西宁南山4种灌木根际和非根际土壤微生物、酶活性和养分特征

西宁南山区植被退化情况严重,人工造林植被恢复被看作是最有效的恢复手段,其中选择合适造林树种尤为关键。选择人工种植的唐古特白刺Nitraria tangutorum、柠条Caragana korshinskii、西北小蘗Berberis vernae和短叶锦鸡儿Caragana brevifolia共4种灌木树种造林试验区为研究对象,通过测定根际和非根际土壤微生物数量、酶活性及养分含量,综合比较种植4种灌木树种根际和非根际土壤肥力差异,科学评价其对土壤的改善效果。研究表明:(1)土壤微生物数量和酶活性总体呈现出根际高于非根际的规律,仅放线菌数量和脲酶活性出现了根际低于非根际现象。(2)土壤养分方面,4种灌木根际土壤和非根际土壤p H值、全N、全P、全K含量差异不显著,有机质、有效P、速效K含量均呈现出根际非根际,而碱解N则是根际非根际。(3)土壤酶活性与土壤微生物数量相关性不显著,土壤有机质含量与土壤细菌、真菌数量呈极显著正相关,有效P含量与土壤细菌、真菌和放线菌数量呈极显著正相关,速效K含量与过氧化氢酶、酸性磷酸酶活性呈显著正相关,全N、碱解N含量均与脲酶活性呈显著正相关。(4)从土壤肥力综合水平来看,根际非根际,其中根际土壤中西北小蘗柠条短叶锦鸡儿唐古特白刺,研究结果表明西北小蘗和柠条能大幅提高土壤肥力,改良土壤效果较好。     

干旱荒漠区不同灌木根际与非根际土壤氮素的含量特征

选取广泛分布于阿拉善干旱荒漠区的白刺、霸王、红砂、沙冬青、沙木蓼、梭梭和驼绒藜7种不同的旱生灌木,研究其根际与非根际土壤各种形态氮素、有机碳的含量特征及土壤pH的变化.结果表明,相对于非根际土壤,根际土壤全氮、铵态氮、硝态氮分别平均高24.9%、24.5%和65.1%,土壤有机碳平均高出18.5%,土壤pH值平均低0.14个单位.根际与非根际土壤的全氮、铵态氮、硝态氮、有机碳和pH之间都呈现出了极显著差异(p<0.01).7种灌木根际土壤全氮、硝态氮和有机碳含量均比非根际土壤含量高.除沙冬青根际铵态氮含量较非根际低以外,其余6种灌木根际土壤铵态氮含量均高于非根际土壤.梭梭的根际土壤pH高于非根际,其它6种灌木均是根际pH低于非根际土壤.在根际与非根际,土壤有机碳与土壤全氮之间均呈显著相关,二者表现为线性关系.而土壤全氮与铵态氮在根际与非根际则均无相关性,全氮与硝态氮在根际和非根际土壤均显著相关,且二者也呈线性相关.     

施氮量对夏玉米根际和非根际土壤酶活性及氮含量的影响

在华北平原潮土上进行田间试验,研究施氮量对夏玉米根际和非根际土壤酶活性及氮含量的影响.结果表明: 不同施氮水平下土壤酶活性均表现出一致的季节性变化趋势.与不施氮处理相比,施氮处理能显著提高根际和非根际土壤硝态氮含量及根际土壤铵态氮含量,显著增强土壤几丁质酶、β-葡萄糖苷酶、纤维素酶和木聚糖酶活性.在整个玉米生育期内,非根际土壤硝态氮含量显著高于根际土壤;非根际土壤铵态氮含量在灌浆期显著高于根际土壤,但在苗期和完熟期则显著低于根际土壤;根际土壤几丁质酶、β-葡萄糖苷酶、纤维素酶和木聚糖酶活性都显著高于非根际土壤.施氮对土壤有机质含量没有显著影响;在0～180 kg·hm^-2施氮范围内,施氮可明显增加土壤全氮含量,但当施氮量超过180 kg·hm^-2时,土壤全氮含量则明显下降.综上,适量施氮能显著增强土壤酶活性,提高土壤全氮含量,改善土壤生化性质.     

套作棉根际与非根际土壤酶活性和养分的变化

在棉麦两熟双高产条件下研究了棉花根际与非根际土壤酶活性和养分含量的变化.结果表明,套作棉土壤脲酶、蔗糖酶、蛋白酶及过氧化氢酶活性随生育进程的变化趋势与单作棉表现一致,但整个生育期套作棉根际与非根际土壤各种酶活性均明显高于单作棉.套作棉根际与非根际土壤养分含量在麦棉共生期低于单作棉或差异较小,而在麦收后则显著高于单作棉.套作棉土壤养分含量随生育进程的变化趋势与单作棉大体相同,但一些养分的吸收高峰晚于单作棉.无论套作棉还是单作棉,根际土壤酶活性和养分含量高于非根际.土壤各养分含量与土壤脲酶、蔗糖酶和蛋白酶活性呈显著(P=0.0,n=32)或极显著(P=0.01,n=32)相关,与土壤过氧化氢酶活性相关不显著.     

黄土丘陵区不同植被根际土壤微量元素含量特征

为了解黄土高原不同植被土壤微量元素的根际效应,分析了该地区柠条、沙棘、沙打旺、柳枝稷、阿尔泰狗娃花和茵陈蒿6种植被根际与非根际土壤中有机碳、全氮、Mn、Cu、Fe、Zn含量.结果表明： 6种植被中,柠条、阿尔泰狗娃花和茵陈蒿根际土壤的有机碳、全氮含量高于非根际土壤;除柠条和沙棘外,其余4种植被非根际土壤pH值均显著高于根际土壤.6种植被根际土壤有效Mn含量均低于非根际;柠条、沙打旺和柳枝稷根际有效Cu含量显著高于非根际,表现出强烈根际富集现象.除沙打旺外,其他5种植被根际有效Fe含量均略高于非根际.沙打旺、柳枝稷、茵陈蒿和阿尔泰狗娃花表现出强烈的有效Zn根际富集现象.根际与非根际土壤有机碳、全氮与有效Mn、有效Zn,以及有效Mn与有效Zn呈极显著正相关.根际土壤pH值与有效Mn和有效Zn呈显著负相关.由于不同植物根系的生长特征、根际pH值及微生物种类等的差异,不同植被根际的微量元素含量不同,茵陈蒿根际4种微量元素含量高于其他植被.     

南方根结线虫对不同砧木嫁接番茄苗活性氧清除系统的影响

采用盆栽人工接种方法,对番茄嫁接苗进行了抗性评价,研究了番茄嫁接苗叶片中抗氧化酶活性和活性氧代谢的动态变化。结果表明,接种南方根结线虫(J2)后,砧木嫁接苗表现为高抗,自根嫁接苗为高感。通过嫁接换根,与自根嫁接苗相比,砧木嫁接苗明显提高了接穗叶片的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性,降低了超氧阴离子(O.2-)产生速率以及过氧化氢(H2O2)和丙二醛(MDA)含量。表明番茄植株体内的活性氧水平和抗氧化酶活性的高低与其抗根结线虫的能力密切相关,较低的活性氧水平和较高的抗氧化酶活性有利于减轻对膜系统的伤害,提高番茄植株的抗根结线虫能力。     

构树(Broussonetia papyrifera)幼苗氮、磷吸收对接种AM真菌的响应

对石灰岩适生植物构树(Broussonetia papyrifera)进行菌根真菌摩西球囊霉(Glomus mosseea)、地表球囊霉(G.versiforme)、透光球囊霉(G.diaphanum)的单独接种、混合接种和不接种处理,幼苗生长3个月后测定其根茎叶N、P含量和土壤酶活性,结果表明:接种AM真菌后构树幼苗生物量显著增加,植株根茎叶N含量较对照组显著提高,其含量为根<茎<叶。各处理中除了透光球囊霉处理的茎含量与对照差异不显著外,其余各处理含量均呈显著或极显著差异。AM真菌对构树苗P的促进效应主要体现在根、茎的利用上,而叶片P含量除混合接种外则有所降低,但M (接种处理)与M-(非接种处理)间无显著差异。构树苗根茎叶等量干物质P含量依次为叶>根>茎。进一步研究表明,接种AM真菌显著提高了土壤酶活性,这种显著性主要体现在蛋白酶和碱性磷酸酶上,植株N含量与土壤蛋白酶和碱性磷酸酶活性有显著相关性,而P含量只是根部吸收与多酚氧化酶活性显著相关。结果表明,接种AM真菌促进了宿主植物构树生物量的积累,提高了根际土壤酶活性,增加了植株对N、P的吸收。     

施硒对水稻土壤硒有效性的影响

硒在华南稻区酸性土壤中极易被固定使其有效性较低.本研究旨在通过盆栽试验,探明施用硒肥对水稻根际和非根际土壤硒有效性的影响.结果表明: 施硒能提高水稻产量,增加籽粒硒含量;水稻根际土壤中水溶态硒、交换态硒、铁锰氧化物结合态硒、有机物-硫化物结合态硒和残渣态硒含量均低于非根际土壤.各施硒处理之间,根际和非根际土壤中硒的迁移系数没有显著差异;施硒对根和叶片之间硒的迁移系数也没有显著影响,但是施硒提高了叶片和籽粒之间硒的迁移系数.施用0.5 mg·kg^-1硒增加了水稻根系有机酸的分泌,而施用1.0、5.0 mg·kg^-1硒则降低了有机酸的分泌.根系有机酸的分泌对根际土壤pH值影响不大,根际土壤pH值反而高于非根际土壤,但施硒显著降低了根际土壤pH值.随着施硒水平的提高,根际土壤黏土矿物(高岭石)的红外吸收光谱不断增强.施入土壤中的硒多转化为水稻难以吸收利用的形态,且不易向根际移动.根系分泌的有机酸也并不是通过影响土壤pH值来提高土壤硒的有效性.     

丘陵红壤茶园根际氮磷转化对不同强度酸雨胁迫的响应

南方丘陵红壤茶园长期受到酸沉降的胁迫,但茶树根际氮(N)、磷(P)转化过程对酸雨的响应及其机制尚不清楚.以江西典型丘陵红壤25年茶园为对象,开展pH 4.5、pH 3.5、pH 2.5及对照4种不同强度酸雨处理的原位模拟试验,于试验第3年测定根际和非根际土壤矿质N、速效P和相关酶的活性,并估测土壤N、P矿化速率,计算各变量的根际效应.结果表明: 与对照相比,pH 4.5、pH 3.5和pH 2.5处理根际土壤NO₃^--N含量分别降低了7.1%、42.1%和49.9%,矿质N分别降低了6.4%、35.9%和40.3%,速效P分别降低了10.5%、41.1%和46.9%;根际氨化速率分别降低了18.7%、30.1%和44.7%,N净矿化速率分别降低了3.6%、12.7%和38.8%,P矿化速率分别降低了31.5%、41.8%和63.0%,但不同处理之间根际硝化速率差异不显著;根际土壤脲酶和酸性磷酸酶活性均表现为随酸雨加重呈增强的趋势(P<0.05).非根际土壤除NH₄⁺-N外,其他有效N和P含量未随酸雨加重而改变;不同酸雨处理对非根际土壤氨化、硝化、N净矿化速率和P矿化速率的影响差异均不显著.根际NH₄⁺-N、NO₃^--N、矿质N、氨化和净矿化速率均随着酸雨强度加重由正效应转变为负效应,而脲酶和酸性磷酸酶活性由负效应转变为正效应,但速效P和P矿化速率始终表现为负效应,硝化速率始终为正效应.综上所述,连续酸雨加重总体上抑制了根际N、P转化,降低其有效性,且不同程度改变其根际效应,从而影响茶园养分循环.     

秦岭太白山区6种中草药根际与非根际土壤化学性质及酶活性

以秦岭太白山区不同生境下鹿蹄草、三尖杉、玉竹、银露梅、珠芽蓼和金露梅6种中草药为对象,研究其根际与非根际土壤的化学性质及酶活性.结果表明:6种中草药根际土壤的有机质、全氮、有效氮、有效磷含量和阳离子交换量(CEC)均高于非根际土壤,呈现明显的根际聚集现象;土壤酶活性总体上表现出根际较强的特性;土壤有机质、全氮、全磷含量与中性磷酸酶呈显著正相关;土壤CEC与中性磷酸酶和酸性磷酸酶均呈显著正相关.6种中草药非根际土壤的有机质、全氮与脲酶、过氧化氢酶和中性磷酸酶均呈显著正相关;土壤CEC与脲酶、过氧化氢酶、中性磷酸酶和酸性磷酸酶均呈显著正相关.根际土壤肥力水平综合得分总体上大于非根际土壤.其中,金露梅、珠芽蓼和银露梅的根际与非根际土壤肥力水平综合得分较高,而鹿蹄草、玉竹和三尖杉得分较低.土壤有机质和CEC在评价6种中草药根际与非根际土壤肥力中起重要作用,而中性磷酸酶是首选土壤酶指标.     

Restoration,soil organisms,and soil processes: emerging approaches

Better understanding of the connection between aboveground plant communities and belowground soil organisms and processes has led to an explosion in recent research on the applications of this link to the field of ecological restoration. Research is only beginning to have the capacity to link soil organisms and specific ecosystem functions. Establishing general ecological principles of the role microbial communities have during ecological restoration is also still in its infancy. As such, the literature is at a critical point to generate a Special Feature that brings together novel approaches of linking soil and restoration to promote more regular inclusion and consideration of soil organisms and soil‐based processes in ecological restoration. In this special feature, we bring together nine research articles from different ecosystems that study the relationship between restoration activities, soil microbial communities, and soil properties. From these research articles, we describe two primary themes: (1) research on the impacts of ecosystem‐specific restoration activities on soil organisms and processes and (2) research testing methods of soil manipulation to improve restoration outcomes. We hope to inspire readers and restoration practitioners to consider soil microbes and soil processes in their research, restoration projects, and world views.     

Harvester ant nests, soil biota and soil chemistry

Many ant species accumulate organic debris in the vicinity of their nests. These organic materials should provide a rich resource base for the soil biota. We examined the effect of harvester ant nests (Pogonomyrmex barbatus) on the soil community and soil chemistry. Ant nest soils supported 30-fold higher densities of microarthropods and 5-fold higher densities of protozoa than surrounding, control soils. The relative abundances of the major groups of protozoa differed as well: amoebae and ciliates were relatively overrepresented, and flagellates underrepresented, in ant nest versus control soils. Densities of bacteria and fungi were similar in the two soil types. Concentrations of nitrate, ammonium, phosphorus, and potassium were significantly higher in ant nest soils, while concentrations of magnesium, calcium, and water were similar in nest and control soils. Ant nest soils were marginally more acidic than controls. The results demonstrate that P. barbatus nests constitute a significant source of spatial heterogeneity in soil biota and soil chemistry in arid grasslands. Received: 17 March 1997 / Accepted: 10 June 1997     

植物、土壤及土壤管理对土壤微生物群落结构的影响

土壤微生物是土壤生态系统的重要组成部分,对土壤微生物群落结构多样性的研究是近年来土壤生态学研究的热点。本文综述了有关植物、土壤类型以及土壤管理措施对土壤微生物群落结构影响的最新研究结果,指出植物的作用因植物群落结构多样性、植物种类、同种植物不同的基因型,甚至同一植物不同根的区域而异;而土壤的作用与土壤质地和有机质含量等因素有关;植物和土壤类型在对土壤微生物群落结构影响上的作用存在互作关系。不同的土壤管理措施对土壤微生物群落结构影响较大,长期连作、大量的外援化学物质的应用降低了土壤微生物的多样性;而施用有机肥、免耕可以增加土壤微生物群落结构多样性,有利于维持土壤生态系统的功能。     

Evaluation of soil saturation, soil chemistry, and early spring soil and air temperatures as risk factors in yellow-cedar decline

Yellow‐cedar (Callitropsis nootkatensis (D. Don) Oerst.) is a valuable tree species that is experiencing a widespread decline and mortality in southeast Alaska. This study evaluated the relative importance of several potential risk factors associated with yellow‐cedar decline: soil saturation, soil aluminum (Al) toxicity or calcium (Ca) deficiency, and air and soil temperature. Data were collected from permanent vegetation plots established in two low‐elevation coastal forests exhibiting broad ranges of cedar mortality. Measurements of each risk factor were contrasted among classified forest zones to indicate if there were strong links with decline. Hydrology alone is weakly associated with yellow‐cedar decline, but could have a predisposing role in the decline by creating exposed conditions because of reduced forest productivity. Yellow‐cedar decline is not strongly associated with soil pH and extractable Al and Ca, but there appears to be Ca enrichment of surface soils by feedback from dead yellow‐cedar foliage. Air and soil temperature factors are strongly associated with decline. Based on these results, an hypothesis is presented to explain the mechanism of tree injury where exposure‐driven tree mortality is initiated in gaps created by soil saturation and then expands in gaps created by the tree‐mortality itself. The exposure allows soils to warm in early spring causing premature dehardening in yellow‐cedar trees and subsequent freezing injury during cold events. Yellow‐cedars growing in the protection of shade or snow are not preconditioned by this warming, and thus not as susceptible to cold injury. Yellow‐cedar decline appears to be associated with regional climate changes, but whether the cause of these changes is related to natural or human‐induced climate shifts remains uncertain. Management implications, the possible role of climate, and recommended research are discussed.     

Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO₂ concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open, gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO₂ concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material.Root respiration was strongly affected by diurnal fluctuations in temperature (Q₁₀ = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO₂ concentrations (400 to 25000 ppm CO₂; pH around 6). Soil CO₂ was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO₂ concentration to that of incoming air. Irrigation caused a temporary reduction in CO₂ diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.     

Interpreting,measuring, and modeling soil respiration

This paper reviews the role of soil respiration in determining ecosystem carbon balance, and the conceptual basis for measuring and modeling soil respiration. We developed it to provide background and context for this special issue on soil respiration and to synthesize the presentations and discussions at the workshop. Soil respiration is the largest component of ecosystem respiration. Because autotrophic and heterotrophic activity belowground is controlled by substrate availability, soil respiration is strongly linked to plant metabolism, photosynthesis and litterfall. This link dominates both base rates and short-term fluctuations in soil respiration and suggests many roles for soil respiration as an indicator of ecosystem metabolism. However, the strong links between above and belowground processes complicate using soil respiration to understand changes in ecosystem carbon storage. Root and associated mycorrhizal respiration produce roughly half of soil respiration, with much of the remainder derived from decomposition of recently produced root and leaf litter. Changes in the carbon stored in the soil generally contribute little to soil respiration, but these changes, together with shifts in plant carbon allocation, determine ecosystem carbon storage belowground and its exchange with the atmosphere. Identifying the small signal from changes in large, slow carbon pools in flux dominated by decomposition of recent material and autotrophic and mycorrhizal respiration is a significant challenge. A mechanistic understanding of the belowground carbon cycle and of the response of different components to the environment will aid in identifying this signal. Our workshop identified information needs to help build that understanding: (1) the mechanisms that control the coupling of canopy and belowground processes; (2) the responses of root and heterotrophic respiration to environment; (3) plant carbon allocation patterns, particularly in different forest developmental stages, and in response to treatments (warming, CO₂, nitrogen additions); and (4) coupling measurements of soil respiration with aboveground processes and changes in soil carbon. Multi-factor experiments need to be sufficiently long to allow the systems to adjust to the treatments. New technologies will be necessary to reduce uncertainty in estimates of carbon allocation, soil carbon pool sizes, and different responses of roots and microbes to environmental conditions.     

Ammonium, nitrate, and total nitrogen in the soil water of feedlot and field soil profiles

A level feedlot, located in an area consisting of Wann silt loam changing with depth to sand, appears to contribute no more NO₃^- nitrogen, NH₄⁺ nitrogen, and total nitrogen to the shallow water table beneath it than an adjacent cropped field. Soil water samples collected at 46, 76, and 107 cm beneath the feedlot surface generally showed NO₃^- nitrogen concentrations of less than 1 μg/ml. During the summer months, soil water NO₃^- nitrogen increased at the 15-cm depth, indicating that nitrification took place at the feedlot surface. However, the low soil water NO₃^- nitrogen values below 15 cm indicate that denitrification takes place beneath the surface.     

微生物多样性对土壤氮磷钾转化、酶活性及油菜生长的影响

采用灭菌土壤分别接种不同稀释倍数(1、10~(-2)、10~(-4)和10~(-6))未灭菌土壤悬浊液的方法,研究了土壤微生物多样性降低对油菜生长和养分吸收、土壤养分有效性和酶活性的影响。结果表明:(1)随着接种土壤悬浊液稀释倍数增加,油菜生物量逐渐降低,10-4的油菜生物量显著低于1和10~(-2),10~(-6)仅为1的26%;(2)油菜氮、磷和钾的吸收量与油菜生物量呈现相同的变化规律;(3)土壤铵态氮浓度随接种土壤悬浊液稀释倍数增加而降低;而土壤硝态氮则以10~(-4)为最高,其它处理间没有显著差异;土壤有效磷未发生显著变化;有效钾反而有上升趋势;(4)土壤多酚氧化酶(PhO X)活性随接种土壤悬浊液稀释倍数增加逐渐升高;β-1,4-葡萄糖苷酶(βG)活性以10~(-6)为最高,而其它处理差异不显著;土壤亮氨酸酶氨肽酶(LAP)活性和酸性磷酸酶(AP)活性变化不显著;(5)相关分析表明,油菜生物量与土壤铵态氮浓度的对数显著正相关;与多酚氧化酶、葡萄糖苷酶和亮氨酸氨肽酶活性显著负相关。研究表明,微生物多样性降低主要通过抑制土壤氮素释放影响植物生长。