Abundance of Alnus incana ssp. rugosa in Adirondack Mountain shrub wetlands and its influence on inorganic nitrogen.

The purpose of this research was to determine the abundance of the nitrogen-fixing shrub, Alnus incana ssp. rugosa (speckled alder), in shrub wetlands of the Adirondack Mountain region of New York State and to determine whether its abundance affects the concentration or accumulation of inorganic nitrogen in wetland substrates. Alder/willow wetlands are the second most common wetland type in the Adirondack region. The Adirondack Park Agency's digital GIS database of wetland types was used to determine the areal extent of alder/willow wetlands in the Adirondacks. Randomly selected wetlands were sampled to determine the size and abundance of alder. Alder densities averaged approximately 7000 stems ha(-1) and alder was present in 75% of the wetlands. As an indication of short-term accumulation of NO(3-) and NH4(+) in wetland substrates, ion exchange resins were used to sample ground water in high and low alder density wetlands as well as from wetlands lacking alder and dominated by conifers. Additionally, NO(3-) and NH(4+) concentrations in ground water samples were measured. NH(4+) accumulation levels from exchange resins were low for all wetland types while groundwater NH(4+) concentration was highest in the low-density alder sites. Wetlands with high alder density had approximately six times higher NO(3-) accumulation than other wetlands. Substrate groundwater NO(3-) concentrations in wetlands of high-density alder exceeded by three times levels in low or no alder wetlands, showing the importance of alder to local N budgets. To assess the recovery of shrub wetlands from acidification, future studies should determine the fate of fixed N in wetland systems.

Influence of nutrient availability and tree wildling density on nutrient uptake by Oxalis acetosella and Acer saccharum.

Loss of nutrients following pulses of nutrient input in northern hardwood forests and the general effects of atmospheric deposition on forest communities are of concern. Uptake of nutrients by ground layer vegetation, including herbs and tree wildlings, may be important in both of these processes. We brought plants from the field (Catskill Mts, New York) and grew them under controlled environment conditions at two nutrient input levels to determine responses of Oxalis acetosella and Acer saccharum to increased nutrient input and tree wildling density. Oxalis nutrient concentration increased for many nutrients compared to field plants. Both species doubled their P concentration when P input doubled. Biomass of Oxalis was unaffected by both nutrient input level and Acer wildling density. Acer showed a similar response to increased nutrient input and its density did not affect the response of Oxalis to increased nutrient input. Results indicate that both species may be important to nutrient retention in northern hardwood forests.

Symbiotic N2 fixation of Alnus incana ssp. rugosa in shrub wetlands of the Adirondack Mountains, New York, USA.

Surface waters in forested watersheds in the Adirondack Mountains and northern New York State are susceptible to nitrogen (N) saturation. Atmospheric deposition of N to watersheds in this region has been measured but the extent of internal N inputs from symbiotic N2 fixation in alder-dominated wetlands is not known. We estimated N2 fixation by speckled alder in these wetlands by the 15N natural abundance method and by acetylene reduction using a flow-through system. Foliar N derived from fixation (%Ndfa) was estimated for five wetlands. The δ15N of speckled alder foliage from four of the five sites did not differ significantly (P≤0.05) from that of nodulated speckled alders grown in N-free water culture (-1.2±0.1‰). Estimates from the 15N natural abundance method indicated that alders at these sites derive 85-100% of their foliar N from N2 fixation. At one of the sites, we also measured biomass and N content and estimated that the alder foliage contained 43 kg N ha-1 of fixed N in 1997. This estimate was based on a foliar N content of 55.4±7 kg N ha-1 (mean±SE), 86±4%Ndfa, and an assumption that 10% of foliar N was derived from reserves in woody tissues. At this site, we further estimated via acetylene reduction that 37±10 kg N ha-1 was fixed by speckled alders in 1998. This estimate used the theoretical 4:1 C2H2 reduction to N2 fixation ratio and assumed no night-time fixation late in the season. Nitrogen inputs in wet and dry deposition at this site are approximately 8 kg N ha-1 year-1. We conclude that speckled alder in wetlands of northern New York State relies heavily on N2 fixation to meet N demands, and symbiotic N2 fixation in speckled alders adds substantial amounts of N to alder-dominated wetlands in the Adirondack Mountains. These additions may be important for watershed N budgets, where alder-dominated wetlands occupy a large proportion of watershed area.

Response of tree seedlings to aluminum.

This review focuses on the mechanisms underlying aluminum (Al) toxicity in trees. The major topics discussed include the uptake and localization of Al, effects of Al on growth and composition, factors determining the response to Al, proposed mechanisms of Al resistance, and the occurrence of Al phytotoxicity under field conditions.

Sensitivity of red oak (Quercus rubra L.) and American beech (Fagus grandifolia Ehrh.) seedlings to sodium salts in solution culture.

Sodium salt sensitivity of red oak (Quercus rubra L.) and American beech (Fagus grandifolia Ehrh.) was evaluated in solution culture. Both species showed symptoms of salt injury when grown in the presence of less than 10 mM Na. In red oak, leaf symptoms first appeared at a sodium concentration of 6.0 mM and leaf weight was significantly reduced at 7.5 mM Na. Leaf, stem and root dry weights of American beech were significantly reduced in the presence of 4.0 mM sodium. In both species, browning of leaf margins and necrosis were evident in the Na-treated plants. The observed symptoms were associated with high concentrations of sodium in the tissues. Neither species appears to have control over sodium uptake and translocation.

Effects of aluminum on growth, development, and nutrient composition of honeylocust (Gleditsia triacanthos L.) seedlings.

Hydroponic experiments were conducted to determine the effects of aluminum (Al) on root development, shoot morphology and the nutrient composition of honeylocust seedlings (Gleditsia triacanthos L.). Seedlings were grown at pH 4 in a nutrient solution containing 0, 50, 150, 600 or 1500 microM Al. Within seven days, there were significant differences in root growth and root nutrient composition between control seedlings and seedlings grown in the presence of 150 or 600 microM Al. By day 14, significant reductions in leaf production and plant height were observed in seedlings treated with 1500 microM Al. At the lowest Al concentration, 50 microM, leaf size and expansion rates were significantly lower than in the controls. By the third week of the experiment, Ca and Mg concentrations in young leaves of the Al-treated seedlings were significantly lower than in leaves of control plants. Analysis of old leaf tissue, however, revealed no consistent pattern of nutrient concentration with Al treatment.