Root growth and carbohydrate responses in bearing citrus trees following partial canopy removal

In August, eight 4-m tall citrus trees were pruned by removing the top third of their canopy. Eight unpruned trees served as controls. Root growth, which was examined nondestructively with minirhizotrons over a four-month period, tended to be less in the pruned than unpruned trees seven days after pruning and this difference was significant (P < 0.05) from 14 to 49 days after pruning. Total reducing and ketone sugars (includes free fructose, sucrose and fructans) in the fine roots were less in pruned than unpruned trees 20 days after pruning, but not thereafter. By 30 days after pruning, at least 20% of the roots of the pruned trees at a soil depth of 9 to 35 cm apparently died. By 63 days after pruning, root length density had recovered to that of the unpruned trees, although starch reserves were 18% less in the fine roots of pruned than unpruned trees at this time. Nine to eleven months after pruning (May to July), total biomass of leaves and fine roots to a depth of 1 m were similar in pruned and unpruned trees. However, fruit biomass harvested in April from pruned trees was only 24% of that in the unpruned trees. In May, nonstructural carbohydrates in the fine and coarse roots of pruned trees were generally greater than in unpruned trees, possibly reflecting previous differences in fruit production.     

Dynamics of non-structural carbohydrate reserves in pruned <Emphasis Type="Italic">Erythrina poeppigiana</Emphasis> and <Emphasis Type="Italic">Gliricidia sepium</Emphasis> trees

In alley cropping systems, fast growing leguminous trees are pruned to reduce competition with crops for light and to provide organic inputs for crop nutrition. Tree regrowth depends on non-structural carbohydrate reserves in the remaining tree parts. In this study, the dynamics of starch and soluble carbohydrates in roots and stems of completely pruned (all shoots removed), partially pruned (one branch retained on the pruned stump) and unpruned Erythrina poeppigiana (Walp.) O.F. Cook and Gliricidia sepium (Jacq.) Kunth ex Walp. trees were studied under humid tropical conditions in Turrialba, Costa Rica. Measurements on starch and soluble carbohydrates in roots and stems were made at 0, 2, 6 and 12 weeks after pruning during both a “rainy” and a “dry” season. In general, the dynamics of non-structural carbohydrates in roots and stems of pruned E. poeppigiana and G. sepium trees were similar. Starch concentration was highest in unpruned trees and higher in roots than in stems of pruned trees. The effect of pruning intensity was first observed in stems, and starch reserves were more depleted in stems than in roots, an effect more evident during the “dry” season. The critical tree regrowth stage for starch mobilisation was that of vigorous sprout development at six or four weeks after pruning particularly in completely pruned trees. At this time, fine root biomass and length and nodule biomass in pruned trees decreased. Survival of fine roots and nodules was greater in partially pruned than in completely pruned trees. Starch accumulation in roots recommenced at 12 weeks after pruning in G. sepium, and later than 12 weeks after pruning in E. poeppigiana roots. This study showed that E. poeppigiana responded better to pruning regimes than G. sepium. Recovery of trees after pruning is better when trees are partially pruned than when completely pruned.     

A carbon balance model of peach tree growth and development for studying the pruning response

We modeled tree responses to pruning on the basis of growth rules established on unpruned trees and a simple principle governing root-shoot interactions. The model, which integrates architectural and ecophysiological approaches, distinguishes four types of anatomical organs in a tree: rootstock, main axis, secondary axes and new roots. Tree structure is described by the position of secondary axes on the main axis. The main processes considered are plastochronal activity, branching, assimilate production, respiration and assimilate partitioning. Growth and development rules were based on measurements of two unpruned trees. The model was used to simulate growth of peach trees (Prunus persica (L.) Batsch) in their first growing season. Assuming that the equilibrium between roots and shoots tends to be restored after pruning, the response to removal of the main axis above the twentieth internode in mid-July was simulated and compared to the response measured in three pruned trees. The model fit the unpruned tree data reasonably well and predicted the main traits of tree behavior after pruning. Dry matter growth of the secondary axes of pruned trees was increased so that shoot seasonal carbon balance was hardly modified by pruning. Rhythmicity of growth was enhanced by pruning, and might result from variations induced in the root:shoot ratio. Variation in pruning severity had greater effects than variation in pruning date. A sensitivity analysis indicated that: (1) root-shoot partitioning was a critical process of the model; (2) tree growth was mainly dependent on assimilate availability; and (3) tree shape was highly dependent on the branching process.     

The effect of root and shoot pruning on early growth of hybrid poplars

Planting stock type and quality can have an important impact on early growth rates of plantations. The goal of this study was to evaluate early growth and root/shoot development of different planting materials in typical heavy clay soils of northwestern Quebec. Using one-year-old bareroot hybrid poplar dormant stock, four planting materials were compared: (1) regular bareroot stock, (2) rootstock (stem pruned before planting), (3) whips (roots pruned before planting), and (4) cuttings (30 cm stem sections taken from the basal portion of bareroot trees, i.e. roots and shoot pruned). Rooted stock types (bareroot and rootstock) produced, on average, 1.2 times larger trees than unrooted stock types (cuttings and whips). However, shoot-pruned stock types (rootstocks and cuttings) reached similar heights and basal diameters as unpruned stock types (bareroots and whips), during the first growing season. Shoot pruning reduced leaf carbon isotopic ratios, suggesting that unpruned stock types were water-stressed during the first growing season. The stress was most likely caused by early leaf development while root growth occurred later in the summer. We conclude that shoot pruning bareroot stock is a useful management option to reduce planting stress without compromising early growth rates of hybrid poplars.     

Effects of curtain-like pruning on distribution and seasonal patterns of carbohydrate reserves in plane (Platanus acerifolia Wild) trees

The maintenance of plane trees (Platanus acerfolia Wild) by regular curtain-like pruning during the vegetative period induced modifications in the distribution and seasonal patterns of carbohydrate reserves in the perennial parts. The unpruned trees were characterized by high and fairly constant concentrations of starch in roots > 5 cm in diameter and a decreasing gradient of starch from the base to the top of the trunk. Starch also accumulated at the trunk-branch junction and at the base of large branches. Curtain-like pruning caused the starch gradient in the trunk to disappear and induced well marked seasonal variations in the starch concentration of roots > 5 cm in diameter. Pruning also eliminated the accumulation of starch at the trunk-branch junction during summer, but it had no effect on the accumulation of starch at the base of large branches. Concentrations and seasonal fluctuations of carbohydrates in roots < 0.5 cm in diameter were similar in both pruned and unpruned trees. Repeated cuts or "short head pruning" induced the formation of excrescences at the tips of branches that accumulated starch.     

The influence of severe shoot pruning on growth,carbon and nitrogen status in young peach trees (Prunus persica)

One-year-old peach trees (Prunus persica (L.) Batsch) were severely pruned in July by removing 60% of the shoots. Tree responses were analyzed in terms of architecture and nutritional status. Tree growth was recorded from July to September by nondestructive (leaf production, thickening and branching of the remaining secondary axes) and destructive measurements (biomass partitioning and concentrations of total nitrogen (N) and nonstructural carbohydrates (NC) in specific tissues). The dry weights of pruned trees were lower than those of control trees at the end of the growing season (i.e., 2.5 months after pruning), whereas shoot:root ratios were restored to the initial values. Tree response occurred in two stages. During the first 24 days following pruning, the growth components of the remaining secondary axes were similar to the control, and new secondary axes were produced. During the next 17 days, increases in both diameter and branching of secondary axes contributed to the maintenance of pruned tree growth rate (similar to that of control trees) and restoration of initial shoot:root ratios. No significant effect of pruning was observed on NC concentrations, whereas N concentrations increased in several organs of the pruned trees during the first growth period. The transient increase in internal N availability contributed to the initiation of new axes and the restoration of a more functional biomass partitioning between shoots and roots.     

人工整形对观赏果树生长发育的影响

为了科学而有效地利用苹果树资源,以促进休闲观光农业的发展,采用不同的整形处理方法,就苹果树的树体造型及其造型后的生长发育状况进行了试验与观测,结果表明:双环处理的致矮效应最好;"S"树形最为均衡,其平均干粗明显地高于其它处理,其长、中、短枝的比例适宜;双环处理的高效叶最多,其新梢能够及时停止生长,树体积累的养分多,对形成花芽有利;双环、单环和"S"形处理能够促使苹果树形成优美独特的景观。     

Impact of artificial pruning on growth and secondary shoot development of wild cherry (Prunus avium L.)

Producing high value veneer wood requires that the tree bole be branch-free. This can be accomplished by natural or artificial pruning. Since wild cherry does not self prune well, pruning artificially is the only practical option. The study analysed the effect of conventional whorl-wise pruning and selective pruning, on height growth, diameter growth and secondary shoot development of wild cherry. Four pruning treatments were applied on cherry trees in summer 2007, one group of cherries was left unpruned to serve as a control: treatment C1 (upper 5 whorls left), C2 (upper 3 whorls left), S1 (removal of branches larger than 3 cm or with an angle to the stem < 40°), S2 (removal of branches larger than 2 cm or with an angle to the stem < 40°), N (unpruned). Data showed that height growth was not affected by pruning. In contrast, diameter growth at breast height of the C2 pruned cherry was reduced by approximately 5% (SE = 2.7%) in the year of pruning (trees were pruned in July). This pruning treatment produced significant (p = 0.028) nine percent less diameter growth than the control in the second year following pruning. The diameter increment of the C1 pruned trees with five whorls left after pruning and the selective pruned cherries were only about 4% (SE = 4.0%) smaller than the control after two years. This loss was statistically not significant. Analyses showed that on selective pruned trees the survival rate of secondary shoots was significantly reduced compared to those on whorl-wise pruned trees. Significant differences in the size of the secondary shoots were only found between the C1 and S1 (p < 0.05) pruned trees. We did not find differences in the total number of secondary shoots per tree among pruning treatments. Solely from a tree growth perspective, the moderate whorl-wise pruning treatment C1 and the selective prunings were equally effective in minimizing the reduction of diameter growth and are recommended in practice. However it was found that the survival of secondary shoots was reduced on selective pruned trees although the amount of pruning work needed in selective pruning was slightly greater than conventional moderate pruning.     

Pruning effects on root distribution and nutrient dynamics in an acacia hedgerow planting in northern Kenya

Tree pruning is a common management practice in agroforestry for mulching and reducing competition between the annual and perennial crop. The below-ground effects of pruning, however, are poorly understood. Therefore, nutrient dynamics and root distribution were assessed in hedgerow plantings of Acacia saligna (Labill.) H.L. Wendl. after tree pruning. Pruning to a height of 1.5 m was carried out in March and September 1996. In July and October 1996, the fine root distribution (< 2 mm) and their carbohydrate contents were determined at three distances to the tree row by soil coring. At the same time, foliar nutrient contents were assessed, whereas nutrient leaching was measured continuously. The highest root length density (RLD) was always found in the topsoil (0–0.15 m) directly under the hedgerow (0–0.25 m distance to trees). Pruning diminished the RLD in the acacia plots at all depths and positions. The relative vertical distribution of total roots did not differ between trees with or without pruning, but live root abundance in the subsoil was comparatively lower when trees were pruned than without pruning. In the dry season, the proportion of dead roots of pruned acacias was higher than of unpruned ones, while the fine roots of unpruned trees contained more glucose than those of pruned trees. Pruning effectively reduced root development and may decrease potential below-ground competition with intercropped plants, but the reduction in subsoil roots also increased the danger of nutrient losses by leaching. Leaching losses of such mobile nutrients as NO₃^– were likely to occur especially in the alley between pruned hedgerows and tended to be higher after pruning. The reduced size of the root system of pruned acacias negatively affected their P and Mn nutrition. Pruning also reduced the function of the trees as a safety net against the leaching of nutrients for both NO₃^– and Mn, though not for other studied elements. If nutrient capture is an important aim of an agroforestry system, the concept of alley cropping with pruning should be revised for a more efficient nutrient recycling in the system described here.This revised version was published online in November 2005 with corrections to the Cover Date.     

Growth and yield of sorghum or cowpea in an agrisilviculture system in semiarid India

This study was conducted near Hyderabad, India during 1991–1994 to quantify the effects of shoot pruning, fertilization, and root barriers around Leucaena leucocephala trees on intercropped sorghum(Sorghum bicolor) or cowpea (Vigna unguiculata) crop production under rainfed conditions. Crop plants grown with pruned trees attained higher dry matter and leaf area index than did those with unpruned trees. Two-year mean grain yields of sorghum with no root barriers were76% and 39% of pure crop yield (1553 kg ha–1)for pruned and unpruned trees, respectively. Corresponding values for cowpea were 49% and 26% of pure crop yield (1075 kgha–1). Sorghum or cowpea intercropped with trees responded to fertilizer application more strongly than did their respective pure crops, suggesting an increased need for fertilizer application in this agrisilviculture system over that currently used for pure crops. Impact of root barriers was small on either crop. Irrespective of root barriers, a high response to tree pruning suggested above ground competition for light dominated tree/crop interactions in this agrisilviculture system. This revised version was published online in June 2006 with corrections to the Cover Date.     

The dynamics of rooting in Triplochiton scleroxylon cuttings: their relation to leaf area, node position, dry weight accumulation, leaf water potential and carbohydrate composition

Single-node, leafy stem cuttings of Triplochiton scleroxylon K. Schum. were collected from successive nodes down the uppermost shoot of 2-shoot stockplants. The leaves were trimmed to 10, 50 and 100 cm(2) before the cuttings were set under intermittent mist to root. Batches of cuttings were harvested after 0, 14, 28 and 42 days to assess leaf water potential, dry weight and carbohydrate content of their leaf and stem portions. Cuttings with leaf areas of 10, 50 and 100 cm(2) increased in total dry weight by 29, 61 and 90%, respectively, during the 6-week period. The increase in dry weight was accompanied by increases in reflux-extracted soluble carbohydrates (RSC), water-soluble carbohydrates (WSC) and starch. By contrast, increase in leaf area reduced leaf water potential of cuttings before root emergence. Fewer large-leaved cuttings rooted than smaller-leaved cuttings, suggesting that rooting ability is at least partially determined by the balance between photosynthesis and transpiration. Fewer roots per cutting were produced on cuttings with 10 cm(2) leaves than on cuttings with larger leaves. Node position affected increments in dry weight, carbohydrate content and leaf water potential, with differences between nodes on day 0 generally being lost or slightly reversed by day 14. Rooting ability was not related to initial (day 0) carbohydrate content, suggesting that rooting is dependent on carbohydrates formed after severance. During the rooting period, the proportions of total non-structural carbohydrate as WSC and starch were reversed, from mostly WSC on day 0 to mostly starch by day 42. These changes in WSC and starch occurred most rapidly in large-leaved cuttings.     

Influence of controlled water supply on shoot and root development of young peach trees

Three controlled water supply treatments were applied to 1-year-old peach trees grown in root observation boxes. The treatments were: I(0), growth medium maintained at 50% field capacity; I(1), water supplied when daily net tree stem diameter change was negative or zero for 1 day; I(3) as for I(1) except that water was applied after net daily stem diameter change was negative or zero for 3 consecutive days. Trees in treatment I(0) had the greatest mean daily first-order shoot growth rates, and trees in treatment I(3) had the lowest shoot growth rates. Because leaf production rate (apparent plastochron) of first-order shoots was unaffected by treatment, differences in shoot length were due to differences in internode extension and not to the number of internodes. Trees in treatment I(0) had a greater number of second-order shoot axes than trees in treatment I(1) or I(3). Furthermore, an increase in the rate of growth of the first-order shoot axis was associated with an increased tendency for branching (i.e., the development of sylleptic second-order shoots). Increased leaf length was also associated with more frequent watering. Trees in treatment I(0) had the greatest root lengths and dry weights, and this was attributed to a greater number of first-and second-order (lateral) root axes compared with trees in the I(1) and I(3) treatments. The extension rate and apical diameter of first-order roots were reduced by the I(3) treatment. The density of second-order roots along primary root axes was not affected by any of the treatments.     

Changes in shoot allometry with increasing tree height in a tropical canopy species,Elateriospermum tapos

Allometry of shoot extension units (hereafter termed "current shoots") was analyzed in a Malaysian canopy species, Elateriospermum tapos Bl. (Euphorbiaceae). Changes in current shoot allometry with increasing tree height were related to growth and maintenance of tree crowns. Total biomass, biomass allocation ratio of non-photosynthetic to photosynthetic organs, and wood density of current shoots were unrelated to tree height. However, shoot structure changed with tree height. Compared with short trees, tall trees produced current shoots of the same mass but with thicker and shorter stems. Current shoots with thin and long stems enhanced height growth in short trees, whereas in tall trees, thick and short current shoots may reduce mechanical and hydraulic stresses. Furthermore, compared with short trees, tall trees produced current shoots with more leaves of lower dry mass, smaller area, and smaller specific leaf area (SLA). Short trees adapted to low light flux density by reducing mutual shading with large leaves having a large SLA. In contrast, tall trees reduced mutual shading within a shoot by producing more small leaves in distal than in proximal parts of the shoot stem. The production of a large number of small leaves promoted light penetration into the dense crowns of tall trees. All of these characteristics suggest that the change in current shoot structure with increasing tree height is adaptive in E. tapos, enabling short trees to maximize height growth and tall trees to maximize light capture.     

Genetic and environmental control of seasonal carbohydrate dynamics in trees of diverse Pinus sylvestris populations

We explored environmental and genetic factors affecting seasonal dynamics of starch and soluble nonstructural carbohydrates in needle and twig cohorts and roots of Scots pine (Pinus sylvestris L.) trees of six populations originating between 49 degrees and 60 degrees N, and grown under common garden conditions in western Poland. Trees of each population were sampled once or twice per month over a 3-year period from age 15 to 17 years. Based on similarity in starch concentration patterns in needles, two distinct groups of populations were identified; one comprised northern populations from Sweden and Russia (59-60 degrees N), and another comprised central European populations from Latvia, Poland, Germany and France (49-56 degrees N). Needle starch concentrations of northern populations started to decline in late spring and reached minimum values earlier than those of central populations. For all populations, starch accumulation in spring started when minimum air temperature permanently exceeded 0 degrees C. Starch accumulation peaked before bud break and was highest in 1-year-old needles, averaging 9-13% of dry mass. Soluble carbohydrate concentrations were lowest in spring and summer and highest in autumn and winter. There were no differences among populations in seasonal pattern of soluble carbohydrate concentrations. Averaged across all populations, needle soluble carbohydrate concentrations increased from about 4% of needle dry mass in developing current-year needles, to about 9% in 1- and 2-year-old needles. Root carbohydrate concentration exhibited a bimodal pattern with peaks in spring and autumn. Northern populations had higher concentrations of fine-root starch in spring and autumn than central populations. Late-summer carbohydrate accumulation in roots started only after depletion of starch in needles and woody shoots. We conclude that Scots pine carbohydrate dynamics depend partially on inherited properties that are probably related to phenology of root and shoot growth.     

Dynamics of nonstructural carbohydrates and biomass yield in a fodder legume tree at different harvest intensities

Tropical tree fodder is harvested by frequent prunings, and resprouting depends on nonstructural carbohydrate reserves in the remaining tree parts. We studied the effects of three pruning intensities (removal of all leaves and branches leaving 1 m of stem once a year (T-12), or every 6 months (T-6), and about 50% pruning every 2 months (P-2)) on regrowth and the dynamics of soluble sugars and starch in the legume tree Gliricidia sepium (Jacq.) Walp. growing under humid tropical conditions in Guadeloupe, Lesser Antilles. Carbohydrates were sampled in roots, stems and branches. Among pruned trees, trees in the T-6 harvest regime had the highest leaf fodder yield (0.73 kg tree(-1) year(-1)). High litter loss reduced leaf yield of T-12 trees, but compared with the other treatments, T-12 trees produced the most branch biomass (3.43 kg tree(-1)). Among treatments, P-2 trees had an intermediate leaf fodder yield and the lowest branch production. Sucrose, glucose and fructose were the most common sugars in all biomass compartments. Mannose, pinitol and an unidentified cyclitol were relatively abundant in branches. Root sugar and starch concentrations were unaffected by harvest regime. There was a significant interactive effect of harvest intensity and regrowth time on stem sugar concentration. Stem starch concentration was highest in T-12 trees. After a year of fodder harvesting, whole-tree reserves of nonstructural carbohydrates were highest in T-12 trees; however, a larger proportion of reserves were located in roots and stems of T-6 and P-2 trees. These reserves, which were not lost in pruning and contributed to regrowth of G. sepium after pruning, may explain the relatively small effects of harvesting regime on soluble sugar and starch concentrations.     

Regrowth and dry matter allocation in Quercus robur (L.) seedlings root pruned prior to transplanting

Two-year seedlings of Quercus robur (pedunculateoak) were root-pruned before transplanting in order toevaluate the importance of coarse versus fine roots onregrowth. Root systems were pruned by leaving c. 19,13 or 7 cm root from the root collar. Alternatively,coarse roots (>2 mm in diameter) were removed, leaving only the taproot and the fine roots (<2 mm)attached, or fine roots were removed from coarse rootsand taproot. Growth of shoots and roots after onegrowing season was compared to an unpruned controlunder standard nursery conditions. Seedlings rootpruned to 19, 13 or 7 cm were further tested undercompetition achieved by transplanting into a mixtureof clover and grass. Pruning of the root systemsignificantly reduced regrowth in terms of total plantDW in accordance with the severity of pruning, shootDW being more affected than root DW. Removal of coarseroots depressed final root DW whereas removal of fineroots reduced shoot DW and hence root:shoot ratioincreased. The study suggests that fine and coarseroots have different roles in root:shoot allocation.The competition test increased root:shoot ratioindicating that competition induced seedlings toallocate more of their resources into growth of theroot system.     

Carbon allocation and partitioning in aspen clones varying in sensitivity to tropospheric ozone

Clones of aspen (Populus tremuloides Michx.) were identified that differ in biomass production in response to O(3) exposure. (14)Carbon tracer studies were used to determine if the differences in biomass response were linked to shifts in carbon allocation and carbon partitioning patterns. Rooted cuttings from three aspen Clones (216, O(3) tolerant; 271, intermediate; and 259, O(3) sensitive) were exposed to either charcoal-filtered air (CF) or an episodic, two-times-ambient O(3) profile (2x) in open-top chambers. Either recently mature or mature leaves were exposed to a 30-min (14)C pulse and returned to the treatment chambers for a 48-h chase period before harvest. Allocation of (14)C to different plant parts, partitioning of (14)C into various chemical fractions, and the concentration of various chemical fractions in plant tissue were determined. The percent of (14)C retained in recently mature source leaves was not affected by O(3) treatment, but that retained in mature source leaves was greater in O(3)-treated plants than in CF-treated plants. Carbon allocation from source leaves was affected by leaf position, season, clone and O(3) exposure. Recently mature source leaves of CF-treated plants translocated about equal percentages of (14)C acropetally to growing shoots and basipetally to stem and roots early in the season. When shoot growth ceased (August 16), most (14)C from all source leaves was translocated basipetally to stem and roots. At no time did mature source leaves allocate more than 6% of (14)C translocated within the plant to the shoot above. Ozone effects were most apparent late in the season. Ozone decreased the percent (14)C translocated from mature source leaves to roots and increased the percent (14)C translocated to the lower stem. In contrast, allocation from recently mature leaves to roots increased. Partitioning of (14)C among chemical fractions was affected by O(3) more in source leaves than in sink tissue. In source leaves, more (14)C was incorporated into the sugar, organic acid and lipids + pigments fractions, and less (14)C was incorporated into starch and protein fractions in O(3)-treated plants than in CF-treated plants. In addition, there were O(3) treatment interactions between leaf position and clones for (14)C incorporation into different chemical fractions. When photosynthetic data were used to convert percent (14)C transported to the total amount of carbon transported on a mass basis, it was found that carbon transport was controlled more by photosynthesis in the source leaves than proportional changes in allocation to the sinks. Ozone decreased the total amount of carbon translocated to all sink tissue in the O(3)-sensitive Clone 259 because of decreases in photosynthesis in both recently mature and mature source leaves. In contrast, O(3) had no effect on carbon transport from recently mature leaves to lower shoots of either Clone 216 or 271, had no significant effect on transport to roots of Clone 216, and increased transport to roots of Clone 271. The O(3)-induced increase in transport to roots of Clone 271 was the result of a compensatory increase in upper leaf photosynthesis and a relatively greater shift in the percent of carbon allocated to roots. In contrast to those of Clone 271, recently mature leaves of Clone 216 maintained similar photosynthetic rates and allocation patterns in both the CF and O(3) treatments. We conclude that Clone 271 was more tolerant to O(3) exposure than Clone 216 or 259. Tolerance to chronic O(3) exposure was directly related to maintenance of high photosynthetic rates in recently mature leaves and retention of lower leaves.     

Biomass dynamics of Erythrina lanceolata as influenced by shoot-pruning intensity in Costa Rica

Pruning of agroforestry trees, while reducing shade of the crops, usually reduces both biomass production and nitrogen fixation. Short pruning cycles are often not sustainable on the long run, because tree production declines over subsequent pruning cycles. We compared biomass and labile carbohydrate dynamics of Erythrina lanceolata Standley (Papilionaceae) shade trees under total and partial pruning regimes in a vanilla (Vanilla planifolia L.) plantation in South-western Costa Rica. The highest biomass production was measured in the unpruned control, followed by trees with 50% of the leaf pruned every three months, while total pruning every six months resulted in the lowest biomass pruduction. In the more productive treatments, a higher proportion of the production was in branches. Because, the N content of woody branches was high, they were important for nitrogen cycling. In the partial pruning treatment more nitrogen was returned to the soil from litter and woody branches than from pruned leaf. Sugar concentrations were not different between treatments and the dynamics of non-structural carbohydrates (sugar and starch) seems to depend more on plant phenology than pruning treatment. However, the starch concentrations in the total pruning were lower than in the other treatments.This revised version was published online in November 2005 with corrections to the Cover Date.     

Root distribution of Pinus pinaster, P. radiata, Eucalyptus globulus and E. kochii and associated soil chemistry in agricultural land adjacent to tree lines

We quantified the extent and distribution of roots of four commonly planted tree species (Eucalyptus globulus Labill., Pinus radiata D. Don, P. pinaster Aiton and E. kochii Maiden & Blakely subsp. plenissima C.A. Gardner) in agricultural land adjacent to tree lines, and examined the effect of soil type and root pruning on root morphology. Root distribution in soil adjacent to tree lines was mapped by a trench profile method at 13 sites on the south coast of Western Australia. Soil samples were collected to determine water content and fertility. The lateral extent of tree roots ranged from 10 m for E. kochii to 44 m for P. pinaster. This equated to between 1.5 and 2.5 times tree height (H) for E. globulus and Pinus spp. to 4H for E. kochii. Root density declined logarithmically with distance from the trees and was greatest for P. pinaster and least for E. globulus (P < 0.001). The rate of decrease in root density with distance from the trees was greatest for the Pinus spp. and least for E. kochii (P < 0.05). Root density was generally greatest in the top 0.5 m of the soil profile and decreased with increasing depth. This decrease was relatively gradual in the deep sands, but abrupt in clay subsoil. Root dry mass in the sandy top soil beyond 0.5H ranged between 1.0 and 55.5 Mg km(treeline) (-1) for 6-year-old E. kochii and 50-year-old P. pinaster, respectively. Soil water content generally increased with distance from the trees (P < 0.001). There was no evidence of reduced soil fertility in the top 1.4 m of the soil profile adjacent to the trees. Two to four years after trees had been root pruned, both the lateral extent and vertical distribution of roots were similar for pruned and unpruned trees. The density of roots < 2 mm in diameter was greater for root-pruned trees than for unpruned trees (P < 0.05). We conclude that the study species can compete with agricultural crops based on the lateral extent of their roots and the occurrence of greatest root density within 0.5 m of the soil surface.     

Carbon and phosphorus partitioning in Pinus serotina seedlings growing under hypoxic and low-phosphorus conditions

Ten-week-old pond pine (Pinus serotina Michx.) seedlings were grown in solution culture at 5 or 100 microM P and under aerobic or hypoxic solution conditions. After 6 and 10 weeks in the treatments, changes in relative growth rate (RGR), P acquisition and allocation, and carbohydrate partitioning were determined by analyzing tissue for total P, soluble sugars and starch. Six weeks of low-P growth conditions decreased seedling dry weight and the ratio of shoot dry weight to root dry weight (S/R) by 39 and 51%, respectively, in comparison to seedlings from the aerobic, high-P (control) treatment. Mean RGRs of shoots in the low-P treatment were reduced by 33%, whereas root growth was unaffected. After 10 weeks of low-P growth conditions, however, both shoot and root RGRs were significantly reduced, and plants had lower S/R ratios than in any other treatment. Slowed shoot growth was accompanied by starch and nonstructural carbohydrate accumulation in needles, indicating that needle growth was not limited by carbohydrate supply. Six weeks of low-P growth conditions decreased total seedling P by 75%, reflecting a 97% reduction in the net uptake rate (NUR). Shoot NUR as a fraction of seedling NUR was also greatly reduced in the low-P treatment, indicating that low-P growth conditions affected P translocation to the shoot more than P accumulation by roots. In contrast, 6 weeks of hypoxic growth conditions decreased total dry weight of seedlings in the high-P treatment by 41% relative to their aerobic counterparts. Root growth was affected more than shoot growth, however, and S/R ratios increased. After 10 weeks, S/R ratios doubled, primarily because of the reduction in root RGR. Nevertheless, roots of hypoxic seedlings contained a higher percentage of total seedling P than their aerobic counterparts. Net P acquisition per seedling decreased by more than 50% under hypoxic growth conditions, as a result of reductions in both root RGR and seedling NUR. Starch accumulation in shoots of hypoxic seedlings reflected reductions both in root growth and in transport of carbohydrates to nonwoody roots. Carbohydrate availability did not appear to be limiting growth of hypoxic woody roots, which are well-aerated internally, but it may have limited metabolic processes in nonwoody roots of seedlings from the high-P treatment.