间伐和改变凋落物输入对华北落叶松人工林土壤呼吸的影响

作为森林生态系统的第二大碳通量,土壤呼吸在全球碳循环和气候变化中发挥着重要作用。通过探究土壤呼吸对间伐和改变凋落物的响应规律以及响应之间的联系,能够为准确评价森林碳循环提供依据。针对不同强度(对照、轻度、中度、重度)间伐后的华北落叶松人工林,2016年5月至10月采用LI-8100土壤碳通量测量系统对其原状、凋落物去除、凋落物加倍的土壤呼吸进行观测。结果表明:土壤呼吸在生长季的8月份达到最高值,呈现出明显的季节动态。不同林分间伐处理下,中度间伐显著促进了土壤呼吸,使平均土壤呼吸速率升高了15.66%,轻度间伐和重度间伐对土壤呼吸的影响不显著;不同凋落物处理下,去除凋落物使平均土壤呼吸速率降低了40.16%,加倍凋落物使平均土壤呼吸速率升高了16.06%。中度间伐使土壤呼吸生长季通量增加了55.06 g C/m~2;去除凋落物使土壤呼吸生长季通量减少了153.48 g C/m~2,加倍凋落物使土壤呼吸生长季通量增加了79.87 g C/m~2。土壤呼吸速率与土壤温度呈显著指数相关,而与土壤湿度无显著相关。不同林分间伐处理下,土壤呼吸的温度敏感性指数(Q10)为2.36—3.46,轻度间伐下Q10值最高;凋落物去除和加倍均降低了土壤呼吸的温度敏感性。土壤温湿度对土壤呼吸存在着显著影响,能够解释土壤呼吸28.7%—62.3%的季节变化。研究结果表明间伐和凋落物处理对华北落叶松人工林土壤CO_2释放的影响表现出一定的交互作用,中度间伐和加倍凋落物的交互作用对土壤呼吸的促进作用显著大于单一因子。可见,间伐作业通过改变土壤微环境和凋落物量,对土壤呼吸以及森林生态系统碳循环产生着重要影响。     

中国森林的地下碳分配

通过收集国内33个森林样地的土壤呼吸和年凋落物量数据，分析中国森林地下碳分配（TBCA）模式。结果表明，中国森林土壤呼吸年通量与年凋落物量呈显著的线性相关（R^2=0．3319，P=0．000），其中成熟林土壤呼吸与年凋落物量间呈显著的线性相关（R^2=0．3245，P=0．004），但未成熟林土壤呼吸与年凋落物量间的线性相关不显著（R^2=0．3485，P=0．092）。中国森林的地下碳分配变化范围1．460～25．100tChm^-2a^-1，平均值为9．217tChm^-2a^-1；中国森林的TBCA与年均气温相关关系不显著（P=0．196），但与年均降水量则呈显著正相关（R=0．480，P=0．021）。中国森林TBCA和凋落物对土壤呼吸的平均贡献分别为74．2％和25．8％；中国森林TBCA对土壤呼吸的贡献随土壤呼吸增大而增大，而凋落物对土壤呼吸的贡献则随土壤呼吸的增大而降低。     

氮沉降对森林生态系统土壤碳库的影响

森林土壤碳库是陆地生态系统碳库的重要组成部分,对维持全球碳平衡具有重要意义。不断加剧的全球氮沉降有可能改变森林生态系统中碳元素的地球化学循环过程,从而引起森林土壤碳储量的变化。本文从森林土壤碳收支的角度,将氮沉降对森林生态系统土壤碳库影响的复杂过程划分为凋落物分解、细根周转、土壤呼吸和土壤可溶性有机碳淋失4个相对独立的过程。综合国内外研究现状,对其进行了简要评述,指出了目前研究的不足,并探讨了这一研究领域的发展方向。     

土壤动物对森林凋落物分解的影响:机制和模拟

土壤动物是森林生态系统的重要组成部分。本文综述了土壤动物在不同森林生态系统中对凋落物分解过程的贡献大小及影响因素、土壤动物影响凋落物分解的作用机制以及凋落物分解模型的研究进展,以期为更好地理解森林生态系统中土壤动物在地上、地下生态过程中的作用。我们试图建立一个概念模型来模拟土壤动物在凋落物分解过程中的贡献。土壤动物可以通过直接作用于凋落物(包括移动、破碎、取食等),或间接作用于土壤(穿梭、掘穴等影响凋落物分解微环境)和微生物(影响定殖于凋落物中的微生物群落种类、数量和活性)影响凋落物的分解过程。温度和水分条件是影响土壤动物活动的重要因素,普遍认为热带森林中的土壤动物作用要大于亚热带森林、温带森林和高山/亚高山森林。未来该领域的研究应注重如何在凋落物分解模型中体现土壤动物的作用机制以及利用野外实验数据量化土壤动物对凋落物分解过程的贡献等。     

张广才岭西坡45年生不同起源林分碳储量研究

以五常凤凰山林场皆伐迹地上45年生不同起源(人工造林、人天混更新、天然更新)形成的落叶松纯林、落叶松与阔叶树混交林和次生阔叶林3种林分为研究对象,调查分析不同林型林分乔木层、灌草层、凋落物层、土壤层碳储量以及3种林型林分总碳储量,分析不同更新方式对森林碳储量的影响,探究具有高固碳能力的森林更新方式。研究结果表明:人天混交林能增加林分灌草层碳储量(P<0.05);凋落物未分解层碳储量、半分解层碳储量和凋落物总碳储量均以落叶松纯林最高,且半分解层碳储量和凋落物总碳储量在3个林型间差异显著(P<0.05);土壤总碳储量以及森林生态系统总碳储量针阔混交林均略高于其它两种林分,但差异并不显著(P>0.05)。研究表明人天混更新有利于植被碳汇和土壤碳汇能力的提高。人工针叶纯林具有较高的凋落物碳储量。     

暖温带落叶阔叶林碳循环的初步估算

 森林生态系统碳循环过程与大气中二氧化碳含量有密切的关系,直接影响着大气成分的组成,进而对全球气候变化有重要影响。以我国暖温带落叶阔叶林生态系统近10年的定位研究为基础,初步建立了该类生态系统碳循环数值模式。结果表明：暖温带落叶阔叶林典型生态系统每年从外界主要是大气中吸收的碳是10.3 t·hm-2·a-1,植物呼吸释放到大气中的碳通量为5.5 t·hm-2·a-1。森林植物干物质积存的碳量为4.8 t·hm-2·a-1,通过凋落物分解释放到大气中的碳通量为2.46 t·hm-2·a-1。森林同化的碳绝大部分以活生物呼吸和凋落物分解的形式释放到大气中去了,存留在活生物体和凋落物中的很少。通过对碳现存量的研究发现,所研究的森林生态系统碳现存量为165.05 t·hm-2,其中活生物体碳现存量为61.2 t·hm-2,死生物体碳现存量为104.05 t·hm-2 (包括土壤中碳),土壤碳现存量为96 t·hm-2。土壤碳储量占总碳储量的58%,土壤是该地区森林生态系统主要的碳库,森林生态系统土壤中碳储量的变化必然引起整个区域碳储量整体动态的变化。     

西藏高原主要森林类型凋落物碳储量及空间分布格局

凋落物是森林生态系统的重要组成部分,其作为养分的基本载体,在养分循环中是连接植物与土壤的"纽带",其碳库直接影响着土壤碳库及森林生态系统的碳库。本文以西藏高原冷杉、云杉、高山松、云南松、高山栎、柏木森林类型为研究对象,采用直接收获法对森林凋落物碳储量进行研究。结果显示:凋落物碳储量随着龄级的增大而增加;凋落物碳储量随海拔的升高而增加,在3200~3600 m碳储量最大,随后碳储量开始下降;林芝地区凋落物碳储量最大,其次是山南地区和日喀则地区,最小的是昌都地区。     

陆地生态系统地下碳输入与输出过程研究进展

生态系统地下碳输入与输出过程是陆地生态系统碳分配和转化的核心,并直接影响着全球碳循环。陆地生态系统凋落物、根系周转、根系分泌物、土壤有机碳、土壤微生物和土壤呼吸是地下碳输入与输出过程中的重要组成部分。由于这些组分非常复杂且其研究技术和方法受到限制,目前人们对陆地生态系统地下碳输入与输出过程尚缺乏全面的认识,故在陆地生态系统碳循环研究中存在诸多的不确定性。该文概述了凋落物、根系周转、根系分泌物、土壤有机碳、土壤微生物和土壤呼吸的研究方法,以及它们对气候变化的响应,探讨了陆地生态系统地下碳输入与输出过程中的研究难点,并对未来需要深入探究的一些领域进行了展望。     

中国森林和草地凋落物现存量的空间分布格局及其控制因素

凋落物是陆地生态系统的重要组成部分,它对生态系统的养分循环非常重要。凋落物现存量是凋落物输入量与分解量的净累积量,理论上影响凋落物输入过程和分解过程的因素都会对凋落物现存量产生重要影响。目前,我国科学家对部分区域典型陆地生态系统凋落物现存量及其影响因素进行了探讨,但迄今为止,全国尺度下的关于凋落物现存量评估的结果还未见报道。因此,如何准确地评估凋落物现存量对揭示生态系统应对全球变化具有重要意义。收集了2000—2014年公开发表文献中的森林和草地凋落物现存量数据(共1864个样点),并结合气候、土壤和地上生产力探讨了中国森林和草地凋落物现存量的空间格局及其主要控制因素,此外,还利用森林和草地凋落物的碳氮含量,结合凋落物现存量估算了不同区域和全国尺度的凋落物的碳氮贮量。分析结果表明:中国森林和草地的凋落物现存量存在较弱的经度和纬度格局,然而按照不同经度和纬度间隔整理数据后凋落物现存量表现出显著的空间分布格局。森林的凋落物现存量表现为随着经度和纬度的增加而逐渐增加,主要控制因素为温度。草地的凋落物现存量表现为随着经度的增加而逐渐升高,其主要影响因素为降水。森林和草地凋落物现存量在局部(或区域内)存在非常大的变异,这是造成其大尺度格局较弱的重要原因。结合1∶100万中国植被图的森林和草地面积数据,估算出中国森林的凋落物现存量约为1135.56 Tg,其碳氮贮量约为517.93 Tg C和15.33 Tg N;此外,中国草地的凋落物现存量约为119.63 Tg,其碳氮贮量分别为47.11 Tg C和1.59 Tg N。首次尝试对全国尺度森林和草地凋落物现存量及其碳氮贮量进行估算,其研究结论有助于揭示凋落物在碳氮循环中的重要作用,并可为准确评估中国陆地生态系统碳氮贮量提供重要参考。     

中国南方灌丛凋落物现存量

凋落物是陆地生态系统的重要组成部分,在区域尺度上阐明其现存量的分布特征及其影响因子有助于理解陆地生态系统碳循环的机理。该研究采用分层随机抽样调查方法分析了中国南方灌丛生态系统凋落物现存量的空间分布格局及其影响因子。结果发现:该区域灌丛凋落物现存量的平均值为0.32 kg·m~(–2),是中国森林凋落物现存量(0.47 kg·m~(–2))的68%,是中国草地凋落物现存量(0.06 kg·m~(–2))的5倍;凋落物现存量呈现出明显的纬度格局,随着纬度的增加而升高;该区域的灌丛生态系统凋落物现存量的碳转换系数为0.41,显著低于植被活体转换系数0.50;凋落物现存量与年平均气温、土壤全磷含量和土壤pH值显著负相关,与年降水量、土壤碳、氮以及有机碳含量相关性不显著。研究表明:该区域灌丛凋落物现存量是中国陆地生态系统碳库不可忽视的组分;年平均气温是影响该区域内灌丛生态系统凋落物现存量的重要环境因子;采用常用的植被活体碳转换系数可能会高估凋落物现存量碳库的22%。     

Establishing and validating individual-based carbon budget model FORCCHN of forest ecosystems in China

According to the principles of plant physiology, forest ecology and soil environment, the individual-based carbon budget model of forest ecosystems in China was established. The model process included two timesteps: the primary daily process comprises photosynthesis, plant respiration, allocation and litter production, and soil respiration and transfer; the primary annual process consists of allocation between stands, increase of tree height and breast diameter, and production of large amount of litter fall. Through validating net primary productiviry (NPP) and net ecosystem productivity (NEP) at the plot level and at the country level, it was demonsteated that the model can well simulate carbon budget of forest ecosystems in China, so it can also simulate dynamics of carbon budget of forest ecosystems in the past and in the future.     

Establishing and validating individual-based carbon budget model FORCCHN of forest ecosystems in China

According to the principles of plant physiology, forest ecology and soil environment, the individual-based carbon budget model of forest ecosystems in China was established. The model process included two timesteps: the primary daily process comprises photosynthesis, plant respiration, allocation and litter production, and soil respiration and transfer; the primary annual process consists of allocation between stands, increase of tree height and breast diameter, and production of large amount of litter fall. Through validating net primary productiviry (NPP) and net ecosystem productivity (NEP) at the plot level and at the country level, it was demonsteated that the model can well simulate carbon budget of forest ecosystems in China, so it can also simulate dynamics of carbon budget of forest ecosystems in the past and in the future.     

Modeling the effects of nitrogen deposition on carbon budget in two temperate forests

The NO_x input terrestrial ecosystems are increasing significantly induced by human activities, yet the understanding of the responses of carbon cycle to nitrogen deposition is still poor. The northern temperate forest ecosystems have seen the greatest changes in nitrogen inputs from atmosphere. It is necessary for us to understand how the carbon cycle would change under the nitrogen addition in temperate forests, as an important carbon sink. In this study, we present a biogeochemical process model, CEVSA2, and use this model to elucidate the key processes that may strongly influence the carbon budget response to anthropogenic nitrogen addition. The CEVSA2 model has included the effect of nitrogen on photosynthesis, carbon allocation, soil organic matter decomposition, etc. Our simulations show nitrogen addition stimulates the photosynthesis, net carbon sequestration, carbon accumulation in vegetation and soil, by contrary, the low level of nitrogen addition decreases the heterotrophical and total respiration. The long-term chronic nitrogen addition experiments show that the low and high level nitrogen addition would reduce the carbon sequestration and accumulation. The model failed to simulate the effect of nitrogen addition on plant mortality, the de-coupling of nitrogen and photosynthesis when nitrogen saturates. In addition, the responses of soil respiration to nitrogen deposition involve so many complex biochemical processes; however, we have little knowledge about them. Sequentially, there is large uncertainty of model simulation on the effect of nitrogen deposition on soil respiration. With increasing rates of anthropogenic nitrogen deposition, there is a strong need to understand links between nitrogen inputs and carbon cycle.     

Allometric constraints on,and trade‐offs in,belowground carbon allocation and their control of soil respiration across global forest ecosystems

To fully understand how soil respiration is partitioned among its component fluxes and responds to climate, it is essential to relate it to belowground carbon allocation, the ultimate carbon source for soil respiration. This remains one of the largest gaps in knowledge of terrestrial carbon cycling. Here, we synthesize data on gross and net primary production and their components, and soil respiration and its components, from a global forest database, to determine mechanisms governing belowground carbon allocation and their relationship with soil respiration partitioning and soil respiration responses to climatic factors across global forest ecosystems. Our results revealed that there are three independent mechanisms controlling belowground carbon allocation and which influence soil respiration and its partitioning: an allometric constraint; a fine‐root production vs. root respiration trade‐off; and an above‐ vs. belowground trade‐off in plant carbon. Global patterns in soil respiration and its partitioning are constrained primarily by the allometric allocation, which explains some of the previously ambiguous results reported in the literature. Responses of soil respiration and its components to mean annual temperature, precipitation, and nitrogen deposition can be mediated by changes in belowground carbon allocation. Soil respiration responds to mean annual temperature overwhelmingly through an increasing belowground carbon input as a result of extending total day length of growing season, but not by temperature‐driven acceleration of soil carbon decomposition, which argues against the possibility of a strong positive feedback between global warming and soil carbon loss. Different nitrogen loads can trigger distinct belowground carbon allocation mechanisms, which are responsible for different responses of soil respiration to nitrogen addition that have been observed. These results provide new insights into belowground carbon allocation, partitioning of soil respiration, and its responses to climate in forest ecosystems and are, therefore, valuable for terrestrial carbon simulations and projections.     

未来气候情景下中国东北森林生态系统碳收支变化

应用FGOALS模式输出的未来气候情景数据驱动中国森林生态系统碳循环模型FORCCHN,模拟了东北地区森林生态系统碳收支未来可能的时空变化。预测结果表明：未来平衡发展情景（A1B）气候变化情景下,2003—2049年东北森林生态系统净初级生产力（NPP）和土壤呼吸在达到饱和状态前均呈波动上升趋势,将分别增加10.84%、134.43%,且土壤呼吸的增加速率远远大于NPP的增加速率;2003—2049年,东北森林生态系统可能仍将具有明显碳汇功能,但强度呈下降趋势,将下降95.64%;未来47年东北森林虽然碳汇能力在减弱,但吸碳总量还在不断增加,说明未来47年东北森林对降低大气中温室气体浓度上升以及缓解气候变化将会起到积极作用。     

Distinct responses of soil respiration to experimental litter manipulation in temperate woodland and tropical forest

Global change is affecting primary productivity in forests worldwide, and this, in turn, will alter long‐term carbon (C) sequestration in wooded ecosystems. On one hand, increased primary productivity, for example, in response to elevated atmospheric carbon dioxide (CO₂), can result in greater inputs of organic matter to the soil, which could increase C sequestration belowground. On other hand, many of the interactions between plants and microorganisms that determine soil C dynamics are poorly characterized, and additional inputs of plant material, such as leaf litter, can result in the mineralization of soil organic matter, and the release of soil C as CO₂ during so‐called “priming effects”. Until now, very few studies made direct comparison of changes in soil C dynamics in response to altered plant inputs in different wooded ecosystems. We addressed this with a cross‐continental study with litter removal and addition treatments in a temperate woodland (Wytham Woods) and lowland tropical forest (Gigante forest) to compare the consequences of increased litterfall on soil respiration in two distinct wooded ecosystems. Mean soil respiration was almost twice as high at Gigante (5.0 μmol CO₂ m^?2 s^?1) than at Wytham (2.7 μmol CO₂ m^?2 s^?1) but surprisingly, litter manipulation treatments had a greater and more immediate effect on soil respiration at Wytham. We measured a 30% increase in soil respiration in response to litter addition treatments at Wytham, compared to a 10% increase at Gigante. Importantly, despite higher soil respiration rates at Gigante, priming effects were stronger and more consistent at Wytham. Our results suggest that in situ priming effects in wooded ecosystems track seasonality in litterfall and soil respiration but the amount of soil C released by priming is not proportional to rates of soil respiration. Instead, priming effects may be promoted by larger inputs of organic matter combined with slower turnover rates.     

Soil Respiration and Belowground Carbon Allocation in Mangrove Forests

Mangrove forests cover large areas of tropical and subtropical coastlines. They provide a wide range of ecosystem services that includes carbon storage in above- and below ground biomass and in soils. Carbon dioxide (CO₂) emissions from soil, or soil respiration is important in the global carbon budget and is sensitive to increasing global temperature. To understand the magnitude of mangrove soil respiration and the influence of forest structure and temperature on the variation in mangrove soil respiration I assessed soil respiration at eleven mangrove sites, ranging from latitude 27°N to 37°S. Mangrove soil respiration was similar to those observed for terrestrial forest soils. Soil respiration was correlated with leaf area index (LAI) and aboveground net primary production (litterfall), which should aid scaling up to regional and global estimates of soil respiration. Using a carbon balance model, total belowground carbon allocation (TBCA) per unit litterfall was similar in tall mangrove forests as observed in terrestrial forests, but in scrub mangrove forests TBCA per unit litter fall was greater than in terrestrial forests, suggesting mangroves allocate a large proportion of their fixed carbon below ground under unfavorable environmental conditions. The response of soil respiration to soil temperature was not a linear function of temperature. At temperatures below 26°C Q10 of mangrove soil respiration was 2.6, similar to that reported for terrestrial forest soils. However in scrub forests soil respiration declined with increasing soil temperature, largely because of reduced canopy cover and enhanced activity of photosynthetic benthic microbial communities.     

杉木林年龄序列地下碳分配变化

  森林地下碳分配在森林碳平衡和碳吸存中具有重要作用, 而揭示人工林生长过程中地下碳分配变化对于人工林碳汇估算和碳汇管理等有重要意义。通过采用年龄序列方法研究了杉木(Cunninghamia lanceolata)林生长过程中地下碳分配变化特点。年龄序列为福建省南平7 a生(幼龄林)、16 a生(中龄林)、21 a生(近熟林)、41 a生(成熟林)和88 a生(老龄林)的杉木林。细根净生产力测定采用连续土芯法, 根系呼吸测定采用壕沟法, 生物量增量测定采用异速生长方程, 地上年凋落物量采用凋落物收集框测定。结果表明: 杉木林细根净生产力在中龄林前没有显著差异, 维持在较高水平; 但此后则显著下降。细根净生产力/地上凋落物量比值随林龄增加而显著下降。老龄林的根系呼吸显著低于其它林龄林分, 根系呼吸与细根生物量间呈显著线性相关。中龄林和近成熟林的地下碳分配(Total belouground carbon allocation, TBCA)显著高于幼龄林和成熟林, 而老龄林的则最低。中龄林、近成熟林和成熟林的地上部分净生产力/TBCA比值显著高于幼龄林和老龄林, 而杉木林的根系碳利用效率(RCUE)则呈现出随林龄增加而降低的趋势。     

森林生态系统碳氮循环功能耦合研究综述

在大气CO2浓度升高和氮沉降增加等全球变化背景下,森林生态系统减缓CO2浓度升高的作用及其对全球变化的响应和反馈存在诸多不确定性.森林生态系统碳氮循环相互作用及功能耦合规律的研究是揭示这些不确定性的基础,也是反映森林生态系统生物产量与养分之间作用规律,涉及林地持久生产力（sustainability of long-term site productivity）的生态学机理问题.森林生态系统碳氮循环的耦合作用表现在林冠层光合作用的碳固定过程,森林植物组织呼吸、土壤凋落物与土壤有机质分解、地下部分根系周转与呼吸等碳释放过程,这些过程存在反馈机理和非线性作用,最终决定森林生态系统的碳平衡.着重在生态系统尺度上,综述了碳氮循环耦合作用研究的一些进展与存在的问题,对今后研究方向进行了展望.     

干旱半干旱区不同环境因素对土壤呼吸影响研究进展

土壤呼吸是全球陆地生态系统碳循环的重要环节,也是全球气候变化的关键生态过程。阐明和探讨影响土壤呼吸的各类环境因素,对准确评估陆地生态系统碳收支具有重要意义。干旱半干旱区是陆地生态系统的重要组成部分,研究该区域影响土壤呼吸的环境因素有助于深刻了解干旱半干旱区土壤碳循环过程。就土壤温度、土壤水分、降水、土壤有机质等非生物因子及植被类型、地上、地下生物量、土壤凋落物等生物因子两个方面对土壤呼吸的影响进行了综述。以干旱半干旱区的研究进展为主要论述对象,在上述因素中重点阐述了土壤温度、水分及其耦合作用下土壤呼吸的响应,并就土壤呼吸的Q10值及各影响因素间的交互作用进行归纳总结。在此基础上,说明了土壤温度和水分是影响干旱半干旱区土壤呼吸的主要因素。为了更准确的估算干旱半干旱区土壤呼吸速率,综合分析多种因子的交互影响,提出目前土壤呼吸研究存在的问题和今后重点关注的方向:1)不同尺度下干旱半干旱区土壤呼吸的研究;2)荒漠生态系统土壤呼吸研究;3)非生长季土壤呼吸研究;4)多因素协同作用土壤呼吸模型建立;5)测量方法的改进与完善。