Environmental Effects during Early Life-History Stages and Seed Development on Seed Functional Traits of an Australian Native Legume Species.

Understanding how seed functional traits interact with environmental factors to determine seedling recruitment is critical to assess the impact of climate change on ecosystem restoration. This study focused on the effects of environmental factors on the mother plant during early plant life history stages and during seed development. Desmodium brachypodum A. Gray (large tick trefoil, Fabaceae) was used as a model species. Firstly, this study analyzed seed germination traits in response to temperature and moisture stress. Secondly, it investigated how seed burial depth interacts with temperature and soil moisture to influence seedling emergence traits. Finally, it determined if contrasting levels of post-anthesis soil moisture could result in changes in D. brachypodum reproductive biology and seed and seedling functional traits. The results showed that elevated temperature and moisture stress interacted to significantly reduce the seed germination and seedling emergence (each by >50%), while the seed burial improved the seedling emergence. Post-anthesis soil moisture stress negatively impacted the plant traits, reducing the duration of the reproductive phenology stage (by 9 days) and seed production (by almost 50%). Unexpectedly, soil moisture stress did not affect most seed or seedling traits. In conclusion, elevated temperatures combined with low soil moisture caused significant declines in seed germination and seedling emergence. On the other hand, the reproductive output of D. brachypodum had low seed variability under soil moisture stress, which might be useful when sourcing seeds from climates with high variability. Even so, a reduction in seed quantity under maternal moisture stress can impact the long-term survival of restored plant populations.

Datasets supporting the adoption of multifunctional cover crops related to soil water and nitrogen in water-limited environments.

Crop diversification with cover crops could deliver a wide range of agroecosystem services including water conservation, nutrient cycling, biodiversity, and crop productivity as well as reducing the negative environmental footprint of conventional fallows. However, the potential competition of cover crops and subsequent cash crops on plant available water and soil mineral nitrogen (N) has limited the adoption of cover cropping for fallow replacement in water-limited environments. This article provides datasets for understanding the multifunctional role of cover crops as an alternative paradigm to conventional fallow in water-limited environments. The dataset is divided into four components comprising measured cover crop parameters (21 variables, n = 144), soil water (4 variables, n = 2,159), soil mineral N (4 variables, n = 1440), and site characteristics (8 variables). The datasets consist of crop resource quantity (biomass, N uptake, δ¹5N (‰), fixed shoot N, and water use), resource quality (C/N ratio, lignin, acid detergent fibre, and N concentration), and soil status (plant available water and mineral N) at field scale. The data supports the framework of the continuous development of alternative innovative cropping systems that have the potential to increase and maintain crop yield while minimizing the adverse effects of conventional fallowing in the context of sustainable intensification. The datasets are associated with the original research article published in Agriculture, Ecosystem, and Environment entitled "Fallow replacement cover crops impact soil water and nitrogen dynamics in a semi-arid sub-tropical environment" as Garba et al. [1].

Cropping System Diversification Influences Soil Microbial Diversity in Subtropical Dryland Farming Systems.

Conventional dryland cropping systems are characterised by low crop diversity and frequent fallows. This has significant impacts on soil microbes that underpin soil function. Diversifying crop rotations can potentially counter these effects; however, limited data exists on the impacts of diversified crop rotations on soil microbes in drylands. Using phylogenetic marker gene sequencing, we characterised soil microbial diversity in conventional and diversified dryland crop rotations in subtropical Australia. This included winter and summer dominant rotations. Conventional systems were cereal-dominant with a crop-fallow rotation. Diversified systems included greater crop diversity, double crops, cover crops, and a multi-year ley pasture. In summer rotations with increased crop diversity and cover crops, bacterial and fungal richness increased, and distinct communities were formed compared to fallow land. Often, these community shifts were associated with greater soil organic carbon (SOC) and nitrogen. All winter rotations had distinct fungal communities and ley pasture resulted in greater fungal diversity compared to other rotations. No effects of the winter rotations were evident on bacterial communities. Our results show that diversification of dryland crop rotations leads to significant shifts in soil microbial communities in both winter and summer cropping systems. Both summer and winter rotations incorporating cover crops and ley pasture had greater soil respiration and nitrogen, indicating increases in soil fertility. These rotations may offer an alternative to conventional crop-fallow rotations to counter ongoing declines in soil health.

Effect of Soil Moisture Regimes on the Glyphosate Sensitivity and Morpho-Physiological Traits of Windmill Grass (Chloris truncata R.Br.), Common Sowthistle (Sonchus oleraceus L.), and Flaxleaf Fleabane [Conyza bonariensis (L.) Cronq.].

The glasshouse study was conducted with the objectives of (i) investigating the effect of soil moisture variations on the control efficiency of glyphosate on windmill grass (Chloris truncata R.Br.), common sowthistle (Sonchus oleraceus L.), and flaxleaf fleabane [Conyza bonariensis (L.) Cronq.], (ii) evaluating the tolerance of tested weed species under soil moisture variations, and (iii) determining the morphological and physiological characteristics of these species to partially explain herbicide tolerance under periods of reduced soil moisture availability (RSM). The species' tolerance to glyphosate increased significantly under reduced soil moisture availability (p < 0.001). The lethal dose to cause herbicide injury or biomass reduction by 50% (LD50) and 80% (LD80) in relation to untreated control for water-stressed plants [i.e., moderate soil moisture availability (MSM) and RSM] was significantly higher than that of plants grown under high soil moisture availability (HSM). The tolerance factor (TF) for C. truncata, S. oleraceus, and C. bonariensis, in terms of biomass reduction under RSM, was 2.6, 2.4, and 2.6, respectively, as compared to HSM. The results showed that the glyphosate sensitivity, especially at the sub-lethal rates, of the three weed species under study decreased as soil moisture availability reduced (p< 0.01). Overall glyphosate efficacy, in relation to the recommended rate, was unaffected, except for C. truncata; the weed survived the highest tested glyphosate rate [750 g active ingredient (a.i.) ha-1] under RSM. There was significant interaction between weed species and soil moisture regimes for weed morpho-physiological traits (p < 0.001), with reduced soil moisture having a more influential impact on the growth of C. bonariensis and S. oleraceus compared to C. truncata. Changes in the leaf characteristics, such as increased leaf thickness, higher leaf chlorophyll content, reduced leaf area, and limited stomatal activity for all the tested weed species under MSM and RSM in relation to HSM, partially explain the tolerance of species to glyphosate at sublethal rates.

Root architecture for improved resource capture: trade-offs in complex environments.

Root architecture is a promising breeding target for developing resource-efficient crops. Breeders and plant physiologists have called for root ideotypes that have narrow, deep root systems for improved water and nitrate capture, or wide, shallower root systems for better uptake of less mobile topsoil nutrients such as phosphorus. Yet evidence of relationships between root architecture and crop yield is limited. Many studies focus on the response to a single constraint, despite the fact that crops are frequently exposed to multiple soil constraints. For example, in dryland soils under no-till management, topsoil nutrient stratification is an emergent profile characteristic, leading to spatial separation of water and nutrients as the soil profile dries. This results in spatio-temporal trade-offs between efficient resource capture and pre-defined root ideotypes developed to counter a single constraint. We believe there is need to identify and better understand trade-offs involved in the efficient capture of multiple, spatially disjunct soil resources. Additionally, how these trade-offs interact with genotype (root architecture), environment (soil constraints), and management (agronomy) are critical unknowns. We argue that identifying root traits that enable efficient capture of multiple soil resources under fluctuating environmental constraints is a key step towards meeting the challenges of global food security.

Confronting herbicide resistance with cooperative management.

BACKGROUND: Resistance of pathogens and pests to antibiotics and pesticides worldwide is rapidly reaching critical levels. The common-pool-resource nature of this problem (i.e. whereby the susceptibility to treatment of target organisms is a shared resource) has been largely overlooked. Using herbicide-resistant weeds as a model system, we developed a discrete-time landscape-scale simulation to investigate how aggregating herbicide management strategies at different spatial scales from individual farms to larger cooperative structures affects the evolution of glyphosate resistance in common waterhemp (Amaranthus tuberculatus). RESULTS: Our findings indicate that high-efficacy herbicide management strategies practiced at the farm scale are insufficient to slow resistance evolution in A. tuberculatus. When best practices were aggregated at large spatial scales, resistance evolution was hindered; conversely, when poor management practices were aggregated, resistance was exacerbated. Tank mixture-based strategies were more effective than rotation-based strategies in most circumstances, while applying glyphosate alone resulted in the poorest outcomes. CONCLUSIONS: Our findings highlight the importance of landscape-scale cooperative management for confronting common-pool-resource resistance problems in weeds and other analogous systems. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A regionally-adapted implementation of conservation agriculture delivers rapid improvements to soil properties associated with crop yield stability.

Climate models predict increasing weather variability, with negative consequences for crop production. Conservation agriculture (CA) may enhance climate resilience by generating certain soil improvements. However, the rate at which these improvements accrue is unclear, and some evidence suggests CA can lower yields relative to conventional systems unless all three CA elements are implemented: reduced tillage, sustained soil cover, and crop rotational diversity. These cost-benefit issues are important considerations for potential adopters of CA. Given that CA can be implemented across a wide variety of regions and cropping systems, more detailed and mechanistic understanding is required on whether and how regionally-adapted CA can improve soil properties while minimizing potential negative crop yield impacts. Across four US states, we assessed short-term impacts of regionally-adapted CA systems on soil properties and explored linkages with maize and soybean yield stability. Structural equation modeling revealed increases in soil organic matter generated by cover cropping increased soil cation exchange capacity, which improved soybean yield stability. Cover cropping also enhanced maize minimum yield potential. Our results demonstrate individual CA elements can deliver rapid improvements in soil properties associated with crop yield stability, suggesting that regionally-adapted CA may play an important role in developing high-yielding, climate-resilient agricultural systems.

Long-term agricultural fertilization alters arbuscular mycorrhizal fungal community composition and barley (Hordeum vulgare) mycorrhizal carbon and phosphorus exchange.

Agricultural fertilization significantly affects arbuscular mycorrhizal fungal (AMF) community composition. However, the functional implications of community shifts are unknown, limiting understanding of the role of AMF in agriculture. We assessed AMF community composition at four sites managed under the same nitrogen (N) and phosphorus (P) fertilizer regimes for 55 yr. We also established a glasshouse experiment with the same soils to investigate AMF-barley (Hordeum vulgare) nutrient exchange, using carbon (13 C) and 33 P isotopic labelling. N fertilization affected AMF community composition, reducing diversity; P had no effect. In the glasshouse, AMF contribution to plant P declined with P fertilization, but was unaffected by N. Barley C allocation to AMF also declined with P fertilization. As N fertilization increased, C allocation to AMF per unit of P exchanged increased. This occurred with and without P fertilization, and was concomitant with reduced barley biomass. AMF community composition showed no relationship with glasshouse experiment results. The results indicate that plants can reduce C allocation to AMF in response to P fertilization. Under N fertilization, plants allocate an increasing amount of C to AMF and receive relatively less P. This suggests an alteration in the terms of P-C exchange under N fertilization regardless of soil P status.

Soil Water Holding Capacity Mitigates Downside Risk and Volatility in US Rainfed Maize: Time to Invest in Soil Organic Matter?

Yield stability is fundamental to global food security in the face of climate change, and better strategies are needed for buffering crop yields against increased weather variability. Regional- scale analyses of yield stability can support robust inferences about buffering strategies for widely-grown staple crops, but have not been accomplished. We present a novel analytical approach, synthesizing 2000-2014 data on weather and soil factors to quantify their impact on county-level maize yield stability in four US states that vary widely in these factors (Illinois, Michigan, Minnesota and Pennsylvania). Yield stability is quantified as both 'downside risk' (minimum yield potential, MYP) and 'volatility' (temporal yield variability). We show that excessive heat and drought decreased mean yields and yield stability, while higher precipitation increased stability. Soil water holding capacity strongly affected yield volatility in all four states, either directly (Minnesota and Pennsylvania) or indirectly, via its effects on MYP (Illinois and Michigan). We infer that factors contributing to soil water holding capacity can help buffer maize yields against variable weather. Given that soil water holding capacity responds (within limits) to agronomic management, our analysis highlights broadly relevant management strategies for buffering crop yields against climate variability, and informs region-specific strategies.

Soil Functional Zone Management: A Vehicle for Enhancing Production and Soil Ecosystem Services in Row-Crop Agroecosystems.

There is increasing global demand for food, bioenergy feedstocks and a wide variety of bio-based products. In response, agriculture has advanced production, but is increasingly depleting soil regulating and supporting ecosystem services. New production systems have emerged, such as no-tillage, that can enhance soil services but may limit yields. Moving forward, agricultural systems must reduce trade-offs between production and soil services. Soil functional zone management (SFZM) is a novel strategy for developing sustainable production systems that attempts to integrate the benefits of conventional, intensive agriculture, and no-tillage. SFZM creates distinct functional zones within crop row and inter-row spaces. By incorporating decimeter-scale spatial and temporal heterogeneity, SFZM attempts to foster greater soil biodiversity and integrate complementary soil processes at the sub-field level. Such integration maximizes soil services by creating zones of 'active turnover', optimized for crop growth and yield (provisioning services); and adjacent zones of 'soil building', that promote soil structure development, carbon storage, and moisture regulation (regulating and supporting services). These zones allow SFZM to secure existing agricultural productivity while avoiding or minimizing trade-offs with soil ecosystem services. Moreover, the specific properties of SFZM may enable sustainable increases in provisioning services via temporal intensification (expanding the portion of the year during which harvestable crops are grown). We present a conceptual model of 'virtuous cycles', illustrating how increases in crop yields within SFZM systems could create self-reinforcing feedback processes with desirable effects, including mitigation of trade-offs between yield maximization and soil ecosystem services. Through the creation of functionally distinct but interacting zones, SFZM may provide a vehicle for optimizing the delivery of multiple goods and services in agricultural systems, allowing sustainable temporal intensification while protecting and enhancing soil functioning.