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Pyrolyzed organic matter, or biochar, generally increases the growth of established plants; in some cases, biochar also promotes seed germination in agricultural species, but comparable effects on tree species have received little attention. Potential biochar effects on seed germination and early seedling development were examined in a field experiment involving 14 species of temperate forest trees. Replicated sets of seeds with and without biochar (at 5 t * [ha.sup.- 1]) were placed in mesh bags beneath leaf litter near the time of autumnal leaf fall and retrieved the following spring. Pooled analyses show a positive but small average effect of biochar on germination. Effects on seedling radicle extension growth were more pronounced, with more than a doubling in growth observed overall and large increases observed in some species, including both conifers (e.g., Picea mariana (Mill.) Britton, Sterns & Poggenb. and Pinus resinosa Sol. ex Aiton) and angiosperms (Betula papyrifera Marsh., Prunus virginiana L., and Ulmus americana L.). Species varied in responses, but differences were not related to fire or shade tolerance. The results indicate that biochar can substantially enhance early seedling development in temperate trees; likely mechanisms involve 'priming' effects resulting from increased pH and potassium availability or sorption of germination-inhibiting phenolics in the litter layer. Key words: biochar, conifers, fire adaptation, hardwoods, seed germination, seed size, shade tolerance, temperate trees. La matiere organique pyrolysee, ou biocharbon, augmente generalement la croissance des plantes etablies; dans certains cas le biocharbon favorise aussi la germination des graines chez les especes agricoles, mais peu d'attention a ete accordee a de tels effets chez les especes arborescentes. Les effets potentiels du biocharbon sur la germination des graines et le developpement initial des semis ont ete etudies dans une experience terrain impliquant 14 especes d'arbres de foret temperee. Des ensembles repetes de graines avec ou sans biocharbon (5 t * [ha.sup.-1]) ont ete places dans des sacs- filets sous la litiere de feuilles pres du moment de la chute automnale des feuilles et retires au printemps suivant. Les analyses regroupees montrent un effet moyen positif quoique faible du biocharbon sur la germination. Les effets sur la croissance en longueur des radicules des semis etaient plus prononces alors qu'elle a plus que double dans l'ensemble et que de fortes augmentations ont ete observees chez certaines especes, incluant des coniferes (p. ex., Picea mariana (Mill.) Britton, Sterns & Poggenb. et Pinus resinosa Sol. ex Aiton) et des angiospermes (Betula papyrifera Marsh., Prunus virginiana L. et Ulmus americana L.). La reaction variait selon l'espece mais les differences n'etaient pas reliees a la tolerance au feu ou tolerance a l'ombre. Les resultats indiquent que le biocharbon peut ameliorer le developpement initial des semis des arbres de la zone temperee. Les mecanismes responsables impliquent probablement des effets de stimulation resultant de l'augmentation du pH et de la disponibilite du potassium, ou de sorption des composes phenoliques qui inhibent la germination dans la couche de litiere. [Traduit par la Redaction]. Mots-cles : biocharbon, coniferes, adaptation au feu, feuillus, germination des graines, taille des graines, tolerance a l'ombre, arbres des zones temperees., Introduction Biochar is the term applied in recent years to charcoal used as a soil amendment (Lehmann et al. 2006), with its use being motivated by the potential to ameliorate [...]

Nitrogen (N) deposition from anthropogenic sources can facilitate the encroachment of plant species with high-N demands into nutrient-poor ecosystems such as sphagnum bogs. Prior research has demonstrated that altered leaf morphology of the carnivorous pitcher plant Sarracenia purpurea L. can serve as a biological indicator of increased bog nitrification. Our objective was to assess the effect of N addition on the root morphology of S. purpurea. To make this assessment, nine S. purpurea plants were grown in microcosms with their roots positioned on transparent acrylic tubes so that root growth could be monitored. Three replicate microcosms received either a high-N treatment (1.0 mg N[H.sub.4]-Nx[L.sup.-1]), low-N treatment (0.1 mg N[H.sub.4]-Nx[L.sup.-1]), or no additional N. After 7 weeks, we scanned the roots with WinRhizo Pro software, recorded leaf dimensions, and measured the dry mass of the roots and leaves. The high-N treatment had significantly greater root length, surface area, and dry biomass than the controls. In contrast, we found no difference in leaf dimensions or aboveground biomass among treatments. The results of this study support our hypothesis that S. purpurea increases root growth to uptake nutrients from the soil under conditions of increased N deposition. Key words: bog, minirhizotron, nitrogen deposition, Sarracenia purpurea, wetland ecology. Le depot d'azote (N) a partir de sources anthropogenes peut faciliter l'empietement d'especes vegetales dont le besoin en N est eleve dans des ecosystemes pauvres en nutriments comme les tourbieres a sphaigne. Une recherche precedente a demontre que la modification de la morphologie des feuilles de la sarracenie pourpre, Sarracenia purpurea L., peut servir d'indicateur biologique de l'accroissement de la nitrification d'une tourbiere. L'objectif des auteurs etait d'evaluer l'effet d'un ajout d'azote sur la morphologie racinaire de S. purpurea. Afin de realiser cette evaluation, neuf plants de S. purpurea ont ete cultives en microcosme de facon a ce que la croissance de leurs racines, disposees dans des tubes d'acrylique transparents, puisse etre suivie. Les microcosmes en trois replicats ont recuun traitement riche enN(1,0 mg N[H.sub.4]-Nx[L.sup.-1), faible en N(0,1 mg N[H.sub.4]-Nx[L.sup.-1]), ou sans ajout de N. Apres 7 semaines, les auteurs ont analyse les racines a l'aide du logiciel WinRhizo Pro, compile les dimensions des feuilles et mesure la masse seche des feuilles et des racines. Le traitement riche en N provoquait un allongement significatif des racines et un accroissement de l'aire de surface et de la biomasse seche, comparativement aux controles. Par contre, les auteurs n'ont pas trouve de difference sur le plan des dimensions des feuilles ou de la biomasse hors-sol en fonction des traitements. Les resultats de cette etude corroborent leur hypothese a l'effet que S. purpurea allonge ses racines afin de capter les nutriments a partir du sol lorsque le depot d'azote est accru. [Traduit par la Redaction] Mots-cles : mini-rhizotron, depot d'azote, Sarracenia purpurea, ecologie des milieux humides., Introduction In the last hundred years, human activity such as industrial fertilizer production, fossil fuel combustion, and planting monocultures of nitrogen-fixing crops has doubled the amount of fixed nitrogen (N) [...]

We evaluated variation in root turnover across five root orders in sugar maple (Acer saccharum Marsh.) saplings growing in a northern hardwood forest in central New York, USA. We used a stable isotope approach in which root systems were labeled with [.sup.13]C and root structural C sequentially sampled for [.sup.13]C enrichment. Turnover of first- and second-order roots was apparently rapid with only about 5% of the [.sup.13]C retained in living roots after two growing seasons. Although third-to fifth-order roots appeared to persist longer, differences among root orders were not statistically significant, probably mostly because of highly nonuniform initial labeling. This nonuniform labeling constrains the precision of root turnover quantification using this approach. Resume: Nous avons evalue la variation du taux de remplacement des racines du [1.sup.er] au [5.sup.e] ordre chez des gaules d'erable a sucre (Acer saccharum Marsh.) croissant dans une foret de feuillus nordiques dans le centre de l'Etat de New York, aux Etats-Unis. Nous avons utilise une approche qui consiste a marquer le systeme racinaire avec l'isotope stable [.sup.13]C et a echan-tillonner sequentiellement leC structural des racines pour mesurer leur enrichissement en [.sup.13]C. Le remplacement des racines de [1.sup.er] et [2.sup.e] ordre etait apparemment rapide alors que seulement environ 5% du [.sup.13]C etait retenu dans les racines vivantes apres deux saisons de croissance. Bien que les racines du 3e au 5e ordre semblaient persister plus longtemps, les differences entre les ordres de racines n'etaient pas statistiquement significatives probablement a cause d'un marquage initial tres heterogene. Ce marquage non uniforme nuit a la precision de la quantification du taux de remplacement des racines avec cette approche. [Traduit par la Redaction], Introduction Accurate measurement of the turnover of fine roots is important for understanding the nutrient and organic matter dynamics of forest ecosystems, but methodological difficulties have limited the conclusiveness of [...]

Long regeneration periods, which result in two-layered or multilayered forest stands, are an important element of the close-to-nature forest management paradigm in central Europe. Such extended regeneration periods, however, may lead to undesirable development of advance regeneration, specifically in species such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) where root growth is strongly curtailed under competition. We hypothesized that root systems of naturally regenerated Douglas-fir that had grown under closed canopy for prolonged periods would be inhibited in their capacity to develop adequate structural root systems following release through removal of the canopy. Complete root systems of six approximately 25-year-old Douglas-fir that had grown for at least 12 years underneath a closed canopy before overstory removal were excavated using subterranean explosives. Root elongation, radial increment of primary lateral and vertical roots, and aboveground stem growth were investigated using retrospective analysis of growth rings. Structural roots of the previously suppressed Douglas-fir were capable of strongly responding to release from competition relative to growth prior to removal, but this response, particularly in the form of root elongation, was delayed. However, since the growth response of roots was not stronger than that above ground, an imbalanced root to shoot ratio, likely developed in trees when grown under the canopy, was not reverted. Generalizing interpretation of the derived findings of this study is limited because of the small sample size and the lack of freely grown control trees. Whether or not previously suppressed trees can develop the same physical stability as open-grown individuals therefore deserves further investigation. Resume: De longues periodes de regeneration qui produisent des peuplements forestiers bietages ou multietages sont un element important du paradigme de l'amenagement forestier proche de la nature en Europe centrale. Cependant, de telles periodes prolongees de regeneration peuvent entrainer le developpement de regeneration preetablie indesirable telle que le douglas vert (Pseudotsuga menziesii (Mirb.) Franco) dans les endroits ou la croissance des racines est fortement limitee par la competition. Nous avons formule l'hypothese que le systeme racinaire de la regeneration naturelle de douglas vert qui s'etait developpee sous couvert ferme pendant de longues periodes inhiberait leur capacite a developper un systeme racinaire structural adequat a la suite du degagement cause par l'elimination de la canopee. Le systeme racinaire complet de six arbres de douglas vert ages d'environ 25 ans qui s'etaient developpes pendant au moins 12 ans sous un couvert ferme avant l'elimination de l'etage dominant a ete excave a l'aide d'explosifs souterrains. L'elongation des racines, l'accroissement radial des racines primaires laterales et verticales, ainsi que l'accroissement de la tige audessus du niveau du sol ont ete etudies par l'analyse retrospective des cernes annuels. Les racines structurales des douglas vert qui avaient ete supprimes etaient capables de reagir fortement a l'elimination de la competition relativement a leur croissance anterieure au degagement mais cette reaction, particulierement sous forme d'elongation racinaire, etait differee. Cependant, etant donne que la reaction en croissance des racines n'etait pas plus prononcee que celle de la partie aerienne, un rapport racine--tige debalance qui s'etait probablement developpe lorsque les arbres croissaient sous couvert n'a pas ete modifie. L'interpretation des resultats de cette etude ne peut etre generalisee a cause de la taille reduite de l'echantillon et l'absence d'arbres temoins cultives sans contraintes. D'autres etudes sont par consequent necessaires pour determiner si des arbres precedemment supprimes peuvent ou non developper la meme stabilite physique que des arbres croissant a decouvert. [Traduit par la Redaction], Introduction In the past three decades, management of public and many private forests in central Europe has undergone a paradigm shift from traditionally even-aged management to 'close-to-nature silviculture' characterized by [...]

Selection cutting, where approximately 30% of the trees are removed every 30 years, is the main silvicultural treatment used in temperate deciduous forests of Quebec (Canada). Concerns have been raised that the use of heavy machinery is creating soil disturbances that are negatively affecting the growth and survival of remaining trees. The aim of the study was to determine if heavy machinery is affecting the growth, morphology, and architecture of sugar maple (Acer saccharum Marsh.) fine roots in and around machinery tracks left after selection logging. The study site, a sugar maple dominated stand, was located in southern Quebec. Root ingrowth bags and standard root cores were used to compare fine root growth, morphology, and architecture in and around machinery tracks one year after logging. Fine root growth of maple was reduced fivefold in both primary (multiple trip) and secondary (only one trip) machinery tracks compared with the control. There was a nonstatistical reduction in fine root growth within 1 m of the tracks. Because machinery tracks cover between 15% and 25% of a stand after selection logging, such reduction in fine root growth could be significant for the growth and survival of the remaining mature maple trees. Resume: La coupe jardinatoire, qui consiste a recolter environ 30 % du peuplement a tous les 30 ans, represente le traite-ment sylvicole le plus utilise dans la foret feuillue temperee au Quebec (Canada). Des inquietudes ont ete soulevees au sujet des effets nefastes que les perturbations du sol causees par la machinerie lourde pourraient avoir sur la croissance et la survie des arbres residuels. L'objectif de l'etude etait de determiner si la machinerie lourde affecte la croissance, la morpholo-gie et l'architecture des racines fines de l'erable a sucre (Acer saccharum Marsh.) dans et pres des sentiers laisses par la machinerie lors d'une coupe jardinatoire. Une erabliere ayant subi une coupe jardinatoire a la fin de l'ete 2006 a ete selec-tionnee dans le sud du Quebec. Des sacs de croissance ainsi que des carottes de sol ont ete utilises afin de comparer la croissance, la morphologie et l'architecture des racines fines dans et pres des sentiers, au cours de l'annee suivant la coupe jardinatoire. La croissance des racines fines de l'erable a sucre a ete reduite de cinq fois, autant dans les sentiers primaires (utilises plusieurs fois) que secondaires (utilises une seule fois) par rapport au temoin. Une diminution non significative de la croissance racinaire a une distance d'un metre et moins du sentier a ete observee. Considerant que les sentiers primaires et secondaires couvrent habituellement 15 a 25 % d'un peuplement a la suite a d'une coupe jardinatoire, il est probable qu'une telle reduction de la croissance des racines fines affecte negativement la croissance et la survie des erables residuels situes pres des sentiers., Introduction Little is known about the impacts of heavy machinery used in usual forestry operations on the below-ground components of trees, particularly the fine roots. Yet, with the development of [...]

The stem cell niche in the root meristem is critical for the development of the plant root system. The plant hormone auxin acts as a versatile trigger in many developmental processes, including the regulation of root growth, but its role in the control of the stem cell activity remains largely unclear. Here we show that local auxin levels, determined by biosynthesis and intercellular transport, mediate maintenance or differentiation of distal stem cells in the Arabidopsis thaliana roots. Genetic analysis shows that auxin acts upstream of the major regulators of the stem cell activity, the home-odomain transcription factor WOX5, and the AP-2 transcription factor PLETHORA. Auxin signaling for differentiation of distal stem cells requires the transcriptional repressor IAA17/AXR3 as well as the ARF10 and ARF16 auxin response factors. ARF10 and ARF16 activities repress the WOX5 transcription and restrict it to the quiescent center, where WOX5, in turn, is needed for the activity of PLETHORA. Our investigations reveal that long-distance auxin signals act upstream of the short-range network of transcriptional factors to mediate the differentiation of distal stem cells in roots. Arabidopsis | root | auxin | columella differentiation doi/ 10.1073/pnas.1000672107

Quantitative trait loci analysis of natural Arabidopsis thaliana accessions is increasingly exploited for gene isolation. However, to date this has mostly revealed deleterious mutations. Among them, a loss-of-function allele identified the root growth regulator BREVIS RADIX (BRX). Here we present evidence that BRX and the paralogous BRX-LIKE (BRXL) genes are under selective constraint in monocotyledons as well as dicotyledons. Unexpectedly, however, whereas none of the Arabidopsis orthologs except AtBRXL1 could complement brx null mutants when expressed constitutively, nearly all monocotyledon BRXLs tested could. Thus, BRXL proteins seem to be more diversified in dicotyledons than in monocotyledons. This functional diversification was correlated with accelerated rates of sequence divergence in the N-terminal regions. Population genetic analyses of 30 haplotypes are suggestive of an adaptive role of AtBRX and AtBRXL1. In two accessions, Lc-0 and Lov-5, seven amino acids are deleted in the variable region between the highly conserved C-terminal, so-called BRX domains. Genotyping of 42 additional accessions also found this deletion in Kz-1, Pu2-7, and Ws-0. In segregating recombinant inbred lines, the Lc-0 allele ([AtBRX.sup.Lc-O]) conferred significantly enhanced root growth. Moreover, when constitutively expressed in the same regulatory context, [AtBRX.sup.Lc-O] complemented brx mutants more efficiently than an allele without deletion. The same was observed for AtBRXL1, which compared with AtBRX carries a 13 amino acid deletion that encompasses the deletion found in [AtBRX.sup.Lc-O]. Thus, the [AtBRX.sup.Lc-O] allele seems to contribute to natural variation in root growth vigor and provides a rare example of an experimentally confirmed, hyperactive allelic variant. Brachypodium | BREVIS RADIX | adaptation doi/ 10.1073/pnas.0913207107

To establish the relationship between the soil resistance, depth, and root density of durum wheat (Triticum turgidum L. var. durum) genotypes, the root distribution and penetration performance of 103 genotypes were characterized at three distinct Moroccan fields, namely Safi, Marrakech, and Settat. At each site, a cone penetrometer was used to characterize the penetration resistance profile, and the root distribution was assessed using the horizontal profile method. Marrakech and Safi soils showed a high degree of soil resistance, reaching up to 4 MPa at 170 mm and 220 mm, respectively. In contrast, in Settat soil, 4 MPa resistance was reached at 380 mm, and resistance showed the best linear relationship with depth. Root density decreased with increasing depth. At Settat, the root density of three cultivars was compared at 100, 200, 300, 400, and 500 mm. For the cultivar Haurani, 27% of the roots reached 400 mm, while only 16 and 9% did so for Cham1 and Karim, respectively. Root performance of 103 durum wheat genotypes was assessed at 400 mm depth. Root density varied between 380 and 2568 roots/[m.sup.2]. In addition, principal component analysis of some agrophysiological parameters for the 103 genotypes showed significant genotypic variation. The early maturing genotypes were dwarf and produced small spikes, and 47% of them exhibited less than 1200 roots/[m.sup.2]. doi: 10.2135/cropsci2009.04.0190

Inadequate availability of inorganic phosphate (Pi) in the rhizosphere is a common challenge to plants, which activate metabolic and developmental responses to maximize Pi acquisition. The sensory mechanisms that monitor environmental Pi status and regulate root growth via altered meristem activity are unknown. Here, we show that PHOSPHATE DEFICIENCY RESPONSE 2 (PDR2) encodes the single [P.sub.5]-type ATPase of Arabidopsis thaliana. PDR2 functions in the endoplasmic reticulum (ER) and is required for proper expression of SCARECROW (SCR), a key regulator of root patterning, and for stem-cell maintenance in Pi-deprived roots. We further show that the multicopper oxidase encoded by LOW PHOSPHATE ROOT 1 (LPR1) is targeted to the ER and that LPR1 and PDR2 interact genetically. Because the expression domains of both genes overlap in the stem-cell niche and distal root meristem, we propose that PDR2 and LPR1 function together in an ER-resident pathway that adjusts root meristem activity to external Pi. Our data indicate that the Pi-conditional root phenotype of pdr2 is not caused by increased Fe availability in low Pi; however, Fe homeostasis modifies the developmental response of root meristems to Pi availability. multicopper oxidase | P5-type ATPase | phosphate deficiency | root development | SCARECROW

All organisms must find and consume resources to live, and the strategies an organism uses when foraging can have significant impacts on their fitness. Models assuming optimality in foraging behavior, and which quantitatively account for the costs, benefits, and biological constraints of foraging, are common in the animal literature. Plant ecologists on the other hand have rarely adopted an explicit framework of optimality with respect to plant root foraging. Here, we show with a simple experiment that the marginal value theorem (MVT), one of the most classic models of animal foraging behavior, can provide novel insights into the root foraging behavior of plants. We also discuss existing data in the literature, which has not usually been linked to MVT to provide further support for the benefits of an optimal foraging framework for plants. As predicted by MVT, plants invest more time and effort into highly enriched patches than they do to low-enriched patches. On the basis of this congruency, and the recent calls for new directions in the plant foraging literature, we suggest plant ecologists should work toward a more explicit treatment of the idea of optimality in studies of plant root foraging. Such an approach is advantageous because it forces a quantitative treatment of the assumptions being made and the constraints on the system. While we believe significant insight can be gained from the use of preexisting models of animal foraging, ultimately plant ecologists will have to develop taxa-specific models that account for the unique biology of plants. optimal foraging | plant behavior | root foraging | root movement | giving up time

Abstract: Roots encounter a plethora of microorganisms in the soil environment that are either deleterious, neutral, or beneficial to plant growth. Root endophytic fungi are ubiquitous. These include dark septate [...]

Chicory (Cichorium intybus L.), a deep-rooted forb, has potential for inclusion in pasture mixtures because of its reported drought tolerance and high productivity during summer months. This study examined how adding chicory to pasture mixtures affected forage yield, root growth, and soil moisture extraction under drought. The experiment was planted in August 2002. Movable rainout shelters were used to control water application in the field. Adding chicory to orchardgrass (Dactylis glomerata L.)-white clover (Trifolium repens L.) or perennial ryegrass (Lolium perenne L.)--white clover mixtures increased drought tolerance in 2003 when chicory constituted 24 to 39% of harvested forage biomass. Chicory mortality was high, decreasing from 39% of harvested forage yield under drought stress in early summer 2003 to 9% in late summer 2004. Improved yield under drought stress was not observed in 2004 when chicory constituted only 9 to 16% of the mixture. The three-species mixtures in 2003 had greater root counts than the two-species mixtures at soil depths below about 70 cm under well-watered conditions, but a greater proliferation of roots at depths below 70 cm was observed for the two-species mixture under drought stress. Both mixtures appeared capable of nighttime transfer of soil water from deep to shallow soil layers, thereby improving water availability to shallow roots. However, improved drought tolerance of the three-species mixture was probably related to improved water use efficiency rather than to greater access to and extraction of deep soil moisture.

Root hairs show highly localized cell expansion focused to their growing tips. This growth pattern is accomplished through restriction of secretion to the elongating apex and modulation of cell wall properties, with the wall just behind the tip becoming rigidified to resist the lateral expansive forces of turgor. In this report we show that root hairs exhibit oscillating growth that is associated with oscillating increases in extracellular pH and reactive oxygen species (ROS), which lag growth by [approximately equal to]7 s. Consistent with a role for these changes in growth control, artificially increasing extracellular pH arrested root hair elongation, whereas decreasing pH elicited bursting at the tip. Similarly, application of exogenous ROS arrested elongation, whereas scavenging of ROS led to root hair bursting. Roots hairs of the root hair-defective rhd2-1 mutant, which lack a functional version of the NADPH oxidase ATRBOH C, burst at the transition to tip growth. This phenotype could be rescued by elevating the pH of the growth medium to [greater than or equal to]6.0. Such rescued root hairs showed reduced cytoplasmic ROS levels and a lack of the oscillatory production of ROS at the tip. However, they exhibited apparently normal tip growth, including generation of the tip-focused [Ca.sup.2+] gradient thought to drive apical growth, indicating that ATRBOH C is not absolutely required to sustain tip growth. These observations indicate that root hair elongation is coupled to spatially distinct regulation of extracellular pH and ROS production that likely affect wall properties associated with the polarized expansion of the cell. NADPH oxidase | AtRBOH C | rhd2 | proton flux

The Arabidopsis HOBBIT (HBT) gene encodes a homolog of the CDC27 anaphase-promoting complex/cyclosome subunit and is essential for postembryonic development. We induced loss-of-function clones by Cre/Iox-mediated recombination of a single complementing HBT transgene in a background homozygous for the strong mutant allele [hbt.sub.2311]. Defects in cell division and cell expansion are the primary consequences of ubiquitous postembryonic HBTexcision. In roots, both cell division and cell expansion are rapidly affected. In contrast, in leaf primordia, cell division and cell expansion halt after a lag phase, which results in different severities of defects in the proximodistal and mediolateral axes. Surprisingly, small clones reveal non-cell-autonomous rescue of hbt mutant cells, indicating a previously unrecognized compensation mechanism for reduced activity of an anaphase-promoting complex/cyclosome component critical for cell cycle progression. cell cycle | clona| analysis | growth control | root development

Abstract: Systems theory has been applied to process analysis in a variety of scientific disciplines from engineering to evolutionary biology. In the recent postgenomic era, the accumulation of an enormous [...]

Determining fine-root dynamics is fundamental to forest soil nutrient management yet root development of fast-wowing loblolly pine (Pinus taeda L.) is poorly documented. The objectives of this study were to (i) investigate the spatial and temporal root development of loblolly pine; (ii) evaluate the relationship between root length, number of roots exiting a trench face, and root mass densities; and (iii) determine if there is a relationship between line root and foliage mass as well as root and shoot mass during the early stages of stand development. Thirteen forest sites in southeastern Georgia covering ages 1 to 4 yr old were used. Roots temporal and spatial distributions were investigated using a trench method. The value of [N.sub.x] (# roots [cm.sup.-2] was measured in August/September during the first 4 yr of stand development. Root density depth distributions fit a natural logarithm relationship with soil depth. An empirical model for root development over time was developed. A two-dimensional evaluation of root development showed that roots were present in 13 to >60% of the soil volume front Year 1 to Year 4. Regressions between root length density, [L.sub.v] (cm root [cm.sup.3]soil), and [N.sub.x] were weak until root mass and soil depth were included. Lastly, it was shown that the ratio of fine root mass/foliage mass was stable after the establishment phase, as was the ratio of root to shoot.

The formation of adventitious branch roots in the secondary tissues of parental root axes is a widespread and frequent occurrence under field conditions. Anatomical features diagnostic for the recognition of adventitious roots were utilized to confirm the occurrence of adventitious roots on roots of 22 species from 12 families in nine orders of dicotyledonous plants. Adventitious roots may play an important role in generating the population of fine roots as part of root turnover in the soil. Key words: adventitious roots; branching; root turnover; roots.