Previous studies have shown that there is heterogeneity of structure and function across surfaces in leaves of small-leaved plants. However, little is known of the hydraulic and photosynthetic design of giant leaves. Prof. CAO Kunfang of Xishuangbanna Tropical Botanical Garden (XTBG) and his students chose Alocasia macrorrhiza as their study material to test the hypothesis that the heterogeneity of structure and function might be very strong in large-leaved plant species.

Alocasia macrorrhiza (L.) Schott. (Araceae) is a perennial herbaceous species which bears giant leaves of up to 1–2 m in length and width. This species provides a model system for studying the heterogeneity of leaf structure and function within a large leaf.

The researchers tested the hypothesis that the heterogeneity in leaf structure and function would contribute to higher temperatures and a lower gas exchange rate in the outer lamina regions, given increased hydraulic path length and resistance in the distal parts. Such an effect could be particularly strong in large leaves, and may correspond with greater stomatal closure and/or the development of fewer and/or smaller stomata, and thus induced a lower photosynthetic rate in the leaf outer regions. To test the hypothesis, they examined stomatal conductance, photosynthetic rate and PSII function, as well as leaf water potential, and leaf temperature at midday, as well as leaf structural and anatomical traits, along length and width transects from the center to the outer regions within the large leaves of A. macrorrhiza.

As hypothesized, the researchers found a strong heterogeneity in structure and physiology across giant leaves in Alocasia macrorrhiza. Leaves appeared to function typically with diminished function in the marginal areas, and giant leaves had especially steep within-leaf gradients in their structure and physiology.

The study entitled “The Heterogeneity and Spatial Patterning of Structure and Physiology across the Leaf Surface in Giant Leaves of Alocasia macrorrhiza” has been published in PLoS ONE, 8(6): e66016. doi:10.1371/journal.pone.0066016