Plant-based mulch has been proposed as a sustainable way of maintaining soil fertility. However, the role of mulch diversity, quality, and size in decomposition dynamics, and their effect on crop ...yield, has not been fully explored. We investigated how mulch quality, proxied by the constituent plant species diversity, and residue size drive mulch decomposition, nutrient release, crop nutrition, and yield. A rhizotron experiment was set up with barley as a model crop, with the addition of mulch of two particle sizes (1.5 and 30 cm) and four different plant residue mixes of differing biodiversity (17, 12, 6, and 1 species) in a fully factorial design. Soil nutrient dynamics were measured at advanced decomposition stages, together with residue quality, arbuscular mycorrhizal fungal (AMF) root colonisation, and crop yield. Residue mass loss was significantly affected by its chemical composition. Initial NDF content was more restricted factor in C and N mineralisation than C:N or lignin. Long residues retained significantly higher C and N content, than short residues. Crop yield was not affected by residue type or size. Residue size significantly affected barley growth rate, influencing seed protein content. Soil available K was significantly increased by residues with a higher initial C:N ratio. Short residues resulted in higher soil Zn. Residues of higher diversity resulted inhigher AMF root colonisationof the barley plants. Generally, long residue mulches maintain higher fertilisation capacity at advanced stage of decomposition than short ones, without a deleterious effect on crop yield. Further investigation should evaluate the effect of continuous application of long residue mulches on soil fertility and microbial symbiosis.
A decline in soil biodiversity is generally considered to be the reduction of forms of life living in soils, both in terms of quantity and variety. Where soil biodiversity decline occurs, it can ...significantly affect the soils' ability to function, respond to perturbations and recover from a disturbance. Several soil threats have been identified as having negative effects on soil biodiversity, including human intensive exploitation, land-use change and soil organic matter decline. In this review we consider what we mean by soil biodiversity, and why it is important to monitor. After a thorough review of the literature identified on a Web of Science search concerning threats to soil biodiversity (topic search: threat* "soil biodiversity"), we compiled a table of biodiversity threats considered in each paper including climate change, land use change, intensive human exploitation, decline in soil health or plastic; followed by detailed listings of threats studied. This we compared to a previously published expert assessment of threats to soil biodiversity. In addition, we identified emerging threats, particularly microplastics, in the 10 years following these knowledge based rankings. We found that many soil biodiversity studies do not focus on biodiversity sensu stricto, rather these studies examined either changes in abundance and/or diversity of individual groups of soil biota, instead of soil biodiversity as a whole, encompassing all levels of the soil food web. This highlights the complexity of soil biodiversity which is often impractical to assess in all but the largest studies. Published global scientific activity was only partially related to the threats identified by the expert panel assessment. The number of threats and the priority given to the threats (by number of publications) were quite different, indicating a disparity between research actions versus perceived threats. The lack of research effort in key areas of high priority in the threats to soil biodiversity are a concerning finding and requires some consideration and debate in the research community.
In Sabah, Malaysia, ultramafic rock outcrops are widespread (totalling 3500km2, one of the main outcrops in the tropical zone), and predominantly of the peridotite type. However, strongly ...serpentinised peridotite is also locally common, particularly along fault lines in the Mt. Kinabalu area. This study aimed to determine the extent of chemical variation in ultramafic soils in relation to the degree of serpentinisation and the weathering intensity, and consequent potential ecological implications linked to resulting soil chemical fertility. It was hypothesized that young soils and soils derived from bedrock with a significant degree of serpentinisation strongly differ from typical Geric Ferralsols and result in soil chemistries with more adverse properties to plant life (e.g. low availability of the essential nutrients N, P, K and Ca and high concentrations of potentially phytotoxic Mg and Ni). Ultramafic soil diversity linked to the age of the soil or the degree of serpentinisation would thus be a main factor of plant diversity and distribution. The diverse topography of Kinabalu Park (ultramafic soils present between 400 and 2950masl) has given rise to high pedodiversity with the broad overall ultramafic soil types being: (i) deep laterite soils (Geric Ferralsols); (ii) moderately deep montane soils (Dystric Cambisols) with mor humus; (iii) shallow skeletal soils at high altitude (Eutric Cambisols Hypermagnesic); and (iv) bare serpentinite soils (Hypereutric Leptosols Hypermagnesic) at low altitude (200–700masl). Leptosols on serpentinite and Eutric Cambisols have the most extreme chemical properties in the whole Kinabalu Park area both with very high Mg:Ca molar quotients, with either high available Ni (Cambisols) or high pH (Leptosols). These soils host specific and adapted vegetation (high level of endemism) that tolerates geochemical peculiarities, including Ni hyperaccumulators. Geric Ferralsols present far less chemical constraints than Hypermagnesian Cambisols soils to the vegetation and host a tall and very diverse rainforest, not so different than that on non-ultramafic soils. It therefore appears that altitude, soil age and degree of bedrock serpentinisation are the main determining factors of soil properties: the qualifier “ultramafic” alone is not sufficient to define soil geochemical and ecological conditions in the Kinabalu Park area, probably more than in any other ultramafic region in the world.
•The diverse topography of Kinabalu Park hosts high ultramafic pedodiversity.•Soil age and serpentinised bedrock are important determinants for soil properties.•Leptosols on serpentinite and montane Eutric Cambisols have extreme chemistry.•Despite extreme geochemical properties, these soils support high plant diversity.•Ultramafic Ferralsols have very tall tropical forest comparable to other soils.
Poplars have been identified as heavy metals hyperaccumulators and can be used for phytoremediation. We have previously established that their symbiosis with arbuscular mycorrhizal fungi (AMF) may ...alter their uptake, tolerance and distribution to excess concentrations of heavy metals in soils. In this study we hypothesised that mycorrhizal symbiosis improves the tolerance of poplars to lethal copper (Cu) concentrations, but this influence may vary among different AMF species. We conducted an experiment in a growth chamber with three Cu application levels of control (0 mg kg−1), threshold-lethal (729 mg kg−1) and supra-lethal (6561 mg kg−1), and three mycorrhizal treatments (non-mycorrhizal, Rhizophagus irregularis, and Paraglomus laccatum) in a completely randomized design with six replications. The poplars did not grow after application of 729 mg Cu kg−1 substrate, and mycorrhizal symbiosis did not help plants to tolerate this level of Cu. This can be explained by the toxicity suffered by mycorrhizal fungi. Translocation of Cu from roots to shoots increased when plants were colonised with R. irregularis and P. laccatum under threshold-lethal and supra-lethal applications of Cu, respectively. This result shows that mycorrhizal mediation of Cu partitioning in poplars depends on the fungal species and substrate Cu concentration. Multi-model inference analysis within each mycorrhizal treatment showed that in plants colonised with R. irregularis, a higher level of mycorrhizal colonisation may prevent Cu transfer to the shoots. We did not observe this effect in P. laccatum plants probably due to the relatively low colonisation rate (14%). Nutrient concentrations in roots and shoots were impacted by applied substrate Cu levels, but not by mycorrhizas. Magnesium (Mg), potassium (K), and manganese (Mn) concentrations in roots reduced with enhancing applied substrate Cu due to their similar ionic radii with Cu and having common transport mechanism. Synergistic effect on shoot concentration between applied substrate Cu levels and Mg, K, calcium, iron (Fe), and zinc was observed. Root Cu concentration was inversely related with root K and Mn concentrations, and shoot Cu concentration had a positive correlation with shoot Fe and K concentrations. Overall, mycorrhizal symbiosis has the potential to enhance plant health and their resilience to Cu toxicity in contamination events. However, it is important to note that the effectiveness of this symbiotic relationship varies among different mycorrhizal species and is influenced by the level of contamination.
•Poplars did not grow at 729 mg Cu kg−1 substrate.•Mycorrhizal symbiosis did not help plants to tolerate very toxic Cu levels.•Mycorrhizal mediation of Cu partitioning in poplars depends on the fungal species.•Nutrient partitioning in poplars was impacted by Cu levels, but not by mycorrhizas.
The global decade of restoration brings into sharp focus the need to rehabilitate lands damaged by mining, to provide safe, stable, and productive landscapes. For the majority of mines, the required ...final land use is some form of natural, semi-natural or managed ecosystem, such as agriculture, aquaculture or forestry. Mining activities lead to new highly altered landscapes that require rehabilitation. These comprise various on-land stores of waste material and mined land itself. The repair of damaged ecosystems is described by many terms including restoration, rehabilitation, revegetation, ecological restoration, and reclamation. These terms overlap in meaning, have regional biases, and all fall short of what is really required: ecosystem reconstruction. This requires a highly multidisciplinary approach drawing on many disciplines including geotechnical engineering, social science, soil science, law, hydrology, botany, geology, pollination biology, financial planning, alongside ecology. Ideally, mine rehabilitation should be progressive, start early in the life of the mine, and employ a strict regime of characterising and tracking waste materials for use in creating safe and stable post-mining landscapes. These actions will limit risks and optimise outcomes, especially when waste materials contain toxic metals or have high levels of acidity, alkalinity or salinity. Some mine sites are appropriate for the restoration of native ecosystems and biodiversity that existed pre-mining, but many, including landscape features created from waste materials, are not. Criteria for successful land rehabilitation are complex, multivariate, and highly contingent on the agreed final land use. Future advances in mine rehabilitation include the use of geomorphic landscape design and emerging thinking on cradle-to-cradle mining. This primer will discuss the complex factors that need to be considered in ecosystem reconstruction after mining and outlines approaches for optimising land rehabilitation outcomes.
Mark Tibbett discusses the complex factors that need to be considered in ecosystem reconstruction after mining and outlines approaches for optimising land rehabilitation outcomes.
•Under excess, P. trichocarpa restricts Cd transport to shoots but not Zn.•Expression patterns of HMA4 and ZIP1 suggest they transport both Cd and Zn.•Arbuscular mycorrhizal fungus modulates Cd/Zn ...accumulation and distribution in poplar.•Symbiosis up-regulates metallothionein PtMT2b in roots regardless of contamination.•PtMT2b greatly increases Cd tolerance in transgenic yeast under Cd stress.
We investigated how arbuscular mycorrhizal symbiosis can alter trace element uptake, distribution and toxicity in plants by examining some of the molecular mechanisms behind Populus trichocarpa tolerance to Cd and Zn, and the effects of AMF in metal homeostasis. Plants were grown under Cd and Zn contamination, with and without Rhizophagus irregularis inoculation. We determined organ metal concentrations, the expression of genes involved in trace element homeostasis, and the function of metallothionein PtMT2b by heterologous expression in yeast. P. trichocarpa was highly tolerant to both elements, with AMF increasing Zn accumulation. AMF altered the partitioning of Cd, but maintained the same patterns for Zn, indicating that despite being geochemically similar and carried mostly by the same transporters, the nutrient metal (Zn) is handled differently from the non-essential metal (Cd). High Zn and Cd down-regulated PtHMA4 (roots), and up-regulated PtZIP1 (leaves), suggesting their involvement in transporting both metals in poplar. PtMT2b was highly up-regulated in mycorrhizal roots and enhanced Cd tolerance in transformed yeast. R. irregularis reduced Cd transfer to poplar shoots, but did not affect Zn partitioning. The gene expression patterns observed offer a glimpse into the mechanisms behind trace element uptake/translocation dynamic in poplars, influenced by AMF symbiosis.
Predominant frameworks for understanding plant ecology have an aboveground bias that neglects soil micro-organisms. This is inconsistent with recent work illustrating the importance of soil microbes ...in terrestrial ecology. Microbial effects have been incorporated into plant community dynamics using ideas of niche modification and plant–soil community feedbacks. Here, we expand and integrate qualitative conceptual models of plant niche and feedback to explore implications of microbial interactions for understanding plant community ecology. At the same time we review the empirical evidence for these processes. We also consider common mycorrhizal networks, and propose that these are best interpreted within the feedback framework. Finally, we apply our integrated model of niche and feedback to understanding plant coexistence, monodominance and invasion ecology.
This book explores the interface between geology and botany, and mining and conservation. Many areas of unusual geology that contain ore-bearing bodies also support unique ecological communities of ...plants and animals. Increasing demand to exploit rich mineral deposits can lead to a conflict between mining and conservation interests in such landscapes. This book brings together experts in the field of mining and conservation to grapple with this pressing issue and to work toward a positive outcome for all. Chapters are grouped into four themes: Introduction, Concepts and Challenges; Endemism in Ironstone Geosystems; Progress in Bauxite Mining; and Ways Forward.
Root-fungal symbioses such as mycorrhizas and endophytes are key components of terrestrial ecosystems. Diverse in trophy habits (obligate, facultative or hemi-biotrophs) and symbiotic relations (from ...mutualism to parasitism), these associations also show great variability in their root colonization and nutritional strategies. Specialized interface structures such as arbuscules and Hartig nets are formed by certain associations while others are restricted to non-specialized intercellular or intracellular hyphae in roots. In either case, there are documented examples of active nutrient exchange, reinforcing the fact that specialized structures used to define specific mycorrhizal associations are not essential for reciprocal exchange of nutrients and plant growth promotion. In feremycorrhiza (with
and eucalypts), the fungal partner markedly enhances plant growth and nutrient acquisition without colonizing roots, emphasizing that a conventional focus on structural form of associations may have resulted in important functional components of rhizospheres being overlooked. In support of this viewpoint, mycobiome studies using the state-of-the-art DNA sequencing technologies have unearthed much more complexity in root-fungal relationships than those discovered using the traditional morphology-based approaches. In this review, we explore the existing literature and most recent findings surrounding structure, functioning, and ecology of root-fungal symbiosis, which highlight the fact that plant fitness can be altered by taxonomically/ecologically diverse fungal symbionts regardless of root colonization and interface specialization. Furthermore, transition from saprotrophy to biotrophy seems to be a common event that occurs in diverse fungal lineages (consisting of root endophytes, soil saprotrophs, wood decayers etc.), and which may be accompanied by development of specialized interface structures and/or mycorrhiza-like effects on plant growth and nutrition.
Aim: Most vascular plants on Earth form mycorrhizae, a symbiotic relationship between plants and fungi. Despite the broad recognition of the importance of mycorrhizae for global carbon and nutrient ...cycling, we do not know how soil and climate variables relate to the intensity of colonization of plant roots by mycorrhizal fungi. Here we quantify the global patterns of these relationships. Location: Global. Methods: Data on plant root colonization intensities by the two dominant types of mycorrhizal fungi world-wide, arbuscular (4887 plant species in 233 sites) and ectomycorrhizal fungi (125 plant species in 92 sites), were compiled from published studies. Data for climatic and soil factors were extracted from global datasets. For a given mycorrhizal type, we calculated at each site the mean root colonization intensity by mycorrhizal fungi across all potentially mycorrhizal plant species found at the site, and subjected these data to generalized additive model regression analysis with environmental factors as predictor variables. Results: We show for the first time that at the global scale the intensity of plant root colonization by arbuscular mycorrhizal fungi strongly relates to warm-season temperature, frost periods and soil carbon-to-nitrogen ratio, and is highest at sites featuring continental climates with mild summers and a high availability of soil nitrogen. In contrast, the intensity of ectomycorrhizal infection in plant roots is related to soil acidity, soil carbon-to-nitrogen ratio and seasonality of precipitation, and is highest at sites with acidic soils and relatively constant precipitation levels. Main conclusions: We provide the first quantitative global maps of intensity of mycorrhizal colonization based on environmental drivers, and suggest that environmental changes will affect distinct types of mycorrhizae differently. Future analyses of the potential effects of environmental change on global carbon and nutrient cycling via mycorrhizal pathways will need to take into account the relationships discovered in this study.
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