Nutritional status of a Norway spruce stand in SW Sweden in response to compensatory fertilization

The response of a Norway spruce (Picea abies L. Karst.) forest, located in SW Sweden, to various combinations of nitrogen, phosphorus, potassium and dolomite was investigated two and five years after fertilization in a semi-factorial experiment. The aim has been to apply a diagnostic field test as a base for development of suitable composition of compensatory or vitality fertilizers within an area showing nutritional imbalances. Different ways of describing foliar analysis were tested: current needle (C) critical concentrations, Deviation from Optimum Percentage (DOP), and nutrient/N percentage ratios. The graphical Relative Concentration and Content change (RCC) technique was also used. Nutritional status of the control plots showed deficiency in N, P and K. According to the analyses, N alone or N together with P are the growth-limiting elements. Fertilization with N alone induced limitation of K or P. Based on our results, NPK is a suitable compensatory fertilizer at the site. The only significant difference between dolomite and non-dolomite treatments was in Ca and Mg concentrations. The effect of dolomite on Ca and Mg became more evident during the fifth season following fertilization. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of fertilization and liming on the chemical soil conditions and element distribution in forest soils

Summary The distribution and storage of major elements in acid soils from a spruce and a beech forest was investigated after fertilization of NH₄NO₃ and KCl followed by Ca and Mg fertilization by 2 liming applications. All fertilizers were applied on top of the soil without mixing. Most of the added Ca and Mg was detected in the humus layer, a significant part of it still in carbonatic form. The effect of liming on mineral soil pH is very low, and was only observed in the 0–10 cm layer. However, base saturation of the mineral soil increased. The storage of C and N of the humus layer was not affected. N fertilization increased the N storage of the soil only under beech, but was followed by heavy NO₃-losses with seepage water under spruce. High leaching rates for K were also found in the spruce stand. The amount of K that was not leached increased the pool of exchangeable K in the deeper soil layer.     

陕南秦巴山区水稻施肥现状评价

为了解陕南秦巴山区水稻施肥现状及农户养分资源投入中存在的问题,提出解决问题的对策,对测土配方施肥项目2006-2009年的11个县2854户调查数据进行了分析和评价.结果表明: 陕南秦巴山区水稻平均产量为7822 kg·hm^-2,中等产量农户所占比例为509%.总氮(N)、磷(P₂O₅)、钾(K₂O)养分投入量分别为169、68、54 kg·hm^-2,其中化肥氮(N)、磷(P₂O₅)、钾(K₂O)养分投入量分别为159、62、45 kg·hm^-2,偏生产力分别为51.52、135.69和158.26 kg·kg^-1.根据养分分级等级,农户化肥氮、磷、钾投入合理比例分别为48.0%、42.4%和7.2%,过量比例分别为22.6%、11.2%和0.6%,不足比例分别为29.4%、46.5%和92.2%.如果化肥养分投入不足的农户将施肥量增加到合理水平,陕南秦巴山区水稻可增产7.70万t.该区域水稻施肥存在的问题主要包括:氮肥和磷肥投入过量和不足并存,钾肥和有机肥投入不足.今后该区域水稻施肥的重点是平衡氮肥和磷肥用量,增加钾肥和有机肥用量,增加追肥尤其是钾肥的施用.     

Nutritional Status of the Cauliflower Cultivar ‘Verona’ Grown with Omission of out Added Macronutrients

Knowledge of plant nutritional status allows an understanding of the physiological responses of plants to crop fertilization. A hydroponic experiment evaluated the symptoms of macronutrient deficiency in cauliflower ‘Verona’ and determined: a) the macronutrient contents of foliar tissues when visual symptoms were observed, b) macronutrients content of foliar and inflorescence tissues at harvest. The effect of nutrient deficiency on inflorescence mass was also evaluated. Nitrogen deficiency caused chlorosis followed by purple color in the old leaves, while P deficiency caused only chlorosis in old leaves. Chlorosis at the edge of old leaves progressing to the center of the leaves was observed with the omission of K, and after was observed necrosis in the chlorotic areas. Ca deficiency caused tip burn in new leaves, while Mg deficiency caused internerval chlorosis in old leaves. The omission of each macronutrient reduced inflorescence dry matter. This deleterious effect was larger for N, P, and K deficiencies, reducing inflorescence dry matter by 87, 49, and 42%, respectively. When the nutrient solutions without N, P, K, Ca, or Mg were supplied to cauliflower plants, the macronutrient contents at harvest were 8.8, 0.6, 3.5, 13.0, and 0.8 g kg^-1 in the foliar tissues and 27.3, 2.2, 21.6, 1.1, and 0.7 g kg^-1 in the inflorescence tissues, respectively.     

Mineralization of carbon and nitrogen in soil samples taken from three fertilized pine stands: Long-term effects

Seven years after fertilization the rate of CO₂ production in the soil samples taken from the organic horizons of a poor pine forest site (Calluna vulgaris site type), treated with urea or ammonium nitrate with lime, was lower than that in the unfertilized soil. The same trend was also observed in samples of theEmpetrum-Calluna site type 14 years after fertilization. In the more fertileVaccinium myrtillus site type these rapidly-soluble N fertilizers had a long-term enhancing effect on the production of CO₂. Apatite and biotite eliminated the decreasing effect of urea on the production of CO₂. One reason for this might be the long-term increase in soil pH caused by apatite and biotite, or their constituents (Ca, Mg, K, P). Nitroform (a slow-releasing N fertilizer) had no statistically significant effect on the production of CO₂ in soil samples from any of the forest types. Despite the high N mineralization in the samples from nitroform fertilized soils there was no nitrification, and the high content of total N indicated that after nitroform fertilization the losses of N were low.The correlation between the net mineralization values for C (CO₂ production) and N was poor. However, multiple linear regression analysis, which also took into account the effect of nutrients and pH, indicated that there was a link between the mineralization of C and N.     

Land use intensity,rather than plant species richness,affects the leaching risk of multiple nutrients from permanent grasslands

The intensification of land use constitutes one of the main drivers of global change and alters nutrient fluxes on all spatial scales, causing landscape‐level eutrophication and contamination of natural resources. Changes in soil nutrient concentrations are thus indicative for crucial environmental issues associated with intensive land use. We measured concentrations of NO₃–N, NH₄–N, P, K, Mg, and Ca using 1,326 ion‐exchange resin bags buried in 20 cm depth beneath the main root zone in 150 temperate grasslands. Nutrient concentrations were related to land use intensity, that is, fertilization, mowing, grazing intensities, and plant diversity by structural equation modeling. Furthermore, we assessed the response of soil nutrients to mechanical sward disturbance and subsequent reseeding, a common practice for grassland renewal. Land use intensity, especially fertilization, significantly increased the concentrations of NO₃–N, NH₄–N, K, P, and also Mg. Besides fertilization (and tightly correlated mowing) intensity, grazing strongly increased NO₃–N and K concentrations. Plant species richness decreased P and NO₃–N concentrations in soil when grassland productivity of the actual year was statistically taken into account, but not when long‐term averages of productivity were used. Thus, we assume that, in the actual study year, a distinct drought period might have caused the observed decoupling of productivity from fertilization and soil nutrients. Breaking up the grassland sward drastically increased NO₃–N concentrations (+146%) but reduced NH₄–N, P, and K concentrations, unbalancing soil nutrient stoichiometry and boosting the risk of N leaching. Reseeding the sward after disturbance did not have a short‐term effect on nutrient concentrations. We conclude that renewal of permanent grassland should be avoided as far as possible and future grassland management has to strongly rise the effectiveness of fertilization. Additionally, grassland management might have to increasingly taking care of periods of drought, in which nutrient additions might not increase plant growth but potentially only facilitate leaching.     

Litter production and forest floor nutrient dynamics in pine and hardwood stands of New Brunswick, Canada

Biomass and nutrient transfer (N, P, K, Ca, Mg) of overstory (branches and leaves) and understory litter fall were examined over a two year period in four jack pine stands aged 16, 29, 49 and 57 years and four mixed hardwood stands aged 7, 17, 20 and 29 years. Relative amounts of the five nutrients in litter fall for both series of stands were N > K ≷ Ca > P = Mg. Return of mineral elements to the forest floor was generally twice as high on the hardwood stands as for similarly aged pine stands. Overall return of nutrients plotted versus stand age generally exhibited a plateau relationship, with relatively little difference among stands; however, some exceptions occurred. Understory contribution to litter fall was very important on these stands, since in most cases the nutrient mass in understory litter was usually similar to or higher than that from the tree layer. Data on forest floor biomass, nutrient distribution and turnover rates of these stands were also presented; mobility of nutrients in the forest floor was in the order K > Mg ≥ P ≥ Ca ≥ N.     

Long-term availability of nutients in forest soil derived from fast- and slow-release fertilizers

The availability of P, K and Mg was studied in boreal forest soil treated 10 years earlier with slow- and fast-release fertilizers. Fast release superphosphate, potassium chloride and magnesium sulphate and slow-release apatite (P) and biotite (K, Mg) were applied alone or together with urea or urea+limestone. The concentrations of total and exchangeable nutrients in the organic horizon and the concentration of exchangeable nutrients in the uppermost mineral horizon were measured. CO₂ production during aerobic laboratory incubation was used to estimate the microbial activity and substrate-induced respiration to determine the microbial biomass C in soil. Biotite caused a moderate but persistent increase in pH in the organic horizon, but this increase was smaller than with lime. The fast-release fertilizers had no effects on the nutrient status of the soil 10 years after the fertilization. However, apatite and biotite still increased the total content of Mg, K and P and the concentrations of exchangeable Mg and soluble P in soil. On the other hand, simultaneous addition of lime and biotite reduced the release of soluble P from apatite. The reduction in soil microbial activity found with urea and the fast-release salts soon after application was no longer evident 10 years later. There was no increase in nitrification in the fertilized soils, not even with the urea+lime treatment. The previous results right after the application and the results presented here do not indicate major leaching of nutrients from the slow-release fertilizers to the deeper soil profiles.     

Nutrient resorption of two evergreen shrubs in response to long-term fertilization in a bog

Plant resorption of multiple nutrients during leaf senescence has been established but stoichiometric changes among N, P and K during resorption and after fertilization are poorly understood. We anticipated that increased N supply would lead to further P limitation or co-limitation with N or K [i.e. P-(co)limitation], decrease N resorption and increase P and K resorption, while P and K addition would decrease P and K resorption and increase N resorption. Furthermore, Ca would accumulate while Mg would be resorbed during leaf senescence, irrespective of fertilization. We investigated the effect of N, P and K addition on resorption in two evergreen shrubs (Chamaedaphne calyculata and Rhododendron groenlandicum) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada. In general, N addition caused further P-(co)limitation, increased P and K resorption efficiency but did not affect N resorption. P and K addition did not shift the system to N limitation and affect K resorption, but reduced P resorption proficiency. C. calyculata resorbed both Ca and Mg while R. groenlandicum resorbed neither. C. calyculata showed a higher resorption than R. groenlandicum, suggesting it is better adapted to nutrient deficiency than R. groenlandicum. Resorption during leaf senescence decreased N:P, N:K and K:P ratios. The limited response of N and K and the response of P resorption to fertilization reflect the stoichiometric coupling of nutrient cycling, which varies among the two shrub species; changes in species composition may affect nutrient cycling in bogs.     

Multiple nutrients limit litterfall and decomposition in a tropical forest

To explore the importance of 12 elements in litter production and decomposition, we fertilized 36 1600 m²-plots with combinations of N, P, K, or micronutrients (i.e. B, Ca, Cu, Fe, Mg, Mn, Mo, S, Zn) for 6 years in a lowland Panamanian forest. The 90% of litter falling as leaves and twigs failed to increase with fertilization, but reproductive litter (fruits and flowers) increased by 43% with N. K enhanced cellulose decomposition; one or more micronutrients enhanced leaf-litter decomposition; P enhanced both. Our results suggest tropical forests are a non-Liebig world of multiple nutrient limitations, with at least four elements shaping rates of litterfall and decomposition. Multiple metallomic enzymes and cofactors likely create gradients in the break down of leaf litter. Selection favours individuals that make more propagules, and even in an N-rich forest, N is a non-substitutable resource for reproduction.     

林地覆盖经营对雷竹鞭根主要养分内循环的影响

为了给林地覆盖经营雷竹(Phyllostachys violascens)林可持续经营提供理论参考,探讨了休养式覆盖经营(覆盖3a后休养3a)、长期覆盖经营(覆盖6a)和不覆盖雷竹林(CK)2年生壮龄竹鞭及其1级、2级根N、P、K、Mg、Ca、Fe浓度和养分迁移、内循环率的差异。结果表明:不同覆盖经营年限雷竹林N、P、K、Mg、Ca和Fe浓度总体上1级根显著高于2级根。1级根和2级根中均存在N、P、K、Mg的养分内循环,且1级根养分内循环率大于2级根,Fe、Ca内循环不明显。N、P、K、Mg养分浓度与养分迁移速率随时间的推延,1级根为持续降低,2级根为先升高后降低。与不覆盖雷竹林相比,休养式林地覆盖经营总体上提高了1级、2级根的N、P、K、Ca的浓度和P、K、Mg的迁移速率、N、P、K的迁移量、P、K的养分内循环率以及1级根Mg的浓度和迁移量、2级根N的迁移速率和Mg的内循环率;长期林地覆盖经营虽提高了雷竹1级根N、K的浓度和N的迁移量及2级根N的浓度和内循环率,但总体上降低了1级根P、K、Mg和2级根N、P、Mg的迁移量与1级、2级根P、Mg的迁移速率及P、K、Mg的养分内循环率。研究表明:雷竹林鞭根中存在明显的养分内循环,且1级根对养分内循环的贡献较大。休养式林地覆盖经营利于雷竹林对养分的循环利用,而长期覆盖经营阻碍了根系对养分的平衡吸收,减弱了根系养分的内循环,不利于雷竹林的生长更新。     

Effectiveness of wood ash containing charcoal as a fertilizer for a forest plantation in a temperate region

Amendment of forest soils with mixed wood ash (MWA) generated in biomass power plants can prevent the depletion of soil nutrients that results from the intensive harvesting of forest plantations. Unlike fly wood ash, MWA contains charcoal and is characterized by a lower release of nutrients, so that it might be useful as a long term source of nutrients and soil organic matter. However, in order to use MWA as a fertilizer in forest systems, its effectiveness as regards supplying P and N must be improved. These aspects were studied in a 4 year-trial carried out in a Pinus radiata plantation. MWA was added alone or with mineral P, and the results were compared with those obtained with a combination of Ca(OH)₂ and mineral P. The application of MWA together with mineral P fertilizer increased the nutrient supply to the trees, as revealed by the changes in nutrient concentrations, lower values of resorption efficiencies and improved tree growth. The results showed that the amounts of Ca, Mg and K supplied by the MWA were suitable for maintenance of soil reserves. However, the presence of charcoal may have decreased the availability of P. The application of the MWA led to lower soil N mineralization rates and mineral N concentrations, which may affect N-limited systems. The use of density-dependent single tree increment models enabled the positive effects on tree growth of fertilization and thinning to be distinguished. For the treatments supplemented with mineral P, multiplicative factors of 1.13 to 1.15 can be applied to obtain post-thinning predictions of 4-year single-tree basal area increments. Although MWA can be used as a long term source of nutrients, charcoal temporarily reduces the availability of P and N.     

Cultivation of Miscanthus under West European conditions: Seasonal changes in dry matter production,nutrient uptake and remobilization

There is increasing interest in cultivation of Miscanthus as a source of renewable energy in Europe, but there is little information on its nutrient requirements. Our aim was to determine the nutrient requirement of an established Miscanthus crop through a detailed study of nutrient uptake and nutrient remobilization between plant parts during growth and senescence. Therefore dry matter of rhizomes and shoots as well as N, P, K and Mg concentration under three N fertilizer rates (0, 90, and 180 kg N ha-1) were measured in field trials in 1992/93 and at one rate of 100 kg N h-1 in 1994/95.Maximum aboveground biomass in an established Miscanthus crop ranged between 25-30 t dry matter ha-1 in the September of both trial years. Due to senescence and leaf fall there was a 30% loss in dry matter between September and harvest in March. N fertilization had no effect on crop yield at harvest. Concentrations of N, P, K and Mg in shoots were at a maximum at the beginning of the growing period in May and decreased thereafter while concentrations in rhizomes stayed fairly constant throughout the year and were not affected by N fertilization.Nutrient mobilization from rhizomes to shoots - defined as the maximum change in nutrient content in rhizomes from the beginning of the growth period measured in 1992/93 was 55 kg N ha-1, 8 kg P ha-1, 39 kg K ha-1 and 11 kg Mg ha-1. This is equivalent to 21 N, 36 P, 14 K and 27 Mg of the maximum nutrient content of the shoots. Nutrient remobilization from shoots to rhizomes defined as the increase in nutrient content of rhizomes between September and March measured in 1994/95 was 101 kg N ha-1, 9 kg P ha-1, 81 kg K ha-1 and 8 kg Mg ha-1 equivalent to 46 N, 50 P, 30 K and 27 Mg of nutrient content of shoots in September. Results showed that nutrient remobilization within the plant needs to be considered when calculating nutrient balances and fertilizer recommendations.     

Litterfall Dynamics Under Different Tropical Forest Restoration Strategies in Costa Rica

In degraded tropical pastures, active restoration strategies have the potential to facilitate forest regrowth at rates that are faster than natural recovery, enhancing litterfall, and nutrient inputs to the forest floor. We evaluated litterfall and nutrient dynamics under four treatments: plantation (entire area planted), tree islands (planting in six patches of three sizes), control (same age natural regeneration), and young secondary forest (7–9‐yr‐old natural regeneration). Treatments were established in plots of 50 × 50 m at six replicate sites in southern Costa Rica and the annual litterfall production was measured 5 yr after treatment establishment. Planted species included two native timber‐producing hardwoods (Terminalia amazonia and Vochysia guatemalensis) interplanted with two N‐fixing species (Inga edulis and Erythrina poeppigiana). Litter production was highest in secondary forests (7.3 Mg/ha/yr) and plantations (6.3), intermediate in islands (3.5), and lowest in controls (1.4). Secondary forests had higher input of all nutrients except N when compared with the plantation plots. Inga contributed 70 percent of leaffall in the plantations, demonstrating the influence that one species can have on litter quantity and quality. Although tree islands had lower litterfall rates, they were similar to plantations in inputs of Mg, K, P, Zn, and Mn. Tree islands increased litter production and nutrient inputs more quickly than natural regeneration. In addition to being less resource intensive than conventional plantations, this planting design promotes a more rapid increase in litter diversity and more spatial heterogeneity, which can accelerate the rate of nutrient cycling and facilitate forest recovery.     

Effect of N,K, and P fertilization,N source,and clipping on potential tetany hazard of bromegrass

Summary The objective of this field study was to determine early-season effects of N source, N, K, and P fertilization, and clipping (to simulate grazing) on potential tetany hazard of bromegrass (Bromus inermis L.) as indicated by the chemical composition of its forage. Tetany is a metabolic disorder of ruminants resulting from forage with low Mg availability. Chemical components considered in the forage were inorganic cations, organic acids, aconitate, and per cent total N/per cent total water soluble carbohydrate (N/TWSC). Differences between the sum (in meq/kg) of inorganic cations (Mg, Ca, K, and Na) and inorganic anions (Cl, NO₃, H₂PO₄, and SO₄) in forage were defined as the concentration of organic acids (C-A). Soil was Parshall fsl, a Pachic Haploboroll. Yields and chemical composition of oven-dried forage from previously unclipped and reclipped plots were determined at 3-week intervals beginning May 22 and June 12, respectively. A water budget was determined using soil-water and rainfall data.Forage yields were increased 2- to 3-fold by N fertilization with the NO₃-N source generally outyielding the NH₄-N source. A slight additional yield response to that obtained with N alone was obtained with K+P fertilization but not with K or P alone with or without N. Much less total forage was removed from reclipped plots than from unclipped plots. Forage Mg content was decreased only slightly by K or NH₄-N fertilization. Soil analysis indicated that high NH₄-N levels were present at the May 22 harvest. Magnesium and Ca concentrations were only slightly affected by N fertilization; however, K, K/(Ca+Mg), total N, C-A, and aconitate were increased. Reclipping increased Mg, N, K, N/TWSC, C-A, and aconitate. Estimates of blood-plasma Mg concentrations were obtained by using the data for plant N, K, and Mg. These estimates did not indicate increased tetany hazard as a result of reclipping, but did indicate increased tetany hazard from N fertilization. Forage C-A and aconitate concentrations were decreased by fertilization with KCl which seemed to have been caused by the increased Cl concentrations in the forage. Estimates of quantities of Mg, arriving at the root surfaces from the soil by mass flow, far exceeded amounts of Mg in the forage. Mass flow seemed to be the principal mechanism by which Mg and Ca arrived at root surfaces but this mechanism was much less important for K.This study indicated an increased potential tetany hazard resulting primarily from N fertilization with either NH₄-N or NO₃-N sources. However, the potential for increased forage and livestock-carrying capacity with N fertilization is very large. Therefore, management practices corroborated by livestock data are vitally needed to minimize tetany hazard while increasing bromegrass yields by N fertilization.Contribution from Soil, Water, and Air Sciences, North Central and Northeastern Regions, ARS-USDA.Follett, Power, and Grunes are soil scientists and Kleinis a biological laboratory technician. Follett is now National Program Staff Scientist, ARS, BARC-West, Beltsville, MD 20705. Power and Klein are at the USDA Northern Great Plains Research Center, Mandan, ND 58554, as formerly was Follett. Grunes is at the U.S. Plant, Soil and Nutrition Laboratory, Ithaca, NY 14853.     

Effects of Long-Term Fertilization on Leaf Photosynthetic Characteristics and Grain Yield in Winter Wheat

Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000–2001 and 2001–2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (P _N), maximal activity of photosystem 2, PS2 (F_v/F_m), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as P _N×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK.     

不同施肥模式下潮棕壤稻田的速效养分状况和水稻的养分分配

研究了不同施肥模式下下辽河平原潮棕壤稻田土壤速效养分的供应能力及水稻的养分分配.结果表明:各处理0～20 cm速效养分供应能力均高于20～40 cm,其变异也大于20～40 cm(速效氮除外);有机、无机肥相结合有利于提高土壤速效养分的供应能力;水稻氮和磷的分配主要集中在籽实中,钾的分配则主要集中在秸秆中.采用秸秆还田措施有利于缓解钾肥资源的不足,保持钾素的循环再利用,维持土壤钾库,减少钾肥投入,降低农业生产成本,减轻环境污染.     

尾叶桉叶片氮磷钾钙镁硼元素营养诊断指标

采用临界值法对尾叶桉幼林材积生长进行叶片营养诊断,试验结果表明,氮,磷,钾,钙,镁和硼等营养元素的临界浓度分别为15.3g/kg,1.2g/kg,4.2g/kg,16.1g/kg,2.5g/kg和0.019g/kg;最适浓度范围分别为15.3-18.1g/kg,1.2-1.7g/kg,4.2-5.6g/kg,16.1-19.8g/kg,2.5-3.0g/kg和0.019-0.031g/kg,而对树高生长进行营养诊断时,上选结果稍微有些变化,试验还得到各营养元素比值的临界值和最适范围。     

模拟氮沉降对杉木幼苗养分平衡的影响

为研究氮沉降对植物养分平衡的影响,对1a生杉木（Cunninghamia lanceolata（Lamb.）Hook.）幼苗进行了室内模拟试验。以NH4NO3作为外加氮源,设计了N0（0 g N m-2?a-1）、N1（6 g N m-2?a-1）、N2（12 g N m-2?a-1）、N3（24 g N m-2?a-1）和N4（48g N m-2?a-1）等5种氮沉降水平,每处理重复6次。通过1a的试验发现,杉木幼苗叶、茎、粗根和细根中的N、K、Mg含量随氮处理水平的增加而上升,但Ca在各器官中的含量则呈下降趋势;中低氮（N1,N2）对叶、茎和粗根中P的含量表现为促进作用,而高氮（N3,N4）则表现为抑制作用。幼苗各器官中的N与其他养分元素的比值随氮处理水平的增加而普遍升高,但粗根中的N/K、N/Mg则表现为下降。与对照（N0）相比,在N1、N2、N3、N4处理中,幼苗对外加氮素的表观利用率分别为60.7%、57.9%、43.3%和27.9%,随氮处理水平增加,利用率呈明显下降趋势。随着氮处理水平的增加,幼苗体内的氮分配到叶和细根中的比例增加,而分配到茎和粗根中的比例下降。因此,氮沉降明显增加了杉木幼苗各器官的氮含量,影响了幼苗的养分平衡。     

Macro- and micronutrient effects on decomposition of leaf litter from two tropical tree species: inferences from a short-term laboratory incubation

While a large number of studies have investigated the effects of macronutrients such as nitrogen (N) or phosphorus (P) on litter decomposition, recent studies suggest that micronutrients including zinc (Zn) may also limit decomposition rates. Our goal was to compare the effects of nutrient addition on decomposition of two leaf litter types from tropical dry forest trees in a short-term laboratory microcosm experiment. Single nutrients (N, P, Zn, potassium, magnesium, and nickel) were applied to leaf litter in solution at low or high concentrations (to mimic in situ availability or to alleviate nutrient limitation, respectively), and decomposition was assessed as final mass remaining and carbon dioxide mineralization. Both mass remaining and CO₂ mineralization were affected by nutrient identity and concentration, and these effects varied by species. In general, P and Zn addition increased decomposition, Mg and N inhibited it, and K and Ni had no significant effects. Future studies should consider the interactions between decomposition processes, decomposer communities, and a wider range of macro- and micronutrients.