Positive feedback between acidification and organic phosphate mineralization in the rhizosphere of maize (Zea mays L.)

To test the hypothesis that rhizosphere acidification would enhance the hydrolyzation of organic phosphates by increasing phosphatase activity. A Petri dish experiment with sterile agar and a pot experiment with a low P soil were used. In the Petri dish experiment, roots of each plant were cultured in two compartments, each of which contained agar with one of three nitrogen combinations: NH ₄ ⁺ /N0 (N0 = nitrogen free), NH ₄ ⁺ /NO ₃ ^- , and NO ₃ ^- /N0. Phytin was supplied as the sole phosphorus (P) source to all compartments. In the pot experiment, the soil in each pot was treated with N0, KNO₃, or (NH₄)₂SO₄) together with 0 or 75 mg kg^?1 phytin-P. Dry weight, P concentration, and P content of roots were highest in the NH ₄ ⁺ compartments in the Petri dish experiment. In the pot experiment, dry weight, P concentration, and P content of both shoots and roots were higher with NH ₄ ⁺ than with NO ₃ ^- . NH ₄ ⁺ treatments reduced rhizosphere pH, promoted the hydrolization of phytin, enhanced acid phosphatase activity in the rhizosphere, and increased phytin-P utilization relative to N0 and NO ₃ ^- treatments. Phosphatase activity was negatively correlated with rhizosphere pH but was positively correlated with plant P content in both experiments. Rhizosphere acidification optimized the activity of acid phosphatase excreted by maize roots and promoted phytin mineralization. NH ₄ ⁺ -induced acidification in the maize rhizosphere improved the growth of maize roots by improving P uptake from phytin; the improved growth, in turn, increased NH ₄ ⁺ uptake and acidification.     

Selenium accumulation in durum wheat and spring canola as a function of amending soils with selenite, selenate and or sulphate

Aims

A comparison was performed between plant species to determine if extractable, rather than total soil Se, is more effective at predicting plant Se accumulation over a full growing season.

Methods

Durum wheat (Triticum turgidum L.) and spring canola (Brassica napus L.) were sown in potted soil amended with 0, 0.1, 1.0, or 5.0 mg kg^?1 Se as SeO₄ ^2? or SeO₃ ^2?. In addition, SeO₄ ^2?-amended soils were amended with 0 or 50 mg kg^?1 S as SO₄ ^2?. Soils were analyzed for extractable and total concentration of Se ([Se]). Twice during the growing season plants were harvested and tissue [Se] was determined.

Results

Plants exposed to SeO₃ ^2? accumulated the least Se. Fitted predictive models for whole plant accumulation based on extractable soil [Se] were similar to models based on total [Se] in soil (R²?=?0.73 or 0.74, respectively) and selenium speciation and soil [S] were important soil parameters to consider. As well, soil S amendments limited Se toxicity.

Conclusions

Soil quality guidelines (SQGs) based on extractable Se should be considered for risk assessment, particularly when Se speciation is unknown. Predictive models to estimate plant Se uptake should include soil S, a modifier of Se accumulation.     

On the presence of sulphate in pituitary lutropin

The presence of sulphate in the carbohydrate of pituitary lutropin from different species has been investigated using a biosynthetic approach. Pituitaries from rats, rabbits, goats, and buffaloes were incubated in the presence of³⁵SO ₄ ^- and the³⁵SO ₄ ^- -labelled proteins in the tissue immunoprecipitated with a well characterized anti-sheep lutropin serum. The incorporation into immunoreactive lutropin was low in the case of rat, rabbit and goat pituitaries while, it was considerable in the case of buffalo pituitaries. Hence further characterization studies were carried out on³⁵SO ₄ ^- -labelled proteins of buffaloes. The physico-chemical, immunological and biological properties of radio-labelled buffalo pituitary material were shown to be similar to those of standard lutropin. Inin vitro conditions of incubations, most of the incorporation of³⁵SO ₄ ^- was observed into tissue lutropin while under similar conditions of incubation, [¹⁴C]-amino acids were found to get incorporated mostly into medium lutropin. The physiologically specific releasing hormone, lutropin-releasing hormone was found to stimulate the release of³⁵SO ₄ ^- -labelled lutropin from the rabbit pituitaries into the medium. These results give indirect evidence that sulphate could be present in pituitary lutropin.     

Selenium improves recovery of wheat seedlings at rewatering after drought stress

Rewatering after drought is beneficial to plants subjected to moderate drought stress, and selenium (Se) could increase the tolerance of plants to stressful environment. The role of Se in rewatering of drought-treated wheat seedlings (Triticum aestivum L., cv Hengmai5229) was studied. The objective was to elucidate whether Se could improve recovery of wheat seedlings at rewatering after drought stress. Drought stress induced a significant reduction in growth parameters, total chlorophyll and soluble protein contents, and increased the rate of superoxide radical (O ₂ ^·? ) production, MDA content, and the activities of peroxidase, catalase (CAT), and superoxide dismutase in wheat seedlings. Rewatering after drought did not significantly affect biomass accumulation of seedlings over drought treatment, although it decreased the rate of O ₂ ^·? production and MDA content. However, the combined treatment of rewatering and Se evidently promoted biomass accumulation of seedlings over drought treatment and rewatering alone; and the rate of O ₂ ^·? production, MDA content, soluble protein content and CAT activity were recovered to the control values. This indicates that Se improved recovery of wheat seedlings at rewatering after drought stress.     

Biofortification of rice grain with zinc through zinc fertilization in different countries

Aims and background

The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Earlier, we reported that sorghum roots release higher BNI-activity when grown with NH ₄ ⁺ , but not with NO ₃ ^- as N source. Also for BNI release, rhizosphere pH of <5.0 is needed; beyond this, a negative effect on BNI release was observed with nearly 80% loss of BNI activity at pH >7.0. This study is aimed at understanding the inter-functional relationships associated with NH ₄ ⁺ uptake, rhizosphere-pH and plasma membrane H⁺-ATPase (PM H⁺-ATPase) activity in regulating the release of BNIs (biological nitrification inhibitors) from sorghum roots.

Methods

Sorghum was grown hydroponically and root exudates were collected from intact plants using a pH-stat system to separate the secondary acidification effects by NH ₄ ⁺ uptake on BNIs release. A recombinant luminescent Nitrosomonas europaea bioassay was used to determine BNI-activity. Root plasma membrane was isolated using a two-phase partitioning system. Hydrolytic H⁺-ATPase activity was determined. Split-root system setup was deployed to understand the localized responses to NH ₄ ⁺ , H⁺-ATPase-stimulator (fusicoccin) or H⁺-ATPase-inhibitor (vanadates) on BNI release by sorghum.

Results

Presence of NH ₄ ⁺ in the rhizosphere stimulated the expression of H⁺-ATPase activity and enhanced the release of BNIs from sorghum roots. Fusicoccin, which stimulates H⁺-ATPase activity, also stimulated BNIs release in the absence of NH ₄ ⁺ ; vanadate, which suppresses H⁺-ATPase activity, also suppressed the release of BNIs. NH ₄ ⁺ levels (in rhizosphere) positively influenced BNIs release and root H⁺-ATPase activity in the concentration range of 0-1.0 mM, indicating a close relationship between BNI release and root H⁺-ATPase activity with a possible involvement of carrier-mediated transport for the release of BNIs in sorghum.

Conclusion

Our results suggest that NH ₄ ⁺ uptake, PM H⁺-ATPase activity, and rhizosphere acidification are functionally inter-connected with BNI release in sorghum. Such knowledge is critical to gain insights into why BNI function is more effective in light-textured, mildly acidic soils compared to other soil types.     

Partitioning of previously-accumulated nitrate to translocation,reduction, and efflux in corn roots

The effect of nitrate uptake, or its absence, on the utilization of nitrate previously accumulated by dark-grown, decpitated maize (Zea mays L., cv. DeKalb XL-45) seedlings was examined. Five-d-old plants that had been pretreated with 50 mM ¹⁴NO ₃ ^? for 20 h were exposed for 8 h to nutrient solutions containing either no nitrate or 50 mM ¹⁵NO ₃ ^? , 98.7 atom % ¹⁵N. The ambient solution, xylem exudate, and plant tissue were analyzed to determine the quantities of previously-accumulated (endogenous) ¹⁴NO ₃ ^? that were translocated to the xylem, lost to the solution, or reduced within the tissue during the 8-h period. Energy was continuously available to the roots from the attached endosperm. In the absence of incoming nitrate, appreciable reduction and translocation of the endogenous ¹⁴NO ₃ ^? occurred, but efflux of ¹⁴NO ₃ ^? to the external solution was minimal. In contrast, during ¹⁵NO ₃ ^? uptake, there was considerable efflux of ¹⁴NO ₃ ^? as well as translocation of ¹⁴NO ₃ ^? to the xylem, but little ¹⁴NO ₃ ^? was reduced. Thus there appeared to be an inverse relationship between ¹⁴NO ₃ ^? efflux and reduction. The data are tentatively interpreted on the basis of a model which envisages (a) two storage locations within roots, one of which primarily supplies nitrate for translocation and the other of which primarily supplies nitrate for outward passage through plasmalemma, and (b) the majority of nitrate reduction as occurring during or immediately following influx across the plasmalemma, with endogenous ¹⁴NO ₃ ^? initially moving outward being recycled inward and thereby being reduced.     

Ammonium nutrition increases water absorption in rice seedlings (Oryza sativa L.) under water stress

Water stress is a primary limitation on plant growth. In previous studies, it has been found that ammonium enhances the tolerance of rice plants to water stress, but how water is related to nitrogen form and water stress remains unknown. To study the effects of nitrogen form (NH ₄ ⁺ , NO ₃ ^? , and a mixture of NH ₄ ⁺ and NO ₃ ^? ) on the growth and water absorption of rice (Oryza sativa L.) seedlings, a hydroponic experiment with water stress, simulated by the addition of polyethylene glycol (PEG, 10% w/v, MW 6000), was conducted in a greenhouse. The results showed that, compared with non-water stress, under water stress, the fresh weight of rice seedlings increased by 14% with NH ₄ ⁺ nutrition, whereas it had decreased by about 20% with either NO ₃ ^? or mixed nitrogen nutrition. No significant difference was found in the transpiration rate of excised shoots or in xylem exudation of excised roots in NH ₄ ⁺ supply between the two water situations, whereas xylem flow decreased by 57% and 24% under water stress in NO ₃ ^? and mixed nutrition, and root hydraulic conductivity decreased by 29% and 54% in plants in NH ₄ ⁺ and NO ₃ ^? nutrition conditions, respectively. Although water absorption ability decreased in both NH ₄ ⁺ and NO ₃ ^? nutrition, aquaporin activity was higher in NH ₄ ⁺ than in NO ₃ ^? nutrition, regardless of water stress. We conclude that NH ₄ ⁺ nutrition can improve water handling in rice seedlings and subsequently enhance their resistance to drought.     

Alteration of nitrogen metabolism in rice variety 'Nipponbare' induced by alkali stress

Aims

Alkali stress (AS) is an important agricultural contaminant and has complex effects on plant metabolism, specifically root physiology. The aim of this study was to test the role of nitrogen metabolism regulation in alkali tolerance of rice variety 'Nipponbare'.

Methods

In this study, the rice seedlings were subjected to salinity stress (SS) or AS. Growth, the contents of inorganic ions, NH ₄ ⁺ -nitrogen (free amino acids), and NO ₃ ^? -nitrogen in the stressed seedlings were then measured. The expression of some critical genes involved in nitrogen metabolism were also assayed to test their roles in the regulation of nitrogen metabolism during adaptation of rice variety 'Nipponbare' to AS.

Results

AS showed a stronger inhibiting effect on rice variety 'Nipponbare' growth than SS. AS may have more complex effects on nitrogen metabolism than SS.

Conclusions

Effects of AS on the nitrogen metabolism of rice variety 'Nipponbare' mainly comprised two mechanisms. Firstly, in roots, AS caused the reduction of NO ₃ ^? content, which caused two harmful consequences, the large downregulation of OsNR1 expression and the subsequent reduction of NH ₄ ⁺ production in roots. On the other hand, under AS (pH, 9.11), almost all the NH ₄ ⁺ was changed to NH₃, which caused a severe deficiency of NH ₄ ⁺ surrounding the roots. Both events might cause a severe deficiency of NH ₄ ⁺ in roots. Under AS, the increased expression of several OsAMT family members in roots might be an adaptative response to the reduction of NH ₄ ⁺ content in roots or the NH ₄ ⁺ deficiency in rhizosphere. Also, the down-regulation of OsNADH-GOGAT and OsGS1;2 in roots might be due to NH ₄ ⁺ deficiency in roots. Secondly, in shoots, AS caused a larger acuumulatiuon of Na⁺, which possibly affected photorespiration and led to a continuous decrease of NH ₄ ⁺ production in shoots, and inhibited the expression of OsFd-GOGAT and OsGS2 in chloroplasts.     

Dark induction of nitrate reductase in the halophilic alga Dunaliella salina

The effect of nitrogen starvation on the NO₃-dependent induction of nitrate reductase (NR) and nitrite reductases (NIR) has been investigated in the halophilic alga Dunaliella salina. When D. salina cells previously grown in a medium with NH ₄ ⁺ as the only nitrogen source (NH ₄ ⁺ -cells) were transferred into NO ₃ ^? medium, NR was induced in the light. In contrast, when cells previously grown in N-free medium were transferred into a medium containing NO ₃ ^? , NR was induced in light or in darkness. Nitrate-dependent NR induction, in darkness, in D. salina cells previously grown at a photon flux density of 500 umol · m^?2 s^?1 was observed after 4 h preculture in N-free medium, whilst in cells grown at 100 umol · m^?2 s^?1 NR induction was observed after 7–8 h. An inhibitor of mRNA synthesis (6-methylpurine) did not inhibit NO ₃ ^? -induced NR synthesis when the cells, previously grown in NH ₄ ⁺ medium, were transferred into NO ₃ ^? medium (at time 0 h) after 4-h-N starvation. However, when 6-methylpurine was added simultaneously with the transfer of the cells from NH ₄ ⁺ to NO ₃ ^? medium (at time 0 h), NO ₃ ^? induced NR synthesis was completely inhibited. The activity of NIR decreased in N-starved cells and the addition of NO ₃ ^? to those cells greatly stimulated NIR activity in the light. The ability to induce NR in darkness was observed when glutamine synthetase activity reached its maximal level during N starvation. Although cells grown in NO ₃ ^? medium exhibited high NR activity, only 0.33% of the total NR was found in intact chloroplasts. We suggest that the ability, to induce NR in darkness is dependent on the level of N starvation, and that NR in D. salina is located in the cytosol. Light seems to play an indirect regulatory role on NO ₃ ^? uptake and NR induction due to the expression of NR and NO ₃ ^? -transporter mRNAs.     

Influence of different mineral nitrogen sources (NO 3 − -N vs. NH 4 + -N) on arbuscular mycorrhiza development and N transfer in a Glomus intraradices–cowpea symbiosis

Labeled nitrogen (¹⁵?N) was applied to a soil-based substrate in order to study the uptake of N by Glomus intraradices extraradical mycelium (ERM) from different mineral N (NO ₃ ^? vs. NH ₄ ⁺ ) sources and the subsequent transfer to cowpea plants. Fungal compartments (FCs) were placed within the plant growth substrate to simulate soil patches containing root-inaccessible, but mycorrhiza-accessible, N. The fungus was able to take up both N-forms, NO ₃ ^? and NH ₄ ⁺ . However, the amount of N transferred from the FC to the plant was higher when NO ₃ ^? was applied to the FC. In contrast, analysis of ERM harvested from the FC showed a higher ¹⁵?N enrichment when the FC was supplied with ¹⁵NH ₄ ⁺ compared with ¹⁵NO ₃ ^? . The ¹⁵?N shoot/root ratio of plants supplied with ¹⁵NO ₃ ^? was much higher than that of plants supplied with ¹⁵NH ₄ ⁺ , indicative of a faster transfer of ¹⁵NO ₃ ^? from the root to the shoot and a higher accumulation of ¹⁵NH ₄ ⁺ in the root and/or intraradical mycelium. It is concluded that hyphae of the arbuscular mycorrhizal fungus may absorb NH ₄ ⁺ preferentially over NO ₃ ^? but that export of N from the hyphae to the root and shoot may be greater following NO ₃ ^? uptake. The need for NH ₄ ⁺ to be assimilated into organically bound N prior to transport into the plant is discussed.     

Characterization of ammonium and nitrate uptake and assimilation in roots of tea plants

It has been pointed out that tea (Camellia sinensis (L.) O. Kuntze) prefers ammonium (NH ₄ ⁺ ) over nitrate (NO ₃ ^? ) as an inorganic nitrogen (N) source. ¹⁵N studies were conducted using hydroponically grown tea plants to clarify the characteristics of uptake and assimilation of NH ₄ ⁺ and NO ₃ ^? by tea roots. The total ¹⁵N was detected, and kinetic parameters were calculated after feeding ¹⁵NH ₄ ⁺ or ¹⁵NO ₃ ^? to tea plants. The process of N assimilation was studied by monitoring the dynamic ¹⁵N abundance in the free amino acids of tea plant roots by GC-MS. Tea plants supplied with ¹⁵NH ₄ ⁺ absorbed significantly more ¹⁵N than those supplied with ¹⁵NO ₃ ^? . The kinetics of ¹⁵NH ₄ ⁺ and ¹⁵NO ₃ ^? influx into tea plants followed a classic biphasic pattern, demonstrating the action of a high affinity transport system (HATS) and a low affinity transport system (LATS). The V _max value for NH ₄ ⁺ uptake was 54.5 nmol/(g dry wt min), which was higher than that observed for NO ₃ ^? (39.3 nmol/(g dry wt min)). K_M estimates were approximately 0.06 mM for NH ₄ ⁺ and 0.16 mM for NO ₃ ^? , indicating a higher rate of NH ₄ ⁺ absorption by tea plant roots. Tea plants fed with ¹⁵NH ₄ ⁺ accumulated larger amounts of assimilated N, especially glutamine (Gln), compared with those fed with ¹⁵NO ₃ ^? . Gln, Glu, theanine (Thea), Ser, and Asp were the main free amino acids that were labeled with ¹⁵N under both conditions. The rate of N assimilation into Thea in the roots of NO ₃ ^? -supplied tea plants was quicker than in NH ₄ ⁺ -supplied tea plants. NO ₃ ^? uptake by roots, rather than reduction or transport within the plant, seems to be the main factor limiting the growth of tea plants supplied with NO ₃ ^? as the sole N source. The NH ₄ ⁺ absorbed by tea plants directly, as well as that produced by NO ₃ ^? reduction, was assimilated through the glutamine synthetase-glutamine oxoglutarate aminotransferase pathway in tea plant roots. The ¹⁵N labeling experiments showed that there was no direct relationship between the Thea synthesis and the preference of tea plants for NH ₄ ⁺ .     

Nitrogen turnover in fresh Douglas fir litter directly after additions of moisture and inorganic nitrogen

The effects of wetting and drying and inorganic nitrogen (N) addition on carbon (C) and N turnover in fresh Douglas fir litter (Speuld forest, the Netherlands) were investigated. Litter was incubated for 9 days in the laboratory, receiving different moisture and N addition treatments. Following the additions, a series of reactions were observed of which most notable were a rapid retention of added ammonium and nitrate (NO ₃ ^- ) and a sudden increase in CO₂ respiration. For the rewetted-and-moist incubations, respiration levels remained elevated, N was net immobilized and nitrous oxide (N₂O) production increased throughout the experiment. About 80% of the NO ₃ ^- produced was lost again as N₂O. In the rewetted-and-dried incubations, respiration decreased during the drying phase; no clear patterns in N mineralization were detected; and N₂O production remained at constant levels, but still resulted in gaseous loss for half of the NO ₃ ^- net produced. The experiments thus revealed two important NO ₃ ^- sinks in LF1 litter, namely rapid retention of added NO ₃ ^- and gaseous loss as N₂O. The maximum NO ₃ ^- loss via these sinks was estimated at 2 kg-N ha^-1 yr^-1, which is small compared to annual NO ₃ ^- leaching at 90 cm soil depth (31 kg-N ha^-1 yr^-1).     

Respiration costs associated with nitrate reduction as estimated by 14CO2 pulse labeling of corn at various growth stages

Utilization of nitrogen in the form of either nitrate (NO ₃ ^? ) or ammonium (NH ₄ ⁺ ) ions may affect the carbohydrate metabolism and energy budget of plants. Recent studies showed that greater expenses of NO ₃ ^? to NH ₄ ⁺ reduction mostly occur in the roots and during darkness. Fertilization of corn with ¹⁵N-labeled nitrate and ammonium, combined with pulse labeling of plants in a ¹⁴CO₂ atmosphere at the V6 and V8 growth stages, allowed us to evaluate the effect of N form on the CO₂ efflux from soil. NH ₄ ⁺ oxidation was inhibited by adding dicyandiamide. In respect to ammonium, nitrate addition increased root-derived CO₂ efflux from corn by 2.6 times at stage V6 and by 1.8 times at stage V8. The time of peak ¹⁴CO₂ efflux from soil also differed between two growing stages: at V6, efflux peaked only on the second day after pulse labeling, while at V8 this occurred within the first 6 h. The strong effect of NO ₃ ^? and NH ₄ ⁺ on root respiration requires considering the N form in the soil and the nitrate reduction site location in a plant when modeling soil respiration changes and when separately estimating individual CO₂ sources that contribute to the total soil CO₂ efflux.     

Responses of CO2 efflux from an alpine meadow soil on the Qinghai Tibetan Plateau to multi-form and low-level N addition

Aims

To assess the effects of atmospheric N deposition on the C budget of an alpine meadow ecosystem on the Qinghai–Tibetan Plateau, it is necessary to explore the responses of soil-atmosphere carbon dioxide (CO₂) exchange to N addition.

Methods

Based on a multi-form, low-level N addition experiment, soil CO₂ effluxes were monitored weekly using the static chamber and gas chromatograph technique. Soil variables and aboveground biomass were measured monthly to examine the key driving factors of soil CO₂ efflux.

Results

The results showed that low-level N input tended to decrease soil moisture, whereas medium-level N input maintained soil moisture. Three-year N additions slightly increased soil inorganic N pools, especially the soil NH ₄ ⁺ -N pool. N applications significantly increased aboveground biomass and soil CO₂ efflux; moreover, this effect was more significant from NH ₄ ⁺ -N than from NO ₃ ^? -N fertilizer. In addition, the soil CO₂ efflux was mainly driven by soil temperature, followed by aboveground biomass and NH ₄ ⁺ -N pool.

Conclusions

These results suggest that chronic atmospheric N deposition will stimulate soil CO₂ efflux in the alpine meadow on the Qinghai–Tibetan Plateau by increasing available N content and promoting plant growth.     

Effect of salt stress on antioxidant system of plants as related to nitrogen nutrition

In plants of wheat (Triticum aestivum L.) grown in the media with nitrate (NO ₃ ^? plants), ammonium (NH ₄ ⁺ plants), and without nitrogen (N-deficient plants), the response to oxidative stress induced by the addition of 300 mM NaCl to the nutrient solution was investigated. Three-day-long salinization induced chlorophyll degradation and accumulation of malondialdehyde (MDA) in the leaves. These signs of oxidative stress were clearly expressed in NO ₃ ^? and N-deficient plants and weakly manifested in NH ₄ ⁺ plants. In none of the treatments, salinization induced the accumulation of MDA in the roots. Depending on the conditions of N nutrition, salt stress was accompanied by diverse changes in the activity of antioxidant enzymes in the leaves and roots. Resistance of leaves of NH ₄ ⁺ plants to oxidative stress correlated with a considerable increase in the activities of ascorbate peroxidase and glutathione reductase. Thus, wheat plants grown on the NH ₄ ⁺ -containing medium were more resistant to the development of oxidative stress in the leaves than those supplied with nitrate.     

Culture medium optimization for improved puerarin production by cell suspension cultures of Pueraria tuberosa (Roxb. ex Willd.) DC.

The effects of carbon, nitrogen, phosphate, and copper on cell growth and production of the isoflavone puerarin by suspension cultures of Pueraria tuberosa (Roxb. ex. Willd.) DC were investigated. Among the various sugars evaluated (glucose, galactose, fructose, maltose, and sucrose), use of sucrose in the medium led to the maximum accumulation of puerarin. A sucrose-feeding strategy in which additional sucrose was added to the flasks 15?d into the culture cycle stimulated both cell biomass and puerarin production. The maximum production of puerarin was obtained when a concentration balance of 20:60?mM NH ₄ ⁺ /NO ₃ ^? was used as the nitrogen source. Alteration in the concentration balance of nitrogen components (NH ₄ ⁺ /NO ₃ ^? 60:20?mM) or the use of either NH ₄ ⁺ or NO ₃ ^? alone decreased biomass production and puerarin accumulation compared with the control culture (NH ₄ ⁺ /NO ₃ ^? 20:20?mM). High amounts of phosphate (2.5 and 5?mM) in the medium inhibited puerarin production whereas 0.625?mM phosphate promoted puerarin production (68.3???g/g DW on day?25). An increase in Cu²⁺ concentration from 0.025 to 0.05?mg/l in the P. tuberosa cell culture medium resulted in a 2.2-fold increase in puerarin production (up to 141???g/g DW on day?25) but reduced cell culture biomass.     

Nitrous oxide emissions and nitrate leaching from a rain-fed wheat-maize rotation in the Sichuan Basin, China

Aims

A 3-year field experiment (October 2004–October 2007) was conducted to quantify N₂O fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China.

Methods

Static chamber-GC techniques were used to measure soil N₂O fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha^?1 yr^?1 or 150 kg N?ha^?1 per crop); N250 (500 kg N fertilizer ha^?1 yr^?1 kg or 250 kg N?ha^?1 per crop). Nitrate (NO ₃ ^? ) leaching losses were measured at nearby sites using free-drained lysimeters.

Results

The annual N₂O fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg N?ha^?1 yr^?1 corresponding to an N₂O emission factor ranging from 0.12 % to 1.06 % (mean value: 0.61 %). The relationship between monthly soil N₂O fluxes and NO ₃ ^- leaching losses can be described by a significant exponential decaying function.

Conclusions

The N₂O emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO ₃ ^? , is an underrated regulating factor of soil N₂O fluxes from cropland, especially in the regions where high NO ₃ ^- leaching losses occur.     

Limnology of Gallocanta Lake,Aragon, northeastern Spain

A limnological study was sustained from September 1980 to October 1981 to show the evolution of Gallocanta Lake (N.E. Spain) under very dry climatic conditions. It is the physical terminus within an endorheic basin of 500 km² situated 1 000 m over the sea level. In 1977 its maximum depth was 2.5 m but it decreased to 60 cm in 1981 as a consequence of the last very dry years. It is actually 6 km long and 2.5 km wide, and its area is approximately 12 km². Salt concentration was quite constant (32–43 g l^-1) since September 1980 until June 1981. The equivalent ratio Cl^-:SO _inf4 ^sup2- varied between 2.2 and 2.8. From June through October 1981 salinity increased up to 105 g l^-1 and Cl^-:SO _inf4 ^sup2- equivalent ratio varied between 2.5 and 3.4. The relative concentrations of ions were retained all year ordinated as follows: Cl^- > SO _inf4 ^sup2- > HCO _inf3 ^sup- >. CO _inf3 ^sup2- ; Na⁺ > Mg²⁺ ? Ca²⁺ > K⁺. Total reactive phosphorus was less than 1.5 µg-at l^-1 from September 1980 to January 1981. During the rest of the studied period it varied between 2 and 8 µg-at l^-1 (the maximum, in February 1981). Nitrogen oxidized forms were relatively high in winter (4–8 µg-at N-NO _inf3 ^sup- l^-1; 0.5–2.5 µg-at N-NO _inf2 ^sup- l^-1), and early May 1981 (25 µg-at N-NO _inf3 ^sup- l^-1; 1 µg-at N-NO _inf2 ^sup- l^-1). Neither reached 1 µg-at l^-1 from September through December 1980, or from June through October 1981. Planktonic algae increased in density during the period of the study from 10³ to 5 10⁵ cells ml^-1. Chromulina sp. was the main species during autumn and winter (>50% in number of cells ml^-1) while the copepod Arctodiaptomus salinus decreased its population. Lobocystis dichotoma increased its density from December 1980 to May 1981 and was dominant in spring (>90%), when a typical reproductive activity was observed in the Arctodiaptomus population. This species disappeared in late spring. In June 1981 Brachionus plicatilis reached up to near 2 000 individuals ml^-1. This species was not observed after August 1981. Then the ciliate Fabrea salina was the only zooplankter staying in the free waters of the lake and Nannochloris sp. the dominant alga (>90%). Dense macrophytic beds constituted of Lamprothamnium papulosum and Chara galioides covered the bottom of the lake in September 1980 and before that date since the observations began in 1977. They decreased in covered area since October 1980 and disappeared during summer 1981. Gallocanta Lake is in a very stressed situation produced by prolonged drought. The increased salt concentration together with the extremely cold and hot temperatures, and the lack of nitrogen relative to phosphorus are the main environmental factors that controlled the biological populations during the period of the present study.     

Denitrification in soil amended with thermophile-fermented compost suppresses nitrate accumulation in plants

NO ₃ ^? is a major nitrogen source for plant nutrition, and plant cells store NO ₃ ^? in their vacuoles. Here, we report that a unique compost made from marine animal resources by thermophiles represses NO ₃ ^? accumulation in plants. A decrease in the leaf NO ₃ ^? content occurred in parallel with a decrease in the soil NO ₃ ^? level, and the degree of the soil NO ₃ ^? decrease was proportional to the compost concentration in the soil. The compost-induced reduction of the soil NO ₃ ^? level was blocked by incubation with chloramphenicol, indicating that the soil NO ₃ ^? was reduced by chloramphenicol-sensitive microbes. The compost-induced denitrification activity was assessed by the acetylene block method. To eliminate denitrification by the soil bacterial habitants, soil was sterilized with γ irradiation and then compost was amended. After the 24-h incubation, the N₂O level in the compost soil with presence of acetylene was approximately fourfold higher than that in the compost soil with absence of acetylene. These results indicate that the low NO ₃ ^? levels that are often found in the leaves of organic vegetables can be explained by compost-mediated denitrification in the soil.