青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析

基于2008—2016年青海海北站9年净初级生产力及气候因子监测数据,分析了青藏高原高寒小嵩草草甸和高寒金露梅灌丛两种植被净初级生产力年际动态,并探讨了气候因子对其影响及其不同土层深度根系周转值特征。结果表明:(1)年际尺度上,小嵩草草甸地上净初级生产力表现为显著增加趋势,增幅为7.02 g m~(-2) a~(-1),而金露梅灌丛地上净初级生产力相对较为稳定;对于其地下净初级生产力和总生产力,小嵩草草甸和金露梅灌丛均表现为增加趋势(P0.05),9年间小嵩草草甸地上、地下和总净初级生产力平均值分别为(217.55±9.95)、(1882.75±161.33) g m~(-2) a~(-1)和(2100.30±163.38) g m~(-2) a~(-1),金露梅灌丛地上、地下和总净初级生产力9年间平均值分别为(256.27±11.4)、(1614.31±173.03) g m~(-2) a~(-1)和(1870.58±177.93) g m~(-2) a~(-1)。(2)不同植被类型地上净初级生产力对气候因素响应不同,金露梅灌丛地上净初级生产力主要受温度影响,而温度对小嵩草草甸地上净初级生产力无显著影响。此外,降水不是限制高寒生态系统草地地上净初级生产力主要因子,相比于降水影响,高寒生态系统地上净初级生产力更受温度调控。(3)年均温和年降水对金露梅灌丛和小嵩草草甸地下净初级生产力均无显著影响(P0.05),表明高寒生态系统,其地下生产力受外界气候条件变化影响微弱,是一个稳定的碳库。(4)两种植被类型其根系周转值均随着土壤深度的增加呈逐渐增加趋势,且高寒灌丛根系周转值明显高于高寒草甸根系周转值。研究表明,在全球气候变暖背景下将会增加金露梅灌丛地上净初级生产力,而对小嵩草草甸地上净初级生产力无显著影响。     

青藏高原矮嵩草草甸和金露梅灌丛草甸CO2通量变化与环境因子的关系

利用涡度相关技术观测了青藏高原两个典型的生态系统即矮嵩草(K obresia hum ilis)草甸和金露梅(P oten-tilla f ruticosa)灌丛草甸的CO2通量,并就2003年8月份的数据,分析了生态系统通量变化与环境因子的关系.8月份是这两个生态系统的叶面积指数达到最高也是相对稳定的时期,在此期间矮嵩草草甸和金露梅灌丛草甸净碳吸收量分别达56.2和32.6 g C.m-2,日CO2吸收量最大值分别为12.7μm o l.m-2.-s 1和9.3μm o l.m-2.-s 1,排放量最大值分别为5.1μm o l.m-2.-s 1和5.7μm o l.m-2.-s 1.在相同光合有效光量子通量密度(PPFD)条件下,矮嵩草草甸CO2吸收速度大于金露梅灌丛草甸;在PPFD高于1 200μm o l.m-2.s-1的条件下,随气温增加,两生态系统的CO2吸收速度都下降,但矮嵩草草甸的下降速度(-0.086)比金露梅灌丛草甸(-0.016)快.土壤水分影响土壤呼吸,并且影响差异因植被类型不同而不同.生态系统日CO2吸收量随昼夜温差增加而增大;较大的昼夜温差导致较高的净CO2交换量;植物反射率与CO2通量之间存在负相关关系.     

青海高寒金露梅灌丛碳密度及其分配格局

灌丛面积增加引起的碳储量增加被认为是我国陆地生态系统碳储量增加的重要原因,也是陆地生态系统碳汇研究中的一个不确定因素。为了揭示高寒灌丛的碳密度及其分配格局,该文对青海省不同样地8个金露梅(Potentilla fruticosa)灌丛生态系统各组分的碳密度及分布特征进行了研究。结果表明:金露梅灌丛的生物碳密度、凋落物碳密度、土壤有机碳密度和总碳密度分别为:5 088.54、542.1、35 903.76和41 534.4 kg·hm~(–2)。金露梅灌丛灌木层碳主要分配在根部(49.5%–56.1%),灌木层碳密度占总生物量碳密度的68%以上。草本层碳也主要分配在根部(59.6%–75.1%),草本层碳密度占总生物量碳密度的22.5%。金露梅灌丛的生物碳密度明显低于中国6种主要灌丛的平均值(10.88 t·hm~(–2))。在金露梅灌丛中,土壤碳密度占有最大比例,约占总碳密度的86.4%。     

内蒙古草甸草原与典型草原地下生物量与生产力季节动态及其碳库潜力

地下根系是草原生态系统的重要组成部分,其生物量及其净生产力对地下碳库具有直接与间接作用,分析地下生物量季节动态与周转对深入揭示草原生态系统碳库动态及其固碳速率与潜力具有重要意义。应用钻土芯法对不同利用方式或管理措施下内蒙古草甸草原、典型草原地下生物量动态及其与温度、降水的相关性研究表明:草甸草原和典型草原地上生物量季节动态均为单峰型曲线,与上月降水显著正相关(P0.05),但地下生物量季节动态表现为草甸草原呈"S"型曲线,典型草原则是双峰型曲线,与温度、降水相关性均不显著(P0.05);两种草原根冠比和地下生物量垂直分布均为指数函数曲线,根茎型草原地下生物量集中在土壤0—5 cm,丛生型草原地下生物量集中于土壤5—10 cm,根冠比值在生长旺季(7—8月份)最小。草甸草原地下净生产力及碳储量范围分别为2167—2953 g m-2a-1和975—1329 gC m-2a-1,典型草原为2342—3333 g m-2a-1和1054—1450 gC m-2a-1,地下净生产力及其碳储量约为地上净生产力及其碳储量的10倍,具有较大的年固碳能力,且相对稳定;地下净生产力与地上净生产力呈显著负相关性(P0.05);地下生物量碳库是地上生物量碳库的10倍左右,适度放牧可增加地下生产力,但长期过度放牧显著降低其地下生物量与生产力,并使其垂直分布趋向于浅层化。     

三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放

利用静态箱-碱液吸收法研究了三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放速率,讨论了影响CO2释放的环境因素,估算了枯落物分解的CO2释放对于总释放的贡献.结果表明,生长季,小叶章沼泽化草甸和小叶章湿草甸各部分CO2释放均具有明显的时间变化特征,温度和水分是重要制约因素.两类草甸湿地的平均土壤呼吸速率分别为4.33g·m-2·d-1和6.15g·m-2·d-1,枯落物分解的CO2平均释放速率分别为1.76g·m-2·d-1和3.10g·m-2·d-1,枯落物分解的CO2释放占总释放量的31%和35%,说明在碳素由地上植物碳库转移到地下土壤碳库的过程中,湿地枯落物是一个不可忽略的碳损失源.     

宁夏天然草地植被碳储量特征及构成

以宁夏广泛分布的温性草甸草原、温性草原、温性草原化荒漠和温性荒漠草原为研究对象,采用实地调查采样的方法,研究了宁夏天然草地植被总碳储量。结果表明: 宁夏天然草地地上植被、地下根系及主要灌木平均含碳率为0.40,枯落物平均含碳率为0.39。草甸草原、温性草原、草原化荒漠和荒漠草原的植被总碳储量分别为470.26、192.23、117.17和83.36 g·m^-2,其中,地上植被碳储量分别为87.35、68.50、59.32和40.05 g·m^-2,地下根系碳储量分别为344.29、108.83、50.65和30.29 g·m^-2,枯落物碳储量分别为38.62、14.91、7.19和13.03 g·m^-2,且均表现为草甸草原＞温性草原＞草原化荒漠＞荒漠草原。地下根系碳储量是构成草甸草原和温性草原植被总碳储量的主体,地上植被碳储量是构成草原化荒漠和荒漠草原植被总碳储量的主体,且地下根系碳储量均随土层深度加深而递减。宁夏天然草地植被总碳储量空间分布呈现草甸草原和温性草原分布的南部区域碳储量明显高于荒漠草原和草原化荒漠分布的中北部区域。     

基于静态箱式法和生物量评估海北金露梅灌丛草甸碳收支

高寒灌丛是青藏高原重要植被类型,因特殊生物学性质致使其系统碳功能较难评估。采用静态箱式法测定高寒金露梅(Potentilla fruticosa)灌丛草甸的生态系统呼吸,结合生物量收获法估测生态系统净初级碳量。结果表明,高寒金露梅灌丛草甸生态系统呼吸、土壤呼吸和植物呼吸具有明显的季节动态变化,其年总量分别为886.28、444.93 gC/m2和441.36 gC/m2;灌丛区、草本区以及土壤区的呼吸均与5 cm地温具有极显著的指数关系(R2分别为0.95、0.94和0.83),各区温度敏感系数Q10分别为4.40、4.13和3.16;8a(2003—2010)植被净初级生产力平均为468.55 gC/m2。结合系统土壤呼吸,生态系统年均净固碳量为27.19 gC/m2,即高寒金露梅灌丛草甸生态系统为碳汇。对比涡度相关标准方法连续观测数据表明该方法评估生态系统碳功能具有较大可信度。     

围栏放牧下土壤-植被碳密度空间分布格局

对围封13年且放牧的冷季高寒矮嵩草草甸,进行了从围栏入口到内部不同距离植被和土壤碳密度状况的调查.结果表明:1)入口到50 m植被现存碳密度平均为1298.0gC·m-2,60～180m有所下降(平均为997.3 g C·m-2),200～300 m反而升高(平均为1285.5 g C·m-2).当年净初级生产碳密度分布趋势与其相同,0～50 m、60 ～180 m和200～300 m平均分别为742.5、571.0和745.7 g C·m-2.这种分布趋势与放牧过程中绵羊觅食频度和强度有关.一般在中央地带放牧强度大,绵羊觅食时间长,边缘地带受围栏效应或围栏外环境因素影响,放牧强度相对较弱,一定程度上对植被生长发育起到了保护作用,使边缘地带植被碳密度得到提高.2)从围栏入口到草场内部土壤碳密度变化趋势表现复杂,入口到100 m增加,100～170 m减小,然后略有升高.土壤碳密度最高值出现在95 m处(15.42 g C·m-2),最低值出现在170 m处(14.12 gC· m-2).目前尚不清楚为何出现这种格局,但至少认为,土壤有机质的动态转化过程受多种因素影响,与植被碳密度相比具有一定的迟滞效应.具体如何影响有机质的动态转化及其迟滞效应,有待进一步研究.     

青藏高原高寒草甸初级生产力及其主要影响因素

青藏高原有各类天然草地14×108hm2,其中高寒草甸和高寒灌丛约占青藏高原天然草地面积的50%,占全国草地总面积的16.2%。嵩草草甸是高寒草甸的主体,包括矮嵩草草甸、金露梅灌丛草甸、藏嵩草草甸、小嵩草草甸和高山嵩草草甸等,这5类高寒草甸平均地上生物量分别为354.2、422.4、445.1、227.3和368.5g/m2,地下生物量分别为3389.6、3548.3、11922.7、4439.3、5604.8g/m2,地下与地上生物量的比例分别为10.55、10.15、27.82、14.82和15.21,远大于IPCC(2006)报告中地下/地上生物量比例的默认值(2.8±95%)。地下生物量对气候变化和放牧的反应比地上生物量更敏感,干旱和重度放牧均降低了地下/地上生物量的比例。在极度退化状态下地下/地上生物量的比例2。对于轻度和中度退化的高寒草甸应以围封禁牧为主要恢复措施,但如果结合补播和施肥,则恢复速率会加快;对于重度和极度退化的高寒草甸,由于草地植物群落中优良牧草的比例极低,仅靠自然恢复很难进行恢复或需要的年限很长,所以必须采用人工重建的措施,并结合毒杂草防除和施肥等措施进行恢复,通过建立人工或半人工草地的措施予以重建。     

膜下滴灌对新疆棉田生态系统净初级生产力、土壤异氧呼吸和CO2净交换通量的影响

2009年4-10月,通过田间试验,以传统无膜漫灌为对照,研究了膜下滴灌对我国新疆棉田生态系统净初级生产力、土壤异氧呼吸和CO2净交换通量的影响.结果表明:膜下滴灌和无膜漫灌处理下,棉田生态系统净初级生产力、土壤异氧呼吸通量和CO2净交换通量均呈先增大后减小的变化趋势.与无膜漫灌相比,膜下滴灌显著提高了棉花地上、地下生物量和净初级生产力,降低了土壤异氧呼吸通量.在整个生长季节,膜下滴灌处理的年土壤异氧呼吸通量为214 g C·m-2,低于无膜漫灌处理的317 g C·m-2;膜下滴灌处理的棉花年净初级生产力为1030 g C·m-2,显著高于无膜漫灌处理的649 g C·m-2;膜下滴灌处理比无膜漫灌处理多固定大气CO2479 g C·m-2.膜下滴灌栽培措施既提高了作物生产力,又降低了土壤CO2排放,是干旱地区一种重要的农业固碳减排措施.     

The role of shrub (Potentilla fruticosa) on ecosystem CO2 fluxes in an alpine shrub meadow

Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO₂ sinks. On the plateau, alpine shrub meadow is one of typical grassland ecosystems. The major alpine shrub on the plateau is Potentilla fruticosa L. (Rosaceae), which is distributed widely from 3 200 to 4 000 m. Shrub species play an important role on carbon sequestration in grassland ecosystems. In addition, alpine shrubs are sensitive to climate change such as global warming. Considering global warming, the biomass and productivity of P. fruticosa will increase on Qinghai-Tibetan Plateau. Thus, understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau. However, the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear. The objectives of the present study were to evaluate the magnitude of CO₂ exchange of P. fruticosa shrub patches around the upper distribution limit and to elucidate the role of P. fruticosa on ecosystem CO₂ fluxes in an alpine meadow.Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity (NEP), ecosystem respiration (R e), and gross primary productivity (GPP) of P. fruticosa shrub patches at three elevations around the species' upper distribution limit. Ecosystem CO₂ fluxes and environmental factors were measured from 17 to 20 July 2008 at 3 400, 3 600, and 3 800 m a.s.l. We examined the maximum GPP at infinite light (GPP max) and maximum R e (R emax) during the experimental time at each elevation in relation to aboveground biomass and environmental factors, including air and soil temperature, and soil water content.Important findings Patches of P. fruticosa around the species' upper distribution limit absorbed CO₂, at least during the daytime. Maximum NEP at infinite light (NEP max) and GPP max of shrub patches in the alpine meadow varied among the three elevations, with the highest values at 3 400 m and the lowest at 3 800 m. GPP max was positively correlated with the green biomass of P. fruticosa more strongly than with total green biomass, suggesting that P. fruticosa is the major contributor to CO₂ uptake in the alpine shrub meadow. Air temperature influenced the potential GPP at the shrub-patch scale. R emax was correlated with aboveground biomass and R emax normalized by aboveground biomass was influenced by soil water content. Potentilla fruticosa height (biomass) and frequency increased clearly as elevation decreased, which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.     

Carbon density and its spatial distribution in the Potentilla fruticosa dominated alpine shrub in Qinghai,China

Aims Shrub recovery is recognized as an important cause of the increase of carbon stocks in China, and yet there are great uncertainties in the carbon sink capacities of shrubs. Our objectives were to estimate carbon density and its spatial distribution in alpine shrubs.
Methods Eight sites in Potentilla fruticosa dominated shrublands across Qinghai, China were investigated. Plant biomass and carbon content in leaves, branches and stems, and roots were measured to analyze the biomass allocation and carbon density.
Important findings Mean carbon densities in biological carbon, litter, soil and whole ecosystem of P. fruticosa shrublands were 5088.54, 542.1, 35903.76 and 41534.4 kg·hm^-2, respectively. Carbon density in the shrub layer was more than 68% of the biological carbon density of the whole ecosystem and was mainly distributed in roots (49.5%-56.1%). Carbon density of the herbaceous layer was 22.5% of the biological carbon density of the whole ecosystem and was also mainly distributed in roots (59.6%-75.1%). The biological carbon density of P. fruticosa shrublands (5.08 t·hm^-2) was lower than the average carbon density of shrub communities in China (10. 88 t·hm^-2). Soil carbon density contributed the largest proportion (85.8%) of total carbon density in P. fruticosa shrublands.     

黄土丘陵区油松人工林生态系统碳密度及其分配

以子午岭林区油松(Pinus tabulaeformis)人工林为研究对象,通过野外调查与室内分析,探讨了幼龄9a、中龄23a、近熟33a和成熟47a等不同林龄林分的生物量、含碳率、碳密度及其时空分布特征。结果表明:(1)油松林各群落平均生物量大小排序为:乔木层(76.12 t/hm2)枯落物层(14.56 t/hm2)林下植被层(3.66 t/hm2)。乔木层生物量随林龄增大而持续增加,各器官中树干所占比例最大(38%—46%),其次为叶和根,枝和皮所占比例最小;林下植被层生物量随林龄增大呈先降低后增加趋势;枯落物层生物量随林龄增大则明显增加。(2)油松乔木、林下灌木、草本、枯落物平均含碳率依次为50.2%、44.5%、43.8%和40.6%。林龄对乔木各器官含碳率无显著影响,不同器官之间含碳率存在显著性差异,具体表现为叶(53.3%)枝(51.4%)皮(50.6%)干(49.8%)根(47.3%);灌木各器官含碳率表现为枝(46.0%)叶(44.8%)根(42.5%),草本则是地上(45.2%)地下(40.2%)。土壤(0—100 cm)含碳率在0.3%—2.7%之间,且具有明显的垂直分布特征:表层含碳率高,并随土壤深度的增加逐渐降低。(3)9、23、33和47年生油松林生态系统碳密度分别为70.49、100.48、167.71和144.26 t/hm2,其空间分布序列表现为土壤层植被层枯落物层,且植被层和土壤层是油松人工林的主要碳库。林龄是影响油松林木及群落碳密度积累的主导因子之一。随林龄增加,土壤碳密度所占生态系统碳密度份额逐渐降低,乔木层和枯落物层则逐渐增加。     

西南地区草地群落灌木植物盖度对生态系统碳库的影响

中国西南地区草地主要为暖性及热性草丛、灌草丛, 约占全国草地面积的1/10, 分析灌木植物盖度与草地碳库及其构成的关系对于准确评估尚处于次生演替阶段的南方草地碳储量具有重要意义。该研究基于野外实地调查, 将西南地区不同地貌类型的41个代表性草地样地依据灌木植物盖度划分为3种类型: 无灌木植物草地群落(灌木植物盖度为0)、低灌木植物盖度草地群落(灌木植物盖度0-10%)和高灌木植物盖度草地群落(灌木植物盖度10%-30%), 测定了群落地上、地下生物量和凋落物生物量以及植物和土壤碳含量, 计算碳密度。结果表明: 随着草地群落灌木植物盖度增大, 生态系统植被碳密度从0.304 kg·m ^-2增加到1.574 kg·m ^-2, 其中根系和凋落物碳库也呈增长趋势; 土壤碳密度从7.215 kg·m ^-2增加到9.735 kg·m ^-2, 生态系统碳密度从7.519 kg·m ^-2增加到11.309 kg·m ^-2。草地碳库构成中, 低灌木植物盖度草地群落的土壤碳库占生态系统碳库比例最小。草地群落灌木植物盖度增加改变了草地生态系统碳库构成并导致生态系统碳库增加, 建议在估算草地生态系统碳库时, 需要统筹考虑并兼顾南方地区草地群落灌木植物盖度变化。     

添加铜尾矿矿砂的栽培基质对黄花苜蓿幼苗生长及部分生理指标的影响

采用盆栽法对种植于添加铜尾矿矿砂(体积分数0%、25%、50%、75%和100%)栽培基质中的黄花苜蓿(Medicago falcata Linn.)幼苗的生长及部分生理指标的变化进行了分析。结果表明:随栽培基质中铜尾矿矿砂体积分数的提高,黄花苜蓿的株高、根长、地上和地下部分干质量以及耐性指数均呈逐渐下降的趋势且总体上低于对照,但仅在铜尾矿矿砂体积分数较高(75%和100%)的条件下株高和地上部分干质量与对照差异显著(P<0.05);地上和地下部分的CAT活性和叶片光合色素(包括叶绿素a、叶绿素b和类胡萝卜素)含量均逐渐下降且总体上低于对照,而地上和地下部分的POD活性、GSH含量和O-·2含量则总体上呈逐渐增加的趋势且高于对照。在铜尾矿矿砂体积分数25%~75%的条件下,地上和地下部分的SOD活性逐渐增加且显著高于对照;而在铜尾矿矿砂体积分数100%的条件下,地上部分的SOD活性显著低于对照,而地下部分的SOD活性则略降低但显著高于对照。各处理组幼苗地上和地下部分的MDA含量均不低于对照;而各处理组AsA含量变化则呈波动趋势。综合分析结果表明:黄花苜蓿对铜尾矿矿砂具有一定的适应性,可用于铜尾矿矿砂的绿化固着以及铜污染环境的植物修复。     

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。     

大兴安岭火烧迹地不同恢复方式碳储量差异

为了探讨不同恢复方式对大兴安岭重度火烧迹地碳储量的影响,以人工恢复(兴安落叶松、樟子松)和天然恢复的林分为研究对象,采用干烧法对乔木层、灌木层、草本层和枯枝落叶层含碳率进行测定.采用全收获法和平均标准木法获得林分各组分生物量估算森林植被的碳储量,分析不同恢复方式下林分各组分碳储量的分配特征.结果表明： 人工恢复和天然恢复的林分灌木层平均含碳率高于乔木层和草本层.兴安落叶松人工林灌木层平均含碳率为45.8%、枯枝落叶层为45.3%、乔木层为44.4%、草本层为33.6%.樟子松人工林灌木层和乔木层平均含碳率高于50%.天然次生林乔木层、灌木层和枯枝落叶层平均含碳率在42%左右.森林植被层中,生物量贡献率从大到小依次为乔木层、灌木层和草本层.兴安落叶松人工林森林植被层和枯枝落叶层生物量总和为123.90 t·hm^-2,远高于樟子松人工林和天然次生林.火烧后人工恢复23年的兴安落叶松人工林森林植被碳储量为50.97 t·hm^-2,其中,乔木层碳储量为49.87 t·hm^-2,占森林植被层总碳储量的97.8%,草本层所占比重仅为0.02%.人工恢复的林分植被层总碳储量高于天然恢复的林分,火烧迹地在这一时段内采用人工恢复的方式较天然恢复碳汇能力更强.     

Above- and Belowground Biomass Allocation in Shrub Biomes across the Northeast Tibetan Plateau

Biomass partitioning has been explored across various biomes. However, the strategies of allocation in plants still remain contentious. This study investigated allocation patterns of above- and belowground biomass at the community level, using biomass survey from the Tibetan Plateau. We explored above- and belowground biomass by conducting three consecutive sampling campaigns across shrub biomes on the northeast Tibetan Plateau during 2011–2013. We then documented the above-ground biomass (AGB), below-ground biomass (BGB) and root: shoot ratio (R/S) and the relationships between R/S and environment factors using data from 201 plots surveyed from 67 sites. We further examined relationships between above-ground and below-ground biomass across various shrub types. Our results indicated that the median values of AGB, BGB, and R/S in Tibetan shrub were 1102.55, 874.91 g m^-2, and 0.85, respectively. R/S showed significant trend with mean annual precipitation (MAP), while decreased with mean annual temperature (MAT). Reduced major axis analysis indicated that the slope of the log-log relationship between above- and belowground biomass revealed a significant difference from 1.0 over space, supporting the optimal hypothesis. Interestingly, the slopes of the allometric relationship between log AGB and log BGB differed significantly between alpine and desert shrub. Our findings supported the optimal theory of above- and belowground biomass partitioning in Tibetan shrub, while the isometric hypothesis for alpine shrub at the community level.     

中国寒温带不同林龄白桦林碳储量及分配特征

为了解中国寒温带地区不同林龄白桦林生态系统碳储量及固碳能力, 在样地调查基础上, 以大兴安岭地区25、40与61年白桦(Betula platyphylla)林生态系统为研究对象, 对其乔木层、林下地被物层(灌木层、草本层、凋落物层)、土壤层(0-100 cm)碳储量与分配特征进行调查研究。结果表明白桦林乔木层各器官碳含量在440.7-506.7 g·kg ^-1之间, 各器官碳含量随着林龄的增长而降低; 灌木层、草本层碳含量随林龄的增加呈先降后升的变化趋势; 凋落物层碳含量随林龄增加而降低; 土壤层(0-100 cm)碳含量随林龄增加而显著升高, 随着土层深度的增加而降低。白桦林生态系统各层次碳储量均随林龄的增加而明显升高。25、40与61年白桦林乔木层碳储量分别为11.9、19.1和34.2 t·hm ^-2, 各器官碳储量大小顺序表现为树干>树根>树枝>树叶, 树干碳储量分配比例随林龄增加而升高。25、40与61年白桦林生态系统碳储量分别为77.4、180.9和271.4 t·hm ^-2, 其中土壤层占生态系统总碳储量的81.6%、87.7%和85.9%, 是白桦林生态系统的主要碳库。随林龄增加, 白桦林年净生产力(2.0-4.4 t·hm ^-2·a ^-1)、年净固碳量(1.0-2.1 t·hm ^-2·a ^-1)均出现增长, 老龄白桦林仍具有较强的碳汇作用。     

Estimation of biomass allocation and carbon density of Rhododendron simsii shrubland in the subtropical mountainous areas of China

Aims As an important potential carbon sink, shrubland ecosystem plays a vital role in global carbon balance and climate regulation. Our objectives were to derive appropriate regression models for shrub biomass estimation, and to reveal the biomass allocation pattern and carbon density in Rhododendron simsii shrubland.
Methods We conducted investigations in 27 plots, and developed biomass regression models for shrub species to estimate shrub biomass. The biomass of herb and litterfall were obtained through harvesting. Plant samples were collected from each plot to measure carbon content in different organs.
Important findings The results showed that the power and linear models were the most appropriate equation forms. The D and D²H (where D was the basal diameter (cm) and H was the shrub height (m)) were good predictors for organ biomass and total biomass of shrubs. All of the biomass models reached extremely significant level, and could be used to estimate shrub biomass with high accuracy. It was more difficult to predict leaf and annual branch biomass than stem biomass, because leaf and annual branch were susceptible to herbivores and inter-plant competition. The mean biomass of the shrub layer was 20.78 Mg·hm^-2, in which Rhododendron simsii and Symplocos paniculata biomass accounted for 93.63%. Influenced by both environment and species characteristics, the biomass of the shrub layer organs was in the order of stem > root > leaf > annual branch. The root:shoot ratio of the shrub layer was 0.32, which was less than other shrubs in subtropical regions. The relative higher aboveground biomass allocation reflected the adaptation of plants to the warm and humid environment for more photosynthesis. The mean total community biomass was 26.26 Mg·hm^-2, in which shrub layer, herb layer and litter layer accounted for 79.14%, 7.62% and 13.25%, respectively. Litter biomass was relatively high, which suggested that this community had high nutrient return. There were significant correlations among aboveground biomass, belowground biomass and total biomass of shrub layer and herb layer. The mean biomass carbon density of the community was 11.70 Mg·hm^-2 and the carbon content ratio was 44.55%. The carbon density was usually obtained using the conversion coefficient of 0.5 in previous studies, which could overestimate carbon density by 12.22%.