Population Trends and Vertical Distribution of Plant-Parasitic Nematodes Associated with Vitis labrusca L. in Michigan

Nematode population trends and vertical distribution were monitored in a southwest Michigan vineyard (Vitis labrusca cv. Concord) from 1976 through 1983. Shallow (20 cm) and deep (90 cm) applications of 1,3-dichloropropene applied at 281 (shallow) plus 658 or 1,122 (deep) liters/ ha provided excellent control of Xiphinema americanum, Criconemella xenoplax, and Meloidogyne hapla. Populations of X. americanum remained below detectable levels for the entire 8-year experimental period where the fumigant was applied. X. americanum and C. xenoplax populations exhibited multiyear cycling in nonfumigated plots. M. hapla was first detected in 1978 and increased in prominence from 1980 through 1982. Criconemella spp. were commonly parasitized by an endoparasitic fungus. Parasitism was monitored and reported as an indication of nematode population quality.     

Ozone-3,6-dihydroxynaphtha-2,7-disulphonate chemiluminescence system is used for online ozone detection

The chemiluminescence (CL) reaction between ozone and 3,6-dihydroxynaphtha-2,7-disulphonate (DNDS) was found under alkaline conditions. Therefore, a novel CL system for ozone detection was established. The CL signal of the CL system is weak, and the CL signal is enhanced by adding nonionic surfactants. It was found that adding 16.4 g/l Triton X-100 can enhance the CL signal. The CL reagent activated by ultraviolet (UV) light produced a CL signal was nearly 10 times stronger than the CL reagent not activated by UV light; the CL signal was enhanced by adding 8 g/l NaHCO₃ to the CL reagent irradiated by UV light. Through the optimization of these test conditions, a high-selectivity, high-sensitivity online detection method for ozone CL was established. The linear range was 0.5–150 ppbv, and the limit of detection (LOD) was 0.092 ppbv (S/N = 3).     

A new gas injection method to enhance spatial utilization within a Free-Air CO2 Enrichment (FACE) system

Visual observations of smoke dispersion in a wind tunnel and a computational fluid dynamics (CFD) model were used to evaluate methods of improving the performance of Free-Air COT Enrichment (FACE) Systems for field studies of the effects of elevated CO₂ on vegetation. A special baffle, named an Enhanced Local Mixing (ELM) system, was observed to increase the turbulence and consequent dilution of fumigant gas in the atmosphere. Modelling results suggest that the ELM design reduces the spatial variation of fumigant gas concentration in small experimental plots. The potential reduction in CO₂ use and costs warrants further evaluation under Held conditions.     

Effects of increased UV-B radiation and elevated levels of tropospheric ozone on physiological processes in European beech (Fagus sylvatica)

As a consequence of the ongoing reduction of the stratospheric ozone layer, the vegetation is exposed to increasing levels of UV-B radiation (280–320 nm). In addition ozone in the troposphere is a pollutant and also capable of affecting the photosynthetic machinery. In this study, 5-year-old European beech trees were exposed from 1 July to October 1993 to two levels of UV-B radiation and two levels of ozone, alone and in combination, in open-top chambers equipped with lamps. The simulated UV-B levels corresponded to either clear sky ambient level or a 14% decrease in the stratospheric ozone column over eastern Denmark, resulting in a 23% difference in biologically effective UV-B (UV-B_BE) irradiance. The maximum UV-Bbe given was 8.61 kJ m⁻² day⁻¹. The ozone levels were either the ambient (average 32 nl l⁻¹) or ambient with ozone addition (average resulting concentration 71 nl l⁻¹). Compared to the control treatment (ambient UV-B, ambient O₃) the elevated levels of UV-B and O₃ affected the trees negatively, expressed as declines in net photosynthesis (P_n), stomatal conductance (g_s), chlorophyll fluorescence (F_v/F_m) and acceleration of senescence, measured as yellowing of the leaves. The UV-B treatment induced stomatal closure before the other treatments did. The magnitude of the decreases in P_n and F_v/F_m occurred in the order: control 3 3. Compared to the control, the combination treatment with high levels accelerated the visual senescence processes by ca 27 days, while for high UV-B and O₃ alone, there was an acceleration by 14 and 21 days, respectively. UV-B and O₃ in combination enhanced the negative effects compared with UV-B and O₃ alone. The P_n and F_v/F_m results could be related to this acceleration process. The chamber effect was investigated by comparing the control plots with a plot without open-top chamber. The trees in the chambers showed a higher P_n and F_v/F_m and a 14-day delayed senescence compared to the trees outside, probably caused by higher temperatures, a more protected environment and altered conditions inside the chambers.     

An experimental facility for free air humidity manipulation (FAHM) can alter water flux through deciduous tree canopy

A facility for free air humidity manipulation (FAHM) was established to investigate the effect of increased air humidity on trees’ performance and their canopy functioning with respect to rising air humidity predicted for Northern Europe. The FAHM system enables air relative humidity (RH) to be increased up to 18 units (%) over the ambient level during mist fumigation, depending on the wind speed inside the experimental stand. Water was dispersed inside 14 × 14 m experimental plots in the form of mist with an average particle size of 50 μm from June to August in 2008, and from May to September in 2009. The average increase in RH was 7 units (%) over the whole period of humidification in 2008 (P < 0.05). The average diurnal stem sap flux density per unit projected leaf area (F) in silver birch (Betula pendula Roth.) trees was 24.8% (P < 0.05) and 27.2% (P < 0.01) higher in control (C) plots compared to humidification (H) plots during misting in 2008 and 2009, respectively. However, the difference between C and H plots was statistically insignificant (P > 0.05) in silver birch on the days without misting. In hybrid aspen (Populus tremula L. × P. tremuloides Michx.) the average difference in F between C and H plots was 61.1% (P < 0.001) during mist fumigation in the summer of 2009. Nevertheless, the difference was considerable (38.8%; P < 0.001) also on the days without misting, reflecting the impact of plant inner factors on F as a result of long-term acclimation to fumigation. The leaves of silver birch in a humidified plot demonstrated up to 2.4 °C lower (P < 0.05) leaf temperature (T_L) compared to the control plot in 2009. The decline in T_L decreased the humidity gradient between leaf and air by about 1/3, whereas 2/3 of the effect was caused directly by changes in air humidity in the leaf boundary layer. Our preliminary data suggest that the FAHM experimental facility enables water fluxes through a deciduous tree canopy to be reduced and this effect is attributable both to the increased air humidity and decreased leaf temperature. Changes in these two basic factors may create considerable differences in the physiology, anatomy and nutrition of a whole tree, also affecting forest functioning in the light of global climate change.