较长时间内15N标记的氨态氮和硝态氮在小嵩草草甸中的运移规律

运用15N稳定性同位素技术,对15N标记的硝酸盐和铵盐在输入小嵩草(Kobresia pygaea C.B.Clarke)草甸11～13个月后的运移规律进行了研究.在经历11～13个月后,进入无机氮库中的15N很少,一般不超过所输入氮素的l%,而较多的1 5N为土壤有机质、土壤微生物和植物所固持.NO3--15N和NH4 -1 5N在小嵩草草甸中的运移规律差异很大.在11、12和13个月后,NO3--15N的总恢复率分别为92.83%、92.64%和79.96%;而NH4 -15N的则分别为49.6%、63.33%和66.22%.两者的差异在土壤有机质、土壤微生物和植物等库之间的分配中更加明显.输入NO3--15N时在11、12个月后植物所固持的15N最多,而土壤微生物和土壤有机质所固持的15N比较接近,而在13个月后,土壤有机质和植物所固持的15N接近,而土壤微生物所固持的15N下降许多;当输入NH4 -15N,土壤有机质所固持的1 5N比植物和土壤微生物所固持的都多,而且植物所固持的15N比较稳定,而土壤微生物所固持的15N则有较大变化.这表明在较长的时间内嵩草草甸对NO3-和NH4 的固持能力是不一样的.     

草甸草原土壤与植物系统自然丰度氮稳定同位素的年际变化及其指示作用

氮是陆地生态系统生产力的首要限制性养分,利用自然丰度δ¹⁵N(¹⁵N/¹⁴N)可以有效指示生态系统氮循环过程。本试验研究了内蒙古草甸草原土壤与植物系统自然丰度δ¹⁵N、土壤净氮矿化潜势的年际变化。结果表明: 2017—2020年,土壤NO₃^--N含量(9.83～14.79 mg·kg^-1)均显著高于NH₄⁺-N含量(3.92～5.00 mg·kg^-1);土壤NH₄⁺的δ¹⁵N值(13.3‰～18.3‰)显著高于NO₃^-的δ¹⁵N值(3.76‰～6.14‰),土壤NO₃^-的δ¹⁵N值与土壤NO₃^-含量呈显著负相关;干旱年NH₄⁺的δ¹⁵N值相对较高,降水较高或较低年NO₃^-的δ¹⁵N值显著降低。干旱年土壤净氮矿化速率、净氨化速率显著高于湿润年,而土壤硝化速率与年降水量无显著相关性。植物δ¹⁵N值与土壤δ¹⁵N值无显著相关性,但与植物N含量呈显著负相关;豆科植物与非豆科植物δ¹⁵N值、N含量均呈显著正相关,在一定程度上表明豆科植物对非豆科植物的N吸收具有促进作用。研究结果可为草原土壤-植物系统氮循环过程及其对降水变化的响应提供数据支撑。     

东北森林两种典型阔叶树种子和幼苗对15N同位素的富集响应

以东北森林两种典型的阔叶树种风力传播种子——花曲柳和色木槭种子为研究对象,通过室内¹⁵N尿素浸泡试验和温室盆栽试验,设置4个浓度(0、0.05、0.1和0.2 g·L^-1)、3个浸泡时间(4、8和12 d)与4个叶期(2、4、6和8叶)处理,研究种子浸泡浓度、浸泡时间和幼苗叶期对种子和幼苗¹⁵N富集的影响.结果表明: 浸泡浓度和浸泡时间对两树种种子δ¹⁵N值均有显著的正反馈作用,高浓度和长时间(0.2 g·L^-1+12 d)更有利于种子¹⁵N总量的富集,花曲柳和色木槭种子¹⁵N同位素最大富集倍数的浸泡浓度和浸泡时间组合分别为0.1 g·L^-1+(4、8 d)和0.05 g·L^-1+(4、8 d);δ¹⁵N值稀释率随幼苗株高的增加先急剧减少(2~6叶)后趋于稳定,幼苗从8叶开始叶片¹⁵N总量降低,表明6叶幼苗更适合追踪幼苗的来源;幼苗叶片δ¹⁵N值与种子浸泡浓度、浸泡时间和种子的δ¹⁵N值呈显著正相关.花曲柳和色木槭种子及幼苗均能成功富集到¹⁵N信号,采用0.1 g·L^-1+8 d+6叶组合最适合追踪花曲柳和色木槭种子和幼苗.     

Responses of plant 15N natural abundance and isotopic fractionation to N addition reflect the N status of a temperate steppe in China

Aims Elevated anthropogenic nitrogen (N) deposition could alter N status in temperate steppe. However, threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems. Research on the natural abundance of¹⁵N (δ¹⁵N) could greatly help provide integrated information about ecosystem N status. The goal of this study was to investigate the suitability of measurements of δ¹⁵N of major ecosystem N pools and several key species, plant¹⁵N fractionation, together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia.     

施钾对甘薯氮素转移分配及氮代谢酶活性的影响

利用¹⁵N示踪技术,研究了施钾对甘薯发根结薯期、薯块膨大期地上和地下部氮素转移分配、光合特性及氮代谢酶活性的影响.结果表明: 在发根结薯期,施钾显著提高¹⁵N向地上部的转移分配,其中K₃(K₂O, 300 mg·kg^-1)处理与对照相比¹⁵N向叶片转移速率提高了76.2%,¹⁵N积累量提高了92.1%.在薯块膨大期,随施钾量增加地上部叶片¹⁵N总分配率由33.7%降低至24.4%,块根¹⁵N分配率由5.8%升高至17%,其中K₃处理块根¹⁵N积累量是对照的3倍.两个关键生长期硝酸还原酶、谷氨酸脱氢酶、谷氨酰胺合酶、谷氨酸合酶和净光合速率(P_n)均随施钾量的增加而提高.逐步回归分析表明,氮代谢酶活性和P_n是影响甘薯¹⁵N转移和分配的主要因素(R分别为0.965和0.942),通径分析表明,在发根结薯期主要通过促进硝酸还原酶和谷氨酸脱氢酶介导的氮素催化能力促进氮素向地上部分配;在薯块膨大期主要通过提高谷氨酰胺合酶/谷氨酸合酶循环介导的氮素同化能力促进氮素向地下部分配.     

Improvement of the 15N dilution method for estimation of absorption of NOx by plants supplied with 15N-labelled fertilizer

To develop further the methods for estimation of NOx absorption by plants supplied with ¹⁵N-labelled fertilizer, we proposed a new calculation method, total N fixed method (TNF), and compared with the ¹⁵N dilution method and the classical mass balance method (MB).
Hydroponically grown soybean plants were supplied with ¹⁵N-labelled nitrate and exposed to 200–250 nl l⁻¹ NO₂ for 7 d. The proportions of the N derived from NO₂ to total N in exposed plants were estimated by the three methods.
The reported rates of NO₂ absorption by several plant species, estimated by the ¹⁵N dilution method, were recalculated using the TNF method. The results of the two methods were compared and showed that: (1) The ¹⁵N dilution method overestimated the content of NO₂-N in exposed plants compared with the MB method whilst the TNF method produced estimations of NO₂-N closer to those by the MB method when the plants were supplied with 5 m M nitrate. (2) The differences in estimations between the MB method and either the ¹⁵N dilution method or the TNF method increased with decreasing supply of ¹⁵N-labelled nitrate to roots.     

Nitrogen assimilation in Lolium perenne colonized by the arbuscular mycorrhizal fungus Glomus fasciculatum

To investigate nitrogen assimilation in Lolium perenne L. colonized by the arbuscular mycorrhizal (AM) fungus Glomus fasciculatum (Thax. sensu Gerd.), nitrate uptake, key enzyme activities, and ¹⁵N incorporation into free amino acids were measured. After a 4-h labelling period with [¹⁵N]nitrate, ¹⁵N content was higher in roots and shoots of AM-plants than in those of control plants. Glutamine synthetase (GS) and nitrate reductase (NR) activities were increased in shoots of AM-plants, but not in roots. More label was incorporated into amino acids in shoots of AM plants. Glutamine, glutamate, alanine and γ-aminobutyric acid were the major sinks for ¹⁵N in roots and shoots of control and AM plants. Interactions between mycorrhizal colonization, phosphate and nitrate nutrition and NR activity were investigated in plants which received different amounts of phosphate or nitrate. In shoots of control plants, NR activity was not stimulated by high levels of phosphate nutrition but was stimulated by high levels of nitrate. At 4 m M nitrate in the nutrient solution, NR activity was similar in control and AM plants. We concluded that mycorrhizal effects on nitrate assimilation are not mediated via improved phosphate nutrition, but could be due to improved nitrogen uptake and translocation.     

铵盐和硝酸盐稳定同位素丰度测定方法及其应用案例

综述了过去几十年来铵盐和硝酸盐稳定同位素丰度测定方法的历史发展变化,分析了各种方法的优缺点,并对新方法作了介绍和推荐.目前铵盐稳定同位素丰度的最新测定方法为次溴酸盐氧化结合羟胺还原法,硝酸盐氮氧同位素丰度主流的测定方法为反硝化细菌法和镉粉叠氮酸还原化学法.这些方法的主要共同特点是以N₂O为分析物,分析精度高,对样品的含氮量需求小,一般只需要10～60 nmol N,适用于低浓度样品.新方法的建立对于国内外开展氮素循环研究将起到极大的推动作用.     

不同黄腐酸用量对‘红将军’苹果产量、品质和15N-尿素去向的影响

以15年生红将军/八棱海棠为试材,运用¹⁵N同位素示踪技术,设置单施尿素(CK)及尿素配施不同用量黄腐酸处理(黄腐酸用量分别为75、150、300和450 kg·hm^-2,分别以NF₁、NF₂、NF₃和NF₄表示),研究不同黄腐酸用量对苹果植株¹⁵N-尿素吸收、利用、残留、损失及果实产量和品质的影响.结果表明: 至果实成熟期,苹果根系、一年生枝和叶片的Ndff值(植株器官从肥料中吸收分配到的¹⁵N量对该器官全氮量的贡献率)均为NF₃>NF₄>NF₂>NF₁>CK,且各处理间差异显著.植株全氮量和¹⁵N吸收量均以NF₃处理最大,其次为NF₄处理,CK处理最低.与CK处理相比,NF₁、NF₂、NF₃和NF₄处理¹⁵N利用率分别提高了14.2%、33.5%、64.2%和50.0%,而¹⁵N损失率分别降低了9.1%、18.5%、37.1%和28.7%.不同处理土壤¹⁵N残留量不同.配施黄腐酸处理0～60 cm土层¹⁵N残留量显著高于CK处理,其中以NF₃处理最多,而在60～100 cm土层显著低于CK处理.NF₃处理单株产量和纯收益较CK处理增幅最大,分别为15.8%和20.2%,其次为NF₄处理,同时,NF₃处理果实硬度、可溶性固形物含量和糖酸比均达到最高水平.通过对果实产量和氮素利用率与黄腐酸施用量进行拟合分析,得出本试验条件下适宜的黄腐酸用量为326.41～350.61 kg·hm^-2.     

外生菌根真菌菌丝对马尾松苗氮素传递的影响

为探究外生菌根真菌菌丝对马尾松Pinus massoniana幼苗氮素的吸收、传递及分配规律的影响,本研究应用¹⁵N示踪技术,采用四室隔网系统进行盆栽试验。研究表明：供体接种外生菌根真菌后,根外菌丝能够穿过粘土层和隔离层到达受体室,在供、受体植株之间形成菌丝桥。接种不同外生菌根真菌均显著增加供体植株苗高、地径及生物量(P<0.05),但对受体植株的影响有差异,其中接种橙黄硬皮马勃Scleroderma citrinum (Sc)对植株苗高、地径及生物量具有显著的促进作用(P<0.05)。接种对供、受体植株全氮含量无显著性的规律(P>0.05),只有接种东方豆马勃Pisolithus orientalis (Po)的植株全氮含量显著高于其他处理。接种能够显著提高供体植株根、茎、叶的吸氮量,且叶>根>茎,受体植株中,接种Po、Sc和褐环乳牛肝菌Suillus luteus (Sl)的植株总吸氮量较不接种(NE)显著增加(P<0.05),而接种混合菌(Sm)的植株与NE无显著差异(P>0.05)。接种Sl的植株¹⁵N传递率最高(75.86%),受体植株对¹⁵N吸收量最大(91.68 μg/pot),Po次之。供体植株中,除接种Sl的植株¹⁵N主要分配在叶外,其他处理的¹⁵N分配中心均在根部,在受体植株中,接种Po、Sl、Sm的植株¹⁵N主要分配在根部,而NE和接种Sc的植株¹⁵N主要分配在茎。综上,在马尾松供、受体苗木间能形成菌丝桥,接种外生菌根真菌能够促进马尾松供体植株苗高、地径的生长及生物量的积累,提高植株吸氮量,对于受体植株不同菌种的作用有差异,其中接种Sc的苗木表现最好。此外,不同的菌种菌丝对植株的全氮含量、¹⁵N吸收量、传递率及分配率的影响也不同,其中,以接种Po和Sl的苗木表现较好。     

DNA buoyant density shifts during 15N-DNA stable isotope probing

DNA-based stable isotope probing (SIP) is a novel technique for the identification of organisms actively assimilating isotopically labeled compounds. Herein, we define the limitations to using ¹⁵N-labeled substrates for SIP and propose modifications to compensate for these shortcomings. Changes in DNA buoyant density (BD) resulting from ¹⁵N incorporation were determined using cultures of disparate GC content (Escherichia coli and Micrococcus luteus). Incorporation of ¹⁵N into DNA increased BD by 0.015±0.002 g mL⁻¹ for E. coli and 0.013±0.002 g mL⁻¹ for M. luteus. The DNA BD shift was greatly increased (0.045 g mL⁻¹) when dual isotope (¹³C plus ¹⁵N) labeling was employed. Despite the limited DNA BD shift following ¹⁵N enrichment, we found the use of gradient fractionation, followed by a comparison of T-RFLP profiles from fractions of labeled and control treatments, facilitated detection of enrichment in DNA samples from either cultures or soil.     

硝酸盐供应水平对平邑甜茶幼苗生长、光合特性与15N吸收、利用的影响

以霍格兰营养液为培养基质,采用¹⁵N同位素示踪技术,研究不同浓度¹⁵NO₃^--N (0、2.5、5、10和20 mmol·L^-1,分别以N₀、N₁、N₂、N₃和N₄表示)对平邑甜茶幼苗生长、光合作用、¹⁵N吸收、利用及分配的影响.结果表明:与其他处理相比,N₂处理幼苗叶绿素含量、叶面积及各器官干质量最大.叶片净光合速率(P_n)随¹⁵NO₃^--N浓度的增加显著增大,但¹⁵NO₃^--N浓度超过N₂处理后P_n略有下降.处理20 d时,N₂处理幼苗根系活力最大,根系长度、根系总表面积和根尖数也显著高于其他处理.各处理间¹⁵N分配率差异显著,N₂处理幼苗各器官间¹⁵N分配率最均衡,¹⁵N利用率也较高;随¹⁵NO₃^--N浓度增加,各处理幼苗全氮量和¹⁵N吸收量呈先升高后降低的趋势,且在N₂处理时最大,分别为103.77和21.57 mg.处理12 d后,叶片硝酸还原酶(NR)活性以N₂处理最高,N₄处理最低,至第16天时,N₄处理较N₂处理降低了84.9%.因此,¹⁵NO₃^--N供应过低抑制幼苗光合作用及氮素吸收,¹⁵NO₃^--N供应过高则抑制幼苗体内硝态氮同化及根系生长,均不利于苹果幼苗生长及氮素营养吸收利用,适量供氮有利于苹果幼苗的生长、光合作用的提高,以及氮素的吸收、利用和分配.     

Nitrogen delivery to maize via mycorrhizal hyphae depends on the form of N supplied

Arbuscular mycorrhizal fungi can enhance nutrient acquisition by a plant via their extraradical hyphae. This is particularly true for phosphorus, but the case for nitrogen (N) has been less clear. In our growth systems there was a small air-gap between root and hyphal compartments, which eliminated diffusion of nutrients between compartments. Moreover, our methods allowed us to distinguish between nitrate and ammonium. We found that N transfer to Zea maize L. depends on the sources fed to the hyphae of Glomus aggregatum Schenck & Smith. In experiment 1, despite the fact that plant demand for N was already met, plants received 10 times as much ¹⁵N from ammonium than from nitrate. In experiment 2, 74% of shoot-N was derived from the slow-release urea added to the hyphal compartment while only 2.9% was derived from the nitrate-N. Intraradical hyphae isolated from roots contained a considerable amount of ¹⁵N in the cell wall even when ¹⁵N-nitrate was the source. We conclude that the mycorrhizal fungus can rapidly deliver ammonium-N to the plants, and that while the fungus can absorb nitrate, it apparently lacks the capacity to transfer it to the plant.     

Differential uptakes of different forms of soil nitrogen among major tree species in subalpine coniferous forests of western Sichuan,China

Aims Although acquisition of soil organic nitrogen (N)(mainly amino acids) by plants is a widespread ecological phenomenon in many terrestrial ecosystems, the rate of organic N uptake and their contributions to plant nutrient supply are poorly understood. Our objective was to determine the relative contributions of inorganic N (NO₃^–-N and NH₄⁺-N) and organic N (amino acids) to plant N uptake in a high-frigid forest ecosystem.Methods The differences in the uptake rate of three different forms of N (NO₃^–-N, NH₄⁺-N and glycine) were quantified by exposing seedlings of two dominant tree species (Picea asperata and Betula albo-sinensis) in subalpine coniferous forests of western Sichuan, China, to trace quantities of K¹⁵NO₃,¹⁵NH₄Cl and (U-¹³C₂/¹⁵N) glycine.Important findings Both ¹³C and ¹⁵N were significantly enriched in fine roots 2 h after tracer application, indicating the occurrence of glycine uptake in P. asperata and B. albo-sinensis seedlings. The seedlings of two tree species had a significant preference for NO₃^–-N compared with glycine and NH₄⁺-N, and the uptake rate of NO₃^–-N was 5 to 10 times greater than that of glycine and NH₄⁺-N. The roots of seedlings in the two species took up glycine more rapidly than NH₄⁺-N, implying that soil organic N (i.e., amino acids) could be an important N source for the two species in subalpine coniferous forests. The results of this study are of great theoretical significance for understanding N utilization strategies and nutrient regulation processes in plants of the high-frigid forest ecosystems.     

土壤碳氮比对平邑甜茶幼苗生长和碳氮分配的影响

为探讨土壤碳氮比(C:N)对苹果(Malus pumila)植株生长和碳氮分配特性的影响, 采用碳氮双标记示踪技术, 以二年生平邑甜茶(Malus hupehensis)幼苗为试验材料, 研究了6个不同土壤C:N处理(T1-T6分别为4.70、9.78、14.70、19.96、25.60和28.83)下平邑甜茶的生长状况和氮素吸收、利用分配以及碳水化合物的运转特性。结果表明, 随着土壤C:N的逐渐增大, 平邑甜茶幼苗根系干重逐渐增加, 而株高、茎粗、地上部干重和植株总干重呈先增加后降低的趋势, 以T4处理最大。土壤C:N显著影响了平邑甜茶幼苗的 ¹⁵N利用率, 从T1到T4处理, 植株的 ¹⁵N利用率逐渐升高, T4处理(18.46%)是T1处理(10.65%)的1.73倍; 随着土壤C:N的进一步增加, 植株的 ¹⁵N利用率逐渐降低, T5和T6处理分别比T4处理降低了1.59%和2.58%。土壤C:N较低的T1和T2处理, 平邑甜茶幼苗各器官从肥料中吸收分配到的 ¹⁵N量对该器官全氮量的贡献率(Ndff)大小顺序为根>叶>茎, 随着土壤C:N的进一步增大, 叶片的Ndff均为最大, 其次是根, 茎最少。随着土壤C:N的增大, 叶片 ¹⁵N分配率逐渐升高, ¹³C分配率逐渐降低; 而根系 ¹⁵N分配率逐渐降低, ¹³C分配率逐渐升高。综合考虑植株生长和氮素利用状况, 本试验条件下适宜平邑甜茶生长的土壤C:N为21-23。     

P effects on N uptake and remobilization during regrowth of Italian ryegrass (Lolium multiflorum)

The influence of P deficiency on the utilization of two sources of N, mineral N (exogenous N) and reserved N (endogenous N), for regrowth of Italian ryegrass (Lolium multiflorum) was studied. P-sufficient (+P) or P-free (−P) nutrition solution was applied from 7 days before defoliation to 24 days of regrowth and the N flows derived from two different N sources within the plant were quantified by ¹⁵N pulse-chase labeling. Shoot regrowth significantly reduced by 12 days of regrowth, while root growth was more in −P plants. Inorganic P (P_i) concentration was highly reduced by P deprivation more in the stubble and regrowing shoots and less in the roots. At defoliation, P deprivation had induced a higher accumulation for all N compounds in the stubble and for amino acids in the roots. The previously incorporated ¹⁵N in stubble and roots as nitrate and amino acids was much decreased in −P plants especially for the first 6 days of regrowth. Total N content in the regrowing leaves was not significantly different between +P and −P plants, but percentage contribution of remobilized N for total leaf N formation was significantly higher in −P plants (78%) than in +P plants (69%) at 6 days of regrowth. From day 12, the utilization of both endogenous and exogenous N was apparently inhibited in −P plants.     

15N natural abundance during early and late succession in a middle-European dry acidic grassland

δ¹⁵N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N₂-fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and δ¹⁵N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed δ¹⁵N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific δ¹⁵N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant–mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N₂-fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N₂-fixing legumes.     

施肥深度对矮化苹果15N尿素吸收、利用及损失的影响

以5年生烟富3/M26/平邑甜茶为试材,采用¹⁵N同位素示踪技术,研究表层(0 cm)、上层(20 cm)和中层(40 cm)3个施肥深度对矮化苹果¹⁵N 尿素吸收、分配及利用特性的影响.结果表明： 20 cm施肥处理的叶面积、叶绿素含量和叶片全氮含量显著高于0和40 cm施肥处理.不同施肥处理各器官从肥料中吸收分配到的¹⁵N量对该器官全氮量的贡献率(Ndff)存在显著差异,盛花期均以根的Ndff最高,多年生枝次之;新梢旺长期和花芽分化期根部吸收的¹⁵N优先向新生营养器官转运;果实膨大期各器官Ndff均达到较高水平;果实成熟期均以果实中的Ndff最高.果实成熟期不同施肥处理的¹⁵N分配率存在显著差异,20 cm施肥处理生殖器官和营养器官的¹⁵N分配率显著高于0和40 cm施肥处理,而贮藏器官的¹⁵N分配率显著低于0和40 cm施肥处理.在果实成熟期,20 cm施肥处理¹⁵N肥料利用率为24.0%,显著高于0 cm(14.1%)和40 cm施肥处理(7.6%),而¹⁵N损失率为54.0%,显著低于0 cm(67.8%)和40 cm施肥处理(63.5%).不同施肥深度土壤¹⁵N残留量随施肥深度的增加而显著增加.     

N NMR studies of the binding of CN with gold(I) drugs

¹⁵N NMR studies of the interaction of ¹⁵N cyanide ion with gold(I)-thiomalate (Autm) and gold(I)-thioglucose (Autg) have been carried out at pH* 7.40. The chemical shifts of the two ¹⁵N ions containing species Au(C¹⁵N)₂⁻ and RS-Au-C¹⁵N⁻ (where RS⁻ = tm⁻ or tg⁻) were identified at 265.94 and 260.30 ppm, respectively. From the broadened ¹⁵N NMR signals, approximate life times of the RS-Au-CN⁻ species were calculated.