Contribution of plants to N 2 O emissions in soil-winter wheat ecosystem: pot and field experiments

Outdoor pot and field experiments were conducted to assess the role of growing plants in agricultural ecosystem N₂O emissions. N₂O emissions from plants were quantified as the difference in soil-crop system N₂O emissions before and immediately after cutting plants during the main growth stages in 2001–02 and 2002–03 winter wheat seasons. Emissions of N₂O from plants depended on biomass within the same plant developmental status. Field results indicated that the seasonal contribution of N₂O emissions from plants to ecosystem fluxes averaged 25%, ranging from 10% at wheat tillering to 62% at the heading stage. The fluxes of N₂O emissions from plants varied between 0.3 and 3.9 mg N₂O-N m⁻² day⁻¹ and its seasonal amount was equivalent to 0.23% of plant N released as N₂O. A N₂O emission coefficient (N₂O_E, mg N₂O-N g⁻¹ C day⁻¹), defined as N₂O-N emission in milligrams from per gram carbon of plant dry matter within a day, was represented by a 5-fold variation ranging from 0.021 to 0.004 mg N₂O-N g C⁻¹ day⁻¹. A linear relationship (y=0.4611x+0.0015, r ²=0.9352, p < 0.001) between N₂O_E (y) and plant dark respiration rate (x, mg CO₂-C g C⁻¹ day⁻¹) suggested that in the absence of photosynthesis, some N₂O production in plant N assimilation was associated with plant respiration. Although this study could not show whether N₂O was produced or transferred by winter wheat plants, these results indicated an important role for higher plant in N₂O exchange. Identifying its potential contribution is critical for understanding agricultural ecosystem N₂O sources.     

Amendment of vanadium-contaminated soil with soil conditioners: A study based on pot experiments with canola plants (Brassica campestris L.)

We performed pot experiments with canola plants (Brassica campestris L.) to evaluate the effect of eight soil conditioners on the amendment of vanadium (V)-contaminated soil based on analysis of the growth of canola plants and the uptake, bioaccumulation, and translocation of heavy metals. Tested soil conditioners included polyacrylamide (PAM), sepiolite, humic acid (HAC), peat, sludge compost (SC), bentonite, lime, and fly ash. Results from the analysis of the growth of canola plants and the analysis of variance showed that the best soil conditioners for V-contaminated soil were 0.05–0.1 wt% PAM, 1 wt% peat, 1 wt% HAC, and 1 wt% SC; moderately effective soil conditioners included sepiolite and lime. The best combination of soil conditioners was 0.1 wt% PAM, 1 wt% HAC, and 0.15 wt% lime, in addition of 1% ZVI, which increased the biomass and height of canola plants by 1.18-fold and 59.49%, respectively. We conclude that the best combination of soil conditioners determined from this study is promising for mitigating V contamination in soil.     

A new sampler for extracting undisturbed surface peat cores for growth pot experiments

The sampler extracts uncompressed cores of 13·3 cm in diameter, up to 70 cm long, from the surface layers of peat. It has two close-fitting concentric cylindrical tubes, the outer one acting as a cutter and the inner one as a collector. As the outer tube is introduced by rotation into the peat, the cut core is collected in the inner tube which is maintained in a fixed position during the rotation phase and then pushed down stepwise. This limits friction between the peat core and the wall of the corer and prevents compression or distortion of the peat. These problems are also reduced by means of three skew cutters allowing the peat to be supported during the slicing action. Air can penetrate between the tubes to the lower end of the core, suppressing any suction effect during withdrawal. The sampler has been tested and has worked satisfactorily in many different peat types.     

Lead uptake and translocation by willows in pot and field experiments

Plant growth and lead (Pb) uptake by seven willow varieties were investigated in pot and field experiments to assess the suitability of willows for phytoremediation of Pb at heavily contaminated sites such as skeet ranges. Differences in uptake and translocation of Pb in Salix were observed between pot and field experiments. In the pot experiment, willows grown in Pb-contaminated field soil for 6 months showed tolerance to very high soil Pb concentration (21,360 mg kg(-1)), and with the addition of EDTA were able to take up and translocate more than 1000 mg kg(-1) Pb into above-ground tissues. In the field experiment, all willow varieties showed tolerance to heterogeneously high soil Pb concentrations. Plants were also able to take up and translocate Pb into above-ground tissues. However, after 4.5 months, the lead concentration in the above-ground tissues of willows grown in soil amended with EDTA was less than 200 mg kg(-1). The results from the pot experiment suggest that Salix varieties have the potential to take up and translocate significant amounts of Pb into above-ground tissues using EDTA. However, to verify the phytoextraction abilities of Salix in the field, additional research is needed.     

陆地生态系统野外增温控制实验的技术与方法

由于人类活动导致的碳排放急剧增加, 工业革命以来全球地表温度显著增加约1 ℃, 未来全球气候还将持续变暖, 到21世纪末最高可升温4 ℃。这种前所未有的气候变化不仅影响陆地植被的适应策略, 也深刻影响生态系统的结构和功能。其中陆地生态系统碳收支对全球变暖的反馈, 是决定未来气候变化强度的关键因素, 因此全球已经开展了大量的生态系统尺度的野外增温控制实验, 研究生态系统碳收支对气温升高的响应, 从而提高地球系统模型的预测精度。然而由于增温技术和方法的不同, 不同研究的结果之间难以进行比较。该文系统总结了常见的野外增温技术和方法, 包括主动增温和被动增温, 阐述了其优缺点、适用对象以及相关研究成果。同时简要介绍了野外增温控制实验的前沿研究方向——新一代野外增温技术(包括全土壤剖面增温和全生态系统增温)和基于新一代增温技术开展的野外增温联网实验。     

Transpiration and metabolisation of TCE by willow plants – a pot experiment

Willows were grown in glass cylinders filled with compost above water-saturated quartz sand, to trace the fate of TCE in water and plant biomass. The experiment was repeated once with the same plants in two consecutive years. TCE was added in nominal concentrations of 0, 144, 288, and 721 mg l^?1. Unplanted cylinders were set-up and spiked with nominal concentrations of 721 mg l^?1 TCE in the second year. Additionally, ¹³C-enriched TCE solution (δ¹³C = 110.3 ‰) was used. Periodically, TCE content and metabolites were analyzed in water and plant biomass. The presence of TCE-degrading microorganisms was monitored via the measurement of the isotopic ratio of carbon (¹³C/¹²C) in TCE, and the abundance of ¹³C-labeled microbial PLFAs (phospholipid fatty acids). More than 98% of TCE was lost via evapotranspiration from the planted pots within one month after adding TCE. Transpiration accounted to 94 to 78% of the total evapotranspiration loss. Almost 1% of TCE was metabolized in the shoots, whereby trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) were dominant metabolites; less trichloroethanol (TCOH) and TCE accumulated in plant tissues. Microbial degradation was ruled out by δ¹³C measurements of water and PLFAs. TCE had no detected influence on plant stress status as determined by chlorophyll-fluorescence and gas exchange.     

Techniques for the removal of marker genes from transgenic plants

The presence of marker genes encoding antibiotic or herbicide resistances in genetically modified plants poses a number of problems. Various techniques are under development for the removal of unwanted marker genes, while leaving required transgenes in place. The aim of this brief review is to describe the principal methods used for marker gene removal, concentrating on the most recent and promising innovations in this technology.     

EUF-N fractions in different soils during a vegetation period in pot and field experiments

Summary Mobilization of soil-borne N, N fertilization and N removal by crops influence EUF-NO₃-N contents as well as EUF-N_org contents in the course of a vegetation period. N mobilization alone (no N fertilization) increases the EUF-N_org contents only temporarily (mainly in May and July), while in December they are almost the same as in March (Table 1). The EUF-NO₃ contents, on the contrary, increase during the vegetation period, so that an increment in NO₃ is registered in unplanted pots in December. This increment is larger the higher the EUF-N_org contents are in March (Table 2).N fertilization increases the contents of both EUF-N_org and EUF-NO₃, so that there is an increment in EUF-N_org as well as EUF-NO₃ in December (Table 2). This finding also applies to field experiments under fallow (Figs. 4 and 5). However, in contrast to the pot experiment, the EUF-N contents in the field experiment were only temporarily increased by N mobilization alone. This means that N immobilization had taken place which had not been observed in the pot experiment under stable moisture conditions (Fig. 4 and Table 1).A close correlation between hot-water-soluble N contents and EUF-N_org is found only under uniform management conditions (uniform N-fertilizer rates). Depending on the time of sampling different regression equations are, however, obtained because of changes in EUF-N_org due to N mobilization, whereas the hot-water-soluble N contents hardly show any variations during the vegetation period (Fig. 6 and Table 3).     

Exploratory pot experiments on sensitiveness of different crops to sodium: A. Spinach

Summary In orientating pot trials, carried out partly on soil and partly on an artificial soil-mixture, spinach showed a pronounced ability to take up sodium when dressed with sodium nitrate. The crop benefited much by this type of fertilizer both in yield and outward appearance, as compared with controls receiving calcium nitrate.In spinach sodium can replace potassium to a large extent, but it appears that, when receiving an equal supply of sodium and potassium, this plant prefers potassium. The use of sodium, supplied as a secondary constituent of nitrate fertilizers, is found to have economic importance, because it reduces the plant's need of potassium and improves the yields, even in presence of adequate potassium.In pot experiments with soil the dressing of potassium chloride in combination with Chilean nitrate gave negative results. Chilean nitrate alone, however, produced the highest yields of the series. Combined with nitrate of lime, potassium chloride initially depressed the growth, but showed in the end a slight increase of yield. As the water supplying power of this soil was more or less deficient, it is deemed possible that the negative effect of potassium chloride is due to the action of salt-concentration.It is pointed out that the normally grown spinach from the market-gardening centres destined for consumption may contain very high contents of potassium.These experiments were commenced at the Laboratory for Agricultural Chemistry of the Agricultural College at Wageningen, in concert with Prof. Ir. J. Hudig, Director of the Institute. The experiments could not be finished there owing to interference of war conditions.     

Exploratory pot experiments on sensitiveness of different crops to sodium: C. flax

Summary In three pot experiments the effect of sodium on the development of flax and its fibre quality was investigated. Sodium, applied either in the nitrate form or as dusarit in an artificial soil complex, stimulated the vegetative development, even in the presence of an ample K-supply. It also had a favourable effect on the quality of the fibre, which was greatest when 6 percent of the exchangeable bases were in form of sodium but gradually decreased at higher percentages. Overdosage of sodium, especially in combination with high potassium, induced a condition of calcium deficiency as diagnosed by the drooping of the heads (wilting of the apex), and resulted in lower grain yields.     

Exploratory pot experiments on sensitiveness of different crops to sodium: B. Oats

Summary Two pot experiments with oats are described: 1. on an artificial soil complex (sand-dusarit mixture) and 2. on a humic sandy soil, in which the Na effect of nitrate of soda was studied by comparison with calcium nitrate. On the Na-free sand-dusarit mixture a positive Na effect on grain and straw was obtained at all K levels. On the other hand, the Na effect in the soil experiment was confined to the pots without K dressing. The soil itself however, had an appreciable K content and a high Na content.A further study of the literature on pot experiments with oats leads to the conclusion that the Na effect was incorrectly interpreted in the past as a K-replacing effect, whereas the results point mostly to an independent function of Na by itself (positive yield effects in the presence of sufficient potassium). Out of 12 available examples, only 3 turn out to be in favour of a mere K-replacing action. Moreover, 2 of them cannot be called conclusive, because of unmistakable presence of fairly large amounts of Na in the growing medium.