Quantification of the carbon and nitrogen cycles in long‐term field experiments in Prague

The oldest still existing long‐term field experiments in Czech Republic were founded in 1955. In Prague Ruzyné, there are five of nine experiments founded by ?karda. Data of two of these experiments (Block III and Block B) were used to evaluate the carbon and nitrogen cycles in time period 1966–1997. These two experiments have a similar design. They differ in the crop rotation. Four variants of organic and mineral fertilisation, receiving similar doses of fertilisers, have been selected. The same was calculated for the same time period for a mini‐plot bare fallow field experiment founded in 1958 by Novák.

The results of these experiments conducted in one locality (the same soil and climatic conditions) show the effect of the cultivated crops on the carbon and nitrogen cycles (comparing bare fallow experiment with the cropped ones), the effect of organic and mineral fertilisation (among all experiments), and the effect of crop rotation (comparing Block III to Block B) on these cycles.     

Soil Organic Matter Content and Quality in Polyfactorial Field Experiments

The polyfactorial long-term field experiments founded in 1979 exist in four different sites till the present time. The experimental design and selected variants have been described in our previous paper (Lipavsky et al. 2002). Besides of the organic carbon and nitrogen contents in soil, dry matter of the main and second products, nitrogen uptake by the main and second products presented in our previous paper (Lipavsky et al, 2002), hot water soluble carbon (C hwl ), humic substances, e.g. humic and fulvic acids have been determined in soil samples taken in autumn each year from six selected variants of organic and mineral fertilisation. The results of the hot water soluble carbon content and humic and fulvic acids contents in the air dried soil samples have been evaluated in this paper. It was shown that humic substances are rather conservative and site specific soil properties that are not much affected by the cropping and fertilisation systems. Hot water soluble carbon, on the other hand, seems to be a dynamic part of the soil organic matter.     

Comparison of factors limiting bacterial growth in different soils

Lack of carbon has been assumed to be the most common limiting factor for bacterial growth in soil, although there are reports of limitation by other nutrients, e.g. nitrogen and phosphorus. We have studied which nutrient(s) limited instantaneous growth rates of bacteria in 28 Swedish soils using the thymidine or leucine incorporation technique to measure increased growth rate after adding different combinations of organic carbon (glucose), nitrogen and phosphorus. The soils ranged in pH between 3.1 and 8.9, in organic matter content between 1% and 91% and in soil C/N ratio between 10 and 28. We also tested the effect of adding different amounts of carbon on the bacterial change in growth rate for two soils with different organic matter content. We found that bacterial growth in most of the 28 soils was limited by a lack of carbon, indicated by an increased bacterial growth rate 48 h after adding glucose. In some soils, adding carbon together with nitrogen increased the bacterial growth rates even further. In three soils no effects were seen upon adding nutrients separately, but adding carbon and nitrogen together increased bacterial growth rates. Nitrogen addition tended to decrease bacterial growth rates, while phosphorus addition had little effect in most soils. No correlations were found between the soil C/N ratio, ammonium or nitrate content in soil and bacterial growth limitation, indicating that even soils with a C/N ratio of 28 could be carbon limited. Although the interpretation of the effects of a single limiting nutrient was in most cases straightforward, an interaction between the amount of carbon added and the organic matter content of the soil confounded the interpretation of the extent of a second limiting nutrient.     

Experimental snowpack reduction alters organic matter and net N mineralization potential of soil macroaggregates in a northern hardwood forest

Climate change is predicted to reduce or delay annual wintertime snow pack formation in the forests of the northeastern US. Any delay in snowpack formation could increase soil freezing in winter and, thereby, alter soil characteristics and processes. We examined the hypothesis that delayed snowpack would disrupt soil structure and change organic matter bioavailability in an experimental snow removal study at the Hubbard Brook Experimental Forest (HBEF), NH, USA. Pairs of reference and snow removal treatment plots were studied in four different sites at HBEF. Snow was removed from November–January of two winters, inducing soil freezing throughout both winters. Size class distribution and organic matter concentration and content of aggregates, and carbon and nitrogen mineralization potential of size fractions were quantified for surface mineral soils in the spring of both years immediately after snowmelt. In the first year of sampling, the only significant effect of snow removal was an increase in the smallest (<53 μm) size fraction of mineral soil. In the second year, snow removal increased organic matter concentrations of macroaggregate (250–2,000 μm) and microaggregate (53–250 μm) size fractions. This change corresponded to an increase in net N mineralization potential and the ratio of N to C mineralized in the macroaggregate fraction, but there were no effects of snow removal on C mineralization. We propose that soil freezing increases the movement of organic matter from organic to mineral soil horizons and increases the N content of mineralizable substrates in mineral soil following years with delayed snowpack formation.     

Soil fauna alter the effects of litter composition on nitrogen cycling in a mineral soil

Plant chemical composition and the soil community are known to influence litter and soil organic matter decomposition. Although these two factors are likely to interact, their mechanisms and outcomes of interaction are not well understood. Studies of their interactive effects are rare and usually focus on carbon dynamics of litter, while nutrient dynamics in the underlying soil have been ignored. A potential mechanism of interaction stems from the role fauna plays in regulating availability of litter-derived materials in the mineral soil. We investigated the role of soil fauna (meso, macro) in determining the effect of surface-litter chemical composition on nitrogen mineralization and on the micro-food web in mineral soils. In a field setting we exposed mineral soil to six types of surface-applied litter spanning wide ranges of multiple quality parameters and restricted the access of larger soil animals to the soils underlying these litters. Over six months we assessed litter mass and nitrogen loss, nitrogen mineralization rates in the mineral soils, and soil microbes and microfauna. We found evidence that the structure of the soil community can alter the effect of surface-litter chemical composition on nitrogen dynamics in the mineral soil. In particular, we found that the presence of members of the meso- and macrofauna can magnify the control of nitrogen mineralization by litter quality and that this effect is time dependent. While fauna were able to affect the size of the micro-food web they did not impact the effect of litter composition on the abundance of the members of the micro-food web. By enhancing the strength of the impact of litter quality on nitrogen dynamics, the larger fauna can alter nitrogen availability and its temporal dynamics which, in turn, can have important implications for ecosystem productivity. These findings contribute to evidence demonstrating that soil fauna shape plant litter effects on ecosystem function.     

Sensitivity analysis and calibration of CN-SIM to simulate the mineralisation of liquid dairy manures

Scientific knowledge of carbon and nitrogen dynamics incorporated into soil organic matter (SOM) dynamic simulation models can be tested using experimental data from decomposition experiments. This possibility is particularly interesting for liquid animal manures, which are very heterogeneous materials. CN-SIM is a SOM model that was successfully applied for the short- and long-term simulation of C and N dynamics in the soil. The objective of this research was to test this model using results of a 180-d laboratory incubation of five liquid dairy manures in three soils. Initial sensitivity analysis indicated that model parameters that mostly impact net CO₂ and soil mineral nitrogen concentration (SMN) are those that allocate manure C and N to model pools, their decomposition constants and soil parameters that describe microbial biomass and its residues. Automatic parameter optimisation was carried out with the downhill simplex method separately for 15 manure by soil combinations. After optimisation, CO₂ respiration was well simulated for the entire period, while SMN was overestimated after day 40. Simulations overestimated the remineralisation of immobilised N in the first weeks. Simulated initial microbial immobilisation was the only possibility for the model to match the experimental decrease of SMN, while simulated N remineralisation after day 40 was necessary to enable a good simulation of respired CO₂. Further work is needed to test whether these simulations can be improved by adding SMN sinks (such as denitrified N and clay-fixed ammonium).     

Importance of Soil Organic Matter (SOM) for Biomass Production and Environment (a review)

The aim of sustainable agricultural land use is to reach high and rising crop yields and to minimise environmental pollution. Soil organic matter (SOM) plays a key role in maintaining soil productivity and also in protection of environment. At least two SOM fractions can be distinguished, one being relatively inert, the other being decomposable. High yields are only attainable on an environmentally acceptable way in combination of organic and mineral fertilization. The ranges for the optimal content of the decomposable organic carbon is between 0.2 and 0.6% and that of nitrogen 0.02 and 0.06%. The hot water extractable carbon has proved to be an appropriate criterion for the characterisation of the decomposable carbon. When considering the current state of knowledge consistently, the use of mineral fertiliser has a positive effect on the environment and supports a considerable gain of energy by the cultivated crops. Too high humus content in soil can contribute to environmental pollution. Between organic carbon content and soil physical properties there is nearly functional relation.     

西南地区喀斯特干热河谷地带不同植被类型下小生境土壤碳氮分布特征

通过对西南地区典型喀斯特干热河谷地带乔木林、灌木林及草丛下所覆盖的土面、石面、石沟、石洞、石缝、石槽和石坑7类小生境土壤样品碳氮含量分布特征进行研究,结果表明:研究区域内小生境表层土壤中有机碳和全氮的含量分别介于10.6~103.7 g/kg和1.16~6.39 g/kg之间,变幅较大;不同植被类型下小生境土壤碳氮的含量分布存在明显差异,乔木林下小生境土壤碳氮平均含量较草丛增加100%以上,灌木林下小生境土壤碳氮的空间变异性最小,小生境土壤碱解氮在各植被类型下服从正态分布,有机碳及全氮则服从右偏态分布;小生境相对开放的土面、石面、石坑及石沟普遍较石槽、石缝及石洞土壤有机碳和全氮的含量高,而碱解氮的变化规律不明显。在同种植被类型下,土壤有机碳与全氮、碱解氮、速效磷和碳氮比均表现出良好的相关性。     

Fungi mediate long term sequestration of carbon and nitrogen in soil through their priming effect

It is increasingly recognized that soil microbes have the ability to decompose old recalcitrant soil organic matter (SOM) by using fresh carbon as a source of energy, a phenomena called priming effect (PE). However, efforts to determine the consequences of this PE for soil carbon and nitrogen dynamics are in their early stage. Moreover, little is known about the microbial populations involved. Here we explore the consequences of PE for SOM dynamics and mineral nitrogen availability in a soil incubation experiment (161 days), combining the supply of dual-labeled (¹³C and ¹⁴C) cellulose and mineral nutrients. The microbial groups involved in PE were investigated using molecular fingerprinting techniques (FAMEs and B- and F-ARISA). We show that mean residence time of SOM pool controlled by the PE decreased from 3130 years in the subsoil, where the availability of fresh carbon is very low, to 17-39 years in the surface layer. This result suggests that the decomposition of this recalcitrant soil C pool is strictly dependent on the presence of fresh C and is not an energetically viable mean of accessing C for soil microbes. We also suggest that fungi are the predominant actors of cellulose decomposition and induced PE and they adjust their degradation activity to nutrient availability. The predominant role of fungi can be explained by their ability to grow as mycelium which allows them to explore soil space and mine large reserve of SOM. Finally, our results support the existence of a bank mechanism that regulates nutrient and carbon sequestration in soil: PE is low when nutrient availability is high, allowing sequestration of nutrients and carbon; in contrast, microbes release nutrients from SOM when nutrient availability is low. This bank mechanism may help to synchronize the availability of soluble nutrients to plant requirement and contribute to long-term SOM accumulation in ecosystems.     

氮输入对陆地生态系统碳库的影响研究进展

碳氮循环是生物地球化学的重要过程。陆地生态系统碳循环在全球碳收支中占有重要的地位,人类活动导致生态系统中氮含量增加,影响土壤和植物体中碳的积累与重新分配,对陆地生态系统不同的碳过程产生不同的影响。本文综述了近年来氮输入的研究现状,并对未来的研究方向做了展望,提出今后重点研究的方向。     

不同供氮水平对玉米秸秆降解初期碳素矿化及微生物量的影响

采用室内恒温(25℃)培养方法研究了不同无机态氮供应水平(0、30、60、80、100Nmgkg-1土)对玉米秸秆降解初期的影响。试验结果表明:碳素的矿化量随着添加无机氮源数量的增加而增加,其中两个高氮添加量(80、100mgkg-1)处理的碳素矿化量要高于不加氮源和两个低氮添加量处理(30、60mgkg-1)。不同氮量添加条件下微生物量碳的变化呈相同趋势。利用土壤呼吸和微生物量碳计算而得的微生物代谢商在低量氮素处理条件下高于较高量氮源添加处理,表明高量氮素添加可提高微生物对秸秆碳素的利用效率。以上结果说明:对C/N比较大的玉米秸秆而言,土壤中无机氮素的供给对残体碳素的初始矿化有明显的影响,相对较低的氮源供给量不能满足微生物快速生长代谢对氮素的需求,使秸秆降解过程受到一定程度的抑制,不利于土壤氮素截获。因此在大田条件下,秸秆还田时要考虑氮素的供应问题,根据实际需要确定秸秆还田时间及肥料氮素施用水平。     

外源氮输入对土壤有机碳矿化和凋落物分解的影响

目前,由人类活动造成的陆地生态系统氮输入量已经远远超过了其自身的生物固氮,外源氮输入的增多已经并将继续对土壤有机碳矿化和凋落物分解产生影响。本文分析了国内外有关氮输入增多对土壤有机碳矿化和凋落物分解的影响及其机理:由于研究点环境状况不同,凋落物性质的差异和分解阶段的不同等原因,氮输入对土壤有机碳矿化的结果主要表现为抑制或促进作用;对凋落物分解的影响表现为促进、无影响和抑制三种效果,有关其作用机理还有待进一步深入研究。着重指出对于作为大气CO2"汇"的沼泽湿地,氮输入的增多能够对其碳"汇"功能产生影响,因此进行氮输入对湿地土壤有机碳矿化和凋落物分解方面的研究,对于探讨湿地碳循环对外源氮输入的响应及其机理非常重要。     

Soil organic carbon and nitrogen in aggregates in response to over seven decades of farmyard manure application

The study aimed to evaluate the effects of long-term fertilisation on soil aggregation and the associated changes in soil organic carbon (SOC) and nitrogen (N) pools in aggregates. The combined application of mineral fertiliser and manure improved soil aggregation, SOC and N content in aggregates, compared to manure or mineral fertiliser alone, and thus proved to be a suitable fertilisation strategy to increase C sequestration in agroecosystems.     

Nutrient limitations to soil microbial biomass and activity in loblolly pine forests

We performed an assay of nutrient limitations to soil microbial biomass in forest floor material and intact cores of mineral soil collected from three North Carolina loblolly pine (Pinus taeda) forests. We added solutions containing C, N or P alone and in all possible combinations, and we measured the effects of these treatments on microbial biomass and on microbial respiration, which served as a proxy for microbial activity, during a 7-day laboratory incubation at 22 °C. The C solution used was intended to simulate the initial products of fine root decay. Additions of C dramatically increased respiration in both mineral soil and forest floor material, and C addition increased microbial biomass C in the mineral soil. Additions of N increased respiration in forest floor material and increased microbial biomass N in the mineral soil. Addition of P caused a small increase in forest floor respiration, but had no effect on microbial biomass.     

同位素稀释分析在土壤氮素循环利用研究中的应用

同位素稀释分析是研究氮素在土壤植物体系中转化和迁移特征的有效方法。本文对国内外近十年利用同位素稀释技术研究土壤微生物和植物对不同形态的氮素的利用与竞争进行了总结,强调了土壤在植物和微生物养分利用中的双重作用。利用同位素稀释分析还可以研究所施氮肥的转化、迁移、和流失,推断土壤-植物系统N肥平衡状况,对提高肥料利用率,科学施肥,减少氮素污染有着科学的指导作用。     

Microbial carbon dynamics in nitrogen amended Arctic tundra soil: Measurement and model testing

We examined the responses of grazers (protozoa and nematodes) and their main food sources to low levels of nitrogen (N) fertilisation and applied carbon (C) flux models to our data. Replicate plots of tundra soil adjacent to the Kongsfjorden (Svalbard 78°N) were amended with ammonium and nitrate at concentrations of 1 and 5 kg N ha⁻¹ to assess the impact of anthropogenic N deposition over three summers. Bacterial abundance as determined using the fluorochrome SYBR Green and epifluorescence microscopy ranged between 9.73×10⁸ and 102.49×10⁸ cells/g dry wt of soil, with a significant response to N addition occurring only during the second sampling in 2001. Despite little change in bacterial biomass, bacterial production (measured by the incorporation of ³H thymidine into DNA) during the second sampling in 2002, increased in NH₄ enriched plots compared to control and NO₃ amended plots, indicating that NH₄ was the preferred source of inorganic N. The main bacterial predators were heterotrophic flagellates (HNAN) and naked amoebae, which showed no significant response to the N addition. HNAN showed a correlation with bacterial abundance suggesting a dependence on bacteria as a food source. The inability of a microbial C flux model to fit our data (RWSS/data=18.6, r²=0.088) was at least partly due to insufficient bacterial production to meet the C demands of predator taxa, and high variability in the data over time. This is reflected in the performance statistics for model variants where select microbial taxa and data were removed. The optimal model in terms of predictive utility was a model with data from 2002 only, minus naked amoebae (RWSS/data=2.45, r²=0.806).     

氮营养水平对烤烟根际土壤酶活性及烟叶内在品质的影响

田间试验研究了不同时期烤烟根际各土层土壤酶活性变化规律及其不同施氮量对烟叶品质的影响。结果表明:0~20 cm土层范围内,施氮可以提高圆顶期、采烤期及采烤结束后土壤脲酶、转化酶的活性,但当施氮量超过52.5 kg hm-2时,脲酶、转化酶的活性反而降低;土壤蛋白酶活性均在37.5 kg hm-2处理达到最大值,且随着施氮量的增多大都呈现降低的趋势。20~80 cm土层范围内,土壤脲酶、转化酶、蛋白酶活性变化规律并不一致。对于烤后烟叶,施氮量为52.5 kg hm-2的烟叶,糖碱比、氮碱比、钾氯比均比较适宜,化学成分较为协调,燃烧性较好,有利于优质烟叶品质的形成。说明在该地区的试验条件下,水稻土种植烤烟最适宜的施氮量为52.5 kg hm-2。     

亚热带地区土壤硝酸盐异化还原成铵速率的空间差异和驱动因素

土壤硝酸盐异化还原成铵(DNRA)是生态系统土壤氮转化的重要途径，理清环境因素对土壤DNRA速率的影响意义重大。本研究通过收集246项试验观测值采用整合分析方法(Meta-analysis)研究了亚热带地区不同生态系统中DNRA速率的变化范围及其影响因素。结果表明：纬度对亚热带土壤DNRA速率无显著影响；土壤p H、全氮(TN)、SOC/NO₃^–-N、Fe(Ⅱ)、阳离子交换量(CEC)、易氧化有机碳(EOC)、有效磷(AP)、黏粒含量和年平均气温(MAT)的增加均会促进DNRA速率；年平均降水量(MAP)和土壤NH₄⁺-N含量的增加会抑制土壤DNRA速率。此外，环境因子对DNRA速率的影响随生态系统的不同表现出较大差异。结构方程模型分析结果显示，SOC/NO₃^–-N是DNRA主要驱动因素，p H、NH₄⁺-N、MAP和MAT对土壤DNRA也有较大影响。     

秸秆还田对土壤有机质和氮素有效性影响及机制研究进展

秸秆还田作为全球有机农业的重要环节, 对维持农田肥力, 减少化肥使用, 提高陆地土壤碳汇能力具有积极作用。秸秆还田主要通过增加土壤有机质和提高氮肥利用率来改善农田生产环境, 获得高农业生产能力。有效的秸秆还田能为土壤中的微生物提供丰富的碳源, 刺激微生物活性, 提高土壤肥力; 同时矿化的秸秆组分能促进土壤氮循环和矿化, 提高氮素有效性。秸秆还田能够促使集约化高氮输入的农田生态系统维持正常的碳氮比例, 减少氮素淋洗损失, 改善土壤结构板结和连作障碍等现象。目前我国农田秸秆还田率不足50%, 与欧美国家高达90%多的秸秆还田率相比, 还具有很大的发展潜力。因此加强我国秸秆还田率能够逐渐改变我国耕地土壤存在的有机质含量和品质下降、氮素损失严重等现象。目前应进一步深入研究秸秆还田对有机质及氮素有效性的影响机制, 并结合长期监测试验, 以及多种秸秆还田技术进行比较研究, 发展适合当地秸秆还田模式, 促进我国农业生态系统的可持续性。