202 to 54 mol/ha-yr, and throughfall plusstemflow decreased from 220 to 110 mol/ha-yr in 1964–69 and1987–92, respectively. These ecosystem response patterns were relatedto acidification and to decreases in net biomass accretion during the study.Calcium return to soil by fine root turnover was about 270 mol/ha-yr, with190 mol/ha-yr returning to the forest floor and 80 mol/ha-yr to the mineralsoil. A lower content of Ca was observed with increasing elevation for mostof the components of the watershed-ecosystems at HBEF. Possibly as a result,mortality of sugar maple increased significantly during 1982 to 1992 at highelevations of the HBEF. Interactions between biotic and abiotic controlmechanisms were evident through elevational differences in soil cationexchange capacity (the exchangeable Ca concentration in soils wassignificantly and directly related to the organic matter content of thesoils), in soil/till depth, and in soil water and in streamwaterconcentrations at the HBEF, all of which tended to decrease with elevation.The exchangeable pool of Ca in the soil is about 6500 mol/ha, and itsturnover time is quite rapid, about 3 yr. Nevertheless, the exchangeablepools of Ca at HBEF have been depleted markedly during the past 50 years orso, >21,125 mol/ha during 1940–1995. The annual gross uptake oftrees is about 26–30% of the exchangeable pool in the soil.Some 7 to 8 times more Ca is cycled through trees than is lost in streamwater each year, and resorption of Ca by trees is negligible at HBEF. Of thecurrent inputs to the available nutrient compartment of the forestecosystem, some 50% was provided by net soil release, 24% byleaching from the canopy, 20% by root exudates and 6% byatmospheric deposition. Clear cutting released large amounts of Ca tostream water, primarily because increased nitrification in the soilgenerated increased acidity and NO , a mobileanion in drainage water; even larger amounts of Ca can be lost from theecosystem in harvested timber products. The magnitude of Ca loss due towhole-tree harvest and acid rain leaching is comparable for forests similarto the HBEF, but losses from harvest must be superimposed on losses due toacid rain.     

Modelling yield losses of aluminium-resistant and aluminium-sensitive wheat due to subsurface soil acidity: effects of rainfall, liming and nitrogen application

Subsurface soil acidity reduces the growth of roots, which can potentially decrease crop yields. However, the magnitude of these yield reductions is dependent on interactions between factors such as the depth and severity of subsurface soil acidity, plant resistance to acidity, and water and nutrient availability. The Agricultural Production Systems Simulator (APSIM) was used to examine effects of these factors and their interactions on wheat yields in the Mediterranean climatic regions of Western Australia. The model was linked to historical meteorological data of the region (up to 90 different seasons), and was run for three locations representing low, medium and high rainfall zones and three constant but contrasting soil acidity profiles in a deep sandy soil with two wheat cultivars differing in aluminium (Al) resistance. The simulated results showed inherently high variability between seasons in grain yield, rooting depth and nitrogen leaching. Subsurface soil acidity could decrease average grain yields by up to 60%, particularly in soil profiles with acidity in deep layers. The adverse effects of acidity on wheat yields were greater in the high than the low rainfall zone. Amelioration of acidity by 75% in the entire profile or in the top 20-cm layer improved the yield of the Al-sensitive wheat cultivar. Growing Al-resistant wheat partially eliminated the negative effects of acidity on yields in soils with severe subsurface acidity and almost fully eliminated these negative effects in soils with moderate subsurface acidity. The yield benefits arising from growing Al-resistant wheat were greater than those from ameliorating acidity in the 0–20 cm layer by liming. Increasing nitrogen input increased yields of both Al-sensitive and Al-resistant wheat grown in acid soils in all the rainfall zones, but the yield increments were much greater in the high than the low rainfall zones. Applications of nitrogen fertilisers mitigate the effect of acidity on yields of Al-sensitive wheat in soils with shallow (10–40 cm) subsurface acidity. Furthermore, the improved yield by growing Al-resistant wheat and amelioration of acidity was correlated with increased rooting depth and was associated with decreased nitrogen leaching. Possible agronomic management options to combat the subsurface acidity problem are discussed.     

Soil Base Saturation Combines with Beech Bark Disease to Influence Composition and Structure of Sugar Maple-Beech Forests in an Acid Rain-Impacted Region

Sugar maple, an abundant and highly valued tree species in eastern North America, has experienced decline from soil calcium (Ca) depletion by acidic deposition, while beech, which often coexists with sugar maple, has been afflicted with beech bark disease (BBD) over the same period. To investigate how variations in soil base saturation combine with effects of BBD in influencing stand composition and structure, measurements of soils, canopy, subcanopy, and seedlings were taken in 21 watersheds in the Adirondack region of NY (USA), where sugar maple and beech were the predominant canopy species and base saturation of the upper B horizon ranged from 4.4 to 67%. The base saturation value corresponding to the threshold for Al mobilization (16.8%) helped to define the species composition of canopy trees and seedlings. Canopy vigor and diameter at breast height (DBH) were positively correlated (P < 0.05) with base saturation for sugar maple, but unrelated for beech. However, beech occupied lower canopy positions than sugar maple, and as base saturation increased, the average canopy position of beech decreased relative to sugar maple (P < 0.10). In low-base saturation soils, soil-Ca depletion and BBD may have created opportunities for gap-exploiting species such as red maple and black cherry, whereas in high-base saturation soils, sugar maple dominated the canopy. Where soils were beginning to recover from acidic deposition effects, sugar maple DBH and basal area increased progressively from 2000 to 2015, whereas for beech, average DBH did not change and basal area did not increase after 2010.     

Calcium as a plant nutrient

Abstract. Calcium occurs as a relatively large, divalent ion which readily enters the apoplast and is bound in exchangeable form in cell walls and on the exterior surface of the plasmalemma. It occurs in only very low concentrations in the cytoplasm and chloroplasts and appears to have a limited role as an enzymatic cofactor. The soil solution usually provides an adequate supply of Ca to plants. The well known physiological disorders resulting from localized Ca deficiencies within the plant are thus attributable to poor Ca distribution rather than restriction in uptake. Calcium is moved largely in the xylem and only to a very limited extent in the phloem. The phloem/xylem ratio of the solute input can be particularly critical in organs which are naturally low in Ca, such as fruits and young leaves. Factors which influence the distribution of Ca such as humidity, root pressure, phytohormone activity, can also affect the occurrence of these disorders.     

Base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics

The nutritional benefits that mycorrhizal associations provide to plants may be constrained by acidic soil conditions resulting in decreased photosynthetic function. Sugar maple (Acer saccharum) and red maple (Acer rubrum) seedlings were grown on a native acidic (pH 4.1) soil both unamended and amended with base cations (pH 6.2). In a second study a fungicide treatment was included. Foliar nutrition, mycorrhizal colonization, photosynthesis and their relationships were assessed. On the native soil, red maple maintained higher levels of mycorrhizal colonization and photosynthesis than sugar maple but showed little response to base cation amendments. Mycorrhizal colonization and photosynthesis of sugar maple increased significantly in response to base cation amendments. Correlations were observed among mycorrhizal colonization, foliar nutrition and photosynthesis. The fungicide treatment indicated that 50% of the base cation-induced increase in sugar maple photosynthesis was mycorrhiza related. The results suggest that base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics. Red maple exhibits much less sensitivity to these same edaphic conditions.     

Does soil acidity reduce subsoil rooting in Norway spruce (Picea abies)?

Increasing evidence suggests that forest soils in central and northern Europe as well as in North America have been significantly acidified by acid deposition during the last decades. The present investigation was undertaken to examine the effect of soil acidity on rooting patterns of 40-year-old Norway spruce trees by comparing fine and coarse roots among four stands which differed in soil acidity and Mg (and Ca) nutrition. The coarse root systems of four to five 40-year-old Norway spruce trees per stand were manually excavated. The sum of cross sectional area (CSA) at 60 cm soil depth and below of all vertical coarse roots, as a measure of vertical rooting intensity, was strongly reduced with increasing subsoil acidity of the stands. This pattern was confirmed when 5 additional acidic sites were included in the analysis. Fine root biomass in the mineral soil estimated by repeated soil coring was strongly reduced in the heavily acidified stands, but increased in the humic layer. Using ingrowth cores and a screen technique, we showed that the higher root biomass in the humic layer of the more acidic stands was a result of higher root production. Thus, reduced fine root biomass and coarse root CSA in deeper soil layers coincided with increased root growth in the humic layer. Root mineral analysis showed Ca/Al ratios decreased with decreasing base saturation in the deeper mineral soil (20–40 cm). In the top mineral soil, only minor differences were observed among stands. In general, low Ca/Al ratios coincided with low fine root biomass. Calcium/aluminum ratios determined in cortical cell walls using X-ray microanalysis showed a similar pattern as Ca/Al ratios based on analysis of whole fine roots, although the amplitude of changes among the stands was much greater. Aluminum concentrations and Ca/Al ratios in cortical cell walls were at levels found to inhibit root growth of spruce seedlings in laboratory experiments. The data support the idea that Al (or Ca/Al ratios) and acid deposition-induced Mg (and possibly Ca) deficiency are important factors influencing root growth and distribution in acidic forest soils. Changes in carbon partitioning within the root system may contribute to a reduction in deep root growth.     

Calcium sulfate or coal combustion by-product spread on the soil surface to reduce evaporation, mitigate subsoil acidity and improve plant growth

Removal of sulfur dioxide from flue gas produced by coal-burning power plants has increased the availability of by-products that may be useful as soil amendments for agriculture. We studied the effects of surface layers (caps) of fluidized bed combustion residue-fly ash mixture (FBCR-FA) or calcium sulfate on reduction of evaporative water losses and improvements in subsurface acid soil chemical characteristics. Caps 3.8 cm thick of porous FBCR-FA, hydrated commercial calcium sulfate (CCS), or soil (check) were placed on columns of coarse-loamy, mixed, mesic Umbric Dystrochrept soil of pH 4.2. After the addition of 40 cm of water during a 16-week period, mean daily water loss from the column with the FBCR-FA cap was 0.51 mm compared to 0.98 mm in the check. Mean increase in soil exchangeable Ca in the 5- to 40-cm depth for the CCS treatment was 0.83 cmol_c kg^–1 and mean pH (H₂O) increase was 0.21 units. Mean KCl-extractable Al decreased from 6.08 to 5.52 cmol_c kg^–1. Roots of sudangrass (Sorghum bicolor (L.) Moench) planted in the columns after removal of the caps reached 2 cm depth in the control, 18 cm in the FBCR-FA and 38 cm in the CCS treated columns after 47 days of growth. The gypsum cap was effective in improving deep rooting in acid soils and the FBCR-FA cap reduced evaporative water losses.Abbreviations FBCR-FA fluidized bed combustion residue-fly ash mixture - CCS hydrated commercial calcium sulfate - ICP inductively coupled plasma - GLM general linear models.     

Long-term records of strontium isotopic composition in tree rings suggest changes in forest calcium sources in the early 20th century

Many studies made in Europe and North America have shown an increasing depletion of exchangeable base cations that may cause tree nutritional deficiencies in sensitive soils. We use radial variation of strontium isotope in tree-rings (⁸⁷Sr/⁸⁶Sr ratio) to monitor possible changes in Ca sources for tree nutrition (Sr is used as an analog to Ca). The two main sources of Ca in forest stands are mineral weathering release and atmospheric inputs. Measurements in several forest stands in temperate regions show a steep decrease from pith to outer wood of the Sr isotope ratio from∼1870 to∼1920 except for stands developed on soils with a higher Ca status. This suggests a decrease of the weathering contribution (high ⁸⁷Sr/⁸⁶Sr ratio) when cations are displaced from the soil exchange complex by acid deposition at a rate faster than the replenishment of the cation pool by mineral weathering. This displacement enhances the atmospheric contribution, which is characterized by a low ⁸⁷Sr/⁸⁶Sr ratio. Tree-ring chronologies are an exceptional historic-timing record of chemical changes in the soil environment induced by atmospheric pollution. The reliability of the tree-ring recorder has been verified with a well-controlled nutritional perturbation in the context of a limed forest stand (with a known liming Sr isotopic signature). Our data suggest that forest ecosystems were affected by atmospheric inputs of strong acids earlier than previously thought.     

A comparison between Ca and Sr cycling in forest ecosystems

In favourable conditions, the ⁸⁷Sr/⁸⁶Sr isotope ratios of the Sr delivered by rain and soil mineral weathering differ. Assuming that Ca and Sr behave similarly in forest ecosystems, several authors have used the ⁸⁷Sr/⁸⁶Sr variation in forest compartments to calculate the contribution of rain and mineral weathering to Ca fluxes and pools. However, there are a number of experimental reports showing that Ca and Sr may behave differently in the soil and in the plant. We have tested this Ca–Sr analogy in the field by measuring the variation of Sr and Ca concentrations, fluxes and pools in spruce, beech and maple stands on granite, sandstone and limestone. Results show that (1) variations of Ca and Sr concentrations are generally correlated at each level of the ecosystems. (2) In spruce on acid soils, a preferential uptake of Ca over Sr occurs (Aubure spruce Sr/Ca = 0.8×10⁻³; soil exchangeable Sr/Ca between 2 and 6×10⁻³). On calcareous soils, a preferential uptake of Sr over Ca by spruce may occur. (3) In spruce and beech on acid and calcareous soils, a preferential translocation of Ca over Sr from roots to leaves occurs ((Sr/Ca) in leaves was between 10 and 90% of that in roots). (4) The biological cycling of Ca and Sr leads to an enrichment of the upper soil layers in Ca and Sr. Compared to Sr, Ca accumulates in the upper layer of acid soils because Ca cycling through litterfall is favoured over Sr cycling, and possibly because of the selectivity of acid organic exchangers for Ca. This revised version was published online in June 2006 with corrections to the Cover Date.