SILICON MITIGATES ULTRAVIOLET-B RADIATION STRESS ON SOYBEAN BY ENHANCING CHLOROPHYLL AND PHOTOSYNTHESIS AND REDUCING TRANSPIRATION

The aim of this study was to investigate the potential of silicon (Si) for alleviating Ultraviolet-B (UV-B) radiation stress based on changes in biomass, physiological attributes and photosynthetic characteristics of two soybean (Glycine max L.) cultivars, Kenjiandou 43 (‘K 43’) and Zhonghuang 35 (‘ZH 35’). The cultivars were raised with and without Si in the greenhouse, and then subjected to ambient, ambient + 2.7 kJ m^?2d^?1and ambient + 5.4 kJ m^?2d^?1of UV-B radiation. Depending on cultivar, plants suffered severe growth limitations under UV-B radiation, but the application of Si alleviated the adverse effects on growth and development by increasing the stem length, net photosynthetic rate (P_N) and leaf chlorophyll content. Concurrently, it decreased the stomatal conductance (Sc) and intercellular carbon dioxide (CO₂) concentration (Ci). In response to the UV-B radiation stress, the antioxidant enzyme activities of superoxide dismutase (SOD) increased by 41.2–72.7%, peroxidases (POD) by 49.5–85.7%, malodialdehyde (MDA) by 6.7–20.4% and soluble protein by 4.2–7.6%. The overall results indicated that media treatment with Si might improve soybean growth under elevated UV-B radiation through positive changes in biomass and some physiological attributes that were dependent on cultivar.     

Auswaschung von Nährstoffen durch sauren Nebel aus jungen intakten Fichten (Picea abies)

Leaching of nutrients out of young intact spruce (Picea abies) by acid fog The effect of acid fog on the leaching of minerals and carbohydrates out of needles of five year old spruce trees (Picea abies) was studied. The fogs were prepared from H₂SO₄ and HNO₃ (2:1) with a pH of 2.75 (acid treatment) and 5 (control treatment). The acid fog leached significantly higher amounts of K, Ca, Mg, Mn, and Zn as well as carbohydrates as compared with the control fog. The absolute quantities of minerals leached, however, were low and amounted to only some percent of the minerals generally present in needles. Except Zn, of which the quantity leached was about as high as the Zn needle content. Nevertheless the Zn concentration in the needles treated with acid fog was not lower than the Zn concentration in the control needles suggesting that the lost Zn was quickly compensated by Zn uptake. In the treatments with acid fog damage symptoms appeared at the end of the experimental period. In the older needles a weak chlorosis occurred; from the needles of the 1^st year some turned redish brown. In the acid fog treatments all needles lacked brightness while the control needles looked bright. These symptoms were similar to those under field conditions of older spruce trees with the ?lametta syndrom”?. Electron microscopic investigation revealed that the wax layer of the needles treated with acid fog was badly damaged.     

Der Einfluß von Fichtennadelwachs auf Nadelzersetzung und Erlenkeimung

The influence of spruce needle wax on the degradation of the needles and the germination of alder seeds 1- and 3-year old needles of Picea abies, each untreated or with the wax layer removed, were burried in a field. Dry-weight of needles without wax decreased faster during an exposition period of 1 to 5 months. Because the wax proved to be a highly selective substrate for microbial colonisation, it retarded the needle degradation. Wax on 1-year old needles slowed degradation down during 2 months, wax on 3-year old needles during 5 months. Degradation time varied for different wax components. The site of wax decomposition was determined by analysing the lipids eluted from different soil layers (depth 0–30 cm) in a natural spruce forest. Lipids forming the wax decreased in depth 1–5 cm and were missing in depth 7–14 cm. Microorganisms isolated from 3 soil layers (depth 1–7 cm) were able to use fatty acids and fatty alcohols out of the wax as a carbon source. But only microorganisms from depth 7–14 cm degraded all wax components. Wax of 1-year old needles delayed seed germination (Alnus glutinosa) for 6 days. Wax of 3-year old needles delayed and inhibited germination for at least 12 days. Pure stearic acid did not influence germination. The different effects show the importance of the chemical wax composition rather than of the water repellent property.     

Forest decline in the boreal montane ecosystems of the southern Appalachian Mountains

Research was initiated in 1984 in an attempt to quantify and test possible hypotheses for the systematic decline and mortality of red spruce (Picea rubens Sarg.) observed in the southern Appalachian Mountains. Field surveys have documented increases in decline symptoms. By 1986, 7% of all tagged red spruce trees in permanent plots were dead. This number, partially due to the effects of severe weather, increased to 41% in 1987. An insect and disease survey initiated in 1985 on 100 permanent plots has yielded little significant pathology or insect infestation. With the exception of the balsam wooly adelgid (Adelges picea (Ratz)), few signs or symptoms of disease or insect attack were noted on either Fraser fir (Abies fraseri) (Pursh Poir) or red spruce populations. Cultures from destructively-sampled root systems yielded few significant pathogens that could contribute to decline symptoms. Measurements of throughfall in 1986 yielded estimates of total wet deposition for NO₃ ^? and SO₄ ^2? of 25 and 75 kg ha^?1 yr^?1 respectively. Using net throughfall quantities, we estimate that between 40 and 60% of this input was due to cloud impact. Mean-volume-weighted pH per cloud event was 3.5. Over 75% of the cloud events sampled had a pH < 4.0. Cloud and rain water was dominated by H⁺, NH₄ ⁺, NO₃ ^?,, and SO₄ ^2? ions. Interaction with the forest canopy resulted in an enrichment of throughfall with base cations (K⁺, Ca²⁺, and Mg²⁺) and a loss of H⁺ and NH₄ ⁺. Mean-volume-weighted pH for throughfall was 3.9. The effects of simulated acidic cloud water on the epicuticular waxes of red spruce needles were studied during the summer of 1987. The cuticle proper of both 1986 and 1987 needles did not appear to be damaged by the treatments. The wax crystals which constitute the stomatal wax plugs, however, exhibited substantial degradation by simulated treatments at or below pH 3.5.     

Nitrogen Mobility at the Sediment-Water Interface of Lake Maracaibo,Venezuela

Nitrogen is one of the two most important elements in the metabolism of aquatic ecosystems. At low concentrations it can limit primary productivity and when present at very high concentrations it can participate in the eutrophication process of these environments. The mechanism of nitrogen transport in sediments is almost unknown, nevertheless it is of vital importance for establishing mass balances in aquatic systems. In the study presented here, we assessed the nitrogen flux in sediments of the central part of tropical Lake Maracaibo, Venezuela, in particular with regard to dissolved oxygen concentrations. Experiments were performed under laboratoryconditions in a batch system, and at varying dissolved oxygenregimes (aerobic and anaerobic). Every two days, during 3 months,overlying water samples were taken to analyze nitrite, nitrate,ammonium and Kjeldahl total nitrogen. Average release rates oftotal nitrogen were 0.86 in aerobic, and 1.06 mmol N m^-2 d^-1 in anaerobic systems corresponding to 41.7% of total N input to the lake. The behavior of nitrogen was strongly influenced by nitrate concentrations under aerobic conditions, and by organic nitrogen under anaerobic conditions during the course of the experiment. A major trend for the release of organic nitrogen during anaerobic conditions, and of nitrate, during aerobic conditions, was observed. Also fluxes of NO₃ ^-, NH₄ ⁺, organic N and Total N across the sediment-water interface were measured. In anaerobic conditions, which are predominant in the hypolimnetic cone of LakeMaracaibo, denitrification was estimated to be 0.02 mmol N m^-2 d^-1, which corresponds to 1.89% of the total N released from sediments.This is to our knowledge the first study of nitrogen fluxes insediments from Lake Maracaibo. The laboratory data presented herereflects conditions in the lake when major nutrients accumulation occurs.     

Carbon dynamics in Appalachian peatlands of West Virginia and Western Maryland

Abundant production of organic matter that decomposes slowly under anaerobic conditions can result in substantial accumulation of soil organic matter in wetlands. Tedious means for estimating production and decomposition of plant material, especially roots, hampers our understanding of organic matter dynamics in such systems. In this paper, I describe a study that amended typical estimates for both production and decomposition of organic matter by measuring net flux of carbon dioxide (CO₂) over the peat surface within a conifer swamp, a sedge-dominated marsh, and a bog in the Appalachian Mountain region of West Virginia and western Maryland, USA. The sites are relatively productive, with net primary production (NPP) of 30 to 82.5 mol C m^?2 yr^?1, but peat deposits are shallow with an average depth of about 1 m. In summer, all three sites showed net CO₂ flux from the atmosphere to the peat during the daytime (?20.0 to ?30.5 mmol m^?2 d^?1), supported by net photosynthesis, which was less than net CO₂ flux from the peat into the atmosphere at nighttime (39.2 to 84.5 mmol m^?2 d^?1), supported by ecosystem respiration. The imbalance between these estimates suggests a net loss of carbon (C) from these ecosystems. The positive net CO₂ flux seems to be so high because organic matter decomposition occurs throughout the peat deposit — and as a result concentrations of dissolved inorganic carbon (DIC) in peat pore waters reached 4,000 Μmol L^?1 by late November, and concentrations of dissolved organic carbon (DOC) in peat pore waters reached 12,000 Μmol L^?1. Comparing different approaches revealed several features of organic matter dynamics: (i) peat accretion in the top 30 cm of the peat deposit results in a C accumulation rate of about 15 mmol m^?2 d^?1; however, (ii) the entire peat deposit has a negative C balance losing about 20 mmol m^?2 d^?1.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

The Influence of Hydrochemistry on Methane Emissions from Two Contrasting Northern Wetlands

Methane emissions from an acidic bog and a forested swamp in north Wales, U.K., were measured over a 12 month period. Along with the emission, hydrochemistry (DOC, SO₄ ^2- and NO₃ ^-) and physical factors (temperature, water table level) were determined. At the bog site, the methane emission ranged from 0.15 mg m^-2 day^-1 to 6.39 mg m^-2 day^-1, having two peaks in spring and late summer. In contrast, high emission was observed in October (38.95 mg m^-2 day^-1) and November (75.37 mg m^-2 day^-1)at the swamp site, which is concurrent with leaf litter production and high DOC concentrations. During the remaining months, the flux varied between –1.33 mg m^-2 day^-1 and 3.05 mg m^-2 day^-1. Correlation analyses showed that the methane emission from the acidic bog had a positive correlation with soil temperature, and negative correlations with sulfate and nitrate concentrations in the pore-water. However, a correlation with water table level was absent. Methane emission from the swamp exhibited a negative correlation with sulfate concentration. Our results confirm that methane emissions vary substantially between different types of wetlands, and suggest that under certain conditions, hydrochemistry may be a more critical controlling variable for methane emissions than temperature and water table level.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

The Behavior of Nitrogen Isotopes in Acidified Forest Soils in the Czech Republic

The effects of atmospheric deposition on N cycling in acidified soils were studied at three spruce and one beech forested sites in the Czech Republic. Nitrogen content and δ¹⁵N were monitored in bulk and throughfall precipitation, needles, leaves, soils and soil solutions. Changes in soil NO₃ ^- production, effect of admixing of atmospheric N in spruce forest and N consumption in deciduous forest are described using changes in ¹⁵N fractionation of mineralized N in soil. Admixing of atmospheric NH4+ can be identified at low concentrations of exchangeable NH₄ ⁺. The δ¹⁵N ratio of atmospheric NO₃ ^- input is on average by 2‰ less negative than the δ5N ratio in soil water; admixing changes the δ¹⁵N of soil NO₃ ^- detected in lysimeters.     

Nutrient Fluxes in Sediment (NH4 + and PO4 -3) in N.W. Coastal Lagoon Mexico Associated with an Agroindustrial Basin

In order to balance the impact of agricultural development on land around coastal lagoons with the protection of aquatic resources, knowledge of the role of the sedimentary phase in the entrapment or availability of nutrients in the water column in areas affected by agroindustrial outlets is important. The Ensenada del Pabellon coastal on the Pacific coast of Mexico was chosen to be analyzed. The input of ammonium and orthophosphate from sediment using semicontrolled benthic chambers near a sugar cane factory outlet was compared to non altered sediment. Phosphate and ammonia loading from agroindustrial outlets has been the primary cause of eutrophication. The inputs of ammonium and orthophosphates from the sediment to the water column depend on their concentration in the agroindustrial outlet's waste water, the local morphology, the tide, and biotic assimilation, in order of importance. Sediment in non-altered revealed maxima of 7.8 mg m^-2 d^-1 of NH⁺ ₄ and 1.4 mg m^-2 d^-1 of PO^-3_₄, whereas in one outlet that greatly transfigures the environment, maxima of 223 mg m^-2 d^-1 of NH⁺ ₄ and 67 mg m^-2 d^-1 of PO^-3_₄ were recorded, which represent an increase greater than 20 times the normal diffusion. These figures varied markedly in space and time. Results from the study indicated that existing levels of nutrient could endanger the future of this ecosystem, including its sustainable fisheries.     

我国北方地区几种主要作物氮营养诊断及追肥推荐研究 Ⅳ.冬小麦─夏玉米轮作制度下氮素诊断及追肥推荐的研究

研究了冬小麦夏玉米轮作制度下二苯胺法和反射仪法在两种作物氮营养诊断中的应用。提出冬小麦的最佳氮营养诊断时期和诊断部位为拔节前茎基部节间组织，夏玉米为拔节前功能叶叶脉。确定了两种作物采用两种方法进行氮素营养诊断的临界值，冬小麦为2.00（NO3-N色阶，二苯胺法）、1500mgkg-1（NO3-，反射仪法）;夏玉米为2.40（NO3--N色阶，二苯胺法）和1240mgkg-1（NO3-，反射仪法）。同时建立了两种作物基于氮素营养诊断的作物追肥推荐模型:冬小麦:Nd＝220.2-95.8Td（二苯胺法）Nd＝220.2-0.147Tr（反射仪法）夏玉米:Nd＝185.9-72.5Td（运城，二苯胺法）Nd＝185.9-0.13Tr（运城，反射仪法）Nd＝176.2-80.5Td（永济，二苯胺法）     

Short-term effects of clearfelling on soil CO2, CH4, and N2O fluxes in a Sitka spruce plantation

We examined the effects of forest clearfelling on the fluxes of soil CO₂, CH₄, and N₂O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO₂, CH₄, N₂O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO₂ efflux, with an average efflux rate of 4.0 g m⁻² d⁻¹ in the mature stand (40-year) and 2.7 g m⁻² d⁻¹ in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m⁻² d⁻¹) for CH₄ to a net source (2.01 mg m⁻² d⁻¹). For the same period, soil N₂O fluxes averaged 0.57 mg m⁻² d⁻¹ in the CF and 0.23 mg m⁻² d⁻¹ in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO₂ remained the dominant greenhouse gas in terms of its greenhouse warming potential.     

Changes in the structure and protein binding ability of condensed tannins during decomposition of fresh needles and leaves

Alterations of the chemical structure of condensed tannins (CT) during decomposition of Norway spruce (Picea abies) needles and white willow (Salix alba) leaves were investigated by gel permeation chromatography (GPC), ¹³C nuclear magnetic resonance (NMR) spectroscopy, and matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS). The effect of these alterations on their protein binding capacity was determined by radial diffusion assay on an agarose plate. For these studies an incubation experiment was performed with spruce needles and willow leaves. From the fresh foliage and its decomposed materials obtained after 4-days, and 1-, 2-, 4-, and 8-weeks of incubation, CT were extracted and analyzed.Dynamics of CT alterations during decomposition of the fresh foliage were different for the two plant species, although the amount of extractable CT for both decreased soon after incubation and only slight amounts of CT were extractable after 8 weeks of incubation. The decrease was faster for the willow leaves than for the spruce needles. Solution ¹³C NMR revealed alterations of CT isolated from both degrading plant materials, but only to a small extent. However, considerable changes in chemical composition and chain length of the CT were detected by MALDI-TOF MS. Changes in the chemical composition of CT are expected to decrease the protein binding capacity. Applying the radial diffusion assay, this assumption was confirmed for spruce CT, but not for willow CT. This may be explained by (1) higher reactivity of prodelphinidin (PD) than procyanidin (PC), the former is contained in spruce CT but not in willow CT and (2) the slower decomposition rate of spruce needles than willow leaves. Thus, CT in spruce needles may have suffered a greater extent of chemical alteration, which formed partially altered CT with less protein binding capacity. Further, since the decomposition rate of spruce needles was slower than that of willow leaves, the partially altered CT remained extractable for a longer incubation period compared with the willow leave's CT.     

Annual Variations of Needle Surface Characteristics of Pinus Sylvestris Growing Near the Emission Source

In present study, pollutant effects on needle surface characteristics of Pinus sylvestris in the area affected by a nitrogen fertilizer plant have been investigated over 1994–1997 year period. Near the factory, sites with 15–25-year-old trees on a 0.5–22 km interval were chosen. Mean monthly concentrations of NO₂ and NH₃ varied across the transect in the range of 1.8–8.8 µg m^?3 and 1.8 – 69.3 µg m^?3, respectively. NH₃ concentrations exceeded the critical level (>23 µg m^?3) only in the 0.5 km vicinity. Assessment of needle surface wettability by measuring contact angles (CA) of water droplets and surface quality by measuring stomatal area covered by structural wax (SW) revealed significant (p<0.05) needle age, site, and year of sampling related differences. Comparison of SW between sites showed reliably (p<0.05) higher surface wax erosion on one-year-old needles sampled in the area, where ammonia concentration exceeds critical level. Significant correlations between site SW on one-year-old needles and distance from the pollution source, NO₂ and NH₃ concentrations were detected (r = 0.539; r = ? 0.495; r = ? 0.426; p<0.001, respectively). Correlations between CA and factors mentioned were lower.     

ACCUMULATION OF SULPHUR IN AND ON SCOTS PINE NEEDLES IN THE SUBARCTIC

Total S concentrations of Scots pine (Pinus sylvestris L.) needles studied in the Finnish subarctic (66–70°N, 24–30°E) in 1990/1992 ranged from 573 to 1153 μg g^-1. Levels were found to be ≈ 900 μg g^-1 (i.e. 1.3–1.8 times the ‘normal’ level of 500–700 μg g^-1) in areas where the long-term ambient SO₂ concentration was ≈ 2–5 μg m^-3, particulate SO₄ ^2- ≈ μg m^-3 and total S deposition ≈ 0.5 g m^-2. A statistically significant increase in needle total S concentrations was found towards the east, i.e. towards the smelters of the Kola Peninsula in Russia, which emit SO₂. The increase in needle total S concentrations to over 900 μg g^-1 close to the Russian border is thought to result mainly from exposure to high short-term SO₂ concentrations. The results also suggest that wintertime S deposition may have an impact on the needle total S content. It is suggested that the UNECE long-term critical level of 15 μg SO₂ m^-3 for forestry in boreal and high mountain climates in Europe is too high for the pine forests in the extreme north, where the proportion of dry-deposited S may be 60–80%.     

Effects of rainfall pattern on carbon and nitrogen dynamics in soil amended with biogas slurry and composted cattle manure

Soil moisture affects the degradation of organic fertilizers in soils considerably, but less is known about the importance of rainfall pattern on the turnover of C and N. The objective of this study was to determine the effects of different rainfall patterns on C and N dynamics in soil amended with either biogas slurry (BS) or composted cattle manure (CM). Undisturbed soil cores without (control) or with BS or CM, which were incorporated at a rate of 100 kg N ha^–1, were incubated for 140 d at 13.5°C. Irrigation treatments were (1) continuous irrigation (cont_irr; 3 mm d^–1); (2) partial drying and stronger irrigation (part_dry; no irrigation for 3 weeks, 1 week with 13.5 mm d^–1), and (3) periodic heavy rainfall (hvy_rain; 24 mm d^–1 every 3 weeks for 1 d and 2 mm d^–1 for the other days). The average irrigation was 3 mm d^–1 in each treatment. Cumulative emissions of CO₂ and N₂O from soils amended with BS were 92.8 g CO₂‐C m^–2 and 162.4 mg N₂O‐N m^–2, respectively, whereas emissions from soils amended with CM were 87.8 g CO₂‐C m^–2 and only 38.9 mg N₂O‐N m^–2. While both organic fertilizers significantly increased CO₂ production compared to the control, N₂O emissions were only significantly increased in the BS‐amended soil. Under the conditions of the experiment, the rainfall pattern affected the temporal production of CO₂ and N₂O, but not the cumulative emissions. Cumulative NO leaching was highest in the BS‐amended soils (9.2 g NO ‐N m^–2) followed by the CM‐amended soil (6.1 g NO ‐N m^–2) and lowest in the control (4.7 g NO ‐N m^–2). Nitrate leaching was also independent of the rainfall pattern. Our study shows that rainfall pattern may not affect CO₂ and N₂O emissions and NO leaching markedly provided that the soil does not completely dry out.     

Field crop responses to ultraviolet-B radiation: a review

This paper provides an overview of existing literature on the ultraviolet-B (UV-B) radiation effects on field crops. Earlier reviews on field crop responses to UV-B considered few physiological processes or crops. For this review, we easily located about 129 studies on 35 crop species published since 1975. Here, we report the effects of UV-B radiation on visual symptoms, leaf ultrastructure and anatomy, photosynthetic pigments, UV-B absorbing compounds, photosynthesis, growth and development, yield, genotypic differences, and finally, interactions of UV-B with abiotic and biotic factors of crop plants. Experiments conducted in glasshouses, in closed and open top chambers, and under field conditions, with varying source (solar or artificial) and intensity of photosynthetically active radiation (PAR, 50–1800 μmol m⁻² s⁻¹) and UV-B (0–50 kJ m⁻² per day) are included. It is easy to conduct experiments that purport to evaluate the effects of projected UV-B intensities on crop species by providing supplemental irradiance with lamps or by reducing UV-B with filters; however, it is very difficult to simulate UV-B irradiance spectral changes that are likely to occur in nature. Collated results for each process are presented as percent change from control along with the experimental conditions in tabular format. Many of the studies showed dramatic effects of UV-B radiation, but under conditions with supplemental UV-B irradiance that was higher than would ever occur outside experimental conditions or in which the longer wavelengths in the PAR and UV-A, which moderate UV-B effects, were greatly reduced. Only 25 of the studies reviewed used experimental conditions and supplemental UV-B irradiance that approached realism. However, unrealistic the experimental conditions might be, an increase in understanding of basic plant physiology was gained from most of the studies.Visual symptoms consisting of chlorotic or necrotic patches on leaves exposed to UV-B were not unique. Both vegetative and reproductive morphology were altered by UV-B radiation. Leaf anatomy was altered due to changes in thickness of epidermal, palisade, and mesophyll layers. Enhanced UV-B generally decreased chlorophyll content (10–70%), whereas it increased UV-B absorbing compounds (10–300%) in many crops. Decrease in photosynthesis (3–90%), particularly at higher UV-B doses, was due to both direct (effect on photosystem) and indirect (decrease in pigments and leaf area) effects. The decreases in chlorophyll pigments and photosynthesis resulted in lower biomass and yield of most crop plants. Genotypes of crop species exhibited variability in leaf wax layer thickness, loss of chlorophyll, and increase in phenolics as mechanisms of tolerance to enhanced UV-B radiation resulting in changes in biomass/yield. Results from the few studies on interaction of UV-B with other abiotic and biotic factors did not lead to useful conclusions. Studies are needed to quantify the effects of UV-B radiation on crops in order to develop dose response functions that can facilitate development of dynamic simulation models for use in UV-B and other environmental impact assessments.     

CO2 efflux by rapid decomposition of low molecular organic substances in soils

Decomposition rates of the [2-¹⁴C]-glucose and [2-¹⁴C]-glycine in four different soils of the long-term field trial of Moscow were investigated in a 3-months laboratory experiment in which ¹⁴CO₂ respiration was measured. A model with three decomposition components and two distribution parameters was developed and validated with the data of the experiment. The decay rate constants of free [2-¹⁴C]-glucose (4–32 day^-1) were slower than those of [2-¹⁴C]-glycine (16–44 day^-1). The calculated use efficiency for microbial biosynthesis of the second carbon atom was 47% for glucose and 31% for glycine. The potential half-life of labelled carbon in the microbial soil biomass ranged from 0.6 to 4.4 days, depending on the soil type and the initial amount of added substrate. The calculated total utilisation of carbon by the soil biomass from glycine was about 2–5 times lower than that of glucose.The modelled ¹⁴C incorporation into the microbial soil biomass reached its maximum on the first day of the incubation experiment and did not exceed 22% of the ¹⁴C input. Both of the investigated substances decomposed most rapidly in the soil samples from sites that have not being fertilised with organic or mineral fertilisers during an 81-years period.     

Cotton responses to ultraviolet-B radiation: experimentation and algorithm development

The potential impact of an increase in solar ultraviolet-B (UV-B) radiation due to human activity on higher plants has been the subject of many studies. Little work has been carried out so far on cotton responses to enhanced UV-B radiation. The objective of this study was to determine whether or not the current and projected increases in UV-B levels affect cotton growth and development, and to quantify and develop UV-B radiation functional algorithms that can be used in simulation models. Two experiments were conducted during the summer of 2001 using sunlit plant growth chambers in a wide range of UV-B radiations under optimal growing conditions. Leaves exposed to UV-B radiation developed chlorotic and necrotic patches depending on the intensity and length of exposure. Along with changes in visible morphology, cotton canopy photosynthesis declined with increased UV-B radiation. The decline in canopy photosynthesis was partly due to loss of photosynthetic pigments and UV-B-induced decay of leaf-level photosynthetic efficiency (maximum photosynthesis) and capacity (quantum yield) as the leaves aged. The total leaf area was less due to smaller leaves and fewer leaves per plant. Less plant height was closely related to a shorter average internode length rather than a fewer mainstem nodes. The UV-B did not affect cotton major developmental events such as time taken to square, time to flower, and leaf addition rates on the mainstem. Lower biomass was closely related to both smaller leaf area and lower photosynthesis. The critical limit, defined as 90% of optimum or the control, for stem elongation was lower (8.7 kJ m⁻² per day UV-B) than the critical limit for leaf expansion (11.2 kJ m⁻² per day UV-B), indicating that stem elongation was more sensitive to UV-B than leaf expansion. The critical limits for canopy photosynthesis and total dry weight were 7 and 7.3 kJ m⁻² per day, respectively. The identified UV-B-specific indices for stem and leaf growth and photosynthesis parameters may be incorporated into cotton simulation models such as GOSSYM to predict yields under present and future climatic conditions.