Aboveground biomass and nitrogen in four short-rotation woody crop species growing with different water and nutrient availabilities

We quantified the effect of water and nutrient availability on aboveground biomass and nitrogen accumulation and partitioning in four species from the southeastern United States, loblolly pine (Pinus taeda), slash pine (Pinus elliottii), sweetgum (Liquidambar styraciflua), and sycamore (Platanus occidentalis). The 6-year-old stands received five levels of resource input (control, irrigation with 3.05 cm water week⁻¹, irrigation + 57 kg N ha⁻¹ year⁻¹, irrigation + 85 kg N ha⁻¹ year⁻¹, and irrigation + 114 kg N ha⁻¹ year⁻¹). Irrigation significantly increased foliage, stem, and branch biomass for sweetgum and sycamore, culminating in 103% and 238% increases in total aboveground biomass. Fertilization significantly increased aboveground components for all species resulting in 49, 58, 281, and 132% increases in total aboveground biomass for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Standing total aboveground biomass of the fertilized treatments reached 79, 59, 48, and 54 Mg ha⁻¹ for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Fertilization increased foliar nitrogen concentration for loblolly pine, sweetgum, and sycamore foliage. Irrigation increased total stand nitrogen content by 6, 14, 93, and 161% for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Fertilization increased total nitrogen content by 62, 53, 172, and 69% with maximum nitrogen contents of 267, 212, 237, and 203 kg ha⁻¹ for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Growth efficiency (stem growth per unit of leaf biomass) and nitrogen use efficiency (stem growth per unit of foliar nitrogen content) increased for the sycamore and sweetgum, but not the loblolly or slash pine.     

Mean canopy stomatal conductance responses to water and nutrient availabilities in Picea abies and Pinus taeda

We compared sap-flux-scaled, mean, canopy stomatal conductance (GS) between Picea abies (L.) Karst. in Sweden and Pinus taeda (L.) in North Carolina, both growing on nutritionally poor soils. Stomatal conductance of Picea abies was approximately half that of Pinus taeda and the sensitivity of GS in Picea abies to vapor pressure deficit (D) was lower than in Pinus taeda. Optimal fertilization increased leaf area index (L) two- and threefold in Pinus taeda and Picea abies, respectively, regardless of whether irrigation was increased. Although it increased L, fertilization did not increase GS in Picea abies unless irrigation was also provided. In Pinus taeda growing on coarse, sandy soils, the doubling of L in response to fertilization reduced GS sharply unless irrigation was also provided. The reduction in GS with fertilization in the absence of irrigation resulted from the production of fine roots with low saturated hydraulic conductivity. When Pinus taeda received both fertilization and irrigation, the increase in L was accompanied by a large increase in GS. In Pinus taeda, a reference GS (defined as GS at D = 1 kPa; GSR) decreased in all treatments with decreasing volumetric soil water content (theta). In Picea abies, theta varied little within a treatment, but overall, GSR declined with theta, reaching lowest values when drought was imposed by the interception of precipitation. Despite the large difference in GS both between Picea abies and Pinus taeda and among treatments, stem growth was related to absorbed radiation, and stem growth response to treatment reflected mostly the changes in L.     

Growth versus storage: responses of Mediterranean oak seedlings to changes in nutrient and water availabilities

We compare dry mass (DM) and storage of starch (St) and nitrogen (N) in seedlings of three Mediterranean oaks, two evergreens (Quercus coccifera L. and Q. ilex L. subsp. ballota (Desf.) Samp) and one deciduous (Q. faginea Lam.), across different scenarios of nutrient and water availabilities. Three fertilization (5, 50 and 200 mg of N per plant and growing period) and watering (28–39, 55–71 and 70–85 g H₂O 100 g _soil ^?1 gravimetric soil water) treatments were applied to current-year seedlings between May and October 2002 in two independent experiments. The three species showed a similar response to fertilization, storing nitrogen instead of increasing biomass, in agreement with adaptations to nutrient-poor habitats. However, they differed in their responses to water, reflecting the different water requirements in the field: Q. coccifera, from arid zones, showed no response to water regarding DM and St; Q. faginea, from humid zones, required higher water availability to simultaneously increase growth and storage; while Q. ilex, spanning over most of the water availability range, exhibited a balanced increase of both functions when water increased moderately. In the two evergreen species, N concentration increased with water supply, whereas the reverse occurred in Q. faginea. The latter species favoured growth over storage at moderate water supply (according to its more competitive strategy), although it was the species which accumulated more St and N at the end of the experiments (autumn).     

Free amino acids and protein in Scots pine seedlings cultivated at different nutrient availabilities

Scots pine (Pinus sylvestris L.) seedlings of a provenance from northern Sweden were cultivated hydroponically for 7 weeks in a climate chamber. The nutrient solution contained either 2.5 (low-N) or 50 (high-N) mg N l(-1) with other essential elements added in a fixed optimal proportion to the nitrogen. After 5 and 7 weeks, the seedlings were analyzed for growth, total nitrogen and other essential nutrients, protein and free amino acids. Low-N seedlings grew more slowly and had higher root/shoot ratios than high-N seedlings. With respect to total nitrogen, the effect of the lower nutrient supply was mainly on the nitrogen content of the whole plant and the allocation of nitrogen among tissues, not on tissue nitrogen concentration. This was also the case for potassium, phosphorus, calcium and magnesium. The proportions by weight among these macronutrients in the whole seedlings were similar in both nutrient regimes. The proportion and concentration of sulfur were significantly lower in low-N seedlings than in high-N seedlings, because of a lower net uptake of sulfur than of other macronutrients. The shoot, needles and stem of low-N seedlings had higher concentrations of free amino acids and lower concentrations of protein than the shoot, needles and stem of high-N seedlings. Arginine dominated the pool of free amino acids in the low-N seedlings, whereas glutamine predominated in the high-N seedlings. We conclude that Scots pine seedlings accumulated soluble nitrogen as arginine when net protein synthesis was limited by factors other than nitrogen availability. Nutritional imbalance, as revealed by growth characteristics and a suboptimal proportion and concentration of sulfur in the seedlings, probably affected synthesis of S-amino acids, resulting in the diversion of assimilated nitrogen to arginine instead of protein.     

Production of micro-cuttings from acorns to test the plasticity of response to contrasting soil water regimes

We collected acorns from selected Quercus robur and Quercus petraea mother trees growing at stations with different depths to the water table. We produced pairs of micro-cuttings from these single acorns. The obtained pairs of cuttings represented phenotypes of high similarity according to photosynthetic parameters. These pairs of cuttings were used to test the plasticity of response to contrasting water regimes. For each pair, one cutting was submitted to drought and the other was submitted to waterlogging. Drought response was recorded according to gas exchange traits (stomatal closure and water use efficiency). The response to waterlogging was recorded according to the capacity to form hypertrophied lenticels and to maintain the CO₂ assimilation rate. Intermediary phenotypes presenting both high water use efficiency and the capacity to develop hypertrophied lenticels were expected.     

Citrus response to salinity: growth and nutrient uptake

To determine the effects of salinity on relative growth rate (RGR), net assimilation rate on a leaf weight basis (NAR(w)), leaf weight ratio (LWR), and nutrient uptake and utilization of citrus, we grew four citrus rootstocks (sour orange, Cleopatra mandarin, Carrizo citrange and Citrus macrophylla) in nutrient solutions containing 0, 10, 20, 40 or 80 mM NaCl for 20, 40 or 60 days. For each element analyzed, specific absorption rate (SAR) and specific utilization rate on a leaf basis (SUR(L)) were calculated for the period between Days 40 and 60. Relative growth rate decreased with time for all treatments and rootstocks. Salt treatment significantly reduced both RGR and NAR(w), whereas LWR showed no definite trend. In all rootstocks, NAR(w), but not LWR, was significantly correlated with RGR, indicating that NAR(w) was an important factor underlying the salinity-induced differences in RGR among the citrus rootstocks. At Day 60, salinity had a significant effect on leaf concentrations of Cl, Na, K, Ca, Mg, P, Fe, Mn and Zn and on the SAR and SUR(L) of most elements. In general, RGR was correlated with SAR and SUR(L). Therefore, in addition to osmotic effects and the inhibitory effects of high concentrations of Cl(-) and Na(+), an imbalance of essential nutrients may also contribute to the reduction in plant growth under saline conditions.     

Growth,nutrient, water relations,and gas exchange in a holm oak plantation in response to irrigation and fertilization

Eighty 6-years-old Quercus ilex L. subsp. ballota seedlings planted on a former agricultural land were subjected during two growing seasons to one of four treatments: fertilization and irrigation, irrigation, fertilization, and control. Seasonal and between-treatment variations on water relations, gas exchange parameters, growth and nutrient status were analyzed. Water potential () was related to climatic conditions. Thus, the frequent rain storms during the summer allow seedlings to maintain relatively high values, joined to moderate photosynthetic activity. Differences on , photosynthesis and stomatal conductance due to irrigation were shown at the onset and end of growth, related with lower water availability. Fertilization had a greater effect on growth than irrigation. Both fertilization and irrigation positively affected the relative increment on leaf nutrient concentration at the end of the second year. The results indicate that water availability was not a limited factor, thus irrigation is not justified; while fertilization improve growth.     

Interactive effects of nitrogen and water availabilities on gas exchange and whole-plant carbon allocation in poplar

Cuttings of balsam spire hybrid poplar (Populus trichocarpa var. Hastata Henry x Populus balsamifera var. Michauxii (Dode) Farwell) were grown in sand culture and irrigated every 2 (W) or 10 (w) days with a solution containing either 3.0 (N) or 0.5 (n) mol nitrogen m(-3) for 90 days. Trees in the WN (control) and wn treatments had stable leaf nitrogen concentrations averaging 19.4 and 8.4 mg g(-1), respectively, over the course of the experiment. Trees in the Wn and wN treatments had a similar leaf nitrogen concentration, which increased from 12.0 to 15.8 mg g(-1) during the experiment. By the final harvest, mean stomatal conductances of trees in the wN and wn treatments were less than those of trees in the Wn and WN treatments (1.8 versus 4.6 mm s(-1)). Compared to the WN treatment, biomass at the final harvest was reduced by 61, 72 and 75% in the Wn, wN and wn treatments, respectively. At the final harvest, WN trees had a mean total leaf area of 4750 +/- 380 cm(2) tree(-1) and carried 164 +/- 8 leaves tree(-1) with a specific leaf area of 181 +/- 16 cm(2) g(-1), whereas Wn trees had a smaller mean total leaf area (1310 +/- 30 cm(2) tree(-1)), because of the production of fewer leaves (41 +/- 6) with a smaller specific leaf area (154 +/- 2 cm(2) g(-1)). A greater proportion of biomass was allocated to roots in Wn trees than in WN trees, but component nitrogen concentrations adjusted such that there was no Wn treatment effect on nitrogen allocation. Compared with WN trees, rates of photosynthesis and respiration per unit weight of tissue of Wn trees decreased by 28 and 31%, respectively, but the rate of photosynthesis per unit leaf nitrogen remained unaltered. The wN and Wn trees had similar leaf nitrogen concentrations; however, compared with the Wn treatment, the wN treatment decreased mean total leaf area (750 +/- 50 cm(2) tree(-1)), number of leaves per tree (29 +/- 2) and specific leaf area (140 +/- 6 cm(2) g(-1)), but increased the allocation of biomass and nitrogen to roots. Net photosynthetic rate per unit leaf nitrogen was 45% lower in the wN treatment than in the other treatments. Rates of net photosynthesis and respiration per unit weight of tissue were 48 and 33% less, respectively, in wN trees than in Wn trees.     

Soil water response to precipitation in different microtopographies on the semi-arid Loess Plateau,China

Soil water is an important factor restricting afforestation on the semi-arid Loess Plateau.The microtopography of the loess slope has changed the distribution pattern of soil water on the slope.To improve water utilization efficiency and optimize afforestation configuration patterns,the relationship between soil water and precipitation at micro-topographic scale must be studied.We used time series analysis to study the temporal variation of soil water and its response to precipitation in four kinds of micro-topographies and undisturbed slope on loess slopes.Micro-topographies significantly influenced soil water distribution and dynamics on the slopes.Soil water stored in the platform,sinkhole,and ephemeral gully influenced subsequent soil water for 4 weeks,whereas soil water stored in the scarp and undisturbed slope could influence soil water for 2 weeks.It took 12 weeks,10 weeks,18 weeks,6 weeks,and 12 weeks for precipitation to reach the deeper soil layer in the platform,sinkhole,scarp,ephemeral gully,and undisturbed slope,respectively.These soil water characteristics in different micro-topographies are vital factors that should be taken into consideration when undertaking afforestation on the Loess Plateau.     

不同水分管理措施对抽梢期油茶树体养分含量的影响

为探讨不同水分管理对抽梢期油茶树体养分状况的影响,从而为油茶水分管理提供科学依据。以‘长林4号’5年生油茶为试材,设置滴灌+花生秆+稻草、滴灌+生态膜、滴灌+油茶壳、滴灌、滴灌+黑地膜、花生秆+稻草、生态膜、油茶壳、黑地膜、不覆盖不灌水(CK)共10种水分管理措施,测定不同水分管理措施下抽梢期树体各器官氮、磷、钾养分含量,并对各养分分布特征进行了分析。结果表明:不同水分管理措施对抽梢期油茶老叶和根N、P、K含量、新叶P、K含量以及枝条P养分含量影响差异显著。不同水分管理措施对抽梢期老叶、根养分含量具有明显促进作用,对当年生新叶和枝条的影响比较小。滴灌+花生秆+稻草处理和滴灌+黑地膜处理更有利于养分的积累,滴灌+花生秆+稻草处理是最经济最环保的水分管理措施。     

Seasonal nutrient dynamics in white pine and white spruce in response to environmental manipulation

Seasonal retranslocation in white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) was examined in response to silvicultural treatments (scarification, annual fertilization application, and annual control of competing vegetation with herbicide) that changed both environmental conditions and the growth rate of the trees. Four years after plantation establishment and initial treatment, nutrient accumulation in current-year needles of white pine and retranslocation from 1-year-old needles were increased following the vegetation control treatment, which increased resource availability (nutrients, water and light) and, hence, growth rate. Nutrient accumulation also increased in current-year white spruce needles following the same treatment, whereas retranslocation decreased in 1-year-old white spruce needles. Correlations of retranslocation (N, P and K) with growth rate (shoot biomass increment) showed a strong positive relationship for white pine and a negative relationship for white spruce. Retranslocation of K was correlated with foliar and soil K concentrations; the availability of this nutrient was also significantly reduced by vegetation control. A general theory for the control of nutrient retranslocation in conifers, which is not based exclusively on either sink strength or soil nutrient availability, is proposed. We conclude that retranslocation response is species specific and related to the potential phenotypic growth response to changing environmental conditions and to short-term imbalance in the supply versus the demand for nutrients.     

Management of water and nutrient relations in European forests

The term ‘Europe’ covers a wide range of forest types and scientific philosophies, effectively preventing generalised statements. Water is regularly deficient only in Mediterranean regions and, apart from careful weeding, little active management is undertaken. In more-northern and western regions, much effort has been directed towards removal of excess soil water or providing locally drained planting sites. By contrast, nutrition is relatively amenable to the dictates of management, and relevant research dates back over a century. The greatest demands for soil nutrients occur while the green crown is being formed; thereafter efficient cycling within the tree means a much-reduced uptake. In consequence, responses to fertilizer are most likely at the establishment phase; in Europe, deficiencies have been identified for N, P, K, Mg, B and Cu. Most forest departments have now drawn up guidelines for fertilizer applications based on empirical experimentation, sometimes making use of foliar analysis. A particular feature of northern and western coniferous forests is a late-rotation N deficiency resulting from immobilization of this element in the humus layer. This was the first nutritional problem to attract the attention of forest scientists and it has now been very thoroughly explored.

It seems unlikely that the future will see any heightened interest in the management of water. In relation to nutrition management, the search must be to develop diagnostic and ameliorative measures that ensure minimum adverse effects on the environment.     

Water-use efficiency in cork oak (Quercus suber) is modified by the interaction of water and light availabilities

We studied the interaction of light and water on water-use efficiency in cork oak (Quercus suber L.) seedlings. One-year-old cork oak seedlings were grown in pots in a factorial experiment with four light treatments (68, 50, 15 and 5% of full sunlight) and two irrigation regimes: well watered (WW) and moderate drought stress (WS). Leaf predawn water potential, which was measured at the end of each of two cycles, did not differ among the light treatments. Water-use efficiency, assessed by carbon isotope composition (delta(13)C), tended to increase with increasing irradiance. The trend was similar in the WW and WS treatments, though with lower delta(13)C in all light treatments in the WW irrigation regime. Specific leaf area increased with decreasing irradiance, and was inversely correlated with delta(13)C. Thus, changes in delta(13)C could be explained in part by light-induced modifications in leaf morphology. The relationship between stomatal conductance to water vapor and net photosynthesis on a leaf area basis confirmed that seedlings in higher irradiances maintained a higher rate of carbon uptake at a particular stomatal conductance, implying that shaded seedlings have a lower water-use efficiency that is unrelated to water availability.     

Functional traits and plasticity in response to light in seedlings of four Iberian forest tree species

We investigated the differential roles of physiological and morphological features on seedling survivorship along an experimental irradiance gradient in four dominant species of cool temperate-Mediterranean forests (Quercus robur L., Quercus pyrenaica Willd., Pinus sylvestris L. and Pinus pinaster Ait.). The lowest photochemical efficiency (F(v)/F(m) in dark-adapted leaves) was reached in deep shade (1% of full sunlight) in all species except Q. robur, which had the lowest photochemical efficiency in both deep shade and 100% of full sunlight. Species differed significantly in their survival in 1% of full sunlight but exhibited similar survivorship in 6, 20 and 100% of full sunlight. Shade-tolerant oaks had lower leaf area ratios, shoot to root ratios, foliage allocation ratios and higher rates of allocation to structural biomass (stem plus thick roots) than shade-intolerant pines. Overall phenotypic plasticity for each species, estimated as the difference between the minimum and the maximum mean values of the ecophysiological variables studied at the various irradiances divided by the maximum mean value of those variables, was inversely correlated with shade tolerance. Observed morphology, allocation and plasticity conformed to a conservative resource-use strategy, although observed differences in specific leaf area, which was higher in shade-tolerant species, supported a carbon gain maximization strategy. Lack of a congruent suite of traits underlying shade tolerance in the studied species provides evidence of adaptation to multiple selective forces. Although the study was based on only four species, the importance of ecophysiological variables as determinants of interspecific differences in survival in limiting light was demonstrated.     

Leaf water relations of Eucalyptus cloeziana and Eucalyptus argophloia in response to water deficit

Leaf water relations responses to limited water supply were determined in 7-month-old plants of a dry inland provenance of Eucalyptus argophloia Blakely and in a humid coastal provenance (Gympie) and a dry inland provenance (Hungry Hills) of Eucalyptus cloeziana F. Muell. Each provenance of E. cloeziana exhibited a lower relative water content at the turgor loss point, a lower apoplastic water content, a smaller ratio of dry mass to turgid mass and a lower bulk modulus of elasticity than the single provenance of E. argophloia. Osmotic potential at full turgor and water potential at the turgor loss point were significantly lower in E. argophloia and the inland provenance of E. cloeziana than in the coastal provenance of E. cloeziana. There was limited osmotic adjustment in response to soil drying in E. cloeziana, but not in E. argophloia. Between-species differences in water relations parameters were larger than those between the E. cloeziana provenances. Both E. cloeziana provenances maintained turgor under moderate water stress through a combination of osmotic and elastic adjustments. Eucalyptus argophloia had more rigid cell walls and reached lower water potentials with less reduction in relative water content than either of the E. cloeziana provenances, thereby enabling it to extract water from dryer soils.     

Response of water and nutrient fluxes to improvement fellings in a tropical montane forest in Ecuador

Management of natural forests might be one option to reduce the high deforestation rate in Ecuador. We therefore evaluated the response of water and nutrient cycles in a natural tropical montane forest to improvement fellings with the aim of favoring economically valuable target trees which will later be harvested with additional ecosystem impacts not considered here.     

Photosynthetic capacity of leaves of Eucalyptus globulus (Labill.) growing in the field with different nutrient and water supplies

A technique was tested for obtaining water relations parameters from individual fascicles of loblolly pine needles by the pressure-volume curve method. Comparisons were made between parameters derived from (1) individual fascicles that were rehydrated in a pressure chamber after being removed from the shoot and (2) fascicles that were rehydrated on the shoot. Estimates of tissue osmotic potential for needles rehydrated by the two methods were significantly different for needles from terminal shoots, but not significantly different for needles from lateral shoots. Similarly, a significant difference in the estimated tissue elasticity at zero water potential was noted for needles on terminal shoots, but not for those on lateral shoots. It is suggested that differences due to rehydration method are related to the duration of the rehydration period and not the choice of technique. The use of fascicles of needles, rehydrated after detachment, allows repeated estimation of the tissue water relations of a single conifer shoot.     

Long term growth responses of loblolly pine to optimal nutrient and water resource availability

A factorial combination of four treatments (control (CW), optimal growing season water availability (IW), optimum nutrient availability (FW), and combined optimum water and nutrient availability (FIW)) in four replications were initiated in an 8-year-old Pinus taeda stand growing on a droughty, nutrient-poor, sandy site in Scotland County, NC and maintained for 9 years. Results for the first 4 years after treatment initiation at this study were first reported by Albaugh et al. [For. Sci. 44 (1998) 317]. The site is primarily nutrient limited and all measured stand parameters (height, basal area, leaf area index, live crown length, stem mass accumulation, current annual stem mass increment) were increased with fertilization throughout the study period. Irrigation effects were also positive for these parameters but the increases were much smaller than those found with fertilization. For example, 9 years after treatment initiation, standing stem mass was increased 100 and 25% by fertilization and irrigation, respectively, while current annual increment of stem biomass production was increased 119 and 23% by fertilization and irrigation, respectively. Interestingly, stem density (stems ha⁻¹) was not significantly affected by treatment in any year of the study. Growth efficiency (stem mass increment per unit leaf area index) was 1.9 Mg ha⁻¹ per year per LAI for CW and influenced by treatment with IW, FW, and FIW achieving growth efficiencies of 2.4, 2.7 and 2.9 Mg ha⁻¹ per year per LAI, respectively. Growth efficiency appeared to be relatively stable in the last 4 years of the study. Ring specific gravity was measured in the third, fourth, and fifth years after treatment initiation. An average reduction in ring specific gravity of 7.5% was observed with fertilization while irrigation had little effect on specific gravity in any year measured. The continuation of high growth rates with no observable growth decline in the treated stands throughout the 9-year study may be a function of the age of the stands when treatments were initiated (8 years), the very poor initial nutrient and moisture availability, and/or the application of an ongoing optimum nutrient regime at the site. The fertilized plots are now at or near an age and a size when a commercial harvest would be feasible. For the stand conditions at this site, then, the optimum nutrient availability plots have achieved high productivity throughout the economic life of the stand without measurable declines in stand productivity.     

Foraging ability and growth performance of four subtropical tree species in response to heterogeneous nutrient environments

Considering the ubiquitous heterogeneity in spatial distribution of soil nutrients, we conducted a pot experiment to investigate the foraging traits and growth performance of four important subtropical tree species in a heterogeneous nutrient environment. The tested species exhibited large differences in foraging traits as well as growth benefits obtained from root foraging. Pinus massoniana, Schima superba and Liriodendron chinese all showed a higher degree of root morphological plasticity (expressed as relative fine root mass difference; RFRMD) than Cunninghami lanceolata (P < 0.05). P. massoniana exhibited the largest degree of morphological plasticity, followed by L. chinese and S. superba, whereas there were no significant differences in RFRMD among the three species. S. superba was the only species that exhibiting both morphological plasticity and physiological plasticity. Both P. massoniana and S. superba exhibited greater whole-seedling biomass and high sensitivity in response to nutrient heterogeneity, resulting from both types of plasticity. In contrast, both types of root plasticity were poor for C. lanceolata, resulting in poor growth benefit in heterogeneous environments. As for L. chinese, the root proliferation in nutrient-rich patches occurred at the expense of depressed root growth in other parts of the root system, leading to the lack of increment in total root biomass and nutrient absorption in heterogeneous environments. Our results provide insight and practical advice for silviculture and forest management.     

Leaf nutrient variation in mature carob (Ceratonia siliqua) trees in response to irrigation and fertilization

Seasonal variations in leaf nitrogen, phosphorus and potassium concentrations were studied in a mature carob (Ceratonia siliqua L. cv "Mulata") orchard subjected to a 4-year irrigation and fertilization experiment. Three irrigation regimes (0, 50 and 100%), based on the evaporation values obtained from a class A pan, were tested in combination with two nitrogen (N) supply regimes in which 21 kg ha(-1) year(-1) (low-N) and 63 kg ha(-1) year(-1) (high-N) were supplied as ammonium nitrate. Leaf nitrogen concentration increased throughout the experiment, independently of treatments. There were no significant differences in leaf N concentration between trees in the high-N and low-N treatments. Irrigation regimes had no effect on leaf mineral concentration but influenced the amount of leaves shed and slightly modified the pattern of leaf shedding that occurred during the summer drought period. Nutritional balances between N and P and N and K were both closely and significantly correlated. Potassium was translocated from leaves to fruits during spring, independently of treatments. Severe water stress periods occurring during spring or autumn induced shedding of leaves leading to nutrient mobilization. Nutrient retranslocation during these drought periods may represent an adaptive mechanism. Nitrogen retranslocation was higher for trees in the high-N treatments than for trees in the low-N treatments, whereas phosphorus retranslocation was independent of the irrigation and fertilization treatments.