Detrimental effects of vines on tree growth in successional environments have been frequently reported. Little is known, however, about the relative importance of below and aboveground competition from vines on tree growth. The objective of this study was to quantify and compare the growth responses of Liquidambar styraciflua saplings to below and/or aboveground competition with the exotic evergreen vine, Lonicera japonica (Japanese honeysuckle), and the native deciduous vine, Parthenocissus quinquefolia (Virginia creeper). Soil trenching and/or vine-trellising were used to control the type of vine competition experienced by trees. Comparisons among untrenched treatments tested for effects of belowground competition. Comparisons among trenched treatments tested for effects of aboveground competition. After two growing seasons, Lonicera japonica had a greater effect on the growth of L. styraciflua than did P. quinquefolia. This effect was largely due to root competition, as canopy competition only had a negative effect on tree growth when it occurred in combination with root competition. Leaf expansion was consistently and similarly affected by all treatments which involved belowground competition.

The role of Brazilian pine (Araucaria angustifolia) in the process of forest succession is a topic of increasing controversy. While some authors consider the species to be pioneer, others consider it to be a climax species in relict temperate forests. We designed a field experiment to assess the role of light availability on the regeneration of A. angustifolia. The following three forests, with contrasting patterns of the species regeneration, were selected at a National Forest in southern Brazil: a Pinus plantation, an Araucaria plantation and a native araucarian forest. We analysed the population structure of Brazilian pine, the vegetation architecture, the light regime experienced by seedlings and the height growth of seedlings and sprouts. Brazilian pine colonisation and regeneration were observed in the Pinus and Araucaria plantations, respectively. No seedlings were found in the native forest. The greatest foliage area index and canopy cover were found in the native forest and the smallest in the Pinus plantation. In spite of the architectural differences, the native forest and the Araucaria plantation had similar light conditions and they both had lower levels of irradiances than the Pinus plantation. Seedlings and sprouts of Brazilian pine were found to occupy spots in the Araucaria plantation with canopy cover greater than the average forest conditions. Considering the similarity of understorey light conditions between the Araucaria plantation and the native forest (where no regeneration was taking place), we concluded that light availability was not limiting the regeneration of the species. Tolerance to shading and other aspects of the species indicate that Brazilian pine is not strictly heliophyllous and pioneer and is able to be established in the forest understorey.

No abstract

Brazilian pine (Araucaria angustifolia [Bert.] O.Ktze.) is an indigenous conifer of the southern region of South America, typically regarded as a sun-loving species. However, there is insufficient information on the species’ behaviour under different irradiances to characterise its plasticity to light. The purpose of this work was to measure some ecophysiological responses of Brazilian pine seedlings to three irradiance levels: 100, 45 and 10% full sunlight. Thirty seedlings were grown under each of the irradiance treatments and, after 5 months, growth parameters, leaf chlorophyll concentration and in vivo nitrate reductase activity, in both leaves and roots, were analysed. There was no increase in shoot biomass allocation in response to shading, in contrast to results from other experiments. Only low-light seedlings showed significant increase in specific leaf area, as well as in the ratio of height to shoot biomass. Chlorophyll content and the ratio of chlorophyll a to chlorophyll b did not vary among treatments. Nitrate reductase activity was detected only in roots and was reduced in the low-light treatment. An overall analysis of the results points to a normal growth of Brazilian pine seedlings at both high- and medium-light sites, at least in their initial stages of development.

Background and aims Foliar water uptake has been reported for different species, including conifers living in drought-prone environments. We conducted three experiments to determine whether leaves might absorb mist water and how this affects the water relations of well-watered and water-stressed young plants of Araucaria angustifolia. Methods Three independent experiments were conducted using well-watered and water-stressed plants: immersion of shoot in water for the quantification of water uptake, the short-term exposure of plants to deuteriumenriched artificial mist, followed by the evaluation of plant water status and δ 2 H of xylem and soil water, and the use of the heat ratio method to measure the sap flow in saplings submitted to artificial mist. Results Foliar water uptake was demonstrated in both groups of plants, but only water-stressed plants showed a significant improvement of shoot water status. Isotope analyses indicated release of mist water in waterstressed plants rhizosphere's, and measurements of sap flow pointed to flow reversals in saplings exposed to mist, after a soil drought period. Conclusions The results confirm the capacity of A. angustifolia for absorbing water deposited in its leaves and demonstrate that leaf-absorbed water can be transported through the xylem to the soil close to the roots and improve plant water status.

This 2‐year field study examined stomatal conductance, photosynthesis, and biomass allocation of Liquidambar styraciflua saplings in response to below‐ and aboveground competition with the vines Lonicera japonica and Parthenocissus quinquefolia. Vine competition did not affect stomatal conductance of the host trees. The leaf photosynthetic capacity and photosynthetic nitrogen‐use efficiency were significantly reduced by root competition with vines, either singly or in combination with aboveground competition, early in the second growing season. However, such differences disappeared by the end of the second growing season. Trees competing below ground with vines also had lower allocation to leaves compared with steins. Aboveground competition with vines resulted in reduced photosynthetic capacity per unit leaf area, but not per unit leaf weight, in trees. No correlation was found between single leaf photosynthetic capacity and tree growth. In contrast, a high positive correlation existed between allocation to leaves and diameter growth. Results from this study suggest that allocation patterns are more affected than leaf photosynthesis in trees competing with vines.

Competitive effects of vines on their tree hosts are well documented, but the mechanisms involved in these interactions are poorly understood. The objectives of this study were to measure the effects of below‐ and/or aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on availability of light, water, and nitrogen to the host tree Liquidambar styraciflua, and to examine the relationship between resource availability and tree growth. Light penetration through tree canopies, pre‐dawn leaf water potential, and leaf nitrogen concentration were used as predictors of light, water, and nitrogen availability to the tree, respectively. Vine presence significantly reduced light penetration through the tree canopies, but this reduction was not clearly related to the growth responses of trees. Vines did not reduce the pre‐dawn leaf water potential of competing trees, which was consistently above ‐0.5 MPa for the duration of the study. Leaf nitrogen concentration of trees, on the other hand, was significantly reduced by belowground competition with L. japonica. The positive correlation between the annual average leaf nitrogen concentration and tree diameter growth suggested that competition for nitrogen mediated the effects of belowground competition of vines on tree growth.

Competitive effects of vines on their tree hosts are well documented, but the mechanisms involved in these interactions are poorly understood. The objectives of this study were to measure the effects of below‐ and/or aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on availability of light, water, and nitrogen to the host tree Liquidambar styraciflua, and to examine the relationship between resource availability and tree growth. Light penetration through tree canopies, pre‐dawn leaf water potential, and leaf nitrogen concentration were used as predictors of light, water, and nitrogen availability to the tree, respectively. Vine presence significantly reduced light penetration through the tree canopies, but this reduction was not clearly related to the growth responses of trees. Vines did not reduce the pre‐dawn leaf water potential of competing trees, which was consistently above ‐0.5 MPa for the duration of the study. Leaf nitrogen concentration of trees, on the other hand, was significantly reduced by belowground competition with L. japonica. The positive correlation between the annual average leaf nitrogen concentration and tree diameter growth suggested that competition for nitrogen mediated the effects of belowground competition of vines on tree growth.