Exposed roots as indicators of geomorphic processes: A case-study from Polylepis mountain woodlands of Central Argentina

Soil erosion is a serious problem of land degradation in many parts of the world, and particularly in mountain rangelands. To understand this process it is necessary to develop methods to assess soil erosion rate in a quick, economic and accurate manner. Based on the analysis of exposed Polylepis australis roots, we tested a dendrogeomorphological method for determining soil loss rate in rills and gullies. Few studies considered non-coniferous tree rings in soil erosion analysis and we used, for the first time, an experimental procedure of root exposure and provided a comparison with roots exposed by gully erosion. Our main results showed that as a consequence of soil erosion, exposed roots changed from root-like to a more stem-like wood anatomical structure. The percentage of vessel area per tree-ring area decreases by an average of 22% to 43% during the first and second year after exposure, respectively. Moreover, and during the same time interval, the mean vessel area decreased 32% and 65%, and the number of vessels increased 7% and 48%, respectively. Scars formed at the upper side of the exposed roots are coincident with changes in wood anatomy, and both evidences may be applied to reconstruct an erosion process. This study confirms that the wood anatomy analysis of partially exposed roots can be used to determine the year in which roots are exposed and provides a useful tool to monitor soil erosion rates with a high accuracy.     

Wood anatomical changes in roots of European ash (Fraxinus excelsior L.) after exposure

Global changes have distinct influence on fluvial processes in torrents causing erosion on slopes and riverbanks even in forested areas. Continuous as well as discontinuous erosion of riverbanks covered by trees frequently results in destabilisation and finally cause the trees affected to tip over. These uprooted trees may lead to a blockage of the river and, in the case of a collapse of the resulting dam, resulting in severe flooding or even debris-flow surges. Dating the time of root exposure along riverbanks allows the reconstruction of erosion dynamics. In the previous studies, roots of coniferous trees have shown anatomical changes (cell size reduction in earlywood) after exposure. This anatomical feature in the xylem of exposed roots has helped to determine the time of exposure at an annual resolution. In the current study, this methodology is now applied for the first time to European ash (Fraxinus excelsior L.) to determine its specific reactions to root exposure.

First results show different reactions in vessel and fibre dimensions. Fibres show a distinct decrease in lumen area due to exposure, whereas vessel lumen area displays more variability ranging from 50% size reduction to no changes. It is discussed that vessel size characteristics are also related to ecophysiological and climatic patterns.     

Application of growth rings and scars in exposed roots of Schizolobium parahyba as a tool for dating geomorphic processes in the State of São Paulo,Brazil

Water erosion is an important degradation process, which results in loss of soil, reduction in agricultural productivity, and causes severe environmental impact. Dendrogeomorphology has methods in which the structure of the wood of the stem and roots of tree and shrub species affected by sediment deposition or by root exposure is analysed, to establish the chronology of erosive events. The objective of the present work was to describe the modifications and scar formation in Schizolobium parahyba growth rings, attributed to the effect of roots exposure for determining the first year of exposure. The study area presents erosion features, such as gullies, with the consequent exposure of tree roots. The growth rings and the scars formed by the flow of water and soil particles were analysed in cross-sections of exposed roots to date the erosion processes. This paper demonstrates the potential of S. parahyba for dendrogeomorphological studies, validating dendrogeomorphology as a research tool in tropical climate. Scars used for erosion dating in cross-sections have been proven as good indicators of geomorphic processes. The relevance of this work is to become the first attempt in tropical regions to date erosion processes using dendrogeomorphological techniques on exposed roots.     

Bordered pit structure and function determine spatial patterns of air-seeding thresholds in xylem of Douglas-fir (Pseudotsuga menziesii; Pinaceae) trees

The air-seeding hypothesis predicts that xylem embolism resistance is linked directly to bordered pit functioning. We tested this prediction in trunks, roots, and branches at different vertical and radial locations in young and old trees of Pseudotsuga menziesii. Dimensions of bordered pits were measured from light and scanning electron micrographs, and physiological data were from published values. Consistent with observations, calculations showed that earlywood tracheids were more resistant to embolism than latewood tracheids, mainly from earlywood having stretchier pit membranes that can distend and cover the pit aperture. Air seeding that occurs in earlywood appears to happen through gaps between the torus edge and pit border, as shown by the similar calculated pressures required to stretch the membrane over the pit aperture and to cause embolism. Although bordered pit functioning was correlated with tracheid hydraulic diameter, pit pore size and above all pit aperture constrained conductivity the most. From roots to branches and from the trunk base to higher on the trunk, hydraulic resistance of the earlywood pit membrane increased significantly because of a decrease in the size of the pit aperture and size and number of margo pores. Moreover, overall wood conductivity decreased, in part due to lower pit conductivity and a decrease in size and frequency of pits. Structural and functional constraints leading to the trade-off of efficiency against safety of water transport were also demonstrated at the individual pit level, with a positive correlation between pit membrane resistance on an area basis and the pressure differential required to cause membrane stretching, a characteristic that is essential for pit aspiration.     

Coarse root biomass for eucalypt plantations in Tasmania,Australia: sources of variation and methods for assessment

This study develops a feasible method for evaluating coarse root biomass (roots >2 mm diameter) of well established plantations of eucalypts and then examines coarse root biomass variability across tree age and size, fertilization treatment, species and site for Eucalyptus globulus and E. nitens in Tasmania, Australia. The most efficient sampling protocol consisted of rootball excavation and soil coring for bulk coarse roots, which when compared with total tree excavation estimated total coarse root biomass contained inside the sampled area to within 10%. Across all treatments, an average of 76% of the coarse root biomass was located within the rootball. The majority (>65%) of the coarse roots outside the rootball were located in the surface 20 cm of soil. When size class distribution was examined, 75% of coarse root biomass was found to occur in the larger (20+ mm) diameter size class, a size class that displayed considerable spatial heterogeneity. At the stand level, coarse root biomass ranged from 2.18 to 7.38 kg m ^-2 depending primarily on tree size but also on fertilization treatment, species and site. It is estimated that allocation to coarse root biomass production was around 0.2 kg m ^-2 year ^-1 (around 6% of estimated NPP) for the E. nitens stands examined in this study and around 1 kg m ^-2 year ^-1 (around 20% of estimated NPP) for the E. globulus stand examined. Robust relationships using above-ground parameters could be used to predict coarse root biomass regardless of fertilization or site, but species changed the relationship.     

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.     

Fine root dynamics in a Norway spruce forest (Picea abies (L.) Karst) in eastern Sweden

The annual dynamics of live and dead fine roots for trees and the field layer species and live/dead ratios were investigated at a coniferous fern forest (Picea abies L. Karts) in Sweden. Our methods of estimating the average amount of fine roots involved the periodic sampling of fine roots in sequential cores on four sampling occasions. The highest live/dead ratio was found in the upper part of the humus layer for both tree and field-layer species and decreased with depth. Most tree fine roots on the four sampling occasions were found in the mineral soil horizon, where 86, 81, 85 and 89% of <1 mm and 89, 88, 89 and 92% of <2 mm diameter of the total amounts of live fine roots in the soil profile were found. The mean amounts of live fine roots of tree species for the total soil profile on the four sampling occasions was 317, 150, 139 and 248 g m^?2 for <1 mm and 410, 225, 224 and 351 g m^?2 for <2 mm diameter fine roots. The related amount of dead fine roots was 226, 321, 176 and 299 g m^?2 and 294, 424, 282 and 381 g m^?2, respectively. Average amounts of live and dead fine-roots and live/dead ratios from other Picea abies forest ecosystems were within the range of our estimates. The production of fine roots, <1 and <2 mm in diameter, estimated from the annual increments in live fine roots, was 207 and 303 g m^?2. The related accumulation of dead fine roots was 257 and 345 g m^?2, The turnover rate of tree fine roots <1 mm in diameter in the total soil profile amounted to 0.7 yr^?1 for live and 0.8 yr^?1 for dead fine roots. The related turnover rates for tree fine roots <2 mm were 0.4 yr^?1 and 0.7 yr^?1. Our data, although based on minimum estimates of the annual fluxes of live and dead fine roots, suggests a carbon flow to the forest soil from dead fine-roots even more substantial than from the needle litter fall. Fine-root data from several Picea abies forest ecosystems, suggest high turnover rates of both live and dead tree fine-roots.     

Do roots mind the gap?

Aims

Roots need to be in good contact with the soil to take up water and nutrients. However, when the soil dries and roots shrink, air-filled gaps form at the root-soil interface. Do gaps actually limit the root water uptake, or do they form after water flow in soil is already limiting?

Methods

Four white lupins were grown in cylinders of 20 cm height and 8 cm diameter. The dynamics of root and soil structure were recorded using X-ray CT at regular intervals during one drying/wetting cycle. Tensiometers were inserted at 5 and 18 cm depth to measure soil matric potential. Transpiration rate was monitored by continuously weighing the columns and gas exchange measurements.

Results

Transpiration started to decrease at soil matric potential ψ between ?5 kPa and ?10 kPa. Air-filled gaps appeared along tap roots between ψ?=??10 kPa and ψ?=??20 kPa. As ψ decreased below ?40 kPa, roots further shrank and gaps expanded to 0.1 to 0.35 mm. Gaps around lateral roots were smaller, but a higher resolution is required to estimate their size.

Conclusions

Gaps formed after the transpiration rate decreased. We conclude that gaps are not the cause but a consequence of reduced water availability for lupins.     

Root distribution of different mature tree species growing on contrasting textured soils in temperate windbreaks

Aim

We studied the vertical and lateral root distribution of tree species from three genera (Populus spp. - poplar, Picea spp. - spruce, Salix spp. - willow) that were planted in temperate windbreaks and assessed the effects of soil texture on root density.

Methods

Root distribution to depths of up to 1 m was assessed using the trench-profile method at different distances from the tree rows (2, 6 and 9 m) in 18 mature (average age, 25 years-old) windbreak-sites that were located on light- or heavy-textured agricultural soils in southeastern Québec, Canada. Roots were classified into three diameter classes: fine (<1 mm), medium-size (1–5 mm), and coarse (>5 mm).

Results

Tree fine-root density in poplar and willow windbreaks was higher than in spruce windbreaks at 2 m from the tree row. Root densities were higher in light compared to heavy soils, but these differences were specific to poplar and spruce. Across species groups and soil types, 67 % of the roots occurred in the uppermost 30 cm. In this soil zone, different soil fertility variables (pH, clay content, CEC) were negatively correlated with root density. Densities of spruce and willow roots at 6 m from the tree row were much lower (and often unobserved) than that of poplar. At 9 m, low root densities were observed at only two sites.

Conclusions

We conclude that tree identity and soil type are important drivers of root distribution in temperate agroforestry systems. These results may have important implications for the management of tree competition in agroforestry systems and several ecosystem services that are provided by roots, including C-sequestration, erosion control and water infiltration.     

X-ray microdiffraction reveals the orientation of cellulose microfibrils and the size of cellulose crystallites in single Norway spruce tracheids

The microfibril angle (MFA) distribution and the size of cellulose crystallites in isolated double cell walls of Norway spruce (Picea abies [L.] Karst.) tracheids were determined by synchrotron X-ray microdiffraction using the reflections 200 and 004. Samples were 25 μm thick longitudinal sections of earlywood from annual rings 6–18 of several stems. The asymmetric MFA distributions extended from ?20° to 90°. The mean MFA of tangential cell walls decreased from an average of 24° into 19° from the pith to the bark. The mode of the MFA distribution was about 10° smaller than the mean MFA. The standard deviation of the MFA distribution varied between 18° and 25°. The mean MFA and the mode of the MFA distribution were larger in radial than in tangential cell walls. MFA distributions of mature wood samples exhibited a separate small peak at around 90°. The average width and length of cellulose crystallites varied between 28.9–30.9 Å and 192–284 Å, respectively. Both increased slightly as a function of annual ring number from the pith up to the 15th annual ring. An irrigation–fertilisation treatment of some of the stems resulted in longer cellulose crystallites compared to the untreated stems.     

Quantitative effects of wind erosion on the soil texture and soil nutrients under different vegetation coverage in a semiarid steppe of northern China

Many studies reported the influence of wind erosion on soil degradation and the effect of vegetation coverage on preventing wind erosion. However, fewer studies have quantitatively measured the grassland soil particle size fractions and nutrients’ loss caused by wind erosion under different vegetation coverage. Aims: We conducted a field experiments to (1) to explore the effect of vegetation coverage on soil wind erosion; (2) examine quantitatively the effects of wind erosion on soil texture, and determine the most erodible particles fraction of soil; (3) to examine quantitatively the soil carbon, nutrients such as nitrogen and phosphorus loss caused by wind erosion under different vegetation coverage. Methods: Six vegetation coverage treatments (0 %, 15 %, 35 %, 55 %, 75 % and 95 %) were constructed. To be able to monitor wind erosion status under more diverse weather conditions, three consecutive repeat experiments under different weather condition were conducted. Results: The results show that all the residue soil samples after wind erosion became coarser than that of original soil samples. The degree of change for the soil particle size distribution before and after wind erosion gradually increased with the less of vegetation coverage. The critical particle size for distinguishing the original soil sample and the residue soil after wind erosion occurred in the range of 125 μm and 210 μm depending on the vegetation cover. The fractions below or above the critical particle size are either easy to deplete or favoured by wind erosion, respectively. The most reduction occurs between 50 and 90 μm depending on the different weather condition and vegetation coverage. Due to the disproportionately greater amounts of nutrients in the fine soil particles, the preferential depletion of fine particles directly lead to a preferentially significant depletion of organic carbon and nutrients. The organic carbon and nutrient contents in the residue soil after erosion decreased significantly compared to that in the original soil. The soil nutrient loss ratio decrease significantly with the increase of vegetation coverage. Conclusions: Wind erosion is an important factor to affect the evolution of soil texture and soil nutrient. Vegetation coverage has a major impact on both preventing wind erosion and decreasing loss ratio of fine particles and nutrients. If we want to effectively protect the fine particles and nutrients, the vegetation cover should be maintained at least above 35 %.     

Spatial distribution of rhizodeposit carbon of maize (Zea mays L.) in soil aggregates assessed by multiple pulse 13C labeling in the field

Background and aims

Rhizosphere effect is controlled by spatial distribution of rhizodeposits, which may be influenced by soil aggregation and soil moisture regime in relation to water uptake by roots. The objectives of this study were to measure soil organic carbon (SOC) concentration and its δ¹³C abundance by aggregate size in the rooted bulk soil and by distance in the root-free soil vertically and horizontally away from roots, and to measure DOC concentration and its δ¹³C abundance in pore water in the rooted bulk soil after a seasonal pulse labelings of ¹³CO₂ to maize (Zea mays L.).

Methods

Pulse labeling was conducted in the field once a week for 11 weeks. Soil cells (50 mm in diameter and 100 mm long) mimicking root-free soils were imbedded vertically and horizontally 25–50 mm away from the main root of a maize crop. The rooted bulk soils were sampled to extract soil pore water at different suctions and to fractionate aggregates by wet sieving. The root-free soil cells were sliced by 1 mm intervals from the root end to 20 mm away. All the sampling was 12 days after the last labeling after the crop was harvested.

Results and discussion

The δ¹³C abundance before and after the continuous labeling was ?24.20?±?0.05?‰ and ?23.80?±?0.05?‰ in the rooted bulk soil. The labeling caused increases in δ¹³C abundance in all the aggregates in the rooted bulk soil and down to 14 mm away from the roots in both the root-free cells. The δ¹³C abundance was enriched in the >2 mm and 1–2 mm aggregates (?23.17?±?0.12?‰ and ?23.26?±?0.05?‰) though the SOC concentration was not different among the >0.25 mm aggregates, indicating that rhizodeposits or their metabolites were protected and distributed widely in whole soil through soil aggregation. The δ¹³C abundance in pore water (?24.0?±?0.01?‰) was much lower than those soil aggregates and greatest from the >2 μm soil pores though the DOC concentration was greater from the <20 μm soil pores. The δ¹³C abundance was in general greater in the horizontal cell than in the vertical cell. The δ¹³C abundance decreased with the increasing distance to the roots in the vertical cell and peaked at the 5 and 6 mm distance to the roots in the horizontal cell (?23.66?±?0.11?‰ and ?23.5?±?0.10?‰), possibly due to the drier condition unfavorable to microbial decomposition in the horizontal cell. The higher δ¹³C abundance in the horizontal cell than in the vertical cell was accompanied by a lower SOC concentration and a lower C: N ratio within 3 mm away from the roots, suggesting a stronger priming effect due to the longer residence time of rhizodeposits in the horizontal cell than in the vertical cell.

Conclusions

Rhizodeposits or their metabolites were protected during soil aggregation and distributed to 14 mm beyond the rhizosphere in the natural soil-plant system. This extension is of significance in regulating the formation of soil structure and the priming of soil organic matter during the whole life cycle of plants, which needs further study.     

Linking above- and belowground phenology of hybrid walnut growing along a climatic gradient in temperate agroforestry systems

Background and aims

Plant phenology is a sensitive indicator of plant response to climate change. Observations of phenological events belowground for most ecosystems are difficult to obtain and very little is known about the relationship between tree shoot and root phenology. We examined the influence of environmental factors on fine root production and mortality in relation with shoot phenology in hybrid walnut trees (Juglans sp.) growing in three different climates (oceanic, continental and Mediterranean) along a latitudinal gradient in France.

Methods

Eight rhizotrons were installed at each site for 21 months to monitor tree root dynamics. Root elongation rate (RER), root initiation quantity (RIQ) and root mortality quantity (RMQ) were recorded frequently using a scanner and time-lapse camera. Leaf phenology and stem radial growth were also measured. Fine roots were classified by topological order and 0–1 mm, 1–2 mm and 2–5 mm diameter classes and fine root longevity and risk of mortality were calculated during different periods over the year.

Results

Root growth was not synchronous with leaf phenology in any climate or either year, but was synchronous with stem growth during the late growing season. A distinct bimodal pattern of root growth was observed during the aerial growing season. Mean RER was driven by soil temperature measured in the month preceding root growth in the oceanic climate site only. However, mean RER was significantly correlated with mean soil water potential measured in the month preceding root growth at both Mediterranean (positive relationship) and oceanic (negative relationship) sites. Mean RIQ was significantly higher at both continental and Mediterranean sites compared to the oceanic site. Soil temperature was a driver of mean RIQ during the late growing season at continental and Mediterranean sites only. Mean RMQ increased significantly with decreasing soil water potential during the late aerial growing season at the continental site only. Mean root longevity at the continental site was significantly greater than for roots at the oceanic and Mediterranean sites. Roots in the 0–1 mm and 1–2 mm diameter classes lived for significantly shorter periods compared to those in the 2–5 mm diameter class. First order roots (i.e. the primary or parents roots) lived longer than lateral branch roots at the Mediterranean site only and first order roots in the 0–1 mm diameter class had 44.5% less risk of mortality than that of lateral roots for the same class of diameter.

Conclusions

We conclude that factors driving root RER were not the same between climates. Soil temperature was the best predictor of root initiation at continental and Mediterranean sites only, but drivers of root mortality remained largely undetermined.

     

植物根系固坡抗蚀的效应与机理研究进展

植物根系对抵抗坡体浅层滑坡和表土侵蚀起着巨大的作用.植物根系通过增强土体的抗剪强度发挥固坡效应.目前有关植物根系固坡机理的模型较多,普遍接受的是Wu-Waldron模型.该模型表明,植物根系产生的土体抗剪强度的增量与根系的平均抗拉强度和根面积比成正比,应用该模型评价根系固坡效应的2个最重要因素是根系的平均抗拉强度和根面积比.研究发现,土壤抗侵蚀性随着植物根系数量的增加而提高,但未有一致的定量函数关系.植物根系提高土壤抗侵蚀性主要通过直径小于1mm的须根起作用.须根通过增加土壤水稳性团聚体的数量与粒径等作用来提高土壤的稳定性,以抵抗水流分散;须根还能有效地增强土壤渗透性,减少径流,从而达到减少土壤冲刷的目的.     

Decomposition of roots and twigs: Effects of wood type (beech and ash), diameter,site of exposure and macrofauna exclusion

Carbon loss and nitrogen dynamics in beech roots (Fagus sylvatica L.), beech twigs and ash roots (Fraxinus excelsior L.) of 0–3, 3–10 and 10–40 mm diameter were investigated during 36 months of exposure in litter bags of 1 and 4 mm mesh. Four experiments were set up: (1) Beech and ash roots (three size classes) were placed in a soil depth of ca 5 cm in a beechwood on limestone; (2) beech twigs (three size classes) were placed on the soil surface of the beechwood; (3) beech roots (3–10 mm) were placed on the soil surface of the beechwood: (4) beech twigs (3–10 mm) were placed on the soil surface of four sites representing different stages of secondary succession (wheat field, 13 year old fallow, ca 50 year old fallow, beechwood). Ash roots generally lost more C than beech roots. Loss in C of ash roots was similar for each of the size classes, whereas in beech roots and beech twigs C loss was in the order large roots > medium roots > small roots. Beech roots (3–10 mm) placed on the soil surface lost considerably less C than beech twigs (3–10 mm). Decomposition of beech twigs varied among ecosystems but generally did not follow clear patterns with successional stages. The fit of linear vs exponential models of decay is compared and in most materials exponential models fitted the data better. In each of the wood materials an accumulation of N occurred. Irrespective of wood type, root and twig diameter, mineralization of N of wood materials placed in the beechwood started uniformly after 12 months. Multiple regression analysis indicated a negative relationship between initial N content and C loss in beech roots and twigs but not in ash roots. The analysis also indicated a significant influence of the degree of white rot and of the amount of mineral soil deposited in the litter bags on C loss of certain wood materials. Generally, mesh size affected C loss and N dynamics only slightly, which is attributed to the comparatively short exposure time.     

Fine root dynamics along a 2,000-m elevation transect in South Ecuadorian mountain rainforests

Fine root turnover plays an important role in the cycling of carbon and nutrients in ecosystems. Not much is known about fine root dynamics in tropical montane rainforests, which are characterized by steep temperature gradients over short distances. We applied the minirhizotron technique in five forest stands along an elevational transect between 1,050 and 3,060 m above sea level in a South Ecuadorian montane rainforest in order to test the influence of climate and soil parameters on fine root turnover. Turnover of roots with diameter <?2.0 mm was significantly higher in the lowermost and the uppermost stand (0.9 cm cm^?1 year^?1) than in the three mid-elevation stands (0.6 cm cm^?1 year^?1). Root turnover of finest roots (d?<?0.5 mm) was higher compared to the root cohort with d?<?2.0 mm, and exceeded 1.0 cm cm^?1 year^?1 at the lower and upper elevations of the transect. We propose that the non linear altitudinal trend of fine root turnover originates from an overlapping of a temperature effect with other environmental gradients (e.g. adverse soil conditions) in the upper part of the transect and that the fast replacement of fine roots is used as an adaptive mechanism by trees to cope with limiting environmental conditions.     

The function of intercellular spaces along the ray parenchyma in sapwood, intermediate wood, and heartwood of Cryptomeria japonica (Cupressaceae)

? Premise of the study: Intercellular spaces along ray parenchyma (ISRP) are common in many conifer xylems, but their function is uncertain because the in-situ structural network among ISRP, ray parenchyma, and tracheids has not been evaluated. Analysis of water distribution in ISRP from sapwood to heartwood is needed to elucidate the function of ISRP in sapwood, intermediate wood, and heartwood. ? Methods: We used cryo-scanning electron microscopy, x-ray photography, and water content measurement in xylem to analyze the presence of liquids in ISRP, ray parenchyma, and tracheids from sapwood to heartwood in Cryptomeria japonica (Cupressaceae). ? Key results: In sapwood, almost all ISRP were empty. "Cingulate-cavitated regions", which lose water along the tangential direction within one annual ring, formed in the earlywood tracheids, and their frequency increased toward the inner annual rings, whereas ray parenchyma cells were alive and not involved in the partial cavitation. In intermediate wood, almost all ISRP and earlywood tracheids and many of the ray cells were empty, and only some latewood tracheids retained liquid in their lumina. The ISRP were connected with tracheids via gas-filled ray parenchyma cells. ? Conclusions: The ISRP work as a pathway of gas for aspiration of ray parenchyma cells in sapwood. On the other hand, the occurrence of a gas network between ISRP, ray parenchyma, and tracheids facilitates cavitation of tracheids, resulting in the generation of low-moisture, intermediate wood.     

Biomass of extramatrical ectomycorrhizal mycelium and fine roots in a young Norway spruce stand — a study using ingrowth bags with different substrates

Background and aims

The partitioning of below ground carbon inputs into roots and extramatrical ectomycorrhizal mycelium (ECM) is crucial for the C cycle in forest soils. Here we studied simultaneously the newly grown biomass of ECM and fine roots in a young Norway spruce stand.

Methods

Ingrowth mesh bags of 16 cm diameter and 12 cm height were placed in the upper soil and left for 12 to 16 months. The 2 mm mesh size allowed the ingrowth of fungal hyphae and roots whereas a 45 μm mesh size allowed only the ingrowth of hyphae. The mesh bags were filled with either EA horizon soil, pure quartz sand or crushed granite. Controls without any ingrowth were established for each substrate by solid tubes (2010) and by 1 μm mesh bags (2011). The fungal biomass in the substrates was estimated by the PLFA 18:2ω6,9 and ECM biomass was calculated as difference between fungal biomass in mesh bags and controls.

Results

The maximum ECM biomass was 438 kg ha^?1 in October 2010 in 2 mm mesh bags with EA substrate, and the minimum was close to zero in 2011 in 45 μm mesh bags with quartz sand. The high P content of the crushed granite did not influence the ECM biomass. Fine root biomass reached a maximum of 2,343 kg ha^?1 in October 2010 in mesh bags with quartz sand after 16 months exposure. In quartz sand and crushed granite, ECM biomass correlated positively with fine root biomass and the number of root tips, and negatively with specific root length.

Conclusion

The ratio of ECM biomass/fine root biomass in October ranged from 0.1 to 0.3 in quartz sand and crushed granite, but from 0.7 to 1.8 in the EA substrate. The results for the EA substrate suggest a large C flux to ECM under field conditions.     

Further evidence for slow decomposition of very fine roots using two methods: litterbags and intact cores

Background and aims

Root decomposition studies have rarely considered the heterogeneity within a fine-root system. Here, we investigated fine root (< 0.5 and 0.5–2 mm in diameter) decomposition and accompanying nutrient dynamics of two temperate tree species—Betula costata Trautv and Pinus koraiensis Sieb. et Zucc.

Methods

Both litterbag and intact-core techniques were used to examine decomposition dynamic and nutrient release of the two size class roots over a 498-day period. Moreover, we examined differences between the two approaches.

Results

The very fine roots (< 0.5 mm) with an initially lower C:N ratio, decomposed more slowly than 0.5–2 mm roots of both tree species. The differences in mass loss between size classes were smaller when using the intact-core technique compared with litterbag technique. In contrast to root biomass loss, net N release was much higher in the fine roots (< 0.5 mm). All fine roots initially released N (0–75 days), but immobilized N to varying extent in the following days (75–498 days) during decomposition.

Conclusions

Our results suggest that the slow decomposition rate of very fine roots (< 0.5 mm) may be determined by their high concentration of acid-unhydrolyzable structural components. Additionally, the heterogeneity within a bulk fine-root system could lead to differences in their contribution to soil in terms of carbon and nitrogen dynamics.     

Seasonal and perennial changes in the distribution of water in the sapwood of conifers in a sub-frigid zone

An analysis was made of progressive changes in patterns of cavitation in the sapwood of three species of conifer (Larix kaempferi, Abies sachalinensis, and Picea jezoensis) that were growing in a sub-frigid zone. In all three conifers, all tracheids of the newly forming outermost annual ring were filled with water or cytoplasm during the period from May to August. However, many tracheids in the transition zone from earlywood to latewood lost water in September, presumably through drought-induced cavitation. Cavitated tracheids tended to be continuously distributed in a tangential direction. Subsequently, some earlywood tracheids of the outermost annual ring lost water during the period from January to March. This was associated with freeze-thaw cycles. In the second and third annual rings from the cambium of all three conifers, the lumina of most tracheids in the transition zone from earlywood to latewood contained no water. In contrast, some latewood tracheids near the annual ring boundary and many earlywood tracheids retained water in their lumina. The third annual ring had more cavitated tracheids than the second annual ring. Our observations indicated that cavitation progressed gradually in the tracheids of the conifers and that they were never refilled once cavitation had occurred. The region involved in water transport in conifers did not include the entire sapwood and differed among annual rings.