Incorporation and remobilization of ¹³C within the fine-root systems of individual Abies alba trees in a temperate coniferous stand

Forest ecosystems have a large carbon (C) storage capacity, which depends on their productivity and the residence time of C. Therefore, the time interval between C assimilation and its return to the atmosphere is an important parameter for determining C storage. Especially fine roots (≤2 mm in diameter) undergo constant replacement and provide a large biomass input to the soil. In this study, we aimed to determine the residence time of C in living fine roots and the decomposition rates of dead fine roots. Therefore, we pulse-labelled nine 20-year-old individual silver fir trees (Abies alba Miller; ～70 cm tall) with 13CO? in situ to trace the assimilated C over time into the fine-root systems. Whole trees were harvested at different time points after labelling in autumn, biomass was determined and cellulose and starch of fine roots were extracted. Moreover, soil cores were taken and ingrowth cores installed, in which fine roots were genetically identified, to assess incorporation and remobilization of 13C in the fine roots of silver fir trees; litterbags were used to determine fine-root decomposition rates. The 13C label was incorporated in the fine-root system as cellulose within 3 days, with highest values after 30 days, before reaching background levels after 1 year. The highest δ13C values were found in starch throughout the experiment. 13C recovery and carbon mean residence times did not differ significantly among fine-root diameter classes, indicating size-independent C turnover times in fine roots of A. alba trees of ～219 days. Furthermore, carbon was remobilized from starch into newly grown fine roots in the next spring after our autumn labelling. One year after installation, litterbags with fine roots revealed a decrease of biomass of ～40% with relative 13C content in fine-root bulk biomass and cellulose of ～50%, indicating a faster loss of 13C-labelled compounds compared with bulk biomass. Our results also suggest that genetic analysis of fine-root fragments found in soil and ingrowth cores is advisable when working in mixed forest stands with trees of similar fine-root morphology. Only then can one avoid dilution of the labelling signal by mistake, due to analysis of non-labelled non-target species roots.     

Drought resistance of two hybrid Populus clones grown in a large-scale plantation

Poplar hybrids were grown with irrigation in a large-scale plantation to investigate the mechanisms underlying clonal differences in drought resistance. Beginning in spring 1992, Populus trichocarpa x P. deltoides (TD) and P. deltoides x P. nigra (DN) cuttings received 46, 76, or 137 cm year(-1) of irrigation to supplement the 18-20 cm of annual precipitation, and all trees received the same fertilization regime. Stem volume, assessed as the square of stem diameter at breast height times tree height (D(2)H), and water relations of the trees were studied from the end of their second growing season until the end of their fifth growing season. By the end of the second growing season, stem volume of Clone TD was 40-146% larger than that of Clone DN, but stem volume growth was independent of irrigation in excess of 46 cm year(-1) in both clones. During the third growing season, stem volume growth of both clones was limited by both the 46- and 76-cm irrigation treatments, so that by the end of the third growing season trees in the 46-cm irrigation treatment were only half the size of trees in the 137-cm irrigation treatment. These treatment differences were maintained through the fifth growing season. Although stem volumes of Clone TD trees in the 76- and 137-cm irrigation treatments were larger than the corresponding values for Clone DN trees at the end of the third growing season (1994), these clonal differences gradually decreased in subsequent years and were not detectable after 5 years, because stem volume relative growth rate of Clone DN was greater than that of Clone TD in all treatments. Although both clones exhibited similar predawn leaf water potentials, Clone DN typically maintained higher midday leaf water potentials, suggesting better stomatal control of water loss. Clonal and treatment differences in osmotic potential at full turgor were minimal and could not explain the clonal differences in drought resistance. Root density and root density to stem volume ratio increased more in response to moderate drought in Clone DN than in Clone TD, resulting in enhanced drought resistance (high stem volume growth rate under moderate drought conditions) and an increased capacity to withdraw water from the soil. We conclude that the greater drought resistance of Clone DN compared with Clone TD was the result of the maintenance of a more favorable water balance by stomatal regulation and greater carbon allocation to roots during the early stages of drought. However, the low root density to stem volume ratio in Clone DN growing in the 46-cm irrigation treatment suggests that severe water limitation restricted the preferential allocation of carbon to belowground tissues, so that both root and shoot growth were constrained by severe drought.     

Importance of weed control, fertilization, irrigation, and genetics in slash and loblolly pine early growth on poorly drained spodosols

Research reported here has evaluated interactions of factors limiting the biological potential of slash pine (Pinus elliottii var. elliottii Engelm.) and loblolly pine (P. Taeda L.). Water and nutrients were manipulated by irrigation, weed control, and intensive fertilization. Genetic factors were incorporated as (1) improved loblolly seedlings from a commercial clonal seed orchard and (2) slash seedlings from four fast-growing, open-pollinated seed-orchard clones. Three replications of a 2 × 2 × 2 factorial experiment were established on a Typic Haplaquod soil in northern Florida using four cultural treatments: no treatment (F0H0); weed control (F0H1); fertilizer (F1F0); and combination of weed control and fertilizer (F1H1) for each species. During the first year there were large, sustained responses to all cultural practices. Loblolly and slash pine showed similar growth responses and had a lengthened growing season (60–100 days). Slash pine growth was superior to that of loblolly. Growth responses observed during the first year continued. After 4 years, irrigation had no measurable effect on tree growth. Both pine species responded equally to F1H0 and F0H1, but slash retained a slight edge. Extra nutrients]available via fertilizer, reduced competition, or additional rooting space, increased slash-pine volume index from an average of 2.0 m³ ha⁻¹ (F0H0) to 11.90 and 13.59 m³ ha⁻¹ (F0H1 and F1H0, respectively). The F1H1 treatment produced the largest slash-pine response, diameter at breast height (D_bh) averaged 9.84 cm, height reached 5.02 m, and volume index rose to about 22.94 m³ ha⁻¹. With teh F1H1 treatment, average loblolly-pine height and volume exceeded that of the average slash pine. At age 4, the growth response due to increased nutrient supply was 13–29 times that of the best genetic response within F0H0 trees of the four slash-pine progenies. The best-growing slash-pine family (6–56) exceeded loblolly-pine growth under all four treatments and approximated the vigor shown by slash pine in the southern hemisphere.     

Phosphorus and potassium depletion by roots of field-grown slash pine: Aerobic and hypoxic conditions

Slash pine (Pinus elliottii Engelm. var. elliottii) is planted extensively on flatwood and coastal savanna soils of the southeastern USA. Pine roots growing in these soils encounter shallow water tables. Although the fine-root system of pine trees growing in the surface 20–26 cm of those soils will not be continuously submerged, they will encounter short-term reduced soil conditions, with a severely reduced O₂ supply which might affect their ability for ion uptake from the soil solution. The objectives were: (i) to compare P and K depletion by lateral root systems of slash pine roots subjected to a short-term hypoxic treatment, and (ii) to document K and P depletion patterns by lateral root systems of slash pine roots following the removal of the hypoxic treatment. Our purpose was to evaluate the uptake ability of these roots of changing aeration. For the experiment, 17 intact lateral roots from twelve-year-old slash pine trees were inserted into nutrient-uptake root chambers. The chambers were filled with a nutrient solution containing 6.25 μM P (phosphate), and 25.66 μM K. P and K depletion rates were monitored in six consecutive treatments, each lasting five days. Treatments of aerobic and hypoxic conditions were sequentially applied in the following order: aerobic–hypoxic–aerobic. This sequence was repeated twice. Uptake of P and K by slash pine roots was affected by oxygen availability, but the degree of response differed. Under hypoxic nutrient solution conditions, K depletion from solution by pine roots was totally inhibited, resulting in net efflux of K. In contrast, P depletion was not inhibited under hypoxic nutrient solution conditions. Results suggest that pine roots grown in aerobic soil conditions of surface horizons are capable of P depletion when reduced soil conditions are present.     

Water and nutrient dynamics and tree growth

The balance in the investment of assimilate at any time into leaves and roots may depend on whether water, nutrients or radiation are limiting to growth. Also, for the same investment of assimilate into roots, the root configuration may range from intensive to extensive in both space and time, to take best advantage of the distribution and amount of water and nutrients. Intensive root configurations, which include mycorrhizas and proteoid roots, assist in the uptake of nutrients (such as phosphorus) which are rate-limiting in soil. Mycorrhizas may assist in water uptake in dry or coarse textured soils with low unsaturated hydraulic conductivities.

Adaptations which assist trees to survive in dry and nutrient-deficient environments are discussed. These mechanisms may reduce, maintain or increase growth. In production forestry, it is desirable to exploit those mechanisms which increase growth. When soil water and nutrients limit tree growth, productivity may be improved by increasing the amount of uptake of water and nutrients, or by increasing the efficiency by which they are used in growth. Maximizing water-use efficiency when soil water supply is limiting may be dependent on whether the trees are in mixed stands or in monoculture. Selecting trees with relatively less root may improve productivity in monocultures when weeds are controlled and fertilizer is added. It is well known that trees can ‘re-use’ nutrients by retranslocating them within the tree to zones of demand. Relatively little is known, though, about differences in the biochemical involvement of nutrients at the cellular and subcellular level which contribute to differences in nutrient-use efficiency in trees.     

Effects of coppicing on the root and stump carbohydrate dynamics in birches

Whole birch stems were cut off in order to determine how coppicing affects root and stump starch, glucose, fructose and sucrose concentrations and their correlation with shoot regeneration capacity. The Betula pubescens Ehrh. and B. pendula Roth studied included intact trees, trees that had been coppiced 8 years earlier, trees coppiced at the beginning of the experimental season, and birches that had been coppiced twice, 8 years earlier and at the beginning of the experimental season. Carbohydrate accumulation differed between 8 years earlier coppiced and intact trees. Recent coppicing clearly decreased the starch and sugar concentrations of the roots, which were often highest in the thin roots. The concentrations of these compounds in the stumps were always low, although the carbohydrate concentrations of stumps, in particular, correlated with shoot regeneration capacity. Starch was the most labile of the carbohydrates measured and most clearly reacted to coppicing. Differences in starch- and sugar-reserve dynamics indicate a difference between these birch species in the use and replenishing of root and stump reserves. This information may also be of help when the effects of other stresses, for example, severe animal damage or burning, on the regrowth of young birch stands are estimated.     

Carbon allocation and nitrogen acquisition in a developing Populus deltoides plantation

We established Populus deltoides Bartr. stands differing in nitrogen (N) availability and tested if: (1) N-induced carbon (C) allocation could be explained by developmental allocation controls; and (2) N uptake per unit root mass, i.e., specific N-uptake rate, increased with N availability. Closely spaced (1 x 1 m) stands were treated with 50, 100 and 200 kg N ha(-1) year(-1) of time-release balanced fertilizer (50N, 100N and 200N) and compared with unfertilized controls (0N). Measurements were made during two complete growing seasons from May 1998 through October 1999. Repeated nondestructive measurements were carried out to determine stem height and diameter, leaf area and fine-root dynamics. In October of both years, above- and belowground biomass was harvested, including soil cores for fine-root biomass. Leaves were harvested in July 1999. Harvested tissues were analyzed for C and N content. Nondestructive stem diameter and and fine-root dynamic measurements were combined with destructive harvest data to estimate whole-tree biomass and N content at the end of the year, and to estimate specific N-uptake rates during the 1999 growing season. Shoot growth response was greater in fertilized trees than in control trees; however, the 100N and 200N treatments did not enhance growth more than the 50N treatment. Root biomass proportions decreased over time and with increasing fertilizer treatment. Fertilizer-induced changes in allocation were explained by accelerated development. Specific N-uptake rates increased during the growing season and were higher for fertilized trees than for control trees.     

Initial sprouting, growth and mortality of European aspen and birch after selective coppicing in central Sweden

For reasons of aesthetics, sheltering, biodiversity, and children’s need of playgrounds, selective coppicing could be a useful and effective silvicultural method in urban areas. A randomised block experiment was carried out in three broad-leaved coppices situated within the fenced area of Arlanda Airport to compare a selective coppice regime (SCR), where all trees above a certain height limit were cut, with a traditional coppice regime, where all trees were felled. The effects of the treatments of the dominating tree species European aspen (Populus tremula L.) and birch (Betula pendula Roth and B. pubescens Ehrh.) were studied. During three growing seasons after performed treatment, the proportion of sprouting stools and root shooting of European aspen were reduced in SCR. Birch stools had fewer sprouts stool⁻¹, and sprouts of both birch and European aspen tended to be shorter in SCR. There was a tendency that the sprout mortality was lower in SCR for both birch and European aspen. Residual stands of SCR consisted of proportionally less birch, and more rowan, bird cherry, oak and other species. Coppicing with single tree selection from above suppressed light demanding tree species and promoted the more shade-tolerant species compared to traditional coppicing.     

Remobilization and uptake of N by newly planted apple (Malus domestica) trees in response to irrigation method and timing of N application

Environmentally sound management of N in apple orchards requires that N supply meets demand. In 1997, newly planted apple trees (Malus domestica Borkh. var. Golden Delicious on M.9 rootstock) received daily applications of N for six weeks as Ca(15NO3)(2) through a drip irrigation system at a concentration of 112 mg l(-1) at 2-8, 5-11 or 8-14 weeks after planting. Irrigation water was applied either to meet estimated evaporative demand or at a fixed rate. In 1997, trees were harvested at 5, 8, 11 and 14 weeks after planting; and in 1998 at 3 weeks after full bloom. The amount of fertilizer N recovered was similar in trees in both irrigation treatments, but efficiency of fertilizer use was greater for trees receiving demand-controlled irrigation than fixed-rate irrigation. This was attributed to lower N inputs, greater retention time in the root zone and less N leaching in the demand-controlled irrigation treatments compared with fixed-rate irrigation treatments. Less fertilizer N was recovered by trees receiving an early application of N than a later application of N and this was related to the timing of N supply with respect to tree demand. Demand for root-supplied N was low until 11 weeks after planting, because early shoot and root growth was supported by N remobilized from woody tissue, which involved 55% of the total tree N content at planting. Rapid development of roots > 1 mm in diameter occurred between 11 and 14 weeks after planting, after remobilization ended, and was greater for trees receiving an early application of N than for trees receiving a later application of N. Late-season tree N demand was supplied by native soil N, and uptake and background soil solution N concentrations were higher for trees receiving demand-supplied irrigation compared with fixed-rate irrigation. Total annual N uptake by roots was unaffected by treatments and averaged 6-8 g tree(-1). Nitrogen applications in 1997 affected growth and N partitioning in 1998. Trees receiving early applications of N had more flowers, spur leaves and bourse shoots than trees receiving later applications of N. Consequently, more N was remobilized into fruits in trees receiving early applications of N compared with fruits in trees receiving later applications of N. Demand for N in the young apple trees was low. Early season demand was met by remobilization from woody tissues and the timing of demand for root-supplied N probably depends on whether flowering occurs. Method of N delivery affected the efficiency of N use. We conclude that N demand can be met at soil solution N concentrations of around 20 mg l(-1).     

Fine root dynamics, coarse root biomass, root distribution, and soil respiration in a multispecies riparian buffer in Central Iowa, USA

By influencing belowground processes, streamside vegetation affects soil processes important to surface water quality. We conducted this study to compare root distributions and dynamics, and total soil respiration among six sites comprising an agricultural buffer system: poplar (Populus × euroamericana‘ Eugenei), switchgrass, cool-season pasture grasses, corn (Zea mays L.), and soybean (Glycine max (L.) Merr.). The dynamics of fine (0--2 mm) and small roots (2--5 mm) were assessed by sequentially collecting 35 cm deep, 5.4 cm diameter cores from April through November. Coarse roots were described by excavating 1 × 1 × 2 m pits and collecting all roots in 20 cm depth increments. Root distributions within the soil profile were determined by counting roots that intersected the walls of the excavated pits. Soil respiration was measured monthly from July to October using the soda-lime technique. Over the sampling period, live fine-root biomass in the top 35 cm of soil averaged over 6 Mg ha^-1 for the cool-season grass, poplar, and switchgrass sites while root biomass in the crop fields was < 2.3 Mg ha^-1 at its maximum. Roots of trees, cool-season grasses, and switchgrass extended to more than 1.5 m in depth, with switchgrass roots being more widely distributed in deeper horizons. Root density was significantly greater under switchgrass and cool-season grasses than under corn or soybean. Soil respiration rates, which ranged from 1.4--7.2 g C m^-2 day^-1, were up to twice as high under the poplar, switchgrass and cool-season grasses as in the cropped fields. Abundant fine roots, deep rooting depths, and high soil respiration rates in the multispecies riparian buffer zones suggest that these buffer systems added more organic matter to the soil profile, and therefore provided better conditions for nutrient sequestration within the riparian buffers. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of tree shelters,irrigation and branch pruning on early field performance of micropropagated wild cherry cv. F12/1

The growth potential of micropropagated wild cherry cv. F12/1 under field conditions was assessed. Relatively short trees (19–22 cm tall) were planted in the field just seven months after transfer from tissue culture to soil. Irrigation and shelters promoted shoot heights in the first (establishment) year. If planting techniques can be developed which reduce branch production, then the cost of corrective pruning to achieve clean stems is also reduced. Shelters, but not irrigation almost totally inhibited outgrowth of branches produced in spring. Outgrowth of spring branches by unsheltered trees was strongly influenced by tree height at planting, with shorter trees producing fewer branches. In the second and third years of the trial, pruning branches from trees that had been planted in shelters, resulted in taller trees. By the end of the third year, pruned trees had smaller stem diameters than unpruned trees. These results are discussed with respect to using cv. F12/1 as a productive timber tree.     

Influence of soil temperature and water content on fine-root seasonal growth of European beech natural forest in Southern Alps,Italy

In tree species, fine-root growth is influenced by the interaction between environmental factors such as soil temperature (ST) and soil moisture. Evidences suggest that if soil moisture and nutrient availability are adequate, rates of root growth increase with increasing soil temperature up to an optimum and then decline at supraoptimal temperatures. These optimal conditions vary between different taxa, the native environment and the fine-root diameter sub-classes considered. We investigated the effects of seasonal changes of both ST and soil water content (SWC) on very fine (d < 0.5 mm) and fine-root (0.5 < d < 2 mm) mass (vFRM, FRM) and length (vFRL, FRL) in Italian Southern Alps beech forests (Fagus sylvatica L.). Root samples were collected by soil core method. Turnover rate was higher for the very fine (0.51) than for the fine (0.36) roots. vFRM, FRM, vFRL and FRL displayed a complex seasonal pattern peaking in summer when SWC was around 40 % and ST was around 14 °C. Above this temperature, under almost constant SWC, all above mentioned root traits decreased. vFRM, FRM, vFRL and FRL showed significant second-order polynomial relationship (p < 0.05) with SWC for both diameter classes, with the only exception of SRL. ST showed the same kind of relationship significant only with vFRM and vFRL, the latter within the 12–16 °C smaller range. Interpolation analysis between root mass and length for both diameter classes and investigated soil environmental characteristics (ST and SWC) showed a clear roundish delineation only for vFRM. In conclusion, these findings clarified the occurrence of a bimodal fine-root growth seasonal pattern for our beech forest. The optimal growth ST and SWC ranges were delineated only for very fine roots, giving further evidence on this root category as the more responsiveness to soil environmental changes. Furthermore, F. sylvatica seems to adopt an intensive strategy to cope with decreasing SWC. Finally, fine-root growth, mainly radial type, seems to be driven by SWC, whereas very fine-root growth, mainly longitudinal type, seems to be driven by ST.     

Nutrient concentrations in roots, leaves and wood of seedling and mature sugar maple and American beech at two contrasting sites

Differences in sensitivity to soil conditions across tree species and developmental stage are important to predicting forest response to environmental change. This study was conducted to compare elemental concentrations in leaves, stems, and roots of (1) sugar maple (Acer saccharum Marsh.) seedlings vs. mature trees and (2) mature sugar maple vs. mature American beech (Fagus grandifolia Ehrh.) in two sites that differ in soil base saturation and pH. Both sites are located in Huntington Forest, NY, USA; one site (hereafter ‘H’) has higher soil pH and Ca, Mg, and Mn concentrations than the other site (hereafter ‘L’). Sugar maple growth at H (14.8 cm² year⁻¹ per tree) was much greater than at L (8.6 cm² year⁻¹ per tree), but the growth of beech was not different between the two sites. Leaves, roots, and stem wood of mature beech trees and sugar maple seedlings and mature trees were sampled for nutrient analysis. Foliar Ca, K, and Al concentrations were positively correlated with soil elements, but Mn concentrations were negatively correlated. Sugar maple differed more than beech between sites in foliar K and Mn concentrations. Root Mg and P concentrations reflected soil chemistry differences, in contrast to foliar concentrations of Mg and P, which were indistinguishable between the sites. In sugar maple, seedlings differed more than in mature trees in nutrient concentrations in roots, especially for Mg and Mn. Although beech was not as responsive to nutrient availability as sugar maple in foliar and root nutrient concentrations, Ca and Mg concentrations in beech wood were higher in H (52% higher for Ca and 68% higher for Mg), while sugar maple did not differ between sites. Sugar maple regeneration failure on acidic soils in the same region is consistent with our finding that sugar maple seedlings were very sensitive to nutrient availability. This sensitivity could ultimately contribute to the replacement of sugar maple by American beech in regions of low pH and base cations if base cation leaching by anthropogenic deposition and tree harvesting continues.     

Effects of simulated drought stress on the fine roots of Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) in a plantation forest on the Kanto Plain,eastern Japan

Drought stress was simulated in a 28-year-old Japanese cedar plantation (Kanto Plain, Japan) between April and October 2004 by removing throughfall using rain shelters. Changes in fine-root parameters caused by this drought treatment were examined by sequential soil coring. Drought effects on fine roots were analyzed separately for particular soil depths (0–5, 5–15, and 15–25 cm) and root diameters (<1 and 1–2 mm). Generally, fine-root biomass and root tip numbers decreased by the drought treatment. Drought stress was most intense for fine roots in the topsoil and weakest for fine roots in the deepest soil layer. Fine roots less than 1 mm in diameter were affected more severely than 1- to 2-mm roots. The effect of drought treatment was most remarkable for the number of white root tips, which decreased to 17% of the control at the soil depth of 0–5 cm. These results suggest that white root tip is the most suitable indicator of drought stress. Simulated drought reduced production of fine roots less than 1 mm and 1–2 mm in diameter. Fine-root mortality was stimulated for roots less than 1 mm, but not for 1- to 2-mm roots. These results suggest that fine roots with larger diameters can survive drought stress at a level simulated in this study, but processes of fine-root production were inhibited regardless of the diameter classes. The duration of drought stress and phenology of fine roots should also be considered in diagnosing the effects of drought on fine-root parameters.     

平欧杂种榛细根空间分布特征

目的 探讨单作系统下平欧杂种榛根系空间分布特征,揭示影响细根（吸收根,0 < d ≤ 2 mm）分布的关键土壤因子,为平欧杂种榛的地下水肥高效管理提供理论参考。 方法 采用田间分层挖掘法和根系形态结构分析系统,研究平欧杂种榛根系径级构成以及垂直与水平分布特征。 结果 表明：平欧杂种榛根系主要由细根构成,其中,细根表面积和细根长度分别占测定总根系的60. 8%和93.2%,表明平欧杂种榛只有维持足够庞大的细根表面积和长度才能摄取更多的养分和水分以保障正常的生长需求。垂直方向上,平欧杂种榛根系生物量密度、表面积密度和根长密度均随土层深度的增加呈先升高后降低的趋势,各根系密度参数最大值均在10~20 cm土层。水平方向上,平欧杂种榛根系生物量密度、表面积密度和根长密度均表现为随距树干基部水平距离的增加而减小,且各根系密度参数在水平距离上差异显著。细根密度的空间分布特征表明,距树干基部水平距离0~150 cm以内的0~50 cm土层为细根表面积和根长密度的集中分布区,二者分别占测定总细根的54.16%和48.83%。相关分析表明：平欧杂种榛细根表面积密度和根长密度均与土壤含水量呈极显著正相关,表明细根分布对土壤水分的响应敏感,细根“逐水性”特征明显。 结论 在平欧杂种榛单作系统下,从节水节肥的角度考虑,距树干基部水平距离0~150 cm以内的0~50 cm土层可作为土壤水肥管理的重要区域     

Effects of irrigation deprivation during the harvest period on nonstructural carbohydrate and nitrogen contents of dormant, mature almond trees

Effect of irrigation deprivation during the harvest period on the nonstructural carbohydrate (NC) content of dormant, mature, field-grown almond (Prunus dulcis (Mill.) D.A. Webb cv. Nonpareil) trees was studied. Roots, trunk, branches, spurs and stems of 12 trees were subsampled in February 1997, across a gradient of irrigation treatments (FI = fully irrigated, MS = moderately stressed and SS = severely stressed) to relate NC concentration to the degree of water stress experienced by individual trees during the previous (1996) harvest period. To assess the effect of water stress on whole-tree NC content, three dormant FI trees and three dormant SS trees were excavated on December 10, 1997, and dry weights and NC and N concentrations of the tree components were determined. Whole-tree biomass did not differ significantly between FI and SS trees, although SS trees tended to have less total dry weight. Although roots constituted just 13% of tree biomass, they stored 36 and 44% of tree NC and N contents, respectively. There were negative relationships between the seasonal minimum values of both midday (Psi(ms)) and predawn (Psi(pd)) stem water potentials during the harvest period and root NC content of dormant trees. Severe water stress during the harvest period resulted in a 26% reduction in NC content and a 50% reduction in biomass of current-year stems (> 5 cm in length) per tree. The reduction in NC content is consistent with the previously reported late season reductions in leaf function and persistence. The SS trees exhibited a reduction in NC content but not in N content per tree, indicating that late season accumulation of NC and N were uncoupled in trees subjected to severe harvest-period water stress.     

The effect of coppiced teak regrowth on soil in a teak-maize agroforest

The effects on soil of canopy and roots of coppiced teak (Tectona grandis L.f.) regrowth in a maize-teak mixture were investigated experimentally by trenching and coppice shoot control. Nitrogen, potassium, magnesium and calcium content of soil were not significantly affected by either treatment throughout the first season of cropping the soil with maize. It is suggested that soil nutrient changes due to canopy or surface roots of coppiced teak regrowth are probably too small to influence the performance of intercropped maize in the first season following coppicing.     

Characteristics of root growth in a fast-growing and high-yield poplar plantation under subsurface drip-irrigation

The characteristics of root growth in the fast-growing and high-yield plantation of poplar I-214 (Populus × euramericana cv. ‘I-214’) were studied under two contrasting conditions, subsurface drip-irrigation (SDI) and normal irrigation (CK), on the sandy soil of Chaobai River, Beijing. The results showed that in the soil layer of 20–50 cm, there was a considerable increase in the amount of roots less than 10 mm in diameter (especially those of less than 2mm) under SDI, which was three times as much as that under CK. The absorbing roots under SDI were concentrated in the soil layer of 20–50 cm, while the roots under CK were distributed evenly in each layer. With respect to horizontal distribution, roots (d<10 mm) under SDI were distributed mainly near the subsurface emitters and the amount of roots in 3 m in a row under SDI were 50% less than under CK. Therefore, it is suggested that subsurface emitters with the shape of “#” should be collocated in the middle of two rows and two individual trees to increase the distributing and absorbing range of roots under SDI, and further increase the plantation productivity. __________ Translated from Journal of Beijing Forestry University, 2007, 29(2): 34–40 [译自: 北京林业大学学报]     

Water and nutrient supply regimes and the water relations of juvenile leaves of Eucalyptus globulus

Pressure-volume analysis was used to study effects of irrigation and fertilization on the water relations of newly expanded juvenile leaves of Eucalyptus globulus Labill. seedlings growing in Portugal's Atlantic region. In May, at the beginning of the dry season, fertilization and irrigation treatments had no significant effects on the water relations parameters investigated. In September, at the end of the dry season, leaves from non-irrigated plants had a significantly higher apoplasmic water content and a higher dry weight/turgid weight ratio than leaves of similar physiological age from irrigated trees. The osmotic potential at full turgor and the water potential at the wilting point were lower in non-irrigated than in irrigated plants. Changes in osmotic potential at full turgor were negatively correlated with changes in dry weight/turgid weight ratio, suggesting that reductions in osmotic potential at full turgor were largely the result of decreases in cell size. Fertilization had no detectable effect on these variables or on leaf tissue bulk modulus of elasticity. Tissue elasticity was also unaffected by irrigation. Independently of water and nutrient supplies, leaf elasticity was higher and relative water content at the wilting point lower in leaves sampled in May than in leaves sampled in September. In non-irrigated plants, leaves sampled in September had a lower tissue elasticity and a lower osmotic potential at full turgor than leaves sampled in May, indicating that leaves produced at the end of the dry season generate lower water potentials as turgor is lost than leaves expanded early in the season.     

Growth patterns and morphology of fine roots of size-controlling and invigorating peach rootstocks

We compared growth patterns and morphology of fine roots of size-controlling and invigorating peach (Prunus persica (L.) Batsch) rootstocks. Peach trees were grafted on five rootstocks: a vigorous control (Nemaguard), three intermediate vigor rootstocks (K119-50, P30-135 and Hiawatha), and a semi-dwarfing rootstock (K146-43). Minirhizotron tubes were installed at the base of trees on each rootstock and root images captured with a minirhizotron digital camera system. Number, visible length, and diameter of new roots were recorded at fixed soil depths from April 19, 2000 to December 19, 2001. Root diameter, specific root length, root tissue density and root length density were also measured periodically for each rootstock on roots collected from in-growth cores. Rootstocks had similar seasonal patterns of new root production. Fine root production was lowest in winter and appeared to decline during the final stages of fruit growth. A rootstock with almond in its genetic background (K119-50) produced the greatest quantity of fine roots and had the greatest number of new roots below 69 cm, whereas there were no differences among the other four rootstocks in the total number of roots produced. Rootstock K146-43 had thicker fine roots than the other rootstocks. Independent of rootstock, fine roots produced during spring had greater specific root length than those produced later in the season. The seasonal pattern of fine root production did not appear to be associated with the previously reported effects of these dwarfing rootstocks on shoot growth and stem water potential early in the growing season.