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Mucilage produced by myxodiaspores has been mainly studied for its role in seed ecology. This work investigates changes due to mucilage in soil structure and stability in the spermosphere of the myxodiaspore crop chia (.Salvia hispanica L.). In sandy-loam (S) repacked soil sown with chia and subjected to wetting-drying (DW), Computer Assisted X-ray micro tomography showed that extrusion of a mucilage capsule formed a pore of volume twice that of the seed, surrounded by a shell of particles with higher porosity and lower pore size than the bulk soil. In three soils (S; loam, L; and clay-loam, C) the aggregate stability index to wet sieving (Stw) decreased with one and two DW cycles. Application of 2% w/w mucilage increased Stw before and after DW, from 29% in C to more than 60-fold in S. Mucilage-amended samples after DW had higher or equal Stw compared with unamended soil before DW. Soil retained at the surface of hydrated diaspores exposed to water flow changed with soil texture (11.3, 90.5 and 91.7 mg on each hydrated seed for S, L and C respectively) and chia genotype (6.7, 9.9 and 12.8 mg per hydrated seed in BC and G8 long-day flowering mutants and commercial Black chia respectively). Our results showed that myxodiaspores affected soil structure by providing a microenvironment of altered porosity and high stability around the mucilage capsule extruded by the hydrated seed. This finding characterises a transient but crucial time of crop production around sowing when physical properties of soil surrounding seeds are relevant to stability, germination and plant-microorganism relations. Additional keywords: aggregate stability, germination, soil-plant interactions, soil porosity., Introduction Soil structure and related properties are affected by plants (Roose et al. 2015). Many studies focus on the effect of roots or polysaccharides produced by roots and associated microorganisms [...]

The effects of Vetiver grass (Chrysopogon zizanioides) roots on the soil-water retention curves (SWRCs), permeability (k) function, and saturated permeability, [k.sub.sat], have been investigated on clayey sand (SC) and low-plasticity silt (ML). For ML soil, when the root biomass per soil volume was lower than 6.5 kg/[m.sup.3], the saturated permeability increased, the air-entry suction decreased slightly, and the SWRC became steeper with increasing root contents, probably due to the formation of cracks caused by wetting and drying cycles during the plant growing period. Nevertheless, roots appeared to decrease the saturated permeability and increase the air-entry suction of ML soil, after reaching this threshold with a root content of about 6.5 kg/[m.sup.3] as roots occupied the macropores and tended to suppress cracks and swelling. For SC soil for all root contents, only a slight variation of the saturated permeability with root content could be observed for the upper bounds on saturated permeability. However, the lower bounds on saturated permeability appeared to decrease as root content increased. It has also been shown that for a suction range beyond 30 kPa, the influence of roots on permeability appeared to be less significant. Key words: soil-water retention curve, permeability function, grass root, soil bio-engineering. Les effets de racines de l'herbe Vetiver (Chrysopogon zizanioides) sur les courbes de retention sol-eau (SWRCs), sur la fonction de permeabilite (k) et sur la permeabilite saturee, [k.sub.sat], ont ete etudies sur du sable argileux (SC), et sur du limon a faible plasticite (ML). Pour du sol ML, lors de la biomasse racinaire par volume de sol etait inferieure a 6,5 kg/[m.sup.3], l'augmentation de permeabilite saturee, l'aspiration d'entree d'air legerement diminuee et le SWRC sont devenu de plus en plus forte avec une augmentation dans le contenu de racine, probablement due a la formation de fissures dues aux cycles d'humidification et de sechage pendant la periode de croissance des vegetaux. Neanmoins, les racines semblaient reduire la permeabilite saturee et augmenter l'aspiration d'entree d'air du sol ML, apres avoir atteint ce seuil avec un contenu de racine d'environ 6,5 kg/[m.sup.3] lorsque les racines ont occupe les macrospores et avaient tendance a reprimer les fissures et l'enflure. Pour les sols SC pour tout contenu de racine, seulement une legere variation de la permeabilite saturee avec le contenu de la racine peut etre observee pour les limites superieures de permeabilite saturee. Cependant, la limite inferieure de la permeabilite saturee semblait diminuer avec l'augmentation du contenu de la racine. Il a egalement ete montre que pour l'aspiration au-dela de 30 kPa, l'influence des racines sur la permeabilite semble moins importante. [Traduit par la Redaction] Mots-cles: courbe de retention sol-eau, fonction de la permeabilite, racine d'herbe, bio-ingenierie du sol., Introduction Vegetation has been used to prevent shallow slides and erosion in various geotechnical and geo-environmental structures, such as embankments, landfill cover systems, and mine facilities. This technique has received [...]

Logging residues, such as tops and branches, can provide a useful biofuel for large-scale energy production. However, increasing the harvest intensity may affect the soil nutrient stores and water quality. Here, effects on soil-water chemistry after stem-only and whole-tree harvesting were investigated using data from five experimental sites in Sweden, representing medium-to high-fertility sites. They were located in recharge areas on mineral soil and harvested between the years 1995 and 2001. Soil-water samples had previously been collected from below the main part of the root zone in study plots subjected to stem-only or whole-tree harvest. Soil-water chemistry data from the five sites were jointly analyzed by ANOVA using seasonal mean concentrations from the first six seasons after clear-cutting. The concentrations of N[O.sub.3.sup.-]-N, [K.sup.+], and [Mg.sup.2+] were significantly different (p < 0.05) between the two harvest regimes, indicating lower levels after whole-tree harvest than after stem-only harvest. No significant differences were detected for electrical conductivity, pH, or the concentrations of N[H.sub.4.sup.+]-N, Al, [Ca.sup.2+], S[O.sub.4.sup.2-]-S, and [Cl.sup.-]. Measurements at one site suggested that the logging residues left on the ground increased the influx of [Cl.sup.-] to the soil. Simple budget calculations indicated that the nutrient export by logging-residue harvest was greater than the export by leaching during the regeneration phase. Key words: clear-cutting, forest, logging residue, Norway spruce, soil solution. Les residus d'exploitation, tels que les houppiers et les branches, peuvent fournir un biocarburant utile pour la production d'energie a grande echelle. Cependant, augmenter l'intensite de la recolte peut avoir un effet sur les pools de nutriments du sol et la qualite de l'eau. Dans cet article, les effets de l'exploitation par tronc entier ou arbre entier sur les caracteristiques chimiques de l'eau du sol ont ete etudies a l'aide de donnees provenant de cinq stations experimentales en Suede, representatives de stations dont la fertilite variait de moyenne a elevee. Ces stations etaient situees dans des zones d'alimentation de la nappe phreatique sur un sol mineral et ont ete recoltees entre les annees 1995 et 2001. Des echantillons d'eau du sol avaient precedemment ete recoltes au-dessous de la zone principale des racines dans des parcelles soumises a une exploitation par tronc entier ou arbre entier. Les donnees au sujet des caracteristiques chimiques de l'eau du sol provenant des cinq stations ont ete analysees conjointement par l'ANOVA en utilisant les concentrations moyennes saisonnieres des six premieres saisons suivant la coupe rase. Les concentrations de N-N[O.sub.3.sup.-], [K.sup.+] et [Mg.sup.2+] etaient significativement differentes (p < 0,05) selon le regime d'exploitation: les concentrations etaient plus faibles suivant l'exploitation par arbre entier que par tronc entier. Aucune difference significative n'a ete detectee pour la conductivite electrique, le pH ou les concentrations de NN[H.sub.4.sup.+], Al, [Ca.sup.2+], S-S[O.sub.4.sup.2-] et [Cl.sup.-]. Les mesures dans une station indiquaient que les residus d'exploitation laisses sur place ont augmente l'afflux de [Cl.sup.-] dans le sol. Des calculs simples de bilan indiquent que l'exportation de nutriments via la collecte des residus d'exploitation etait plus elevee que l'exportation par lessivage durant la phase de regeneration. [Traduit par la Redaction] Mots-cles: coupe rase, foret, residus d'exploitation, epicea commun, solution du sol., Introduction To develop strategies for reducing the environmental impact of forestry on water, it is essential to know the effects of common forestry operations at different sites and scales (cf. [...]

Losses in forest productivity through poor soil management are typically evaluated by changes in crop production, but conflicting growth responses among co-occurring species can challenge criteria for sustainability. In this study, we evaluate species response to compaction and organic matter removal by contrasting the growth and foliar attributes at age 20 of lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca x engelmannii (Moench) Voss) in sub-boreal forests of central British Columbia. Bole volume increment was stable for lodgepole pine, averaging a 6 % difference across treatments. White spruce, in contrast, often had large growth increases on forest floor retained--compacted plots (average of 63 % gain) but reductions in productivity on the forest floor removed--compacted plots (40 % decline). Foliar nitrogen concentrations converged across treatments for both species, despite the removal of over 50 % of the site N capital. Some key differences in species traits were suggested by foliar [delta][sup.15]N, attributed to deeper rooting of pine, and foliar [delta][sup.13]C, indicating possibly higher C[O.sub.2] assimilation potential for spruce. The implication is that standard metrics of sustainable forestry are contingent upon tree autecology and that comprehensive assessments of land management require a measure of collective species response. Key words: compaction, whole-tree harvest, [sup.13]C, Pinus contorta, Picea glauca. Les pertes de productivite forestiere due a une mauvaise gestion des sols sont habituellement evaluees par les changements dans la production vegetale, mais les reactions en croissance contradictoires parmi les especes qui cohabitent peuvent remettre en question les criteres de durabilite. Dans cette etude, nous evaluons le reaction des especes a la compaction et a l'enlevement de la matiere organique en comparant la croissance et les attributs foliaires a l'age de 20 ans du pin tordu (Pinus contorta Dougl. ex Loud.) et de l'epinette blanche hybride (Picea glauca x engelmannii (Moench) Voss) dans les forets subboreales du centre de la Colombie-Britannique. L'accroissement en volume du tronc etait stable chez le pin tordu avec une difference moyenne de 6% entre les traitements. Chez l'epinette blanche, au contraire, il y avait souvent de fortes augmentations de croissance (moyenne de 63%) dans les parcelles ou la couche holorganique avait ete conservee et le sol avait ete compacte mais des baisses de productivite (diminution de 40%) dans les parcelles ou la couche holorganique avait ete enlevee et le sol avait ete compacte. Chez les deux especes, la concentration d'azote foliaire tendait vers la meme valeur peu importe le traitement et malgre l'enlevement de plus de 50% des stocks de N de la station. Les rapports isotopiques laissaient entrevoir certaines differences cles entre les caracteristiques des especes attribuees a l'enracinement plus profond du pin dans le cas de [delta][sup.15]N foliaire et possiblement a une plus grande capacite d'assimilation du C[O.sub.2] de l'epinette dans le cas de [delta][sup.13]C foliaire. En consequence, les metriques standards de foresterie durable dependent de l'autecologie des arbres et les evaluations approfondies de la gestion des terres exigent une mesure de la reaction collective des especes. [Traduit par la Redaction] Mots-cles: compaction, recolte par arbre entier, [sup.13]C, Pinus contorta, Picea glauca., Introduction The postharvest maintenance of soil productivity is a widely accepted and fundamental principle of sustainable forestry (Powers et al. 1999; Schoenholtz et al. 2000; Moffat 2003) and the impetus [...]

Abstract: Invasive, non-native plant species can alter soil microbial communities in ways that contribute to their persistence. While most studies emphasize mycorrhizal fungi, invasive plants also may influence communities of [...]

Intensive horticultural practices in the greenhouse can cause proliferation of soil phytopathogenic organisms and pollution of groundwater from nitrate leaching. Among the different soil disinfection techniques, bio-disinfection through the addition of organic amendments (OA), with subsequent solarisation (biosolarisation) or without (biofumigation), is an efficient and economically viable alternative for the control of soil pathogens. This greenhouse experiment was conducted to initiate the process of conversion of a conventional tomato culture to organic farming. The effects of OA applied through biofumigation and biosolarisation in the first season on soil nitrate concentration and tomato fruit yield and quality were evaluated with the following treatments: control, no OA; [T.sub.1] 0.3 kg [m.sup.-2] of dehydrated pellets of Brassica carinata seed meal; [T.sub.2], 0.8 kg [m.sup.-2] of packaged and dehydrated B. oleracea var. italica; [T.sub.3], [T.sub.2] + 0.15 kg [m.sup.-2] of dehydrated poultry manure; [T.sub.4], [T.sub.1] + 0.16 L [m.sup.-2] of microbial cocktail. The experiment was carried out over the autumn crop cycle of two seasons (2011-12, 2012-13). Addition of OA increased soil nitrate concentration, more so with biosolarisation. Total and marketable yield of tomato and number of marketable fruits were higher in the biosolarised plots in the first crop after treatments. No effects were observed in the second crop after treatments. Except for tomato fruit firmness, quality attributes (size, soluble solids, acidity and colour) improved with some OA treatments. The supply of OA through biosolarisation is a soil disinfection technique with potential to minimise the impact of nitrate leaching and to provide improved yield and quality of tomatoes. Additional keywords: biofumigation, biosolarisation, organic amendment, organic farming, nitrate leaching, tomato crop., Introduction Agriculture based on mono-cropping and intensive production has favoured the proliferation of soil phytopathogenic organisms, resulting in substantial yield losses in many crops (Messiaen and Lafon 1967; Messiaen et [...]

Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for assessing the potential for carbon sequestration of managed pine forests. This study used a sequential exclusion of aboveground litter inputs (L, litter exclusion) and aboveground plus belowground inputs (LR, litter and root exclusion) to segregate carbon sources contributing to the development and maintenance of SOC in the surface soil supporting juvenile loblolly pine (Pinus taeda L.) in its rapid growth phase. The study spanned the 7th to 10th year of stand growth. Soil physical size fractions (>2 mm, ≤2 mm, 2000-250 µm, 250-150 µm, 150-53 µm, and Key words: carbon accretion, leaf litter, mineralization, Pinus taeda L., soil size fraction. Il est essentiel de quantifier les apports de carbone organique du sol (COS) dans le sol de surface pour evaluer le potentiel de sequestration du C dans les forets de pin amenagees. Dans cette etude nous avons eu recours a l'exclusion sequentielle des apports aeriens de litiere (L, exclusion de la litiere) et des apports aeriens et souterrains (LR, exclusion de la litiere et des racines) pour separer les sources de C qui contribuent au developpement et au maintien du COS dans le sol de surface qui supporte le pin a encens (Pinus taeda L.) juvenile dans sa phase de croissance rapide. L'etude couvrait de la 7e a la 10e annee de croissance du peuplement. Les classes granulometriques du sol (>2 mm, ≤2 mm, 2000-250 µm, 250-150 µm, 150-53 µm et Mots-cles: accumulation du carbone, litiere de feuilles, mineralisation, Pinus taeda L., classes granulometriques du sol., Introduction Soil organic carbon (SOC) content is a keystone soil quality parameter and plays a significant role in the global carbon (C) cycle. Yet, the role of root turnover and [...]

For a given evapotranspiration (ETr), both soil evaporation and plant transpiration (Tr) would induce soil suction. However, the relative contribution of these two processes to the amount of suction induced is not clear. The objective of this study is to quantify ETr- and Tr-induced suction by a selected tree species, Scheffllera heptaphylla, in silty sand. The relative contribution of transpiration and evaporation to the responses of suction is then explored based on observed differences in Trand ETr-induced suction. In total, 12 test boxes were used for testing: 10 for vegetated soil with different values of leaf area index (LAI) and root area index (RAI), while two were for bare soil as references. Each box was exposed to identical atmospheric conditions controlled in a plant room for monitoring suction responses over a week. Due to the additional effects of soil evaporation, ETr-induced suction could be 3%-47% higher than Tr-induced suction, depending on LAI. The significance of evaporation reduced substantially when LAI was higher, as relatively less radiant energy fell on the soil surface for evaporation. For a given LAI, the effects of evaporation were less significant at deeper depths within the root zone. The effects of RAI associated with root-water uptake upon transpiration were the dominant process of ETr affecting the suction responses. Key words: suction, evapotranspiration, transpiration, evaporation, root area index, leaf area index. Pour une valeur donnee d'evapotranspiration (ETr), l'evaporation du sol et la transpiration vegetale (Tr) seraient toutes deux responsables du phenomene de succion capillaire dans le sol. Cependant, on ne connait pas avec precision la contribution relative de chacun de ces deux mecanismes a l'intensite de la force de succion. La presente etude a pour objectif de quantifier la force de succion induite par l'ETr et la Tr, dans le cas d'une espece d'arbre specifique, Scheffllera heptaphylla, poussant dans du sable limoneux. Les contributions relatives de la transpiration et de l'evaporation au phenomene de succion sont analysees a partir des differences observees entre les valeurs de la force de succion induite par la Tr et l'ETr. Des essais ont ete realises a l'aide de 12 boites d'essai, dont 10 contenaient un sol vegetalise recouvert de plantes ayant differentes valeurs d'indice de surface foliaire (ISF) et d'indice de surface racinaire (ISR) et deux contenaient un sol nu et servaient de boites de reference. On a place les boites dans une salle de culture vegetale, en les exposant a des conditions atmospheriques identiques et controlees, afin de surveiller pendant une semaine le mecanisme de succion. En raison des autres effets de l'evaporation du sol, la force de succion induite par l'ETr pourrait etre superieure de 3% a 47% a celle induite par la Tr, en fonction de la valeur de l'ISF. L'intensite de l'evaporation diminue de maniere importante lorsque l'ISF augmente, puisqu'une quantite relativement plus faible d'energie provenant du rayonnement solaire arrive a la surface du sol. Pour une valeur donnee d'ISF, les effets de l'evaporation sont moins importants lorsque se situe a de plus grandes profondeurs dans le sol au niveau des racines. Les effets de l'ISR combines au mecanisme d'absorption d'eau par les racines sont les deux principaux facteurs, dans le processus d'ETr, qui influent sur le phenomene de succion. [Traduit par la Redaction] Mots-cles: succion, evapotranspiration, transpiration, evaporation, indice de surface racinaire, indice de surface foliaire., Introduction Evapotranspiration (ETr) is a natural process of the sum of evaporation from the soil surface and plant transpiration (Tr) through root-water uptake. The associated changes in soil moisture and [...]

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 [...]