Mycorrhizal Status of Chinese Tallow, An Exotic Invasive Tree.

Chinese tallow tree (Triadica sebifera) is highly invasive in the coastal prairies of the Gulf of Mexico, altering the structure and function of these endangered ecosystems.  The objectives of this study were to: (1) Assess the mycorrhizal status of tallow tree; and (2) Examine the degree to which mycorrhizal symbiosis might contribute to the invasive success of tallow trees.  Research was conducted in a semi-green house at the University of Houston Coastal Center, (La Marque, Texas).  Tallow seeds from the study area were collected and planted in 3.8L pots containing local soil.  Half of the plants were grown in soils to which fungicide (Rovral) was added regularly, while the other half served as untreated controls, (n = 33 plants/treatment).  After nine months, we recorded shoot height, shoot diameter and leaf count.  Soil cores containing root samples were obtained, and root tissues were stained with trypan blue and examined microscopically to assess mycorrhizal status.  In addition, leaf tissues were analyzed for δ¹⁵N by isotope ratio mass spectrometry to provide an additional assessment of mycorrhizal status.  Microscopy revealed that tallow trees grown in both control and fungicide treated soils possessed arbuscular mycorrhizal (AM) fungi,  and that mycorrhizal colonization increased significantly in fungicide treated soils (p<0.001).  Shoot height, and leaf count both increased significantly with fungicide addition (p<0.05).  Foliar δ¹⁵N values of fungicide treated plants were significantly higher than plants in the control group (p<0.0001), suggesting that the more extensive mycorrhizal infection of fungicide treated plants may have altered sources of plant N and/or their mode of acquisition and uptake.  Results indicate that tallow trees possess AM fungi, that this mycorrhizal relationship is somehow enhanced by regular treatment with a commercial fungicide, and that fungicide treatment appeared to alter N sources and/or mode of N uptake by this invasive tree species.