Increased contribution of microbial necromass to soil organic carbon in solar farms on the Tibetan Plateau

Solar farms have been rapidly expanding on the Qinghai-Tibetan Plateau.However,the effects of photovoltaic arrays on the contribution of microbial necromass carbon(MNC)to soil organic carbon(SOC),along with the underlying mechanisms,remain unclear.To address this,we collected soil samples from the top 20 cm in under-panel,inter-panel and control plots at five solar farms constructed between 2012 and 2014 in the dry Yarlung Tsangpo and Lhasa River valleys on the Qinghai-Tibetan Plateau.We determined SOC,fungal and bacterial necromass and relevant soil properties.We found that the concentration of MNC in the under-panel plots(3.93±0.79 mg g-1)was significantly higher compared to the control plots(2.28±0.79 mg g-1)across all five solar farms.The proportion of MNC to SOC in the under-panel plots(34.7±2.4%)was also significantly higher than that in the control plots(27.5±1.4%).Specifically,the contribution of fungal necromass to SOC in the under-panel plots(26.4±2.2%)was significantly larger than that in the control plots(19.7±1.6%),while the increase in the bacterial necromass proportion was insignificant.Partial least squares structural equation modeling(PLS-SEM)indicated a significant and positive effect of increased soil moisture in the under-panel plots on the proportion of fungal necromass to SOC.These results highlight that beyond their economic benefits,solar farms in the arid regions on the Qinghai-Tibetan Plateau can enhance soil C sequestration by improving soil moisture and promoting microbial necromass accumulation.

Profound loss of microbial necromass carbon in permafrost thaw-subsidence in the central Tibetan Plateau

Climate warming is causing rapid permafrost degradation,including thaw-induced subsidence,potentially resulting in heightened carbon release.Nevertheless,our understanding of the levels and variations of carbon components in permafrost,particularly during the degradation process,remains limited.The uncertainties arising from this process lead to inaccurate assessments of the climate effects during permafrost degradation.With vast expanses of permafrost in the Tibetan Plateau,there is limited research available on SOC components,particularly in the central Tibetan Plateau.Given remarkable variations in hydrothermal conditions across different areas of the Tibetan Plateau,the existing limited studies make it challenging to assess the overall SOC components in the permafrost across the Tibetan Plateau and simulate their future changes.In this study,we examined the properties of soil organic carbon(SOC)and microbial necromass carbon(MicrobialNC)in a representative permafrost thaw-subsidence area at the southern edge of continuous permafrost in the central Tibetan Plateau.The results indicate that prior to the thaw-subsidence,the permafrost had a SOC content of 72.68±18.53 mg g^(-1),with MicrobialNC accounting for 49.6%.The thaw-subsidence of permafrost led to a 56.4%reduction in SOC,with MicrobialNC accounting for 70.0%of the lost SOC.MicrobialNC constitutes the primary component of permafrost SOC,and it is the main component that is lost during thaw-subsidence formation.Changes in MicrobialNC are primarily correlated with factors pH,plant input,and microbial properties.The present study holds crucial implications for both the ecological and biogeochemical processes associated with carbon release from permafrost,and it furnishes essential data necessary for modeling the global response of permafrost to climate warming.Based on this study and previous research,permafrost thawing in the Tibetan Plateau causes substantial loss of SOC.However,there's remarkable heterogeneity in SOC component changes across different regions,warranting further in-depth investigation.

Soil microbial necromass carbon in forests:A global synthesis of patterns and controlling factors

Boreal and temperate forests had higher MNC and FNC/BNC than other forest biomes.Mixed forests had higher MNC and lower FNC/BNC than other forest types.The dependence of MNC on forest type varied among forest biomes.MAT and soil total N were the important factors on MNC and MNC/SOC.MAT,soil pH,and clay content were identified as direct factors on FNC/BNC.Soil microbial necromass carbon(MNC)is an important contributor to soil organic carbon(SOC)and plays a vital role in carbon sequestration and climate change mitigation.However,it remains unclear whether the content,contribution to SOC(MNC/SOC),and fungal-to-bacterial necromass carbon ratio(FNC/BNC)of MNC vary across forest biomes and types.By summarizing data from 1704 points across 93 forest sites,we explored the spatial patterns of MNC,MNC/SOC,and FNC/BNC in the surface layer of 0–20 cm of forest soils,as well as the controlling factors involved.Overall,boreal and temperate forests had higher MNC and FNC/BNC values than tropical,subtropical,and Mediterranean forests,whereas both boreal and Mediterranean forests had low MNC/SOC values.Mixed forests had higher MNC and lower FNC/BNC than broadleaved and coniferous forests,whereas MNC/SOC was higher in broad-leaved forests than that in coniferous forests.Interestingly,the dependence of MNC on forest type also varies among forest biomes.Regression analyses identified soil total N as one of the most important factors affecting MNC and MNC/SOC;whereas MAT,soil pH,and clay content were identified as the important factors affecting FNC/BNC.This synthesis is critical for managing soil MNC to mitigate climate change in forests.

MICROBIAL NECROMASS WITHIN AGGREGATES STABILIZES PHYSICALLY-PROTECTED C RESPONSE TO CROPLAND MANAGEMENT

The interactions of soil microorganisms and structure regulate the degradation and stabilization processes of soil organic carbon(SOC). Microbial necromass is a persistent component of SOC, and its magnitude of accumulation dependent on management and aggregate sizes. A meta-analysis of 121 paired measurements was conducted to evaluate the management effects on contributions of microbial necromass to SOC depending on aggregate fractions. Results showed that the contribution of fungal necromass to SOC increased with aggregate sizes, while bacterial necromass had a higher proportion in silt and clay. Cropland management increased total and fungal necromass in large macroaggregates(47.1% and 45.6%), small macroaggregates(44.0% and 44.2%), and microaggregates(38.9% and 37.6%).Cropland management increased bacterial necromass independent of aggregate fraction sizes. Greater fungal necromass was increased in macroaggregates in response to manure(26.6% to 28.5%) and no or reduced tillage(68.0% to 73.5%). Cover crops increased bacterial necromass by 25.1%in small macroaggregates. Stimulation of microbial necromass was proportional to the increases of SOC within soil aggregates, and the correlation was higher in macroaggregates. Increasing microbial necromass accumulation in macroaggregates can, therefore, be considered as a central component of management strategies that aim to accelerate C sequestration in agricultural soils.

凋落物添加与去除对米槠天然林土壤微生物残体碳的影响

【目的】研究森林凋落物输入变化对土壤微生物残体碳的影响,为全面认识植物、土壤与微生物间的相互作用对森林长期碳固存的影响提供科学依据。【方法】以亚热带米槠天然林为研究对象,采用随机区组试验设计,设置3种凋落物处理(去除凋落物、双倍凋落物和对照),测定土壤理化性质、氨基糖含量及微生物残体碳含量,采用Pearson分析和路径分析(PLS-PM)探讨微生物残体碳含量的影响因素。【结果】去除凋落物后,土壤中总氨基糖、氨基葡萄糖、氨基半乳糖和甘露糖胺含量分别降低了14.7%、33.4%、9.3%和16.1%;凋落物添加处理后,甘露糖胺含量降低了21.7%。去除凋落物后,真菌残体碳和总微生物残体碳含量分别降低了16.2%和16.1%,而细菌残体碳含量无显著变化;凋落物添加后,总微生物残体碳含量显著降低了9.2%,但2种处理下微生物残体碳对土壤有机碳的贡献无差异。路径分析表明,凋落物输入变化下的微生物生物量碳、土壤含水量和微生物生物量是驱动土壤微生物残体碳累积的关键因子。【结论】改变凋落物的输入可显著调控土壤微生物残体的积累,尤其是对真菌残体碳的影响较大,而对细菌残体碳的影响较小。凋落物在微生物残体碳积累中具有重要作用,适度维持地表凋落物贮量有助于保持土壤碳库的稳定。

氮肥配施生物质碳点对潮土微生物残体碳含量的影响

为探明碳氮投入下土壤微生物残体对有机碳积累的相对贡献,采用培养试验方法探究氮肥配施生物质碳点(简称碳点)对潮土微生物残体碳含量的影响。研究设置4个处理:空白(CK)、施碳点(CDs)、施氮(N)、施氮和碳点(N+CDs)。结果表明:与CK处理相比,CDs处理的无机氮(SIN)含量显著下降29.1%;与N处理比较,N+CDs处理的SIN含量显著下降32.8%,土壤脲酶和亚硝酸还原酶活性均显著下降(P<0.05)。CDs处理的土壤溶解性有机碳(DOC)含量略高于CK处理,且CDs处理改变了DOC的官能团结构;N+CDs处理的DOC含量比N处理显著提高28.8%,N+CDs也提高了DOC中胺类和芳香类化合物含量。与N处理比较,N+CDs处理的细菌残体碳(BNC)和真菌残体碳(FNC)含量显著增加29.5%和17.7%(P<0.05),且提高了土壤微生物残体对有机碳积累的相对贡献。回归分析表明,总的细菌和真菌残体碳与土壤理化性质存在相关性。通过结构方程模型进一步验证,发现DOC中的芳香族化合物是调控BNC的主要因素,FNC主要受土壤氮净硝化速率和DOC的平均分子量调控,N+CDs处理主要通过改变潮土溶解性有机碳及官能团结构和氮转化速率影响微生物残体碳积累。

不同气候条件下土壤有机碳水热响应驱动机制研究

土壤有机碳(SOC)是陆地生态系统中最大的碳库,其对气候变化的响应直接影响全球碳循环。然而,关于土壤有机碳对长期水热变化的响应及其微生物调控机制尚不清楚。借助跨气候带土壤移置试验平台,开展了一项8年的土壤移置试验,其中将寒温带地区(中国海伦)的黑土剖面移置到温带和中亚热带地区(即封丘和鹰潭)来模拟土壤水热条件增加。水热增加提高了植被生物量,地上部植株C/N与微生物酶活性;降低了土壤有机碳、全氮、微生物残体碳(MNC)和活性矿物的相对含量。并且,微生物残体碳对有机碳的贡献也随着水热条件的增加而降低。通过计算ΔMNC/ΔSOC以表征水热增加后微生物残体碳损失速率。结果发现,ΔMNC/ΔSOC随着水热条件的增加而显著增加,封丘地区为72.50%±9.35%,而在鹰潭达到了82.67%±2.37%。重要的是,土壤活性矿物的变化与ΔMNC/ΔSOC呈强烈的负相关关系,突出了矿物保护在调控ΔMNC/ΔSOC发挥的关键作用。这些结果表明,水热增加降低了土壤矿物对微生物残体碳的保护和/或刺激了土壤中微生物对微生物残体碳的利用,通过减少微生物残体碳促进了有机碳的显著损失。

湖泊湿地土壤有机碳形成、周转及稳定性研究进展

湖泊湿地生态系统作为重要的陆地碳汇之一,其土壤有机碳(SOC)储量变化将对全球气候产生显著影响。当前全球变化背景下,湖泊湿地经历的水位降低、水域面积缩小等生态问题使其碳汇功能面临严重威胁。尽管已有大量文献研究了湖泊湿地SOC的动态变化,但由于研究地点、实验方法和关注重点的不同,难以形成一致的结论,因此详细阐明湖泊湿地SOC存储和转化过程的演化趋势尤为重要。综述国内外湖泊湿地SOC的研究成果,从其形成、周转及稳定性三个方面进行归纳,总结现阶段湖泊湿地SOC的研究热点和不足,并结合当前湖泊湿地面临的现状,阐述影响其有机碳动态变化的因素。现有研究表明,植物源碳尤其是凋落物碳是湖泊湿地SOC的主要来源,但微生物碳在湖泊湿地SOC形成中的作用不容忽视,且植物和微生物碳对湖泊湿地碳储量的贡献比可能具有空间异质性。湿地SOC周转主要受微生物的调控,但中小型区系的土壤动物也扮演着重要的角色,它们可能既是驱动者也是贡献者,研究提示将土壤动物纳入湿地SOC的周转模型才可更准确地评估湖泊湿地的碳周转过程。有机物-矿物化学结合态保护是维持湖泊湿地SOC稳定的最重要机制,多种生物和非生物(气候、水环境等)因素会直接或间接影响SOC的稳定储存。目前维持湖泊湿地SOC稳定性的机制仍延用陆地或海洋生态系统的理论模型,需进一步评估其在湖泊湿地中的适用性。研究旨在总结湖泊湿地中SOC形成和转化的研究进展,为研究提供文献参考和思路。

黄土高原不同人工林型微生物残体碳对土壤有机碳组分的积累贡献及影响因素

为探究不同人工林型微生物残体碳(Microbial necromass carbon,MNC)对土壤有机碳组分的积累贡献及影响因素,在黄土高原选取刺槐林、山杏林、油松林为研究对象,分析了三种人工林0—60 cm土层真菌残体碳(Fungal necromass carbon,FNC)、细菌残体碳(Bacterial necromass carbon,BNC)、MNC对颗粒态有机碳(Particulate organic carbon,POC)和矿物结合态有机碳(Mineral—associated organic carbon,MAOC)的积累贡献及其影响因素。结果表明:(1)三种人工林POC、MAOC中FNC、BNC、MNC含量均随土层深度的增加而降低;(2)刺槐林和山杏林MNC对MAOC的积累贡献(60.9%,52.0%)高于POC(33.5%,49.5%),其中FNC对MAOC的积累贡献分别是BNC的4.4和2.5倍,油松林在0—10 cm土层MNC对POC的积累贡献(73.8%)高于MAOC(48.2%),其中FNC对POC的积累贡献是BNC的3.5倍,而在10—60 cm土层MNC对MAOC的积累贡献(30.9%)高于POC(24.4%),其中FNC对MAOC的积累贡献是BNC的3.4倍;(3)总有机碳和全氮含量与MNC/POC、MNC/MAOC呈显著正相关关系(P<0.05),黏粒含量与MNC/MAOC呈显著正相关关系(P<0.05),pH值、砂粒含量与MNC/MAOC呈显著负相关关系(P<0.05)。说明黄土高原三种人工林0—60 cm土层MNC主要贡献MAOC的积累,油松林0—10cm土层除外,且与细菌残体碳相比,真菌残体碳在土壤有机碳组分积累中的贡献更大,土壤总有机碳、全氮、黏粒、砂粒含量、pH值是影响该区不同人工林型微生物残体碳贡献土壤有机碳组分积累的主要因素。

宁夏不同草地类型土壤微生物残体碳积累特征及其影响因素

为探究不同草地类型土壤微生物残体碳积累特征,明确微生物残体碳对土壤有机碳(SOC)的贡献及影响因素。研究利用生物标记物的方法,测定宁夏草甸草原(MS)、典型草原(TS)、荒漠草原(DS)、草原化荒漠(SD)和荒漠(D)5种草地类型0—20 cm土壤的理化性质、微生物群落组成及氨基糖含量,进一步分析微生物残体碳含量与土壤理化性质和微生物群落的关系。结果表明:MS和TS土壤有机碳、全氮、铵态氮、硝态氮、微生物量碳、微生物量氮、真菌、细菌、放线菌和原生动物含量显著高于其他草地类型(P<0.05)。土壤氨基葡萄糖(GluN)、氨基甘露糖(ManN)、氨基半乳糖(GalN)和胞壁酸(MurA)含量均表现为MS最大,D最小(P<0.05);不同草地类型土壤氨基葡萄糖含量((0.62±0.18)μg/mg)最高,胞壁酸含量((0.04±0.01)μg/mg)最低。不同草地类型土壤细菌残体碳(BNC)、真菌残体碳(FNC)和总残体碳(TNC)变化范围为0.12—5.74μg/mg、0.22—15.31μg/mg和0.34—21.05μg/mg;BNC、FNC和TNC对SOC贡献分别为9.0%—17.8%、22.0%—48.2%和33.5%—66.0%;FNC对SOC的贡献是BNC的1.8—3.8倍。相关性分析显示,微生物残体碳含量与海拔、年降雨量、干旱指数、地上生物量、地下生物量以及土壤有机碳、全氮、铵态氮、硝态氮、全磷、微生物生物量(微生物量碳、微生物量氮、微生物量磷、真菌、细菌、放线菌和原生动物)显著正相关(P<0.05),与年均温及土壤容重、pH显著负相关(P<0.05)。细菌残体碳和真菌残体碳含量分别随细菌和真菌含量的增大而增大(P<0.001),微生物残体碳含量随真菌/细菌值的增大而增大(P<0.05),随革兰氏阳性/革兰氏阴性细菌(GP/GN)值的增大而减小(P<0.01)。随机森林模型预测显示,土壤全氮和pH是土壤微生物残体碳的主要影响因子。研究分析了宁夏不同草地类型微生物来源有机碳的积累特征及影响因素,可为进一步探讨干旱半干旱草地生态系统土壤有机碳固存的微生物学机制提供数据支撑。

丛枝和外生菌根森林土壤微生物残体碳对有机碳贡献的整合分析

土壤微生物残体碳在有机碳(SOC)形成过程中具有重要作用。为了量化评估不同菌根类型森林土壤微生物残体碳对SOC的贡献,对80篇已发表的文献进行了Meta分析,明确了丛枝菌根(AM)和外生菌根(EM)树种占优势的森林土壤细菌和真菌残体碳含量及其在SOC中的占比差异。结果表明,EM森林表层土壤微生物、真菌、细菌残体碳含量及其对SOC的贡献均显著高于AM森林;而EM和AM森林底层土壤中三者含量及其占SOC比例差异均不显著。两种森林表层土壤微生物残体碳含量均显著高于底层土壤,且表层土壤真菌残体碳含量均显著高于细菌残体碳含量。在表层土壤中,EM森林土壤微生物残体碳含量变化范围为0.08—89.17 g/kg,其中,真菌和细菌残体碳平均含量分别为12.75 g/kg和3.98 g/kg,对SOC的平均贡献分别为27.78%和10.68%;AM森林土壤微生物残体碳含量变化范围为0.54—71.64 g/kg,其中,真菌和细菌残体碳平均含量为6.42 g/kg和2.31 g/kg,占SOC比例分别为22.65%和8.84%。环境因子调控着土壤微生物残体碳的积累,SOC、总氮(TN)和年平均温度(MAT)是影响AM和EM森林土壤微生物残体碳的重要因素,EM森林中较高的SOC和TN含量及较低的MAT有利于微生物残体碳的积累,而AM森林中较高的pH和MAT促进了微生物残体的分解。

长期氮磷添加对滨海湿地土壤微生物残体碳和酶活性的影响

滨海湿地土壤氮磷水平及比例的变化影响了滨海湿地生态系统的结构和功能。目前长期氮磷添加对滨海湿地土壤微生物群落的影响已有一定的研究,但其对滨海湿地生态系统碳循环中土壤微生物残体碳和酶活性的影响机制尚不清楚。因此,基于黄河三角洲滨海湿地为期7 a(2014—2021年)的氮磷添加野外原位实验(包括低、中、高3种氮磷供应水平,每种氮磷供应水平设置5∶1、15∶1、45∶1这3种氮磷供应比例),探究了氮磷供应水平及比例对土壤微生物残体碳、酶活性及土壤有机碳(SOC)、速效氮、速效磷等含量及其之间相互关系的影响。结果表明,氮磷供应水平及比例对土壤微生物总残体碳、细菌残体碳、真菌残体碳及其与SOC的比值,SOC、速效氮、速效磷含量,土壤β-1,4-N-乙酰氨基葡萄糖苷酶、亮氨酸氨基肽酶和碱性磷酸酶活性均无显著影响。氮磷供应水平及比例仅显著影响β-1,4-葡萄糖苷酶含量,氮磷供应比例为15∶1时的高氮磷供应水平处理较对照降低约40%。在不同氮磷供应比例及水平添加条件下,土壤微生物残体碳、酶活性及土壤碳氮磷含量之间存在显著相关性。该研究强调了土壤微生物残体碳和酶活性在维持滨海湿地有机碳储量方面的重要性,研究结果对提升滨海湿地土壤有机碳变化的预测能力具有重要意义。

华北马铃薯连作土壤微生物残体氮对氮肥用量的响应

【目的】微生物残体氮作为一种稳定而重要的土壤氮组分,在维持土壤肥力方面发挥着重要作用。氮肥施用量影响土壤微生物残体氮的转化和积累,研究微生物残体氮对不同施氮量的响应对于优化施氮管理以提高土壤肥力至关重要。【方法】马铃薯氮肥管理试验始于2017年,在内蒙古自治区武川旱作试验站进行。种植模式为马铃薯连作,试验设置4个处理:NE [肥料用量用NE (Nutrient Expert,养分专家系统)推荐确定]、NE-N(不施氮肥)、NE-1/2N (氮肥用量较NE处理减少1/2)和NE+1/2N (氮肥用量较NE处理增加1/2)。于2023年马铃薯收获期,采集0—20和20—40 cm土层土壤样品,测定土壤矿质氮和微生物残体氮含量,分析马铃薯连作下不同氮肥用量对土壤矿质氮和微生物残体氮的影响。【结果】氮肥施用处理较NE-N处理增加了土壤全氮(TN)和NO-_(3)^(-)-N含量。在20—40 cm土层,土壤NO_(3)^(-)-N和NH_(4)^(+)-N随着施氮量的增加而增加;但在0—20 cm土层,土壤TN、NO_(3)^(-)-N和NH_(4)^(+)-N在3个施氮处理之间没有显著差异。与NE处理相比,NE-N和NE-1/2N处理降低了土壤细菌、真菌和微生物残体氮含量,而NE+1/2N处理并没有增加这些残体氮含量。在所有处理中,真菌残体氮与细菌残体氮的比值随着施氮量的增加而逐渐降低,并且20—40 cm土层中的比值高于0—20 cm土层。在所有处理中,微生物残体氮与土壤全氮的比值达64.2%~73.2%,不同施氮量对0—20 cm深度的比值没有影响;然而,NE-N、NE-1/2N、NE+1/2N处理20—40 cm土层微生物残体氮与土壤全氮的比值较NE处理降低了4.1%~13.2%。NE处理维持了较好的土壤氮平衡,而NE+1/2N处理导致了极大的土壤氮盈余。【结论】在内蒙古马铃薯连作体系,土壤微生物残体氮随氮肥用量逐步增加,在NE推荐施氮量下获得了较高的微生物残体氮积累。因此,基于NE系统推荐施肥能维持土壤肥力和氮素平衡。

基于Meta分析的增温对土壤微生物残体积累影响

增温对微生物残体积累的影响对土壤碳库收支平衡具有重要意义。目前关于增温背景下微生物残体的响应规律和主要影响因素尚未明确。为此,以土壤氨基糖为微生物残体标识物,筛选国内外已发表的12篇文献,收集总氨基糖数据29组,氨基葡萄糖35组,胞壁酸39组,氨基半乳糖25组,利用Meta分析方法,探讨了增温对土壤微生物残体积累的影响及主控因素。结果表明:整体上,增温背景下微生物残体积累有所增加,但响应规律具有生态系统特异性,其中,农田生态系统中微生物残体对增温的响应更为敏感。增温对不同来源氨基糖的影响程度不同,表现为增温显著增加了土壤中氨基半乳糖和胞壁酸的含量,增幅分别为10.3%和5.0%。相应地,增温显著降低了氨基葡萄糖与胞壁酸的比值,说明增温有利于细菌残体的积累。增温背景下,细菌残体占土壤有机碳(SOC)比例显著增加,微生物残体和真菌残体对SOC的贡献比例无显著改变,暗示增温后真菌残体对有机碳库的贡献有所削弱。Meta分析发现,增温幅度是影响微生物残体积累的主要因子,增温幅度小于或等于2℃时,微生物残体的积累数量会增加,增加比例为2.7%~14.6%,而增温幅度大于2℃则会降低微生物残体在土壤中的积累,降低比例为8.0%~14.3%。此外,增温的时间尺度不同(短期、中期、长期)也会对微生物残体产生不同的影响效应。综上,增温会显著影响微生物残体在土壤中的积累动态及其对有机碳库的贡献比例,影响强度和方向又与生态系统类型和土壤深度有关,而增温幅度、增温时间和年均降水量是影响微生物残体积累的重要因素。

微塑料参与下的土壤碳循环过程评述

土壤有机碳固定是驱动土壤肥力演变和陆地生态系统碳平衡的关键过程。鉴于微塑料在土壤生态系统中的持久性和生态环境风险,其对土壤性质和过程的影响日益受到关注,但基于土壤碳循环视角关注微塑料介导作用的研究仍相对匮乏。赋存于土壤中的微塑料能够通过间接影响土壤理化性质和直接参与碳循环的方式影响土壤有机碳固存、矿化与消长,这进一步加剧了土壤有机碳循环过程的不确定性,也突出了相关研究的迫切性。以此为背景,本文概述了土壤有机碳固定途径的理论发展,总结了土壤中微塑料的来源特征,阐述了微塑料对不同土壤碳库的影响,并深入探讨了微塑料调控土壤碳循环的可能机制,最后对微塑料参与下的土壤有机碳循环相关研究进行了展望。结果表明微塑料能够通过影响土壤物理结构、微生物群落结构多样性、酶活性与功能基因、生物膜的形成、动物的繁殖与生长、植物的生长和根系沉积等对土壤碳的平衡起到介导作用,同时通过自身参与到土壤全链条生物地球化学循环中而直接影响土壤有机碳循环。但相关研究仍处于起步阶段,如何选取科学方法将微塑料周转与有机碳循环过程进行区分与耦合是未来研究的难点。因此,在现有研究基础上,通过先进土壤学研究手段的嵌套与改良,以及研究思路的革新与交叉,可进一步精准区分微塑料源碳在不同有机碳库中的贡献潜力,探明微塑料直接和间接影响土壤有机碳循环的耦合作用机制,并推进多因素影响下微塑料参与土壤碳循环过程的研究。

Variations in fine root dynamics and turnover rates in five forest types in northeastern China

Quantifying fi ne root(≤ 2.0 mm in diameter) distribution and turnover is essential for accurately estimating forest carbon budgets. However, fi ne root dynamics are poorly understood, possibly because of their inaccessibility. This study quantifi es fi ne root distribution and turnover rates for fi ve representative Chinese temperate forests types. Fine root number, diameter, biomass, necromass, production, mortality, and turnover rates were measured using a minirhizotron over a 12-month period. More than 90% of the fi ne roots were < 0.5 mm in diameter, with thin fi ne roots at shallow layers, and thicker ones in deeper soil layers. The fi ne root dynamics were signifi cantly diff erent among the forest types. Coniferous plantations had fewer fi ne roots, less biomass, necromass, production and mortality but greater average diameters than fi ne roots of broadleaved forests. All traits, except for diameter, decreased along the soil profi le. Fine root numbers and production exhibited a unimodal seasonal pattern with peaks occurring in summer, whereas biomass, necromass and mortality progressivelyincreased over the growing season. The turnover rates of roots < 0.5 mm varied from 0.4 to 1.0 a-1 for the fi ve forest types, 0.5–1.0 a-1 for the soil layers and 0.2–1.1 a-1 for the seasons, with the largest turnover rate at the 0–10 cm depth in summer. The patterns of fi ne root numbers, biomass, necromass, production, mortality, and turnover rates varied with forest types, soil depths, growing season and diameter classes. This study highlights the importance of forest types and diameters in quantifying fi ne root turnover rates.

Forest management causes soil carbon loss by reducing particulate organic carbon in Guangxi, Southern China

Background: The loss of soil organic carbon(SOC) following conversion of natural forests to managed plantations has been widely reported. However, how different SOC fractions and microbial necromass C(MNC) respond to forest management practices remains unclear.Methods: We sampled 0–10 cm mineral soil from three different management plantations and one protected forest in Guangxi, Southern China, to explore how forest management practices affect SOC through changing mineralassociated C(MAOC) and particulate organic C(POC), as well as fungal and bacterial necromass C.Results: Compared with the protected forest, SOC and POC in the abandoned, mixed and Eucalyptus plantations significantly decreased, but MAOC showed no significant change, indicating that the loss of SOC was mainly from decreased POC under forest management. Forest management also significantly reduced root biomass, soil extractable organic C, MNC, and total microbial biomass(measured by phospholipid fatty acid), but increased fungi-to-bacteria ratio(F:B) and soil peroxidase activity. Moreover, POC was positively correlated with root biomass, total microbial biomass and MNC, and negatively with F:B and peroxidase activity. These results suggested that root input and microbial properties together regulated soil POC dynamics during forest management.Conclusion: Overall, this study indicates that forest management intervention significantly decreases SOC by reducing POC in Guangxi, Southern China, and suggests that forest protection can help to sequester more soil C in forest ecosystems.

Carbon stock measurements of a degraded tropical logged-over secondary forest in Manokwari Regency,West Papua,Indonesia

Several studies have been conducted in the past on carbon stock measurements in the tropical forests of Indonesia. This study is the first related research conducted in the New Guinea Island. In a degraded logged-over secondary forest in Manokwari Regency （West Papua, Indonesia）, carbon stocks were measured for seven parts, i.e., above-ground biomass （AGB）, below-ground biomass （BGB）, under-storey biomass （B）, necromass of dead leaves （N~）, necromass of dead trees （Art）, litter （L） and soil （S） using appropriate equations and laboratory analysis. Total carbon stocks were measured at 642.8 tC.h~~ in the low disturbance area, 536.9 tC＇ha-~ in the moderate disturbance area and 490.4 tC＇ha ~ in the high disturbance area. Bu, N1 and N were not significant in the carbon stock and were collectively categorized as a total biomass complex. The carbon stock of litter was nearly equal to that of the total biomass complex, while the total carbon stock in the soil was eight times larger than the total biomass complex or the carbon stock of the litter. We confirmed that the average ratio of AGB and BGB to the total biomass （TB） was about 84.7% and 15.3%, respectively. Improvements were made to the equations in the low disturbance logged-over secondary forest area, applying corrections to the amounts ofbiomass of sample trees, based on representative commercial trees of category one. TB stocks before and after correction were estimated to be 84.4 and 106.7 tC.ha-~, indicating that these corrections added significant amounts of tree biomass （26.4%） dur- ing the sampling procedure. In conclusion, the equations for tree biomass developed in this study, will be useful for evaluating total carbon stocks, especially TB stocks in logged-over secondary forests throughout the Papua region.

连年秸秆覆盖对玉米产量及土壤微生物残体碳积累的影响

为明确连年秸秆覆盖对玉米产量及土壤微生物残体碳的影响,从而揭示秸秆覆盖条件下土壤有机碳积累的微生物学机制,该研究基于田间8 a长期定位小区试验,比较了不覆盖秸秆(CK)和覆盖秸秆(SM)两处理中玉米产量,同时利用一阶动力学模型对土壤(0~10 cm和>10~20 cm)中有机碳、微生物残体碳及两者比例的年际变化进行了拟合。结果表明:1)秸秆覆盖在前5 a内没有显著提高玉米产量,第6年开始产量显著增加;在前2~3 a没有显著提高土壤有机碳和微生物残体碳含量;2)利用一阶动力学模型参数得到,SM处理显著提高了表层土壤有机碳、微生物残体碳以及两者比例的最大值,较CK处理分别高12%、39%、6%;3)SM处理显著延长了表层土壤有机碳、微生物残体碳以及两者比例达到最大值的时间,较CK处理分别多13、12和2.5 a,然而SM处理并没有显著影响下层土壤有机碳、微生物残体碳及两者比例的变化。因此,秸秆覆盖能够通过显著提高表层微生物残体碳及其对土壤有机碳的贡献,进而有利于对整个耕层土壤有机碳的固持。

丛枝菌根真菌介导的土壤有机碳稳定机制研究进展

土壤有机碳(SOC)的稳定是陆地生态系统碳循环的关键过程之一,对维持土壤肥力和减少温室气体排放具有重要意义。以往认为植物残体中难降解性物质的物理保护和腐殖质影响土壤中有机碳库的稳定性。最近的研究结果表明,微生物介导的碳循环过程在土壤有机碳稳定中发挥着重要作用。丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)作为土壤中一类重要的共生微生物,参与植物光合碳向土壤的转运和分配,是陆地生态系统碳循环的重要一环,但其在土壤有机碳稳定中的作用潜力还未得到充分挖掘。基于此,本文估算了植物光合碳在AMF根外菌丝的分配量;总结了AMF介导的土壤有机碳稳定机制,主要包括AMF活体菌丝对碳的截留,分泌物及残体的分子结构抗性和土壤矿物吸附,提高植物源碳的质量和数量,菌丝分泌物及残体的激发效应和稳定土壤团聚体;探讨了影响AMF介导的稳定性有机碳形成的非生物(气候因子、土壤养分和土壤矿物)和生物因子(植物和AMF种类);提出了AMF与土壤有机碳周转互作机理进一步的研究方向,包括探究菌根植物光合碳转化为稳定性SOC的机制,解析不同生态系统中AMF对稳定性SOC的贡献及影响因素,并厘清不同管理措施下AMF生物量、多样性与稳定性SOC的关系。以期为更好地利用AMF提升陆地生态系统碳汇和缓解全球气候变化提供理论依据。