Norway Maple (Acer platanoides) Invasion of a Natural Forest Stand: Understory Consequence and Regeneration Pattern

Norway maple (Acer platanoidesis) is invasive in a natural stand in suburban Ithaca, NY. To determine the understory pattern and consequences of a Norway maple invasion, I compared density and species richness under Norway maples and sugar maples (Acer saccharum). Mean sapling density was significantly lower (P<0.0027) under Norway maples (3.64/100 m²±1.6 SE) than under sugar maples (19.4/100 m²±4.4 SE). Mean sapling species richness was significantly lower (P<0.0018) under Norway maples (0.7/32 m²±0.18 SE) than under sugar maples (2.6/32 m²±0.48 SE). Likewise, Norway maple regeneration is more frequent under sugar maples than sugar maple regeneration: 57% of sugar maple plots had Norway maple saplings while 0% of Norway maple plots had sugar maple saplings. Two significant plot effects were found for presence–absence: Norway maple saplings grow under Norway maples with a significantly lower frequency (P<0.03) than under sugar maples; sugar maple saplings grow under Norway maples with a significantly lower frequency (P<0.000) than under sugar maples. Across the site, Norway maple saplings were the most abundant (29 saplings for 480 m²). The success of Norway maple regeneration and the reductions in total stem density beneath Norway maples is most likely the result of its strong competitive abilities, notably its high shade tolerance and abundant seed crops.     

Soil N mineralization and nitrification in relation to nitrogen solution chemistry in a small forested watershed

Spatial variations in soil processes regulating mineral N losses to streams were studied in a small watershed near Toronto, Ontario. Annual net N mineralization in the 0–8 cm soil was measured in adjacent upland and riparian forest stands using in situ soil incubations from April 1985 to 1987. Mean annual rates of soil N mineralization and nitrification were higher in a maple soil (93.8 and 87.0 kg.ha^–1) than in a pine soil (23.3 and 8.2 kg.ha^–1 ). Very low mean rates of mineralization (3.3 kg.ha^–1) and nitrification (3.4 kg.ha^–1) were found in a riparian hemlock stand. Average NO₃-N concentrations in soil solutions were 0.3–1.0 mg.L^–1 in the maple stand and >0.06mg.L^–1 in the pine stand. Concentrations of NO₃–N in shallow ground water and stream water were 3–4× greater in a maple subwatershed than in a pine subwatershed. Rapid N uptake by vegetation was an important mechanism reducing solution losses of NO₃–N in the maple stand. Low rates of nitrification were mainly responsible for negligible NO₃–N solution losses in the pine stand.     

Response to inoculation and N fertilization for increased yield and biological nitrogen fixation of common bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is able to fix 20–60 kg N ha^–1 under tropical environments in Brazil, but these amounts are inadequate to meet the N requirement for economically attractive seed yields. When the plant is supplemented with N fertilizer, N₂ fixation by Rhizobium can be suppressed even at low rates of N. Using the ¹⁵N enriched method, two field experiments were conducted to compare the effect of foliar and soil applications of N-urea on N₂ fixation traits and seed yield. All treatments received a similar fertilization including 10 kg N ha^–1 at sowing. Increasing rates of N (10, 30 and 50 kg N ha^–1) were applied for both methods. Foliar application significantly enhanced nodulation, N₂ fixation (acetylene reduction activity) and yield at low N level (10 kg N ha^–1). Foliar nitrogen was less suppressive to nodulation, even at higher N levels, than soil N treatments. In the site where established Rhizobium was in low numbers, inoculation contributed substantially to increased N₂ fixation traits and yield. Both foliar and soil methods inhibited nodulation at high N rates and did not significantly increase bean yield, when comparing low (10 kg N ha^–1) and high (50 kg N ha^–1) rates applied after emergence. In both experiments, up to 30 kg N ha^–1 of biologically fixed N₂ were obtained when low rates of N were applied onto the leaves.     

Effects of soil freezing disturbance on soil solution nitrogen, phosphorus, and carbon chemistry in a northern hardwood ecosystem

Reductions in snow cover undera warmer climate may cause soil freezing eventsto become more common in northern temperateecosystems. In this experiment, snow cover wasmanipulated to simulate the late development ofsnowpack and to induce soil freezing. Thismanipulation was used to examine the effects ofsoil freezing disturbance on soil solutionnitrogen (N), phosphorus (P), and carbon (C)chemistry in four experimental stands (twosugar maple and two yellow birch) at theHubbard Brook Experimental Forest (HBEF) in theWhite Mountains of New Hampshire. Soilfreezing enhanced soil solution Nconcentrations and transport from the forestfloor. Nitrate (NO₃ ^–) was thedominant N species mobilized in the forestfloor of sugar maple stands after soilfreezing, while ammonium (NH₄ ⁺) anddissolved organic nitrogen (DON) were thedominant forms of N leaching from the forestfloor of treated yellow birch stands. Rates ofN leaching at stands subjected to soil freezingranged from 490 to 4,600 mol ha^–1yr^–1, significant in comparison to wet Ndeposition (530 mol ha^–1 yr^–1) andstream NO₃ ^– export (25 mol ha^–1yr^–1) in this northern forest ecosystem. Soil solution fluxes of P_i from the forestfloor of sugar maple stands after soil freezingranged from 15 to 32 mol ha^–1 yr^–1;this elevated mobilization of P_i coincidedwith heightened NO₃ ^– leaching. Elevated leaching of P_i from the forestfloor was coupled with enhanced retention ofP_i in the mineral soil Bs horizon. Thequantities of P_i mobilized from the forestfloor were significant relative to theavailable P pool (22 mol ha^–1) as well asnet P mineralization rates in the forest floor(180 mol ha^–1 yr^–1). Increased fineroot mortality was likely an important sourceof mobile N and P_i from the forest floor,but other factors (decreased N and P uptake byroots and increased physical disruption of soilaggregates) may also have contributed to theenhanced leaching of nutrients. Microbialmortality did not contribute to the acceleratedN and P leaching after soil freezing. Resultssuggest that soil freezing events may increaserates of N and P loss, with potential effectson soil N and P availability, ecosystemproductivity, as well as surface wateracidification and eutrophication.     

Translocation from leaves to fruits of a legume,studied by a phloem bleeding technique: Diurnal changes and effects of continuous darkness

Summary Diurnal changes in the carbohydrates of leaf laminae and fruits and in the bleeding of sugar and amino acids from fruit phloem were followed by successive sampling from a population of Lupinus albus L. plants. Phloem sap was collected for a standard 5 min period from cut distal tips of attached fruits. Daily fluctuations in leaf dry matter resulted largely from changes in starch and sugar. Leaf sugar rose to a maximum in the afternoon, starch to a maximum at, or shortly after, dusk. Leaves lost sugar and starch from dusk to dawn. Phloem bleeding rate varied little over a daily cycle but sucrose levels fluctuated from a noon maximum of 12–13% (w/v) to a dawn minimum of 9–10%. The rhythm of phloem sugar levels matched closely those of fruit and leaf. Phloem amino acid levels fluctuated in phase with that of sucrose: the relative composition of the amino fraction did not vary significantly over the daily cycle. Pulse feeding of source leaves with ¹⁴CO₂ at different times in the photoperiod allowed study of the pattern of release of labelled photosynthate to the fruit phloem and the build up and depletion of ¹⁴C starch in leaves. Plants transferred to continuous darkness showed a rapid decline in output and concentration of phloem sap solutes, and translocated nitrogen to their fruits at only one quarter of the rate of control plants retained in natural daylight. The combined data from the experiments showed that the rate of output of sugar from cut phloem of a fruit was directly related to the current level of sugar in leaves. When leaf sugar levels were low (5–10 mg ml tissue water^-1) sugar in phloem was 10–11 times more concentrated than in source leaves, but at high leaf sugar levels (25–30 mg ml^-1) this concentration difference was only 3–4 fold.     

Fertilizer nitrogen budgets of two doses of Na15NO3 dressings split-applied to winter wheat in microplots on a loam soil

In a field experiment performed in microplots, winter wheat was fertilized at two different total N dressings (135 and 180 kg ha^–1) split-applied as Na¹⁵NO₃ in three equal applications at tillering, stem elongation, and flag leaf.No significant differences were found in the percentage recovery values for the entire plant at the three split applications between the two N dressings. The total percentage recovery of fertilizer N by the plant was high and practically equal at both fertilization levels (76.65% and 75.84% for 135 and 180 kg N ha^–1, respectively); crop yields were also similar. In contrast, gaseous losses calculated after drawing up the balance sheet were, in absolute values, higher for the tillering and stem elongation split applications when using the 180 kg N ha^–1 dressing (7.67 and 4.84 kg N ha^–1, respectively) than for the 135 kg N ha^–1 dressing (3.45 and 1.26 kg N ha^–1, respectively). They were found to be zero at flag leaf at both fertilization levels. The amount of applied fertilizer N did not influence the amount of N taken up from the soil which was about 143 kg ha^–1.     

Nitrogen fixation of field-inoculatedLeucaena leucocephala (Lam.) de Wit estimated by the15N and the difference methods

The amount of nitrogen fixed byLeucaena leucocephala (Lam.) de Wit was assessed on an Alfisol at the International Institute of Tropical Agriculture located in southwestern Nigeria. Estimated by the difference method, nitrogen fixation of leucaena inoculated with Rhizobium strain IRc 1045 was 133 kg ha^–1 in six months. Inoculation with Rhizobium strain IRc 1050 gave a lower nitrogen fixation of 76 kg ha^–1. Fertilization with 40 and 80 kg N ha^–1 inhibited nitrogen fixation by 43–76% and 49–71%, respectively. Estimates with the¹⁵N dilution method gave nitrogen fixation of 134 kg ha^–1 in six months when leucaena was inoculated with Rhizobium strain IRc 1045 and 98 kg ha^–1 for leucaena inoculated with Rhizobium strain IRc 1050. This nitrogen fixation represented 34–39% of the plant nitrogen. Inoculated leucaena derived 5–6% of its nitrogen from applied fertilizer and 56–54% from soil.     

Sugar beet and barley yields in relation to inoculation with N2-fixing and phosphate solubilizing bacteria

Recently, there has been a resurgence of interest in bioorganic fertilizers as part of sustainable agricultural practices to alleviate drawbacks of intensive farming practices. N₂-fixing and P-solubilizing bacteria are important in plant nutrition increasing N and P uptake by the plants, and playing a significant role as plant growth-promoting rhizobacteria in the biofertilization of crops. A study was conducted in order to investigate the effects of two N₂-fixing (OSU-140 and OSU-142) and a strain of P-solubilizing bacteria (M-13) in single, dual and three strains combinations on sugar beet and barley yields under field conditions in 2001 and 2002. The treatments included: (1) Control (no inoculation and fertilizer), (2) Bacillus OSU-140, (3) Bacillus OSU-142, (4) Bacillus M-13, (5) OSU-140 + OSU-142, (6) OSU-140 + M-13, (7) OSU-142 + M-13, (8) OSU-140 + OSU-142 + M-13, (9) N, (10) NP. N and NP plots were fertilized with 120 kg N ha^–1 and 120 kg N ha^–1 + 90 kg P ha^- for sugar beet and 80 kg N ha^–1 and 80 kg N ha^–1 + 60 kg P ha^–1 for barley. The experiments were conducted in a randomized block design with five replicates. All inoculations and fertilizer applications significantly increased leaf, root and sugar yield of sugar beet and grain and biomass yields of barley over the control. Single inoculations with N₂-fixing bacteria increased sugar beet root and barley yields by 5.6–11.0% depending on the species while P-solubilizing bacteria alone gave yield increases by 5.5–7.5% compared to control. Dual inoculation and mixture of three bacteria gave increases by 7.7–12.7% over control as compared with 20.7–25.9% yield increases by NP application. Mixture of all three strains, dual inoculation of N₂-fixing OSU-142 and P-solubilizing M-13, and/or dual inoculation N₂-fixing bacteria significantly increased root and sugar yields of sugar beet, compared with single inoculations with OSU-140 or M-13. Dual inoculation of N₂-fixing Bacillus OSU-140 and OSU-142, and/or mixed inoculations with three bacteria significantly increased grain yield of barley compared with single inoculations of OSU-142 and M-13. In contrast with other combinations, dual inoculation of N₂-fixing OSU-140 and P-solubilizing M-13 did not always significantly increase leaf, root and sugar yield of sugar beet, grain and biomass yield of barley compared to single applications both with N₂-fixing bacteria. The beneficial effects of the bacteria on plant growth varied significantly depending on environmental conditions, bacterial strains, and plant and soil conditions.     

Effect of snow removal on leaf water potential,soil moisture,leaf and soil nutrient status and leaf peroxidase activity of sugar maple

Effect of removal of snow cover in winter was investigated in an 80-year-old sugar maple (Acer saccharum Marsh.) stand in southern Quebec. We hypothesized that winter soil frost would induce some of the decline symptoms observed in sugar maple stands in southern Quebec in the early 1980's. Snow was continuously removed from around trees for a one week (partial removal) or for a four-month period (complete removal) during the 1990–1991 winter. Foliage and soils were sampled periodically during the summer of 1991. The complete snow removal treated trees showed decreased leaf water potential and increased peroxidase activity over most of the growing season. Foliar Ca was reduced in both snow removal treatments early in the growing season while foliar N was reduced in the complete snow removal trees late in the growing season. Soil NO ₃ ^– and K⁺ were elevated in both snow removal treatments at various times throughout the growing season. Prolonged soil frost in a sugar maple stand can induce lower leaf water potential, higher leaf peroxidase activity and early leaf senescence during the following growing season. Soil frost may have reduced nutrient uptake without affecting significantly the leaf nutrient status.     

Non-structural carbohydrate pools in a tropical forest

The pool size of mobile, i.e. non-structural carbohydrates (NSC) in trees reflects the balance between net photosynthetic carbon uptake (source) and irreversible investments in structures or loss of carbon (sink). The seasonal variation of NSC concentration should reflect the sink/source relationship, provided all tissues from root to crown tops are considered. Using the Smithsonian canopy crane in Panama we studied NSC concentrations in a semi-deciduous tropical forest over 22 months. In the 9 most intensively studied species (out of the 17 investigated), we found higher NSC concentrations (starch, glucose, fructose, sucrose) across all species and organs in the dry season than in the wet season (NSC 7.2% vs 5.8% of dry matter in leaves, 8.8/6.0 in branches, 9.7/8.5 in stems, 8.3/6.4 in coarse and 3.9/2.2 in fine roots). Since this increase was due to starch only, we attribute this to drought-constrained growth (photosynthesis less affected by drought than sink activity). Species-specific phenological rhythms (leafing or fruiting) did not overturn these seasonal trends. Most of the stem volume (diameter at breast height around 40 cm) stores NSC. We present the first whole forest estimate of NSC pool size, assuming a 200 t ha^–1 forest biomass: 8% of this i.e. ca. 16 t ha^–1 is NSC, with ca. 13 t ha^–1 in stems and branches, ca. 0.5 and 2.8 t ha^–1 in leaves and roots. Starch alone (ca. 10.5 t ha^–1) accounts for far more C than would be needed to replace the total leaf canopy without additional photosynthesis. NSC never passed through a period of significant depletion. Leaf flushing did not draw heavily upon NSC pools. Overall, the data imply a high carbon supply status of this forest and that growth during the dry season is not carbon limited. Rather, water shortage seems to limit carbon investment (new tissue formation) directly, leaving little leeway for a direct CO₂ fertilization effects.     

Exchange of N-gases at the Höglwald Forest – A summary

During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Höglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N₂-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO₂-deposition was in a range of –1.6 –2.9 kg N ha^–1 yr^–1 and no huge differences between the different sites could be demonstrated. In contrast to NO₂-deposition, NO- and N₂O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha^–1 yr^–1), lowest at the beech site (2.3–3.5 kg N ha^–1 yr^–1) and intermediate at the limed spruce site (3.4–5.4 kg N ha^–1 yr^–1). With regard to N₂O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha^–1 yr^–1) >> spruce limed (0.7–4.0 kg N ha^–1 yr^–1) > spruce control (0.4–3.1 kg N ha^–1 yr^–1). Average N-trace gas emissions (NO, NO₂, N₂O) for the years 1994–1997 were 6.8 kg N ha^–1 yr^–1 at the spruce control site, 3.6 kg N ha^–1 yr^–1 at the limed spruce site and 4.5 kg N ha^–1 yr^–1 at the beech site. Considering N₂-losses, which were significantly higher at the beech (12.4 kg N ha^–1 yr^–1) than at the spruce control site (7.2 kg N ha^–1 yr^–1), the magnitude of total gaseous N losses, i.e. N₂-N + NO-N + NO₂-N + N₂O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha^–1 yr^–1 at the spruce control site and 15.5 kg N ha^–1 yr^–1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input.     

The effect of nitrogen fertilization on nitrogen use efficiency of irrigated and non-irrigated tobacco (Nicotiana tabacum L.).

Burley tobacco (Nicotiana tabacum L.) plants were grown in the field with or without irrigation and fertilized with 0, 120, 240 or 360 kg N ha^–1 over two growing seasons to assess nitrogen use under Mediterranean climate conditions. Kjeldahl-N and NO₃-N in leaves and stems and NO₃-N and NH₄-N in the soil at two depths (0–0.3 and 0.3–0.6 m) were determined. The effect of N fertilization on total N accumulated in the canopy biomass was markedly different between irrigated and non-irrigated plants. Under non-irrigated conditions N accumulated in the plant did not depend on the amount of N applied. In both years, the amount of N in irrigated plants increased in response to the amount of N applied, starting from 49 to 56 days after transplanting (DAT). The average amount of total N in the canopy of irrigated plants, measured across all sampling dates of both years, ranged from 30 kg ha^–1 of the unfertilized control to 88 kg ha^–1 of the 360 kg ha^–1 of N applied. The average amount of plant NO₃-N was 2.6 and 4.4 kg ha^–1 for non-irrigated and irrigated plots across all N treatments (means of 1996 and 1997). Nitrogen uptake rate (NUR) of non-irrigated plants was high between seedling establishment and the period of rapid stem elongation in 1996 (from 36 to 50 DAT) and until flowering in 1997 (from 42 to 71 DAT), but much less or negligible at later stages of plant development. Irrigation increased NUR dramatically in the second part of the growing season. Maximum NUR was estimated for plants receiving 240 or 360 kg N ha^–1 in both years. The year of study did not affect the recovery fraction (RF), physiological efficiency (PE) or agronomic efficiency (AE). Irrigation and N fertilization had significant effects on both RF and AE, but not on PE. Maximum values of RF were 45 and 22% for irrigated and non-irrigated treatments, respectively. In irrigated plots there was a negative relationship between RF and increasing N levels at all sampling dates.     

Forest vegetation in relation to surface water chemistry in the North Branch of the Moose River,Adirondack Park,N.Y.

The Regional Integrated Lake-Watershed Acidification Study (RILWAS) was conducted to identify and to quantify the environmental factors controlling surface water chemistry in forested watersheds of the Adirondack region of New York. The RILWAS vegetation research was designed to: (1) compare the quantitative patterns of forest cover and tree community structure in the study catchments of the Moose River drainage system; and (2) identify important vegetation differences among study watersheds that might help to explain inter-watershed differences in water chemistry and aquatic responses to acidic deposition. Field transect data indicated that the overall drainage system includes 50% mixed forest cover, 38% hardwood forest, 10% coniferous forest, and 2% wetland cover. Major tree species include yellow birch, red spruce, American beech, sugar maple, eastern hemlock, and red maple. Analysis of forest structure indicated that mean weighted basal area estimates ranged two-fold from 24–48 m²ha^–1 among watersheds. Likewise, mean weighted estimates for aboveground biomass and aboveground annual productivity ranged among watersheds from 160 to 320 MT ha^–1 and from 8 to 18 MT ha^–1 yr^–1, respectively. Results showed that differences in surface water chemistry were independent of vegetation differences among watersheds.     

An attempt to predict long-term effects of atmospheric nitrogen deposition on the yield of Norway spruce stands (Picea abies (L.) Karst.) in southwestern Sweden

Long-term field experiments in Norway spruce stands on fertile sites (site indices 27–35 m) in southwestern Sweden were analysed with respect to volume increment. Three treatments were included (0=No fertilization, N = Fertilization with N, NP = Fertilization with N and P).Volume growth was monitored for 18 years in 10 blocks. No significant differences in annual volume increment between the treatments were detected. Volume increments in the N treatment were 97%, 99% and 107% as high as those in the 0 treatment for the periods 1–5, 6–10 and 11–15 years after the first fertilization. Corresponding values for the NP treatment were 104%, 108% and 110%, indicating that P has a small positive effect.The amount of N-fertilization would correspond to an annual N deposition of 20 kg ha^-1 during the next 30 years in southwestern Sweden. For this period, the results imply that this N deposition would not affect the growth of Norway spruce stands on fertile sites.     

The phosphorus status of northern hardwoods differs by species but is unaffected by nitrogen fertilization

Northern hardwood forests in the eastern US exhibit species-specific influences on nitrogen (N) cycling, suggesting that their phosphorus (P) cycling characteristics may also vary by species. These characteristics are increasingly important to understand in light of evidence suggesting that atmospheric N deposition has increased N availability in the region, potentially leading to phosphorus limitation. We examined how P characteristics differ among tree species and whether these characteristics respond to simulated N deposition (fertilization). We added NH₄NO₃ fertilizer (50 kg ha^?1 year^?1) to single-species plots of red oak (Quercus rubra L.), sugar maple (Acer saccharum Marsh.), eastern hemlock (Tsuga canadensis (L.) Carr.), American beech (Fagus grandifolia Ehrh.), and yellow birch (Betula alleghaniensis Britt.), in the Catskill Mountains, New York from 1997 to 2007. Species differences were observed in foliar, litter and root P concentrations, but all were unaffected by a cumulative N fertilization of 550 kg/ha. Similarly, measures of soil P availability and biotic P sufficiency differed by species but were unaffected by N fertilization. Results suggest species exhibit unique relationships to P as well as N cycles. We found little evidence that N fertilization leads to increased P limitation in these northern hardwood forests. However, species such as sugar maple and red oak may be sufficient in P, whereas beech and hemlock may be less sufficient and therefore potentially more sensitive to future N-stimulated P limitation.     

Water chemistry and nutrient budgets in an undisturbed evergreen rainforest of southern Chile

In a pristine evergreen rainforest of Nothofagus betuloides, located at the Cordillera de los Andes in southern Chile (41 °S), concentrations and fluxes of nutrients in bulk precipitation, cloud water, throughfall water, stemflow water, soil infiltration and percolation water and runoff water were measured. The main objectives of this study were to investigate canopy-soil-atmosphere interactions and to calculate input-output budgets. From May 1999 till April 2000, the experimental watershed received 8121 mm water (86% incident precipitation, 14% cloud water), of which the canopy intercepted 16%. Runoff water volume amounted 9527 mm. Bulk deposition of inorganic (DIN) and organic (DON) nitrogen amounted 3.6 kg ha^–1 year^–1 and 8.2 kg ha^–1 year^–1 respectively. Occult deposition (clouds + fog) contributes for 40% to the atmospheric nitrogen input (bulk + occult deposition) of the forest. An important part of the atmospheric ammonium deposition is retained within the canopy or converted to nitrate or organic nitrogen by epiphytic bacteria or lichens. Also the export of inorganic (0.9 kg ha^–1 year^–1) and organic (5.2 kg ha^–1 year^–1) nitrogen via runoff is lower than the input to the forest floor via throughfall and stemflow water (3.2 kg DIN ha–1 year^–1 and 5.6 kg DON ha^–1 year^–1). The low concentrations of NO ₃ ^– and NH ₄ ⁺ under the rooting depth suggest an effective biological immobilization by vegetation and soil microflora. Dry deposition and foliar leaching of base cations (K⁺, Ca²⁺, Mg²⁺) was estimated using a canopy budget model. Bulk deposition accounted for about 50% of the total atmospheric input. Calculated dry and occult deposition are both of equal value (about 25%). Foliar leaching of K⁺, Ca²⁺, and Mg²⁺ accounted for 45%, 38% and 6% of throughfall deposition respectively. On an annual basis, the experimental watershed was a net source for Na⁺, Ca²⁺ and Mg²⁺.     

The effect of elevated carbon dioxide and fertilization on primary and secondary metabolites in birch,Betula pendula (Roth)

Seedlings of European white birch (Betula pendula Roth) were grown in growth chambers for one growth season under four carbon dioxide regimes (350, 700, 1050 and 1400 ppm) and at three fertilization levels (0, 100 and 500 kg ha^–1 monthly). The soluble carbohydrates and secondary phenolics in the leaves and stems were analysed. It was found that fertilizer addition reduced the amounts of glucose and fructose while sucrose remained almost unaffected. The sugar content of leaves increased at 700 ppm and 1050 ppm of CO₂ and decreased at the highest CO₂ concentration (1400 ppm). The amounts of proanthocyanidins and flavonoids in leaves decreased with fertilization addition and increased with CO₂ enrichment. The production of simple phenolic glucosides varied according to the fertilization and CO₂ treatments. The triterpenoid content of stems seemed to increase with fertilization and CO₂-addition. Our results indicate that the production of phytochemicals in the birch seedlings is very sensitive to both fertilization and CO₂ addition, which is in agreement with earlier studies, and thus provide some support for the hypothesis of carbon allocation to plant defence when there is an excess of carbon and nutrient. The considerable variation in the production of secondary components may indicate that the synthesis of these defensive metabolites can be regulated by a plant to certain extent, depending on the ability of the plant to acclimate to changes in the physical environment.     

Response of field-grown chickpea (Cicer arietinum L.) to phosphorus fertilization for yield and nitrogen fixation

Application of phosphorus at 40, 60, 80 and 100 kg P₂O₅ ha^–1 in the presence of a uniform dressing of nitrogen (N) and potash (K₂O) each applied at 20 and 24 kg ha^–1 to chickpea (CM-88) grown in sandy loam soil in a replicated field experiment improved the nodulation response of the crop, increased its grain yield (ka ha^–1) by 18, 59, 40 and 14 percent, biomass yield (ka ha^–1) by 32, 32, 54 and 14 percent, biomass N (kg ha^–1) by 31, 48, 49, 19 percent, and biomass P (kg ha^–1) by 26, 40, 41 and 11 percent, respectively. The effect of phosphorus on the nitrogenase activity of the excised roots of chickpea was, however, inconsistent.     

Effects of soil applied herbicides on leaf nitrate reductase and crude protein in the leaf and seed of two cowpea cultivars

A glass-house study was conducted to determine the effects of four commonly used herbicides (pendimethalin, metobromuron, metolachlor and prometryne) applied pre-emergence at rates of 0, 0.125, 0.625 and 1.25 kg ha^–1, on leaf nitrate concentration (NO₃–C), nitrate reductase activity (NRA), leaf crude protein and seed protein in two cowpea cultivars, 60 day (60D) and Ife brown (IB).Control and treated plants of both cultivars showed separate peaks for NO₃–C and NRA, 49 days after planting (DAP) and 35 DAP for 60D and IB respectively. Herbicide treatment generally enhanced NO₃–C but tended to decrease NRA in both cultivars. Howver, metobromuron at 0.625 kg ha^–1 increased NRA throughout the growth period with an optimum increase of 52.5%, over the control, at 35 DAP. Pendimethalin increased NO₃–C NRA and leaf protein but did not influence seed protein appreciably. In contrast metobromuron increased NO₃–C, decreased NRA, but increased seed protein by 29.6% over the control at 0.125 kg ha^–1 in 60D. Metolachlor and prometryne were most inhibitory to seed protein development. In addition, metolachlor reversed the interdependence of NO₃–C and NRA.     

Effects of boron fertilization on `Conference' pear tree vigor, nutrition, and fruit yield and storability

The aim of the study was to examine the response of pear (Pyrus communis L.) trees to soil and foliar applications of boron (B). The experiment was carried out during 2000–2001 in a commercial orchard in Central Poland on mature `Conference' pear trees grafted on Pyrus communis var. caucasica seedlings planted at a spacing of 4 × 2.5 m on a sandy loam soil with a low hot water-extractable B status. Annually, foliar sprays with B were applied. (i) before full bloom (at green and white bud stage, and when 1–5% of flowers was at full bloom), (ii) after flowering (at petal fall, and 7 and 14 days after the end of flowering), or (iii) postharvest in fall (approximately 6 weeks before leaf fall). Spray treatments involved application of B at a rate of 0.2 kg ha^–1 in spring or 0.8 kg ha^–1 in fall. Additionally, other trees were supplied with soil-applied B at the bud break stage at a rate of 2 kg ha^–1. Trees untreated with B served as the control. The results revealed that foliar applications of B before full bloom or after harvest increased fruit set and fruit yield. Tree vigor, mean fruit weight, firmness, soluble solids concentration and titratable acidity of fruits at harvest were not affected by B treatments. Foliar B sprays before full bloom or after harvest increased B concentrations in flowers, and both leaves and fruitlets at 40 days after flowering. Only the foliar treatments after flowering and soil fertilization with B increased the content of this microelement in fruit and leaves at 80 and 120 days after full bloom. Foliar B application before full bloom or after harvest increased calcium (Ca) in fruitlets at 40 days after full bloom, in fruit, and in leaves at 80 and 120 days after full bloom. Nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) in plant tissues were not affected by B fertilization. After storage, and also after the ripening period, fruits from the trees sprayed with B before full bloom or after harvest had higher firmness and titratable acidity than those from the control trees. After the ripening period, fruits from the trees sprayed with B before full bloom or after harvest had lower membrane permeability and were less sensitive to internal browning than the control fruits. These findings indicate that prebloom and postharvest B sprays are successful in increasing pear tree yielding and in improving fruit storability under the conditions of low B availability in the soil.