Effect of Soil Water Contents on Arsenic Accumulation in Phytoliths of Pteris Multifida and Phragmites Australis

Purpose: The encapsulation of toxic metal(loid)s in phytoliths represents a new area of research. The accumulation of metal(loid)s in phytoliths can alter the fate and toxicity of soil metal(loid). Pteris multifida is a well-known As hyperaccumulator which also harbors phytoliths. However, As accumulation in phytoliths has not yet been studied. Soil water content is considered the main factor influencing phytolith accumulation and also remains unexplored with respect to As accumulation in phytoliths. In this study, As concentration in the phytoliths of P. multifida was compared with that in Phragmites australis phytoliths as a function of the soil water content. Methods: P. multifida and P. australis were grown under different soil water contents. The As concentration in phytoliths, roots, and shoots of plants was then determined.Results: The range of As concentration in the phytoliths of P. multifida was 414.70 - 1610.74 mg kg-1, and that for P. australis phytoliths was 41.67 - 126.54 mg kg-1. In P. multifida, higher soil water content increased As accumulation in phytoliths but did not affect phytolith content in the plant. In P. australis, the higher soil water content increased phytolith content in the plant but decreased As concentration in phytoliths. Conclusion: This study suggests that P. multifida has higher As content in phytoliths than P. australis, and this accumulation can be affected by soil water content. The current findings provide insight into the accumulation of As in phytoliths and provide a theoretical basis for our understanding on the fate of As in the environment.

Experimental Research on Evaluation of Soil Water Content Using Ground Penetrating Radar and Wavelet Packet-Based Energy Analysis

Soil water content is one of the most important factors affecting the safety and stability of buildings or structures, especially in roadbeds, slopes, earth dams and foundations. Accurate assessments of soil water content can ensure the quality of construction, reduce construction costs and prevent accidents, among other benefits. In this study, ground penetrating radar (GPR) was used to detect and evaluate changes in soil water content. The GPR signal is usually nonstationary and nonlinear; however, traditional Fourier theory is typically suitable for periodic stationary signals, and cannot reflect the law of the frequency and energy of the GPR signal changing with time. Wavelet transform has good time-frequency localization characteristics, and therefore represents a new method for analyzing and processing GPR signals. According to the time-frequency characteristics of GPR signals, in this paper, a new biorthogonal wavelet basis which was highly matched with the GPR waveform was constructed using the lifting framework of wavelet theory. Subsequently, an evaluation method, namely, the wavelet packet-based energy analysis (WPEA) method, was proposed. The method was utilized to calculate the wavelet packet-based energy indexes (WPEI) of the GPR single-channel signals for clay samples with water contents ranging from 10% to 24%. The research results showed that there was a highly correlated linear relationship between the WPEI and the soil water contents, and the relationship between the two was fitted with a linear fitting function. The feasibility of the method was verified by comparing our results with those obtained using classical wavelet bases to perform the wavelet packet transform. The large-area, continuous scanning measurement method of GPR was shown to be suitable for evaluations of soil water contents in roadbeds, slopes, earth dams, and foundations.

MITIGATION YIELD SCALED METHANE EMISSION FROM RICE GROWN IN WATER STRESS CONDITIONS WITH BIOCHAR AND SILICATE AMENDMENTS

Climate change and water scarcity may badly affect existing rice production system in Bangladesh. With a view to sustain rice productivity and mitigate yield scaled CH4 emission in the changing climatic conditions, a pot experiment was conducted under different soil water contents, biochar and silicate amendments with inorganic fertilization (NPKS). In this regard, 12 treatments combinations of biochar, silicate and NPKS fertilizer along with continuous standing water (CSW), soil saturation water content and field capacity (100% and 50%) moisture levels were arranged into rice planted potted soils. Gas samples were collected from rice planted pots through Closed Chamber technique and analyzed by Gas Chromatograph. This study revealed that seasonal CH4 emissions were suppressed through integrated biochar and silicate amendments with NPKS fertilizer (50–75% of the recommended doze), while increased rice yield significantly at different soil water contents. Biochar and silicate amendments with NPKS fertilizer (50% of the recommended doze) increased rice grain yield by 10.9%, 18.1%, 13.0% and 14.2%, while decreased seasonal CH4 emissions by 22.8%, 20.9%, 23.3% and 24.3% at continuous standing water level (CSW) (T9), at saturated soil water content (T10), at 100% field capacity soil water content (T11) and at 50% field capacity soil water content (T12), respectively. Soil porosity, soil redox status, SOC and free iron oxide contents were improved with biochar and silicate amendments. Furthermore, rice root oxidation activity (ROA) was found more dominant in water stress condition compared to flooded and saturated soil water contents, which ultimately reduced seasonal CH4 emissions as well as yield scaled CH4 emission. Conclusively, soil amendments with biochar and silicate fertilizer may be a rational practice to reduce the demand for inorganic fertilization and mitigate CH4 emissions during rice cultivation under water stress drought conditions.

Soil Water Availability Changes in Amount and Timing Favor the Growth and Competitiveness of Grass Than a Co-dominant Legume in Their Mixtures

The grasslands on the semi-arid Loess Plateau of China are expected to be particularly responsive to the size and frequency changes of extreme precipitation events because their ecological processes are largely driven by distinct soil moisture pulses. However, the plant growth and competitiveness of co-dominant species in response to the changes in the amount and timing of soil water are still unclear. Thus, two co-dominant species, Bothriochloa ischaemum and Lespedeza davurica, were grown in seven mixture ratios under three watering regimes [80 ± 5% pot soil capacity (FC) (high watering), 60 ± 5% FC (moderate watering), and 40 ± 5% FC (low watering)] in a pot experiment. The soil water contents were rapidly improved from low to moderate water and from moderate to high water, respectively, at the heading, flowering, and maturity stages of B. ischaemum, and were maintained until the end of the growing season of each species. The biomass production of both species increased significantly with the increased soil water contents, particularly at the heading and flowering periods, with a more pronounced increase in B. ischaemum in the mixtures. The root/shoot ratio of both species was decreased when the soil water availability increased at the heading or flowering periods. The total biomass production, water use efficiency (WUE), and relative yield total (RYT) increased gradually with the increase of B. ischaemum in the mixtures. The relative competition intensity was below zero in B. ischaemum, and above zero in L. davurica. The competitive balance index calculated for B. ischaemum was increased with the increase of the soil water contents. Bothriochloa ischaemum responded more positively to the periodical increase in soil water availability than L. davurica, indicating that the abundance of B. ischaemum could increase in relatively wet seasons or plenty-rainfall periods. In addition, the mixture ratio of 10:2 (B. ischaemum to L. davurica) was the most compatible combination for the improved biomass production, WUE, and RYTs across all soil water treatments.

Non-microbial methane emissions from tropical rainforest soils under different conditions

Non-microbial methane (NM-CH4), emissions from soil might play a significant role in carbon cycling and global climate change. However, the production mechanisms and emission potential of soil NM-CH4 from tropical rainforest remain highly uncertain. In order to explore the laws and characteristics of NM-CH4 emission from tropical rainforest soils. Incubation experiments at different environmental conditions (temperatures, soil water contents, hydrogen peroxide) and for soils with different soil organic carbon (SOC) contents were conducted to investigate the NM-CH4 emission characteristics and its influence factors of soils (0-10cm) that collected from a tropical rainforest in Hainan, China. Incubation results illustrated that soil NM-CH4 release showed a linear increase with the incubation time in the first 24 hours at 70 °C, whereas the logarithmic curve increase was found in 192 h incubation. Soil NM-CH4 emission rates under aerobic condition were significantly higher than that of under anaerobic condition at first 24 h incubation. The increasing of temperature, suitable soil water contents (0–100%), and hydrogen peroxide significantly promoted soil NM-CH4 emission rates at the first 24 h incubation. However, excessive soil water contents (200%) inhibited soil NM-CH4 emissions. According to the curve simulated from the NM-CH4 emission rates and incubation time at 70 °C of aerobic condition, soil would no longer release NM-CH4 after 229 h incubation. The NM-CH4 emissions were positively corelated with SOC contents, and the average soil NM-CH4 emission potential was about 6.91 ug per gram organic carbon in the tropical mountain rainforest. This study revealed that soils in the tropical rainforest could produce NM-CH4 under certain environment conditions and it supported production mechanisms of thermal degradation and reactive oxygen species oxidation. Those results could provide a basic data for understanding the soil NM-CH4 production mechanisms and its potential in the tropical rainforest.

Moment Analysis for Modeling Soil Water Distribution in Furrow Irrigation: Variable vs. Constant Ponding Depths

Despite increasing use of pressurized irrigation methods, most irrigation projects worldwide still involve surface systems. Accurate estimation of the amount of infiltrating water and its spatial distribution in the soil is of great importance in the design and management of furrow irrigation systems. Moment analysis has previously been applied to describe the subsurface water distribution using input data from numerical simulations rather than field measured data, and assuming a constant ponding depth in the furrow. A field experiment was conducted in a blocked-end level furrow at Maricopa Agricultural Center, Arizona, USA, to study the effect of time-variable ponding depths on soil water distribution and the resulting wetting bulb under real conditions in the field using moment analysis. The simulated volumetric soil water contents run with variable and constant (average) ponding depths using HYDRUS 2D/3D were almost identical, and both compared favorably with the field data. Hence, only the simulated soil water contents with variable ponding depths were used to calculate the moments. It was concluded that the fluctuating flow depth had no significant influence on the resulting time-evolving ellipses. This was related to the negligible 10-cm variation in ponding depths compared to the high negative matric potential of the unsaturated soil.

Spatial variability of greenhouse gas fluxes in two drained Northern peatlands

<p>Peatlands store large amounts of organic carbon, which is subject to microbial decomposition and mineralization to either CO<sub>2</sub> or CH<sub>4</sub>.  Drained peatlands are characterized by large horizontal variability in soil water contents and saturation, with dryer parts closer to the drainage ditches. The greenhouse gas (GHG) production in these systems is expected to be sensitive to temperature, substrate chemistry, oxygen concentration thus on soil water contents. Methane production should take place in the wetter parts, while respiration should dominate in drier parts. The seasonality of weather conditions modulates the spatial variability. In this complex situation, we are interested in how the seasonal weather variability triggers the microbial processes in the different micro-topographical situations and how this affects the overall GHG budgets of such sites.</p><p>We investigate two neighboring, drained ombrotrophic bogs in Norway close to Trysil, Innlandet, 61.1N- 12.25E, 640 m a. s. l.. One site (South) on an upper slope is about 45 m higher than the other site (North) in a saddle like flattening.  We use an automated chamber method to examine the seasonality of GHG production at microsites that cover some contrasting local situations with in the large range of small scale spatial heterogeneity. With eddy covariance CO<sub>2</sub> and CH<sub>4</sub> flux measurements, we integrate over a larger spatial scale, with, however, shifting footprints depending on weather conditions and wind direction. We present a comparative  analysis of 1.5 years continuous measurements, where we examine shifting spatial patterns of GHG production at different scales and relate them to soil conditions.</p><p>While the CO<sub>2</sub> fluxes compared very well between the two investigated sites, the CH<sub>4</sub> fluxes in the lower and wetter of the two sites (North) was higher and their spatial variability was lower than in the South site. Only in the South site, the CH<sub>4</sub> fluxes correlated with the coverage of well drained versus less well drained areas. We will present results on how the spatial variability changed with the seasonality of soil temperatures and the water table.</p><p>The automated chambers (five chambers within each footprint of the eddy flux towers) showed higher spatial variability for CH<sub>4</sub> fluxes than for CO<sub>2</sub> with higher CH<sub>4</sub> emissions in the wetter plots furthest away from ditches, i.e. CH<sub>4</sub> fluxes correlate well to ground water depth at both sites. N<sub>2</sub>O emissions were observed in short events during the early summer season. Overall, there was a good alignment of fluxes measured with eddy flux and chamber technologies.</p><p>Information on factors that constrain the spatio-temporal variability are important for estimating areal GHG budgets and for predicting possible effects of peatland management, such as draining or re-wetting on the climate effects from these ecosystems.  From the results, we expect higher effects of peatland restoration on GHG budgets in the South site.</p>

The Effect of Irrigation Rate on the Water Relations of Young Citrus Trees in High-Density Planting

The availability and proper irrigation scheduling of water are some of the most significant limitations on citrus production in Florida. The proper volume of citrus water demand is vital in evaluating sustainable irrigation approaches. The current study aims to determine the amount of irrigation required to grow citrus trees at higher planting densities without detrimental impacts on trees’ water relation parameters. The study was conducted between November 2017 and September 2020 on young sweet orange (Citrus sinensis) trees budded on the ‘US-897’ (Cleopatra mandarin x Flying Dragon trifoliate orange) citrus rootstock transplanted in sandy soil at the Southwest Florida Research and Education Center (SWFREC) demonstration grove, near Immokalee, Florida. The experiment contained six planting densities, including 447, 598, and 745 trees per ha replicated four times, and 512, 717, and 897 trees per ha replicated six times. Each density treatment was irrigated at 62% or 100% during the first 15 months between 2017 and 2019 or one of the four irrigation rates (26.5, 40.5, 53, or 81%) based on the calculated crop water supplied (ETc) during the last 17 months of 2019–2020. Tree water relations, including soil moisture, stem water potential, and water supplied, were collected periodically. In addition, soil salinity was determined. During the first year (2018), a higher irrigation rate (100% ETc) represented higher soil water contents; however, the soil water content for the lower irrigation rate (62% ETc) did not represent biological stress. One emitter per tree regardless of planting density supported stem water potential (Ψstem) values between −0.80 and −0.79 MPa for lower and full irrigation rates, respectively. However, when treatments were adjusted from April 2019 through September 2020, the results substantially changed. The higher irrigation rate (81% ETc) represented higher soil water contents during the remainder of the study, the lower irrigation rate (26.5% ETc) represents biological stress as a result of stem water potential (Ψstem) values between −1.05 and −0.91 MPa for lower and higher irrigation rates, respectively. Besides this, increasing the irrigation rate from 26.5% to 81%ETc decreased the soil salinity by 33%. Although increasing the planting density from 717 to 897 trees per hectare reduced the water supplied on average by 37% when one irrigation emitter was used to irrigate two trees instead of one, applying an 81% ETc irrigation rate in citrus is more efficient and could be managed in commercial groves.

Modulations in Functional Traits Improve Phragmites australis Adaptation under Different Soil Water Contents in Marshes of Arid Middle-Lower Reaches of Shule River Basin, China

Variations in plant functional traits might reveal the adaptation strategies of vegetation under changing environment. However, few studies have focused on the variation of dominant plant functional traits in changing soil water content in marsh wetland of the arid regions. In this study, functional traits were investigated in the dominant species Phragmites australis growing at distinct soil water contents in marshes of the arid middle-lower reaches of the Shule River Basin in Northwest China. Three soil water gradients (33.38 ± 1.40, 15.97 ± 1.99 and 10.22 ± 1.61%) were identified from three marsh sites. Results showed that leaf thickness, specific leaf area, maximum height and leaf phosphorous content in P. australis were significantly varied from the high soil water to low soil water in arid marshes. Soil water content driven variations in functional traits of P. australis, mainly by its effect on soil salinity and available nitrogen, affected the functional traits of P. australis. In conclusion, in marshes of arid regions, P. australis adapted well to resource-poor habitats through the coordinated combination of multiple functional traits i.e., low specific leaf area, leaf nitrogen content and leaf phosphorous content, high leaf dry matter content and leaf thickness, which reflected that P. australis had conservative strategy. © 2021 Friends Science Publishers