六种温带森林类型凋落物量长期动态及其环境驱动

阐明凋落物动态及其环境控制机制,可以为森林生态系统生产力及碳汇功能的维持提供重要的数据支持和理论依据。以长白山系余脉张广才岭西坡林龄相近但立地条件不同的4种天然次生林（即硬阔叶林、杨桦林、杂木林和蒙古栎林）和2种人工林（落叶松人工林和红松人工林）为研究对象,对其地上凋落物产量及其组分以及相关环境因子进行了14年（2008-2021年）的连续测定,旨在揭示森林凋落物量及其组分的时空变化（林型间和年际变异）及其环境驱动机制。结果表明：6种森林类型的凋落总量（TL）无显著差异,波动范围为500.5-556.1 g m^-2 a^-1;但其叶凋落量（LL）、繁殖组织凋落量（RT）和其他组织凋落量（OT）均存在显著差异,波动范围依次分别为333.9-391.8 g m^-2 a^-1、8.43-69.93 g m^-2 a^-1和93.4-185.9 g m^-2 a^-1。6种森林类型的TL均存在显著的年际变化;其中LL和OT年际变化的显著性因森林类型而不同,而RT的年际变化不显著。除落叶松人工林外,其余5种森林类型的LL与生长季平均气温、日最低气温均值、土壤10 cm深度处的平均温度、最低温度（Ts_min）和土壤5 cm含水量（Ms）均呈显著正相关。杂木林、硬阔叶林和红松人工林的RT与Ms呈显著负相关;杂木林、杨桦林和硬阔叶林的OT与Ts_min呈显著负相关。样地水平的LL与土壤10 cm处含水量存在显著的正相关关系,而RT和OT则与其呈现显著负相关关系。这些结果表明林龄相似的温带森林地上凋落物总量有趋同趋势,但其通过改变组分分配格局来适应立地条件的变化;土壤湿度和温度变化会引起凋落物量的年际变化,但不同森林类型的凋落物量对环境波动的敏感性不同。     

Above- and Below-Ground Carbon Stocks in an Indigenous Tree (Mytilaria laosensis) Plantation Chronosequence in Subtropical China

More than 60% of the total area of tree plantations in China is in subtropical, and over 70% of subtropical plantations consist of pure stands of coniferous species. Because of the poor ecosystem services provided by pure coniferous plantations and the ecological instability of these stands, a movement is under way to promote indigenous broadleaf plantation cultivation as a promising alternative. However, little is known about the carbon (C) stocks in indigenous broadleaf plantations and their dependence on stand age. Thus, we studied above- and below-ground biomass and C stocks in a chronosequence of Mytilaria laosensis plantations in subtropical China; stands were 7, 10, 18, 23, 29 and 33 years old. Our assessments included tree, shrub, herb and litter layers. We used plot-level inventories and destructive tree sampling to determine vegetation C stocks. We also measured soil C stocks by analyses of soil profiles to 100 cm depth. C stocks in the tree layer dominated the above-ground ecosystem C pool across the chronosequence. C stocks increased with age from 7 to 29 years and plateaued thereafter due to a reduction in tree growth rates. Minor C stocks were found in the shrub and herb layers of all six plantations and their temporal fluctuations were relatively small. C stocks in the litter and soil layers increased with stand age. Total above-ground ecosystem C also increased with stand age. Most increases in C stocks in below-ground and total ecosystems were attributable to increases in soil C content and tree biomass. Therefore, considerations of C sequestration potential in indigenous broadleaf plantations must take stand age into account.     

黄土高原子午岭地区人工油松林碳氮磷生态化学计量特征

分析人工植被重建背景下,森林植物、枯落物与土壤的碳(C)、氮(N)、磷(P)化学计量特征有助于深入理解森林生态系统养分循环规律和系统稳定机制。以黄土高原子午岭地区的3个林龄(10、25 a和40 a)的人工油松林为对象,通过测定油松林叶片、枯落物和土壤的碳(C)、氮(N)、磷(P)含量,研究人工油松林不同林龄叶片、枯落物和土壤的化学计量学特征。结果表明,不同林龄油松叶片C、N、P含量分别为538.85—560.54 g/kg、9.00—10.47 g/kg和1.04—1.13 g/kg。在3个林龄油松林中,除叶片C含量外,叶片N、P含量存在显著差异(P0.05);枯落物层以及土壤层的C、N、P含量均存在显著差异(P0.05),且枯落物层含量大于土壤层。随着林龄的增加,叶片C∶N比呈现先减小后增大的变化,N∶P和C∶P比呈显著增加趋势,而枯落物层C∶N、C∶P和N∶P比无显著差异。同时,随着林龄的增加,除10—20 cm土层的C∶N比外,土壤的C∶N比在0—10 cm土层和C∶P和N∶P比在0—10和10—20 cm皆呈显著增加趋势。研究区油松林叶片N∶P比平均值为9.13,低于14,表明油松林生长主要受氮的限制。土壤的N含量与叶片和枯落物层的N含量、以及三者间N∶P比呈显著线性相关(P0.05),充分体现了油松林植物、枯落物与土壤之间的互动关系。研究结果可为我国黄土高原脆弱生态区的生态功能恢复与植被重建提供科学依据。     

不同林龄马尾松凋落物基质质量与土壤养分的关系

凋落物的质量、数量及分解速率在一定程度上代表了土壤的营养状况。为了精确估算凋落物分解对土壤碳库的年净归还量及凋落物-土壤生物化学连续体的深层理解,从凋落物基质质量的角度分析了三峡库区不同林龄马尾松凋落物基质质量与土壤养分的作用关系,结果表明:中龄林、近熟林、成熟林马尾松凋落物基质质量中的C、C/N比、C/P比、木质素/N比、木质素/P比差异显著,其中近熟林凋落物叶木质素/N分别比中龄林和成熟林的高33.65%、39.24%,N、P、K、木质素含量差异不显著;但各组织器官的N、P、K含量差异显著,均是皮<枝<叶<杂物,C/N比、C/P比的变化则相反。不同林龄马尾松0-20 cm(0-5 cm、5-10 cm、10-20 cm)土壤有机质、总氮、有效磷含量均表现出近熟林<中龄林<成熟林,0-5 cm最大,10-20 cm最小,且随着土壤深度的增加而明显降低,总磷则是中林龄最低,成熟林最大,pH值则各土层均表现为中龄林<成熟林<近熟林,平均pH值为4.55-5.51。凋落物基质质量指标与土壤养分之间冗余分析(RDA)表明:马尾松凋落物基质质量和土壤养分之间关系紧密,N、P、纤维素、半纤维素、木质素、木质素/N比、C/N比对土壤养分影响比较大;凋落物中木质素/N比、C/N比与土壤有机质呈显著负相关,其含量越高越不利于土壤有机质的形成,土壤养分积累的越慢;凋落物基质质量氮含量与土壤氮含量呈显著正相关;土壤pH值、容重与N含量呈显著负相关,与凋落物C/N比、木质素/N比呈显著正相关。马尾松土壤表面有机质、N、P养分含量与凋落物基质质量对应养分含量变化规律一致,土壤养分高,凋落物基质质量相对较高,土壤贫瘠,凋落物基质质量相对较低。     

Nutrients and mass in litter and top soil of ten tropical tree plantations

The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha^-1 in the H. sonora stand to 27.2 Mg ha^-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing leaf litter generally increased in the order of recently fallen <old intact< fragmented. Nutrient concentration of standing leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have had different influences on the concentration of available nutrients in soil.     

科尔沁沙地典型固沙人工林地土壤水分时空特征及其对环境因子的响应

土壤水分时空动态特征对于干旱地区人工林的可持续经营与管理起着至关重要的作用。以位于科尔沁沙地南缘的樟子松和柠条固沙人工林为对象,于2018年11月-2019年11月连续观测了林地0-200 cm土壤剖面的含水量、温度及微气象因子,系统分析了土壤水分的时空变化特征及其对环境因子的响应。研究期内,两种林地土壤水分的季节变化可分为冻结期、补充期、消耗期和稳定期;依据土壤剖面的水分特征可分为易变层、活跃层和稳定层,但两种林地的分层深度有一定差异。在生长季内（5-10月）,土壤含水量对大气降雨的响应随着土层深度的增加而减弱;降雨对樟子松人工林0-20 cm层土壤水分的影响极显著（P<0.01）,对柠条人工林0-10 cm层的影响极显著（P<0.01）、20-60 cm层显著（P<0.05）。在土壤冻融周期内（2018年11月-2019年4月）,两种林地的土壤均表现为"单向冻结"和"双向融化"的特点;土壤温度是影响冻融期内土壤含水量的关键因素,两者呈极显著的指数函数关系;樟子松和柠条人工林土壤的最大冻结深度分别为170 cm和190 cm,前者10 cm土层解冻时间要比后者晚11 d,可能与乔木树冠的遮阴作用有关。潜在蒸散与柠条林0-60 cm层、樟子松林0-20 cm和200 cm层的土壤水分呈极显著相关（P<0.01）,而与樟子松林60 cm和160 cm层呈显著相关（P<0.05）,这与树木蒸腾和土壤蒸发等综合作用有关。研究表明,由于两种人工林的树种组成、树冠大小、郁闭程度和根系分布等结构特征不同会导致林地土壤水分时空特征的异质性及其对环境因素响应的差异。     

The effects of simulated nitrogen deposition on extracellular enzyme activities of litter and soil among different-aged stands of larch

Aims Nitrogen (N) addition could affect the rate of forest litter and soil organic matter decomposition by regulating extracellular enzyme activity (EEA). The impact of N addition on EEA may differ across different age stands with different organic matter quality. We were interested in whether the impact of N addition on EEA in litter and mineral soil during the growing season was dependent on stand age of a larch plantation in North China.Methods We added three levels of N (0, 20 and 50kg N ha^-1 year^-1) in three age stands (11, 20 and 45 years old) of Larix principis-rupprechtii plantation in North China. We measured potential activities of β-1,4-glucosidase (BG), cellobiohydrolase (CB), β-1,4-N-acetyl-glucosaminidase (NAG) and phenol oxidase (PO) in litter (organic horizon) and mineral soil (0–10cm) during the second growing season after N amendment. We also measured C and N concentrations, microbial biomass C and N, and KCl-extractable ammonium and nitrate in both litter and mineral soil.Important findings We observed unimodal patterns of EEA during the growing season in all three stands, consistent with the seasonal variations of soil temperature. Stand age had a strong effect on EEA in both litter and mineral soil, and this effect differed between litter and mineral soil as well as between different enzymes. N addition did not significantly affect the activities of BG or CB but significantly suppressed the activity of NAG in litter. We also found stand age-specific responses of PO activity to N addition in both litter and mineral soil. N addition suppressed PO activity of the high C:N ratio litters in 20- and 45-year-old stands but had no significant effect on PO activity of the low C:N ratio litter in 11-year-old stand. Moreover, N addition inhibited PO activity of the high C:N ratio soil in 20-year-old stand but had no significant impact on PO activity of the low C:N ratio soils in 11- and 45-year-old stands. Overall, stand age had a greater effect on EEA in litter and mineral soil compared to 2 years of N addition. Moreover, the effect of N addition on PO activity is stand age dependent, which may affect the long-term soil carbon storage in this forest.     

Microbial biomass C and N,and mineralizable-N,in litter and mineral soil under Pinus radiata on a coastal sand: Influence of stand age and harvest management

Microbial biomass C and N, and anaerobically mineralizable-N, were measured in the litter and mineral soil (0–10 cm and 10–20 cm depth) of Pinus radiata plantations in two trials on a nitrogen-deficient coastal sand. The trials comprised (a) stands of different age (1 to 33 years), with five of the seven stands studied being second rotation, and (b) a harvest-management trial, with stands established after different harvesting treatments of the first-rotation trees and understorey development controlled by manual weeding and chemical sprays. The harvest-management stands were sampled in the fifth year after the second-rotation establishment.In the stands of different age, the levels of microbial biomass C and N, and also mineralizable-N, in the litter and mineral soil showed no relationship with tree age and were similar to those in the oldest (33 years) stands of P. radiata. In the harvesting trial, five years after establishment of the second rotation, levels of microbial N and mineralizable-N in the litter and mineral soil were generally lowest where whole trees and the original forest floor had been removed; they were higher in associated plots in which the original forest floor had been removed but fertilizer N was regularly applied. No marked differences were then found between the other harvest treatments, viz. whole-tree harvest, stem-only harvest with slash remaining on site, and stem-only harvest plus extra added slash materials. In each trial, levels of microbial C and N and mineralizable-N were closely related to total C, and especially total N, in 0–10 cm depth mineral soil, but not generally in litter. Respiratory measurements strongly suggest that the microbial populations in mineral soil had a high metabolic activity.On an area basis in the harvest-management trial, total tree N and microbial N in the litter and mineral soil were lowest in stands where the original forest floor had been removed. In this particular treatment, microbial N in the litter plus mineral soil (0–20 cm depth) after five years of second-rotation growth comprised 7.3% of the total ecosystem N; values in the other treatments ranged between 5.6 and 6.0%.Our results emphasise the importance of slash and litter, and probably volunteer shrubs and herbaceous under-storey species, in conserving pools of potentially available N during the early stages of tree development.     

Carbon, nitrogen and phosphorus in volcanic soils following afforestation with native birch (Betula pubescens) and introduced larch (Larix sibirica) in Iceland

Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth) and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed to a slow accumulation of organic matter. Soil N concentrations and soil P_tot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material (400 Mg soil ha⁻¹ in 0–10 cm depth and 600 Mg soil ha⁻¹ in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average 23.6 Mg ha⁻¹ in the upper soil layer and 16.9 Mg ha⁻¹ in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha⁻¹ year⁻¹ in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha⁻¹ in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass of the growing trees. Soil P_tot pools were in average 220 and 320 kg P ha⁻¹ in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence on the availability of N and P to the trees. Responsible Editor: Hans Lambers.     

Nitrogen dynamics of a boreal black spruce wildfire chronosequence

This study examined the nitrogen (N) dynamics of a black spruce (Picea mariana (Mill.) BSP)-dominated chronosequence in Manitoba, Canada. The seven sites studied each contained separate well- and poorly drained stands, originated from stand-killing wildfires, and were between 3 and 151 years old. Our goals were to (i) measure total N concentration ([N]) of all biomass components and major soil horizons; (ii) compare N content and select vegetation N cycle processes among the stands; and (iii) examine relationships between ecosystem C and N cycling for these stands. Vegetation [N] varied significantly by tissue type, species, soil drainage, and stand age; woody debris [N] increased with decay state and decreased with debris size. Soil [N] declined with horizon depth but did not vary with stand age. Total (live + dead) biomass N content ranged from 18.4 to 99.7 g N m⁻² in the well-drained stands and 37.8–154.6 g N m⁻² in the poorly drained stands. Mean soil N content (380.6 g N m⁻²) was unaffected by stand age. Annual vegetation N requirement (5.9 and 8.4 g N m⁻² yr⁻¹ in the middle-aged well- and poorly drained stands, respectively) was dominated by trees and fine roots in the well-drained stands, and bryophytes in the poorly drained stands. Fraction N retranslocated was significantly higher in deciduous than evergreen tree species, and in older than younger stands. Nitrogen use efficiency (NUE) was significantly lower in bryophytes than in trees, and in deciduous than in evergreen trees. Tree NUE increased with stand age, but overall stand NUE was roughly constant (∼ ∼150 g g⁻¹ N) across the entire chronosequence.     

The ectomycorrhizal flora of primary and secondary stands of Pinus sylvestris in relation to soil conditions and ectomycorrhizal succession

Abstract. Ectomycorrhizal species composition and sporocarp abundance in two 15–20-yr old primary stands of Pinus sylvestris in the central part of the Netherlands was compared with those in two 16- and 27-yr old secondary stands of P. sylvestris in the Northeast of the country. The trees of the primary stands were spontaneously seeded in a drifting sand area. Only thin litter and humus layers were present. The trees of the 16-yr old secondary stand were planted on podzolic sandy soil and those of the 27-yr old stand on non-podzolic sandy soil. In both secondary stands thick litter and humus layers had developed. The litter and humus partly originated from former stands at the same sites and partly from the present stands. In the secondary stands the thick litter and humus layers and herb vegetation were removed (‘sod-cutting’) in order to simulate the thin litter and humus layers in the primary stands. Control treatments were present. Surveys in 1991, 1992 and 1993 showed that sod-cutting enhanced both abundance and diversity of ectomycorrhizal fungi. However, species richness and diversity were higher in the primary stands than in the secondary ones, also even in the sod-cut plots. High species richness and diversity were associated with low concentrations of nitrogen and relatively high pH in the litter and humus layers, and in the mineral soil.     

Responses of litter decomposition to temperature along a chronosequence of tropical montane rainforest in a microcosm experiment

We conducted a microcosm experiment for studying the decomposition of Altingia obovata leaf litter by the decomposer community at 20 and 30°C from three forest stands (namely a 35-year-old secondary forest, a 47-year-old secondary forest, and a primary forest) of a tropical montane rainforest. Our results showed that rank-order of the litter decomposition among the three forest stands was not parallel to the stand age. At 20°C, the mass loss of A. obovata leaf litter from the primary forest was higher than those from the two secondary forests, of which the younger stand showed higher mass loss than did the older one. However, there were no differences in mass loss among these three stands at 30°C. The mass loss for the two secondary forest stands, but not for the primary forest stand, increased significantly from 20 to 30°C. The level of lignin decomposition among the three stands at 20°C corresponded to their forest stand age, i.e., the primary forest > the 47-year-old secondary forest > the 35-year-old secondary forest. A rise of 10°C in temperature significantly increased lignin decomposition for the two secondary forests, while the reverse was true for the primary forest. Carbohydrate decomposition was positively related to the temperature but not to the stand age. The different responses of litter decomposition to the forest stand age and temperature might be due to the differences in the microbial activities among the three forest stands.     

Stand age-related effects on soil respiration in a first rotation Sitka spruce chronosequence in central Ireland

The effect of stand age on soil respiration and its components was studied in a first rotation Sitka spruce chronosequence composed of 10‐, 15‐, 31‐, and 47‐year‐old stands established on wet mineral gley in central Ireland. For each stand age, three forest stands with similar characteristics of soil type and site preparation were used. There were no significant differences in total soil respiration among sites of the same age, except for the case of a 15‐year‐old stand that had lower soil respiration rates due to its higher productivity. Soil respiration initially decreased with stand age, but levelled out in the older stands. The youngest stands had significantly higher respiration rates than more mature sites. Annual soil respiration rates were modelled by means of temperature‐derived functions. The average Q ₁₀ value obtained treating all the stands together was 3.8. Annual soil respiration rates were 991, 686, 556, and 564 g C m^?2 for the 10‐, 15‐, 31‐, and 47‐year‐old stands, respectively. We used the trenching approach to separate soil respiration components. Heterotrophic respiration paralleled soil organic carbon dynamics over the chronosequence, decreasing with stand age to slightly increase in the oldest stand as a result of accumulated aboveground litter and root inputs. Root respiration showed a decreasing trend with stand age, which was explained by a decrease in fine root biomass over the chronosequence, but not by nitrogen concentration of fine roots. The decrease in the relative contribution of autotrophic respiration to total soil CO₂ efflux from 59.3% in the youngest stand to 49.7% in the oldest stand was explained by the higher activity of the root system in younger stands. Our results show that stand age should be considered if simple temperature‐based models to predict annual soil respiration in afforestation sites are to be used.     

Ectomycorrhizal root growth in scots pine stands in response to manipulation of litter and humus layers

 The effect on ectomycorrhizal root growth in a nitrogen-enriched planted stand of Scots pine (Pinus sylvestris L.) on podzolic sandy soil to manipulation of litter and humus layers (removal, doubling and control treatments) was examined, and compared to ectomycorrhizal root growth in an untreated naturally established Scots pine stand on nutrient-poor non-podzolic sandy soil. Half a year after manipulation of litter and humus layers in the planted stand, ingrowth-cores to a depth of 60 cm were installed in both stands. Scots pine roots were sampled four times during two growing seasons. Ectomycorrhizal roots were found at all sampled soil depths to 60 cm in all plots. Root growth and ectomycorrhizal development were greater in the naturally established stand than in all plots in the planted stand. Numbers of ectomycorrhizal root tips in the litter and humus removal plots were generally higher than in the control plots in the planted stand until May 1992. Doubling litter and humus did not significantly affect root length or the numbers of ectomycorrhizal root tips. The N _dissolved , NH₄ ⁺ and NO₃ ^– concentrations and the organic matter content in the upper 5 cm of the mineral soil in the planted stand on podzolic sandy soil were generally higher and the pH significantly lower than in the naturally established stand on non-podzolic sandy soil. Root growth and ectomycorrhizal development in the secondary stand may have been negatively affected by the chemical composition of the podzolic sandy soil. Accepted: 19 March 1997     

高寒沙地乌柳防护林碳库随林龄的变化

植被恢复是改善脆弱生态系统的有效方式。长期的植被恢复能够提高沙地生态系统的服务功能。以青海共和高寒沙地不同林龄乌柳(Salix cheilophila)防护林生态系统为研究对象,研究植被恢复过程中植被碳库与土壤碳库的动态变化,探讨乌柳防护林生态系统的碳汇功能。结果表明:随林龄增加,乌柳各组分碳浓度变化规律并不显著(P0.05),而碳贮量显著增加(P0.05),且不同林龄乌柳各组分碳库的分配比例不同,树干碳贮量占林分碳贮量的百分比最高。各林龄(6、11、16、21a)乌柳林碳贮量分别为4.95、9.93、14.67 t/hm2和21.99 t/hm2。土壤碳库随植被恢复时间的增加而增加,各林龄土壤碳库(0—200cm)分别为9.54、13.03、17.18和19.05 t/hm2。较之6、11a土壤碳库增加26.78%,16a较之11a提高24.16%,21a较16a提高9.82%。地被物层(植被残体)固碳量分别为0.27、0.29、0.33、0.43 t/hm2。不同林龄乌柳林生态系统碳库分别为14.76、23.25、32.18 t/hm2和41.48 t/hm2。各林龄乌柳植被层碳库分别占该林龄总碳库的33.54%、42.71%、45.59%和53.01%,土壤碳库分别占该林龄总碳库的64.63%、56.04%、53.39%和45.93%,而地被物层分别占该林龄总碳库的1.83%、1.25%、1.03%和1.03%。较之恢复前的,各林龄碳库依次增加57.05%、36.52%、27.75%和22.42%。植被恢复各阶段年净碳累积速率分别为1.41、1.70、1.79、1.86 t C hm-2a-1。乌柳防护林生态系统具有"碳汇"功能。     

黄土丘陵区人工柠条种植年限和坡位对土壤团聚体稳定性的影响

柠条(Caragana korshinskii Kom.)种植是黄土高原地区生态环境建设中重要的人工植被恢复措施。选择黄土丘陵区条带种植15、25和35年的柠条坡地,以荒草坡地为对照,运用Le Bissonnais法分析柠条种植不同年限和坡位对0—40 cm土层团聚体分布及其稳定性的影响。结果表明:长时间柠条种植对土壤团聚体稳定性的影响主要在0—20 cm土层;不同处理下土壤大团聚体(0.25 mm)含量总体表现为柠条35年柠条25年柠条15年荒草地,表明柠条种植年限增加促进了大团聚体的形成。从坡面尺度看,柠条平均重量直径整体表现为坡下坡上坡中;在上坡的柠条35年样地具有最大值(3.08 mm),但在下坡荒草地显著高于柠条林地(P0.05)。基于相对消散指数和相对机械破碎指数,上中坡土壤团聚体均对消散作用和机械破碎作用较敏感,而下坡的下层土壤团聚体对破碎作用更敏感。冗余分析表明,土壤有机碳和粘粒含量与柠条平均重量直径呈显著正相关关系(P0.05)。种植年限是影响土壤团聚体稳定性的主要因素,解释了30.4%的变异;其次是土层(2.75%)和坡位(0.61%)。总体而言,柠条种植年限增加有利于促进黄土丘陵区土壤团聚体稳定性提升,但这种影响在不同坡位具有差异:在上中坡团聚体稳定性均随种植年限增加而增强,在下坡则先降后增。     

林地覆盖对雷竹林土壤碳氮磷化学计量特征的影响

林地覆盖措施可明显促进雷竹笋芽提早萌发,显著提高竹林经济效益,但长期连年覆盖会导致雷竹林退化为雷竹林。对不同覆盖年限(1、3、6 a)雷竹林和不覆盖雷竹林土壤C、N、P含量和化学计量比及相关性进行了研究。结果表明:不同覆盖年限雷竹林和不覆盖雷竹林土壤C、N、P含量均随土壤深度的增加而极显著降低。不同土层土壤C、N、P含量不同覆盖年限雷竹林极显著地高于不覆盖雷竹林。随覆盖年限的延长,雷竹林0～20 cm土壤C、N含量极显著提高。覆盖1 、3 a雷竹林和不覆盖雷竹林0～50 cm土壤P含量和20～50 cm土壤C、N含量差异均不显著,均显著地低于覆盖6 a雷竹林土壤。不同覆盖年限雷竹林各土层土壤C:N差异不显著,而C:P、N:P随覆盖年限的延长呈升高趋势。随覆盖年限的延长,土壤C、N、P间正相关关系减弱,C与N、P协同变化速率降低。研究表明:雷竹鞭根系统主要分布区0～20 cm土壤养分过量积累及引起的土壤养分失衡是林地覆盖雷竹林退化的主要原因。应实行轮闲覆盖和测土配方平衡施肥,并在雷竹自然出笋开始时(3月上旬)及时撤除有机覆盖物。为雷竹林可持续经营提供理论依据。     

不同林龄格木人工林碳储量及其分配特征

在生物量调查的基础上,对广西7、29和32 a格木人工林生态系统碳储量及其分配特征进行了研究.结果表明: 格木各器官碳含量在509.0～572.4 g·kg^-1,大小顺序为:树干>树枝>树根>树皮>树叶;不同林龄间格木人工林的灌木层、草本层和凋落物层碳含量无显著差异;土壤层(0～100 cm)碳含量随土层深度的增加而降低,随林龄的增加而增大.7、29和32 a格木人工林乔木层碳储量分别为21.8、100.0和121.6 t·hm^-2,各器官碳储量大小顺序与碳含量一致;生态系统碳储量分别为132.6、220.2和242.6 t·hm^-2,乔木层和土壤层为主要碳库,占生态系统碳储量的97%以上.乔木层碳储量分配随着林龄的增加而增大,土壤碳储量分配则减小,而林龄对灌木层、草本层和凋落物层碳储量分配的影响无明显规律.     

Soil carbon fluxes and stocks in a Great Lakes forest chronosequence

We measured soil respiration and soil carbon stocks, as well as micrometeorological variables in a chronosequence of deciduous forests in Wisconsin and Michigan. The chronosequence consisted of (1) four recently disturbed stands, including a clearcut and repeatedly burned stand (burn), a blowdown and partial salvage stand (blowdown), a clearcut with sparse residual overstory (residual), and a regenerated stand from a complete clearcut (regenerated); (2) four young aspen ( Populus tremuloides ) stands in average age of 10 years; (3) four intermediate aspen stands in average age of 26 years; (4) four mature northern hardwood stands in average age of 73 years; and (5) an old-growth stand approximately 350-years old. We fitted site-based models and used continuous measurements of soil temperature to estimate cumulative soil respiration for the growing season of 2005 (days 133–295). Cumulative soil respiration in the growing season was estimated to be 513, 680, 747, 747, 794, 802, 690, and 571 g C m⁻² in the burn, blowdown, residual, regenerated, young, intermediate, mature, and old-growth stands, respectively. The measured apparent temperature sensitivity of soil respiration was the highest in the regenerated stand, and declined from the young stands to the old-growth. Both, cumulative soil respiration and basal soil respiration at 10 °C, increased during stand establishment, peaked at intermediate age, and then decreased with age. Total soil carbon at 0–60 cm initially decreased after harvest, and increased after stands established. The old-growth stand accumulated carbon in deep layers of soils, but not in the surface soils. Our study suggests a complexity of long-term soil carbon dynamics, both in vertical depth and temporal scale.     

Production,standing biomass and natural abundance of <Superscript>15</Superscript>N and <Superscript>13</Superscript>C in ectomycorrhizal mycelia collected at different soil depths in two forest types

Nutrient uptake by forest trees is dependent on ectomycorrhizal (EM) mycelia that grow out into the soil from the mycorrhizal root tips. We estimated the production of EM mycelia in root free samples of pure spruce and mixed spruce-oak stands in southern Sweden as mycelia grown into sand-filled mesh bags placed at three different soil depths (0–10, 10–20 and 20–30 cm). The mesh bags were collected after 12 months and we found that 590±70 kg ha^–1 year^–1 of pure mycelia was produced in spruce stands and 420±160 kg ha^–1 year^–1 in mixed stands. The production of EM mycelia in the mesh bags decreased with soil depth in both stand types but tended to be more concentrated in the top soil in the mixed stands compared to the spruce stands. The fungal biomass was also determined in soil samples taken from different depths by using phospholipid fatty acids as markers for fungal biomass. Subsamples were incubated at 20°C for 5 months and the amount of fungal biomass that degraded during the incubation period was used as an estimate of EM fungal biomass. The EM biomass in the soil profile decreased with soil depth and did not differ significantly between the two stand types. The total EM biomass in the pure spruce stands was estimated to be 4.8±0.9×10³ kg ha^–1 and in the mixed stands 5.8±1.1×10³ kg ha^–1 down to 70 cm depth. The biomass and production estimates of EM mycelia suggest a very long turnover time or that necromass has been included in the biomass estimates. The amount of N present in EM mycelia was estimated to be 121 kg N ha^–1 in spruce stands and 187 kg N ha^–1 in mixed stands. The ¹³C value for mycelia in mesh bags was not influenced by soil depth, indicating that the fungi obtained all their carbon from the tree roots. The ¹³C values in mycelia collected from mixed stands were intermediate to values from pure spruce and pure oak stands suggesting that the EM mycelia received carbon from both spruce and oak trees in the mixed stands. The ¹⁵N value for the EM mycelia and the surrounding soil increased with soil depth suggesting that they obtained their entire N from the surrounding soil.