Amazon Basin forest pyrogenic carbon stocks: First estimate of deep storage

Amazon Basin forest soils contain considerable soil organic carbon stocks; however, the contribution of soil pyrogenic carbon (PyC) to the total is unknown. PyC is derived from local fires (historical and modern) and external inputs via aeolian deposition. To establish an initial estimate of PyC stocks in non-terra preta forest with no known history of fire, to assess site and vertical variability, as well as to determine optimal sampling design, we sampled 37 one hectare forest plots in the Amazon Basin and analysed PyC via hydrogen pyrolysis of three individual samples per plot and of bulked samples to 200 cm depth. Using our data and published total organic carbon stocks, we present the first field-based estimate of total PyC stock for the Amazon Basin of 1.10 Pg over 0–30 cm soil depth, and 2.76 Pg over 0–100 cm soil depth. This is up to 20 times higher than previously assumed. Three individual samples per 1 ha are sufficient to capture the site variability of PyC in our plots. PyC showed significant, large-scale variability among plots. To capture 50% of the PyC in 200 cm soil profiles, soil must be sampled to a depth of at least 71 cm. PyC represents a significant (11%) portion of total organic carbon in soil profiles 0–200 cm depth. This finding highlights the potentially important role that historical fire has played in modifying soil C stocks. Our data suggest that PyC is an important carbon pool for long-term storage, involved in millennial scale biogeochemical cycling, particularly in the subsurface soil

Interactions between mycorrhizal fungi and mycorrhizosphere bacteria during mineral weathering: Budget analysis and bacterial quantification

International audienceThe impact of ectomycorrhizal fungi or rhizosphere bacteria on tree seedling growth and nutrient uptake is well known. However, few studies have combined those microorganisms in one experiment to clarify their relative contribution and interactions in nutrient acquisition. Here, we monitored the respective contributions of pine roots, two ubiquitous forest ectomycorrhizal fungi Scleroderma citrinum and Laccaria bicolor, and two S. citrinum-mycorrhizosphere bacterial strains of Burkholderia glathei and Collimonas sp., on mineral weathering, nutrient uptake, and plant growth. Pinus sylvestris plants were grown on quartz–biotite substrate and inoculated or not with combinations of mycorrhizal fungi and/or bacterial strains. Magnesium and potassium fluxes were measured and nutrient budgets were calculated. Both ectomycorrhizal fungi significantly increased Mg plant uptake. No significant effects of the two bacterial strains were detected on the K and Mg budgets, but co-inoculating the mycorrhizal fungus S. citrinum and the efficient mineral-weathering B. glathei bacterial strain significantly improved the Mg budget. Similarly, co-inoculating S. citrinum with the Collimonas sp. bacterial strain significantly improved the pine biomass compared to non-inoculated pine plants. In order to better understand this process, we monitored the survival of the inoculated bacterial strains in the quartz–biotite substrate, the pine rhizosphere, and the mycorrhizal niche. The results showed that the two bacterial strains harboured different colonization behaviours both of which depended on the presence of the ectomycorrhizal partner. The populations of the Burkholderia strain were maintained in all these environments with a significantly higher density in the mycorrhizal niche, especially of S. citrinum. In contrast the population of the Collimonas strain reached the detection level except in the treatment inoculated with S. citrinum. These results highlight the need for taking into account the ecology of the microorganisms, and more specifically the fungal–bacterial interactions, when studying mineral weathering and plant nutrition

Mycorrhizas in changing ecosystems

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155731/1/Dickie_et_al_2014_Mycorrhizas_in_changing_ecosystems.pd

Ecological significance of mineral weathering in ectomycorrhizal and arbuscular mycorrhizal ecosystems from a field-based comparison

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155740/1/Koele_et_al_2013_Ecological_significance.pd

No globally consistent effect of ectomycorrhizal status on foliar traits

The concept that ectomycorrhizal plants have a particular foliar trait suite characterized by low foliar nutrients and high leaf mass per unit area (LMA) is widely accepted, but whether this trait suite can be generalized to all ectomycorrhizal clades is unclear. We identified 19 evolutionary clades of ectomycorrhizal plants and used a global leaf traits dataset comprising 11 466 samples across c. 3000 species to test whether there were consistent shifts in leaf nutrients or LMA with the evolution of ectomycorrhiza. There were no consistent effects of ectomycorrhizal status on foliar nutrients or LMA in the 17 ectomycorrhizal/non-ectomycorrhizal pairs for which we had sufficient data, with some ectomycorrhizal groups having higher and other groups lower nutrient status than non-ectomycorrhizal contrasts. Controlling for the woodiness of host species did not alter the results. Our findings suggest that the concepts of ectomycorrhizal plant trait suites should be re-examined to ensure that they are broadly reflective of mycorrhizal status across all evolutionary clades, rather than reflecting the traits of a few commonly studied groups, such as the Pinaceae and Fagales

Mycorrhizas and mycorrhizal fungal communities throughout ecosystem development

Background and scope: Plant communities and underlying soils undergo substantial, coordinated shifts throughout ecosystem development. However, shifts in the composition and function of mycorrhizal fungi remain poorly understood, despite their role as a major interface between plants and soil. We synthesise evidence for shifts among mycorrhizal types (i.e., ectomycorrhizas, arbuscular and ericoid mycorrhizas) and in fungal communities within mycorrhizal types along long-term chronosequences that include retrogressive stages. These systems represent strong, predictable patterns of increasing, then declining soil fertility during ecosystem development, and are associated with coordinated changes in plant and fungal functional traits and ecological processes. Conclusions: Mycorrhizal types do not demonstrate consistent shifts through ecosystem development. Rather, most mycorrhizal types can dominate at any stage of ecosystem development, driven by biogeography (i.e., availability of mycorrhizal host species), plant community assembly, climate and other factors. In contrast to coordinated shifts in soil fertility, plant traits and ecological processes throughout ecosystem development, shifts in fungal communities within and among mycorrhizal types are weak or idiosyncratic. The consequences of these changes in mycorrhizal communities and their function for plant-soil feedbacks or control over long-term nutrient depletion remain poorly understood, but could be resolved through empirical analyses of long-term soil chronosequences

Safeguarding human and planetary health demands a fertilizer sector transformation

Fertilizer nutrients are essential for food and nutrition security, but a large proportion of nutrients applied to soil are lost because they are unavailable to plants. The extent of these nutrient losses exceeds safe and sustainable limits. Societal awareness of this is limited because it can take many seasons for nutrient‐loss impacts to become visible. We propose that Innovative Fertilizers and Application Technologies (IFAT) could help reduce nutrient losses and thus reduce pressure on resources, and provide important micronutrients for human health. However, transformation of the fertilizer sector through stakeholder engagement, policy interventions, and public–private initiatives will be required to unlock the full potential of IFAT. Summary Strategies for delivering sustainable food systems require significant reduction in yield gaps and food system inefficiencies. Mineral fertilizers will play a critical role in achieving both of these aims. However, reduction in nutrient losses from mineral fertilizer use to levels that are considered sustainable has not been achieved and has been estimated to be unachievable, even with optimized practices for current products. We argue that Innovative Fertilizers and Application Technologies (IFAT) are needed to address the daunting and interlinked food, agricultural, and environmental challenges facing humanity and the planet. We define IFAT as a set of fertilizer products and technologies that are designed by taking the physiological needs of plants (such as nutrient uptake, redistribution, and utilization) as the entry point in the fertilizer development process, rather than starting first with chemistry. This approach aims for the timely and targeted delivery of nutrients in balanced quantities. We propose that this can result in multiple food, agricultural, and environmental benefits, including increased yield, improvements in nutritional quality, enhanced crop resilience, and reduced emission of greenhouse gases (GHG), and leaching losses. However, the benefits of IFAT for human and environmental health have remained elusive. The major challenge for optimal use of IFAT is a transformation of the vast fertilizer sector by means of government policy interventions, societal responses, and significant investment in public and private research and development

No globally consistent effect of ectomycorrhizal status on foliar traits

The concept that ectomycorrhizal plants have a particular foliar trait suite characterized by low foliar nutrients and high leaf mass per unit area (LMA) is widely accepted, but whether this trait suite can be generalized to all ectomycorrhizal clades is unclear. We identified 19 evolutionary clades of ectomycorrhizal plants and used a global leaf traits dataset comprising 11 466 samples across c. 3000 species to test whether there were consistent shifts in leaf nutrients or LMA with the evolution of ectomycorrhiza. There were no consistent effects of ectomycorrhizal status on foliar nutrients or LMA in the 17 ectomycorrhizal/non-ectomycorrhizal pairs for which we had sufficient data, with some ectomycorrhizal groups having higher and other groups lower nutrient status than non-ectomycorrhizal contrasts. Controlling for the woodiness of host species did not alter the results. Our findings suggest that the concepts of ectomycorrhizal plant trait suites should be re-examined to ensure that they are broadly reflective of mycorrhizal status across all evolutionary clades, rather than reflecting the traits of a few commonly studied groups, such as the Pinaceae and Fagales