Soil Oxygen Content Research Articles

Aerated Irrigation of Different Irrigation Levels and Subsurface Dripper Depths Affects Fruit Yield, Quality and Water Use Efficiency of Greenhouse Tomato

Aerated irrigation (AI) is a method to mitigate rhizosphere hypoxia caused by the wetting front from subsurface drip irrigation (SDI). This study evaluated the impacts of AI on soil aeration, plant growth performance, fruit yield (tomato), irrigation water use efficiency (IWUE), fruit nutrition (lycopene and Vitamin C (VC)) and taste (soluble sugar, organic acid and sugar–acid ratio) quality. A three-factorial experiment including AI and SDI at three irrigation levels (W0.6, W0.8 and W1.0, corresponding with crop-pan coefficients of 0.6, 0.8 and 1.0) and two dripper depths (D15 and D25, burial at 15 and 25 cm, respectively), totaling 12 treatments overall, was conducted in a greenhouse during the tomato-growing season (April–July) in 2016. The AI improved soil aeration conditions, with significantly increased soil oxygen concentration and air-filled porosity relative to SDI. Moreover, the AI improved crop growth performance, with increased root morphology (diameter, length density, surface area and volume density), delayed flowering time, prolonged flowering duration and increased shoot (leaf, stem and fruit) dry weight, and harvest index. Fruit yield per plant, fruit weight, IWUE, the contents of lycopene, VC and soluble sugar, and sugar–acid ratio significantly increased under AI treatments (P < 0.05). As the irrigation level increased, fruit yield, number, and weight increased (P < 0.05), but IWUE and fruit lycopene, soluble sugar, and organic acid content decreased (P < 0.05). The dripper depth had no significant impact on fruit yield, nutrition and taste quality. Principal component analysis revealed that the optimal three treatments in terms of fruit yield, IWUE, and nutrition and taste quality were the treatments W0.6D25AI, W1.0D25AI and W1.0D15AI. These results suggest that AI can improve tomato growth performance and increase fruit yield, nutrition and taste quality, and IWUE through enhancing soil aeration conditions.

Natural Nitrogen Isotope Ratios as a Potential Indicator of N2O Production Pathways in a Floodplain Fen

Nitrous oxide (N2O), a major greenhouse gas and ozone depleter, is emitted from drained organic soils typically developed in floodplains. We investigated the effect of the water table depth and soil oxygen (O2) content on N2O fluxes and their nitrogen isotope composition in a drained floodplain fen in Estonia. Measurements were done at natural water table depth, and we created a temporary anoxic environment by experimental flooding. From the suboxic peat (0.5–6 mg O2/L) N2O emissions peaked at 6 mg O2/L and afterwards decreased with decreasing O2. From the anoxic and oxic peat (0 and >6 mg O2/L, respectively) N2O emissions were low. Under anoxic conditions the δ15N/δ14N ratio of the top 10 cm peat layer was low, gradually decreasing to 30 cm. In the suboxic peat, δ15N/δ14N ratios increased with depth. In samples of peat fluctuating between suboxic and anoxic, the elevated 15N/14N ratios (δ15N = 7–9‰ ambient N2) indicated intensive microbial processing of nitrogen. Low values of site preference (SP; difference between the central and peripheral 15N atoms) and δ18O-N2O in the captured gas samples indicate nitrifier denitrification in the floodplain fen.

Effect of Municipal Solid Waste Disposal on the Engineering Properties of Soil from a Non-Engineered Landfill

The presents study showed the effect of open dumping on soil characteristics and biodegradation settlement analysis of soil in non-engineered landfill. The contaminated soil is referred to as waste soil which has different settlement rates due to the various categories and complex characteristics of waste. The degradation of waste causing percolation of leachate into soil affecting the strength and stability of soil. This paper includes the analysis of geotechnical properties and settlement analysis of waste soil and its comparison was done with natural soil. The geochemical analysis was carried out by Energy Dispersive X- Ray Spectroscopy (EDX) and Scanning Electron Microscopy (SEM). The elemental analysis of soil exhibited presence of high oxygen and silica content in uncontaminated soil. The analysis depicted that specific gravity, maximum dry density (MDD), permeability and California bearing ratio (CBR) showed decreasing trend variation for polluted soil. It was observed that cohesion for contaminated soil was found to be increased thereby increasing the shear strength of soil. Additionally, temperature, pH and moisture content hold a significant position for assessing the settlement. The settlement of soil due to biodegradation of MSW is estimated using empirical mathematical model for dump site depending upon pH, moisture content and temperature. Additionally, settlement is evaluated keeping in view the settlement due to biodegradation of MSW on soil, which further helped in determination of the suitability of the site for the construction and other recreational purposes.

Aerated Irrigation Promotes Soil Respiration and Microorganism Abundance around Tomato Rhizosphere

Core Ideas Aerated irrigation improved soil aeration, increasing oxygen concentration and air‐filled porosity. Aerated irrigation enhanced soil, microbial, and root respiration and microbe abundance. Soil oxygen, air‐filled porosity correlated with respiration, microbe abundance. Aerated irrigation has economic benefits, promoting fruit yield and IWUE. Aerated irrigation (AI), by which aerated water is supplied to soil through subsurface drip irrigation (SDI), has shown high yield potential and application prospects. This study evaluated the impact of AI on soil aeration, respiration components, and microorganism abundance to determine the relationships between these parameters. Four treatments (W1AI, W2AI, W1CK, and W2CK) combining AI and nonaerated SDI (CK) and two irrigation levels (W1 and W2, with crop‐pan coefficients of 0.6 and 1.0) were conducted in a greenhouse during two tomato (Lycopersicon esculentum Mill.) growing seasons in April to July in 2015 and 2016. The results showed that AI improved soil aeration conditions, with soil oxygen concentration and air‐filled porosity significantly increasing by 5.86 and 5.16%, respectively, compared with CK. The W1AI treatment increased soil, microbial, and root respiration as well as bacteria, actinomycetes, and fungi abundance by 18.8, 10.0, 23.4, 30.1, 29.4, and 30.1%, respectively, compared with W1CK, and W2AI significantly increased these by 24.2, 15.3, 28.7, 39.2, 39.3, and 37.1%, respectively, compared with W2CK. Moreover, the abundance of bacteria, actinomycetes, and fungi with W2AI significantly increased by 26.9, 27.1, and 24.8%, respectively, compared with W1AI. Soil oxygen concentration (under controlled soil temperature) and air‐filled porosity positively correlated with soil respiration and microorganism abundance. Mean fruit yield with AI was 22.4% higher than CK. Aerated irrigation therefore stimulated soil respiration and microbial proliferation by improving soil aeration conditions. Enhanced soil aeration, respiration, and microorganism abundance under AI provide economic benefit by improving fruit yield.

Corrosion Behavior of Steel Buried in Soil Under Natural Rainfall Conditions at Outdoor Test Field

Introduction Buried steel structures generally deteriorate due to soil corrosion. The corrosion rate depends on various soil environment factors such as the water content, pH value, resistivity, and oxygen concentration (1, 2). It is well known that these factors in shallow ground usually change with rainfall. However, the relationship between these factors and the corrosion rate of buried steel under natural rainfall conditions has not been clarified. Therefore, in this study, we used electrochemical impedance spectroscopy to evaluate the corrosion behavior of steel buried in shallow ground under natural rainfall conditions at outdoor test fields. Experimental The electrode cell for the AC impedance measurements was fabricated from a carbon steel plate with dimensions of 10 × 10 mm and embedded in epoxy resin. It was buried at a depth of 90 cm in the gley soil of the experimental system at outdoor test field. The soil conditions changed with rainfall. The AC impedance measurements were carried out at constant time interval to evaluate the changes in the corrosion rate with rainfall. They were conducted over the frequency range of 0.05 Hz to 10 kHz at the AC voltage of ± 50 mV. Results and discussion Figure 1 shows the Nyquist plot of the buried steel obtained from the AC impedance measurement with different voltage conditions. The equivalent circuit is also shown in Fig. 1, where R s, R ct, C dl, and Z w are the resistance in soil, charge transfer resistance, double-layer capacitance, and Warburg impedance, respectively. At the low AC voltage of ± 5 mV, the Nyquist plot could not be measured due to exogenous noise. On the other hand, as shown in Fig. 1, it could be obtained by increasing the AC voltage to ± 50 mV. It has been confirmed that the influence of the applied voltage of ± 50 mV on the Nyquist plot is small. Therefore, we set the AC voltage during the impedance experiments to ± 50 mV. Figure 2 shows the changes in the 1/R ct value of the buried steel over time under natural rainfall conditions. As shown in Fig. 2, the value of 1/R ct, which is proportional to the corrosion rate, decreased during rainfall and gradually increased over time after the rain stopped. During this experiment, the soil water content and oxygen concentration were kept almost constant at around 54% and 0.9%, respectively. In extremely low-oxygen soil, it is considered that the cathodic reaction on the steel surface is a reduction reaction of water, not a reduction reaction of oxygen. Since both the soil water content and oxygen concentration were almost constant, it is suggested that the cathodic reaction stayed constant during experiment. Therefore, in this study, the change in the corrosion rate with rainfall was thought to be due to changes in anodic reactions. Conclusion The corrosion rate of steel buried at a depth of 90 cm in gley soil under natural rainfall conditions at outdoor test fields was monitored by electrochemical impedance spectroscopy. It was observed that the 1/R ct value, which is proportional to the corrosion rate, decreased during rainfall and gradually increased over time after the rain stopped. From the changes in the AC impedance and soil environment factors with rainfall, it was found that the corrosion rate in gley soil was closely related to anodic reactions on the steel surface. References (1) R. Akkouche, C. Rémazailles, M. Barbalat, R. Sabot, M. Jeannin and Ph. Refait, J. Electrochem. Soc., 164(12). C626-C634 (2017). (2) S. Mineta, S. Ohki, M. Mizunuma, S. Oka, ECS Trans., 85(13), 599-604 (2018). Figure 1

Interactive effects of nitrate and oxygen on methane oxidation in three different soils

The ability of soil to uptake methane is regulated by several factors affecting soil microbial activity. The soil oxygen concentration is usually lower than the concentration of atmospheric air, and nitrogen fertilization contributes to a significant increase in nitrate-N in soil. Therefore, we selected three agricultural soils (Eutric Cambisol, Haplic Podzol, Mollic Gleysol) to investigate interactive effects of oxygen and nitrate (KNO3) on CH4 oxidation including different gradients of O2 (20%, 10%, 5%, 2%) and nitrate (0, 100, 200 mg N kg−1). The soils varied in their response to O2 and nitrate treatments. In the absence of nitrate, all soils completely oxidized added CH4 (1%) under the oxygen concentrations used (except 2%O2); however, low oxygen (5%; 10%O2) was optimal. Both nitrate doses strongly stimulated methane oxidation at 2%O2 in Podzol and Gleysol, but generally inhibited CH4 uptake in Cambisol.

Micro-nano bubble water oxygation: Synergistically improving irrigation water use efficiency, crop yield and quality

Coordination of water saving, yield and quality increase remains an attractive problem in agricultural production. Transporting irrigation water rich in micro-nano bubbles and fertilizers to the crop root zone through subsurface drip irrigation is expected to be an effective technique. In present study, cucumber and tomato cultivated in greenhouse were subjected to investigate the effects of three mixing ratios of micro-nano bubble water and groundwater combined with three different oxygation frequencies on irrigation water use efficiency, crop yield and quality. The results indicated that micro-nano bubble water oxygation could significantly increase their yield, irrigation water use efficiency and fruit quality (p < 0.05) without increasing the amounts of irrigation water and fertilizer, which demonstrated a cleaner production being friendly to soil ecological environment and sustainability using water saving technology. In the optimal treatment, the yield, irrigation water use efficiency, vitamin C, and soluble sugar of tomatoes increased by 16.9%, 16.9%, 17.7% and 39.2%, while those for cucumbers were 22.1%, 22.1%, 16.7% and 19.4%, respectively. This was mainly due to the increased soil oxygen content, longer retention time and stronger mass transfer ability of micro-nano bubbles. The recommended micro-nano bubble water oxygation mode for tomato plantation was the mixing ratio of 1:4 combined with the frequency of once every 5d, while that of cucumber being the mixing ratio of 1:0 with the same frequency with tomato. The study aims to provide a novel concept for the synergistic realization of water saving, yield increases and quality improvements in greenhouse crop production using subsurface drip irrigation.

Effects of film mulching and nitrogen fertilization on rhizosphere soil environment, root growth and nutrient uptake of winter oilseed rape in northwest China

The ridge film mulching and furrow planting (RFMF) pattern has been increasingly applied to the production of wheat, maize, and potato in arid and semiarid regions of northwest China because it can significantly improve crop yield. How RFMF affects the productivity and whether it can improve the rhizosphere soil environment of winter oilseed rape (Brassica napus L.) is not clear. The main objective of the present study was to determine whether RFMF can improve rhizosphere soil environment and winter oilseed rape productivity in comparison to the conventional flat planting (FP) pattern in a three-year (2014-2017) field experiment. In combination with each planting pattern, we determined an optimal nitrogen (N) application rate among six levels: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240) and 300 (N300) kg N ha−1. Results showed that the RFMF pattern significantly improved the rhizosphere soil environment by increasing soil moisture by 0.3–5.6% and soil temperature by 0.6–3.0 °C. However, soil oxygen concentration decreased by 0.03–5.66% during the flowering stage of winter oilseed rape. In addition, the RFMF pattern markedly improved rhizosphere soil enzyme activity and microorganism abundance and thus promoted root growth, nutrient uptake, and seed yield of winter oilseed rape. The resulting optimal N application rates remarkably improved rhizosphere soil enzyme activity, microorganism abundance, root growth, nutrient uptake, and yield of winter oilseed rape in both RFMF and FP treatments. In the RFMF treatment, N240 obtained significantly greater rhizosphere soil enzyme activity, microorganism abundance, root growth parameters, nutrient uptake, and seed yield than N0, N60, N120, and N180, with no significant differences observed between N240 and N300. In conclusion, the RFMF pattern in combination with the optimal N-application rate of 240 kg ha−1 has great potential to improve rhizosphere environment and winter oilseed rape productivity in arid and semiarid regions of northwest China.

Straw amendment with nitrate-N decreased N2O/(N2O+N2) ratio but increased soil N2O emission: A case study of direct soil-born N2 measurements

Straw application in combination with synthetic N fertilizer could increase crop yield and improve soil fertility, however, contradictory observations have been reported on the effects of straw addition on soil N2O emission. Straw application can affect both denitrification rate and its product stoichiometry (N2O/(N2O + N2) ratio), whereas the latter remains rather unclear since the ratio is strongly regulated by other soil parameters, e.g. nitrate and oxygen concentrations at denitrifying micro-sites. In this context, we conducted an incubation experiment with a robotized continuous flow incubation system using a He/O2 atmosphere and measured N2O and direct N2 fluxes over 22 days. Soil amended with and without rice straw (2.5 g kg−1 soil) in conjunction with nitrate fertilizer (10 mM KNO3) and non-amended control soil were incubated under 85% water-filled pore space. To simulate a short soil anoxic period, three different O2 partial pressures phases were set (20%, 5% and 10%). Additionally, N2O site preference signatures of soil-emitted N2O were analyzed to identify the processes contributing to N2O fluxes. Addition of nitrate increased cumulative N2O fluxes and decreased cumulative N2 fluxes compared with non-fertilized control, while rice straw amendment increased both N2O and N2 emissions drastically compared with the nitrate only treatment. The N2O SP values ranged from 0.4 to 2.7‰ among all treatments, indicating denitrification/nitrifier denitrification was the dominating source. The results suggest that straw amendment can trigger high denitrification rate, whereas the effect of straw amendment on the amount of emitted N2O and the N2O/(N2O + N2) product ratio strongly depends on soil NO3− concentration. As a conclusion, the present study suggests that straw amendment in conjunction with nitrate-N can increase soil N2O emissions under conditions favoring denitrification, even though it may decrease the overall N2O/(N2O + N2) product ratio.

Effects of wheel traffic and farmyard manure applications on soil CO 2 emission and soil oxygen content

This 2-year field study investigated the effects of different wheel traffic passes, manure amounts, and manure application methods on soil temperature, soil moisture, CO 2 emission, and soil O 2 content. To achieve this purpose, three different wheel traffic applications (no traffic, one pass, and two passes) were used. In the experiments, two different methods of manure applications (surface and subsurface) and three different farmyard manure amounts were used with a control plot (N0), 40 Mg ha -1 (N40), and 80 Mg ha -1 (N80). Manure was applied in both years of the experiment in the first week of April. For the subsurface application, the manure was mixed in at approximately 10 cm of soil depth with a rotary tiller. According to the results, soil temperature, soil moisture, penetration resistance, and bulk density increased with increasing wheel traffic except CO 2 emission for 2014 and 2015. CO 2 emission values decreased with traffic. Subsurface manure application caused more CO 2 emission compared to surface application. The increase in manure amounts led to an increase in CO 2 emission and soil moisture content. The effects on soil O 2 content were observed only during 2015. Maximum oxygen values were obtained in the plots where compaction was not applied. In addition, surface manure application caused more soil O 2 content compared to subsurface application.

Survival of Salmonella and Escherichia coli in Two Different Soil Types at Various Moisture Levels and Temperatures

With the increased consumption of fresh produce, a proportional increase in numbers of produce-related foodborne illness has been observed. An estimate of foodborne illness during 1998 to 2008 attributed ∼46% of the incidences to produce. Any foodborne illness associated with produce can have devastating consequences to the industry. The most recent data from the Centers for Disease Control and Prevention implicate leafy vegetables, vine-stalk vegetables, root vegetables, and sprouts as the most common cause of produce-related foodborne outbreaks. Excess rainfall or flooding, mainly by altering levels of soil moisture and oxygen content, affects the microbial community in soil. The goal of this research was to determine the survivability of a three-serovar Escherichia coli and a five-serovar Salmonella enterica cocktail in microcosms prepared with Candler sand (CS) and Orangeburg sandy loam (OSL) soils. Microcosms were prepared with low, medium, and high volumetric water contents and were incubated at 20 and 30°C. Serotyping was used to determine which E. coli or Salmonella serovar(s) from each cocktail persisted. Microcosm inoculation levels were ∼7.0 log CFU/g. Sampling for CS and OSL microcosms incubated at 20°C ended on day 364 and 357, respectively. The reduction of Salmonella and E. coli to below the limit of detection (extinction) in CS microcosms (incubated at 30°C at all volumetric water content [VWC] levels) was reached on day 168 and 56, respectively. Extinction of Salmonella and E. coli in OSL microcosms (incubated at 30°C at all VWCs) was reached on day 168 and 224, respectively. Of the Salmonella and E. coli serovars analyzed, Salmonella Javiana persisted the longest in both soil types, whereas E. coli O104:H4 and E. coli O145 persisted the longest in CS and OSL microcosms, respectively. Results from the current study suggest that soil type and temperature influenced pathogen persistence in CS and OSL soils more than moisture level and pathogen type.

NUMERICAL SOLUTION OF THE DIFFUSION EQUATION FOR OXYGEN DIFFUSION IN SOIL

By solving the diffusion equation using the explicit finite difference method, oxygen concentrations inside the soil are determined for various periods of time. Two different cases are investigated, with constant and daily changing air oxygen concentrations. It was concluded that the influence of the periodical change of the air oxygen concentration on the oxygen concentration in the soil was more pronounced for smaller diffusion times at smaller lengths of the soil profile.

Aeration of clayey soils by injecting air through subsurface drippers: Lysimetric and field experiments

We examined the effects of air injection into clayey-soil, with and without a perforated sphere around the dripper, on oxygen concentrations and pepper yields in a barrel experiment, and on soil oxygen concentrations and stem growth of young mango trees in a field experiment. The perforated sphere was intended to reduce soil resistance to air flow and to enhance the efficiency of air spreading in the soil. The main findings were that injecting atmospheric air did not contribute much to aeration of soils with high existing oxygen concentrations, i.e., about 80% of the atmospheric 21%, in the barrel experiments, and did not contribute at all in the field experiment, where oxygen concentration was about 95% of atmospheric. Furthermore, it was found that an oxygen concentration of about 80% did not decrease pepper yield in the absence of other stresses such as salinity or nutrients deficiency. A perforated sphere increased soil oxygen concentration when both water and air were applied through the sphere. A positive effect of air injection on pepper yields was found in soils with high volumetric water contents, i.e., average above 0.4 throughout the growth period. Conversely, air injection decreased pepper yields in barrels where water contents were lower.

A process-based model of methane consumption by upland soils

This study combines a literature survey and field observation data in an ad initio attempt to construct a process-based model of methane sink in upland soils including both the biological and physical aspects of the process. Comparison is drawn between the predicted sink rates and chamber measurements in several forest and grassland sites in the southern part of West Siberia. CH4 flux, total respiration, air and soil temperature, soil moisture, pH, organic content, bulk density and solid phase density were measured during a field campaign in summer 2014. Two datasets from literature were also used for model validation. The modeled sink rates were found to be in relatively good correspondence with the values obtained in the field. Introduction of the rhizospheric methanotrophy significantly improves the match between the model and the observations. The Q10 values of methane sink observed in the field were 1.2–1.4, which is in good agreement with the experimental results from the other studies. Based on modeling results, we also conclude that soil oxygen concentration is not a limiting factor for methane sink in upland forest and grassland ecosystems.

Gross nitrous oxide production drives net nitrous oxide fluxes across a salt marsh landscape.

Sea level rise will change inundation regimes in salt marshes, altering redox dynamics that control nitrification - a potential source of the potent greenhouse gas, nitrous oxide (N2 O) - and denitrification, a major nitrogen (N) loss pathway in coastal ecosystems and both a source and sink of N2 O. Measurements of net N2 O fluxes alone yield little insight into the different effects of redox conditions on N2 O production and consumption. We used insitu measurements of gross N2 O fluxes across a salt marsh elevation gradient to determine how soil N2 O emissions in coastal ecosystems may respond to future sea level rise. Soil redox declined as marsh elevation decreased, with lower soil nitrate and higher ferrous iron in the low marsh compared to the mid and high marshes (P<0.001 for both). In addition, soil oxygen concentrations were lower in the low and mid-marshes relative to the high marsh (P<0.001). Net N2 O fluxes differed significantly among marsh zones (P=0.009), averaging 9.8±5.4μgNm(-2) h(-1) , -2.2±0.9μgNm(-2) h(-1) , and 0.67±0.57μgNm(-2) h(-1) in the low, mid, and high marshes, respectively. Both net N2 O release and uptake were observed in the low and high marshes, but the mid-marsh was consistently a net N2 O sink. Gross N2 O production was highest in the low marsh and lowest in the mid-marsh (P=0.02), whereas gross N2 O consumption did not differ among marsh zones. Thus, variability in gross N2 O production rates drove the differences in net N2 O flux among marsh zones. Our results suggest that future studies should focus on elucidating controls on the processes producing, rather than consuming, N2 O in salt marshes to improve our predictions of changes in net N2 O fluxes caused by future sea level rise.

Spatiotemporal dynamics of phosphorus release, oxygen consumption and greenhouse gas emissions after localised soil amendment with organic fertilisers

Organic fertilisation inevitably leads to heterogeneous distribution of organic matter and nutrients in soil, i.e. due to uneven surface spreading or inhomogeneous incorporation. The resulting localised hotspots of nutrient application will induce various biotic and abiotic nutrient turnover processes and fixation in the residuesphere, giving rise to distinct differences in nutrient availability, soil oxygen content and greenhouse gas (GHG) production. In this study we investigated the spatiotemporal dynamics of the reaction of manure solids and manure solids char with soil, focusing on their phosphorus (P) availability, as current emphasis on improving societal P efficiency through recycling waste or bio-based fertilisers necessitates a sound understanding of their behaviour. Soil layers amended at a constant P application rate with either pig manure solids or char made from pig manure solids were incubated for three weeks between layers of non-amended, P-depleted soil. Spatial and temporal changes in and around the amendment layers were simultaneously investigated in this study using a sandwich sensor consisting of a planar oxygen optode and multi-element diffusive gradients in thin films (DGT) gels, combined with GHG emission measurements. After three weeks of incubation, the soil containing a layer amended with manure solids had a lower overall O2 content and had emitted significantly more CO2 than the non-amended control or the char-amended soil. The P availability from manure solids was initially higher than that from the char, but decreased over time, whereas from the char-amended layer P availability increased in the same period. In both treatments, increases in P availability were confined to the amended soil layer and did not greatly affect P availability in the directly adjacent soil layers during the three-week incubation. These results highlight the importance of placing organic P fertilisers close to where the plant roots will grow in order to facilitate optimal fertiliser use efficiency.

Effects of different sediment type and burial depth on growth traits and biomass accumulation of Spartina anglica

Soils in salt marsh ecosystems have been undergoing certain changes including those related to sediment types and burial depths due to tidal activity and a variety of biotic factors. The changes in sediment type affect water-retaining properties, permeability and organic content while those in burial depth alter soil humidity, nutrition content, oxygen content, light intensity and temperature. Although many previous studies have focused on the effects of soil properties on plant growth and reproduction, few have explicitly tested the impacts of sediment type and burial depth on plants in salt marsh ecosystems. The exotic species Spartina anglica found in coastal China has been experiencing increased mortality over the past decade, however the mechanism of this mortality remains unclear. This study mainly focused on the effects of sediment type and burial depth on growth traits and biomass accumulation of S. anglica and was conducted under greenhouse conditions. The experiment included two types of sediments with clay and clay-sand mixtures (the volume of 1:1). Furthermore, four treatments were established with burial depths from 0 cm to one quarter of the plant height, one half of the plant height and three quarters of the plant height. Results indicated that clay increased leaf area, number of leaves, number of rhizomes, total length of rhizomes, rhizome mass and aboveground mass, while the clay-sand mixture led to an increase in the number of ramets, total mass, underground mass •研究报告• 1280 生 物 多 样 性 Biodiversity Science 第 24 卷 and root mass. All of the measures, except for leaf area, peaked at one half of the plant height burial treatment among all treatments. Overall, burial depth at one half of the plant height in clay was the most suitable combination for S. anglica. The results indicate that changes in sediment properties and subsequent changes in burial depth for S. anglica may assist with management of its populations over the species range.

Improved Empirical Representation of Plant Responses to Waterlogging for Simulating Crop Yield

Waterlogging causes apparent reductions in crop yields around the world. Crops undergo plant responses and adaptations due primarily to the reduction in soil oxygen concentrations in the plant root zone that occur during waterlogged conditions. Current methods of assessing and quantifying crop yield reductions due to waterlogging, such as the sum of excess water (SEW) and stress day index (SDI) accumulating methods, and the models DRAINMOD, Agricultural Production Systems Simulator (APSIM), and Salt Water And Groundwater MANagement (SWAGMAN) Destiny (Destiny) do not include plant physiological adaptation processes that may limit or avoid reductions in crop yield. This paper analyses results from field trials to create a unifying concept that recognizes the various responses and adaptations of crops to waterlogging. We propose an empirical three stage representation of crop responses and adaptations during waterlogging. Stage one represents increased plant function with unlimited water and adequate soil oxygen concentrations for root respiration for up to 3 d. Stage two follows and represents plant response to declining soil oxygen concentrations often resulting in decreased plant function. Finally, stage three represents species dependant plant adaptations. We test the sensitivity of SWAGMAN Destiny using our three stage empirical representation to estimate yield reductions due to waterlogging. Results are consistent with field trial observations, with decreased yield compared to simulations using 10% air‐filled pore space as the waterlogging criteria. We suggest the three stage empirical representation for specific crops can be used to improve simulation model estimations of crop yields due to waterlogging.

Influence of rhizosphere ventilation on soil nutrient status, root architecture and the growth of young peach trees

The peach tree root respiration rate is high, which requires large amounts of oxygen. When the rhizosphere oxygen content is poor, the root respiration and energy metabolism are restrained which will have negative impacts on peach trees growth, fruit quality and yield, especially during high temperature and rainy season. Our objectives were to investigate the relationship between rhizosphere ventilation and orchard soil enzyme activity, nutrient status, root architecture and growth of young peach trees. Two-year-old ‘Chunmei’ peach (Prunus persica L. Batsch) was subjected to various treatments (Treatment 1 [T1]: ventilation every three days; T2: ventilation every six days; T3: natural ventilation; Control: no ventilation) under field cultivation conditions. The soil oxygen content decreased and subsequently increased during the growth period, reaching a minimum in August. The rhizosphere soil oxygen content was higher under ventilation treatment than control, and T1 markedly increased the rhizosphere soil oxygen content. The rhizosphere soil available K and organic matter decreased while the rhizosphere soil available N and available P content increased and the soil enzyme activity was improved under ventilation treatments. The root activity and root nitrate reductase activity increased under ventilation treatments. Under T1, the total root surface area, total root length and number of first lateral root and second lateral root were increased significantly, but the average root diameter and the average length of first lateral root was reduced significantly, the branching angle between first lateral root and vertically downward direction was decreased, the number of small angle was increased. T1improved leaf functions and increased the net photosynthetic rate. Under T1, the leaf chlorophyll content and leaf protective enzyme activity (Superoxide dismutase, Guaiacol peroxidase and Catalase) increased markedly in the middle- and late-growth period and leaf senescence was postponed. The total nitrogen, phosphorus and potassium contents of young peach roots, shoots and leaves, as well as shoot growth, leaf weight and leaf area, increased under T1.

Inhibition of tomato shoot growth by over‐irrigation is linked to nitrogen deficiency and ethylene

Although physiological effects of acute flooding have been well studied, chronic effects of suboptimal soil aeration caused by over-irrigation of containerized plants have not, despite its likely commercial significance. By automatically scheduling irrigation according to soil moisture thresholds, effects of over-irrigation on soil properties (oxygen concentration, temperature and moisture), leaf growth, gas exchange, phytohormone [abscisic acid (ABA) and ethylene] relations and nutrient status of tomato (Solanum lycopersicum Mill. cv. Ailsa Craig) were studied. Over-irrigation slowly increased soil moisture and decreased soil oxygen concentration by 4%. Soil temperature was approximately 1°C lower in the over-irrigated substrate. Over-irrigating tomato plants for 2 weeks significantly reduced shoot height (by 25%) and fresh weight and total leaf area (by 60-70%) compared with well-drained plants. Over-irrigation did not alter stomatal conductance, leaf water potential or foliar ABA concentrations, suggesting that growth inhibition was not hydraulically regulated or dependent on stomatal closure or changes in ABA. However, over-irrigation significantly increased foliar ethylene emission. Ethylene seemed to inhibit growth, as the partially ethylene-insensitive genotype Never ripe (Nr) was much less sensitive to over-irrigation than the wild type. Over-irrigation induced significant foliar nitrogen deficiency and daily supplementation of small volumes of 10 mM Ca(NO3 )2 to over-irrigated soil restored foliar nitrogen concentrations, ethylene emission and shoot fresh weight of over-irrigated plants to control levels. Thus reduced nitrogen uptake plays an important role in inhibiting growth of over-irrigated plants, in part by stimulating foliar ethylene emission.