Low Soil Moisture Research Articles

Water availability rather than temperature control soil fauna community structure and prey–predator interactions

AbstractThe ongoing climate change may strongly impact soil biodiversity with cascading effects on the processes they drive. Thus, it is of prime interest to improve our knowledge about responses by soil organisms such as collembolans to expected shifts in environmental conditions by considering communities comprising both detritivores and predators.The aim of the present study was to evaluate how simulated climate change and predation under laboratory conditions alter a collembolan community.To infer the impact of climate change, we applied a decreased level of soil moisture (60% vs. 30% soil water holding capacity) and an increasing air temperature (15°C vs. 25°C) to a collembolan community constituted by four species (Folsomia candida,Protaphorura fimata,Proisotoma minutaandMesaphorura macrochaeta) exhibiting distinct functional traits, for example, body size and furca presence, in the presence or absence of a predatory gamasid AcariStratiolaelaps scimitusduring 2 months in a microcosm experiment.We observed that decreasing soil moisture altered the collembolan community with species‐specific responses. Interaction between soil moisture, temperature and predation indicates that low soil moisture reduced total collembolan abundance especially (a) by suppressing the positive effect of increasing temperature and (b) by increasing the predatory control on collembolan abundance.These results highlight that soil moisture is the major driver of Collembola community and by consequence, a shift in climatic parameters with the ongoing climate change should strongly modify the Collembola community structure and the predator–prey interaction. Our findings are highly important since a strengthening of predation impact on Collembola prey could have major consequences on the whole soil food web being able to lead to a slowdown of key ecosystem processes they drive (e.g. litter decomposition and nutrient recycling). Finally, our study promotes the need to study more complex systems considering distinct soil‐dwelling species, their functional traits and their trophic interactions to better predict the ecosystem responses to the ongoing climate change.A freePlain Language Summarycan be found within the Supporting Information of this article.

Combined effect of temperature and water stress on seed germination of four Leptocereus spp. (Cactaceae) from Cuban dry forests

AbstractCactus seeds have developed adaptations to survive with high temperatures and low soil moisture in their habitats. We studied the effect of the combination of four water potentials (0, −0.2, −0.4 and −0.6 MPa) and two temperatures (25°C and 35°C) on germination and seedling mass of four endemic Leptocereus species from Cuba. There were two semi‐arid coast species (L. arboreus and L. santamarinae) and two species inhabiting dry inland karstic hills (L. ekmanii and L. scopulophilus). We hypothesized that: (a) a decrease in water potential and an increase in temperature would result in low and slow germination, as well as in low seedling mass, and (b) ungerminated cactus seeds after exposure to combined water and temperature stress would have a high recovery capacity. The minimum time required for the seeds to start germination (Tmin), mean germination time (MGT) and germinability were evaluated. In addition, seed mass, the recovery after treatments of non‐germinated seeds, and the seedling fresh mass obtained under different treatments were compared between species. In general, germination was only obtained at 25°C and germinability and seedling mass were drastically affected by the reduction from 0 MPa to −0.2 MPa. Seeds showed thermoinhibition at 35°C at all water potentials. There was a tendency to increase the MGT with decreasing water potential in three species. Low seed recovery occurred at all combined treatments for three species. If the predictions of increased temperature and decreased rainfall for the Caribbean region occur, a reduction in the germination of the Leptocereus species studied is expected.

Yield and botanical composition of four dryland pastures at Ashley Dene Research Farm over 8 years

Dry matter yield and botanical composition of four grazed dryland pasture types were compared over 8 years in summer-dry conditions at Ashley Dene, Canterbury, New Zealand. The experiment was sown in March 2013 to evaluate cocksfoot (CF)- or meadow fescue/ryegrass hybrid (RG)-based pastures established with either subterranean (Sub) or subterranean and balansa (S+B) clovers. Plantain was included in all pasture types. Perennial ryegrass established poorly on the low soil moisture holding capacity Lismore soil and in Year 2 was re-broadcast into the RG pastures. Despite this, plantain was the main sown species in RG pastures beyond Year 3. Total spring yield was greatest in Year 5 at 6720 kg DM/ha and varied with spring rainfall. Cocksfoot-based pastures had 60% of sown species present in the spring of Year 8, compared with 28% in RG-based pastures. Balansa clover was only present up to Year 5 after a managed seeding event in the first spring. White clover did not persist in the dryland environment past Year 2. Sub clover yield depended on the time and amount of autumn rainfall but contributed up to 45% of the spring yield. Cocksfoot-sub clover pastures appear to be most resilient in this summer-dry environment with variable spring rainfall.

Effects of thinning intensity and understory removal on soil microbial community in Pinus massoniana plantations of subtropical China

Monitoring the soil microbial communities following forest management practices is vital since soil microorganism play a critical role in sustaining forest productivity, nutrient cycling and soil CO2 emission. Here, biomass and the structures of soil microbial communities in aerially seeded Pinus massoniana plantations across three growing and three non-growing seasons following canopy tree thinning and understory removal were investigated using PLFA method, and soil environmental factors were analyzed. Both overall microbial community structures and mean microbial biomass did not significantly differ among control (CK), heavily thinning (HT), light thinning (LT) and understory removal (UR), but were significantly affected by time following treatment. In spite of non-significant effects of treatment, thinning and UR tended to decrease soil microbial biomass in non-growing seasons, and to increase the microbial biomass in the 2nd and 3rd growing seasons following treatment. Soil moisture, carbon to nitrogen ratio and nitrogen (i.e. total N and mineral N) were the main drivers of soil microbial community changes. Lower soil moisture and higher soil nitrogen led to significant differences in soil microbial biomass in the 2nd year after treatment. Thinning significantly increased fungi to bacteria ratio (FB ratio), which was significantly positively correlated with soil heterotrophic respiration. Our study confirms that forest management practices such as thinning and understory removal exert strong effects on environmental conditions (i.e. microclimate and soil nutrient availability), which further influences FB ratio, and consequently might impact soil C cycling and forest productivity.

Prolonged Usage of Herbicides Reduces Heterotrophic Aerobic Bacteria and Fungi Population and Alters Soil Physicochemical Parameters

The study aimed to examine the effect of commonly used herbicides on soil microbiota (bacteria and fungi) as well as its physiochemical properties. Topsoil (0 to 5cm depth) samples were collected from different plots at Ayepe, Iwaro Oka Akoko, Ondo State, Nigeria with known prior herbicide treatments. The plots had different history of glyphosate, paraquat and both combination application. The soil samples were serially diluted and cultured on nutrient agar and potato dextrose agar for bacteria and fungi, respectively. The physicochemical properties of the soil samples showed that all the soil samples had pH values which ranged from 7.4 to 9.4. The moisture contents ranged from 2.6 to 15 with soil sample without prior usage of herbicide having the highest moisture content. The average total bacterial counts ranged from 4.0 x 108 to 2.5 x 109 cfu/g while the average total fungal counts ranged from 3.0 x 103 to 3.1 104 cfu/g with the untreated soil containing the highest loads. Soil samples with prolonged use of herbicides generally contained lower soil moisture contents, organic matter contents, as well as lower microbial loads. It could be concluded from the study that the pattern of change in the bacteria and fungi population vary as a result of differences in the composition of herbicides and year of usage.

Conservation tillage and nutrient management practices in summer rice (Oryza sativa L.) favoured root growth and phenotypic plasticity of succeeding winter pea (Pisum sativumL.) under eastern Himalayas, India

Low soil moisture during dry season, poor soil properties and lack of adequate crop varieties are the major constraints for sustainable intensification of eastern Himalayas in changing climate. Suitable varieties, tillage alteration and integrated nutrient management with emphasis on locally available crop residues/plant biomass may help addressing these issues. The role of minimum tillage (MT) and no-till (NT), and organic matter substitution on conferring of favourable root environment, improvement in morpho-physiology and subsequent productivity of the crops are not objectively studied in Himalayan ecosystems. Thus, a six year field study was conducted for examining the residual effect of tillage and nutrient management (NM) practices applied to summer (rainy) rice (Oryza sativa L) on root growth-attributes and impact on morpho-physiology of succeeding winter pea (Pisums ativum L.) grown uniformly under NT. Higher root surface area, total root length, root volume, root length ratio (RLR) and root tissue densityin pea crop were observed under residual effect of conventional tillage (CT) relative to NT and MT. In addition, significantly higher values of functional root traits viz., root length ratio (RLR), root mass ratio and root finenessin pea were observed under CT and application of 50% NPK and 100% NPK relative to other tillage and NM practices. However, increased root exudation was observed under NT and MTalong with organic residue addition. Noticeable changes in stress responsive morpho-physiological traits like enhanced chlorophyll pigmentation and favourable leaf characteristics were observed in pea crop grown under NT with 50% NPK+weed biomass (WB)/green leaf manure (GLM) applications. Higher leaf area expansion and thickness were recorded with optimum turgidity under NT and MT than that under CT. Comparative increase in green pod and stover yield of pea with enhanced partition efficiency and harvest index were recorded under MT/NT along with 50% NPK+WB/GLM application than that under CT and other NM practices. Thus, adoption of MT/NT along with 50% NPK+WB/GLM in summer rice is recommended for inducing favourable root environment and optimised pea production in succeeding winter season in study region of the Eastern Himalayas, India and other similar agro-ecosystems.

Using isotopes to understand landscape‐scale connectivity in a groundwater‐dominated, lowland catchment under drought conditions

AbstractThe Demnitzer Millcreek catchment (DMC), is a 66 km2 long‐term experimental catchment located 50 km SE of Berlin. Monitoring over the past 30 years has focused on hydrological and biogeochemical changes associated with de‐intensification of farming and riparian restoration in the low‐lying landscape dominated by rain‐fed farming and forestry. However, the hydrological function of the catchment, which is closely linked to nutrient fluxes and highly sensitive to climatic variability, is still poorly understood. In the last 3 years, a prolonged drought period with below‐average rainfall and above‐average temperatures has resulted in marked hydrological change. This caused low soil moisture storage in the growing season, agricultural yield losses, reduced groundwater recharge, and intermittent streamflows in parts of an increasingly disconnected channel network. This paper focuses on a two‐year long isotope study that sought to understand how different parts of the catchment affect ecohydrological partitioning, hydrological connectivity and streamflow generation during drought conditions. The work has shown the critical importance of groundwater storage in sustaining flows, basic in‐stream ecosystem services and the dominant influence of vegetation on groundwater recharge. Recharge was much lower and occurred during a shorter window of time in winter under forests compared to grasslands. Conversely, groundwater recharge was locally enhanced by the restoration of riparian wetlands and storage‐dependent water losses from the stream to the subsurface. The isotopic variability displayed complex emerging spatio‐temporal patterns of stream connectivity and flow duration during droughts that may have implications for in‐stream solute transport and future ecohydrological interactions between landscapes and riverscapes. Given climate projections for drier and warmer summers, reduced and increasingly intermittent streamflows are very likely not just in the study region, but in similar lowland areas across Europe. An integrated land and water management strategy will be essential to sustaining catchment ecosystem services in such catchment systems in future.

Functional relationship between photosynthetic leaf gas exchange in response to silicon application and water stress mitigation in sugarcane

BackgroundWater stress is one of the serious abiotic stresses that negatively influences the growth, development and production of sugarcane in arid and semi-arid regions. However, silicon (Si) has been applied as an alleviation strategy subjected to environmental stresses.MethodsIn this experiment, Si was applied as soil irrigation in sugarcane plants to understand the mitigation effect of Si against harmful impact of water stress on photosynthetic leaf gas exchange.ResultsIn the present study we primarily revealed the consequences of low soil moisture content, which affect overall plant performance of sugarcane significantly. Silicon application reduced the adverse effects of water stress by improving the net photosynthetic assimilation rate (Anet) 1.35–18.75%, stomatal conductance to water vapour (gs) 3.26–21.57% and rate of transpiration (E) 1.16–17.83%. The mathematical models developed from the proposed hypothesis explained the functional relationships between photosynthetic responses of Si application and water stress mitigation.ConclusionsSilicon application showed high ameliorative effects on photosynthetic responses of sugarcane to water stress and could be used for mitigating environmental stresses in other crops, too, in future.

Effects of degraded grassland conversion to mango plantation on soil CO2 fluxes

Land use changes are of serious concern due to its effects on soil carbon stock, which is second largest anthropogenic source of atmosphere CO2. To better understand these effects in typical and fragile ecosystems like dry-hot valley regions, we quantified changes in soil properties (pH, organic carbon, total nitrogen, phosphorus, microbial biomass carbon contents, activities of β-glucosidase, beta-N-acetyl-glucosaminidase, acid phosphatase) and CO2 efflux before (degraded grassland) and after (mango plantation) land use change in a dry-hot valley region. Most soil chemical properties remained unaffected after conversion due to generally low regional nutrient levels. Principal component analysis revealed the decline of soil heterogeneity of the selected properties (pH, SOC, TN, TP, AP), which will be useful for future unified management. Compared to grassland, CO2 efflux in mango plantation increased by 20–69% after land use change, more factors and their interactions were responsible for CO2 efflux from soil in mango plantations. The temperature sensitivity (Q10: 0.68–1.98) of CO2 efflux in both land use types was low due to the low soil moisture at high temperatures. Soil water content was the primary factor affecting CO2 efflux in the dry-hot valley region, followed by microbial biomass carbon. In summary, the CO2 efflux increased shortly after the land use change (within first year), even though absence of significant quantitative change of soil properties, and low temperature sensitive (Q10) before and after conversion and its difference between land use types is opposite in dry and wet season.

Macrophomina phaseolina : General Characteristics of Pathogenicity and Methods of Control.

Macrophomina phaseolina is a generalist soil-borne fungus present all over the world. It cause diseases such as stem and root rot, charcoal rot and seedling blight. Under high temperatures and low soil moisture, this fungus can cause substantial yield losses in crops such as soybean, sorghum and groundnut. The wide host range and high persistence of M. phaseolina in soil as microsclerotia make disease control challenging. Therefore, understanding the basis of the pathogenicity mechanisms as well as its interactions with host plants is crucial for controlling the pathogen. In this work, we aim to describe the general characteristics and pathogenicity mechanisms of M. phaseolina, as well as the hosts defense response. We also review the current methods and most promising forecoming ones to reach a responsible control of the pathogen, with minimal impacts to the environment and natural resources.

The effects of stump size and within-gap position on sprout non-structural carbohydrates concentrations and regeneration in forest gaps vary among species with different shade tolerances

BackgroundTo restore secondary forests (major forest resources worldwide), it is essential to accelerate the natural regeneration of dominant trees by altering micro-environments. Forest gaps are products of various disturbances, ranging from natural storms or wildfires to anthropogenic events like logging and slashing-and-burning, and sprouts of most tree species with non-structural carbohydrates (NSCs) storage can regenerate from stumps after gap formation. However, how the stump sprouts with diverse NSCs storages and stump sizes (i.e., diameters) adapt to various micro-environments of within-gap positions remains unclear. Therefore in this study, we monitored the stump sprout regeneration (density, survival, and growth) and NSCs concentrations of three dominant tree species with different shade tolerances and varying stump diameters at five within-gap positions for the first two consecutive years after gap formation.ResultsStump diameter was positively correlated with sprout density, growth, and survival of all three tree species, but insignificantly related with sprout NSCs concentrations at the early stage after gap formation. The effect of within-gap position on sprout NSCs concentrations was different among species. After an environmental adaptation of two growing seasons, the north of gap (higher light availability and lower soil moisture habitat) was the least conducive for shade-intolerant Quercus mongolica to accumulate leaf NSCs, and the east of gap (shadier and drier habitat) was conducive to increasing the leaf NSCs concentrations of shade-tolerant Tilia mandshurica.ConclusionsWithin-gap position significantly affected leaf NSCs concentrations of all three tree species, but most of the sprout growth, survival, and stem NSCs concentrations were independent of the various within-gap positions. Besides stump diameter, the NSCs stored in stump and root systems and the interspecific differences in shade tolerance also contributed more in sprout regeneration at the early stage (2 years) of gap formation. A prolonged monitoring (> 10 years) is needed to further examine the long-term effects of stump diameter and within-gap position on sprout regeneration. All of these findings could be applied to gap-based silviculture by promoting sprout regeneration of dominant tree species with different shade tolerances, which would help accelerate the restoration of temperate secondary forests.

An improved microelectrode method reveals significant emission of nitrous oxide from the rhizosphere of a long-term fertilized soil in the North China Plain

Microsensors are able to accurately quantify nitrous oxide (N2O) emissions in microenvironments at high spatio-temporal resolution; yet, limited studies have been conducted on agricultural soils due to the inability to obtain electrical signal under conditions of low soil moisture. This study improved the calibration of a microelectrode for measuring N2O emissions from agricultural soil. The microelectrode was applied to evaluate the effect of long-term fertilization with mineral fertilizer (NPK), complemented with pig manure (MNPK), straw (SNPK), or without fertilizer (CK), all with and without urea addition, on N2O emissions from the soil, with explicit separation of the rhizosphere and the bulk soil compartments. The use of soil solution instead of pure water for calibration of the microelectrode doubled the signal and significantly improved the sensor sensitivity. The optimal electrolytic concentration of the soil solution, expressed as water: soil ratio, was found at the maximum vertex of the quadratic equation fitted on the slope values of the calibration equations for different soil solutions. The application of the calibrated microelectrode revealed significantly higher N2O emission from the rhizosphere compared to the bulk soil, accounting for 60% of the total emission. For the bulk soil, MNPK significantly increased N2O emissions compared to SNPK and NPK, whereas the differences between these treatments for the rhizosphere soil were insignificant. The statistical modeling revealed significant relation of the N2O emission with soil inorganic nitrogen contents and an additive effect of treatment (MNPK and SNPK), urea addition and rhizosphere soil. This study provides novel insights into the use of microelectrodes for measuring N2O emissions from the soil microenvironment and also points on the rhizosphere compartment and the management practices of agroecosystems able to reduce the N2O emission from agriculture.

Delimitation of low topsoil moisture content areas in a vineyard using remote sensing imagery (Sentinel-1 and Sentinel-2) in a Mediterranean-climate region

Irrigation can be responsible for salt accumulation in the root zone of grapevines when late autumn and winter precipitation is not enough to leach salts from the soil upper horizons, turning the soil unsuitable for grape production. The aim of this work is to present a novel methodology to outline areas, within a drip-irrigated vineyard, with a low soil moisture content (SMC) during, and after, an 11-month agricultural drought. Soil moisture (SM) field measurements were performed in two plots at the vineyard, followed by a geostatistical method (indicator kriging) to estimate the SM class probabilities according to a threshold value, enlarging the training set for the classification algorithms. The logistic regression (LR) and Random Forest (RF) methods used the features of the Sentinel-1 and Sentinel-2 images and terrain parameters to classify the SMC probabilities at the vineyard. Both methods classified the highest SMC probabilities above 14% that is located close to the stream at the lower altitudes. The RF method performed very well in classifying the topsoil zones with a lower SMC during the autumn-winter period. This delineation allows the prevention of the occurrence of areas affected by salinisation, indicating which areas will need irrigation management strategies to control the salinity, especially under climate change, and the expected increase in droughts.

Relationships among carbon isotope composition, growth, and foliar nitrogen in soybean

ABSTRACT Interactions between carbon isotope composition (δ13C), foliar nitrogen concentration (foliar N), and biomass accumulation (growth) merit further investigation in soybean (Glycine max (L.) Merr.) and other species as these metrics may be valuable for assessing moisture stress and for screening of drought-resistant varieties. To this end, we examined the response of six soybean genotypes to water-deficit stress in a greenhouse study. Two treatments were imposed: low soil moisture (5–10% volumetric water content) and high soil moisture (30–38% volumetric water content). Above-ground biomass accumulation, foliar N, and δ13C were measured at the end of the experiment. Leaf water potential and midday gas exchange (net assimilation, stomatal conductance, and transpiration) were measured multiple times throughout the experiment. All measurements were affected by water-deficit stress. Significant, but weak, positive relationships were found between δ13C and biomass accumulation in both soil moisture treatments. Foliar N was significantly, but weakly, correlated to growth in the high soil-moisture treatment, but not in the low soil-moisture treatment. The data suggest that selection for genotypes with higher δ13C values could result in improved biomass accumulation. The relationship between foliar N and δ13C was negative under high soil-moisture conditions and positive under low soil-moisture conditions. The relationships between δ13C and foliar N could be a highly informative metric to help understand the effects of water-deficit stress and may further indicate whether water or nitrogen acquisition is limiting in a specific environment, which should help in breeding improved soybean cultivars.

Representation of Plant Hydraulics in the Noah‐MP Land Surface Model: Model Development and Multiscale Evaluation

AbstractPlants are expected to face increasing water stress under future climate change. Most land surface models, including Noah‐MP, employ an idealized “big‐leaf” concept to regulate water and carbon fluxes in response to soil moisture stress through empirical soil hydraulics schemes (SHSs). However, such schemes have been shown to cause significant uncertainties in carbon and water simulations. In this paper, we present a novel plant hydraulics scheme (PHS) for Noah‐MP (hereafter, Noah‐MP‐PHS), which employs a big‐tree rather than big‐leaf concept, wherein the whole‐plant hydraulic strategy is considered, including root‐level soil water acquisition, stem‐level hydraulic conductance and capacitance, and leaf‐level anisohydricity and hydraulic capacitance. Evaluated against plot‐level observations from a mature, mixed hardwood forest at the University of Michigan Biological Station and compared with the default Noah‐MP, Noah‐MP‐PHS better represents plant water stress and improves water and carbon simulations, especially during periods of dry soil conditions. Noah‐MP‐PHS also improves the asymmetrical diel simulation of gross primary production under low soil moisture conditions. Noah‐MP‐PHS is able to reproduce different patterns of transpiration, stem water storage and root water uptake during a 2‐week dry‐down period for two species with contrasting plant hydraulic behaviors, i.e., the “cavitation risk‐averse” red maple and the “cavitation risk‐prone” red oak. Sensitivity experiments with plant hydraulic capacitance show that the stem water storage enables nocturnal plant water recharge, affects plant water use efficiency, and provides an important buffer to relieve xylem hydraulic stress during dry soil conditions.

Modulation of Compound Extremes of Low Soil Moisture and High Vapor Pressure Deficit by Irrigation in India

AbstractCompound extremes of low soil moisture and high vapor pressure deficit (VPD) have implications on terrestrial carbon sequestration, vegetation growth, and net primary productivity (NPP). Yet, the role of irrigation on the occurrence of compound extremes remains unexplored in India. Here, we use satellite observations, reanalysis data sets, and high‐resolution simulations from the Weather Research and Forecasting (WRF) model to show that irrigation significantly reduces the frequency of compound extremes of low soil moisture and high VPD in India. The Indo‐Gangetic plain witnessed a significant (p < 0.05) increase in mean annual soil moisture while a substantial reduction in VPD during 1979–2018. Moreover, irrigation caused considerable cooling over the Indo‐Gangetic plain during 1982–2018. The increase in soil moisture and the decline in VPD partly contributed to a substantial rise in Normalized Difference Vegetation Index (NDVI) and NPP. We conducted high‐resolution simulations using the WRF model to examine the role of irrigation in modulating the frequency of compound extremes during 1979–2018. The WRF simulations under the irrigation‐on show a considerably reduced frequency of the compound extremes compared to the irrigation‐off (control) simulations. Irrigation modulates compound extremes by changing the land surface energy budget and planetary boundary layer height. Therefore, there is a need to consider irrigation for reliable projections of compound extremes under a warming climate in intensively irrigated regions.

Low soil moisture predisposes field-grown chickpea plants to dry root rot disease: evidence from simulation modeling and correlation analysis

Rhizoctonia bataticola causes dry root rot (DRR), a devastating disease in chickpea (Cicer arietinum). DRR incidence increases under water deficit stress and high temperature. However, the roles of other edaphic and environmental factors remain unclear. Here, we performed an artificial neural network (ANN)-based prediction of DRR incidence considering DRR incidence data from previous reports and weather factors. ANN-based prediction using the backpropagation algorithm showed that the combination of total rainfall from November to January of the chickpea-growing season and average maximum temperature of the months October and November is crucial in determining DRR occurrence in chickpea fields. The prediction accuracy of DRR incidence was 84.6% with the validation dataset. Field trials at seven different locations in India with combination of low soil moisture and pathogen stress treatments confirmed the impact of low soil moisture on DRR incidence under different agroclimatic zones and helped in determining the correlation of soil factors with DRR incidence. Soil phosphorus, potassium, organic carbon, and clay content were positively correlated with DRR incidence, while soil silt content was negatively correlated. Our results establish the role of edaphic and other weather factors in chickpea DRR disease incidence. Our ANN-based model will allow the location-specific prediction of DRR incidence, enabling efficient decision-making in chickpea cultivation to minimize yield loss.

Water balance of the turn-of-the-century drought in the Southwestern United States

Analysis of the water balance of the southwestern United States (SWUS) during 1900 through 2018 was used to evaluate the magnitude of the turn-of-the-century (TOC) drought in the SWUS. Results indicate that the warm season (April through September) soil moisture and runoff during the TOC drought were among the lowest values of the 1900 through 2018 period. Additionally, increases in temperature were identified as a significant driver of low soil moisture and runoff conditions during the warm season. In contrast, during the cool seasons (October through March) and the water year (October 1 through September 30) during the TOC drought, soil moisture and runoff did not indicate extremely dry conditions even though temperatures were the highest of the 1900 through 2018 period.

Skid Trail Effects on Soil Methane and Carbon Dioxide Flux in a Selection-Managed Northern Hardwood Forest

Temperate forest soils are an important sink for methane (CH4); however, disturbance through forest management and the creation of skid trails may significantly decrease soil’s ability to uptake CH4 or in some cases cause CH4 emissions. Skid trails might also be expected to show reductions in carbon dioxide (CO2) flux due to anaerobic conditions and reduced root activity. Studies to date have investigated skid trail greenhouse gas flux dynamics on experimentally created skid trails, which may not experience the full extent of traffic intensity or contain the various microsites found in actual harvested areas. We investigated variation of CH4 and CO2 fluxes based on traffic intensity, trail topography, and trail microsites in selection-managed hardwood forests in the Haliburton Highlands of Ontario, Canada. Skid trail soils showed reduced CH4 uptake, and primary and secondary trails were found to commonly be a CH4 source, especially on lower slope locations and on wheel track and trail middle ridge microsites. Skid trails also showed high CO2 emissions in the same areas. CH4 emissions on skid trails were correlated with low surface soil porosities and high soil moisture contents, which were found to occur most frequently on highly impacted trails, in low-lying areas, and in the wheel tracks and trail middle ridges. Scaling up, skid trails offset ~ 45% of CH4 uptake in untrafficked soils, an effect that should be accounted for in future greenhouse gas budgets of managed forests.

Sustainable effect of a symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti on nodulation and photosynthetic traits of four leguminous plants under low moisture stress environment.

Sustainable effect of a nitrogen-fixing bacterium Sinorhizobium meliloti on nodulation and photosynthetic traits (phenomenological fluxes) in four leguminous plants species under low moisture stress (20-25% soil moisture content) environment was studied. Sinorhizobium meliloti was isolated from fenugreek (Trigonella foenum-graecum) root nodules, and later, it was cultured and purified. Nodulation and photosynthetic ability in the presence of S. meliloti were tested in four leguminous plant species, that is, kidney bean (cv. lobia-2000), black bean (cv. NM-97), mung bean (cv. NM-2006) and chickpea (cv. Pb-2008). Plants of each species were grown in sterilized soil that was previously treated with 25ml suspension containing S. meliloti at 41×106 CFUml-1 kg-1 pot. One-month-old plants were subjected to low soil moisture stress conditions for 15days, and soil moisture contents were maintained to 20-25% throughout the experimental period. The ability to fix nitrogen, nodule formation, and their subsequent effect on phenomenological fluxes in low moisture treated legumes were studied.