Fungal biomass development in a chronosequence of land abandonment

Based on biomass size, the contribution of fungi to nutrient cycling and soil properties is in general more important in natural ecosystems than in agro-ecosystems. Therefore, we expect an increase of fungal biomass after cessation of cultivation to values of a natural ecosystem. However, so far, information on fungal dynamics in ex-arable land is limited. We quantified fungal biomass in a chronosequence of 26 ex-arable fields in the Netherlands ranging from 1-34 years of abandonment. Agricultural lands and semi-natural heathlands were included as reference sites for initial and final stages of succession, respectively. Fungal biomass values were low at the start of land abandonment and increased during the first 2 years after abandonment. After this initial increase of fungal biomass no further increase was apparent, neither did we find any relations with time since abandonment and changes in soil acidity, organic matter content or organic matter quality (quantity of recalcitrant C and C:N ratio). Therefore, we conclude that the initial increase of fungal biomass is caused by stopping agricultural management activities. A phase of stabilization occurs for at least three decades in which the size of the fungal biomass did not change significantly. We observed much higher values for fungal biomass, total and recalcitrant carbon in the heathland sites. We propose that a change in abiotic soil properties is a prerequisite for further increase of fungal biomass towards levels of representative heathlands.     

Relative abundance and activity of melanized hyphae in different soil ecosystems

Here we report on the frequency of melanized fungal hyphae in 323 soils, covering different land use types. The proportion of total hyphae that was melanized averaged 61%. Arable fields with loamy sand, heathlands and city parks on sandy soils had the highest percentage of melanized hyphae. In addition to the frequency determinations, a microcosm study was performed on the role of melanized hyphae in two different ecosystems: an ex-arable field and a forest. Melanized hyphae appeared to be part of the active hyphae in the forest soil but not in the ex-arable soil. In conclusion, our results indicate that (1) melanized hyphae represent a large proportion of the total fungal biomass in soils and that (2) their function might differ between ecosystems.     

The establishment of heathland vegetation on ex-arable land: the response of Calluna vulgaris to soil acidification

The UK Biodiversity Action Plan has identified the creation of lowland heathland as an important objective. Heathland restoration studies have identified soil pH, elevated soil nutrients and large weed seed banks as major problems in the restoration of heathland vegetation on ex-arable land. Heathland vegetation is usually found on nutrient-poor acidic soils. Creating acidic soil conditions on ex-arable sites thus may produce a suitable environment for the establishment of heath vegetation. Soil acidification by the addition of sulphur has been shown to reduce the soil pH and the availability of nutrients in arable soils. A series of experiments was established to investigate the effects of soil acidification using sulphur on the establishment of Calluna vulgaris and the development of weed vegetation. The application of sulphur at 0.24 kg m⁻² to an arable soil was found to increase the survival rate of C. vulgaris cuttings planted in it. The mechanism of increased C. vulgaris survival appeared to be by sulphur application significantly reducing the cover of arable weeds arising from the soil seed bank. Higher rates of sulphur application (0.36 and 0.48 kg m⁻²) resulted in the death of many C. vulgaris plants. However C. vulgaris seedlings were able to establish successfully on these ex-arable soils within 18-24 months following the addition of these levels of sulphur. The application of sulphur appears to offer a practical solution to heathland creation on ex-arable land. However, it may be necessary to provide an interval of between 18 and 24 months between the application of sulphur and the addition of C. vulgaris plants or seeds for the successful establishment of heathland vegetation.     

侵蚀环境撂荒地植物群落恢复动态研究

以侵蚀环境不同退耕撂荒年限样地为研究对象,采用空间代替时间序列的方法调查植物群落特征,分析植物恢复过程。结果表明：植物群落覆盖度和地上生物量随退耕撂荒年限的增加,恢复演替的推进逐渐增大;群落物种多样性指数与撂荒年限呈正相关,而群落优势度指数与撂荒年限呈负相关;物种多样性指数能极好地反映群落物种丰富度,并能客观表达物种的动态变化,其演变呈升—降—升的趋势,退耕撂荒3、10和25 a左右时为物种多样性指数的高峰。植物群落结构稳定性与物种多样性、群落生物量、覆盖度和优势度关系密切,随着退耕撂荒地植被恢复演替的进展,植被结构稳定性呈阶梯式增强,从而为侵蚀环境生态恢复提供了基础保障。     

Restoration of species-rich grasslands on ex-arable land: Seed addition outweighs soil fertility reduction

A common practice in biodiversity conservation is restoration of former species-rich grassland on ex-arable land. Major constraints for grassland restoration are high soil fertility and limited dispersal ability of plant species to target sites. Usually, studies focus on soil fertility or on methods to introduce plant seeds. However, the question is whether soil fertility reduction is always necessary for getting plant species established on target sites. In a three-year field experiment with ex-arable soil with intensive farming history, we tested single and combined effects of soil fertility reduction and sowing mid-successional plant species on plant community development and soil biological properties. A controlled microcosm study was performed to test short-term effects of soil fertility reduction measures on biomass production of mid-successional species. Soil fertility was manipulated by adding carbon (wood or straw) to incorporate plant-available nutrients into organic matter, or by removing nutrients through top soil removal (TSR). The sown species established successfully and their establishment was independent of carbon amendments. TSR reduced plant biomass, and effectively suppressed arable weeds, however, created a desert-like environment, inhibiting the effectiveness of sowing mid-successional plant species. Adding straw or wood resulted in short-term reduction of plant biomass, suggesting a temporal decrease in plant-available nutrients by microbial immobilisation. Straw and wood addition had little effects on soil biological properties, whereas TSR profoundly reduced numbers of bacteria, fungal biomass and nematode abundance. In conclusion, in ex-arable soils, on a short-term sowing is more effective for grassland restoration than strategies aiming at soil fertility reduction.     

Changes in physical properties and carbon stocks of gray forest soils in the southern part of Moscow region during postagrogenic evolution

Changes in carbon stocks and physical properties of gray forest soils during their postagrogenic evolution have been studied in the succession chronosequence comprising an arable, lands abandoned 6, 15, and 30 years ago; and a secondary deciduous forest (Experimental Field Station of the Institute of Physicochemical and Biological Problems of Soil Science, Russian Academy of Sciences, Pushchino, Moscow region). It is found that carbon stocks in the upper 60-cm soil layer gain with increasing period of abandonment, from 6.17 kg C/m² on the arable land to 8.81 kg C/m² in the forest soil, which represents the final stage of postagrogenic succession. The most intensive carbon accumulation occurs in the upper layer of the former plow (0- to 10-cm) horizon. It is shown that the self-restoration of gray forest soils is accompanied by a reliable decrease of bulk density in the upper 10-cm layer from 1.31 ± 0.01 g/cm³ on the arable to 0.97 ± 0.02 g/cm³ in the forest. In the former plow horizon of the arable–abandoned land–forest succession series, the portion of macroaggregates increases from 73.6 to 88.5%; the mean weighted diameter of aggregates, by 1.6 times; and the coefficient of aggregation, by 3.8 times. Thus, the removal of lands from agricultural use results in a gradual restoration of their natural structure, improvement of soil agronomical properties, and carbon sequestration in the upper part of the soil profile.     

Successional trajectories of soil nematode and plant communities in a chronosequence of ex-arable lands

Conversion of arable land into semi-natural grassland or heath land is a common practice for restoring and conserving plant diversity. However, little is known about the effectiveness of land conversion for restoring and conserving taxonomic and functional diversity in the soil. We studied soil nematode community development in a chronosequence of abandoned fields and related this to plant community development. The taxonomic and functional composition of the soil nematode community was analyzed to detect changes in soil food web structure, using semi-natural sites and theoretical plant and soil communities as references.While plant communities clearly developed towards the semi-natural references, there was less direction in succession of nematode taxa. The number of fungal feeding nematodes increased after land abandonment. Numbers of omni-carnivorous nematodes expanded only during the first years, after which there were no substantial changes for the next three decades. Plant communities on the ex-arable fields developed towards the theoretical reference plant associations Galio hercynici-Festucetum ovinae and Genisto anglicae-Callunetum. Nematode communities developed away from a theoretical community indicative of arable land, but there was no clear development towards a theoretical (semi-)natural reference. Our results show that restoration and conservation of plant communities is of limited indicative value for developments belowground: successful restoration of plant diversity does not necessarily imply successful restoration of belowground diversity. Assessing the impact of conservation measures on restoring soil biodiversity requires information on belowground community composition of (semi-)natural areas in order to establish proper references for restoration sites.     

Changes in soil microbial community structure following the abandonment of agricultural terraces in mountainous areas of Eastern Spain

In Eastern Spain, almond trees have been cultivated in terraced orchards for centuries, forming an integral part of the Mediterranean forest scene. In the last decades, orchards have been abandoned due to changes in society. This study investigates effects of changes in land use from forest to agricultural land and the posterior land abandonment on soil microbial community, and the influence of soil physico-chemical properties on the microbial community composition (assessed as abundances of phospholipids fatty acids, PLFA). For this purpose, three land uses (forest, agricultural and abandoned agricultural) at four locations in SE Spain were selected. Multivariate analysis showed a substantial level of differentiation in microbial community structure according to land use. The microbial communities of forest soils were highly associated with soil organic matter content. However, we have not found any physical or chemical soil property capable of explaining the differences between agricultural and abandoned agricultural soils. Thus, it was suggested that the cessation of the perturbation caused by agriculture and shifts in vegetation may have led to changes in the microbial community structure. PLFAs indicative of fungi and ratio of fungal to bacterial PLFAs were higher in abandoned agricultural soils, whereas the relative abundance of bacteria was higher in agricultural soils. Actinomycetes were generally lower in abandoned agricultural soils, while the proportions of vesicular–arbuscular mycorrhyzal fungi were, as a general trend, higher in agricultural and abandoned agricultural soils than in forests. Total microbial biomass and richness increased as agricultural < abandoned agricultural < forest soils.     

侵蚀环境退耕撂荒地水稳性团聚体演变特征及土壤养分效应

研究了侵蚀环境退耕撂荒地生态恢复过程中水稳性团聚体的变化规律及其与土壤养分状况及土壤微生物量的关系，结果表明，侵蚀环境退耕撂荒地土壤水稳性团聚体含量迅速提高，在退耕撂荒的第一个10年，水稳性团聚体增大约253．45％。随着退耕撂荒年限的延长，其增大幅度趋缓，第10～50年，水稳性团聚体仅增大16．42％，之后增大幅度更加缓慢，接近一个稳定的水平。相关性分析和回归分析表明侵蚀环境退耕地撂荒后土壤中〉0．25mm水稳性团聚体与土壤的有机碳、全氮、速磷、碳酸钙、微生物量（C，N，P）、CEC关系密切，达到显著（P〈0．05）或极显著水平（P〈0．01），而与速钾没有明显的相关性。要保持侵蚀环境退耕撂荒土壤良好的结构状况，必须坚持长期封禁，维持土壤有机碳变化处于平衡状态。     

Effect of vegetation manipulation of abandoned arable land on soil microbial properties

 The effect of vegetation composition on various soil microbial properties in abandoned arable land was investigated 2 years after agricultural practice had terminated. Microbial numbers and processes were determined in five replicate plots of each of the following treatments: continued agricultural practice (monoculture of buckwheat in 1997), natural colonization by the pioneer community (arable weeds), and manipulated colonization from low (four species, three functional groups: grasses, forbs and legumes) or high diversity (15 species, three functional groups) seed mixtures from plant species that are characteristic of abandoned fields in later successional stages. The results indicated that differences in above-ground plant biomass, plant species composition and plant species diversity had no significant effect on soil microbial processes (net N mineralization, short-term nitrification, respiration and Arg ammonification), microbial biomass C and N (fumigation-incubation) or colony-forming units of the major microbial groups. Hence, there were no indications that soil microbial processes responded differently within 2 years of colonization of abandoned arable land by later successional plants as compared to that by plants from the natural pioneer weed community. Therefore, it seems that during the first few years after arable field abandonment, plants are more dependent on the prevailing soil microbiological conditions than vice versa. Received: 8 April 1999     

Contrasted Impact of Land Abandonment on Soil Erosion in Mediterranean Agriculture Fields

Abandonment of agricultural land results in on-and off-site consequences for the ecosystem. In this study, 105 rainfall simulations were carried out in agriculture lands of the Mediterranean belt in Spain(vineyards in Málaga, almond orchards in Murcia, and orange and olive orchards in Valencia) and in paired abandoned lands to assess the impact of land abandonment on soil and water losses. After abandonment, soil detachment decreased drastically in the olive and orange orchards, while vineyards did not show any difference and almond orchards registered higher erosion rates after the abandonment. Terraced orchards of oranges and olives recovered a dense vegetation cover after the abandonment, while the sloping terrain of almond orchards and vineyards enhanced the development of crusts and rills and a negligible vegetation cover resulted in high erosion rates. The contrasted responses to land abandonment in Mediterranean agricultural lands suggest that land abandonment should be programmed and managed with soil erosion control strategies for some years to avoid land degradation.     

Fungal presence in paired cultivated and uncultivated soils in central Iowa, USA

 Amounts of fungal biomass in adjacent cultivated and uncultivated soils in central Iowa were estimated and compared by quantifying soil ergosterol concentrations and lengths of fungal hyphae present. Both indices of fungal biomass, with one exception, indicated that there was at least twice as much fungal biomass in uncultivated soil as in cultivated soil. Levels of microbial biomass carbon in uncultivated soils were also determined to be at least twice that in cultivated soils. Data collected in this study indicate that fungi may be more significantly affected by agricultural soil management practices than other components of the soil microbial community. For two of the soils examined, calculated estimates denote that fungal biomass carbon represented approximately 20% of the total microbial biomass carbon in cultivated soil and about 33% of the microbial biomass carbon in uncultivated soil. Results of this study indicate that conventional agricultural practices result in a significant reduction of fungal biomass production in soil. Implications of differences in fungal biomass between the soils are discussed. Received: 12 October 1997     

侵蚀环境人工刺槐林土壤水稳性团聚体演变及其养分效应

采用时空互代法,以典型侵蚀环境纸坊沟流域生态恢复过程中不同年限的人工刺槐林为研究对象,选取坡耕地和天然侧柏林为参照,分析了植被恢复过程中土壤水稳性团聚体变化规律及其与土壤养分状况之间的相互关系。结果表明,侵蚀环境下的坡耕地由于人为耕作干扰,土壤水稳性团聚体含量低下,抗蚀性能较差。营造刺槐林前5a土壤水稳性团聚体含量较坡耕地显著快速增加,随后增幅变缓,成对数增长,恢复25a后土壤水稳性团聚体含量已经达到天然侧柏林水平。在植被恢复过程中土壤小粒径的水稳性团聚体逐渐聚集转变形成大粒径的团聚体。相关性分析和回归分析表明,植被恢复过程中〉0．25mm土壤水稳性团聚体与有机碳、全氮、碱解氮、速效钾、容重等相关性达到显著（P〈0．05）或极显著水平（P〈0．01）,与全磷和速效磷相关性较弱。坡耕地退耕营造刺槐林后可以减少人为干扰,增加碳素和氮素供给,提高水稳性团聚体含量,使土壤抗蚀性能提高。     

土地利用和轮作方式对旱地红壤生化性质的影响

研究不同土地利用和轮作方式对旱地红壤肥力的影响对提高红壤质量具有十分重要的指导意义。本研究以湖南省桃源县的林地、大豆-油菜轮作、玉米-休闲轮作土壤为研究对象,明确了林地、农地土壤及农地不同轮作方式对土壤化学和生物性质的影响。结果表明,林地土壤的pH、有机碳、速效养分、微生物生物量碳及酶活性(纤维素酶、酸性磷酸酶、转化酶、蛋白酶)均显著高于农地土壤;大豆-油菜轮作土壤的pH、养分含量、微生物生物量碳含量及其微生物熵在大多数情况下高于玉米-休闲轮作,但轮作处理对各酶活性的影响并不完全一致。这种不一致性可能与不同酶对由不同利用和轮作方式导致的土壤性质差异的敏感性不同所致。土壤有机碳和pH与各生物指标均呈显著正相关关系,表明提高该地区的土壤有机碳含量对于维持土壤的生化性质具有重要的作用。     

沂蒙山区小流域坡耕地土壤颗粒结构与养分退化特征

为探讨坡耕地土壤退化程度及其与坡度的关系,在沂蒙山区选择典型小流域,通过测定流域内不同坡度坡耕地、弃耕地与生态林地的土壤颗粒组成、分形维数、土壤养分质量分数的变化及其相关性,研究坡耕地土壤颗粒结构与养分退化特征。结果表明：1）所有土地利用类型,土壤砂粒体积分数最高,黏粒体积分数最低,平均值分别为70．81％、0．75％;2）土壤颗粒分形维数、有机质质量分数为生态林地〉弃耕地〉坡耕地;3）坡耕地土壤颗粒分形维数随坡度增加而减小,其大小与土壤粉粒和黏粒体积分数分别呈极显著、显著正相关;4）所有土地利用类型,土壤有机质质量分数与砂粒体积分数显著负相关,与粉粒和黏粒体积分数显著正相关,土壤氮、磷、钾养分质量分数与土壤颗粒体积分数相关性不显著;5）研究区土壤具有粗骨性砂土的物理特性,坡耕地耕作或坡度加大会增强土壤粉粒和黏粒的流失,导致土壤颗粒分布的均匀性及其分维数下降,水肥保蓄性能和养分质量分数降低。     

Low importance for a fungal based food web in arable soils under mineral and organic fertilization indicated by Collembola grazers

We investigated the Collembola community at an arable field where mineral and organic fertilizers have been applied at low and high rates for 27 years. As food resources for Collembola, the soil microbial community was analyzed using phospholipid fatty acids (PLFAs). A special focus was put on AM fungi, which were estimated by the marker 16:1ω5 in PLFA (viable hyphae) and neutral lipid fatty acid (NLFA – storage fat in spores) fractions. Additionally, whole cellular lipids in crop plant tissues and manure were assessed. Greater Collembola species richness occurred in plots where mineral fertilizer was added. In contrast, soil microbial biomass including AM fungal hyphae increased with addition of organic fertilizer, while the amount of AM fungal spores and biomass of saprotrophic fungi were not affected by fertilizer type. The lipid pattern in wheat roots was altered by fertilizer type, application rate and their interaction, indicating different rhizosphere communities. In sum, the availability and composition of food resources for Collembola changed considerably due to farm management practice. The major diet of three dominant Collembola species, Isotoma viridis, Willemia anophthalma and Polyacanthella schäffer was determined by lipid profiling. Multivariate analysis demonstrated species specific lipid patterns, suggesting greater importance of species than management practice on the diet choice. Nevertheless, feeding strategy was affected by fertilizer type and availability of resources, as trophic biomarker fatty acids indicated feeding on wheat roots (and to some extent saprotrophic fungi) with mineral and a shift to soil organic matter (litter, detritus) with organic fertilization. Although AM fungi dominated the soil fungal community, the AMF marker 16:1ω5 was not detected in Collembola lipids, indicating that these were not consumed. The very low amount of saprotrophic fungi in the soil and the fact that Collembola as major fungal grazers did not feed on AM fungi indicates that the fungal energy channel in the investigated arable field is of little importance to the faunal food web.     

Effects of cultivation and abandonment on soil carbon content of subalpine meadows, northwest China

Purpose

Land use changes have a significant impact on soil carbon emission and sequestration worldwide. Accurate evaluation of the effect of land use change (cultivation and abandonment) on soil carbon content of subalpine meadows is required to monitor the soil carbon dynamics of rangeland ecosystems in China.

Materials and methods

Based on collection of soil cores and vegetation, investigations of four types of land use (undisturbed natural meadow, land cultivated for 20?years, land abandoned for 3?years following cultivation, and land abandoned for 10?years following cultivation) were undertaken in the headwater area of the Heihe River in northwest China. Three soil carbon fractions [soil organic carbon (SOC), light fraction organic carbon (LFOC), and microorganism biomass carbon (MBC)] were determined in the laboratory, and the relative abundances of LFOC/SOC and MBC/SOC were calculated.

Results and discussion

Repeated cultivation by ploughing reduced the carbon content of the top soil layer, resulting in more uniform vertical distribution of soil organic matter. Ten years after cessation of cultivation, the organic carbon content within the top 10-cm soil layer (0?C10?cm) had reached 90?% of the content in native meadows, equivalent to a mean annual sequestration rate of 1.73?t?C?ha^?1. The rate of LFOC restoration was faster than that of SOC restoration. The variation in the ratio of MBC to SOC (0.91?C1.07?%) was small.

Conclusions

The activity of cultivation reduced all indicators of soil carbon status, which were not completely restored to the level of natural meadow, even after abandonment of cultivation for 10?years. Nevertheless, abandonment of cultivation is a practical, even if long-term, means of improving carbon sequestration in subalpine meadow of China.     

The coarse‐soil fraction is the main living space of fungal hyphae in the BhBs horizon of a Podzol

In acidified forest soils, the coarse‐soil fraction is a potential nutrient source. Plant nutrient uptake from the coarse‐soil fraction is aided by ectomycorrhiza. Similarly, (recalcitrant) organic matter (OM) is an important nutrient source largely made plant‐available through (symbiotic) microorganisms, especially in the topsoil. We hypothesized that in a podzol profile, fungal hyphae would concentrate in nutrient hotspots, either OM or the coarse‐soil fraction. Absolute hyphal length, base saturation, and organic‐C content of a Podzol profile were determined in the fine‐earth and coarse‐soil fractions. In the fine‐earth fraction, hyphae were attracted by the organic‐C content and relative high base saturation. In the coarse‐soil fraction of the BhBs horizon, the absolute hyphal length exceeded the hyphal length in the fine earth by factor 3, yet C content and base saturation were lowest. We could not determine to what fungi the hyphae belonged. Most likely ectomycorrhiza, ericoid mycorrhiza and saprotrophic fungi dominate the upper soil layers of this profile and all utilize OM for nutrition. In the deeper mineral horizons and especially in the coarse‐soil fraction, ectomycorrhiza are better adapted than other fungi to harvest nutrients from inorganic sources. Additionally, favorable physical properties may explain the high amount of fungal hyphae in the coarse‐soil fraction of the BhBs horizon. Both the coarse‐soil fraction and deeper mineral soil horizons may play a more active role in microbial nutrient cycling than previously assumed.     

Impact of land-use change on nitrogen mineralization in subalpine grasslands in the Southern Alps

 A field study was conducted to investigate the effect of abandonment of management on net N mineralization (NNM) in subalpine meadows. NNM, soil microbial biomass N (SMBN), fungal biomass and physicochemical characteristics (total C, total N, dissolved organic carbon (DOC) and pH) were determined in surface (0–10 cm) soil from May to October 1997 in an intensively managed and an abandoned meadow at 1770 m a.s.l.. The cumulative NNM was lower in the abandoned area and ranged from 150 to 373 and from 25 to 85 μg N g^–1 soil in the intensively managed and the abandoned areas, respectively. The total organic C increased in the abandoned area, while total N showed no difference between abandoned and managed meadow. SMBN showed no difference between the investigated sites, whereas ergosterol, a measure of fungal biomass, increased significantly at the abandoned site. The cumulative NNM was negatively correlated with total organic C, C : N ratio, DOC and ergosterol content, and positively correlated with the NH₄ ⁺-N content of soil. The decrease in NNM at the abandoned site may be explained by the lower availability of N in substrates characterized by a high C : N ratio which, together with a decrease in pH in the litter layer, may have increased fungal biomass. Received: 8 January 1999