高寒草甸土地退化及其恢复重建对植被碳、氮含量的影响

以青海省达日县高寒草甸原生高寒嵩草(Kobresia)草甸封育系统为对照,研究了土地退化对植被生产力的影响,检验了不同人工重建措施(两个人工种植处理:混播(HB)、翻耕单播(DBF)和1个退化草地封育自然恢复处理(NR)及1个退化草地自然状态(SDL))对植被生产力的相对影响程度。结果表明,原生植被封育处理(YF)地上总生物量为265.1 g·m^-2,混播(HB)和翻耕单播(DBF)处理中地上总生物量分别为原生植被封育处理的116%和68%。退化草地封育自然恢复处理(NR)和重度退化自然状态下地上总生物量分别为原生植被封育的76%和53%。YF处理根系生物量远大于其它处理。原生植被封育系统中植被地上部分碳储量为 110.14 g·m^-2,地下根系(0~30 cm)碳储量为2 957 g·m^-2,植被总碳储量为 3 067.14 g·m^-2;重度退化草地系统中植被地上部分碳储量为 57.07 g·m^-2,地下根系(0~30 cm)碳储量为 357 g·m^-2,植被总碳储量为 414.07 g·m^-2。由此可见,高寒草甸严重退化后,通过植物组织流失的碳达到2 653.35 g·m^-2,即86.5%的碳损失;原生植被封育系统植被总氮储量为 56.85 g·m^-2,而重度退化草地植被总氮储量为 18.02 g·m^-2,高寒草甸严重退化使植物组织68.30%氮损失。与重度退化地相比,由于恢复重建措施增加了植物的生物量输入和群落组成,除翻耕单播处理外,其它恢复重建措施均能恢复系统植被的碳氮储量。这些恢复重建措施将会逐步改善土壤的物理和化学特性,最终使这些生态系统逐步由碳源向碳汇方向的转变成为可能。     

藏北高寒草地植被的碳密度与碳贮量

采用实地调查与查阅文献相结合的方法估算藏北高寒草地植被碳密度和碳贮量。结果表明:1)藏北高寒草地总面积约39.059×106 hm²,植被地上平均碳密度12.158±4.7g·m^-2,植被地下平均碳密度84.458±20.38g·m^-2,植被地上部碳贮量5.171±0.95Tg,植被地下部碳贮量25.223±2.96Tg,植被总碳贮量为30.394±3.91Tg;2)不同草地组间植被碳密度和碳贮量差异显著。其中不同草地组间植被碳密度以丛生禾草组碳密度值最低,地上和地下碳密度分别为6.13±1.51g·m^-2和26.04±5.8g·m^-2,具灌木的半灌木组碳密度最高,地上和地下碳密度分别为31±3.4 g·m^-2和244.59±6.9g·m^-2;而不同草地组间,草地植被碳贮量以小莎草组最大,植被地上和地下碳贮量分别为2.24±0.32Tg和9.52±0.89Tg,半灌木组碳贮量最小,其地上和地下碳贮量分别为0.012 4±0.002Tg和0.098 1±0.002Tg。3)藏北高寒草地分布各县(区)碳密度和碳贮量的分布也存在显著差异。从碳密度来看,革吉县、札达县、噶尔县和措勤县碳密度较高,植被平均碳密度分别相当于藏北平均植被碳密度的1.76,1.47,1.11和1.06倍,从碳贮量来看,碳贮量集中分布于双湖特别区、札达、尼玛、日土、革吉和改则6县(区),六县(区)草地植被碳贮量为25.2±2.31Tg,占藏北总植被碳量的82.89%。     

宁夏典型温性天然草地固碳特征

本文研究了宁夏草甸草原、温性草原、草原化荒漠和荒漠草原4种温性典型天然草地生态系统碳储量及其构成特征。结果表明: 草甸草原、温性草原、草原化荒漠和荒漠草原植被总生物量分别为1178.91、481.22、292.80和209.09 g·m^-2。其中,地下根系生物量是构成草甸草原和温性草原植被总生物量的主体,分别占总生物量的73.1%和56.6%;地上植被生物量是构成草原化荒漠和荒漠草原植被总生物量的主体,分别占总生物量的50.3%和47.6%;枯落物生物量占比较低,分别仅为8.5%、8.0%、6.4%和16.2%。草甸草原、温性草原、草原化荒漠和荒漠草原4种天然草地生态系统碳储量分别为13.90、5.94、2.69和2.37 kg·m^-2,其中植被碳储量分别为470.26、192.23、117.17、83.36 g·m^-2,0～40 cm土层土壤有机碳储量分别为13.43、5.75、2.58和2.29 kg·m^-2,土壤有机碳储量是构成宁夏典型天然草地碳储量的主体,分别占到了生态系统碳储量的96.6%、96.8%、95.6%和96.5%。4种草地类型植被总生物量、植被碳储量、土壤有机碳储量和生态系统碳储量均表现为:草甸草原＞温性草原＞草原化荒漠＞荒漠草原。     

青藏高原高寒草甸生态系统碳增汇潜力

为了揭示青藏高原高寒草甸生态系统植被变化对碳储量的影响,以原生矮嵩草草甸、退化草甸、人工草地以及农田为研究对象,对比分析了该4种不同土地格局下生态系统的有机碳现状.以原生矮嵩草草甸土壤碳储量为基准对不同类型高寒生态系统的碳增汇潜力进行了估算.结果表明:不同类型生态系统的碳储量和碳增汇潜力有很大差异,在0-40cm土层中,(1)原生草甸碳储量最高,达到17098 g C/m2,退化草甸、人工草地和农田的有机碳汇增加潜力分别为:5637、3823、1567 g C/m2.(2)对于退化草甸和人工草地,土壤有机碳含量和密度明显低于原生草甸和农田.(3)地下生物量碳储量主要集中在0-20cm,且原生草甸地下生物量的碳储量比其他3个植被类型高3.6-5倍.总体上,青藏高原草地生态系统存在巨大的碳增汇潜力.     

陕西黄河湿地自然保护区碳储量估算

湿地生态系统的固碳及其调节气候等生态系统服务十分重要,准确评估黄河流域自然保护地的碳储量有助于碳中和研究和区域生态保护与高质量发展。该研究基于野外采样和室内分析,并结合遥感数据,评估了陕西黄河湿地省级自然保护区光滩和典型自然植被区的地上植被和0–50 cm土壤碳储量。碳储量评估区总面积13 086.52 hm²,占保护区面积的23.87%。结果表明,高草植被的地上碳储量显著高于低草植被和矮灌丛植被,其碳密度分别为496.73、23.45和138.38g·m^–2;土壤0–50 cm的碳密度为7.15–11.98 kg·m^–2,高草植被区的土壤碳储量(5.02×10⁵ t)显著高于光滩(2.09×10⁵ t)、低草植被区(3.40×10⁵t)和矮灌丛植被区(1.45×10⁵t);最终核算出陕西黄河湿地省级自然保护区典型植被区的地上植被和0–50cm土壤总碳储量约为1.22×10⁶ t,其中光滩区、低草植被区、矮灌丛植...     

黑河中游荒漠草地地上和地下生物量的分配格局

草地生态系统中地上和地下生物量的分配方式对于研究生态系统碳储量和碳循环有着重要的意义。为了解黑河中游荒漠草地的地上和地下生物量分配格局, 从群落和个体两个水平对黑河中游的地上和地下生物量进行了调查。结果表明: 群落水平上地上生物量介于3.2-559.2 g·m^-2之间, 地下生物量介于3.3-188.2 g·m^-2之间, 个体水平上地上生物量介于6.1-489.0 g·株^-1之间, 地下生物量介于2.4-244.2 g·株^-1之间, 群落水平上的根冠比(R/S)为0.10-2.49, 个体水平上为0.07-1.55, 地下生物量均小于地上生物量, 群落水平上R/S值大于个体水平。群落和个体水平地上和地下生物量的拟合斜率分别为1.1001和0.9913, 与1没有显著差异, 说明地上与地下生物量呈等速生长关系。群落和个体水平土壤表层0-20 cm和0-30 cm的根系生物量分别占全部根系生物量的89.81%、96.95%和81.42%、93.62%, 表明地下生物量主要集中在0-20 cm和0-30 cm土壤表层。     

河南典型暖(热)性草地固碳特征及区域差异

通过野外调查取样与室内分析,研究了河南两种气候区内分布的典型草地(豫西北的暖性草丛和暖性灌草丛,豫南的暖性草丛、暖性灌草丛、热性草丛和热性灌草丛)植被与土壤碳密度特征及碳分布差异.结果表明: 豫西北与豫南地区草地植被地上平均生物量分别为327.4和221.4 g·m^-2,呈北高南低趋势,差异显著;而根系平均生物量分别为1.58×10³和1.94×10³ g·m^-2,呈南高北低趋势,且差异显著.豫西北和豫南地区地上平均碳密度分别为113.75和77.35 g C·m^-2.豫西北地区暖性草丛植被地上碳密度大于暖性灌草丛,但差异不显著;而豫南地区热性草丛活体碳密度显著低于其他3种类型草地.豫西北与豫南地区地下平均碳密度分别为6.35×10³和5.14×10³ g C·m^-2.豫西北地区2种类型草地根系碳密度和土壤碳密度差异均不显著;豫南地区热性灌草丛根系碳密度显著低于其他3种类型草地,而热性草丛土壤碳密度显著大于其他3种类型草地.豫西北和豫南地区草地生态系统平均碳密度分别为6.46×10³和5.22×10³ g C·m^-2,呈北高南低趋势,且土壤贡献最大(78%～90%).豫西北地区2种类型草地生态系统碳密度差异不显著;豫南地区热性草丛生态系统碳密度最高为9.70×10³ g C·m^-2,显著大于其他3种类型草地.本研究结果为准确计算河南不同类型草地生态系统碳储量及评估其固碳潜力提供基础数据.     

宁夏回族自治区森林生态系统固碳现状

根据宁夏回族自治区森林资源清查资料以及野外调查和室内分析的结果,研究了宁夏地区森林生态系统固碳现状,估算了该区森林生态系统的碳密度、碳储量,并分析了其空间分布特征.结果表明: 宁夏森林各植被层生物量大小顺序为: 乔木层(46.64 Mg·hm^-2)>凋落物层(7.34 Mg·hm^-2)>细根层(6.67 Mg·hm^-2)>灌草层(0.73 Mg·hm^-2).云杉类(115.43 Mg·hm^-2)和油松(94.55 Mg·hm^-2)的单位面积植被生物量高于其他树种.不同林龄乔木层碳密度中,过熟林最高,但由于幼龄林面积所占比例最大,其乔木层碳储量(1.90 Tg C)最大.宁夏地区森林生态系统平均碳密度为265.74 Mg C·hm^-2,碳储量为43.54 Tg C,其中,植被层平均碳密度为27.24 Mg C·hm^-2、碳储量为4.46 Tg C,土壤层碳储量是植被层的8.76倍.宁夏地区的森林碳储量整体呈南高北低分布,总量较低.这与其森林面积小和林龄结构低龄化有很大关系.随着林龄结构的改善和林业生态工程的进一步实施,宁夏森林生态系统将发挥巨大的固碳潜力.     

广西不同林龄喀斯特森林生态系统碳储量及其分配格局

基于广西喀斯特地区45块1000 m²样地的调查,研究幼龄林、中龄林、近熟林、成熟林、过熟林5个林龄阶段喀斯特森林植被与土壤碳储量的分配格局.结果表明: 广西不同林龄喀斯特森林总碳储量表现为幼龄林(86.03 t·hm^-2)＜近熟林(110.63 t·hm^-2)＜中龄林(112.11 t·hm^-2)＜成熟林(149.1 t·hm^-2)＜过熟林(244.38 t·hm^-2);各林龄阶段植被不同层碳储量分配均不同,乔木层所占比例占绝对优势,达到92.3%～98.7%,随林龄的增加而增长,灌木层、草本层、凋落物层所占比例分别为0.3%～1.9%、0.3%～1.2%和0.3%～2.5%,细根所占比例为0.3%～3.3%.土壤有机碳密度随土层深度的增加而递减,土壤层碳储量为51.75～81.21 t·hm^-2,所占生态系统比例为33.2%～66.2%,其随林龄的增大呈减小趋势.生态系统地上、地下部分碳储量分别为22.80～141.72和62.30～102.66 t·hm^-2,除过熟林外均为地下部分＞地上部分,地上碳储量随林龄的增大呈逐渐增加的趋势,地下碳储量的变化规律与土壤碳储量变化趋势一致.土壤层和乔木层为生态系统的主要碳库,二者所占比例达到了96%以上.     

内蒙古森林生态系统碳储量及其空间分布

内蒙古森林面积居全国第一位, 林木蓄积量居第五位, 准确地估算该区域森林碳储量对于评估中国森林碳储量以及制定森林资源管理措施均具有重要意义。该研究基于内蒙古森林资源野外样方调查和室内分析, 评估了内蒙古森林生态系统的固碳现状, 估算了内蒙古森林生态系统不同林型和不同碳库(乔木、灌木、草本、凋落物和土壤碳库)的碳密度大小, 揭示了其空间分布特征。在此基础上估算了内蒙古森林碳储量大小及空间格局。结果表明: 1)内蒙古森林植被层碳储量为787.8 Tg C, 乔木层、凋落物层、草本层和灌木层分别占植被层总碳储量的93.5%、3.0%、2.7%和0.8%。内蒙古森林植被层平均碳密度为40.4 t·hm^-2, 其中, 乔木层、凋落物层、草本层和灌木层的碳密度分别为35.6 t·hm^-2、2.9 t·hm^-2、1.2 t·hm^-2和0.6 t·hm^-2。2)内蒙古森林土壤层(0-100 cm)碳储量为2449.6 Tg C, 其中0-30 cm的土壤碳储量最高, 占总碳储量的79.8%。0-10 cm、10-20 cm和20-30 cm的土壤碳储量分别占0-30 cm土壤碳储量的38.8%、34.1%和27.1%。内蒙古森林土壤平均碳密度为144.4 t·hm^-2。黑桦(Betula davurica)林土壤碳密度最高, 云杉(Picea asperata)林最小。土壤碳密度随土壤深度的增加而降低。3)内蒙古森林生态系统碳储量为3237.4 Tg C, 植被层和土壤层碳储量分别占森林生态系统碳储量的24.3%和75.7%。落叶松(Larix gmelinii)林总碳储量最高, 其次为白桦(Betula platyphylla)林、夏栎(Quercus robur)林、黑桦林、榆树(Ulmus pumila)疏林和山杨(Populus davidiana)林。内蒙古森林生态系统平均碳密度为184.5 t·hm^-2。土壤碳密度与植被碳密度呈显著正相关关系。4)内蒙古森林生态系统碳储量和碳密度的空间分布总体上为东部地区高、西部地区低的趋势。在降水量充沛的东部地区和降水偏少的中西部地区, 有针对性地开展森林保护区建设和人工造林, 可显著提升区域的碳汇能力。     

Biomass carbon stocks and their changes in northern China’s grasslands during 1982–2006

Grassland covers approximately one-third of the area of China and plays an important role in the global terrestrial carbon (C) cycle. However, little is known about biomass C stocks and dynamics in these grasslands. During 2001–2005, we conducted five consecutive field sampling campaigns to investigate above-and below-ground biomass for northern China’s grasslands. Using measurements obtained from 341 sampling sites, together with a NDVI (normalized difference vegetation index) time series dataset over 1982–2006, we examined changes in biomass C stock during the past 25 years. Our results showed that biomass C stock in northern China’s grasslands was estimated at 557.5 Tg C (1 Tg=10¹² g), with a mean density of 39.5 g C m⁻² for above-ground biomass and 244.6 g C m⁻² for below-ground biomass. An increasing rate of 0.2 Tg C yr⁻¹ has been observed over the past 25 years, but grassland biomass has not experienced a significant change since the late 1980s. Seasonal rainfall (January–July) was the dominant factor driving temporal dynamics in biomass C stock; however, the responses of grassland biomass to climate variables differed among various grassland types. Biomass in arid grasslands (i.e., desert steppe and typical steppe) was significantly associated with precipitation, while biomass in humid grasslands (i.e., alpine meadow) was positively correlated with mean January-July temperatures. These results suggest that different grassland ecosystems in China may show diverse responses to future climate changes.     

The impact of land degradation on the C pools in alpine grasslands of the Qinghai-Tibet Plateau

Aims

To determine the effect of grassland degradation on the soil carbon pool in alpine grassland.

Methods

In this study, we calculated the carbon pool in the above-and below-ground biomass, the soil microbial biomass carbon pool, the total organic carbon pool and the soil total carbon.

Results

Grassland degradation has resulted in decreases in biomass and carbon content and has changed the ratio of roots to shoots. However, there was less influence of degradation on dead root biomass. There was most likely a lag effect of changes in dead root biomass following grassland degradation. In the alpine grassland ecosystem, the carbon pool in soil accounts for more than 92 % of the total carbon both in vegetation and soil. The carbon in alpine grassland is stored primarily in the form of total organic carbon below-ground. As organic carbon decreases, the ratio of the microbial biomass carbon pool to the total organic carbon pool increases and then declines with increasing degradation level. Along the grassland degradation gradient, the total vegetation biomass (above-and below-ground) and the soil carbon pool (microbial biomass C, total organic C and total C) all decreased.     

高寒草原不同植物群落地上-地下生物量碳分布格局

高寒草原具有独特的自然生境和生物资源,对高寒草原开展系统研究对于减缓气候变化与草原恢复具有重要实践意义。以往研究主要针对高寒草原生物量碳开展整体评估,缺乏对不同群落类型间的定量比较。本文分析了高寒草原10种主要典型植物群落地上-地下生物量碳分布格局以及对总生物量碳的贡献差异。结果表明:高寒草原面积为167.33×10^6hm^2,总生物量碳为1.53 Pg(1 Pg=1015g),其中地上生物量碳0.19 Pg,地下生物量碳1.34 Pg;紫花针茅、青藏苔草和紫花针茅-小蒿草群落面积大,生物量碳密度高,为高寒草原贡献了69.3%的生物量碳。高寒草原平均生物量碳密度为690.80 g C·m^-2,其中紫花针茅群落(196.14 g C·m^-2)和蔷薇群落(177.93 g C·m^-2)具有最高的地上生物量碳密度(AGC);蔷薇(1491.18 g C·m^-2)和紫花针茅-小蒿草群落(1306.51 g C·m^-2)则具有最高的地下生物量碳密度(BGC),且显著高于其他群落类型(P<0.05)。不同群落的BGC在土壤中的垂直分布格局存在较大差异,驼绒藜、盐爪爪、金露梅、紫花针茅、青藏苔草、紫花针茅-小蒿草、蔷薇、固沙草、砂生槐等群落的BGC主要集中在表层土壤(0~10 cm),分布曲线呈指数函数,而华扁穗草群落的BGC则集中在40~60 cm土壤层,分布曲线呈二次函数关系。对草原植物群落的地上-地下生物量碳开展评估,可以提高生物量碳的估算精度,为草原生态管理提供更有力的数据支持。     

黄土高原人工苜蓿草地固碳效应评估

苜蓿草地作为黄土高原草地的重要组成部分,在黄土高原草地生态系统碳循环占有重要地位。同时由于苜蓿具有固氮和固碳的双重作用,使它在低碳农业的发展中具有重要意义。本文以一年生（建植初期）、三年生（盛产期）、五年生（稳产期）和十年生（衰败期）的人工苜蓿草地为研究对象,利用地上地下生物量和土壤碳贮量,定量分析了人工苜蓿草地不同发育阶段的固碳能力;结合种植面积,对黄土高原区人工苜蓿草地的总固碳效应进行了评价。研究结果表明：苜蓿草地地上生物固碳能力以三年生和五年生最强,并显著高于其他年限;地下生物固碳和土壤固碳量均以十年苜蓿草地最高,且显著高于其他年限。总体而言,人工苜蓿草地以土壤固碳为主,并集中在0~80cm土壤,各年限0-80cm土层土壤固碳量分别占到总固碳量的41.02%、39.43%、41.56%、39.59%;而地下生物固碳主要发生在0~20cm土层,各年限该层生物固碳量分别占到地下生物总固碳量的45.74%、 55.68%、53.12%和 43.28%。苜蓿草地在整个生命周期中总固碳量随生长年限逐年增长,但增长速度不明显,各年限单位面积总固碳量分别为12.69kg/m2、13.49 kg/m2、13.31 kg/m2和14.83 kg/m2。估算得到黄土高原的人工苜蓿草地年总固碳量为1.430?1011 Kg（143.0 Tg）,其中地上、地下、土壤分别为5.43Tg、1.15Tg和136.4Tg。本研究结果为正确分析区域碳循环和发展低碳大农业提供了重要理论参考。     

不同放牧强度下短花针茅荒漠草原植被-土壤系统有机碳组分储量特征

草地生态系统作为陆地生态系统的重要组成部分,在全球碳循环中发挥着重要作用。以内蒙古短花针茅荒漠草原不同放牧强度样地为研究对象,通过分析地上植物、凋落物、根系、土壤中有机碳和土壤轻组有机碳,研究草原植被-土壤系统有机碳组分储量的变化特征,从碳储量角度为合理利用草原提供指导。研究结果表明:(1)不同放牧强度荒漠草原地上植物碳储量为11.98—44.51 g/m~2,凋落物碳储量10.43—36.12 g/m~2,根系(0—40cm)碳储量502.30—804.31 g/m~2,且对照区(CK)均显著高于中度放牧区(MG)、重度放牧区(HG);(2)0—40cm土壤碳储量为7817.43—9694.16 g/m~2,其中轻度放牧区(LG)碳储量为9694.16 g/m~2,显著高于CK、HG(P0.05);(3)植被—土壤系统的碳储量为8342.14—10494.80 g/m~2,LGMGCKHG,有机碳主要储存于土壤当中,占比约90.54%—93.71%,适度放牧利用有利于发挥草地生态系统的碳汇功能;(4)土壤轻组有机碳储量为484.20—654.62 g/m~2,LG储量最高,表明适度放牧有助于草原土壤营养物质的循环和积累。     

青海省森林土壤有机碳氮储量及其垂直分布特征

森林土壤在调节森林生态系统碳、氮循环和减缓全球气候变化中起着关键的作用。但是,由于林型、林龄以及环境因子(海拔)的差异,至今对于森林土壤碳、氮储量的估算依然存在极大的不确定性。因此,利用森林土壤实测数据估算了青海森林土壤有机碳、氮密度和碳、氮储量,分析了土壤有机碳、氮密度的垂直分布格局。结果表明:1)土壤有机碳密度随海拔的增加呈单峰曲线变化,在海拔3100—3400 m达到最大34.33 kg/m~2;氮密度随海拔的增加而增加,范围为1.39—2.93 kg/m~2。2)在0—30 cm土层,土壤有机碳、氮密度均随土层的增加而降低,范围分别为3.84—4.63 kg/m~2、0.22—0.27 kg/m~2。3)青海省森林土壤碳储量为1098.70 Tg,氮储量为61.78 Tg。4)海拔与氮含量和密度之间存在极显著正相关关系(P0.01,P0.01)。土层深度与有机碳含量存在极显著负相关关系(P0.01);与有机碳密度、氮密度存在极显著正相关关系(P0.01,P0.01)。说明海拔和土层是影响青海省森林土壤有机碳、氮分布的关键因子。     

Carbon,nitrogen, and phosphorus storage in alpine grassland ecosystems of Tibet: effects of grazing exclusion

In recent decades, alpine grasslands have been seriously degraded on the Tibetan Plateau and grazing exclusion by fencing has been widely adopted to restore degraded grasslands since 2004. To elucidate how alpine grasslands carbon (C), nitrogen (N), and phosphorus (P) storage responds to this management strategy, three types of alpine grassland in nine counties in Tibet were selected to investigate C, N, and P storage in the environment by comparing free grazing (FG) and grazing exclusion (GE) treatments, which had run for 6–8 years. The results revealed that there were no significant differences in total ecosystem C, N, and P storage, as well as the C, N, and P stored in both total biomass and soil (0–30 cm) fractions between FG and GE grasslands. However, precipitation played a key role in controlling C, N, and P storage and distribution. With grazing exclusion, C and N stored in aboveground biomass significantly increased by 5.7 g m⁻² and 0.1 g m⁻², respectively, whereas the C and P stored in the soil surface layer (0–15 cm) significantly decreased by 862.9 g m⁻² and 13.6 g m⁻², respectively. Furthermore, the storage of the aboveground biomass C, N, and P was positively correlated with vegetation cover and negatively correlated with the biodiversity index, including Pielou evenness index, Shannon–Wiener diversity index, and Simpson dominance index. The storage of soil surface layer C, N, and P was positively correlated with soil silt content and negatively correlated with soil sand content. Our results demonstrated that grazing exclusion had no impact on total C, N, and P storage, as well as C, N, and P in both total biomass and soil (0–30 cm) fractions in the alpine grassland ecosystem. However, grazing exclusion could result in increased aboveground biomass C and N pools and decreased soil surface layer (0–15 cm) C and P pools.     

青海湖流域矮嵩草草甸土壤有机碳密度分布特征

通过对青海湖流域不同退化程度矮嵩草草甸土壤容重和有机碳含量的测定,确定了其土壤有机碳密度。结果表明:不同退化程度下矮嵩草草甸土壤有机碳含量和变化特征各有不同。从未退化-重度退化,0—100 cm土壤剖面平均有机碳含量分别为(25.17±4.73)g/kg,(17.51±3.06)g/kg,(20.79±1.30)g/kg和(14.53±1.20)g/kg,即未退化中度退化轻度退化重度退化;0—20 cm土壤平均有机碳含量从(64.47±11.70)g/kg减少为(14.52±1.52)g/kg,减少了77.48%。土壤剖面有机碳密度变化趋势与其有机碳含量变化趋势一致。0—100 cm土壤剖面有机碳密度分别为(18.16±4.12)kg/m3,(14.24±3.52)kg/m3,(18.64±2.82)kg/m3和(13.27±2.28)kg/m3,即中度退化未退化轻度退化重度退化;土壤有机碳集中分布在0—40 cm深度,从未退化到严重退化,该深度有机碳密度分别为(32.06±6.41)kg/m3,(25.10±4.20)kg/m3,(22.68±3.17)kg/m3和(17.10±2.77)kg/m3,比整个剖面有机碳密度高出76.53%,76.25%,21.68%和28.88%。不考虑其他因素,以空间尺度代替时间尺度,这一结果说明矮嵩草草甸的退化导致土壤逐渐释放有机碳,其作为储存碳的功能在减弱,必须加强对矮嵩草草甸生态系统的保护,以防止其碳库变为碳源。     

Spatio-Temporal Variation in Vegetation Biomass and Its Relationships with Climate Factors in the Xilingol Grasslands,Northern China

Knowledge about grassland biomass and its dynamics is critical for studying regional carbon cycles and for the sustainable use of grassland resources. In this study, we investigated the spatio-temporal variation of biomass in the Xilingol grasslands of northern China. Field-based biomass samples and MODIS time series data sets were used to establish two empirical models based on the relationship of the normalized difference vegetation index (NDVI) with above-ground biomass (AGB) as well as that of AGB with below-ground biomass (BGB). We further explored the climatic controls of these variations. Our results showed that the biomass averaged 99.01 Tg (1 Tg=10¹² g) over a total area of 19.6×10⁴ km² and fluctuated with no significant trend from 2001 to 2012. The mean biomass density was 505.4 g/m², with 62.6 g/m² in AGB and 442.8 g/m² in BGB, which generally decreased from northeast to southwest and exhibited a large spatial heterogeneity. The year-to-year AGB pattern was generally consistent with the inter-annual variation in the growing season precipitation (GSP), showing a robust positive correlation (R²=0.82, P<0.001), but an opposite coupled pattern was observed with the growing season temperature (GST) (R²=0.61, P=0.003). Climatic factors also affected the spatial distribution of AGB, which increased progressively with the GSP gradient (R²=0.76, P<0.0001) but decreased with an increasing GST (R²=0.70, P<0.0001). An improved moisture index that combined the effects of GST and GSP explained more variation in AGB than did precipitation alone (R²=0.81, P<0.0001). The relationship between AGB and GSP could be fit by a power function. This increasing slope of the GSP–AGB relationships along the GSP gradient may be partly explained by the GST–GSP spatial pattern in Xilingol. Our findings suggest that the relationships between climatic factors and AGB may be scale-dependent and that multi-scale studies and sufficient long-term field data are needed to examine the relationships between AGB and climatic factors.