开垦年限对黑土氮初级转化速率和净转化速率的影响

以东北黑土区开垦2 a和开垦30 a的典型旱作土壤为研究对象,采用15N同位素成对标记技术开展室内培养试验,利用数值计算模型(FLUAZ)计算不同开垦年限土壤的氮初级转化速率,以比较不同开垦年限黑土氮初级转化速率和净转化速率的差异,明确开垦年限对黑土氮转化过程的影响。结果表明,与开垦2a土壤相比,开垦30a土壤的有机碳和水溶性有机碳含量显著降低,导致土壤氮初级矿化速率和初级固定速率也显著降低。但开垦30a土壤的初级硝化速率、净硝化速率和净氮矿化速率却显著高于开垦2a土壤。两个开垦年限土壤的初级硝化速率分别为净硝化速率的1.15倍和1.02倍,说明土壤微生物对硝态氮的固定很少。开垦30a土壤的m/i值(氮初级矿化速率与初级固定速率之比)和n/ia值(初级硝化速率与初级铵态氮固定速率之比)均显著大于1,而开垦2 a土壤的m/i值和n/ia值均接近1。表明开垦2 a土壤的氮矿化与固定过程紧密偶联,氮素损失的风险较小,而开垦30 a土壤中氮矿化量超过了固定量,这为硝化作用的进行提供了底物,增加了硝酸盐反硝化和淋溶风险。     

Is N‐feedback involved in the regulation of nitrogenase activity in Medicago truncatula?

To determine whether senescing leaves provoke an active nitrogen (N) remobilization that results in the reduction of nitrogenase activity, 60% of Medicago truncatula lower leaves were either darkened or individually excised for two weeks. Although a considerable amount of N was remobilized, N₂ fixation activity was found to be increased to maintain the N source/sink balance, indicating an absence of the negative N‐feedback regulation of nitrogenase activity in the senescing M. truncatula.     

Mineralization of Organic Nitrogen in Soils with Contrasting Fertility Was Regulated Differently by Addition of Biochar and Animal Manures

ABSTRACT

How to restore the soil fertility and productivity in a damaged and then reclaimed area with extremely low fertility is a big concern worldwide. To explore the method of soil restoration in the coal mining subsidence area, the effects of biochar application coupled with organic fertilizer (animal manures) on the process of organic nitrogen (N) mineralization were studied in a 149 days leaching experiment. Biochar were applied (wt/wt) at the rates of 0%, 1%, and 3%. Two organic fertilizers with different C/N ratio (chicken and sheep manures) were applied at the rate of 200 mg N·kg^?1 soil. A vegetable soil with high-fertility was used as the comparison. The results showed that when treated with chicken manure, the reclaimed soil had 11.13% lower mineralization potential and 20.00% lower inorganic nitrogen production from mineralization than the vegetable soil. Compared with the non-biochar treatment, biochar at both application rates decreased N leaching in chicken manure-treated reclaimed soil, i.e., by 21.49% (1% biochar) and 28.31% (3% biochar), respectively, whereas only high rate of biochar application decreased N leaching in chicken manure-treated vegetable soil by 8.10%. However, N leaching in sheep manure-treated reclaimed soil was unaffected by the biochar application. Thus, the effect of the biochar on the organic nitrogen mineralization was affected by both soil and organic fertilizer type.     

Carbon and nitrogen stocks and their mineralization potentials are higher under organic than conventional farming practices in Japanese Andosols

ABSTRACT

This study aimed at understanding whether and how long-term organic rice farming affects soil carbon (C) and nitrogen (N) stocks and their mineralization potentials in submerged rice paddies in Tochigi, Japan. An incubation experiment was carried out to assess the impacts of internal nutrient cycling after organic farming (OF) for 4–5 years (4OF), 8–9 years (8OF), and 12 years (12OF), compared with a conventional rice field (CF). Soil samples were collected at 0–15 cm and 15–20 cm in flooded rice fields after harvest in October 2013. pH and bulk density at 0–15 cm were significantly lower in 12OF fields than in CF fields (by 0.22 unit pH and 17.5%, respectively). Compared with CF, 12OF fields showed significant differences in soil organic carbon (SOC) and total nitrogen (TN), but 4OF and 8OF fields did not. In 8OF fields, the C decomposition (Co) and N mineralization (No) potentials were significantly higher (by 34.0% and 35.6%, respectively, at 0–15 cm, and by 67.1% and 24.5% at 15–20 cm) than in CF fields. Similarly, in 8OF fields at 0–15 cm, the Co:SOC and No:TN ratios were 19.8% and 23.2% higher, respectively, than in CF fields. Co, No, Co:SOC, and No:TN in 12OF fields were higher than those in CF fields, demonstrating the effects of prolonged organic rice farming. Additionally, in 12OF fields, C and N stocks were significantly higher (by 15.5% and 17.2%, respectively, at 0–15 cm, and by 4.8% and 12.1% at 15–20 cm) than in CF fields. Our findings suggest that long-term organic rice farming increases soil C and N stocks as well as C and N mineralization in Japanese Andosols.     

Stable carbon isotope ratios of water-extractable organic carbon affected by application of rice straw and rice straw compost during a long-term rice experiment in Yamagata,Japan

ABSTRACT

Hot-water- and water-extractable organic matter were obtained from soil samples collected from a rice paddy 31 years after the start of a long-term rice experiment in Yamagata, Japan. Specifically, hot-water-extractable organic carbon and nitrogen (HWEOC and HWEON) were obtained by extraction at 80°C for 16 h, and water-extractable organic carbon and nitrogen (WEOC and WEON) were obtained by extraction at room temperature. The soil samples were collected from surface (0–15 cm) and subsurface (15–25 cm) layers of five plots that had been treated with inorganic fertilizers alone or with inorganic fertilizers plus organic matter, as follows: PK, NPK, NPK plus rice straw (RS), NPK plus rice straw compost (CM1), and NPK plus a high dose of rice straw compost (CM3). The soil/water ratio was 1:10 for both extraction temperatures. We found that the organic carbon and total nitrogen contents of the bulk soils were highly correlated with the extractable organic carbon and nitrogen contents regardless of extraction temperature, and the extractable organic carbon and nitrogen contents were higher in the plots that were treated with inorganic fertilizers plus organic matter than in the PK and NPK plots. The HWEOC and WEOC δ¹³C values ranged from ?28.2% to ?26.4% and were similar to the values for the applied rice straw and rice straw compost. There were no correlations between the HWEOC or WEOC δ¹³C values and the amounts of HWEOC or WEOC. The δ¹³C values of the bulk soils ranged from ?25.7% to ?23.2% and were lower for the RS and CM plots than for the PK and NPK plots. These results indicate that HWEOC and WEOC originated mainly from rice plants and the applied organic matter rather than from the indigenous soil organic matter. The significant positive correlations between the amounts of HWEOC and HWEON and the amount of available nitrogen (P < 0.001) imply that extractable organic matter can be used as an index for soil fertility in this long-term experiment. We concluded that the applied organic matter decomposed more rapidly than the indigenous soil organic matter and affected WEOC δ¹³C values and amounts.     

稳定碳、氮同位素在牛肉加工过程中的分馏效应

为了探究牛肉及副产物中稳定碳、氮同位素在加工过程中的变化规律,确证稳定碳、氮同位素在牛肉加工制品产地溯源中的稳定性和有效性。本试验通过对牛肉进行不同时间的水煮、烤制和油炸3种处理,其中水煮和烤制加工时间分别为5、10、15、20、25和30 min,油炸加工时间分别为1、2、3、4和5 min;采用元素分析仪-稳定同位素比率质谱仪(EA-IRMS)测定脱脂牛肉、粗脂肪及副产物中δ¹³C和δ¹⁵N值。结果表明,脱脂牛肉中δ¹³C值在水煮、烤制和油炸3种加工方式不同加工时间之间均无显著差异,水煮和烤制后粗脂肪中δ¹³C值无显著变化,油炸后的牛肉粗脂肪δ¹³C值主要受植物油的影响,加工方式及加工时间对其无显著影响;水煮脱脂牛肉δ¹⁵N值在加工25、30 min时与对照组牛肉存在显著差异,但平均差值仅为0.3‰~0.9‰。牛肉稳定碳、氮同位素在不同加工过程中分馏效应较小,可有效用于牛肉加工半成品及成品的原产地溯源。     

Impacts of wetting-drying cycles on short-term carbon and nitrogen dynamics in Amynthas earthworm casts

Effects of earthworm casts on soil nutrient dynamics and their responses to changing moisture availability in subtropical ecosystems remain poorly understood. This study aimed to examine short-term carbon(C) and nitrogen(N) dynamics and their interactions with wetting-drying cycles in three different structural forms(i.e., granular, globular, and heap-like) of Amynthas earthworm casts. The rates of C and N mineralization in the earthworm casts were examined under two different wetting-drying cycles(i.e., 2-d and 4-d wetting intervals) using a rainfall simulation experiment. After three simulated rainfall events, subsamples of the earthworm casts were further incubated for 4 d for the determination of CO_2 and N_2O fluxes. The results of this study indicated that the impacts of wetting-drying cycles on the short-term C and N dynamics were highly variable among the three cast forms, but wetting-drying cycles significantly reduced the cumulative CO_2 and N_2O fluxes by 62%–83% and 57%–85%, respectively, when compared to the control without being subjected to any rainfall events. The C mineralization rates in different cast forms were affected by the amount of organic substrates and N content in casts, which were associated with the food preference and selection of earthworms. Meanwhile, the cumulative N_2O fluxes did not differ among the three cast forms. Repeated wetting and drying of casts not only enhanced aggregate stability by promoting bonds between the cast particles, but also inhibited microbial survival and growth during the prolonged drying period, which together hindered decomposition and denitrification. Our findings demonstrated that the interactions between the structural forms, aggregate dynamics, and C and N cycling in the earthworm casts were highly complex.     

尿素氮形态转化对腐殖酸的响应

通过模拟试验研究了不同用量腐殖酸对土壤中尿素氮形态转化的影响。结果表明,腐殖酸对尿素态氮形态转化的影响受其施用量的制约。与对照相比,低浓度腐殖酸(<15gkg-1)对尿素水解及以后的氮转化过程抑制作用较小,有时甚至促进了尿素水解;高浓度腐殖酸(15gkg-1和20gkg-1)则能明显的抑制尿素水解,延长尿素态氮在土壤中的停留时间,增加铵态氮含量,减少硝态氮的生成及氮素损失量,大大提高尿素利用效率。由此可见,腐殖酸不仅是一种脲酶抑制剂,还是一种硝化抑制剂。     

设施菜田不同施氮处理对硝酸盐迁移和积累的影响

在设施菜地条件下,研究了氮肥减施及配施抑制剂处理在黄瓜生长期对土壤NO3--N迁移累积的影响。结果表明,氮肥减施处理可显著降低土壤表层和整个土体的NO3--N含量。常规施氮量时0~40 cm土层的NO3--N含量均高于其它处理,减氮30%后0~40 cm土层未出现NO3--N显著积累现象;氮肥配施抑制剂处理不同程度降低了土壤NO3--N含量,且抑制硝态氮向下层土壤淋失,其中抑制剂组合的效果最好。氮肥配施抑制剂,可以有效控制NO3--N在土壤和植物体内的过量累积,减少硝态氮淋溶损失。     

Involvement of Bradyrhizobium japonicum denitrification in symbiotic nitrogen fixation by soybean plants subjected to flooding

Denitrification by Bradyrhizobium japonicum bacteroids contributes to nitric oxide (NO) production within soybean nodules in response to flooding conditions. However, the physiological relevance of NO production by denitrification in B. japonicum-Glycine max symbiosis is still unclear. In this work, soybean plants were inoculated with B. japonicum strains lacking the nirK or norC genes which encode the copper-containing nitrite reductase and the c-type nitric oxide reductase enzymes, respectively. 14 days flooding increased nodule number of plants inoculated with the WT and norC strains, but not of plants inoculated with the nirK mutant. However, nodule dry weight was not affected by 14 days flooding regardless of the strain used for inoculation. Supporting this observation, individual nodule growth was significantly higher in plants inoculated with nirK than those inoculated with WT or norC after 14 days flooding. Nodule functioning was strongly inhibited by flooding since leghemoglobin content of the nodules induced by any of the strains was significantly decreased after 7 or 14 days flooding compared to control plants. However, this effect was more relevant in nodules of plants inoculated with the WT or norC mutant than in those inoculated with the nirK mutant. Nitrogen fixation was also estimated by analyzing nitrogen content derived from biological nitrogen fixation in shoots, using the ¹⁵N isotope dilution technique. By using this approach, we observed that the negative effect of 14 days flooding on nitrogen fixation was more pronounced in plants inoculated with the norC mutant. However, nitrogen fixation of plants inoculated with nirK showed the highest tolerance to 14 days flooding. These findings allowed us to demonstrate the previously proposed hypothesis which suggests that NO formed by copper-containing nitrite reductase in soybean nodules, in response to flooding, has a negative effect on nitrogenase activity. We propose that inoculation of soybeans with a B. japonicum nirK mutant, which does not produce NO from nitrate, increases the tolerance of symbiotic nitrogen fixation to flooding.