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There are few studies focused on spore and pollen clumps in paleopalynological samples, and these are only reports from the Northern Hemisphere. These aggregates may be of animal or floral origin. The goal of this contribution is to provide the first detailed study of spore and pollen clumps from the Southern Hemisphere, and to discuss their possible origin, botanical affinities, and pollination modes, based on their morphological characteristics, preservation and comparison with putative living representatives. Three fern spore clumps and 18 angiosperm pollen clumps were recognized in Maastrichtian-Danian La Colonia Formation sediments that outcrop at Chubut Province, Patagonia, Argentina. Most clumps are monospecific and composed of undamaged elements but some of them have two types of spore/pollen with corroded and/or fragmented exines. These findings represent the most diverse and abundant record of fern and angiosperm clumps from the Late Cretaceous and early Paleocene so far known from South America and the Southern Hemisphere. These results are indicative of the need for comprehensive large-scale studies on pollination of modern taxa and careful processing of palynological samples to lessen the already large bias in paleopalynological interpretations. The paucity of information on clumps in the fossil record has impaired our comprehension of dispersion/pollination in deep time. Keywords Floral origin * Coprolites * Monospecific clumps * Pollination modes Hay pocos estudios enfocados en agregados de esporas y polen procedentes de muestras palinologicas, y estos han sido reportados unicamente en el Hemisferio Norte. Estos agregados pueden ser de origen animal o floral. El objetivo de esta contribucion es proveer el primer estudio detallado de agregados de esporas y polen del Hemisferio Sur, y discutir sus posibles origenes, afinidades botanicas y modos de polinizacion, basados en sus caracteristicas morfologicas, preservacion y comparacion con posibles analogos modernos. Tres agregados de esporas de helechos y 18 de polen de angiospermas fueron reconocidos en los sedimentos del Maastrichtiano-Daniano de la Formacion La Colonia, aflorantes en la Provincia de Chubut, Patagonia, Argentina. La mayoria de los agregados son monoespecificos y estan compuestos por elementos en general bien preservados, aunque algunos tienen dos tipos de esporas/polen con exinas corroidas y/o fragmentadas. Estos hallazgos constituyen el registro mas diverso y abundante de agregados esporopolinicos del Cretacico Tardio y Paleoceno temprano de Sudamerica y del Hemisferio Sur. Los resultados de este trabajo indican la necesidad de realizar estudios exhaustivos a gran escala sobre polinizacion en taxones modernos y de desarrollar nuevas tecnicas palinologicas menos destructivas que permitan recuperar los agregados de las paleoasociaciones. Claramente, la escasez de informacion sobre agregados polinicos en el registro fosil afecta nuestra interpretacion acerca de la dispersion/polinizacion y su evolucion en el tiempo. Palabras clave Origen floral * Coprolitos * Agregados monoespecificos * Modos de polinizacion, Introduction Pollen and spores have major roles in plant sexual reproduction as they are fundamental to maintaining plant populations and successfully colonizing of new habitats. Floral and pollen traits are [...]

Alberta's forests are becoming increasingly disturbed and fragmented by the cumulative effects of anthropogenic disturbances exacerbated by the enduring footprint of seismic lines on the landscape. Forest harvesting and subsequent reforestation activities (e.g., site preparation and tree planting) may facilitate tree growth on seismic lines when forestry companies incorporate them into management areas. In this study, forest regeneration was assessed along transects on and off seismic lines within four cutblocks in northwestern Alberta. Tree, sapling, and shrub characteristics were measured, and tree cookies from a subset of trees on and off seismic lines were used to model height growth. No difference in total tree, sapling, or shrub counts on and off seismic lines was found although trees on seismic lines were growing at slightly slower rates compared to the adjacent cutblock, and Alnus viridis was more abundant on seismic lines. Our results suggest that, despite some species-level differences and modest differences in tree growth rates, trees on seismic lines within cutblocks are regenerating similarly to other trees growing in the post-harvest stand. These findings indicate that forest harvesting, and subsequent reforestation, could represent an important tool in conducting landscape-level restoration in mixedwood forests where seismic lines have not naturally recovered. Key words: seismic lines, forest harvesting, linear restoration, forest regeneration, boreal forest, 1. Introduction The cumulative effects of anthropogenic disturbances including oil and gas activities, forestry, agriculture, transportation, and communication corridors have been contributing to the fragmentation of Alberta's forests for decades [...]

An individual-based, multiple-growthform gap model of forest stand development and succession (ZELIG.MGF) of the JABOWA and FORET lineage was modified to simulate long-term changes in 'ohi'a-hapu'u montane rain forests on the island of Hawai'i. Based on the autecology, architecture, and life history of the two dominant species, we were able to re-create some of the stand dynamics and population structures observed in these forests. The phenomenon of displacement dieback, which occurs only on rich sites with persistent cloud cover, is portrayed as a natural successional consequence of 'ohi'a lehua (Metrosideros polymorpha Gaud.) senescence and shade intolerance, which contrasts with the shorter stature, clonal reproduction, and shade tolerance of hapu'u pulu tree fern (Cibotium glaucum (Sm.) Hook. & Arn.). ZELIG.MGF predicts that 'ohi'a will achieve a maximum basal area of 27 [m.sup.2]/ha in stands 80-90 years old, after which basal area is projected to decline to levels of 8-11 [m.sup.2]/ha that persist after 220 years. Alternating phases of 'ohi'a and hapu'u may dominate individual gaps, but overall old-growth 'ohi'a populations do not recover to earlier levels. 'Ohi'a overstory mortality is consistent with senescence or a growing imbalance of respiratory to photosynthetic tissue in large trees. Understory mortality as modeled is largely due to shading by adults and by hapu'u tree ferns, although mechanical damage from dead hapu'u fronds, which was not modeled, may also be important. 'Ohi'a stand rejuvenation can occur when the density of hapu'u is reduced by harvesting or wind storms. Keywords: displacement dieback, gap dynamics, plant competition, forest regeneration, 'ohi'a dieback, hapu'u harvesting, ZELIG, rapid 'ohi'a death, THE ENDEMIC 'OHI'A lehua (Metrosideros polymorpha Gaud.) is the most widespread tree species of the largest Hawaiian Islands, colonizing recent volcanic deposits, but also dominating or sharing dominance in montane [...]

Plant roots affect the soil shear strength, but the temporal dynamics of roots such as growth and decay due to different mortality means have rarely been considered. This study investigates the effects of root growth and decay on the changes in root biomechanical properties and the shearing behaviour of vegetated soils. Columns of compacted soils were grown with a grass species, Cynodon dactylon. The grass was grown for 6 months, followed by burning or herbicide applications to introduce root decay. The top part of each column was used for direct shear tests, whilst the roots collected from the bottom part were used for the measurements of root tensile and chemical properties. The vegetated soils displayed greater shear strength and larger dilatancy, which were attributable to the growth-induced increase in the root cellulose content, and thus the root tensile strength and modulus. Root decay, upon burning or herbicide use, caused significant declines in the root tensile properties, which translated to the reductions in soil dilatancy and soil shear strength lower than those of the fallow soil. Herbicide use introduced a much faster and significant loss of root reinforcement than burning because of the more severe decay and loss of root biomechanical properties. Key words: soil bioengineering, root reinforcement, root biomechanics, root decay, shear strength, dilatancy Les racines des plantes affectent la resistance au cisaillement du sol, mais la dynamique temporelle des racines, telle que la croissance et la decomposition dues a differents moyens de mortalite, a rarement ete prise en compte. Cette etude examine les effets de la croissance et de la decomposition des racines sur les changements des proprietes biomecaniques des racines et le comportement de cisaillement des sols vegetalises. Des colonnes de sols compactes ont ete cultivees avec une espece de graminee, Cynodon dactylon. L'herbe a ete cultivee pendant 6 mois, suivis d'un brulage ou d'applications d'herbicides pour introduire la decomposition des racines. La partie superieure de chaque colonne a ete utilisee pour les tests de cisaillement direct, tandis que les racines collectees dans la partie inferieure ont ete utilisees pour les mesures des proprietes de traction et chimiques des racines. Les sols vegetalises presentaient une plus grande resistance au cisaillement et une plus grande dilatation, qui etaient attribuables a l'augmentation, induite par la croissance, de la teneur en cellulose des racines et donc de la resistance a la traction et du module des racines. La decomposition des racines, lors du brulage ou de l'utilisation d'herbicides, a entraine une baisse significative des proprietes de traction des racines, qui s'est traduite par des reductions de la dilatance et de la resistance au cisaillement du sol inferieures a celles du sol en jachere. L'utilisation d'herbicides a entraine une perte beaucoup plus rapide et significative du renforcement des racines que le brulage, en raison de la decomposition plus severe et de la perte des proprietes biomecaniques des racines. [Traduit par la Redaction] Mots-cles : bio-ingenierie des sols, renforcement des racines, biomecanique des racines, decomposition des racines, resistance au cisaillement, dilatation, Introduction Plants in soil bioengineering have been used to reinforce shallow soils against landslides (Ng et al. 2019). Fibrous roots, as they grow, form a composite material, which displays greater [...]

Alberta wildfires vary greatly in severity, resulting in a mosaic of burnt, partially burnt, and unburnt forest. These unburnt patches (refugia) within the fire perimeter are critical for the survival of organisms during the fire and the regeneration process. We examined the literature to identify how the fire regimes and landscape features found in Alberta affect the creation and persistence of refugia, the role of refugia for the flora and fauna of Alberta, how climate change is likely to affect refugia, how humans may alter the creation and effectiveness of refugia, and management implications moving forward. Refugia can vary in scale from small areas of unburnt soil or boulders (centimetres to a few metres), to large stands of unburnt trees (many hectares) with different taxa using these refugia across all the spatial scales. Species reliant on habitat connectivity or old growth forest also benefit from refugia as they can use them as stepping-stones between intact habitats or as a lifeboat to recolonize from. The factors influencing what areas remain unburnt are complex and poorly understood but are likely tied to topography, aspect, proximity to waterbodies, weather changes (precipitation and wind direction), time of day during burning, and vegetation type. Areas with the right combination of topography, aspect, and proximity to water have cooler microclimates and higher moisture than the surrounding areas and may remain unburnt throughout multiple fire events, making them persistent refugia. Other areas may remain unburnt by a chance result of weather changes or having the fire pass through at night, making them random refugia. Many of the features that make persistent refugia unlikely to burn (cooler microclimate and higher moisture) will also buffer the effects of climate change. As a result, it is essential we manage the landscape in such a way as to protect areas that act as persistent refugia from industrial activities. In addition, we must restore fire in the landscape to maintain the mosaic of forest caused by mixed-severity fire, especially in the face of climate change, which is projected to increase the severity and frequency of wildfires in Alberta. Key words: refugia, remnant, unburnt, wildfire, legacies Les incendies de forêt en Alberta varient grandement en gravité, ce qui donne lieu àune mosaïque de forêts brûlées, partiellement brûlées et non brûlées. Ces îlots non brûlés, ou refuges, situés dans le périmètre du feu, sont essentiels àla survie des organismes pendant le feu et au processus de régénération. Les auteurs ont examiné la littérature afin de déterminer comment les régimes de feu et les caractéristiques du paysage en Alberta influencent la création et la persistance de refuges, le rôle des refuges pour la flore et la faune en Alberta, comment les changements climatiques sont susceptibles d'affecter les refuges, comment les humains peuvent modifier la création et l'efficacité des refuges, et les implications de gestion pour l'avenir. L'échelle des refuges peut varier de petites zones de sol ou de blocs rocheux non brûlés (de quelques centimètres àquelques mètres) àde grands peuplements d'arbres non brûlés (plusieurs hectares), différents taxons utilisant ces refuges àtoutes les échelles spatiales. Les espèces qui dépendent de la connectivité des habitats ou des forêts anciennes bénéficient également des refuges, car elles peuvent les utiliser comme étapes entre des habitats intacts ou comme canots de sauvetage pour se recoloniser. Les facteurs qui déterminent les zones qui restent non brûlées sont complexes et mal compris, mais sont probablement liés àla topographie, àl'aspect, àla proximité des cours d'eau, aux changements météorologiques (précipitations et direction du vent), àl'heure de la journée pendant le brûlage et au type de végétation. Les zones présentant la bonne combinaison de topographie, d'aspect et de proximité de l'eau ont des microclimats plus frais et une humidité plus élevée que la zone environnante et peuvent rester non brûlées pendant de multiples incendies, ce qui en fait des refuges persistants. D'autres zones peuvent rester non brûlées par le hasard des changements météorologiques ou du passage du feu la nuit, ce qui en fait des refuges aléatoires. Bon nombre des caractéristiques qui rendent les refuges persistants peu susceptibles de brûler (microclimat plus frais et humidité plus élevée) les aideront également àamortir les effets des changements climatiques. Par conséquent, il est essentiel que nous gérions le paysage de manière àprotéger les zones qui agissent comme des refuges persistants des activités industrielles. En outre, nous devons rétablir le feu dans le paysage afin de maintenir la mosaïque de forêts causée par les feux de gravité mixte, surtout face aux changements climatiques qui devraient accroître la gravité et la fréquence des feux en Alberta. Mots-clés : refuges, vestiges, non brûlés, incendies de forêt, héritages, Introduction Forests throughout Alberta experience wildfire as a naturally occurring disturbance that has dominated and molded the landscape over time. However, the relationship between fire and the landscape is highly [...]

Aims. P-mobilising microbes may effectively increase soil P availability. These experiments investigated soil P mobilisation and pepper (Capsicum annuum L.) P uptake in response to the wood-rot fungus Fomitopsis palustris CQ2018. Methods. F. palustris CQ2018 was incubated in liquid media and soil to study P mobilisation, and pepper plants with fungal inoculation were grown in a greenhouse experiment to observe the agronomic performances. Key results. F. palustris CQ2018 secreted protons, organic acids, and phosphatase to convert AlP[O.sub.4], [Ca.sub.3][(P[O.sub.4]).sub.2], FeP[O.sub.4] and lecithin into soluble P in liquid culture and increased P availability in three soils with pH 5.53, 7.36 and 8.67. It grew in the roots or on the root surfaces, stimulated root growth, increased dehydrogenase activity in the roots, and solubilised water-insoluble P. Soil inoculated with F. palustris CQ2018 exhibited higher Olsen P and phosphatase activity than uninoculated soil, and there was a positive linear correlation between Olsen P and phosphatase activity (r = 0.788). F. palustris CQ2018 increased pepper P uptake and fruit yield in both unfertilised and fertilised soils even under the condition of reduced fertilisers. Fruit quality was also improved by the increase in P, potassium, and vitamin C but decrease in nitrate. Conclusions. F. palustris CQ2018 can mobilise soil P and improve plant P uptake and fruit yield and quality in pepper. Implications. F. palustris CQ2018 may be developed into a new, effective, and environmentally friendly biofertiliser. Its effect on different plants in various soils needs further study. Keywords: biofertiliser, Fomitopsis palustris, fungus, H+, organic acids, P absorption, phosphatases, phosphorus., Introduction Soil phosphorus (P) and P fertiliser Approximately 5.7 billion ha of agricultural soils on our earth are lacking in readily available P for plants because there is only 0.1-10 [...]

Relatively few comparative studies exist of nitrogen (N) uptake by ectomycorrhizal (EM) and nonmycorrhizal roots under controlled conditions. Instantaneous and long-term N uptake by EM and nonmycorrhizal roots of lodgepole pine seedlings (Pinus contorta (Douglas) var. latifolia (Engelm.)) were compared after 9-12 months of preconditioning under high or low N supply, with N[H.sub.4.sup.+] and N[O.sub.3.sup.-] in proportions of 90:10 and 10:90. EM roots were inoculated with Amphinema byssoides or Laccaria bicolor. Instantaneous net N[H.sub.4.sup.+], N[O.sub.3.sup.-], and [H.sup.+] fluxes were measured simultaneously on seedling roots with a microelectrode ion flux measurement system, and seedling organ biomass and N content were measured to infer long-term N uptake. Net N[H.sub.4.sup.+] uptake was observed in EM roots of lodgepole pine but N[H.sub.4.sup.+] efflux was observed in nonmycorrhizal roots. Greater instantaneous N uptake in EM roots was supported by higher root and shoot N contents in seedlings associated with L. bicolor than in noninoculated seedlings. Absence of N[H.sub.4.sup.+] efflux in EM roots suggests that root colonization by EM fungi has the potential to reduce futile cycling of N[H.sub.4.sup.+]. EM lodgepole pine appeared to prefer N[H.sub.4.sup.+] over N[O.sub.3.sup.-] as an N source and instantaneous N[H.sub.4.sup.+] uptake rates were higher in N[H.sub.4]-starved roots. [H.sup.+] efflux was observed in most roots. Future work should focus on a greater variety of EM species to explore differences among species in N uptake. Key words: conifer, ectomycorrhizae, ammonium, nitrate, nitrogen ion flux, futile ammonium cycling Il existe relativement peu d'etudes comparatives sur l'absorption de l'azote (N) par les racines ectomycorhiziennes (EM) et non mycorhiziennes dans des conditions controlees. L'absorption instantanee et a long terme d'azote par les racines ectomycorhiziennes et non-mycorhiziennes de semis de pin tordu (Pinus contorta (Douglas) var. latifolia (Engelm.)) a ete comparee apres 9 a 12 mois de preconditionnement sous un apport eleve ou faible d'azote, avec N[H.sub.4.sup.+] et N[O.sub.3.sup.-] dans des proportions de 90:10 et 10:90. Les racines EM ont ete inoculees avec de l'Amphinema byssoides ou du Laccaria bicolor. Les flux nets instantanes de N[H.sub.4.sup.+], N[O.sub.3.sup.-] et [H.sup.+] ont ete mesures simultanement sur les racines des semis a l'aide d'un systeme de mesure des flux ioniques a microelectrodes. Une absorption nette de N[H.sub.4.sup.+] a ete observee dans les racines EM du pin tordu, mais un efflux de N[H.sub.4.sup.+] a ete observe dans les racines non mycorhiziennes. Une plus grande absorption instantanee d'azote dans les racines EM a ete soutenue par des teneurs en azote plus elevees dans les racines et les pousses des semis associes au L. bicolor que dans les semis non inocules. L'absence d'efflux de N[H.sub.4.sup.+] dans les racines EM suggere que la colonisation des racines par les champignons EM a le potentiel de reduire le cycle futile du N[H.sub.4.sup.+]. Les RE du pin tordu semblent preferer le N[H.sub.4.sup.+] au N[O.sub.3.sup.-] comme source d'azote et les taux d'absorption instantanee de N[H.sub.4.sup.+] sont plus eleves dans les racines privees de N[H.sub.4]. Un efflux de [H.sup.+] a ete observe dans la plupart des racines. Les travaux futurs devraient se concentrer sur une plus grande variete d'especes d'EM pour explorer les differences entre les especes dans l'absorption de l'azote. [Traduit par la Redaction] Mots-cles : conifere, ectomycorhizes, ammonium, nitrate, flux d'ions d'azote, cycle futile de l'ammonium, Introduction In coniferous forests, tree roots are typically in intimate, symbiotic association with a variety of mycorrhizal fungi. Tree species in the Pinaceae commonly associate with ectomycorrhizae (Smith and Read [...]

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 [...]

In naturally regenerated managed forests, silvicultural methods leverage timing and intensity of harvesting activities to align with species-specific reproduction mechanisms. With contemporary emphasis on complex stand structure and diverse composition, there is uncertainty in the continued use of timber-oriented management practices in meeting evolving objectives. In the northern hardwood region of North America, contemporary theory is that selection regeneration systems result in homogenization of structure and composition through increasing dominance of Acer saccharum Marsh. Given the coupling of soils and vegetation in northern hardwoods, trends in site conditions that may be more resilient and (or) facilitative to community diversity may be of value to silviculturists. Remote-sensing products and inventory records were integrated to assess tree communities across site variables in northern Michigan, USA. The results reveal that composition is stabilized by local landforms and that diversity increases with hydrologic catchment area. Time since treatment (1-54 years) appeared negatively correlated with catchment area, reflecting lowlands with high diversity not managed or harvested infrequently, due to equipment access and operational logistics. Broad interpretations of selection regeneration systems may be invalidated by the influence of site conditions not previously accounted for, and the results highlight a novel technique to capture the effect of topography on species assemblages. Key words: northern hardwoods, single-tree selection, group selection, site, silviculture. Dans les forets amenagees qui sont naturellement regenerees, les methodes sylvicoles ajustent le calendrier et l'intensite des activites de recolte pour qu'elles concordent avec les mecanismes de reproduction des especes. Puisqu'on met presentement l'accent sur la complexite de la structure des peuplements et la diversite de leur composition, il n'est pas certain que de continuer a utiliser des pratiques d'amenagement axees sur la production de bois permette d'atteindre des objectifs en evolution. Dans la region des feuillus nordiques de l'Amerique du Nord, la theorie contemporaine veut que les systemes de regeneration par jardinage menent a une homogeneisation de la structure et de la composition a cause de la dominance croissante d'Acer saccharum Marsh. Parce que les sols et la vegetation sont intimement lies dans les peuplements de feuillus nordiques, les tendances faisant en sorte que les conditions de la station peuvent etre plus resilientes ou facilitantes pour la diversite de la communaute pourraient etre utiles aux sylviculteurs. Des outils de teledetection et des donnees d'inventaire ont ete integres pour evaluer les communautes forestieres selon une gamme de variables de la station dans le nord du Michigan, aux Etats-Unis. Les resultats revelent que la composition est stabilisee par les reliefs locaux et que la diversite augmente avec la superficie du bassin versant. Le temps ecoule depuis l'application d'un traitement (entre 1 et 54 ans) est apparu negativement correle a la superficie du bassin versant, refletant que les basses terres ou la diversite est elevee ne sont pas amenagees ou rarement recoltees en raison de l'acces des equipements et de la logistique operationnelle. L'interpretation generale des systemes de regeneration par jardinage peut etre invalidee par l'influence des conditions de la station qui n'ont pas ete prises en compte auparavant, et les resultats mettent en evidence une nouvelle technique pour detecter l'effet de la topographie sur les assemblages d'especes. [Traduit par la Redaction] Mots-cles : feuillus nordiques, jardinage par pied d'arbre, jardinage par groupe, station, sylviculture., Introduction Forest composition and site productivity correspond to gradients in soil properties and local climatic conditions. In naturally regenerated forests, vegetation communities reflect specie-specific functional traits across successional trajectories interwoven [...]

Most forest soils contain substantial amounts of gravel. However, unlike the more widely known root resource uptake behaviors which respond to resource patches in substrate without gravels, how roots respond to substrate containing different gravel levels is poorly understood. We grew roots in substrates with five gravel levels (0%, 10%, 20%, 30%, and 40% of volume) in a subtropical Schima superba Gardn. et Champ plantation, determined fine root dynamics and turnover rate with minirhizotrons, measured fine root morphological, architectural, mycorrhizal colonization, chemistry, and mass allocation. The presence of gravel in the substrate delayed the timing of peak root growth. In the substrate with higher gravel content, plants produced more in roots in autumn, but there were fewer roots in summer and the roots tended to exhibit lower fine root turnover rate and mycorrhizal colonization, but higher root biomass allocation. The higher root biomass in the substrate with higher gravel content was associated with higher root carbon/nitrogen ratio. Our findings emphasize the complexity of root resource uptake behavior in response to gravel content and suggest that incorporating substrate gravel content into root studies may help to improve the prediction of patch exploitation and nutrient acquisition in stony soils. Key words: heterogeneous patches, root phenology, root morphology, root architecture, mycorrhizal colonization. La plupart des sols forestiers contiennent des quantites substantielles de gravier. Cependant, contrairement aux comportements plus largement connus concernant le prelevement des ressources par les racines qui reagissent a des ilots riches en ressources dans un substrat exempt de gravier, la facon dont les racines reagissent a un substrat qui contient differentes quantites de gravier est mal connue. Nous avons fait croitre les racines dans des substrats contenant differentes proportions (cinq) de gravier (0%, 10%, 20%, 30% et 40% du volume) dans une plantation subtropicale de Schima superba Gardn. et Champ; determine la dynamique et le taux de renouvellement des racines fines a l'aide de minirhizotrons; mesure la morphologie, l'architecture, la colonisation mycorhizienne et les caracteristiques chimiques des racines fines ainsi que la repartition de la biomasse. La presence de gravier dans le substrat a retarde le moment ou la croissance des racines a atteint son niveau maximum. Dans le substrat contenant le plus de gravier, la plus forte croissance est survenue dans les racines a l'automne. Par contre les racines etaient moins abondantes durant l'ete et le taux de renouvellement ainsi que la colonisation mycorhizienne des racines fines avaient tendance a etre plus faibles, mais l'allocation de biomasse racinaire etait plus prononcee. La biomasse racinaire plus elevee dans le substrat contenant le plus de gravier etait associee a un rapport carbone:azote plus eleve dans les racines. Nos resultats font ressortir la complexite du comportement relie au prelevement des ressources par les racines en reaction a la teneur en gravier et indiquent que l'incorporation de la teneur en gravier du substrat dans les etudes portant sur les racines pourrait contribuer a ameliorer la prediction de l'exploitation des ilots riches en ressources et l'acquisition des elements nutritifs dans les sols pierreux. [Traduit par la Redaction] Mots-cles : ilots heterogenes, phenologie racinaire, morphologie racinaire, architecture racinaire, colonisation mycorhizienne., 1. Introduction Resources in soil are heterogeneously distributed. Understanding fine root resource uptake strategies in heterogeneous patches is of primary importance for predicting plant growth and adaptation to changing environments [...]

Azospirillum spp. are plant-growth-promoting rhizobacteria. The surface lectins of A. brasilense strain Sp7 and A. baldaniorum strain Sp245 can attach to specific carbohydrates, and ensure the binding of the bacteria to the root surface. We investigated possible effects of A. brasilense Sp7 and A. baldaniorum Sp245 lectins on the activities of antioxidant enzymes and on the content of low-molecular-weight antioxidants in the roots of 4-day-old wheat seedlings. The roots were exposed to a number of simulated abiotic stresses: hypothermic, hyperthermic, drought, and salinity stresses. Under all stresses, both lectins increased peroxidase and superoxide dismutase activities and decreased catalase activity. The lectins differed in the intensity of induction of changes in the amounts of the low-molecular-weight antioxidants in wheat roots. They also differed in functional activity owing to their different carbohydrate specificities and structures. The data suggest broader possibilities of lectins in terms of the effect on the metabolism of host plants, and they permit adjustments to be made to the current understanding of the mechanisms that control the associative interactions between plants and bacteria. Keywords: abiotic stresses, antioxidants, Azospirillum, bacterial proteins, plant-growth-promoting rhizobacteria, plants, wheat roots., Introduction Microorganisms play an important part in biogeochemical cycles and have recently been assumed to have considerable potential for use in agriculture (Robe et al. 2003). Most soil microorganisms are [...]

Plant roots are known to provide mechanical reinforcement to soils upon shearing and seismic loading. However, the effects of different stress paths on root reinforcement remain unclear. Moreover, whether and how roots provide resistance to soil liquefaction upon cyclic loading have rarely been studied. The objective of this study is to conduct a series of undrained triaxial tests to investigate the monotonic and cyclic behaviour of rooted sand. Roots of vetiver grass (Chrysopogon zizanioides L.), which has been advocated for use in shallow slope stabilisation purposes, were used for testing. The root diameters ranged between 0.3 and 1.5 mm, while the root volume ratios (RVRs) were 0.23%, 0.45%, and 0.67%. It was discovered that the root reinforcement effect was anisotropic and path-dependent. Along the extension path, when the major principal stress was perpendicular to the predominant root orientation, the root-induced increase in soil friction angle was approximately 10[degrees]. This increase was much greater than that along the compression path, where the change was minimal. The presence of roots prevented the limited flow failure at some RVRs and cyclic stress ratios (CSRs) (which occurred in the unreinforced sand) and the failure mode of the root-reinforced soil switched to cyclic mobility. The liquefaction resistance was improved with an increase in root volume, and this improvement was more remarkable at higher CSRs. Key words: vegetation, root reinforcement, soil-root interaction, stress paths, liquefaction. Les racines des plantes sont connues pour apporter un renforcement mecanique aux sols en cas de cisaillement et de charge sismique. Cependant, les effets des differentes voies de stress sur le renforcement des racines ne sont pas clairs. En outre, on a rarement etudie si, et comment, les racines offrent une resistance a la liquefaction du sol en cas de charge cyclique. L'objectif de cette etude est de mener une serie de tests triaxiaux non draines pour etudier le comportement monotone et cyclique du sable enracine. Des racines de vetiver (Chrysopogon zizanioides L.), dont l'utilisation a ete preconisee pour la stabilisation des pentes peu profondes, ont ete utilisees pour des essais. Le diametre des racines variait entre 0,3 et 1,5 mm, tandis que les rapports de volume des racines (RVR) etaient de 0,23 %, 0,45 % et 0,67 %. On a decouvert que l'effet de renforcement des racines etait anisotrope et dependant de la voie. Le long du trajet d'extension, lorsque la contrainte principale majeure etait perpendiculaire a l'orientation predominante des racines, l'augmentation de l'angle de frottement du sol induite par les racines etait d'environ 10[degrees]. Cette augmentation a ete beaucoup plus importante que dans le cas du chemin de compression oU le changement a ete minime. La presence de racines a empeche la defaillance de l'ecoulement limite a certaines RVR et taux de stress cyclique (CSR) (qui s'est produite dans le sable non renforce), et le mode de defaillance du sol renforce par les racines est passe a la mobilite cyclique. La resistance a la liquefaction a ete amelioree par une augmentation du volume des racines, et cette amelioration a ete plus remarquable a des CSR plus eleves. [Traduit par la Redaction] Mots-cles : vegetation, renforcement des racines, interaction sol-racine, parcours de stress, liquefaction., Introduction Soil bioengineering using vegetation is considered an environmentally and ecologically friendly bioremediation technique for resisting shallow soil slope failure resulting from excessive rainfall (Stokes et al. 2014; Ni et [...]

Growth regulation tailors development in plants to their environment. A prominent example of this is the response to gravity, in which shoots bend up and roots bend down.sup.1. This paradox is based on opposite effects of the phytohormone auxin, which promotes cell expansion in shoots while inhibiting it in roots via a yet unknown cellular mechanism.sup.2. Here, by combining microfluidics, live imaging, genetic engineering and phosphoproteomics in Arabidopsis thaliana, we advance understanding of how auxin inhibits root growth. We show that auxin activates two distinct, antagonistically acting signalling pathways that converge on rapid regulation of apoplastic pH, a causative determinant of growth. Cell surface-based TRANSMEMBRANE KINASE1 (TMK1) interacts with and mediates phosphorylation and activation of plasma membrane H.sup.+-ATPases for apoplast acidification, while intracellular canonical auxin signalling promotes net cellular H.sup.+ influx, causing apoplast alkalinization. Simultaneous activation of these two counteracting mechanisms poises roots for rapid, fine-tuned growth modulation in navigating complex soil environments. Auxin rapidly modulates root growth through simultaneous activation of two opposing mechanisms--TMK1-mediated apoplast acidification and TIR1/AFB-mediated apoplast alkalinization., Author(s): Lanxin Li [sup.1] , Inge Verstraeten [sup.1] , Mark Roosjen [sup.2] , Koji Takahashi [sup.3] [sup.4] , Lesia Rodriguez [sup.1] , Jack Merrin [sup.1] , Jian Chen [sup.5] [sup.6] [...]

Mast year occurrence in trees is often synchronized across large regions. In this study, we used dendrochronological methods based on cone scar characteristics on tree branches in order to reconstruct male and female cone production in balsam fir (Abies balsamea (L.) Mill.) during the period 1988-2018. Results indicate that mast years generally occur every second year and can be synchronized across distances >1000 km. The main predictors of current-year cone abundance were cone abundance during the two previous years, which can be considered a proxy for resource availability for cone bud development during the current year, together with relatively warm temperature during cone bud development. Presence of aborted male cones was positively correlated with the occurrence of relatively cold episodes during cone bud development. This finding suggests that the influence of weather on cone crop abundance is at least partly mediated by growth cessation in the developing cone buds. We also suggest that a change in weather patterns before and after the 2005-2010 period is responsible for a switch in mast years from even to uneven calendar years around that time. Key words: balsam fir, boreal forest, conifers, female cones, large-scale synchrony, male cones, mast years. Les annees semencieres chez les arbres sont souvent synchronisees sur de larges territoires. Dans cette etude, nous avons utilise des methodes dendrochronologiques en mesurant les caracteristiques des cicatrices laissees sur les branches pour reconstruire la production de cones males et femelles chez le sapin baumier (Abies balsamea (L.) Mill.) durant la periode 1988-2018. Les resultats indiquent que les annees semencieres surviennent a tous les deux ans en general, et ce de facon synchronisee sur des distances >1000 km. Les principaux predicteurs de l'abondance des cones durant une annee donnee sont l'abondance de cones durant les deux annees precedentes, soit un indicateur de la disponibilite en ressources pour le developpement des bour geons de cones durant l'annee courante, ainsi que des temperatures relativement chaudes durant le developpement de ces memes bourgeons. La presence de cones males ayant avorte est correlee positivement avec l'occurrence d'episodes relativement froids durant le developpement des bourgeons de cones. Ceci suggere que l'influence des conditions meteorologiques sur la production de cones depend en partie d'interruptions de croissance lors du developpement des bourgeons. Nous suggerons egalement qu'un changement dans les patrons meteorologiques avant et apres la periode 2005-2010 explique une transition des annees semencieres depuis les annees paires vers les annees impaires au cours de la periode d'etude. Mots-cles: annees semencieres, cones femelles, cones males, coniferes, foret boreale, sapin baumier, synchronisme a grande echelle., 1. Introduction Mast seeding can be described as large-scale synchronized fluctuations in the reproductive output of perennial plants (Kelly and Sork 2002). A better understanding of the processes driving these [...]

Understanding microsite preferences of species at the sapling stage is crucial for successful forest restoration, as efforts can be concentrated onto the most promising sites, and invaded sites can be manipulated toward more suitable conditions for target species. The Hawaiian Lowland Wet Forest is a highly endemic and endangered ecosystem that has received limited attention in terms of research on recruitment dynamics. Our study combined density records and sapling-based measurements within a forest reserve, an invaded forest, a traditional restoration project and a novel restoration project. We recorded substrate type, soil depth, surface roughness, and light availability for 382 saplings of the four native tree species Metrosideros polymorph'a, Myrsine lessertiana, Pipturus albidus, and Psychotria hawaiiensis, and 146 spots where the target species were absent. The invaded forest had the lowest native sapling density, lower light availability, and lower surface roughness than the remaining management units. The novel restoration project had more moss/nurselog sites and higher light availability than the remaining management units. The traditional restoration project was mainly characterized by rocky substrate. Metrosideros and Pipturus showed significantly higher light demand than Myrsine and Psychotria. Pipturus was associated with rough microsites and Metrosideros with moss/nurselog substrates. Our findings suggest that restoration strategies considering manipulation of the canopy light environment and microsite preferences of target species can better facilitate native recruitment into heavily invaded forests. Keywords: abiotic microsite preferences, restoration ecology, Metrosideros polymorpha, Psychotria hawaiiensis, Pipturus albidus, Myrsine lessertiana, forest restoration planning, THE ABUNDANCE AND DIVERSITY OF SAPLINGS in a forest ecosystem provide information about future forest conditions as forest composition and dynamics are predominantly influenced by variation in the survival of [...]

Soil-borne plant root disease caused by Rhizoctonia solani AG8 is prevalent in cereal farming systems worldwide, particularly in semiarid agricultural regions. A controlled environment study was undertaken using three Australian soils to test the hypothesis that OM input from crop roots and residues decreases infection by Rhizoctonia root rot via biologically mediated disease suppression. The specific aim was to determine the relative effect of two different OM inputs (wheat stubble or roots) on (a) abundance (DNA) of the pathogen R. solani AG8 and soil organisms putatively associated with disease suppression, and (b) incidence of Rhizoctonia root rot infection of wheat seedlings (% root infected). An increase in microbial biomass carbon (C) following OM amendment indicated a potential for enhanced general biological disease suppression in all soils. OM inputs also increased the population size (DNA) of certain bacteria and fungi putatively associated with specific suppression for Rhizoctonia root rot, suggesting a C resource-mediated change in microbial functions related to disease suppression. There were no significant changes to measured pathogens with stubble addition. However, OM inputs via root residues and rhizodeposits from living roots increased the populations of R. solani AG8 and Gaeumannomyces graminis var. tritici so that in subsequently planted wheat there was greater incidence of root disease infection and reduced plant shoot and root DM compared with that following OM input as stubble. Differences between soils in terms of plant and soil organism responses to each OM input suggest that abiotic factors modify the development of biological disease suppression and the expression of the disease. Additional keywords: beneficial soil organisms, microbial biomass, Rhizoctonia, soil-borne disease suppression. Received 20 November 2018, accepted 4 March 2019, published online 24 April 2019, Introduction Soil-borne plant root disease caused by Rhizoctonia solani AG8 is prevalent in cereal farming systems worldwide, particularly in agricultural regions in Australia with Mediterranean type climate (MacNish and Neate [...]

Root turnover is an important contributor to ecosystem nutrient and carbon cycling, but seasonal aspects of root mortality are not well known. This study tests the hypothesis that in strongly seasonal climates, such as in Northern Ontario, Canada, perennial wetland monocots fall into two distinct categories with respect to their root overwintering strategy: complete senescence or survival over the winter. Root survival in late winter and early spring was tested for a total of 26 species using vitality staining with tetrazolium chloride. Root survival in spring was either over 85% (18 species) or 0% (8 species). Lateral root survival was marginally lower than that of basal roots. In some species, low nutrient supply slightly increased root winter mortality, but did not change the seasonal pattern. We conclude that in a northern temperate climate, the overwintering strategies of roots of herbaceous monocots are binary: either avoidance or tolerance of the long unfavourable season, similar to deciduous and evergreen leaves among woody plants. Roots do not gradually die during the unfavourable season, but either completely senesce in the autumn or survive the winter. The distinct root overwintering strategies presumably affect the species' resource economics and ecosystem processes. Keywords: phenology, root mortality, root turnover, seasonal climate, wetland. Resume : Le renouvellement racinaire contribue de maniere importante aux nutriments et au cycle du carbone d'un ecosysteme, mais les aspects saisonniers de la mortalite racinaire ne sont pas bien connus. Cette etude teste l'hypothese que dans des climats fortement saisonniers comme dans le nord de l'Ontario, Canada, les monocotyledones vivaces des milieux humides se distribuent en deux categories selon leur strategie de survie hiemale des racines : une senescence complete ou une survie au cours de l'hiver. La survie des racines tard dans l'hiver ou tot au printemps a ete mesuree chez 26 especes a l'aide de la coloration vitale au chlorure de tetrazolium. La survie des racines au printemps etait soit superieure a 85 % (18 especes), soit a 0%(8 especes). La survie des racines laterales etait un peu plus faible que celle des racines basales. Chez certaines especes, un faible apport nutritionnel augmentait legerement la mortalite des racines en hiver, mais ne changeait pas le patron saisonnier. Les auteurs concluent que dans un climat tempere nordique, les strategies de survie hiemale des racines des monocotyledones herbacees sont binaires : soit un evitement ou une tolerance a la longue saison froide, semblable a la strategie des feuilles decidues et sempervirentes des plantes ligneuses. Les racines ne meurent pas graduellement durant la saison froide, mais soit elles entrent completement en senescence a l'automne, soit elles survivent a l'hiver. Les strategies de survie hiemale des racines affectent probablement l'economie des ressources des especes et les processus des ecosystemes. [Traduit par la Redaction] Mots-cles : phenologie, mortalite racinaire, renouvellement racinaire, climat saisonnier, milieu humide., Introduction Understanding the relationships between plant species' functional traits and their ecological behaviour is necessary to predict species' responses to different environmental conditions, and to be able to develop appropriate [...]

The effects of magnetized water irrigation on the growth and ionic movements of one-year-old potted seedlings of Populus x euramericana 'Neva' were investigated. A magnetic treatment device was used to treat the plants. The contents of [K.sup.+], [Na.sup.+], [Ca.sup.2+], and [Mg.sup.2+] in leaves and roots were analyzed by atomic absorption spectrophotometry (AAS), and the fluxes of [K.sup.+], [Na.sup.+], [Ca.sup.2+], [Mg.sup.2+], and [H.sup.+] in mesophyll cells and in meristematic zones were measured using a noninvasive micro -test technique (NIMT) after 30 days of treatment. After 90 days, the plants were harvested, and their growth indices and root morphology were measured. The results showed that (i) compared with nonmagnetic treatments (NMT), the magnetic treatments (MT) led to higher [K.sup.+] and [Mg.sup.2+] contents and lower [Ca.sup.2+] content in roots and leaves, while the [Na.sup.+] content was lower and the [K.sup.+]/[Na.sup.+] ratio was higher; (ii) MT enhanced [Na.sup.+] efflux, increased [H.sup.+] influx, and decreased [K.sup.+] and [Mg.sup.2+] efflux compared with NMT; (iii) MT resulted in greater height, diameter, and leaf area of the plants and increased the length, surface area, and number of root tips compared with NMT; and (iv) stomatal conductance (Gs), net photosynthetic rate (Pn), intercellular C[O.sub.2] concentration (Ci), and water use efficiency (WUE) were increased in MT, whereas both transpiration rate (Tr) and stomatal limiting value (Ls) were decreased compared with NMT. The results indicate that the use of magnetized water can promote plant quality and regulate the ion absorption, transpiration, and distribution. Thus, MT is conducive to the re-establishment of ionic homeostatic mechanisms via ion-selective absorption and transportation under salt stress. Key words: ionic homeostasis, ion content, ion flux, magnetization, Populus x euramericana 'Neva'. Les effets de l'irrigation avec de l'eau magnetisee sur la croissance et la circulation des ions chez des semis en pot ages d'un an de Populus x euramericana 'Neva' ont ete etudies. Un appareil de magnetisation a ete utilise pour traiter les plants. Les teneurs en [K.sup.+], [Na.sup.+], [Ca.sup.2+] et [Mg.sup.2+] des feuilles et des racines ont ete analysees par spectrophotometrie d'absorption atomique et les flux de [K.sup.+], [Na.sup.+], [Ca.sup.2+], [Mg.sup.2+] et [H.sup.+] dans les cellules du mesophylle et dans les zones meristematiques ont ete mesures apres 30 jours a l'aide d'une technique non invasive de mesure par microelectrodes. Apres 90 jours, les plants ont ete recoltes et leurs indices de croissance et leur morphologie racinaire ont ete mesures. Les resultats montrent que : (i) comparativement a l'absence de magnetisation (AM), l'eau magnetisee (EM) a augmente la teneur en [K.sup.+] et [Mg.sup.2+] et reduit la teneur en [Ca.sup.2+] dans les racines et les feuilles tandis que la teneur en [Na.sup.+] etait plus faible et le rapport [K.sup.+] a [Na.sup.+] etait plus eleve; (ii) l'EM a ameliore le flux sortant de [Na.sup.+], augmente l'afflux de [H.sup.+] et reduit le flux sortant de [K.sup.+] et [Mg.sup.2+] comparativement a l'AM; (iii) l'EM a entraine une augmentation de la hauteur, du diametre et de la surface foliaire des plants ainsi qu'une augmentation de la longueur, de la surface et du nombre d'apex racinaires comparativement a l'AM; et (iv) la conductance stomatique (Gs), le taux de photosynthese nette (Pn), la concentration intracellulaire de C[O.sub.2] (Ci) et l'efficacite d'utilisation de l'eau (EUE) ont ete accrus par l'EM tandis que tant le taux de transpiration (Tr) que la valeur de la limitation stomatique de la photosynthese (Ls) ont diminue comparativement a l'AM. Les resultats indiquent que l'utilisation de l'EM peut ameliorer la qualite des plants et reguler l'absorption, la transpiration et la distribution des ions. Par consequent, l'EM est propice au retablissement des mecanismes homeostatiques ioniques via l'absorption et le transport selectifs des ions en situation de stress salin. [Traduit par la Redaction] Mots-cles: homeostasie ionique, teneur en ions, flux ionique, magnetisation, Populus x euramericana 'Neva'., Introduction Soil salinization resulting from water shortages and irrational irrigation has become an important limiting factor for agricultural production, ecological security, and sustainable economic development (Jesus et al. 2015; Zhu [...]

The vertical distribution of belowground herbivores plays an important role in determining the performance of an individual plant, but we still do not know the effects of this distribution on plant populations. A grass (Lolium perenne L.) was, therefore, grown at two densities with three vertical distributions of the belowground herbivore Anomala cuprea Hope (Coleoptera: Scarabaeidae). The population yield decreased significantly in the treatments with a herbivore, and decreased most when the herbivore was in the top feeding zone (i.e., the shallowest soil). Plants only died when the herbivore was in the top zone or was free to move within the pot. At low plant density, the biomass of the three largest shoots decreased significantly in the presence of a herbivore, but that of shoots in the fourth and smaller ranks did not. At high plant density, shoot biomass was not significantly affected by herbivory, irrespective of plant size. The standard deviation of shoot size was larger at low densities than at high densities. At low, but not high plant densities, the standard deviation decreased when herbivory occurred in the shallowest soil layer. To our knowledge, this study is the first to demonstrate that the vertical distribution of a belowground herbivore can markedly affect the size dynamics of a plant population. Key words: belowground herbivory, plant-herbivore interaction, plant-soil interaction, population dynamics, population size structure. La distribution verticale des herbivores du sous-sol joue un role important dans la determination de la performance d'un plant individuel, mais on ne connait pas encore les effets de cette distribution sur les populations de vegetaux. Une herbe (Loliumperenne L.) a ete ainsi cultivee a deux densites avec trois distributions verticales de l'herbivore du sous-sol Anomala cuprea Hope (Coleoptera: Scarabaeidae). Le rendement de la population diminuait significativement en fonction des traitements en presence de l'herbivore, et diminuait davantage lorsque l'herbivore se trouvait dans la zone d'alimentation superieure (c'est-a-dire le sol le moins profond). Les plants mouraient seulement lorsque l'herbivore se trouvait dans la zone superieure ou qu'il etait libre de circuler a l'interieur du pot. A faible densite de vegetaux, la biomasse des trois plus grandes pousses diminuait significativement en presence d'un herbivore, contrairement a celle des pousses du 4ieme rang et moins. A haute densite de vegetaux, la biomasse des pousses n'etait pas significativement affectee par l'herbivorisme, peu importe la taille du plant. L'ecart-type de la taille des pousses etait plus grand a faible densite qu'a haute densite. A faible densite mais pas a haute densite de vegetaux, l'ecart-type diminuait en fonction de l'herbivorisme dans la couche de sol la moins profonde. A la connaissance des auteurs, leur etude est la premiere a demontrer que la distribution verticale d'un herbivore du sous-sol peut affecter de maniere importante la dynamique de la taille d'une population vegetale. [Traduit par la Redaction] Mots-cles : herbivorisme du sous-sol, interaction plante-herbivore, interaction plante-sol, dynamique de population, structure de la taille de la population., Introduction Soil organisms can markedly affect plant population and community dynamics (De Deyn et al. 2003; Bardgett and Wardle 2010; Dighton and Krumins 2014), because most of them feed on [...]

Belowground herbivory under nutrient-poor conditions is known to significantly decrease plant biomass and root:shoot ratios. However, the mechanisms behind the changes in belowground plant-herbivore interactions that occur under different nutrient conditions remain unclear. We performed a pot experiment using Lolium perenne L. and the third-instar larva of Popillia japonica Newman. The experiment used a three-way factorial randomized-block design; the three factors were nutrient amount (rich/poor), nutrient heterogeneity (homogeneous/heterogeneous), and belowground herbivore (present/absent). Relative water content (RWC) of shoots under nutrient-poor conditions was smaller than that under nutrient-rich conditions, and a single herbivory significantly reduced the RWC under the nutrient-poor conditions. Plant biomass was larger under nutrient-rich conditions than under nutrient-poor conditions. A herbivore decreased plant biomass more under nutrient-poor conditions than under nutrient-rich conditions. Nutrient heterogeneity had no effect on plant biomass, but herbivory and nutrient amount interactively affected root proliferations to nutrient patches. Plants were smaller under nutrient-poor conditions; thus, a larger proportion of the roots was removed by a belowground herbivore. A loss of a larger proportion of roots would cause the small RWC, which restricts compensatory growth. Consequently, growth of L. perenne is more severely limited by a belowground herbivore under nutrient-poor conditions. Keywords: nutrient patches, plant-herbivore interactions, relative water content, root foraging, root:shoot ratio. L'herbivorisme souterrain dans des conditions pauvres en nutriments est connu pour diminuer de maniere tres importante la biomasse vegetale et les ratios racine : pousse. Cependant, les mecanismes derriere les changements dans les interactions souterraines plante-herbivore qui surviennent dans differentes conditions nutritives demeurent flous. Les auteurs ont realise une experience en pot avec Lolium perenne L. et la larve du troisieme stade de Popillia japonica Newman. Ils ont utilise un plan experimental factoriel aleatoire triple; les trois facteurs etaient la quantite de nutriments (riche/pauvre), l'heterogeneite des nutriments (homogene/heterogene) et l'herbivore souterrain (present/absent). Le contenu relatif en eau (RWC pour << relative water content >>) des pousses dans des conditions pauvres en nutriments etait similaire a celui obtenu dans des conditions riches en nutriments, et un herbivore unique reduisait de maniere tres importante le RWC dans des conditions pauvres en nutriments. La biomasse vegetale etait plus importante dans des conditions riches en nutriments que dans des conditions pauvres en nutriments. L'herbivore diminuait davantage la biomasse vegetale dans des conditions pauvres en nutriments que dans des conditions riches en nutriments. L'heterogeneite en nutriments n'avait pas d'effet sur la biomasse vegetale, mais l'herbivorisme et la quantite de nutriments affectaient de maniere interactive la proliferation des racines vers les patchs de nutriments. Les plants etaient plus petits dans des conditions pauvres en nutriments; ainsi, une plus grande proportion de racines etait eliminee par un herbivore souterrain. La perte d'une plus grande proportion de racines pourrait etre la cause du faible RWC, ce qui restreint la croissance compensatoire. Consequemment, la croissance de L. perenne est plus severement limitee par un herbivore souterrain dans des conditions pauvres en nutriments. [Traduit par la Redaction] Mots-cles: patchs de nutriments, interactions plante-herbivore, contenu relatif en eau, ravitaillement des racines, ratio racine/pousse., Introduction The belowground parts of plants, such as roots, rhizomes, and storage organs, are estimated to account for over 80% of total plant biomass in temperate grasslands, tundra, and deserts [...]