Gains and losses in soil nutrients associated with harvesting and burning eucalypt rainforest

In mixed eucalypt/rainforest in southern Tasmania, samples of surface soil 0 to 2 cm, 2 to 5 cm, and 5 to 10 cm were taken from a clear-felled coupe before and after burning in 1982, from a similar coupe after burning in 1979, and from an uncut area adjacent to each coupe. Factors compared were bulk density; total organic C, N, P, Ca, Mg, and K; pH; exchangeable Ca, Mg, and K; cation exchange capacity; extractable P; and N-mineralisation rates. The effect of burning was found to be restricted mainly to the upper 2 cm of soil. The combustion of organic matter caused losses of 7360 kg organic C and 211 kg N/ha; 348 kg Ca and 282 kg Mg and 151 kg K/ha were added to the soil in ash. Burning caused significant increases in pH, exchangeable Ca, Mg, and K, and in extractable P; cation exchange capacity was reduced. In the 6 months after burning only K was leached from the upper 2 cm of soil. Equilibrium levels of NH₄?N increased initially after the fire, but between 6 and 18 months, equilibrium levels and rate of production of NH₄?N during anaerobic incubation in soil of burned coupes differed little from that in adjacent uncut forest. Rates of production of NO₃?N during aerobic incubation were very low throughout the period of study. It is concluded that for soils developed on dolerite in mixed eucalypt/rainforest, a single regeneration burn probably improves the nutritional status of the soil. Nutrients lost from the area as particulate ash are in quantities that will probably be replaced in rainfall in 15 to 20 years.     

Nutrient stocks in managed and natural humid tropical fallows

Managed fallows which recover nutrients more rapidly than natural secondary vegetation may improve the performance of shifting agriculture systems operating under inadequately long fallow cycles. Our objective was to construct nutrient balances for the soil, vegetation, and litter compartments of six planted leguminous fallows and natural secondary vegetation during 53 months. The fallows were planted on a previously cultivated Ultisol (Acrisol) in the Peruvian Amazon and included:Centrosema macrocarpum (Centrosema),Pueraria phaseoloides (Pueraria),Stylosanthes guianensis (Stylosanthes),Desmodium ovalifolium (Desmodium),Cajanus cajan (Cajanus), andInga edulis (Inga). In addition, in the natural fallow treatment secondary vegetation was allowed to establish and grow naturally. Quantities of extractable P, K, Ca, and Mg, total N, and organic C in soil to a 45 cm depth, and macrouttrients in aboveground biomass, roots, and litter were estimated at fallow planting, at 8, 17, and 29 months afterward, and at fallow clearing (53 months). Total N stocks increased by 10% in the Stylosanthes, Desmodium, Pueraria, and Inga treatments, but changed little in the Cajanus, Centrosema and natural fallows. This difference was largely due to greater net increases in both soil and vegetation compartments in the former group of treatments. In the Inga, Desmodium, and natural fallows, total stocks of P and K at 53 months were about 40% to 80% greater and 12% greater, respectively, than initial values, but Ca and Mg stocks were reduced by 25% to 40%. In the other treatments, there was generally little change in P stocks, but large (30% to 60%) reductions in K, Ca, and Mg during the course of the fallow. Although there were net decreases of stocks of P, K, Ca, and Mg in soil in all treatments during the fallow, storage of P and K in vegetation and litter in the Inga, Desmodium, and natural fallows offset losses of these nutrients from soil. These treatments also tended to accumulate more Ca and Mg in biomass and litter than the other treatments. These results suggest that leguminous fallow vegetation that accumulates large amounts of biomass may increase N, P, and K stocks, but that incomplete recuperation of Ca and Mg may limit the sustainability of short-rotation fallow-based systems on acidic, infertile soils. ei]Section editor: G R Stewart     

Changes in the soil after clearing tropical forest

Summary About one-and-a-half acres of tropical forest, of known mass and chemical composition, was cleared and burned. Soil changes during clearing and two years' cropping were studied.Following burning, approximately all the K, Ca, and Mg in the vegetation were accounted for by the rise in exchangeable K, Ca, and Mg in the soil. There was a marked rise in soil pH. A small but significant increase in C and N was attributed to admixture of parts of the vegetation with the soil.Following cultivation, there was a rapid loss of nutrients by leaching and erosion during the first year and a substantial loss of K and Mg, but smaller loss of Ca in the second year. Losses of calcium were less and of potassium more under the local practice of shifting cultivation than under cultivation treatments involving clearing of roots followed by bare fallow or a maize-cassava rotation. Depths of cultivation had little effect on nutrient losses. Losses of organic matter in the first year were rapid due to oxidation of unhumified material. They were much reduced in the second year. Greater production of food was obtained from the maize-cassava rotation than by local practice.     

Fire and soil-plant nutrient relations in a pine-wiregrass savanna on the coastal plain of North Carolina

Summary Changes in soil and plant nutrient conditions were evaluated following various burn and clip treatments in a longleaf pine-wiregrass savanna in Bladen Co., N.C., USA. Ground fires were found to add substantial quantities of N, P, K, Ca, and Mg to the soil, though not necessarily in forms immediately available to plants. Less than 1% of the total nitrogen in the charred residue (ash) is present as nitrate or ammonium. Considerable quantities of all nutrients examined were lost to the atmosphere during burning. Green leaf tissue in recently burned areas was consistently higher in N, P, K, Ca, and Mg compared to unburned areas. Howerver, when compared to similar tissues from clipped plots, burned area tissues were significantly higher in N, Ca, and Mg only. Data presented here suggest that tissue age significantly affects nutrient content and must be considered in any analysis of tissue nutrient content following burning. Within 4–6 months following fire, burned-area tissue nutrient content decreases to concentrations found in the unburned area. Burning resulted in initial enrichment of available soil nutrients including PO₄, K⁺, Ca⁺⁺, and Mg⁺⁺, however, NO₃ ^-, and NH₄ ⁺ concentrations in burned soil were not significantly different from unbruned soil. Soil and plant nutrient changes in an area burned two years in succession indicate that repeated burning may diminish nutrient availability. Plant response to various nutrient enrichment treatments of the soil indicated that nitrogen is limiting growth in both burned and unburned soils and that burning may alter some factors other than nutrients which may retard plant growth in unburned areas.     

Base cation biogeochemistry and weathering under oak and pine: a controlled long-term experiment

Large earthen-walled lysimeters at the San Dimas Experimental Forest in southern California present a unique opportunity to assess vegetation effects on biogeochemical processes and cation release by weathering in controlled soil-vegetation systems where archived samples of soil parent material are available for comparison. The lysimeters were filled in 1937 with homogenized fine sandy loam derived on site from the weathering of diorite, and planted in 1946 with scrub oak (Quercus dumosa) and Coulter pine (Pinus coulteri). Changes in base cation contents were measured in above-ground biomass, and total and exchangeable soil pools to a depth of 1 meter. All cations in the non-exchangeable soil pool decreased relative to the initial fill material, indicating release by weathering. Sodium and K were depleted from both exchangeable and non-exchangeable pools of the soils. Plant uptake of Na was minimal, whereas K storage in vegetation exceeded the loss from the exchangeable soil pool. In both soil-vegetation systems, but especially for oak, there was an increase in exchangeable Ca and Mg. For all base cations, storage in above-ground biomass was greater for oak, whereas losses by weathering from the non-exchangeable soil pool were greater under pine. Strong evidence supports biocycling as a controlling mechanism resulting in greater Ca and Mg release by weathering under pine. In addition, decreases in non-exchangeable Ca and Mg were strongly correlated to decrease in Si under oak, whereas no correlation was observed under pine. We conclude that weathering reactions or stoichiometry differed between vegetation types.Corresponding author     

Young secondary vegetation and soil interactions in Izabal,Guatemala

Summary A study of the relationships of soils and vegetation was undertaken in the humid tropical region of Lake Izabal, Guatemala, Central America. Soils and associated 10-month-old secondary growth were analyzed for N, P, K, Ca, and Mg. In addition, organic matter, Al and pH were determined in the soil samples and plant biomass for the secondary growth were calculated. The secondary growth biomass averaged 9,710 kg/ha for the 10-month growth period. Total nutrient content of the vegetation increased linearly with the biomass, except for Mg. The antagonism of Mg on K and Ca nutrition was quite significant when Mg exceeded Ca in the soil under shifting cultivation. Pure stands ofHeliconia sp. andGynerium sp. appeared to be more efficient in accumulating P than stands of mixed vegetation. Chemical composition and dry matter production of native vegetation may provide additional information to evaluate soil fertility in the humid tropics.     

The effect of Mg on Ca,K and P content of date palm seedlings under mycorrhizal and non-mycorrhizal conditions

The effects of the presence or absence of Mg in the nutrient solution and of vesicular-arbuscular mycorrhizal fungi (VAMF) on the content and partitioning of Ca, K and P between root and shoot of date palm (Phoenix dactylifera) seedlings were examined under greenhouse conditions using soil as basal medium. Mg content of the soil was 14.95 µmol/g dry soil. The infection percentages after inoculation of VAMF were 66.0% and 55.5%, respectively, on application of –Mg and +Mg nutrient solution. Ca content of both roots and shoots did not change by these treatments; but a highly significant decrease in shoots was recorded on –Mg and +VAMF treatment. K content of root was significantly elevated by –Mg and +VAMF treatment but no changes were observed in shoots. P content of both roots and shoots increased significantly with +VAMF regardless of the presence or absence of Mg.     

Relations of soil properties to topography and vegetation in a subtropical rain forest in southern Taiwan

Soil chemical properties for a subtropical rain forest in the Nanjenshan Reserve, southern Taiwan, were examined to determine soil-landscape and soil-vegetation relationships. Soil sampling sites were separated into four groups based on landscape features and exposure to the prevailing northeasterly monsoon winds. Corresponding vegetation types were delimited along the first DCA axis. The forest showed a drastic change both in structure and floristic composition along the wind-stress gradient. Redundancy analysis (RDA) showed that both topographic variables and vegetation types were needed to explain the variation in soil data. Soil properties that differed significantly among landforms were pH, available N, CEC, exchangeable Al, K, Ca and Mg. Levels of pH, exchangeable Ca and Mg increased in a downslope direction, and exchangeable Al tended to be higher in the upper slope soils. These trends pointed to the importance of slope processes in redistribution of soil minerals. The main differences in soil properties attributed to the influence of the occupying vegetation were apparently aspect dependent. The contents of available N, exchangeable K, and CEC in the 0–40 cm depth of soils under windward low-stature (mostly sclerophyllous) forest were consistently lower compared to those under the leeward forest. For a given catena, however, soil variability associated with vegetation differences seemed to be confounded by the slope processes.     

Urease activity in soils

Summary The availability of Ca from different levels of gypsum and calcium carbonate in a non-saline sodic soil has been investigated. Different levels of tagged gypsum (Ca⁴⁵SO₄.2H₂O) and calcium carbonate (Ca⁴⁵CO₃) (i.e. 0, 25, 50, 75, and 100 per cent of gypsum requirement) were mixed thoroughly in 3.5 Kg of a non-saline alkali soil (ESP, 48.4; ECe, 2.68 millimhos/cm). Dhaincha (Sesbania aculeata) — a legume and barley (Hordeum vulgare L.) — a cereal were taken as test crops. Increasing levels of gypsum caused a gradual increase in the yield of dry matter, content of Ca and K in the plant tops and Ca:Na and (Ca+Mg):(Na+K) ratios in both the crops. Application of calcium carbonate caused a slight increase in the dry matter yield, content of Ca and Mg and Ca:Na and (Ca+Mg):(Na+K) ratios in barley, however, in case of dhaincha there was no such effect. Gypsum application caused a gradual decrease in the content of Na and P in both the crops. Total uptake of Ca, Mg, K, N and P per pot increased in response to gypsum application. The effect of calcium carbonate application on the total uptake of these elements was much smaller on dhaincha, but in barley there was some increasing trend.Increasing application of tagged gypsum and calcium carbonate caused a gradual increase in the concentration and per cent contribution of source Ca in both the crops, although, the rate of increase was considerably more in dhaincha. The availability of Ca from applied gypsum was considerably more than that from applied calcium carbonate. Efficiency of dhaincha to utilize Ca from applied sources was considerably more (i.e. about five times) than that of barley     

云雾山典型草原火烧不同恢复年限土壤化学性质变化

云雾山典型草原处于黄土高原半干旱地区,也是草原火灾多发区,试验比较了未烧地与新烧地、火烧后3 a和火烧后11 a土壤有机碳(SOC)、全N、全P和速效K含量的变化过程。测量的土壤深度为50 cm,每10 cm一层,比较了4个样地0—10 cm、10—20 cm、20—30 cm、30—40 cm、40—50 cm土壤养分的变化。结果表明:(1)新烧地土壤剖面各层SOC、全N、全P和速效K含量都显著高于未烧地。(2)火烧后3 a样地土壤剖面各层SOC、全N、全P和速效K含量与未烧地差异不显著。(3)火烧后11 a样地土壤剖面各层全N含量都显著高于未烧地,SOC、全P和速效K含量除了0—10 cm层与未烧地差异不显著外,其它土层均显著增加。(4)4个样地的土壤剖面各层从上到下SOC、土壤全N、全P和速效K含量呈递减趋势。(5)3个火烧样地土壤表层(0—10 cm)的pH值和未烧地差异不显著。     

Nutrient pools and fluxes of the ground vegetation in coniferous forests due to fertilizing,liming and amelioration

The effects of fertilization and amelioration treatments on some nutrient pools and fluxes of ground vegetation in mature pine and spruce stands on acid soils in South Germany are described. In N-limited pine forests with moderate canopy density and with Deschampsia flexuosa an additional N-accumulation in biomass of 20–40 kg ha^-1 occurred 3 years after pure N-fertilization. The N, P, K-cycling through ground vegetation was stimulated more than 10 years by a combined N + CaCO₃ + P treatment leading toa shift in dominance from cryptogams and Ericaceae towards Deschampsia flexuosa and ruderal species like Epilobium angustifolium. The effect of a lupine treatment (combined with initial soil preparation, liming and P supply) was far stronger than the effect of the other experimental procedures. But the fertilizer and amelioration effects on the herb layer of pine forests tended to decline after two decades for different reasons.The shade-tolerant ground vegetation in a nitrogen-saturated spruce forest was not able to prevent heavy additional nitrate losses from upper mineral soil after dolomitic liming. But the Ca, Mg and K fluxes through ground vegetation were strongly elevated in the third year after treatment.     

Biogeochemical consequences of the transformation of native Cerrado into Pinus caribaea plantations in Brazil

Under the same climatic and edaphic conditions, native savanna vegetation in Brazil, the Cerrado, shows a lower stature and canopy cover than planted Pinus caribaea Morelet forests. To assess the differences in biogeochemical element cycling we compared the nutrient economy of Cerrado and Pinus on three replicate plots of each forest type. The mean nutrient storage in the soil organic layer under Pinus (N: 2630; P: 141; K: 103; Ca: 131; Mg: 20 kg ha^–1) was substantially higher than under Cerrado (N: 23; P: 1.2; K: 0.83; Ca: 5.8; Mg: 1.0 kg ha^–1) probably because the Pinus roots explored a larger soil volume. The Pinus trees had a higher nutrient-use efficiency as indicated by higher mean litter mass per unit nutrient in litter (N: 108; P: 2290; K: 729; Ca: 1360; Mg: 5420; S: 1190; Fe: 2960; Mn: 9990, Zn: 145000) than the Cerrado trees (N: 94; P: 1810; K: 619; Ca: 302; Mg: 938, S: 746; Fe: 1800; Mn: 7880; Zn: 63700). Mean annual small litterfall collected in 0.25-m² samplers between May 1997 and April 1999 was 2.1 Mg ha^–1 in Cerrado and 7.8 in Pinus. The litterfall rates of the 1–3 week collection intervals correlated negatively with the soil matric potential indicating that litterfall was partly related to water stress. The fluxes of N (73 kg ha^–1 year^–1), P (3.7), K (11), S (7.0), and Mn (0.83) to the soil with litterfall under Pinus were greater than the litterfall+turnover of the grass/herbs layer under Cerrado (N: 39, P: 2.8, K: 8.6, S: 5.4, Mn: 0.79 kg ha^–1 year^–1), those of Zn (0.06–0.07) were similar, and those of Ca (Pinus: 5.9/Cerrado: 10), Mg (1.5/4.4), and Fe (2.9/4.0) were smaller. Mean residence times of the organic matter and of all elements were longer in the soil organic layer under Pinus (3.7–26 years in the Oi horizon, 8.1–907 years in the whole organic layer) than under Cerrado (0.22–3.6 years in the Oi horizon, the only organic horizon under Cerrado). Our results demonstrate that the main differences in biogeochemical element cycling between the Pinus forest and the Cerrado consisted of a larger nutrient storage in the organic layer, a higher nutrient-use efficiency, and slower nutrient release rates from the organic layer in the Pinus forest than in the Cerrado. Nutrient cycling as assessed by the nutrient fluxes with litterfall was only partly faster in the Pinus forest than in the Cerrado.     

Effects of water and nutrient applications in a Scots pine stand to tree growth and nutrient cycling

In a Scots pine forest stand, demineralized water and a complete set of nutrients with water were applied to the soil by means of frequent irrigation for four years in order to eliminate water and nutrient shortage of the trees. Apart from this optimization, dissolved (NH₄)₂SO₄ was irrigated at a rate of 120 kg N ha^-1 y^-1 to create a situation of N excess. Effect of treatments on tree growth and chemical composition of soil water and vegetation were monitored. From the first treatment year onwards basal area growth increased by ca. 35% as a result of the increased water supply. Nutrient applications increased K and P concentrations in pine needles immediately, but growth was enhanced only in the fourth treatment year and coincided with an improved K supply. Most of the applied P and K was retained in the soil, and only 6% was recovered in the vegetation. Tree nutrient status did not respond on Ca and Mg applications, whereas Ca and Mg seepage losses were increased with ca. 5 kg ha^-1 y^-1. The applied NH₄ was mostly retained in the 0–20 cm surface soil and caused a drastic increase of Al in soil solution. Tree growth was stimulated initially by extra NH₄, but was hampered after three years obviously because of a decreased P nutrition. The applied base cations were absorped to the soil and the accompanying anions were leached, thus temporarily increasing the acidification of the soil solution.     

Soil physiochemical changes following 12 years of annual burning in a humid–subtropical tallgrass prairie: a hypothesis

Burning is known to stimulate growth of grassland vegetation, promote species diversity, and inhibit natural invasion by woody plants. However, the frequency at which grasslands are burned as part of their management can affect soil nutrient content and, ultimately, productivity. The objective of this study was to characterize changes in soil physical and chemical properties in a native tallgrass prairie after 12 years of annual burning. In 1989, five soil samples from the 0 to 10 cm depth were collected along a transect through a 3 ha parcel of native tallgrass prairie in central Arkansas. Soil sampling was repeated in 2001 to assess changes over time. Results showed that soil bulk density, electrical conductivity, extractable P, Na, Fe, and Mn decreased significantly (P < 0.05), while soil organic matter, total N and C, and the C/N ratio increased significantly (P < 0.05) within the 12-year period during which annual burning was the only imposed management practice. Mean extractable K, Ca, Mg, S, and Zn levels were all lower in 2001 than in 1989, but differences were not significant, while soil pH did not change. The results of this study indicate that annual export of several essential plant nutrients during prescribed burning of relatively small, remnant prairie fragments exceeds annual imports from atmospheric deposition and/or organic matter mineralization. Annual prescribed burning may be too frequent to maintain optimal ecosystem functioning and productivity. Decreasing the frequency of prescribed burning for native grassland management may help to retain more soil nutrients to sustain a higher level of productivity.     

Effects of forest clear-cutting on the sulphur, phosphorus and base cations fluxes through podzolic soil horizons

Clear-cutting considerably alters the flow of nutrients through the forest ecosystem. These changes are reflected in soil solution concentrations and fluxes. The effects of clear-cutting (stems only) on the fluxes of water soluble phosphorus (P), sulphur (S) and base cations (Ca, Mg and K) through a podzolic soil were studied in a Norway spruce dominated mixed boreal forest in eastern Finland. Bulk deposition, total throughfall (throughfall + stemflow) and soil percolate from below the organic (O), eluvial (E) and illuvial (B) horizons were collected for 4 years before and for 3 years after cutting. Annual deposition loads (kg ha^–1) to the forest floor were less after clear-cutting, averaging 1.7 S, 0.84 Ca, 0.14 Mg, 0.64 K and 0.10 P. Before cutting, the loads were 4.6 S, 2.7 Ca, 0.70 Mg, 6.2 K and 0.20 P. Annual fluxes of total S and sulphate (SO ₄ ^2– ) from below the O-horizon were also lower (33%) after clear-cutting, total S averaging 2.0 kg ha^–1, the flux from below the B-horizon also diminished after clear-cutting. The flux of total P (mainly inorganic) from below the O-horizon increased threefold (6.9 kg ha^–1; sum over the 3-year period) compared to period before cutting. The fluxes of base cations from below the O-horizon increased twofold. The flux of K⁺ from below the O- and E-horizons was most strongly correlated with that of phosphate (PO ₄ ^3– ) and those of Ca²⁺ and Mg²⁺ with the DOC flux. Increased fluxes of P and base cations to the mineral soil generated only slightly increased fluxes from below the B-horizon. The retention of base cations and P in the mineral soil indicates there was little change in leaching to ground and surface waters after clear-cutting.     

Soil chemical properties as related to forest succession in a highland area in north-east Tasmania

The relationship between vegetational type and a number of soil chemical factors was examined in secondary successions from fire-maintained eucalypt/grass to climax rainforest communities growing on uniform granitic soil parent material. Canonical variates analysis, which utilized the following variables: pH; loss on ignition; total N, P, K, Ca, and Mg; cation exchange capacity and exchangeable Ca, K, and Mg; and potentially mineralizable N, revealed close overall similarity between surface soils of adjacent types, and significant differences among those of types distant from each other in the successional sequences. Exchangeable Ca, mineralizable N, total N. P, and Mg, and pH all differed significantly among soils of the vegetational types. However, the only identifiable gradients in soil properties that were detected within a successional sequence were in total and mineralizable N, which tended to increase, and pH, which generally tended to decrease with progression towards the climax vegetation. Nitrification was promoted by the presence of Acacia dealbata and apparently inhibited by the presence of Leptospermum lanigerum; it was more rapid in soils beneath late successional vegetation than in those from climax vegetation or early stages of succession, and was inhibited in soil from old (> 200 years) grassland. It was concluded that differences among soils in chemical composition and rates of mineralization of N were due to differences in species composition of the vegetational types that they carried for the time being.     

Seasonal fluctuations of the mineral concentration of alder (Alnus glutinosa (L.) Gaertn.) from the field

Summary The seasonal fluctuation of N, P, K, Ca, Mg, Fe, Mn, Mo, and Co, in leaves, roots and nodules of 40–50 year oldAlnus glutinosa trees growing at four different locations along the banks of the Tormes river, in the province of Salamanca, was studied. Also, the evolution of the soil organic matter under the trees sampled was evaluated. The data obtained for the various nutrient elements in the three plant parts are statistically treated at the significance levels of 99–95 per cent, and some remarks as to the nutritional status of the European alder in respect to the nutrients and its contribution to soil nutrient-cycling are provided. A positive correlation was found between N–P, N–K, N–Mg, and N–Mo, in leaves, and between N–P, N–K, N–Fe, N–Mn, and N–Mo in root nodules. In roots only, no significance at any level was obtained between N and any of the elements analyzed.     

Mg2+ blocks myogenic tone but not K+-induced constriction: role for SOCs in small arteries

The effects of Mg(2+) and nifedipine (Nif) on vasoconstriction and Ca(2+) transients were studied in intact, pressurized rat mesenteric arteries with myogenic tone. Changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) were measured with confocal microscopy in fluo 4-AM loaded, individual myocytes. Myogenic tone was abolished by 10 mM Mg(2+) or 0.3 microM Nif. Contractions induced by 75 mM K(+) depolarization were blocked by 0.3 microM Nif, but not by 10 mM Mg(2+). Phenylephrine (PE; 5 microM) evoked sustained [Ca(2+)](cyt) elevation and vasoconstriction with superimposed Ca(2+) oscillations and vasomotion. The subsequent addition of 10 mM Mg(2+) or 0.3 microM Nif reduced [Ca(2+)](cyt) and abolished plateau vasoconstriction. When added before PE, both Mg(2+) and Nif abolished the PE-evoked Ca(2+) oscillations and vasomotion. Mg(2+) dilated the PE-constricted arteries after a brief (< or =180-240 s) vasoconstriction, but Nif did not. Both agents also abolished the vasoconstriction attributed to Ca(2+) entry through store-operated channels (SOCs) during internal Ca(2+) store refilling that followed store depletion. The data suggest that Ca(2+) entry through SOCs helps maintain both myogenic tone and alpha(1)-adrenoceptor-induced tonic vasoconstriction.     

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

镉胁迫下草莓幼龄期叶、根矿质元素积累和分布的变化

采用水培实验,研究重金属镉对草莓幼龄期叶、根矿质元素含量和分布的影响。结果表明,高量镉降低草莓根中K、Ca、Mg、P、Cu、Zn、Mn、Fe的积累,叶片相应元素以及B、Mo含量也随镉浓度增大而呈降低趋势;但镉浓度较低时,K、Mg、P、Zn在叶、根中的含量均增加,而后才随镉处理浓度提高而降低。在镉胁迫下,同一元素在草莓叶、根之间的分布也受到影响,而且某些矿质元素含量间有显著相关性。