施用生物炭对华北平原农田土壤容重、阳离子交换量和颗粒有机质含量的影响

以华北平原高产农田3年定位试验为基础,研究了生物炭与矿质肥配施对土壤容重、阳离子交换量和颗粒有机质组分中碳、氮含量的影响.试验共设4个处理：单施氮磷钾肥（CK）;氮磷钾肥+2250 kg·hm^-2生物炭（C₁）;氮磷钾肥+4500 kg·hm^-2生物炭（C₂）;炭基缓释肥（750 kg·hm^-2,CN）.结果表明： 与CK相比,C₁和C₂处理显著降低了0～7.5 cm土层容重,降低幅度分别为4.5%和6.0%;施用生物炭增加了0～15 cm土层的阳离子交换量,其中C₂处理增加了24.5%;在0～7.5 cm土层,C₁处理土壤颗粒有机质组分中的碳、氮浓度较CK处理分别增加了250%和85%,C₂处理分别增加了260%和120%.施用生物炭3年后土壤理化特性得到明显改善,并在碳增汇和温室减排方面具有潜在积极效应.     

黄土高原不同生态治理小流域土壤有机质、容重及黏粒含量的对比

为探讨不同生态治理小流域土壤性质的差异,本研究分别从坡向、坡位、区段和土层4个方面分析了人工刺槐林流域杨家沟(YJG)与封禁荒草地流域董庄沟(DZG)土壤有机质(SOM)、土壤容重(BD)和黏粒含量(CC)的空间分异.结果表明: YJG与DZG的SOM、BD、CC分别为12.78 g·kg^-1、1.24 g·cm^-3、19.2%与11.13 g·kg^-1、1.21 g·cm^-3、18.2%,前者均略高,但差异不显著.各指标均为东坡大于西坡;SOM和CC顺坡向下有增加趋势,BD变异最小;SOM由上游至下游呈增大趋势,BD和CC不断减小;由土表向下至60 cm土深,BD和CC不断增大,SOM不断减小.各指标的空间敏感性依次为CC＞SOM＞BD,空间因素的影响效用依次为土层＞区段＞坡向＞坡位.上游CC、中游BD和CC在两流域间的差异显著,各指标对坡位、区段、土层的敏感性均为YJG＜DZG.     

Bi-directional soil/atmosphere N2O exchange over two mown grassland systems with contrasting management practices

Nitrous oxide (N₂O) fluxes from soil under mown grassland were monitored using static chambers over three growing seasons in intensively and extensively managed systems in Central Switzerland. Emissions were largest following the application of mineral (NH₄NO₃) fertilizer, but there were also substantial emissions following cattle slurry application, after grass cuts and during the thawing of frozen soil. Continuous flux sampling, using automatic chambers, showed marked diurnal patterns in N₂O fluxes during emission peaks, with highest values in the afternoon. Net uptake fluxes of N₂O and subambient N₂O concentrations in soil open pore space were frequently measured on both fields. Flux integration over 2.5 years yields a cumulated emission of +4.7 kgN₂O‐N ha^?1 for the intensively managed field, equivalent to an average emission factor of 1.1%, and a small net sink activity of ?0.4 kg N₂O‐N ha^?1 for the unfertilized system. The data suggest the existence of a consumption mechanism for N₂O in dry, areated soil conditions, which cannot be explained by conventional anaerobic denitrification. The effect of fertilization on greenhouse gas budgets of grassland at the ecosystem level is discussed.     

间作对旱地CO2和N2O排放影响的研究进展

农田温室气体排放是近年来科学界的研究热点,采用合适的种植模式是减少农田温室气体排放的有效途径之一.本文综述了作物间作对旱地土壤CO₂和N₂O排放的影响及机理.合理间作能够提高土壤有机碳(SOC)含量、促进不同作物秸秆向SOC转化、降低SOC矿化速率,从而减少CO₂排放.禾本科与豆科作物间作能够在维持作物产量的情况下,减少化学氮肥投入、土壤有效氮残留及还田秸秆产生的无机氮,降低N₂O排放.间作作物的互作、田间小气候环境的改善也是影响土壤温室气体排放的重要因素.今后,要增加土壤温室气体监测时长并对影响因子进行综合、全面的分析,尤其是从分子水平探究间作模式下土壤微生物对温室气体产生过程的作用机理,为构建环境友好型农业模式提供科学依据.     

Environmental manipulation treatment effects on the reactivity of water-soluble phenolics in a subalpine tundra ecosystem

Low soil organic matter content and limited soil water holding are the major natural constraint of dryland cropping on sandy soils in the Quebec boreal regions. We conducted a 3-yr (1994–1996) study in a boreal sandy soil, Ferro-Humic Podzol (Spodosols), to determine the potential of Sphagnum peat for improving soil organic matter (SOM), water holding capacity, bulk density (BD), plant leaf nutrient status, and potato and barley yields. The cropping was a rotation of 2-yr potato (Solanum tuberosum L. Superior) and 1-yr barley (Hordeum vulgare L. Chapais). The treatments consisted of Sphagnum peat at rates of 0, 29, 48, and 68 Mg ha^–1 3-yr^–1 on a dry weight basis, and granular N-P-K fertilizers (12-7.5-7) at rates of 1.4, 1.6, and 1.8 Mg ha^–1 yr^–1, respectively, arranged in a split-block design. The peat-amended soils were higher in water content (SWC), SOM and total porosity but lower in BD and N than neighboring non-peat soils (P < 0.05). Effects of peat and fertilizer treatments and their interaction were significant on potato leaf N, Ca, Mg, and P, tuber yield, dry weight, harvested N and tuber specific gravity (P < 0.05), depending on year. Potato tuber yield and N increased simultaneously up to 30% (compared to the control), and were significantly correlated with SWC, SOM, BD, and NO₃-N (–0.52 r 0.80). In the 3rd year, the linear effect of peat treatments was significant on barley grain yield. In 1995 there was a decline of 4.5–7.3% of SOM of the previous year level. It is suggested that Sphagnum peat at a rate of 48 Mg ha^–1 had the potential for improving sandy soil productivity. A longer-term investigation of soil water, N, SOM pool and crop yield changes is necessary to better understand the physical, chemical and biological processes of peat in cropping systems and to maximize the benefits of peat applications.     

Soil 13C–15N dynamics in an N2-fixing clover system under long-term exposure to elevated atmospheric CO2

Reduced soil N availability under elevated CO₂ may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N₂‐fixing system. We studied the effects of Trifolium repens (an N₂‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO₂ under FACE conditions. ¹⁵N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha^?1 yr^?1 and the CO₂ concentration was increased to 60 Pa pCO₂ using ¹³C‐depleted CO₂. The total soil C content was unaffected by elevated CO₂, species and rate of ¹⁵N fertilization. However, under elevated CO₂, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (f_N) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO₂, had a significant effect on f_N values of the total soil N pool. The fractions of newly sequestered C (f_C) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO₂, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more ¹⁵N fertilizer than T. repens: 179 vs. 101 kg N ha^?1 for the low rate of N fertilization and 393 vs. 319 kg N ha^?1 for the high N‐fertilization rate. As the loss of fertilizer‐¹⁵N contributed to the ¹⁵N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N₂ fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N₂‐fixing L. perenne system. This suggests that N₂ fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.     

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.     

蒙古栎叶片及其土壤碳、氮同位素自然丰度对大气CO2浓度升高的响应

大气CO₂浓度升高对土壤氮素转化过程产生重要影响,研究其变化有助于更好地预测陆地生态系统的固碳潜力.氮同位素自然丰度作为生态系统氮素循环过程的综合指标能够有效地指示CO₂浓度升高对土壤氮素转化过程的影响.本研究采用开顶箱CO₂ 熏蒸法研究连续10年的大气CO₂ 浓度升高对我国东北地区蒙古栎及其土壤和微生物生物量碳、氮同位素自然丰度的影响.结果表明: 大气CO₂浓度升高改变了土壤氮循环过程,增加了土壤微生物和植物叶片δ¹⁵N;促进了富¹³C土壤有机碳分解,中和了贫¹³C植物光合碳输入的效果,导致土壤可溶性有机碳和微生物碳δ¹³C在CO₂升高条件下没有发生显著变化.这些结果表明,CO₂浓度升高很可能促进了土壤有机质矿化过程,并加剧了系统氮限制的状态.     

氮添加对森林土壤有机碳库固存及CO2排放的影响研究进展

氮添加会引起土壤理化性质和养分有效性的改变。受此影响,森林植物的地上碳同化能力和地下碳分配格局也会相应地发生变化,总体表现为促进植物生长固碳,增加凋落物和植物根系沉积碳输入土壤,并改变上述植物源有机质的数量和化学成分。与此同时,土壤微生物的群落结构和生态功能也会受到氮添加的影响,由于土壤中的有机碳分解、转化和稳定等过程均受到微生物的驱动,因此,氮添加所引起的底物供应差异和微生物响应会影响森林土壤有机碳的矿化,并最终影响森林土壤有机碳库固存、稳定和CO₂排放。但目前关于氮添加对森林土壤有机碳库固存能力和CO₂排放特征的影响机制仍不清楚,为此,以森林土壤的碳循环过程为线索,综述了氮添加对底物供应、土壤有机碳激发效应、微生物碳代谢等过程的影响,并尝试梳理在氮添加影响下森林土壤有机碳分解、转化和稳定的微生物驱动机制。这有助于预测氮添加对森林土壤\"氮促碳汇\"的实际效果,以便研究人员在未来氮沉降日益严重背景下更好地预测森林土壤的碳循环特征,寻找提高森林土壤有机碳库固存能力和降低CO₂排放相关途径提供参考。同时,还分析了目前相关研究中存在的问题,并对该领域未来的研究热点进行了展望。     

21st‐century biogeochemical modeling: Challenges for Century‐based models and where do we go from here?

21st‐century modeling of greenhouse gas (GHG) emissions from bioenergy crops is necessary to quantify the extent to which bioenergy production can mitigate climate change. For over 30 years, the Century‐based biogeochemical models have provided the preeminent framework for belowground carbon and nitrogen cycling in ecosystem and earth system models. While monthly Century and the daily time‐step version of Century (DayCent) have advanced our ability to predict the sustainability of bioenergy crop production, new advances in feedstock generation, and our empirical understanding of sources and sinks of GHGs in soils call for a re‐visitation of DayCent's core model structures. Here, we evaluate current challenges with modeling soil carbon dynamics, trace gas fluxes, and drought and age‐related impacts on bioenergy crop productivity. We propose coupling a microbial process‐based soil organic carbon and nitrogen model with DayCent to improve soil carbon dynamics. We describe recent improvements to DayCent for simulating unique plant structural and physiological attributes of perennial bioenergy grasses. Finally, we propose a method for using machine learning to identify key parameters for simulating N₂O emissions. Our efforts are focused on meeting the needs for modeling bioenergy crops; however, many updates reviewed and suggested to DayCent will be broadly applicable to other systems.