Soil Moisture Treatments Research Articles

The importance of priority effects for riparian plant community dynamics

AbstractQuestionsThe order of plant species arrival can affect recruitment and subsequent plant community development via priority effects, but is often overlooked. Priority effects occur when early‐colonizing plant species affect the establishment of later‐arriving species, and are hypothesized to depend on species identity and habitat conditions. In riparian ecosystems on the banks of rivers, a strong moisture gradient induces a zonation of plant species with different degrees of adaptation to soil moisture. Further, riparian zones receive seeds during floods and later in the season via wind dispersal. As such, we questioned if recruitment in riparian zones is primarily affected by (1) environmental conditions (i.e. soil moisture), (2) arrival order, and (3) species identity, or an interaction between these factors.LocationRiparian zones of tributaries in the Vindel River catchment, northern Sweden.MethodWe designed a controlled greenhouse experiment and a large‐scale field experiment where we sowed five plant species representing different dispersal events and habitat moisture preferences. We sowed seeds in three arrival order treatments (all species simultaneously, species group A phased 3 wk before group B, and vice versa) and under different soil moisture treatments in the greenhouse (dry, dry‐after‐wet and wet) and under a range of moisture conditions in the field.ResultsWe found strong priority effects as early‐arriving species grew bigger and often produced higher seedling densities compared to later‐arriving species, both in the greenhouse and after two growing seasons in the field. Priority effects in the greenhouse were strongest in the dry and dry‐after‐wet treatments and weaker under wet conditions. Consistent but weaker patterns were observed in the field after the first growing season. The relative abundance of species in plant communities assembled without phased arrival interacted with soil moisture and species identity. Priority effects were strongest for species with a low relative abundance (i.e. less competitive species).ConclusionsOur findings that priority effects influenced recruitment and interacted with soil moisture suggest that priority effects should be considered when addressing riparian vegetation changes after shifts in flooding regimes. This is especially important because floods will not only affect habitat conditions, but also the phasing of seed arrival.

The effect of environmental conditions and soil physicochemistry on phosphate stabilisation of Pb in shooting range soils

The stabilisation of Pb in the soil by phosphate is influenced by environmental conditions and physicochemical properties of the soils to which it is applied. Stabilisation of Pb by phosphate was examined in four soils under different environmental conditions.The effect of soil moisture and temperature on stabilisation of Pb by phosphate was examined by measurement of water extractable and bioaccessible Pb, sequential fractionation and X-ray absorption spectroscopy. The addition of humic acid, ammonium nitrate and chloride was also examined for inhibition or improvement of Pb stability with phosphate treatment.The effect of moisture level varied between soils. In soil MB and DA a soil moisture level of 50% water holding capacity was sufficient to maximise stabilisation of Pb, but in soil TV and PE reduction in bioaccessible Pb was inhibited at this moisture level. Providing moisture at twice the soil water holding capacity did not enhance the effect of phosphate on Pb stabilisation. The difference of Pb stability as a result of incubating phosphate treated soils at 18 °C and 37 °C was relatively small. However wet–dry cycles decreased the effectiveness of phosphate treatment. The reduction in bioaccessible Pb obtained was between 20 and 40% with the most optimal treatment conditions. The reduction in water extractable Pb by phosphate was substantial regardless of incubation conditions and the effect of different temperature and soil moisture regimes was not significant.Selective sequential extraction showed phosphate treatment converted Pb in fraction 1 (exchangeable, acid and water soluble) to fraction 2 (reducible). There were small difference in fraction 4 (residual) Pb and fraction 1 as a result of treatment conditions. X-ray absorption spectroscopy of stabilised PE soil revealed small differences in Pb speciation under varying soil moisture and temperature treatments. The addition of humic acid and chloride produced the greatest effect on Pb speciation in phosphate treated soils.

The invasive annual cheatgrass releases more nitrogen than crested wheatgrass through root exudation and senescence.

Plant-soil feedbacks are an important aspect of invasive species success. One type of feedback is alteration of soil nutrient cycling. Cheatgrass invasion in the western USA is associated with increases in plant-available nitrogen (N), but the mechanism for this has not been elucidated. We labeled cheatgrass and crested wheatgrass, a common perennial grass in western rangelands, with (15)N-urea to determine if differences in root exudates and turnover could be a mechanism for increases in soil N. Mesocosms containing plants were either kept moist, or dried out during the final 10days to determine the role of senescence in root N release. Soil N transformation rates were determined using (15)N pool dilution. After 75 days of growth, cheatgrass accumulated 30% more total soil N and organic carbon than crested wheatgrass. Cheatgrass roots released twice as much N as crested wheatgrass roots (0.11 vs. 0.05mgN kg(-1) soil day(-1)) in both soil moisture treatments. This occurred despite lower root abundance (7.0 vs. 17.3g dry root kg(-1) soil) and N concentration (6.0 vs. 7.6gN kg(-1) root) in cheatgrass vs. crested wheatgrass. We propose that increases in soil N pool sizes and transformation rates under cheatgrass are caused by higher rates of root exudation or release of organic matter containing relatively large amounts of labile N. Our results provide the first evidence for the underlying mechanism by which the invasive annual cheatgrass increases N availability and establishes positive plant-soil feedbacks that promote its success in western rangelands.

高温干旱复合胁迫对构树幼苗抗氧化酶活性和活性氧代谢的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 高温干旱复合胁迫对构树幼苗抗氧化酶活性和活性氧代谢的影响 DOI: 10.5846/stxb201409201862 作者: 作者单位: 南京林业大学,南京林业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 江苏省自然科学基金项目(BK2012819);江苏省高校自然科学研究重大项目(15KJA180003);江苏省生物学优势学科建设项目 Effects of combined elevated temperature and drought stress on anti-oxidative enzyme activities and reactive oxygen species metabolism of Broussonetia papyrifera seedlings Author: Affiliation: Jiangsu Key Laboratory of Forestry and Ecological Engineering,Nanjing Forestry University,Jiangsu Key Laboratory of Forestry and Ecological Engineering,Nanjing Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:近年来,全球气温不断升高,亚热带部分地区夏季高温和临时性干旱现象日益显著,高温与干旱严重威胁着植物的生存与生长。采用盆栽和人工气候室方式模拟不同的温度和土壤水分梯度,研究了高温与干旱复合胁迫对构树幼苗超氧化物歧化酶(SOD)、过氧化物酶(POD)与过氧化氢酶(CAT)活性、活性氧代谢和丙二醛(MDA)含量的影响。结果表明:(1)高温或干旱单一胁迫下,构树幼苗SOD、POD、CAT活性增加,复合胁迫下,SOD和POD酶活性高于单一胁迫,且随着复合胁迫时间延长而升高。SOD活性受温度和土壤水分双因素影响极其显著,复合胁迫对SOD活性有一定程度的叠加效应;(2)复合胁迫下,活性氧代谢物与MDA含量均显著高于单一胁迫,表明复合胁迫加剧对植物的伤害。通过改变抗氧化酶活性以减轻膜脂过氧化的伤害作用是有限的。 Abstract:In recent years, under the global climate change scenario, the occurrence of seasonal high temperature and temporal drought phenomena has increased in some subtropical regions. Consequently, the survival and growth of plants are restrained under the combined stress of elevated temperature and drought. In the present study, a pot experiment was performed at the Xiashu Forest Station of Nanjing Forestry University in 2013. One-year-old Broussonetia papyrifera seedlings were grown in 27-cm pots with brown loam soil, using a completely randomized design with four replicates. Seedlings were initially grown in the field environment and then transferred to a controlled greenhouse with three elevated-temperature and soil-moisture treatments, and the effects of combined elevated temperature and drought stress on anti-oxidative enzyme activities and reactive oxygen species(ROS) metabolism were measured in B.papyrifera seedling leaves. The results indicated that under either elevated temperature or drought stress, the superoxide dismutase(SOD), peroxidase(POD), and catalase(CAT) activities of seedlings increased with the increase of stress level. Under the combined elevated temperature and drought stress, the activities of SOD and POD were higher than those under single temperature or drought stress, and increased over stress exposure time. Significant variation was observed in SOD activity of the seedlings between combined stress treatments, revealing the synergistic effects of combined stress on SOD activities. Under the combined elevated temperature and drought stress, ROS, including O2- production rates and hydrogen peroxide(H2O2) and malondialdehyde(MDA) contents, were significantly higher than those under the single temperature or drought stress treatment, which suggests the limited role of antioxidant enzyme activities in alleviating the damage of the cell membrane of seedlings due to differences in ROS metabolite accumulation. 参考文献 相似文献 引证文献

Effect of SiO2 nanoparticles on drought resistance in hawthorn seedlings

Abstract Drought is a significant factor limiting crop production in arid regions while hawthorns (Crataegus sp.) are an important component of such region’s forests. Therefore, treatments that increase hawthorn drought resistance may also increase transplanting success. Thus, the physiological and biochemical responses of hawthorn seedlings to a factorial combination of different concentrations of silica nanoparticles (SNPs at 0, 10, 50 and 100 mg L−1) and three soil moisture treatments (without stress, moderate stress and severe stress) were investigated. Seedlings were irrigated with one of the four concentrations of SNPs for 45 days before exposing them to drought stress. Photosynthesis parameters, malondialdehyde (MDA), relative water content (RWC), membrane electrolyte leakage (ELI) as well as chlorophyll, carotenoid, carbohydrate and proline content were determined. At the end of the experiment, positive effects by SNP pre-treatment on physiological indexes were observed during drought stress. Under drought conditions, the effect of SNPs on photosynthetic rate and stomatal conductance was evident. Although the SNPs increased plant biomass, xylem water potential and MDA content, especially under drought conditions, RWC and ELI were not affected by the SNP pre-treatments. Seedlings pre-treated with SNPs had a decreased carbohydrate and proline content under all water regimes, but especially so under drought. Total chlorophyll content and carotenoid content did not change among the treatments. Generally, the findings imply that SNPs play a positive role in maintaining critical physiological and biochemical functions in hawthorn seedlings under drought stress conditions. However, more studies are needed before the physiological and biochemical basis of induced drought resistance can be determined.

Earthworm activities increase the leaching of salt and water from salt-affected agricultural soil during the wet–dry process under simulated rainfall conditions

The objectives of this study were to (1) evaluate earthworm-induced leaching of water and salt from salt-affected agricultural soils with constant and fluctuating soil moisture conditions and (2) determine the effects of earthworms on the distribution of soil salt in casts, burrow walls, and surrounding soils responsible for salt leaching. Soils were kept in mesocosms at constant moisture (CM) or underwent one wet–dry process (WD). Each soil moisture treatment had three earthworm treatments, including (1) inoculation with high abundance of earthworms (five endogeic Aporrectodea trapezoides), (2) inoculation with moderate abundance of earthworms (three endogeic A. trapezoides), and (3) no earthworm treatment. The presence of earthworms significantly increased total leaching water volume compared to the same treatment without earthworms in both moisture treatments. In the treatment following the wet–dry process, more than 65 % of water leaching occurred during the rainfall event, whereas in the treatment following constant moisture, more than 60 % of water leaching occurred after the rainfall event. The presence of earthworms produced a higher salt amount in the leaching water than the same moisture treatment without earthworms, but only the low number of earthworms (three endogeic A. trapezoides) caused a significantly higher total amount of leached salt than the same moisture treatment without earthworms. The percentage of leached salt in leaching water during the rainfall event ranged from 75.31 to 79.93 % in the wet–dry treatment and from 41.28 to 50.65 % in the constant moisture treatment. The wet–dry process significantly increased the total amount of leached salt from salt-affected agricultural soil compared to the constant moisture treatment when earthworms were present, which may be due to the significantly higher electrical conductivity of saturation extract (ECe) of earthworm casts than those of burrow walls and surrounding soils in the 0- to 10-cm soil layer.

Variation Among Genotypes and Source Habitats in Growth and Fecundity of the Wetland Invasive Plant Phalaris arundinacea L

The spread of invasive wetland plants has resulted in a number of negative impacts to wetland habitats including reductions in biodiversity, displacement of native plants, and altered water flow. Phalaris arundinacea L. (Reed canarygrass) is a highly competitive invasive plant in North American wetlands. While research has focused on growth characteristics and competitive ability of P. arundinacea in wetland habitats, little is known about how its growth in upland conditions differs from that in wetlands. To characterize differences in growth between upland and wetland habitats, we conducted a 13-month field experiment of unconstrained growth of P. arundinacea in upland and wetland conditions. A suite of traits was measured in genotypes collected from upland and wetland habitats. Although P. arundinacea most often occurs in wetlands, there was significantly higher growth and fecundity in the dry soil treatment. All of the growth traits measured varied among genotypes, a few varied between the habitats of origin, and significant interactions were found between habitat of origin and soil moisture treatment for several traits. The significant genetic variation observed suggests that there is potential for local adaptation to upland habitats. The higher growth and fecundity in upland conditions highlights the need for additional research to investigate P. arundinacea establishment capacity and competitiveness in upland habitats.

Uso da subirrigação para imposição de estresse hídrico em sistema semi-contínuo para medição de CO2

The objectives of this work were to evaluate the effects of distinct moisture contents to trigger subirrigation on salvia photosynthesis and plant growth, and to verify the feasibility of subirrigation use in water stress imposition research in this crop. We evaluated two substrate volumetric water contents (VWC) as treatments (0.2 and 0.4 m3 m-3) to trigger subirrigation, with 4 replications. Each replication was composed of 10 plants. An automated semi-continuous multi-chamber crop CO2-exchange system was used, with capacitance soil moisture sensors for continuous moisture monitoring. Manual subirrigation with nutrient solution was performed when VWC dropped below the thresholds. In both treatments, the values of net photosynthesis, daily carbon gain and carbon use efficiency reduced over time, from 2 to 1.1 μmol s-1 from 2.2 to 1 μmol d-1 from 0.7 to 0.45 mol mol-1, respectively, in both soil moisture treatments. Total shoot dry mass (p=0.0129), shoot height in the tip of the highest flower (p<0.0001) and total leaf area (p=0.0007) were statistically higher at 0.4 m3 m-3 treatment. The subirrigation system was not efficient to impose water stress, due to excessive variation on VWC values after each irrigation event in both treatments. Higher soil moisture promoted positive plant growth responses in salvia cultivated by subirrigation.

Phosphorus Removal With Grass In An Apple Orchard Under Influence Of Mulch And Irrigation

Phosphorus leaching from intensive agriculture systems is one of major contributors responsible for pollution of ground-water and surface water bodies. The aim of this study was to determine the content of phosphorus in orchard lawn for reduction of phosphorus fertilizer application and to include the phosphorus from mown grass into P balance and turnover calculation. The investigation was done at the Latvia State Institute of Fruit–Growing in 2009. Three treatments were compared: control, mulch and fertigation. Inter-row strips were covered by grass vegetation. Grass samples were collected at the time of grass mowing. The removal of phosphorus was calculated as kilograms per hectare area. The concentration of phosphorus in the lawn and the height of grass growth were significantly influenced by the mowing time and the soil moisture treatment. These results can be a base for further studies of phosphorus turnover in an orchard, as well as for fertilizer planning and management.

Malate as a key carbon source of leaf dark-respired CO2 across different environmental conditions in potato plants.

Dissimilation of carbon sources during plant respiration in support of metabolic processes results in the continuous release of CO2. The carbon isotopic composition of leaf dark-respired CO2 (i.e. δ (13) C R ) shows daily enrichments up to 14.8‰ under different environmental conditions. However, the reasons for this (13)C enrichment in leaf dark-respired CO2 are not fully understood, since daily changes in δ(13)C of putative leaf respiratory carbon sources (δ (13) C RS ) are not yet clear. Thus, we exposed potato plants (Solanum tuberosum) to different temperature and soil moisture treatments. We determined δ (13) C R with an in-tube incubation technique and δ (13) C RS with compound-specific isotope analysis during a daily cycle. The highest δ (13) C RS values were found in the organic acid malate under different environmental conditions, showing less negative values compared to δ (13) C R (up to 5.2‰) and compared to δ (13) C RS of soluble carbohydrates, citrate and starch (up to 8.8‰). Moreover, linear relationships between δ (13) C R and δ (13) C RS among different putative carbon sources were strongest for malate during daytime (r(2)=0.69, P≤0.001) and nighttime (r(2)=0.36, P≤0.001) under all environmental conditions. A multiple linear regression analysis revealed δ (13) C RS of malate as the most important carbon source influencing δ (13) C R . Thus, our results strongly indicate malate as a key carbon source of (13)C enriched dark-respired CO2 in potato plants, probably driven by an anapleurotic flux replenishing intermediates of the Krebs cycle.

Role of spring soil moisture in the formation of large-scale droughts in the East European Plain in 2002 and 2010

Using COSMO-CLM (a nonhydrostatic atmospheric model designed for climate experiments), we simulate the summer anomalies in the meteorological regime of 2010 and 2002 over the central part of the East European Plain. The module of soil moisture treatment is shown to demonstrate reliable results and the radiation module of the model needs to incorporate the optical properties of haze generated by the smoke of forest and peat fires. It is shown that the soil moisture content formed in the spring can (due to its inertial behavior and by changing the heat balance structure) participate in the formation of temperature and humidity anomalies over 3–4 months. The extremeness of the thermal regime in the summer of 2010 in the central part of the East European Plain is due to (all other conditions being equal) the specific values of soil moisture content w 0 = 0.6–0.65. The revealed fine dependence of the phenomenon on the spring state of soil moisture makes it important to improve the monitoring of soil moisture as a key factor in the dynamics of extreme weather anomalies.

Flood Tolerance in Common Buckthorn (Rhamnus cathartica)

ABSTRACT: Rhamnus cathartica is a Eurasian shrub that has invaded woodland habitats of eastern North America. While historically known from more mesic habitats, it is often found in wetland habitats in Illinois, Minnesota, and Wisconsin, USA. This study assessed R. cathartica's growth, architecture, and biomass allocation across multiple flooding treatments representing a soil moisture gradient spanning upland (mesic soil moisture) to wetland habitats (saturated within 30 cm of the soil surface, periodic flooding, and permanently flooded conditions) for two age classes of saplings of R. cathartica. Our results on plant growth patterns under these treatments show that young R. cathartica saplings were able to tolerate saturated soil conditions, while old saplings were able to tolerate periodic flooding. Allocation of biomass to above- versus below-ground tissues showed that both young and old saplings have similar biomass allocation patterns in relation to soil moisture treatments. Collectively, our result...

Effects of Soil Moisture and Fertilization Treatments on the Agronomic Traits of Teff (<i>Eragrosis tef</i>) in Southern Kyushu, Japan

This study investigated the agronomic characteristics of pot-cultured teff (Eragrostis tef) under soil moisture and fertilization treatments in southern Kyushu, Japan. In experiments examining the effects of soil moisture and fertilization, growth of teff and Setaria (Setaria sphacelata) as a reference species was compared under six treatments combining two soil moisture regimes, control (C) and high moisture (H) treatment, and three fertilizer applications, chemical fertilizer with manure (CF + M), chemical fertilizer (CF) and doubled level of manure (DM). H treatment did not decrease dry matter yield in teff two months after transplanting, except when combined with CF + M, compared with a decreasing tendency in Setaria. Top and underground dry matter yields and harvest index in teff increased significantly (P 0.05) at CF application levels above 6.2 gN m-2 two months after sowing, suggesting that the optimum CF level of teff in southern Kyushu was comparable with that in the USA, and that teff had potential as an early-harvest forage crop two months after planting to replace summer forage in paddy fields of this region.

Planting pattern and pre-sowing soil moisture effect on yield of soybean

This study aimed to investigate the effects of planting patterns and pre-sowing soil moisture on the yield of summer soybean [Glycine max (L.) Merr.] in northern China from 2009 to 2010. The experiment comprised three planting patterns, namely, 30 cm uniform row spacing pattern (U), “20 + 40” wide-narrow row planting pattern (WN), and “20 + 40” furrow planting pattern (F). Three pre-sowing soil moisture treatments were performed at 90, 135, and 180 mm and involved irrigation during the winter wheat growth season. The leaf area index and chlorophyll content index of F were higher than those of U and WN under the same pre-sowing soil moisture treatment (P < 0.05). The accumulation of dry matter and the grain yield of F were significantly higher than those of U and WN (P < 0.05) irrespective of water content. The increase in grain yields of summer soybean was significant in 2009 (P < 0.05) but not in 2010 (P > 0.05) for 135 and 180 mm pre-sowing soil moisture under F. In conclusion, F and 180 mm pre-sowing soil moisture treatments were good agronomic measures to increase the yield of summer soybean in northern China.

Metabolite profile, antioxidant capacity, and inhibition of digestive enzymes in infusions of peppermint (Mentha piperita) grown under drought stress.

Peppermint (Mentha piperita) infusions represent an important source of antioxidants, which can be enhanced by inducing abiotic stress in plants. The aim of this study was to evaluate the effect of drought stress on peppermint cultivation as well as the metabolite profile, antioxidant capacity, and inhibition of digestive enzymes of resulting infusions. At 45 days after planting, irrigation was suppressed until 85 (control), 65, 35, 24, and 12% soil moisture (SM) was reached. The results showed that 35, 24, and 12% SM decreased fresh (20%) and dry (5%) weight. The 35 and 24% SM treatments significantly increased total phenolic and flavonoid contents as well as antioxidant capacity. Coumaric acid, quercetin, luteolin, and naringenin were detected only in some drought treatments; however, in these infusions, fewer amino acids and unsaturated fatty acids were identified. The 24 and 12% SM treatments slightly improved inhibition of pancreatic lipase and α-amylase activity. Therefore, induction of moderate water stress in peppermint is recommended to enhance its biological properties.

English

The objective of this study was to evaluate the effects of glyphosate on soil microbial activity under appropriate and water deficit conditions. The factors consisted of four treatments with different Roundup Ready® soybean cultivars, two herbicidal treatments [glyphosate (1.080 and 1.800 g a.e. ha-1) + control] and two soil moisture treatments (appropriate and water deficit conditions), plus two soybean conventional varieties subject only to the soil moisture treatments. It was evaluated total organic carbon (TOC), basal respiration rate (CO2), microbial carbon biomass (MCB), metabolic quotient (qCO2), microbial quotient (qmic), nodule number (NN), and dry weight of nodules per plant (DWNP). Except for TOC, all other microbiological parameters were significantly influenced by the application of glyphosate, and the effects are more evident at a 1.800 g a.e. ha-1 dose in Roundup Ready® soybean cultivars associated to water deficit condition. The soil microbiota stability was favored by the absence of glyphosate application and water deficit condition on soil. MCB and qCO2 showed to be quite sensitive to changes resulting from the use of glyphosate. In general, in conventional cultivars there was lesser effect of water deficit conditions on the microbiological attributes, when compared to treatments with glyphosate application under the same conditions. Key words: Glycine max (L.) Merrill, inhibitors of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs), microbiota, Roundup Ready® soybean seed.

Effects of Soil Chemistry on Plant Germination and Growth in a Northern Everglades Peatland

Vegetation patterns across the Florida Everglades peatland are influenced by anthropogenic gradients in both hydrology and chemistry. These gradients often overlap, making it difficult to isolate specific causes of vegetation change. We examined whether differences in plant communities between the minimally impacted interior and the impacted perimeter of the northern Everglades could be attributed to soil chemistry as opposed to other factors such as hydrology or seed-bank composition. Seedling establishment from soil seed banks collected from interior locations was examined under conditions that reflected either the phosphorus (P)- and calcium-carbonate (CaCO3)-depleted chemistry of the peatland interior or enriched conditions around the perimeter. Three soil moisture treatments were used to increase seed-bank expression. The interior seed bank contained viable seeds of both interior and perimeter taxa, but distinct plant assemblages established in the two chemistry treatments. Perimeter species germinated in both chemistry treatments, but only survived under enriched conditions. Establishment of these species in the interior is likely limited by low P availability. Germination and survival of some interior species were reduced by enrichment, likely due to elevated CaCO3 levels. Protection from both increased P and CaCO3 loads thus appears important to maintain plant communities in mineral-poor remnants of the Everglades.

Effects of Soil Moisture on Nitrogen Mineralization in a Typical 10-Year Floodplain Wetland

Soil profiles from 0 to 80 cm depth were collected and a 14-day incubation experiment at three soil moisture levels (initial moisture, water holding capacity, and flooding) was carried out at 25°C in the dark to reveal the effects of soil moisture on nitrogen mineralization rates in a 10-yr floodplain wetland. Our results showed that nitrogen mineralization rates decreased with depth along soil profiles and the maximal nitrogen mineralization rates appeared at the 10-20cm soil layer. The nitrogen mineralization rates were higher under flooding treatment compared to another two soil moisture treatments. Nitrogen mineralization rates in the top 20cm soils exhibited an increasing tendency with increasing soil moisture. Additionally, nitrogen mineralization rates were significantly correlated with electrical conductivity, total soluble salt, and salinity under three soil moisture treatments.

Growth, developmental, and physiological responses of two sweetpotato (Ipomoea batatas L. [Lam]) cultivars to early season soil moisture deficit

Soil moisture deficit at early season is detrimental for sweetpotato growth and development affecting final yield. This study investigated the effects of different soil moisture regimes on early season growth, developmental, and physiological responses of two sweetpotato cultivars, ‘Beauregard’ and ‘Evangeline’, grown in a greenhouse environment. Five levels of soil moisture treatments, 0.256, 0.216, 0.164, 0.107, and 0.058m3m−3 of VWC, were maintained through sensor-based soil moisture monitoring, and semi-automated programmed irrigation. Midday leaf water potential (LWP), gas exchange, and fluorescence were measured weekly from 30 to 50 days after transplanting (DAT). Growth and development of plants were evaluated through harvesting four plants at 5-day intervals from 14 to 50 DAT. Leaf pigments and cell and chlorophyll stability indices were also determined. Midday LWP of sweetpotato declined linearly with decreasing soil moisture levels. The photosynthetic rate also declined linearly in Beauregard and quadratically in Evangeline with decreasing soil moisture. Both cultivars had a close association between photosynthetic rate and stomatal conductance over the soil moisture treatments, suggesting that stomatal closure is a key limitation for the drop in photosynthesis. Chlorophyll concentration was significantly lower at extreme soil moisture deficit conditions. Significant difference was found in water use efficiency between cultivars and among soil moisture treatments. Rates of vine elongation and leaf formation of Evangeline decreased more rapidly than Beauregard with declining soil moisture levels. Also with decreasing soil moisture, the shoot biomass declined more rapidly than root biomass. The results showed that maintaining soil moisture closer to field capacity (0.256m3m−3 of VWC) during early season is beneficial for early development of both root and shoot system and thus better crop performance. The data and the inferences derived from the functional algorithms developed in this study will be useful for crop modelling, field-level irrigation scheduling, and planting decisions.

Soil moisture and soil-litter mixing effects on surface litter decomposition: A controlled environment assessment

Recent studies suggest the long-standing discrepancy between measured and modeled leaf litter decomposition in drylands is, in part, the result of a unique combination of abiotic drivers that include high soil surface temperature and radiant energy levels and soil-litter mixing. Temperature and radiant energy effects on litter decomposition have been widely documented. However, under field conditions in drylands where soil-litter mixing occurs and accelerates decomposition, the mechanisms involved with soil-litter mixing effects are ambiguous. Potential mechanisms may include some combination of enhanced microbial colonization of litter, physical abrasion of litter surfaces, and buffering of litter and its associated decomposers from high temperatures and low moisture conditions. Here, we tested how soil-litter mixing and soil moisture interact to influence rates of litter decomposition in a controlled environment. Foliar litter of two plant species (a grass [Eragrostis lehmanniana] and a shrub [Prosopis velutina]) was incubated for 32 weeks in a factorial combination of soil-litter mixing (none, light, and complete) and soil water content (2, 4, 12% water-filled porosity) treatments. Phospholipid fatty acids (PLFAs) were quantified one week into the experiment to evaluate initial microbial colonization. A complementary incubation experiment with simulated rainfall pulses tested the buffering effects of soil-litter mixing on decomposition.Under the laboratory conditions of our experiments, the influence of soil-litter mixing was minimal and primarily confined to changes in PLFAs during the initial stages of decomposition in the constant soil moisture experiment and the oscillating soil moisture conditions of the rainfall pulse experiment. Soil-litter mixing effects on CO2 production, total phospholipid concentrations, and bacterial to total PLFA ratios were observed within the first week, but responses were fairly weak and varied with litter type and soil moisture treatment. Across the entire 32-week incubation experiment, soil moisture had a significant positive effect on mass loss, but soil-litter mixing did not. The lack of strong soil-litter mixing effects on decomposition under the moderate and relatively constant environmental conditions of this study is in contrast to results from field studies and suggests the importance of soil-litter mixing may be magnified when the fluctuations and extremes in temperature, radiant energy and moisture regimes common dryland field settings are in play.