Do propagation methods affect the fine root architecture of African plum (Dacryodes edulis)?

Belowground tree growth attributes determine whether associations will be complementary or competitive in an agroforestry context. A study on fine root (d?≤?2?mm) distribution patterns of Dacryodes edulis based on root density (RD), root length density (RLD) and root weight density (RWD) was conducted to evaluate the effect of propagation methods on rooting distribution. Results showed that D. edulis trees of seed origin had greater RD (P?≤?0.001) than trees of vegetative origin (cuttings and marcots) in the upper soil stratum (0–30?cm). Similarly, in the uppermost soil stratum (0–10?cm), RLD and RWDs varied significantly (P?<?0.01). Trees of seed origin had an exponential distribution pattern for fine RD, RLD and RWD with depth to 80?cm. In contrast, the distribution pattern of fine roots of trees of vegetative origin (cuttings and marcots) were quadratic for the same variables which increased in the 20–30?cm soil depth stratum before declining steadily to a depth of 80?cm. The findings of this study suggest that D. edulis trees of vegetative origin (cuttings and marots) are likely to be less competitive than trees of seed origin when intercropped with shallow-rooted annual plants in an agroforestry system for belowground resources.     

Root suckering patterns in Populus euphratica (Euphrates poplar, Salicaceae)

To understand the spatial structure of monospecific Tugai forests (Xinjiang Province, China) growing as gallery woods nourished by ground water, root suckering in Populus euphratica was studied by a combination of morphological and molecular analyses. Seedlings grow a deep tap root and keep this as adult trees, whereas root suckers never develop a tap root but utilize the horizontally stretching root of their parent trees. The resulting reverse “T” root architecture distinguishes reliably even adult root suckers from generatively grown trees. Due to assimilate input from the root sucker, the distal root (pointing away from the parent tree) becomes thicker soon than its proximal root, which allows determination of the direction of vegetative growth. One stand including 279 young trees germinated from seeds and 267 root suckers was mapped completely, and selected suckers were assigned to parent trees by genotyping with microsatellite DNA. Root suckers develop up to 40 m away from parent trees on horizontal “spacer” roots, usually originating not deeper than 20 cm below surface. Trees begin with root suckering between 10 and 15 years, shortly before reaching flowering age. Cutting experiments indicated reduced survival of young root suckers disconnected from the parent tree. Without a tap root and with a rooting point close to the surface, declining ground water levels should lower the fitness of root suckers even more than that of generatively grown trees.     

Root distribution of poplar at varying densities on pastoral hill country

Spaced poplar (Populus spp.) trees are used widely in New Zealand for soil conservation on erodible pastoral hill country. Their root distribution in this environment, and factors that affect it, are poorly understood. Robust recommendations on effective tree spacing depend on knowledge of root systems. This study determined the effect of tree density, position between trees, and soil depth (0–90 cm) on root number, root diameter distribution, root area ratio (RAR), and cross sectional area per root for young trees on slopes. Data were collected for lateral roots using trenches. Greater than 80% of roots were < 5 mm diameter and root attributes were highest in shallow soil. Trees at 770 stems per hectare (sph) had 3–12 times more roots and 3–9 times greater RAR than those at densities of ≤ 237 sph, representative of most tree-pasture systems. Mean cross sectional area per root was similar across densities. Positions close to trees had twice as many roots (46 vs. 23/m²) and RAR (109 vs. 52 mm²/m²) as positions midway between trees. The study provided quantitative understanding of variation in root distribution with tree density and information useful for supporting and strengthening recommendations on densities for effective erosion control.     

Is it possible to manipulate root anchorage in young trees?

The optimal root system architecture for increased tree anchorage has not yet been determined and in particular, the role of the tap root remains elusive. In Maritime pine (Pinus pinaster Ait.), tap roots may play an important role in anchoring young trees, but in adult trees, their growth is often impeded by the presence of a hard pan layer in the soil and the tap root becomes a minor component of tree anchorage. To understand better the role of the tap root in young trees, we grew cuttings (no tap root present) and seedlings where the tap root had (?) or had not (+) been pruned, in the field for 7 years. The force (F) necessary to deflect the stem sideways was then measured and divided by stem cross-sectional area (CSA), giving a parameter analogous to stress during bending. Root systems were extracted and root architecture and wood mechanical properties (density and longitudinal modulus of elasticity, E _L ) determined. In seedlings (?) tap roots, new roots had regenerated where the tap root had been pruned, whereas in cuttings, one or two lateral roots had grown downwards and acted as tap roots. Cuttings had significantly less lateral roots than the other treatments, but those near the soil surface were 14% and 23% thicker than plants (+) and (?) tap roots, respectively. Cuttings were smaller than seedlings, but were not relatively less resistant to stem deflection, probably because the thicker lateral roots compensated for their lower number. Apart from stem volume which was greater in trees (+) tap roots, no significant differences with regard to size or any root system variable were found in plants (?) or (+) tap roots. In all treatments, lateral roots were structurally reinforced through extra growth along the direction of the prevailing wind, which also improved tap root anchorage. Predictors of log F/CSA differed depending on treatment: in trees (?) tap roots, a combination of the predictors stem taper and %volume allocated to deep roots was highly regressed with log F/CSA (R ² = 0.83), unlike plants (+) tap roots where the combined predictors of lateral root number and root depth were best regressed with log F/CSA (R ² = 0.80). In cuttings, no clear relationships between log F/CSA and any parameter could be found. Wood density and E _L did not differ between roots, but did diminish with increasing distance from the stem in lateral roots. E _L was significantly lower in lateral roots from cuttings. Results showed that nursery techniques influence plant development but that the architectural pattern of Maritime pine root systems is stable, developing a sinker root system even when grown from cuttings. Anchorage is affected but the consequences for the long-term are still not known. Numerical modelling may be the only viable method to investigate the function that each root plays in adult tree anchorage.     

Effect of aboveground intervention on fine root mass, production, and turnover rate in a Chinese cork oak (Quercus variabilis Blume) forest

Aims

Fine root is an important part of the forest carbon cycle. The growth of fine roots is usually affected by forest intervention. This study aims to investigate the fine root mass, production, and turnover in the disturbed forest.

Methods

The seasonal and vertical distributions of fine root (diameter ≤2 mm) were measured in a Chinese cork oak (Quercus variabilis Blume) forest. The biomass and necromass of roots with diameters ≤1 mm and 1-2 mm in 0-40 cm soil profiles were sampled by using a sequential soil coring method in the stands after clear cutting for 3 years, with the stands of the remaining intact trees as the control.

Results

The fine root biomass (FRB) and fine root necromass (FRN) varied during the growing season and reached their peak in August. Lower FRB and higher FRN were found in the clear cutting stands. The ratio between FRN and FRB increased after forest clear cutting compared with the control and was the highest in June. The root mass with diameter ≤1 mm was affected proportionately more than that of diameter 1-2 mm root. Clear cutting reduced FRB and increased FRN of roots both ≤1 mm and 1-2 mm in diameter along the soil depths. Compared with the control, the annual fine root production and the average turnover rate decreased by 30.7 % and 20.7 %, respectively, after clear cutting for 3 years. The decline of canopy cover contributed to the dramatic fluctuation of soil temperature and moisture from April to October. With redundancy discriminate analysis (RDA) analysis, the first axis was explained by soil temperature (positive) and moisture (negative) in the control stands. Aboveground stand structure, including canopy cover, sprout height, and basal area, influenced FRB and FRN primarily after forest clear cutting.

Conclusions

This study suggested that the reduction of fine root biomass, production, and turnover rate can be attributed to the complex changes that occur after forest intervention, including canopy damage, increased soil temperature, and degressive soil moisture.     

Root hydraulic conductivity and vessel structure modification with increasing soil depth of two oak species: Quercus pubescens and Quercus robur

There are numerous studies on water transport characteristics of trees from the base to tops, but only few deal with the variation in xylem conduit diameters from shallow to deep roots. This study compares variation in root conduit properties as a function of increasing soil depths for two oak species (Quercus pubescens Willd and Quercus robur L.) growing on two different plots. We measured root vessel characteristics at three soil depths including 0, 50 and 100 cm, and calculated the associated root-specific hydraulic conductivities. Vessel diameter and specific hydraulic conductivity increased with increasing soil depth from 0 to 50 cm, but did not change in the deeper soil layer in both species. We conclude that freeze–thaw events in upper soil layer limit vessel diameters and thus hydraulic conductivity of roots.     

The vertical distribution of N and K uptake in relation to root distribution and root uptake capacity in mature Quercus robur, Fagus sylvatica and Picea abies stands

We have measured the uptake capacity of nitrogen (N) and potassium (K) from different soil depths by injecting ¹⁵N and caesium (Cs; as an analogue to K) at 5 and 50 cm soil depth and analysing the recovery of these markers in foliage and buds. The study was performed in monocultures of 40-year-old pedunculate oak (Quercus robur), European beech (Fagus sylvatica) and Norway spruce (Picea abies (L.) Karst.) located at an experimental site in Palsgård, Denmark. The markers were injected as a solution through plastic tubes around 20 trees of each species at either 5 or 50 cm soil depth in June 2003. After 65 days foliage and buds were harvested and the concentrations of ¹⁵N and Cs analysed. The recovery of ¹⁵N in the foliage and buds tended to be higher from 5 than 50 cm soil depth in oak whereas they where similar in spruce and beech after compensation for differences in immobilization of ¹⁵N in the soil. In oak more Cs was recovered from 5 than from 50 cm soil depth whereas in beech and spruce no difference could be detected. Out of the three investigated tree species, oak was found to have the lowest capacity to take up Cs at 50 cm soil depth compared to 5 cm soil depth also after compensating for differences in discrimination against Cs by the roots. The uptake capacity from 50 cm soil depth compared with 5 cm was higher than expected from the root distribution except for K in oak, which can probably be explained by a considerable overlap of the uptake zones around the roots and mycorrhizal hyphae in the topsoil. The study also shows that fine roots at different soil depths with different physiological properties can influence the nutrient uptake of trees. Estimates of fine root distribution alone may thus not reflect the nutrient uptake capacity of trees with sufficient accuracy. Our study shows that deep-rooted trees such as oak may have lower nutrient uptake capacity at deeper soil layers than more shallow-rooted trees such as spruce, as we found no evidence that deep-rooted trees obtained proportionally more nutrients from deeper soil layers. This has implications for models of nutrient cycling in forest ecosystems that use the distribution of roots as the sole criterion for predicting uptake of nutrients from different soil depths.     

How does the root system inhibit windthrow in thinned black spruce sites in the boreal forest?

Key message

The root shape and the angle between roots play an important role to prevent windthrow occurrence.

Abstract

Partial cutting is frequently applied to increase the volume growth of residual stems. However, the opening of the forest increases the wind speed within the site, and consequently, the risk of windthrow. In the case of black spruce, uprooted trees are normally characterized by a lifting of the root plate. This research was conducted to compare the root systems of standing and uprooted black spruces, after commercial thinning, by looking at root architecture, volume and radial growth. For this purpose, data from a pool of 18 standing and 18 uprooted trees from three study areas were analyzed. The distribution of roots around the stump was compared between both types of trees, standing and uprooted. The radial growth was measured at 30 cm in the stem, 10 cm and 60 cm in the roots. The shape (I and T-beam) and volume were recorded for each root system. The structure of the roots was also mapped to obtain a spatial overview of the angle between roots. The root shape (at 10 and 60 cm) and the angle between roots combined with the diameter of the stem at stump height seem to determine the vulnerability of black spruce to windthrow. Uprooted trees developed fewer roots, with a large sector around the stump without lateral roots which suggests its major implication in the resistance to windthrow.     

Soil organic carbon and root distribution in a temperate arable agroforestry system

Aim

To determine, for arable land in a temperate area, the effect of tree establishment and intercropping treatments, on the distribution of roots and soil organic carbon to a depth of 1.5 m.

Methods

A poplar (Populus sp.) silvoarable agroforestry experiment including arable controls was established on arable land in lowland England in 1992. The trees were intercropped with an arable rotation or bare fallow for the first 11 years, thereafter grass was allowed to establish. Coarse and fine root distributions (to depths of up to 1.5 m and up to 5 m from the trees) were measured in 1996, 2003, and 2011. The amount and type of soil carbon to 1.5 m depth was also measured in 2011.

Results

The trees, initially surrounded by arable crops rather than fallow, had a deeper coarse root distribution with less lateral expansion. In 2011, the combined length of tree and understorey vegetation roots was greater in the agroforestry treatments than the control, at depths below 0.9 m. Between 0 and 1.5 m depth, the fine root carbon in the agroforestry treatment (2.56 t ha^-1) was 79% greater than that in the control (1.43 t ha^?1). Although the soil organic carbon in the top 0.6 m under the trees (161 t C ha^?1) was greater than in the control (142 t C ha^?1), a tendency for smaller soil carbon levels beneath the trees at lower depths, meant that there was no overall tree effect when a 1.5 m soil depth was considered. From a limited sample, there was no tree effect on the proportion of recalcitrant soil organic carbon.

Conclusions

The observed decline in soil carbon beneath the trees at soil depths greater than 60 cm, if observed elsewhere, has important implication for assessments of the role of afforestation and agroforestry in sequestering carbon.     

Effects of local scouring and saturation of soil due to flooding on maximum resistive bending moment for overturning Robinia pseudoacacia

The effects on Robinia pseudoacacia (an exotic and invasive plant in Japanese rivers) of local scouring and saturation of the soil in the root-anchoring zone due to flooding were investigated. Scouring has been defined as the removal of substrate in the root-anchoring zone, exposing the tree roots. Tree-pulling experiments were conducted, simulating flood action, and the resulting damage was examined in order to assess the effect of local scouring on the maximum resistive bending moment (M _max) for overturning. Scouring was artificially created to three different depths, 0, 25, and 50 cm. A nonlinear model was developed that included soil strength characteristics to calculate the critical overturning moment (M _cri) under dry and saturated soil conditions. Significant correlations (p < 0.05) of M _max with different tree and root–soil plate characteristics, such as diameter at breast height (D _bh), tree weight, root depth, and root–soil plate radius, were developed in order to elucidate the effects of scouring on M _max. M _max was slightly reduced with scouring depth for trees with D _bh <10 cm (small) trunks, and it was significantly and negatively (p < 0.05) correlated with scouring depth for trees with 10 < D _bh < 20 cm (medium) trunks. However, M _max did not change significantly with scouring depth for trees with a D _bh >20 cm (big) trunks. The nonlinear model was useful for determining the M _cri of R. pseudoacacia under dry and saturated soil conditions. The overturning moments of all (small, medium, and big) trees were considerably reduced under the saturated soil condition. It could be concluded that medium-sized trees were greatly affected by scouring, and that small and big trees were mainly affected by saturation of the soil under severe flooding conditions.     

The Increase in Anchorage with Tree Size of the Tropical Tap Rooted TreeMallotus wrayi, King (Euphorbiaceae)

The mechanical development of the anchorage system of the taprooted tropical speciesMallotus wrayiKing (Euphorbiaceae) wasinvestigated by pulling over and examining trees with a diameterat breast height (d_bh) of 4.2 cm to 14.3 cm. The mode of mechanicalfailure depended upon the size of the tree: thicker trees (d_bhapprox.9 cm) failed in the ground with their tap roots pushing intothe soil on the winchward side; in smaller trees (d_bhapprox.7 cm) the trunk snapped before anchorage failure; and in verysmall trees (of d_bh<6 cm) neither type of failure occurredand the trees returned to their original upright position undamagedafter the test. The anchorage strength of the trees was correlatedwith the second power of trunk diameter rather than with thethird power that theory suggests is optimal because tap rootsdid not show an isometric increase in length or diameter. Thereforeas trees grow larger the ‘factor of safety’ againstanchorage failure falls, making them prone to fail in theirroots. These results suggest that only relatively small treespecies can rely solely on the tap root to prevent uprooting.It may be for this reason that most larger trees develop thicklateral roots.Copyright 1998 Annals of Botany Company Anchorage, tap roots, scaling,Mallotus wrayi, isometric growth, functional development, windthrow, root systems.     

Relationships between tree dimension and coarse root biomass in mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies[L.] Karst.)

Relationships between tree parameters above ground and the biomass of the coarse root system were examined in six mixed spruce-beech stands in the Solling Mountain region in northwest Germany. The selected stands were located on comparable sites and covered an age range of 44 to 114 years. Coarse roots (d?\ge?2 mm) of 42 spruce and 27 beech trees were sampled by excavating the entire root system. A linear model with logarithmic transformation of the variables was developed to describe the relationship between the coarse root biomass (CRB, dry weight) and the corresponding tree diameter at breast height (DBH). The coefficients of determination (R ²) attained values between 0.92 for spruce and 0.94 for beech; the logarithmic standard deviation values were between 0.29 and 0.43. A significantly different effect of tree species on the model estimates could not be detected by an analysis of co-variance (ANCOVA). For spruce, the derived relationships were similar to those reported in previous studies, but not for beech. Biomass partitioning in the tree compartments above and below ground differs significantly between spruce (coarse root/shoot ratio 0.16±0.06) and beech (coarse root/shoot ratio 0.10±0.03) in the mixed stands. These results are similar to those given in other studies involving pure spruce and beech stands on comparable sites in the region, although the ratios of pure stands in other regions growing under different site conditions are somewhat higher. Comparing trees of the same DBH classes, root/shoot ratios of spruce are 1.2 to 3 times higher than those of beech. Dominant spruce trees (DBH>60 cm) attained the highest ratios, suppressed beech trees (DBH<10 cm) the lowest. Site conditions of varying climate and soils and interspecific tree competition are likely to affect root/shoot ratio and DBH-coarse root biomass relationships. The greater variability in beech compared with spruce indicates a high 'plasticity' and adaptability of beech carbon allocation. Thus, the derived equations are useful for biomass estimates of coarse roots involving trees of different ages in mixed stands of spruce and beech in the Solling Mountains. However, application of these relationships to stands in other regions would need further testing.     

Root niche partitioning among grasses, saplings, and trees measured using a tracer technique

Niche partitioning of resources by plants is believed to be a fundamental aspect of plant coexistence and biogeochemical cycles; however, measurements of the timing and location of resource use are often lacking because of the difficulties of belowground research. To measure niche partitioning of soil water by grasses, planted saplings, and trees in a mesic savanna (Kruger National Park, South Africa), we injected deuterium oxide into 102,000 points in 15, 154-m² plots randomly assigned to one of five depths (0–120 cm) and one of three time periods during the 2008/2009 growing season. Grasses, saplings and trees all demonstrated an exponential decline in water uptake early in the season when resources were abundant. Later in the season, when resources were scarce, grasses continued to extract the most water from the shallowest soil depths (5 cm), but saplings and trees shifted water uptake to deeper depths (30–60 cm). Saplings, in particular, rapidly established roots to at least 1 m and used these deep roots to a greater extent than grasses or trees. Helping to resolve contradictory observations of the relative importance of deep and shallow roots, our results showed that grasses, saplings and trees all extract the most water from shallow soils when it is available but that woody plants can rapidly shift water uptake to deeper soils when resources are scarce. Results highlight the importance of temporal changes in water uptake and the problems with inferring spatial and temporal partitioning of soil water uptake from root biomass measurements alone.     

Fine root biomass in two black spruce stands in interior Alaska: effects of different permafrost conditions

Key message

In black spruce stands on permafrost, trees and understory plants showed higher biomass allocation especially to ‘thin’ fine roots (diam. < 0.5 mm) when growing on shallower permafrost table.

Abstract

Black spruce (Picea mariana) forests in interior Alaska are located on permafrost and show greater below-ground biomass allocation than non-permafrost forests. However, information on fine roots (roots <2 mm in diameter), which have a key role in nutrient uptake and below-ground carbon flux, is still limited especially for effects of different permafrost conditions. In this study, we examined fine root biomass in two black spruce stands with different depths to the permafrost table. In the shallow permafrost (SP) plot, fine root biomass of black spruce trees was 70 % of that in the deep permafrost (DP) plot. In contrast, ratio of the fine root biomass to above-ground biomass was greater in the SP plot than in the DP plot. Understory plants, on the other hand, showed larger fine root biomass in the SP plot than in the DP plot, whereas their above-ground biomass was similar between the two plots. In addition, biomass proportion of ‘thin’ fine roots (diam. <0.5 mm) in total fine roots was greater in the SP plot than in the DP plot. These results suggest that black spruce trees and understory plants could increase biomass allocation to fine roots for efficient below-ground resource acquisition from colder environments with shallower permafrost table. In the SP plot, fine roots of understory plants accounted for 30 % of the stand fine root biomass, suggesting that understory plants such as Ledum and Vaccinium spp. would have significant contribution to below-ground carbon dynamics in permafrost forests.

     

Effects of litter types, microsite and root diameters on litter decomposition in Pinus sylvestris plantations of northern China

Background and aims

Litter decomposition is a major process in the carbon (C) flow and nutrient cycling of terrestrial ecosystems, but the effects of litter type, microsite, and root diameter on decomposition are poorly understood.

Methods

Litterbags were used to examine the decomposition rate of leaf litter and roots at three soil depths (5, 10 and 20 cm) over a 470-day period in Pinus sylvestris plantations in northern China.

Results

Leaves and the finest roots decomposed more quickly at 5 cm depth and coarser roots (>1-mm) decomposed more quickly at 10 and 20 cm depth. Roots generally decomposed more quickly than leaf litter, except at 5 cm deep; leaves decomposed more quickly than the coarsest roots (>5-mm). Root decomposition was strongly influenced by root diameter. Leaves experienced net nitrogen (N) immobilization and coarse roots (>2-mm) experienced more N release than fine roots. Significant heterogeneity was seen in N release for fine-roots (<2-mm) with N immobilization occurring in smaller (0.5–2-mm) roots and N release in the finest roots (<0.5-mm).

Conclusions

Soil depth of litter placement significantly influenced the relative contribution of the decomposition of leaves and roots of different diameters to carbon and nutrient cycling.     

Role of aquaporin activity in regulating deep and shallow root hydraulic conductance during extreme drought

Key message

Deep root hydraulic conductance is upregulated during severe drought and is associated with upregulation in aquaporin activity.

Abstract

In 2011, Texas experienced the worst single-year drought in its recorded history and, based on tree-ring data, likely its worst in the past millennium. In the Edwards Plateau of Texas, rainfall was 58 % lower and the mean daily maximum temperatures were >5 °C higher than long-term means in June through September, resulting in extensive tree mortality. To better understand the balance of deep and shallow root functioning for water supply, we measured root hydraulic conductance (K _R) in deep (~20 m) and shallow (5–10 cm) roots of Quercus fusiformis at four time points in the field in 2011. Deep roots of Q. fusiformis obtained water from a perennial underground (18–20 m) stream that was present even during the drought. As the drought progressed, deep root K _R increased 2.6-fold from early season values and shallow root K _R decreased by 50 % between April and September. Inhibitor studies revealed that aquaporin contribution to K _R increased in deep roots and decreased in shallow roots as the drought progressed. Deep root aquaporin activity was upregulated during peak drought, likely driven by increased summer evaporative demand and the need to compensate for declining shallow root K _R. A whole-tree hydraulic transport model predicted that trees with greater proportions of deep roots would have as much as five times greater transpiration during drought periods and could sustain transpiration during droughts without experiencing total hydraulic failure. Our results suggest that trees shift their dependence on deep roots versus shallow roots during drought periods, and that upregulation of aquaporin activity accounts for at least part of this increase.     

Vegetative Life History of a Dominant Rain Forest Canopy Tree1

Tetramerista glabra has a remarkable combination of life history traits. It is a dense-wooded, large, common canopy tree in primary peat swamp rain forest. Its seedlings, although shade tolerant, can grow rapidly in high light conditions, but frequently lack structural stability. Most juvenile stems (94% in the understory and 38% in canopy gaps) collapse under their own weight or from branchfalls. Fallen stems then ramify into vegetative sprouts, which in turn may collapse, perpetuating a vegetative juvenile cycle. Most recruitment is from sprouts rather than from seed. Structural analysis of stem dimensions shows that stems 2–8 cm DBH (diameter at breast height) are close to the theoretical buckling limit, especially for those dependent on neighboring vegetation to maintain vertical form. Trees > 4 cm DBH persisting as upright stems develop stilt root support and become structurally independent at ca 8 cm DBH. Eventually, as stems thicken, stilt roots anastamose and trees adopt the cylindrical growth form of mature canopy trees (up to 150 cm DBH). Thus, the vegetative life history strategy of the species is to: (i) regenerate a large “ramet bank” from the majority of juveniles that fail structurally while suppressed in the understoty, and (ii) to maximize height growth at the expense of diameter growth in high light conditions. The growth pattern and plastic form of T. glabra shows how a shade tolerant species may adapt to utilize the ephemeral light resource in canopy gaps. The growth strategy of this species allows it to circumvent the normal trade-off between shade tolerance and rapid growth in canopy gaps.     

Reactive Oxygen Species and Relative Enzyme Activities in the Development of Aerial Roots of Chinese Banyan (Ficus microcarpa)

Although previous research has indicated that reactive oxygen species (ROS) regulate cell extension and tissue ontogenesis, the functions of ROS in aerial roots have not been previously studied. This research evaluated ROS production and dissipation in aerial roots of Chinese banyan (Ficus microcarpa). Aerial root segments (4 cm long) were cut from trees and divided into developmental zones 1, 2, and 3 (0–5, 5–15, and 15–25 mm from root tip, respectively). According to histochemical and biochemical determinations, production of the superoxide radical (O ₂ ^·– ), hydrogen peroxide (H₂O₂), and the hydroxyl radical (^·OH) decreased from zone 1 to zone 3. The detected ROS increased with the application of exogenous stimulators of ROS generation and decreased with the application of exogenous inhibitors of ROS generation. Based on protein content, superoxide dismutase (SOD) activity increased but peroxidase (POD) and catalase (CAT) activities decreased from zone 1 to zone 3, whereas based on root segment fresh weight, SOD and CAT activities did not differ among the zones but POD activity decreased from zone 1 to 3. We conclude that ROS are generated mainly in the rapidly developing zones of aerial roots and suggest that NADPH oxidase, POD, and SOD control ROS generation. POD activity and the hydroxyl cycle seem particularly important in ROS generation in aerial roots.     

Relation of fine root distribution to soil C in a Cunninghamia lanceolata plantation in subtropical China

Background and aims

Growth and distribution of fine roots closely depend on soil resource availability and affect soil C distribution in return. Understanding of relationships between fine root distribution and soil C can help to predict the contribution of fine root turnover to soil C accumulation.

Methods

A study was conducted in a subtropical Cunninghamia lanceolata plantation to assess the fine root mass density (FRMD), fine root C density (FRCD) of different fine root groups as well as their relations with soil C.

Results

The FRMD and FRCD of short-lived roots, dead roots and herb roots peaked in the 0–10 cm soil layer and decreased with soil depth, while FRMD, FRCD of long-lived roots peaked in the 10–20 cm soil layer. Soil C was positively related to FRMD and FRCD of total fine roots (across all three soil layers), dead roots (0–10 cm) and herb roots (10–20 cm) as well as FRCD of short-lived roots (20–40 cm) (P <0.05).

Conclusions

Soil C was mainly affected by herb roots in upper soil layers and by woody plant roots in deeper soil layers.     

The function of buttress roots: a comparative study of the anchorage systems of buttressed (Aglaia and Nephelium ramboutan species) and non-buttressed (Mallotus wrayi) tropical trees

The anchorage mechanics of mature buttressed trees of Aglaiaand Nephelium, and of non-buttressed Mallotus wrayi have beeninvestigated by combining a study of the morphology of theirroot systems with a series of anchorage tests. Both types possessed tap roots, but only buttressed trees possessedsinker roots, which branched from the ends of the buttresses.The anchorage strength of the buttressed trees was almost double(10.6 kNm) that of the unbuttressed ones (4.9 kNm), and themaximum moment was generated at lower angles. In but tressedtrees, the leeward buttresses were pushed into the soil beforebending and eventually breaking towards their tip, whilst thewindward buttresses pulled out of the soil or delaminated ifthey possessed sinker roots. The tap root rotated in the soilto windward. In contrast, during failure of unbuttressed treesthe tap root both moved and bent towards the leeward, the windwardroots were pulled out of the soil, and the leeward lateralssimply buckled. Strains along but tresses were much higher thanalong the laterals of unbuttressed trees. These results suggest that buttresses act in both tension andcompression and make a much larger contribution to anchoragethan the thin laterals of non-buttressed trees. The relativecontribution of the but tresses was determined by carrying outa further series of anchorage tests in which both buttressedand unbuttressed trees were pulled over after all their lateralshad been cut away. These trees were therefore only anchoredby their taproot. Failure of both types was similar to intactunbuttressed trees, and they had similar anchorage strengthstoeach other, 4 kNm, around 80% of the value for intact non-buttressedtrees, but only 40% of the strength of intact buttressed trees.Buttresses therefore contribute around 60% of the anchorageof buttressed trees, producing around six times more anchoragethan the thin laterals of unbuttressed trees. Key words: Anchorage, root architecture, sinker roots, tap roots, root bending strength, buttresses