氮、磷养分添加对高寒草甸土壤酶活性的影响

本试验以典型的青藏高原高寒矮嵩草草甸(Kobresia humilis meadow)为研究平台,以表征土壤碳、氮、磷、硫养分循环的6种土壤酶为研究对象,研究土壤酶以及土壤速效养分在4年氮、磷养分添加的累积效应下的变化规律,分析和评价氮、磷养分添加对土壤养分循环方面的影响。试验结果为:氮、磷养分添加改变了土壤中速效养分的含量;氮添加与010 cm土层中的碱性磷酸酶活性有正效应,磷添加抑制了010 cm土层中的碱性磷酸酶活性;氮、磷养分添加均抑制了010 cm土层中的脲酶活性;氮添加抑制了2个土层中的纤维素酶活性;芳基硫酸酯酶活性和蔗糖酶活性没有表现出显著差异性;1020 cm土层中的几丁质酶活性在氮、磷养分添加处理下均增强,其中磷添加对几丁质酶活性的增幅最显著。结果表明:外源添加的氮在调控磷的矿化方面有促进作用,磷的添加对氮素的释放也有一定的作用;青藏高原高寒草甸受磷限制的程度可能更大。     

基于高通量测序的准噶尔盆地荒漠土壤细菌多样性及群落结构特征

荒漠草地占新疆草地总面积的46.9%,不同荒漠类型的气候差异显著,植被和土壤类型也各不相同。以准噶尔盆地大面积分布的3种代表性荒漠植被类型(南缘伊犁绢蒿荒漠、腹地白梭梭荒漠和北缘盐生假木贼荒漠)为研究对象,应用高通量测序技术,分析比较3种荒漠植被类型的土壤细菌群落组成和多样性特征。结果表明:放线菌门、变形菌门、绿弯菌门、酸杆菌门、芽单胞菌门和拟杆菌门是准噶尔盆地荒漠土壤中6个主要优势类群细菌,其相对丰度累计超过94%。放线菌门在3种荒漠类型中相对丰度最高,均超过50%,但差异不显著(P>0.05);酸杆菌门在伊犁绢蒿荒漠中相对丰度最高,厚壁菌门在白梭梭荒漠丰度最高,拟杆菌门在盐生假木贼荒漠丰度最高,且这3种菌门在3种荒漠类型中差异显著(P<0.05);在3种荒漠类型中,白梭梭荒漠细菌操作分类单元(OTU)数最少,多样性最低。Pearson相关性分析和RDA分析结果均表明,年均降水量和土壤有机碳是影响细菌群落结构组成和多样性最显著的环境因子。     

不同封育年限对宁夏荒漠草原土壤粒径及碳氮储量的影响

封育禁牧的时间效应已经成为科学和政府决策关注的焦点,研究以宁夏盐池县典型荒漠草原围封6、10、15年样地的围栏内外2种主要土壤类型——灰钙土和风沙土为研究对象,基于样线调查法及方差分析法,探究不同封育年限对荒漠草原颗粒组成及土壤碳氮储量的影响。结果表明:1)封育会导致灰钙土及风沙土土壤细颗粒含量增加,灰钙土封育6年样地土壤细颗粒较围栏外增加量最明显,后随封育年限的增加而呈现增幅减少的趋势;风沙土封育15年样地围栏内土壤细颗粒增加量高于封育6年样地。2)灰钙土及风沙土封育6年样地均表现为围栏内土壤碳氮(有机碳、全碳、全氮)含量高于围栏外,而围封10年及15年样地围栏内外土壤碳氮含量没有明显差异。3)灰钙土围封6年样地围栏内土壤碳氮比高于围栏外,而围封10年及15年样地无此规律,围封不会影响风沙土土壤碳氮比。围封可以有效使土壤颗粒细化,但不同土质对封育年限的响应有所差异,人工封育的最佳时间尺度应根据草原退化程度和草原不同土壤条件而定。     

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。     

Salinity an Environmental “Filter” Selecting for Plant Invasiveness? Evidence from Indigenous Lepidium alyssoides on Chihuahuan Desert Shrublands

A better understanding of site-specific factors such as soil salinity that regulate plant invasions is needed. We conducted a 3-mo greenhouse study to evaluate the salinity responses of three local maternal sources of Lepidium alyssoides, which is an indigenous species shown to aggressively colonize disturbed shrubland sites in the southwestern United States, including those affected by high salinity and sodicity. Results indicated that there were little or no population effects on plant evapotranspiration (ET), growth, and tissue Na and Cl concentrations. Significant reductions in seedling growth and ET were largely independent of various isosmotic saline irrigation solutions that included NaCl, Na₂SO₄, and CaCl₂, each at ? 0.1 MPa and ? 0.2 MPa, suggesting that ET and growth were controlled by solution osmotic potential. The combined Na and Cl concentrations in leaves were 9–10% of dry weight with no visible sign of injury. However, increasing leaf mortality and abscission as a proportion of total leaf production was observed in the high-salt treatments (? 0.2 MPa), with a combined Na and Cl concentration reaching 16% with high NaCl. Under saline conditions, considerable foliage salt loads of this species could deposit high-salt litter to potentially alter a landscape to its own favor and to the detriment of other salt-sensitive species. Results of this study add to a limited quantitative database on site-specific salinity factors governing plant invasions by showing the potential for these populations to behave invasively under saline conditions and, thus, potential for soil salinity assessment to predict incipient populations. However, due to its halophytic traits and indigenous status, L. alyssoides may alternatively provide ecosystem services to salinized shrublands of the arid and semiarid southwestern United States.     

柴达木盆地弃耕地盐渍状况的主分量分析

采用主分量分析（PCA）方法对柴达木盆地弃耕地盐渍化状况进行了研究，结果表明，该地属于中重度氯化物盐渍地、耕作层含盐量在0．5％－4．0％之间，盐分表聚强烈，基本无自然淋溶过程。耕作层第一、二主分量显著，累计贡献率高达95．0％左右，反映了该区土壤含盐量及盐离子分布规律，认为全盐量、Cl^-,Mg^2＋是该弃耕地盐渍环境的特征因子。     

Local evidence for tolerance of birdsfoot trefoil (lotus corniculatus) to acid soils

Abstract

The pattern of yield response of birdsfoot trefoil (Lotus corniculatus) cv. San Gabriel to soil amendment with lime and superphosphate on a virgin acid soil indicated that this legume is tolerant of local acid soils and moderately tolerant of low levels of extractable phosphorus.     

Status of selenium and vitamin E on Norwegian organic sheep and dairy cattle farms

Herbage selenium (Se) concentration is generally low in Norway. It is unknown whether feeding practices on Norwegian organic farms fulfil the dietary needs of Se and vitamin E for sheep and dairy cattle. Therefore we analysed Se in soil and herbage, and Se and vitamin E in animal blood in the indoor feeding season at 14 organic dairy and 14 organic sheep farms. The herbage Se concentration was low. Approximately 50 and 35% of all samples in the first and second cut, respectively, had Se concentrations below the detection limit of 0.01 mg/kg dry matter (DM). The median (10th, 90th percentile) Se concentrations were <0.01 (<0.01, 0.03) and 0.02 (<0.01, 0.06) mg/kg DM in the first and second cuts, respectively. Whole blood Se concentrations were 0.10 (0.04, 0.15) μg/g in dairy cattle and 0.14 (0.03, 0.26) μg/g in sheep. Vitamin E concentrations were 4.2 (2.7, 8.4) mg/l in dairy cattle and 1.3 (0.9, 2.4) mg/l in sheep. None of the soil or plant variables explained the variation in herbage Se concentration, although Se in soil and plant tended to be correlated. Herbage Se concentration was inadequate to meet the dietary Se requirements. Vitamin E requirement was only met in dairy herds. We recommend Se and vitamin E supplementation to ruminants on organic farms.     

Grass species composition,yield and quality under and outside tree crowns in a semi‐arid rangeland in south‐western Zimbabwe

Abstract

A two‐year study was conducted in lightly grazed areas of Matopos Research Station, Zimbabwe, to evaluate the impact of widely spaced trees on understorey grass composition, yield and quality. The study trees were Terminalia sericea and Acacia karroo. Ordination techniques using grass density and biomass as indices separated quadrats according to soil type but not grass species according to understorey or open areas or according to tree species. Grass yield under tree crowns was similar to open areas, in contrast with most reports where understorey areas had higher yields. The high understorey grass quality that has been reported from savanna areas exhibiting grass composition differences was not expressed. Selective grazing of palatable perennial grasses growing in association with tree crowns and their eventual replacement by low‐yielding and less‐palatable grasses that normally grow in open areas is proposed as an explanation of the unique tree‐grass interaction scenario of this study. In areas where this replacement has occurred, recovery may require management interventions.     

星星草的生长对盐碱土磷素营养的影响

研究不同生长年限星星草对盐碱土全磷、速效磷、有机磷和无机磷含量及磷酸酶活性的影响.结果表明:土壤全磷、速效磷、有机磷和无机磷含量增加,三龄时达到最高值.星星草对盐碱土速效磷和有机磷含量有明显的影响;土壤磷素各项指标及磷酸酶活性之间都存在着一定的相关关系,其中磷酸酶活性与磷素各指标之间呈极显著相关.