Shredder abundance and leaf breakdown in an Appalachian Mountain stream

SUMMARY.

• 1 Breakdown rates of dogwood (Cornus florida L.), red maple (Acer rubrum L.) and white oak (Quercus alba L.) leaves were investigated at two first-order and two second-order sites in an Appalachian Mountain stream.
• 2 Leaves exposed in mesh bags were sampled on eight occasions over a 207 day period and breakdown rates were compared using an exponential decay model.
• 3 There was a consistent ranking in leaf breakdown rate within each site, i.e. dogwood > red maple > white oak, and all species broke down faster at second-than at first-order sites.
• 4 Our data suggest that differences in species-specific leaf breakdown rates were largely a function of shredder abundance on the leaves.

     

Bottomland hardwood productivity: case study in a rapidly subsiding,Louisiana, USA,watershed

The Verret basin was formerly an overflow area between the Mississippi and Atchafalaya rivers and contains about 41,000ha of forested wetlands. Water levels are rising at the rate of over 1 cm/year in this area, and the forests are subjected to longer and deeper flooding. Tree growth, litterfall, and species composition were monitored across a flooding gradient during January 1985–December 1986. The driest area was only 20 cm higher in elevation than the wettest area, but the structure of the forest changes greatly over this range. The drier area was dominated by sweetgum (Liquidambar styraciflua L.), oaks (Quercus spp.), and sugarberry (Celtis laevigata Willd.), while green ash (Fraxinus pennsylvanica Marsh.), red maple (Acer rubrum L.), and baldcypress (Taxodium distichum (L.) Rich.) were dominant in the wetter area. Green ash and bitter pecan (Carya aquatica (Michaux. f.) Nutt.) were found in all plots, but these two species are under severe stress in the more flooded area as evidenced by dead and dying trees. Stem wood production increased from 1985 to 1986 in the driest (392 to 473 g/m²/yr) and wettest (199 to 399 g/m²/yr) plots, but remained relatively unchanged in the transitional area (386 to 380g/m²/yr). Leaf litter production decreased across the gradient from dry to flooded plots during both years. Over 40% of the litterfall in the drier plot was from flood-tolerant shrub species. In the flooded plots, red maple and baldcypress were major contributors to total litterfall. Increased flooding of dry bottomland forests in the future could lead to decreased litterfall and increased tree death over the entire watershed.     

Branch growth and leaf numbers of red maple (Acer rubrum L.) and red oak (Quercus rubra L.): response to defoliation

Summary Branch growth and leaf formation from terminal and from lateral buds of red maple (Acer rubrum L.) and red oak (Quercus rubra L.) were measured in response to simulated insect defoliation. A single large branch representative of the crown of each tree was used for enumeration of growth and of bud numbers throughout three successive years of 0, 50, 75, and 100% leaf removal for the entire tree. Leaf number per tree for both species after the last year of defoliation was reduced in direct proportion to the severity of defoliation, in comparison to the predefoliation status of the trees. Bud number per tree for red maple, but not for red oak, was also reduced in proportion to severity of defoliation.Averaged over all defoliation treatments, defoliation reduced branch growth more than leaf production. Furthermore, the reduction in branch growth and leaf production was greater in red oak than in red maple. Three years of successive defoliation reduced the mean lateral plus terminal branch growth by 40% in red oak and by 23% in red maple, while leaf number was reduced 22% in red oak and remained unchanged in red maple. In red maple, 100% defoliation caused greater branch death than the 50 or 75% defoliation treatments, and the amount of death was greater after each successive year of defoliation. In contrast to red maple, undefoliated red oak incurred a substantial amount of branch death throughout the study which was little affected by defoliation treatment.     

Fine root production of astringent phenolics

Summary Chemical quality of fine roots (<1 mm diameter) was determined over a gradient of species composition in the Mixed Mesophytic Forest Region. Ash-free nitrogen, calcium, and phosphorus concentrations of roots declined by 49, 41, and 72%, respectively, over a gradient of increasing soil acidity (pH 5.3 to 4.7). Lignin concentration was unrelated to either the vegetation gradient or any of the soil changes it encompassed; however, astringent phenolics increased by 275% over the same gradient. Trends in the chemical constituency of fine roots suggest that the production of phenolics in below-ground plant parts is increased on nutrient-poor sites. This response is best related to changes in species composition, especially increasing importancy of Quercus spp.This investigation (No. 88-8-36) is connected with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

Increasing Red Maple Leaf Litter Alters Decomposition Rates and Nitrogen Cycling in Historically Oak-Dominated Forests of the Eastern U.S.

Without canopy-opening fire disturbances, shade-tolerant, fire-sensitive species like red maple (Acer rubrum L.) proliferate in many historically oak-dominated forests of the eastern U.S. Here, we evaluate potential implications of increased red maple dominance in upland oak forests of Kentucky on rates of leaf litter decomposition and nitrogen (N) cycling. Over 5 years, we evaluated mass loss of leaf litter and changes in total N and carbon (C) within six leaf litter treatments comprised of scarlet oak, chestnut oak, and red maple, and three mixed treatments of increasing red maple contribution to the leaf litter pool (25, 50, and 75% red maple). Over a 1.5-year period, we conducted a plot-level leaf litter manipulation study using the same treatments plus a control and assessed changes in net nitrification, ammonification, and N mineralization within leaf litter and upper (0–5 cm depth) mineral soil horizons. Red maple leaf litter contained more “fast” decomposing material and initially lost mass faster than either oak species. All litter treatments immobilized N during initial stages of decomposition, but the degree of immobilization decreased with decreasing red maple contribution. The leaf litter plot-level experiment confirmed slower N mineralization rates for red maple only plots compared to chestnut oak plots. As red maple increases, initial leaf litter decomposition rates will increase, leading to lower fuel loads and more N immobilization from the surrounding environment. These changes may reduce forest flammability and resource availability and promote red maple expansion and thereby the “mesophication” of eastern forests of the U.S.     

Allocation of extracellular enzymatic activity in relation to litter composition, N deposition, and mass loss

Decomposition of plant material is a complex process that requiresinteraction among a diversity of microorganisms whose presence and activity issubject to regulation by a wide range of environmental factors. Analysis ofextracellular enzyme activity (EEA) provides a way to relate the functionalorganization of microdecomposer communities to environmental variables. In thisstudy, we examined EEA in relation to litter composition and nitrogendeposition. Mesh bags containing senescent leaves of Quercusborealis (red oak), Acer rubrum (red maple) andCornus florida (flowering dogwood) were placed on forestfloor plots in southeastern New York. One-third of the plots were sprayedmonthly with distilled water. The other plots were sprayed monthly withNH₄NO₃ solution at dose rates equivalent to 2 or 8 g N m^–2 y^–1. Mass loss, litter composition, fungal mass, and the activities ofeight enzymes were measured on 13 dates for each litter type. Dogwood wasfollowed for one year, maple for two, oak for three. For each litter type andtreatment, enzymatic turnover activities were calculated from regressions of LN(%mass remaining) vs. cumulative activity. The decomposition of dogwood litterwas more efficient than that of maple and oak. Maple litter had the lowestfungal mass and required the most enzymatic work to decompose, even though itsmass loss rate was twice that of oak. Across litter types, N amendment reducedapparent enzymatic efficiencies and shifted EEA away from N acquisition andtoward P acquisition, and away from polyphenol oxidation and towardpolysaccharide hydrolysis. The effect of these shifts on decomposition ratevaried with litter composition: dogwood was stimulated, oak was inhibited andmaple showed mixed effects. The results show that relatively small shifts intheactivity of one or two critical enzymes can significantly alter decompositionrates.     

Elevated CO2 differentially alters the responses of coocurring birch and maple seedlings to a moisture gradient

Summary To determine the effects of elevated CO₂ and soil moisture status on growth and niche characteristics of birch and maple seedlings, gray birch (Betula populifolia) and red maple (Acer rubrum) were experimentally raised along a soil moisture gradient ranging from extreme drought to flooded conditions at both ambient and elevated atmospheric CO₂ levels. The magnitude of growth enhancement due to CO₂ was largely contingent on soil moisture conditions, but differently so for maple than for birch seedlings. Red maple showed greatest CO₂ enhancements under moderately moist soil conditions, whereas gray birch showed greatest enhancements under moderately dry soil conditions. Additionally, CO₂ had a relatively greater ameliorating effect in flooded conditions for red maple than for gray birch, whereas the reverse pattern was true for these species under extreme drought conditions. For both species, elevated CO₂ resulted in a reduction in niche breadths on the moisture gradient; 5% for gray birch and 23% for red maple. Species niche overlap (proportional overall) was also lower at elevated CO₂ (0.98 to: 0.88: 11%). This study highlights the utility of of experiments crossing CO₂ levels with gradients of other resources as effective tools for elucidating the potential consequences of elevated CO₂ on species distributions and potential interactions in natural communities.     

Stem hypoxia and root respiration of flooded maple and birch seedlings

Some researchers have attributed flood tolerance of woody plants to air entering the shoot through stems, leaves, or lenticels and diffusing to the roots to sustain aerobie respiration. The purpose of this study was to determine if internal aeration of roots by lower stems, changes in gross morphology of lower stems, or both, contribute to flood tolerance of certain tree species. Greenhouse-grown seedlings of red maple ( Acer rubrum L.) and river birch ( Betula nigra L.) tolerated at least 30 days of flooding, where as sugar maple ( Acer saccharum Marsh) and European white birch (also called silver birch, Betula pendula Roth) were intolerant. Flood treatment induced lentieel intumescences and adventitious root formation on red maple stems, but only adventitious roots formed on river birch stems. Stem morphology of sugar maple and European birch was unchanged by flooding. Flood stress decreased oxygen consumption capacity of excised roots from both tolerant and intolerant species. Exclusion of oxygen from the lower stems of flooded red maple and river birch prevented lenticel intumescence and adventitious root formation, but flood tolerance and root respiration capacity were unchanged. Neither internal aeration nor changes in stem morphology appear to account for flood tolerance of red maple and river birch.     

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.     

Subtle differences in environmental stress along a flooding gradient affect the importance of inter-specific competition in an annual plant community

Empirical evidence suggests that the direction and intensity of plant–plant interactions may depend on the favourability of the environment. Previous studies have mainly focused on steep gradients of environmental stress or disturbance, while the interplay of competition and environment has not been tested for subtle environmental differences. Here, we present results from a study on plant communities of temporary wetlands in East-German farmland. Due to yearly ploughing in autumn, the vegetation is composed of annual species. Flooding does not affect adult plants and the elevation on the gradient expresses differences in the length of the growing season rather than in disturbance intensity or severe environmental stress. We tested whether such subtle differences in environmental stress may affect the importance of interspecific competition by the dominant species. Two treatments were applied at two elevations: removal of the dominant species (Matricaria maritima ssp. inodora) and reciprocal transplants of the seed-bank of the two elevations. At both elevations, removal of Matricaria inodora led to an increase in total species richness and number of wetland species, but the effects were substantially stronger at high elevations. Removal and the elevation on the flooding gradient significantly influenced the plant community composition. In particular, the weed communities became more similar to the wetland communities after the removal. Transplanted weed species did not emerge at low elevations. While two of four target species had significantly higher densities after the removal at high elevations, none of them was influenced by removal at low elevations. This indicates that, consistent with previous studies from other habitat types, competition by the dominant species was more intense under conditions of low environmental stress. The overall results suggest that both flooding as well as interspecific competition are important in structuring the plant communities along the freshwater gradient studied.     

Changes in abscisic acid levels in embryo axes of Norway maple and sycamore seeds during maturation and dehydration

Changes in the abscisic acid (ABA) levels in embryo axes of seeds, belonging to the orthodox (Norway maple — Acer platanoides L.) and recalcitrant (sycamore — Acer pseudoplatanus L.) categories, were investigated throughout maturation using an ELISA (enzyme-linked immunosorbent assay) test. Concentration of ABA in embryo axes substantially differed depending on species and sampling date. ABA was always higher in Norway maple except at the end of seed maturation when ABA content was similar in both species. During maturation ABA decreased in both species but the decline was more marked in Norway maple than in sycamore (11 vs. 3 fold). These species also differed in the pattern of ABA changes, which in sycamore embryo axes was very regular, while in Norway maple a sharp decrease was recorded after acquisition by the seeds of tolerance to desiccation. Dehydration of embryo axes of Norway maple caused a further significant decrease of ABA level. In contrast, in dehydrated sycamore embryo axes ABA content did not decrease, but slightly increased. The role of ABA in desiccation tolerance and dormancy of Norway maple and sycamore seeds is discussed.     

A sporulation medium forDiscula destructiva,the dogwood anthracnose fungus

A growth medium incorporating finely ground oak or maple leaf tissue was developed for the purpose of increasing in vitro conidium production by the dogwood anthracnose pathogen,Discula destructiva.     

First-year growth response of trees in an intact forest exposed to elevated CO2

Although elevated atmospheric CO₂ has been shown to increase growth of tree seedlings and saplings, the response of intact forest ecosystems and established trees is unclear. We report results from the first large-scale experimental system designed to study the effects of elevated CO₂ on an intact forest with the full complement of species interactions and environmental stresses. During the first year of exposure to ^ 1.5 Ë ambient CO₂, canopy loblolly pine (Pinus taeda, L.) trees increased basal area growth rate by 24% but understorey trees of loblolly pine, sweetgum (Liquidambar styraciflua L.), and red maple (Acer rubrum L.) did not respond. Winged elm (Ulmus alata Michx.) had a marginally significant increase in growth rate (P = 0.069). These data suggest that this ecosystem has the capacity to respond immediately to a step increase in atmospheric CO₂; however, as exposure time increases, nutrient limitations may reduce this initial growth stimulation.     

Light absorption by anthocyanins in juvenile, stressed, and senescing leaves

The optical properties of leaves from five species, Norway maple (Acer platanoides L.), cotoneaster (Cotoneaster alaunica Golite), hazel (Corylus avellana L.), Siberian dogwood (Cornus alba L.), and Virginia creeper (Parthenocissus quinquefolia (L.) Planch.), differing in pigment composition and at different stages of ontogenesis, were studied. Anthocyanin absorption maxima in vivo, as estimated with spectrophotometry of intact anthocyanic versus acyanic leaves and microspectrophotometry of vacuoles in the leaf cross-sections, were found between 537 nm and 542 nm, showing a red shift of 5-20 nm compared with the corresponding maxima in acidic water-methanol extracts. In non-senescent leaves, strong anthocyanin absorption was found between 500 nm and 600 nm (with a 70-80 nm apparent bandwidth). By and large, absorption by anthocyanin in leaves followed a modified form of the Lambert-Beer law, showing a linear trend up to a content of nearly 50 nmol cm(-2), and permitting thereby a non-invasive determination of anthocyanin content. The apparent specific absorption coefficients of anthocyanins at 550 nm showed no substantial dependence on the species. Anthocyanin contribution to total light absorption at 550 nm was followed in maple leaves in the course of autumn senescence. Photoprotection by vacuolar anthocyanins is discussed with special regard to their distribution within a leaf; radiation screening by anthocyanins predominantly localized in the epidermal cells in A. platanoides and C. avellana leaves was also evaluated.     

Inadequate Cold Tolerance as a Possible Limitation to American Chestnut Restoration in the Northeastern United States

The American chestnut (Castanea dentata (Marshall) Borkh.), once a major component of eastern forests from Maine to Georgia, was functionally removed from the forest ecosystem by chestnut blight (an exotic fungal disease caused by Cryphonectria parasitica (Murr.) Barr), first identified at the beginning of the twentieth century. Hybrid‐backcross breeding programs that incorporate the blight resistance of Chinese chestnut (Castenea mollissima Blume) and Japanese chestnut (Castenea crenata Sieb. & Zuc.) into American chestnut stock show promise for achieving the blight resistance needed for species restoration. However, it is uncertain if limitations in tissue cold tolerance within current breeding programs might restrict the restoration of the species at the northern limits of American chestnut's historic range. Shoots of American chestnut and hybrid‐backcross chestnut (i.e., backcross chestnut) saplings growing in two plantings in Vermont were tested during November 2006, February 2007, and April 2007 to assess their cold tolerance relative to ambient low temperatures. Shoots of two potential native competitors, northern red oak (Quercus rubra L.) and sugar maple (Acer saccharum L.), were also sampled for comparison. During the winter, American and backcross chestnuts were approximately 5°C less cold tolerant than red oak and sugar maple, with a tendency for American chestnut to be more cold tolerant than the backcross chestnut. Terminal shoots of American and backcross chestnut also showed significantly more freezing damage in the field than nearby red oak and sugar maple shoots, which showed no visible injury.     

Stand history is more important than climate in controlling red maple (Acer rubrum L.) growth at its northern distribution limit in western Quebec,Canada

Aims We examined growth of red maple (Acer rubrum L.) to evaluate environmental controls of its northern distributional limit in Eastern North America and its potential response to future climate change.Methods We collected growth data from nine sites located along a 300-km transect (47–49°N), which included frontier population of red maple and covered three bioclimatic domains in western Quebec. We analyzed three growth variables: growth rates during the first 30 years of maple lifespan, cumulative basal area increment (BAI) over the most recent decade (2000–2009) and annual growth rate over the whole tree lifespan ranging from 58 to 112 years. We also examined growth sensitivity to climate by using response function analysis.Important findings Three different proxies of maple absolute growth (initial growth rate, BAI during 2000–09 and mean diameter growth rate) indicated a better growth with an increase in latitude. We speculate that stand history effectively overrode the direct effects of colder climate on maple growth along the S-N gradient. Regeneration of maple in the southern sites likely occurred in canopy gaps, whereas in the north it was contingent upon large disturbances such as stand-replacing fires, which apparently provided more favorable light environment for maple growth than canopy gaps. The annual growth variability, which reflects effects of annual weather on growth and is largely independent from the absolute growth rate, was significantly affected by monthly climate, suggesting a positive effect of higher summer temperature in the northern part of the transect (48–49°N) and a negative effect of summer drought in the south (47–48°N). In the future, the natural and human disturbance regimes will be dominant controls of the actual biomass productivity of red maple at the northern limit of its present distribution range. Direct effects of climate on maple growth would likely be less important in this context, and will likely entail negative effect of increased summer drought in the southern part of the study area and positive effects of increased temperatures in the north.     

Phenotypic effects of the nurse Thylacospermum caespitosum on dependent plant species along regional climate stress gradients

Contrasting phenotypes of alpine cushion species have been recurrently described in several mountain ranges along small‐scale topography gradients, with tight competitive phenotypes in stressful convex topography and loose facilitative phenotypes in sheltered concave topography. The consistency of phenotypic effects along large‐scale climate stress gradients have been proposed as a test of the likely genetic bases of the differences observed at small‐scale. Inversely, plastic phenotypic effects are more likely to vanish at some points along climate stress gradients. We tested this hypothesis for two phenotypes of the alpine cushion species Thylacospermum caespitosum at four points along regional gradients of cold and drought stress in northwest China. We measured the traits of the two cushion phenotypes and quantified their associated plant communities and environmental variables along the regional temperature and aridity gradients. Cushion height, convexity and stem density overall showed significant effect of phenotypes. Difference in tightness of cushions between phenotypes was consistent across climate conditions, whereas differences in cushion convexity and height between phenotypes increased with increasing cold stress. Phenotypic effects on species richness and abundance were consistent along both climate gradients but not effects on species composition, while there were no phenotypic effects on environmental variables. Additionally, RII (relative interaction index) curves were linear along the drought gradient but unimodal along the temperature gradient, likely due to the occurrence of contrasting species pools at the different sites. We conclude that the consistency of phenotypic effects of T. caespitosum was high for species richness and abundance and mainly explained by differences in interference mediated by likely heritable differences in cushion tightness. Additionally, our study shows that the shapes of the relationship between plant responses to neighbours and environmental stresses are not necessarily driven by niche‐based deterministic factors.     

Membrane phospholipid composition during maturation of seeds of Acer platanoides and Acer pseudoplatanus in relation to desiccation tolerance

Membrane phospholipid composition was investigated in seeds of two species from the genus Acer: Norway maple (Acer platanoides L.) — tolerant to desiccation, and sycamore (Acer pseudoplatanus L.) — intolerant to desiccation, during their maturation, from 1 August to 25 September 1995, at weekly intervals. Seeds of Norway maple acquire tolerance to desiccation at the end of August ie. about 125 days after flowering (DAF). Phospholipid composition during development revealed marked differences between studied seeds. Seeds of Norway maple after acquiring tolerance to desiccation contained much more phosphatidylcholine (PC) and phosphatidylethanolamine (PE), compared to sycamore. The ratio of PC/PE in mature Norway maple seeds was evidently higher than those in sycamore. The level of unsaturated fatty acids in the phospholipid fraction substantially increased in Norway maple seeds during development and the saturation of PC and PE was less than in sycamore. The results suggest that phospholipid composition may be involved in desiccation tolerance of Norway maple seeds.     

SPECIES RESPONSE TO A MOISTURE GRADIENT IN CENTRAL ILLINOIS FORESTS

Polar and Gaussian ordination applied to data collected from 37 forest sites in central Illinois resulted in a continuous and gradual change in species composition along a moisture gradient. A series of overlapping species success curves formed by plotting Importance Values over stands ordered along the gradient varied continuously in modal location and habitat width. Blackjack oak and black oak dominated upland sandy sites. Black oak, white oak, and shagbark hickory were the most important species on exposed, upper slope positions or ridge tops with silt-loam soils. Red oak, sugar maple, American elm, and bur oak dominated sheltered locations on lower slope positions and stream terraces. Sycamore, silver maple, and cottonwood were leading tree species in floodplain forests. Conversion of black, white, and red oak forests on silt-loam sites to sugar maple, white ash, and red elm dominance is evident by high densities of these shade tolerant species in the understory. Composition of forests at the extreme ends of the moisture gradient is more stable than the mesic sites. Maximum tree diversity occurred on mesic sites and decreased toward the extreme ends of the moisture gradient. However, competitive exclusion of shade intolerant species by sugar maple and other species has caused a decrease in understory diversity on mesic sites. Diversity decreased from canopy to understory strata in lowland forests and increased on xeric sites.     

The Association of Discula destructiva (Red.) Hyphae With Cornus florida (L.) Trichomes

Detached, surface-dismfested flowering dogwood (Cornus florida L.) leaves were inoculated with a Discula destructiva (Red.) spore suspension in an effort to identify inoculation and pre-penetration phenomena in the dogwood anthracnose pathosystem. Scanning electron micrographs show an association of D. destructiva hyphae with trichomes on the flowering dogwood upper leaf surface. The basal area of these leaf hairs may provide an entry point for Discula spp. colonization of and penetration into the dogwood leaf; however, the possible significance of this area as a unique ecological niche on the dogwood phylloplane should not be ignored.