Nonfertilized Trees Research Articles

Modeling branch attributes and biomass for Catalpa bungei plantations under various fertilization regimes

The development and morphology of branches, a crucial step in producing high-quality large-diameter lumber, may be influenced by fertilization. The response of branch attributes to different fertilization regimes, however, is still poorly understood. The Catalpa bungei plantations, which had been growing for 6 years in northern China, were chosen to study how various fertilization measures affected branch attributes. The two fertilization techniques used were hole fertilization (HF) and water and fertilizer integration (WF), with no fertilization (CK) as a control. The quantity, density, morphology (e.g., diameter, length, and angle), and position (e.g., height and orientation) of branches, and organ biomass of 18 standard trees (total of 516 branches) were investigated. The results demonstrated a considerable increase in tree height, diameter at breast height (DBH), canopy ratio, branch quantity, and organ biomass following the addition of fertilizer. Both the maximum branch diameter and the number of branches rose with fertilization. Following fertilization, the number of branches rose by 16% (HF) and 28% (WF) compared to non-fertilized trees, while the maximum branch diameter increased by 3.5% (HF) and 17.3% (WF), respectively. WF led to an increase in the number of branches and largest branch diameter in comparison to CK and HF. The length, angle, and diameter of branches, however, were not affected significantly by different fertilization treatments. There were roughly equal amounts of branches in four orientations. The mixed-model analysis revealed that the number of branches was positively correlated with branch density and tree height. The branch diameter increased with the increase of branch length and angle. The branch length was negatively correlated with branch height and angle. The branch angle showed a larger angle at the bottom of the canopy. Tree height plus diameter at breast height combined, or just the diameter at breast height indicator alone, can both reliably predict the total biomass of trees. The branch models created in this research may offer some theoretical backing for understanding the crown dynamics of valuable tree species in northern China.

Effects of fertilization on radial growth of Pinus pinea explored hourly using dendrometers

BackgroundStone pine (Pinus pinea), a drought-resistant species, has significant socio-economic benefits and increasing interest for the establishment of productive plantations in several countries, especially in a climate change context. Monitoring hourly stem diameter variations contributes to the understanding of the tree-growth response to changes in environmental conditions and management. By monitoring the diameter expansion of tree stems, high-resolution band dendrometers were used to study the development of adult trees growing in a semi-arid coastal environment of central Chile under fertilized and non-fertilized soil conditions through the span of a year.ResultsShort cycles (< 21 h) were few in fertilized and non-fertilized trees (6 and 4, respectively), whereas long cycles (> 28 h) occurred at a higher frequency in fertilized trees (16 vs 6). Most of the circadian cycles were regular (24 ± 3 h). The longest cycle duration (59 h) was observed in fertilized trees during spring. In all seasons, each phase of the circadian cycle, especially during the stem diameter increment phase (P3, irreversible growth), started earlier in fertilized than in control trees. P3 duration was significantly longer in fertilized than in control trees in springtime. The maximum shrinkage (P1) was observed in summer for both treatments. Stem diameter increased faster in fertilized than in control trees throughout the year, with the highest accumulation occurring in spring and the lowest in autumn. The daily variability pattern showed lower growth under high temperature across seasons.ConclusionsThis study highlights the importance of fertilization in enhancing stone pine diameter growth. This cultural practice should be further explored to contribute to the mitigation of climate change effects in semi-arid environments.

Nutrient Uptake in Huanglongbing-affected Sweet Orange: Transcriptomic and Physiological Analysis

Since the advent of Huanglongbing [HLB (Candidatus Liberibacter asiaticus)] in Florida, several preliminary reports have emerged about the positive effects of mineral nutrition on the performance of HLB-affected citrus (Citrus sp.) trees. HLB-affected trees are known to undergo significant feeder root loss. Therefore, studies have focused on foliar nutrient application instead of soil-applied nutrients speculating that the HLB-affected trees root systems may not be competent in nutrient uptake. Some studies also suggest that HLB-affected trees benefit from micronutrients at higher than the recommended rates; however, the results are often inconclusive and inconsistent. To address this, the goal of the present study was to evaluate the nutrient uptake efficiency and the quantitative and qualitative differences in nutrient uptake of HLB-affected trees. HLB-affected and healthy sweet orange (Citrus sinensis) trees were grown in a 100% hydroponic system with Hoagland solution for 8 weeks. The trees were deprived of any fertilization for 6 months before the transfer of trees to the hydroponic solution. Altogether, the four treatments studied in the hydroponic system were healthy trees fertilized (HLY-F) and not fertilized (HLY-NF), and HLB-affected trees fertilized (HLB-F) and not fertilized (HLB-NF). HLY-F and HLY-NF trees were found to have similar levels of leaf nutrients except for N, which was found to be low in nonfertilized trees (HLY and HLB). Both HLB-F and HLB-NF trees had lower levels of Ca, Mg, and S compared with HLY trees. In addition, HLB-NF trees had significantly lower levels of micronutrients Mn, Zn, and Fe, compared with HLY-NF trees. The hydroponic solution analysis showed that HLB-F and HLY-F trees had similar uptake of all the nutrients. Considering that HLB-affected trees have a lower root-to-shoot ratio than healthy trees, nutrient uptake efficiency per kilogram of root tissue was significantly higher in HLB trees compared with HLY trees. Under nutrient-deficient conditions (day 0) only nine genes were differentially expressed in HLB roots compared with HLY roots. On the other hand, when fertilizer was supplied for ≈1 week, ≈2300 genes were differentially expressed in HLB-F roots compared with HLY-F roots. A large number of differentially expressed genes in HLB-F were related to ion transport, root growth and development, anatomic changes, cell death, and apoptosis compared with HLY-F trees. Overall, anatomic and transcriptomic analyses revealed that HLB-affected roots undergo remarkable changes on transitioning from no nutrients to a nutrient solution, possibly facilitating a high uptake of nutrients. Our results suggest the roots of HLB-affected trees are highly efficient in nutrient uptake; however, a small root mass is a major limitation in nutrient uptake. Certain micronutrients and secondary macronutrients are also metabolized (possibly involved in tree defense or oxidative stress response) at a higher rate in HLB-affected trees than healthy trees. Therefore, a constant supply of fertilizer at a slightly higher rate than what is recommended for micronutrients and secondary macronutrients would be beneficial for managing HLB-affected trees.

Interactions between the mechanical and hydraulic properties of Eucalyptus trees under different environmental conditions of fertilization and water availability

Water and potassium are limiting factors for tree growth. Their influence on morphology and anatomy are well known, but their combined effects on tree growth remain to be clarified. A single clone of Eucalyptus grandis was analyzed under different treatments of rainfall exclusion and fertilization. Eight trees per treatment were sampled to investigate the influence of these treatments on the morphological, mechanical, and anatomical traits. The results showed that the fertilization mainly influenced the morphological and anatomical characteristics. Considering the difference between the fertilized and non-fertilized trees, the function of mechanical support was provided through increasing the diameter and the stiffness. Considering the fertilized trees, two different mechanisms occurred inducing a high stiffness: the wood density was higher for trees with rainfall exclusion; the specific modulus was higher for trees with a normal water supply.

Fertilization increases the functional specialization of fine roots in deep soil layers for young Eucalyptus grandis trees

Functional specialization of fine roots was found for Eucalyptus grandis trees at harvesting age (6 years) on tropical soils. Aiming to elucidate whether functional specialization is a ubiquitous feature of eucalypts, we focused on its changes with ontogeny, tree nutrient status and soil depth. We studied the potential uptake of N, K and Ca by 2-year-old E. grandis trees, as a function of soil depth and NPK fertilization. We injected NO−3-15N, Rb+ (K+ analogue) and Sr2+ (Ca2+ analogue) tracers simultaneously in a solution at depths of 10, 50, 150 and 300 cm in a sandy Ferralsol soil. A complete randomized block design was set up with three replicates of paired trees per injection depth, in fertilized and non-fertilized plots. Recently expanded leaves were sampled at 70 days after tracer injection. Determination of foliar Rb, Sr concentrations and x(15N) allowed estimating the relative uptake potential (RUP) and the specific RUP (SRUP), defined as the ratio between RUP and fine root length density (RLD) in the corresponding soil layer. Various root traits were measured at each depth. Foliar N and K concentrations were higher in fertilized than in non-fertilized trees. The RUP of NO3–-15N decreased sharply with soil depth and the highest values of the SRUP of NO3–-15N were found at a depth of 50 cm. The RUP of Rb+ and Sr2+ did not change with soil depth, whilst the SRUP of Rb+ and Sr2+ were higher at the depth of 300 cm than in the topsoil, concomitant with an increase in root diameter and a decrease in root tissue density with depth. The SRUP of Rb+ and Sr2+ at a depth of 300 cm were on average 136 and 61% higher for fertilized trees than for non-fertilized trees, respectively. Fine roots of young E. grandis trees showed contrasting potential uptake rates with soil depth depending on the nutrient. Fertilization increased the uptake rate of Rb+ and Sr2+ by unit of root length in deep soil layers. Functional specialization of fine roots for cations of low mobility depending on depth previously shown at harvesting age also occurs in young E. grandis plantations and increases with fertilization application. This mechanism helps explaining very low amounts of cations lost by leaching in Eucalyptus plantations established in deep tropical soils, even in highly fertilized stands.

Initial Effects of Fertilization and Canopy Management on Flowering and Seed and Oil Yields of Jatropha curcas L. in Malawi

Appropriate canopy management, including planting density and pruning, and application of fertilizer may increase flowering success and seed and oil yields of Jatropha curcas L. Two field experiments were performed from 2009 to 2011 in Balaka, Malawi, to assess the effect of planting density and pruning regime and single fertilizer application (N, P, and K) on male and female flower number and seed and oil yields of J. curcas. Planting density influenced flower sex ratio and female flower number. Branch pruning treatments did not influence the flower sex ratio but reduced seed and final oil yield by 55 % in the following year. It is claimed that J. curcas can be grown on soils with low nutrient content, but this study revealed that yield was low for non-fertilized trees. We observed higher seed and oil yields at higher N application rates (up to 203 ± 42 % seed and 204 ± 45 % oil yield increase) compared with the non-fertilized control. The study suggests thatcurrently used heavy pruning practice is not recommended for J. curcas cultivation, although it needs further longer term investigation. Applying nitrogen fertilizer is effective in increasing yield.

Terpene production and growth of three Pacific Northwest conifers in response to simulated browse and nutrient availability

Natural variation in ungulate browsing behavior interferes with the understanding of plant morphological and biochemical responses to herbivory. To investigate mechanisms for recovery from herbivory, we examined growth patterns and biosynthesis of terpenoids under simulated browse (three clipping intensities) and supplemental mineral nutrition (four levels of controlled-release fertilization) for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock (Tsuga heterophylla Raf. Sarg.), and western red-cedar (Thuja plicata Donn ex D. Don) seedlings on a reforestation site in Northwestern Oregon, USA, that was fenced to exclude ungulates. Higher clipping intensities increased relative height growth (at cost of diameter growth) for all the species. Only western red-cedar showed a decline in monoterpene concentrations with increasing clipping severity, suggesting prioritization in biosynthesis of terpenoids for this species. Douglas-fir and western hemlock responded to fertilization mostly through increased growth. Western red-cedar growth responses to fertilization were less pronounced, but monoterpene concentrations were 2–3 times higher compared to non-fertilized trees. Douglas-fir and western hemlock browse recovery and responses to fertilization consisted primarily of increased growth, while western red-cedar balanced growth promotion with production of chemical defense compounds. Our data suggests the evolution of species-dependent resource allocation strategies in response to both browse and soil nutrient availability.

Erythroneura lawsoni abundance and feeding injury levels are influenced by foliar nutrient status in intensively managed American sycamore

Abundance and feeding injury of the leafhopper Erythroneura lawsoni Robinson was measured in an intensively‐managed American sycamore Platanus occidentalis L. plantation. Trees were planted in spring 2000 in a randomized complete block design, and received one of three annual treatments: (i) fertilization (120 kg N/ha/year); (ii) irrigation (3.0 cm/week); (iii) fertilization + irrigation; or (iv) control (no treatment). Foliar nutrient concentrations were significantly influenced by the treatments because only sulphur and manganese levels were not statistically greater in trees receiving fertilization. Over 116 000 E. lawsoni were captured on sticky traps during the study. Leafhopper abundance was highest on nonfertilized trees for the majority of the season, and was positively correlated with foliar nutrient concentrations. Significant temporal variation in E. lawsoni abundance occurred, suggesting five discrete generations in South Carolina. Significant temporal variation occurred in E. lawsoni foliar injury levels, with the highest injury ratings occurring in late June and August. Foliar injury was negatively correlated with foliar nutrient content, and higher levels of injury occurred more frequently on nonfertilized trees. The results obtained in the present study indicated that increased E. lawsoni abundance occurred on trees that did not receive fertilization. Nonfertilized trees experienced greater foliar injury, suggesting that lower foliar nutrient status may have led to increased levels of compensatory feeding.

The impact of forest fertilization on growth of mature Norway spruce affected by Sirococcus shoot blight

The effects of forest fertilization and Sirococcus shoot blight on growth of mature Norway spruce ( Picea abies (L.) Karst.) were studied in a field experiment. The single tree fertilization experiment was established with 144 sample trees in the year 2000. These trees were selected among the dominant and co-dominant trees of the stand in a way that half of the trees exhibited symptoms of Sirococcus shoot blight and the other half did not. One-third of the sample trees were fertilized with dolomitic lime, one-third with kieserite and gypsum and one-third were left unfertilized as control. The treatments were randomly assigned to the sample trees. As the experimental design became unbalanced due to tree mortality caused by bark beetle infestation final analyses were performed with the volume growth data of 125 sample trees only. An analysis of covariance was used to evaluate the effect of fertilization and Sirococcus shoot blight on volume growth. The average volume increment of the period 1977–1980 was used as a covariate attribute, assuming that during this period growth was not yet affected by Sirococcus shoot blight. Indeed an effect of Sirococcus shoot blight on growth turned out to start after 1980 and the analysis revealed that over the whole period 1981–2006 trees with shoot blight symptoms had a significantly lower increment. The increment reduction of the nonfertilized trees by Sirococcus was 7.46 ± 2.90 % in 1981 and was continuously increasing with time to 37 ± 3.78 % by the year 2000. A significant positive effect of fertilization was only found for the kieserite + gypsum variant from 2002 to 2006, with the highest surplus increment in 2004 with 31.6 ± 15.2 %, calculated as average over the diseased and healthy group. However, a mitigation of the Sirococcus-caused increment loss via fertilization with kieserite and gypsum was statistically significant only for the year 2003. A moderate relationship between basal area increment and disease severity was found, indicating decreasing basal area increment with increasing disease severity.

Cold acclimation of Norway spruce roots and shoots after boron fertilization

Boron deficiency, manifested as shoot dieback, is a problem in conifer stands growing on soils with high nitrogen availability in Fennoscandia. Earlier observations on Norway spruce (Picea abies L. Karst.) suggest that freezing tolerance is decreased by boron deficiency. Here, the effect of boron fertilization on cold acclimation of Norway spruce was studied in a young stand with initially low boron status two years after fertilization. Buds, stems, needles and roots were collected at five sampling times during cold acclimation and subsequently exposed to series of freezing temperatures. Lethal temperatures of organs were assessed by electrolyte leakage method (EL) and visual scoring of damage (VS). Freezing tolerance of buds was measured also by differential thermal analysis (DTA). The mean boron (B) concentration in needles was 4 mg kg–1 in unfertilized and 21 mg kg–1 in B-fertilized trees while critical level of B deficiency is considered to be 5 mg kg–1. The risk for increased freezing injuries in the low-B trees was not evident since all trees achieved cold hardiness that would be sufficient in central Finland. At two sampling times out of five, shoots or stem of B-fertilized trees were slightly more freezing tolerant than non-fertilized trees. However, the present study does not give strong evidence for the hypothesis that decreased freezing tolerance in B deficiency would be a triggering factor for leader dieback in Norway spruce at the B levels studied.

The Influence of Nitrogen Fertilization on Waterlogging Stresses in Fagus sylvatica L. and Quercus robur L.

The aims of this study were to determine the influence of nitrogen (N) fertilizers on tree tolerance under prolonged waterlogging conditions and investigate the effect of N fertilization on aiding tree recovery from waterlogging damage using containerized English oak (waterlogging-intermediate) and European beech (waterlogging-sensitive) as test species. English oak proved to be more waterlogging-tolerant than European beech. Tree vitality as measured by chlorophyll fluorescence, photosynthetic rates, leaf chlorophyll content, stomatal conductance, leaf and root protein concentration, and foliar N content was consistently higher in trees in which N fertilizers were added to the waterlogged solutions compared with trees waterlogged with tapwater only for 18 days. Measurement of light absorbance, light trapping, electron transport, and dissipation fluxes per leaf cross-section of photosystem II after the 18-day waterlogging period indicated a beneficial influence of N fertilization on leaf photosynthetic processes at the cessation of the waterlogging period. Addition of N induced greater resource allocation in favor of roots over shoots in both tree species. At the cessation of the 18-day waterlogging period and after a 10-day regeneration period, growth (leaf area, shoot, root, total plant dry weight) was constantly higher in N waterlogged trees compared with non-N waterlogged ones. In a separate study, recovery rates of trees as measured by chlorophyll fluorescence, photosynthetic rates, leaf chlorophyll content, and stomatal conductance over a 6-week period after the cessation of 18 days waterlogging were 30% to 50% higher in N-fertilized trees compared with non-N-fertilized trees irrespective of species. In all cases, nonfertilized trees had the least capacity for recovery. In addition, leaf area, shoot, root, and total plant dry weight were higher in N-fertilized trees compared with nonfertilized ones. Results of this investigation indicate 1) applications of N fertilizers enhance the tolerance of trees under prolonged waterlogged conditions; and 2) applications of N fertilizers after waterlogging stress would be of benefit to improve tree recovery rates and growth. From a practical point of view, N fertilization 14.5 g (0.51 oz) or greater N per liter (0.26 gal) of water is tentatively suggested based on preliminary results of this study.

Influence of nitrogen on leaf chlorophyll content and photosynthesis of ‘Golden Delicious’ apple

The aim of the present study was to estimate the influence of different rates of soil-applied nitrogen on leaf N and chlorophyll content and photosynthesis in ‘Golden Delicious’ apple trees. Three different treatments were included: the trees were either fertilized with 80 kg N ha−1 (N-80), 250 kg N ha−1 (N-250) or left unfertilized (CON). Fertilization increased leaf nitrogen content, with a more prominent effect in high N application level treatment. In all treatments, a slight seasonal decrease in leaf nitrogen content was observed. N-250 treatment resulted in higher chlorophyll content; a similar effect was found late in the season for N-80 treatment. Measurements of A-C i curves, performed on spur leaves, revealed a higher CO2 saturated photosynthetic rate in N-250 trees compared with low application level fertilized or unfertilized trees. No effect of N fertilization on carboxylation efficiency was found, as revealed by comparisons of the initial slopes of A-C i curves. The lack of positive effect is rather surprising, since the leaf N content was efficiently increased with application of fertilizer. Obviously, the existing pool of leaf nitrogen in non-fertilized trees does not limit Rubisco activity and efficiency.

Effect of Thawing Time, Cooling Rate and Boron Nutrition on Freezing Point of the Primordial Shoot in Norway Spruce Buds

Effects of cooling rates on bud frost hardiness have been studied but there is little information on bud responses to thawing. Since the cell wall pore size has been found to increase with boron (B) deficiency, B deficiency may affect the supercooling ability of buds in winter. The effects of duration of thawing time and rate of cooling on bud frost hardiness of Norway spruce (Picea abies) were studied in a B fertilization trial in February 2003 and March 2005. Frost hardiness of apical buds was determined by differential thermal analysis (DTA) and visual scoring of damage. In 2003, the freezing point of primordial shoots of buds (T(f)), i.e. the low-temperature exotherm (LTE), was, on average, -39 degrees C when buds were thawed for less than 3 h and the T(f) increased to -21 degrees C after 18 h of thawing. During the first 4 h of thawing, the rate of dehardening was 6 degrees C h(-1). In 2005, buds dehardened linearly from -39 degrees C to -35 degrees C at a rate of 0.7 degrees C h(-1). In 2003, different cooling rates of 1-5 degrees C h(-1) had a minor effect on T(f) but in 2005 with slow cooling rates T(f) decreased. In both samplings, at cooling rates of 2 and 1 degrees C h(-1), T(f) was slightly higher in B-fertilized than in non-fertilized trees. By contrast, at very short thawing times in 2003, T(f) was somewhat lower in B-fertilized trees. There was little evidence of reduced frost hardiness in trees with low B status. This study showed that buds deharden rapidly when exposed to above-freezing temperatures in winter, but if cooled again they reharden more slowly. According to this study, rapid dehardening of buds has to be taken into account in assessments of frost hardiness.

Long-term effects of thinning and fertilization on growth of red fir in northeastern California

To determine the impact of fertilization and thinning on growth and development of red fir (Abies magnifica A. Murr.) stands, we established an experiment in a 60-year-old stand using a 2 × 3 factorial design with nitrogen-fertilized and nonfertilized treatments and three stocking levels. Plots were established in 1976 and were measured every 5 years for 26 years. The periodic annual increment in basal area was 97%, 51%, 38%, and 33% greater in fertilized trees than in nonfertilized trees during the first, second, third, and fourth 5-year periods, respectively. After 20 years, annual basal area increment was greater in nonfertilized trees. The response of annual volume increment to fertilization was not statistically significant until the fourth period. Yet, volume increases of the fertilized plots were 25%–92% greater than those of the nonfertilized plots from 1976 to 1996. Similarly, basal area increment was greater in lightly thinned plots than in unthinned plots from the second period on, until heavy mortality during 1996–2002. Basal area increment was greater in the heavily thinned plots from the fourth period on. Results indicate that red fir can respond to fertilization and thinning quickly and that both treatments speed stand development. In addition, fertilization increases the stand's carrying capacity. Therefore, forest managers can use these silvicultural practices to improve stand growth, to reduce fire fuels, and to accelerate stand development.

Interaction Between Nitrogen-Fertilized Peach Trees and Expression ofsyrB, a Gene Involved in Syringomycin Production inPseudomonas syringaepv.syringae

ABSTRACT The in vitro expression of the syrB gene that controls the synthesis of syringomycin, a non-host-specific phytotoxin produced by Pseudomonas syringae pv. syringae van Hall, was studied using aqueous extracts derived from bark tissues collected from nitrogen-fertilized and nonfertilized peach trees. Expression of the syrB gene was quantified as beta- galactosidase activity expressed by P. syringae pv. syringae B3AR-132 containing a syrB::lacZ fusion. Gene expression was significantly less in three of four paired comparisons using extracts derived from fertilized versus nonfertilized trees; however, canker lengths were significantly different in only one of four comparisons. Expression was negatively correlated with plant tissue nitrogen content and positively correlated with a plant carbon/nitrogen ratio. Bark tissue from ring nematodeinfested trees had significantly higher concentrations of total soluble phenolic compounds and carbon/nitrogen ratios than bark samples from trees without nematodes, and canker size was significantly greater in trees growing in ring nematode-infested soil compared with noninfested soil. Nitrogen fertilization significantly decreased the plant carbon/nitrogen ratio, which was positively correlated with the concentration of total soluble phenolic compounds. Canker size developing after bacterial inoculation was positively correlated with higher plant carbon/nitrogen ratios and total soluble phenolic compounds. These results support the hypothesis that one reason why nitrogen fertilization decreases host susceptibility to bacterial canker is by either reducing the amount of plant metabolites that can induce syrB gene expression, or producing or increasing the concentration of compounds that antagonize syrB inducing compounds.

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

AbstractThe objective of the present study was to investigate the interactive effects of elevated [CO2] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO2] in whole‐tree chambers. Elevated [CO2] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO2] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO2]. In the latter, the CO2 effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO2] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.

Leaf potassium concentration, CO 2 exchange and light interception in almond trees ( Prunus dulcis (Mill) D.A. Webb)

The goal of this study was to determine the effect of tree potassium status on CO 2 exchange and light interception of field-grown almond trees ( Prunus dulcis (Mill) D.A. Webb). Treatments consisted of four levels of potassium fertilization applied for three consecutive seasons. Potassium deficiency negatively affected tree light interception. Defoliation after mechanical harvesting indicated that potassium deficiency accelerated premature leaf senescence and premature leaf abscission. CO 2 exchange rates were curvilinearly related to leaf potassium concentration during mid-summer after most vegetative shoot growth was completed. Leaf potassium concentrations less than 0.5–0.6% appeared to limit leaf CO 2 exchange rate. Large variations in leaf potassium concentration were found in the non-fertilized trees. Indeed, most of the response curve of leaf CO 2 exchange rate to leaf potassium concentration could be described by analyzing the leaves of non-fertilized trees. Stomatal conductance was not affected significantly by leaf potassium concentration and leaves with low potassium concentration had the highest calculated internal CO 2 concentrations. Thus it appears that potassium deficiency in almond affected the leaf photosynthetic capacity via biochemical limitations and not through an effect on stomatal conductance.

Changes in fine root production and longevity in relation to water and nutrient availability in a Norway spruce stand in northern Sweden.

The PEACH computer simulation model of reproductive and vegetative growth of peach trees (Grossman and DeJong 1994) was adapted to estimate seasonal nitrogen (N) dynamics in organs of mature peach (Prunus persica (L.) Batsch cv. O'Henry) trees grown with high and low soil N availability. Seasonal N accumulation patterns of fruits, leaves, stems, branches, trunk and roots of mature, cropping peach trees were modeled by combining model predictions of organ dry mass accumulation from the PEACH model with measured seasonal organ N concentrations of trees that had been fertilized with either zero or 200 kg N ha(-1) in April. The results provided a comparison of the N use of perennial and annual organs during the growing season for trees growing under both low and high N availability. Nitrogen fertilization increased tree N content by increasing organ dry masses and N concentrations during the fruit growing season. Dry mass of current-year vegetative growth was most affected by N fertilization. Whole-tree N content of fertilized trees was almost twice that of non-fertilized trees. Although N use was higher in fertilized trees, calculated seasonal N accumulation patterns were similar for trees in both treatments. Annual organs exhibited greater responses to N fertilization than perennial organs. Estimated mean daily N use per tree remained nearly constant from 40 days after anthesis to harvest. The calculations indicated that fertilized trees accumulated about 1 g N tree(-1) day(-1), twice that accumulated by non-fertilized trees. Daily N use by the fertilized orchard was calculated to be approximately 1 kg N ha(-1), whereas it was approximately 0.5 kg N ha(-1) for the non-fertilized trees. During the first 25-30 days of the growing season, all N use by growing tissues was apparently supplied by storage organs. Nitrogen release from storage organs for current growth continued until about 75 days after anthesis in both N treatments.

Effect of pine needle removal and fertilization on tree growth and soil P availability in a Pinus elliottii Engelm. var. elliottii stand

Pine-needle raking and fertilization effects on tree growth nutrition and soil inorganic phosphorus availability were examined in a 13-year-old slash pine ( Pinus elliottii Engelm. var. elliottii) stand in Clay County, Florida. Fertilized and nonfertilized treatments were applied to main plots. Sixteen of the 32 plots were unfertilized, while the remaining 16 plots received fertilizer application with 280 kg ha diammonium phosphate (DAP) in August 1991 and again in September 1992. Four raking frequency treatments: no raking; rake-every-year; rake-every-2-years; and rake-every-4-years were applied to split-plots within these main plots. Diameter at breast height and tree heights were measured annually from 1991 to 1995. Raking every-year treatment significantly reduced diameter growth by 5.2 mm. Fertilizer had a significant negative effect on tree heights; nonfertilized trees in the stand grew more than fertilized trees in all diameter classes. Annual needlefall production rate was 8735 kg ha −1 with a maximum of 50 kg N ha −1 and 5 kg P ha −1 removed through litter raking. During 1 year, a maximum yield of 737, 934, and 1093 bales/ha were produced in the rake-every-year, every-2, and every-4-year plots. N and P concentration in the raked needles was 0.59 and 0.052%, respectively. Needlefall P concentration was significantly lower among trees raked more frequently. Fertilizer significantly increased needlefall N concentration. Availability of soil inorganic phosphorus detected by anion-exchange membranes was significantly higher in the plots raked every-4-years followed by the control compared to the plots that were raked every-year. These results indicate that removal of pine needles does not have an immediate effect on old-field sites with high residual fertility, but removing 50 kg ha −1 of N and 5 kg ha −1 of P annually may eventually deplete the site.

Distribution of leaf mass per unit area and leaf nitrogen concentration determine partitioning of leaf nitrogen within tree canopies.

Distribution of leaf nitrogen with respect to leaf mass per unit area (M(a)), nitrogen per unit mass (N(m)) and nitrogen per unit area (N(a)) within peach (Prunus persica L.) tree canopies was studied in two field experiments. In one experiment, leaf light exposure and M(a) were measured on leaves from different canopy positions of peach trees subjected to five nitrogen (N) fertilization treatments. Leaf light exposure and M(a) were linearly related and the relationship was independent of N fertilization. In a subsequent experiment, N fertilizer was applied to previously unfertilized trees in midsummer, after shoot growth had terminated. Application of N fertilizer did not affect mean canopy M(a). Fertilization increased N(m) of all leaves throughout the canopy compared with non-fertilized trees. No significant relationship between N(m) and M(a) was found in either fertilized or control trees. There was a linear relationship between N(a) and M(a) and the slope of the relationship was increased by N fertilizer application. We conclude that distribution of N(a) in peach tree canopies is primarily a function of M(a) partitioning with light and N(m), which is related to soil N availability.