Effects of elevated O3 concentration on winter wheat and rice yields in the Yangtze River Delta, China.

The effects of a continuing rise of ambient ozone on crop yield will seriously threaten food security in China. In the Yangtze River Delta, a rapidly developing and seriously air polluted region in China, innovative open-top chambers have been established to fumigate winter wheat and rice in situ with elevated O(3). Five years of study have shown that the yields of wheat and rice decreased with increasing O(3) concentration. There were significant relationships between the relative yield and AOT40 (accumulated hourly O(3) concentration over 40 ppb) for both winter wheat and rice. Winter wheat was more sensitive to O(3) than rice. O(3)-induced yield declines were attributed primarily to 1000-grain weight and harvest index for winter wheat, and attributed primarily to grain number per panicle and harvest index for rice. Control of ambient O(3) pollution and breeding of O(3) tolerant crops are urgent to guarantee food security in China.

Soil temperature and moisture sensitivities of soil CO2 efflux before and after tillage in a wheat field of Loess Plateau, China.

As a conventional farming practice, tillage has lasted for thousands of years in Loess Plateau, China. Although recent studies show that tillage is a prominent culprit to soil carbon loss in croplands, few studies have investigated the influences of tillage on the responses of soil CO2 efflux (SCE) to soil temperature and moisture. Using a multi-channel automated CO2 efflux chamber system, we measured SCE in situ continuously before and after the conventional tillage in a rain fed wheat field of Loess Plateau, China. The changes in soil temperature and moisture sensitivities of SCE, denoted by the Q10 value and linear regression slope respectively, were compared in the same range of soil temperature and moisture before and after the tillage. The results showed that, after the tillage, SCE increased by 1.2-2.2 times; the soil temperature sensitivity increased by 36.1%-37.5%; and the soil moisture sensitivity increased by 140%-166%. Thus, the tillage-induced increase in SCE might partially be attributed to the increases in temperature and moisture sensitivity of SCE.

Stability of soil organic carbon changes in successive rotations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations.

The importance of soil organic carbon (SOC) under forests in the global carbon cycle depends on the stability of the soil carbon and its availability to soil microbial biomass. We investigated the effects of successive rotations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations on the stability of SOC and its availability to microbes by adopting the two-step hydrolysis with H2SO4 and density fractionation. The results showed that successive rotations of Chinese fir decreased the quantity of total SOC, recalcitrant fraction, and carbohydrates in Labile Pool I (LP I), and microbial properties evidently, especially at 0-10 cm horizon. However, cellulose included in Labile Pool II (LP II) and the cellulose/total carbohydrates ratio increased in successive rotations of Chinese fir. The non-cellulose of carbohydrates included in LP I maybe highly available to soil microbial biomass. Hence the availability of SOC to microbial biomass declined over the successive rotations. Although there was no significant change in recalcitrance of SOC over the successive rotations of Chinese fir, the percentage of heavy fraction to total SOC increased, suggesting that the degree of physical protection for SOC increased and SOC became more stable over the successive rotations. The degradation of SOC quality in successive rotation soils may be attributed to worse environmental conditions resulted from disturbance that related to "slash and burn" site preparation. Being highly correlated with soil microbial properties, the cellulose/total carbohydrates ratio as an effective indicator of changes in availability of SOC to microbial biomass brought by management practices in forest soils.

Comparison of a diurnal vs steady-state ozone exposure profile on growth and yield of oilseed rape (Brassica napus L.) in open-top chambers in the Yangtze Delta, China.

Most available exposure-response relationships for assessing crop loss due to elevated ozone (O(3)) have been established using data from chamber and open-top chamber experiments, using a simulated constant O(3) concentration exposure (square wave), which is not consistent with the diurnal variation of O(3) concentration that occurs in nature. We investigated the response of oilseed rape (Brassica napus L.) to O(3) as affected by two exposure regimes: one with a diurnal variation (CF100D) and another with a constant concentration (CF100). Although the two exposure regimes have the same mean O(3) concentration and accumulated O(3) concentration above 40 ppb (AOT40), our results show that O(3) at CF100D reduced biomass and number of pods/plant more than O(3) at CF100. Both O(3) exposures resulted in larger seed weights/100 pods compared to CF. Numbers of seeds/100 pods were reduced by CF100, while numbers of seeds/100 pods in the CF100D chambers were comparable to those in CF. Our results suggest that chamber experiments that use a constant O(3) exposure may underestimate O(3) effects on biomass and yields.

[Effects of elevated ozone on rice (Oryza sativa L.) leaf lipid peroxidation and antioxidant system].

With rice (Oryza sativa L.) cultivar 3694 Fan as test material, and by using open top chambers, the effects of different ozone (O3) concentration on the leaf soluble protein content, lipid peroxidation, and antioxidant system were applied. Three treatments were applied, i.e., charcoal-filtered air (CF, 20 nl O3 x L(-1)), non-filtered ambient air (NF, 40 nl O3 x L(-1)), and elevated O3 (EO, 75 nl O3 x L(-1)). The results showed that there were no significant differences in the test variables between treatments CF and NF. Compared with CF, EO induced a significant decrease of soluble protein content and significant increases of H2O2 and ASA contents and SOD, CAT and POD activities. In treatment EO, the SOD, CAT and POD activities increased by 93.7%, 39.9% and 312.4%, respectively, as compared with treatment CF, while the APX activity tended to increase at first and decrease then. MDA content had no significant differences among the treatments, indicating that leaf antioxidant system could significantly prevent the lipid peroxidation induced by elevated O3, and rice cultivar 3694 Fan could resist O3 to some extent.

Ground-level ozone in China: distribution and effects on crop yields.

Rapid economic development and an increasing demand for food in China have drawn attention to the role of ozone at pollution levels on crop yields. Some assessments of ozone effects on crop yields have been carried out in China. Determination of ozone distribution by geographical location and resulting crop loss estimations have been made by Chinese investigators and others from abroad. It is evident that surface level ozone levels in China exceed critical levels for occurrence of crop losses. Current levels of information from ozone dose/response studies are limited. Given the size of China, existing ozone monitoring sites are too few to provide enough data to scale ozone distribution to a national level. There are large uncertainties in the database for ozone effects on crop loss and for ozone distribution. Considerable research needs to be done to allow accurate estimation of crop losses caused by ozone in China.

[Estimation models of understory shrub biomass and their applications in red soil hilly region].

With 16 familiar species of understory shrub at Qianyezhou ecological experimental station in red soil hilly region under Chinese Academy of Sciences as test objects, crown area (A(c)) and projected volume (V(c)) were used as the variables for building quadratic and power allometric equations, respectively, to estimate the biomass of individual populations, and mixed-model was used to estimate the biomass of the 16 species. The best-fit models were applied to estimate the biomass of understory shrub in different forest types. The results showed that the biomass of shrub layer varied significantly among different stand types. With species-specific models, the biomass in deciduous, secondary, and coniferous forests was estimated as 4 773, 3 175 and 733 kg x hm(-2), respectively; while with mixed model, the estimation result was a little lower, being 3 946, 2 772 and 840 kg x hm(-2), respectively. Under the conditions of species-specific models being not established, mixed model was more convenient and practical in estimating the biomass of understory shrub.

[A simulation model of ozone stress on photosynthetic production and its allocation of winter wheat].

Assessing and predicting the impacts of ozone (O3) concentration on crop production have been drawing great attention in the scientific community. The ambient O3 concentration above the winter wheat field was observed with ML9810B O3 Analyzer in Jiaxing, Zhejiang Province. The impact of O3 on the wheat leaf photosynthesis was measured in open-top chamber. Based on the observed parameters, a numerical model for simulating the impact of O3 on the winter wheat development and yield was established, by added the effects of O3 on ear photosynthesis and leaf area. The results showed that the model properly simulated the impacts of O3 on wheat growth in field. The relative error of predicted biomass was 10.3%. The accumulated loss of photosynthate was 11.4% and yield loss was 17.8% at ambient O3 concentration in the wheat growth period under sufficient moisture and fertilizer supplies.

[Effect of elevated atmospheric O3 on arbuscular mycorrhizaL (AM) and its function].

In order to understand the possibility of AM in protecting crops from O3 pollution, simulated experiment was carried out to investigate effect of increased atmospheric O3 (0.02 microL x L(-1), 0.1 microL x L(-1) and 0.2 microL x L(-1)) on AM and its function. The results indicate that mycorrhizal colonization was slightly affected by elevated atmospheric O3, but spore and hypahe growth were significantly impacted. Spore number at high O3 level increased I times than that at ambient O3; hypahe length of AM at low and high O3 level decreased 48.7% and 85.6% than that at ambient O3, respectively. Root biomass, nodule number, horsebean pod and grain weight (excluding the treatment-- S + M) significantly decreased with elevated atmospheric O3, but they markedly increased after inoculation with AM fungi. Compared with the uninoculated treatment, nodule number increased by 2-5 times and grain weight of horsebean increased by 3-6 times after inoculation with AM fungi. Relative function of AM was slightly impacted by elevated atmospheric O3. Although indigenous microbes competed with inoculated AM fungi, inoculation with AM fungi could decrease the stress of O3 on plant, which was positive significant to alleviate crop loss resulted from O3 pollution.

[NO3(-)-N dynamics in a spring wheat and radish multiple-crop system in the Hetao Irrigation District].

The NO3(-)-N dynamics of the soil, soil solution and groundwater were studied under spring wheat and radish multiple-crop system in Hetao Irrigation District over two years. A strong tendency of NO3(-)-N to move from upper layer to deeper layer could be observed and soil NO3(-)-N was increased at the layer of 100 approximately 150cm. NO3(-)-N concentration of soil solution at the depth of 70 and 120 cm was significantly higher than that at the depth of 30 cm, especially in the radish growth season. NO3(-)-N leaching amount was correlated with deep percolation at both different crop growth seasons and different years and it accounted for higher than 30% of total N input across two years. In the fertilizer plot, the concentration of NO3(-)-N in groundwater was far higher than that in the non-fertilizer plot, and 65.5% samples were over the safe standard of WHO (11.3mg/L) in the fertilizer plot. The topsoil NO3(-)-N content was markedly decreased during the two years multiple-crop system. However, NO3(-)-N leaching was inevitable in the near future due to a large amount of residual NO3(-)-N in the middle and deeper soil profiles.

Variation in photosynthetic photon flux density within a tropical seasonal rain forest of Xishuangbanna, south-western China.

The effects of canopy development, solar angle, and weather conditions on temporal variation in photosynthetic photon flux density(PPFD) at three heights within a tropical rain forest canopy in Xishuangbanna, China, were examined. PPFD was measured every second and stored as 10-min averages from 1 December 2002 to 30 November 2003. PPFD variability was examined at three different temporal scales. Specific days in March, September, and December with clear and overcast sky conditions were selected to separate the effects of leaf area index (LAI) and solar angle on diurnal variability. On both clear and overcast days, mean daily average PPFD was significantly different between March and September at all heights, except 10 m on clear days, suggesting that LAI directly influences PPFD. In contrast, the differences in daily average PPFD among three heights between September and December were likely due to variation in solar angle. In addition, daily average PPFD at all locations were significantly lower under overcast than clear sky conditions in March, September and December. Over the year-long study, the mean daily total PPFD at 21 m, 10 m and 4 m was 2.8, 2.7 and 0.7 mol/(m2 x d), which accounted for 9.7%, 9.4% and 2.4% of the daily PPFD above the canopy, respectively. Significant differences in mean daily total PPFD occurred at the same heights among different seasons, and diurnal, day-to-day and seasonal PPFD varied at different heights within the canopy. The possible effects of light variability on physiological and morphological responses of plants are discussed.

[Conservation priorities for plant species of forest-meadow ecotone in Sanjiangyuan Nature Reserve].

Based on field survey, information collection and experts consultation, the quantitative grading index system and assessment standards for preference conservation of rare and endangered plant species of forest-meadow ecotone in Sanjiangyuan Nature Reserve were established by using the methods and principles of systematical analysis. The quantitative grading index system included endangered coefficient, genetic coefficient, and useful value coefficient. In addition, 10 indicators used to evaluate endangered grading and conservation priorities sequenc, were also included in 3 subsystems respectively. Furthermore, the weights of 3 subsystem and 10 indicators were given through experts consultation and analytic hierarchy process. Endangered coefficient and conservation priorities coefficient, which respectively described the endangered grading, and preferential conservation of plant species were calculated by mathematic models and computer program. Contrasting to the standards of endangered grading and conservation priorities for plant species, we quantitatively evaluated the status of endangered and conservation priorities of plant species. The results showed that the number of endangered species was 4, vulnerable species 68, lower risk species 179, safety species 695; the number of the first class species was 8, the second class species 78, the third class species 164, and the delayed conservation species 696. Finally, we discussed the problems of indicator system and its weight, the relationship between endangered grading and conservation priorities sequence, and the spatial scale problem of plant species assessment.

[An overview on studies of soil organic matter in Chinese fir plantation].

Soil organic matter (SOM) is an important component of soil and an important carbon pool of terrestrial ecosystems, which plays an important role in soil nutrient cycling and in the balance of global carbon cycle. This paper discussed the SOM quality in Chinese fir plantation, the influence of rotation on SOM content, the change of SOM during Chinese fir growth, and the effect of human activities such as burning, site preparations and fertilization on SOM. Human activities changed soil environment including soil moisture, temperature, total porosity and nutrient contents, and hence, made the turnover of SOM slower or quicker. The content and quality of SOM in mixed forests were higher than those in pure Chinese fir plantations, and decreased with rotation. In the last part of this paper, some issues to be further researched were put forward, including the turnover model of SOM, its components, and its relationship with global carbon cycle.

[Soil quality assessment of forest stand in different plantation esosystems].

After a clear-cutting of the first generation Cunninghamia lanceolata plantation in 1982, three plantation ecosystems, pure Michelia macclurei stand (PMS), pure Chinese-fir stand (PCS) and their mixed stand, were established in spring 1983, and their effects on soil characteristics were evaluated by measuring some soil physical, chemical, microbiological and biochemical parameters. After 20 years' plantation, all test indices showed differences among different forest management models. Both PMS and MCM had a favorable effect on soil fertility maintenance. Soil quality assessment showed that some soil functions, e.g., water availability, nutrient availability, root suitability and soil quality index were all in a moderate level under the mixed and pure PMS stands, whereas in a relatively lower level under successive PCS stand. The results also showed that there existed close correlations between soil total organic C (TOC), cation exchange capacity (CEC), microbial biomass-C (Cmic) and other soil physical, chemical and biological indices. Therefore, TOC, CEC and Cmic could be used as the indicators in assessing soil quality in this study area. In addition, there were also positive correlations between soil microbial biomass-C and TOC, soil microbial biomass-N and total N, and soil microbial biomass-P and total P in the present study.

Effects of ground-level ozone (O3) pollution on the yields of rice and winter wheat in the Yangtze River Delta.

Effects of elevated O3 on the yields of rice and winter wheat were studied by using open-top chambers (OTCs). Results showed that compared to the control treatment, 200 ppb, 100 ppb, 50 ppb treatments caused a 80.4%, 58.6% and 10.5% decrease in grain yields per winter wheat plant and a 49.1%, 26.1% and 8.2% decrease in grain yield per rice plant, respectively. According to the dose-response relation educed from OTCs experiment and the monitor data of O3 concentrations in spots, it was estimated that the yield losses of rice and winter wheat resulted by O3 pollution in the Yangtze River Delta region in 1999 were 0.599 million ton and 0.669 million ton, economic losses were 0.539 billion RMB Yuan and 0.936 billion RMB Yuan, respectively.

Effects of lignin on nitrification in soil.

The effects of two lignins isolated from black liquor from pulping process on nitrification in soils after addition of urea, (NH4)2SO4 and (NH4)2HPO4 were investigated by incubation at 20 or 30 degrees C for 7 or 14 d. The effects of lignin on nitrous oxide emissions from soil were also determined. Results showed that both lignins were more effective for inhibiting nitrification of NH4(+)-N as (NH4)2SO4 or (NH4)2HPO4 as compared to urea-N. The effectiveness of lignin on nitrification was markedly affected by different soil type and temperature. Nitrous oxide emissions from soil declined when lignin was used. Urea plus 20 and 50 g/kg lignin reduced N2O emissions by about 83% and 96%. respectively, while (NH4)2HPO4 plus 20 and 50 g/kg lignin respectively reduced emissions by 83% and 93%. Because of its low cost and nonhazardous characteristics, lignin has potential value as a fertilizer amendment to improve N fertilizer efficiency.

[Effect of triadimefon on cucumber seedlings growth and their resistance to chilling injury].

Studies on the effects of different concentrations of triadimefon on cucumber seedlings growth and their resistance to chilling injury showed that 20-100 mumol.L-1 triadimefon inhibited the shoot or root length of cucumber seedlings, and increased their root weight or root/shoot ratio and chlorophyll content significantly. After at low temperature for 3 days, a higher chlorophyll content, lower membrane relative permeability and higher SOD activity were observed in the leaves of cucumber seedlings soaked with 10-50 mumol.L-1 triadimefon. 50 mumol.L-1 triadimefon could retard the accumulation of MDA at low temperature stress. It was also observed that 50 mumol.L-1 triadimefon enhanced the accumulation of praline at the first day of chilling treatment. However, higher concentrations(> 100 mumol.L-1) of triadimefon were unfavorable for cucumber seedlings to defense against low temperature. It was thus concluded that triadimefon protected the cucumber seedlings against low temperature.

Effects of acid deposition on terrestrial ecosystems and their rehabilitation strategies in China.

South China has become the third largest region associated with acid deposition following Europe and North America, the area subject to damage by acid deposition increased from 1.75 million km2 in 1985 to 2.8 million km2 in 1993. Acid deposition has caused serious damage to ecosystem. Combined pollution of acid rain and SO2 showed the obvious multiple effects on crops. Vegetable was more sensitive to acid deposition than foodstuff crops. Annual economic loss of crops due to acid deposition damage in eleven provinces of south China was 4.26 billion RMB Yuan. Acid deposition caused serious damage to forest. Annual economic loss of wood volume was about 1.8 billion RMB Yuan and forest ecological benefit loss 16.2 billion in eleven provinces of south China. Acid deposition in south China was typical "sulfuric acid type". According to the thoughts of sustainable development, some strategies were brought forward as follows: (1) enhancing environmental management, specifying acid-controlling region, controlling and abating the total emission amount of SO2; (2) selecting practical energy technologies of clean coal, for example, cleansing and selecting coal, sulfur-fixed-type industrial briqutting, abating sulfur from waste gas and so on; (3) developing other energy sources to replace coal, including water electricity, atomic energy and the new energy such as solar energy, wind energy and so on; (4) in acid deposition region of south China, selecting acid-resistant type of crop and tree to decrease agricultural losses, planting more green fertilizer crops, using organic fertilizers and liming, in order to improve buffer capacities of soil.

[Effect of triadimefon on activity of peroxidase and soluble protein content in detached cucumber cotyledons].

Contents of chlorophyll a, chlorophyll b, soluble protein and proline, as well as the ratio chlorophyll a/b in detached cotyledons of cucumber were distinctly increased by treating with 20 mg/L triadimefon, which suggested that triadimefon can effectively retard the senescence of detached cotyledons in cucumber. Triadimefon could inhibit the increase of peroxide (POD) activity and H2O2 content in different degree. It was found that contents of chlorophyll and protein were markedly negative correlated with the activity of POD and with the content of H2O2 respectively during the senescence of cotyledons. These results indicated triadimefon inhibit the degradation of chlorophyll and protein in cucumber cotyledons through POD- H2O2 enzyme system.