Life at the interface: above- and below-ground responses of a grazed pasture soil to reforestation

Conversion of agricultural lands to mixed species woody plantings is increasingly being undertaken as ameans of sequestering C and increasing biodiversity. The implications of such changes in land use for soilcommunities, and the ecosystem services they provide (e.g., nutrient and C cycling), are relatively littleunderstood. Results of a detailed study of vegetation, soil physicochemical properties and soilcommunities (primarily microbial) to reforestation of a pasture (15 years post reforestation), and itsimmediately adjacent un-restored pasture, are presented. Whereas the reforested portion of the site hadsignificantly higher levels of tree canopy cover and a well-developed litter layer than the immediatelyadjacent pasture, the reverse was true for grass biomass. Although there were no differences in total rootbiomass between the sampling zones, the pasture zone was dominated by fine roots and the reforestedzone by coarse roots. Reforestation had a significant impact on soil physicochemical properties, with soilC, C:N and mineral N being higher than in the pasture. The reforestation also supported a greatermicrobial PLFA, a higher Fungal:Bacterial PLFA ratio and a different microbial community (based on PLFAprofiles) from that of the adjacent pasture. There were also differences in earthworm abundance, withearthworms present and absent in soils from the pasture and reforested zones, respectively. All of thechanges in vegetation, soil physicochemical properties and biotic communities occurred abruptly at theinterface between the land-use types, with no evidence of an interaction between side of fence(reforested versus pasture zones) and distance from the fence. Results are discussed in the context ofchanges in land-use on soil ecology and their potential functional significance.T.R. Cavagnar

Pastures to woodlands: changes in soil microbial communities and carbon following reforestation

Reforestation of agricultural lands has the potential to sequester C, while providing other environmentalbenefits. It is well established that reforestation can have a profound impact on soil physicochemicalproperties but the associated changes to soil microbial communities are poorly understood. Therefore,the objective of this study was to quantify changes in soil physicochemical properties and microbialcommunities in soils collected from reforested pastures and compare then to remnant vegetation and un-reforested pastures. To address this aim, we collected soil from two locations (pasture and its adjacentreforested zone, or pasture and its adjacent remnant vegetation) on each of ten separate farms thatcovered the range of planting ages (0–30 years and remnant vegetation) in a temperate region ofsoutheastern Australia. Soils were analysed for a range of physicochemical properties (including C andnutrients), and microbial biomass and community composition (PLFA profiles). Soil C:N ratios increasedwith age of tree planting, and soil C concentration was highest in the remnant woodlands. Reforestationhad no clear impact on soil microbial biomass or fungal:bacterial ratios (based on PLFA’s). Reforestationwas associated with significant changes in the molecular composition of the soil microbial community atmany farms but similar changes were found within a pasture. These results indicate that reforestation ofpastures can result in changes in soil properties within a few decades, but that soil microbial communitycomposition can vary as much spatially within pastures as it does after reforestation.T.R. Cavagnaro, S.C. Cunningham, S. Fitzpatric

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.Bahareh Bicharanloo, Timothy R. Cavagnaro, Claudia Keitel and Feike A. Dijkstr

The incorporation of fungal to bacterial ratios and plant ecosystem effect traits into a state-and-transition model of land-use change in semi-arid grasslands

Feedbacks between plants, microbes and their growth traits are important in the maintenance of nutrient cycling functions. Despite this, there is little understanding of the role of these relationships in the transitions between alternate vegetation states in semi-arid and arid lands. We investigated the relationships between vegetation, soil nutrients and soil microbes across grasslands and agricultural fields described within an existing conceptual state-and-transition model of agricultural de-intensification in the semi-arid Riverine Plains grasslands of south-eastern Australia. Sites represented the proposed transition from annual exotic pastures to native perennial grasslands with agricultural de-intensification. Microbial community composition was assessed using phospholipid fatty acid analysis (PLFA). The native grassland state and the native pasture state were characterized by a higher fungal to bacterial ratio (F:B). The native grassland state had a slightly lower bacterial PLFA biomass whilst the native pasture state had a slightly higher fungal PLFA biomass, although these differences were non-significant. Only the recently cultivated, heavily grazed state was characterized by high soil nutrient availability (soil P and K) and leaf traits indicating rapid growth and resource utilization (high SLA, low LDMC). Thus, the association of these ecosystem properties with a lower F:B was not as close as expected. States with a higher F:B were not characterized by higher total soil C or C:N as hypothesized. This study further extends our knowledge of the association between fungal dominance and agricultural de-intensification to a semi-arid system with relatively old, nutrient poor soils. It highlights the need for a better understanding of the mechanistics behind this association and the implications for C cycling and storage in such systems.Megan R. Wong, John W. Morgan, Nathan K. Wong, Timothy R. Cavagnar

A concise review on multi-omics data integration for terroir analysis in Vitis vinifera

Mini reviewVitis vinifera (grapevine) is one of the most important fruit crops, both for fresh consumption and wine and spirit production. The term terroir is frequently used in viticulture and the wine industry to relate wine sensory attributes to its geographic origin. Although, it can be cultivated in a wide range of environments, differences in growing conditions have a significant impact on fruit traits that ultimately affect wine quality. Understanding how fruit quality and yield are controlled at a molecular level in grapevine in response to environmental cues has been a major driver of research. Advances in the area of genomics, epigenomics, transcriptomics, proteomics and metabolomics, have significantly increased our knowledge on the abiotic regulation of yield and quality in many crop species, including V. vinifera. The integrated analysis of multiple ‘omics’ can give us the opportunity to better understand how plants modulate their response to different environments. However, ‘omics’ technologies provide a large amount of biological data and its interpretation is not always straightforward, especially when different ‘omic’ results are combined. Here we examine the current strategies used to integrate multi-omics, and how these have been used in V. vinifera. In addition, we also discuss the importance of including epigenomics data when integrating omics data as epigenetic mechanisms could play a major role as an intermediary between the environment and the genome.Pastor Jullian Fabres, Cassandra Collins, Timothy R. Cavagnaro and Carlos M. Rodríguez Lópe

Scales that matter: guiding effective monitoring of soil properties in restored riparian zones

Considerable effort has been directed at restoring riparian zones to ensure they continue to provide ecosystem services and one of the most common aims of these activities is to reduce nutrients (in either water or soil) entering waterways. Vegetation plays a major role in nutrient interception, but nutrients in terrestrial ecosystems are strongly influenced by edaphic factors. Therefore understanding the effectiveness of riparian restoration efforts is dependent on knowledge of the complex and highly dynamic nature of nutrient cycling processes in riparian soils and their adjacent landscapes. Our primary aim was to assess the potential utility of a range of common soil indicators for monitoring responses to riparian restoration, and to use this information to provide guidance for more effective monitoring. A range of soil physiochemical properties in riparian zones and adjacent paddocks as a comparison were measured, incorporating both structural (e.g., bulk density) and functional (e.g., nitrogen) variables likely to differ in terms of both their responsiveness to restoration, and degree of natural spatial and temporal variation. Soil properties across the three spatial scales considered here (among creeks, among sites and within sites) varied considerably, particularly levels of phosphorus, ammonium and nitrate. Total organic carbon and total nitrogen were less variable and more uniform across all scales. Potential explanations for these patterns were explored by examining relationships between soil properties and vegetation measures, and between a subset of the most promising indicators (carbon, total nitrogen and bulk density, based on inherently low spatial variability) and adjacent land-use. Fertiliser inputs appear to be a strong determinant of soil phosphorus but otherwise soil properties were not strongly related to vegetation or adjacent land-use. For mineral N this is likely a reflection of the highly spatiotemporally dynamic nature of nutrient cycling in riparian zone soils. A better understanding of natural variability in soil properties will greatly aid in developing more effective monitoring programmes to assess potential changes in riparian soil properties. Management of riparian systems to recover soil ecosystem services will depend upon identifying effective ecological indicators that can be used as measures of progress towards restoration goals. This study represents a necessary first step towards guiding meaningful monitoring of soil properties at riparian zones subject to restoration efforts.Robin Hale, Paul Reicha, Tom Daniel, Philip S. Lake, Timothy R. Cavagnar

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

Advance access publication 8 March 2023High-throughput phenotyping was used to track real-time plant growth of tomato plants and their responses to nutrients supplied from different sources and rates of phosphorus (P). The results suggest that the combined use of P-rich chicken litter (organic matter) and inorganic P sources can be used to close the growth gap between the sole use of organic fertilizer and the use of conventional P fertilizer. Furthermore, organic P fertilizers could reduce the need for additional nitrogen fertilizer.Hue T. T. Ngo, Timothy R. Cavagnaro, Nathaniel Jewell, Christopher J Brien, Bettina Berger and Stephanie J. Watts-William

Frequency versus quantity: phenotypic response of two wheat varieties to water and nitrogen variability

Due to climate change, water availability will become increasingly variable, affecting nitrogen (N) availability. Therefore, we hypothesised watering frequency would have a greater impact on plant growth than quantity, affecting N availability, uptake and carbon allocation. We used a gravimetric platform, which measures the unit of volume per unit of time, to control soil moisture and precisely compare the impact of quantity and frequency of water under variable N levels. Two wheat genotypes (Kukri and Gladius) were used in a factorial glasshouse pot experiment, each with three N application rates (25, 75 and 150 mg N kg−1 soil) and five soil moisture regimes (changing water frequency or quantity). Previously documented drought tolerance, but high N use efficiency, of Gladius as compared to Kukri provides for potentially different responses to N and soil moisture content. Water use, biomass and soil N were measured. Both cultivars showed potential to adapt to variable watering, producing higher specific root lengths under low N coupled with reduced water and reduced watering frequency (48 h watering intervals), or wet/dry cycling. This affected mineral N uptake, with less soil N remaining under constant watering × high moisture, or 48 h watering intervals × high moisture. Soil N availability affected carbon allocation, demonstrated by both cultivars producing longer, deeper roots under low N. Reduced watering frequency decreased biomass more than reduced quantity for both cultivars. Less frequent watering had a more negative effect on plant growth compared to decreasing the quantity of water. Water variability resulted in differences in C allocation, with changes to root thickness even when root biomass remained the same across N treatments. The preferences identified in wheat for water consistency highlights an undeveloped opportunity for identifying root and shoot traits that may improve plant adaptability to moderate to extreme resource limitation, whilst potentially encouraging less water and nitrogen use

Effects of silver sulfide nanomaterials on mycorrhizal colonization of tomato plants and soil microbial communities in biosolid-amended soil

We investigated effects of Ag2S engineered nanomaterials (ENMs), polyvinylpyrrolidone (PVP) coated Ag ENMs (PVP-Ag), and Ag+ on arbuscular mycorrhizal fungi (AMF), their colonization of tomato (Solanum lycopersicum), and overall microbial community structure in biosolids-amended soil. Concentration-dependent uptake was measured in all treatments. Plants exposed to 100 mg kg−1 PVP-Ag ENMs and 100 mg kg−1 Ag+ exhibited reduced biomass and greatly reduced mycorrhizal colonization. Bacteria, actinomycetes and fungi were inhibited by all treatment classes, with the largest reductions measured in 100 mg kg−1 PVP-Ag ENMs and 100 mg kg−1 Ag+. Overall, Ag2S ENMs were less toxic to plants, less disruptive to plant-mycorrhizal symbiosis, and less inhibitory to the soil microbial community than PVP-Ag ENMs or Ag+. However, significant effects were observed at 1 mg kg−1 Ag2S ENMs, suggesting that the potential exists for microbial communities and the ecosystem services they provide to be disrupted by environmentally relevant concentrations of Ag2S ENMs.Jonathan D. Judy, Jason K. Kirby, Courtney Creamer, Mike J. McLaughlin, Cathy Fiebiger, Claire Wright, Timothy R. Cavagnaro, Paul M. Bertsc

Impact of herbicides on soil biology and function

There is a growing awareness among farmers about the importance of soil for sustaining crop production and providing beneficial ecosystem services. Over the last 2 decades, global herbicide use has increased as farmers have shifted to more sustainable conservation tillage practices and have adopted herbicide-tolerant crop cultivars. The implications of increased herbicide use for soil biology are being questioned, but a comprehensive review on this topic is lacking. In this chapter we outline the chemistry and use of the major herbicide classes, and review the soil functions relevant to crop production. We then collate and critically evaluate the evidence for herbicide effects on soil biota and activity. In general, most studies suggest that the impacts of herbicide application on soil function are only minor and/or temporary. However, there are some instances where findings consistently suggest effects that could significantly alter soil function. These include disruptions to earthworm ecology in soils exposed to glyphosate and atrazine; inhibition of soil N-cycling (including biological N2-fixation, mineralization and nitrification) by sulfonylurea herbicides in alkaline or low organic matter soils; and site-specific increases in disease resulting from the application of a variety of herbicides. Issues with extrapolating these findings to broadacre farming include the lack of a consistent framework for assessing herbicide risk to soil biology, the relevance of the magnitude of herbicide impacts compared with the impacts of other soil management practices such as tillage or crop rotation, the complexity of herbicide formulations and mixtures, and the limited number of long-term field studies.Michael T. Rose, Timothy R. Cavagnaro, Craig A. Scanlan, Terry J. Rose, Tony Vancov, Stephen Kimber, Ivan R. Kennedy, Rai S. Kookana, Lukas Van Zwiete