Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U-Th series and REEs

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 mm inland. Pedogenic carbonates occur in the MAR range of 500-1200 mm. In the semi-arid zone (MAR: 500-900 mm), carbonates occur (i) as rhick hardpan calcretes on pediment slopes and (ii) as nodular horizons in polygenic black soils (i.e. vertisols). In the sub-humid zone (MAR: 900-1500 mm), pedogenic carbonates are disseminated in the black soil matrices either as loose, irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size. They also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate-cemented lumps of centimetric to decimetric size. Chemical and isotopic (Sr-87/Sr-86) compositions of the carbonate fraction were determined after leaching with 0.25 N HCl. The corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed. The trend defined by the Sr-87/Sr-86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition. Considering the residual fraction of each sample as the most likely lithogenic source of Ca in carbonates, it is estimated that from 24% to 82% (55% on average) of Ca is derived from local bedrock weathering, leading to a consumption of an equivalent proportion of atmospheric CO2. These values indicate that climatic conditions were humid enough to allow silicate weathering: MAR at the time of carbonate formation likely ranged from 400 to 700 mm, which is 2- to 3-fold less than the current MAR at these locations. The Sr, U and Mg contents and the (U-234/U-238) activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation. The relatively high concentrations of Sr, U and Mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite, possibly due to a better confinement of the pore waters which is supported by their high (U-234/U-238) signatures, and/or to higher content of dissolved carbonates in the pore waters. The occurrence of Ce, Mn and Fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation. The carbonate ages determined by the U-Th method range from 1.33 +/- 0.84 kyr to 7.5 +/- 2.7 kyr and to a cluster of five ages around 20 kyr, i.e. the Last Glacial Maximum period. The young occurrences are only located in the black soils, which therefore constitute sensitive environments for trapping and retaining atmospheric CO2 even on short time scales. The maximum age of carbonates depends on their location in the climatic gradient: from about 20 kyr for centimetric nodules at Mule Hole (MAR = 1100 mm/yr) to 200 kyr for the calcrete at Gundlupet (MAR = 700 mm/yr, Durand et al., 2007). The intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils. (C) 2010 Elsevier Ltd. All rights reserved.

Biotic vs. Abiotic Control of Decomposition: A Comparison of the Effects of Simulated Extinctions and Changes in Temperature

The loss of species is known to have significant effects on ecosystem functioning, but only recently has it been recognized that species loss might rival the effects of other forms of environmental change on ecosystem processes. There is a need for experimental studies that explicitly manipulate species richness and environmental factors concurrently to determine their relative impacts on key ecosystem processes such as plant litter decomposition. It is crucial to understand what factors affect the rate of plant litter decomposition and the relative magnitude of such effects because the rate at which plant litter is lost and transformed to other forms of organic and inorganic carbon determines the capacity for carbon storage in ecosystems and the rate at which greenhouse gasses such as carbon dioxide are outgassed. Here we compared how an increase in water temperature of 5 degrees C and loss of detritivorous invertebrate and plant litter species affect decomposition rates in a laboratory experiment simulating stream conditions. Like some prior studies, we found that species identity, rather than species richness per se, is a key driver of decomposition, but additionally we showed that the loss of particular species can equal or exceed temperature change in its impact on decomposition. Our results indicate that the loss of particular species can be as important a driver of decomposition as substantial temperature change, but also that predicting the relative consequences of species loss and other forms of environmental change on decomposition requires knowledge of assemblages and their constituent species' ecology and ecophysiology.

Biotic vs. Abiotic Control of Decomposition: A Comparison of the Effects of Simulated Extinctions and Changes in Temperature

The loss of species is known to have significant effects on ecosystem functioning, but only recently has it been recognized that species loss might rival the effects of other forms of environmental change on ecosystem processes. There is a need for experimental studies that explicitly manipulate species richness and environmental factors concurrently to determine their relative impacts on key ecosystem processes such as plant litter decomposition. It is crucial to understand what factors affect the rate of plant litter decomposition and the relative magnitude of such effects because the rate at which plant litter is lost and transformed to other forms of organic and inorganic carbon determines the capacity for carbon storage in ecosystems and the rate at which greenhouse gasses such as carbon dioxide are outgassed. Here we compared how an increase in water temperature of 5 degrees C and loss of detritivorous invertebrate and plant litter species affect decomposition rates in a laboratory experiment simulating stream conditions. Like some prior studies, we found that species identity, rather than species richness per se, is a key driver of decomposition, but additionally we showed that the loss of particular species can equal or exceed temperature change in its impact on decomposition. Our results indicate that the loss of particular species can be as important a driver of decomposition as substantial temperature change, but also that predicting the relative consequences of species loss and other forms of environmental change on decomposition requires knowledge of assemblages and their constituent species' ecology and ecophysiology

Análisis biofísico y social de los servicios ecosistémicos de la reseva de Biosfera de Urdaibai

[es]Conocer la distribución de la biodiversidad y de los servicios de los ecosistemas (SE), así como la demanda por parte de la población es la base para realizar una gestión sostenible en la Reserva de la Biosfera de Urdaibai. En este trabajo se analizan los valores ecológicos de la biodiversidad y de cinco SE (regulación del ciclo hidrológico, almacenamiento de carbono, polinización, uso recreativo y disfrute estético del paisaje) en las seis unidades ambientales/ecosistemas presentes en la zona (encinar, marisma, plantaciones forestales, fondos y prados de valles, bosques naturales y hábitat costeros). Se compara esta evaluación con la percepción que la población tiene de dichos servicios y con la demanda que manifiestan los habitantes/usuarios de la reserva. De los resultados obtenidos se concluye que existe una gran demanda de los servicios de abastecimiento y regulación por parte de la población; sin embargo, la población percibe que Urdaibai ofrece principalmente servicios culturales. También se observa que la población no discrimina las diferentes contribuciones que los diferentes ecosistemas realizan a los servicios y que en general las valoraciones de los servicios suministrados asignadas por la población a los diferentes ecosistemas son superiores a las obtenidas con los datos biofísicos, con la excepción de los bosques los cuales son infravalorados. Castellano.

我国主要森林生态系统碳循环研究

作者广泛收集了近二十年来我国森林生物量生产力、土壤剖面有机质含量、凋落物现存量、年凋落量、凋落物分解等方面的研究资料，以及国内外土壤呼吸的相关资料，把森林作为一个自然的生态系统，从生物自身循环的角度系统地研究了我国森林在全球变化中的地位和作用提供了基础数据。主要得到以下几个方面的研究结果： 1、基于上述资料，采用林业部规划院1989-1993年的最新统计的我国不同森林类型的面积（不包括经济林和竹林，台湾省未计入），估算了我国森林生态系统总碳贮量。森林生态系统有机碳库包括植被、土壤和凋落物层三个分室，我国主要森林生态系统的碳贮量为281.16 * 10~8吨，其中植被碳库为62.00 * 10~8吨，占总碳库的22.2%;土壤碳库为210.23 * 10~8吨，占总碳库的74.6%;凋落物层的碳贮量为8.92 * 10~8吨，占总量的3.2%。我国森林生态系统碳贮量由大到小的顺序是：落叶阔叶林、暖性针叶林、常绿和常绿落叶阔叶林、云冷杉林、落叶松林、硬叶常绿阔叶林、温性针叶林、针叶和针阔混交林、阔叶红松林、热带林、樟子松林，前5类森林碳贮量占总贮量的87%，是我国森林主要的碳库。 2、分析了我国森林生态系统各个分室的碳密度特点。我国森林生态系统的平均碳密度是258.83t/ha，基本趋势是随纬度的增加而增加。其中植被的平均碳密度是57.07t/ha，随纬度的增加而减小;土壤碳密度约是植被碳密度3.4倍，其区域特点与植被碳密度呈相反趋势，随纬度升高而增加，作者根据所选117个样本建立了土壤有机碳密度与水热因子的模拟方程;凋落物层平均碳密度是8.21t/ha，随水热因子的改善而减小。这些结果为研制森林生态系统仿真模型提供了基础。 3、分析了我国森林生态系统的主要碳平衡通量，对中国森林生态系统的碳源与碳汇作初步评价，为减缓我国二氧化碳排放提供理论基础。结果表明我国森林生态系统在与大气的气体交换中表现为碳汇，年通量为4.80 * 10~8吨C/年。基本规律是随纬度的升高，即从热带向寒带，碳汇功能下降，这取决于系统碳收支的各个通量之间的动态平衡;阔叶林的固碳能力大于针叶林。 4、初步评价了我国森林生态系统在碳循环中的作用。我国生物物质燃烧、化石燃料燃烧、人口呼吸每所释放的总碳量为9.87 * 10~8吨/年，而我国森林生态系统可以吸收其中的48.7%。

中国主要森林生态系统碳储量和碳收支评估

森林作为陆地生态系统中主要的植被类型在全球碳循环研究中有着十分重要的作用，而森林资源清样调查资料以其系统性、科学性、连续性等优点在森林生态系统碳循环研究中具有十分重要的地位。本研究以中国主要森林植被类型为研究对象，基于中国森林资源清样调查资料（FID），采用建立的生物气候生产力模型和反映林龄和蓄积量共同影响的生产力回归模型分别估计了中国油松林和主要造林树种的生产力;利用改进的材积源生物量法估算了中国主要森林植被类型的碳储量;并基于多元线性回归方法和因子分析法探讨了林业用地以及气候因子对中国森林植被碳储量的影响;同时，结合生物地球化学循环模型CENTURY模型评估了中国森林生态系统的碳收支。主要研究结果如下： 1建立了中国油松林生物气候生产力模型NPPa=［0.331n（V／A）+0.18］*3000（1-e-0.00096‘哪，根据油松林的森林资源清样调查资料和气候资料估算的中国油松林生产力平均为7.82Mg•ha-1•yr-1，其变化幅度为3.32-11.87Mg•ha-1•yr-1，其分布表现为南高北低的趋势。生产力较高的区域主要分布在东部和南部（四川、湖北、河南、辽宁等省），均大于7.7Mg•ha-1•yr-1;生产力较低的区域主要分布在北部和西部较为干旱的区域（内蒙古），NPP均低于5.5Mg•ha-1•yr-1：油松林集中分布区（陕西、山西）生产力处于中等水平，在5.5-7.7Mg•ha-1•yr-1之间。 2基于森林资源清样调查资料评估了中国五种主要造林树种（落叶松Larix，油松Pinusstabulaeformis，马尾松Pinusmassoniana，杉木Cunninghamialanceolata，杨树Populus）的生产力，分别为8.43、5.75、4.42、4.41、7.33Mg•ha-1•yr-1，低于世界平均生产力水平，主要原因可能是这五种造林树种大都处于未成熟阶段，表明中国造林树种在提高中国森林生态系统的固碳能力方面有很大的潜力。 3基于两次（第三次和第四次）森林资源清查资料和改进的材积源生物量法评估了中国森林的碳储量，分别为3.48和3.78PgC（1Pg＝1015g）。 基于多元线性回归模型探讨了林业用地变化对森林植被碳储量的影响。分析表明：在森林平均林龄减小的情况下，森林植被碳储量有增加的趋势;而森林碳储量随森林面积的增加而增加。当平均林龄增加10年，全国森林面积增加1*104ha时，全国森林植被的碳储量将增加54.51Tg（1Tg＝1012g），表明我国森林植被碳储量取决于自然和人为因素共同作用。 采用因子分析方法探讨了气候变化对森林植被碳储量的影响，分析表明：气温是森林植被碳储量的主要限制因子。当气温升高时，森林植被碳储量有降低的趋势;降水与森林植被碳储量呈正相关，随降水的增加森林植被碳储量增加。在年均温升高4℃，年降水量增加10％;年均温升高4℃，年降水量不变;年均温升高4℃，年降水量减少10％三种气候变化情景下，我国森林植被碳储量的增加量分别为：9.19Tg、6.67Tg和4.15Tg。 4基于生物地球化学循环模型模拟的中国森林生态系统的碳收支为0.17PgC，中国森林表现为一个巨大的碳汇。其中，西南地区森林碳收支占44％，华东及西北地区的森林碳收支总和不足14%。

长白山自然保护区北坡森林结构、植物多样性与碳储量40余年的变化

长白山自然保护区始建于1960年，位于北坡的红松针阔叶混交林森林生态系统是我国东北地区典型温带地带性森林植被之一，面临着全球气候变化和人类干扰的双重影响。 本研究以间隔43年的野外调查数据为基础，对1963年和2006年的长白山自然保护区北坡海拔800~1700m的森林植物群落进行对比分析，得到该区域的森林结构、植物多样性与碳储量的变化特点，讨论森林动态变化与人类活动、气候变化的关系，评价长白山自然保护区的保护效果： 对长白山北坡森林沿海拔梯度的森林结构和植物多样性的分析表明：群落的整体空间格局保存完好，植物种类变化不大，乔木层的建群种的种类基本不变，植物多样性与海拔高度呈负相关关系;林下层植物多样性受小环境影响，与海拔高度无明显相关。 以红松（Pinus koraiensis）针阔混交林、红松针叶混交林和云冷杉暗针叶林三种类型为单元分别研究各森林类型的多样性变化：α多样测度选择物种丰富度、Shannon-Wiener和Pielou均匀度指数，较好体现了样地内发生的多样性变化，灌木层和草本层多样性明显下降，一些稀有种和药用物种消失，红松等原优势物种有衰退趋势，阔叶树比例增大;β多样性测度选取Cody指数，体现出海拔梯度上的植被空间格局细节变化，演替层特别是阔叶树的物种更替变化有向高海拔移动的趋势。 对森林生态系统各层次碳储量进行估算：乔木层和灌木层采用维量法，对灌木层自建生长回归方程;草本层、枯枝落叶层采取收获法;植物细根采取根钻法;土壤采取土壤深度加权法。碳密度估算结果都与前人研究结果相似。各类型植被碳库总碳密度都达到170 t/hm2，远远高于国内平均森林植被碳库密度值44.9 t/hm2。 乔木层43年来的碳储量变化都无显著性差异，但仍表现出：阔叶树种碳储量上升，特别在高海拔类型这种变化更加明显;针叶树种碳储量在暗针叶林内大幅下降;树干的碳库分配比例都有所减少，表明植被碳库正存在向不稳定性方向发展的趋势。针阔混交林和暗针叶林的土壤碳储量，与植被碳库出现相反的变化趋势，整体碳库保持在一个相对平衡的状态。 推测造成这种变化的原因是：禁止砍伐等保护措施的实施，基本保存了乔木层垂直分布格局，而气候变暖使阔叶树种比例大幅增加，采集松籽等人类生产及旅游活动对林下层植被影响破坏较大。提议加强保护区内管理力度和规划，以减缓长白山北坡森林群落的不稳定变化趋势。

暖温带地区典型森林群落叶面积指数、生产力和树木年轮特征的分析

以辽东栎(Quercus liaotungensis)为主的落叶阔叶林、华北落叶松林(Larix principisrupprechtii)和油松(Pinus tabulaeformis)林是我国暖温带地区具有代表性的森林群落类型。本研究：1）应用国内外流行的半球图方法，通过对这三种森林群落叶面积指数和林冠开阔度的测定和综合比较，分析了叶面积指数和林冠开阔度的季节动态，揭示了暖温带地区不同类型森林群落叶面积指数和林冠开阔度的特征;2）基于野外调查的样地资料，利用维量分析法估算了中国科学院北京森林生态系统定位研究站三种森林群落乔木层的生物量和生产力，并揭示生产力和叶面积指数之间的相关关系;3）利用油松森林群落和落叶松森林群落采集树芯作为研究对象，用树木年轮学方法，建立相应的年表，联系气候资料进行相关分析，揭示树木生长的限制因子。 研究结果表明：1）落叶阔叶林(优势种为：辽东栎、棘皮桦(Betula dahurica)、五角枫(Acer mono))和华北落叶松林两种落叶森林群落的叶面积指数值均随生长季的到来而呈现增长的趋势，最大值出现在8月;林冠开阔度值随着生长季的到来而下降，最大值出现在11月。落叶阔叶林的叶面积指数和林冠开阔度的季节动态较之华北落叶松林明显。油松是常绿树种，其群落叶面积指数和林冠开阔度的变化程度均不明显，但林冠开阔度的变化趋势也是与叶面积指数的变化趋势相反。通过计算得出叶面积指数和林冠开阔度相关显著，并且呈现指数回归的关系。2） 油松、落叶松、落叶阔叶林三种森林群落乔木层的生物量和生产力分别为93.59 t•hm-2、119.36 t•hm-2 、169.94 t•hm-2和4.02 t•hm-2•a-1、5.58 t•hm-2•a-1、7.04 t•hm-2•a-1;三种森林群落乔木层生产力和叶面积指数回归曲线分析显示，生产力和叶面积指数呈现线性正相关关系。3）油松和落叶松生长与气候因子相关分析结果显示，两种群落树木的生长受当地降水和气温的影响，油松与5月份的温度显著负相关，落叶松与2月份和5月份的降水显著正相关。 以上研究结果为以遥感途径获取暖温带地区叶面积指数提供了地面校正依据，为研究该地区利用LAI估算生产力以及利用遥感途径得到的NDVI测定生产力、研究气候因子对树木年轮宽度形成的影响，以及进一步对该地区林分、景观和区域尺度上碳、水、通量等方面的模拟提供了基础数据。

退耕草地演替过程中的碳储量变化

退耕草地演替的研究对了解现有退耕草地的变化趋势有重要意义,也可以为退耕地的植被恢复提供科学依据。本研究采用以空间代替时间的方法,对处于不同演替时间阶段退耕草地的土壤碳储量以及植被的地上部分与根系生物碳储量变化进行了研究,结果表明,退耕草地演替过程中,地上部分生物碳储量呈阶梯式上升趋势,演替初期地上部分生物碳储量先降后升,并在演替的22~32年,保持相对平稳,之后在演替的40~60年,达到第2个相对平稳的阶段。根系生物碳储量也呈分阶段的阶梯式上升趋势,但第1个相对平稳的阶段出现在演替的第12~28年,在演替的第32~60年出现第2个相对平稳的阶段。退耕草地的土壤碳储量在退耕演替的初期下降,且在演替的第1~12年一直小于农地,在演替的第15年之后,土壤碳储量逐步上升。在0~150 cm的不同土层中,土壤有机碳含量以0~15 cm最高,在演替的1~12年,各土层有机碳含量均小于农地,之后在演替的第15~60年,各土层土壤有机碳含量均随演替时间的增加有所增加,且0~50 cm表层土壤有机碳含量在演替第34~60年迅速积累,增幅较大。在演替初期,草地地上部分生物碳储量、根系生物碳储量和土壤碳储量较演替第1年均表现为下降...

不同放牧强度下高山草甸生态系统碳氮分布格局和循环过程研究

本研究针对川西北高山草甸缺乏科学管理，过度放牧导致草场退化，并由此引发的一系列生态环境问题，选取红原县瓦切乡1996 年草地承包后形成的四个放牧强度草场，即不放牧、轻度（1.2 头牦牛hm-1）、中度（2.0 头牦牛hm-1）和重度放牧（2.9 头牦牛hm-1），作为研究对象，研究了不同放牧强度对草地植物-土壤系统中碳、氮这两个最基本物质的分布格局和循环过程的影响，并探讨了放牧干扰下高山草甸生态系统的管理。 1．放牧对草地植物群落物种组成，尤其是优势种，产生了明显的影响。不放牧、轻度、中度和重度放牧草地群落物种数分别为22，23，26，20 种，群落盖度分别是不放牧96.2%＞中度93.6%＞轻度89.7%＞重度73.6%。随放牧强度的增加， 原植物群落中的优势种垂穗鹅冠草（ Roegneria nutans ）、发草（Deschampsia caespitosa）和垂穗披碱草（Elymus nutans）等禾草逐渐被莎草科的川嵩草（Kobresia setchwanensis）和高山嵩草（Kobresia pygmaea）所取代成为优势种。同时，随放牧强度的增加，高原毛茛（Ranunculus brotherusii）、狼毒（Stellera chamaejasme）、鹅绒委陵菜（Potentilla anserina）和车前（Plantagodepressa）等杂类草的数量也随之增加。 2．生长季6～9 月份，草地植物地上和地下生物量（0～30cm）都是从6 月份开始增长，8 月份达到最高值，9 月份开始下降。每个月份，通常地上生物量以不放牧为最高，重度放牧总是显著小于不放牧；地下生物量随放牧强度的增加表现为增加的趋势，通常重度和中度放牧显著高于不放牧和轻度放牧草地。不放牧、轻度、中度和重度放牧草地6～9 月份4 个月的植物总生物量平均值分别是1543、1622、2295 和2449 g m-2，但随放牧强度的增加越来越来多的生物量被分配到了地下部分，地下生物量占总生物量比例的大小顺序分别是重度88%＞中度82%＞轻度76%＞不放牧69%。生物量这种变化主要是由于放牧使得群落优势种发生改变而引起的，其分配比例的变化体现了草地植物对放牧干扰的适应策略。 3．植物碳氮贮量的季节变化类似与生物量的变化。每个月份，不同放牧强度间植物地上碳氮的贮量有所不同，一般重度放牧会显著减少植物地上碳氮贮量。植物根系(0～30cm)碳氮贮量随放牧强度的增加表现为增加的趋势，通常重度和中度放牧显著高于不放牧和轻度放牧草地。不放牧、轻度、中度和重度放牧草地6～9 月份4 个月的植物总碳平均值分别是547、586、847 和909 g m-2，根系碳贮量占植物总碳的比例大小顺序分别是重度88%＞中度82%＞轻度76%＞不放牧69%；放牧、轻度、中度和重度放牧草地6～9 月份4 个月的植物总氮平均值分别是17、17、23 和26 g m-2，根系氮贮量占植物总氮的比例大小顺序分别是重度79%＞轻度71%＞中度70%＞不放牧65%。 4. 土壤有机碳贮量（0～30cm）的季节变化表现为7 月份略有下降，8 月开始增加，9 月份达到的最大值。土壤氮贮量的季节变化表现为随季节的推移逐渐增加的趋势。增加的放牧强度不同程度的增加土壤有机碳氮的贮量。不放牧、轻度、中度和重度放牧6～9 月份4 个月的土壤有机碳贮量的平均值分别是9.72、10.36、10.62 和11.74 kg m-2，土壤氮贮量分别为1.45、1.56、1.66 和1.83 kg m-2。土壤中有机碳（氮）的贮量都占到了植物-土壤系统有机碳（氮）的90%以上，但不同放牧强度之间的差异不明显。 5. 土壤氮的总硝化和反硝化，温室气体N2O 和CO2 的释放率的季节变化表现为从6 月份开始增加，7 月份达到最大值，8 月份开始下降，9 月份降为最小值。增加的放牧强度趋向于增加土壤氮的总硝化和反硝化作用，温室气体N2O和CO2 的释放率，通常情况下，中度放牧和重度放牧显著地加强了这些过程。 6．垂穗鹅冠草（Roegneria nutans）和川嵩草（Kobresia setchwanensis）凋落物在不同放牧强度下经过1 年的分解，两种凋落物的失重率及其碳氮的损失率3都随放牧增加表现为增加的趋势。在同一放牧强度下，川嵩草凋落物的失重率和碳氮的损失率都高于垂穗鹅冠草凋落物。 7. 尽管重度放牧显著增加了土壤碳氮的贮量，但同时也显著降低了植被群落盖度，降低了植物地上生物量，因此，久而久之会减少植物向土壤中的碳氮归还率；与不放牧和轻度放牧相比，重度放牧又显著增加了土壤CO2 和NO2 的排放量，这是草地生态系统碳氮损失的重要途径。由此可见，对于这些地处青藏高原的非常脆弱的高山草甸生态系统，长期重度放牧不仅导致植物生产力降低，而且将导致草地生态系统退化，甚至造成土壤中碳氮含量减少。 Long-term overgrazing has resulted in considerable deterioration in alpine meadowof the northwest Sichan Province. In order to explore management strategies for thesustainability of these alpine meadows, we selected four grasslands with differentgrazing intensity (no grazing-NG: 0, light grazing-LG: 1.2, moderate grazing-MG: 2.0,and heavy grazing-HG: 2.9 yaks ha-1) to evaluate carbon, nitrogen pools and cyclingprocesses within the plant-soil system in Waqie Village, Hongyuan County, Sichuan Province. 1. Grazing obviously changed the plant species composition, especially ondominant plant species. Total number of species is 22, 23, 26, and 20 for NG, LG, MGand HG, respectively. Vegetation coverage under different grazing intensity ranked inthe order of 96.2% for HG＞93.6% for MG＞89.7% for LG＞73.6% for NG. Thedominator of HG community shifted from grasses-Roegneria nutans andDeschampsia caespitosa dominated in the NG and LG sites into sedges-Kobresiapygmaea and K. setchwanensis. At the same time, with the increase of grazingintensity, the numbers of forbs, such as Ranunculus brotherusii, Stellera chamaejasme,Potentilla anserine and Plantago depressa, increased with grazing intensity. 2. Over the growing season, aboveground and belowground biomass showed a 5single peak pattern with the highest biomass in August. For each month, abovegroundbiomass usually was the highest in the NG site and lowest in the HG site.Belowground biomass showed a trend of increase as grazing intensity increased and itwas significantly higher in the HG and MG site than in the NG and LG sites. Totalplant biomass averaged over the growing season is 1543, 1622, 2295 and 2449 g m-2for NG, LG, MG and HG, respectively. The proportion of biomass to total plantbiomass for NG, LG, MG and HG is 88%, 82%, 76% and 69%, respectively. Higherallocation ratio for is an adaptive response of plant to grazing. 3. Carbon and nitrogen storage in plant components followed the similar seasonalpatterns as their biomass under different grazing intensities. Generally, heavy grazingsignificantly decreases aboveground biomass carbon and nitrogen compared to nograzing. Carbon and nitrogen storage in root tended to increase as grazing increasedand they are significantly higher in the HG and MG sites compared to the LG and NGsite. Total Carbon storage in plant system averaged over the growing season is 547,586, 847 and 909 g m-2 for NG, LG, MG and HG, respectively, while 17, 17, 23 and 26g m-2 for nitrogen. The proportion of carbon storage in root to total plant carbon forNG, LG, MG and HG is 88%, 82%, 76%, 69%, respectively, while 65%, 71%, 70%and 79% for nitrogen. 4. Carbon storage in soil (0-30cm) decreased slightly in July, then increased inAugust and peaked in September. Nitrogen storage in soil tended to increase withseason and grazing intensity. Total Carbon storage in soil averaged over the growingseason is 9.72, 10.36, 10.62 and11.74 kg m-2 for NG, LG, MG and HG, respectively,while 1.45, 1.56, 1.66 and 1.83 for nitrogen. The proportion of carbon (nitrogen)storage in soil to plant-soil system carbon (nitrogen) storage for NG, LG, MG and HGis more than 90%, which is not markedly different among different grazing intensities. 5. Gross nitrification, denitrification, CO2 and N2O flux rates in soil increasedfrom June to July and then declined until September, all of which tended to increasewith the increase of grazing intensity. Generally, heavy and moderate grazing intensitysignificantly enhanced these process compared to no and light grazing intensity. 6. After decomposing in situ for a year, relative weight, carbon and nitrogen loss in the litter of Roegneria nutans and Kobresia setchwanensis tended to increase asgrazing intensity increased. Under the same grazing intensity, relative weight, carbonand nitrogen loss in the litter of Kobresia setchwanensis were higher than these in thelitter of Roegneria nutans. 7. Although heavy grazing intensity resulted in higher levels of carbon andnitrogen in plant and soil, it decreased vegetation coverage and aboveground biomass,which are undesirable for livestock production and sustainable grassland development.What is more, heavy grazing could also introduce potential carbon and nitrogen lossvia increasing CO2 and N2O emission into the atmosphere. Grazing at moderateintensity resulted in a plant community dominated by forage grasses with highaboveground biomass productivity and N content. The alpine meadow ecosystems inTibetan Plateau are very fragile and evolve under increasing grazing intensity by largeherbivores; therefore, deterioration of the plant-soil system, and possible declines insoil C and N, are potential without proper management in the future.

黄土高原淤地坝土壤性质剖面变化规律及其功能探讨

为分析淤地坝土壤性质的剖面变化规律及其在非点源污染工程治理方面的可能性,采用经典统计学方法研究了黄土高原典型淤地坝土壤性质在5.20 m剖面上的变化规律,并探讨了淤地坝作为碳储存库以及养分富集库的独特功能.结果表明,①坝前土壤剖面容重、砂粒含量低于坝尾,而土壤含水率、有机碳、粘粒、粉粒、速效磷、硝态氮以及铵态氮均大于坝尾;容重随剖面的变异情况为弱变异性,其余指标为中等变异性;除坝前砂粒含量和坝尾土壤含水率外,其余指标均呈正态分布;②坝前和坝尾剖面土壤含水率随土层深度的增加均呈锯齿型变化趋势,在剖面上的分布表现为波动型;土壤有机碳、速效磷、铵态氮随剖面的变化规律与土壤水分的趋势相同;③除坝尾容重与硝态氮、铵态氮及速效磷与铵态氮的相关性未达到显著水平外,土壤含水率、有机碳、容重、粘粒、粉粒、砂粒、速效磷、硝态氮以及铵态氮之间的相关性均达到了显著水平(p<0.05),并且坝前与坝尾剖面土壤各个性质之间所表现的正相关性或负相关性是一致的;④淤地坝作为黄土高原的一个重要碳储存库,坝前有机碳储量高于坝尾,且坝前在400~520 cm储量最高,坝尾在0~100 cm储量最高;⑤淤地坝对速效养分具有富集效应,坝前储量大于坝尾...

Depression of net ecosystem CO2 exchange in semi-arid Leymus chinensis steppe and alpine shrub

Uptake and release of carbon in grassland ecosystems is very critical to the global carbon balance and carbon storage. In this study, the dynamics of net ecosystem CO2 exchange (FNEE) of two grassland ecosystems were observed continuously using the eddy covariance technique during the growing season of 2003. One is the alpine shrub on the Tibet Plateau, and the other is the sem-arid Leymus chinensis steppe in Inner Mongolia of China. It was found that the FNEE of both ecosystems was significantly depressed under high solar radiation. Comprehensive analysis indicates that the depression of FNEE in the L. chinensis steppe was the results of decreased plant photosynthesis and increased ecosystem respiration (R-eco) under high temperature. Soil water stress in addition to the high atmospheric demand under the strong radiation was the primary factor limiting the stomatal conductance. In contrast, the depression of FNEE in the alpine shrub was closely related to the effects of temperature on both photosynthesis and ecosystem respiration, coupled with the reduction of plant photosynthesis due to partial stomatal closure under high temperature at mid-day. The R,c of the alpine shrub was sensitive to soil temperature during high turbulence (u* > 0.2 m s(-1)) but its FNEE decreased markedly when the temperature was higher than the optimal value of about 12 degrees C. Such low optimal temperature contrasted the optimal value (about 20 degrees C) for the steppe, and was likely due to the acclimation of most alpine plants to the long-term low temperature on the Tibet Plateau. We inferred that water stress was the primary factor causing depression of the FNEE in the semi-arid steppe ecosystem, while relative high temperature under strong solar radiation was the main reason for the decrease of FNEE in the alpine shrub. This study implies that different grassland ecosystems may respond differently to climate change in the future. (c) 2006 Elsevier B.V All rights reserved.

冰期间冰期转换过程中陆地碳库的演化规律研究

Terrestrial carbon pool mainly consists of three parts: the active carbon pool of the vegetation，soil carbon pools and the lithosphere carbon pool of less activity. Under natural conditions，vegetation carbon pools，soil carbon exchange with atmospheric carbon pool directly，the lithosphere participate in the global carbon cycle by weathering Our research have coverd the soil organic carbon density，plant biomass (carbon density)，plant net primary productivity of past 40 ka，and the magnetic susceptibility，grain size，weathering of silicate carbon consumption of past 140 ka. This study has achieved a number of conclusions as shown below. 1 Silicate weathering CO2 consumption in the long-term fluctuations with a similar deep-sea δ18O record，demonstate that it not only can be used as one of the instructions of terrestrial carbon pool，even can be used as indicators of global environmental change; silicate weathering CO2 consumption and susceptibility shown a clear relationship between lag or lead at different times，it maybe lies on how the climate change. 2 Soil carbon pools in line with the global climate on long-term，but the relationship between soil carbon density and climate change was not obvious in short-term change，generally lags behind the changes in other climatic proxies. 3 Carbon density of vegetation and other proxy indicators of climate have good consistency. In the study period，perform the cycle of glacial and interglacial completely，but because of the ancient vegetation of accurate information is difficult to obtain，it did not reflect rapid response to climate change. 4 Cooling events is conducive to soil organic carbon accumulation but not conducive to weathering and vegetation growth. High temperature environment is not conducive to the accumulation of soil organic carbon. 5 In the deglacial time from the last glacial maximum to the Holocene，weathering carbon consumption seems earlier than vegetation and soil organic carbon in the fluctuant increase.Does it imply that the effects of silicate weathering is an important factor to the global carbon cycle and global climate change? It is worth further research.

末次盛冰期以来中国陆地生态系统碳储量变化研究

Carbon is an essential element for life, food and energy. It is also a key element in the greenhouse gases and therefore plays a vital role in climatic changes. The rapid increase in atmospheric concentration of CO_2 over the past 150 years, reaching current concentrations of about 370 ppmv, corresponds with combustion of fossii fuels since the beginning of the industrial age. Conversion of forested land to agricultural use has also redistributed carbon from plants and soils to the atmosphere. These human activities have significantly altered the global carbon cycle. Understanding the consequences of these activities in the coming decades is critical for formulating economic, energy, technology, trade, and security policies that will affect civilization for generations. Under the auspices of the International Geosphere-Biosphere Programme (IGBP), several large international scientific efforts are focused on elucidating the various aspects of the global carbon cycle of the past decade. It is only possible to balance the global carbon cycle for the 1990s if there is net carbon uptake by terrestrial ecosystems of around 2 Pg C/a. There are now some independent, direct evidences for the existence of such a sink. Policymarkers involved in the UN Framework Convention on Climate Change (UN-FCCC) are striving to reach consensuses on a 'safe path' for future emissions, the credible predictions on where and how long the terrestrial sink will either persist at its current level, or grow/decline in the future, are important to advice the policy process. The changes of terrestrial carbon storage depend not only on human activities, but also on biogeochemical and climatological processes and their interaction with the carbon cycles. In this thesis, the climate-induced changes and human-induced changes of carbon storage in China since the past 20,000 years are examined. Based on the data of the soil profiles investigated during China's Second National Soil Survey (1979-1989), the forest biomass measured during China's Fourth National Forest Resource Inventory (1989-1993), the grass biomass investigated during the First National Grassland Resource Survey (1980-1991), and the data collected from a collection of published literatures, the current terrestrial carbon storage in China is estimated to -144.1 Pg C, including -136.8 Pg C in soil and -7.3 Pg C in vegetation. The soil organic (SOC) and inorganic carbon (SIC) storage are -78.2 Pg C and -58.6 Pg C, respectively. In the vegetation reservoir, the forest carbon storage is -5.3 Pg C, and the other of-1.4 Pg C is in the grassland. Under the natural conditions, the SOC, SIC, forest and grassland carbon storage are -85.3 Pg C, -62.6 Pg C, -24.5 Pg C and -5.3 Pg C, respectively. Thus, -29.6 Pg C organic carbon has been lost due to land use with a decrease of -20.6%. At the same time, the SIC storage also has been decreased by -4.0 Pg C (-6.4%). These suggest that human activity has caused significant carbon loss in terrestrial carbon storage of China, especially in the forest ecosystem (-76% loss). Using the Paleocarbon Model (PCM) developed by Wu et al. in this paper, total terrestrial organic carbon storage in China in the Last Glacial Maximum (LGM) was -114.8 Pg C, including -23.1 Pg C in vegetation and -86.7 Pg C in soil. At the Middle Holocene (MH), the vegetation, soil and total carbon were -37.3 Pg C, -93.9 Pg C and -136.0 Pg C, respectively. This implies a gain of-21.2 Pg C in the terrestrial carbon storage from LGM to HM mainly due to the temperature increase. However, a loss of-14.4 Pg C of terrestrial organic carbon occurred in China under the current condition (before 1850) compared with the MH time, mainly due to the precipitation decrease associated with the weakening of the Asian summer monsoon. These results also suggest that the terrestrial ecosystem in China has a substantial potential in the restoration of carbon storage. This might be expected to provide an efficient way to mitigate the greenhouse warming through land management practices. Assuming that half of the carbon loss in the degraded terrestrial ecosystem in current forest and grass areas are restored during the next 50 years or so, the terrestrial ecosystem in China may sequestrate -12.0 Pg of organic carbon from the atmosphere, which represents a considerable offset to the industry's CO2 emission. If the ' Anthropocene' Era will be another climate optimum like MH due to the greenhouse effect, the sequestration would be increased again by -4.3 - 9.0 Pg C in China.

Rapid Losses of Surface Elevation following Tree Girdling and Cutting in Tropical Mangroves.

Discussion Conclusions Materials and Methods Acknowledgments Author Contributions References Reader Comments (0) Figures Abstract The importance of mangrove forests in carbon sequestration and coastal protection has been widely acknowledged. Large-scale damage of these forests, caused by hurricanes or clear felling, can enhance vulnerability to erosion, subsidence and rapid carbon losses. However, it is unclear how small-scale logging might impact on mangrove functions and services. We experimentally investigated the impact of small-scale tree removal on surface elevation and carbon dynamics in a mangrove forest at Gazi bay, Kenya. The trees in five plots of a Rhizophora mucronata (Lam.) forest were first girdled and then cut. Another set of five plots at the same site served as controls. Treatment induced significant, rapid subsidence (−32.1±8.4 mm yr−1 compared with surface elevation changes of +4.2±1.4 mm yr−1 in controls). Subsidence in treated plots was likely due to collapse and decomposition of dying roots and sediment compaction as evidenced from increased sediment bulk density. Sediment effluxes of CO2 and CH4 increased significantly, especially their heterotrophic component, suggesting enhanced organic matter decomposition. Estimates of total excess fluxes from treated compared with control plots were 25.3±7.4 tCO2 ha−1 yr−1 (using surface carbon efflux) and 35.6±76.9 tCO2 ha−1 yr−1 (using surface elevation losses and sediment properties). Whilst such losses might not be permanent (provided cut areas recover), observed rapid subsidence and enhanced decomposition of soil sediment organic matter caused by small-scale harvesting offers important lessons for mangrove management. In particular mangrove managers need to carefully consider the trade-offs between extracting mangrove wood and losing other mangrove services, particularly shoreline stabilization, coastal protection and carbon storage.