Proportion Of Aboveground Biomass Research Articles

Biomass Allocation of China’s Forests as Indicated by a Literature-Based Allometry Database

Allometry reflects the quantitative relationship between the allocation of resources among different organs. Understanding patterns of forest biomass allocation is critical to comprehending global climate change and the response of terrestrial vegetation to climate change. By collecting and reorganizing the existing allometric models of tree species in China, we established a database containing over 3000 empirical allometric models. Based on this database, we analyzed the model parameters and the effect of climate on forest biomass allocation under the context of ‘optimal allocation theory’. We showed that (1) the average and median exponent of power functions for above-ground biomass were 2.344 and 2.385, respectively, which significantly deviated from the theoretical prediction of 2.667 by metabolic theory (p < 0.01). (2) The parameters of the allometric model were not constant, and not significantly correlated with temperature, precipitation, latitude, and elevation (p > 0.05), but were more closely related to individual size (p < 0.01). (3) Among different types of forests, the proportion of above-ground biomass in tropical rainforests and subtropical evergreen rainforests was significantly higher than that in temperate forests and boreal forests (p < 0.05). The proportion of trunk and branch biomass allocated to tropical rainforest was significantly higher than that of boreal forest (p < 0.05), while the proportion of root and leaf biomass allocated to tropical rainforest was significantly lower than that of boreal forest (p < 0.05). (4) The abiotic environment plays a crucial role in determining the allocation of plant biomass. The ratio of below-ground/above-ground biomass is significantly and negatively correlated with both temperature and rainfall (p < 0.01), and significantly and positively correlated with altitude and latitude (p < 0.01). This means that as temperature and rainfall increase, there is a decrease in the amount of biomass allocated to below-ground structures such as roots. On the other hand, as altitude and latitude increase, there is an increase in below-ground biomass allocation. These findings highlight the importance of considering the influence of abiotic factors on plant growth and development.

Propagation strategies of Deyeuxia angustifolia in heterogeneous habitats

Plants utilize different strategies in different environments to maximize population expansion. Understanding plant reproductive strategies in heterogeneous habitats is therefore important for explaining plant ecological adaptability, and for effectively managing and conserving ecosystems. We wanted to explore the reproductive strategy transformation of D. angustifolia in heterogeneous habitats, as well as the environmental factors driving and affecting its reproductive characteristics. To do this we measured the reproductive characteristics of D. angustifolia, as well as the soil physical and chemical properties of these heterogeneous habitats. The density, biomass per unit area, and proportion of aboveground biomass in swampy meadows were significantly higher compared to other habitats. The proportion of rhizome node buds gradually increased from swampy to typical to miscellaneous grass meadows, while the proportion of tillering node buds decreased. The allocation of sexual reproduction within D. angustifolia populations was significantly and positively correlated with plant rhizome biomass and negatively correlated with the number of tillering node buds. The propagation strategies of D. angustifolia in heterogeneous habitats were consistent with CSR theory (Competitor, Stress-tolerator, and Ruderal). The proportions of inflorescence (2.07 ± 0.52%; 1.01 ± 0.15%) and root (23.8 ± 1.5%; 19.6 ± 1.4%) biomass in miscellaneous and typical meadows were high, which tended toward the “Ruderal” adaptation strategy. In swampy meadow, D. angustifolia invested mostly in vegetative growth to produce tiller node buds (14426.67 buds/m2; 46%) and ramets (1327.11 ± 102.10 plants/m2), which is characteristic of the “Competitor” strategy. Swamp D. angustifolia resisted flooding by maintaining a resource balance in its body, and was therefore biased toward the “Stress-tolerator” strategy. Environmental factors accounted for 74.63% of reproductive characteristic variation, in which the interpretative proportions of soil water content, dissolved organic carbon, ammonia nitrogen, and nitrate nitrogen were significant (p < 0.01). When soil water content, dissolved organic carbon, and nitrate nitrogen increased, D. angustifolia tended toward the C strategy; in contrast, when soil water content decreased, amine nitrogen and available phosphorus increased, and D. angustifolia tended toward the R strategy. In a stressful environment, the escape mechanism constitutes an increased rhizome and sexual reproduction investment. In contrast, for suitable habitats, tillering node buds increased in order to expand the population via new plant production, which was the propagation strategy of D. angustifolia in heterogeneous habitats.

高寒条件下根际环境对极小种群大理白前竞争能力的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 高寒条件下根际环境对极小种群大理白前竞争能力的影响 DOI: 10.5846/stxb202203270754 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 第四次全国中药资源普查(2019PC001) Effects of rhizosphere environment on the competitive ability of extremely small population of Cynanchum forrestii Schltr under alpine conditions Author: Affiliation: Fund Project: the fourth national survey of traditional Chinese medicine resources (Grant No. 2019PC001) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大理白前(Cynanchum forrestii Schltr)是中国无危极小种群野生植物,研究高寒环境下大理白前-根际土壤系统的化学计量特征及其元素吸收,有助于解析极小种群的生存策略及其对环境的适应能力。以川西九龙县高寒草甸中的大理白前为对象,研究了其种群特征、光合色素特性、植物体和土壤的化学元素、根际土/非根际土的养分和细菌多样性。结果表明:与非根际土相比,根际土P、C/P和N/P较高而C/N较低,有机质(SOM)、全磷(TP)、全氮(TN)、速效氮(AN)、速效磷(AP)、速效钾(AK)增加;大理白前根际土P与茎的N、C/P、N/P呈正相关,而与P、C/N呈负相关。高通量测序表明,根际土/非根际土的优势细菌包括6个类群。根际土的变形菌门、芽单胞菌门相对丰度较高,而酸杆菌门、拟杆菌门、放线菌门、厚壁菌门的相对丰度较低,拟杆菌门相对丰度降低了45.53%,变形菌门相对丰度增加了32.89%。RDA分析结果显示,变形菌门相对丰度与土壤C、N、P呈正相关。在高寒草甸中,大理白前株丛呈均匀分布,平均株高(27 cm)高于群落其他植物的平均水平,地上生物量占比高达41.24%,种群密度和生态位宽度较大;随着株高增加,叶面积增大,光合色素含量和Chla/Chlb先增加后下降,但比叶质量变化不大;根茎叶对土壤元素均具有富集作用,其中对Ca、Mn、Na、K、P富集能力和对P、Ca、K转移能力较强。叶的C/N、C/P和N/P高于根、茎,各器官的N/P均小于14,表明养分主要分配到根、茎且受N限制。上述结果表明,大理白前富集有益的土壤微生物以改善根际土壤养分状况,提高植物体对Ca、Mn、Na、K、P等元素的吸收和转移能力,增强抗冻和抗辐射能力,并借助株高和叶面积的优势,弥补了光合色素含量较低的缺陷,从而提高了大理白前在高寒环境中的种间竞争能力和适合度,但却加剧种内竞争,导致其株丛呈均匀分布。推测种内竞争激烈是大理白前局限分布的原因之一。 Abstract:Cynanchum forrestii Schltr, an erect perennial herb of Asclepiadaceae, is a wild plant with extremely small population(WPESP) in China. This unique plant grows in a variety of habitats such as plateau and mountain at altitudes of 1000-3500 m. The root of C. forrestii is often used as a substitute for the traditional Chinese medicine "Baiwei". In Jiulong County, Ganzi Tibetan Autonomous Prefecture, western Sichuan Province, China, this plant is confined to alpine meadows in valleys at the altitude of 3100-3500 m. The rhizosphere is a part of the soil ecosystem where plant roots, soil and the soil microorganisms interact with each other. Soil microorganisms actively participate in soil material transformation and play a leading role in nutrient cycling by influencing the transformation of mineral elements. Most of the nutrients needed of plants come from soil and enter plants through rhizosphere interaction. The chemical element characteristics of plants can reflect the supply of nutrients to the soil. The study of plant and soil stoichiometric characteristics helps to understand the growth strategies of plants and their adaptability to the environment. Investigating the stoichiometric characteristics and element enrichment of the C. forrestii-rhizosphere soil system under the alpine environment will help to analyze the survival strategies of the extremely small populations and their adaptability to the environment. In this study, we investigated the effects of rhizosphere soil nutrients and bacterial community on population characteristics and photosynthetic characteristics of C. forrestii in the alpine meadow of Jiulong County by using plot and line transect sampling methods, physiological and biochemical analysis and Illumina-MiSeq high-throughput sequencing technology. The results showed that compared with the non-rhizosphere soil, the rhizosphere soil had higher P, C/P and N/P and lower C/N, and increased soil organic matter (SOM), total phosphorus (TP), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), and available potassium (AK). The Pearson correlation analysis showed that the value of N, C/P, N/P in C. forrestii stem were significantly positively correlated with the rhizosphere soil P, while the value of P and C/N were significantly negatively correlated with the rhizosphere P. High-throughput sequencing showed that the dominant bacteria in rhizosphere soil/non-rhizosphere soil included 6 groups. Compared with non-rhizosphere soil, the relative abundance of Proteobacteria and Gemmatimonadetes in rhizosphere soil was higher, while the relative abundance of Acidobacteria, Bacteroidetes, Actinobacteria and Firmicutes was lower. The relative abundance of Bacteroidetes decreased by 45.53%, and the relative abundance of Proteobacteria increased by 32.89%. Redundancy analysis (RDA) results showed that the relative abundance of Proteobacteria was positively correlated with soil C, N and P contents. The average plant height of C. forrestii was 27 cm, which was higher than the average height of other plants in the community. The proportion of above ground biomass reached 41.24%, and the population density and niche width also were larger than those of other plants. With the increase of plant height and leaf area, the photosynthetic pigment contents and Chla/Chlb raised first and then decreased, but leaf mass per area (LMA) had little change. Plants had enrichment effect on soil elements, the relatively high enrichment capacity for Ca, Mn, Na, K and P, and high transfer capacity for P, Ca, and K. Analysis of C, N, P stoichiometry showed that the C/N, C/P and N/P in C. forrestii leaves were higher than those of roots and stems, and the N/P of each organ was less than 14, indicating that N was the limit factor. In general, C. forrestii enriched beneficial soil microorganisms to improve the nutrient status of the rhizosphere soil, enhanced the absorption and transfer of elements such as Ca, Mn, Na, K, and P in plants, and promoted the ability to resist freezing and radiation. With the advantages of plant height and leaf area, it made up for the defect of low photosynthetic pigment content, thereby improving the interspecific competition ability and fitness of C. forrestii in the alpine environment, but intraspecific competition was intensified, which resulted in uniform distribution of plant clusters. It was speculated that the intense intraspecific competition was one of the reasons for the limited distribution of C. forrestii. 参考文献 相似文献 引证文献

Belowground bud bank of invasive plants contributes to their successful invasion in coastal wetlands

The capacity of vegetative regeneration can contribute to the invasion success of alien plant species in introduced ranges. Belowground bud bank is a trait closely related to vegetative regeneration, but it is still unknown whether belowground bud bank can help invasive alien plants to successfully invade into native plant communities. We measured bud bank density and aboveground biomass of invasive alien and native plants, and species diversity in four wetlands along a soil moisture gradient in Zhejiang Province in East China. Overall, bud bank density, aboveground biomass, and plant diversity differed significantly among the four wetlands along the soil moisture gradient. Bud bank density, aboveground biomass, and the relative dominance of invasive plants increased with increasing soil moisture, whereas bud bank density and the relative dominance of the native plants showed the opposite trend. For invasive plants, both the proportion of aboveground biomass and the relative dominance were significantly positively related to their bud proportion. These results suggest that belowground bud bank of invasive alien plant species can contribute to their successful invasion in native plant communities. Therefore, measures such as plowing and raking could be taken to destroy or restrict belowground bud bank of invasive alien plants to prevent their invasion and to restore native vegetation.

Exploring genetic diversity for grain partitioning traits to enhance yield in a high biomass spring wheat panel

Abstract Breeding to raise yield potential through enhancing photosynthesis will have limited impact unless harvest index (HI: proportion of above-ground biomass as grain yield) is maintained or ideally increased. Boosting grain dry matter (DM) partitioning will require increased allocation of assimilates to sink organs to enhance spike growth. A high biomass spring wheat panel of 150 genotypes encompassing elite, landrace-derived and synthetic-derived lines was grown under yield potential conditions in two seasons in NW Mexico. Results showed that the incorporation of landrace-derived and synthetic-derived backgrounds into elite lines resulted in higher expression of above-ground biomass (AGDM), leaf lamina and stem DM partitioning at anthesis. However, no grain yield advantage was observed over elite lines, due to lower grain number per unit area (GN) and decreased harvest index (HI). Positive linear associations were found among spike fertility-related traits - fruiting efficiency (grains per unit of spike DM at anthesis; FE), GN and HI - which were, in turn, related positively with grain yield (GY). Stem-internode 3 length and internode 3 DM partioning were negatively associated with spike partitioning index (SPI: ratio of spike DM to total above-ground DM at anthesis) and GN, suggesting an enhanced competition for assimilates between the spike and stem internode 3 during stem elongation. Within-spike DM partitioning analysis (glume, lemma, palea, rachis, awn) showed decreased partitioning to awns was associated with increased FE and thousand grain weight (TGW). While the use of exotic material can enhance biomass, special attention needs to be paid in the selection for novel DM partitioning traits that raise HI and GN coming from the elite genepool. The selection for grain partitioning traits in wheat breeding combined with sources expressing high biomass can potentially allow breeders to increase grain carbon assimilation that will deliver higher yields.

Models for estimating aboveground biomass of four dryland woody species in Burkina Faso, West Africa

Reliable estimates of carbon stocks for drylands are constrained by a limited number of biomass models for predicting accurately the biomass of dominant tree and shrub species. In this study, 119 trees with a diameter at breast height (dbh) between 3.82 and 45.48 cm were destructively sampled to evaluate aboveground biomass (AGB) allocation and prediction for four dryland species (Senegalia dudgeonii, Senegalia gourmaensis, Vachellia nilotica and Vachellia tortilis) commonly found in the Sudanian and Sahelian zones of Burkina Faso. Biomass allocation to leaf, branch and stem was examined using a classmometric analysis. Allometric equations relating biomass to dbh alone, and to dbh in combination with height and/or crown area were developed with and without consideration of the additivity property. Branches stored the largest (up to 90%) proportion of AGB. For three of the species, the branch mass fraction increased with increasing tree size at the expense of stem and leaf mass fractions. The statistical evaluations of the selected additive and non-additive models were satisfactory with no severe deficiencies. Diagnostics of model performance revealed that non-additive models performed better than additive models. The biomass models developed can be used for improved quantification of carbon stock and dynamics in dry savanna ecosystems.

Optimizing dry-matter partitioning for increased spike growth, grain number and harvest index in spring wheat

Improving biomass is an important goal for future genetic gains in yield potential in wheat, but it will also be crucial to identify physiological traits to maximize harvest index (HI, proportion of aboveground biomass in grain). Increased grain partitioning will require increased dry-matter (DM) partitioning to the spikes at anthesis as well as enhanced fruiting efficiency (FE, grains per g spike dry matter at anthesis or chaff dry matter at harvest), whilst optimizing the partitioning amongst the non-grain components to maintain post-anthesis photosynthetic capacity and soluble carbohydrate translocation. The objectives of this study were to: i) quantify genetic variation in DM partitioning among plant organs at anthesis (GS65) + 7 days and associations with spike growth and FE and ii) identify optimized partitioning traits associated with enhanced HI and grain yield, in CIMMYT elite spring wheat backgrounds. Two field experiments were conducted in 2011-12 and 2012-13 testing 26 CIMMYT spring wheat cultivars in NW Mexico in irrigated conditions in which DM partitioning was assessed in plant organs at anthesis + 7 days, and within-spike (glume, palea, lemma, rachis and awn) partitioning was assessed at harvest for a subset of 17 cultivars. Grain yield, yield components, HI and FE were assessed at harvest. Our results identified new traits for HI (decreased DM partitioning to stem internodes 2 (top down, peduncle -1) and 3, and decreased rachis DM partitioning and rachis specific weight (rachis DM per rachis unit length) and increased lemma DM partitioning), potentially allowing breeders to maximize the exploitation of enhanced carbon assimilation for grain biomass. Further work will focus on understanding the role of soluble carbohydrate re-translocation in these relationships and establishing high-throughput and cost-effective phenotyping methods for these traits for deployment in breeding.

Variation in carbon, nitrogen and phosphorus partitioning between above- and belowground biomass along a precipitation gradient at Tibetan Plateau

Precipitation is a potential factor that significantly affects plant nutrient pools by influencing biomass sizes and nutrient concentrations. However, few studies have explicitly dissected carbon (C), nitrogen (N) and phosphorus (P) pools between above- and belowground biomass at the community level along a precipitation gradient. We conducted a transect (approx. 1300 km long) study of Stipa purpurea community in alpine steppe on the Tibet Plateau of China to test the variation of N pool of aboveground biomass/N pool of belowground biomass (AB/BB N) and P pool of aboveground biomass/P pool of belowground biomass (AB/BB P) along a precipitation gradient. The proportion of aboveground biomass decreased significantly from mesic to drier sites. Along the belt transect, the plant N concentration was relatively stable; thus, AB/BB N increased with moisture due to the major influences by above- and belowground biomass allocation. However, P concentration of aboveground biomass decreased significantly with increasing precipitation and AB/BB P did not vary with aridity because of the offset effect of the P concentration and biomass allocation. Precipitation gradients do decouple the N and P pool of a S. purpurea community along a precipitation gradient in alpine steppe. The decreasing of N:P in aboveground biomass in drier regions may indicate much stronger N limitation in more arid area.

Chloride content and biomass partitioning in Eucalyptus hybrids grown on saline sites

Eucalyptus camaldulensis × globulus and E.camaldulensis × grandis hybrids have been developed to combine the salt–waterlogging tolerance and high-quality wood fibre of their respective parents. The aim is to develop trees that will grow in relatively dry and/or saline environments and provide commercial wood products. Previous studies indicate that the hybrids exhibit faster growth than either of their pure species parents, and that there are significant differences in growth rates between them. We undertook a comparative study of the partitioning of above-ground biomass (AGB) to examine biomass and chloride (Cl) allocation of trees growing on two saline-irrigated sites in south-eastern Australia. Eucalyptus camaldulensis × globulus had a higher proportion of AGB in leaves (20–29% cf. 15–16%), and lower proportion in live branches (3–10% cf. 6–14%) than E.camaldulensis × grandis. The concentration of Cl was highest in the stembark (4.2–9.6 g kg−1) and lowest in the stemwood (0.6–2.0 g kg−1), suggesting that trees can export Cl through bark shedding. Total Cl content was strongly related to volume under bark (R2 = 0.99), and differences in partitioning of Cl into tree components differed between the hybrids in the same way as AGB. Preferential partitioning of Cl to live branches rather than foliage in E. camaldulensis × grandis suggests that this hybrid may be compartmentalising Cl to reduce the risk of Cl toxicity in the leaves.

Responses of a Dominant Temperate Grassland Plant (Leymus chinensis) to Elevated Carbon Dioxide and Nitrogen Addition in China

The impact of elevated atmospheric CO(2) concentration on plant communities is varied and strongly dependent on the dominant species response, as well as nutrient conditions. Responses of a dominant species (Leymus chinensis) to elevated CO(2) and N application were examined with open-top chambers in a typical temperate grassland in northern China for 3 yr. The significant effect of elevated CO(2) on L. chinensis growth was mainly reflected in the higher photosynthetic rates, increased leaf number, larger shoot and root biomass, and higher root/shoot (R/S) ratio. Enhancement of root biomass induced by elevated CO(2) was larger (40%) than that of shoot biomass (9%). In contrast, N application had a significant impact on most growth indices examined in this study, which was reflected in the enhanced aboveground growth and depressed belowground growth. Nitrogen application significantly reduced the R/S ratio by an average of 40%. Nitrogen addition significantly enhanced the proportion of senescent biomass and decreased the proportion of green leaf biomass under elevated CO(2). There were no CO(2) x N interactions on most of the measured variables, except on photosynthetic rate and the proportion of aboveground biomass. Plant growth variables showed high interannual variation. These results indicate that belowground growth of L. chinensis is more sensitive to elevated CO(2) than is the aboveground. Aboveground growth of L. chinensis is much more sensitive to N application than to CO(2) enrichment. Therefore, the effect of elevated CO(2) on L. chinensis steppe is more likely to be underestimated if only aboveground parts are considered.

Proportion of above-ground biomass in commercial logs and residues following the harvest of five commercial forest species in Australia

A significant factor influencing the contribution of wood products to carbon (C) storage is the proportion of above-ground tree biomass (AGB) recovered in commercial logs at harvest. This study examined the proportion of AGB in logs and residues at the harvest of radiata pine, cypress pine, blackbutt, spotted gum and messmate. Messmate and spotted gum had the highest variation in stem diameter and height. The average AGB ranged from 2000 to 3000 kg for the hardwoods and 220–1000 kg for the softwoods. Blackbutt had the overall lowest proportion of AGB recovered in commercial logs (45.5%) and radiata pine the highest (65%). The proportion of AGB in the bark of the hardwoods was significantly lower than in the softwoods. The proportion of the AGB in forest residues following harvest ranged from 30 to 55% depending on the species. The proportion of AGB recovered in high quality commercial logs ranged from 15% for spotted gum to 63% for radiata pine. The differences were due to the natural characteristics of the selected species and variations in regional market availability. The highest retention rates of AGB in high quality hardwood commercial logs were obtained for trees with DBH between 500 and 600 mm (messmate and blackbutt) and greater than 600 mm for spotted gum. The mean moisture content of the wood of the different species ranged from 35 to 50%. Messmate and radiata pine logs had the highest moisture content (48 and 50%, respectively). The C concentration of blackbutt, radiata pine and cypress pine was slightly higher than 50%. The softwoods had significantly higher C concentration than the hardwoods. The C concentration between positions (cross-section, sapwood and heartwood) also varied for the different species. The highest proportion of the above-ground C was in the debarked log for all species with the exception of blackbutt. The cellulose concentration of the wood ranged from 56 to 64% for hardwoods and 40–52% for the two softwoods. The lignin concentration of the wood ranged from 16 to 19% for the hardwoods and 25–35% for the two softwoods. The hardwood species could not be distinguished from one another based on the cellulose, hemicellulose and lignin concentration, but within the softwood species, cypress pine and radiata pine formed separate clusters.

Total above-ground biomass and biomass in commercial logs following the harvest of spotted gum (Corymbia maculata) forests of SE NSW

Summary Total stand above-ground biomass (AGB) was measured at three sites of varying productivity in the Batemans Bay region of NSW. All trees with diameter at breast height (dbh) > 10 cm on three plots of 0.4–0.6 ha were weighed. Spotted gum was the dominant tree species across all sites. The basal area ranged from 29 to 43 m ha−1 depending on site quality. The total dry AGB was 220, 287 and 397 t ha−1 for the low, medium and high-quality sites (LQS, MQS and HQS), respectively. Spotted gum accounted for 66–79% of the AGB. The proportion of AGB in larger trees (dbh >50 cm) increased significantly with increased site quality. Bark accounted for about 7% of the weight of all spotted gum logs. The only significant differences in the proportion of bark in the logs were between trees with dbh >70 cm and those with dbh <40 cm. Ironbark had the highest proportion of the log biomass in the bark (12.4%). The mean moisture content of spotted gum logs was similar to that of Sydney blue gum and yellow stringybark logs. The moisture content of ironbark logs was significantly lower than that of all other species tested, whereas its basic density was higher than that of all other species. A strong correlation (r = 0.947) was found between tree diameter and AGB for spotted gum across all sites. Most trees on all sites were < 30 cm in diameter (particularly at the low-quality site), and the variance of AGB increased with tree size. The fraction of biomass in all spotted gum commercial logs was 58.2%. The biomass in commercial logs at the MQS was significantly greater than that at both the LQS and the HQS. An average 0.8 t of residues was generated per tree as a result of selective harvesting of commercial spotted gum forests. The largest fraction of biomass in commercial spotted gum logs (64.1%) was found in large trees (55–65 cm dbh), although the only significant differences were between trees with dbh between 35 and 40 cm and those with dbh between 55 and 65 cm. Pulp logs accounted for 55% of the AGB harvested in spotted gum commercial logs. The proportion of higher-quality commercial logs increased with increased site quality.

Nutrient and Carbon Additions to the Microbial Soil Community and its Impact on Tree Seedlings in a Boreal Spruce Forest

We have added glucose and nutrients to manipulate soil microbial activity and nutrient availability in a boreal spruce forest to study the performance of birch and spruce seedlings in relation to the soil microbial community. The proportion of aboveground biomass in the seedlings was largest in plots amended with extra nutrients, while ectomycorrhizal (ECM) colonisation was low in these plots. ECM appeared beneficial for growth of both species, but only at low levels of colonisation (<25% ECM colonised root-tips). The soil microbial biomass, as determined by total PLFA, was largest in plots treated with glucose and there was a significant negative relationship between birch seedling size and levels of total PLFA in soil. This could be taken to suggest that poor seedling growth was due to nutrient limitation caused by microbial assimilation. However, the treatment response of the birch seedlings was generally weak, and spruce often showed no response at all to the addition of nutrients and glucose. The most consistent parameter for the variation in plant performance, as well as for the microbial soil community, was the block-effect. This suggests a strong spatial structure in the soil microbial community, and that this structure was robust with respect to our treatments even though they continued over a 3-year period.

Distribution and increment of biomass in adjacent young Douglas-fir stands with different early growth rates

Total biomass increments were determined for three adjacent 22-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations in the Oregon Coast Range that had widely different early growth rates. Estimated total aboveground biomass of the stands, designated slow, intermediate, and fast, was 98.7, 148.7, and 203.7 Mg•ha−1, respectively; estimated mean biomass increment in the 5 years previous to sampling was 8.9, 12.6, and 12.3 Mg•ha−1•year−1. The slow stand had a greater proportion of aboveground biomass in branches and a smaller proportion in stem wood than the intermediate and fast stands. Differences in biomass increment were primarily due to stem rather than crown growth. Total below ground biomass was highest in the fast stand, the difference being due to roots &gt;5 mm in diameter; weight of roots &lt;5 mm was greater in the slow and intermediate stands. Roots &gt;5 mm comprised about 77% of the total root system in those stands and 90% in the fast stand. Increment of roots &gt;5 mm was 2.2, 2.5, and 3.0 Mg•ha−1•year−1 in the slow, intermediate, and fast stands. The ratio of productivity to total leaf nitrogen suggests that nitrogen is a principal limiting resource in the intermediate stand. The fast stand, with a leaf area index 50% greater than the others, is probably limited by light. The slow stand has anaerobic soils during at least part of the year, which may restrict rooting depth and thereby induce water stress during summer drought.