草地灌丛化土壤碳氮地球化学循环

灌丛化(shrub encroachment)是全球陆地生态系统重要的生态现象之一,是影响草地碳库的重要过程。灌丛化由全球气候变化、降雨、火烧和生物活动等多因素共同作用形成,对区域环境、气候、土壤性质和碳循环影响显著。目前灌丛化对生态系统的影响仍存在分歧,表现在不同气候和降雨梯度下灌丛化后土壤有机碳/氮储量、养分循环和土壤温室气体排放等差异。本文总结和归纳了灌丛化形成与控制因素、灌丛化对团聚体稳定性、酶活性和土壤碳、氮循环的影响。灌丛化改变了土壤团聚体稳定性和酶活性,进而影响土壤呼吸以及土壤生源物质的存储、分解和循环,这将显著影响区域乃至全球气候变化。因此分析提出,今后应进一步加强对灌丛化形成过程长期的定位观察研究,以便了解灌丛化的可控因素,并加强对灌丛化后土壤有机碳库、土壤团聚体稳定性变化对碳氮循环进程和全球气候变化的影响研究。     

长期施肥对高原农业生态系统土壤有机碳和氮的影响

The effects of fertilization on the distributions of organic carbon (OC) and nitrogen (N) in soil aggregates and whether these effects vary with cropping system have not been well addressed.Such information is important for understanding the sequestration of OC and N in agricultural soils.In this study,the distributions of OC and N associated with soil aggregates were analyzed in different fertilization treatments in a continuous winter wheat cropping system and a legume-grain rotation system in a 27-year field experiment,to understand the effects of long-term fertilization on the distributions of OC and N in aggregates and to examine the recovery of soil OC and N in a highland agroecosystem.Manure fertilizer significantly decreased soil bulk density but increased the amount of coarse fractions and their associated OC and N stocks in the soils of both systems.Fertilizers N + phosphorus (P) and manure had similar effects on total soil OC and N stocks in both systems,but had larger effects on the OC and N stocks in ＞ 2 mm aggregates in the legume-grain rotation system than in the continuous winter wheat system.The application of P increased the OC and N stocks in ＞ 2 mm aggregates and decreased the loss of N from chemical fertilizers in the legume-grain rotation system.The results from this study suggested that P fertilizer should be applied for legume-included cropping systems and that manure with or without chemical fertilizers should be applied for semiarid cropping systems in order to enhance OC and N accumulation in soils.     

不同土层复配方案对土壤水稳性团聚体及有机质的影响

为探究“治沟造地”重大工程项目（GLCP）中新增耕地快速改良的方法，达到营造良好土壤、提升新增耕地生产能力的目的，以延安羊圈沟流域的GLCP为背景，利用马兰黄土（ML）和红黏土（RC）对新造耕地0~30 cm土层进行复配试验。结果表明：当RC为20 cm、ML为10 cm（T3处理）时，复配层土壤孔隙度较对照处理增加了16.7%，容重下降了11.1%。与对照组相比，T3处理0~10、10~20、20~30 cm土层中>0.25 mm水稳性团聚体含量（W_0.25）显著增加，分别增加了11.8、12.3倍和27.9倍；T2（RC为25 cm、ML为5 cm）、T3处理更利于大团聚体的形成，较对照组除在0.25~0.5、0.5~1 mm的粒级有较大增加外，在2~5 mm和>5 mm粒径范围也有明显增加。0~20 cm土层中，即使在考虑对照组前期土壤有机质积累的情况下，T3处理的土壤有机质也与对照组相近甚至更高，且高于其他试验组，表现出更好的有机质赋存能力。T3处理的玉米生长状况较好，其地上生物量最高，较对照组提高了23.9%。研究表明，当复配土壤RC为20 cm、ML为10 cm时，土壤具有最佳的性状和生产力。试验初步证明土层复配是一种可行的快速营造高质量土壤的方法，该方法可为GLCP新造地的改良及类似土地整治工程的实施提供实践参考。     

Impacts of natural polymer derivative neutral polysaccharide Jag S and cationic hydroxypropyl polysaccharide Jag C162 on rainfall infiltration on an experimental loess hillslope

ABSTRACT

Developing effective measures to improve soil structure and increase soil infiltration in the Loess Plateau located in arid and semiarid areas is important for soil and water conservation. Simulated rainfall experiments were conducted to determine the effects of two new natural polymer derivatives, namely neutral polysaccharide (Jag S) and cationic hydroxypropyl polysaccharide (Jag C162), on rainfall infiltration and their underlying mechanisms. The proportions of different sizes of water-stable soil aggregates were analyzed after spraying four different concentrations (0, 1, 3, and 5 g m^?2) of Jag S and Jag C162 under rainfall intensities of 1, 1.5, and 2 mm min^?1 and a slope gradient of 15°. Treatments with Jag S and Jag C162 significantly improved the rainfall infiltration rates (IRs) compared with the control. Moreover, applying 1 and 3 g m^?2 Jag S effectively increased the IRs by 22.81% and 13.69%, respectively. Treatment with Jag C162 also increased the rainfall IRs by 39.47%, 46.59%, and 46.50%. Furthermore, the content of >0.25 mm water-stable soil aggregates increased from 27.19% to 90.42% before rainfall and from 9% to 50% after rainfall. Compared with Jag C 162, treatment with Jag S was less effective on improving rainfall infiltration and aggregate content. In particularly, application of 5 g m^?2 Jag S improved the soil aggregate content but weakened rainfall infiltration because of the higher viscidity and consistency of the Jag S solution. Overall, spraying appropriate amounts of Jag C162 and Jag S on the loess slope surface can increase the water-stable soil aggregate content, resulting in improved rainfall infiltration and reduced soil erosion. Thus, application of two new natural polymer derivatives is a possible alternative conservation practice in the Loess Plateau.     

长期定位施肥和地膜覆盖对棕壤团聚体稳定性及其有机碳含量的影响

以沈阳农业大学长期定位试验（29年）不同施肥与地膜覆盖处理棕壤为研究对象，采用湿筛方法，研究了覆膜和不覆膜条件下不同施肥措施对棕壤各粒级团聚体分布及其有机碳含量的影响，为揭示施肥措施对土壤地力形成演变的影响机制提供理论基础。选取的试验处理包括：不施肥对照（CK）、单施高量氮肥（N4）、氮磷肥配施（N4P2）、单施高量有机肥（M4）、有机-氮肥配施（M2N2）、有机-氮磷肥配施（M4N2P1）以及所有相对应的覆膜处理。结果表明，连续29年的不同施肥和覆膜处理显著影响了土壤团聚体的含量、稳定性及团聚体有机碳的含量。不覆膜条件下，长期施肥处理使>2 mm团聚体的含量显著增加，而0.25~2 mm粒级团聚体含量显著下降，其中有机肥和氮磷肥处理变幅最大。有机肥的施入（M4、M2N2、M4N2P1）均显著增加了不覆膜土壤各粒级团聚体的有机碳含量，且单施有机肥能显著增加不覆膜土壤团聚体平均重量直径，说明长期有机物料投入有利于增加土壤团聚体的稳定性及有机碳在团聚体中的固持。覆膜条件下，各施肥处理也显著影响土壤团聚体的稳定性及有机碳含量，但是不同施肥处理之间的差异变小，说明相同施肥模式下覆膜与不覆膜处理对土壤团聚体的形成和稳定性会产生不同的影响。覆膜条件下，与对照相比，只有高量有机肥（M4和M4N2P1）处理能显著增加土壤团聚体的平均重量直径和各粒级团聚体有机碳含量，说明在覆膜条件下，需要投入更多的有机物质才能维持土壤团聚体的稳定性及较高的有机碳含量。不同施肥和覆膜处理下，氮磷肥配施可以显著提高土壤团聚体的平均重量直径，但对团聚体有机碳含量的影响表现为显著降低或不显著。各处理土壤中水稳性大团聚体是土壤有机碳的主要载体，施用有机肥及有机无机配施有利于促进土壤各粒级水稳性团聚体的有机碳含量，是改善土壤团聚体结构、维持和提高棕壤地力的有效措施。     

Effects of conservation tillage drills on soil quality indicators in a wheat–oilseed rape rotation: organic carbon,earthworms and water-stable aggregates

The effects of five conservation tillage drills with crop residue levels covering between 17% and 79% of the soil, and tillage depths ranging from 25 to 200 mm, were examined over 3 years. The tillage systems ranged from a relatively disruptive Farm System to a Low Disruption system, with three intermediate treatments labelled Sumo DTS, Claydon and Mzuri. The study involved field sites on a clay or clay loam soil, where winter wheat and oilseed rape were grown in rotation. In the clay field, the Mzuri and Low Disruption treatments, which produced the highest residue coverage, showed the greatest increase in surface total soil organic carbon (1.1 and 0.48 Mg C ha⁻¹, respectively) between years 1 and 3. The least disruptive tillage system also resulted in the highest density of earthworms (181–228 m⁻²), and the most disruptive system produced the lowest densities (75–98 m⁻²). In the third year, the least disruptive system also showed a higher proportion of water-stable aggregates (29.8%) than the other treatments (22.7%–25.3%). Linear regressions showed positive relationships of both soil organic carbon and earthworm density with surface residue cover, and of the proportion of water-stable aggregates with soil organic carbon.     

基于REE示踪的土壤团聚体破碎转化路径定量表征

土壤团聚体破碎转化路径是坡面侵蚀过程研究的难点问题之一。目前团聚体破碎转化路径的定量表征仍不明晰,一定程度上限制了土壤侵蚀过程中泥沙分选搬运机制的深入研究。基于大样带调查选取6种不同质地的典型农耕地土壤为研究对象,结合稀土元素(Rare Earth Elements,REE)示踪方法,综合分析不同粒径土壤团聚体(5~2,2~1,1~0.5,0.5~0.25,<0.25 mm)和不同径流扰动周期(24 h,7天)对REE吸附和解吸能力的影响,探究REE示踪不同粒径土壤团聚体破碎转化的可行性,定量表征了土壤团聚体破碎转化路径。结果表明:REE与土壤团聚体的实际吸附浓度低于施放浓度,2~1,1~0.5,0.5~0.25,<0.25 mm土壤团聚体的REE吸附浓度与黏粒含量呈显著正相关(P<0.05);径流扰动影响对吸附于土壤团聚体的REE解吸作用十分微弱,解吸浓度仅占REE实际吸附浓度的0.001%~0.139%。5~2,2~1,1~0.5,05~0.25,<0.25 mm土壤团聚体经过湿筛后向各粒径转化的路径基本相同,向<0.25 mm微团聚体转化为土壤团聚体破碎的主要路径。相较于粉粒、黏粒含量较高的土壤团聚体,砂粒含量较高的土壤团聚体向1~0.5,0.5~0.25 mm粒径的转化贡献率整体偏低。基于REE示踪得到的>0.25 mm各粒径团聚体质量整体被低估,低估范围为-27.96%^-11.08%;而<0.25 mm团聚体质量则被高估,高估范围为3.65%~22.73%。基于各粒径土壤团聚体的REE量化值建立了校正关系,可将计算相对误差降低至0.04%~16.24%。     

秸秆和地膜覆盖对黄土高原旱作小麦田土壤团聚体氮组分的影响

利用田间定位试验研究旱作农田不同覆盖措施对土壤团聚体氮组分的影响。基于黄土高原8年冬小麦覆盖定位试验,试验设置生育期秸秆覆盖(SM)、生育期地膜覆盖(PM)和无覆盖对照(CK)3个处理。采用干筛法测定团聚体分布特征及不同粒径团聚体中全氮(STN)、微生物量氮(MBN)和潜在可矿化氮(PNM)含量。结果表明:(1)与CK处理相比,2种覆盖处理均未在各粒径团聚体全氮含量有显著变化,但SM处理相较于PM处理提高了0—10 cm土层的1.00～0.25 mm粒径团聚体STN含量(12.88%,P0.05)。(2)与CK处理相比,SM处理在0—10 cm土层中2.00,2.00～1.00,0.25 mm粒径团聚体MBN含量分别提高18.67%,24.05%,20.08%(P0.05),且各粒径团聚体PNM含量分别提高35.13%,30.03%,42.88%(P0.05);SM处理在10—20 cm土层中2.00 mm粒径团聚体MBN含量提高23.02%(P0.05),分别提高2.00,2.00～1.00,0.25 mm粒径团聚体PNM含量28.59%,31.31%,32.48%(P0.05)。(3)PM处理较CK处理提高0—10 cm土层中0.25 mm粒径团聚体PNM含量(32.34%,P0.05)。(4)微团聚体(0.25 mm)氮组分含量均高于大团聚(0.25 mm)氮组分含量,但大团聚体氮组分贡献率为81.88%～87.66%。可见,SM处理可提高土壤表层大团聚体氮组分的贡献率,使更多的氮素储存在大团聚体中,而PM处理对团聚体氮素贡献率的影响作用较小。总体而言,与CK和PM处理相比,SM处理可提高总土壤氮组分含量,提高微团聚体和大团聚体氮组分含量,使更多的氮储存在大团聚体中,促进土壤氮素周转。     

植物根系对土壤团聚体形成作用机制研究回顾

土壤团聚体是土壤结构的基本单元,土壤水力侵蚀的微观描述即为土壤团聚体的破裂过程。研究表明:植物根系可以改变土壤的力学以及水文特征,促进土壤团聚体的形成和稳定。因此,对近20年国内外的相关研究成果进行较为系统的回顾,从根系对土壤团聚体的物理、生物、电化学作用3个研究视角,分析了植物根系对土壤团聚体形成的作用机制,提出了现有研究中存在的问题及研究趋势,这对深入认识植物根系对土壤团聚体的影响及其作用机制、发展根-土相互作用的土壤侵蚀过程模型具有重要的意义。     

不同施肥措施及复垦年限下土壤团聚体的大小分布及其稳定性

土壤团聚体的数量和质量直接影响着土壤性质和有机碳固存。研究长期不同施肥措施及复垦年限对采煤塌陷区土壤团聚体的重量分布比例及其稳定性的影响,为该区域的农业生产和土壤质量提升提供科学依据。采集复垦6年和11年定位试验不同施肥处理耕层土样,选取不施肥(CK)、平衡施氮磷钾肥(NPK)、单施有机肥(M)、有机无机肥配施(MNPK)4个处理,利用干筛法和湿筛法获得4种粒径的团聚体/粉黏粒组分(> 2 mm、0.25-2 mm、0.053-0.25 mm和< 0.053 mm),用> 0.25 mm团聚体含量(R_0.25)、平均重量直径(MWD)、团聚体破坏率(PAD)和土壤不稳定团粒指数(E_LT)表示团聚体的稳定性,并测定了土壤有机碳含量。结果表明：复垦年限对土壤团聚体的含量及稳定性影响产生了显著影响。干筛条件下,复垦6年和11年均显著降低了各处理0.053-0.25 mm团聚体和< 0.053 mm组分的含量,降幅分别为68.39%-87.37%、69.63%-78.32%(6年)和90.01%-93.68%、78.29%-83.93%(11年)；湿筛条件下,复垦11年显著提高了各处理> 2 mm团聚体的含量,增幅达473.35%-645.16%,但是显著降低了0.053-0.25 mm团聚体的含量,降幅为43.67%-57.54%。土壤团聚体的稳定性也随着复垦年限的增加而逐渐增强,表现为DR_0.25、WR_0.25和MWD值呈增加趋势,而PAD和E_LT值呈降低趋势。土壤有机碳含量与DR_0.25、WR_0.25、MWD_水稳性呈极显著正相关关系,而它与PAD和E_LT呈极显著负相关关系。本研究表明,该区域连续复垦11年提高了土壤大团聚体的含量而伴随着微团聚体含量的显著减少,导致土壤结构越来越稳定。它对提高采煤塌陷区复垦土壤肥力、改善土壤结构效果最佳。