黄土高原生物土壤结皮发育过程中颗粒态和矿物结合态有机碳变化特征

土壤颗粒态有机碳(POC)和矿物结合态有机碳(MAOC)是重要的土壤碳库,其比例的变化决定土壤有机碳的周转速率及稳定性。探讨沙地生物土壤结皮发育过程中颗粒态有机碳和矿物结合态有机碳的含量、分配比例和差异性特征,对于深刻认识初始土壤形成过程中有机碳库形成、稳定机制具有重要意义。选择神木市六道沟流域生物土壤结皮4个发育阶段(藻结皮、藻结皮+少量藓结皮、藓结皮+少量藻结皮、藓结皮)为研究对象,裸沙作为对照,研究生物结皮层及结皮层下层0—2 cm, 2—10 cm, 10—20 cm土层土壤颗粒态和矿物结合态有机碳的变化特征。结果表明：(1)在BSCs土层,POC的增加速率大于MAOC,MAOC处于饱和状态;(2)在BSCs和0—2 cm土层,以微生物源有机碳为主导的MAOC主要贡献有机碳积累,在2—10 cm和10—20 cm土层,以植物源有机碳为主导的POC主要贡献有机碳积累;(3) POC和MAOC含量随土层增加而降低,随着生物土壤结皮发育而增加;(4) POC和MAOC与SOC均有显著的正相关关系,表明结皮定殖和发育显著促进了土壤有机碳积累。这些结果表明生物土壤结皮的定殖和发育能够显著...     

降雨对荒漠草原生物土壤结皮化学计量的影响

生物土壤结皮是干旱地区地表景观的基本组成部分,对生物地球化学循环具有重要影响。在中国北方荒漠化地区,生物土壤结皮化学计量在很大程度上是未知的,特别是降雨如何影响荒漠草原生物土壤结皮化学计量仍然不确定。该研究以自然降雨为对照,通过使用遮雨棚和喷灌系统控制降水输入,开展增水和减水处理野外控制性试验,研究降雨量对荒漠草原生物土壤结皮化学计量的影响。试验结果表明:1)减水处理增加了结皮层C∶N、C∶P和N∶P的比率,增水处理增加了结皮层下垫面C∶N、C∶P和N∶P比率;2)减水处理增大了结皮层与下垫面之间C含量的差异,同时减小了N和P含量的差异,增水处理增大了结皮层与下垫面之间N和P含量的差异,减水处理有利于结皮层C的积累,而增水后结皮层中磷的有效性降低;3)适宜的土壤水分条件促进了结皮层及下垫面土壤微生物生物量碳(Soil Microbial Biomass Carbon,SMBC)和土壤微生物生物量氮(Soil Microbial Biomass Nitrogen,SMBN)的积累,而过高的降雨量导致土壤养分损失,不利于SMBC和SMBN的积累。相对干旱的土壤环境有利于结皮层土壤C、N的富集,为土壤微生物呼吸提供较多的营养物质,有利于SMBC和SMBN的积累。总之,在中国北方荒漠化地区,生物土壤结皮和下垫面的C∶N∶P化学计量对降雨量有不同的响应。     

苔藓结皮及其下层土壤的胞外酶活性与微生物CUE特征

为进一步明确苔藓结皮对下层土壤养分的影响及微生物对养分的利用特征,以黄土丘陵区典型退耕地上发育的苔藓结皮及其下层土壤(0—2 cm,2—5 cm,10—20 cm)为研究对象,分析在剖面尺度下土壤碳(C)、氮(N)、磷(P)养分状况、胞外酶活性以及微生物CUE特征。结果表明:苔藓结皮显著提高了表层土壤养分含量,结皮层的SOC,TN,TP,DOC,DON和Olsen-P含量分别是10—20 cm土壤养分的2.58,2.34,1.13,2.30,4.30,7.36倍。与养分含量特征一致,微生物生物量随土层深度的增加逐渐降低。在整个剖面尺度上,微生物群落存在较为稳定的元素内稳态以保持自身C,N,P的计量平衡。参与C,N,P循环的相关胞外酶活性在剖面尺度上表现出差异,β-1,4-葡萄糖苷酶(BG)随深度增加逐渐降低,而β-1,4-N-乙酰氨基葡萄糖苷酶(NAG)和碱性磷酸酶(AP)则表现为先降低后增加的趋势,底层土壤较高的NAG和AP酶活性反映出N,P养分的匮乏。微生物CUE在剖面尺度上表现为先降低后增加的趋势,平均水平为0.25,表明表层与深层土壤更有助于C的固存。此外,方差分解(VPA)和线性模型结果均指出养分状况和土壤酶是影响微生物CUE的关键因素。总的来说,苔藓结皮对表层土壤的养分和微生物代谢产生积极作用,尽管底层土壤养分匮乏,但仍保持较高的微生物C利用效率。     

毛乌素沙地植被类型对生物结皮及其下伏土壤养分的影响

为了解旱区荒漠生物结皮的养分效应及其同植被灌丛间的关系,研究以毛乌素沙地广泛分布的苔藓、藻结皮为对象,选取4类典型植被样地,深入探讨了植被对生物结皮及其下伏土壤的养分分布的影响。结果表明:(1)沙蒿植被冠层下的藻结皮及其下伏土壤的全氮、全磷、有机质含量显著高于植被冠层间,沙柳、柠条群落则为植被冠层下的相应值显著低于植被冠层间(p0.05)。(2)沙蒿、沙柳、柠条3种群落的生物结皮及下伏土壤养分含量均随土层加深逐渐降低,而草地则表现为5—10 cm土层的土壤养分显著高于上层土壤;苔藓结皮的全氮、有机质表现为:柠条草地沙柳沙蒿,苔藓结皮的全磷以及藻结皮的养分含量均表现为:草地柠条沙蒿沙柳。(3)总体上,各类型植被下的苔藓及藻结皮均能够显著增加表层0—10 cm土壤的养分含量,且苔藓结皮的养分富集作用优于藻结皮。     

生物土壤结皮对荒漠区土壤微生物生物量的影响

为探明生物土壤结皮对土壤微生物生物量碳和氮的影响,以腾格里沙漠东南缘的人工植被固沙区生物土壤结皮覆盖的沙丘土壤为研究对象,根据固沙时间的不同将样地分为4个不同的区进行采样(55、47、30和20 a固沙区),以流沙区(0 a)和天然植被区(100 a)为对照。研究表明:人工植被固沙区的藻-地衣结皮和藓类结皮均可显著提高土壤微生物生物量碳(SMBC)和氮(SMBN)含量(p0.05),且固沙年限与SMBC和SMBN含量存在显著的正相关关系(p0.05);结皮类型显著影响土壤微生物生物量,藓类结皮下SMBC和SMBN含量显著高于藻-地衣结皮下SMBC和SMBN含量(p0.05);此外,生物土壤结皮可显著提高0~20 cm土层SMBC和SMBN含量(p0.05),且这种影响随土层的增加而减弱。而且,生物土壤结皮下SMBC和SMBN含量表现明显的季节变化,表现为夏季春季秋季。水热因子是决定土壤微生物生物量季节变化的主要因子,而生物土壤结皮通过调节土壤温度和湿度而影响土壤微生物生物量的季节变化。     

毛乌素沙地南缘沙丘生物土壤结皮发育特征

生物土壤结皮广泛分布于干旱和半干旱区,它的形成和发育对荒漠生态系统生态修复过程产生重要的影响。采用野外调查、测定和室内分析相结合的方法,对毛乌素沙地南缘沙丘生物土壤结皮发育特征进行研究。结果表明:不同地貌部位生物土壤结皮的厚度、各类型结皮盖度、机械组成和结皮及其下层剖面土壤容重均发生不同程度的变化。生物土壤结皮的发育对不同地貌部位具有一定的选择性,丘顶微生物结皮少量分布,迎风坡以浅灰色的藻类结皮为主,背风坡以黑褐色的藻类结皮为主,丘间地以苔藓结皮为主。不同地貌部位结皮层微生物总数存在较大差异。不同发育阶段生物土壤结皮的优势成分不同,表现出明显的阶段性特点,其形成和发育是生物过程和非生物过程的统一。     

生物结皮发育对风沙土盐基离子释放和矿物风化的影响

为探明生物结皮发育对风沙土盐基离子释放和矿物风化的影响,以进一步明确生物结皮的风化成土作用。以典型风沙土上发育的生物结皮为对象,通过模拟淋溶试验比较不同类型生物结皮(藻结皮、藻—藓混生结皮和藓结皮)覆盖土壤的盐基离子释放规律,探究盐基离子释放量随淋溶液pH的变化趋势,以及量化生物结皮覆盖土壤的矿物风化速率。结果表明:矿物风化反应阶段不同种类盐基离子的淋出量均较为平缓,生物结皮覆盖土壤的各盐基离子总淋出量表现为Ca²⁺＞K⁺＞Mg²⁺＞Na⁺,其中藻结皮覆盖土壤的盐基离子总淋出量最高,比无结皮、混生结皮和藓结皮分别增加了112.0%,31.2%,27.1%。淋溶液pH显著影响盐基离子的淋溶释放,且其作用程度因离子种类和结皮类型而异。生物结皮覆盖提升了土壤的易风化矿物含量、风化程度和速率,藻结皮、混生结皮和藓结皮覆盖土壤的风化速率相比无结皮分别提升了61.2%,27.1%,152.6%,并且风化速率随淋溶液pH降低而提升。综上,生物结皮能显著促进风沙土矿物风化,其对风沙土改良和修复具有积极意义。     

人工林建设对沙地土壤结皮发育及其表土理化特性的影响

为了了解人工林建设对土壤结皮发育和表土特征的影响,2006年在科尔沁沙地调查了不同年龄杨树林地的土壤结皮及结皮下0-5.0cm土壤的理化特性,分析研究了植被固沙区土壤结皮及其表土的发育特征。结果表明:(1)在科尔沁沙地,人工林的建设有利于流动沙地土壤结皮的形成、发育和结皮下0-5.0cm表土性状的改善;(2)随着人工林的生长发育,土壤结皮覆盖度、厚度、硬度、土壤细颗粒和有机质、养分含量均明显增加,并从物理结皮逐步演变成地衣结皮和苔癣结皮;(3)随着人工林的生长发育,结皮下0-2.5cm和2.5-5.0cm表土的细颗粒、有机质和养分含量大幅增加,但其含量随着表土深度增加而下降;(4)人工植被建设对沙地土壤结皮形成发育和下层表土成土过程的作用机制,一方面源于人工植被具有降风滞尘,维护沙面稳定,增加地表粘粉粒含量的作用;另一方面源于凋落物的生产与沉降,以及对局部水热环境的改善,增加了结皮与表土的有机质和养分含量,促进了微生物和微管植物的侵入。     

荒漠区生物土壤结皮对土壤酶活性的影响

在干旱的沙漠生态系统中,生物土壤结皮对于沙丘的固定和土壤生物的维持起着相当重要的作用。土壤酶活性能敏感地指示土壤的恢复程度,是衡量沙区生态恢复与健康的重要生物学属性,而目前关于生物土壤结皮与土壤酶活性的关系研究很少。为探明生物土壤结皮对土壤酶活性的影响,以腾格里沙漠东南缘的人工植被固沙区生物土壤结皮覆盖的沙丘土壤为研究对象,根据固沙时间的不同将样地分为4个不同的区进行采样(57、49、32和22 a固沙区),以流沙区(0 a)和红卫天然植被区(100 a)为对照。研究表明:人工植被固沙区的藻-地衣结皮和藓类结皮均可显著提高土壤碱性磷酸酶、蛋白酶和纤维素酶的活性(p0.05);结皮类型显著影响土壤酶的活性,发育晚期的藓类结皮下土壤碱性磷酸酶、蛋白酶和纤维素酶的活性显著高于发育早期的藻-地衣结皮下土壤酶的活性(p0.05);固沙年限显著影响土壤碱性磷酸酶、蛋白酶和纤维素酶的活性,且与这三种土壤酶活性均存在显著的线性正相关关系(p0.05);目前,生物土壤结皮可显著提高0~20 cm土层碱性磷酸酶、蛋白酶和纤维素酶的活性(p0.05),且这种影响随土层的增加而减弱。而且,生物土壤结皮下土壤碱性磷酸酶、蛋白酶和纤维素酶的活性表现明显的季节变化,表现为夏季秋季春季和冬季。腾格里沙漠东南缘的人工植被固沙区生物土壤结皮的存在与演替提高了土壤酶的活性,生物土壤结皮有利于该区土壤及其相应生态系统的恢复。     

铜尾矿生物结皮的生物固氮及其影响因素研究

在铜尾矿生态系统自然恢复过程中,生物结皮广泛存在并成为尾矿生态系统演替早期的重要阶段。本文采用乙炔原位还原法对藻类结皮、藻藓混合结皮和藓类结皮的生物固氮特征进行了系统研究。结果表明:(1)生物结皮显著提高了铜尾矿总氮含量,同时降低了铜的含量。(2)不同类型生物结皮的固氮能力差别较大,其中藻藓混合结皮的生物固氮量最高,在N 4.36～30.39 kg hm2 a–1之间;藻类结皮和藓类结皮的固氮量分别为N 1.32～8.78、0～16.34 kg hm2 a–1。(3)生物固氮能力随季节变化明显,夏季的生物固氮量最高,春季次之,秋冬季节相对较低。(4)铜尾矿基质pH、NH4+-N和水溶性有机碳(WSOC)等与生物固氮量呈显著正相关(p<0.05),而土壤容重、NO3--N和总铜等与生物固氮量呈显著负相关(p<0.05)。     

Responses of soil microbial biomass and community composition to biological soil crusts in the revegetated areas of the Tengger Desert

As a key component of desert ecosystems, biological soil crusts (BSCs) play an important role in dune fixation and maintaining soil biota. Soil microbial properties associated with the colonization and development of BSCs may indicate soil quality changes, particularly following dune stabilization. However, very little is known about the influence of BSCs on soil microbes in sand dunes. We examined the influence of BSCs on soil microbial biomass and community composition in revegetated areas of the Tengger Desert. BSCs increased soil microbial biomass (biomass C and N), microbial phospholipid fatty acid (PLFA) concentrations and the ratio of fungal to bacterial PLFAs. The effects varied with crust type and crust age. Moss crusts had higher microbial biomass and microbial PLFA concentrations than cyanobacteria-lichen crusts. Crust age was positively correlated with microbial biomass C and N, microbial PLFA concentrations, bacterial PLFA concentrations, fungal PLFA concentrations and the ratio of fungal to bacterial PLFAs. BSCs significantly affected microbial biomass C and N in the 0–20 cm soil layers, showing a significant negative correlation with soil depth. The study demonstrated that the colonization and development of BSCs was beneficial for soil microbial properties and soil quality in the revegetated areas. This can be attributed to BSCs increasing topsoil thickness after dunes have been stabilized, creating suitable habitats and providing an essential food source for soil microbes.     

氮素有机替代对东北黑土区土壤微生物碳磷资源限制的影响

  【目的】  土壤微生物数量和结构普遍受到碳 (C)，氮 (N)、磷 (P)等养分有效性的影响，研究不同施肥措施对东北黑土区土壤理化性质、微生物量和酶活性的影响，深入了解土壤微生物养分资源限制状况及其变化规律，为提高土壤生物肥力提供理论依据。  【方法】  试验设在黑龙江省哈尔滨市，土壤类型为黑土，种植制度为玉米单作。试验开始于2019年，共设9个处理:不施肥 (CK)、习惯施肥 (FP)、推荐施肥 (OPT)、推荐施肥不施氮 (–N)；有机氮替代推荐施氮量的10% (M1)、20% (M2)、30% (M3)、40% (M4) 和50% (M5)。玉米收获后，采集0—20 cm土壤样品，测定土壤含水量、pH、有机质、全氮、速效磷、速效钾、可溶性有机碳、可溶性有机氮、微生物量碳、微生物量氮和4种土壤酶 (酸性磷酸酶、β-D-葡萄糖苷酶、L-亮氨酸氨基肽酶、β-N-乙酰氨基葡萄糖苷酶) 活性。  【结果】  与OPT处理相比，有机氮替代化肥氮处理提高了土壤速效养分含量 (可溶性有机碳、有效磷、速效钾) 和微生物量 (微生物量碳、微生物量氮)，其中可溶性有机碳、有效磷和速效钾的含量随替代比例的增加分别增加了15.5%～46.6%、1.4%～18.5%和2.4%～18.8%；MBC和MBN的含量随有机替代比例的增加分别增加了1.4%～19.9%和0.04%～22.7%。PCA分析显示出CK、化肥处理 (FP、OPT、–N) 和有机氮替代化肥氮处理 (M1、M2、M3、M4、M5) 下的土壤酶活性具有显著差异；RDA分析进一步表明有效磷 (F = 14.1，P = 0.002) 是影响酶活性变化的主要理化因子，解释了不同处理间酶活性差异的36.1%。酶化学计量散点图显示出试验点的土壤微生物均受到磷的限制，FP处理下的土壤微生物还受到碳的限制。此外，与CK相比，有机氮替代化肥氮显著提高了β-D-葡萄糖苷酶与酸性磷酸酶的比值，但是矢量角度在不同有机替代处理间并无显著差异。  【结论】  在本试验区中，未施肥处理下土壤微生物受到碳和磷的共同限制，习惯施肥和优化施肥均会加剧微生物的碳限制。有机氮替代化肥氮可以显著提高土壤的养分含量与生物肥力，解除土壤微生物的碳限制，并显著减轻土壤微生物的磷限制。但是磷限制的减轻效果并未随有机氮替代化肥氮比例的增加而显著增加，考虑到有机肥养分释放较为缓慢，具体的有机替代比例还需开展长期试验。     

不同施肥处理对水稻养分吸收和稻田土壤微生物生态特性的影响

在水稻长期定位肥料试验条件下研究了不同施肥处理对水稻养分吸收动态变化和土壤微生物生态特性的影响。该长期定位试验设有CK(不施肥对照)和PK、NK、NP、NPK五个肥料处理和常规稻、杂交稻品种对比处理。研究结果表明,水稻产量分别与水稻吸氮总量、吸磷总量和吸钾总量显著相关;在连续种植水稻条件下,水稻对所缺养分的吸收量呈逐年下降趋势,表明缺肥区土壤相应的有效养分库消耗很快。土壤微生物特性测定表明,不平衡施肥降低了土壤微生物量N,使微生物量C/N比增加。与缺肥区相比较,NPK配施处理促进了土壤微生物的功能多样性,同时增加了土壤微生物总量。可见,土壤中养分不足或供应不平衡,不仅影响水稻养分的吸收,而且对土壤微生物总量和群落多样性产生重要影响。     

Dynamics of soil microbial biomass C, N and P in disturbed and undisturbed stands of a tropical wet-evergreen forest

To understand the spatial and temporal dynamics of soil microbial biomass and its role in soil organic matter and nutrient flux in disturbed tropical wet-evergreen forests, we determined soil microbial biomass C, N and P at two soil depths (0–15 and 15–30 cm), along a disturbance gradient in Arunachal Pradesh, northeastern India. Disturbance resulted in considerable increase in air temperature and light intensity in the forest and decline in the soil nutrients concentration, which affected the growth of microbial populations and soil microbial biomass. There were significant correlations between bacterial and fungal populations and microbial biomass C, N and P. Soil microbial population was higher in the undisturbed (UD) forest stand than the disturbed forest stands during post-monsoon and less during rainy season due to heavy rainfall. Greater demand for nutrients by plants during rainy season limited the availability of nutrients to soil microbes and therefore, low microbial biomass C, N and P. Microbial biomass was negatively correlated with soil temperature and pH in all the forest stands. However, there were significant positive relationships among microbial biomass C, N and P. Percentage contribution of microbial C to soil organic C was higher in UD forest, whereas percentage contribution of microbial biomass N and P to total N and total P was higher in the moderately disturbed site than in the highly disturbed (HD) site. These results reveal that the nutrient retention by soil microbial biomass was greater in the selective logged stand and would help in the regeneration of the forest upon protection. On the other hand, the cultivated site (HD) that had the lowest labile fractions of soil organic matter may recover at a slower phase. Further, minimum and maximum microbial biomass C, N and P during rainy and winter seasons suggest the synchronization between nutrient demand for plant growth and nutrient retention in microbial biomass that would help in ecosystem recovery following disturbance.     

Effect of Soil Drying Intensity During an Experimental Drying-Rewetting Event on Nutrient Transformation and Microbial Community Composition

Soil drying-rewetting(DRW) events affect nutrient transformation and microbial community composition; however, little is known about the influence of drying intensity during the DRW events. Therefore, we analyzed soil nutrient composition and microbial communities with exposure to various drying intensities during an experimental drying-rewetting event, using a silt loam from a grassland of northern China, where the semi-arid climate exposes soils to a wide range of moisture conditions, and grasslands account for over 40% of the nation's land area. We also conducted a sterilization experiment to examine the contribution of soil microbes to nutrient pulses. Soil drying-rewetting decreased carbon(C) mineralization by 9%–27%. Both monosaccharide and mineral nitrogen(N) contents increased with higher drying intensities(drying to ≤ 10% gravimetric water content), with the increases being 204% and 110% with the highest drying intensity(drying to 2% gravimetric water content), respectively, whereas labile phosphorus(P)only increased(by 105%) with the highest drying intensity. Moreover, levels of microbial biomass C and N and dissolved organic N decreased with increasing drying intensity and were correlated with increases in dissolved organic C and mineral N, respectively,whereas the increases in labile P were not consistent with reductions in microbial biomass P. The sterilization experiment results indicated that microbes were primarily responsible for the C and N pulses, whereas non-microbial factors were the main contributors to the labile P pulses. Phospholipid fatty acid analysis indicated that soil microbes were highly resistant to drying-rewetting events and that drought-resistant groups were probably responsible for nutrient transformation. Therefore, the present study demonstrated that moderate soil drying during drying-rewetting events could improve the mineralization of N, but not P, and that different mechanisms were responsible for the C, N, and P pulses observed during drying-rewetting events.     

Litter, warming and plants affect respiration and allocation of soil microbial and plant C, N and P in arctic mesocosms

In a mesocosm experiment, we studied decomposition rates as CO₂ efflux and changes in plant mass, nutrient accumulation and soil pools of nitrogen (N) and phosphorus (P), in soils from a sub-arctic heath. The soil was incubated at 10 °C and 12 °C, with or without leaf litter and with or without plants present. The purpose of the experiment was to analyse decomposition and nutrient transformations under simulated, realistic conditions in a future warmer Arctic.Both temperature enhancement and litter addition increased respiration rates. Temperature enhancement and surprisingly also litter addition decreased microbial biomass carbon (C) content, resulting in a pronounced increase of specific respiration. Microbial P content increased progressively with temperature enhancement and litter addition, concomitant with increasing P mineralisation, whereas microbial N increased only in the litter treatment, at the same time as net N mineralisation decreased. In contrast, microbial biomass N decreased as temperature increased, resulting in a high mobilisation of inorganic N.Plant responses were closely coupled to the balance of microbial mineralisation and immobilisation. Plant growth and N accumulation was low after litter addition because of high N immobilisation in microbes and low net mineralisation, resulting in plant N limitation. Growth increased in the temperature-enhanced treatments, but was eventually limited by low supply of P, reflected in a low plant P concentration and high N-to-P ratio. Hence, the different microbial responses caused plant N limitation after litter addition and P limitation after temperature enhancement. Although microbial processes determined the main responses in plants, the plants themselves influenced nutrient turnover. With plants present, P mobilisation to the plant plus soil inorganic pools increased significantly, and N mobilisation non-significantly, when litter was added. This was presumably due to increased mineralisation in the rhizosphere, or because the nutrients in addition to being immobilised by microbes also could be absorbed by plants. This suggests that the common method of measuring nutrient mineralisation in soils incubated without plants may underestimate the rates of nutrient mobilisation, which probably contributes to a commonly observed discrepancy of measured lower rates of net nutrient mineralisation than uptake rates in arctic soils.     

Coupling of nutrient cycling and carbon dynamics in the Arctic,integration of soil microbial and plant processes

Most studies of nutrient cycling in arctic ecosystems have either addressed questions of plant nutrient acquisition or of decomposition and mineralization processes, while few studies have integrated processes in both the soil and plant compartments. Here, we synthesize information on nutrient cycling within, and between, the soil/microbial and the plant compartments of the ecosystems and integrate the cycling of nutrients with the turnover of organic matter and the carbon balance in tundra ecosystems. Based on this compilation and integration, we discuss implications for ecosystem function in response to predicted climatic changes.Many arctic ecosystems have high amounts of nutrients in the microbial biomass compared to the pools in the plant biomass both due to large nutrient-containing organic deposits in the soil and low plant biomass. The microbial pools of N and P, which are the most commonly limiting nutrients for plant production, may approach (N) or even exceed (P) the plant pools. Net nutrient mineralization is low, the residence time of nutrients in the soil is long and the nutrients are strongly immobilized in the soil microorganisms. This contributes to pronounced nutrient limitation for plant productivity, implies that the microbial sink strength for nutrients is strong and that the microbes may compete with plants for nutrients, but also that they are a potential source of plant nutrients during periods of declining microbial populations. The extent of this competition is poorly explored and it is uncertain whether plants mainly take up nutrients continuously during the summer when the microbial activity and, presumably, also the microbial sink strength is high, or whether the main nutrient uptake occurs during pulses of nutrient release when the microbial sink strength declines.Improved knowledge of mechanisms for plant-microbial interactions in these nutrient-limited systems is important, because it will form a basis also for our understanding of the C exchange between the ecosystems and the atmosphere under the predicted, future climatic change. High microbial nutrient immobilization, i.e. low release of plant-available nutrients, paired with high microbial decomposition of soil organic matter will lead to a loss of C from the soil to the atmosphere, which may not be compensated fully by increased plant C fixation. Hence, the system will be a net source of atmospheric C. Conversely, if plants are able to sequester extra nutrients efficiently, their productivity will increase and the systems may accumulate more C and turn into a C sink, particularly if nutrients are allocated to woody tissues of low nutrient concentrations.     

长期平衡施肥对潮土微生物活性和玉米养分吸收的影响

利用中国科学院封丘农业生态实验站农田生态系统养分平衡长期定位试验地,研究氮磷钾平衡施肥(NPK)与缺素施肥(NK、PK、NP)对土壤微生物生物量、酶活性、呼吸强度以及玉米养分吸收的影响。结果发现,与不施肥对照(CK)相比,NPK处理玉米根系与茎叶生物量、籽粒产量以及植株氮磷钾吸收量均大幅提高,NP处理次之,PK与NK处理则无显著影响;同一处理玉米茎叶与根系养分含量接近,而籽粒的全氮和全磷含量较高、全钾含量偏低;与NPK处理相比,缺施氮、磷或钾肥均直接导致玉米植株相应养分的明显亏缺或其他养分的过量富集,但在根系、茎叶和籽粒部位的累积情况存在一定差异。与CK相比,所有施加磷肥的处理(NPK、NP、PK)土壤微生物生物量(碳、氮、磷)、脱氢酶、转化酶、脲酶与碱性磷酸酶活性以及土壤微生物代谢活性和土壤基础呼吸强度均显著升高(p<0.05),土壤微生物代谢熵则显著下降(p<0.05),而缺施磷肥的NK处理除显著提高脲酶活性外(p<0.05),对其他指标均无显著影响。结果表明,氮磷钾平衡施肥在促进土壤微生物繁育和保育微生物代谢活性以及促进作物生长和保证养分吸收等方面显得非常重要,而缺素施肥中以缺施磷肥的不利影响最为突出。     

红壤水稻土累积酶活性及养分对长期不同施肥处理的响应

本研究基于鹰潭农田生态系统国家野外科学观测研究站24年的长期定位试验,揭示对照(不施肥,CK)、有机肥(C)、化学氮磷钾肥(NPK)、化学氮磷钾肥+有机肥(NPKC)等不同施肥处理对红壤水稻土酶活性及土壤养分的影响。于晚稻收获后采集各小区耕层土壤,测定红壤水稻土中转化酶、脲酶活性(测定时并设加0.5 ml甲苯与不加甲苯处理)及转化酶动力学特征,同时测定土壤养分含量及微生物生物量碳,分析酶活性与养分含量及微生物生物量碳间的关系,明确土壤中累积酶活性及土壤养分对长期不同施肥处理的响应。结果发现,与对照相比,施肥处理下土壤转化酶活性显著提高了31.3%~131.7%,微生物生物量碳显著提高了84.9%~125.1%;在没有甲苯抑制微生物活性下,施肥处理的转化酶底物蔗糖转化速率增加量提高了89.5%~153.7%,脲酶底物尿素转化增加量提高了59.2%~98.9%,表明微生物显著影响两种累积酶表观酶活性;转化酶活性、脲酶活性与微生物生物量碳呈显著正相关。与对照处理相比,施肥处理显著增加了土壤有机碳(30.1%~36.3%)、全磷(28.6%~102.9%)、速效磷(62.2%~445.0%)、碱解氮(35.9%~56.4%)含量;统计分析显示,转化酶活性、脲酶活性均与碱解氮、有机碳含量显著正相关。与对照相比,各施肥处理土壤的转化酶米氏常数(Km)差异并不显著,而转化酶表观活性(Vmax)及转化系数(Vmax/Km)均显著增加。长期施肥处理增加了土壤养分含量和微生物生物量碳,提高了土壤中累积酶的活性。