Carbonservation with Demonstrated Biodiversity and Carbon Gains: Carbon Can Pay But Biodiversity Must Lead.

Land use has a critical role to play in both climate change mitigation and biodiversity conservation, and increasingly there have been calls to integrate policies for concurrently meeting Paris Agreement commitments and the UN decade on ecosystem restoration 2021-2030. Currently however, investment activities have been dominated by climate change mitigation activities, including through the development of carbon markets (both voluntary and compliance markets). Whilst climate change mitigation is to be welcomed, the prioritization of carbon in avoided deforestation and reforestation can lead to suboptimal or negative outcomes for biodiversity. Restoration of degraded native vegetation may provide an opportunity for concurrent production of both carbon and biodiversity benefits, by harnessing existing carbon markets without the need to trade-off biodiversity outcomes. Here we demonstrate that carbon sequestered by restoring degraded temperate woodland can pay the price of the restored biodiversity. This is shown using conservative carbon prices in an established market (during both a voluntary and compliance market phase), and the restoration price revealed by a 10-year conservation incentive payment scheme. When recovery rates are high, market prices for carbon could pay the full price of restoration, with additional independent investment needed in cases where recovery trajectories are slower. Using carbon markets to fund restoration of degraded native vegetation thereby provides a solution for constrained resources and problematic trade-offs between carbon and biodiversity outcomes. Multi-attribute markets offer the potential to greatly increase the extent of restoration for biodiversity conservation, while providing an affordable source of carbon sequestration and enhancing economic benefits to landowners.

High-throughput shoot phenotyping reveals temporal growth responses to nitrogen and inorganic and organic phosphorus sources in tomato.

The application of nitrogen (N) and phosphorus (P) fertilizers to soils is required to maintain crop yields, so the sufficient and timely delivery of nutrients to match crop demand is important in fertilizer management. We quantified temporal growth responses of tomato plants with different rates of N and P application using high-throughput shoot phenotyping. The tomato plants were grown in soil that had organic, inorganic or a combination of sources of P incorporated. Additional N was added to each pot at low and high rates, 13 days after planting. At the same rate of total P application, the inorganic P source resulted in greater shoot growth at the early time points. Later on, the plants supplied with organic or mixed P sources grew faster than those that received the inorganic P source, resulting in comparable shoot biomass in all treatments at the time of destructive harvest. The shoot phenotyping data demonstrated that readily available soil P was important for early tomato growth while available N was more important in later stages of vegetative growth. These results suggest that a fertilizer formulation of combined inorganic and organic P sources may be able to sustain rapid and great shoot growth in tomato plants, while also reducing additional N input.

Establishing a quality management framework for commercial inoculants containing arbuscular mycorrhizal fungi.

Microbial inoculants containing arbuscular mycorrhizal (AM) fungi are potential tools in increasing the sustainability of our food production systems. Given the demand for sustainable agriculture, the production of such inoculants has potential economic value and has resulted in a variety of commercial inoculants currently being advertised. However, their use is limited by inconsistent product efficacy and lack of consumer confidence. Here, we propose a framework that can be used to assess the quality and reliability of AM inoculants. First, we set out a range of basic quality criteria which are required to achieve reliable inoculants. This is followed by a standardized bioassay which can be used to test inoculum viability and efficacy under controlled conditions. Implementation of these measurements would contribute to the adoption of AM inoculants by producers with the potential to increase sustainability in food production systems.

Nitrogen addition and defoliation alter belowground carbon allocation with consequences for plant nitrogen uptake and soil organic carbon decomposition.

Grassland plants allocate photosynthetically fixed carbon (C) belowground to root biomass and rhizodeposition, but also to support arbuscular mycorrhizal fungi (AMF). These C allocation pathways could increase nutrient scavenging, but also mining of nutrients through enhanced organic matter decomposition. While important for grassland ecosystem functioning, methodological constraints have limited our ability to measure these processes under field conditions. We used 13CO2 and 15N pulse labelling methods to examine belowground C allocation to root biomass production, rhizodeposition and AMF colonisation during peak plant growth in a grassland field experiment after three years of N fertilisation (0 and 40 kg N ha-1 year-1) and defoliation frequency treatments ("low" and "high", with 3-4 and 6-8 simulated grazing events per year, mimicking moderate and intense grazing, respectively). Moreover, we quantified the consequences for plant nitrogen (N) uptake and decomposition of soil organic C (SOC). Nitrogen fertilisation increased rhizodeposition and AMF colonisation (by 63 % and 54 %), but reduced root biomass (by 25 %). With high defoliation frequency, AMF colonisation increased (by 60 %), but both root biomass and rhizodeposition declined (by 35 % and 58 %). Plant N uptake was highest without N fertilisation and low defoliation frequency, and positively related to root biomass and the number of root tips. Therefore, when N supply is low and the capacity to produce C through photosynthesis is high, belowground C allocation to root production and associated root tips was important to scavenge for N in the soil. In contrast, the strong positive relationship between the rate of rhizodeposition and SOC decomposition, suggests that rhizodeposition may help plants to mine for nutrients locked in SOC. Taken together, the results of this study suggest that belowground C allocation pathways affected by N fertilisation and defoliation frequency affect plant N scavenging and mining with important consequences for long-term grassland C dynamics.

Arbuscular mycorrhizas increased tomato biomass and nutrition but did not affect local soil P availability or 16S bacterial community in the field.

While interest in arbuscular mycorrhizal (AM) fungal effects on soil phosphorus (P) have recently increased, field experiments on this topic are lacking. While microcosm studies provided valuable insights, the lack of field studies represents a knowledge gap. Here, we present a field study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) with and without additional fertiliser, using a drip-irrigation system to examine the impacts of the AM symbiosis on soil P availability and plant growth and nutrition. AM effects on fruit biomass and nutrients, soil nutrient availability, soil moisture and the soil bacterial community were examined. At the time of harvest, the AM tomato plants without fertiliser had the same early season fruit biomass and fruit nutrient concentrations as plants that received fertiliser. The presence of roots reduced the concentration of available soil P, ammonium and soil moisture in the top 10 cm soil layer. Arbuscular mycorrhizas did not significantly affect soil P availability, soil moisture, or 16S bacterial community composition. These findings suggest an indirect role for AM fungi in tomato production but not necessarily a direct role in determining soil physicochemical traits, during the one season that this experiment was conducted. While longer-term field studies may be required in the future, the present study provides new insights into impacts of AM fungi on P availability and uptake in a field soil system.

Development of an organomineral fertiliser formulation that improves tomato growth and sustains arbuscular mycorrhizal colonisation.

Achieving sustainable agricultural development requires the efficient use of nutrient resources for crop production. Recovering nutrients from animal manures may play a key role in achieving this. Animal manures typically have low nutrient concentrations, and in ratios that are often not ideal for balanced crop nutrition. Here, combinations of organic and inorganic phosphorus (P) were formulated as granular products (organomineral fertilisers) with granule size suitable for transport and spreading. The fertilisers were produced by granulating powdered chicken litter with MAP and urea powders making the following formulations: 0:4, 1:3, 2:2, 3:1, 4:0. The kinetics of NH4+-N and P release from the fertilisers, and the effects on tomato growth and nutrition, as well as arbuscular mycorrhizal formation in roots following fertiliser application, were determined. Cumulative NH4+-N release ceased within 12 h, and was lower in the formulations with higher proportions of chicken litter. The cumulative P released reached approximately 80% of total P in all formulations, and the time to obtain maximum P dissolution was 19 days in the formulation that contained only chicken litter. The organomineral fertilisers increased tomato shoot growth by 15-28% compared to the chicken litter only, MAP only and MAP/urea formulations. Reasonable levels of mycorrhizal colonisation of tomato roots was achieved with the organomineral fertilisers. The results demonstrated that optimum plant growth does not depend solely on immediately available P, and that timing of nutrient supply to match plant demand is important. The combination of chicken litter with MAP sustained nutrient supply and improved plant growth. Taken together, organomineral fertiliser formulations are potential alternatives to inorganic P fertilisers that can improve crop growth and nutrition, while provide a sustainable use for animal production wastes.

Nitrogen Fertilisation Increases Specific Root Respiration in Ectomycorrhizal but Not in Arbuscular Mycorrhizal Plants: A Meta-Analysis.

Plants spend a high proportion of their photosynthetically fixed carbon (C) belowground to support mycorrhizal associations in return for nutrients, but this C expenditure may decrease with increased soil nutrient availability. In this study, we assessed how the effects of nitrogen (N) fertiliser on specific root respiration (SRR) varied among mycorrhizal type (Myco type). We conducted a multi-level meta-analysis across 1,600 observations from 32 publications. SRR increased in ectomycorrhizal (ECM) plants with more than 100 kg N ha-1 applied, did not change in arbuscular mycorrhizal (AM) and non-mycorrhizal (NM) plants, but increased in plants with a dual mycorrhizal association in response to N fertilisation. Our results suggest that high N availability (>100 kg N ha-1) could disadvantage the growth of ECM plants because of increased C costs associated with maintaining higher root N concentrations, while the insensitivity in SRR by AM plants to N fertilisation may be because AM fungi are more important for phosphorus (P) uptake.

Global data on earthworm abundance, biomass, diversity and corresponding environmental properties.

Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change.

Current carbon prices do not stack up to much land use change, despite bundled ecosystem service co-benefits.

Biological sources of carbon sequestration such as revegetation have been highlighted as important avenues to combat climate change and meet global targets by the global community including the Paris Climate Agreement. However, current and projected carbon prices present a considerable barrier to broad-scale adoption of tree planting as a key mitigation strategy. One avenue to provide additional economic and environmental incentives to encourage wider adoption of revegetation is the bundling or stacking of additional co-beneficial ecosystem services that can be realized from tree planting. Using the World's largest land-based carbon credit trading scheme, the Australian Emissions Reduction Scheme (ERF), we examine the potential for three pairs of ecosystem services, where the carbon sequestration value of land use change is paired with an additional co-benefit with strong prospects for local tangible benefits to land owners/providers. Two cases consider agricultural provisioning values that can be realized by the landowners in higher returns: increased pollination services and reduced lamb mortality. The third case examined payments for tree plantings along riparian buffers, with payments to farmers by a water utility who realizes the benefit from reduced treatment cost due to water quality improvements. Economic incentives from these co-benefit case studies were found to be mixed, with avoided treatment costs from water quality paired with carbon payments the most promising, while pollination and reduced lamb mortality paired with carbon payments were unable to bridge the economic gap except under the most optimistic assumptions. We conclude that the economics case for significant land use change are likely to be geographically dispersed and only viable in relatively niche landscape positions in high establishment, high opportunity cost areas even when carbon payments are augmented with the value of co-benefits classified as providing direct and local benefits.

A novel 13 C pulse-labelling method to quantify the contribution of rhizodeposits to soil respiration in a grassland exposed to drought and nitrogen addition.

Rhizodeposition plays an important role in below-ground carbon (C) cycling. However, quantification of rhizodeposition in intact plant-soil systems has remained elusive due to methodological issues. We used a 13 C-CO2 pulse-labelling method to quantify the contribution of rhizodeposition to below-ground respiration. Intact plant-soil cores were taken from a grassland field, and in half, shoots and roots were removed (unplanted cores). Both unplanted and planted cores were assigned to drought and nitrogen (N) treatments. Afterwards, shoots in planted cores were pulse labelled with 13 C-CO2 and then clipped to determine total below-ground respiration and its δ13 C. Simultaneously, δ13 C was measured for the respiration of live roots, soils with rhizodeposits, and unplanted treatments, and used as endmembers with which to determine root respiration and rhizodeposit C decomposition using two-source mixing models. Rhizodeposit decomposition accounted for 7-31% of total below-ground respiration. Drought reduced decomposition of both rhizodeposits and soil organic carbon (SOC), while N addition increased root respiration but not the contribution of rhizodeposit C decomposition to below-ground respiration. This study provides a new approach for the partitioning of below-ground respiration into different sources, and indicates that decomposition of rhizodeposit C is an important component of below-ground respiration that is sensitive to drought and N addition in grassland ecosystems.

Effects of plant roots and arbuscular mycorrhizas on soil phosphorus leaching.

While the impact of arbuscular mycorrhizal fungi (AMF) on phosphorus (P) uptake is well understood, the mechanism(s) of how these fungi affect P leaching from soil is still unclear. Here we present results of a study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) in microcosms containing non-sterile soil, to examine the influence of roots and AMF on P leaching. More P was leached from the planted microcosms as compared to the plant-free controls. Further, although there was more plant biomass and greater P uptake in the mycorrhizal plant treatments, these treatments were associated with the most leaching of total P, reactive P, and dissolved organic carbon (DOC). There was a strong correlation between the total P and DOC leached, suggesting that root and fungal exudates may have affected P leaching. These findings provide new insights into the impact of roots and AMF on nutrient leaching in soils.

The effect of zinc fertilisation and arbuscular mycorrhizal fungi on grain quality and yield of contrasting barley cultivars.

Zinc is essential for the functioning of many enzymes and plant processes and the malting process. Arbuscular mycorrhizal fungi (AMF) can improve zinc (Zn) uptake in the important cereal crop barley (Hordeum vulgare) on Zn-deficient soils. Here we investigated the impacts of Zn fertilisation and AMF on the yield and grain quality of malting barley cultivars. Five barley genotypes were inoculated or not with the AMF Rhizophagus irregularis, and grown in pots either fertilised with Zn or not. Measurements of Zn nutrition and yield were made for all cultivars. Further analyses of grain biochemical composition, including starch, ß-glucan and arabinoxylan contents, and analysis of ATR-MIR spectra were made in two contrasting cultivars. Mycorrhizal colonisation generally resulted in decreased biomass, but increased grain dimensions and mean grain weight. Barley grain yield and biochemical qualities were highly variable between cultivars, and the ATR-MIR spectra revealed grain compositional differences between cultivars and AMF treatments. Mycorrhizal fungi can affect barley grain Zn concentration and starch content, but grain biochemical traits including ß-glucan and arabinoxylan contents were more conserved by the cultivar, and unaffected by AMF inoculation. The ATR-MIR spectra revealed that there are other grain characteristics affected by AMF that remain to be elucidated.

Wine Terroir and the Soil Bacteria: An Amplicon Sequencing-Based Assessment of the Barossa Valley and Its Sub-Regions.

A wines' terroir, represented as wine traits with regional distinctiveness, is a reflection of both the biophysical and human-driven conditions in which the grapes were grown and wine made. Soil is an important factor contributing to the uniqueness of a wine produced by vines grown in specific conditions. Here, we evaluated the impact of environmental variables on the soil bacteria of 22 Barossa Valley vineyard sites based on the 16S rRNA gene hypervariable region 4. In this study, we report that both dispersal isolation by geographic distance and environmental heterogeneity (soil plant-available P content, elevation, rainfall, temperature, spacing between row and spacing between vine) contribute to microbial community dissimilarity between vineyards. Vineyards located in cooler and wetter regions showed lower beta diversity and a higher ratio of dominant taxa. Differences in soil bacterial community composition were significantly associated with differences in fruit and wine composition. Our results suggest that environmental factors affecting wine terroir, may be mediated by changes in microbial structure, thus providing a basic understanding of how growing conditions affect interactions between plants and their soil bacteria.

Soil Microbial Community Responses After Amendment with Thermally Altered Pinus radiata Needles.

Post-fire litter layers are composed of leaves and woody debris that predominantly fall during or soon after the fire event. These layers are distinctly different to pre-fire litters due to their common origin and deposition time. However, heterogeneity can arise from the variable thermal conditions in the canopy during fire. Therefore, in this study, we used thermally altered pine needles (heated to 40 °C, 150 °C, 260 °C and 320 °C for 1 h) in a laboratory incubation study for 43 days. These samples were measured for respiration throughout and extracted for DNA at the experiment's end; soil ribosomal RNA was analysed using Illumina sequencing (16S and internal transcribed spacer amplicons). The addition of pine needles heated to 40 °C or 150 °C caused a substantial shift in community structure, decreased alpha diversity and significantly increased soil respiration relative to the control treatment. In contrast, pine needles heated to 260 °C or 320 °C had little effect on microbial community structure or soil respiration. These results indicate that highly thermally altered needles are not microbially decomposed during the first 43 days of exposure and therefore that biomass temperature may have significant effects on post-fire litter decomposition and carbon flux. This research outlines an important knowledge gap in forest fire responses that may affect post-fire carbon emission estimates.

Variable water cycles have a greater impact on wheat growth and soil nitrogen response than constant watering.

Current climate change models project that water availability will become more erratic in the future. With soil nitrogen (N) supply coupled to water availability, it is important to understand the combined effects of variable water and N supply on food crop plants (above- and below-ground). Here we present a study that precisely controls soil moisture and compares stable soil moisture contents with a controlled wetting-drying cycle. Our aim was to identify how changes in soil moisture and N concentration affect shoot-root biomass, N acquisition in wheat, and soil N cycling. Using a novel gravimetric platform allowing fine-scale control of soil moisture dynamics, a 3 × 3 factorial experiment was conducted on wheat plants subjected to three rates of N application (0, 25 and 75 mg N/kg soil) and three soil moisture regimes (two uniform treatments: 23.5 and 13% gravimetric moisture content (herein referred to as Well-watered and Reduced water, respectively), and a Variable treatment which cycled between the two). Plant biomass, soil N and microbial biomass carbon were measured at three developmental stages: tillering (Harvest 1), flowering (Harvest 2), and early grain milk development (Harvest 3). Reduced water supply encouraged root growth when combined with medium and high N. Plant growth was more responsive to N than the water treatments imposed, with a 15-fold increase in biomass between the high and no added N treatment plants. Both uniform soil water treatments resulted in similar plant biomass, while the Variable water treatment resulted in less biomass overall, suggesting wheat prefers consistency whether at a Well-watered or Reduced water level. Plants did not respond well to variable soil moisture, highlighting the need to understand plant adaptation and biomass allocation with resource limitation. This is particularly relevant to developing irrigation practices, but also in the design of water availability experiments.

The effects of soil phosphorus and zinc availability on plant responses to mycorrhizal fungi: a physiological and molecular assessment.

The positive effects of arbuscular mycorrhizal fungi (AMF) have been demonstrated for plant biomass, and zinc (Zn) and phosphorus (P) uptake, under soil nutrient deficiency. Additionally, a number of Zn and P transporter genes are affected by mycorrhizal colonisation or implicated in the mycorrhizal pathway of uptake. However, a comprehensive study of plant physiology and gene expression simultaneously, remains to be undertaken. Medicago truncatula was grown at different soil P and Zn availabilities, with or without inoculation of Rhizophagus irregularis. Measures of biomass, shoot elemental concentrations, mycorrhizal colonisation, and expression of Zn transporter (ZIP) and phosphate transporter (PT) genes in the roots, were taken. Mycorrhizal plants had a greater tolerance of both P and Zn soil deficiency; there was also evidence of AMF protecting plants against excessive Zn accumulation at high soil Zn. The expression of all PT genes was interactive with both P availability and mycorrhizal colonisation. MtZIP5 expression was induced both by AMF and soil Zn deficiency, while MtZIP2 was down-regulated in mycorrhizal plants, and up-regulated with increasing soil Zn concentration. These findings provide the first comprehensive physiological and molecular picture of plant-mycorrhizal fungal symbiosis with regard to soil P and Zn availability. Mycorrhizal fungi conferred tolerance to soil Zn and P deficiency and this could be linked to the induction of the ZIP transporter gene MtZIP5, and the PT gene MtPT4.

Resource allocation to growth or luxury consumption drives mycorrhizal responses.

Highly variable phenotypic responses in mycorrhizal plants challenge our functional understanding of plant-fungal mutualisms. Using non-invasive high-throughput phenotyping, we observed that arbuscular mycorrhizal (AM) fungi relieved phosphorus (P) limitation and enhanced growth of Brachypodium distachyon under P-limited conditions, while photosynthetic limitation under low nitrogen (N) was exacerbated by the fungus. However, these responses were strongly dependent on host genotype: only the faster growing genotype (Bd3-1) utilised P transferred from the fungus to achieve improved growth under P-limited conditions. Under low N, the slower growing genotype (Bd21) had a carbon and N surplus that was linked to a less negative growth response compared with the faster growing genotype. These responses were linked to the regulation of N : P stoichiometry, couples resource allocation to growth or luxury consumption in diverse plant lineages. Our results attest strongly to a mechanism in plants by which plant genotype-specific resource economics drive phenotypic outcomes during AM symbioses.

Arbuscular mycorrhizal fungal inoculation and soil zinc fertilisation affect the productivity and the bioavailability of zinc and iron in durum wheat.

There is a growing recognition of the role of arbuscular mycorrhizal fungi (AMF) in food security, specifically the potential for AMF to enhance the yield and mineral nutrition-including phosphorus, zinc (Zn), and iron (Fe)-of food crops. However, the bioavailability of Zn and Fe for humans in the grain of cereal crops can be overestimated by failing to consider the abundance of phytic acid (PA). This is because PA can chelate the micronutrients, making them difficult to absorb. In order to understand the effect of an AM fungus and soil Zn concentration on the productivity and nutritional quality of food parts, this study examined the growth and nutritional responses of durum wheat, with and without inoculation with Rhizophagus irregularis, at five soil Zn concentrations. Growth and nutrient responses of the plants to soil Zn amendment was stronger than responses to AMF. However, the protective effect of AMF under soil Zn toxicity conditions was observed as reduced Zn concentration in the mycorrhizal durum wheat grain at Zn50. Here, AMF inoculation increased the concentration of PA in durum wheat grain but had no effect on the concentration of Zn and Fe; this consequently reduced the predicted bioavailability of grain Zn and Fe, which could lead to a decrease in nutritional quality of the grain. This research suggests that in soil with low (available) phosphorus and Zn concentrations, AMF may reduce the food quality of durum wheat because of an increase in PA concentration, and thus, a decrease in the bioavailability of Zn and Fe.

Impact of an arbuscular mycorrhizal fungus on the growth and nutrition of fifteen crop and pasture plant species.

The formation of arbuscular mycorrhizas (AM) can result in positive, neutral or negative responses in the growth and mineral nutrition of host plants, particularly that of P, Zn and other micronutrients. This study examined the growth and nutritional responses of 15 agriculturally important plant species, including cereals, legumes and vegetables, with and without inoculation with the AM fungus (AMF) Rhizophagus irregularis. Furthermore, we explored whether the responses differed between different functional groups of plants such as monocots and dicots, C3 and C4 plants, and N-fixing and non-N-fixing plants. We found that that mycorrhizal colonisation of roots, plant growth and plant nutrient responses differed between plant species. Among the species analysed, leek (Allium ampeloprasum L. var. porrum) was the most mycorrhiza-responsive, displaying the highest mycorrhizal colonisation and biomass response, and the greatest increases in most mineral nutrients. In other plant species, the concentration of P, Cu, Zn and S were generally enhanced by inoculation with AMF. Furthermore, ionomes differed more greatly between plant species than in response to inoculation with AMF. This research further improves our understanding of the responses of different and diverse plant species to the formation of AM in terms of growth and ionomics under standardised growth conditions. The results of this study may be used in further studies and to inform agricultural practices.