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1.
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.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
In New Zealand poplars are commonly planted on moist, unstable pastoral hill country to prevent or reduce soil erosion, thereby maintaining hillslope integrity and pasture production. Mechanical reinforcement by poplar root systems aids slope stabilisation. Root mass and distribution were determined for three Populus deltoides × nigra ‘Veronese’ trees aged 5, 7 and 9.5 year planted as 3 m poles at 8 m × 8 m spacing on a hillslope near Palmerston North in the southern North Island. Most of the structural roots (≥2 mm diameter) were distributed in the top 40 cm of soil. Vertical roots penetrated to about 1.0 m, being the depth of the soil above a fragipan. Total structural root dry masses (excluding root crown) were 0.57, 7.8 and 17.90 kg for the trees aged 5, 7 and 9.5 year, respectively. Total structural root length was 79.4 m for the 5 year tree and 663.5 m for the 9.5 year tree. Surrounding trees were estimated to increase root mass density to 3 times and root length density to 4–5 times the contribution of the single tree at 9.5 year. The study indicated that root development of wide-spaced poplar trees on hillslopes was minimal in the first 5 years but then increased rapidly. These results suggest that poplar trees established from poles may take at least 5 years to develop a structural root network that will effectively bind soil.  相似文献   

5.
Fifteen, 1-year-old Populus maximowiczii Henry x P. nigra L. 'MN9' trees were decapitated and allowed to sprout. After 8 weeks, all had 6 to 10 coppice shoots. All shoots, except the tallest (dominant) shoot, were removed from five of the trees (pruned treatment), and shoot growth, gas exchange and carbohydrate status were compared in the pruned and unpruned trees. Although photosynthetic rate of recently mature leaves of pruned trees was approximately 50% greater than that of leaves on the dominant shoot of unpruned trees, and the dry weight of leaves of pruned trees was 37% greater than that of the leaves on the dominant shoot of unpruned trees, the shoot dry matter relative growth rate did not differ between treatments. Concentrations of water-soluble carbohydrates and starch in the uppper stem and leaves of the dominant shoot were similar in pruned and unpruned trees. However, relative to that of the dominant shoot in unpruned trees, the lower stem in pruned trees was depleted in both soluble carbohydrates and starch. Starch deposition, assessed as the quantity of (14)C-starch in tissues 24 h after a fully expanded source leaf was labeled with (14)CO(2), was 3.9 times greater in roots of pruned trees than in roots of unpruned trees. We conclude that early removal of all but the dominant shoot reduces the carbohydrate status of the roots and the lower portion of the stem by eliminating the excised shoots as a source of photosynthate.  相似文献   

6.
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.  相似文献   

7.
Tree root pruning is a potential tool for managing belowground competition when trees and crops are grown together in agroforestry systems. We investigated the effects of tree root pruning on shoot growth and root distribution of Alnus acuminata (H.B. & K.), Casuarina equisetifolia L., Grevillea robusta A. Cunn. ex R. Br., Maesopsis eminii Engl. and Markhamia lutea (Benth.) K. Schum. and on yield of adjacent crops in sub-humid Uganda. The trees were 3 years old at the commencement of the study, and most species were competing strongly with crops. Tree roots were pruned 41 months after planting by cutting and back-filling a trench to a depth of 0.3 m, at a distance of 0.3 m from the trees, on one side of the tree row. The trench was reopened and roots recut at 50 and 62 months after planting. We assessed the effects on tree growth and root distribution over a 3 year period, and crop yield after the third root pruning at 62 months. Overall, root pruning had only a slight effect on aboveground tree growth: height growth was unaffected and diameter growth was reduced by only 4%. A substantial amount of root regrowth was observed by 11 months after pruning. Tree species varied in the number and distribution of roots, and C. equisetifolia and M. lutea had considerably more roots per unit of trunk volume than the other species, especially in the surface soil layers. Casuarina equisetifolia and M. eminii were the tree species most competitive with crops and G. robusta and M. lutea the least competitive. Crop yield data provided strong evidence of the redistribution of root activity following root pruning, with competition increasing on the unpruned side of tree rows. Thus, one-sided root pruning will be useful in only a few circumstances.  相似文献   

8.
Although hydraulic redistribution has been observed for a range of tree species, including Eucalyptus kochii subsp. borealis (C. Gardner) D. Nicolle, there is limited direct evidence that water taken up by deep roots in moist soil is in fact exuded by shallow roots in dry soil. This paper reports an experiment designed to test this hypothesis. Water enriched with deuterium was added to the groundwater via a slotted tube at 4.5 m depth below 5-year-old E. kochii subsp. borealis trees. Nocturnal sap flow increased markedly immediately after deep irrigation, indicating that the trees were using water from this depth. Two weeks later, samples of surface soil and xylem water were found to contain levels of deuterium up to 30% higher than soils and xylem water from a control plot upslope of the main treatment plot. This is strong evidence that trees used groundwater and that efflux of important amounts of hydraulically redistributed water occurred via the roots of E. kochii subsp. borealis.  相似文献   

9.
Growth of graded sweetgum 3 years after root and shoot pruning   总被引：1，自引：0，他引：1  
Nursery grown 1–0 bareroot sweetgum seedlings were lifted and graded into two diameter classes (12–16 and 4–8 mm) during the dormant season. Large and small grades were top and/or root pruned and then outplanted on two sites in the lower Coastal Plain of the southeastern United States. Seedling shoots were pruned to 50% of tree height, a 5 cm stump, or no pruning. Seedling roots were pruned to a 15 cm length or left unpruned. Site affected survival but not growth. Smaller, top pruned seedlings performed worse on one site, probably due to greater weed competition. Large seedlings increased survival and growth which increased 3 year average plot volumes by 89%. Top pruning stimulated height growth, but reduced diameter growth and decreased third year seedling volumes. Root pruning did not affect seedling growth. Diameter growth may better indicate treatment impact that height, which has been most commonly used in previous studies.  相似文献   

10.
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.  相似文献   

11.
Swamy  S.L.  Mishra  A.  Puri  S. 《New Forests》2003,26(2):167-186
A study of an agrisilviculture system comprising Gmelina arborea and soybean (Glycine max) was conducted in the subhumid region of Central India. Above- and below-ground biomass production and distribution of coarse and fine roots were studied in 4-year-old G. arborea, planted at a spacing of 2 × 2 m, 2 × 3 m, 2 × 4 m and 2 × 5 m. The total biomass varied from 10.89 Mg ha–1 to 3.65 Mg ha–1 depending on the tree density. Among the different tree components, stemwood contributed maximum biomass (54.3–79.4%), followed by branches and leaves. Root distribution pattern showed that most of the coarse roots were distributed in the top 40 cm of soil, whereas fine roots were concentrated in the top 20 cm. Coarse root biomass decreased with an increase in spacing. The spread of roots was asymmetrical in trees planted at 2 × 2 m and 2 × 3 m spacings, while it was symmetrical in trees planted at wide spacings. No significant difference was observed in the fine root biomass in different stands. The root:shoot ratio increased with an increase in spacing. Crop (soybean) growth and productivity varied significantly and it increased with a decrease in tree density. Soybean yield varied between 1.5 Mg ha–1 to 2.1 Mg ha–1. The role of root architecture of G. arborea trees on productivity of crops under agri-silviculture system is discussed.  相似文献   

12.

Faidherbia albida is one of the scattered trees commonly intercropped with most cereals in Ethiopia due to its positive impacts. The tree is pruned for various purposes including for fencing and fuelwood. In this study, the impact of pruning on water relations of F. albida and on understorey wheat productivity was investigated. The on-farm study was conducted in Ejerssa Joro, semi-arid Ethiopia. Six mature trees were selected; three were fully pruned and three were left unpruned. Sap flow and leaf water potential were measured on these trees. Crop gas exchange, aboveground biomass and grain yield were measured under and outside tree canopies. The highest and the lowest sap volumes, recorded from unpruned F. albida, during the dry period, were 153 L day?1 and 20 L day?1, respectively. The highest and the lowest sap volumes were 13.4 L day?1 and 0.04 L day?1 recorded during the wet period. Wheat CO2 assimilation was highest (7.8 µmolm?2 s?1) at 1 m distance and declined away from the tree trunk under unpruned trees. Aboveground biomass and grain yield under unpruned treatments were significantly (P?<?0.05) higher than outside of canopy of same tree and outside canopies of pruned trees. Pruning reduced aboveground biomass and grain yield by 30% and 27%, respectively; despite the higher water uptake by unpruned trees. We recommend that intensive pruning of F. albida be discouraged and propose further studies on optimal pruning for increased food production and provision of tree products to meet farmers’ needs.

  相似文献   

13.
Root morphology, biomass, and (14)C distribution were studied in two 2-year-old Populus trichocarpa x P. deltoides hybrids, which originated from hardwood cuttings, to determine the pattern of root distribution in a plantation and to refine methods for root recovery. The trees were labeled with (14)CO(2) and harvested after a 72-hour chase period. Roots attached to each labeled tree were analyzed for morphological traits at the time of harvest. Detached roots from within a 1-m(3) volume of soil surrounding each tree were separated from the soil and sorted on the basis of rooting depth and root diameter. Lateral roots > 2 mm in diameter had a largely horizontal orientation at their point of origin from the cutting and extended horizontally up to 4 m from the cutting. This resulted in considerable overlap of root systems in the plantation. Results from (14)C labeling indicated that 24 +/- 4% (+/- SD) of the carbon exported from branches-labeled within two weeks after branch budset-was translocated to the root system. Dilution of the root (14)C label indicated that from 0 (> 5 mm diameter roots) to 75% (< 2 mm diameter roots) of the roots recovered from within the 1-m(3) volume of soil surrounding a harvested tree originated from other trees. Total root biomass was 6 +/- 1 Mg ha(-1) for both hybrids. Sixty percent of the root biomass was recovered directly from excavation, 16% from coarse-sieving excavated soil, and 24% from re-sorting sieved soil. The study indicated that root growth of hybrid poplars may be rapid and extensive and that detailed sorting of soil subsamples substantially improves the recovery of fine roots < 2 mm in diameter.  相似文献   

14.
Biomechanical characteristics of the root system of hornbeam (Carpinus betulus) were assessed by measuring Root Area Ratio (RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran. RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m. In total 123 root specimens were analyzed for tensile strength. Results indicate that in general, RAR decreases with depth, following a power function. The RAR values in up and down slopes have no significant statistical differences. In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m. The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively. The number of roots in the up and down slope trenches was not significantly different. In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function. The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively. Results of Spearman's bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots. The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, following a power law equation. Using ANCOVA, we found intraspecies variation of tensile strength.  相似文献   

15.
McJannet D  Vertessy R 《Tree physiology》2001,21(12-13):1001-1008
We conducted thinning trials in a 5-year-old Eucalyptus globulus ssp. globulus Labill plantation near Warrenbayne, northeastern Victoria, Australia, where soil salinization and waterlogging are common, and assessed treatment effects on tree growth, water use and survival. Half-hectare plots were thinned from the original density of 1100 stems ha(-1) to densities of 800, 600 and 400 stems ha(-1), and stem diameter increment, leaf area index, transpiration, canopy interception and depth of tree water source monitored for 21 months. Two drought periods occurred during the study, rainfall was 30% below the long-term average and there was severe mortality in all three plots. Analysis of deuterium abundance in soil and xylem water indicated that the trees accessed water only from the top meter of the soil profile. Transpiration rates were higher in the most heavily thinned plot than in the least thinned plot, which underwent a reduction in basal area during the study. The most heavily thinned plot increased in basal area by 10% during the study. Edge trees had significantly greater diameters than trees from the middle of the plots.  相似文献   

16.
The active root distribution pattern of mature rubber (Hevea brasiliensis Muell. Arg.) up to a lateral distance of 250 cm from the tree and to a soil depth of 90 cm was studied in an oxisol by employing 32P soil injection technique in Kerala, the state which accounts for 83% of rubber cultivation in India. The trees were aged 18 years and grown at a spacing of 4.9 × 4.9 m. The extent of absorption of applied 32P by the tree from various placements was assessed by radio assay of leaf and latex serum. Latex serum registered higher counts and variability was less compared to leaf indicating the suitability of latex serum as a potential source for radio assay for 32P studies in rubber. The results revealed that rubber is a surface feeder with 55% of the root activity confining to the top 10 cm of soil layer. Root activity declined with increasing depths and the concentration of physiologically active roots at 90 cm depth was only 6%. A more or less uniform distribution of root activity was noticed with respect to lateral distance indicating more extensive spread of lateral roots. Concentration of physiologically active roots in the surface layer suggests the possibility for competition under intercropped situation in mature plantations.  相似文献   

17.
Adventitious rooting is essential for vegetative propagation of woody species. We studied the effects of auxin and light on the development of adventitious roots in cuttings obtained from seedlings of Eucalyptus saligna Smith and E. globulus Labill in an attempt to characterize the adventitious rooting process and identify factors controlling rhizogenesis. Root development was scored as rooting percentage, root density (roots per rooted cutting), mean rooting time and root length. In both species, rooting time was reduced in the presence of auxin. Cuttings from 2-month-old E. saligna seedlings were responsive to lower auxin concentrations than comparable cuttings from E. globulus seedlings. Cuttings from 3-month-old E. saligna seedlings rooted promptly and rooting was not significantly affected by light conditions. In contrast, rooting of cuttings from 3-month-old E. globulus seedlings exhibited recalcitrant behavior and no roots were formed if illuminated during the root formation phase. Effective root regeneration of E. globulus cuttings was obtained by a 4-day exposure to 10 mg l(-1) IBA and culture in darkness during the root formation step. Loss of rooting capacity with seedling age was more pronounced in E. globulus than in E. saligna. The possibility of switching adventitious rooting off and on by manipulating light regime and exogenous auxin supply in E. globulus, and the constitutive nature of rooting in E. saligna may provide useful models for examining the rooting process at the biochemical and molecular levels in Eucalyptus.  相似文献   

18.
Fine root and nodule production and turnover in pruned 2- and 8-yr-old Erythrina poeppigiana (Walp.) O.F. Cook trees were estimated under humid tropical conditions by applying the compartment flow model (CFM) to fine root and nodule biomass and necromass measured in sequentially taken core samples. Shoot pruning intensities compared were complete pruning (i.e., complete removal of shoots) and partial pruning (i.e., retention of one branch on the pruned stump). The CFM provided reasonable estimates of nodule dynamics but did not apply to fine root data. Over a five-month observation period, nodule production in completely and partially pruned 2-yr-old trees was 58.2 and 115 g tree–1, respectively, and the corresponding values in 8-yr-old trees were 26.8 and 26.4 g tree–1. Senescent nodules and fine roots pass to soil organic matter via decomposition. Partially and completely pruned 2-yr-old trees added 95.4 and 50.4 g tree–1 decomposed nodules to soil, respectively. The respective value for 8-yr-old trees were 26.7 and 36.5g tree–1. Nodule and fine root turnover was compensated for by new production at 10–14 weeks after pruning. The retention of a branch on the pruned E. poeppigiana tree stump allows better fine root and nodule survival, and enhances tree biomass production.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

19.
Planting trees, in farm forestry enterprises, to control rising watertables is an increasing practice for both economic and environmental benefits. One central biophysical issue which determines the effectiveness of trees to control groundwater is the ability of trees to grow roots through degraded soils and take up groundwater. We investigated the effect of soil properties, especially the presence of shallow watertables and site preparation practice, on the vertical and horizontal distributions of Eucalyptus grandis W. Hill ex Maiden and Corymbia maculata (Hook.) K.D. Hill and L.A.S. Johnson roots. In order to improve the reliability of root data, we measured root growth and distribution by three different methods – (i) number of roots intercepting the vertical plane of the soil profile, (ii) root length density in soil cores taken at different depths but in the horizontal plane of the profile, and (iii) root length density in soil cores in the vertical plane at different radial positions from trees and compared the results. Two experimental sites were established in flood-irrigated, farm forestry plantations on contrasting soils in the Murray Riverina region of south-eastern Australia. At one site (Norwood Park), we studied a 58-month-old stand of E. grandis growing in clay loam overlaying medium clay, saline, sodic and alkaline subsoil with a saline (11.5 dS m−1) watertable at 2.8 m depth. Here, there were few roots growing above the watertable. The Karawatha site had adjacent stands of 46-month old E. grandis and C. maculata growing in a sandy, neutral and non-saline soil with a shallow (3.1 m deep) non-saline (2.8 dS m−1) watertable. Here roots proliferated above the watertable in both species but to a much greater extent under C. maculata than under E. grandis. Root distributions in the surface soil were similar at all sites but differences in root growth in the capillary zones paralleled differences in groundwater uptake by trees. We conclude (i) that appropriate matching of species with site characteristics, especially soil and groundwater properties, will enhance tree growth and groundwater uptake and (ii) that extensive planting of C. maculata over non-saline watertables maximises the chances of achieving the multiple objectives of regional groundwater control, fast growth rates and reduced irrigation demand.  相似文献   

20.
Fast-growing exotic trees are widely planted in the tropics to counteract deforestation; however, their patterns of water use could be detrimental to overall ecosystem productivity through their impact on ecosystem water budget. In a comparative field study on seasonal soil-plant water dynamics of two exotic species (Cupressus lusitanica Mill. and Eucalyptus globulus Labill.) and the indigenous Podocarpus falcatus (Thunb.) Mirb. in south Ethiopia, we combined a 2.5-year record for climate and soil water availability, natural-abundance oxygen isotope ratios (delta(18)O) of soil and xylem water, destructive root sampling and transpiration measurements. Soil was generally driest under C. lusitanica with its dense canopy and shallow root system, particularly following a relatively low-rainfall wet season, with the wettest soil under E. globulus. Wet season transpiration of C. lusitanica was twice that of the other species. In the dry season, P. falcatus and C. lusitanica reduced transpiration by a factor of six and two, respectively, whereas E. globulus showed a fivefold increase. In all species, there was a shift in water uptake to deeper soil layers as the dry season progressed, accompanied by relocation of live fine root biomass (LFR) of C. lusitanica and P. falcatus to deeper layers. Under P. falcatus, variability in soil matric potential, narrow delta(18)O depth gradients and high LFR indicated fast water redistribution. Subsoil water uptake was important only for E. globulus, which had low topsoil LFR and tap roots exploiting deep water. Although P. falcatus appeared better adapted to varying soil water availability than the exotic species, both conifers decreased growth substantially during dry weather. Growth of E. globulus was largely independent of topsoil water content, giving it the potential to cause substantial dry-season groundwater depletion.  相似文献   

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