High-density Treatment Research Articles

High plant density optimizes leaf stomatal traits for accelerating the stomatal response rate at the lower cotton canopy

AbstractPlants are often exposed to fluctuating light from a few seconds to a few minutes due to cloud movements, mutual shading of leaves, and change in the angle of the sun. Slow stomatal response to fluctuating light leads to carbon loss, but the influence of planting density on light fluctuation frequency and on stomatal response and carbon gain has yet to be fully explored. To fill this knowledge gap, we investigated leaf morphology, stomatal anatomy and response rate, nitrogen content, biomass, and yield under low density, moderate density, and high density (HD) of cotton cultivar (Gossypium hirsutum L.). The results showed that higher planting density significantly increased light fluctuation frequency at the lower canopy. Stomatal size significantly decreased with the increase in planting density, while total stomatal density was consistent. Stomatal density had greater plasticity of determining maximum stomatal conductance than stomatal size. Faster stomatal response rate to fluctuating light under HD was attributed to smaller and denser stomata in the abaxial leaf side. Therefore, cotton under HD treatment had faster photosynthetic induction rate under light induction, resulting in greater carbon gain. We conclude that faster stomatal response rate achieved by the optimization of stomatal anatomy, especially the abaxial side, plays a crucial role in obtaining more carbon gain, biomass, and yield under HD cotton field. This finding indicates that selecting varieties with rapid stomatal response traits and planting at appropriate densities may optimize fluctuating light use to achieve higher yields.

The Effect of Prey Size and Prey Density on Paralarval Feeding Success of the Common Sydney Octopus, Octopus tetricus

ABSTRACTGlobal demand for octopus seafood has been increasing over the past 30 years. This demand is projected to increase further as coastal communities and seafood consumers seek alternative sources of protein as finfish stocks decline. The establishment of a sustainable octopus aquaculture would have the potential to alleviate fishing pressures from wild populations. Commercial‐scale octopus aquaculture, however, has not been achieved due to the difficulty of successfully rearing octopus paralarvae on an efficacious diet. This study investigated the prey size and density preferences of Octopus tetricus paralarvae to understand the characteristics that improve food acquisition during rearing. Groups of octopus paralarvae from multiple broods were observed for a range of feeding behaviour including positioning, attack, capture loss, successful capture and handling time when given different treatments of Artemia prey. Prey size experiments used treatments of Artemia with total lengths of < 0.5, 0.9–1.0 and 1.4–1.6 mm, while prey density experiments used 0.2, 0.6, 1.0, 1.4, 1.8 and 2.2 Artemia mL−1. Increased numbers of successful feeding behaviours (e.g., positionings, attacks and successful captures) were directly observed with increasing prey size. Octopus paralarvae performed 52% more positionings, 100% more attacks and 175% more successful captures when given large Artemia (1.4–1.6 mm) than when given small Artemia (< 0.5 mm). Likewise, the number of observed successful feeding behaviours tended to increase with increasing Artemia density but sharply decreased at the highest density treatment (2.2 Artemia mL−1). Paralarvae performed up to 109% more positionings, 307% more attacks and 300% more successful captures when given prey densities of 1.0–1.8 Artemia mL−1 than when given lower prey density treatments and 2.2 Artemia mL−1. The results from this study indicate that prey size and density are crucial for the successful feeding of octopus paralarvae. Based on the greatest numbers of successful feeding behaviours, O. tetricus paralarvae prefer prey between 1.4 and 1.6 mm in length and at densities between 1.0 and 1.8 prey mL−1. The use of these optimal prey characteristics can be used to promote efficient paralarval octopus prey capture and feeding to greatly increase food intake in octopus paralarvae when reared in aquaculture.

Thinning Modulates the Soil Organic Carbon Pool, Soil Enzyme Activity, and Stoichiometric Characteristics in Plantations in a Hilly Zone

Thinning, a core forest management measure, is implemented to adjust stand density and affect soil biogeochemical processes by changing biotic and abiotic properties. However, the responses of soil organic carbon (SOC), soil enzyme activity (EEA), and stoichiometry (EES) in plantations in hilly zones to thinning have received little attention. To test the hypothesis that thinning has regulatory effects on the SOC pool, EEA, and EES characteristics, field sampling and indoor analysis were conducted 9 years after thinning. Thinning significantly influenced the soil properties, especially in the topsoil, and significantly greater SOC and mineral-associated organic carbon (MAOC) contents were observed in the high-density treatment. The EEAs in the topsoil tended to increase with increasing density. SOC, MAOC, and C to phosphorus (C:P) had the greatest influence on the soil EEAs and EESs. Microbial metabolic limitations tended to change from nitrogen to phosphorus with increasing density. The soil properties, SOC fractions, available nutrients, and elemental stoichiometry drove microbial metabolic limitations and were significantly positively correlated with β-glucosidase, elemental stoichiometry, and EES. This study deepens our understanding of EEAs, SOC, and nutrient dynamics under thinning practices and elucidates how forest tending measures affect soil biogeochemical processes, thereby providing ideas for developing strategies to mitigate the adverse impacts of human interventions.

Dense aquatic vegetation can reduce parasite transmission to amphibians

Submerged aquatic vegetation (macrophytes) can provide prey with refuges from predators and may perform a similar role for interactions with other natural enemies such as parasites. This could occur by interfering with the ability of free-swimming infectious parasite stages to locate or move towards hosts, reducing infections. Alternatively, infections may increase if macrophytes reduce host anti-parasite behaviours such as detection or evasion. Both scenarios could be affected by macrophyte density and structural complexity. Here we investigated whether experimental infection of tadpoles (Rana sylvatica and Rana pipiens) by parasitic flatworms (the trematodes Ribeiroia ondatrae and Echinostoma spp. was affected by the presence of artificial vegetation with varying density and complexity (simple versus branching), as well as tadpole activity under these conditions. Macrophyte presence significantly reduced tadpole infection loads only in the highest density treatment, but there was no effect of structural complexity. Related to this, tadpoles spent significantly more time near aquatic vegetation when it was dense but showed no preference for either structural type. Our results indicate that aquatic vegetation can reduce parasite transmission in certain scenarios, with further studies needed to explore how structural complexity in natural systems can affect host-parasite interactions, considering the massive physical alterations possible through eutrophication and the introduction of invasive plant species.

Effects of High-Density Mixed Planting in Artificial Grassland on Microbial Community

The construction level of artificial grassland is an important index of the development degree of grassland animal husbandry. Therefore, improving the productivity level of artificial grassland and promoting the sustainable utilization of artificial grassland have become important tasks that need to be urgently addressed. There have been numerous studies on the effects of monoculture on the soil microbial community structure in artificial grassland, but there is limited research on the effects of mixed sowing on the soil microbial community structure and the related patterns. In this study, Elymus nutans (En), Festuca sinensis (Fs), Avena sativa (As), and Poa pratensis (Pp) were used as common herbage materials in an alpine grassland pastoral area of the eastern Tibetan Plateau. Multi-density monoculture and mixed seeding were employed to establish artificial grassland communities with varying structures. By comparing the soil microbial community structure of the differently treated artificial planting grass, degraded grassland with bald spots, and natural grassland, it was confirmed that plant community diversity significantly influences the microbial community structure. The high-density planting treatment of multiple forage grasses had a more pronounced impact on the soil microbial community structure compared to that of the high-density planting treatment of a single variety of forage grass. The soil microbial community diversity index of the four mixed-planting treatments was higher than those of the other artificial grassland treatments and the natural grassland treatments, and the soil microbial community structure was most similar to that of the natural grassland. Avena sativa planting increased the abundance of Actinobacteria and Basidiomycota and decreased the number of Acidobacteria by increasing the soil pH value. The AFP (As+Fs+Pp) treatment reduced the proportion of Mortierellomycota in the soil by decreasing the content of available phosphorus. The AEFP (As+En+Fs+Pp) treatment increased the number of Proteobacteria by raising the soil total phosphorus content and reduced the abundance of Acidobacteria by lowering the soil pH value. Additionally, a machine learning method was used to evaluate the comprehensive performance of 21 artificial grassland treatments on nine soil physical and chemical properties. It was found that the AEFP mixed-planting and high-density planting treatments had the greatest improvement effect on the nine soil physical and chemical properties, which was conducive to sustainable land use.

Above- and Below-Ground Interactions and Interspecific Relationships in Wheat/Maize Systems

Above- and below-ground interactions play a crucial role in achieving higher yields in intercropping systems. Nonetheless, it remains unclear how these interactions impact intercropping crop growth and regulate interspecific relationships. This study aimed to quantify the impact of above- and below-ground interactions on crop yield by determining the dynamics of dry matter accumulation, photosynthetically active radiation (PAR) transmittance, and leaf area index (LAI) in intercropped wheat and maize. Three below-ground intensities were set for an intercropping system: no root separation (CI: complete interaction below ground), 48 μm nylon mesh separation (PI: partial interaction below ground), and 0.12 mm plastic sheet separation (NI: no interaction below ground). Two densities were set for maize: low (45,000 plants hm−2) and high (52,500 plants hm−2). At the same time, corresponding monoculture treatments were established. The grain yields in the CI and PI treatments were, on average, 23.7% and 13.7% higher than those in the NI treatment at high and low maize densities, respectively. Additionally, the grain yield for high density was 12.3% higher than that of low density in the CI treatment. The dry matter accumulation of intercropped wheat under the CI and PI treatments was, on average, 9.1%, 14.5%, and 9.0% higher than that in the NI treatment at the flowering, filling, and maturity stages, respectively. The dry matter accumulation of intercropped maize at the blister, milk, and physiological maturity stages increased by 41.4%, 32.1%, and 27.8%, respectively, under the CI treatment compared to the NI treatment. The PAR transmittance and LAI of maize at the V6 stage were significantly increased by increasing the intensity of below-ground interactions. This study showed that complete below-ground interaction contributed to a significant increase in the competitiveness of intercropped wheat with respect to maize (Awm) under the high-density maize treatment, especially at the filling stage of wheat. Moreover, the CI treatment enhanced the recovery effects of maize (Rm) after wheat harvesting. Increasing the intensity of below-ground interactions can significantly enhance the Awm and Rm in intercropping systems, favoring the accumulation of crop dry matter mass and light energy utilization to increase system yields.

Achieving Stress Relief in Martensitic Stainless Steel Via High-Density Pulsed Electric Current Treatment

Achieving Stress Relief in Martensitic Stainless Steel Via High-Density Pulsed Electric Current Treatment

Influences of Stocking Density on Antioxidant Status, Nutrients Composition, and Lipid Metabolism in the Muscles of Cyprinus carpio under Rice-Fish Co-Culture.

Cyprinus carpio is a significant freshwater species with substantial nutritional and economic value. Rice-carp co-culture represents one of its principal cultivation methods. However, in the system, the optimal farming density for carp and the impact of high stocking density on their muscle nutritional composition have yet to be explored. Thus, the objective of the current study was to investigate the influences of stocking density on the muscle nutrient profiles and metabolism of C. carpio in rice-fish co-culture systems. Common carp were cultured at three stocking densities, low density (LD), medium density (MD), and high density (HD), over a period of 60 days. Following this, comprehensive analyses incorporating physiological, biochemical, and multi-omics sequencing were conducted on the muscle tissue of C. carpio. The results demonstrated that HD treatment led to a reduction in the antioxidant capacity of C. carpio, while resulting in elevated levels of various fatty acids in muscle tissue, including saturated fatty acids (SFAs), omega-3 polyunsaturated fatty acids (n-3 PUFAs), and omega-6 polyunsaturated fatty acids (n-6 PUFAs). The metabolome analysis showed that HD treatment caused a marked reduction in 43 metabolites and a significant elevation in 30 metabolites, primarily linked to lipid and amino acid metabolism. Additionally, transcriptomic analysis revealed that the abnormalities in lipid metabolism induced by high-stocking-density treatment may be associated with significant alterations in the PPAR signaling pathway and adipokine signaling pathway. Overall, our findings indicate that in rice-fish co-culture systems, high stocking density disrupted the balance of antioxidant status and lipid metabolism in the muscles of C. carpio.

Effects of different stocking densities on growth, nutritional quality, stress and antioxidant response in Labeo rohita; cultured in in-pond raceway system.

A 171-day long experimental trial was undertaken to study intricate physiological response of rohu (Labeo rohita) under stress caused by high stocking density in In-pond raceways system (IPRS). Fingerlings of rohu (initial body weight: 250 ± 1.20 g) were cultured at three different stocking densities; low density (LD) (2.27 kg/m3), medium density (MD) (3.79 kg/m3) and high density (HD) (5.30 kg/m3) in raceways of IPRS production system. Each treatment was in triplicate. Fish growth exhibited a decline in HD treatment statistically as its average weight gain/fish/day was 4.21 g as compared to MD (4.82 g) and LD (4.74 g). Nutritional profile of rohu indicated by the content of crude protein, fatty acids, and profile of amino acids was up to the set dietary benchmarks. Survival rate of fish in all the treatment groups was greater than 99%. The elevated cortisol levels observed in the HD treatment in contrast to the other treatments suggested the presence of stress. The levels of superoxide dismutase, catalase and glutathione peroxidase were also higher in HD as compared to other treatments. However, there were no difference in the level of MDA between the three treatments. Activity of amylase, protease was significantly different in treatment whereas the difference in lipase activity was found to be insignificant. It can be concluded that medium stocking density i.e. 3.79 kg/m3 outperformed the high density (5.30 kg/m3) in different aspects of this study. Nevertheless, additional research is imperative to ascertain whether any intermediate stocking density between medium (3.79 kg/m3) and high (5.30 kg/m3) such as 4 kg/m3, 4.5 kg/m3, or 5 kg/m3, could potentially serve as suitable options for rohu. It is also suggested that brood stock of rohu should be genetically improved to obtain stress resilient fingerlings which will perform better at high stocking density at large scale production level.

The genotypic variation in the positive response of sorghum to higher sowing density is linked to an increase in water use efficiency

In semi-arid tropical areas, sorghum is sown at very low planting densities. Hence, increasing plant density represents an opportunity to improve productivity. However, assessing the expected increase in water needs is critical prior to testing higher densities under rainfed conditions. This was tested with a panel of elite cultivars in field and lysimiter experiments, and testing the effects of two density treatment, high (HD, 22 plants.m-²) and low (LD, 11 plants.m-²), on grain and biomass yield and on water use and water use efficiency (WUE). Doubling the conventional sowing density significantly increased biomass and grain yield, with a genotypic variability in the biomass response. No link was found between the response to density and the maintenance of the tillering capacity, whereas the response to density was somewhat explained by a differential increase in the leaf area index under high density (r=0.43 P<0.05). Lysimeter experiments showed that, compared with the conventional density, the high-density treatment had 62% increase in biomass vs a 38% increase in water use, resulting in a 17% higher WUE on average of the genotypes tested. There was an appreciable genotypic variability in this degree of WUE increase under high density. The most striking result was the very tight positive link between the biomass response to density and the differential increase in WUE in the dry season (r=0.91 P<0.0001), whereas in the wet season this link was negative (r=-0.48 P<0.02). This work shows that intensifying sorghum production by increasing sowing density is possible, in the short term using cultivars that show the largest WUE increase under high density, in the longer term by breeding high-density adapted cultivars, targeting plant traits that explain the tight link between higher WUE and higher yield under high density.

Analysis of cell growth, photosynthetic behavior and the fatty acid profile in Tetraselmis subcordiformis under different lighting scenarios

Tetraselmis has been investigated as a potential source of lipids. This microalga possesses good growth characteristics and can be used to develop viable platforms for fatty acid production. This research aims to evaluate the effect of high photon flux density with light-dark cycles and light wavelength on biomass production and fatty acid profile in Tetraselmis subcordiformis. A low light control and treatments with high photon flux density with different light-dark cycles (24:0 h, 12:12 h, 1:1 h, and 15:15 min) and different light wavelength (white, green, red, and blue) were evaluated to determine cell concentration, nutrient consumption, chlorophyll content, photosynthetic yields, lipid content, and fatty acid profile. Significant differences were found in all variables, except for phosphate consumption. High photon flux density promotes cell growth with T. subcordiformis reaching biomass productivities of 0.10 g L-1 day-1 when continuous white light is used. However, no differences were observed in biomass productivities and lipid content for all high photon flux density treatments. On the other hand, red light resulted in higher cell growth, with a productivity of 0.12 g L-1 day-1, and the highest lipid content was achieved under white light. There was a significant effect on the fatty acid profile under different light conditions, with palmitic acid, oleic acid, and eicosapentaenoic acid being the most abundant. This study demonstrated that cellular growth and fatty acid profiles in T. subcordiformis can be influenced by different lighting schemes in the cultivation.

Growth of juvenile red abalone (Haliotis rufescens) co-cultivated with two densities of warty sea cucumber (Apostichopus parvimensis)

ABSTRACT Co-culture of abalone and sea cucumber can result in benefits. This study investigated for 131 days the growth of juvenile red abalone (Haliotis rufescens) co-cultured with two densities of warty sea cucumbers (Apostichopus parvimensis). The initial mean (± SE) shell length of 1080 red abalone was 26.74 ± 1.04 mm, with a wet weight of 5.64 ± 0.12 g. The average weight of nine sea cucumbers was 175.26 ± 2.22 g. One experimental treatment had low density (LD) of sea cucumbers with a ratio of 1 gram of abalone to 0.25 grams of sea cucumber. The other, high density (HD) with a ratio of 1 gram of abalone to 0.50 grams of sea cucumber and a control treatment without sea cucumbers. There were no differences in abalone growth between treatments and the control; the only differences were among HD and LD. Abalone from the HD treatment had 19.40% higher growth than the control and 20.94% than the LD. Overall, the sea cucumbers in both treatments showed a decrease in body weight, 17.15% in the HD and 6.13% in the LD. We hope our results encourage further studies for developing multitrophic aquaculture in the Northeastern Pacific.

Elevating fatigue life in nickel-based superalloys through suppression of persistent slip bands/markings via high-density pulsed electric current treatment

Elevating fatigue life in nickel-based superalloys through suppression of persistent slip bands/markings via high-density pulsed electric current treatment

Interaction between drinker density and cow social dominance affects drinking behavior

Dairy cow welfare and milk production levels can be negatively affected when animals lack access to sufficient amounts of good-quality drinking water. Farms vary greatly in how well they meet this standard. Here, we explored how the interaction between drinker density and social dominance level influenced the drinking behaviors of a group of 40 mid-lactation cows. We recorded cow drinking behavior and competitive outcomes (i.e., number of replacements) at the drinkers during the final 5 d of 2 drinker density treatments, applied successively (12 drinkers, then 4 drinkers available). Four social dominance categories were defined by applying the quartile classification method to the normalized David's score obtained from the low-density treatment data (NormDS values). The high- and low-density treatments used approximately 56 (±16) versus 119 (±31) replacements per drinker per day. Subordinate cows were lighter and younger than dominant cows. Dominant cows drank around 5 L more per day in the low- versus high-density treatment. Furthermore, both drinking rate and daily drinking frequency were higher in the low-density treatment, with the most pronounced differences seen for subordinate cows. In the low-density treatment, mid-subordinate cows shifted their drinking times, visiting the drinkers 1 to 2 h after peak water consumption by the group. The results for the low-density treatment thus indicate that the cows were experiencing more intense competition for water, leading to behavioral responses that were related to social dominance. Our findings underscore the need to more broadly explore the effects of increasing drinker numbers under a variety of rearing conditions to provide farmers with better technical recommendations.

Ultrahigh deformability of Ti-6Al-4V assisted by high-density pulsed electric current treatment

In this study, the mechanical properties and microstructural evolution of the pre-strained titanium alloy Ti‐6Al‐4V under high-density pulsed electric current (HDPEC) treatment were investigated. The results showed that the HDPEC treatment successfully restored the plastic deformation or strain hardening of the pre-strained Ti‐6Al‐4V without deteriorating its strength. In addition, multi-HDPEC treatments were conducted to examine the cumulative effect on plastic recovery, and ultrahigh deformability with an increasing rate of 287% was achieved at a current density of 250 A/mm2 for 20 ms. Microstructural characterization indicated that dislocations and the associated sub-grain boundaries were remarkably reduced after the HDPEC treatment, contributing to ductility enhancement. Additionally, the rapidly heat-treated sample with a thermal history curve similar to that of the HDPEC-treated samples did not show obvious microstructural changes, indicating that the athermal effect of the HDPEC treatment plays an important role in modifying the microstructure of the material. The α'/α'' martensite phases were formed in the β phase after the HDPEC treatment, which is possibly related to the high cooling rate and diffusion of the V element (β phase stabilizer element). Specifically, at the current condition of 250 A/mm2 for 20 ms, some tiny martensite phases precipitated in the β phase without heavily deteriorating the microstructure and mechanical properties. Therefore, owing to its low cost and high efficiency, the HDPEC treatment can be applied to Ti-alloy components with internal plastic deformation to realize rapid restoration or achieve long service periods without significantly altering the microstructure.

Mechanical characteristics and reservoir stimulation mechanisms of the Gulong shale oil reservoirs, the northern Songliao Basin

Shale oil of the Qingshankou Formation of the Gulong Sag, the northern Songliao Basin, represents the first attempt at large-scale development of pure-shale-type shale oil in China. By integrating the multi-scale refined reservoir characterization with macro-micro-scale mechanical testing, it is clarified that the Gulong shale is characterized by high clay mineral content, high rock plasticity, highly-developed bedding, and prominent mechanical anisotropy. A three-dimensional (3D) fracture propagation model of hydraulic fracturing was built for the Gulong shale, which fully captures the hydraulic fracture distribution pattern affected by the high bedding density, in-situ stress, and fracturing treatment parameters. Our research showed that due to influences of bedding, hydraulic fracturing in the Gulong shale forms a complex fracture morphology featuring the main fracture with multiple perpendicular branches that have different lengths (like the outdoor directional TV antenna); however, the vertical propagation of fractures is inhibited, and the fracture height is commonly less than 10 m. The limited stimulated reservoir volume (SRV) is the main problem facing the fracturing stimulation of the Gulong shale oil. Bedding density has vital effects on fracture morphology, so case-specific fracturing designs shall be developed for shale intervals with different bedding development degrees. For reservoirs with well-developed bedding, it is suggested to properly increase the perforation cluster spacing and raise the volume and proportions of viscous fluids of the pad, so as to effectively promote vertical fracture propagation and improve reservoir stimulation performance. This study integrates multi-scale fine reservoir characterization and macro-micro-scale mechanical testing, as well as the construction and numerical simulation of hydraulic fracturing models for high-density layered shale reservoirs, providing a new approach and methodological framework for the fracturing research of high-density layered shale reservoirs.

Density-dependent within-patch movement behavior of two competing species.

Movement behavior is central to understanding species distributions, population dynamics and coexistence with other species. Although the relationship between conspecific density and emigration has been well studied, little attention has been paid to how interspecific competitor density affects another species' movement behavior. We conducted releases of two species of competing Tribolium flour beetles at different densities, alone and together in homogeneous microcosms, and tested whether their recaptures-with-distance were well described by a random-diffusion model. We also determined whether mean displacement distances varied with the release density of conspecific and heterospecific beetles. A diffusion model provided a good fit to the redistribution of T. castaneum and T. confusum at all release densities, explaining an average of >60% of the variation in recaptures. For both species, mean displacement (directly proportional to the diffusion rate) exhibited a humped-shaped relationship with conspecific density. Finally, we found that both species of beetle impacted the within-patch movement rates of the other species, but the effect depended on density. For T. castaneum in the highest density treatment, the addition of equal numbers of T. castaneum or T. confusum had the same effect, with mean displacements reduced by approximately one half. The same result occurred for T. confusum released at an intermediate density. In both cases, it was total beetle abundance, not species identity that mattered to mean displacement. We suggest that displacement or diffusion rates that exhibit a nonlinear relationship with density or depend on the presence or abundance of interacting species should be considered when attempting to predict the spatial spread of populations or scaling up to heterogeneous landscapes.

AM fungus promotes wheat grain filling via improving rhizospheric water & nutrient availability under drought and low density

Arbuscular mycorrhizal fungi (AMF) are widely considered as ecosystem engineers to positively affect the adaptation of plants to adverse environments, but whether AMF can commonly promote root-soil relationships and reproductive allocation is unclear in dryland crops. It is crucial to reveal if AMF can promote grain filling via mediating rhizosphere interactions regardless of soil water regimes and planting densities in dryland crops for the application of AMF regarding more precise management. To address this issue, Funneliformis mosseae was inoculated in pot-cultured wheat to examine the inoculation effects on wheat growth, yield formation, rhizospheric moisture and nutrient status across four planting densities under the drought and well-watered conditions. As expected, under drought stress, wheat grain filling, shoot biomass, rhizospheric soil water content (SWC), water use efficiency (WUE), soil organic carbon (SOC) content and the ratio of SOC to soil total nitrogen (TN) contents were significantly lowered in the soils without AMF inoculation across four planting densities. Under well-watered conditions, the SWC ranged from 10.30 % to 16.64 %, while under water stress conditions, the values ranged from 5.77 % to 9.61 %. Soil mineralized nitrogen (NO3−-N and NH4+-N) contents were decreased with AMF regardless of soil water status and planting densities. Under drought stress, AMF inoculation increased wheat productivity, WUE, SWC, SOC content, the ratio of SOC to TN, and promoted the absorption of mineralized nitrogen. Particularly, AMF inoculation substantially promoted the soil easily oxidizable organic carbon (EOC) content by 58.5 % and 55.6 % in the two highest densities, respectively. The soil microbial biomass carbon (MBC) content was totally >50 mg kg−1, whereas that of the non-AMF group was <40 mg kg−1. AMF inoculation significantly promoted grain yield up to 28.5 % under drought stress. Such a trend was tightly associated with higher WUE, rhizosphere C/N ratio and labile SOC (EOC and MBC) content owing to the enhanced absorption of soil mineralized nitrogen under drought stress with AMF. The above trend tended to become weaker with increasing densities. However, under a sufficient water supply, AMF inoculation had no such significant effect on the above parameters in low densities, and turned to generate negative effects under high densities (P < 0.05). For example, compared with well-watered, AMF inoculation reduced wheat grain yield and shoot weight by 9.78 % and 4.83 % in high planting density treatment (HC), respectively. Therefore, the inoculation effects of AMF were highly dependent on planting density and soil moisture, and the mechanism was that AMF optimized the rhizospheric interactions for better water and nutrient status under drought and low density. Our findings may provide novel insights into the application of AMF regarding agricultural sustainability under climate change.

Submersed Macrophyte Density Regulates Aquatic Greenhouse Gas Emissions

AbstractShallow freshwater ecosystems emit large amounts of greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), yet emissions are highly variable. The role that aquatic macrophytes play in regulating aquatic GHG emissions is uncertain despite their ability to dominate shallow waterbodies. Here, we studied the effects of submersed macrophyte (Ceratophyllum demersum) density on CO2 and CH4 concentrations and fluxes. We conducted a 61‐days experiment using mesocosms containing one of the following C. demersum density treatments: 0, 10, 20, or 30 individual shoots (n = 3). We found that high density C. demersum had the highest CO2 and CH4 surface water concentrations and emissions while there was no significant difference in CH4 in the low and medium densities and no plant control. The high density treatment lost biomass over the course of the experiment, indicating die‐off and additions of organic matter to the sediment. High organic matter loading and low dissolved oxygen likely stimulated GHG production in the high density treatment. Our results emphasize that submersed macrophyte density and periods of growth and dieback are important in regulating GHG emissions, which may help explain why shallow waterbodies are high yet variable sources of GHGs to the atmosphere.

Plant Density Recommendations and Plant Nutrient Status for High Tunnel Tomatoes in Virginia

Open-field tomatoes in Virginia are traditionally planted in a single row with 2 ft (0.60 m) of in-row spacing, resulting in a plant density of 4356 plants per acre (10,890 plants/ha). However, there has been increasing interest among small and medium-sized farmers in high tunnel production. In order to be profitable, farmers must maximize their yield per unit area and take advantage of the potential benefits of producing under high tunnels. A common approach under greenhouse conditions is to increase the planting density to enhance yield per area. However, high tunnel farmers often extrapolate open-field practices to their high tunnels as they believe both systems are closer related together than to greenhouse production. In those cases, high tunnel farmers could potentially be neglecting yield increases due to their planting density selection. Additionally, irrigation and fertilization management (fertigation) under high tunnels tend to be more efficient than open-field systems, as the frequency of application is increased with a lower volume per application. A higher efficiency of fertigation could alter plant yield responses, especially under traditional planting-density systems. Hence, this study aimed to identify the effect of high planting density on high tunnel tomatoes and their nutrient status on the Eastern Shore of Virginia. The experiment was established on a completely randomized block design with four replications, with 20 ft (6.09 m) experimental plots. We evaluated the combination of two in-row distances and single and double planting rows, with treatments consisting of 2 ft of in-row distance in a single row (4356 plants/acre—current open-field recommendation), 1.5 ft (0.45 m) of in-row distance in a single row (5808 plants/acre [14,520 plants/ha]), 2 ft of in-row distance in a double row (8712 plants/acre [21,780 plants/ha]), and 1.5 ft of in-row distance in a double row (11,616 plants/acre [29,040 plants/ha]). Summer-grown tomatoes produced on the Eastern Shore of Virginia under high tunnel conditions should be planted with 2 ft of in-row spacing and with a single row of plants per planting bed. Increasing the plant density or modifying the current recommended plant distribution could result in yield losses per plant between 32% and 46% and substantial increases in production costs compared with the traditional planting density. Throughout all treatments, tomato plants did not show deficient nutrient status. We hypothesized that irrigation water and pollination were the limiting factors that promoted a decrease in yield per plant for the high-density treatments.