Joseph E. Miller

Assessment of crop loss from ozone

The National Crop Loss Assessment Network (NCLAN) was set up to determine more accurately crop loss from ozone, sulfur dioxide, and nitrogen dioxide. The NCLAN consists of a group of government and nongovernment organizations cooperating in field work, crop production modeling, and economic studies to assess the immediate and long-term economic consequences of the effects of air pollution on crop production. The program will define the relationships between yields of major agricultural crops and doses of O/sub 3/, SO/sub 2/, NO/sub 2/ and their mixtures. These relationships will be used to assess the primary economic consequences of the exposure of agricultural crops to these pollutants. The program is also designed to advance the understanding of cause-effect relationships with the intent of developing simulation models. These nationally-coordinated field studies are designed to provide crop dose-response data that are as free of artifact as is currently possible using state-of-the-art technology. The basic exposure technique utilizes open-top chambers. These chambers have been well tested and permit control of gas(es) around the plant canopy, allowing specific pollution regimes to be imposed on experimental plants. (JMT)

Effects on photosynthesis, carbon allocation, and plant growth associated with air pollutant stress

Over the past 30 to 50 years, extensive literature has accumulated concerning air pollutant effects on plants. The relative degree of phytotoxicity of the common pollutant gases is known, and the potential for effects on many botanical classes of plants is understood somewhat. Knowledge is at a point where attempts are being made to assess and predict the effects of current or projected air pollutant levels on the growth or productivity of vegetation. The most successful attempts have been made with crops because the most extensive data are available in this area. The National Crop Loss Assessment Network (NCLAN) has made noteworthy contributions in the areas of generating empirical, field-based, dose—response data and of economic assessments (Heck et al., 1982; 1984; Adams et al., 1985). But, even in the case of assessment of crop losses due to air pollutants, it has become apparent that insufficient data or understanding exist to make predictions with a high degree of confidence. The NCLAN effort has clearly identified the need for additional information in the form of dose—response data concerning the interaction of air pollutants with other environmental variables and the need to establish the functional relationships between air pollution stress and plant growth and yield.

Is UV-B a Hazard to Soybean Photosynthesis and Yield? Results of an Ozone-UV-B Interaction Study and Model Predictions

Current levels of tropospheric ozone suppress photosynthesis and yield in soybean. Also, it has been suggested that increased ground-level UV-B as a result of stratospheric ozone depletion may have additional deleterious effects. A three-year field study, conducted in open-top chambers, was undertaken to uncover possible interactions between these putative stressors. Ozone treatments resulted in the expected and well-documented reductions in photosynthesis, yield and acceleration of senescence. However, UV-B treatments not only failed to induce any significant interactions, but did not induce any significant reductions in photosynthesis or yield, even at levels simulating a 35% column ozone depletion. Reconciliation of our data with other predictions of physiological dysfunction and crop losses due to increased UV-B was attempted by examining the models used to predict ground-level UV-B, ground truthing, and critically reviewing the literature. Comparison of ground-based measurements at our location with the Green et al. (9) model, frequently used to predict ground-level UV-B, showed consistent over-predictions of clear-sky UV-B of 32% on an annual basis. We believe that similar over-predictions have led some researchers to underestimate the actual dosages used, with the result that the effects reported would normally only occur at much higher UV-B levels and are much greater than would occur at the reported dosages. Lack of ground-level UV-B monitoring in many experiments has obscured and perpetuated this problem. Also, there generally has been no adjustment of enhancement levels for either season or weather conditions, except where modulated systems have been used, so that effects are additionally exaggerated for these reasons. Interpretation of experimental results is confounded by these four factors (model over-prediction, seasonal changes, weather changes, and failure to monitor UV-B) and made much more difficult when UV-B enhancement experiments are conducted under greenhouse growth conditions. Additional illustrative calculations for greenhouse conditions are included for consideration. Examination of the literature in light of these findings indicates there is little evidence that increased ground-level UV-B, well in excess of current predictions for the next century, will pose any hazard to soybean growth and productivity.

Response of soluble sugars and starch in field-grown cotton to ozone, water stress, and their combination

Abstract Ozone (O3) stress is known to reduce the growth and yield of a number of crops, and water stress can modify the extent of these effects. Both O3 and water stress alter the carbohydrate status of plants. Little is known, however, concerning O3 effects on carbohydrate pools of field-grown plants and whether water stress will modify the carbohydrate response to O3. Cotton (Gossypium hirsutum L. “McNair-235”) plants were exposed to five O3 concentrations in open-top field chambers for 12 hr/day throughout the growing season at two levels of soil water (well-watered or periodically water-stressed). The O3 concentrations ranged from 0.021 to 0.073 μl/l (seasonal mean 12 hr/day concentration). Plants were sampled from each plot on four occasions encompassing the early- to late-reproductive stages of growth. Soluble sugars (glucose, fructose and sucrose) and starch were measured in leaves, stems and roots at each sampling date. Analysis of variance was performed for main effects and interactions of O3 and water treatments at each sampling date (O3 effects were partitioned in linear and quadratic components). Effects of O3 and water stress on soluble carbohydrates and starch were most common in stems and roots. Ozone suppressed carbohydrate concentrations in all cases where significant O3 effects were detected in the absence of O3 × water interactions. On the other hand, soluble carbohydrate concentrations were greater in water-stressed plant tissues when effects were significant and in the absence of interactions. Water-stress effects on starch were variable. Interactions of O3 and water stress were not consistent but often included interaction with the quadratic O3 component.

Effects of continuous, low levels of ethylene on growth and flowering of Easter lily

Abstract Easter lilies (Lilium longiflorum Thunb. cultivar ‘Nellie White’) were continually exposed to 0, 0.01, 0.05 or 0.1 μl l−1 ethylene in air during growth and flowering. Shoot length was drastically reduced with 0.05 or 0.1 μl l−1 ethylene, but was increased by 0.01 μl l−1. Plants grown at 0.05 and 0.1 μl l−1 ethylene were unmarketable, while 0.01 μl l−1 treated plants were commercially acceptable. All ethylene levels caused reduction in total shoot and flower dry weights. Leaf unfolding rate was similar in all treatments, indicating that height differences were due to ethylene effects on internodal length rather than rate of leaf development. Flower numbers were reduced and buds abnormally curved on plants grown at 0.05 and 0.1 μl l−1 ethylene.

Model analysis of interactive effects of ozone and water stress on the yield of soybean

The interactive effects of ozone and water stress on the yield of soybean (Glycine max (L.) Merr. Davis) were addressed with a growth model of soybean. Two simulations were conducted, using the data from the exposures of soybean to ozone in open-top chambers under two soil moisture regimes, and the results of the simulations were compared. In the original simulation, soil moisture content was calculated based on a water budget using the actual precipitation and irrigation data. In the modified simulation, the soil water content was given as input data. In this case, soil moisture content was maintained at the same level across the ozone treatments regardless of different water use by the plants. Both simulations included the effect of reduced ozone flux to the leaves due to water stress, whereas only the original simulation included the effect of mitigated water stress due to reduced water use by the plants under higher ozone concentration. The water stress reduced ozone impact on soybean yield in the original simulation on the basis of the ozone dosecrop yield response relationship, but not in the modified simulation. The ozone uptake rate was reduced by water stress in the original simulation, but the relationship between seasonal mean ozone uptake rate and relative yield still showed reduced impact of ozone due to water stress. These results indicated that the alleviation of water stress by ozone due to reduced plant water use in ozone-treated plots can be a contributing factor in the reduction of ozone impact by water stress. The above conclusion was partly confirmed by the actual data for soil water content, which was significantly lower in the lowest ozone treatment than in the higher ozone treatments. Further experimental and modelling studies are needed to elucidate the mechanism of the ozone X water stress interaction.

Modeling the effects of ozone on soybean growth and yield.

A simple mechanistic model was developed based on an existing growth model in order to address the mechanisms of the effects of ozone on growth and yield of soybean [Glycine max. (L.) Merr. Davis] and interacting effects of other environmental stresses. The model simulates daily growth of soybean plants using environmental data including shortwave radiation, temperature, precipitation, irrigation and ozone concentration. Leaf growth, dry matter accumulation, water budget, nitrogen input and seed growth linked to senescence and abscission of leaves are described in the model. The effects of ozone are modeled as reduced photosynthate production and accelerated senescence. The model was applied to the open-top chamber experiments in which soybean plants were exposed to ozone under two levels of soil moisture regimes. After calibrating the model to the growth data and seed yield, goodness-of-fit of the model was tested. The model fitted well for top dry weight in the vegetative growth phase and also at maturity. The effect of ozone on seen yield was also described satisfactorily by the model. The simulation showed apparent interaction between the effect of ozone and soil moisture stress on the seed yield. The model revealed that further work is needed concerning the effect of ozone on the senescence process and the consequences of alteration of canopy microclimate by the open-top chambers.

Effects of rooting medium and fertilizer rate on response of white clover to tropospheric ozone

Two white clover (Trifolium repens L.) clones with varying sensitivity to O(3) are being developed as a system to indicate effects of ambient concentrations of tropospheric O(3) on plants. One clone (NC-S) is highly sensitive to O(3) and the other (NC-R) is highly resistant. The system relies on periodic measurement of foliar injury, foliar chlorophyll, and forage production of NC-S and NC-R grown in 15-liter pots throughout a summer season. Relative amounts of foliar injury and ratios (NC-S/NC-R) for chlorophyll and forage weight can be used to estimate biologically effective ambient O(3) concentrations. The effect of variation in rooting media formulation and fertilizer rate on response of NC-S and NC-R to ambient O(3) was determined in the present study. In the rooting medium experiment, clover was grown in three mixtures of sandy loam topsoil:course washed sand:Metro Mix 220 (ratios (by volume) of 2:1:1, 2:1:5, and 6:1:1). In the fertilizer experiment, clover was grown in the 2:1:1 medium at four fertilizer rates (soluble 5-11-26 (N-P-K) at 0.0, 0.5, 1.0, or 2.0 g per pot). Ozone caused more foliar injury, more chlorosis, and a greater decrease in forage production of NC-S than of NC-R in all studies. Rooting media treatments affected both clones similarly and occasional clone x media interactions were judged to be random. Forage production by NC-S, relative to that of NC-R, was generally greater in the 0.0 fertilizer treatment, but the forage ratios were similar at all other fertilizer treatments. The relative response of NC-S and NC-R to O(3) is fairly stable under cultural conditions that support normal plant growth.

Effects of ozone and water stress on net photosynthetic rate of field-grown soybean leaves

Detailed physiological measurements were taken in controlled field experiments to better elucidate how environmental stresses interact to affect a soybean plants physiology and growth. Nondestructive techniques were used to measure weekly and diurnal effects of ozone and water stress on net photosynthesis, stomatal resistance, and water status of field-grown soybean leaves. Open-top field chambers were used to expose soybeans to seasonal 12-h/day mean concentrations of 0.018 (CF), 0.059 (1.3NF) and 0.085 (1.9NF) ppm ozone. Soil water levels were well watered (WW) and water stressed (WS). Net carbon exchange-rate measurements (CER) were taken between 1000 and 1230h EST on center trifoliates with uniform exposure to sunlight. Average CER rates expressed as percent of CF over the growing season were 75% and 55% for WW 1.3NF, and 1.9NF and 90% and 61% for WS 1.3NF and 1.9NF, respectively. Measured mean seasonal photosynthesis rates of the WS CF treatments were 68% of those for the WW CF treatments.