Search

Since the mid-1990s, several empirical unsaturated shear strength equations have been proposed for use in geotechnical engineering practice. Most of the equations have been based on information associated with the measured drying soil- water characteristic curve (SWCC) in combination with the effective shear strength parameters of the saturated soil. There have been few studies, however, undertaken on verifying and comparing the suitability of the proposed unsaturated shear strength equations. This study involves consideration of a wide range of possible drying SWCCs plotted as a relationship between the degree of saturation and suction (saturation soil-water characteristic curve (S-SWCC)). The study forms the basis for comparing five methodologies that have been proposed for the estimation of the shear strength of unsaturated soils. The SWCCs are defined by the fitting parameters for the Fredlund and Xing (1994) sigmoidal equation. This study supports the use of unsaturated soil shear strength empirical estimation methods using the S-SWCC anchor points of air-entry value and residual suction of the soil. Key words: unsaturated shear strength, unsaturated soil, soil-water characteristic curve, shear strength function, anchor conditions, air-entry value, residual suction, Introduction Soils founded above the water table have increased shear strength due to negative pore-water pressures or matric suctions. The soil experiences an increase in shear strength upon drying (provided [...]

Soil water saturation affects soil behavior when subjected to external loads and thus buried pipe deformation. To investigate this effect, full-scale tests were conducted on a buried steel pipe with a diameter of 600 mm. The deformed pipe ring transforms from a 'heart' shape into an inclined 'heart' shape due to the load redistribution within the soil after increasing soil water saturation. Then, a three-dimensional finite element model was created and validated based on the experimental data. A parametric study was thereafter performed to investigate the impact of factors including soil water saturation, cover depth, and pipe wall-thickness on buried pipe responses when subjected to external loads. Soil might be simply modeled as a linear elastic material at a large cover depth (>0.6 m) or a water saturation < 80%. Soil plasticity should be considered at a relatively low cover depth ([less than or equal to] 0.6 m) and a high water saturation ([greater than or equal to] 80%). The pipe circumferential stress is inversely proportional to the square of pipe wall-thickness when the pipe-soil stiffness ratio is equal to or greater than 0.13. Key words: X52 steel, static load, saturation, cover depth, wall-thickness, 1. Introduction Steel pipe has been widely used in oil and gas industry because of its outstanding properties of high yield and ultimate strengths, ability to take a load while [...]

Between 1954 and the mid-1980s, about 50,000 ha of native montane rainforest on the island of Hawai'i experienced a decline in canopy trees (''ohi'a dieback'), leading to great concern about the future of Hawai'i's rainforests. Dieback symptoms particularly affected the dominant tree species, the endemic Metrosideros polymorpha. Early hypotheses postulated that the forest decline was caused by a virulent pathogen or a combination of biotic disease and pest agents. This was ruled out after a decade of intensive disease research in the 1970s. Instead, it turned out that dieback patterns were significantly related to the physical environment, particularly the slope, topography, relative position on the hill slope, annual rainfall, and the type of substrate. Thus, an alternative hypothesis proposed that dieback is initiated by climate anomalies that manifest through soil moisture regimes under certain conditions of forest stand demography. Ironically, scientific perception of this interdisciplinary ground-breaking research that stimulated a global perspective on forest decline vanished while the awareness of climate change and its potential impact on the world's forests started to grow, rapidly becoming a major focus of research in recent years. In this paper, we reinforce memory of the world's first complex discussion on the natural causes of forest dieback as a showcase for the complexity of modern forest mortality research. This case demonstrates the need to rigorously identify, quantify, and fully understand all drivers of tree mortality to realistically project future climate-driven and other risks to forest ecosystem functions and services. Moreover, we summarize recent findings on forest mortality and climate change in the Pacific islands and beyond. Keywords: cavitation, climate change, dieback, Metrosideros polymorpha, montane rainforest, novel ecosystem, tree mortality, vulnerability, CLIMATE IS THE DOMINANT FACTOR determining the distribution of vegetation (Woodward and Woodward 1987). Climatic factors, in particular temperature, precipitation, and humidity, play a fundamental role in the physiology of [...]

The Leeward Kohala Field System (LKFS) on Hawai'i Island once featured over 60 [km.sup.2] of productive, rain-fed croplands. For several centuries, its occupants cultivated 'uala (Ipomoea batatas, sweet potato) as a staple crop between kuaiwi (earthen or rock walls) planted with ko (Saccharum officinarum, sugarcane). These raised ko rows could have influenced 'uala growth through an array of microclimatic processes, including wind abatement, shading, and the redistribution of moisture. While such effects are frequently mentioned in the literature, efforts to directly quantify them and relate them to 'uala production have been lacking. We measured wind speeds, precipitation rates, solar illuminance, soil moisture, and 'uala yields along a transect through three ko rows within the LKFS. Ko rows proved effective windbreaks, reducing near-surface wind speeds by up to 90% and for distances of up to 10 m. The rows also concentrated wind-blown moisture at their upwind edges while creating rain shadows 5-6 m in length. 'Uala yields peaked at 3.8-6.0 kg [m.sup.-2] near the center of inter-row space, probably because 'uala were energy-limited during the wet study period and grew slowly when shaded by the ko. A zone of low turbulence leeward of each ko row also appeared to benefit 'uala growth. Additional measurements are needed to investigate the landscape-level hydrologic effects of ko row planting. Our findings will help guide ongoing efforts to expand agricultural and educational activities in the LKFS. Keywords: sugarcane, sweet potato, traditional agriculture, windbreaks, row planting, microclimates, traditional ecological knowledge, land stewardship, HAWAIIANS WERE UNIQUE within pre-contact Polynesia for their reliance on--and mastery of--dryland agriculture (Lincoln and Vitousek 2017). After beginning to farm in fertile lowlands and river valleys, Hawaiians expanded their [...]

The Eucalyptus genus is extensively planted in Brazil for industrial use, and with the expansion of forest frontiers and climate changes, studies are needed on how these changes affect wood density (WD). The aim of this study was to evaluate the effect of some climate variables on WD of an Eucalyptus urophylla clone for a 4-5 year period. WD from trees collected in 12 sites were evaluated. Five growth rings were identified using a magnifying glass, X-ray densitometry, and forest inventory. WD was correlated with temperature (T), precipitation (P), soil water deficit, ring width, and current annual increment. There was no variation in WD in the first 20 months among sites. From that age on, WD was mainly correlated with T (r > 0.6). The 1 [degrees]C increase in T resulted in a WD reduction of 0.014 g [cm.sup.-1], and increases of 10 [m.sup.-3] [ha.sup.-1] in the final volume were related to an increase of 0.004 g [cm.sup.-1] in WD. Researchers and managers should continue to put efforts into broad experimental networks to assess the effects of climate change on the adaptation and wood quality of Eucalyptus clones. Highlights The influence of climate on E. urophylla wood density was greater after the third year of growth. The mean air temperature was the best correlated climatic variable with E. urophylla wood density. The cross-site climatic gradient was more important in wood density variation of E. urophylla than the variability among the years. Key words: wood quality, climate conditions, annual growth, densitometry, forest expansion, 1. Introduction Plant secondary (radial) growth is a dynamic process and related to external factors such as climate and soil (Pillai et al. 2013; Zhang et al. 2014; Mendivelso et [...]

Drought is a costly natural disaster characterized by water shortages that impact water availability, agriculture, ecosystems, and the economy. The driving mechanisms of drought operate on a wide range of spatial scales, from the movement of soil water on a hillslope to global atmospheric circulation. Additionally, drought impacts vary across spatial scales, from drought induced crop stress on a specific agricultural field to widespread continental water shortages. As a result, multiscalar drought monitoring and early warning systems are needed to utilize observational data sets obtained at different spatial scales and to communicate drought impacts to various levels of decision-makers in government and industry. However, scaling must be employed to translate information across scales, either to fix incongruencies in the spatial scale of input data sets or to modify the model output scale. These scaling techniques have several challenges and limitations that hinder drought accuracy and interpretability, such as the Modifiable Areal Unit Problem (MAUP) and increased model uncertainty. This paper reviews the role of spatial scale in drought monitoring and early warning systems, the associated challenges, and techniques to minimize their impact. Finally, this review identifies several knowledge gaps and future directions. Key words: drought, spatial scale, scaling, MAUP. La sécheresse est une catastrophe naturelle coûteuse caractérisée par des pénuries d'eau qui ont un impact sur la disponibilité de l'eau, l'agriculture, les écosystèmes et l'économie. Les mécanismes moteurs de la sécheresse opèrent sur un large spectre d'échelles spatiales, allant du mouvement de l'eau du sol sur une pente de colline àla circulation atmosphérique globale. De plus, les impacts de la sécheresse varient selon les échelles spatiales, allant du stress des cultures induit par la sécheresse dans un champ agricole spécifique aux pénuries d'eau généralisées àl'échelle du continent. Par conséquent, des systèmes de surveillance de la sécheresse et d'alerte précoce multi-scalaires sont nécessaires pour utiliser les ensembles de données d'observation obtenus àdifférentes échelles spatiales et pour communiquer les impacts de la sécheresse àdifférents niveaux de décideurs au gouvernement et dans l'industrie. Cependant, la mise àl'échelle doit être utilisée pour traduire l'information àtravers les échelles, soit pour corriger les incongruités dans l'échelle spatiale des ensembles de données d'entrée, soit pour modifier l'échelle de sortie du modèle. Ces techniques de mise àl'échelle présentent plusieurs défis et limites qui nuisent àla précision et au potentiel d'interprétation de la sécheresse, comme le problème d'agrégation spatiale (MAUP ; Modifiable Areal Unit Problem) et l'incertitude accrue du modèle. Cet article examine le rôle de l'échelle spatiale dans la surveillance de la sécheresse et les systèmes d'alerte précoce, les défis associés, et les techniques pour minimiser leur impact. Enfin, cette synthèse identifie plusieurs lacunes dans les connaissances et les orientations futures. [Traduit par la Rédaction] Mots-clés : sécheresse, échelle spatiale, mise àl'échelle, MAUP., 1. Introduction Drought is a pervasive and insidious natural disaster marked by a prolonged lack of precipitation relative to normal conditions, resulting in complex and costly impacts that permeate a [...]

Context. Soil water availability, as characterised by the integral water capacity, uses weighting functions based on models not yet evaluated using plants, especially in the context of saline soils. Without plant evaluation such weighting functions remain theoretical at best. Aims. We aimed to use maize plants to evaluate Mohammadi and Khataar's (2018) conceptual model for a salinity weighting function, against those used in Hydrus 1D. Methods. We conducted glasshouse experiments with large columns of two sandy loams planted with maize irrigated using different salinities, and repeated without plants. Soil matric suction ranged between saturation and 100 cm, and we measured or predicted plant height, transpiration, evaporation, drainage, storage, and solute concentration over time. The soil water retention curve was measured and the weighted mean hydraulic conductivity was obtained using the van Genuchten model. Key results. We found a correlation between our salinity weighting function and the relative transpiration rate of maize (grown in two different soils using irrigation water of three different salinities), particularly in the first few days of growth but not thereafter; errors were related to uncertainties in predicting drainage, salt concentration, and soil water storage in planted columns. Conclusions. The deviation of transpiration rate from that predicted by our salinity weighting function at higher salinities may relate to the linear nature of the Maas-Hoffman salinity weighting function plus heterogeneity of soil water and solute distributions. Implications. Improving the estimates of drainage and soil water storage in future would make our physical model more useful in larger scale hydrological predictions. Keywords: drainage, evapotranspiration, field capacity, irrigation, modeling, root water uptake, salinity, soil hydraulic properties, soil water availability., Introduction Agricultural production in all regions depends directly on the amount of plant water use (Feng et al. 2021). Water uptake depends on the soil moisture conditions as well as [...]

In situ wetting-drying cycles significantly and repeatedly influence the soil water content in the active zone but not in the steady zone. To investigate effects of in situ wetting-drying cycles on the mechanical behaviour of intact loess, a series of pressure plate tests was carried out with an intact loess sampled from the active and steady zones. Results show that the specimens from the steady zone have higher yield stresses at given suctions and a larger inclination of normalized loading collapse (LC) curve than the specimens from the active zone. As evidenced by the scanning electron microscopy results, the clay particles accumulating around the contacts between silt particles are widely observed in the former specimens but not in the latter specimens. The distribution of clay particles in the former specimens results in a stabilized skeleton with mechanical properties sensitive to suction variations. On the other hand, the maximum collapse potential of the specimen from the steady zone is 37% larger than that of the specimen from the active zone, mainly because of the larger inclination of normalized LC curve owned by the former specimen. Key words: intact loess, compression, collapse, in situ wetting-drying cycles. Les cycles de mouillage-sechage in situ influencent de maniere significative et repetitive la teneur en eau du sol dans la zone active, mais pas dans la zone stable. Pour etudier les effets des cycles de mouillage-sechage in situ sur le comportement mecanique du loess intact, une serie d'essais sur plaque de pression a ete realisee avec un loess intact echantillonne dans les zones actives et stables. Les resultats montrent que les specimens de la zone stable ont des contraintes d'elasticite plus elevees a des suctions donnees et une plus grande inclinaison de la courbe d'effondrement normalisee (LC) que les specimens de la zone active. Comme le montrent les resultats de la microscopie electronique a balayage, les particules d'argile qui s'accumulent autour des contacts entre les particules de limon sont largement observees dans les premiers specimens, mais pas dans les seconds. La repartition des particules d'argile dans les anciens specimens donne lieu a un squelette stabilise dont les proprietes mecaniques sont sensibles aux variations de la succion. D'autre part, le potentiel d'effondrement maximal de l'eprouvette de la zone stable est 37 % plus eleve que celui de l'eprouvette de la zone active, principalement en raison de la plus grande inclinaison de la courbe LC normalisee appartenant a la premiere eprouvette. [Traduit par la Redaction] Mots-cles: loess intact, compression, effondrement, cycles de mouillage-sechage in situ., 1. Introduction Loess is distributed over vast arid and semiarid regions in the People's Republic of China and many other countries (Munoz-Castelblanco et al. 2012; Ng et al. 2018). Active [...]

Context. The combination of no-till and stubble retention has been shown to preserve old crop roots, which behave as pathways for water infiltration into water repellent soil, by-passing repellent surface soil layers. Aim. To evaluate the benefits to soil properties and crop performance of seeding close to the previous season's crop rows (near-row sowing) compared with inter-row sowing on water repellent soils. Methods. At four field sites, near Moora, Pingrup and Calingiri in Western Australia and Wanilla in South Australia, measurements were made of: (1) crop performance of near- and inter-row sown crops (Moora and Wanilla); and (2) differences in soil properties between the crop row and inter-row at Wanilla, Calingiri and Pingrup. Key results. Biomass accumulation (Moora) and grain yields (Moora and Wanilla) were significantly improved by near-row sowing compared with inter-row sowing, particularly under no-till and stubble retention, but these differences were reduced after cultivation, which either buried repellent surface soils or disrupted root pathways. At Calingiri and Pingrup, where near-row sowing had been practised for [greater than or equal to] 4 years, and at Wanilla, soil water contents were higher in the crop row than the inter-row by up to 4% v/v, and this was associated with significantly reduced repellency (Calingiri and Pingrup) and larger communities of wax-degrading bacteria (Pingrup). Conclusions. Near-row sowing may enhance crop production directly through improved water infiltration down root pathways, and indirectly by reduced soil water repellency in the row. Implications. Near-row sowing is potentially a low-cost management for enhanced crop production on water repellent soils. Keywords: crop establishment, crop row placement, non-wetting soils, on-row sowing, preferential water infiltration, siliceous sand, soil water repellency, soil water repellence, strategic tillage, wax-degrading bacteria., Introduction Soil water repellency associated with the surface layers of coarse sandy soils restricts crop and pasture production on 10 million ha of agricultural land in south-west Western Australia (WA) [...]

Black spruce (Picea mariana (Mill.) BSP) is the main tree species growing within peatlands. The difficult growing conditions within peatlands are associated with low individual wood productivity, and only tree species tolerant to high ground water level can survive. We examine the effect of water-saturated soil on the growth potential of black spruce trees and specific adaptation of the root system. Experimental mesocosms were constructed with two drainage regimes (saturated and well-drained soil conditions). We measured biomass, height, and diameter at stem base of 55 black spruce saplings and noted the location of each horizontal root. Black spruce exhibited a very shallow root system located above saturated commercial peat 19 years after the experiment was initiated. Most roots were adventitious in the water- saturated mesocosms. Overall aerial and root biomass accumulation of the black spruce trees growing under saturated soil conditions was significantly lower than that of the well-drained mesocosms. Interestingly, root-shoot ratios were similar across the two drainage regimes. Soil conditions induced adaptation of the root system in black spruce trees, and physiological stress affected the entire individual with lower biomass productivity in all components (stem, branches, root system). However, biomass distribution remained similar to that of trees growing in well-drained mesocosms. Key words: peatland, black spruce, root system, adventitious root, biomass, root-shoot ratio. L'epinette noire (Picea mariana (Mill.) BSP) est la principale espece d'arbre poussant dans les tourbieres. Les conditions de croissance difficiles dans les tourbieres sont associees a une faible productivite du bois, et seules les especes d'arbres tolerantes aux niveaux eleves de la nappe phreatique peuvent survivre. Nous examinons l'effet d'un sol sature en eau sur le potentiel de croissance des epinettes noires et l'adaptation specifique du systeme racinaire. Experimental mesocosms were constructed with two drainage regimes (saturated and well-drained soil conditions). Nous avons mesure la biomasse, la hauteur et le diametre a la base du tronc de 55 gaules d'epinette noire et note l'emplacement de chaque racine horizontale. L'epinette noire presentait un systeme racinaire tres peu profond situe au-dessus de la tourbe commerciale saturee, 19 ans apres le debut de l'experience. La plupart des racines etaient adventives dans les mesocosmes satures d'eau. L'accumulation globale de biomasse aerienne et racinaire des epinettes noires poussant dans des conditions de sol sature etait significativement plus faible que celle des mesocosmes bien draines. Il est interessant de noter que les ratios racinespousses etaient similaires pour les deux regimes de drainage. Les conditions du sol ont entraine une adaptation du systeme racinaire chez l'epinette noire, et le stress physiologique a affecte l'ensemble de la plante avec une baisse de la productivite de la biomasse dans toutes les composantes (tige, branches, systeme racinaire). Cependant, la distribution de la biomasse est restee similaire a celle des arbres poussant dans des mesocosmes bien draines. [Traduit par la Redaction] Mots-cles : tourbiere, epinette noire, systeme racinaire, racine adventive, biomasse, rapport racines-pousses., Introduction Extensive peatlands occur in Canada, accounting for more than 13% of its terrestrial surface. They are mostly located (more than 85%) northward of the 51st parallel in the boreal [...]

Context. Biochar and pumice have potential to improve soil water retention and mitigate salinity. However, little is known about their effect on salt transport in sandy soils. Aims. We investigated the influence of the porosity and pore size distribution of soil amendments with pumice and biochar on the mobile water content of a New Zealand sandy soil. Methods. Pumice and biochar (1.5-cm, 3-cm and 6-cm in diameter, [empty set]) were characterised using scanning electron microscope technology. The fraction of mobile water present in these amendments, previously added to a sandy soil at different application rates and particle sizes, was determined using a tracer ([Na.sup.+]) technique. Key results. (I) Pumice exhibited a wider pore-size span than biochar; and (2) both materials had a predominance of pores with [empty set] < 30 [micro]m; but (3) the total porosity in pumice and biochar was not significantly different; (4) pumice had a significantly larger (P < 0.05) mean absolute micro-scale porosity than biochar; and (5) a significantly greater (P < 0.05) relative resident [Na.sup.+] concentration than biochar, irrespective of the particle size. Conclusions. These results reflect a larger fraction of the mobile water in pumice than that of biochar under near-saturated conditions, irrespective of the biochar particle size; and this increased as the pumice particle size increased. Implications. While both materials are expected to contribute to water retention and thus might alleviate salt-stress by diluting salt concentration, pumice may perform better than this specific biochar on improving the retention of plant-available water. Keywords: dilution, miscible displacement, mobile-water fraction, particle size, physical properties, porosity, salinity, scanning electron microscopy., Introduction The sustainability of agriculture in arid regions is challenged by the limited availability of water, and the need to manage salinity in soils and irrigation-water. This demands long-term interventions, [...]

Invasive plant species can alter litter decomposition rates through changes in litter quality, environment conditions, and decomposer organisms (microflora and soil fauna), but limited research has examined their direct impact on soil fauna. We assessed the abundance and relative contribution of soil meso- and macrofauna to litter decomposition in a forest invaded by Ligustrum lucidum W.T. Aiton and in a noninvaded forest in a subtropical mountain forest in northwestern Argentina, using litterbags (0.01, 2, and 6 mm mesh size). Additionally, we analyzed the litter quality and soil properties of both forest types. Soil fauna abundance was lower in the invaded forest than in the noninvaded forest. The contribution of soil macrofauna to litter decomposition was important in both forest types, but soil mesofauna contribution was significant only in noninvaded forest. Litter decomposition was significantly faster in the invaded forest, consistent with its higher quality litter compared with the uninvaded forest. Invaded forest had significantly lower litter accumulation, lower soil moisture, and greater soil pH than noninvaded forest. Our results showed that although soil fauna was less abundant and played a less pronounced role in litter decomposition in invaded forest, these changes did not translate into a reduced litter decomposition rate due to the higher quality of litter produced in the invaded forest. Key words: glossy privet, invasive alien species, litter decomposition, soil mesofauna and macrofauna, subtropical montane forest. Les especes vegetales envahissantes peuvent modifier le taux de decomposition de la litiere par le biais de changements dans la qualite de la litiere, les conditions du milieu et les organismes responsables (microflore et faune du sol) de sa decomposition, mais peu de travaux de recherche ont etudie leur impact direct sur la faune du sol. Nous avons evalue l'abondance et la contribution relative de la mesofaune et de la macrofaune a la decomposition de la litiere dans la foret envahie par Ligustrum lucidum W.T. Aiton et la foret non envahie dans une foret subtropicale de montagne du nord-ouest de l'Argentine a l'aide de sacs a litiere (mailles de 0,01, 2 et 6 mm). De plus nous avons analyse la qualite de la litiere et les proprietes du sol dans les deux types de foret. L'abondance de la faune du sol etait plus faible dans la foret envahie que dans la foret non envahie. La contribution de la macrofaune du sol a la decomposition de la litiere etait importante dans les deux types de foret mais la contribution de la mesofaune du sol etait significative seulement dans la foret non envahie. La decomposition de la litiere etait significativement plus rapide dans la foret envahie ou la litiere est de meilleure qualite que dans la foret non envahie. La foret envahie accumulait significativement moins de litiere, avait un sol moins humide et un pH du sol plus eleve que la foret non envahie. Nos resultats montrent que, meme si la faune du sol est moins abondante et joue un role moins important dans la decomposition de la litiere dans la foret envahie, ces changements n'ont pas entrarne de reduction du taux de decomposition etant donne la plus grande qualite de la litiere dans la foret envahie. [Traduit par la Redaction] Mots-cles : troene luisant, especes exotiques envahissantes, decomposition de la litiere, mesofaune et macrofaune du sol, foret subtropicale de montagne., Introduction One of the characteristics of the Anthropocene is that no place seems immune to biological invasions. Invasion by alien species is, in fact, considered one of the main drivers [...]

Stomatal conductance (SC) and chlorophyll concentration (CC) are sensitive to soil matric suction ([psi]). The relationship between these two plant parameters and [psi] in the root zone can help understand the water uptake efficiency and photosynthetic capacity of a plant. This paper aims to quantify the relationships between SC and CC with [psi], for Schefflera arboricola grown in compacted bare silty sand and biochar amended soil (BAS). Plant parameters (SC, CC, leaf area (LA), root length (RL)) and [psi] were regularly monitored in an atmospheric controlled room. The maximum recorded SC was greater in BAS than that in bare soil due to the higher water demand of LA. Based on measured data upon evapotranspiration, two equations are proposed to interpret the effects of [psi] on plant water uptake and photosynthesis. A fitting equation is established to relate normalized SC with [psi] to identify a threshold suction (CNSC; indicator of drought stress resistance). The magnitude of [[psi].sup.t.sub.NSC] is found to be mainly dependent on LA/RL ratio and root ends. Furthermore, a new relationship between CC and [psi] is observed and developed. A decrease in CC at higher [psi] is attributed to leaf senescence and stomatal closure, restricting plant to produce more chlorophyll. Key words: monitoring, partial saturation, suction, vegetation. La conductance stomatique (SC) et la concentration en chlorophylle (CC) sont sensibles a la succion matricielle du sol ([psi]). La relation entre ces deux parametres vegetaux et [psi] dans la zone racinaire peut aider a comprendre l'efficacite de l'absorption d'eau et la capacite photosynthetique d'une plante. Cet article vise a quantifier les relations entre SC et CC avec [psi], pour Schefflera arboricola cultive dans du sable limoneux nu compacte et dans un sol amende au biochar (BAS). Les parametres des plantes (SC, CC, surface foliaire (LA), longueur des racines (RL)) et [psi] ont ete regulierement controles dans une piece a atmosphere controlee. La SC maximale enregistree etait plus grande dans le BAS que dans le sol nu en raison de la demande en eau plus elevee de LA. Sur la base des donnees mesurees sur l'evapotranspiration, deux equations sont proposees pour interpreter les effets de [psi] sur l'absorption d'eau et la photosynthese des plantes. Une equation d'ajustement est etablie pour relier la SC normalisee a [psi] afin d'identifier un seuil de succion ([[psi].sup.t.sub.NSC]; indicateur de la resistance au stress de la secheresse). La magnitude de [[psi].sup.t.sub.NSC] depend principalement du rapport LA/RL et des extremites des racines. En outre, une nouvelle relation entre CC et [psi] est observee et developpee. Une diminution de la CC a un ft plus eleve est attribuee a la senescence des feuilles et a la fermeture des stomates, ce qui limite la production de chlorophylle par la plante. [Traduit par la Redaction] Mots-cles: surveillance, saturation partielle, aspiration, vegetation., Introduction Vegetation as a 'live protection' layer provides hydrological reinforcement for shallow slope stability in landfill covers and bio-engineered slope (Pagano et al. 2019; Liang et al. 2020). Transpiration by [...]

Context. Success of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is dependent on a range of soil factors including pH and soil organic carbon (OC) content. Aims. This study identified the effect of soil properties and moisture content at the time of DMPP application on the efficiency of DMPP and soil mineral N concentrations. Methods. Soil was collected from paired paddocks with contrasting management, cropping or pasture across three sites. Soil samples were pre-incubated for 7 days with moist (-85 kPa) or air dried soil to simulate sowing into soil with moisture equivalents of post seasonal break or dry sowing. Urea ammonium nitrate (UAN) was applied with and without DMPP to all soils. Key results. DMPP inhibited nitrification in all soils, although decreased inhibitory effectiveness was observed in acidic soils compared to neutral soils. Inhibition efficacy on acidic soils was improved when DMPP was applied to dry rather than wet soils. Neutral soils did not observe the same soil moisture effect having similar inhibition efficiency of DMPP observed between dry and wet soil application. Nitrogen fertilisers applied to dry soils nitrified at a greater rate than when applied to wet soils. DMPP decreased the ammonia oxidising bacteria (AOB) population while the ammonia oxidising archaea (AOA) amoA gene copy numbers were unaffected. Conclusions. This study shows that the lower soil pH and high OC contents can reduce the efficacy of DMPP. Implications. When using DMPP in Australian broad acre agriculture, knowledge of soil properties including soil pH will determine if application of DMPP is suitable for use before or after a seasonal break rainfall event. Keywords: amoA, AOA, AOB, DMPP, mineralisation, nitrification inhibitor, priming effect, pre-incubation., Introduction The biological oxidation of ammonium (N[H.sub.4.sup.+]) is performed by ubiquitous soil microorganisms called nitrifiers. Aerobic, chemoautotrophic ammonia oxidising bacteria (AOB) and archaea (AOA) oxidise N[H.sub.4.sup.+] to the intermediate hydroxylamine [...]

Given the large contribution of forests to terrestrial carbon storage, there is a need to resolve the environmental and physiological drivers of tree-level response to rising atmospheric C[O.sub.2]. This study examines how site-level soil moisture influences growth and intrinsic water-use efficiency in sugar maple (Acer saccharum Marsh.). We construct tree-ring, [[delta].sup.18]O, and [[DELTA].sup.13]C chronologies for trees across a soil moisture gradient in Ontario, Canada, and employ a structural equation modelling approach to ascertain their climatic, ontogenetic, and environmental drivers. Our results support previous evidence for the presence of strong developmental effects in tree-ring isotopic chronologies--in the range of -4.7% for [[DELTA].sup.13]C and +0.8% for [[delta].sup.18]O--across the tree life span. Additionally, we show that the physiological response of sugar maple to increasing atmospheric C[O.sub.2] depends on site-level soil moisture variability, with trees only in relatively wet plots exhibiting temporal increases in intrinsic water-use efficiency. These results suggest that trees in wet and mesic plots have experienced temporal increases in stomatal conductance and photosynthetic capacity, whereas trees in dry plots have experienced decreases in photosynthetic capacity. This study is the first to examine sugar maple physiology using a dendroisotopic approach and broadens our understanding of carbon-water interactions in temperate forests. Key words: tree ring, temperate broadleaf, dendroecology, carbon isotopes, oxygen isotopes, tree physiology, Acer saccharum Marsh. Etant donne l'importance de la contribution des forets au stockage du carbone terrestre, il y a un besoin evident d'identifier les facteurs environnementaux et physiologiques determinants de la reaction a l'augmentation du C[O.sub.2] atmospherique a l'echelle de l'arbre. Cette etude examine de quelle facon l'humidite du sol a l'echelle de la station influence la croissance et l'efficience de l'utilisation de l'eau chez l'erable a sucre (Acer saccharum Marsh.). Nous avons elabore des series dendrochronologiques pour [[delta].sup.18]O et [[DELTA].sup.13]C chez des arbres situes le long d'un gradient d'humidite du sol en Ontario, au Canada, et nous avons utilise une approche de modelisation par equation structurelle pour determiner leurs facteurs climatiques, ontogeniques et environnementaux determinants. Nos resultats supportent les indices anterieurs de la presence d'effets marques lies au developpement dans les chronologies isotopiques, dans l'ordre de -4,7% pour [[DELTA].sup.13]C et +0,8% pour [[delta].sup.18]O, pour la duree de la vie. De plus, nous montrons que la reaction physiologique de l'erable a sucre a l'augmentation du C[O.sub.2] atmospherique depend de la variation de l'humidite du sol a l'echelle de la station alors que seuls les arbres situes dans les parcelles relativement humides montrent des augmentations temporelles de l'efficience de l'utilisation de l'eau. Ces resultats indiquent que les arbres situes dans les parcelles hydriques et mesiques ont connu des augmentations temporelles de la conductance stomatique et de la capacite photosynthetique, tandis que les arbres dans les parcelles xeriques ont connu des diminutions de la capacite photosynthetique. Il s'agit de la premiere etude qui examine la physiologie de l'erable a sucre a l'aide d'une approche dendroisotopique et elle permet d'elargir notre comprehension des interactions entre le carbone et l'eau dans les forets temperees. [Traduit par la Redaction] Mots-cles : cernes annuels, feuillu tempere, dendroecologie, isotopes du carbone, isotopes de l'oxygene, physiologie de l'arbre, Acer saccharum Marsh., 1. Introduction Increasing atmospheric carbon dioxide ([C.sub.a]) is a unique component of global environmental change in that its influence on terrestrial ecosystems is ubiquitous. Since photosynthesis of C3 plants is [...]

Climate warming will influence photosynthesis via thermal effects and by altering soil moisture.sup.1-11. Both effects may be important for the vast areas of global forests that fluctuate between periods when cool temperatures limit photosynthesis and periods when soil moisture may be limiting to carbon gain.sup.4-6,9-11. Here we show that the effects of climate warming flip from positive to negative as southern boreal forests transition from rainy to modestly dry periods during the growing season. In a three-year open-air warming experiment with juveniles of 11 temperate and boreal tree species, an increase of 3.4 °C in temperature increased light-saturated net photosynthesis and leaf diffusive conductance on average on the one-third of days with the wettest soils. In all 11 species, leaf diffusive conductance and, as a result, light-saturated net photosynthesis decreased during dry spells, and did so more sharply in warmed plants than in plants at ambient temperatures. Consequently, across the 11 species, warming reduced light-saturated net photosynthesis on the two-thirds of days with driest soils. Thus, low soil moisture may reduce, or even reverse, the potential benefits of climate warming on photosynthesis in mesic, seasonally cold environments, both during drought and in regularly occurring, modestly dry periods during the growing season.Low soil moisture may reduce, or even reverse, the potential benefits of climate warming on photosynthesis in mesic, seasonally cold environments, both during drought and in regularly occurring, modestly dry periods during the growing season., Author(s): Peter B. Reich [sup.1] [sup.2] , Kerrie M. Sendall [sup.1] [sup.3] , Artur Stefanski [sup.1] , Roy L. Rich [sup.1] [sup.4] , Sarah E. Hobbie [sup.5] , Rebecca A. [...]

Although it is clear that gap thinning significantly increases the soil water content (SWC) of the topsoil, less is known about whether and how this treatment affects deeper layers. From December 2008 to April 2012, we monitored the SWC at depths of 10, 20, 30, 45, 60, and 90 cm in gap creation treatments (small gap size of 30 [m.sup.2], intermediate gap size of 80 [m.sup.2], and unthinned plots) in a typical pine plantation in the eastern Tibetan Plateau. Among gap treatments, differences in SWC and its coefficient of variation (CV) at each depth and the soil water content proportion (SWCP) of the whole soil profile at specific depths were compared. Gap thinning improved SWC and decreased the CV at each depth. The SWCPs in thinned plots were lower at depths from 10 to 30 cm compared with unthinned plots but higher at depths of 45 and 60 cm. Also, in each season, the patterns were similar to the general results. In conclusion, gap thinning improves the SWC, changes the vertical soil water distribution, and decreases the SWC heterogeneity. The soil water conditions in intermediate gaps are more appropriate for local forest restoration. Key words: gap size, precipitation, season, soil layer, understory plant. Bien qu'il soit clair que l'eclaircie par trouees augmente significativement la teneur en eau du sol (TES) de la couche superficielle du sol, les effets de ce traitement sur les horizons du sol plus profonds sont moins bien connus. De decembre 2008 a avril 2012, nous avons mesure la TES a des profondeurs de 10, 20, 30, 45, 60 et 90 cm dans des traitements visant a creer des trouees (petites trouees : 30 [m.sup.2]; trouees intermediaires : 80 [m.sup.2]; et placettes non eclaircies) dans une plantation de pin representative du plateau tibetain oriental. Ces traitements ont fait l'objet d'une comparaison de la TES, du coefficient de variation de la TES (CV) a chaque profondeur, et de la proportion de la teneur en eau du sol (PTES) par rapport a celle du profil de sol complet a des profondeurs specifiques. L'eclaircie par trouees a ameliore la TES et a diminue le CV a chaque profondeur. La PTES des placettes eclaircies etait plus faible aux profondeurs de 10 a 30 cm par rapport aux placettes non eclaircies, mais plus elevee aux profondeurs de 45 et 60 cm. De plus, ce type de resultats qui est semblable aux resultats generaux a ete observe a chaque saison. En conclusion, l'eclaircie par trouees ameliore la TES, modifie la distribution verticale de l'eau du sol et diminue l'heterogeneite de la TES. Les conditions d'eau du sol dans les trouees de taille intermediaire sont plus appropriees pour la restauration des forets locales. [Traduit par la Redaction] Mots-cles : taille des trouees, precipitation, saison, couche du sol, plantes de sous-bois., Introduction Forest gap thinning is an effective protocol to improve understory environmental conditions, thereby contributing to seedling establishment and increasing species diversity (Muscolo et al. 2014). Soil water content (SWC) [...]

ABSTRACT The National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) mission was launched in January 2015 and has been providing science data since April 2015. Though designed [...]

The genus Drosera (sundews) is represented in British Columbia (BC), Canada, by Drosera rotundifolia (L.), Drosera anglica (Huds.), and their hybrid Drosera x obovata (Mert. & W.D.J. Koch). All three can be found in Sphagnum bogs of central BC, including those within the Aleza Lake Research Forest (ALRF) located 60 km east of Prince George. Vegetation patterns in bogs are known to be correlated with light, water, and nutrient gradients, and despite information being available on the influence of light and water on Drosera occurrence, little information is known about the role of nutrients. Here, we focused on a bog containing all three Drosera species, to determine whether nutrient levels are related to the abundance of the widespread species, D. rotundifolia. Univariate regression tree analysis between soil water chemistry and D. rotundifolia numbers indicates that D. rotundifolia is a calcifuge, preferring moderately acidic soil pH (>5.5) and relatively low calcium levels ( Key words: Drosera rotundifolia, Drosera anglica, calcium, Sphagnum peatlands, carnivorous plants. Le genre Drosera (<>) est represente en Colombie-Britannique (CB), au Canada, par Drosera rotundifolia (L.), Drosera anglica (Huds.) et leur hybride Drosera x obovata (Mert. & W.D.J. Koch). Tous trois peuvent se trouver dans les tourbieres du centre de la CB, incluant les tourbieres de la foret d'enseignement et de recherche d'Aleza Lake situee a 60 km a l'est de Prince George. Les patrons de vegetation des tourbieres sont connus pour etre correles avec les gradients de lumiere, d'eau et de nutriments, et malgre le fait que l'information sur l'influence de la lumiere et de l'eau sur la presence de Drosera soit disponible, le role des nutriments est peu connu. Les auteurs se concentrent ici sur une tourbiere comportant les trois especes de Drosera afin de determiner si les niveaux de nutriments sont relies a l'abondance de l'espece repandue D. rotundifolia. L'analyse d'un arbre de regression multivariable entre la chimie de l'eau du sol et le nombre d'individus indique que D. rotundifolia est un calcifuge, preferant les sols a pH moderement acides (5,5) et a niveaux de calcium relativement faibles ( Mots-cles: Drosera rotundifolia, Drosera anglica, calcium, tourbieres, plantes carnivores., Introduction Members of the sundew genus Drosera represent a number of scientifically important species. Widely known for their carnivorous habit, sundews are key models for ecological processes such as plant [...]

'Essentially, we need to stop thinking about returning to normal as a thing that is possible.' --SAMANTHA STEVENSON of the University of California, Santa Barbara, who led a recent study [...]

Most hypotheses about controls over high-altitude forests, including treeline, the elevation for upright woody plants, or timberline, the upper elevation for aggregated forest, suggest that low temperature drives forest dynamics, either through effects on cell division and tree growth or indirectly through frost damage or nutrient availability. However, abiotic factors other than temperature, including water availability, may serve as other important controls at high elevations, particularly for seedlings. To test the hypothesis that the timing and amount of precipitation exerts a strong control over the high-elevation forest boundary on the Wasatch Plateau in central Utah, USA, we conducted a field experiment that manipulated water availability and monitored photosynthesis, growth, and survivorship in Picea engelmannii Parry ex Engelm. seedlings. Survivorship increased from the driest to the wettest conditions, whereas the timing of precipitation did not explain differences in survival. However, we found that large, infrequent rain events increased maximum photosynthetic flux density compared with small, frequent rain events. Our results highlight the potential role of growing season water availability in limiting timberline expansion below the low-temperature thermal limits of P. engelmannii. As a consequence, the infilling of trees below the treeline in this region in response to climate change is likely to be episodic and driven by multiyear periods of high water availability and frequency that overcome drought limitations. Key words: treeline, hydrology, Picea engelmannii, photosynthesis, survivorship. La plupart des hypotheses concernant les controles sur les forets de haute altitude, incluant la limite des arbres, l'altitude a laquelle on retrouve encore des plantes ligneuses dressees, ou la limite de vegetation des arbres, l'altitude superieure a laquelle il y a encore de la foret, indiquent que la basse temperature determine la dynamique forestiere, soit en ayant des effets sur la division cellulaire et la croissance des arbres, soit indirectement a cause des dommages dus au gel ou de la disponibilite des nutriments. Cependant, des facteurs abiotiques autres que la temperature, incluant la disponibilite en eau, pourraient etre d'importants facteurs alternatifs de controle a haute altitude, particulierement pour les semis. Pour tester l'hypothese que le moment et la quantite de precipitation exercent un controle significatif sur la limite de la foret a haute altitude sur le plateau des Wasatch dans le centre de l'Utah, aux Etats-Unis, nous avons realise une experience sur le terrain dans laquelle nous avons manipule la disponibilite en eau et suivi la photosynthese, la croissance et la survie des semis de l'epicea d'Engelmann (Picea engelmannii Parry ex Engelm.). La survie augmentait en passant des conditions les plus seches aux plus humides tandis que le moment des precipitations n'expliquait pas les differences dans la survie. Cependant, nous avons trouve que des episodes peu frequents de forte pluie ont augmente la densite du flux photosynthetique maximum comparativement a des episodes frequents de faible pluie. Nos resultats font ressortir le role potentiel de la disponibilite en eau durant la saison de croissance qui limiterait l'expansion de la limite de vegetation des arbres en deca des limites thermiques de temperature minimale de l'epicea d'Engelmann. En consequence, le recrutement des arbres en deca de la limite des arbres dans cette region en reponse au changement climatique sera probablement episodique et determine par des periodes de plusieurs annees de disponibilite en eau elevee et a une frequence qui surmonte les restrictions imposees par la secheresse. [Traduit par la Redaction] Mots-cles: limite des arbres, hydrologie, Picea engelmannii, photosynthese, survie., Introduction Renewed interest in upper treeline dynamics is, in part, driven by the hope that these systems will help us understand how ecosystems will respond to climate change (Harsch et [...]

Abstract: The eradication of dominant, nonnative trees can alter soil conditions in forest ecosystems by changing the forest's water balance. To test this idea, we measured water in surface soil [...]