New Evidence for the Hypothesis of Reducing Natural Enemy Pressure of Eupatorium adenophorum: Solenopsis invicta Competing with Doxrylus orientalis to Feed on E. adenophorum

Natural enemy insects are important factors in regulating plant invasion. The interactions between multiple insect species resulting from invasive plants remain poorly understood despite their potential. We observed notorious invasive plants Eupatorium adenophorum Sprengel were competedly fed by Solenopsis invicta Buren (Hymenoptera: Formicidae) and Dorylus orientalis Westwood (Hymenoptera: Formicidae) beside the scientific research base of Kunming University. It was first observed that D. orientalis was eating the epidermis, cortex, phloem and other root and stem tissues of E. adenophorum in soil. Two months later, it was observed that S. invicta ate the epidermis, cortex, phloem and other aboveground stem tissues of E. adenophorum. S. invicta attacked D. orientalis and displaced their living space by causing the later dead, injured, or even disabled. This phenomenon suggested that local herbivorous insects have adapted to E. adenophorum well, which will intensify the naturalization process of E. adenophorum in local habitats. In a homogeneous garden planting experiment of E. adenophorum conducted at the experimental base of Kunming University, the biomass of the introduced (China) populations of E. adenophorum was lower than that of the native (Mexico) populations, although there was no statistically significant difference. These results indicate a possible positive correlation between the increase in natural enemy pressure and the decrease in fitness of E. adenophorum.

Role and Mechanism of Action of Exogenous Salicylic Acid and Sodium Molybdate in Improving Cold Tolerance of Bougainvillea glabra

This study was conducted to comprehensively evaluate the effects of salicylic acid and sodium molybdate on cold tolerance of an ornamental plant Bougainvillea glabra and to provide a theoretical guidance for landscape maintenance.B.glabra plants were treated with 0.5 mmol/L salicylic acid and 2.0 μmol/L alone or in combination,and then exposed to low temperature stress before physiological indices were measured.The results showed that all salicylic acid and sodium molybdate treatments reduced the relative conductivity and malondialdehyde( MDA) content of B.glabra to varying extents under the stress of low temperature,and more significant effect was achieved by using the two agents in combination.Oxygen free radicals production rate increased with decreasing temperature from 20 to 6 ℃,but declined with temperature decreasing from 3 to-3 ℃.The SOD activity of the control( CK) was significantly lower than that of other treatments at 0 and-3 ℃.The treatments with salicylic acid and sodium molybdate alone and in combination increased POD activity of B.glabra plants,especially at 0 ℃,as the POD activity of treatments T1,T2 and T3 was significantly higher than that of CK at 0 ℃.In addition,under low temperature stress,the contents of soluble sugar,starch and proline increased initially and decreased subsequently with temperature decreasing.The soluble sugar content at 3 ℃,starch and proline contents at 0 and-3 ℃ in treatments with salicylic acid and sodium molybdate alone and in combination were significantly higher than those of CK.All above results proved that salicylic acid and sodium molybdate are able to improve cold tolerance of B.glabra,and better effect can be achieved by using them together.

Effects of Formaldehyde and Low-light Stress on Growth and Nutrition of Hedera spp.

Potted seedlings of Hedera nepalensis and H. helix were exposed to formaldehyde and low light alone or in combination for four months, before the morphological and nutritive indices of the plants were measured to assess the effects of formaldehyde and low-light stress on the growth and nutrient accumulation of Hedera species. The results showed that treatment with either formaldehyde or low-light stress reduced leaf length, leaf width, stem length, stem diameter, root length and biomass, but increased leaf shape index of the two Hedera species. Treatment with formaldehyde alone increased root-shoot ratio, while treatment with formaldehyde ＋ low light or low light alone decreased root-shoot ratio of the two Hedera species. Under the stress of formaldehyde, soluble sugar content decreased, while starch content increased in roots, stems and leaves of the two Hedera species; total carbon content, proline content and carbon-to-nitrogen （C/N） ratio increased, while protein content and phosphorus content decreased in roots of the two Hedera species; the contents of total carbon, protein and total nitrogen in leaves of the two Hedera species; C/N ratio in roots of H. nepalensis increased; the C/N ratio in roots of H. nepalensis and that in leaves of the two Hedera species significantly increased. Under formaldehyde ＋ low light stress, the soluble sugar content decreased, while starch content increased in stems and leaves of the two Hedera species; starch content in roots of the two Hedera species decreased; the contents of protein and total nitrogen decreased, while C/N ratio increased in leaves of H. nepalensis ; proline content in roots and stems of the two Hedera species significantly increased.