Species Identity and Initial Size Rather Than Neighborhood Interactions Influence Survival in a Response-Surface Examination of Competition.

Questions: (1) What is the water threshold for shrub seedling establishment in arid scrubland? (2) How do seedling root growth morphological traits affect the water threshold required for seedling establishment? Location: Arid scrubland, Atacama Desert, north-central Chile. Methods: We conducted a field experiment with nine native shrub species under a gradient of simulated rainfall to test if species with deep root architecture have higher seedling survival rates and establish more successfully during water pulses. Results: Seedling survival rate was very low; only 2% of the 12150 planted seedlings survived the first summer drought. Seedling survival required at least 206mm of water, which is twice the average rainfall and roughly equivalent to the precipitation during an ENSO (El Ni˜ no Southern Oscillation) event in this region. Seedling survival at the onset of the summer drought was best explained by leaf habit, root length and initial seedling size. However, only Senna cumingii seedlings survived through the first year. S. cumingii seedlings had distinctively longer roots than the other shrub species, enabling them to reach moister soil layers. Conclusions: Water conditions resembling rainy years enhance shrub seedling establishment in the Atacama Desert, but the effects of higher water availability are strongly dependent on the shrub species. Rapid and deep rooting appears to be a very important functional trait for successful first-year survival in this arid system where water availability is highly episodic.

PDF HTML阅读 XML下载 导出引用 引用提醒 三个亚热带森林优势种凋落物非结构性碳水化合物含量的季节动态 DOI: 10.5846/stxb202103050606 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（32022056，31800521，31922052） Seasonal variations of non-structural carbohydrates in fresh litters of three dominant tree species in subtropical forests Author: Affiliation: Fund Project: National Natural Science Foundation of China (32022056, 31800521, 31922052). 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:非结构性碳水化合物（NSC）是凋落物中的易分解组分，在凋落物分解早期快速释放进入土壤并被微生物利用，参与森林土壤生物地球化学循环，因此新鲜凋落物中NSC变化规律是认识森林土壤碳和养分循环的关键之一。选取亚热带常绿阔叶林优势树种米槠（Castanopsis carlesii）和主要造林树种杉木（Cunninghamia lanceolata）、马尾松（Pinus massoniana）为研究对象，分析其新鲜凋落叶和凋落枝中NSC （可溶性糖和淀粉）含量的动态变化规律。结果表明：凋落物中NSC含量在不同月份表现出明显的时间动态，米槠、杉木和马尾松凋落叶和凋落枝中NSC含量总体上在11-12月呈上升趋势，而在2-6月呈缓慢下降趋势。不同类型的凋落物NSC含量存在显著差异，米槠、杉木和马尾松凋落叶中NSC含量分别为3.03%-3.56%、2.18%-4.37%、3.38%-4.89%，凋落枝中NSC含量分别为1.87%-4.22%、2.88%-4.28%、2.75%-5.27%，米槠和马尾松凋落叶中NSC含量高于凋落枝，而杉木凋落枝中NSC含量高于凋落叶。不同树种凋落物NSC含量差异显著，米槠和马尾松凋落叶中NSC含量显著高于杉木，而马尾松凋落枝中NSC含量显著高于米槠。这些结果表明，凋落物中NSC含量受凋落物类型、树种和凋落物生产节律的影响，且亚热带常绿阔叶林转换为杉木和马尾松人工林将改变凋落物中NSC等易分解组分归还，进而影响森林地表生物地球化学过程。 Abstract:Forests retain large amounts of organic carbon mainly through the accumulation of photosynthetic products and the sequestration of soil organic carbon. Plant litter transfers carbon from plants to soils as a more stable pool with high resistance time. Non-structural carbohydrates (NSC), such as soluble sugars and starch, are labile components in plant litter and could be released quickly from decomposing litter and utilized by soil microorganisms. Therefore, the NSC in plant litter could involve in soil biogeochemical cycles and is a key driver for carbon and nutrient cycling in forest soils. In this study, we collected monthly fresh leaf and twig litters of Castanopsis carlesii (a dominant tree species in subtropical evergreen broad-leaved forest), Cunninghamia lanceolata and Pinus massoniana (two main planted trees in subtropical China) in a natural Castanopsis carlesii forest and the Cunninghamia lanceolata and Pinus massoniana plantations over one year to assess the seasonal dynamics of the NSC (including soluble sugars and starch) in fresh litters. The results showed that the NSC content in fresh litter varied significantly among seasons for all studied litter species and between litter types (leaf versus twig). In general, the NSC content in the leaf and twig litters of Castanopsis carlesii, Cunninghamia lanceolate, and Pinus massoniana greatly increased in November and December but decreased dramatically from February to June of the following year. The NSC content differed significantly between litter types:the NSC content in leaf litters of Castanopsis carlesii, Cunninghamia lanceolata and Pinus massoniana showed average values of 3.03%-3.56%, 2.18%-4.37%, 3.38%-4.89%, respectively, while those in the twig litters were 1.87%-4.22%, 2.88%-4.28%, 2.75%-5.27%, for the three litter species, respectively. The NSC contents in leaf litters of Castanopsis carlesii and Pinus massoniana were generally higher than those in the twig litters, and the NSC content in twig litter of Cunninghamia lanceolata was higher than that in the leaf litter. The NSC content in fresh litter also varied significantly among tree species:the NSC contents in leaf litters of Castanopsis carlesii and Pinus massoniana were significantly higher than that of Cunninghamia lanceolata, and the NSC content in twig litter of Pinus massoniana was significantly higher than that of Castanopsis carlesii. The results suggest that the NSC content in fresh litter varied significantly between litter types, tree species and litterfall rhythms. The conversion of subtropical evergreen broad-leaved forests to Cunninghamia lanceolata and Pinus massoniana plantations may change the input of easily decomposable components from seasonal litterfall, and this change in labile carbon input from fresh litterfall may affect soil microbial turnover and microbially mediated biogeochemical cycles in forest soils of subtropical China. 参考文献 相似文献 引证文献

中国人工林面积居世界第一位,而马尾松是中国人工林面积较大的树种之一,广泛分布于中国的亚热带区域。马尾松适应能力强,耐干旱、瘠薄,是南方低山丘陵区群落演替的先锋树种,也是荒山绿化造林的主要树种,马尾松人工林对生态防护、生态治理有着重大的意义。但是,绝大部分马尾松人工林为人工纯林,生态系统比较脆弱,生态服务功能较差。人工林的近自然改造对于增加林地生物多样性,提升人工林的生态服务功能具有重要意义。2005年,对中国林业科学院热带林业试验中心1993年造林的马尾松人工林进行4种不同强度(50%、40%、30%、20%)间伐后,套种大叶栎(<em>Castanopsis fissa</em>)、米老排(<em>Mytilaria laosensis</em>)、润楠(<em>Machilus pingii</em>)、红锥(<em>C. hystrix</em>)4个乡土阔叶树种,各种套种密度皆为120株/hm²。分别于间伐前(2004年)及2010年对群落生物多样性及人工套种树种生态情况进行调查,结果表明:(1)间伐处理后,自然更新至乔木层的物种种类和数量都有显著的增加,600 m²的样方中,物种数由(2.75±2.56)种增加到(11.17±4.32)种,个体数由(5.75±4.31)株增加到(32.17±19.09)株,群落中乔木亚层的优势种变化不大,主要有南酸枣(<em>Choerospondias axillaris</em>)、水锦树(<em>Wendlandia uvariifolia</em>),枫香(<em>Liquidambar formosana</em>)、破布木(<em>Cordia dichotoma</em>)、白背桐(<em>Mallotus paniculatus</em>)等。新增加到乔木层的物种大都为之前群落中灌木层的种类,主要有三桠苦(<em>Evodia lepta</em>)、鸭脚木(<em>Schefflera minutistellata</em>)、白花龙(<em>Styrax faberi</em>)、中平树(<em>Macaranga denticulata</em>)、黄毛榕(<em>Ficus esquiroliana</em>)、华南毛柃(<em>Eurya ciliata</em>)、罗浮柿(<em>Diospyros morrisiana</em>)、猴耳环(<em>Pithecellobium clypearia</em>)、木姜子(<em>Litsea pungens</em>)、毛黄肉楠(<em>Actinodaphne pilosa</em>)等。(2)间伐处理前,600 m²样方中出现的灌草种类数量为(24.63±4.24)种,间伐处理后,600 m²样方中出现的灌草种类数量为(27.58±3.80)种,不同间伐强度处理后林下灌草的优势种与间伐前大致相同,灌木层优势种为三桠苦,草本层优势种为弓果黍(<em>Cyrtococcum patens</em>)。不同间伐强度处理林分间,灌木层和草本层的物种丰富度指数、Shannon-Wiener指数、Simpson指数和Pielou指数均无显著差异,且与间伐前林分也无显著差异。(3)间伐促进了4个乡土树种幼树的生长,随着间伐强度的增加,大叶栎、红锥幼树的高度和胸径显著增长;50%的间伐强度的林分中,阔叶树种幼树的长势要显著好于其他间伐强度,50%的间伐强度最有利于马尾松林下套种的阔叶树种生长。(4)在马尾松林下套种的4个阔叶树种幼树的初期生长有明显差异。总体而言,大叶栎与米老排幼树的早期生长速率要明显高于红锥和润楠。;China has the world's largest total area of plantation resource, among which the most common species is masson pine (<em>Pinus massoniana</em> Lamb). As a pioneer tree species in hill areas of southern China, masson pine is highly resistant to drought and infertile soils and thus plays an important role in the ecological restoration. However, as most masson pine plantations are monocultures, consisting of a single dominant tree species, their ecosystem services are often poor. Close-to-nature management is of great significance for the increase of species diversity and the improvement of ecological service in plantations. In 2005, a thinning experiment was conducted in a 12-year-old masson pine plantation in the Experiment Center of Tropical Forestry of Chinese Academy of Forestry, with four different levels of thinning density (i.e. 50%, 40%, 30%, and 20%). Then, four native broad-leaved tree species, ie. <em>Castanopsis fissa</em>, <em>Mytilaria laosensis</em>, <em>Machilus pingii</em> and <em>C. hystrix</em>, were interplanted with a density of 120 trees/hm² in the thinned masson pine plantation. We investigated the community species diversity and growth conditions before the thinning experiment. Five years later, a re-investigation of the plots showed that: (1) the number of tree layer species were significant increased, with the species richness per plot (600 m²) from 2.75±2.56 to 11.17±4.32 and individual number from 5.75±2.56 to 32.17.17±19.09. In addition to the original dominant species before the experiment, nearly 10 species in original shrub layer grew into tree layer, including <em>Evodia lepta</em>,<em>Schefflera minutistellata</em>,<em>Styrax faberi</em>,<em>Macaranga denticulata</em>,<em>Ficus esquiroliana</em>,<em>Eurya ciliata</em>,<em>Diospyros morrisiana</em>,<em>Pithecellobium clypearia</em>,<em>Litsea pungens</em> and <em>Actinodaphne pilosa</em>. (2) the number of shrub and herb layer species increased only slightly from 24.63±4.24 to 27.58±3.80 per plot (600 m²). Different thinning density treatments had no significant effect on shrub-herb species in terms of Species richness index, Shannon-Wiener index, Simpson index, and Pielou index. The dominant species in shrub and herb layer were <em>Evodia lepta</em> and <em>Cyrtococcum patens</em>, respectively, which are similar with those before the thinning experiment. (3) The saplings of broad-leaved tree species benefited greatly from thinning management. The height and DBH increased significantly with the thinning intensity in <em>Castanopsis fissa</em> and <em>C. hystrix</em>. In the 50% thinning intensity stands, the broad-leaves tree saplings had significantly better performance than those in other stands, suggesting that the 50% thinning management was optimal for the growth of broad-leaves tree species. (4) There were significantly differences in early growth among the four broad-leave tree species in masson pine plantation. Overall, the early growth rates of <em>C. fissa</em> and <em>Mytilaria laosensis</em> were obviously higher than the other two species. Our results highlight the significant effects of close-to-nature management, i.e. thinning of dominant masson pine and interplanting of native tree species, on the increase of species diversity in plantations even in a relative short experimental period. As higher levels of species diversity are essential for community stability (e.g. the resistance of forest to variable disturbances), the close-to-nature management will benefit the supply of high-quality timbers and ecological services in masson pine plantations.

Neighborhood effects and environmental variables drive sapling growth in a young subtropical tree plantation

:We investigated the effects of seed size and microhabitat on the dynamics of seedling establishment in Olea europaea. We tested the hypothesis that the type of microhabitat suitable for O. europaea recruitment is influenced by microhabitat-specific relationships between seed size and seedling growth rate. To test this hypothesis we conducted field experiments evaluating seedling growth and survival as a function of seed size, microhabitat (determined by presence/absence of scrub cover), and competition (established by means of seedling density gradients). Our results show that, first, seed size was related to seedling size and to differential growth rate. Second, seedling growth rate was negatively correlated with initial seedling size, although this correlation varied among microhabitats and temporally. Third, seedling survival differed between microhabitats and was positively affected by initial seedling size until the end of the summer drought. Finally, the effect of seedling size on survival was partly mediated by its negative relationship with growth rate. However, the combined effect of size and growth on seedling survival varied between microhabitats. We conclude that establishment depended on microhabitats through facilitation and inhibition processes, and that seed size-related growth rate strongly affected seedling fate. It is noteworthy that the effectiveness of the size-correlated growth depended on microhabitat.

There is interest in restoring shortleaf pine (Pinus echinata) in pine–oak woodlands where it once was abundant. Because of its shade intolerance and slow initial growth rate, shortleaf pine restoration has remained a challenge because competition from hardwoods exhibits greater initial growth following canopy removal but greater shade tolerance with canopy retention. The study objective was to examine the survival and growth of underplanted shortleaf pine seedlings relative to competing hardwoods as a function of initial seedling size, overstory density, and understory competition. In the Ozark Highlands of southeastern Missouri, USA, 48, 0.4-ha experimental units were each harvested from below to a uniform stocking level from 0 to 90 % and 30, 1–0 improved shortleaf pine seedlings were planted on a 3.7 × 7.3 m spacing. Linear or logistic regression was used to determine how shortleaf pine seedling (1) survival, (2) basal diameter growth, and (3) shoot growth were related to initial seedling size, overstory stocking, and understory competitor height during the first 5 years after underplanting. After five growing seasons, the survival rate of shortleaf pine seedlings was 50 % and was positively related to the initial basal diameter but was not related to overstory stocking or competitor height. Increasing overstory stocking decreased the basal diameter and height growth of shortleaf pine seedlings, explaining >51 % of the variation in basal diameter and 54 % of the variation in seedling height. Although competing hardwood seedlings were consistently taller than the shortleaf pine seedlings throughout the study, shortleaf pine seedlings maintained similar growth rates as competitors from the second to the fifth growing season. The eventual release of shortleaf pine is essential for recruitment, but releases can be delayed for several years after underplanting.

Soil fauna play an important role in key functions of ecosystem such as material cycling. Litter quality and microenvironment of different tree species may regulate soil fauna community structure. In this study, we investigated soil fauna community structure, the differences of taxonomic and functional groups, and the regulatory factors under eight dominant tree species in August 2022. We captured 567 soil fauna (except for termites and ants), belonging to 3 phyla, 10 classes, 26 orders, and 99 families, with Achipteriidae, Trygoniidae, Poduridae, and Isotomidae as the dominant species. Tree species significantly affected soil fauna abundance, following an order: Michelia macclurei > Elaeocarpus decipiens > Castanopsis carlesii > Cunninghamia lanceolata > Lindera communis > Schima superba > Pinus massoniana > Liquidambar formosana. However, the richness, evenness, and diversity of soil fauna under different tree species were significantly different. Richness and diversity of M. macclurei, C. lanceolatas soil fauna were relatively high, while L. formosana, C. carlesii were relatively low. The evenness of meso-microfauna of L. formosana was the highest, which was significantly higher than that of M. macclureis and E. decipiens. The evenness of macrofauna and total soil fauna was not significantly different among the eight tree species. In addition, the abundance of omnivores and herbivores soil fauna was relatively high under M. macclurei, but relatively low under E. decipiens. The abundance of saprophages and predators soil fauna of E. decipiens, M. macclurei was higher than L. formosana, while saprophages was mainly meso-microfauna. Results of redundancy analysis showed that litter N, C:N, and K were the main factors affecting soil fauna community structure. The results indicated that the tree species with thicker litter layer and higher N and K contents may be conducive to enhancing the diversity of soil fauna community and affecting the distribution of different functional groups, thus contributing to the maintenance of forest biodiversity.

Neighborhood competition influences tree growth, which can affect species composition and community succession. However, there is a lack of understanding regarding how dominant tree species at different successional stages of forest communities respond in terms of crown architecture and functional traits during their growth process to neighborhood competition. In this study, we analyzed the responses of average annual basal area increment (BAI), crown architecture, and leaf functional traits of early-successional species (Cunninghamia lanceolata and Pinus massoniana), transitional species (Alniphyllum fortunei and Choerospondias axillaris), and late-successional species (Elaeocarpus duclouxii and Castanopsis carlesii) to neighbor competition in a secondary evergreen broad-leaved forest. We found that the BAI of all species is negatively correlated with competition intensity. Notably, early-successional and transitional species exhibited a more rapid decline in growth rates compared to late-successional species in response to increased competition. Among these tree species, the response of crown structure to neighbor competition exhibited variation. Early-successional and transitional species displayed a negative correlation between the competition index and crown area (CA)/diameter, while a positive correlation emerged between the lowest branch height (LBH)/height. Conversely, late-successional species followed the opposite trend. In terms of leaf functional traits, specific leaf area (SLA) showed heightened sensitivity to neighborhood competition, with a positive correlation between SLA of all tree species and the competition index. Furthermore, water use efficiency (WUE) demonstrated negative correlations with the competition index in early-successional and transitional trees, while a positive correlation emerged with late-successional trees. These findings suggest that early-successional and transitional trees prioritize vertical canopy growth, whereas late-successional trees tend to favor horizontal canopy expansion in response to neighboring competition. Additionally, early-successional and transitional trees experience more significant suppression of radial growth rate. Our research contributes to a deeper understanding of the underlying mechanisms driving changes in species composition and community succession.

In heterogenous landscapes, seeds settle in some microsites more readily than others, independently of whether those microsites are suitable for germination and subsequent growth, and survival of seedlings. Wild seeds and seedlings of Ericameria nauseosa var. oreophila in the sand-dune ecosystem near Mono Lake, California show both concordance and conflict in where seeds are retained and where seedlings flourish. Using a field experiment, we followed performance of seeds and seedlings (i.e., the rate of germination and successful emergence, initial seedling size, seedling growth and survival over first growing season), by planting seeds of known sizes in pre-identified microsites (windward and lee aspects of interspaces between shrubs, under shrub canopies, and under snag canopies, respectively). Heavier seeds were more likely to germinate and emerge successfully and resulted in initially larger seedlings than lighter seeds. These initially larger seedlings subsequently remained larger over the growing season and lived longer than initially smaller seedlings. Independent of seed and initial seedling size, seedlings that germinated under the canopy of adult shrubs grew larger and survived longer than seedlings that germinated in interspaces (open space with little or no vegetation) or under snags (dead adult shrubs). Seedlings grown under the canopy of adult shrubs experienced significantly less solar radiation and wind-deposited sand than seedlings grown in interspace or snag microsites. Sand burial more than 1 cm was lethal for seedlings. The two variables of seed size and microsite type had by far greater impact on eventual growth and survival of seedlings than did aspect, and the effects of the former two variables were independent of each other. This study amplifies the body of work on E. nauseosa at this site demonstrating that the earliest events in the life history of this long-lived perennial shrub appear to persist through time despite the harsh and variable environment.

Effects of neighborhood diversity on herbivory in early-stage forests in southern China.

Lianas have a huge influence on forest structure and function. However, it is unclear how the surrounding environment affects the establishment of liana seedlings in temperate forests. We addressed the following questions: (1) Can current-year seedlings persist under a closed canopy? (2) Do current-year seedlings form aggregated distribution and how has their spatial distribution varied over the years? (3) How does the light condition, soil moisture content, forest floor litter, understory vegetation, and the distance from the conspecific adults affect the establishment and survival of seedlings? We examined the distribution pattern and survivorship of current-year seedlings of the temperate liana species, Wisteria floribunda, across a heterogeneous environment for 6years using 1m2 sub-quadrats (n = 651) in a 6ha plot within the Ogawa Forest Reserve, an old-growth, temperate, deciduous forest in central Japan. In total, 908 current-year seedlings were observed during the study period, 87% of which emerged in 2014. Over half (56%) of these seedlings survived until 1year after germination, which was relatively high compared with other tree species in this forest. The seedlings formed significantly aggregated distribution, but the degree of aggregation decreased over time. The number of emerged seedlings was negatively associated with the presence of dwarf bamboo (Sasa borealis) and the distance from the nearest conspecific adult. However, the survival rate of the seedlings was negatively associated with the presence of dwarf bamboo and soil moisture content and was positively associated with the openness of the canopy and the distance from the nearest conspecific adult. An enhanced survival rate under more intense light conditions and the ability to persist within the shaded understory may be important for the survival of this species in the earlier stage of the life history.

PDF HTML阅读 XML下载 导出引用 引用提醒 南亚热带格木、马尾松幼龄人工纯林及其混交林生态系统碳氮储量 DOI: 10.5846/stxb201401030018 作者: 作者单位: 中国林业科学研究院,中国林业科学研究院,中国林业科学研究院,中国林业科学研究院,中国林业科学研究院热带林业实验中心 作者简介: 通讯作者: 中图分类号: 基金项目: 中国科学院碳专项(XDA05060100);林业公益性行业科研专项(201104006) Carbon and nitrogen storage in monoculture and mixed young plantation stands of Erythrophleum fordii and Pinus massoniana in subtropical China Author: Affiliation: Chinese Academy of Forestry,Chinese Academy of Forestry,Chinese Academy of Forestry,Chinese Academy of Forestry,Experimental Center of Tropical Forestry,Chinese Academy of Forestry Fund Project: 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:研究比较了南亚热带6年生格木(Erythrophleum fordii)、马尾松(Pinus massoniana)幼龄人工纯林及马尾松与格木混交林生态系统碳氮储量及其分配特征。结果表明,生态系统总碳储量依次为马尾松-格木混交林(137.75 t/hm2) >格木纯林(134.07 t/hm2) >马尾松纯林(131.10 t/hm2),总氮储量则为格木纯林(10.19 t/hm2) >马尾松-格木混交林(8.68 t/hm2) >马尾松纯林(7.01 t/hm2)。3种人工林生态系统碳氮库空间分布基本一致,绝大部分储存于0-100 cm土壤层,平均占生态系统总储量的81.49%和96.91%,其次为乔木层(分别占17.52%和2.69%),林下植被和凋落物层所占比例最小。林地土壤碳主要集中于表土层,其中0-30 cm土层平均碳储量为52.52 t/hm2,占土壤总碳储量(0-100 cm)的47.99%,土壤氮的分布则无明显规律。相比于纯林,与固氮树种混交的营林方式表现出更大的碳储存能力。3种幼龄人工林生态系统较低的地上与地下部分碳氮分配比,表明其仍具有较强的碳氮固持潜力。 Abstract:Carbon sequestration in forest ecosystems is recognized as a key mechanism for mitigating the accumulation of atmospheric carbon dioxide. However, both forest carbon pools and sequestration vary according to tree species, age of the stand, soil types, climate, environmental disturbances, and management practices. Tree species composition and management practices are important tools for increasing carbon storage in forest ecosystems. Plantation is becoming a key component of the world's forest resources and is playing an important role in sustainable forest management. Well-designed, multi-purpose plantations can reduce the pressure on natural forests and complement some ecological resources provided by natural forests in addition to mitigating climate change through direct carbon sequestration. Afforestation and reforestation are important measures for managing commercial forests in subtropical China. However, the large-scale development of monoculture plantations of coniferous species (e.g., Pinus massoniana and Cunninghamia lanceolata) and exotic species (Eucalyptus spp.) has caused a number of problems, such as the loss of biodiversity, degradation of soil fertility, reduction of ecosystem stability, and loss of ecological resources. Thus, some broad-leaved tree species with different functions (e.g., indigenous valuable broad-leaved species and nitrogen-fixing species) have been developed for restructuring the plantations. In this study, three young plantation stands (monoculture of Erythrophleum fordii, monoculture of P. massoniana and a mixed stand of the two species) were selected to study carbon and nitrogen storage in these ecosystems and their spatial distribution. The results showed that the total carbon storage of the mixed plantation stand was 137.75 t/hm2, higher than that of monoculture stands of E. fordii (134.07 t/hm2) and P. massoniana (131.10 t/hm2). Nitrogen storage was highest in E. fordii (10.19 t/hm2), followed by the mixed plantation (8.68 t/hm2), and then P. massoniana stands (7.01 t/hm2). The spatial distribution of carbon and nitrogen was identical in the three plantation stands, with the majority found in the 0-100 cm soil (occupying an average 81.49% and 96.91% of the total storage, respectively), followed by the above-ground biomass represented by the trees (17.52% and 2.69%, respectively), and the understory vegetation and litterfall. Soil organic carbon was mainly distributed in the top-soil, while soil nitrogen was irregularly distributed. Average organic carbon storage in 0-30 cm soil was 52.52 t/hm2 (47.99% of the total 0-100 cm soil storage). The mixed plantation stands showed a greater capacity for carbon storage in comparison to the other two monoculture stands. The above-/underground ratio of carbon and nitrogen suggested that these three young plantation stands had a high potential for carbon and nitrogen sequestration. The results are significant in that they provide scientific references for tree species selection and plantation management to enhance productivity and carbon sequestration in subtropical China. 参考文献 相似文献 引证文献

We examined the functional relationship between seed size and seedling performance in the valley oak (Quercus lobata Nee) by means of a 13-year common garden experiment. Acorns were collected from five localities throughout the range of valley oak in autumn 1997, weighed and measured, and planted at Sedgwick Reserve, Santa Barbara County, California, USA. In the short term, larger acorns produced larger seedlings that had lower survival than seedlings from smaller acorns. In the longer term, large seeds correlated positively with both seedling size and survival, with path analyses indicating that the latter effect was primarily indirect via initial seedling size. The longer-term relative growth rate was only weakly related to seed size, being a combination of a slight positive direct influence of seed size on relative growth rate and a comparable negative indirect effect via larger initial seedling size. These results generally matched the predictions of the “seedling size effect hypothesis” (larger seeds yield larger seedlings with greater competitive abilities), the only one of the three hypotheses we examined that predicts an inverse relationship between seed size and initial survival and a positive relationship between seed size and longer-term relative growth rate. The factors influencing the relationships between seed size and seedling performance are complex and may involve both direct effects of seed size and indirect effects mediated through initial seedling size. Although the seedling size effect was the most important in our study, other factors may be important under different environmental conditions and/or at different growth stages.

We used height growth data from a 7-year field experiment with European beech (Fagus sylvatica L.) seedlings to test the hypothesis that the effects of above- and belowground resources on height growth depend on seedling size and age. Photosynthetically active radiation (PAR) was determined by hemispheric photography, and estimates of fine root biomass of the overstory trees were used as an inverse proportional surrogate for belowground resource availability. For recently germinated seedlings growing under the canopy of Picea abies (L.) Karst., belowground resource availability affected height growth more than light. During subsequent stages of seedling development, apart from initial seedling size, PAR increasingly determined seedling growth. Besides initial size, seedling age determined the effects of above- and belowground resources on seedling height growth. In seedlings identical in initial size but differing in age, the increase in height growth with increasing PAR was greater in older seedlings than in younger seedlings. The ranking of seedling height by year showed that small differences in size at the end of the first growing season resulted in continuously increasing differences during the following years. Mortality data indicated that the chances of a seedling surviving intraspecific competition was strongly determined by its dominance ranking within the first 5 years after establishment.

The effects of seasonal drought, belowground competition, and low soil fertility on the survival and growth over 2 years of four native tree species planted on a degraded hillside grassland in Hong Kong were studied in a field transplant experiment using three‐way analysis of variance. The tree species wereSchima superba(Theaceae),Castanopsis fissa(Fagaceae),Schefflera heptaphylla(Araliaceae), andSapium discolor(Euphorbiaceae), and the treatments were dry season irrigation, herbicide, and fertilizer. Each species responded differently to the treatments.Sapiumhad a very low survival rate as a result of wind damage at the exposed study site. All three treatments significantly reduced the survival rate ofCastanopsisseedlings, whereas herbicide reduced it forSapiumbut increased it forSchefflera. The significant effects on seedling growth were all positive, except for a strong negative effect of herbicide onCastanopsisgrowth. Overall, the results suggest that all three factors—seasonal drought, belowground competition, and low soil nutrients—can significantly impair seedling growth on a degraded hillside site in Hong Kong but that their relative importance differs among species. The growth benefits of the three treatments were largest and most consistent forSchima, which as a mature forest dominant would be expected to be particularly sensitive to the environmental conditions on degraded open sites. This study highlights the fact that more systematic planting trials are needed to identify suitable native tree species for cost‐effective reforestation on degraded hillsides in Hong Kong and South China.