AUTHOR=Tong You-Gui , Ding Xiao-Xi , Zhang Kai-Cun , Yang Xin , Huang Wei 

TITLE=Effect of the Gall Wasp Leptocybe invasa on Hydraulic Architecture in Eucalyptus camaldulensis Plants

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00130

DOI=10.3389/fpls.2016.00130

ISSN=1664-462X

ABSTRACT=<p>The gall wasp, <italic>Leptocybe invasa</italic> (Hymenoptera; Eulophidae), is a devastating pest of eucalypt plantations in the Middle East, the Mediterranean basin, Africa, India, South-East Asia, and China. Heavy galling causes the leaves to warp and in extreme cases it may stunt the growth of the trees of <italic>Eucalyptus camaldulensis</italic>. However, the physiological mechanisms underlying how <italic>L. invasa</italic> inhibits the growth of plants of <italic>E. camaldulensis</italic> are unclear. Because the growth rate of plants is mainly dependent on photosynthesis that is largely correlated with hydraulic architecture, we speculate that galling of <italic>L. invasa</italic> depresses hydraulic conductance of stem and leaf. In the present study, we examined the effects of <italic>L. invasa</italic> galling on hydraulic architecture and photosynthetic parameters in <italic>E. camaldulensis</italic> plants. We found that galling of <italic>L. invasa</italic> significantly decreased stem hydraulic conductance (<italic>K</italic><sub>stem</sub>), midday leaf water potential (Ψ<sub>md</sub>), minor vein density, and stomatal density (SD). Furthermore, the stomatal conductance (<italic>g</italic><sub>s</sub>), chlorophyll content, CO<sub>2</sub> assimilation rate (<italic>A</italic><sub>n</sub>) and photosynthetic electron flow were reduced in infected plants. Therefore, the galling of <italic>L. invasa</italic> not only declined the water supply from stem to leaves, but also restricted water transport within leaf. As a result, galled plants of <italic>E. camaldulensis</italic> reduced leaf number, leaf area, SD and <italic>g</italic><sub>s</sub> to balance water supply and transpirational demand. Furthermore, galled plants had lower leaf nitrogen content, leading to decreases in chlorophyll content, CO<sub>2</sub> assimilation rate and photosynthetic electron flow. These results indicate that the change in hydraulic architecture is responsible for the inhibition of growth rate in galled plants.</p>