草地生态系统中土壤氮素矿化影响因素的研究进展

氮素是各种植物生长和发育所需的大量营养元素之一,也是牧草从土壤吸收最多的矿质元素．土壤中的氮大部分以有机态形式存在,而植物可以直接吸收利用的是无机态氮．这些有机态氮在土壤动物和微生物的作用下。由难以被植物直接吸收利用的有机态转化为可被植物直接吸收利用的无机态的过程就是土壤氮的矿化．氮素矿化受多种因子的影响,这些因子可以归结为生物因子和非生物因子．生物因子包括：土壤动物、土壤微生物和植物种类．土壤动物可以促进土壤有机质的矿化;土壤微生物种类、结构及功能与氮的分解、矿化有密切的关系;不同的植物种类对土壤氮素的矿化作用是不相同的,一般来说。有豆科植物生长的土壤比其它种类土氮素矿化的作用大．非生物因素一般可以分为环境因子和人类活动干扰．环境因子中土壤温度和含水量对土壤氮素矿化的影响是国内外众多科学家研究的方向．尽管如此,在此方面的研究还没有取得一致意见,仍然需要进行这方面的研究,而在其他诸如：不同的土壤质地与土壤类型方面,研究报道的结论也很不一致,草地生态系统中人类活动对土壤氮素矿化的影响主要包括,不同强度的放牧,割草以及施肥、火烧强度等．非生物因子对氮素矿化的影响非常直接和明显,尤其是人类活动．本文综述了近年来影响草地生态系统土壤氮素矿化有关因素的一些进展．     

植物吸收利用有机氮营养研究进展

植物矿质营养学问世以后,人们一直认为无机氮是植物吸收氮素的主要形态.随着研究手段的改进和研究内容的不断深入,现已证实许多没有菌根的维管植物都可以直接吸收可溶性有机氮,特别是小分子的氨基酸.由此引起了人们对植物有机营养、植物营养方式多样化问题的重视.研究表明：氨基酸可以通过多种方式释放到土壤溶液中,土壤中的氨基酸主要来源于微生物、动植物及其代谢产物等.土壤氨基酸含量受土壤温湿度、所施的有机肥料、生长的植物种类及其生长发育时期的影响.植物对氨基酸的吸收是一个主动吸收过程,受载体调节,并与能量状况有关,同时受介质中pH和温度的影响.但是有关植物吸收氨基酸的机理及其生态过程还需进行深入的研究.     

川西亚高山针叶林主要树种对土壤中不同形态氮素的吸收差异

在陆地生态系统中,植物对土壤有机氮(主要指氨基酸)的获取是一个普遍的生态学现象,然而植物对土壤有机氮的吸收速率及土壤有机氮在植物养分供应中所占比例仍不清楚。为探究土壤无机氮和有机氮对西南高寒森林植物氮源的贡献效应,以川西亚高山针叶林两个主要树种云杉(Picea asperata)和红桦(Betula albo-sinensis)的幼苗为研究对象,采用稳定同位素标记法对K~(15)NO_3、~(15)NH_4Cl和(U-~(13)C_2/~(15)N)甘氨酸3种氮素进行示踪,分析了两个树种对无机氮(NH_4~+-N和NO_3~--N)和有机氮(甘氨酸)的吸收速率及其差异。结果显示:(1)云杉和红桦幼苗在施加同位素标记物2 h后,两种幼苗细根的13C和~(15)N均出现明显的富集现象,表明两种树种幼苗均能吸收甘氨酸。(2)与甘氨酸和NH_4~+-N相比,云杉和红桦幼苗对NO_3~--N有显著的偏好吸收,其吸收速率为NH_4~+-N和甘氨酸吸收速率的5–10倍。(3)两个树种的幼苗对甘氨酸也有较高的吸收速率,其吸收速率高于对NH_4~+-N的吸收速率,表明土壤有机氮(如氨基酸)也是亚高山针叶林植物养分获取的重要氮源。     

高等植物对氨基酸态氮的吸收与利用研究进展

植物能够在不经矿化的情况下直接吸收利用环境中的分子态氨基酸.氨基酸作为植物和微生物的优良碳源和氮源,二者对其吸收存在着激烈竞争,氨基酸态氮来源广、半衰期短的特点使其具有巨大的流通量.运用氮同位素示踪方法研究氨基酸对植物的氮营养贡献一直是国内外学者研究的热点,对揭示土壤肥力本质具有重要意义.本文对不同生态系统中氨基酸形态特征、代谢机制及营养贡献进行了简要综述,分析了氨基酸态氮在植物-土壤-微生物系统中的循环机制及生物有效性等方面研究现状和发展趋势,并提出了土壤氨基酸生物有效性环境调控、氨基酸碳-氮代谢及提高农田生态系统有机氮管理等待解决的科学问题.     

缺磷条件下的小麦根系酸性磷酸酶活性研究

1　引　　言植物根可向根际分泌许多有机化合物 ,其中有许多物质都能促进植物对矿质养分的吸收 .作为必需大量营养元素的Ｐ ,在土壤中以无机磷酸盐阴离子的形式被吸收 ,而有机磷酸酯必须被水解成无机Ｐ后才能进入植物根 ,在这一过程中有一非常重要的步骤 ,就是由微生物、菌根外真菌和植物根分泌酸性磷酸酶 .土壤中的有机Ｐ一般占全Ｐ的 30 %～ 5 0 % ,有的可达95 % .因此 ,如何发挥植物自身利用土壤有机Ｐ的潜力已成为目前植物营养学研究的热点之一 .Ｇｏｌｄｓｔｅｉｎ等[3 ] 研究Ｐ胁迫条件下悬浮培养细胞时发现 ,抑制植物生长和诱导酸性…     

鱼池生态系统中影响浮游细菌生长制约因素的研究

从溶解有机质及营养盐对细菌生长、细菌利用和矿化营养物质的影响,细菌捕食者和水温对细菌生长的影响等方面就鱼池生态系内影响细菌生长的主要制约因素进行研究。结果表明,向池水中添加P明显促进了细菌的生长和对C、N素的吸收,而添加C和N对细菌数量增长和营养物质吸收的作用不明显,但添加N明显增强了细菌对有机N的矿化能力,表明原池水中C、N供应充足,而无机磷限制了细菌的生长和对营养物质的利用;捕食组的细菌生长速率最低,比对照组减少6.26%-15.4%,且增长结束后细菌数量下降较其它组显著;池塘水体的原有细菌丰度,试验培养中细菌增长数量和生长速率在温度较高的季节也较高,温度升高促进了细菌生长,减弱捕食对细菌生长的负作用。     

植物寡肽运输与硝酸根运输基因家族的研究进展

氮素是植物生长发育的重要营养元素,也是限制植物生物量尤其是经济产量的关键营养元素之一.植物不仅能从外界获取无机氮素(硝酸根、铵根和尿素等),还能以氨基酸、寡肽等形式获取有机氮素.植物已进化出复杂的运输系统来吸收与运输这些含氮化合物.硝酸根运输基因家族分为低亲和力硝酸根运输基因(low-affmity nitrate t...     

植物对有机氮源的利用及其在自然生态系统中的意义

近来大量实验研究表明,许多植物能够在不经矿化的情况下直接吸收、利用环境介质中的生物有机氮,尤其氨基酸类。而且,有些植物利用氨基酸的效率可以与矿质氮源(NH4 、NO3)相当或更高。自然界植物赖以生存的土壤生境中同时存在多种有机氮和矿质氮养分,这是导致植物(至少部分植物)进化产生利用各种不同氮源能力的环境驱动力。土壤中的游离氨基酸尽管含量不高,但其周转快、通量大,理论上可远大于植物的氮需求。尽管植物在与土壤微生物的有机氮源竞争中处于根本性劣势,但土壤中氨基酸的巨大潜在通量和植物相对于微生物的生命周期仍可使植物在长期竞争中获取数量可观的氮。基于植物根对氨基酸的吸收能力、土壤中游离氨基酸库的大小和通量、植物与土壤微生物对氨基酸氮源的竞争以及有关的原位实验结果,近来许多研究者都认为植物有机氮营养在多种生态系统中是重要或潜在重要的。尤其是在一些极地、高山、亚高山、北方针叶林或泰加林生态系统中,由于低温等因素限制有机氮矿化,土壤氨基酸浓度常超过矿质氮(NH4 、NO3-)浓度,氨基酸可能代表着植物的一个主要氮源。认识到现实生态系统中植物对有机氮源利用的重要性意味着传统的矿质营养观念的更新,这将在很大程度上改变人们对某些重要生态过程的理解,并导致对若干生态学中心问题的再认识。研究以森林生态系统为例,阐述了我国开展该领域研究的科学意义和基本框架。     

温度对土壤中外源氨基酸、多肽的矿化及其吸收动力学的影响

研究了不同温度（1 ℃、15 ℃和25 ℃）对3种园艺生产系统（有机生产系统OS、转换期生产系统TS、常规生产系统CS）土壤中外源添加氨基酸、多肽的矿化及其吸收动力学特性的影响.结果表明：随着温度的升高,外源添加的氨基酸和多肽在土壤中的矿化速度加快.在1 ℃、15 ℃和25 ℃下,3种供试土壤中谷氨酸（Glu）的平均半衰期分别为13.3、6.8和5.5 h;而谷氨酰 苯丙氨酸（Glu-Phe）的平均半衰期则分别为29.7、7.5和4.4 h.土壤的氨基酸、多肽的吸收动力学试验表明,土壤对氨基酸、多肽的吸收速率随着外源添加氨基酸和多肽浓度及温度的增加而提高.土壤对氨基酸的最大吸收速率(V_max)和亲和力（K_m）及对多肽的吸收速率（V_h）均随温度的升高而增大.在0～2.5 mmol·L^-1浓度范围内,土壤对氨基酸的吸收动力学曲线遵循经典的米氏动力学曲线,而多肽则表现为线性模式.3种园艺生产系统土壤的氨基酸和多肽的周转速率、吸收动力学参数（V_max、K_m和V_h）均表现为OS>TS>CS.总之,温度显著影响了氨基酸、多肽在土壤中的矿化及其吸收动力学特性.     

丛枝菌根真菌萌发孢子利用不同氮素及外源葡萄糖对其代谢的影响

对各种含氮基质、葡萄糖和(或)根浸出液中培养的丛枝菌根真菌Glomus intraradices孢子,在萌发过程中对不同氮素的利用及其氨基酸的生物合成进行了研究.用稳定同位素标记及质谱仪来分析不同氮素的利用和氨基酸的生物合成.以高效液相色谱测量氨基酸的浓度.在缺少外源氮素的情况下,丛枝菌根真菌孢子萌发时可以利用内部储存的含氮化合物生物合成游离氨基酸.其中,丝氨酸和甘氨酸是大量合成的氨基酸.合成的氨基酸浓度在2周内随着萌发时间的增加而增加.在有可利用的外源无机氮(铵盐、硝酸盐和尿素)和有机氮(氨基酸)时,铵盐和尿素比硝酸盐更容易被AM真菌萌发孢子利用,而其利用氨基酸中的氮比无机氮源慢的多.孢子吸收同化外源无机氮,且将其整合到游离氨基酸中,这些新生氨基酸浓度比无外源氮添加时要高得多.在无葡萄糖添加的硝酸盐培养液中,AM真菌孢子中积累大量天冬酰胺.然而,在含有葡萄糖的培养液中,萌发孢子因葡萄糖的吸收促进了对外源氮的吸收,产生的游离氨基酸是无葡萄糖时的5倍,并且发现精氨酸转为含量最多的游离氨基酸.并且,从外源氮吸收同化的氮可以储存于精氨酸中,随之,精氨酸被整合到AM真菌孢子储存的蛋白质中.此外,根浸出原液在AM真菌孢子萌发2周后对氮的吸收作用不明显.     

Thermo-erosion gullies increase nitrogen available for hydrologic export

Formation of thermokarst features, ground subsidence caused by thaw of ice-rich permafrost, can result in increased export of inorganic nitrogen (N) from arctic tundra to downstream ecosystems. We compared physical characteristics, N pools, and rates of N transformations in soils collected from thermo-erosion gullies, intact water tracks (the typical precursor landform to thermo-erosion gullies), and undisturbed tundra to test potential mechanisms contributing to export of inorganic N. Subsidence exposes mineral soils, which tend to contain higher abundance of inorganic ions relative to surface soils, and may bring inorganic N into contact with flowing water. Alternatively, physical mixing may increase aeration and drainage of soils, which could promote N mineralization and nitrification while suppressing denitrification. Finally, some soil types are more prone to formation of thermokarst, and if these soils are relatively N-rich, thermokarst features may export more N than surrounding tundra. Inorganic N pools in thermo-erosion gullies were similar to the mean for all tundra types in this region, as well as to water tracks when integrated across two sampled depths. Thus, soils prone to thermo-erosion are not intrinsically N-rich, and increased N availability in thermokarst features is apparent only at sub-regional spatial scales. However, vertical profiles of N pools and transformation rates were homogenized within thermo-erosion gullies compared to adjacent intact tundra, indicating that physical mixing brings inorganic N to the surface, where it may be subject to hydrologic export. Increased inorganic N availability caused by formation of thermo-erosion gullies may have acute, localized consequences for aquatic ecosystems downstream of positions within drainage networks that are susceptible to thermo-erosion.     

Interactions between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils

We used long-term laboratory incubations and chemical fractionation to characterize the mineralization dynamics of organic soils from tussock, shrub, and wet meadow tundra communities, to determine the relationship between soil organic matter (SOM) decomposition and chemistry, and to quantify the relative proportions of carbon (C) and nitrogen (N) in tundra SOM that are biologically available for decomposition. In all soils but shrub, we found little decline in respiration rates over 1 year, although soils respired approximately a tenth to a third of total soil C. The lack of decline in respiration rates despite large C losses indicates that the quantity of organic matter available was not controlling respiration and thus suggests that something else was limiting microbial activity. To determine the nature of the respired C, we analyzed soil chemistry before and after the incubation using a peat fractionation scheme. Despite the large losses of soil C, SOM chemistry was relatively unchanged after the incubation. The decomposition dynamics we observed suggest that tundra SOM, which is largely plant detritus, fits within existing concepts of the litter decay continuum. The lack of changes in organic matter chemistry indicates that this material had already decomposed to the point where the breakdown of labile constituents was tied to lignin decomposition. N mineralization was correlated with C mineralization in our study, but shrub soil mineralized more and tussock soil less N than would have been predicted by this correlation. Our results suggest that a large proportion of tundra SOM is potentially mineralizable, despite the fact that decomposition was dependent on lignin breakdown, and that the historical accumulation of organic matter in tundra soils is the result of field conditions unfavorable to decomposition and not the result of fundamental chemical limitations to decomposition. Our study also suggests that the anticipated increases in shrub dominance may substantially alter the dynamics of SOM decomposition in the tundra. Received 31 January 2002; accepted 16 July 2002.     

Treeline shifts in the Ural mountains affect soil organic matter dynamics

Historical photographs document that during the last century, forests have expanded upwards by 60–80 m into former tundra of the pristine Ural mountains. We assessed how the shift of the high‐altitude treeline ecotone might affect soil organic matter (SOM) dynamics. On the gentle slopes of Mali Iremel in the Southern Urals, we (1) determined the differences in SOM stocks and properties from the tundra at 1360 m above sea level (a.s.l.) to the subalpine forest at 1260 m a.s.l., and (2) measured carbon (C) and nitrogen (N) mineralization from tundra and forest soils at 7 and 20 °C in a 6‐month incubation experiment. C stocks of organic layers were 3.6±0.3 kg C m^?2 in the tundra and 1.9±0.2 kg C m^?2 in the forest. Mineral soils down to the bedrock stored significantly more C in the forest, and thus, total soil C stocks were slightly but insignificantly greater in the forest (+3 kg C m^?2). Assuming a space for time approach based on tree ages suggests that the soil C sink due to the forest expansion during the last century was at most 30 g C m^?2 yr^?1. Diffuse reflective infrared spectroscopy and scanning calorimetry revealed that SOM under forest was less humified in both organic and mineral horizons and, therefore, contained more available substrate. Consistent with this result, C mineralization rates of organic layers and A horizons of the forest were two to four times greater than those of tundra soils. This difference was similar in magnitude to the effect of increasing the incubation temperature from 7 to 20 °C. Hence, indirect climate change effects through an upward expansion of forests can be much larger than direct warming effects (Δ0.3 K across the treeline). Net N mineralization was 2.5 to six times greater in forest than in tundra soils, suggesting that an advancing treeline likely increases N availability. This may provide a nutritional basis for the fivefold increase in plant biomass and a tripling in productivity from the tundra to the forest. In summary, our results suggest that an upward expansion of forest has small net effects on C storage in soils but leads to changes in SOM quality, accelerates C cycling and increases net N mineralization, which in turn might stimulate plant growth and thus C sequestration in tree biomass.     

Carbon and Nitrogen Cycling in Soils from Acidic and Nonacidic Tundra with Different Glacial Histories in Northern Alaska

Moist acidic and nonacidic tundra are two of the most common vegetation types of the tundra in the northern foothills of the Brooks Range, Alaska, and they differ considerably in vegetation, soil nutrient availability, and soil pH. Both occur on mesic, gentle slopes, but acidic tundra is more common on older glacial surfaces whereas nonacidic tundra is more common on younger surfaces. Although much prior research has focused on moist acidic tundra, nonacidic tundra is still relatively unstudied. We compared rates of soil carbon (C) and nitrogen (N) cycling and their response to warming and changes in moisture in moist acidic tundra on Itkillik I glacial drift (50,000–120,000 years old, pH = 3–4) and moist nonacidic tundra on Itkillik II glacial drift (11,500–60,000 year old, pH = 6–7). We hypothesized that rates of soil C and N cycling would be faster at the nonacidic site because it has a more favorable pH for microbial activity and higher-quality organic matter inputs arising from its greater herbaceous plant production relative to the acidic site. However, in contrast to our hypothesis, in situ soil respiration, as well as respiration, dissolved organic C production, and net N mineralization in laboratory incubations, was greater for soils from the acidic site. Nevertheless, the sites responded similarly to manipulations of temperature and moisture, exhibiting exponential increases in respiration with warming between 4°C and 15°C but surprisingly little sensitivity to changes in moisture between 300% and 700%. Slower soil organic matter decomposition at the nonacidic site likely results from the stabilization of soil organic matter by high concentrations of calcium. Received 27 August 2001; accepted 3 April 2002.     

Soil carbon and nitrogen dynamics along a latitudinal transect in Western Siberia, Russia

An 1800-km South to North transect (N 53°43′ to 69°43′) through Western Siberia was established to study the interaction of nitrogen and carbon cycles. The transect comprised all major vegetation zones from steppe, through taiga to tundra and corresponded to a natural temperature gradient of 9.5°C mean annual temperature (MAT). In order to elucidate changes in the control of C and N cycling along this transect, we analyzed physical and chemical properties of soils and microbial structure and activity in the organic and in the mineral horizons, respectively. The impact of vegetation and climate exerted major controls on soil C and N pools (e.g., soil organic matter, total C and dissolved inorganic nitrogen) and process rates (gross N mineralization and heterotrophic respiration) in the organic horizons. In the mineral horizons, however, the impact of climate and vegetation was less pronounced. Gross N mineralization rates decreased in the organic horizons from south to north, while remaining nearly constant in the mineral horizons. Especially, in the northern taiga and southern tundra gross nitrogen mineralization rates were higher in the mineral compared to organic horizons, pointing to strong N limitation in these biomes. Heterotrophic respiration rates did not exhibit a clear trend along the transect, but were generally higher in the organic horizon compared to mineral horizons. Therefore, C and N mineralization were spatially decoupled at the northern taiga and tundra. The climate change implications of these findings (specifically for the Arctic) are discussed.     

Vascular plant 15N natural abundance in heath and forest tundra ecosystems is closely correlated with presence and type of mycorrhizal fungi in roots

In this study we show that the natural abundance of the nitrogen isotope 15, δ¹⁵N, of plants in heath tundra and at the tundra-forest ecocline is closely correlated with the presence and type of mycorrhizal association in the plant roots. A total of 56 vascular plant species, 7 moss species, 2 lichens and 6 species of fungi from four heath and forest tundra sites in Greenland, Siberia and Sweden were analysed for δ¹⁵N and N concentration. Roots of vascular plants were examined for mycorrhizal colonization, and the soil organic matter was analysed for δ¹⁵N, N concentration and soil inorganic, dissolved organic and microbial N. No arbuscular mycorrhizal (AM) colonizations were found although potential host plants were present in all sites. The dominant species were either ectomycorrhizal (ECM) or ericoid mycorrhizal (ERI). The δ¹⁵N of ECM or ERI plants was 3.5–7.7‰ lower than that of non-mycorrhizal (NON) species in three of the four sites. This corresponds to the results in our earlier study of mycorrhiza and plant δ¹⁵N which was limited to one heath and one fellfield in N Sweden. Hence, our data suggest that the δ¹⁵N pattern: NON/AM plants > ECM plants ≥ ERI plants is a general phenomenon in ecosystems with nutrient-deficient organogenic soils. In the fourth site, a␣birch forest with a lush herb/shrub understorey, the differences between functional groups were considerably smaller, and only the ERI species differed (by 1.1‰) from the NON species. Plants of all functional groups from this site had nearly twice the leaf N concentration as that found in the same species at the other three sites. It is likely that low inorganic N availability is a prerequisite for strong δ¹⁵N separation among functional groups. Both ECM roots and fruitbodies were ¹⁵N enriched compared to leaves which suggests that the difference in δ¹⁵N between plants with different kinds of mycorrhiza could be due to isotopic fractionation at the␣fungal-plant interface. However, differences in δ¹⁵N between soil N forms absorbed by the plants could also contribute to the wide differences in plant δ¹⁵N found in most heath and forest tundra ecosystems. We hypothesize that during microbial immobilization of soil ammonium the microbial N pool could become ¹⁵N-depleted and the remaining, plant-available soil ammonium ¹⁵N-enriched. The latter could be a main source of N for NON/AM plants which usually have high δ¹⁵N. In contrast, amino acids and other soil organic N compounds presumably are ¹⁵N-depleted, similar to plant litter, and ECM and ERI plants with high uptake of these N forms hence have low leaf δ¹⁵N. Further indications come from the δ¹⁵N of mosses and lichens which was similar to that of ECM plants. Tundra cryptogams (and ECM and ERI plants) have previously been shown to have higher uptake of amino acid than ammonium N; their low δ¹⁵N might therefore reflect the δ¹⁵N of free amino acids in the soil. The concentration of dissolved organic N was 3–16 times higher than that of inorganic N in the sites. Organic nitrogen could be an important N source for ECM and, in particular, ERI plants in heath and forest tundra ecosystems with low release rate of inorganic N from the soil organic matter. Received: 8 June 1997 / Accepted: 28 February 1998     

Rapid analysis of total sulphur in soils and plant material

Summary The Leco high-frequency induction furnace technique was adapted for rapid titrimetric analysis of total S in soils and plant material. Accuracy and precision were tested by standardizing soils and plant material and by measuring recovery of known amounts of inorganic and organic sulphur standards from these. Recovery ranged from 86 to 90 per cent and differed between soils, depending on organic matter and N content.     

Warming of subarctic tundra increases emissions of all three important greenhouse gases – carbon dioxide,methane, and nitrous oxide

Rapidly rising temperatures in the Arctic might cause a greater release of greenhouse gases (GHGs) to the atmosphere. To study the effect of warming on GHG dynamics, we deployed open‐top chambers in a subarctic tundra site in Northeast European Russia. We determined carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes as well as the concentration of those gases, inorganic nitrogen (N) and dissolved organic carbon (DOC) along the soil profile. Studied tundra surfaces ranged from mineral to organic soils and from vegetated to unvegetated areas. As a result of air warming, the seasonal GHG budget of the vegetated tundra surfaces shifted from a GHG sink of ?300 to ?198 g CO₂–eq m^?2 to a source of 105 to 144 g CO₂–eq m^?2. At bare peat surfaces, we observed increased release of all three GHGs. While the positive warming response was dominated by CO₂, we provide here the first in situ evidence of increasing N₂O emissions from tundra soils with warming. Warming promoted N₂O release not only from bare peat, previously identified as a strong N₂O source, but also from the abundant, vegetated peat surfaces that do not emit N₂O under present climate. At these surfaces, elevated temperatures had an adverse effect on plant growth, resulting in lower plant N uptake and, consequently, better N availability for soil microbes. Although the warming was limited to the soil surface and did not alter thaw depth, it increased concentrations of DOC, CO_2, and CH₄ in the soil down to the permafrost table. This can be attributed to downward DOC leaching, fueling microbial activity at depth. Taken together, our results emphasize the tight linkages between plant and soil processes, and different soil layers, which need to be taken into account when predicting the climate change feedback of the Arctic.     

Links between plant community composition,soil organic matter quality and microbial communities in contrasting tundra habitats

Plant communities, soil organic matter and microbial communities are predicted to be interlinked and to exhibit concordant patterns along major environmental gradients. We investigated the relationships between plant functional type composition, soil organic matter quality and decomposer community composition, and how these are related to major environmental variation in non-acid and acid soils derived from calcareous versus siliceous bedrocks, respectively. We analysed vegetation, organic matter and microbial community compositions from five non-acidic and five acidic heath sites in alpine tundra in northern Europe. Sequential organic matter fractionation was used to characterize organic matter quality and phospholipid fatty acid analysis to detect major variation in decomposer communities. Non-acidic and acidic heaths differed substantially in vegetation composition, and these disparities were associated with congruent shifts in soil organic matter and microbial communities. A high proportion of forbs in the vegetation was positively associated with low C:N and high soluble N:phenolics ratios in soil organic matter, and a high proportion of bacteria in the microbial community. On the contrary, dwarf shrub-rich vegetation was associated with high C:N and low soluble N:phenolics ratios, and a high proportion of fungi in the microbial community. Our study demonstrates a strong link between the plant community composition, soil organic matter quality, and microbial community composition, and that differences in one compartment are paralleled by changes in others. Variation in the forb-shrub gradient of vegetation may largely dictate variations in the chemical quality of organic matter and decomposer communities in tundra ecosystems. Soil pH, through its direct and indirect effects on plant and microbial communities, seems to function as an ultimate environmental driver that gives rise to and amplifies the interactions between above- and belowground systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.