Materials on Plant Leaf Surfaces are Deliquescent in a Variety of Environments

Many materials on plant leaf surfaces are hygroscopic, and they impact foliar applied agrochemicals, foliar water uptake, gas exchange and stomatal density. Few studies are available on the nature of these substances, and we quantify how hygroscopic these materials are. Water vapor sorption experiments on twelve leaf washes were conducted and analyzed with inductively coupled plasma-optical emission spectroscopy and X-ray diffraction. Oils were found in all Eucalyptus samples studied. The leaf materials can deliquesce and form an aqueous solution in a variety of environments where plants grow, including glasshouses and by the ocean. All plant materials studied were hygroscopic. For mangroves that excrete salt to the leaf surfaces, significant sorption occurred at high humidity of a total of 316 mg (~0.3 mL) over 6-10 leaves. These fitted a Guggenheim, Anderson, and de Boer isotherm; mostly due to sodium chloride, though other more hygroscopic materials were also present.

Foliar Water Uptake in the Needles of Pinus Torreyana

In semi-arid climate systems that encounter low clouds or fog, many plants have adapted to capture atmospheric moisture on the foliar surface. The natural habitat of Pinus torreyana, the Torrey pine, is restricted to two locales in coastal Southern California that experience substantial fog and low clouds during the dry months of a Mediterranean climate. In this study, droplet contact angles were used to assess surface wettability, and droplet uptake was used to measure the foliar water uptake rate along a needle. We demonstrated that there are only remnants of epicuticular wax on the needle. The results showed that the needle surface of P. torreyana, including under the base sheath, is hydrophilic and capable of direct water uptake. There are small spatial gradients in the uptake pattern, but the variability is high and the statistical significance is not strong. However, the decrease in uptake at higher contact angles can be described by an ordinary linear regression (r2 = 0.45, p = 4 x 10-8). On average, the foliar uptake of the adaxial surface of a one-year-old needle is 2.88 ± 0.60 x 10-2 mg cm–2s–1. In comparison, the uptake rates by the adaxial surfaces of four local broadleaf plants are between 0.05 and 0.6 of that of P. torreyana.

Functional assembly of tropical montane tree islands in the Atlantic forest is shaped by stress-tolerance, bamboo-invasion and facilitation

Aims: Amidst the Campos the Altitude (Highland Grasslands) in the Brazilian Atlantic Forest, woody communities grow either clustered in tree islands or interspersed within the herbaceous matrix. The functional ecology, diversity and biotic processes shaping these communities are largely unstudied. We characterised the functional assembly and diversity of these tropical montane woody communities and investigated how those communities fit within the Grime’s CSR (C – competitor, S – stress-tolerant, R – ruderal) scheme, what trade-offs they exhibit and how traits and functional diversity vary in response to bamboo invasion. Methods: We sampled five leaf traits and wood density along transects covering the woody communities both inside tree islands and outside (i.e. woody plants in the grasslands community) to characterise the functional ecology of the community. We used Kruskal-Wallis test, t-test and variation partitioning to determine effects of inside vs outside the tree island and bamboo invasion on traits, woody species diversity and functional diversity. Results: We found a general SC/S strategy with drought-related functional trade-offs. Woody plants in tree islands had more acquisitive traits, whereas woody plants within the grasslands had more conservative traits. Trait variation was mostly taxonomically driven, and species composition varied between inside and outside tree islands. Leaf thickness, wood density and foliar water uptake were unrelated to CSR-strategies, suggesting independent trait dimensions and multiple drought-coping strategies within the predominant S-strategy. Bamboo-invaded islands showed lower Simpson diversity, lower functional dispersion, lower foliar water uptake and greater leaf thickness than non-invaded tree islands. Conclusions: The observed functional assembly in response to bamboo and facilitation have implications for future forest expansion and response of the communities to climate change. Further studies on eco-physiological and establishment traits and the mechanisms behind biotic interactions are needed to better understand the response of these communities to future environmental changes.