互花米草入侵对漳江口红树林湿地土壤有机碳官能团特征的影响

红树林对全球气候变化敏感, 近年来不少区域又受互花米草(Spartina alterniflora)入侵的影响, 土壤碳库组成发生显著变化, 然而鲜有从有机碳官能团特征角度出发的关于两群落的研究。为了解在红树林群落与互花米草群落下土壤碳库及其有机碳官能团的特征差异, 在福建省云霄县漳江口红树林自然保护区湿地内由内陆到海岸方向选取3条样带, 每条样带依次选取3个样地: 红树林群落(MC)、秋茄(Kandelia obovata)-互花米草过渡带(TC)和互花米草群落(SC), 每个样地选取3个呈品字形分布的采样点, 分5层采集0-100 cm土壤样品, 分析土壤中的总有机碳(TOC)、颗粒有机碳(POC)以及可溶性有机碳(DOC)特征, 并利用核磁共振波谱法测定表层0-15 cm与深层75-100 cm土壤总有机碳官能团特征, 以空间换时间法研究入侵前后土壤碳库变化特征。结果表明: (1)从MC群落到SC群落, 土壤有机碳库显著减小, 各样地总有机碳与颗粒有机碳含量表现为MC > TC > SC, 并随着土层深度增加而减少, DOC含量没有表现出明显的变化趋势。(2)各植被类型土壤有机碳以烷基碳与烷氧碳为主, 其次是芳香碳与羰基碳, N-烷氧碳与酚基碳含量最少, 其中表层0-15 cm土壤从红树林群落到互花米草群落, 烷基碳与烷氧碳含量呈现增加趋势但不显著, 芳香碳与酚基碳含量显著减少, 其余有机碳组分含量无显著差异。在深层75-100 cm随着植被类型的改变, 土壤有机碳组成结构均无显著差异。(3)在0-15 cm土层, 烷基碳/烷氧碳含量表现为: SC > MC > TC; 芳香度表现为SC最小, MC与TC无显著差异; 疏水碳/亲水碳无显著差异; 脂族碳/芳香碳表现为SC显著大于其他两种植被类型, MC与TC无显著差异。在75-100 cm土层, 各比值无显著差异。综上所述, 红树林群落碳储量显著高于互花米草群落, 受植被的影响, 互花米草群落表层土壤有机碳分解程度显著高于红树林群落, 而红树林群落的土壤有机碳分子结构要比互花米草群落更复杂, 以维持其土壤有机碳的稳定性。因此, 互花米草入侵红树林后可能会加快有机碳的分解, 最终稳定在相对简单的分子结构, 降低土壤碳储量。     

Effects of Spartina alterniflora invasion on soil organic carbon composition of mangrove wetland in Zhangjiang River Estuary

红树林对全球气候变化敏感, 近年来不少区域又受互花米草(Spartina alterniflora)入侵的影响, 土壤碳库组成发生显著变化, 然而鲜有从有机碳官能团特征角度出发的关于两群落的研究。为了解在红树林群落与互花米草群落下土壤碳库及其有机碳官能团的特征差异, 在福建省云霄县漳江口红树林自然保护区湿地内由内陆到海岸方向选取3条样带, 每条样带依次选取3个样地: 红树林群落(MC)、秋茄(Kandelia obovata)-互花米草过渡带(TC)和互花米草群落(SC), 每个样地选取3个呈品字形分布的采样点, 分5层采集0-100 cm土壤样品, 分析土壤中的总有机碳(TOC)、颗粒有机碳(POC)以及可溶性有机碳(DOC)特征, 并利用核磁共振波谱法测定表层0-15 cm与深层75-100 cm土壤总有机碳官能团特征, 以空间换时间法研究入侵前后土壤碳库变化特征。结果表明: (1)从MC群落到SC群落, 土壤有机碳库显著减小, 各样地总有机碳与颗粒有机碳含量表现为MC > TC > SC, 并随着土层深度增加而减少, DOC含量没有表现出明显的变化趋势。(2)各植被类型土壤有机碳以烷基碳与烷氧碳为主, 其次是芳香碳与羰基碳, N-烷氧碳与酚基碳含量最少, 其中表层0-15 cm土壤从红树林群落到互花米草群落, 烷基碳与烷氧碳含量呈现增加趋势但不显著, 芳香碳与酚基碳含量显著减少, 其余有机碳组分含量无显著差异。在深层75-100 cm随着植被类型的改变, 土壤有机碳组成结构均无显著差异。(3)在0-15 cm土层, 烷基碳/烷氧碳含量表现为: SC > MC > TC; 芳香度表现为SC最小, MC与TC无显著差异; 疏水碳/亲水碳无显著差异; 脂族碳/芳香碳表现为SC显著大于其他两种植被类型, MC与TC无显著差异。在75-100 cm土层, 各比值无显著差异。综上所述, 红树林群落碳储量显著高于互花米草群落, 受植被的影响, 互花米草群落表层土壤有机碳分解程度显著高于红树林群落, 而红树林群落的土壤有机碳分子结构要比互花米草群落更复杂, 以维持其土壤有机碳的稳定性。因此, 互花米草入侵红树林后可能会加快有机碳的分解, 最终稳定在相对简单的分子结构, 降低土壤碳储量。     

天然常绿阔叶林改造为板栗林对土壤有机碳库的影响

天然林改造为人工林后,由于植被覆盖类型和经营管理措施发生改变,从而显著影响土壤有机碳库的特征.测定浙江省临安市相邻的天然常绿阔叶林和板栗林(板栗林由常绿阔叶林改造而来,集约经营10年)表层(0～20 cm)和亚表层(20～40 cm)土壤有机碳储量和不同形态活性有机碳库,用固态核磁共振方法分析土壤有机碳的化学结构特征,研究天然常绿阔叶林改造为板栗林对土壤有机碳库的影响.结果表明: 常绿阔叶林改造为板栗林后,土壤表层有机碳储量、水溶性有机碳、热水溶性有机碳、微生物生物量碳和易氧化碳含量分别下降19.7%、34.4%、25.8%、30.4%和25.2%,土壤亚表层的各指标分别下降13.5%、38.4%、19.8%、34.1%和22.2%.土壤表层烷氧碳含量、芳香碳含量以及芳香度显著降低,而烷基碳含量、羰基碳含量以及A/O-A值均显著增加;土壤亚表层烷氧碳含量显著降低,而烷基碳含量和A/O-A值显著增加,而芳香碳含量、羰基碳含量以及芳香度无显著变化.天然常绿阔叶林改造为板栗林并长期集约经营后,土壤有机碳储量和活性有机碳库均显著下降,有机碳的化学结构发生显著变化.     

短期降水控制对鼎湖山南亚热带季风林土壤有机碳及官能团碳组分的影响

区域降水特征变化影响森林土壤有机碳积累。2013年6月—2017年1月,设置年降水量减少50%(DP)、年降水总量不变而降水次数增加(IF)、自然降水(CK)3种降水处理,利用¹³CNMR技术研究鼎湖山南亚热带季风林土壤总有机碳及其官能团碳组分对降水变化的响应。结果表明:DP处理显著提高了20—40 cm土壤易氧化有机碳, IF处理显著提高了0—10cm土壤总有机碳和易氧化有机碳;鼎湖山季风林土壤官能团碳结构以烷氧碳为主;DP处理显著提高了20—40 cm土壤烷氧碳和芳香碳含量, IF处理显著提高了0—10 cm土壤的烷氧碳、芳香碳与羰基碳含量;在土壤总有机碳和易氧化有机碳显著变化的土层中惰性指数趋于降低。短期降水控制增加了鼎湖山南亚热带季风林土壤总有机碳和易氧化有机碳,其官能团组分也发生改变,土壤碳结构稳定性下降,不利于季风林土壤有机碳的积累。     

温度和湿度对高寒草甸凋落物分解的影响

多数研究发现增温增湿加快了凋落物失重率,但对如何影响凋落物分解过程中CO₂和可溶性有机碳（DOC）释放的影响研究较少。通过室内培养设置四个温度梯度（0,5,10和20℃）和两个湿度梯度（25%和40%）对高寒草甸凋落物分解进行了96 d的培养试验。结果表明,总体上高寒草甸凋落物分解速率随着温度和湿度的增加而加快;高湿度条件下凋落物分解释放CO₂总量的敏感性是低湿度的2.3倍左右;湿度变化对DOC淋溶的温度敏感性影响较小。在25%和40%的湿度培养下,CO₂总排放量的温度敏感性分别是DOC总淋溶量的温度敏感性的10和20倍左右,表明未来气候变化情境下凋落物中的有机质分解更多的是以CO₂形式排放到大气中。因此,未来需要更系统的研究不同气候变化情境下凋落物积累与分解、DOC淋溶和土壤碳库的动态变化,从而更好的理解这些生态系统碳循环过程的变化及其对气候变化产生的反馈作用和机制。     

互花米草盐沼土壤有机碳库组分及结构特征

在江苏盐城互花米草(Spartina alterniflora)盐沼建立以下样地:光滩(Mudflat)、互花米草建群1a(S.alterniflora flat 2011)、5a(S.alterniflora flat 2007)、12a(S.alterniflora flat 2000)、23a(S.alterniflora flat 1989)以及碱蓬(Suaeda salsa flat 1989),采集表层土壤样品,分析土壤中的活性有机碳(可溶性有机碳、微生物量碳)特征,并利用核磁共振波谱法测定土壤总有机碳的结构图谱,研究互花米草盐沼土壤有机碳库组分及结构特征。结果表明:(1)互花米草建群后,盐沼表层土壤有机碳含量显著增加(P0.05),在0.82—7.6 g/kg之间,各样地表层土壤有机碳含量为:互花米草滩(5.57 g/kg)碱蓬滩(2.4 g/kg)光滩(1.05 g/kg);可溶性有机碳含量为:互花米草滩(36.08 mg/kg)碱蓬滩(17.43 mg/kg)光滩(6.92 mg/kg);微生物量碳含量为:互花米草滩(52.51 mg/kg)碱蓬滩(18.27 mg/kg)光滩(13.56 mg/kg)。互花米草建群后,土壤中活性碳库含量显著增加(P0.05)。(2)土壤有机碳结构以烷氧碳和芳香碳为主,其中芳香碳的平均比例(35.85%)最高,其次为烷氧碳(32.83%)和羧基碳(20.62%),烷基碳的平均比例(10.36%)最低,其中建群5a的互花米草样地(SAF2007)土壤芳香碳、烷氧碳、烷基碳含量最高,建群23a的互花米草样地(SAF1989)土壤羧基碳含量最高。(3)互花米草盐沼土壤中烷基碳/烷氧碳为:SAF2007(0.44)SSF1989(0.43)SAF2000(0.28)SAF2011(0.27)SAF1989(0.22);疏水碳/亲水碳为:SAF2007(0.97)SSF1989(0.87)SAF2000(0.85)SAF2011(0.83)SAF1989(0.81)。烷基碳/烷氧碳在建群5a后达到最高值0.44,烷基化程度最高;疏水碳/亲水碳达到最高值0.97,土壤碳库稳定性高于其它样地。     

喀斯特11种典型生态恢复树种凋落叶分解及其对土壤碳排放的激发效应

旨在探究喀斯特地区退化生态系统植被恢复树种凋落叶分解过程及其对土壤碳排放的激发效应,为选择合适的树种进行植被恢复提供数据支持。以中国林科院热带林业实验中心大青山石山树木园11种适应性强、耐干旱贫瘠的优良石山树种为研究对象,利用¹³C自然丰度法区分凋落叶和土壤来源CO₂并量化土壤激发效应,比较不同生态恢复树种凋落叶分解及其激发效应的差异,探讨凋落物分解及其激发效应与凋落物性状之间的关联。结果表明:(1)11个生态恢复树种凋落叶在碳相关化学性质(水溶性碳、半纤维素和单宁含量等)、养分含量(磷和镁含量等)及化学计量特征(碳磷比和氮磷比)等方面均表现出较高程度变异。(2)不同生态恢复树种凋落叶分解及其诱导的土壤激发效应具有极显著差异(P<0.001);在整个培养实验期间,11个生态恢复树种凋落叶平均分解了35.3%,其中海南椴分解最快,达到50%,而青冈栎分解最慢,仅分解16.5%。(3)总体上看,凋落叶处理的土壤呼吸速率(5.1 mg C kg^-1 土壤 d^-1)是对照土壤呼吸速率(2.3 mg C kg^-1土壤d^-1)的2.2倍,凋落叶添加显著促进土壤有机碳分解,平均达到37.6%;其中海南椴、割舌树和任豆凋落叶输入则抑制土壤有机碳分解(抑制程度分别为-13.2%、-6.9%和-22.5%),产生负激发效应。(4)凋落叶分解与非结构性碳(r=0.63,P=0.04)和水溶性碳(r=0.91,P<0.001)呈显著正相关,与叶干物质含量(r=0.64,P=0.03)、纤维素(r=0.62,P=0.04)和锰含量(r=-0.63,P=0.04)呈显著负相关。多元回归分析结果表明,水溶性碳、钾和钙含量相结合可以解释生态恢复树种凋落叶分解变异的98%;然而,凋落叶性状与土壤激发效应强度之间并没有显著相关性。从土壤养分归还角度考虑,喀斯特退化生态系统恢复树种可以选择光皮梾木、海南椴、顶果木和降香黄檀等凋落叶分解较快的树种,以促进土壤养分循环和植被恢复;另一方面,从土壤碳固持角度来看,海南椴、任豆和割舌树等凋落叶输入会抑制土壤有机碳分解,从而有利于提高退化生态系统土壤碳封存能力。     

天然灌木林改造成板栗林对土壤碳库和氮库的影响

在浙江省安吉县采集了相邻的天然灌木林和板栗林土壤,分析土壤水溶性碳(WSOC)、微生物生物量碳(MBC)、易氧化碳(ROC)、水溶性有机氮(WSON)和微生物生物量氮(MBN),并利用核磁共振方法分析土壤总有机碳的波谱特征,研究天然灌木林改造成板栗林对土壤碳库和氮库的影响.结果表明： 天然灌木林改造成板栗林后,土壤中的碱解氮、有效磷和速效钾显著增加,而WSOC、MBC、ROC、WSON和MBN显著下降.天然灌木林和板栗林土壤有机碳以烷基碳和烷氧碳为主.天然灌木林改造成板栗林后,土壤有机碳中的烷氧碳和羰基碳比例显著下降,而烷基碳和芳香碳比例以及A/O-A值和芳香度均显著增加.天然灌木林改造成板栗林并长期集约经营后,土壤活性碳库和氮库含量均显著下降,而土壤碳库的稳定性显著增加.     

发酵床猪粪腐解菌群筛选

在浙江省安吉县采集了相邻的天然灌木林和板栗林土壤,分析土壤水溶性碳(WSOC)、微生物生物量碳(MBC)、易氧化碳(ROC)、水溶性有机氮(WSON)和微生物生物量氮(MBN),并利用核磁共振方法分析土壤总有机碳的波谱特征,研究天然灌木林改造成板栗林对土壤碳库和氮库的影响.结果表明： 天然灌木林改造成板栗林后,土壤中的碱解氮、有效磷和速效钾显著增加,而WSOC、MBC、ROC、WSON和MBN显著下降.天然灌木林和板栗林土壤有机碳以烷基碳和烷氧碳为主.天然灌木林改造成板栗林后,土壤有机碳中的烷氧碳和羰基碳比例显著下降,而烷基碳和芳香碳比例以及A/O-A值和芳香度均显著增加.天然灌木林改造成板栗林并长期集约经营后,土壤活性碳库和氮库含量均显著下降,而土壤碳库的稳定性显著增加.     

互花米草凋落物有机碳在不同发育阶段盐沼中的分解动态

采用分解袋法,在江苏盐城新洋港互花米草(Spartina alterniflora)盐沼,根据盐沼发育阶段,从海向陆设置以下5个样地:建群3年互花米草盐沼(SAF2011)、5年互花米草盐沼(SAF2009)、11年互花米草盐沼(SAF2003)、25年互花米草盐沼(SAF1989)以及互花米草-碱蓬(Suaeda salsa)盐沼(SAF-SS),研究互花米草凋落物分解过程中总有机碳、惰性有机碳及活性有机碳动态变化。结果表明:(1)各样地凋落物经过1年的分解,其总有机碳、惰性有机碳、活性有机碳残留率逐月下降,惰性有机碳残留率高于活性有机碳残留率,有机碳各组分分解残留率随盐沼建群时间增加而增加;(2)各样地凋落物有机碳分解速率有明显季节变化,总有机碳、惰性有机碳和活性有机碳分解速率分别在8、1和6月最高,总有机碳和活性有机碳分解速率在10和2月较低,惰性有机碳分解速率在12和2月较低;活性有机碳分解速率高于惰性有机碳;凋落物总有机碳和活性有机碳分解速率均随着互花米草盐沼建群时间的增加而下降,建群3年盐沼中凋落物惰性有机碳分解速率最高;(3)凋落物分解后,总有机碳中惰性有机碳比重增高,活性有机碳比重降低,总有机碳中活性有机碳的分解比例大于惰性有机碳;(4)各样地凋落物总有机碳年分解量分别为0.3167、0.2632、0.2608、0.2380和0.2583 g·g-1,建群3年的盐沼中凋落物有机碳分解量高于其余样地。盐沼发育程度对凋落物的分解动态有显著影响。     

Irrigation,fertilization and initial substrate quality effects on decomposing Loblolly pine litter chemistry

Changes in carbon chemistry (i.e., carbon compound classes such as aromatics, phenolics, etc.) of loblolly pine (Pinus taeda L.) litter were examined during three years of decomposition under factorial combinations of irrigation and fertilization treatments. Cross polarization magic angle spinning ¹³C nuclear magnetic resonance revealed that total carbon and nutrient concentrations correlated strongly with carbohydrate and O-alkyl carbon concentrations but did not relate well with concentrations of lignin, aromatic and phenolic carbon, or with lignin-related decomposition indices. The best correlations to carbon and nutrient concentrations occurred with the C/N (R²=0.86, P > 0.0001) and alkyl/O-alkyl (R²=0.75, P > 0.0001) decomposition indices. In all situations, the carbon chemistry of the decomposing litter followed the general pattern of accumulation of alkyl and carbonyl carbon with a loss of O-alkyl and methoxy carbon. Only small variations in the aromatic and phenolic carbon concentrations were detected. Since lignin is composed primarily of aromatic and phenolic carbons, the observation that there were only small changes in the aromatic and phenolic carbons of the litter is consistent with the general stability of lignin in these ecosystems. Trends in carbon chemistry during decomposition suggested that fertilization accelerated the decomposition process by about 100% as compared with the control plots. Irrigation also accelerated the decomposition process but to a lower extent (about 62% greater than control plots). Initial litter quality, as defined by the litter C/N, did not have a significant effect on the carbon chemistry of the decomposing litter. This study demonstrated that the decomposition mechanisms were not altered by the treatments but there were important changes in the relative chemistry of the decomposing litter which impacted the rate of decomposition.     

Aspects of the chemical structure of soil organic materials as revealed by solid-state13C NMR spectroscopy

Solid-state cross-polarisation/magic-angle-spinning³C nuclear magnetic resonance (CP/MAS¹³C NMR) spectroscopy was used to characterise semi-quantitatively the organic materials contained in particle size and density fractions isolated from five different mineral soils: two Mollisols, two Oxisols and an Andosol. The acquired spectra were analysed to determine the relative proportion of carboxyl, aromatic, O-alkyl and alkyl carbon contained in each fraction. Although similar types of carbon were present in all of the fractions analysed, an influence of both soil type and particle size was evident.The chemical structure of the organic materials contained in the particle size fractions isolated from the Andosol was similar; however, for the Mollisols and Oxisols, the content of O-alkyl, aromatic and alkyl carbon was greatest in the coarse, intermediate and fine fractions, respectively. The compositional differences noted in progressing from the coarser to finer particle size fractions in the Mollisols and Oxisols were consistent with the changes noted in other studies where CP/MAS¹³C NMR was used to monitor the decomposition of natural organic materials. Changes in the C:N ratio of the particle size fractions supported the proposal that the extent of decomposition of the organic materials contained in the fine fractions was greater than that contained in the coarse fractions. The increased content of aromatic and alkyl carbon in the intermediate size fractions could be explained completely by a selective preservation mechanism; however, the further accumulation of alkyl carbon in the clay fractions appeared to result from both a selective preservation and anin situ synthesis.The largest compositional differences noted for the entire organic fraction of the five soils were observed between soil orders. The differences within orders were smaller. The Mollisols and the Andosol were both dominated by O-alkyl carbon but the Andosol had a lower alkyl carbon content. The Oxisols were dominated by both O-alkyl and alkyl carbon.A model describing the oxidative decomposition of plant materials in mineral soils is proposed and used to explain the influence of soil order and particle size on the chemical composition of soil organic matter in terms of its extent of decomposition and bioavailability.     

Cultivation effects on the nature of organic matter in soils and water extracts using CP/MAS 13C NMR spectroscopy

The objective of this study was to examine the chemical structure of the organic matter (SOM) of Oxisols soils in slash and burn agriculture, in relation to its biological properties and soil fertility. The CP/MAS ¹³C technique was used to identify the main structural groups in litter and fine roots as SOM precursors; to identify the changes on the nature of the SOM upon cultivation and the proportion of labile and stable components; and to identify the nature of the organics present in water extracts (DOC). Carbohydrates were the main structural components in litter whereas components such as carbonyl C, carboxyl C,O-alkyl C and alkyl C were more common in SOM. Phenolic C and the degree of aromaticity were similar in litter and SOM. Cultivation resulted in a small decrease in the relative proportion of carbohydrates in SOM, little change in the levels of O-alkyl C and carbonyl C, but an increase in carboxyl C, phenolic C and aromaticity of the SOM. The level of alkyl C in soil was higher than the level of O-alkyl C, indicating the importance of long-chain aliphatics along with lignins in the stabilization of the SOM in Oxisols. The SOM of Mollisols from the Canadian Prairies differed from the Oxisol, with a generally stronger expression of aromatic structures, particularly in a cultivated soil in relation to a native equivalent. Carbohydrate components were the predominant structures in the DOC, indicating their importance in nutrient cycling and vertical translocations in the Oxisol.     

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。     

Temperature response of litter and soil organic matter decomposition is determined by chemical composition of organic material

The global soil carbon pool is approximately three times larger than the contemporary atmospheric pool, therefore even minor changes to its integrity may have major implications for atmospheric CO₂ concentrations. While theory predicts that the chemical composition of organic matter should constitute a master control on the temperature response of its decomposition, this relationship has not yet been fully demonstrated. We used laboratory incubations of forest soil organic matter (SOM) and fresh litter material together with NMR spectroscopy to make this connection between organic chemical composition and temperature sensitivity of decomposition. Temperature response of decomposition in both fresh litter and SOM was directly related to the chemical composition of the constituent organic matter, explaining 90% and 70% of the variance in Q₁₀ in litter and SOM, respectively. The Q₁₀ of litter decreased with increasing proportions of aromatic and O‐aromatic compounds, and increased with increased contents of alkyl‐ and O‐alkyl carbons. In contrast, in SOM, decomposition was affected only by carbonyl compounds. To reveal why a certain group of organic chemical compounds affected the temperature sensitivity of organic matter decomposition in litter and SOM, a more detailed characterization of the ¹³C aromatic region using Heteronuclear Single Quantum Coherence (HSQC) was conducted. The results revealed considerable differences in the aromatic region between litter and SOM. This suggests that the correlation between chemical composition of organic matter and the temperature response of decomposition differed between litter and SOM. The temperature response of soil decomposition processes can thus be described by the chemical composition of its constituent organic matter, this paves the way for improved ecosystem modeling of biosphere feedbacks under a changing climate.     

Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter

Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C₄), Sorghastrum nutans (C₄), and Poa pratensis (C₃) plants that were grown in large open-top chambers under ambient or twice ambient CO₂ and with or without nitrogen fertilization (45 kg N ha⁻¹). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO₂ on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter. However, there was a large difference in characteristics of leaf litter decomposition among the species. Poa leaf litter had a different initial chemistry and decayed more rapidly than C₄ grasses. We conclude that an indirect effect of CO₂ on decomposition and nutrient cycling could occur if CO₂ induces changes in the relative aboveground biomass of the prairie species.     

模拟N沉降下不同林龄马尾松林凋落叶分解-土壤C、N化学计量特征

模拟N沉降对森林生态系统的影响是当今全球变化生态学研究的一个热点问题,土壤碳库对N沉降比较敏感,N沉降增加了凋落叶分解过程中外源N含量,间接影响凋落叶分解的化学过程并改变凋落叶分解速率,因此,研究模拟N沉降下凋落叶分解-土壤C-N关系对预测森林C吸存有重要意义。利用原位分解袋法研究了模拟N沉降下三峡库区不同林龄马尾松林(Pinus massoniana)凋落叶分解过程中凋落叶-土壤C、N化学计量响应及其关系;N沉降水平分对照(CK,0 g m~(-2)a~(-1))、低氮(LN,5 g m~(-2)a~(-1))、中氮(MN,10 g m~(-2)a~(-1))和高氮(HN,15 g m~(-2)a~(-1))。结果表明:分解540 d后,N沉降促进20年生和30年生马尾松林凋落叶分解,46年生马尾松林中仅低氮处理促进凋落叶分解,4种处理均是30年生分解最快,说明同一树种起始N含量低的凋落叶对N沉降呈正响应,N沉降处理促进起始N含量低的凋落叶分解,起始N含量高的凋落叶分解过程中易达到"N饱和"。N沉降抑制20年生和46年生凋落叶C释放(低于对照0.62%—6.69%),促进30年生C释放(高于对照0.28%—5.55%);30年生和46年生林分N固持量均高于对照(高于对照0.15%—21.34%),20年生则低于对照(5.70%—13.87%),说明模拟N沉降处理促进起始C含量低的凋落叶C释放和起始N含量低的凋落叶N固持。N沉降处理下仅30年生马尾松林土壤有机碳较对照增加,且土壤有机质与凋落叶C、N和分解速率呈正相关,与凋落叶C/N比呈显著负相关;土壤总氮与凋落叶分解速率、凋落叶N含量呈正相关,土壤有机碳/总氮比与凋落叶C、N含量呈正相关;对照处理中凋落叶分解指标对土壤养分影响顺序是分解速率凋落物C含量凋落物C/N比凋落物N含量,低、中、高氮处理中则是凋落物C含量分解速率凋落物N含量凋落物C/N比。研究表明低土壤养分含量马尾松林对N沉降呈正响应,N沉降促进低土壤养分马尾松林凋落叶分解并提高土壤肥力;凋落叶质量和土壤养分含量低的生态系统土壤C对N沉降响应更显著。     

Sensitivity of organic matter decomposition to warming varies with its quality

The relationship between organic matter (OM) lability and temperature sensitivity is disputed, with recent observations suggesting that responses of relatively more resistant OM to increased temperature could be greater than, equivalent to, or less than responses of relatively more labile OM. This lack of clear understanding limits the ability to forecast carbon (C) cycle responses to temperature changes. Here, we derive a novel approach (denoted Q_10?q) that accounts for changes in OM quality during decomposition and use it to analyze data from three independent sources. Results from new laboratory soil incubations (labile Q_10?q=2.1 ± 0.2; more resistant Q_10?q=3.8 ± 0.3) and reanalysis of data from other soil incubations reported in the literature (labile Q_10?q=2.3; more resistant Q_10?q=3.3) demonstrate that temperature sensitivity of soil OM decomposition increases with decreasing soil OM lability. Analysis of data from a cross‐site, field litter bag decomposition study (labile Q_10?q=3.3 ± 0.2; resistant Q_10?q=4.9 ± 0.2) shows that litter OM follows the same pattern, with greater temperature sensitivity for more resistant litter OM. Furthermore, the initial response of cultivated soils, presumably containing less labile soil OM (Q_10?q=2.4 ± 0.3) was greater than that for undisturbed grassland soils (Q_10?q=1.7 ± 0.1). Soil C losses estimated using this approach will differ from previous estimates as a function of the magnitude of the temperature increase and the proportion of whole soil OM comprised of compounds sensitive to temperature over that temperature range. It is likely that increased temperature has already prompted release of significant amounts of C to the atmosphere as CO₂. Our results indicate that future losses of litter and soil C may be even greater than previously supposed.     

鄱阳湖湿地优势植物枯落物的分解速率及碳、氮、磷释放动态特征

植物枯落物分解对生态系统碳通量和养分循环有至关重要的作用,这一过程主要由3个相互作用的因素决定,即化学(枯落物理化特性)、物理(气候和环境)以及生物(参与枯落物分解的微生物和无脊椎动物)因素。在气候和立地环境条件相同的情况下,枯落物质量是制约分解的内在因素。在鄱阳湖湿地开展了野外定位观测实验,采用分解袋技术研究了鄱阳湖湿地优势植物芦苇(Phragmite)、南荻(Triarrhena lutarioriparia)和薹草(Carex.cinerascens Kükenth)枯落物分解速率及碳(C)、氮(N)、磷(P)元素释放动态特的征差异性。结果表明,在0—150 d内三种植物枯落物的干物质分解速率和残留率以及碳相对归还指数(CRRI)、氮相对归还指数(NRRI)、磷相对归还指数(PRRI)差异性都极其显著。在0—150 d内分解速率都是芦苇的最大,薹草的次之,南荻最小。分解进行150 d后,芦苇、南荻和薹草枯落物干物质残留率依次约为56.57%、67.99%和60.88%,CRRI依次约为57.44%、34.58%和41.75%,NRRI依次约为50.71%、-22.66%、和23....     

Abundance patterns of soil micro-arthropods at aPinus pumila scrub in an alpine range of central Japan

Seasonal changes in abundances of major soil micro-arthropods were assessed at aPinus pumila scrub in an alpine range of central Japan during a period with no snow coverage. The total abundance showed a peak in late August, reaching no less than 140 000 m⁻², which was comparable to that in an evergreen coniferous plantation in the cool-temperate zone. Collembola was the most dominant group of soil micro-arthropods, comprising about 50% of the total, followed by oribatid mites (Acari [O]) occupying 20%. Annual mean air temperature was no more than 2.1 °C and the daily fluctuation in temperature was less in soil layers. The thickness of the A₀ layer reached 9–10 cm and soil organic matter accumulation was estimated to be 45–58 ton dry weight ha⁻¹. The large amount of litterfall and organic matter accumulation in the soil, comparable to those of sub-alpine evergreen coniferous forests, and a lower decomposition rate due to severe environmental conditions, suggest the relative importance of litter processing by soil micro-arthropods such as Collembola and Acari, especially in alpine regions.