Nitrogen in soils beneath 18–65 year old stands of subtropical evergreen broad-leaved forests in Laoshan Mountains in Eastern China

Monitoring of soil nitrogen (N) cycling is useful to assess soil quality and to gauge the sustainability of management practices. We studied net N mineralization, nitrification, and soil N availability in the 0 10 cm and 11 30 cm soil horizons in east China during 2006 2007 using an in situ incubation method in four subtropical evergreen broad-leaved forest stands aged 18-, 36-, 48-, and 65-years. The proper- ties of surface soil and forest floor varied between stand age classes. C:N ratios of surface soil and forest floor decreased, whereas soil total N and total organic C, available P, and soil microbial biomass N increased with stand age. The mineral N pool was small for the young stand and large for the older stands. NO 3 - -N was less than 30% in all stands. Net rates of N mineralization and nitrification were higher in old stands than in younger stands, and higher in the 0 10 cm than in the 11 30 cm horizon. The differences were significant between old and young stands (p < 0.031) and between soil horizons (p < 0.005). Relative nitrification was somewhat low in all forest stands and declined with stand age. N trans- formation seemed to be controlled by soil moisture, soil microbial bio- mass N, and forest floor C:N ratio. Our results demonstrate that analyses of N cycling can provide insight into the effects of management distur- bances on forest ecosystems.     

自然侵入阔叶树对琉球松人工林碳素及氮素动态的影响

对日本冲绳岛北部相同土壤条件下的琉球松纯林及其混交林的土壤氮素及有机碳素、地表凋落物量、枯枝落叶量以及土壤氮素矿化速率进行了比较研究。结果表明 ,琉球松纯林的地表凋落物层氮、碳平均贮量分别为133kg·hm- 2 和 7199kg·hm- 2 ,混交林则分别为 10 5kg·hm- 2 和 6 14 3kg·hm- 2 。然而 ,混交林地表 10cm矿质土层的氮、碳贮量则显著高于纯林 ,氮素比纯林多 4 93kg·hm- 2 ,碳素多 5 5 5 4kg·hm- 2 。在 30d的实验室培养实验中 ,混交林表层土壤的氮素矿化速率高于纯林 18% ;而且 ,混交林的落叶和土壤的碳氮比值亦明显低于松纯林。混交林土壤的年平均矿化氮素 (NH4 NO3- )浓度高于纯林 2 2 %。与松纯林相比 ,混交林通过枯枝落叶年平均氮素归还量多 4 3 7kg·hm- 2 ,碳素归还量多 16 5 5kg·hm- 2 。混交林具有较高的氮素归还量 ,主要是混交林的针叶含氮含量较高以及大量的高含氮量的阔叶落叶所致。上述结果充分说明针阔混交导致了林分氮素循环的变化。     

Effect of vegetation and land use on soil fertility in Wutai Mountains of Shanxi Province

IntroductionSoilpropertiesdependonclimate,vegetationtypes,parentmaterials,landformandsoilderivedage(Bei-jingForestryCoIlege1982).VegetationpIaysasig-nificantroIeintheformationofsoiIparticuIarIyforthepropertiespfSurfBcesoil.PlantsabsorbselectivelynutrientfromsoilandbuiIdtheirbodies.ThenutrientpartofIitterdecomposedgradualIybymicrobeswouldraturntoground-TheroOtsystemOfplantaIsoplaysasignificantroleinsoiIproperties.EffectofpIantsonsoildependonthevegdstiontype,speciescomposi-tion,age,dens…     

坡位对杉木×闽粤栲混交林和杉木纯林养分积累的影响

选择福建省建阳范桥国有林场16年生杉木×闽粤栲混交林与杉木纯林为研究对象,对不同坡位不同林分养分积累量进行分析对比。结果表明:上坡立地条件下,杉木纯林乔木层N、P、K养分积累量均大于杉木×闽粤栲混交林。中坡和下坡林分乔木层养分积累量则表现为混交林大于杉木纯林。不同林分乔木层养分积累量均占整个林分养分积累总量的90%以上,且表现为N>K>P和下坡>中坡>上坡。上坡杉木纯林的灌木层和草本层N、P积累量均大于混交林,下坡林分的灌木层N、P、K养分积累量均表现为杉木×闽粤栲混交林大于杉木纯林。不同林分凋落物的N和P的积累量均大大超过草本层和灌木层的积累量。     

The effect of stand age on the accumulation of nutrients in the aboveground components of an Aleppo pine ecosystem

Nutrient dynamics of an Aleppo pine (Pinus halepensis, Mill.) ecosystem located in the Kassandra peninsula, Central Macedonia, Northern Greece, were studied using a chronosequence approach. The nutrient composition of the Aleppo pine trees, the understory evergreen broadleaves and forest floor in adjacent stands of 23, 48, 70 and over 100 years old was determined to estimate postfire nutrient losses. The concentration of nutrients in the Aleppo pine trees, except of Ca, was reduced with increasing stand age. Ca was the most abundant nutrient in the aboveground vegetation and in forest litter, followed by N, K, Mg and P. The accumulation of nutrients in the aboveground biomass was positively related to stand age. For younger stands nutrient accumulation was considerably larger in the understory vegetation as compared to the pines, due to substantial enhancement of the understory biomass and the number of understory species present. In middle-aged stands, however, nutrient accumulation in the understory and overstory vegetation reached a balance. In addition, considerable quantities of nutrients have been accumulated in the forest floor particularly in stands of 48 years old. Therefore, any destruction during the period of maximum nutrient accumulation in the forest floor will cause degradation of the ecosystem. It is postulated that the competition for nutrients between overstory and understory vegetation may be as important as competition in soil. Forest management practices leading to the direct conversion of the understory biomass into littermass would be of great significance for the sustainability of the Aleppo pine ecosystem.     

杉木、火力楠混交幼林养分位移和循环的研究

杉木(Cunninghamia lanceloata)是我国特有的优良速生树种,分布广,但连栽出现地力和生长衰退现象。为此,许多地方开展了杉木混交林的试验研究。本文试图通过对广东南亚热带5年生杉木纯林和杉木、火力楠(Michelia macclurei)混交林的养分位移和循环及其枯落物量与分解速率的调查研究,揭示树种组成的种间关系,深入认识混交林生态系统的功能。     

Effect of fertilization on the litter fall of pinus sylvestris and betula pubescens on drained peatlands

NPK fertilization on a dwarf shrub pine bog initially increased the amount and nutrient content of the tree litter. Eight years after fertilization, however, the amount of micronutrients decreased compared to the amount of N and P in the litter. Fertilization on a fertile mire also increased the nutrient content of the litter fall, especially in the mature pine and birch stands. The amount of nutrients in the litter fall of the birch stands was considerably greater than that in the pine stand of the same volume.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Belowground carbon pools and processes in different age stands of Douglas-fir

Forest floor material and soil organic matter may act as both a source and a sink in global CO2 cycles. Thus, the ecosystem processes controlling these pools are central to understanding the transfers of carbon (C) between the atmosphere and terrestrial systems. To examine these ecosystem processes, the effect of stand age on temporal carbon source-sink relationships was examined in 20-year-old, 40-year-old and old-growth stands of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in the Cascade Mountains of south-central Washington State. Belowground C and nitrogen (N) storage and soil respiration were measured. In addition, nylon mesh bags containing homogenized soils from each site were buried at the respective sites to quantify root ingrowth and potential C sequestration and loss. The sites supporting the 20- and 40-year-old stands had soil C stores reflecting the C contributions from logging residue, coarse woody debris and stumps left after harvest. Because the N-fixer red alder (Alnus rubra Bong.) comprised 33% of the 40-year-old stand, this site had significantly greater concentrations and pools of N in the forest floor than sites without red alder. This N-rich site had consistently lower soil CO2 efflux rates during the growing season than the sites supporting the 20-year-old and old-growth stands. Estimated annual soil C efflux was 1367, 883 and 1194 g m-2 for the sites supporting the 20-, 40- and old-growth stands, respectively. These values are higher than previously reported values. Root ingrowth was significantly less in the 40-year-old stand than in the 20-year-old stand, and both young stands showed markedly less fine root growth than the old-growth stand. At the sites supporting the young stands, C and N were lost from the soil bags, whereas there was an increase in C and N in the soil bags at the site supporting the old-growth stand. The fine root growth and soil respiration data support the hypothesis that belowground C allocation decreases with increasing fertility. Quantification of the source-sink relationship of soil C at the three stands based on litterfall, relative root ingrowth and soil respiration measurements was compromised because of significant CO2 flux from decaying organic matter in the young stands.     

Branch mortality and potential litterfall from Douglas-fir trees in stands of varying density

Forest floor characteristics influence nutrient cycling and energy flow properties of forest ecosystems, and determine quality of habitat for many forest plants and animals. Differential crown recession and crown development among stands of differing density suggest that an opportunity may exist to control the input of fine woody litter into the system by manipulating stand density. The objective was to measure the rate of branch mortality among stands of differing density and to estimate the range in total per hectare necromass inputs. Although litter traps are reliable for estimating per hectare rates of litterfall, branch mortality dating on sectioned stems uniquely allows assessment of several other litterfall components: (1) individual tree contributions to total litterfall; (2) the amount of branch material released by mortality, regardless of whether the branches are shed to the forest floor; (3) the distribution of basal diameters characterizing the litterfall from a given tree and stand. Twenty-four trees were felled and sectioned on permanent plots that were part of a silvicultural study of stand density regimes in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco.). Whorl branches were dissected out of bole sections to determine the dates of mortality, and a branch biomass equation was applied to estimate potential rate of litterfall. Periodic annual rates were expressed in four ways: (1) number of branches per tree; (2) mass of branches per tree; (3) mass of branches per unit of crown projection area; (4) mass of branches per hectare. For the growth periods investigated, larger trees and trees growing on denser plots tended to release a greater necromass through branch mortality. Average branch basal diameter generally decreased with increasing stand density. Annual branch mortality ranged from 33 to 430 g m⁻² crown projection area for individual trees, and from 236 to 1035 kg ha⁻¹ for individual plots. These rates approached the low end of the range of previously published fine litterfall rates for Douglas-fir. Rates on these plots were relatively low owing to the temporary delay in crown recession imposed by artificial thinning. A conceptual model of branch litter dynamics is presented to depict consistencies with crown development among stands managed under different density regimes.     

The nutrient status of Norway spruce in pure and in mixed-species stands

Atmospheric deposition of N and S appears to have caused nutrient imbalance in Norway spruce stands in southern Sweden. This calls for a change of forest management to procedures that promote nutrient balance. Studies have shown lower soil acidity in Norway spruce/deciduous mixed stands than in spruce monocultures, but the tree nutrient status in such mixtures has not been much investigated so far.

The nutrient status of Norway spruce foliage and top mineral soil chemistry in monocultures and in stands mixed with beech, birch, or oak was investigated through paired comparisons on 30 sites in southern Sweden (27 sites) and eastern Denmark (three sites). In total, 45 mixed stands and 34 pure stands were included in the study.

Spruce needles from mixed stands had higher concentrations and ratios to N of K, P, and Zn than needles from pure spruce stands. Among the mixed stands, the K status appeared to be positively correlated with the percentage of deciduous tree basal area. Soil samples from mixed stands had a higher Mg concentration, base saturation, and BC/Al ratio than soil samples from pure stands. The spruce needle nutrient status was comparable in pure stands on fertile sites and in mixed stands on poor sites. We did not detect any differences in spruce tree growth between pure and mixed stands.

This paper discusses possible reasons for a positive effect on the tree nutrient status in mixed-species stands and the possibility of using mixed-species stands as a forest management procedure to avoid nutrient imbalance.     

Soil organic matter in European forest floors in relation to stand characteristics and environmental factors

Published data on the quantities of organic matter in the forest floor (SOM_fl) of European forest stands were collated. Studies of SOM_fl were included if the total sampled surface was at least 0.15 m², the surface of a single sample was at least 100 cm², live material was sorted out, and ash or carbon content was determined. Data from 59 forest stands were compared with regard to stand characteristics and environment. Using a single variable, tree genus was most important for the amount of SOM_fl (R ² _adj = 0.34). The amounts in spruce stands (41 × 10³ kg ha^?1) were significantly higher than those in larch, Douglas fir, oak and birch stands (4–11 × 10³ kg ha^?1). The best significant multiple model was genus combined with stand age and basal area (R ² _adj. = 0.72). The importance of litter quantity and quality for differentiating the tree genera is discussed.     

土壤水分梯度对阔叶红松林结构的影响

2002年8月,在吉林省白河林业局红石林场(12755E,4230N),沿着一个山坡设置了一个长宽为112m8m、包含14个样方的样带。调查了群落结构、0-10cm和10-20cm的土壤含水量、枯落物现存量及其C、N、P含量,主要树种的叶片和枝条的C、N、P含量。沿着山坡的不同位置土壤含水量的不同导致阔叶红松林的群落结构发生变化。蒙古栎的比例随着土壤含水量的下降而逐渐升高,而其他主要阔叶树种则逐渐减少乃至消失。枯落物的水分变化趋势与土壤一致。在不同坡位枯落物的分解状况不同,干重差异显著。坡下枯落物含量较坡上的丰富,部分原因在于群落结构的变化。水分和养分含量的变化影响了枯落物的成分、降解及其养分的释放,进一步影响了林木的生长速度和林分结构并最终影响整个生态系统。图7表2参14。     

Tree age effect on fine-root and leaf morphology in a silver birch forest chronosequence

The influence of forest ageing on fine-root morphology and relations between fine-root and leaf characteristics is poorly studied. The aim of this study was to analyse age-driven changes in ectomycorrhizal roots (EcM roots) and leaf morphology in a chronosequence of silver birch (Betula pendula Roth.), which would provide a better understanding of adaptation responses and acclimation capacity of tree roots and leaves. The chronosequence included six age classes (3, 6, 14, 32, 45, and 60 years.). All stands had regenerated naturally and grew in a highly productive Oxalis forest site type in Estonia. Most changes in the morphology of EcM roots and leaves of silver birch occur faster at a young age. The functional parameters—mean specific area of EcM root (SRA) and leaf specific area (SLA) as well as leaf N—decreased with age. EcM root SRA and specific root length (SRL) decreased with stand age as a result of increased mean diameter and tissue density. In age classes of 6, 14, and 32 years, the total number of dominating EcM taxa was 34, and the distribution of four different dominating EcM exploration types (contact-, short-, medium-, long-distance) was similar. We conclude that high values of SRA, SLA, and leaf N measured in young silver birch stands indicate high activity of physiological processes necessary for fast-growing young trees. A decrease of SLA and SRA and N in the chronosequence of fertile stands of silver birch is most probably caused by down-regulation of growth, affecting simultaneously leaves and fine roots.     

THE CHARACTERISTICS OF THE NUTRIENT CYCLING IN BIRCH STANDS WITH DIFFERENT AGE STAGES

SuccessionisthedynanucdeveloPInentofecosystemswhichcanbecharactetindbyenergyandndneralcyclings.Eachsuccessionstagehasitscharaceristicsofelementcycling.SomeschOlarshaveStatedbutbrieflawsofnutrienCyclinginsuccessionstagesI"3I.InthespaPer,thenutrientcyclingcharacterishcsofbirchsuccessionseriesinXiaokinganlingwerediscussed.SwrYAasAroarernoDSThestUdyareaislocatedinLiangshniNatUralReservesinthendddieofXiaox-ing'anlilg(l28"53,2o'rE,47olo'5O"N).Theclimat6belongstocontinentalmonsoonclimate,W…     

Nutrient content of standing crop and biological cycling in Pinus patula ecosystem

Nutrient contents were estimated in different components of Pinus patula trees growing in six stands ranging from 8 to 34 years of age in the Darjeeling hills, India. The highest concentrations of most nutrients were found in the leaves but the maximum nutrient pool was contained in the bole which accounted for about 58 to 85% of the total aerial contents of different elements. Among the nutrients, N concentration (2.2%) was the highest, followed by Ca Mg K P Na. Nutrient contents in the standing crop increased with stand age and were nearly 2102 kg Ca, 1911 kg N, 875 kg Mg, 478 kg K, 285 kg P and 82 kg Na per ha in above-ground biomass of the 34-year-old stand. The annual uptake of N is highest but its accumulation in the standing stock is lower than that of Ca in the 34-year-old stand. The uptake and storage of Mg closely resembled those of K. Nutrient return and release were also determined to establish biological cycling in the 34-year-old P. patula ecosystem. Litter is resistent to decay and the forest floor retained a very rich nutrient store over the mineral soil. Turnover rates and times for nutrient fluxes showed the higher efficiency of the return pathway and the greater stability of the soil pool.     

Litter Production in Western Washington Douglas-Fir Stands

Litter production by Douglas-fir stands ranging in age from22 years old to 160 years old, is discussed. Typical leaf litterproduction was 2100 kg ha^–1 yr^–1 while total litterwas 2500 kg ha^–1 yr^–1. Annual fall of leaf litterincreases up to about 40 years of age and then becomes fairlyconstant while total litter continues to increase because ofwood production, although this increase may be quite irregular.Average nutrient returns to the forest floor are 21, 3, 7, 32,4, and 7 kg ha^–1 yr^–1 for N, P, K, Ca, Mg, and Mnrespectively.     

Long-term nutrient cycling patterns in Douglas-fir and red alder stands: a simulation study

Long-term patterns in nutrient cycling in regrowing Douglas-fir (Pseudosuga menziesii Mirb. Franco) and red alder (Alnus rubra Bong.) on native soils plus soils previously occupied by other species were simulated using the nutrient cycling model. Simulations of regrowing stands were also compared with observations of nutrient cycling in mature Douglas-fir and red alder. We hypothesized that (1) prolonged presence of red alder will cause a depletion in soil base cations due to increased nitrification and NO₃⁻ leaching; (2) lower base cation availability under red alder will ultimately cause biomass production to decline; (3) high N availability in red alder soils will favor regrowth of Douglas-fir; (4) higher base cation and P status of the Douglas-fir soils will favor growth of red alder both in the short- and long-term, since N is not limiting to red alder; and (5) in regrowing red alder, NO₃⁻ leaching will increase with time as a result of increased N fixation. All hypotheses were confirmed, but the effect of soil type on biomass production was minimal both for red alder and Douglas-fir. The higher soil organic matter content in the mature red alder stand most likely reflected previous occupation by old-growth Douglas-fir and also a large litter input from the understory vegetation. In general, the nutrient cycling model simulated differences in nutrient cycling patterns at least qualitatively between Douglas-fir and red alder and was helpful in identifying potential gaps in the understanding of biogeochemical cycling as well as uncertainties in the data. The nutrient cycling model did not fully elucidate differences in P cycling between Douglas-fir and red alder and overestimated weathering rates under Douglas-fir. Uncertainties in the data included: (1) temporal patterns in N fixation in the regrowing stands; (2) understory litterfall; and (3) site history and, consequently, presence of pre-existing differences in site conditions.     

赛罕乌拉4种林分林下植被及枯落物的水源涵养功能研究

文章以赛罕乌拉4种典型林分为对象,对其林下植被及枯落物层的水源涵养功能进行了初步研究。结果表明:①林分结构越复杂,林下植被物种多样性越大,其截留降雨的能力也越大。②4种林分枯落物的蓄积量范围在12.44～31.60t/hm2,针叶林枯落物的蓄积量明显高于阔叶林。③枯落物持水率大小顺序为山杨林>白桦林>山杨白桦林>落叶松林,山杨林分枯落物的最大吸水率(511%)为落叶松林分(280%)的1.8倍。④枯落物最大持水量的大小为阔叶混交林>针叶林>阔叶林。枯落物最大拦蓄量大小表现为:针叶林>阔叶混交林>阔叶林。落叶松林的有效拦蓄量最高(为6.56mm),白桦林分有效拦蓄量最小(为3.38mm)。     

马尾松两种林型土壤养分特征及其与凋落物质量的关系

【目的】研究土壤养分和地被层凋落物养分含量的差异,为马尾松人工林营林措施及地力维持提供科学依据。【方法】以鼎湖山两种典型林型(马尾松纯林和马尾松-黧蒴混交林)为研究对象,对比分析0~60 cm土层的土壤养分含量及地被层凋落物养分含量的差异,探索凋落物质量如何影响土壤养分。【结果】1)林型对土壤有机质、全氮和硫酸根含量有显著影响(P<0.05),对土壤全磷、交换性K+、Ca2+和Mg2+有极显著影响(P<0.01),混交林土壤养分含量(除硝态氮含量和交换性H+含量以外)均高于纯林。2)相同林型不同土层间土壤养分含量差异极显著(P<0.01),其中,土壤有机质和全氮含量随土层的加深而递减,且主要聚集在0~10 cm土层,表聚效应十分明显。3)纯林凋落物有机碳、全氮、C/N和全磷等含量高于混交林;相同林型不同分解层凋落物有机碳、全钙和全镁含量有显著差异(P<0.05),均表现为未分解层>半分解层>腐殖质层。4)土壤养分与地被层凋落物质量的RDA分析表明,0~10 cm土层土壤养分与腐殖质层有机碳呈极显著负相关(P<0.01),与腐殖质层C/N呈显著负相关(P<0.05);在10~20 cm土层,土壤养分与腐殖质层有机碳呈极显著负相关(P<0.05)。【结论】纯林的土壤养分低于混交林的主要原因是纯林凋落物具有较高的C/N和有机碳含量。