地理学报, 2024, 79(1): 206-217 doi: 10.11821/dlxb202401013

生物地理

北京森林表土碳组分城郊梯度变化及其影响因素

田越韩,1,2, 郭泓伯1,2, 高晓飞1,2, 夏楠1,2, 杜恩在,1,2

1.北京师范大学地理科学学部,北京 100875

2.北京师范大学地表过程与资源生态国家重点实验室,北京 100875

Changes of forest topsoil carbon fractions across urban-rural transects in Beijing

TIAN Yuehan,1,2, GUO Hongbo1,2, GAO Xiaofei1,2, XIA Nan1,2, DU Enzai,1,2

1. Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China

2. State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China

通讯作者: 杜恩在(1986-), 男, 山东日照人, 教授, 博士生导师, 研究方向为生物地球化学与森林生态学。E-mail: enzaidu@bnu.edu.cn

收稿日期: 2023-07-10   修回日期: 2023-12-22  

基金资助: 中央高校基本科研业务费专项资金(2233200006)
地表过程与资源生态国家重点实验室自主课题(2021-TS-02)

Received: 2023-07-10   Revised: 2023-12-22  

Fund supported: Fundamental Research Funds for the Central Universities(2233200006)
Project of State Key Laboratory of Earth Surface Processes and Resource Ecology(2021-TS-02)

作者简介 About authors

田越韩(1998-), 男, 湖北宜昌人, 硕士生, 主要从事城市森林生物地球化学循环研究。E-mail: 202121051110@mail.bnu.edu.cn

摘要

快速的城市化进程深刻影响了城市森林土壤碳循环,重塑了城郊梯度上森林土壤碳空间分布特征。本文在北京市设置了4条城郊样带,测定了20个城市森林公园表土(表层0~10 cm和亚表层10~20 cm)总碳及其不同碳组分含量,分析了各碳组分空间变化及其影响因素。结果表明,城郊样带森林表土总碳(表层21.0±1.6 g/kg;亚表层18.0±1.3 g/kg)以有机碳为主(表层占比64.6%±4.5%;亚表层占比54.9%±4.5%),有机碳含量从市中心到郊区表现出先下降后增加的非线性变化,无机碳含量在此梯度上呈显著线性下降趋势。城市森林表土有机碳(表层13.8±1.5 g/kg;亚表层10.0±1.2 g/kg)以颗粒态有机碳为主(表层占比71.3%±2.4%;亚表层占比70.5%±2.8%),颗粒态有机碳和矿物结合态有机碳含量在城郊梯度上均表现出先下降后增加的非线性变化;颗粒态有机碳的占比在城区相对更小,而矿物结合态有机碳占比在城区相对更大。土壤质地、土壤pH和公园年龄是解释表土碳组分在城郊梯度上空间变异的重要因素,城郊气候梯度以及树木多样性对城市森林土壤碳组分空间变化的影响并不明显。上述研究结果有助于认识气候变化及人类活动双重干扰下的城市森林土壤碳库特征,也对城市森林土壤管理具有重要的指导意义。

关键词: 城市森林; 城市化; 土壤有机碳; 颗粒态有机碳; 矿物结合态有机碳; 空间格局

Abstract

Rapid urbanization has profoundly altered soil carbon cycling and thereby reshaped the spatial pattern of soil carbon content and fractions across the urban-rural gradients. In this study, we measured the contents of total carbon and its different fractions in the topsoil (surface layer 0-10 cm and subsurface layer 10-20 cm) of twenty parks across four urban-rural transects in Beijing, China. We analyzed the spatial variations of different soil carbon fractions and their potential driving factors across the urban-rural gradients. The results showed that topsoil total carbon (topsoil: 21.0±1.6 g/kg; subsurface soil: 18.0±1.3 g/kg) was dominated by organic carbon (topsoil: 64.6%±4.5%; subsurface soil: 54.9%±4.5%). Topsoil contents of organic carbon showed a nonlinear trend from the urban core to the rural area, while the topsoil inorganic carbon content decreased significantly. Topsoil organic carbon (topsoil: 13.8±1.5 g/kg; subsurface soil: 10.0±1.2 g/kg) was dominated by particulate organic carbon (topsoil: 71.3%±2.4%; subsurface soil: 70.5%±2.9%). The contents of both particulate organic carbon and mineral associated organic carbon showed nonlinear changes across the urban-rural forest transects. The proportion of particulate organic carbon was relatively low in urban areas, while that of mineral associated organic carbon showed an opposite trend. Soil texture, soil pH, and park age were important drivers to shape the spatial variation of topsoil carbon components across the urban-rural transects, while the urban-rural climate gradient and species diversity were found to have an unimportant role. Our findings improve the understanding of how urbanization reshapes soil carbon fractions and have useful implications for soil management in urban forests.

Keywords: urban forest; urbanization; soil organic carbon; particulate organic carbon; mineral associated organic carbon; spatial pattern

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本文引用格式

田越韩, 郭泓伯, 高晓飞, 夏楠, 杜恩在. 北京森林表土碳组分城郊梯度变化及其影响因素. 地理学报, 2024, 79(1): 206-217 doi:10.11821/dlxb202401013

TIAN Yuehan, GUO Hongbo, GAO Xiaofei, XIA Nan, DU Enzai. Changes of forest topsoil carbon fractions across urban-rural transects in Beijing. Acta Geographica Sinica, 2024, 79(1): 206-217 doi:10.11821/dlxb202401013

1 引言

土壤为人类提供了众多关键的生态系统服务[1],尤其在调节植物生长、缓解气候变化等方面起着重要作用。然而,快速的城市化强烈改变了土壤的结构和功能[2-3],导致诸多土壤属性在城市和郊区间呈现明显的梯度变化(即城郊梯度变化)[4-5]。已有研究表明,城市森林土壤与近郊森林土壤相比具有更高的碳含量[6-7]。土壤碳由具有不同周转率的碳组分组成[8],周转较快的碳组分对环境变化和人为干扰更为敏感[9],因此不同碳组分对气候变化与人为干扰的响应可能存在明显差异[10-11]。然而,以往的研究多聚焦于城市化对森林土壤总碳或总有机碳的影响[12-13],关于城市化对森林土壤碳组分的影响尚缺乏深入认识。

土壤碳库可划分为有机碳(SOC)及无机碳(SIC)[14],通常有机碳占比最高且活性更强[15]。越来越多的研究将有机碳分为颗粒态有机碳(POC)和矿物结合态有机碳(MAOC),以更好地认识土壤碳的积累、持久性及其对环境变化的响应[16]。颗粒态有机碳主要来源于半分解的植物残体,是相对不稳定的有机碳组分,而矿物结合态有机碳主要由难分解的微生物代谢物和残体形成,周转缓慢且更为稳定[17]。因此,森林土壤不同碳组分在城郊梯度上的空间变化规律及其驱动因素可能存在明显的差异。

城市森林土壤碳组分的空间格局可能受到多种因素的影响。首先,城市热岛促进了微生物呼吸作用[18],使易分解的活性碳组分发生损失。例如,在美国纽约及巴尔的摩开展的城郊梯度样带研究发现,与郊区相比,城区森林土壤活性有机碳组分减少但惰性有机碳组分增加[2,8]。其次,土壤属性的变化也会导致不同碳组分的变化。例如,由于碱性混凝土的输入[19-20],市区土壤的pH普遍比郊区高[21],而且无机碳的占比增加。因此,人为管理措施可能会通过改变土壤质地进而影响土壤通气性及矿物含量[22],最终影响土壤有机碳及其组分的固存。此外,年龄更老的城市森林由于土壤碳积累时间更久而具有更高的土壤有机碳含量[23-24]。城市森林植被覆盖率也可能通过改变枯落物输入量以及土壤温度和湿度等微环境因子,造成土壤碳组分的变化[25]。除上述因素外,城市森林不同树种组成也可能通过影响凋落物的分解[26]、土壤酶活性[27]、土壤理化性质[28]等,导致土壤碳组分发生变化。然而,目前很少有研究定量揭示上述多种因素对城郊梯度上森林土壤不同碳组分的影响及其相对重要性。

作为中国首都和世界上最大的城市之一,北京在过去40年内经历了快速的城市化进程[29],形成了典型的城郊梯度森林景观[30-31],为研究城郊梯度上森林土壤碳组分的变化提供了良好平台。本文拟通过对北京4条城郊样带上20个城市公园中森林斑块进行调查采样,分析其表土(表层0~10 cm和亚表层10~20 cm)总碳及不同碳组分在城郊梯度上的空间变化特征和影响因素。

2 材料与方法

2.1 研究区域及采样设计

北京(39.43°N~41.05°N, 115.42°E~117.50°E)属于温带大陆性季风气候,年均温约为11~13 ℃,年均降水约为500~600 mm。自然地带性植被类型以温带落叶阔叶林及针阔叶混交林为主[32]。本文从市中心(故宫博物院)到郊区设置4条不同走向(东北、西北、西南和正南)的城郊梯度样带[33],随机选取20个独立的城市森林公园进行采样(图1)。采样公园到市中心的距离在3~79 km之间。从市中心到郊区,主要土地覆盖类型由建设用地转变为农田,再过渡为次生植被。在城郊梯度上,年均温呈下降趋势,年降水无变化规律;土壤pH呈下降趋势,土壤粘粉粒含量呈先降低后增加的趋势;公园年龄在0~40 km范围内随距离增加而下降,超过40 km后则随距离增加而增加;公园植被覆盖度无显著变化。

图1

图1   北京城郊样带及公园采样点分布

Fig. 1   Urban-rural transects and locations of sampling parks


2.2 样品采集与分析

样带调查与采样于2019年6月下旬至7月初进行[31,33]。在每个公园随机选择3块典型森林斑块,去除土壤表层的凋落物,用土钻采集表层(0~10 cm)和亚表层(10~20 cm)土壤样品,每个公园内同层土样分别均匀混合成一个样品。采集土壤样品的同时,记录森林斑块的树种数。土壤样品经自然风干后过2 mm筛,去除石砾、死根及其他植物残体,用于土壤理化性质和土壤碳组分分析。通过pH计法(PB-10, Sartorius, Germany)测定土壤pH;通过全自动激光粒度仪法(Malvern Mastersizer 2000, Worcestershire, UK)测定土壤粘粉粒含量。将土壤样品研磨并过100目筛,用碳氮元素分析仪(CN802, Velp, Italy)测定土壤总碳含量。

土壤有机碳含量通过酸水解法测定。称取土样5.0 g用10%的稀盐酸彻底去除无机碳,之后多次用去离子水洗酸至溶液呈中性,置于65 ℃烘箱内烘干至恒重。随后研磨过100目筛,用碳氮元素分析仪(CN802, Velp, Italy)测定土壤有机碳含量。土壤中无机碳含量通过土壤总碳含量减去有机碳含量的差值计算得出。采用湿筛和粒径分组法将土壤有机质分离为颗粒态有机质(POM,粒径> 53 μm)和矿物结合态有机质(MAOM,粒径< 53 μm)[16,34],分别得到颗粒态和矿物结合态有机质悬浊液,经过沉淀、去除上清液、烘干、称重后,计算其质量回收率。将筛分得到的两类组分样品分别研磨并过100目筛,通过添加稀盐酸去除无机碳后,用碳氮元素分析仪(CN802, Velp, Italy)分别测定其土壤有机碳含量。根据质量守恒定律,结合公式(1)~(3)分别计算得到颗粒态有机碳和矿物结合态有机碳含量[35]

MassRec=MassPOM+MassMAOMMassBuiksoil×100%
POC=MassPOM×OCPOMMassBuiksoil×MassRec
MAOC=MassMAOM×OCMAOMMassBuiksoil×MassRec

式中:MassRec为土壤质量回收率;MassBulk soil为土壤样品质量;MassPOMMassMAOM分别为分离所得颗粒态有机质与矿物结合态有机质的质量;OCPOMOCMAOM分别为颗粒态有机质与矿物结合态有机质中测得的有机碳含量;POCMAOC分别为土壤样品中颗粒态有机碳与矿物结合态有机碳的含量。经计算,筛分后的土壤平均质量回收率为97.3%,物理分组效果较好。

2.3 潜在影响因素数据获取

为分析影响不同土壤碳组分含量空间变异的潜在因素,本文收集了与土壤碳输入及输出过程直接相关的3类影响因素数据,包括气候因素(年均温和年降水)、土壤因素(土壤质地和土壤pH)、植被因素(公园植被覆盖度、公园年龄和树种多样性)。其中,气象数据来自中国气象局(http://data.cma.cn/),土壤理化性质(pH和质地)数据来自实验测试,公园植被覆盖度通过地理国情监测云平台(http://www.dsac.cn/)的卫星遥感图像(空间分辨率为2.5 m)估算得出,公园年龄来自北京市园林绿化管理局网站(http://yllhj.beijing.gov.cn/),树种多样性以采样时所记录的树种数为指标。除上述因素外,人为管理措施(如施肥、灌溉等)也会影响城市森林土壤属性[30],但受限于这类数据的可获得性,本文未能将其纳入影响因素分析。

2.4 统计分析

通过Shapiro-Wilk test对不同土壤碳组分含量数据进行正态性检验,对不符合正态分布的数据进行正态转换。通过线性或非线性回归分析检验城郊梯度上森林表土不同碳组分含量及各类环境因素的空间变化趋势。基于相关分析检验表土不同碳组分含量随气候、土壤和植被因素的变化。使用“rdacca.hp”程序包[36]进行基于层次分割原理的方差分解(VPA),量化各影响因素的综合作用及相对重要性。本文统计分析均基于R软件(version 4.0.5)完成[37],统计分析样本量均为20个,统计显著性水平为P < 0.05。

3 结果

3.1 表土总有机碳和无机碳含量的城郊梯度变化

北京城郊梯度上森林表土总碳(表层21.0±1.6 g/kg;亚表层18.0±1.3 g/kg)以有机碳为主导(表层土壤占比64.6%±4.5%;亚表层土壤占比54.9%±4.5%)。在城郊梯度上,森林表土总有机碳与无机碳含量的空间变化规律存在明显差异(图2)。从市区到郊区,有机碳含量呈先下降后升高的非线性趋势(图2a、2e),有机碳在总碳中的占比(SOC∶STC)总体呈增加趋势(图2b、2f)。无机碳含量在城郊梯度上呈现显著下降趋势(图2c、2g),无机碳在总碳中的占比(SIC∶STC)总体呈下降趋势(图2d、2h)。

图2

图2   北京森林表土有机碳和无机碳含量城郊梯度及其在总碳中占比的变化

Fig. 2   Changes of topsoil organic carbon and inorganic carbon contents and their contributions to total carbon across urban-rural forest transects in Beijing


3.2 表土颗粒态有机碳和矿物结合态有机碳含量的城郊梯度变化

城郊梯度森林表土有机碳(表层13.8±1.5 g/kg;亚表层10.0±1.2 g/kg)以颗粒态有机碳为主导(表层土壤占比71.3%±2.4%;亚表层土壤占比70.5%±2.8%)。从市中心到郊区,矿物结合态有机碳和颗粒态有机碳含量均呈先下降后升高的非线性趋势(图3a、3e)。在城郊梯度上,两种有机碳组分在总有机碳中的占比表现出相反的变化,颗粒态有机碳的占比(POC∶SOC)在市区相对较低,在城郊梯度上呈显著非线性增加趋势(图3b、3f);矿物结合态有机碳的占比(MAOC∶SOC)在市区相对较高,呈显著非线性下降趋势(图3d、3h)。

图3

图3   北京森林表土颗粒态有机碳和矿物结合态有机碳含量城郊梯度及其在总有机碳中占比变化

Fig. 3   Changes of topsoil particulate organic carbon and mineral associated organic carbon content and their contributions to total organic carbon across urban-rural forest transects in Beijing region


3.3 土壤碳组分含量与环境因素的关系以及各影响因素的相对重要性

基于相关分析发现,表层和亚表层土壤有机碳含量均与土壤pH呈显著负相关(表层P < 0.001;亚表层P < 0.01),且与公园年龄呈显著正相关(P < 0.01)(图4a、4c、4d、4f),有机碳含量仅在表层土壤中与粘粉粒含量呈显著正相关(图4b)。无机碳含量仅在表层土壤中与土壤pH呈显著正相关(图4a),亚表层土壤的无机碳含量同各影响因素均无显著相关性(图4d~4f)。

图4

图4   北京森林表土碳组分与土壤pH、土壤粘粉粒含量及公园年龄之间的相关关系

Fig. 4   Correlations between topsoil carbon fractions and soil pH, soil clay and silt content and park age across urban-rural forest transects in Beijing


表层和亚表层土壤的颗粒态有机碳含量均与土壤pH呈显著负相关,且与公园年龄呈显著正相关(图4g、4i、4j、4l)。表层土壤的矿物结合态有机碳含量与土壤pH呈显著负相关,与公园年龄呈显著正相关(图4g、4i)。亚表层土壤的矿物结合态有机碳含量则仅与公园年龄呈显著正相关(图4l)。此外,表层土壤颗粒态有机碳和矿物结合态有机碳含量均与土壤粘粉粒含量呈显著正相关(图4h)。

方差分解(VPA)结果表明,各影响因素总共解释了表层土壤颗粒态有机碳、矿物结合态有机碳及无机碳含量空间变异总方差的71.4%、65.4%和45.5%(图5a~5c)。其中,土壤pH对颗粒态有机碳、矿物结合态有机碳及无机碳含量变异的单独解释率均最大,分别为29.9%、29.6%和15.7%。各影响因素总共解释了亚表层土壤颗粒态有机碳、矿物结合态有机碳及无机碳含量空间变异总方差的63.4%、45.3%和51.8%(图5d~5f)。其中土壤pH对颗粒态有机碳含量变异的单独解释率最高,为29.5%(图5d)。相比之下,公园年龄对于矿物结合态有机碳及无机碳含量变异的单独解释率最高,分别为16.1%和19.9%(图5e~5f)。

图5

图5   不同因素对北京森林表土碳组分城郊梯度空间变异影响的相对重要性

Fig. 5   Relative importance of different drivers in shaping the spatial variation of topsoil carbon fractionsacross urban-rural forest transects in Beijing


4 讨论

4.1 城郊梯度上不同表土碳组分的空间变化规律

本文发现森林表土无机碳含量城郊梯度上表现为线性降低趋势,且无机碳在总碳中的占比也在城区相对更高。前人在北京[38]、上海[39]及美国菲尼克斯[40]等城市的研究也有类似的结论。城市森林表土无机碳含量与土壤pH显著正相关,而且土壤pH对表土无机碳空间变异的方差解释率最高,这可能是因为城区人类活动更密集,产生的城市建筑垃圾(尤其是水泥和混凝土)通常由富含钙和镁元素的碱性物质构成[41],易与土壤溶解的CO2反应生成碳酸盐,从而导致无机碳积累[42]。然而,城郊梯度上表土总有机碳、颗粒态有机碳和矿物结合态有机碳含量均呈先降低后增加的趋势,不同于以往研究发现的土壤总有机碳含量在城郊梯度上的单调递减趋势[38]。这可能是由于本文设置的城郊梯度样带覆盖范围更广,而以往研究主要集中在城区与近郊区的对比(图6)。

图6

图6   森林表土碳组分城郊梯度变化及其影响因素空间变异概念图

Fig. 6   Conceptual diagram of spatial variation of topsoil carbon fractions and potential drivers across urban-rural gradients


在城郊梯度上,城市森林表土有机碳、颗粒态有机碳和矿物结合态有机碳含量的空间变化主要受土壤pH、粘粉粒含量及公园年龄影响。城市森林公园在城郊梯度上建成时间及管理强度的不同影响了上述3种因素在城郊梯度上的变化,进而导致了表土有机碳组分含量的非线性格局(图6)。公园年龄一方面可以直接反映土壤有机碳的积累时间[7,43],另一方面也侧面反映了人类活动干扰的程度[38]。市中心建成时间较长的森林公园管理措施趋于稳定,促进了有机碳的稳定积累,近郊区新建的城市森林公园由于土壤回填及人为踩踏等干扰更为频繁,土壤保持水分与养分的能力较差[23],不利于有机碳的持续积累。相比之下,虽然远郊森林公园很少受到密集的人为管理,但地表丰富的凋落物能够输入丰富的有机质及养分[44],因此有机碳及其组分含量同样较高。此外,表土质地在市中心及远郊相对较细,粒径较小的土壤粘粉粒通常比表面积更大,能够形成更多的有机碳—矿物化学键从而促进有机碳及其组分的固定[45]。市区偏碱性的土壤中钙含量较高,土壤中的Ca2+桥键是土壤有机碳稳定的重要机制[46],能增加对有机碳的固定能力[47]

4.2 颗粒态有机碳对城市森林表土总有机碳的主导性贡献

本文发现城郊梯度上森林表土有机碳组分始终以颗粒态有机碳为主,这可能与城市土壤发育时间较短有关。一般认为颗粒态有机碳主要来源于新鲜的植物残体,而随着土壤的发育,微生物过程主导的矿物结合态有机碳则会逐渐积累[16,48]。然而,本文也发现,与郊区相比,颗粒态有机碳对总有机碳的贡献在城区更小,而矿物结合态有机碳对有机碳的贡献在城区更大,这可能是由于城区土壤有较长的碳累积时间,增加了颗粒态有机碳向矿物结合态有机碳的转化,同时频繁的凋落物移除措施也会减少植物残体向土壤有机碳库的归还[49],从而降低了颗粒态有机碳组分的比例。虽然市中心由于热岛效应(图6)导致大气及土壤温度相对更高[50],可能加速不稳定的颗粒态有机碳组分的分解速率,同时高温会促进土壤微生物活性有利于矿物结合态有机碳的积累。然而,本文并未发现年均温和颗粒态有机碳及矿物结合态有机碳含量存在相关性,这表明在局地小尺度下,温度对土壤有机碳动态的单独效应可能并不明显。

4.3 城郊梯度上不同表土碳组分空间变异的主导因素

本文发现土壤pH和公园年龄是解释表土碳组分含量在城郊梯度上空间变异的最重要因素。以往的研究多强调气候因素(年均温和年降水)[51-53]和植被类型[54-55]对自然土壤碳组分空间格局的决定作用,但这些研究通常是在区域尺度或全球上进行的,涵盖了多样的水热条件和土壤植被类型。相比之下,北京市城郊梯度上的温度和降水变化较小,并且土壤与植被类型也基本一致(图6)。有研究表明城市化较高的地区存在非常明显的城郊经济水平差异[53,56],城区与郊区在森林养护、人群踩踏和垃圾处理等方面的差异会使土壤受干扰时间及土壤属性存在很大差别[57-58]。例如,城区园林管理倾向于增加植被覆盖度,通常进行施肥和灌溉措施,有利于树木生长和土壤净碳固存[59];郊区公园的集约开发则往往会破坏土壤结构并加速土壤养分流失,减弱土壤物理化学保护机制对有机碳的固定作用[43]。总之,我们的研究结果表明,在局地尺度上,人为因素导致的土壤与植被变化相比气候因素对土壤碳组分的空间变异影响更为强烈。

4.4 不确定性与未来研究展望

本文对城市森林表土碳组分空间变异潜在影响因素的分析存在一定不确定性。例如,城市森林通常会受到频繁的园艺管理(如施肥、灌溉和修剪),尤其是在人为活动密集的城市核心区[60]。由于缺乏相应的数据,本文无法量化城市森林管理措施的影响。此外,较高浓度的大气CO2可以刺激城市树木生长[61],增加植物的土壤碳输入;大气氮沉降“城市热点现象”会增加土壤中氮的有效性,影响植物的生长以及微生物群落特征[30],从而影响土壤碳组分的变化。遗憾的是,本文未能测定城市公园样点尺度的大气CO2浓度和大气氮沉降速率,无法进行相关量化分析。因此,在未来的研究中应综合考虑上述多种因素的影响,从而深化对城市森林土壤碳循环过程调控机制的认识。同时,城市公园需要通过更科学的管理措施增强土壤碳的稳定性,从而更好地维持城市森林土壤的功能。

5 结论

本文基于样带调查手段分析了北京森林表土碳组分城郊梯度空间变化特征及其影响因素。结果表明,从市中心到郊区,表土无机碳含量表现为线性下降趋势,总有机碳、颗粒态有机碳和矿物结合态有机碳含量均呈先降低后增加的趋势。城郊梯度上总有机碳组分始终以颗粒态有机碳为主,颗粒态有机碳对总有机碳的贡献在城区更小,而矿物结合态有机碳对总有机碳的贡献在城区更大。土壤质地、pH和公园年龄是解释表土碳组分在城郊梯度上空间变异的主要因素,而气候因素的影响相对较小,表明在局地尺度上人为活动导致的土壤与植被属性变化对城市森林土壤碳组分的影响更为重要。未来研究应更多关注人为影响和气候变化背景下,城市森林土壤碳组分的动态变化及其响应机制。

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In urban areas, anthropogenic drivers of ecosystem structure and function are thought to predominate over larger‐scale biophysical drivers. Residential yards are influenced by individual homeowner preferences and actions, and these factors are hypothesized to converge yard structure across broad scales. We examined soil total C and total δ13C, organic C and organic δ13C, total N, and δ15N in residential yards and corresponding reference ecosystems in six cities across the United States that span major climates and ecological biomes (Baltimore, Maryland; Boston, Massachusetts; Los Angeles, California; Miami, Florida; Minneapolis‐St. Paul, Minnesota; and Phoenix, Arizona). Across the cities, we found soil C and N concentrations and soil δ15N were less variable in residential yards compared to reference sites supporting the hypothesis that soil C, N, and δ15N converge across these cities. Increases in organic soil C, soil N, and soil δ15N across urban, suburban, and rural residential yards in several cities supported the hypothesis that soils responded similarly to altered resource inputs across cities, contributing to convergence of soil C and N in yards compared to natural systems. Soil C and N dynamics in residential yards showed evidence of increasing C and N inputs to urban soils or dampened decomposition rates over time that are influenced by climate and/or housing age across the cities. In the warmest cities (Los Angeles, Miami, Phoenix), greater organic soil C and higher soil δ13C in yards compared to reference sites reflected the greater proportion of C4 plants in these yards. In the two warm arid cities (Los Angeles, Phoenix), total soil δ13C increased and organic soil δ13C decreased with increasing home age indicating greater inorganic C in the yards around newer homes. In general, soil organic C and δ13C, soil N, and soil δ15N increased with increasing home age suggesting increased soil C and N cycling rates and associated 12C and 14N losses over time control yard soil C and N dynamics. This study provides evidence that conversion of native reference ecosystems to residential areas results in convergence of soil C and N at a continental scale. The mechanisms underlying these effects are complex and vary spatially and temporally.

Wang Shaoqiang, Zhou Chenghu, Li Kerang, et al.

Analysis on spatial distribution characteristics of soil organic carbon reservoir in China

Acta Geographica Sinica, 2000, 55(5): 533-544.

DOI:10.11821/xb200005003      [本文引用: 1]

The paper respectively adopted physiochemical properties of every soil stratum from<sup>2</sup> 473 soil profiles of the second soil survey. The corresponding carbon content of soil is estimated by utilizing conversion coefficient 0 58. First, we calculated the carbon content of every stratum of different soil stirp in the same soil subtype. Then, we took soil stratum depth as weight coefficient to acquire the average physiochemical properties of various kinds of soil stirp. Finally, we got the average depth, organic content, duck density and carbon density of different soil subtypes through area averaging. The total carbon quantity of different kinds of soil can be calculated by the following expression: C j=0 58S jH jO W j where j is the soil type, C j is the carbon storage of j soil type, S j is the distribution area of j soil type, H j is the average depth of j soil type, O j is the average organic content of j soil type, and W j is the average bulk density of j soil type. In the second soil survey, the total amount of soil organic carbon is about 924 18?10 8 t and carbon density is about 10 53 kgC/m<sup>2</sup> in China according to the statistic country area 877 63?10<sup>6</sup>hm<sup>2</sup>. The spatial distribution characteristics of soil organic carbon in China are that the carbon storage increases with the increase of latitude in eastern China and the carbon storage decreases with the decrease of longitude in northern China. There is a transition zone where carbon storage varies greatly in China. Moreover, there is an increasing tendency of carbon density with the decrease of latitude in western China. Soil circle has implications on global change, but the difference in soil spatial distribution is substantial in China. Because the structure of soil is inhomogeneous, mistakes will be resulted in estimating soil carbon reservoir. It is thus necessary to farther resolve soil respiration, organic matter conversion and others related problems, and build uniform and normal methods of measurment and sampling.

[王绍强, 周成虎, 李克让, .

中国土壤有机碳库及空间分布特征分析

地理学报, 2000, 55(5): 533-544.]

DOI:10.11821/xb200005003      [本文引用: 1]

土壤有机碳库是陆地碳库的主要组成部分,在陆地碳循环研究中有着重要的作用。根据中国第二次土壤普查实测2473个典型土壤剖面的理化性质,以及土壤各类型分布面积,估算中国土壤有机碳库的储量约为924.18×108t,平均碳密度为10.53kg/m<sup>2</sup>,表明中国土壤是一个巨大的碳库。其空间分布总体规律上表现为:东部地区大致是随纬度的增加而递增,北部地区呈现随经度减小而递减的趋势,西部地区则呈现随纬度减小而增加的趋势。

Song X D, Yang F, Wu H Y, et al.

Significant loss of soil inorganic carbon at the continental scale

National Science Reivew, 2021, 9(2). DOI: 10.1093/nsr/nwab120.

[本文引用: 1]

Lavallee J M, Soong J L, Cotrufo M F.

Conceptualizing soil organic matter into particulate and mineral-associated forms to address global change in the 21st century

Global Change Biology, 2020, 26(1): 261-273.

DOI:10.1111/gcb.14859      PMID:31587451      [本文引用: 3]

Managing soil organic matter (SOM) stocks to address global change challenges requires well-substantiated knowledge of SOM behavior that can be clearly communicated between scientists, management practitioners, and policy makers. However, SOM is incredibly complex and requires separation into multiple components with contrasting behavior in order to study and predict its dynamics. Numerous diverse SOM separation schemes are currently used, making cross-study comparisons difficult and hindering broad-scale generalizations. Here, we recommend separating SOM into particulate (POM) and mineral-associated (MAOM) forms, two SOM components that are fundamentally different in terms of their formation, persistence, and functioning. We provide evidence of their highly contrasting physical and chemical properties, mean residence times in soil, and responses to land use change, plant litter inputs, warming, CO enrichment, and N fertilization. Conceptualizing SOM into POM versus MAOM is a feasible, well-supported, and useful framework that will allow scientists to move beyond studies of bulk SOM, but also use a consistent separation scheme across studies. Ultimately, we propose the POM versus MAOM framework as the best way forward to understand and predict broad-scale SOM dynamics in the context of global change challenges and provide necessary recommendations to managers and policy makers.© 2019 John Wiley & Sons Ltd.

Sokol N W, Sanderman J, Bradford M A.

Pathways of mineral-associated soil organic matter formation: Integrating the role of plant carbon source, chemistry, and point of entry

Global Change Biology, 2019, 25(1): 12-24.

DOI:10.1111/gcb.14482      PMID:30338884      [本文引用: 1]

To predict the behavior of the terrestrial carbon cycle, it is critical to understand the source, formation pathway, and chemical composition of soil organic matter (SOM). There is emerging consensus that slow-cycling SOM generally consists of relatively low molecular weight organic carbon substrates that enter the mineral soil as dissolved organic matter and associate with mineral surfaces (referred to as "mineral-associated OM," or MAOM). However, much debate and contradictory evidence persist around: (a) whether the organic C substrates within the MAOM pool primarily originate from aboveground vs. belowground plant sources and (b) whether C substrates directly sorb to mineral surfaces or undergo microbial transformation prior to their incorporation into MAOM. Here, we attempt to reconcile disparate views on the formation of MAOM by proposing a spatially explicit set of processes that link plant C source with MAOM formation pathway. Specifically, because belowground vs. aboveground sources of plant C enter spatially distinct regions of the mineral soil, we propose that fine-scale differences in microbial abundance should determine the probability of substrate-microbe vs. substrate-mineral interaction. Thus, formation of MAOM in areas of high microbial density (e.g., the rhizosphere and other microbial hotspots) should primarily occur through an in vivo microbial turnover pathway and favor C substrates that are first biosynthesized with high microbial carbon-use efficiency prior to incorporation in the MAOM pool. In contrast, in areas of low microbial density (e.g., certain regions of the bulk soil), MAOM formation should primarily occur through the direct sorption of intact or partially oxidized plant compounds to uncolonized mineral surfaces, minimizing the importance of carbon-use efficiency, and favoring C substrates with strong "sorptive affinity." Through this framework, we thus describe how the primacy of biotic vs. abiotic controls on MAOM dynamics is not mutually exclusive, but rather spatially dictated. Such an understanding may be integral to more accurately modeling soil organic matter dynamics across different spatial scales.© 2018 John Wiley & Sons Ltd.

Pouyat R V, Mcdonnell M J, Pickett S T A.

Litter decomposition and nitrogen mineralization in oak stands along an urban-rural land use gradient

Urban Ecosystems, 1997, 1(2): 117-131.

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Washbourne C L, Renforth P, Manning D A C.

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Science of the Total Environment, 2012, 431(1): 166-175.

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Yang J L, Zhang G L.

Formation, characteristics and eco-environmental implications of urban soils: A review

Soil Science and Plant Nutrition, 2015, 61(1): 30-46.

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Zhang Qingqing, Zhang Guilian, Wu Haibing, et al.

Soil organic carbon distribution and its relationship with soil physicochemical properties in different forest types of Shanghai city

Journal of Zhejiang A&F University, 2019, 36(6): 1087-1095.

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[张青青, 张桂莲, 伍海兵, .

上海市林地土壤有机碳分布特征及其与土壤理化性质的关系

浙江农林大学学报, 2019, 36(6): 1087-1095.]

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Pouyat R V, Szlavecz K, Yesilonis I D, et al.

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//Aitkenhead-Peterson J, Volder A. Urban Ecosystem Ecology. Madison: Agronomy Monograph, 2010: 119-152.

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Liu Zhaoyun, Zhang Mingkui.

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Chinese Journal of Ecology, 2010, 29(1): 142-145.

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[刘兆云, 章明奎.

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Lindén L, Riikonen A, Setälä H, et al.

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Urban Forestry and Urban Greening, 2020, 49: 126633. DOI: 10.1016/j.ufug.2020.126633.

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Lorenz K, Lal R.

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Environment International, 2009, 35(1): 1-8.

DOI:10.1016/j.envint.2008.05.006      PMID:18597848      [本文引用: 1]

The percentage of urban population is projected to increase drastically. In 2030, 50.7 to 86.7% of the total population in Africa and Northern America may live in urban areas, respectively. The effects of the attendant increases in urban land uses on biogeochemical C and N cycles are, however, largely unknown. Biogeochemical cycles in urban ecosystems are altered directly and indirectly by human activities. Direct effects include changes in the biological, chemical and physical soil properties and processes in urban soils. Indirect effects of urban environments on biogeochemical cycles may be attributed to the introductions of exotic plant and animal species and atmospheric deposition of pollutants. Urbanization may also affect the regional and global atmospheric climate by the urban heat island and pollution island effect. On the other hand, urban soils have the potential to store large amounts of soil organic carbon (SOC) and, thus, contribute to mitigating increases in atmospheric CO(2) concentrations. However, the amount of SOC stored in urban soils is highly variable in space and time, and depends among others on soil parent material and land use. The SOC pool in 0.3-m depth may range between 16 and 232 Mg ha(-1), and between 15 and 285 Mg ha(-1) in 1-m depth. Thus, depending on the soil replaced or disturbed, urban soils may have higher or lower SOC pools, but very little is known. This review provides an overview of the biogeochemical cycling of C and N in urban soils, with a focus on the effects of urban land use and management on soil organic matter (SOM). In view of the increase in atmospheric CO(2) and reactive N concentrations as a result of urbanization, urban land use planning must also include strategies to sequester C in soil, and also enhance the N sink in urban soils and vegetation. This will strengthen soil ecological functions such as retention of nutrients, hazardous compounds and water, and also improve urban ecosystem services by promoting soil fertility.

Xu Y D, Ding F, Gao X D, et al.

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Journal of Soils and Sediments, 2019, 19: 1407-1415.

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Lin Yu, Nie Fuyu, Yang Wanqin, et al.

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Chinese Chinese Journal of Applied and Environmental Biology, 2019, 25(3): 634-639.

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[林玉, 聂富育, 杨万勤, .

四川盆地西缘4种人工林土壤氮转化酶的季节动态

应用与环境生物学报, 2019, 25(3): 634-639 ]

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Toriyama J, Ohta S, Ohnuki Y, et al.

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Japan Agricultural Research Quarterly, 2011, 45(3): 309-316.

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Song X M, Zhang J Y, Aghakouchak A, et al.

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Journal of Geophysical Research: Atmospheres, 2014, 119(19): 250-271.

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Du E Z, Xia N, Guo Y Y, et al.

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Frontiers of Agricultural Science and Engineering, 2022, 9(3): 445-456.

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<p> <List> <ListItem><ItemContent><p>● Patterns and effects of N deposition on urban forests are reviewed.</p></ItemContent></ListItem> <ListItem><ItemContent><p>● N deposition generally shows an urban hotspot phenomenon.</p></ItemContent></ListItem> <ListItem><ItemContent><p>● Urban N deposition shows high ratios of ammonium to nitrate.</p></ItemContent></ListItem> <ListItem><ItemContent><p>● N deposition likely has distinct effects on urban and natural forests.</p></ItemContent></ListItem></List> </p> <p>The global urban area is expanding continuously, resulting in unprecedented emissions and deposition of reactive nitrogen (N) in urban environments. However, large knowledge gaps remain in the ecological effects of N deposition on urban forests that provide key ecosystem services for an increasing majority of city dwellers. The current understanding of the spatial patterns and ecological effects of N deposition in urban forests was synthesized based on a literature review of observational and experimental studies. Nitrogen deposition generally increases closer to cities, resulting in an urban hotspot phenomenon. Chemical components of N deposition also shift across urban-suburban-rural gradients, showing higher ratios of ammonium to nitrate in and around urban areas. The ecological effects of N deposition on urban forest ecosystems are overviewed with a special focus on ecosystem N cycling, soil acidification, nutrient imbalances, soil greenhouse gas emissions, tree growth and forest productivity, and plant and soil microbial diversity. The distinct effects of unprecedented N deposition on urban forests are discussed in comparison with the common effects in natural forests. Despite the existing research efforts, several key research needs are highlighted to fill the knowledge gaps in the ecological effects of N deposition on urban forests.</p>

Du E Z, Xia N, Tang Y, et al.

Anthropogenic and climatic shaping of soil nitrogen properties across urban-rural-natural forests in the Beijing metropolitan region

Geoderma, 2022, 406: 115524. DOI: 10.1016/j.geoderma.2021.115524.

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Plant and Soil, 2022, 477(1): 425-437.

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Yuan X, Qin W K, Xu H, et al.

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Soil Biology and Biochemistry, 2020, 150: 107984. DOI: 10.1016/j.soilbio.2020.107984.

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Methods in Ecology and Evolution, 2022, 13(4): 782-788.

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Luo S H, Mao Q Z, Ma K M.

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Xu N Z, Liu H Y, Wei F, et al.

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Du J F, Yu M X, Cong Y G, et al.

Soil organic carbon storage in urban green space and its influencing factors: A case study of the 0-20 cm soil layer in Guangzhou city

Land, 2022, 11(9): 1484. DOI: 10.3390/land11091484.

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Urban soils can contribute to organic carbon sequestration. The socioeconomic drivers of soil organic carbon (SOC) in urban areas may differ between regions due to the different land tenure and its derived green space management regimes. Currently, few studies focus on regions where public ownership of land was implemented. We examined the SOC storage and driving factors of urban green spaces in Guangzhou, China at 0–20 cm depth by variance and regression analysis. Our results showed that the total SOC storage did not vary significantly among green space types, with an average value of 2.59 ± 1.31 kg/m2. SOC increased with plot age (2–87 years) by 0.025 kg/m2/year (p = 0.026) and plot size (63–2058 m2) by 0.001 kg/m2/m2 (p = 0.026). Disturbance intensity was negatively correlated to SOC storage. Green space maintenance practices could promote SOC sequestration, but this benefit may be offset by high-intensity disturbances such as trampling, litter and debris removal and fragmentation of green spaces. To increase urban residential SOC storage, except for remediation of compacted soils, it is essential to promote house owners’ initiative in green space management and conservation by improving the current residential green space management regimes.

Meyer S, Rusterholz H P, Salamon J A, et al.

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Boiteau R M, Kukkadapu R, Cliff J B, et al.

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Georgiou K, Jackson R B, Vinduskova O, et al.

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Nature Communications, 2022, 13(1): 3797. DOI: 10.1038/s41467-022-31540-9.

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Soil is the largest terrestrial reservoir of organic carbon and is central for climate change mitigation and carbon-climate feedbacks. Chemical and physical associations of soil carbon with minerals play a critical role in carbon storage, but the amount and global capacity for storage in this form remain unquantified. Here, we produce spatially-resolved global estimates of mineral-associated organic carbon stocks and carbon-storage capacity by analyzing 1144 globally-distributed soil profiles. We show that current stocks total 899 Pg C to a depth of 1 m in non-permafrost mineral soils. Although this constitutes 66% and 70% of soil carbon in surface and deeper layers, respectively, it is only 42% and 21% of the mineralogical capacity. Regions under agricultural management and deeper soil layers show the largest undersaturation of mineral-associated carbon. Critically, the degree of undersaturation indicates sequestration efficiency over years to decades. We show that, across 103 carbon-accrual measurements spanning management interventions globally, soils furthest from their mineralogical capacity are more effective at accruing carbon; sequestration rates average 3-times higher in soils at one tenth of their capacity compared to soils at one half of their capacity. Our findings provide insights into the world's soils, their capacity to store carbon, and priority regions and actions for soil carbon management.© 2022. The Author(s).

Chen T, Hong X M, Hu Y L, et al.

Effects of litter input on the balance of new and old soil organic carbon under natural forests along a climatic gradient in China

Biogeochemistry, 2022, 160(3): 409-421.

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Vasenev V I, Varentsov M, Konstantinov P, et al.

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Science of the Total Environment, 2021, 786: 147457. DOI: 10.1016/j.scitotenv.2021.147457.

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Jobbágy E G, Jackson R B.

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Wang Chunyan, He Nianpeng, Lv Yuliang.

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Acta Ecologica Sinica, 2016, 36(11): 3176-3188.

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[王春燕, 何念鹏, 吕瑜良.

中国东部森林土壤有机碳组分的纬度格局及其影响因子

生态学报, 2016, 36(11): 3176-3188.]

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Wang Di, Geng Zengchao, She Diao, et al.

Vertical distribution of soil active carbon and soil organic carbon storage under different forest types in the Qinling Mountains

Chinese Journal of Applied Ecology, 2014, 25(6): 1569-1577.

PMID:25223009      [本文引用: 1]

Adopting field investigation and indoor analysis methods, the distribution patterns of soil active carbon and soil carbon storage in the soil profiles of Quercus aliena var. acuteserrata (Matoutan Forest, I), Pinus tabuliformis (II), Pinus armandii (III), pine-oak mixed forest (IV), Picea asperata (V), and Quercus aliena var. acuteserrata (Xinjiashan Forest, VI) of Qinling Mountains were studied in August 2013. The results showed that soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC) decreased with the increase of soil depth along the different forest soil profiles. The SOC and DOC contents of different depths along the soil profiles of P. asperata and pine-oak mixed forest were higher than in the other studied forest soils, and the order of the mean SOC and DOC along the different soil profiles was V > IV > I > II > III > VI. The contents of soil MBC of the different forest soil profiles were 71.25-710.05 mg x kg(-1), with a content sequence of I > V > N > III > II > VI. The content of EOC along the whole soil profile of pine-oak mixed forest had a largest decline, and the order of the mean EOC was IV > V> I > II > III > VI. The sequence of soil organic carbon storage of the 0-60 cm soil layer was V > I >IV > III > VI > II. The MBC, DOC and EOC contents of the different forest soils were significanty correlated to each other. There was significant positive correlation among soil active carbon and TOC, TN. Meanwhile, there was no significant correlation between soil active carbon and other soil basic physicochemical properties.

[王棣, 耿增超, 佘雕, .

秦岭典型林分土壤活性有机碳及碳储量垂直分布特征

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采用野外调查结合室内分析的方法,2013年8月分析了秦岭典型林分锐齿栎(马头滩林区,Ⅰ)、油松(Ⅱ)、华山松(Ⅲ)、松栎混交林(Ⅳ)、云杉(Ⅴ)、锐齿栎(辛家山林区,Ⅵ)土壤剖面上活性有机碳及碳储量的分布规律.结果表明: 研究区各林分土壤的有机碳、微生物生物量碳、水溶性碳、易氧化态碳含量均随着土层深度的增加而不断减小;在整个土壤剖面(0~60 cm)上,云杉和松栎混交林的土壤有机碳和水溶性碳含量明显高于其余林分,不同林分的土壤有机碳和水溶性碳含量的平均值大小均为Ⅴ>Ⅳ>Ⅰ>Ⅱ>Ⅲ>Ⅵ;各林分不同土层的微生物生物量碳在71.25~710.05 mg&middot;kg<sup>-1</sup>,不同林分的土壤微生物生物量碳大小依次为Ⅰ>Ⅴ>Ⅳ>Ⅲ>Ⅱ>Ⅵ;整个土壤剖面上,松栎混交林的土壤易氧化态碳含量降幅最大,不同林分土壤易氧化态碳含量的平均值大小为Ⅳ>Ⅴ>Ⅰ>Ⅱ>Ⅲ>Ⅵ.3种活性有机碳占有机碳的比例在不同林分类型中没有表现出一致的规律性.各林分0~60 cm土层的有机碳储量大小为Ⅴ>Ⅰ>Ⅳ>Ⅲ>Ⅵ>Ⅱ.各林分的土壤微生物生物量碳、水溶性碳、易氧化态碳两两之间均表现为极显著相关,各林分的土壤微生物生物量碳、水溶性碳、易氧化态碳与土壤有机碳、全氮之间的相关性均表现为显著或极显著水平,与碳氮比、pH、土壤水分、土壤容重的相关关系不显著.&nbsp;

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Carbon storage (carbon density; kg C m(2)), concentrations of dissolved organic carbon (DOC) in soil pore water and soil respiration (g C m(2) yr(-1)) were measured in a 35 year old urban lawn soil amended with a surface mulch application of green waste compost and compared to those in two newly created urban soils, manufactured by mixing different volumes of green waste compost with existing soils or soil forming materials. The aim was to determine C storage and calculate annual fluxes in two newly created urban soils compared to an existing urban soil, to establish the potential for maintaining and building carbon storage. In the lawn soil, organic carbon storage was largely limited to the upper 15 cm of the soil, with material below 30 cm consisting of substantial amounts of alkaline building debris augmenting sandstone parent material. Leaching of DOC directly from the surface applied compost mulch amendment was readily mobile within the upper 15 cm of soil beneath, but not to 30 cm depth, indicating limited vertical redistribution of the soluble organic C fraction to the deeper, technic horizons. Only a very small proportion of annual C losses were attributable to DOC export (≤ 0.5%) whilst a much greater amount was accounted for by soil respiration (∼20%). In the two newly created urban soils, ≤ 30% additions of compost mixed with existing soil forming materials trebled C densities from <2 to 6 kg total carbon (TC) m(2), surpassing those of the existing lawn soil (≤ 5 kg TC m(2)). Adding 45% compost served only to reduce bulk density so that C densities did not increase further until >50% compost was applied. Combined increases in soil respiration losses and DOC leaching associated with higher compost application rates suggested that volumes of ∼30% compost were altogether optimal for sustainable C storage whilst minimising annual losses. Thus repeated applications of small amounts, rather than single applications of large amounts of green waste compost could be most effective at maintaining and building C storage in urban soils.Copyright © 2012 Elsevier Ltd. All rights reserved.

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