Tong You-Gui, Ding Xiao-Xi, Zhang Kai-Cun, Yang Xin, Huang Wei
Forestry Bureau of Dongchuan County Kunming, China.
Kunming Forest Resources Administration Kunming, China.
Front Plant Sci. 2016 Feb 15;7:130. doi: 10.3389/fpls.2016.00130. eCollection 2016.
The gall wasp, Leptocybe invasa (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 Eucalyptus camaldulensis. However, the physiological mechanisms underlying how L. invasa inhibits the growth of plants of E. camaldulensis 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 L. invasa depresses hydraulic conductance of stem and leaf. In the present study, we examined the effects of L. invasa galling on hydraulic architecture and photosynthetic parameters in E. camaldulensis plants. We found that galling of L. invasa significantly decreased stem hydraulic conductance (K stem), midday leaf water potential (Ψmd), minor vein density, and stomatal density (SD). Furthermore, the stomatal conductance (g s), chlorophyll content, CO2 assimilation rate (A n) and photosynthetic electron flow were reduced in infected plants. Therefore, the galling of L. invasa not only declined the water supply from stem to leaves, but also restricted water transport within leaf. As a result, galled plants of E. camaldulensis reduced leaf number, leaf area, SD and g s to balance water supply and transpirational demand. Furthermore, galled plants had lower leaf nitrogen content, leading to decreases in chlorophyll content, CO2 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.
桉树枝瘿姬小蜂（Leptocybe invasa，膜翅目；姬小蜂科）是中东、地中海盆地、非洲、印度、东南亚和中国桉树林的一种毁灭性害虫。严重的瘿害会导致树叶卷曲，在极端情况下，可能会阻碍赤桉的树木生长。然而，桉树枝瘿姬小蜂抑制赤桉植物生长的生理机制尚不清楚。由于植物的生长速率主要取决于光合作用，而光合作用在很大程度上与水力结构相关，我们推测桉树枝瘿姬小蜂的瘿害会降低茎和叶的水力导度。在本研究中，我们研究了桉树枝瘿姬小蜂瘿害对赤桉植物水力结构和光合参数的影响。我们发现，桉树枝瘿姬小蜂的瘿害显著降低了茎水力导度（K茎）、午间叶水势（Ψmd）、小叶脉密度和气孔密度（SD）。此外，受感染植物的气孔导度（gs）、叶绿素含量、二氧化碳同化率（An）和光合电子流均降低。因此，桉树枝瘿姬小蜂的瘿害不仅减少了从茎到叶的水分供应，还限制了叶内的水分运输。结果表明，受到瘿害的赤桉植物通过减少叶片数量、叶面积、SD和gs来平衡水分供应和蒸腾需求。此外，受到瘿害的植物叶片氮含量较低，导致叶绿素含量、二氧化碳同化率和光合电子流下降。这些结果表明，水力结构的变化是导致受瘿害植物生长速率受到抑制的原因。
