贵州月亮山不同演替阶段亮叶水青冈林碳储量及其分配格局

林龄对森林生态系统碳储量及其在不同碳组分(植被、木质残体、凋落物和土壤)中的分配有着重要影响。亚热带森林在陆地生态系统碳循环中起着重要作用, 水青冈属(Fagus)植物是我国亚热带广泛分布的重要树种, 而有关水青冈林碳储量随林龄变化的研究在我国鲜有报道。该研究选取贵州月亮山3个演替阶段(林龄分别为33年、82年和208年)的亮叶水青冈(Fagus lucida)林为研究对象, 对其生态系统全组分的碳储量及其分配格局进行了调查与估算。研究发现, 随林龄增加, 亮叶水青冈林生态系统碳储量显著增加, 33年、82年和208年林分别为(186.9 ± 46.0)、(265.8 ± 82.3)和(515.1 ± 176.4) Mg·hm ^-2, 且生态系统碳储量的增加主要由植被碳储量(占比由32%增长至79%)贡献。凋落物与木质残体碳储量随林龄增加亦呈增加趋势, 但二者占生态系统碳储量的比例很小(<1%)。而不同林龄土壤碳储量无显著差异, 其占比由33年林的67%降至208年林的20%。这些结果验证了林龄对森林生态系统各组分碳储量及其分配的重要影响, 同时指出干扰和土地利用历史等对森林植物残体和土壤碳积累的重要作用。     

Advances in the carbon use efficiency of forest

植物碳利用效率(CUE)指净初级生产力与总初级生产力的比率, 它不仅反映了植被生态系统将大气中CO₂转化为生物量的能力和固碳潜力, 而且可确定呼吸对植被生产力的影响。CUE是比较不同生态系统碳循环差异的重要参数, 了解生态系统CUE有助于分析陆地生态系统是碳源还是碳汇, 对于预测全球变化和人类干扰对森林碳收支的影响具有重要意义。我国在森林CUE研究方面还十分欠缺。该文在介绍森林CUE计算方法和测定技术的基础上, 综述了植被、气象、森林经营等因子对森林CUE的影响, 得出主要结论: (1)关于不同森林植被类型CUE变化有两种截然相反的观点, 即: 恒定CUE和变量CUE。越来越多的研究支持第二种观点, 不同生态系统、不同森林类型、不同物种和植物发育阶段的CUE存在较大差异, 森林CUE较灌丛和草地低, 落叶林比混交林和常绿林具有较高的CUE, 热带森林CUE通常低于温带森林, CUE与植被演替和林龄相关, 森林地上、地下部分和不同组织的CUE不同, 以树干为最高; (2)植被的CUE与气温相关, 全球尺度上, 森林植被年平均CUE与年平均气温呈抛物线关系, 温带、寒带、干旱地区植物呼吸的温度适应驱动其较高的CUE; CUE随着降水量的增加而减少, 在水分充足或过剩的地区保持不变; 光照减弱降低维持呼吸系数, 增加生长呼吸系数, 导致植物CUE降低, 生长在高光照下的植物CUE高于低光照下的植物; (3) CO₂浓度升高引起植物CUE的升高或降低, 也有人认为CO₂浓度升高对森林CUE没有影响, CO₂浓度升高对CUE的影响可能取决于树木年龄或基因型; (4)生长在土壤瘠薄、低温、干旱等胁迫环境下的植物CUE通常比生长在适宜环境下的植物具有较大的可塑性, 施肥、灌溉和择伐等管理措施影响森林CUE; (5)植物CUE具有明显的季节变化, 温带森林以春季CUE为最高。建议今后森林CUE研究应着重围绕以下3个关键问题: (1)从不同空间尺度和生态系统层次, 探讨森林CUE的变异特征及其驱动机制; (2)从不同时间尺度, 探讨森林CUE动态过程与机制; (3)森林CUE对气候变化的响应与适应。     

Carbon density characteristics of sparse Ulmus pumila forest and Populus simonii plantation in Onqin Daga Sandy Land and their relationships with stand age

Aims
Sparse Ulmus pumila forest is an intrazonal vegetation in Onqin Daga Sandy Land, while Populus simonii has been widely planted for windbreak and sand dune stabilization in the same region. Our objective was to compare the differences in carbon (C) density of these two forests and their relationships with stand age.
Methods
We measured the C content of tree organs (leaf, twig, stem, and root), herb layers (above ground vegetation and below ground root) and soil layers (up to 100 cm) in sparse Ulmus pumila forests and Populus simonii plantations of different stand ages, and then computed C density and their proportions in total ecosystem carbon density. In addition, we illustrated the variation in carbon density-stand age relationship for tree layer, soil layer and whole ecosystem. We finally estimated the C sequestration rates for these two forests by the space-for-time substitution approach.
Important findings
The average C contents of tree layer and soil layer for sparse Ulmus pumila forests were lower than those for Populus simonii plantations. The total C density of sparse Ulmus pumila forests was half of that of Populus simonii plantations. The carbon density of soil and tree layers accounted for more than 98% of ecosystem C density in the two forests. Irrespective of forest type, the C density ratios of soil to vegetation decreased with stand age. This ratio was 1.66 for sparse Ulmus pumila forests and 1.87 for Populus simonii plantations when they were over-matured. The C density of tree layer, soil layer, and total ecosystem in both forests increased along forest development. There were significantly positive correlations between tree layer’s C density and stand age in both forests and between the total ecosystem C density of sparse Ulmus pumila forests and stand age. The C sequestration rate of tree layer was 5-fold higher in Populus simonii plantation than in sparse Ulmus pumila forest. The ecosystem-level C sequestration rate was 0.81 Mg C·hm^-2·a^-1 for sparse Ulmus pumila forest and 5.35 Mg C·hm^-2·a^-1 for Populus simonii plantation. These findings have implications for C stock estimation of sandy land forest ecosystems and policy-making of ecological restoration and C sink enhancement in the studied area.     

C:N:P stoichiometry in forest floor litter of evergreen broad-leaved forests at different successional stages in Tiantong,Zhejiang, eastern China

地表凋落物在森林物质循环中起着重要作用, 但是目前缺乏对其不同分解层次中碳(C)、氮(N)、磷(P)演替动态的研究。该文以浙江天童常绿阔叶林为研究对象, 用空间代替时间序列的方法, 通过测定5个演替阶段地表凋落物不同分解层次的凋落物量、有机碳库和氮磷养分库的储量及C:N:P化学计量特征, 探讨地表凋落物特征的演替动态。结果表明: 1)随着演替的进行, 地表凋落物量和有机碳储量呈现下降的趋势。2)在各演替阶段, 有机碳含量在各分解层表现出未分解层(L) > 半分解层(F) > 已分解层(Y)的趋势; 有机碳储量均表现为Y < F。3)演替前期群落氮含量和储量显著低于演替中后期群落; 不同分解层的氮含量在各演替阶段皆表现为: Y > F > L, 且各层氮含量随着演替的进行均趋于升高。4)磷含量在演替中期群落最低, 各演替阶段不同分解层的磷含量皆表现为Y > F > L。磷储量的演替趋势不明显。L层磷储量随着演替进行趋于降低。5)随着演替进行, 凋落物C:N、C:P和N:P皆趋于下降(p < 0.05)。在各分解层之间, C:N和C:P皆表现为Y < F < L, N:P差异不显著。总之, 随着演替进行, 天童常绿阔叶林地表凋落物量降低, 有机碳库及氮磷养分库的含量趋于升高, 储量趋向降低, C:N:P趋于下降, 体现了生态系统碳和养分循环随着演替进行在不断优化。     

中国寒温带不同林龄白桦林碳储量及分配特征

为了解中国寒温带地区不同林龄白桦林生态系统碳储量及固碳能力, 在样地调查基础上, 以大兴安岭地区25、40与61年白桦(Betula platyphylla)林生态系统为研究对象, 对其乔木层、林下地被物层(灌木层、草本层、凋落物层)、土壤层(0-100 cm)碳储量与分配特征进行调查研究。结果表明白桦林乔木层各器官碳含量在440.7-506.7 g·kg ^-1之间, 各器官碳含量随着林龄的增长而降低; 灌木层、草本层碳含量随林龄的增加呈先降后升的变化趋势; 凋落物层碳含量随林龄增加而降低; 土壤层(0-100 cm)碳含量随林龄增加而显著升高, 随着土层深度的增加而降低。白桦林生态系统各层次碳储量均随林龄的增加而明显升高。25、40与61年白桦林乔木层碳储量分别为11.9、19.1和34.2 t·hm ^-2, 各器官碳储量大小顺序表现为树干>树根>树枝>树叶, 树干碳储量分配比例随林龄增加而升高。25、40与61年白桦林生态系统碳储量分别为77.4、180.9和271.4 t·hm ^-2, 其中土壤层占生态系统总碳储量的81.6%、87.7%和85.9%, 是白桦林生态系统的主要碳库。随林龄增加, 白桦林年净生产力(2.0-4.4 t·hm ^-2·a ^-1)、年净固碳量(1.0-2.1 t·hm ^-2·a ^-1)均出现增长, 老龄白桦林仍具有较强的碳汇作用。     

Current forest carbon stocks and carbon sequestration potential in Anhui Province,China

Aims
This study was conducted to investigate carbon stocks in forest ecosystems of different stand ages in Anhui Province, and to identify the carbon sequestration potential of climax forests controlled by the natural environment conditions.
Methods
Data were collected based on field investigations and simulations were made with the BIOME4 carbon cycle model.
Important findings
Currently, the total forest carbon stocks in Anhui Province amounts to 714.5 Tg C: 402.1 Tg C in vegetation and 312.4 Tg C in soil. Generally, both the total and vegetation carbon density exhibit an increasing trend with the natural growth of forest stands. Soil carbon density increases from young to near mature forests, and then gradually decreases thereafter. Young and middle-aged forests account for 75% of the total forest area in Anhui Province, with potentially an additional 125.4 Tg C to be gained after the young and middle-aged forests reach near mature stage. Results of BIOME4 simulations show that potentially an additional 245.7 Tg C, including 153.7 Tg C in vegetation and 92 Tg C in soil, could be gained if the current forests are transformed into climax forest ecosystems in Anhui Province.     

华北地区落叶松林的分布、群落结构和物种多样性

华北落叶松(Larix principis-rupprechtii)林、日本落叶松(L. kaempferi)林及太白红杉(L. chinensis)林是华北地区常见的3种落叶松林类型, 其中日本落叶松林为人工林, 华北落叶松林既有天然分布又有人工种植, 太白红杉林则主要是天然林。该研究基于野外调查数据, 对这3种落叶松林的分布、物种组成、群落结构、物种多样性及其与环境间的关系进行了分析。研究发现, 3种落叶松林的分布受年平均气温的影响较大, 随着年平均气温的增加, 落叶松林的天然分布减少而人工种植的分布增加。3种森林中落叶松的林分径级及树高均为右偏分布, 说明3种落叶松林均处于相对稳定的演替阶段。3种落叶松林均拥有较高的物种丰富度且差异显著, 其中太白红杉林的物种丰富度最大(39.3 ± 17.9), 而华北落叶松林的物种丰富度最小(人工林27.2 ± 17.7, 天然林27.5 ± 13.8)。除最大树高与经度的关系不显著以外, 落叶松林的最大胸径和最大树高及物种丰富度均随经纬度的增加而显著降低, 随着年降水量的增加而显著增加。此外, 年平均气温对落叶松林的总物种丰富度影响不大, 但是对其群落结构影响显著。随着年平均气温的升高, 落叶松林的最大胸径显著降低而最大树高却显著增加。落叶松天然林和落叶松人工林物种多样性的地理分布格局及与气候因子间的关系与落叶松林总体的基本一致, 但群落结构的格局不尽相同: 随着经纬度的增加, 落叶松人工林的最大树高增加而天然林的最大树高减小; 落叶松天然林的最大胸径和最大树高分别随年平均气温的升高和年降水量的增加而减小, 而落叶松人工林的最大胸径和最大树高分别随年平均气温的升高和年降水量的增加而增大。     

Effects of nitrogen addition on soil respiration in shrublands in Mt. Dongling,Beijing, China

Aims Soil respiration from terrestrial ecosystems is an important component of terrestrial carbon budgets. Compared to forests, natural or semi-natural shrublands are mostly distributed in nutrient-poor sites, and usually considered to be relatively vulnerable to environmental changes. Increased nitrogen (N) input to ecosystems may remarkably influence soil respiration in shrublands. So far the effects of N deposition on shrubland soil respiration are poorly understood. The aim of this study is to investigate the soil respiration of Vitex negundo var. heterophylla and Spiraea salicifolia shrublands and their response to N deposition. Methods We carried out a N enrichment experiment in V. negundo var. heterophylla and S. salicifolia shrublands in Mt. Dongling, Beijing, with four N addition levels (N₀, control, 0; N₁, low N, 20 kg N·hm^-2·a^-1; N₂, medium N, 50 kg N·hm^-2·a^-1 and N₃, high N, 100 kg N·hm^-2·a^-1). Respiration was measured from 2012-2013 within all treatments.Important findings Under natural conditions, annual total and heterotrophic respiration were 5.91 and 4.23, 5.76 and 3.53 t C·hm^-2·a^-1 for the V. negundo var. heterophylla and S. salicifolia shrublands, respectively and both were not affected by short-term N addition. In both shrubland types, soil respiration rate exhibited significant exponential relationships with soil temperature. Temperature sensitivity (Q₁₀) of total soil respiration in V. negundo var. heterophylla and S. salicifolia shrublands ranged from 1.44 to 1.58 and 1.43 to 1.98, and Q₁₀ of heterotrophic soil respiration ranged from 1.38 to 2.11 and 1.49 to 1.88, respectively. Short-term N addition decreased only autotrophic respiration rate during the growing season, but had no significant effects on total and heterotrophic soil respiration in V. negundo var. heterophylla shrubland. In contrast, N addition enhanced the heterotrophic soil respiration rate and did not influence autotrophic and total soil respiration in S. salicifolia shrubland.     

Season dynamics of carbon use efficiency and its influencing factors in the old-growth Abies fabri forest in Gongga Mountain,western Sichuan,China

碳利用效率(CUE)是植被生态系统的一个重要功能参数, 反映了植被生态系统的固碳能力, 适用于分析不同时间段内器官、个体和群落等不同层次的碳收支趋势, 因而有助于对陆地生态系统碳功能的确定与预测, 引起了广泛关注。该研究采用生物计量法, 测定和计算了川西贡嘎山东坡峨眉冷杉(Abies fabri)成熟林树木不同器官的呼吸与净生产力动态, 分析了乔木层及其各器官CUE动态及主要影响因子, 并估算了乔木层不同径级树木CUE。主要结果: (1)乔木层各器官月呼吸速率与温度呈正相关关系, 以细根月呼吸速率为最大; 不同径级树木年呼吸量无显著差异, 以小径级树木树干的年呼吸量为最小。(2)乔木层细根和树干月净初级生产力(NPP)均随温度增加而增加, 以细根月NPP为最大。小径级树木年NPP最大, 其针叶年NPP也显著高于中径级和大径级树木。(3)林分乔木层及其各器官CUE大多集中在0.30-0.60之间, 其中细根、树干CUE具有相似的月变化动态, 均随温度的升高而上升。不同径级树木CUE及树干和针叶CUE均随树木个体的增大而明显下降。(4)气温和土壤温度与乔木层树干和细根CUE呈正相关关系, 而降水量与针叶CUE呈负相关关系。细根CUE与树干CUE呈正相关关系,与针叶CUE呈负相关关系。峨眉冷杉成熟林乔木层CUE主要取决于树干和细根CUE。该研究证实了川西亚高山暗针叶成熟林仍具有较强的碳汇功能, 在区域碳储存和森林生态系统碳循环中发挥着极其重要的作用。     

中国典型陆地生态系统波文比特征及影响因素

波文比(β)是陆面过程中的重要参数, 影响着地表和大气间的能量交换, 明确β的空间变异规律和影响因素有助于对地表能量平衡和气候间反馈关系的预测。该研究收集了在中国不同生态系统类型开展的用涡度相关法(EC)测量地表能量平衡的公开发表文献, 构建了β和气象环境因子数据库, 分析了β在生态系统之间的差异、空间变异特征及影响因素。主要结果: (1)所有生态系统β平均值为0.95 ± 0.64, 变异系数67%, 偏度1.58, 峰度3.07, 整体服从对数正态分布, β平均值最高为灌木生态系统(1.26), 最低为湿地生态系统(0.49)。(2) β在生态系统类型间差异显著: 森林和湿地生态系统β无显著差异, 灌木生态系统β >草地生态系统 β >森林和湿地生态系统 β, 农田生态系统β介于草地生态系统与森林和湿地生态系统之间。(3) β随着纬度的增加而增加, 不随经度和海拔变化。纬度每增加1°,β增加0.038。(4) β随着年降水量(MAP)、年平均气温(MAT)、净辐射(R_n)、当年降水量(PPT)、当年平均气温(T_a)和叶面积指数(LAI)的增加而降低。(5)不同生态系统中β对生物和非生物因素的响应存在显著差异: 草地、森林和灌木生态系统的β对生物和非生物因素变化较为敏感, 而农田和湿地生态系统的β与所有生物和非生物因素均无显著相关关系。(6) MAP和R_n是β变化的直接影响因素, LAI通过影响R_n间接影响β。结果表明了植被类型与气候因素之间具有交互作用, 能量分配最主要的影响因素是降水, 叶面积对能量分配的调节作用并不显著。     

Effects of nitrogen enrichment on root exudative carbon inputs in Sibiraea angustata shrubbery at the eastern fringe of Qinghai-Xizang Plateau

Aims Understanding the responses of root exudative carbon (C) to increasing nitrogen deposition is important for predicting carbon cycling in terrestrial ecosystems. However, fewer studies have investigated the dynamics of root exudation in shrubbery ecosystems compared to forests and grassland ecosystems. This objective of this study was to determine the effects of nitrogen fertilization on the rate and C flux of root exudates.Methods Three levels of nitrogen addition treatments were applied to a Sibiraea angustata shrubbery ecosystem situated at the eastern fringe of Qinghai-Xizang Plateau, including N₀ (without nitrogen application), N₅ (nitrogen addition rate of 5 g·m^-2·a^-1), and N₁₀ (nitrogen addition rate of 10 g·m^-2·a^-1), respectively, in 5 m ´ 5 m plots. Root exudates were collected in June, August and October of 2015, using a modified culture-based cuvette system. Root biomass in each plot was measured with root core method.Important findings The rates of root exudates on biomass, length, and surface area basis all displayed apparent seasonal variations during the experimental period, with the magnitude ranked in the order of: August > June > October, consistent with changes in soil temperature at 5 cm depth. With increases in the nitrogen addition rate, the rate of root exudates on biomass, length, and area basis all trended lower. Compared with the control (N₀), the N₅ and N₁₀ treatments significantly reduced fine root biomass in the Sibiraea angustata shrubbery, by 23.36% and 33.84%, respectively. The decreasing root exudation and fine root biomass in response to nitrogen addition significantly decreased C flux of root exudates. Our results provide additional evidences toward a robust theoretical foundation for better understanding soil C-nutrient cycling process mediated by root exudation inputs in Alpine shrubbery ecosystems under various environmental changes.     

Testing parameter sensitivities and uncertainty analysis of Biome-BGC model in simulating carbon and water fluxes in broadleaved-Korean pine forests

生态过程模型的发展为研究者在长时间序列和区域尺度的研究提供了便利, 但模型模拟的准确性受到模型自身结构、模型参数估计合理性的影响。敏感性分析能够定量或定性筛选出对模型模拟结果影响较大的敏感参数, 是模型参数校准过程中的重要工具, 也是建模和应用的先决条件。该文以阔叶红松林为研究对象, 采用全局敏感性分析方法——傅里叶幅度灵敏度检验扩展法(EFAST)对Biome-BGC模型的生理生态参数进行了敏感性分析, 分别分析了红松(Pinus koraiensis)和阔叶树的净初级生产力(NPP)、蒸散(ET)对参数变化的敏感性。结果表明: (1)模拟红松NPP的不确定性高于阔叶树, 但二者的模拟ET的不确定性均较小。阔叶树的NPP和ET对生理生态参数的敏感性总体上都小于红松。(2)无论是红松、阔叶或其他植被类型, 模拟NPP均表现出对叶片碳氮比、细根碳氮比、比叶面积(SLA)和冠层截留系数的敏感性, 这4个参数的高敏感性主要是由模型自身结构所决定的, 与植被类型和研究地区的关系较小。对模拟ET而言, 细根与叶片碳分配比、新茎与新叶碳分配比和SLA均是影响红松和阔叶树ET的敏感参数, 但红松ET主要受参数与参数间的二阶或多阶交互作用的间接影响, 而阔叶树ET则主要是受到敏感参数直接效应的影响。(3)除了上述影响红松和阔叶树碳水通量的共性参数外, 诸如核酮糖-1,5-二磷酸羧化酶中叶氮含量、叶片与细根周转率、所有叶面积与投影叶面积之比等也是对模拟结果有影响的重要参数, 但是其敏感程度随物种不同和研究区不同而不同, 所以这类参数可以根据具体情况进行参数本地化, 对于其他不敏感参数则可以采用模型缺省值。     

Current stocks and rate of sequestration of forest carbon in Gansu Province,China

Aims
Carbon sequestration is the basic function and most primary service of forest ecosystems, and plays a vital role in mitigating the global climate change. However, carbon storage and allocation in forest ecosystems have been less studied at regional scales than at forest stand levels, and the results are subject to uncertainty due to inconsistent methodologies. In this study we aim to obtain relatively accurate estimates of forest carbon stocks and sequestration rate at a provincial scale (regional) based on plot surveys of plants and soils.
Methods
In consideration of the areas and distributions of major forest types, 212 sampling plots, covering different age classes and origins (natural forests vs. planted forests), were surveyed in Gansu Province in northern China. Field investigations were conducted for vegetation layers (trees, shrubs, herbs and litter), soil profiles, and sampling of both plant materials and soils for laboratory analyses. Regional carbon stocks were calculated by up-scaling the carbon densities of all forest types with their corresponding areas. Carbon sequestration rate was estimated by referencing the reports of national forest inventory data for different periods.
Important findings Forest carbon stocks at the provincial scale were estimated at 612.43 Tg C, including 179.04 Tg C in biomass and 433.39 Tg C in soil organic materials. Specifically, natural forests stored 501.42 Tg C, approximately 4.52 times than that of the plantations. Biomass carbon density in both natural forests and plantations showed an increasing trend with stand age classes, and was greater in natural forests than in plantations within the same age classes. Soil carbon density also increased with stand age classes in natural forests, but the highest value occurred at the pre-mature stage in plantations. The weighted average of regional biomass carbon density was at 72.43 Mg C·hm^-2, with the average value of 90.52 Mg C·hm^-2 in natural forests and 33.79 Mg C·hm^-2 in plantations, respectively. In 1996, vegetation stored 132.47 Tg C in natural forests and 12.81 Tg C in plantations, respectively, and the values increased to 152.41 and 26.63 Tg C in 2011, with the mean carbon sequestration rates of 1.33 and 0.92 Tg C·a^-1. Given that young and middle-aged forests account for a large proportion (62.28%) of the total forest areas, the region is expected to have substantial potential of carbon sequestration.     

Differential uptakes of different forms of soil nitrogen among major tree species in subalpine coniferous forests of western Sichuan,China

Aims Although acquisition of soil organic nitrogen (N)(mainly amino acids) by plants is a widespread ecological phenomenon in many terrestrial ecosystems, the rate of organic N uptake and their contributions to plant nutrient supply are poorly understood. Our objective was to determine the relative contributions of inorganic N (NO₃^–-N and NH₄⁺-N) and organic N (amino acids) to plant N uptake in a high-frigid forest ecosystem.Methods The differences in the uptake rate of three different forms of N (NO₃^–-N, NH₄⁺-N and glycine) were quantified by exposing seedlings of two dominant tree species (Picea asperata and Betula albo-sinensis) in subalpine coniferous forests of western Sichuan, China, to trace quantities of K¹⁵NO₃,¹⁵NH₄Cl and (U-¹³C₂/¹⁵N) glycine.Important findings Both ¹³C and ¹⁵N were significantly enriched in fine roots 2 h after tracer application, indicating the occurrence of glycine uptake in P. asperata and B. albo-sinensis seedlings. The seedlings of two tree species had a significant preference for NO₃^–-N compared with glycine and NH₄⁺-N, and the uptake rate of NO₃^–-N was 5 to 10 times greater than that of glycine and NH₄⁺-N. The roots of seedlings in the two species took up glycine more rapidly than NH₄⁺-N, implying that soil organic N (i.e., amino acids) could be an important N source for the two species in subalpine coniferous forests. The results of this study are of great theoretical significance for understanding N utilization strategies and nutrient regulation processes in plants of the high-frigid forest ecosystems.     

神农架常绿落叶阔叶混交林碳氮磷化学计量比

生态化学计量学是研究生态过程中化学元素平衡的科学, 碳(C)、氮(N)、磷(P)化学计量比是生态系统过程及其功能的重要特征。该研究测定了神农架常绿落叶阔叶混交林植物器官、凋落物及土壤的C、N、P含量, 利用生物量加权法计算其化学计量比, 并分析该生态系统不同组分间及不同器官间化学计量比的差异。研究结果发现: 在不同组分之间, C含量、C:N及C:P表现为植物>凋落物>土壤; N、P含量及N:P表现为凋落物>植物>土壤。在不同植物器官间, C含量的差异较小, 其变异系数相对N、P含量较低且保持稳定; N、P含量为叶片最高且变异系数最低; N:P为树皮最高, 而枝的变异系数最低。常绿与落叶树种的叶片N、P含量差异显著。与不同森林类型的化学计量比相比, 该常绿落叶阔叶混交林植物群落的C:P及N:P较低, 凋落物的C:P及N:P较高, 土壤的C、N、P化学计量比与亚热带常绿阔叶林基本一致, 生态系统的C:N相对较低。利用生物量加权法计算得到的该森林生态系统不同组分的C、N、P化学计量比的大小关系与前人利用枝叶取样算术平均的结果存在较大差异。C、N、P含量及其化学计量比在不同器官的分配及内稳性与器官的生理功能关系密切。     

Phylogeny and biogeography of Fagus (Fagaceae) based on 28 nuclear single/low-copy loci

Fagus L. is a key component in temperate deciduous broadleaf forests of the Northern Hemisphere. However, its biogeographic history has not been examined under the framework of a fully resolved and reasonably time-calibrated phylogeny. In this study, we sequenced 28 nuclear single/low-copy loci (18 555 bp in total) of 11 Fagus species/segregates and seven outgroups. Phylogenetic trees were reconstructed using both concatenation-based (maximum parsimony, maximum likelihood, and Bayesian inference) and coalescent-based methods (StarBEAST2, ASTRAL). The monophyly of two subgenera (Fagus and Engleriana) and most sections was well supported, except for sect. Lucida, which was paraphyletic with respect to sect. Longipetiolata. We also found a major phylogenetic conflict among North American, East Asian, and West Eurasian lineages of subgen. Fagus. Three segregates that have isolated distribution (F. mexicana, F. multinervis, and F. orientalis) were independent evolutionary units. Biogeographic analysis with fossils suggested that Fagus could have originated in the North Pacific region in late early Eocene. Major diversifications coincided with a climate aberration at the Eocene/Oligocene boundary and the global cooling since mid-Miocene. The late Miocene accelerated global cooling and the Pleistocene glaciations would have driven beeches into East Asia, North America, and West Eurasia. Meanwhile, range reduction and extinction in high latitudes, central Asia, and western North America converged to form the beech modern distribution pattern. This study provides a first attempt to disentangle the biogeographic history of beeches in the context of a nearly resolved and time-calibrated phylogeny, which could shed new insights into the formation of the temperate biome in the Northern Hemisphere.     

Soil carbon storage and its determinants in the forests of Shaanxi Province,China

Aims The bank of soil carbon of forests plays an important role in the global carbon cycle. Our aim is to understand the characteristics of soil carbon storage and its determinants in the forests in Shaanxi Province.Methods The data of forest inventory in 2009 and resampling in 2011 were used to analyze the characteristics of soil carbon storage and its determinants in the forest soil in Shaanxi Province.Important findings The soil carbon storage in the forests in Shaanxi Province was 579.68 Tg. Soil carbon storage of Softwood and Hardwood forests were the highest among all forest types, accounting for 36.35% of the whole province forest soil carbon storage. The forest soil carbon storage was 4.15 times greater in the natural forest (467.17 Tg) than that in the plantations. The young and middle-aged forests were the main contributors to the total carbon storage across all age groups, accounting for about 57.30% of the total forest soil carbon storage. The average soil carbon density of forests in Shaanxi Province was 90.68 t∙hm^-2, in which the soil carbon density of Betula forests was the highest (141.74 t∙hm^-2). Soil carbon density of different forest types were gradually decreased with soil depth. In addition, it was highest in middle-aged forest. Soil carbon density was higher in the natural forest ecosystems than that in the plantations within the each age group, indicating natural forest ecosystems have higher capacity of carbon sequestration. Differences in the spatial patterns between carbon storage and density indicated that carbon storage was related to forest coverage. The soil carbon density and storage of forests in Yulin were the lowest across the province. This suggests that, in order to enhance the regional carbon sequestration capacity in this region, we need to appropriately strengthen artificial afforestation activities and manage them scientifically and rationally. The soil carbon density of forests in Shaanxi Province decreased with the increase of longitude, latitude, and annual temperature, but increased with the increase of altitude and annual rainfall. This study provides data basis for provincial estimation of forest soil carbon bank in China.     

青海森林生态系统中灌木层和土壤生态化学计量特征

灌木层作为森林生态系统的重要组成部分, 了解其生态化学计量特征将有助于揭示森林生态系统物质周转和养分循环等生态功能。该研究选取青海省7种主要优势林分——白桦(Betula platyphylla)林、毛白杨(Populus tomentosa)林、红桦(Betula albosinensis)林、青扦(Picea wilsonii)林、山杨(Populus davidiana)林、圆柏(Sabina chinensis)林、云杉(Picea asperata)林为研究对象, 采用野外取样和室内实验分析相结合的方法, 研究了不同林分林下灌木层不同器官(叶、枝干、根)及其表层(0-10 cm)土壤的碳(C)、氮(N)、磷(P)含量及其相关性。结果表明: 7种林分间灌木(叶、枝干、根) P含量、C:P均没有明显差异性; 山杨林、圆柏林、云杉林的林下灌木(叶、枝干、根) N含量、N:P高于白桦林、毛白杨林、红桦林和青扦林, C:N则相反。圆柏林的林下灌木生长受P限制, 其余6种林分的林下灌木生长受N限制。7种林分间土壤有机碳(SOC)和总氮(TN)含量呈现出明显差异性, 而总磷(TP)含量则差异不明显。相关性分析表明, 林下灌木(叶、枝干、根) N含量、C:N、N:P与土壤TN含量、C:N、N:P呈极显著相关性, 而P含量、C:P与土壤TP含量呈显著相关性。冗余分析表明, 林下灌木层植被C、N、P含量及生态化学计量特征受到土壤化学计量特征及各环境因子的共同影响, 其中土壤C:N、海拔、年平均气温、年降水量为主要影响因子。     

New perspectives on forest soil carbon and nitrogen cycling processes: Roles of arbuscular mycorrhizal versus ectomycorrhizal tree species

Nearly all tree species develop symbiotic relationships with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi to acquire nutrients from soils, and hence influence soil carbon (C) and nitrogen (N) cycles in terrestrial ecosystems. It is crucial to understand the differences in soil C and N cycles between AM and EM forests and the underlying mechanisms. In this review, we first compared the differences in the soil C and N cycles between AM and EM forests, and synthesized the underlying mechanisms from perspectives of the inputs, stabilization, and outputs of soil C and N in forest ecosystems. We also compared the responses of soil C and N cycles between AM and EM forests to global changes. In this field, one major research priority is comparing the structure and function (including the soil C and N cycles) between AM and EM forest ecosystems to provide theoretical basis and solid data for improving forest productivity and ecosystem services. The second research focus is deepening the understanding of the effects of interactions between aboveground litter and belowground mycorrhiza and free-living microbes on soil C and N cycles to reveal the potential underlying mechanisms in forests with different mycorrhizal symbioses. Third, the research methodology and new techniques need refining and applying to explicitly focus on scaling up the fine-scale measurements to better expound and predict the C and N cycles in forest ecosystems. Finally, more studies on the stability of soil organic matter among different mycorrhizal forests are needed to precisely assess responses of the structure and function of forest ecosystems to global changes.     

Stoichiometric characteristics of carbon,nitrogen and phosphorus in Phyllostachys edulis forests of China

Aims Stoichiometric ratios of carbon (C), nitrogen (N) and phosphorus (P) are important characteristics of the ecological processes and functions. Studies on population ecological stoichiometry can refine the content of flora chemometrics, determine the limited nutrient, and provide data for process-based modeling over large scale. Phyllostachys edulis is an important forest type, whose area accounts for 74% of total bamboo forest area in Southern China. However, little is known about the ecological stoichiometric in P. edulis. This study aimed to reveal C:N, C:P and N:P stoichiometry characteristics of the “plant-soil-litter” continuum and to provide a better understanding nutrient cycling and stability mechanisms in P. edulis forest in China. Methods The data were collected from the published literature containing C、N、P content in leaf or surface soil (0-20 cm) or littefall in P. edulis forests. Important findings 1) The leaf C, N, P content were estimated at 478.30 mg·g^-1, 22.20 mg·g^-1, 1.90 mg·g^-1 in P. edulis, and the corresponding C: N, C: P and N: P were 26.80, 299.60 and 14.40, respectively. Soil C, N, and P content in 0-20 cm were 21.53 mg·g^-1, 1.66 mg·g^-1, 0.41 mg·g^-1, with ratios of 14.20 for C:N, 66.74 for C:P and 4.28 for N:P. The C, N and P contents were 438.49 mg·g^-1, 13.39 mg·g^-1, 0.86 mg·g^-1 for litterfall, with the litter C:N, C:P and N:P being 25.53, 665.67, 22.55, respectively. 2) In the plant-soil-litter system in P. edulis forest, leaf had higher C:N, litter had higher C:P and N:P, while soil were the lowest. The N, P resorption rate was 39.68% and 54.74%, indicating that P. edulis forest growth and development was constrained by P or by both of N and P in China. 3) N content and N:P in leaf showed a tendency to increase with latitude, while the C:N of leaf declined with latitude. N:P of leaf increased with longitude, but the P content and the C:N of leaf showed a opposite trend. C: N of soil increased with longitude, whereas the N content of soil declined longitude. The N content of litter declined with longitude. 4) The leaf N content was negatively correlated with mean annual temperature and mean annual precipitation, but being more sensitive to temperature than precipitation. The positive correlations between N content and latitude support “Temperature-Plant Physiological” hypothesis, reflecting an adaptive strategy to environmental conditions.