Biosolids Application and Long‐Term Noxious Weed Dominance in the Western United States

Vegetation characteristics were assessed on three sets of 10‐year‐old test plots and one set of 5‐year‐old plots that received 0, 34, 45, and 67 tons/ha (0, 15, 20, and 30 short tons/acre) of biosolids at a semiarid mine reclamation site in Utah. On average, noxious weed species such as Bromus tectorum L. (cheatgrass) provided two‐thirds of the cover on the biosolids test plots, but only one‐tenth of the cover on adjacent control plots that received no biosolids. Cheatgrass provided more than half of the total cover on every biosolids test plot. Seeded species provided about two times more cover at the control plots than at the biosolids plots. Surfaces treated with 45 tons/ha composted biosolids (one part biosolids and two parts wood chips) had a much lower percentage of noxious weed cover compared to biosolids alone. The relatively heavy initial nitrogen load associated with biosolids application may have promoted cheatgrass dominance. Although the available nitrogen eventually declines, once cheatgrass is established it may maintain its dominance indefinitely. Given the risk of weed invasion, heavy biosolids applications should be used with caution for reclamation projects in semiarid climates if perennial species establishment is desired. Consideration should instead be given to light applications (<45 tons/ha) of biosolids/wood chip compost or forgoing the use of biosolids entirely. The underapplication of nutrients may provide a slower, but ultimately more reliable, strategy for the establishment of a healthy, native perennial vegetation community.     

Vegetation establishment on chalk marl spoil: the role of nurse grass species and fertiliser application

Abstract. The Channel Tunnel workings on the UK side have yielded nearly 4 million m³ of chalk-marl spoil which now forms a 36 ha landscaped reclamation platform. To establish vegetation of amenity and conservation interest on the spoil, seed mixtures of native wild flowers and grasses were sown with Lolium perenne (perennial rye grass) as a nurse species. Potentially, L. perenne is a suitable nurse species for grassland creation on infertile substrates as it provides rapid initial cover and stability, but it is non-persistent and declines in vigour with time, allowing wild flower species sown alongside to expand their cover and spread in the longer term. On very low fertility substrates like chalk marl, an initial application of fertilizer is needed to encourage plant growth. Results are reported of a fertilizer experiment on Channel Tunnel spoil to determine appropriate levels of fertilizer for establishment of species-rich grassland vegetation. An area hydroseeded with L. perenne and wild flowers in autumn 1992 was subjected to factorial treatment of four levels each of N and P in spring 1993. The results the following summer showed significant positive effects of nitrogen and phosphorus on L. perenne biomass and a negative impact of nitrogen on densities of wild flower species, especially legumes, establishing in the L. perenne sward. In general, low fertilizer applications encouraged low productivity and maximal species richness in the vegetation. Conversely high applications encouraged high productivity and competitive exclusion of sown wild flower species. Fertilizer applications must therefore balance encouragement of the stabilising nurse grass sward, while preventing competitive exclusion of wild flowers by the nurse grass.     

Alleviation of Both Water and Nutrient Limitations is Necessary to Accelerate Ecological Restoration of Waste Rock Tips

Hard rock quarries are commonly located close to national parks and special areas of conservation and are generally regarded as visually intrusive. Consequently, restoration strategies that effectively accelerate natural plant regeneration processes are required. Slate waste tips present extreme conditions for plant establishment with multiple potential limiting factors (e.g., lack of organic matter, nutrients, and poor water retention). In this study, we investigated ecological strategies to accelerate natural regeneration at the largest slate quarry in Europe. A field experiment was conducted to assess ecosystem restoration using a contrasting set of native woody species. Treatments included amendments of waste tips with: polyacrylamide gel to increase water‐holding capacity; mineral fertilizer to increase nutrient supply; and two treatments that increased both (organic waste or boulder clay addition). Ecosystem recovery was evaluated through above‐ and below‐ground productivity (plant and microbial, respectively) and soil analyses. Neither increasing nutrient supply (with mineral fertilizer) nor water‐holding capacity (with polyacrylamide gel) was sufficient, alone, to improve plant establishment. However, both boulder clay and organic waste amendment significantly enhanced plant growth. There was a marked positive interaction in the effects on tree growth of the amendment with organic waste and boulder clay. Large interactions occurred between tree species and substrate amendments. The growth of N₂‐fixing species was strongly favored over non‐fixers where there was no addition of material increasing soil nitrogen supply, whereas the growth advantage of pioneer species over non‐pioneers was greatest with fertilizer, organic waste, or clay additions. Organic waste addition had the greatest positive impact on soil processes.     

Critical foliage concentrations of nitrogen and phosphorus as a guide to the nutrient status of araucaria underplanted to pinus

Summary The growth ofAraucaria cunninghamii Ait. planted in lateritic podzolic soils on dry sclerophyll forest sites in southern Queensland is known to be limited primarily by lack of nitrogen; phosphorus is a secondary deficiency. However, Araucaria can be grown without fertilizers on these sites by underplanting to Pinus.A factorial fertilizer trial was used to establish critical levels of foliage nitrogen and phosphorus in Araucaria. The critical level of nitrogen depends     

Nutritional status of different biosolids and their impact on various growth parameters of wheat (Triticum aestivum L.)

Biosolids can be effectively recycled and applied as soil amendments for agricultural crops because they contain several important micro and macronutrients including nitrogen, phosphorus, potassium, manganese. In the current study, we evaluated the effectiveness of seven biosoilds on different growth parameters of wheat crop. The biosolids used were lime stabilized, composted, liquid mesophilic anaerobically digested (liquid MAD), thermally dried mesophilic anaerobically digested (thermally dried MAD), thermally hydrolyzed mesophilic anaerobically digested (thermally hydrolysed MAD), dewatered mesophilic anaerobically digested (dewatered MAD) and thermally dried raw biosolids. We also analysed biosolids for their nutrient contents before application. The results revealed that different types of biosolids differed in nitrogen and phosphorous contents with highest contents observed in dewatered (5.70% nitrogen, 2.32% phosphorous) and liquid biosolids (2.35% phosphorous). The plant height, plant diameter and dry weight yield of wheat was increased with the increase in concentrations of biosolids. Liquid MAD resulted in maximum plant height of 120.35 ± 3.23, 133.2 ± 3.67 and 147.25 ± 3.11 at 3.33, 6.66 and 9.99 tons/ha concentration. The highest plant diameter was recorded (1.05–1.45 cm) where mineral nitrogen was applied. The study will be helpful in replacing the synthetic fertilizer with biosolids to fulfil the nutritional requirements of agricultural crops.     

Arbuscular Mycorrhizal Fungi (AMF) and Biosolids Enhance the Growth of a Native Australian Grass on Sulphidic Gold Mine Tailings

We tested the effect of the addition of biosolids combined with a native mycorrhizal inoculum (Arbuscular Mycorrhizal Fungi [AMF]) on growth of a native Australian grass, and on trace element stabilization of sulphidic gold mine tailings. A glasshouse trial was established on four substrates: tailings (T); tailings with a layer of 5 cm topsoil (TS); tailings amended with 100 dry t ha^?1 biosolids (LB), and tailings amended with 500 dry t ha^?1 biosolids (HB). Pots of 1.2 L of capacity were established; some were inoculated with a mixture of Glomus sp. (WUM51–9227), Scutelospora aurigloba (WUM51–53), and Acaulospora levis (WUM46) culture mix, and others were uninoculated controls. Seeds of the native Australian grass, Bothriochloa macra were sown in the pots. Root infection, plant biomass production, nutrients and trace element concentrations in shoots were investigated. Addition of biosolids significantly increased AMF infection of roots compared to unamended substrates. No clear qualitative differences in colonization were detected. Addition of biosolids and AMF together clearly improved the establishment and growth of the native grass. Similar trends in nutritional status were shown for biosolids and inoculation with AMF treatments. Mycorrhizal inoculation increased plant biomass production and the effectiveness of nutrient uptake. The combined use of biosolids and mycorrhizal inoculation could be a reliable method for phytostabilization purposes in polluted substrates.     

绿肥种植配施减量氮肥对柑橘园杂草群落组成及多样性的影响

以湖北当阳柑橘园杂草群落为对象,研究绿肥种植(自然生草和间种光叶苕子)下配施减量氮肥处理(当地推荐施氮肥量的0%、70%、85%、100%)对橘园杂草群落组成和多样性的影响,并运用Pearson相关分析和典范对应分析探究土壤因子对不同处理下杂草多样性和物种组成的影响。结果显示:(1)经样方调查,试验区共记录杂草植物21科29属30种,以禾本科和菊科为主,稗(Echinochloa crusgalli(L.)Beauv.)、酢浆草(Oxalis corniculata L.)、野老鹳草(Geranium carolinianum L.)等是所有处理中的共有种,自然生草下以匙叶鼠麴草(Gnaphalium pensylvanicum Willd.)和稗为优势种,间种光叶苕子(Vicia villosa Roth.var.glabrescens Koch.)下以酢浆草为优势种;(2)不同氮肥施入量下柑橘园草本物种Margalef指数、Patrick指数、Shannon-Wiener多样性指数和Pielou均匀度指数均无显著差异;相同施肥量下,间种光叶苕子能显著降低柑橘园杂草群落的物种多样性指数;(3)速效磷是显著影响柑橘园草本植物多样性指数的土壤因子;(4)不同处理下影响杂草物种分布的主要土壤因子是速效磷、pH值、含水率和温度。本研究认为无论减施氮肥与否,间种光叶苕子比自然生草更能显著降低杂草群落的物种多样性,从而避免恶性杂草与果树争肥。     

Soil type affects seedling shade response at low light for two Inga species from Costa Rica

Distributions of many humid tropical tree species are associated with specific soil types. This specificity most likely results from processes at the seedling stage, but light rather than nutrient levels is generally considered the dominant limitation for seedling growth in the tropical forest understory. If nutrients are limiting and allocation to belowground resources differs, seedling growth responses to shade should also differ. Here we tested the effects of soil type and light environment on the seedling growth of two canopy tree species in the genus Inga with different soil-type and light-environment affinities as adults. Inga alba is a shade-tolerant soil generalist and I. oestediana is a light-demanding soil specialist. We used four native soils and three light levels (1 and 5% of full sun in shade houses and the forest understory). All growth variables were greatest in 5% full sun, with highest growth rates for the light-demanding soil-type specialist. Soil type significantly affected growth parameters, even at the lower light levels. The specialist grew best on the soils with the most soil phosphorus where adult trees typically occur. Leaf tissue nitrogen:phosphorus ratios suggest increased phosphorus limitation in the low phosphorus soils and with increased light level. Light and soil interacted to significantly affect seedling biomass allocation, growth, and net assimilation rates, indicating that the seedling shade responses were affected by soil type. Seedlings growing on high nutrient soil allocated less to roots and more to photosynthetic tissue. Adult distributions of these two Inga species may be a result of the different growth rates of seedlings in response to the interactive effects of light and soil.     

N limitation increases along a temperate forest succession: evidences from leaf stoichiometry and nutrient resorption

温带森林演替加剧了氮限制：来自叶片化学计量和养分重吸收的证据 森林生产力和碳汇功能在很大程度上取决于土壤氮和磷的有效性。然而,迄今为止,养分限制随森林演替的时间变化仍存在争议。叶片化学计量和养分重吸收是预测植物生长养分限制的重要指标。基于此,本研究测定了温带森林4个演替阶段所有木本植物叶片和凋落叶中氮和磷的含量,并分析了演替过程中非生物因子和生物因子如何影响叶片化学计量和养分重吸收。研究结果表明,在个体尺度上,叶片氮磷含量在演替末期显著增加,而叶片氮磷比无显著变化;氮的重吸收效率随演替显著增加,然而磷的重吸收效率先增加后减少;氮重吸收效率与磷重吸收效率的比值仅在演替末期显著增加。此外,植物氮素循环对土壤养分的响应比磷素循环更弱。在群落尺度上,叶片氮磷含量随森林演替呈现先降低后升高的趋势,主要受香农-维纳多样性指数和物种丰富度的影响;叶片氮磷比随演替而显著变化,主要由胸径的群落加权平均值决定;氮的重吸收效率增加,主要受物种丰富度和胸径的影响,而磷的重吸收效率相对稳定。因此,氮重吸收效率与磷重吸收效率的比值显著增加,表明随着温带森林演替,氮限制加剧。这些结果可能反映了较高生物多样性群落中物种间对有限资源的激烈竞争,强调了生物因子在驱动森林生态系统养分循环中的重要性,为中国温带和北方森林可持续经营的施肥管理提供了参考。     

Limiting nutrients for periphyton growth in sub-alpine, forest, agricultural and urban streams

1. Nutrient-diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub-alpine, forested, agricultural and urban catchments in eastern Victoria, Australia. 2. Chlorophyll a density was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub-alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density. 3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance of Stigeodanium spp. was sometimes increased on substrata containing the limiting nutrient. 4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream-water nitrogen to phosphorus ratios in many instances.     

Rapid nutrient cycling in leaf litter from invasive plants in Hawai’i

Physiological traits that contribute to the establishment and spread of invasive plant species could also have impacts on ecosystem processes. The traits prevalent in many invasive plants, such as high specific leaf areas, rapid growth rates, and elevated leaf nutrient concentrations, improve litter quality and should increase rates of decomposition and nutrient cycling. To test for these ecosystem impacts, we measured initial leaf litter properties, decomposition rates, and nutrient dynamics in 11 understory plants from the Hawaiian islands in control and nitrogen + phosphorus fertilized plots. These included five common native species, four of which were ferns, and six aggressive invasive species, including five angiosperms and one fern. We found a 50-fold variation in leaf litter decay rates, with natives decaying at rates of 0.2–2.3 year^–1 and invaders at 1.4–9.3 year^–1. This difference was driven by very low decomposition rates in native fern litter. Fertilization significantly increased the decay rates of leaf litter from two native and two invasive species. Most invasive litter types lost nitrogen and phosphorus more rapidly and in larger quantities than comparable native litter types. All litter types except three native ferns lost nitrogen after 100 days of decomposition, and all litter types except the most recalcitrant native ferns lost >50% of initial phosphorus by the end of the experiment (204–735 days). If invasive understory plants displace native species, nutrient cycling rates could increase dramatically due to rapid decomposition and nutrient release from invasive litter. Such changes are likely to cause a positive feedback to invasion in Hawaii because many invasive plants thrive on nutrient-rich soils.     

磷素营养对降香黄檀幼苗生长及叶片养分状况的影响

设置0、15、30、60、100、150 mg P·株^-1等6个磷素处理开展降香黄檀幼苗盆栽试验,测定各处理幼苗的生长、生物量、叶片养分含量等指标,采用临界浓度法确定降香黄檀幼苗的适宜施磷量,从而探讨不同磷素水平对降香黄檀幼苗生长和叶片养分状况的影响,揭示其磷素需求规律以及适宜的磷供应范围。结果显示磷肥能促进幼苗生长和生物量的积累,而且随施磷量的增加,各指标呈现先升高后降低的趋势,最高值出现在60 mg P·株^-1处理,其苗高、地径、叶面积、生物量分别为对照的3.07、2.35、49.21和24.25倍。施磷显著降低幼苗叶片氮、钾含量,提高磷、镁含量,其中30、60、100 mg P·株^-13个处理间叶片磷含量差异不显著,约为对照的1.65倍。根据幼苗生物量与叶片磷含量、氮钾含量比、磷钾含量比的抛物线关系,确定叶片最适磷含量范围为1.35~2.32 g·kg^-1,由此推断降香黄檀幼苗最适宜的施磷量为60~100 mg P·株^-1。     

Effects of Tree Guards and Weed Mats on the Establishment of Native Tree Seedlings: Implications for Forest Restoration in Hong Kong, China

The effects of tree guards and weed mats on establishment and growth of native tree seedlings, Thick‐leaved oak (Cyclobalanopsis edithiae (Skan) Schott., Fagaceae), planted in an exposed hillside grassland in Hong Kong, were investigated. The natural regeneration of C. edithiae is poor due to a lack of seed dispersal agents and high seed predation, and therefore, this species is often targeted for forest restoration. The experiment lasted for 3.5 years during which the height, basal diameter, and crown diameter of individual seedlings were measured and survivorship recorded. The use of weed mats alone did not have a significant effect, but a combination of tree guards and weed mats led to a significant improvement in establishment, survivorship, and growth of the seedlings during the experimental period. Initially, the guards promoted rapid height growth of the seedlings, although lateral growth and secondary stem thickening were compromised. After the seedlings grew over the tree guards, the basal diameter and crown diameter increased at a notably faster rate. The combined effect of the tree guard and weed mat on the seedling growth pattern was found to be beneficial and contributed to the high survivorship of the seedlings. Comparing the survivorship data and the costs of various treatments, the use of tree guards in combination with the weed mats was demonstrated to be more cost‐effective than planting the seedlings without tree guards or weed mats. The potential for applying the technique in afforestation programs with native tree species for forest restoration in Hong Kong and other tropical regions is discussed.     

An Evaluation of Reclamation Success on Idaho's Phosphate Mines

To evaluate reclamation success on the Wooley Valley phosphate mine in southeastern Idaho, we compared vegetation structure and soil physical, chemical, and elemental properties of several different reclamation treatments with those of a nearby reference area (a native Artemisia tridentata vaseyana/Festuca idahoensis association) after 14 years. Vegetation data had been collected four years after reclamation, and we were able to compare differences in biomass and species composition between dates on the reclaimed area. Four years after reclamation there were no differences in total biomass between topsoil or spoil or between seed only, seed + mulch, or control treatments on the different soil types. Most treatments were dominated by seeded perennial grasses. Fourteen years after reclamation there were no differences in biomass or cover between spoil and topsoil plots, but on spoil plots the seeded and mulched treatment had higher total biomass and vegetation cover than on control or seed-only treatments. The seeded perennial legume Medicago sativa was codominant with the seeded forage grasses on all of the treatments. High initial fertilization rates probably facilitated the early establishment and dominance of the forage grasses; once nutrient levels, especially nitrogen, began to decline, the legume increased in abundance. Similarity between the reclaimed area and the reference or native area was low. Reclaimed treatments had higher biomass but lower species richness. The topsoil and spoil plots had similar soil texture, bulk density, pH, cation exchange capacity, electrical conductivity, and phosphorus. Differences in organic carbon, total nitrogen, carbon: nitrogen ratios, and available moisture were related more to treatments than to soil type. High biomass and, thus, litter input on the seed + mulch treatment on spoil plots resulted in both higher OC and TN than any on other soil/treatment combination. The reclaimed area had lower OC, TN, and available moisture than did the reference area on all but seed + mulch spoil plots. Bulk density was higher on reclaimed plots. The long-term differences observed between the reclaimed and reference areas parallel those obtained for other western reclamation sites. Although successional trajectories depend on the attribute measured, similarity to native reference areas depends on the initial reclamation methods. We discuss reclamation methods that would increase the structural and functional similarity of reclaimed and reference areas on the Wooley Valley phosphate mine.     

Impact of Fertilizing Pattern on the Biodiversity of a Weed Community and Wheat Growth

Weeding and fertilization are important farming practices. Integrated weed management should protect or improve the biodiversity of farmland weed communities for a better ecological environment with not only increased crop yield, but also reduced use of herbicides. This study hypothesized that appropriate fertilization would benefit both crop growth and the biodiversity of farmland weed communities. To study the effects of different fertilizing patterns on the biodiversity of a farmland weed community and their adaptive mechanisms, indices of species diversity and responses of weed species and wheat were investigated in a 17-year field trial with a winter wheat-soybean rotation. This long term field trial includes six fertilizing treatments with different N, P and K application rates. The results indicated that wheat and the four prevalent weed species (Galium aparine, Vicia sativa, Veronica persica and Geranium carolinianum) showed different responses to fertilizer treatment in terms of density, plant height, shoot biomass, and nutrient accumulations. Each individual weed population exhibited its own adaptive mechanisms, such as increased internode length for growth advantages and increased light interception. The PK treatment had higher density, shoot biomass, Shannon-Wiener and Pielou Indices of weed community than N plus P fertilizer treatments. The N1/2PK treatment showed the same weed species number as the PK treatment. It also showed higher Shannon-Wiener and Pielou Indices of the weed community, although it had a lower wheat yield than the NPK treatment. The negative effects of the N1/2PK treatment on wheat yield could be balanced by the simultaneous positive effects on weed communities, which are intermediate in terms of the effects on wheat and weeds.     

Nitrogen limitation of phytoplankton in a Spanish karst lake with a deep chlorophyll maximum: a nutrient enrichment bioassay approach

An in vitro nutrient addition bioassay was performed to testthe relative inorganic nitrogen (N) and phosphorus (P) limitationof phytoplankton in a Spanish karst lake (El Tejo) during thelast part of the stratification period, when nutrient limitationis most pronounced. Nutrient deficiency was tested in samplesfrom three different layers of the lake: the epilimnion, metalimnionand oxic hypolimnion. Nitrogen additions, either without orcombined with P, increased phytoplankton growth in all threestrata, compared with controls or P treatments. This showedthat N was the nutrient limiting phytoplankton growth in latesummer–early fall. Since both hypolimnetic diffusion andgroundwater fluxes of N-rich waters into the lake are much reducedduring summer, N becomes the limiting nutrient as stratificationadvances. We suggest that in this Mediterranean area with lowatmospheric deposition of anthropogenic N and in lakes relativelyfree of surface run-off, nutrient supply by atmospheric depositionmight be a key factor in controlling nutrient deficiency forphytoplankton growth.     

Post‐fire vegetation dynamics in nutrient‐enriched and non‐enriched sclerophyll woodland

Abstract Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low‐nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run‐off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: ‘Are there differences in post‐fire resprouting and germination of native and exotic species in nutrient‐enriched communities, compared with communities not disturbed by nutrient enrichment?’ We found that in non‐enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient‐enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient‐enriched. In nutrient‐enriched areas after fire, the diversity of native species was lower than in the non‐enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non‐enriched areas. We suggest that although fire can be a useful tool for short‐term removal of exotic plant biomass from nutrient‐enriched areas, it does not promote establishment of native species that were not already present.     

Phosphorus limitation of forest leaf area and net primary production on a highly weathered soil

We tested the hypothesis that P was the nutrient limiting net primary production of a nativeMetrosideros polymorpha forest on a highly weathered montane tropical soil in Hawaii. A factorial experiment used all combinations of three fertilizer treatments: nitrogen (N), phosphorus (P) and a mix of other essential nutrients (OE), consisting primarily of mineral derived cations and excluding N and P. P addition, but not N or OE, increased leaf area index within 12 months, foliar P concentration measured at 18 months, and stem diameter increment within 18 months. Stem growth at 18 months was even greater when trees fertilized with P also received the OE treatment. N and P additions increased leaf litterfall and N and P in combination further increased litterfall. The sequence of responses suggests that increased available P promoted an increase in photosynthetic area which led to increased wood production. P was the essential element most limiting to primary production on old volcanic soil in contrast to the N limitation found on young volcanic soils.     

Extraradical mycelium of arbuscular mycorrhizal fungi radiating from large plants depresses the growth of nearby seedlings in a nutrient deficient substrate

The effect of arbuscular mycorrhiza (AM) on the interaction of large plants and seedlings in an early succession situation was investigated in a greenhouse experiment using compartmented rhizoboxes. Tripleurospermum inodorum, a highly mycorrhiza-responsive early coloniser of spoil banks, was cultivated either non-mycorrhizal or inoculated with AM fungi in the central compartment of the rhizoboxes. After two months, seedlings of T. inodorum or Sisymbrium loeselii, a non-host species colonising spoil banks simultaneously with T. inodorum, were planted in lateral compartments, which were colonised by the extraradical mycelium (ERM) of the pre-cultivated T. inodorum in the inoculated treatments. The experiment comprised the comparison of two AM fungal isolates and two substrates: spoil bank soil and a mixture of this soil with sand. As expected based on the low nutrient levels in the substrates, the pre-cultivated T. inodorum plants responded positively to mycorrhiza, the response being more pronounced in phosphorus uptake than in nitrogen uptake and growth. In contrast, the growth of the seedlings, both the host and the non-host species, was inhibited in the mycorrhizal treatments. Based on the phosphorus and nitrogen concentrations in the biomass of the experimental plants, this growth inhibition was attributed to nitrogen depletion in the lateral compartments by the ERM radiating from the central compartment. The results point to an important aspect of mycorrhizal effects on the coexistence of large plants and seedlings in nutrient deficient substrates.     

Seedling growth of four fire-following Mediterranean plant species deprived of single mineral nutrients

1. Anthyllis vulneraria, Cistus creticus, Hippocrepis unisiliquosa and Pinus brutia are frequent post-fire colonizers whose seedlings are subjected to the mineral conditions imposed by ash in the early stages of growth. We test the hypothesis that the effective internal supply of mineral elements in the seeds of these species may complement the external availability of specific nutrients.
2. Newly germinated seedlings were grown in nutrient solutions, each deficient in one of the following elements: nitrogen, phosphorus or potassium. Control treatments consisted of full nutrients and distilled water. Seedling growth was monitored over 12weeks. The final dry masses of the seedlings were taken as a measure of the availability of each element from the seeds' own stored reserves.
3. For the two legume species nitrogen was the most limiting element followed by phosphorus. Potassium deficiency had no effect on the final legume dry biomass. For Cistus, the order was nitrogen followed by potassium, while phosphorus deprivation had no effect on growth during the 12weeks of the experiment. Deprivation of single minerals had no significant effect on seedling growth of Pinus over the same period. The two legumes and Cistus when denied nitrogen had relatively greater relative root ratios than control plants.
4. The relative seedling requirements of each species for early external supplies of the various nutrients for establishment in the field are discussed with reference to the adaptation of the four species to post-fire regeneration.