No abstract

Many Liriomyza species are pests of agricultural and ornamental plants. In the past two decades, the occurrence and distribution of certain Liriomyza species have changed dramatically, leading to an extensive body of research papers. First, we review the association of thermal tolerance with population dynamics, geographic distribution, and species displacement. Differences in thermal tolerances between species result in their differential geographic locations and overwintering ranges. Displacements among Liriomyza species are associated with their temperature adaptation. We examine the chemical linkage of plants, Liriomyza, and their parasitoids. Chemical compounds from host and nonhost plants mediate the behavior of Liriomyza and their parasitoids. Liriomyza and their parasitoids use chemical cues to locate their hosts. Induced compounds can be used as attractants of parasitoids or repellents of Liriomyza. Thus, understanding the thermal tolerances and chemical ecology of Liriomyza may enable researchers to predict geographic distribution and to develop novel control strategies.

The effects of heat shock on survival and reproduction of two whitefly species, Trialeurodes vaporariorum (Westwood) and Bemisia tabaci (Gennadius) biotype B (Homoptera: Aleyrodidae), were compared in the laboratory. Whitefly adults were exposed to 26 (control), 37, 39, 41, 43 and 45°C for 1 hour, and were then maintained at 26°C. Adult survival was significantly affected when they were exposed at 41°C or higher for B. tabaci or 39°C or higher for T. vaporariorum. All males of T. vaporariorum were killed at 45°C. In both whitefly species, females were more tolerant to high temperatures at 39°C or higher than males. Female fecundity was not significantly different when B. tabaci adults were heat-shocked at all temperatures. In contrast, the fecundity of T. vaporariorum females declined with the increase of temperature, and only a few eggs were oviposited at 43°C. Survival or hatch rates of the F1 nymphs of both whitefly species declined as heat-shock temperature increased, and no T. vaporariorum nymphs were hatched at 43°C. Similarly, percentages of F1 offspring developing to adults for both whitefly species also declined as the heat-shock temperature increased. Sex ratios of the F1 offspring were not significantly affected for T. vaporariorum but were slightly affected for B. tabaci at 43 and 45°C. The significance of heat shock in relation to dispersal, distribution and population dynamics of the two whitefly species is discussed.

To investigate N metabolism of two contrasting Populus species in acclimation to low N availability, saplings of slow-growing species (Populus popularis, Pp) and a fast-growing species (Populus alba × Populus glandulosa, Pg) were exposed to 10, 100, or 1000 μM NH4NO3. Despite greater root biomass and fine root surface area in Pp, lower net influxes of NH4 + and NO3 – at the root surface were detected in Pp compared to those in Pg, corresponding well to lower NH4 + and NO3 – content and total N concentration in Pp roots. Meanwhile, higher stable N isotope composition (δ15N) in roots and stronger responsiveness of transcriptional regulation of 18 genes involved in N metabolism were found in roots and leaves of Pp compared to those of Pg. These results indicate that the N metabolism of Pp is more sensitive to decreasing N availability than that of Pg. In both species, low N treatments decreased net influxes of NH4 + and NO3 –, root NH4 + and foliar NO3 – content, root NR activities, total N concentration in roots and leaves, and transcript levels of most ammonium (AMTs) and nitrate (NRTs) transporter genes in leaves and genes involved in N assimilation in roots and leaves. Low N availability increased fine root surface area, foliar starch concentration, δ15N in roots and leaves, and transcript abundance of several AMTs (e.g. AMT1;2) and NRTs (e.g. NRT1;2 and NRT2;4B) in roots of both species. These data indicate that poplar species slow down processes of N acquisition and assimilation in acclimation to limiting N supply.

To characterize the dynamics of Cd²⁺ flux in the rhizosphere and to study cadmium (Cd) plant-internal partitioning in roots, wood, bark and leaves in relation to energy metabolism, reactive oxygen species (ROS) formation and antioxidants, Populus × canescens plantlets were exposed to either 0 or 50 µM CdSO₄ for up to 20 days in the nutrient solution. A strong net Cd²⁺ influx in root apex was observed after Cd exposure for 24 h, even if net Cd²⁺ influx decreased gradually in roots. A large amount of Cd was accumulated in roots. Cd ions were uploaded via the xylem to leaves and further transported to the phloem where significant accumulation was detected. Cd accumulation led to decreased photosynthetic carbon assimilation but not to the depletion in soluble carbohydrates. Increased levels of ROS were present in all tissues, except the bark of Cd-exposed poplars. To combat Cd-induced superoxide and hydrogen peroxide, P. × canescens appeared to rely mainly on the formation of soluble phenolics as these compounds showed the highest accumulation in the bark and the lowest in wood. Other potential radical scavengers such as proline, sugar alcohols and antioxidant enzymes showed tissue- and exposure time-specific responses to Cd. These results indicate a complex pattern of internal Cd allocation in P. × canescens resulting in higher ROS stress in wood than in bark and intermediate responses in roots and leaves, probably because of differential capacities of these tissues for the production of protective phenolic compounds.

ABSTRACTuptake, transport and detoxification processes were increased in EMs compared to non-mycorrhizal roots. Higher CO2 assimilation, improved nutrient and carbohydrate status, and alleviated oxidative stress were found in mycorrhizal compared to non-mycorrhizal poplars despite higher Cd 2+ accumulation. These results indicate that mycorrhizas increase Cd 2+ uptake, probably by an enlarged root volume and overexpression of genes involved in Cd 2+ uptake and transport, and concurrently enhance Po. × canescens Cd tolerance by increased detoxification, improved nutrient and carbohydrate status and defence preparedness.

Poplar plants are cultivated as woody crops, which are often fertilized by addition of ammonium (NH4(+)) and/or nitrate (NO3(-)) to improve yields. However, little is known about net NH4(+)/NO3(-) fluxes and their relation with H(+) fluxes in poplar roots. In this study, net NH4(+)/NO3(-) fluxes in association with H(+) fluxes were measured non-invasively using scanning ion-selective electrode technique in fine roots of Populus popularis. Spatial variability of NH4(+) and NO3(-) fluxes was found along root tips of P. popularis. The maximal net uptake of NH4(+) and NO3(-) occurred, respectively, at 10 and 15 mm from poplar root tips. Net NH4(+) uptake was induced by ca. 48 % with provision of NO3(-) together, but net NO3(-) uptake was inhibited by ca. 39 % with the presence of NH4(+) in poplar roots. Furthermore, inactivation of plasma membrane (PM) H(+)-ATPases by orthovanadate markedly inhibited net NH4(+)/NO3(-) uptake and even led to net NH4(+) release with NO3(-) co-provision. Linear correlations were observed between net NH4(+)/NO3(-) and H(+) fluxes in poplar roots except that no correlation was found between net NH4(+) and H(+) fluxes in roots exposed to NH4Cl and 0 mM vanadate. These results indicate that root tips play a key role in NH4(+)/NO3(-) uptake and that net NH4(+)/NO3(-) fluxes and the interaction of net fluxes of both ions are tightly associated with H(+) fluxes in poplar roots.

To investigate how N-fertilization affects the growth, carbon and nitrogen (N) physiology, and wood properties of poplars with contrasting growth characteristics, slow-growing (Populus popularis, Pp) and fast-growing (P. alba×P. glandulosa, Pg) poplar saplings were exposed to different N levels. Above-ground biomass, leaf area, photosynthetic rates (A), instantaneous photosynthetic nitrogen use efficiency (PNUE i), chlorophyll and foliar sugar concentrations were higher in Pg than in Pp. Foliar nitrate reductase (NR) activities and root glutamate synthase (GOGAT) activities were higher in Pg than in Pp as were the N amount and NUE of new shoots. Lignin contents and calorific values of Pg wood were less than that of Pp wood. N-fertilization reduced root biomass of Pg more than of Pp, but increased leaf biomass, leaf area, A, and PNUEi of Pg more than of Pp. Among 13 genes involved in the transport of ammonium or nitrate or in N assimilation, transcripts showed more pronounced changes to N-fertilization in Pg than in Pp. Increases in NR activities and N contents due to N-fertilization were larger in Pg than in Pp. In both species, N-fertilization resulted in lower calorific values as well as shorter and wider vessel elements/fibres. These results suggest that growth, carbon and N physiology, and wood properties are more sensitive to increasing N availability in fast-growing poplars than in slow-growing ones, which is probably due to prioritized resource allocation to the leaves and accelerated N physiological processes in fast-growing poplars under higher N levels.