皇甫川流域中小型土壤动物对不同水土治理措施的响应

2007年9月至2008年9月,选择皇甫川流域人工松树林、人工杨树林、人工锦鸡儿灌木林、人工沙打旺草地和撂荒地等不同水土治理措施植被为采样地,以耕作农田为对照,研究了中小型土壤动物对不同水土治理措施的响应。结果表明,共捕获中小型土壤动物14 747只,隶属于5门7纲10类。优势类群为线虫,占群落总个体数的比例为95.53%,常见类群为螨类和弹尾类。不同水土治理措施样地中,中小型土壤动物群落个体数较农田有提高趋势,但无显著差异（P >0.05）;螨类和弹尾类个体数显著提高（P<0.05）;线虫个体数在人工沙打旺草地中显著高于农田（P<0.05）;中小型土壤动物垂直分布的表聚性较农田增强,并以地表凋落物覆盖显著的人工林最为明显。RDA分析表明,中小型土壤动物群落、螨类和弹尾类个体数与凋落物厚度、树（草）高和土壤有机质的变化之间呈显著正相关。以上结果说明,研究地区采取的几种水土治理植被均有利于中小型土壤动物群落的恢复;相比较,地表凋落物层显著的人工松树林、人工杨树林更加有益于螨类和弹尾类的恢复。     

氮沉降与降雨变化下中小型土壤动物对凋落物分解的影响

土壤动物是凋落物分解、养分转化过程的重要调节者,全球变化驱动的氮沉降与降雨变化通过改变其分解环境和土壤动物群落结构,进而影响凋落物分解进程。为了探究中小型土壤动物对凋落物分解的贡献受氮沉降和降雨变化的影响,本研究利用不同网孔(2 mm和0.01 mm)的凋落物分解网袋法,以建群种短花针茅为研究对象进行野外分解试验。试验采用裂区设计,主区为自然降雨(CK)、增雨30%(W)和减雨30%(R)3个水分处理,副区为0(N₀)、30(N₃₀)、50(N₅₀)和100(N₁₀₀) kg·hm^-2·a^-1 4个氮素处理。结果表明: 1)降雨变化显著影响了凋落物的分解速率,增雨处理中凋落物的分解速率加快,且随着氮添加浓度的升高,凋落物重量残留率逐渐降低,100 kg·hm^-2·a^-1时分解速度最快;在减雨处理与对自然降雨处理中凋落物的分解速率则呈先降低后升高的趋势,在50 kg·hm^-2·a^-1时分解速度最快。氮沉降和降雨变化对凋落物分解无显著的交互作用。2)在整个分解过程中,共捕获中小型土壤动物1577只,隶属于1门3纲13目(含亚目)49科,优势类群为蜱螨目、鞘翅目幼虫和弹尾目;增雨施氮提升了中小型土壤动物群落的类群数和个体数。3)凋落物重量残留率与中小型土壤动物类群数、个体数均呈极显著负相关,增雨处理整体提高了中小型土壤动物对凋落物分解的贡献率。综上,荒漠草原上中小型土壤动物对凋落物的分解具有积极作用,且水分和氮素输入的增加提高了中小型土壤动物的类群数及个体数,增加了其对凋落物分解的贡献;在水分不足时,过量的氮素会抑制中小型土壤动物群落的发展,导致中小型土壤动物对凋落物分解的贡献降低。     

内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响

放牧和围封通过影响植物群落结构和土壤微环境来调控草地生态系统的碳循环。该研究在内蒙古温带草原设置轻度放牧后围封、轻度放牧、重度放牧后围封、重度放牧4种样地, 通过测定干旱年(2011年)和湿润年(2012年)地上、地下凋落物产量、质量及其分解速率和土壤养分含量, 分析不同放牧强度对凋落物形成和分解的影响, 以及围栏封育对生态系统恢复的作用。结果表明: 重度放牧地上凋落物产量和分解速率均高于轻度放牧。干旱年轻度放牧样地地下凋落物产量和分解速率高于重度放牧, 湿润年相反。短期围封显著提高了凋落物产量, 轻度放牧样地围封后地上凋落物分解速率和养分循环加快, 而重度放牧样地围封后地上凋落物分解减慢。因此, 与重度放牧相比, 轻度放牧草地的恢复更适合采用围栏封育措施; 而重度放牧草地的恢复可能还需辅以必要的人工措施。降水显著促进地上、地下凋落物形成和分解。地下凋落物的生产和分解受降水年际波动影响较大, 重度放牧草地对降水变化的敏感度比轻度放牧草地高。地上凋落物分解速率与凋落物N含量显著正相关, 与土壤全N显著负相关, 与地上凋落物C:N和木质素:N相关性不大; 地下凋落物分解速率与凋落物C、C:N和纤维素含量显著负相关。该研究结果将为不同放牧强度的草地生态系统恢复和碳循环研究提供理论依据。     

半干旱区封禁草地凋落物的积累与分解

针对我国西部典型草原地带,退化草地封禁后凋落物的积累、分解与水分变化过程,进行了为期20a（1982～2002年）的定位试验研究.结果表明：本氏针茅、百里香、铁杆蒿和大针茅草地群落的凋落物积累与厚度的变化趋势,拟合曲线符合指数方程,无论在植物年生长的初期还是末期,其相关性极为显著.随着气温的升高和降雨量的增加,凋落物的分解速率加快,本氏针茅和大针茅群落凋落物的分解率达到峰值需150d,百里香群落需180d,铁杆蒿群落需210d;凋落物在积累与分解过程中,具有吸水和保水的重要功能,可截留大量天然降水,促进土壤水分的缓慢入渗,通常在植物生长的初期和末期,凋落物在自然状态下饱和含水量,本氏针茅群落为112.30%～124.02%;百里香群落为116.61%～134.09%;铁杆蒿群落为124.76%～144.32%.但草地适宜封禁年限为11～15a,有利于草地自然更新和凋落物的积累.     

我国重要森林群落凋落物层土壤动物群落生态特征

2001年9月～2002年9月,采用凋落袋分解法对我国不同气候带的8种重要森林群落,即黑龙江帽儿山的红松林(Pinus koraiensis)与针阔混交林(落叶松(Larix gmelinii)、白桦(Betula Platyphylla))、北京九龙山辽东栎林(Quercus liaotungensis)与针阔混交林(辽东栎、油松(Pinus tabulaeformis)),江西大岗山杉木林(Cunninghamia lanceolata)与针阔混交林(杉木、鹅掌楸(Liriodendron chinense))林以及广东鼎湖山常绿阔叶林(荷木(Schima superba)-厚壳桂(Cryptocarya chinensis))与针阔混交林(马尾松(Pinus massoniana)、荷木)凋落物层土壤动物群落进行研究.全年74次共采集森林凋落层土壤动物个体29123只,其中大型土壤动物4492只、中小型土壤动物24631只,隶属4门14纲30目,蜱螨类、弹尾类为凋落层的优势群落.非参数Kruskal-Wallis 方差分析表明,8种森林群落凋落层土壤动物群落组成差异性显著 (x2(7)=18.867, P<0.01),且帽儿山、九龙山与鼎湖山之间以及大岗山与鼎湖山阔叶林之间凋落层土壤动物群落组成存在显著性差异(P＜0.001).研究时段内,大型土壤动物月均数量和类群数量随着纬度升高而呈现明显的递减趋势;中小型土壤动物月均数量随纬度升高而基本呈升高的趋势.凋落层土壤动物月均数量、多样性、均匀性均差别显著(X2(66)=37.95、X2(66) = 26.38、X2(66) = 328.97, P＜0.001).多样性分析显示,鼎湖山凋落层土壤动物分布最丰富、分布最均匀;大岗山与鼎湖山典型森林群落凋落层土壤动物群落相似性最高,帽儿山与鼎湖山典型森林群落凋落层土壤动物群落相似性最低.灰色综合关联度分析表明,年均温度对土壤动物影响最大,有机质(表土)次之,土壤pH次于前两者,年均相对湿度影响最小,环境因子对主要土壤动物群落产生不同的影响.     

天童常绿阔叶林五个演替阶段凋落物中的土壤动物群落

为探讨森林凋落物中土壤动物群落的结构特征以及土壤动物群落随植被演替而发生的变化 ,于 2 0 0 3年冬季 ,对浙江天童常绿阔叶林 5个演替阶段凋落物中的土壤动物群落 ,按代表不同分解阶段的新鲜凋落物层、腐叶层和腐殖土层进行了调查研究。共获得土壤动物 13381只 ,分别隶属于 2门 8纲 2 0目。优势类群为蜱螨目 (Arcarina)和弹尾目 (Collem bola) ,二者共占总数的 94 .2 4 % ,A/ C为 7.6 6 ;常见类群为双翅目 (Diptera)。研究结果表明 :(1)凋落物中的土壤动物群落存在明显的有别于真土层的垂直分布 ,类群数和个体数总体表现为向下递增的趋势。共有 19类、5 9.0 3%的土壤动物分布在底部腐殖土层 ,仅 8类、5 .35 %的土壤动物分布在新鲜凋落物层 ,其余共 8类分布在中间腐叶层。而且 ,不同类群在各演替阶段的分布表现出一定的差异 ;(2 )凋落物中土壤动物群落随植物群落的演替而发生明显的变化 :个体总数和类群总数在演替顶极阶段最高 ,其次为中期阶段 ,演替初期最低。但是 ,在目这一分类等级上 ,各演替阶段凋落物中土壤动物群落的主要类群基本一致 ,均为蜱螨目、弹尾目、双翅目和鳞翅目 (L epidoptera) ;(3)相似性分析表明 ,演替中期凋落物中土壤动物群落与顶极阶段最为相似 ;但它们的Shannon- Wiener多样性     

西沙永兴岛抗风桐与海岸桐群落凋落叶分解及中型土壤动物的贡献

我国南海诸岛主要是珊瑚岛。植物凋落物分解是生态系统元素循环的关键环节,但目前关于南海珊瑚岛生态系统凋落物分解的研究还是空白。以我国西沙群岛的优势树种抗风桐（Pisonia grandis）和海岸桐（Guettarda speciosa）为研究对象,采用凋落物袋法,分别于分解期间的第3、6、9、13和15个月取样,探究中型土壤动物对两种植物群落中凋落物分解过程中质量损失和养分释放的影响。结果表明：与没有中型土壤动物存在的情况（0.1 mm凋落物袋）相比,分解开始后的6个月内,中型土壤动物存在（2 mm凋落物袋）使抗风桐和海岸桐凋落叶分解速率分别提高了12.3%和4.8%（P<0.05）;分解6-15个月期间,中型土壤动物存在使抗风桐和海岸桐凋落叶分解速率分别提高了33.0%和12.3%（P<0.05）。中型土壤动物排除显著影响了不同分解阶段凋落叶总碳（Total carbon,TC）、总氮（Total nitrogen,TN）、纤维素、木质素和半纤维素的残留率变化。中型土壤动物群落组成受土壤温度显著影响（P<0.05）,它们对凋落叶分解的贡献可能主要受优势类群如真螨目和寄螨目的影响。相较海岸桐,抗风桐凋落叶的分解周期更短,中型土壤动物对其的贡献更大;选用抗风桐作为南海珊瑚岛退化植被恢复或新建的先锋种对促进生态系统元素循环更有利。     

桉-桤不同混合比例凋落物分解过程中 土壤动物群落动态

采用凋落物分解袋法研究了10:0(TⅠ)、7:3(TⅡ)5:5(TⅢ)、3:7(TⅣ)和0:10(TV)巨桉(Eucalyptus grandis)和台湾桤木(Alnus formosana)混合凋落物分解过程中的土壤动物群落特征.从5种类型、3种规格的810只凋落袋中共收集土壤动物75651只,隶属2门10纲20目,其中弹尾目(Collembola)和蜱螨目(Acarina)为优势类群.土壤动物个体数最高是7-8月,大型土壤动物个体数最高是7月,中小型土壤动物个体数最高是7-8月.大型、中小型土壤动物类群数各月间均波动较小.与30目和6目相比,260目网袋中弹尾目和蜱螨目等中小型土壤动物数量更高.相对台湾桤木(TV)而言,巨桉(TⅠ)凋落物中弹尾目数量更多.啮虫目(Psocoptera)在台湾桤木(TV)凋落物中的数量远远高于其它凋落物,后孔寡毛目(Opisthopora)在混合凋落物中数量较高.不同比例的凋落物混合可改变凋落物中土壤动物的数量和组成.桤木、混合凋落物中大型土壤动物的个体数高于巨桉凋落物,而且上述凋落物的分解速率亦明显快于巨桉凋落物,这意味着大型土壤动物的活动可加速凋落物的分解.因此,在巨桉人工纯林中混栽台湾桤木,可显著提高大型土壤动物的数量,促进凋落物的分解.     

内蒙古武川县农田退耕还草对中小型土壤动物群落的影响

2006年5-9月,以50 mL土壤环刀采集土样,以干、湿漏斗法分离湿生和于生中小型土壤动物,分析了内蒙古武川县农田退耕后不同还草管理措施对中小型土壤动物群落的影响,为退耕还草措施的评价提供依据.试验共捕获中小型土壤动物19845只,隶属于6门8纲8类.优势类群为线虫和线蚓,占总捕获量的比例分别为81.37％和15.68％.与农田比较,不同退耕还草管理方式均导致线虫个体数显著提高(P＜0.05),并以退耕后种植菊芋+蒿属植物提高最为突出,线蚓、螨类和弹尾类个体数提高不显著;退耕后,中小型土壤动物群落垂直分布形式无显著变化,但种植紫花苜蓿导致螨类垂直分布的表聚性升高.结果表明:本研究地区所采取的几种农田退耕还草管理措施均对线虫数量的恢复有益;在退耕还草地的管理中,应该注意地表凋落物的保存和积累,以促进螨类和弹尾类数量的恢复.     

呼伦贝尔草甸草原优势种贝加尔针茅根系组织和地上部分凋落物的分解

采用凋落物分解袋法, 研究了呼伦贝尔草甸草原主要优势种贝加尔针茅(Stipa baicalensis)根系组织和地上部分凋落物分解的季节动态以及凋落物的放置位置(置于地表和15 cm土壤表层)对分解的影响。结果表明, 置于表层土壤中的根系组织和地上部分凋落物的分解速率比置于地表的快, 但是根系组织在两个放置位置分解的差异不显著。无论置于地表还是置于表层土壤中, 地上部分凋落物的分解均快于根系组织的凋落物分解。在分解过程中, 凋落物碳(C)损失的季节变化模式与重量损失相似; 而氮(N)变化模式明显不同, 地上部分凋落物表现为释放—累积—释放, 根系则表现为释放—累积, 并且地上部分或者根系在不同放置位置中N含量变化的差异较小。地上部分和根系组织凋落物的初始化学组成的差异可能是导致其分解过程差异显著的主要原因, 其次的原因才是土壤含水量。因此, 该地区未来环境温度、湿度因子的变化将会显著影响贝加尔针茅地上部分凋落物的分解过程, 而对根系组织凋落物的分解作用较小。     

Ecosystem changes associated with grazing in subhumid South American grasslands

Question: What are the changes in vegetation structure, soil attributes and mesofauna associated with grazing in mesic grasslands? Location: Southern Campos of the Río de la Plata grasslands, in south‐central Uruguay. Methods: We surveyed seven continuously grazed and ungrazed paired plots. Plant and litter cover were recorded on three 5‐m interception lines placed parallel to the fence in each plot. We extracted soil fauna from a 10 cm deep composite sample and analysed the oribatids. Soil attributes included bulk density, water content, organic carbon (in particulate and mineral associated organic matter) and nitrogen content and root biomass at different depths. Changes in floristic, Plant Functional Types and mesofauna composition were analysed by Non‐metric Multidimensional Scaling. Results: Species number was lower in ungrazed than in grazed plots. Of 105 species in grazed plots only three were exotics. Shrub and litter cover were significantly higher inside the exclosures, while the cover of Cyperaceae‐Juncaceae was lower. Grazing treatments differed significantly in plant and oribatid species composition. Grazing exclusion significantly reduced soil bulk density and increased soil water content. Carbon content in particulate organic matter was lower in the upper soil of ungrazed sites, but deeper in the profile, grazing exclosures had 8% more carbon in the mineral associated organic matter. Conclusions Our results generally agree with previous studies but deviate from the results of previous analyses in (1) the increase of shrub cover in ungrazed sites; (2) the redistribution of the soil organic carbon in the profile and (3) the low invasibility of the prairies regardless of grazing regime.     

Grazing history effects on above- and below-ground litter decomposition and nutrient cycling in two co-occurring grasses

Large herbivores may alter carbon and nutrient cycling in soil by changing above- and below-ground litter decomposition dynamics. Grazing effects may reflect changes in plant allocation patterns, and thus litter quality, or the site conditions for decomposition, but the relative roles of these broad mechanisms have rarely been tested. We examined plant and soil mediated effects of grazing history on litter mass loss and nutrient release in two grazing-tolerant grasses, Lolium multiflorum and Paspalum dilatatum, in a humid pampa grassland, Argentina. Shoot and root litters produced in a common garden by conspecific plants collected from grazed and ungrazed sites were incubated under both grazing conditions. We found that grazing history effects on litter decomposition were stronger for shoot than for root material. Root mass loss was neither affected by litter origin nor incubation site, although roots from the grazed origin immobilised more nutrients. Plants from the grazed site produced shoots with higher cell soluble contents and lower lignin:N ratios. Grazing effects mediated by shoot litter origin depended on the species, and were less apparent than incubation site effects. Lolium shoots from the grazed site decomposed and released nutrients faster, whereas Paspalum shoots from the grazed site retained more nutrient than their respective counterparts from the ungrazed site. Such divergent, species-specific dynamics did not translate into consistent differences in soil mineral N beneath decomposing litters. Indeed, shoot mass loss and nutrient release were generally faster in the grazed grassland, where soil N availability was higher. Our results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition. They also indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.     

Are grasslands important habitats for soil microarthropod conservation?

Biodiversity has been a focal aim of environmental protection since the Rio conference, but only with the beginning of the new millennium did soil biodiversity become an important aspect of international policy. Edaphic fauna play a key role in many soil functions, such as organic matter decomposition, humus formation and nutrient element cycling; moreover, affect the porosity, aeration, infiltration and distribution of organic matter in soil horizons, modifying soil structure and improving its fertility. The ecosystem services provided by soil animals are becoming progressively lost due to agricultural practice intensification, which causes a reduction in both abundance and taxonomic diversity of soil communities. In the present study, a permanent grassland habitat was studied in order to evaluate its potential as a soil biodiversity reservoir in agroecosystems. Grassland samples were compared with samples from a semi-natural woodland area and an arable land site. Microarthropod abundances, Acari/Collembola ratio (A/C), Shannon diversity index (H′) and evenness index (E) were calculated. QBS-ar index was used in order to evaluate soil biological quality. Microarthropod communities of the three land use typologies differed in both the observed groups and their abundance. Steady soil taxa characterized both woodland and grassland soils, whereas their abundances were significantly higher in woodland soil. Taxon diversity and soil biological quality in the grasslands did not differ from the woodland samples. The microarthropod community in the arable land showed a reduction both in taxa numbers and soil biological quality compared with the other sites. Soil biological quality and edaphic community composition highlighted the importance of grassland habitats in the protection of soil biodiversity.     

植物凋落物影响土壤有机质分解的研究进展

植物凋落物是土壤动物和土壤微生物的主要生命物质和能量来源,其类型、组成以及物理化学等性质直接决定了土壤有机质的品质。对植物凋落物的类型、品质、物理性质、层效应和激发效应以及根际碳淀积与土壤有机质分解的关系进行了总结,可为研究植物凋落物对土壤有机质的影响提供理论参考,指出要在全球变暖背景下进一步加强凋落物分解过程中土壤微生物和酶活性变化的研究。     

The effect of reindeer grazing on decomposition, mineralization and soil biota in a dry oligotrophic Scots pine forest

Reindeer grazing in the Fennoscandian area has a considerable influence on the ground vegetation, and this is likely in turn to have important consequences for the soil biota and decomposition processes. The effects of reindeer grazing on soil biota, decomposition and mineralization processes, and ecosystem properties in a lichen‐dominated forest in Finnish Lapland were studied inside and outside a large long term fenced reindeer exclosure area. Decomposition rates of Vaccinium myrtillus leaves in litter bags were retarded in the grazed area relative to the ungrazed area, as well as in subplots from which lichens had been artificially removed to simulate grazing. The effect of reindeer grazing on soil respiration and microbial C was positive in the lichen and litter layers of the soil profile, but retarded in the humus layer. There was no effect of grazing on gross N mineralization and microbial biomass N in the humus and upper mineral soil layer, but net N mineralization was increased by grazing. In these layers soil respiration was reduced by grazing, indicating that reindeer effects reduce the ratio of C to N mineralized by soil microorganisms. Grazing stimulated populations of all trophic groupings of nematodes in the lichen layer and microbe feeding nematodes in the litter layer, indicating that grazing by reindeer has multitrophic effects on the decomposer food‐web. Grazing decreased lichen and dwarf shrub biomasses and increased the mass of litter present in the litter layer on an areal basis, but did not significantly alter total C storage per unit area in the humus and mineral soil layers. The N concentration of lichens was increased by grazing, but the N concentrations of both living and dead Pinus sylvestris needles and Empetrum hermaphroditum leaves were not affected.
There was some evidence for each of three mechanisms which could account for the grazing effects that we observed in our study. Firstly, reindeer may have changed the composition and quality of litter input by affecting plant species composition and through addition of N from urine and faeces, resulting in a lack of available C relative to N for decomposer organisms. Secondly, the organic matter in the soil may be older in the grazed area, because of reduction of recent production of lichen litter relative to the ungrazed area. The organic matter in the grazed area may have been in a different phase of decomposition from that in the exclosure. Thirdly, the soil microclimate is likely to be affected by reindeer grazing through physical removal of lichen cover on the ground, and this can have a significant influence on soil microbial processes. This is supported by the strong observed effects of experimental removal of lichens on decomposer processes. The impact of reindeer grazing on soil processes may be a result of complex interactions between different mechanisms, and this could help to explain why the below‐ground effects of reindeer grazing have different consequences to those which have been observed in recent investigations on other grazing systems.     

Grazing‐induced changes in plant–soil feedback alter plant biomass allocation

Large vertebrate herbivores, as well as plant–soil feedback interactions are important drivers of plant performance, plant community composition and vegetation dynamics in terrestrial ecosystems. However, it is poorly understood whether and how large vertebrate herbivores and plant–soil feedback effects interact. Here, we study the response of grassland plant species to grazing‐induced legacy effects in the soil and we explore whether these plant responses can help us to understand long‐term vegetation dynamics in the field. In a greenhouse experiment we tested the response of four grassland plant species, Agrostis capillaris, Festuca rubra, Holcus lanatus and Rumex acetosa, to field‐conditioned soils from grazed and ungrazed grassland. We relate these responses to long‐term vegetation data from a grassland exclosure experiment in the field. In the greenhouse experiment, we found that total biomass production and biomass allocation to roots was higher in soils from grazed than from ungrazed plots. There were only few relationships between plant production in the greenhouse and the abundance of conspecifics in the field. Spatiotemporal patterns in plant community composition were more stable in grazed than ungrazed grassland plots, but were not related to plant–soil feedbacks effects and biomass allocation patterns. We conclude that grazing‐induced soil legacy effects mainly influenced plant biomass allocation patterns, but could not explain altered vegetation dynamics in grazed grasslands. Consequently, the direct effects of grazing on plant community composition (e.g. through modifying light competition or differences in grazing tolerance) appear to overrule indirect effects through changes in plant–soil feedback.     

Distribution of soil organic matter between fractions and aggregate size classes in grazed semiarid steppe soil profiles

Grazed steppe ecosystems are discussed as one of the big global carbon sinks that may have the potential to sequester large amounts of atmospheric CO₂ and mitigate the effects of global change if grazing is abandoned or management improved. But until today, little is known about sequestration potentials and stabilisation mechanisms in complete soil profiles of semiarid grasslands and how these systems react to grazing cessation. We applied a combined aggregate size, density and particle size fractionation procedure to sandy steppe soils under different grazing intensities (continuously grazed = Cg, winter grazing = Wg, ungrazed since 1999 = Ug99, ungrazed since 1979 = Ug79). Higher inputs of organic matter in ungrazed treatments led to higher amounts of OC in coarse aggregate size classes (ASC) and especially in particulate organic matter (POM) fractions across all depth. These processes started in the topsoil and took more than 5 years to reach deeper soil horizons (>10 cm). After 25 years of grazing cessation, subsoils showed clearly higher POM amounts. We found no grazing-induced changes of soil organic matter (SOM) quantity in fine ASC and particle size fractions. Current C-loading of fine particle size fractions was similar between differently grazed plots and decreased with depth, pointing towards free sequestration capacities in deeper horizons. Despite these free capacities, we found no increase in current C-loading on fine mineral soil fractions after 25 years of grazing exclusion. Silt and clay fractions appeared to be saturated. We suppose empirical estimations to overestimate sequestration potentials of particle size fractions or climatic conditions to delay the decomposition and incorporation of OM into these particle size fractions. POM quality was analysed using solid-state ¹³C NMR spectroscopy to clarify if grazing cessation changed chemical composition of POM in different ASC and soil depths via changing litter quality or changing decomposition dynamics. We found comparable POM compositions between different grazing intensities. POM is decomposed hierarchically from coarse to fine particles in all soil depths and grazing cessation has not affected the OM decomposition processes. The surplus of OM due to grazing cessation was predominately sequestered in readily decomposable POM fractions across all affected horizons. We question the long-term stabilisation of OM in these steppe soils during the first 25 years after grazing cessation and request more studies in the field of long-term OM stabilisation processes and assessment of carbon sequestration capacities to consider deeper soil horizons.     

Effects of Grazing on Restoration of Southern Mixed Prairie Soils

A comparative analysis of soils and vegetation from cultivated areas reseeded to native grasses and native prairies that have not been cultivated was conducted to evaluate restoration of southern mixed prairie of the Great Plains over the past 30 to 50 years. Restored sites were within large tracts of native prairie and part of long‐term grazing intensity treatments (heavy, moderate, and ungrazed), allowing evaluation of the effects of grazing intensity on prairie restoration. Our objective was to evaluate restored and native sites subjected to heavy and moderate grazing regimes to determine if soil nutrients from reseeded cultivated land recovered after 30 years of management similar to the surrounding prairie and to identify the interactive influence of different levels of grazing and history of cultivation on plant functional group composition and soils in mixed prairies. For this mixed prairie, soil nitrogen and soil carbon on previously cultivated sites was 30 to 40% lower than in uncultivated native prairies, indicating that soils from restored sites have not recovered over the past 30 to 50 years. In addition, it appears that grazing alters the extent of recovery of these grassland soils as indicated by the significant interaction between grazing intensity and cultivation history for soil nitrogen and soil carbon. Management of livestock grazing is likely a critical factor in determining the potential restoration of mixed prairies. Heavy grazing on restored prairies reduces the rate of soil nutrient and organic matter accumulation. These effects are largely due to changes in composition (reduced tallgrasses), reduced litter accumulation, and high cover of bare ground in heavily grazed restored prairies. However, it is evident from this study that regardless of grazing intensity, restoration of native prairie soils requires many decades and possibly external inputs to adequately restore organic matter, soil carbon, and soil nitrogen.     

Impact of cervid browsing and grazing on the terrestrial gastropod fauna in the boreal forests of Fennoscandia

Selective foraging by cervids can affect vegetation, and that in turn can have far-reaching effects on various components of the boreal forest ecosystem. Since terrestrial gastropods are sensitive to habitat alterations, they can be expected to respond to changes caused by grazing. This study is based on gastropod specimens from two data sets that were collected with pitfall traps in order to study the effects of moose and reindeer on ground-layer invertebrates. Invertebrates were trapped from 23 pairs of plots, where one plot was open to all animals while the other one was fenced to exclude large mammals. Half of the sites were in Finnish Lapland, where reindeer grazing was the main cause of differences between the plots; the rest were located in central Sweden and southern Finland, where moose was the most important cervid grazer. The composition of the gastropod fauna differed between grazed and ungrazed plots in both areas, and the abundance of gastropods in general and that of many species was higher in ungrazed plots (the number of gastropods caught was 17% lower in grazed than in ungrazed plots in moose sites, and 24% smaller in reindeer sites). Species richness differed significantly between grazed and ungrazed plots in the combined data of both site types, and was 15% higher in ungrazed plots. In moose sites the relative diversity (H′/H′_max) of gastropods was 17% higher in grazed plots. In reindeer sites, the means of richness and diversity (H′) were considerably higher in ungrazed plots (35% and 40% respectively) but the differences were only marginally significant. By indirectly modifying the microclimate within the forest, cervids fulfil the criteria for a ‘physical ecosystem engineer’. Since the population density and distribution of terrestrial gastropods depend largely on the physical conditions of the microhabitat, the engineering effects of cervids are the most likely cause of the changes observed in the density and composition of the gastropod fauna in the boreal forest.     

Impact of soil mesofauna on the decomposition of two main species litters in a Pinus koraiensis mixed broad-leaved forest of the Changbai Mountains

In most terrestrial ecosystems, the majority of aboveground net primary productivity enters the decomposition system as plant litter. The decomposition of plant litter plays a critical role in regulating build up of the forest soil organic matter, releasing of nutrients for plant growth, and influencing the carbon cycling. Soil fauna are considered to be an important factor in the acceleration litter decomposition and nutrient transformations. Mechanisms of soil faunal contribution to litter decomposition include digestion of substrates, increase of surface area through fragmentation and acceleration of microbial inoculation into litter. The Pinus koraiensis mixed broad-leaved forest is one of the typical forest vegetation types in Changbai Mountain. Previously, major studies carried here were focused on climate, soil and vegetation; however, on litter decomposition and the role of soil fauna in this forest ecosystem were limited. In this paper, we conducted a litter decomposition experiment using litterbag method to explore the contribution of soil fauna on litter decomposition and provide a scientific basis for maintaining a balanced in P. koraiensis mixed broad-leaved forest in Changbai Mountains. During 2009 and 2010, we used litterbags with different mesh sizes to examine the decomposition of two dominant tree species (P. koraiensis, Fraxinus mandshurica) in studied site. The results showed that the process of litter decomposition can be separated into two apparent stages. The initial decomposition process at former six months was slow, while accelerated the final six months. The former six months (from October 2009 to April 2010) was winter and spring. There was low temperature and almost no activity of soil fauna and microbes. The final six months (from June to October 2010), decomposition rates increased. In summer and autumn, both temperature and moisture increases, abundance of soil fauna was much than before and was most active. The remaining mass of P. koraiensis was higher than that of F. mandshurica in two mesh size litterbags after 1 year decomposition, meanwhile litter in 2 mm mesh size litterbag had higher decomposition rate than that of 0.01 mm for two species litter. The Collembola, Acari, Enchytraeidae Lithobiomorpha and Diptera larvae were mainly fauna groups in the litterbags. The composition of soil fauna community was difference between P. koraiensis and F. mandshurica during litter decomposition. 24 different soil fauna groups and 1431 individual were obtained in P. koraiensis litterbags; Isotomidae, Tomoceridae and Oribatida were dominant groups; while 31 different soil fauna groups and 1255 individual were obtained in F. mandshurica litterbags; Isotomidae, Hypogastruridae Oribatida and Mesostigmata were dominant groups. The rate of litter decomposition was positively correlated with the individual and group density of soil fauna. Contribution rate to litter decomposition was 1.70% for P. koraiensis and 4.83% for F. mandshurica. Repeated measures ANOVA showed that litter species, time and soil fauna had a significant impact on the rate of litter decomposition (P < 0.05). Our results suggested that soil fauna could accelerate litter decomposition and, consequently, nutrient cycling in P. koraiensis mixed broad-leaved forest, Changbai Mountains.