Vertical Growth and Mycorrhizal Infection of Woody Plant Roots as Potential Limits to the Restoration of Woodlands on Landfills

We assessed the vertical growth and mycorrhizal infection of woody plant roots on a closed landfill, using tree and shrub clusters that had been previously installed in patches of increasing size to establish protocols for woodland restoration. The density of the fine roots of shrubs, which had poor-to-moderate mycorrhizal infection, decreased strongly with increasing depth. Oak ( Quercus ) seedlings planted within and outside patches were assessed for ectomycorrhizal infection. Oak root systems were mycorrhizal, but root-tip proliferation was improved and ectomycorrhizal composition was influenced by woody debris in the mineral soil. Most surviving oaks were found within patches, but all seedlings showed poor growth: most taproots were deflected horizontally above the boundary between surface soil and subsoil layers (−15 cm). Abrupt decreases in pH between surface and subsurface horizons (6.9 versus 5.3), together with poor drainage and aeration of the latter soil, were probably responsible for poor root growth. Root growth of greenhouse-grown pine and maple seedlings was similarly restricted in pots packed with topsoil over subsoil material. Our results suggest that many current specifications for the cover of closed landfills will not permit restoration of native woody plant communities because of physical limitations to root growth and infectivity. The structure of the engineered soil must address basic plant growth requirements as well as traditional concerns of drainage and barrier protection.     

Effects of drought stress and arbuscular mycorrhiza on the growth of Gliricidia sepium (Jacq). Walp, and Leucaena leucocephala (Lam.) de Wit. in simulated eroded soil conditions

A greenhouse investigation was conducted to determine the effect of arbuscular mycorrhiza and drought on the growth of two tropical hedgerow legume trees (Gliricidia sepium and Leucaena leucocephala) under simulated eroded soil conditions. It was a factorial design with two levels of watering regime (adequate watering and drought), inoculation with Glomus deserticola (with and without), and two soil types (0-30 cm topsoil and 30-60 cm subsoil). Each treatment was replicated 3 times. After ten drought cycles, the growth of Gliricidia sepium in the subsoil was enhanced by mycorrhizal inoculation under both watering regimes whereas there was no significant contribution of mycorrhizal inoculation to the growth of L. leucocephala in both soil types under the two watering regimes. Drought stress significantly reduced most growth parameters for the two tree species in both soils with or without fungal inoculation. The N-fixing activity of Gliricidia sepium benefited from Glomus deserticola inoculation while that of L. leucocephala was not significantly affected in the topsoil. Mycorrhizal colonization was reduced for both tree species in the subsoil compared to the topsoil while it was significantly increased for both species in the subsoil when compared to the uninoculated subsoil counterpart. In the subsoil, inoculation of Gliricidia sepium with the mycorrhizal fungus increased root colonization by 89% and 73% under adequate watering and drought, respectively, whereas L. leucocephala had only a 38% and 42% increase in root colonization under comparative conditions in the subsoil. Thus Glomus deserticola inoculation may be beneficial to the growth of Gliricidia sepium in a badly eroded site where topsoil is missing.     

Spatial distribution and turnover of root-derived carbon in alfalfa rhizosphere depending on top- and subsoil properties and mycorrhization

Aims

This study analyzed the extent to which root exudates diffuse from the root surface towards the soil depending on topsoil and subsoil properties and the effect of arbuscular mycorrhizal fungal hyphae on root-derived C distribution in the rhizosphere.

Methods

Alfalfa was grown in three-compartment pots. Nylon gauze prevented either roots alone or roots and arbuscular mycorrhizal fungal hyphae from penetrating into the rhizosphere compartments. ¹⁴CO₂ pulse labeling enabled the measurement of ¹⁴C-labeled exudates in dissolved (DOC) and total organic carbon (TOC) in the rhizosphere, distributed either by diffusion alone or by diffusion, root hair and hyphal transport.

Results

Root exudation and microbial decomposition of exudates was higher in the rhizosphere with topsoil compared to subsoil properties. Exudates extended over 28 mm (DOC) and 20 mm (TOC). Different soil properties and mycorrhization, likely caused by the low arbuscular mycorrhizal colonization of roots (13?±?4 % (topsoil properties) and 18?±?5 % (subsoil properties)), had no effect.

Conclusions

Higher microbial decomposition compensated for higher root exudation into the rhizosphere with topsoil properties, which resulted in equal exudate extent when compared to the rhizosphere with subsoil properties. Higher ¹⁴C activity used for labeling compared with previous studies enabled the detection of low exudate concentrations at longer distances from the root surface.     

Characteristic responses of three tropical legumes to the inoculation of two species of VAM fungi in Andosol soils with different fertilities

The growth and mineral nutrition responses were evaluated of three tropical legumes, cowpea (Vigna unguiculata L. cv Kuromame), pigeonpea [Cajanus cajan L. (Millsp.) cv ICPL 86009] and groundnut (Arachis hypogaea cv Nakateyutaka) inoculated with two different species of VAM fungi, Glomus sp. (Glomus etunicatum-like species) and Gigaspora margarita, and grown in Andosols with different fertilities [Bray II-P: topsoil (72 ppm), subsoil (<0.1 ppm)]. Percent fungal root colonization was high in cowpea and groundnut but relatively low in pigeonpea in both soil types. Despite the low rate of root infection, significant growth responses were produced, especially in the inoculated pigeonpea plant. In all legumes, shoot dry matter production was favoured by the inoculations. Increases in shoot biomass due to mycorrhizae were greater in the subsoil than in the topsoil. Mycorrhization raised shoot concentrations of P and Ca (in cowpea and groundnut) and P and K (in pigeonpea) in the topsoil. Whereas the P concentration in shoots in the subsoil was not positively affected by VAM fungi, particularly in cowpea and pigeonpea, the concentration of K in such plants was significantly increased by VAM treatment. The results also showed that mycorrhizal enhancement of shoot micronutrient concentrations was very rare in all plants, with negative effects observed in certain cases. Cu concentration, in particular, was not affected by VAM formation in any of the plants, and Mn and Fe in pigeonpea and groundnut, respectively, remained the same whether plants were mycorrhizal or not. In both soils the three legumes responded to Glomus sp. better than to Gigaspora margarita, and the effects of the VAM fungi on each of the crops relative to the controls were greater in the subsoil than in the topsoil. However, shoot growth of groundnut was not affected as much as cowpea and pigeonpea by the type of soil used. In spite of the relatively low infection of its root, pigeonpea was generally the most responsive of the three legume species in terms of mycorrhizal/nonmycorrhizal ratios.     

The role of arbuscular mycorrhizal fungi in plant community establishment at Samphire Hoe, Kent, UK – the reclamation platform created during the building of the Channel tunnel between France and UK

Samphire Hoe is a newly-created land platform comprising the sub-seabed material excavated during the construction of the Channel tunnel. It represents a unique resource where the arrival and establishment of arbuscular mycorrhizal fungi (AMF) within a sown plant community on a low nutrient substrate can be monitored. Arbuscular mycorrhizal fungi invasion was monitored in a number of ways: by assessing the degree of root colonisation within the roots of plants on the site, by using a successive trap culture technique to determine AMF species richness, and by using sterile substrate bins to determine the extent of wind-borne and rain-dispersed immigration of AMF propagules into the site. Levels of colonisation of indigenous plants by AMF were high in May–June (the pre-flowering phase of growth for many plants) reflecting the important role of the mycorrhizal symbiosis in dry, low nutrient soils. Twelve species of AMF were identified, representing a relatively high diversity for a recently deposited subsoil. An on-site experiment indicated that inoculum of AMF could enter the site within 8 months and that wind dispersal and/or rain were possible vectors. A field experiment compared the outplanting performance of commercially-produced Elymus pycnanthus seedlings (in a commercial compost with added nutrients) with seedlings produced in a low nutrient substrate and inoculated with AMF isolated from the site (a mixture of 5 species of Glomus) or left uninoculated. After 14 months in the field seedlings, inoculated with the indigenous AMF, had the same tiller production as commercially-produced plants, despite slower initial growth. In contrast, non-mycorrhizal controls grew very poorly with a greater frequency of plant mortality compared with the other treatments. Elymus seedlings inoculated with the indigenous AMF ultimately produced approximately seven times the mean number of seed spikes per surviving plant as commercially-produced seedlings and five times greater weight of seed spike. A phyto-microbial approach to the revegetation of nutrient-poor soils is proposed to stimulate plant successional processes as a economically-viable sustainable input for landscaping anthropogenic sites.     

Long-Term Effects of Biosolids on Revegetation of Disturbed Sagebrush Steppe in Northwestern Colorado

A study was conducted to evaluate the long‐term effects of biosolids amendment on restoration of disturbed sagebrush steppe habitat in northwestern Colorado. Twenty‐four years after biosolids amendment, soil fertility and plant community development were studied in replicated plots receiving various biosolids amendments on two different substrates. The two substrates used were a subsoil, determined to have low initial fertility, and a topsoil over retorted shale substrate, determined to have relatively high initial fertility. Results suggest that biosolids amendments have long‐lasting effects on soil fertility and plant community composition, but these effects vary between the two substrates that were utilized. Within the plots established on subsoil, the long‐term effect of biosolids was a reduction in plant species diversity and dominance by perennial grasses. On the topsoil substrate, there was a decrease in perennial grasses and an increase in shrub dominance with increasing biosolids. Results demonstrate the importance of considering initial soil conditions, seed mixture, and biosolids application rate when using biosolids for restoration of disturbed sagebrush steppe habitat. The long‐term effects of the biosolids treatments at this site demonstrate the need to consider restoration treatment effects over longer and more ecologically meaningful time frames.     

Growth and survival of seedlings of native plants in an impoverished and highly disturbed soil following inoculation with arbuscular mycorrhizal fungi

We investigated whether arbuscular mycorrhizas influenced growth and survival of seedlings in an extremely impoverished and highly disturbed soil. Seedlings of four plants species native to the site were either inoculated with native sporocarpic arbuscular mycorrhizal (AM) fungi or fertilised prior to transplanting, and followed over 86 weeks at the site. One treatment was also irrigated with N-rich leachate from the site. In a laboratory experiment, seedlings were fertilised with excess P for 6 weeks, and location of the P store determined. Growth and survival of AM and fertilised seedlings were similar at the site. Inoculated mycorrhizal fungi and roots appeared to extend into the surrounding soil together. P concentration in leaves of all plants was extremely low. Irrigation with leachate increased growth of seedlings. In the laboratory experiment, significantly more P was stored in roots than shoots. We suggest that successful revegetation of extremely disturbed and impoverished sites requires selection of mycorrhizal fungi and plants to suit the edaphic conditions and methods of out-planting.     

The topsoil as the major store of the propagules of vesicular-arbuscular mycorrhizal fungi in southeast Australian sandstone soils

The formation of vesicular-arbuscular mycorrhizae (VAM) in intact soil profiles from two sites in southeastern Australia were measured at two depths using a bioassay grown in intact soil cores. Intact soil cores were taken from (1) topsoil (0–15 cm) and (2) subsoil (15–30 cm) four times during 1990. Seeds of Acacialinifolia (Vent.) Willd. (Mimosaceae) were sown into the cores and plants harvested 8 and 12 weeks after sowing. For 1990, at both sites and in all seasons, VAM most readily developed in the roots of seedlings of A. linifolia grown in topsoil. Limited VAM occurred in roots grown in subsoil cores. Most colonisation of roots by VAM occurred from cores collected during spring and summer. Spore numbers were quantified for each site and depth by wet-sieving 100-g samples of air-dried soil and counting turgid spores containing oil droplets. Three types of spores were found in the soils. Few spores were extracted from all soils sampled, and for the most abundant of the spore types at least twice as many spores occurred in the topsoil than in the subsoil for all seasons examined. As most of the propagules that initiate VAM infection were observed in the topsoil, disturbances which involve the removal and storage of the top 15 cm will adversely affected these fungi.     

Mycorrhizas on nursery and field seedlings of Quercus garryana

Oak woodland regeneration and restoration requires that seedlings develop mycorrhizas, yet the need for this mutualistic association is often overlooked. In this study, we asked whether Quercus garryana seedlings in nursery beds acquire mycorrhizas without artificial inoculation or access to a mycorrhizal network of other ectomycorrhizal hosts. We also assessed the relationship between mycorrhizal infection and seedling growth in a nursery. Further, we compared the mycorrhizal assemblage of oak nursery seedlings to that of conifer seedlings in the nursery and to that of oak seedlings in nearby oak woodlands. Seedlings were excavated and the roots washed and examined microscopically. Mycorrhizas were identified by DNA sequences of the internal transcribed spacer region and by morphotype. On oak nursery seedlings, predominant mycorrhizas were species of Laccaria and Tuber with single occurrences of Entoloma and Peziza. In adjacent beds, seedlings of Pseudotsuga menziesii were mycorrhizal with Hysterangium and a different species of Laccaria; seedlings of Pinus monticola were mycorrhizal with Geneabea, Tarzetta, and Thelephora. Height of Q. garryana seedlings correlated with root biomass and mycorrhizal abundance. Total mycorrhizal abundance and abundance of Laccaria mycorrhizas significantly predicted seedling height in the nursery. Native oak seedlings from nearby Q. garryana woodlands were mycorrhizal with 13 fungal symbionts, none of which occurred on the nursery seedlings. These results demonstrate the value of mycorrhizas to the growth of oak seedlings. Although seedlings in nursery beds developed mycorrhizas without intentional inoculation, their mycorrhizas differed from and were less species rich than those on native seedlings.     

Aboveground environment type, soil nutrient content and arbuscular mycorrhizal fungi explain establishment success of Centaurea jacea on ex-arable land and in late-successional grasslands

We studied the relative importance of the aboveground and belowground environment for survival and growth of emerged seedlings of Centaurea jacea to better understand the general difficulty of establishing late-successional species at restoration sites on ex-arable land. Potted seedlings growing on soil from six late-successional grasslands and from six ex-arable (restoration) sites were reciprocally exchanged, and survival and relative growth rate of the seedlings monitored. In addition, we assessed aboveground herbivory and colonization of roots by arbuscular myccorhizal fungi of all plants, as well as nutrient availability, and microbial biomass and community composition using PLFA techniques in all twelve soils. Seedling survival was higher in restoration habitat and soil than in grassland habitat and soil, but growth did not differ between the aboveground and belowground environment types. Shoot growth rate was initially correlated with soil nutrient content, and later in the experiment with mycorrhizal colonization levels. Our results indicate that arbuscular mycorhizal fungi may be important for the successful establishment of C. jacea and that abiotic soil factors, like K availability and N:P ratio, can promote mycorrhizal colonization. Hence, the belowground environment should be considered when selecting sites for restoring species-rich grasslands.     

Ostryopsis davidiana seedlings inoculated with ectomycorrhizal fungi facilitate formation of mycorrhizae on Pinus tabulaeformis seedlings

Reforestation in China is important for reversing anthropogenic activities that degrade the environment. Pinus tabulaeformis is desired for these activities, but survival and growth of seedlings can be hampered by lack of ectomycorrhizae. When outplanted in association with Ostryopsis davidiana plants on reforestation sites, P. tabulaeformis seedlings become mycorrhizal and survival and growth are enhanced; without O. davidiana, pines often remain without mycorrhizae and performance is poorer. To better understand this relationship, we initiated an experiment using rhizoboxes that restricted root and tested the hypothesis that O. davidiana seedlings facilitated ectomycorrhizae formation on P. tabulaeformis seedlings through hyphal contact. We found that without O. davidiana seedlings, inocula of five indigenous ectomycorrhizal fungi were unable to grow and associate with P. tabulaeformis seedlings. Inocula placed alongside O. davidiana seedlings, however, resulted in enhanced growth and nutritional status of O. davidiana and P. tabulaeformis seedlings, and also altered rhizosphere pH and phosphatase activity. We speculate that these species form a common mycorrhizal network and this association enhances outplanting performance of P. tabulaeformis seedlings used for forest restoration.     

The effects of lime and phosphorus on the function of wheat roots in acid top soils and subsoils

Two wheat varieties with differing aluminium tolerance were grown in pots of acid soil. Liming did not change significantly the amounts of chemically extractable P and K, but caused improved vegetative growth, increased inflow of P and K and reduced uptake of Al. Without lime, roots had a higher content and concentration of P than shoots; liming reversed this. Without lime the sensitive variety with a shorter root length had an Al inflow ten times that of the tolerant one: tolerance involves a mechanism for exlcuding Al. The inflow of P per unit inflow of Al (mol ratio) without lime was three times greater for the tolerant variety which therefore has more P to counteract the effects of Al. The same varieties were grown in two-layer soil columns, with a low P status and a limed topsoil and acid subsoil. Liming the subsoil improved plant growth but this was still restricted by low P availability. Addition of P to the topsoil caused good growth regardless of subsoil acidity: root growth increased in both layers and P (labelled with³²P) taken up from the topsoil was translocated to roots in the subsoil. This P inactivated root Al and allowed the roots to grow and take up more P from the acid subsoil with however a reduction in inflow. The sensitive variety was affected more by the acid subsoil and low P availability, had a similar ability to translocate P to subsoil roots but could not attain the growth rate of the tolerant wheat even with P and lime.     

干旱胁迫条件下AMF促进小马鞍羊蹄甲幼苗生长的机理研究

采用温室水分控制试验,在干旱胁迫条件下,定量化研究优势丛枝菌根真菌(AMF)影响优势乡土植物小马鞍羊蹄甲(Bauhinia faberi var.microphylla)幼苗生长的机理,主要通过研究干旱胁迫条件下摩西球囊霉菌(Funneliformis mosseae)与小马鞍羊蹄甲的共生关系,阐明AMF在植物生长初期的作用。结果表明,干旱胁迫条件下,摩西球囊霉菌能够很好地侵染幼苗,侵染率高达89%—97%,并且不受水分条件影响。接种的幼苗最大光合速率、水分利用效率随着干旱胁迫程度从重度到轻度(水分从低到高)逐渐增大,相反地,叶片脯氨酸含量逐渐减小。接种显著地促进幼苗株高、叶片数、叶面积、根长、根面积等生长指标,提高幼苗各部分生物量、地上地下磷(P)含量。当含水量为60%田间持水量时,AMF促进小马鞍羊蹄甲幼苗吸收P的效果最好。接种还显著影响幼苗的生物量分配,在重度干旱胁迫时影响P分配,水分条件也显著影响幼苗的生物量分配。此外,接种和水分的交互作用对叶生物量、总生物量、生长指标以及地上部氮(N)总量影响显著。结果表明干旱胁迫条件下菌根效应显著,并在干旱条件下显著促进了小马鞍羊蹄甲幼苗的生长,这为进一步干旱河谷植被恢复提供了理论依据。     

Natural revegetation on forest topsoil and subsoil along roadsides in boreal forest

Questions: Does natural revegetation from indigenous soil improve the restoration success of roadside areas? What are the effects of topsoil, subsoil and fertilization on natural revegetation? Location: Akershus county, SE Norway (10°25′ E, 59° 44′ N). Methods: We used a recently constructed road through a boreal coniferous forest for a three year (2000–2002), fully replicated revegetation experiment (six replications). Treatments were soil type (two levels; one topsoil and one subsoil type) and fertilization (two levels; NPK and unfertilized control). Ordination methods, constrained ordination methods as well as univariate statistical methods, such as Wilcoxon's signed‐rank test and correlation analysis, were used to assess the relative importance and significance of treatments on the plant species composition. Results: There was no fertilization effect on species composition. The species composition on both soil types was stabilised by the second year. The species dominating the topsoil were more in accordance with the indigenous vegetation than was the case on the subsoil. The significant difference in species composition among blocks, persisting for the entire study period, indicated that local factors are important determinants of the outcome of revegetation. Conclusions: Unfertilized topsoil provides a revegetation result in better accordance with the indigenous vegetation than does subsoil.     

Fate and stability of dissolved organic carbon in topsoils and subsoils under beech forests

Dissolved organic carbon (DOC) from Oa horizons has been proposed to be an important contributor for subsoil organic carbon stocks. We investigated the fate of DOC by directly injecting a DOC solution from ¹³C labelled litter into three soil depths at beech forest sites. Fate of injected DOC was quantified with deep drilling soil cores down to 2 m depth, 3 and 17 months after the injection. 27 ± 26% of the injected DOC was retained after 3 months and 17 ± 22% after 17 months. Retained DOC was to 70% found in the first 10 cm below the injection depth and on average higher in the topsoil than in the subsoil. After 17 months DOC in the topsoil was largely lost (− 19%) while DOC in the subsoil did not change much (− 4.4%). Data indicated a high stabilisation of injected DOC in the subsoils with no differences between the sites. Potential mineralisation as revealed by incubation experiments however, was not different between DOC injected in topsoil or subsoils underlining the importance of environmental factors in the subsoil for DOC stabilisation compared to topsoil. We conclude that stability of DOC in subsoil is primary driven by its spatial inaccessibility for microorganisms after matrix flow while site specific properties did not significantly affect stabilisation. Instead, a more fine-textured site promotes the vertical transport of DOC due to a higher abundance of preferential flow paths.

     

Effects of Organic Enrichment of Mine Spoil on Growth and Nutrient Uptake in Oak Seedlings Inoculated with Selected Ectomycorrhizal Fungi

Abstract Poor growth of Quercus robur L. (oak) trees has been reported on mine sites where overburden and subsoil have been used in the reinstatement of surface layers. This stunting has been attributed to a lack of macronutrients and to an adverse soil environment for root growth and mycorrhizal development. Growth, mineral nutrition, and ectomycorrhizal colonization of Q. robur seedlings were studied in an experiment carried out under controlled growing conditions in which mine spoil material was enriched with a leaf litter mulch. Enrichment of mine spoil material was found to produce a significant increase in growth and foliar N concentrations of oak seedlings. Inoculation with three taxa of ectomycorrhizal fungi did not benefit seedlings when mine spoil was the only substrate, possibly due to the poor physical properties of the unamended spoil and lack of nutrients. Inoculation with two taxa, Laccaria laccata and Hebeloma crustuliniforme, isolated from 3‐year‐old trees produced a significant stimulation of growth in the organically enriched treatment, which was believed to be due to greater uptake of mineralized N. However, Cortinarius anomalus isolated from fruit bodies associated with a 15‐year‐old tree did not increase biomass. The presence of organic matter was found to result in a significant stimulation of mycorrhizal infection by both inoculum and contaminant mycobionts. Recommendations are made for improving the establishment and growth of oak seedlings on reinstated sites.     

Soil C,N, P and Its Stratification Ratio Affected by Artificial Vegetation in Subsoil,Loess Plateau China

Artificial vegetation restoration can induce variations in accumulation and distribution of soil carbon (C), nitrogen (N) and phosphorus (P). However, little is known about variations in soil C, N and P nutrient fraction stratification following artificial vegetation in Loess Plateau China. Based on the hypothesis that re-vegetated can improve soil quality and stratification ratios (SR) can be used as an indicator to evaluate soil quality. This study measured contents and storages of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and their SRs in topsoil (0–20 cm) and subsoil (20–60 cm) in three 30-year re-vegetated lands that had been converted from arable land (Robinia pseudoacacia L., Caragana Korshinskii Kom. and abandoned cropland with low interferences and few management measures) and one slope cropland (SC) as a control for three soil profiles(0–20 cm, 20–40 cm and 40–60 cm) from June 2009 to June 2013. The results showed that the contents and storages of SOC, TN and TP in re-vegetated land were significantly higher than those in the SC in both topsoil and subsoil. The storages of SOC, TN and TP in the topsoil (0–20 cm) of the re-vegetated lands increased by 16.2%-26.4%, 12.7%-28.4% and 16.5%-20.9%, respectively, and increased by smaller but significant amounts in subsoil from 2009 to 2013. The SRs for SOC, TN and TP in the re-vegetated lands were mostly >2 (either for 0–20:20–40 cm or 0–20:40–60 cm) and greater than that in the SC. The SRs showed an increasing trend with increasing restoration age. The results also showed that the land use type and soil depth were the most influential factors for the SRs and storages, and the SRs of SOC and TN had significantly positive correlations with their storages. The SRs were concluded to be a good indicator for evaluating the soil quality, which can be significantly enhanced through vegetation restoration. Moreover, vegetation restoration can significantly enhance SOC, TN and TP accumulation in both topsoil and subsoil.     

Assimilate transport in maize (Zea mays L.) seedlings at vertical low temperature gradients in the root zone

Even moderate chilling temperatures may cause important modifications in assimilate movement in maize seedlings from the shoot to the roots, but there is no information on long-distance transport of assimilates in plants subjected to vertical gradients of moderately low temperatures in the root zone. Seedlings of a chilling-tolerant (KW1074) and a chilling-sensitive inbred line (CM109) of maize were grown in a system that allowed the maintenance of temperature gradients between the topsoil (0-10 cm) and the subsoil (10-50 cm). After pregrowth at 24C until the third-leaf stage, plants were subjected to chilling-stress regimes for 6 d (17/17/17C, 17/17/12°C, 12/12/12°C, 12/12/17°C, air/topsoil/subsoil). The time taken for the assimilates to enter the phloem from the second leaf increased at low temperatures for both lines, but to a much greater extent in CM109. Although mainly influenced by air and topsoil temperature, low temperature in the subsoil also affected this trait in CM109. The speed of assimilate transport between the second leaf and the mesocotyl in KW1074 was strongly reduced by cool temperatures in the shoot and topsoil as well as by 12°C in the subsoil in CM109, because the latter line had a larger portion of its root system in the subsoil as compared to KW1074. The portion of assimilates allocated to the root decreased at low temperatures in both lines, but to a greater extent in CM109, and was controlled mostly by the subsoil temperature. After rewarming, values of all measured parameters of assimilate transport returned to near pregrowth levels within a few days.Keywords: Assimilate transport, low temperature stress, root growth, vertical soil temperature gradients, Zea mays L.      

Performance of Anisantha (Bromus) tectorum and Rumex acetosella in sandy calcareous soil

Many plants are adapted to an eroded landscape with a large proportion of virgin soil. Open and disturbed soils are today almost only restricted to agricultural fields with high loads of fertilizers. We conducted a pot experiment in order to investigate growth and nutritional constraints of one calcicole species, Anisantha (syn. Bromus) tectorum, and one calcifuge species, Rumex acetosella, in decalcified topsoil and recently exposed calcareous subsoil from a field experiment in sandy grassland. In the pot experiment we implemented one treatment where we limed topsoil with CaCO₃ to the same amount as in subsoil.The subsoil had approximately 10% CaCO₃ and both species grew less in this soil compared to the topsoil, which had less than 1% CaCO₃. Germination rate of A. tectorum was higher in subsoil than in topsoil or limed topsoil. P fertilization of the limed topsoil counteracted the negative liming effect for A. tectorum, but only partly so for R. acetosella. P fertilization of subsoil increased the shoot biomass of A. tectorum, but not of R. acetosella. P concentration in plants was not reduced when growing on subsoil or limed topsoil compared to topsoil. The results show that lime addition may reduce the P availability also to calcicole species such as A. tectorum and we found indications for that Ca toxicity may be a causing factor for the calcifuge behavior of R. acetosella. The significance of the results for conservation management practices in sandy grasslands is discussed.     

森林次生演替和土壤层次对微生物群落结构的影响

森林次生演替与生态系统结构和功能的动态变化密切相关。大多数研究主要关注植物群落以及土壤有机碳(SOC)的变化,然而土壤微生物群落如何响应森林次生演替还需要进一步探究。本研究以长白山森林次生演替序列(20、80、120、200和≥300年)和两个土壤层次为对象,采用磷脂脂肪酸微生物标志物,探究温带森林次生演替过程中地下微生物群落结构变化。森林次生演替改变了土壤微生物群落结构,主要归因于某些特定微生物类群的变化,演替前期革兰氏阴性菌和腐生真菌占主导,而在演替后期革兰氏阳性菌和丛枝菌根真菌占主导。另外,土壤有机质数量和质量差异是影响微生物群落结构和生物量的主要环境因素。森林演替前期和中期增加的SOC含量促进了微生物生物量,而演替后期增加的难分解芳香族有机组分抑制了微生物生物量合成。土壤层次间理化性质的差异导致微生物群落变化,有机质层高的SOC以及氮含量导致更多微生物生物量的合成。微生物群落在时间和空间尺度的变化及其驱动因素反映了生态系统结构和功能对环境变化的响应。