Biomass allocation and leaf stoichiometric characteristics in four desert herbaceous plants during different growth periods in the Gurbantünggüt Desert,China

荒漠草本植物是荒漠生态系统物种多样性的主体, 对其生物量分配及叶片化学计量特征随植物生长的变化规律的研究有助于深入了解荒漠草本植物生存策略和功能特征。该文选择古尔班通古特沙漠4种优势草本(2种短命植物, 2种一年生长营养期植物)为研究对象, 通过野外原位多时段取样, 对比研究了四者生物量分配、叶片N-P化学计量学随植物生长的变化特征, 以及二者之间的关系。结果表明, 在生物量累积过程中, 4种植物根冠比逐渐减小, 地上与地下生物量间的相关生长关系也发生变化, 其中琉苞菊(Hyalea pulchella)和角果藜(Ceratocarpus arenarius)的相关生长指数先增加后减小, 并趋于稳定, 而尖喙牻牛儿苗(Erodium oxyrrhynchum)和沙蓬(Agriophyllum squarrosum)的相关生长指数由小到大并趋于等速生长。琉苞菊叶片N、P含量呈逐渐增长趋势, 而另外3种植物呈下降趋势, 表明所研究的荒漠植物在生长过程中, 叶片N-P化学计量发生改变, 叶片化学计量特征与生物量指标的相关性较弱。     

青藏高原高寒灌丛生态系统草本层生物量分配格局

青藏高原高寒灌丛生态系统生物量分配的研究相对较少,尤其是其草本层。为了探究高寒灌丛生态系统草本层生物量分配特征及其影响因素,分析了青藏高原东北部灌丛生态系统的49个高寒灌丛样地的草本层地上与地下生物量特征及其气候因子之间的关系。结果表明1)草本层地上生物量与地下生物量分别为121.1,342.8 g/m2均大于高寒草地的地上生物量与地下生物量。2)草本层的根冠比为3.6低于高寒草地的根冠比。3)地上生物量与地下生物量之间呈现幂函数的关系y=8.0x0.83(R2=0.48,P0.001)。4)根冠比与年均温度、年均降雨量之间没有显著的相关关系。     

古尔班通古特沙漠中4种荒漠草本植物的生物量与化学计量特征

对于荒漠植物不同生长期生物量分配和化学计量比的研究有助于深入了解荒漠植物的功能结构,更好掌握环境对植物的生存影响。本研究选取古尔班通古特沙漠4种一年生荒漠草本植物沙蓬（Agriophyllum sqarrosum（L.）Moq.）、雾冰藜（Bassssia dasyphylla（Fisch.et Mey.）O.Kuntze）、角果藜（Ceratocarpus arenarius L.）和碱蓬（Suaeda glauca（Bge.）Bge.）对比研究了4种生物量分配与N、P化学计量学随植物生长的变化。结果显示：（1）4种荒漠植物生物量积累配过程中,根冠比随生长季的延长逐渐降低。地上、地上生物量相关生长关系表明,角果藜为等速→异速的变化过程,沙蓬从采样初期至末期的变化过程为异速→等速生长,而沙蓬和碱蓬的相关生长指数相反,分别为异速→等速→异速、等速→异速→等速的变化格局;（2）4种植物N、P含量随生长期的延长逐步降低。在整个生长季节4种植物的N与P含量的变化趋势均为相似。（3）植物N、P含量间达到正相关显著,除沙蓬和雾冰藜的N：P之外其余指标分别与植物的地上、地下生物量及总生物量间呈负相关显著,而根冠比、相关生长指数与化学计量特征间未达到显著水平,表明了二者较弱的相关性。研究表明,4种荒漠草本植物生物量与化学计量特征的相关性不大,说明化学计量比并不是影响植物生物量及生活策略的主要因素,而更多是受植物自身遗传特性的影响。同时也体现了荒漠草本植物在养分匮乏的条件下,形成了自身独特的生理生态特征,且具有相对稳定的适应特性。     

陆生植物生物量分配对模拟氮沉降响应的Meta分析

分析了陆生植物地上、地下各组织中生物量分配对氮沉降的响应,为研究大气氮沉降背景下陆地生态系统的碳、氮循环过程及植物生物量分配、立木收获、定向培育等相关研究和实践提供参考依据。共收集整理了国内外63篇论文的原始数据资料进行Meta分析(Meta-analysis),用以定量评估氮沉降对植物生物量分配的影响,并通过亚组分析进一步探讨了不同生态系统类型、植物种类、氮肥形式、施氮水平和持续时间对生物量分配的影响。结果表明,总体来看施氮会显著促进植物地上部分生物量分配,植物叶生物量和茎生物量在施氮条件下均显著增加;然而地下生物量所受促进作用要低于地上部分,表现为植物细根生物量和粗根生物量在氮输入下并没有显著变化;植物根冠比在氮沉降下显著降低;叶重比、茎重比和根重比在氮沉降下没有显著变化。此外,亚组分析结果表明生态系统类型和植物类型会显著影响植物总生物量和根冠比对氮沉降的响应,草本植物在氮沉降下的生物量累积明显优于木本,这说明短期氮沉降可能会增加草本的覆盖面积;施肥形式对根冠比的影响存在明显差异,相比于尿素,硝酸铵对植物根冠比的作用更显著;不同施氮水平显著影响地上生物量分配,中氮水平(本研究为60—120 kg hm-2a-1)促进作用最大,高氮水平(本研究为≥120 kg hm-2a-1)促进作用明显减弱,这与总生物量的变化一致,表明过高的氮沉降量将抑制植物生长;氮沉降处理时间长短对植物地上生物量的影响也存在显著差异,当施氮时间高于3年,氮沉降对地上生物量的促进作用几乎消失。总之,短期氮沉降会使植物分配更多生物量给地上部分,且氮沉降对草本植物生物量的累积作用明显优于木本,这些发现可为未来大气氮沉降背景下植物地上、地下部分碳存储、植物群落结构、植被动态等相关研究提供科学依据。     

古田山自然保护区地下芽植物多样性及其生物量分配策略

地下芽植物能够通过地下储存器官占据生境资源、储存营养物质等策略来获得生态优势,其地下储存器官多样性以及生物量分配策略,对地下芽植物物种组成以及生态系统功能产生重要影响。然而,以往研究多关注草地生态系统的地下芽植物,对森林地下芽植物的了解仍然缺乏。采集了古田山国家级自然保护区不同海拔分布的693个草本植物个体,分析了地下芽植物及其地下储存器官的类型与多样性,比较了地下芽植物与非地下芽植物的地上、地下各器官的绝对、相对生物量。结果显示：（1）地下芽植物的相对丰富度为69.1%,相对多度为88.2%。大多为根状茎植物,主要由禾本科、莎草科、堇菜科和蕨类植物组成。（2）除茎外,地下芽植物各器官的绝对生物量（叶：1.94g,根：0.65g,地上部分：2.0g,地下部分：4.1g）均大于非地下芽植物（叶：0.26g,根：0.13g,地上部分：0.68g,地下部分：0.13g）。（3）地下芽植物叶（0.40）与茎（0.14）的相对生物量小于非地下芽植物（叶：0.48,茎：0.35）,地下部分相对生物量（0.56）大于非地下芽植物（0.17）。本研究表明,以根状茎植物为主的地下芽植物是古田山亚热带森林生态系统草本植物的主要构成者,且个体普遍较大,倾向于将生物量投资于地下器官。这些结果为认识地下芽植物的生态策略与功能以及草本植物群落管理提供了科学依据。     

青藏高原东部高寒灌丛生物量分配对模拟增温的响应

植物生物量分配特征的变化反映了不同环境条件下植物的适应策略,全球气候变暖正在改变青藏高原高寒生态系统植被动态和生物量分配格局。然而,到目前为止,有关青藏高原高寒灌丛生物量分配特征对气候变暖的响应研究较少。为了探究气候变暖对高寒灌丛生物量分配的影响,以青藏高原东部典型的窄叶鲜卑花高寒灌丛为研究对象,分析了高寒灌丛灌木层、草本层和群落水平生物量分配特征对开顶式生长室（OTC）模拟增温的响应。研究结果表明：整个生长季节,模拟增温使空气温度和表层土壤温度分别升高0.6℃和1.2℃,使表层土壤水分含量下降2.7%。模拟增温使草本层和群落地上生物量显著增加57.8%和7.2%,使灌木层、草本层和群落根系生物量显著增加42.5%、105.6%和45.6%。然而,模拟增温没有显著影响灌木层地上生物量。同时,模拟增温使灌木层、草本层和群落总生物量显著增加25.6%、85.7%和28.4%,使灌木层、草本层和群落根冠比显著增加33.2%、30.4%和36.0%。由此可见,模拟增温在促进高寒灌丛生物量生产的同时将显著提高向地下根系部分的分配比例。Pearson相关分析表明,高寒灌丛生物量分配与空气温度、土壤温度和土壤硝态氮含量呈显著正相关关系;多元线性回归分析结果也表明,空气温度、土壤温度和土壤硝态氮含量解释了高寒灌丛生物量分配变异的50.8%以上。这些结果表明,青藏高原东部高寒灌丛植被能够通过调节生物量分配模式应对未来气候变暖。     

檵木生物量分配特征

生物量是生态系统最基本的数量特征,其在各器官间的分配反映了植物适应环境的生长策略,是物种进化、生物多样性保护和生态系统碳循环研究的核心问题。檵木(Loropetalum chinense)灌丛是中国亚热带灌丛生态系统最具优势的一种灌丛类型。该研究以该灌丛建群种檵木为研究对象,采用整株收获法在个体水平上研究了器官间的异速生长、生物量在各器官间的分配以及与个体大小、灌丛更新起源和生境因子之间的关系。研究发现:檵木地上-地下相对生长关系符合等速生长规律,但随径级增大其等速生长关系可能发生变化;较小径级檵木叶-茎、叶-根为等速生长,随径级增大转换为异速生长。不同灌丛起源间,檵木叶-茎、叶-根相对生长存在显著差异。器官间相对生长的尺度系数与生境因子无显著相关关系,灌木层盖度和坡度通过影响檵木生长初期器官间的相对生长影响其生物量在器官间的分配。檵木平均叶质比为0.11,茎质比为0.55,根质比为0.34,根冠比为0.65。随径级的增大,茎质比(0.50–0.64)逐渐增大,叶质比(0.12–0.08)、根质比(0.38–0.28)和根冠比(0.91–0.43)逐渐减小。在次生灌丛中,檵木叶质比为0.12,根质比为0.33;在原生灌丛中,檵木叶质比为0.07,根质比为0.36。生物量向地上部分的分配与灌木层盖度正相关,叶质比与坡度负相关,根质比与年平均气温正相关。研究结果表明:随个体增大,檵木器官间的相对生长关系由等速生长转换为异速生长,生物量向地上部分的分配增加,地上生物量更多地分配到茎干中;干扰通过影响器官间的相对生长影响生物量在各器官间的分配,干扰导致生物量向叶的分配增加,向根的分配减少;光照减少促进生物量向地上部分的分配,坡度增加导致生物量向叶的分配减少,年平均气温升高促进生物量向根系的分配,年降水量的变化对生物量分配无显著影响。檵木生物量分配策略在一定程度上支持了最优分配假说。     

新疆的短命植物（一）独特的生态生物学特点

短命植物又称短营养期植物、短期生植物。它包括当年完成其生活周期、整个植株干枯死亡,来年春季再由种子形成新个体的一年生短命植物;也包括植株当年生地上部分枯死,而地下器官则处于休眠状态,到第二年春天既可由种子繁殖新个体,也能从地下芽生长出新植物体的多年生短命植物。前者称为短命植物,后者叫做类短命植物。原苏联的中亚地区,是短命植物区系的现代分布中心。在我国,它集中分布于新疆北部的山前平原及低山丘陵地带,是新疆植物区系组成的一个独特类群,在学术上和生产实践中都受到人们的关注。不同的植物适应环境的方式各种…     

四种一年生荒漠植物构件形态与生物量间的异速生长关系

1年生草本植物是古尔班通古特沙漠夏秋季节草本层片的主要组成部分。选择4种藜科1年生草本植物(刺沙蓬、沙蓬、角果藜和对节刺)作为研究对象,对比分析了各物种构件形态特征、生物量分配以及它们之间的异速生长关系。结果表明:沙蓬个体最大,其次为刺沙蓬,角果藜和对节刺个体最小;对节刺具有最大的根冠比(R/S),其次是刺沙蓬,沙蓬和角果藜R/S最小。4种植物构件形态与生物量间均呈显著正相关,表现出强烈的协同变化趋势。R/S与绝大部分指标间呈显著负相关,表明随个体增大地下生物量分配比例逐渐减小。4种植物各构件形态、地上及地下生物量间大部分呈指数1.0的异速生长关系,但各物种间的异速生长指数绝大部分无显著差异且具有共同的异速生长指数。研究表明:尽管物种不同、个体大小迥异,但4种1年生植物构件特征间多具有相同的生长速率和协同变化特征,体现了1年生植物这一生活型内的不同物种对干旱荒漠环境的趋同适应。     

野生和栽培滇龙胆草生物量分配及异速生长

植物地上-地下生物量分配反映了植物的生长策略。草本植物地上-地下生物量是否是等速生长还有争论。养分和密度会影响药用植物地上-地下生物量的分配。本研究比较了野生和栽培滇龙胆草地上-地下生物量分配的差异,分析了栽培年限和密度对栽培滇龙胆草生物量分配的影响。结果表明,野生与栽培滇龙胆草地上-地下生物量分配存在显著差异(P0.05),可能与土壤营养水平和竞争强度有关,但地下生物量和地上生物量为近等速生长关系。密度、密度与生长年限的交互作用均对地下生物量有显著影响(P0.05)。滇龙胆草栽培时需控制密度并研究施肥和土壤微生物等因素对其药用部位产量(地下生物量)的影响。     

Sexual differences in biomass and nutrient allocation of first-year Silene dioica plants

Reproductive and somatic biomass, nitrogen (N), and phosphorus (P) pools were compared between females and males in 1st-year plants of Silene dioica. We estimated irretrievable resources allocated to seeds, pollen, flowers, and unrecovered summer leaf investment by collecting plant parts at abscission throughout the season. At the end of the season, we determined resources lost through senescent stems and autumn leaf turnover and resources stored in perennial roots and overwintering buds. Sexual differences in allocation patterns depended on the resource used for comparison, and whether absolute or proportional resource pools were assessed. Total resource pools in terms of biomass and N were similar for females and males. However, male plants acquired relatively more P. The proportional reproductive investment, i.e., reproductive effort, was similar for males and females in terms of biomass and N. In terms of P, male reproductive effort was higher. There was no difference between sexes in the proportional and relative biomass allocated to perennial roots and overwintering buds. However, in terms of absolute and relative N allocation to below-ground parts, females had larger reserves than males. Females, moreover, had a larger proportion of their P in below-ground parts. However, as male total P pools were larger, absolute P reserves did not differ between sexes. The high reproductive effort and N depletion of below-ground parts in males resulted largely from higher flower production compared to females. In females, seeds were the major component of reproductive effort. These results show that if biomass and nutrient allocation are assessed in parallel for dioecious plants, we obtain a more complete view of their sexual differences. Received: 07 May 1998 / Accepted: 30 October 1998     

Dry matter partitioning and root length/leaf area ratios in herbaceous perennial plants with diverse altitudinal distribution

Summary Partitioning patterns in 22 exclusively low and 27 exclusively high altitude perennial herbaceous species were examined in order to test the hypothesis that plants of high altitudes allocate more dry matter to below-ground parts and in particular to storage organs, than typical low altitude plants. Our results raise some doubts about the general validity of this hypothesis. The mean fractions of total dry matter allocated to green leaves (22±2% s.e. at low and 24±2% at high altitude) and special storage organs (28±4% at both altitudes) do not differ significantly among sites. The mean relative portions of total dry matter allocated to above-ground plant parts amount to 57±3% at low and 42±3% at high elevation (P=0.002) and differ less than often assumed. The greater below-ground fraction at high altitude results from reduced stem and proportionally increased fine root compartments. At high altitude specific root length is increased by 50% and mean individual rooting density is tripled. Fine root length per unit leaf area is 4.5 times greater (P<0.001). However, interspecific variation in all these quantities is considerable and species with quite contrasting partitioning patterns coexist at both elevations. This suggests that the success of perennial herbaceous plants at high elevations does not necessarily depend on a large below ground biomass fraction. The increased fine root length at high altitude may substitute for reduced mycorrhizal infection. Figure 1 provides a graphical summary.     

Effects on soil,microclimate and vegetation of the native-invasive <Emphasis Type="Italic">Retama monosperma</Emphasis> (L.) in coastal dunes

The aim of this study was to analyse and quantify the effects of the canopy of the native-invasive N-fixer woody shrub Retama monosperma in the dune ecosystem, affecting the structure and function of the dune environment as well as plant community, in the context of the facilitation mechanism. Air temperature and relative humidity; soil pH, electric conductivity, organic matter (OM) and nutrient content; above and below-ground vegetation biomass, litter mass, species richness and Shannon diversity were determined and compared from sampling plots below the R. monosperma canopy and in canopy gaps within a coastal dune system in SW Spain. The relationships between soil OM and nutrient contents and above and below-ground vegetation biomass, litter mass, species richness and Shannon diversity were also assessed. A predominance of positive interactions was confirmed. The canopy of R. monosperma ameliorated temperature extremes beneath, and soil OM and nutrient concentrations were increased by 188–466%, compared to those found in gaps. Plant biomass increased by 442% beneath the canopy and was composed almost exclusively of herbaceous annuals. Plant diversity was not affected. Plant communities were clearly structured as fertility islands, distributed in an environmentally stressful dune matrix characterized by scarce vegetation cover and low biomass.     

SEXUAL DIMORPHISM IN BIOMASS ALLOCATION AND CLONAL GROWTH OF XANTHOXYLUM AMERICANUM

Reproduction can have a high resource cost. It has been suggested that greater investments in sexual reproduction by female dioecious plants leads to a lower rate of vegetative growth in females than in males. In this study, we investigated sexual dimorphism in biomass allocation and genet growth of the dioecious clonal shrub, northern prickly ash (Xanthoxylum americanum). The allocation of biomass over the course of one growing season to reproductive tissue, leaves, and growth of aboveground first-year wood, was compared in 18 clones growing in fields and six clones in woods in southeastern Wisconsin during 1985 and 1986. In addition, the number of shoots per clone, and weight of nonfirst-year wood (accumulated biomass) above- and below-ground were estimated. In open field sites, male clones allocated more biomass to new wood and less to reproduction than females, although males allocated more to flowers alone. Accordingly, male clones had significantly more shoots and more accumulated biomass both above- and below-ground than female clones. In the woods, where fruit set was near zero, there were few significant differences between male and female clones in either biomass allocation or accumulated biomass. These results support the hypothesis that the high resource investment in fruit production by females reduces their vegetative growth relative to males.     

古尔班通古特沙漠四种草本植物不同生长期C、N、P化学计量比的动态变化分析

以古尔班通古特沙漠地区广泛分布的4种荒漠草本植物沙蓬（Agriophyllum squarrosum（L.） Moq.）、雾冰藜（Bassia dasyphylla（Fisch.et Mey.） O.Kuntze）、角果藜（Ceratocarpus arenarius L.）和碱蓬（Suaeda glauca（Bge.） Bge.）为对象,对他们在不同生长期的C、N、P含量及计量比的动态变化进行研究。结果显示：4种植物的C、N、P含量以及C：N、C：P、N：P在整个生长期的变化趋势不同,不同生长期各个指标的变异系数在物种间存在明显差异;4种植物的C、N、P含量及计量比的季节性变异分析结果表明,N、P含量及C：N、N：P的季节性变异幅度较大,相反,C含量和C：P的变异幅度较小;4种植物C含量和C：P由季节变化所引起的变异系数范围分别为2.43%~15.80%和6.77%~18.67%,而N、P含量和C：N、N：P的变异系数范围分别为21.26%~34.38%、11.18%~30.26%、18.52%~27.11%、14.90%~25.91%;整个生长季内,4种植物C、N、P含量及计量比的变异系数依次为：N（30.00%） > C：N（22.87%） > N：P （20.12%） > P（17.76%） > C：P（11.72%） > C（9.02%）。研究结果表明4种植物在不同生长周期的C、N、P含量及计量比的变化规律与他们的生长周期和植物种类存在显著相关性。     

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.     

Spatial patterns of desert annuals in relation to shrub effects on soil moisture

Questions: What are the effects of a shrub (Haloxylon ammodendron) on spatial patterns of soil moisture in different seasons? How does productivity of understorey annuals respond to these effects? Are such effects always positive for annuals under shrubs? Location: South Gurbantunggut Desert, northwest China. Methods: Using geostatistics, we explored seasonal patterns of topsoil moisture in a 12 × 9‐m plot over the growing season. To determine spatial patterns of understorey annuals in response to H. ammodendron presence, biomass of annuals was recorded in four 0.2 × 5.0‐m transects from the centre of a shrub to the space between shrubs (interspace). We also investigated vertical distribution of root biomass for annuals and soil moisture dynamics across soil profiles in shrub‐canopied areas and interspaces. Results: Topsoil moisture changed from autocorrelation in the wet spring to random structure in the dry season, while soil moisture below 20 cm was higher in shrub‐canopied areas. Across all microhabitats, soil moisture in upper soil layers was higher than in deeper soil layers during the spring wet season, but lower during summer drought. Topsoil was close to air‐dry during the dry season and developed a ‘dry sand layer’ that reduced evaporative loss of soil water from deeper layers recharged by snowmelt in spring. Aboveground biomass of understorey annuals was lowest adjacent to shrub stems and peaked at the shrub margin, forming a ‘ring’ of high herbaceous productivity surrounding individual shrubs. To acclimate to drier conditions, annuals in interspaces invested more root biomass in deeper soil with a root/shoot ratio (R/S) twice that in canopied areas. Conclusions: Positive and negative effects of shrubs on understorey plants in arid ecosystems are commonly related to nature of the environmental stress and tested species. Our results suggest there is also microhabitat‐dependence in the Gurbantunggut Desert. Soil water under H. ammodendron is seasonally enriched in topsoil and deeper layers. Understorey annuals respond to the effect of shrubs on soil water availability with lower R/S and less root biomass in deeper soil layers and develop a ‘ring’ of high productivity at the shrub patch margin where positive and negative effects of shrubs are balanced.     

Above- and belowground biomass allocation and its regulation by plant density in six common grassland species in China

Above- and belowground biomass allocation is an essential plant functional trait that reflects plant survival strategies and affects belowground carbon pool estimation in grasslands. However, due to the difficulty of distinguishing living and dead roots, estimation of biomass allocation from field-based studies currently show large uncertainties. In addition, the dependence of biomass allocation on plant species, functional type as well as plant density remains poorly addressed. Here, we conducted greenhouse manipulation experiments to study above- and belowground biomass allocation and its density regulation for six common grassland species with different functional types (i.e., C₃ vs C₄; annuals vs perennials) from temperate China. To explore the density regulation on the biomass allocation, we used five density levels: 25, 100, 225, 400, and 625 plant m^?2. We found that mean root to shoot ratio (R/S) values ranged from 0.04 to 0.92 across the six species, much lower than those obtained in previous field studies. We also found much lower R/S values in annuals than in perennials (C. glaucum and S. viridis vs C. squarrosa, L. chinensis, M. sativa and S. grandis) and in C₄ plants than in C₃ plants (C. squarrosa vs L. chinensis, M. sativa and S. grandis). In addition to S. grandis, plant density had significant effects on the shoot and root biomass fraction and R/S for the other five species. Plant density also affected the allometric relationships between above- and belowground biomass significantly. Our results suggest that R/S values obtained from field investigations may be severely overestimated and that R/S values vary largely across species with different functional types. Our findings provide novel insights into approximating the difficult-to-measure belowground living biomass in grasslands, and highlight that species composition and intraspecific competition will regulate belowground carbon estimation.

     

Changes in individual plant traits and biomass allocation in alpine meadow with elevation variation on the Qinghai-Tibetan Plateau

Plant traits and individual plant biomass allocation of 57 perennial herbaceous species, belonging to three common functional groups (forbs, grasses and sedges) at subalpine (3700 m ASL), alpine (4300 m ASL) and subnival (⩾5000 m ASL) sites were examined to test the hypothesis that at high altitudes, plants reduce the proportion of aboveground parts and allocate more biomass to belowground parts, especially storage organs, as altitude increases, so as to geminate and resist environmental stress. However, results indicate that some divergence in biomass allocation exists among organs. With increasing altitude, the mean fractions of total biomass allocated to aboveground parts decreased. The mean fractions of total biomass allocation to storage organs at the subalpine site (7%±2% S.E.) were distinct from those at the alpine (23%±6%) and subnival (21%±6%) sites, while the proportions of green leaves at all altitudes remained almost constant. At 4300 m and 5000 m, the mean fractions of flower stems decreased by 45% and 41%, respectively, while fine roots increased by 86% and 102%, respectively. Specific leaf areas and leaf areas of forbs and grasses deceased with rising elevation, while sedges showed opposite trends. For all three functional groups, leaf area ratio and leaf area root mass ratio decreased, while fine root biomass increased at higher altitudes. Biomass allocation patterns of alpine plants were characterized by a reduction in aboveground reproductive organs and enlargement of fine roots, while the proportion of leaves remained stable. It was beneficial for high altitude plants to compensate carbon gain and nutrient uptake under low temperature and limited nutrients by stabilizing biomass investment to photosynthetic structures and increasing the absorption surface area of fine roots. In contrast to forbs and grasses that had high mycorrhizal infection, sedges had higher single leaf area and more root fraction, especially fine roots.     

PATTERNS OF RESOURCE ALLOCATION IN WILDFLOWER POPULATIONS OF FIELDS AND WOODS

Fifty-two populations of fifty species of wildflowers characteristic of either field or deciduous forest were analyzed to determine pattens of biomass allocation to component organs. These populations' allocation patterns were used to determine generalized allocation patterns of the herb component of earlier (field) and later (deciduous forest) secondary successional communities. The following patterns were determined: (1) The proportion of dry matter allocated to seed reproductive organs was greater in field populations than in woods populations; (2) The herbs of woodland habitats allocated a greater proportion of their resources to leaves and belowground organs than field habitat herbs; (3) The field annuals allocated a greater proportion of their resources to reproduction than field perennials; (4) Introduced species showed a higher reproductive allocation than native species of fields; (5) Regression analysis showed strong correlations of component organ biomass to total biomass and belowground biomass to shoot biomass.