Yield Responses of Wheat to Ozone Exposure as Modified by Drought-Induced Differences in Ozone Uptake

Over a period of two years greenhouse experiments were carried out to quantify the interaction ozone exposure × water stress in winter wheat (Triticum aestivum L. cv. Perlo). Assessment of effects carried out on various yield parameters showed that abundant water supply made the plants most sensitive to ozone exposure. In well-watered plants (75%) of soil water capacity, s.w.c.), the AOT40 ozone exposure doses of 26.8 and 24.9 μmol mol^-1 hr^-1 (ppm.h) caused grain yield reductions by 35 and 39%. No reductions of yields were observed at severe water stress (35% of s.w.c.) condition. The decrease in ozone responsiveness under drought can be explained by a distinct reduction in ozone uptake (18 vs. 2 mmol m^-2 in well-watered vs. severely stressed plants at the same ozone exposure). The calculations of ozone uptake were based onrepeated measurements of leaf conductance. Generally curvi-linear regression functions explained the dependence of relative yield on ozone and on water stress better than multiple simple linear regression functions. The consideration of ozone uptake instead of ozone exposure improved the performances of the models further. For explaining grain yield, 96.8% of the variances could be explained by a model resulting from curvi-linear regression fitting. A suggestion for calculating correction factors to modify critical levels in the case of limited water supply is presented.     

Biochar application to temperate soils: Effects on soil fertility and crop growth under greenhouse conditions

Biochar (BC) application as a soil amendment has aroused much interest and was found to considerably improve soil nutrient status and crop yields on poor, tropical soils. However, information on the effect of BC on temperate soils is still insufficient, with effects expected to differ from tropical soils. We investigated the effects of BC on soil nutrient dynamics, crop yield, and quality in a greenhouse pot experiment. We compared three agricultural soils (Planosol, Cambisol, Chernozem), and BCs of three different feedstocks (wheat straw [WS], mixed woodchips [WC], vineyard pruning [VP]) slowly pyrolyzed at 525°C, of which the latter was also pyrolyzed at 400°C. The BCs were applied at two rates (1% and 3%, which would correspond to 30 and 90 t ha^–1 in the field). Three crops, namely mustard (Sinapis alba L.), barley (Hordeum vulgare L.), and red clover (Trifolium pretense L.) were grown successively within one year. The investigated soil properties included pH, electrical conductivity (EC), cation‐exchange capacity (CEC), calcium‐acetate‐lactate (CAL)–extractable P (P_CAL) and K (K_CAL), C, N, and nitrogen‐supplying potential (NSP). The results show a pH increase in all soils. The CEC increased only on the Planosol. The C : N ratio increased at 3% application rate. Despite improving the soil nutrient status partly, yields of the first crop (mustard) and to a lesser extent of the second crop (barley) were significantly depressed through BC application (by up to 68%); the yield of clover as third crop was not affected. Only the BC from WS maintained yields in the range of the control and even increased barley yield by 6%. The initial yield reduction was accompanied by notable decreases (Cu, Fe, Mn, Zn) and increases (Mo) in micronutrient concentrations of plant tissues while nitrogen concentrations were hardly affected. The results of the pot experiment show that despite additional mineral fertilization, short‐term growth inhibition may occur when applying BC without further treatment to temperate soils.     

Simultaneous analyses of chromosomes in root meristems and of the biochemical status of needle tissues of three different clones of Norway spruce trees challenged with moderate ozone levels

Biochemical effects of both low and high ozone impact in long-term and short-term experiments are well investigated and documented; however, short-term treatments with moderate ozone levels have revealed divergent information concerning the biochemistry of needle tissues. Damage to the meristems of spruce trees have been found for several ozone treatments, in the form of an enhanced number of chromosomal aberrations, which appeared to be persistent for up to 2 years after the ozone challenge. One of the main aims of the present study was to determine whether a moderate ozone concentration is able to induce damage in needle biochemistry and/or only in the genetic material of root meristems. In the experiment three different clones of Norway spruce trees (Picea abies) were challenged with moderate ozone concentrations (up to 80 nl/l) for 11 weeks in greenhouses. Simultaneous investigations of root tip meristematic cells and the biochemical status of needle tissues regarding antioxidants and pigments were performed at two different sampling times: directly after the ozone treatment and 1 year later. Ozone effects in needles were absent both at the end of the fumigation and also after 1 year, but different clonal behaviour was found. Effect of ozone on chromosomal aberration rates in root tip meristems were observed and also the types of persisting chromosomal aberrations changed within the time course and within the different clones.     

Soil organic carbon and microbial communities respond to vineyard management

The farming practices in vineyards vary widely, but how does this affect vineyard soils? The main objective of this study was to evaluate the effects of vineyard management practices on soil organic matter and the soil microbial community. To this end, we investigated three adjacent vineyards in the Traisen valley, Austria, of which the soils had developed on the same parent material and under identical environmental/site conditions but were managed differently (esp. tillage, fertilizer application, cover crops) for more than 10 yrs. We found that topsoil bulk density (BD) decreased with increasing tillage intensity, while subsoil BD showed the opposite trend. Soil organic carbon (SOC) stocks in 0–50 cm depth increased from 10 kg m^?2 in an unfertilized and frequently tilled vineyard to 17 kg m^?2 in a regularly fertilized but less intensively tilled vineyard. Topsoil microbial biomass per unit SOC, estimated by the sum of microbial phospholipid fatty acids (PLFAs), followed this trend, albeit not statistically significantly. Principal component analysis of PLFA patterns revealed that the microbial communities were compositionally distinct between different management practices. The fungal PLFA marker 18:2ω6,9 was highest in the vineyard with the lowest amount of extractable Cu (by 0.01 m CaCl₂), and the bacterial‐to‐fungal biomass ratio was positively correlated with extractable Cu. Our results indicate that tillage and fertilizer application of vineyards can strongly affect vineyard soil properties such as BD and SOC stocks and that the application of Cu‐based fungicides may impair soil fungal communities.     

Harvest Dates, Fertilizer and Varietal Effects on Yield, Concentration and Molecular Distribution of Fructan in Jerusalem Artichoke (Helianthus tuberosus L.)

In a pot experiment two varieties of Jerusalem artichoke ( Helianths tuberosus L., cv. Topianka and cv. Violet de Rennes ) were exposed to different supplies of N, P and K. Nitrogen supply increased tuber yield more than the productivity of aerial parts. Violet de Rennes responded better to N than Topianka. Nutrient regimes without P or K addition but including N to some extent depressed the yields of tubers only (by 8–23 %). Carbohydrate concentrations (78–81 % of d.m.) and molecular fructan distributions were neither influenced by fertilizer regimes nor by mineral concentrations in the tubers.
Genotypic differences were significant for yield, for concentrations of N, P, Ca, S and Cu, and for fructan concentration in the tubers. At harvest time the fructose/glucose ratio in tubers of Violet de Rennes was about 10 % higher than in Topianka and remained on a higher level during storage.
Harvest time had the greatest influence on carbohydrate composition. Depolymerization of fructan proceeded at a high rate in November and slowed down during subsequent storage, accompanied by a decline in polydispersity. Simultaneously osmolanty increased, resulting in a freezing point depression of < 0.5 °C.     

Bush bean (Phaseolus vulgaris L) leaf injury,photosynthesis and stomatal functions under elevated ozone levels

Three bush bean cultivars (Lit, Groffy and Stella) were grown under four levels of ozone exposure (ambient air+50 ppb O₃ ambient air+25 ppb O₃, ambient air and charcoal filtered air) in open- top chambers. Number and leaf injury statistics showed significant reduction in the number of healthy leaves as the level of O₃ increased. The area based leaf injury percentages of the cvs. Lit, Groffy and Stella were 69.8, 57.9 and 71.1% at the highest O₃ level, 24.1, 19.6 and 30.3% at the 2nd highest O₃ level, and 4.5, 0.7 and 5.6% at the ambient air, respectively. The plants grown in the filtered air revealed no injury symptoms. The stomatal conductances were found to decrease gradually in each cultivar as the O₃ level increased. At the highest O₃ level, Chlorophyll fluorescence measurements on the 2nd leaf from the top on 24th day of exposure resulted in significantly the highest Fv/Fm values, the lowest f₀ and the highest F_m values whereas the 4th leaf showed the smallest Fm and correspondingly the smallest F_v/F_m values. This is an indication of photosystem II damage after accumulation of a high ozone dose in the 4th leaf. The photosynthetic rate of the 2nd leaf measured on 30th day of exposure was comparatively higher at the highest exposure but the data taken from the same leaf on 40th day of exposure showed significantly lower photosynthetic rate than the plants in ambient air. Both chlorophyll fluorescence and photosynthetic measurements indicated that ozone stressed leaves experience a stimulation of photosynthesis (possibly due to increased assimilate demand) prior to irreversible damage. Bush bean leaves need to accumulate a critical ozone dose(an AOT40 of presumably > 18 ppm-h) for reduction of the photosynthetic capacitys.     

Ozone effects on dry matter partitioning and chlorophyll fluorescence during plant development of wheat

In closed-chamber fumigation experiments dry matter partitioning and chlorophyll fluorescence of wheat were studied, analysing the effects of ozone during different stages of plant development. Ozone causes enhanced leaf senescence, leading to a loss of green leaf area and, consequently to a decreased supply of assimilates, affecting (in increasing order of severeness) stem, ear and grain productivity because of reduced storage pools for translocation. Leaves of plants before shooting stage were most sensitive but the lack of green leaf area after ear emergence had the most pronounced effects on grain yield.Measurements of photochemical capacity showed that evidence for negative ozone effects could be found in changes of chlorophyll fluorescence parameters in leaf sections not yet showing visible ozone injury. Negative effects on photosynthesis were more distinct with increasing accumulated ozone dose, with increasing age of leaf tissue and with increasing ozone sensitivity of the cultivar. The changes in chlorophyll fluorescence are most likely to be explained by a decreased pool size of plastoquinones caused by ozone.