Acer Saccharum Seedlings Research Articles

Tree seedling functional traits mediate plant-soil feedback survival responses across a gradient of light availability.

1. Though not often examined together, both plant-soil feedbacks (PSFs) and functional traits have important influences on plant community dynamics and could interact. For example, seedling functional traits could impact seedling survivorship responses to soils cultured by conspecific versus heterospecific adults. Furthermore, levels of functional traits could vary with soil culturing source. In addition, these relationships might shift with light availability, which can affect trait values, microbe abundance, and whether mycorrhizal colonization is mutualistic or parasitic to seedlings. 2. To determine the extent to which functional traits mediate PSFs via seedling survival, we conducted a field experiment. We planted seedlings of four temperate tree species across a gradient of light availability and into soil cores collected beneath conspecific (sterilized and live) and heterospecific adults. We monitored seedling survival twice per week over one growing season, and we randomly selected subsets of seedlings to measure mycorrhizal colonization and phenolics, lignin, and NSC levels at three weeks. 3. Though evidence for PSFs was limited, Acer saccharum seedlings exhibited positive PSFs (i.e., higher survival in conspecific than heterospecific soils). In addition, soil microbes had a negative effect on A. saccharum and Prunus serotina seedling survival, with reduced survival in live versus sterilized conspecific soil. In general, we found higher trait values (measured amounts of a given trait) in conspecific than heterospecific soils and higher light availability. Additionally, A. saccharum survival increased with higher levels of phenolics, which were higher in conspecific soils and high light. Quercus alba survival decreased with higher AMF colonization. 4. We demonstrate that functional trait values in seedlings as young as three weeks vary in response to soil source and light availability. Moreover, seedling survivorship was associated with trait values for two species, despite both drought and heavy rainfall during the growing season that may have obscured survivorship-trait relationships. These results suggest that seedling traits could have an important role in mediating the effects of local soil source and light levels on seedling survivorship and thus plant traits could have an important role in PSFs.

Tree Seedling Establishment Under the Native Shrub, Asimina triloba

Abstract Both native and invasive species that form forest understory layers affect tree seedling establishment worldwide. We compared the density and survival of canopy tree seedlings under and outside patches of the native shrub, Asimina triloba (L.) Dunal (Annonaceae) (pawpaw). We also conducted a manipulative experiment to determine whether above ground or below ground competition was more important in seedling growth and survival. Above ground competition was manipulated by tying back pawpaw stems and below ground competition by trenching the perimeter of the study plots. Overstory density (measured by a canopy densiometer) was greater under pawpaw than outside pawpaw. Tree seedling density was approximately three times greater outside pawpaw than under pawpaw over the range of sites. Seedlings under pawpaw were both younger and shorter than those outside of pawpaw. Survival varied by species. Acer saccharum seedlings were about one and a half times more likely to survive outside pawpaw than under pa...

Response of Acer saccharum seedlings to elevated O3 and CO2 concentrations

The effects of three times ambient [O3] (3x) and high [CO2] (650 µL L-1 CO2) alone and in combination were studied on 2-yr-old sugar maple (Acer saccharum) seedlings for 86 days in open top chambers. Sugar maple net CO2 assimilation rate and growth were not decreased by the O3 treatment after one growing season, and the epicuticular wax was not damaged compared with the control. The absence of response to the O3 treatment is attributable to the low stomatal conductance of this species resulting in a low O3 uptake, together with the succession of periods of high and low [O3], which allowed the seedlings to alleviate the oxidative stress. At the end of August, under high [CO2], the growth of the seedlings and net CO2 assimilation to stomatal conductance to CO2 ratio in the second flush of leaves had doubled. Under the environmental growth conditions of the chambers (high light, nutrients and water availabilities), the seedlings may benefit from the availability of CO2. Sugar maple seedlings may have a competitive growth advantage under elevated CO2 conditions and three times ambient [O3] did not decreased the fertilizing effect of CO2.

Response of Native and Exotic Maple Seedling Banks to Removal of the Exotic, Invasive Norway Maple (Acer platanoides)

WEBB, S. L., T H. PENDERGAST IV, AND M. E. DWYER (Drew University, Biology Department, Madison, NJ 07940.) Response of native and invasive maple seedling banks to removal of the exotic, invasive Norway maple (Acer platanoides). J. Torrey Bot. Soc. 128:000-000. 2001.-Acer platanoides is an exotic, invasive tree in eastern deciduous forests of North America where past research shows it to thrive in the forest interior and to suppress understory diversity. To test the efficacy of restoration strategies and to probe dynamics of this tree's seedling bank, trees and seedlings of Acer platanoides were removed in 1997 from a mixed maple forest carpeted by an even mix of exotic Acer platanoides and native Acer saccharum seedlings. The treatments were removal of trees (height > 1.5 m) and removal of small seedlings (height < 1.5 m), using a crossed design with a total of 80 permanent plots, all sampled before removals and two years later. After two years, removal of Acer platanoides trees had caused an increase in native Acer saccharum seedling densities over those in control areas and had caused a decrease of new Acer platanoides recruitment. Conversely, removal of Acer platanoides seedlings initiated far more new Acer platanoides than Acer saccharum seedlings. The Acer platanoides seedling bank was partially, but not fully, replenished two years after its removal. Although removal of canopy trees appears effective as a restoration tool, other exotic species (especially Lonicera japonica, Alliaria petiolata, and Robinia pseudoacacia) proliferated where tree removals opened the canopy. Restoring the pre-invasion community will thus require future intervention.

Soil pH-induced changes in root colonization, diversity, and reproduction of symbiotic arbuscular mycorrhizal fungi from healthy and declining maple forests

Acer saccharum Marsh. (sugar maple) is one of only few arbuscular mycorrhizal trees to form extensive stands in northern temperate biomes. Recent maple decline could result from altered intensity and quality of root colonization by associated mycobionts or possible shifts in symbiotic fungal community composition following environmental stresses. In this study the effects on arbuscular mycorrhizal fungi of soil acidification, one of several proposed causal stresses underlying forest decline, and remedial liming were investigated under glasshouse conditions. Acer saccharum seedlings were grown in unsterilized, pH altered, forest soils from healthy and declining maple stands. Over a range of treatment pHs normally tolerated by A. saccharum, fungal populations and responses to pH changes differed between the two soils. The declining site with more acidic soil had an initially larger spore population but lower taxonomic diversity than the healthy site. However, liming stimulated sporulation of several taxa initially apparently absent from the declining site spore population. The quantity of colonization generally increased with pH for both sites. Five Glomus taxa and Scutellospora calospora (Nicol. &amp; Gerd.) Walker &amp; Sanders are added to the list of fungi known to form arbuscular mycorrhizas with A. saccharum, and the known range of Acaulospora cavernata Blaszkowski is extended from Poland to eastern North America.

Soil pH-induced changes in root colonization, diversity, and reproduction of symbiotic arbuscular mycorrhizal fungi from healthy and declining maple forests

Acer saccharum Marsh. (sugar maple) is one of only few arbuscular mycorrhizal trees to form extensive stands in northern temperate biomes. Recent maple decline could result from altered intensity and quality of root colonization by associated mycobionts or possible shifts in symbiotic fungal community composition following environmental stresses. In this study the effects on arbuscular mycorrhizal fungi of soil acidification, one of several proposed causal stresses underlying forest decline, and remedial liming were investigated under glasshouse conditions. Acer saccharum seedlings were grown in unsterilized, pH altered, forest soils from healthy and declining maple stands. Over a range of treatment pHs normally tolerated by A. saccharum, fungal populations and responses to pH changes differed between the two soils. The declining site with more acidic soil had an initially larger spore population but lower taxonomic diversity than the healthy site. However, liming stimulated sporulation of several taxa in...

Leaf Mass Per Area, Nitrogen Content and Photosynthetic Carbon Gain in Acer saccharum Seedlings in Contrasting Forest Light Environments

Total daily photosynthetic photon flux density (PPFD) varied by two orders of magnitude across forest understorey, gap and clearing habitats for sugar maple (Acer saccharum) seedlings in south-western Wisconsin, USA. Area-based photosynthetic capacity (A max /area) was greater in clearing or gap than in understorey seedlings, but little photosynthetic acclimation was observed between gap and clearing seedlings. We observed significant correlations between A max and leaf nitrogen content (N) among seedling populations from the three habitats when expressed on an area basis, but not on a mass basis because of scaling of leaf mass per unit area (LMA) with N (...)

Water relations and gas exchange of Acer saccharum seedlings in contrasting natural light and water regimes.

Field measurements were made of leaf photosynthesis (A), stomatal conductance (g) and leaf water relations for sugar maple (Acer saccharum Marsh.) seedlings growing in a forest understory, small gap or large clearing habitat in southwestern Wisconsin, USA. Predawn water status, leaf gas exchange and plasticity in field and laboratory water relations characteristics were compared among contrasting light environments in a wet year (1987) and a dry year (1988) to evaluate possible interactions between light and water availability in these habitats. Leaf water potentials (Psi(leaf)) at predawn and midday were lower for clearing than gap or understory seedlings. Acclimation of tissue osmotic potentials to light environment was observed among habitats but did not occur within any of the habitats in response to prolonged drought. During a summer drought in 1988, decreases in daily maximum g (g(max)) and maximum A (A(max)) in clearing seedlings were correlated with predawn Psi(leaf), which reached a seasonal minimum of -2.0 MPa. Under well-watered conditions, diurnal fluctuations in Psi(leaf) of up to 2.0 MPa in clearing seedlings occurred along with large midday depressions of A and g. In a wet year, strong stomatal responses to leaf-to-air vapor pressure difference (VPD) in sunny habitats were observed over nine diurnal courses of gas exchange measurements on seedlings in a gap and a clearing. Increasing stomatal limitations to photosynthesis appeared to be responsible for the reduction in A at high VPD for clearing seedlings. In understory seedlings, however, low water-use efficiency and development of leaf water deficits in sunflecks was related to reduced stomatal limitations to photosynthesis relative to seedlings in sunny habitats. Predawn Psi(leaf) and VPD appear to be important factors limiting carbon assimilation in sugar maple seedlings in light-saturating irradiances, primarily through stomatal closure. The overall results are consistent with the idea that sugar maple seedlings exhibit "conservative" water use patterns and have low drought tolerance. Leaf water relations and patterns of water use should be considered in studies of acclimation and species photosynthetic performance in contrasting light environments.

The Physiological Basis for the Contrasting Distribution Patterns of Acer Saccharum and Thuja Occidentalis at Cliff Edges

(1) Photosynthesis of intact Thuja occidentalls and Acer saccharum seedlings was measured to establish if changes of sensitivity to radiant intensity during early ontogeny could explain their mutually exclusive distribution patterns at cliff edges of the Niagara Escarpment, in southern Ontario, Canada. (2) Measurements of photosynthesis were made following growth at five intensities of photosynthetically active radiation (PAR) and two moisture pre-treatment regimes chosen to simulate conditions found in the field. (3) Two-week-old seedlings (cotyledon stage), six-week-old plants (first adult leaves in Acer and juvenile foliage in Thuja), and two-year-old plants (in Thuja only) were used. (4) Thuja cotyledons had higher net photosynthetic rates and lower specific leaf weights than Acer cotyledons. Thuja may thus rely more on immediate carbon fixation during establishment than Acer, which may rely more on stored metabolites at this stage of development. (5) Thuja seedlings gained more carbon than Acer at lower PAR levels. More Thuja than Acer seedlings survived the first six weeks of growth at the two lowest PAR levels, and were then able to survive an imposed drought for a mean of 5 5 days. (6) Six-week-old Acer seedlings showed low rates of net photosynthesis, biomass production and survival at low PAR and moisture levels, but a greater capacity to respond to favourable conditions. (7) The low net photosynthetic rate of Acer under simulated cliff-edge conditions suggests that it is excluded from the cliff-edge because it is intolerant of hostile conditions that occur there. Unlike Thuja, Acer can benefit from the productive environment in the deciduous forest. Thuja productivity and survival under simulated cliff edge and deciduous conditions were similar. This suggests that Thuja is the more tolerant of cliff-edge conditions but excluded from the deciduous forest zone by other processes.

Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies.

In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 μmol quanta m-2 s-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 μmol m-2 s-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO2 response. At PPFD-saturation CE was 0.018 μmol m-2 s-1/(μl/l). The apparent quantum efficiency (incident PPFD) at saturating CO2 was 0.05-0.08 mol/mol. [Formula: see text] and PPFD-saturated CO2 exchange was 6-8 μmol m-2 s-1. The ratio of internal CO2 concentration to external (C i /C a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C i /C a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO2 exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5-10%.