长期封育对不同类型草地碳贮量及其固持速率的影响

基于4个长期封育草地,采用成对取样方法(封育-自由放牧草地)分析了长期封育和自由放牧草地地上生物量、地表凋落物、0-100 cm根系和土壤的碳氮贮量,探讨了长期封育草地的碳固持速率。实验结果表明:长期封育显著提高了草地碳氮贮量;经30a围封处理后,草地碳固持量为1401-2858 g C m^-2,平均2126 g C m^-2;草地碳固持速率为46.7-129.2 g C m^-2 a^-1,平均84.2 g C m^-2 a^-1。长期封育草地氮固持速率为2.8-14.7 g N m^-2 a^-1,平均7.3 g N m^-2 a^-1。封育草地碳和氮固持速率表现为:针茅草地＜羊草草地＜退化羊草草地＜补播黄花苜蓿+羊草草地。长期封育草地0-40 cm土壤碳固持速率相对较高,但下层土壤对草地碳固持的贡献也比较大,因此,未来的相关研究应给予下层土壤更大关注。内蒙古典型草地具有巨大的碳固持潜力,长期封育(或禁牧)是实现其碳固持效应最经济、最有效的途径之一。     

吊丝单竹林生态系统碳储量及其垂直空间分配特征

利用标准样方法研究了吊丝单竹(Dendrocalamopsis vario-striata)林的碳储量及其空间分布特征。结果表明,吊丝单竹不同器官的碳密度为0.4684~0.5092 g g^-1,依次为竹秆>竹蔸>竹根>竹枝>竹叶;碳储量在吊丝单竹不同器官中的分配以竹秆最大(达50.46%),其次为竹蔸(20.71%),竹叶的最小(仅5.01%)。整个吊丝单竹林生态系统碳库主要由乔木层、灌草层、枯落物层和土壤层4部分组成,总碳贮量为104.9321 t hm^-2,其空间分布为土壤层>乔木层>枯落物层>灌草层,其中土壤层占总碳储量的比例最大(59.74%);整个吊丝单竹林乔木层年固碳量为6.4460 t hm^-2a^-1,相当于每年同化CO₂的量为23.6353 t hm^-2a^-1,这略低于我国森林植被的平均年固碳量,表明吊丝单竹林还有较大的发展空间。     

1981-2019年华北平原农田土壤有机碳储量的时空变化及影响机制

农业土壤具有可观的固碳及减碳潜力,有助于减缓人类温室气体排放导致的气候变化。为了更好地了解华北平原土壤有机碳储量动态及其驱动因子,结合荟萃分析、随机森林机器学习模型和卫星遥感数据,研究了1981-2019年间中国华北平原农田土壤有机碳储量的时空变化及其驱动因子。结果表明,1981-2019年间华北平原0-20 cm农田土壤有机碳储量约为（523.10±79.36） Tg C （（14.56±1.66） Mg C/hm²）,并以5.94 Tg C/a （0.12 Mg C hm^-2 a^-1）的年固持速率稳步增长,占比约为中国农田每年新增土壤有机碳的23.3%。其中,常规农田管理措施,包括无机肥施用、有机肥施用和秸秆还田,对土壤有机碳增长的贡献平均为25.1%,即1.49 Tg C/a （0.03 Mg C hm^-2 a^-1）。相比对照组,氮磷钾无机肥施用可提高22.7%-26.0%的土壤有机碳固定速率,有机肥可提高48.3%,秸秆还田可提高23.4%。同时,上述常规农田管理措施对土壤有机碳的积累作用受到土壤本身理化性质的调控,在温度和降水较高的气候条件下更显著。值得注意的是,无论是无机肥施用、有机肥施用还是秸秆还田,当投入量超过农作物和土壤微生物对碳和养分的需求时,土壤有机碳累积速率会显著下降。这也导致2000年后土壤有机碳固持速率明显减缓,由9.4 Tg C/a下降为3.5 Tg C/a。总的来说,过去几十年农田管理措施的改进显著提高了华北平原农田土壤有机碳的增加速率,而未来华北平原农田系统固碳潜力仍然可观,但亟待明确在保证粮食产量的同时不同气候和土壤环境条件下最佳固碳所需的化肥、有机肥和秸秆投入量。     

林业活动对区域森林生物量碳源汇格局的影响——以南平市为例

林业活动在一定程度上影响着区域森林的时空分布格局和碳汇/源功能。明确并量化林业活动对区域森林碳汇功能的影响与空间分布，对于区域森林碳汇提升和实现区域"碳中和"具有重要意义。以国家级生态示范区福建省南平市为例，以多期森林资源规划调查数据为基础，采用IPCC材积源-生物量法，基于土地利用类型的时空变化和林业活动类型划分，分类分析了南平市森林碳源和碳汇的空间分布特征，并量化了不同林业活动（一直保持为森林、人工造林、自然恢复、毁林和森林退化）对森林碳汇和碳源的影响。研究结果表明，2013年南平市森林碳储量总量为80.84Tg C，2020年森林碳储量总量增加至89.87Tg C，年均变化量为1.29Tg C/a （或4.73Tg CO₂/a）。平均胸径、公顷蓄积等林分因子是当前主要影响森林碳储量的因素。在其他影响因素中，暗红壤分布区的森林生物质碳密度较高而在水稻土分布区则较低；此外，高海拔、中等立地质量土地上的森林碳密度较高。对于不同林业活动，2013-2020年南平市一直保持为森林（森林经营）、自然恢复增加的天然林和人工造林分别使森林生物质碳储量增加了0.34Tg C/a、0.85Tg C/a和1.05Tg C/a，同期因毁林和森林退化导致森林生物质碳储量分别减少0.75Tg C/a和0.42Tg C/a，森林生物质碳储量净增加1.09Tg C/a （或3.98Tg CO₂/a），明显低于2013-2020森林碳储量净增量。对于土地利用变化较剧烈的区域，本文基于土地利用变化且区分林业活动路径的方法，能更准确地反映森林的碳汇和碳源及时空格局。2013-2020年间南平市一直保持为森林的生物质碳密度仅增长0.22Mg C hm^-2 a^-1，成熟林、过熟林面积占比增加使森林平均生长速率下降可能是主要原因。而同期通过自然恢复和人工造林使森林生物质碳密度分别增长4.00Mg C hm^-2 a^-1和4.10Mg C hm^-2 a^-1。优化龄组结构提升森林生长量、减少毁林和防止森林退化可以作为该区域未来森林增汇减排的有效举措。     

中国盐沼湿地蓝碳碳汇研究进展

滨海蓝碳主要指被红树林、盐沼湿地、海草床等蓝碳生态系统所固定的碳,这部分碳对于减缓气候变暖意义重大。其中盐沼湿地作为我国面积最大、分布广泛的滨海湿地,受到人类活动的扰动较多,其碳汇估算的数据缺乏系统性与完整性。通过收集我国的盐沼湿地相关研究与数据,本文对我国盐沼湿地的分布现状及其碳储量、碳埋藏、碳来源、温室气体通量进行了总结,其中我国盐沼湿地的分布面积为(1.27~3.43)×10⁵hm²,总碳储量为(7.5±0.6) Tg,碳埋藏速率为7~955 g C/(m²·a),非CO₂温室气体通量分别为23.6~986 μg CH₄/(m²·h)和1.58~110 μg N₂O/(m²·h)。本文系统梳理了有关我国盐沼湿地碳汇功能的研究,指出我国盐沼湿地碳循环研究仍需加深对机制机理的解析和关键调控因子的探究,以期让盐沼湿地蓝碳为我国的碳达峰与碳中和战略做出更大贡献。     

若尔盖高原泥炭地生态系统碳储量

为了精确估算泥炭地生态系统碳储量,采用土壤剖面法和植被收割法,研究了青藏高原东部边缘的若尔盖3种水位状态下的泥炭地植被碳储量、土壤碳储量(0~200 cm)和生态系统碳储量。结果表明:若尔盖高原3种水位状态下泥炭地生态系统碳储量为761.56~1103.40 t·hm~(-2),平均值为976.49 t·hm~(-2);植被碳储量为13.44~15.23 t·hm~(-2),平均值为14.53 t·hm~(-2);土壤有机碳储量为748.12~1088.17 t·hm~(-2),平均值961.96 t·hm~(-2),是中国湿地土壤有机碳储量的3倍、森林土壤有机碳储量的5倍和草地土壤有机碳储量的11倍。影响泥炭地碳储量估算不确定性的因子主要为泥炭深度、土壤容重和土壤有机碳含量,加强这3种土壤因子数据信息的研究有助于精确估算若尔盖高原泥炭地生态系统碳储量。     

中国亚热带-暖温带过渡区锐齿栎林净生态系统碳交换特征

在2017年1月1日-2017年12月31日期间,采用涡度相关法对位于亚热带-暖温带气候过渡区的河南宝天曼国家级自然保护区的65年生锐齿栎（Quercus aliena）天然次生林的碳通量进行了连续观测。结果表明：在观测期间,该森林生态系统在生长季5-10月份为碳汇,非生长季各月为碳源,净碳吸收量与释放量分别在7月和4月达到最大。净生态系统生产力为569.4 g C m^-2a^-1,生态系统呼吸为529.9 g C m^-2a^-1,总生态系统生产力为1099.3 g C m^-2a^-1。30min尺度上夜间净生态系统碳交换量与5cm深度土壤温度的关系可用指数方程表示（R²=0.21,P < 0.001）,其温度敏感性系数（Temperature sensitivity coefficient,Q₁₀）为2.2。如果排除夜间通量观测的误差,处在海拔较高地区的夜间低温和非生长季的低温抑制了生态系统呼吸排放,可能导致全年生态系统呼吸量较低。在生长季5-10月份,各月的白天净生态系统碳交换量对光合有效辐射的响应符合直角双曲线模型,初始光能利用效率、平均最大光合速率和白天平均生态系统呼吸强度呈明显的季节变化,范围分别是0.06-0.12 μmol CO₂ μmol^-1 photon、0.44-1.47 mg CO₂ m^-2s^-1和0.07-0.19 mg CO₂ m^-2s^-1。夏季7、8月份,较高的饱和水汽压差对白天锐齿栎林的碳吸收有明显的抑制作用;生长季末期9月份较高的土壤含水量对白天锐齿栎林的碳吸收也产生了抑制作用,表明生长末期降水过多影响森林的碳吸收。     

城市森林碳汇及其抵消能源碳排放效果——以广州为例

城市森林及其管理相关政策作为减少CO₂排放的有效策略得到了较为广泛的关注。采用材积源生物量方程与净初级生产力方法来定量分析了广州市城市森林碳储量和碳固定量,根据化石能源使用量及其碳排放因子核算了广州城市能源碳排放,最后评估了城市森林碳抵消效果。结果显示广州市城市森林碳储量为654.42×10⁴t,平均碳密度为28.81 t/hm²,而森林碳固定量为658732 t/a,平均固碳率为2.90 t·hm^-2·a^-1。2005-2010年广州市年均能源碳排放则达到2907.41×10⁴t。广州城市森林碳储量约为城市年均能源碳排放的22.51%,其通过碳固定年均能够抵消年均碳排放的2.27%,不过从城市森林综合效益来看其仍是城市低碳发展重要举措之一。分析了林型组成和林龄结构对于广州森林碳储量和碳固定量的影响,并从森林管理角度为城市森林碳汇提升提出建议。这些结果和讨论有助于评估城市森林碳汇在抵消碳排放中所起的效果。     

连续氮添加14年对温带典型草原土壤碳氮组分及物理结构的影响

全球氮沉降对生态系统造成了深远的影响,研究长时间氮沉降对草地生态系统土壤理化特征的影响有助于加强生态系统对氮沉降响应的长效机制的理解。通过连续14年长期施加N0（0 g N m^-2 a^-1）、N2（2 g N m^-2 a^-1）、N4（4 g N m^-2 a^-1）、N8（8 g N m^-2 a^-1）、N16（16 g N m^-2 a^-1）、N32（32 g N m^-2 a^-1）六种浓度尿素模拟氮沉降,并将土壤分成0-10、10-20和20-40 cm三个深度土层,研究温带草原生态系统土壤碳氮组分及物理结构对氮添加的响应及其相互关系,结果表明：（1）氮添加显著降低0-10 cm土壤酸碱度及土壤微生物量碳含量,N32相比N0分别下降了27.63%和58.40%（P<0.05）;各土层总有机碳和全氮含量对氮添加处理无显著响应,0-10 cm土层显著高于20-40 cm土层。（2）同一土层深度不同梯度氮添加处理显著增加土壤无机氮离子含量（P<0.05）,0-10 cm土层铵态氮含量N32相比N0增加了88.72%,20-40 cm土层硝态氮含量N32相比N0增加了19.55倍,土壤深度与氮添加对无机氮离子含量影响具有显著的交互效应。（3）同一土壤深度不同梯度氮添加处理土壤粒度分形维数及土壤团聚体差异不显著,相关分析表明土壤碳氮元素含量与土壤结构显著相关。土壤碳氮组分在适宜浓度氮添加的增加趋势说明氮添加在一定程度上可能促进土壤理化性质的改良,氮添加对土壤物理结构的影响还需要进一步的深入研究。     

凋落物添加和模拟氮磷沉降对红松凋落物木质素降解和碳释放的影响

通过对阔叶红松林和红松人工林2种林型凋落物处理（分别为不添加凋落物（原样组）、添加凋落物（双倍组）和去除凋落物（去除组）等3个处理）与模拟氮磷沉降（分别为对照CK （0 g N m^-2 a^-1、0 g P m^-2 a^-1）、低浓度氮磷（5 g N m^-2 a^-1、5 g P m^-2 a^-1）、中浓度氮磷（15 g N m^-2 a^-1、10g P m^-2 a^-1）和高浓度氮磷（30 g N m^-2 a^-1、20 g P m^-2 a^-1）等4个强度）原位培养试验,研究凋落物质量的增加与氮磷沉降及两种处理的耦合作用对碳（C）和木质素分解释放的影响。结果表明：凋落物添加在试验前期（6月）抑制人工林L层的C释放,促进H层的C释放;试验后期（10月）促进人工林L层C释放,而抑制H层的C释放。凋落物添加在前期（6月）是促进天然林L层C释放的,但在后期（10月）产生抑制作用。与L层相反,凋落物添加持续促进天然林H层的C释放。低、中浓度氮磷沉降显著促进了红松人工林和阔叶红松林L、H层C释放和木质素降解,但高浓度的氮磷添加会抑制C释放和木质素的降解,两种处理之间无交互作用。     

Carbon balance and radiative forcing of Finnish peatlands 1900–2100 – the impact of forestry drainage

Natural peatlands accumulate carbon (C) and nitrogen (N). They affect the global climate by binding carbon dioxide (CO₂) and releasing methane (CH₄) to the atmosphere; in contrast fluxes of nitrous oxide (N₂O) in natural peatlands are insignificant. Changes in drainage associated with forestry alter these greenhouse gas (GHG) fluxes and thus the radiative forcing (RF) of peatlands. In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry‐drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a^‐‐1 in 1900, when all peatlands were undrained, to 3.6 Tg a^‐‐1 at present, when c. 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH₄‐‐C a^‐‐1, while those of N₂O have increased from 0.0003 to 0.005 Tg N₂O‐‐N a^‐‐1. The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m^‐‐2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO₂ sequestration in peat (‐‐0.5 mW m^‐‐2), tree stands and wood products (‐‐0.8 mW m^‐‐2), decreases in CH₄ emissions from peat to the atmosphere (‐‐1.6 mW m^‐‐2), and only a small increase in N₂O emissions (+0.1 mW m^‐‐2). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be valid also for Scandinavian countries and Russia, where most forestry‐drained peatlands occur outside Finland.     

Carbon sequestration in peatland: patterns and mechanisms of response to climate change

The response of peatlands to changes in the climatic water budget is crucial to predicting potential feedbacks on the global carbon (C) cycle. To gain insight on the patterns and mechanisms of response, we linked a model of peat accumulation to a model of peatland hydrology, then applied these models to empirical data spanning the past 5000 years for the large mire Store Mosse in southern Sweden. We estimated parameters for C sequestration and height growth by fitting the peat accumulation model to two age profiles. Then, we used independent reconstruction of climate wetness and model reconstruction of bog height to examine changes in peatland hydrology. Reconstructions of C sequestration showed two distinct patterns of behaviour: abrupt increases associated with major transitions in vegetation and dominant Sphagnum species (fuscum, rubellum–fuscum and magellanicum stages), and gradual decreases associated with increasing humification of newly formed peat. Carbon sequestration rate ranged from a minimum of 14 to a maximum of 72 g m^?2 yr^?1, with the most rapid changes occurring in the past 1000 years. Vegetation transitions were associated with periods of increasing climate wetness during which the hydrological requirement for increased seepage loss was met by rise of the water table closer to the peatland surface, with the indirect result of enhancing peat formation. Gradual decline in C sequestration within each vegetation stage resulted from enhanced litter decay losses from the near‐surface layer. In the first two vegetation stages, peatland development (i.e., increasing surface gradient) and decreasing climate wetness drove a gradual increase in thickness of the unsaturated, near‐surface layer, reducing seepage water loss and peat formation. In the most recent vegetation stage, the surface diverged into a mosaic of wet and dry microsites. Despite a steady increase in climate wetness, C sequestration declined rapidly. The complexity of response to climate change cautions against use of past rates to estimate current or to predict future rates of peatland C sequestration. Understanding interactions among hydrology, surface structure and peat formation are essential to predicting potential feedback on the global C cycle.     

Holocene radiative forcing impact of northern peatland carbon accumulation and methane emissions

Throughout the Holocene, northern peatlands have both accumulated carbon and emitted methane. Their impact on climate radiative forcing has been the net of cooling (persistent CO₂ uptake) and warming (persistent CH₄ emission). We evaluated this by developing very simple Holocene peatland carbon flux trajectories, and using these as inputs to a simple atmospheric perturbation model. Flux trajectories are based on estimates of contemporary CH₄ flux (15–50 Tg CH₄ yr⁻¹), total accumulated peat C (250–450 Pg C), and peatland initiation dates. The contemporary perturbations to the atmosphere due to northern peatlands are an increase of ∼100 ppbv CH₄ and a decrease of ∼35 ppmv CO₂. The net radiative forcing impact northern peatlands is currently about −0.2 to −0.5 W m⁻² (a cooling). It is likely that peatlands initially caused a net warming of up to +0.1 W m⁻², but have been causing an increasing net cooling for the past 8000–11 000 years. A series of sensitivity simulations indicate that the current radiative forcing impact is determined primarily by the magnitude of the contemporary methane flux and the magnitude of the total C accumulated as peat, and that radiative forcing dynamics during the Holocene depended on flux trajectory, but the overall pattern was similar in all cases.     

Carbon accumulation of tropical peatlands over millennia: a modeling approach

Tropical peatlands cover an estimated 440 000 km² (~10% of global peatland area) and are significant in the global carbon cycle by storing about 40–90 Gt C in peat. Over the past several decades, tropical peatlands have experienced high rates of deforestation and conversion, which is often associated with lowering the water table and peat burning, releasing large amounts of carbon stored in peat to the atmosphere. We present the first model of long‐term carbon accumulation in tropical peatlands by modifying the Holocene Peat Model (HPM), which has been successfully applied to northern temperate peatlands. Tropical HPM (HPMTrop) is a one‐dimensional, nonlinear, dynamic model with a monthly time step that simulates peat mass remaining in annual peat cohorts over millennia as a balance between monthly vegetation inputs (litter) and monthly decomposition. Key model parameters were based on published data on vegetation characteristics, including net primary production partitioned into leaves, wood, and roots; and initial litter decomposition rates. HPMTrop outputs are generally consistent with field observations from Indonesia. Simulated long‐term carbon accumulation rates for 11 000‐year‐old inland, and 5 000‐year‐old coastal peatlands were about 0.3 and 0.59 Mg C ha^?1 yr^?1, and the resulting peat carbon stocks at the end of the 11 000‐year and 5 000‐year simulations were 3300 and 2900 Mg C ha^?1, respectively. The simulated carbon loss caused by coastal peat swamp forest conversion into oil palm plantation with periodic burning was 1400 Mg C ha^?1 over 100 years, which is equivalent to ~2900 years of C accumulation in a hectare of coastal peatlands.     

The large Amazonian peatland carbon sink in the subsiding Pastaza‐Marañón foreland basin,Peru

The carbon (C) dynamics of tropical peatlands can be of global importance, because, particularly in Southeast Asia, they are the source of considerable amounts of C released to the atmosphere as a result of land‐use change and fire. In contrast, the existence of tropical peatlands in Amazonia has been documented only recently. According to a recent study, the 120 000 km² subsiding Pastaza‐Marañón foreland basin in Peruvian Amazonia harbours previously unstudied and up to 7.5 m thick peat deposits. We studied the role of these peat deposits as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 5–13 sites. The basal ages varied from 1975 to 8870 cal yr bp , peat accumulation rates from 0.46 to 9.31 mm yr^?1 and C accumulation rates from 28 to 108 g m^?2 yr^?1. The total peatland area and current peat C stock within the area of two studied satellite images were 21 929 km² and 3.116 Gt (with a range of 0.837–9.461 Gt). The C stock is 32% (with a range of 8.7–98%) of the best estimate of the South American tropical peatland C stock and 3.5% (with a range of 0.9–10.7%) of the best estimate of the global tropical peatland C stock. The whole Pastaza‐Marañón basin probably supports about twice this peatland area and peat C stock. In addition to their contemporary geographical extent, these peatlands probably also have a large historical (vertical) extension because of their location in a foreland basin characterized by extensive river sedimentation, peat burial and subsidence for most of the Quaternary period. Burial of peat layers in deposits of up to 1 km thick Quaternary river sediments removes C from the short‐term C cycle between the biosphere and atmosphere, generating a long‐term C sink.     

Postfire carbon balance in boreal bogs of Alberta, Canada

Boreal peatland ecosystems occupy about 3.5 million km² of the earth's land surface and store between 250 and 455 Pg of carbon (C) as peat. While northern hemisphere boreal peatlands have functioned as net sinks for atmospheric C since the most recent deglaciation, natural and anthropogenic disturbances, and most importantly wildfire, may compromise peatland C sinks. To examine the effects of fire on local and regional C sink strength, we focused on a 12 000 km² region near Wabasca, AB, Canada, where ombrotrophic Sphagnum‐dominated bogs cover 2280 km² that burn with a fire return interval of 123±26 years. We characterized annual C accumulation along a chronosequence of 10 bog sites, spanning 1–102 years‐since‐fire (in 2002). Immediately after fire, bogs represent a net C source of 8.9±8.4 mol m⁻² yr⁻¹. At about 13 years after fire, bogs switch from net C sources to net C sinks, mainly because of recovery of the moss and shrub layers. Subsequently, black spruce biomass accumulation contributes to the net C sink, with fine root biomass accumulation peaking at 34 years after fire and aboveground biomass and coarse root accumulation peaking at 74 years after fire. The overall C sink strength peaks at 18.4 mol C m⁻² yr⁻¹ at 75 years after fire. As the tree biomass accumulation rate declines, the net C sink decreases to about 10 mol C m⁻² yr⁻¹ at 100 years‐since‐fire. We estimate that across the Wabasca study region, bogs currently represent a C sink of 14.7±5.1 Gmol yr⁻¹. A decrease in the fire return interval to 61 years with no change in air temperature would convert the region's bogs to a net C source. An increase in nonwinter air temperature of 2 °C would decrease the regional C sink to 6.8±2.3 Gmol yr⁻¹. Under scenarios of predicted climate change, the current C sink status of Alberta bogs is likely to diminish to the point where these peatlands become net sources of atmospheric CO₂‐C.     

A Tropical Freshwater Wetland: II. Production,Decomposition, and Peat Formation

As much as 10% of the total carbon stored in peatlands occurs in the tropics. Although tropical peatlands are poorly understood scientifically, they are increasingly exploited for a variety of human uses. Our objective was to measure baseline carbon cycling data in one type of tropical peatland in order to understand better how peat accumulates in these ecosystems. Average plant production for two study sites on the island of Kosrae in the Federated States of Micronesia over 2 year was 1122 g C m⁻² year⁻¹, of which 1058 g C m⁻² year⁻¹ was aboveground plant production (bole, buttress and litterfall). Although leaves contributed a high proportion of total plant productivity, their rapid decomposition left little carbon for peat accumulation. In contrast, fine roots only contributed 10% to plant productivity, but their slow decomposition allowed them to accumulate as peat. Wood (branches and stems) probably contributed the most carbon to the formation of peat. Despite being on the soil surface, small branches decomposed more slowly than leaves because of their high C:N and lignin:N ratios. In summary, we suggest that tropical peatlands in Micronesia accumulate peat not because of high plant production but rather because of slow decomposition of roots and wood under anaerobic conditions that result from nearly constant high water levels.     

Comparison of carbon and nitrogen accumulation rate between bog and fen phases in a pristine peatland with the fen-bog transition

Long-term carbon and nitrogen dynamics in peatlands are affected by both vegetation production and decomposition processes. Here, we examined the carbon accumulation rate (CAR), nitrogen accumulation rate (NAR) and δ¹³C, δ¹⁵N of plant residuals in a peat core dated back to ~8500 cal year BP in a temperate peatland in Northeast China. Impacted by the tephra during 1160 and 789 cal year BP and climate change, the peatland changed from a fen dominated by vascular plants to a bog dominated by Sphagnum mosses. We used the Clymo model to quantify peat addition rate and decay constant for acrotelm and catotelm layers during both bog and fen phases. Our studied peatland was dominated by Sphagnum fuscum during the bog phase (789 to −59 cal year BP) and lower accumulation rates in the acrotelm layer was found during this phase, suggesting the dominant role of volcanic eruption in the CAR of the peat core. Both mean CAR and NAR were higher during the bog phase than during the fen phase in our study, consistent with the results of the only one similar study in the literature. Because the input rate of organic matter was considered to be lower during the bog phase, the decomposition process must have been much lower during the bog phase than during the fen phase and potentially controlled CAR and NAR. During the fen phase, CAR was also lower under higher temperature and summer insolation, conditions beneficial for decomposition. δ¹⁵N of Sphagnum hinted that nitrogen fixation had a positive effect on nitrogen accumulation, particular in recent decades. Our study suggested that decomposition is more important for carbon and nitrogen sequestration than production in peatlands in most conditions and if future climate changes or human disturbance increase decomposition rate, carbon sequestration in peatlands will be jeopardized.     

Permafrost thaw causes large carbon loss in boreal peatlands while changes to peat quality are limited

Rapid, ongoing permafrost thaw of peatlands in the discontinuous permafrost zone is exposing a globally significant store of soil carbon (C) to microbial processes. Mineralization and release of this peat C to the atmosphere as greenhouse gases is a potentially important feedback to climate change. Here we investigated the effects of permafrost thaw on peat C at a peatland complex in western Canada. We collected 15 complete peat cores (between 2.7 and 4.5 m deep) along four chronosequences, from elevated permafrost peat plateaus to saturated thermokarst bogs that thawed up to 600 years ago. The peat cores were analysed for peat C storage and peat quality, as indicated by decomposition proxies (FTIR and C/N ratios) and potential decomposability using a 200-day aerobic laboratory incubation. Our results suggest net C loss following thaw, with average total peat C stocks decreasing by ~19.3 ± 7.2 kg C m⁻² over <600 years (~13% loss). Average post-thaw accumulation of new peat at the surface over the same period was ~13.1 ± 2.5 kg C m⁻². We estimate ~19% (±5.8%) of deep peat (>40 cm below surface) C is lost following thaw (average 26 ± 7.9 kg C m⁻² over <600 years). Our FTIR analysis shows peat below the thaw transition in thermokarst bogs is slightly more decomposed than peat of a similar type and age in permafrost plateaus, but we found no significant changes to the quality or lability of deeper peat across the chronosequences. Our incubation results also showed no increase in C mineralization of deep peat across the chronosequences. While these limited changes in peat quality in deeper peat following permafrost thaw highlight uncertainty in the exact mechanisms and processes for C loss, our analysis of peat C stocks shows large C losses following permafrost thaw in peatlands in western Canada.     

Decreased carbon accumulation feedback driven by climate‐induced drying of two southern boreal bogs over recent centuries

Northern boreal peatlands are important ecosystems in modulating global biogeochemical cycles, yet their biological communities and related carbon dynamics are highly sensitive to changes in climate. Despite this, the strength and recent direction of these feedbacks are still unclear. The response of boreal peatlands to climate warming has received relatively little attention compared with other northern peatland types, despite forming a large northern hemisphere‐wide ecosystem. Here, we studied the response of two ombrotrophic boreal peatlands to climate variability over the last c. 200 years for which local meteorological data are available. We used remains from plants and testate amoebae to study historical changes in peatland biological communities. These data were supplemented by peat property (bulk density, carbon and nitrogen content), ¹⁴C, ²¹⁰Pb and ¹³⁷Cs analyses and were used to infer changes in peatland hydrology and carbon dynamics. In total, six peat cores, three per study site, were studied that represent different microhabitats: low hummock (LH), high lawn and low lawn. The data show a consistent drying trend over recent centuries, represented mainly as a change from wet habitat Sphagnum spp. to dry habitat S. fuscum. Summer temperature and precipitation appeared to be important drivers shaping peatland community and surface moisture conditions. Data from the driest microhabitat studied, LH, revealed a clear and strong negative linear correlation (R² = .5031; p < .001) between carbon accumulation rate and peat surface moisture conditions: under dry conditions, less carbon was accumulated. This suggests that at the dry end of the moisture gradient, availability of water regulates carbon accumulation. It can be further linked to the decreased abundance of mixotrophic testate amoebae under drier conditions (R² = .4207; p < .001). Our study implies that if effective precipitation decreases in the future, the carbon uptake capacity of boreal bogs may be threatened.