暖温带落叶阔叶林辽东栎和五角枫生长和光合生理生态特征对模拟氮沉降的响应

暖温带落叶阔叶林在维护区域生态系统功能和平衡中起着重要的作用,研究其在氮添加下的生长和生理生态响应,有助于深入理解暖温带落叶阔叶林在全球氮沉降背景下的生长和变化规律。该研究通过在北京东灵山落叶阔叶林的模拟氮沉降控制实验,以优势种辽东栎(Quercuswutaishanica)和伴生种五角枫(Acerpictumsubsp.mono)为研究对象,设置对照和氮添加2种处理,每种处理4个重复,对照样地不做处理;氮添加样地施加尿素(CO(NH2)2),总的氮添加量为100kg·hm–2·a–1,测定氮添加对其生长和光合生理生态特征的影响。结果显示:氮添加显著提高了两个树种的净光合速率、蒸腾速率、叶绿素含量,同时扩大了叶片光系统II反应中心电子传递体库,增加了基于光合电子流驱动的初级受体醌(QA)被还原的周转次数。氮添加也增加了两个树种当年生枝条的长度和生物量,同时在一定程度上提高了辽东栎种子的质量。辽东栎光合作用氮利用效率、枝条生物量对氮添加的响应程度明显超过五角枫。在未来氮沉降加剧的情景下,东灵山暖温带落叶阔叶林优势种辽东栎的优势地位会进一步加强。     

模拟氮沉降对北京东灵山辽东栎林树木生长的影响

传统的元素限制模型认为氮是温带森林生长的限制元素, 不过该结论更多是从地上生物量以及群落水平进行阐述, 忽视了不同物种以及不同径级树木对外源氮的响应差异。辽东栎(Quercus wutaishanica)林是华北地区常见的森林类型, 该研究以北京东灵山辽东栎林为研究对象, 通过设置3个氮添加水平的实验, 即对照CK (0 kg·hm ^-2·a ^-1), N50 (50 kg·hm ^-2·a ^-1)和N100 (100 kg·hm ^-2·a ^-1), 模拟氮沉降对群落和物种水平以及不同径级树木生长的影响。经过7年氮添加, 实验结果显示: 物种水平上, 氮添加明显促进了优势树种辽东栎的生长; 群落水平上, 树木生长随氮浓度增加有不断上升趋势, 但统计学差异不显著; 氮添加显著抑制了辽东栎以及群落内小径级(3-10 cm)树木生长, 中(10-20 cm)、大径级(>20 cm)树木生长随氮沉降水平增加呈上升趋势, 但统计学差异不显著。表明氮是辽东栎以及温带森林树木生长的限制元素; 不同径级的辽东栎和群落内其他植物对氮添加响应不一致, 氮添加抑制了小径级树木生长, 中、大径级树木生长对氮添加响应不明显。     

暖温带地区3种森林群落叶面积指数和林冠开阔度的季节动态

以辽东栎(Quercus liaotungensis)为主的落叶阔叶林、华北落叶松(Larix principis-rupprechtii)林和油松(Pinus tabulaeformis)林是暖温带林区具有代表性的森林群落类型。该研究应用国内外流行的半球图方法,通过对这3种森林群落叶面积指数和林冠开阔度的测定和综合比较,分析了叶面积指数和林冠开阔度的季节动态,揭示了暖温带地区不同类型森林群落叶面积指数和林冠开阔度的特征。研究结果表明,落叶阔叶林(优势种为辽东栎、棘皮桦(Betula dahurica)和五角枫(Acer mono))和华北落叶松林两种落叶森林群落的叶面积指数值均随生长季的到来而呈现增长的趋势,最大值出现在8月;林冠开阔度值随着生长季的到来而下降,最大值出现在11月。落叶阔叶林的叶面积指数和林冠开阔度的季节动态较之华北落叶松林明显。油松是常绿树种,其群落叶面积指数和林冠开阔度的变化程度均不明显,但林冠开阔度的变化趋势也是与叶面积指数的变化趋势相反。通过计算得出叶面积指数和林冠开阔度相关显著,并且呈现指数回归的关系。此研究结果为以遥感途径获取暖温带地区叶面积指数提供了地面校正依据,为研究该地区植被林冠的异质性及其造成的影响,以及进一步对该地区林分、景观和区域尺度上碳、水分和通量等方面的模拟提供了基础数据。     

模拟氮沉降对北京东灵山辽东栎群落林下植物物种多样性的影响

氮沉降是驱动生物多样性变化的重要因素之一。一般认为氮沉降会改变物种多样性, 而且在外源氮添加条件下, 禾草类植物和落叶灌木比杂类草和常绿灌木更具竞争优势。不过该结论更多是从高寒草甸和荒漠草原等生态系统中得到, 主要是针对同一生活型内植物之间的竞争关系, 不涉及不同生活型植物之间的相互作用, 并且由于草原和草甸等生态系统没有明显的垂直结构, 同一层次中植物的高度差异较小, 有可能高估了光照因素对植物的作用。因此从森林生态系统入手, 可以进一步阐述不同生活型植物对氮沉降的响应。本文以我国北方典型的落叶阔叶林——辽东栎(Quercus wutaishanica)林为研究对象, 设置CK (0 kg N·ha ^-1·yr ^-1)、N50 (50 kg N·ha ^-1·yr ^-1)和N100 (100 kg N·ha ^-1·yr ^-1) 3个梯度氮添加实验, 模拟氮沉降对温带森林生物多样性的影响。8年连续的氮添加实验结果显示: (1)氮添加显著降低了林下植物的物种丰富度和多样性, 改变了群落的物种组成; (2)氮添加提高了灌木植物的物种丰富度和多样性; 降低了草本植物的丰富度; (3)氮添加降低了禾草类植物的重要值, 提高了杂类草的重要值。该研究表明, 长期氮添加会显著改变林下植物的物种组成, 不同生活型植物对氮添加的响应亦有所差别。造成该现象的原因可能是由土壤环境变化(如养分含量提高, pH值下降)和植物获取光照能力强弱(如灌木植物获取光资源要多于草本植物)导致。     

模拟夏季干旱对东灵山森林植被动态的影响

应用LPJ-GUESS植被动态模型, 在耦合不同物种的干旱响应策略的基础上, 研究了夏季干旱化对东灵山地区森林植被的物种组成及其功能的影响。结果表明, 在气候变暖、降水减少、CO₂浓度升高的情况下, 无论树种采取何种策略, 东灵山暖温带森林的总净初级生产力和生物量都有增加的趋势, 降水在未来近一个世纪内尚未成为本地区植被生长的限制因子。但森林植被的树种组成与树种的干旱响应策略密切相关, 不耐旱的物种核桃楸(Juglans mandshurica)的生物量水平在长期干旱条件下并没有降低, 而耐旱的物种辽东栎(Quercus liaotungensis)在受到干旱化长期影响时, 其生物量有下降的趋势。这种响应策略也会导致植被蒸散等生态系统水分循环过程的差异。因此, 降水变化对森林生态系统影响的长期模拟研究应该考虑物种对干旱的不同响应策略。     

北京八达岭林场不同森林类型人工林生物量研究

利用标准地法对八达岭林场人工林主要树种的生物量进行了测定,建立了油松(Pinus tabulaeformis)、黑桦(Betula dahurica Pall)、槺椴(Tilia mandshurica)、五角枫(Acer mono Maxim)及华北落叶松(Larix principis-rupprechtii)的生物量相对生长模型。结果表明,八达岭林场各主要树种生物量分配比例的大小顺序为:五角枫>油松>槺椴>黑桦>落叶松。各树种的生物量值为五角枫93.28 t/hm²>油松86.40 t/hm²>槺椴50.24 t/hm²>黑桦 36.05 t/hm²>落叶松20.21 t/hm²。5 个树种的总生物量为286.17 t/hm²。利用IPCC 模型计算结果表明不同树种在相同的时间下产生的生物量是不同的,并用实际数据指出生长模型的建立方法不同可能带来的生物量计算的差异。此研究结果可用于建立广泛适用的生长模型及在不同树种的生物量计算方面起到重要作用。     

油松 辽东栎混交林地表凋落物与氮添加对土壤微生物生物量碳、氮及其活性的影响

2010年9月-2011年10月,在山西省灵空山油松和辽东栎混交林样地采取随机区组设计,研究了地表凋落物和氮添加处理对土壤微生物生物量碳、氮和微生物活性的影响.凋落物处理包括: 剔除凋落物(N)、叶凋落物加倍(L)、枝果凋落物加倍(B)和混合凋落物加倍(LB);氮添加量分别为0(N₀)、5 g·m^-2·a^-1(N₁)和10 g·m^-2·a^-1(N₂).结果表明: 剔除地表凋落物且无氮添加时,油松和辽东栎混交林地的土壤有机碳(SOC)含量显著降低,其他试验处理间对SOC的影响无显著差异.土壤微生物生物量碳(MBC)、氮(MBN)及其活性(MR)的变化范围依次为: 262.42～873.16 mg·kg^-1、73.55～173.85 mg·kg^-1和2.38～3.68mg·kg^-1·d^-1.MBC、MBN和MR两两间呈极显著正相关.氮添加对MBC、MBN和MR均无显著影响;凋落物处理对MR影响显著,表现为混合凋落物加倍处理的MR最高,叶凋落物加倍处理次之,剔除凋落物处理最低,而对MBC和MBN无显著影响.凋落物和氮添加处理在整个试验过程中未表现出交互作用.短期的氮添加处理和森林地表凋落物变化对土壤微生物过程的影响有限.     

北京东灵山地区植物群落多样性研究Ⅷ.群落组成随海拔梯度的变化

以样带法研究了北京东灵山地区落叶阔叶林物种组成随海拔梯度表现出的变化格局。通过变换分割样带的尺度,考察了环境的局部变化对群落主要组成物种的分布及其优势程度的影响。东灵山落叶阔叶林优势种辽东栎和五角枫几乎遍布整个样带,其它伴生乔木树种表现出明显的分布替代格局。以占据率和单种率考察了尺度对群落特征分析的影响。本区落叶阔叶林１ｍ样带最佳分割尺度为：乔木层４０ｍ,更新层８０ｍ、灌木层２０ｍ。样带法在研究植物群落随环境梯度变化格局中具有重要价值。     

东灵山4种落叶阔叶次生林的物种组成与群落结构

植被的群落构成是决定森林演替方向的重要因素之一.辽东栎林(Quercus wutaishanica forest,QWF)、棘皮桦林(Betula dahurica forest,BDF)、胡桃楸林(Juglans mandshurica forest,JMF)与杂木林(mixed forest,MF)是东灵山地区4种典型的暖温带落叶阔叶次生林.为了更好地了解东灵山地区暖温带落叶阔叶次生林植被动态,我们对该4种林型的物种组成与群落结构进行了综合分析.参照巴拿马(Barro Colorado Island,BCI)50 ha热带雨林样地的技术规范,于2009年在北京东灵山地区以上4个林型中各建立了一块1 ha样地,对样地中所有胸径大于1 cm的木本个体进行了坐标定位和调查.结果表明,QWF样地有22种,属于20科20属;BDF样地共22种,属于16科18属;JMF样地30种,隶属于21科23属;MF样地19种,隶属于14科15属.从物种多度、平均胸径、胸高断面积和重要值等指标来看,各群落具有比较明显的优势种:4个样地所有树种的径级分布均旱倒"J"型,具有良好的更新层;共有树种的径级分布在不同样地有所不同,如辽东栎在QWF样地呈偏态分布,在BDF样地则为倒"J"型分布,而棘皮桦在QWF和BDF样地都呈正态分布,但是径级分布有所差异,表明径级结构与群落类型有密切关系.     

不同氮添加量和添加方式对南亚热带4个主要树种幼苗生长的影响

为阐明南亚热带4个主要树种——海南红豆(Ormosia pinnata)、马占相思(Acacia mangium)、木荷(Schima superba)和马尾松(Pinus massoniana)幼苗生长对不同氮添加量和添加方式的响应差异, 进行了幼苗模拟氮添加实验。实验设置3个氮添加水平(对照: 背景大气氮沉降量5.6 g N·m^-2·a^-1, 中氮: 15.6 g N·m^-2·a^-1, 高氮: 20.6 g N·m^-2·a^-1), 每个水平分两种添加方式(幼苗冠层施氮和土壤表层施氮), 共6个处理: (1)土壤对照(S-CK); (2)土壤中氮(S-MN); (3)土壤高氮(S-HN); (4)冠层对照(C-CK); (5)冠层中氮(C-MN); (6)冠层高氮(C-HN), 每个处理设置6个重复。研究结果表明: 不同氮添加量下, 土壤施氮和冠层施氮对植物幼苗生长的影响不同, 氮添加量、氮添加方式和物种3个因子之间存在显著的交互效应。与对照相比, S-MN增加了马占相思和木荷幼苗的生物量, 降低了马尾松的株高和生物量, 而C-MN仅增加了马占相思的生物量, 对其他3个树种没有影响; S-HN增加了马占相思的生物量, 显著降低了马尾松的基径、株高和生物量(p < 0.01), C-HN增加了马占相思、木荷和马尾松的基径、株高和生物量(p < 0.01)。不同氮添加量和氮添加方式对幼苗生长的影响因物种而异, 所有氮处理下海南红豆和马占相思的生长均明显快于木荷和马尾松; 木荷和马尾松幼苗的生长在两种氮添加方式间差异显著, 冠层施氮比土壤施氮对其幼苗生长的促进作用更大。由此可见: 在氮沉降背景下, 阔叶豆科植物(海南红豆、马占相思)比阔叶非豆科植物(木荷)生长快; 阔叶树种(海南红豆、马占相思和木荷)比针叶树种(马尾松)生长快。在长期氮沉降环境下, 不同物种生长的差异响应有可能导致亚热带森林物种组成发生变化。     

Stoichiometric characteristics of carbon,nitrogen and phosphorus in Phyllostachys edulis forests of China

Aims Stoichiometric ratios of carbon (C), nitrogen (N) and phosphorus (P) are important characteristics of the ecological processes and functions. Studies on population ecological stoichiometry can refine the content of flora chemometrics, determine the limited nutrient, and provide data for process-based modeling over large scale. Phyllostachys edulis is an important forest type, whose area accounts for 74% of total bamboo forest area in Southern China. However, little is known about the ecological stoichiometric in P. edulis. This study aimed to reveal C:N, C:P and N:P stoichiometry characteristics of the “plant-soil-litter” continuum and to provide a better understanding nutrient cycling and stability mechanisms in P. edulis forest in China. Methods The data were collected from the published literature containing C、N、P content in leaf or surface soil (0-20 cm) or littefall in P. edulis forests. Important findings 1) The leaf C, N, P content were estimated at 478.30 mg·g^-1, 22.20 mg·g^-1, 1.90 mg·g^-1 in P. edulis, and the corresponding C: N, C: P and N: P were 26.80, 299.60 and 14.40, respectively. Soil C, N, and P content in 0-20 cm were 21.53 mg·g^-1, 1.66 mg·g^-1, 0.41 mg·g^-1, with ratios of 14.20 for C:N, 66.74 for C:P and 4.28 for N:P. The C, N and P contents were 438.49 mg·g^-1, 13.39 mg·g^-1, 0.86 mg·g^-1 for litterfall, with the litter C:N, C:P and N:P being 25.53, 665.67, 22.55, respectively. 2) In the plant-soil-litter system in P. edulis forest, leaf had higher C:N, litter had higher C:P and N:P, while soil were the lowest. The N, P resorption rate was 39.68% and 54.74%, indicating that P. edulis forest growth and development was constrained by P or by both of N and P in China. 3) N content and N:P in leaf showed a tendency to increase with latitude, while the C:N of leaf declined with latitude. N:P of leaf increased with longitude, but the P content and the C:N of leaf showed a opposite trend. C: N of soil increased with longitude, whereas the N content of soil declined longitude. The N content of litter declined with longitude. 4) The leaf N content was negatively correlated with mean annual temperature and mean annual precipitation, but being more sensitive to temperature than precipitation. The positive correlations between N content and latitude support “Temperature-Plant Physiological” hypothesis, reflecting an adaptive strategy to environmental conditions.     

增温对苔原土壤和典型植物叶片碳、氮、磷化学计量学特征的影响

为探讨苔原植被对气候变暖的响应模式, 采用开顶箱增温法, 研究了3个生长季增温对长白山苔原3种代表植物——牛皮杜鹃(Rhododendron aureum)、笃斯越桔(Vaccinium uliginosum)和东亚仙女木(Dryas octopetala var. asiatica)的叶片及土壤碳(C)、氮(N)、磷(P)含量及其比值的影响。结果表明: 增温使土壤N和P的含量分别增加5.88%和4.83%, C含量降低13.19%; 增温和对照(不增温)条件下, 植物叶片的C、N、P含量及其比值在生长季有明显的变化。增温使笃斯越桔和东亚仙女木叶片的P含量分别增加10.34%和12.87%, 牛皮杜鹃则降低了16.26%, 增温并没有明显改变3种植物叶片的C、N含量, 但牛皮杜鹃和东亚仙女木叶片的C:N值在增温条件下呈现增加趋势。增温使土壤可利用的N、P含量增加。增温对3种植物的C:N值, 牛皮杜鹃、笃斯越桔的P含量, 以及东亚仙女木的C:P值都产生了显著的影响。结果表明增温增加了长白山苔原P元素对植物生长的限制, 且3种植物叶片的C、N、P化学计量学特性对增温的响应模式和尺度没有表现出一致性。     

Storage of carbon,nitrogen and phosphorus in temperate shrubland ecosystems across Northern China

Aims Studying storage of carbon (C), nitrogen (N) and phosphorus (P) in ecosystems is of significance in understanding carbon and nutrient cycling. Previous researches in ecosystem C, N and P storage have biased towards forests and grasslands. Shrubland ecosystems encompass a wide gradient in precipitation and soil conditions, providing a unique opportunity to explore the patterns of ecosystem C, N and P storage in relation to climate and soil properties.
Methods We estimated densities and storage of organic C, N and P of shrubland ecosystems in Northern China based on data from 433 shrubland sites.
Important findings The main results are summarized as follows: the average organic C, N and P densities in temperate shrubland ecosystems across Northern China were 69.8 Mg·hm^-2, 7.3 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively. The average plant C, N and P densities were 5.1 Mg·hm^-2, 11.5 × 10^-2 Mg·hm^-2 and 8.6 × 10^-3 Mg·hm^-2, respectively, and were significantly correlated with precipitation and soil nutrient concentrations. The average litter C, N and P densities were 1.4 Mg·hm^-2, 3.8 ×10^-2 Mg·hm^-2, 2.5 ×10^-3 Mg·hm^-2 and were significantly correlated with temperature and precipitation. The average soil organic C, N and P densities in the top 1 m were 64.0 Mg·hm^-2, 7.1 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively and the former two were significantly correlated with temperature and precipitation. The total organic C, N and P storage of shrublands in Northern China were 1.7 Pg, 164.9 Tg and 124.8 Tg, respectively. The plant C, N and P storage were 128.4 Tg, 3.1 Tg and 0.2 Tg, respectively. The litter C, N and P storage were 8.4 Tg, 0.45 Tg, 0.027 Tg, respectively. Soil is the largest C, N and P pool in the studied area. The soil organic C, N and P storage in the top 1 meter were 1.6 Pg, 161.3 Tg and 124.6 Tg, respectively.     

Changes of the relationships between soil and microbes in carbon,nitrogen and phosphorus stoichiometry during ecosystem succession

AimsThe carbon (C), nitrogen (N) and phosphorus (P) stoichiometry (C:N:P) of soil profoundly influences the growth, community structure, biomass C:N:P stoichiometry, and metabolism in microbes. However, the relationships between soil and microbes in the C:N:P stoichiometry and their temporal dynamics during ecosystem succession are poorly understood. The aim of this study was to determine the temporal patterns of soil and microbial C:N:P stoichiometry and their relationships during ecosystem succession.MethodsAn extensive literature search was conducted and data were compiled for 19 age sequences of successional ecosystems, including 13 forest ecosystems and 6 grassland ecosystems, from 18 studies published up to May 2016. Meta-analyses were performed to examine the sequential changes in 18 variables that were associated with soil and microbial C, N and P contents and the stoichiometry. Important findings (1) There was no consistent temporal pattern in soil C:N along the successional stages, whereas the soil C:P and N:P increased with succession; the slopes of the linear relationships between soil C:N:P stoichiometry and successional age were negatively correlated with the initial content of the soil organic C within given chronosequence. (2) There was no consistent temporal pattern in microbial C:N:P stoichiometry along the successional stages. (3) The fraction of microbial biomass C in soil organic C (qMBC), the fraction of microbial biomass N in soil total N, and the fraction of microbial biomass P in soil total P all increased significantly with succession, in consistency with the theory of succession that ecosystem biomass per unit resource increases with succession. (4) The qMBC decreased with increases in the values of soil C:N, C:P, or N:P, as well as the stoichiometric imbalances in C:N, C:P, and N:P between soil and microbes (i.e., ratios of soil C:N, C:P, and N:P to microbial biomass C:N, C:P, and N:P, respectively). The C:N, C:P, and N:P stoichiometric imbalances explained 37%-57% variations in the qMBC, about 7-17 times more than that explainable by the successional age, illustrating the importance of soil-microbial C:N:P stoichiometry in shaping the successional dynamics in qMBC. In summary, our study highlights the importance of the theories of ecosystem succession and stoichiometry in soil microbial studies, and suggests that appropriately applying macro-ecological theories in microbial studies may improve our understanding on microbial ecological processes.     

Characteristics of nitrogen and phosphorus stoichiometry across components of forest ecosystem in Shaanxi Province

Aims Nitrogen (N) and phosphorus (P) stoichiometry between vegetation, litter, and soil were important for understanding biogeochemical cycles in terrestrial ecosystems, but remain poorly understood. Here, our aims were to study characteristics of N and P stoichiometry for the plant, litter, and soil and the interactions between its components across forest ecosystems in Shaanxi Province.Methods A total of 121 sampling sites, covering the most main forest types in Shaanxi, were established across the whole province in 2012. And N and P concentration of vegetation (tree and understory), litter and soil layers were measured for each site.Important findings 1) There were significant differences in the N and P stoichiometry among the forest ecosystem components (p < 0.05). N and P contents were higher in understory and litter layer, and lower in tree and soil. Whereas the N:P was slightly different, highest in litter and lowest in the soil layer, with little differences among remaining components. The contents of N, P and N:P ranged from 0.72 to11.99 mg·g^-1, 0.47 to 1.07 mg·g^-1, and 1.86 to 14.84, respectively. Within top 1 m soil layer N content and N:P decreased with soil depth (p < 0.05), however the P content did not exhibit significant changes. 2) N and P contents, and N:P of each component were higher in broadleaf forest than in coniferous forest, although the difference is not significant. 3) N was positively correlated with P content except for soil and N:P was negatively correlated with P content, but positively correlated with N content within each component. In addition, there was a significant positive correlation for N and P stoichiometric characteristics between litter layer and tree, herb, soil layer. 4) Although spatial pattern of N and P contents, and N:P differed in relation to longitude, latitude, and elevation for forest ecosystem components, a stable distribution was exhibited in general.     

Carbon,nitrogen and phosphorus stoichiometry in leaves and fine roots of dominant plants in Horqin Sandy Land

Aims The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plant organism is vital to understand plant adaptation to environment. In particular, the correlations of elemental stoichiometric characteristics between leaf and fine root could provide insights into the interaction and balance among the plant elements, nutrient use strategies and plant response to global change.Methods We measured C, N, P contents and C:N, C:P, N:P in leaves and fine roots of 60 dominant plants in Horqin sandy land. The 60 plant species were classified into five life forms and two categories such as perennial forb, annual forb, perennial grass, annual grass, shrub, legume, and non-legume. We statistically analyzed the differences and correlations of C, N and P stoichiometry either between fine root and leaf or among five life forms.Important findings The average C, N and P concentrations in leaves of 60 plant species in Horqin sandy land are 424.20 mg·g^-1, 25.60 mg·g^-1 and 2.10 mg·g^-1, respectively. In fine roots, the corresponding element concentrations are 434.03 mg·g^-1, 13.54 mg·g^-1, 1.13 mg·g^-1. N and P concentrations in leaf are approximately twice as high as averages in fine root. Furthermore, similar N:P between leaf and fine root indicates conservative characteristic of elemental stoichiometry in plant organism, suggesting that nutrients distribution is proportional between aboveground and underground of plants. There are significant difference of C, N, P, C:N, C:P and N:P in leaf and root among five life forms. N and P in forb and C:N and C:P in grass are averagely higher than those in other life forms. N:P in annual forb and grass, however, are lower than those in other life forms. C, N in legume are higher than those in non-legume, while C:N in legume is lower than in non-legume. These results imply that nutrient use strategies are significantly different among plant life forms. Correlations analysis showed that N and P in leaf or fine root positively correlated, but C and N, C and P in fine root negatively correlated, suggesting coupling relationship among C, N and P in leaf and fine root. Subsequently, we detected positively significant correlations in C, N, P and their ratios between leaf and fine root, suggesting proportional distribution of photosynthate and nutrient between aboveground and underground during plant growth. Generally, these results supplied fundamental data to understand mass turnover and nutrients cycling of leaves and roots in sand land.     

Salt accumulation in vegetative organs and ecological stoichiometry characteristics in typical halophytes in Xinjiang,China

AimsStudying salt accumulation in vegetative organs and carbon (C), nitrogen (N), phosphorus (P) stoichiometry in halophytes contributes to understand the adaptive strategy to saline environment and the distribution mechanism of nutrients and salinity of the halophytes.MethodsFour typical dominant species, including three perennial shrubs (Halocnemum strobilaceum, Suaeda microphylla and Kalidium foliatum) and an annual herb (Salicornia europaea) were selected for analyzing the salt accumulation and C, N, P stoichiometry relationships.Important findings 1) The salt accumulation showed “salt island” effect at peak growing stage; Na⁺, Cl^- and electrical conductivity all showed significant positive trends, when salt ions were transported from the root to the shoot of 4 halophytes. 2) P was the limiting growth element of perennial shrubs, while both N and P were limiting factors for the annual herb. 3) Different organs, species and their interactions affected C, N, P stoichiometry and salt icons except Mg²⁺. 4) C was negatively correlated with N and P, but there was a significant positive correlation between N and P. 5) Electrical conductivity, Na⁺and K⁺ were positively correlated with N, N:P ratio, and negatively correlated with C, C:N and C:P ratios, and yet K⁺, CO₃^2- had significant positive correlation with P. These results implied that there were some kind of mutual promoting relationships between nutrients and salinity in halophytes in the saline environment, and fertilizing with N could promote sodium chloride desalination.     

氮肥和种植密度对达乌里胡枝子的生长与生物固氮的影响

氮供给和种植密度是影响植物生长的两个重要因素。豆科植物因其生物固氮能力而在受到氮限制的生态系统中具有重要作用, 氮含量增加促进植物生长的同时也会抑制豆科植物的生物固氮能力, 种植密度会通过种内竞争影响豆科植物的生长和生物固氮能力, 然而少有研究关注氮肥添加和种植密度对豆科植物生长和生物固氮能力的影响。该研究以达乌里胡枝子(Lespedeza davurica)为研究对象, 通过温室盆栽实验, 探究氮肥和种植密度对其生长和生物固氮的影响。实验设置4个氮添加水平(0、5、10、20 g·m^-2·a^-1)和3种种植密度(1、3、6 Ind.·pot^-1, 约32、96、192 Ind.·m^-2)。结果发现: 1)施肥和密度增加均影响了达乌里胡枝子的生长。叶片碳(C)、氮(N)含量、净光合速率随施氮量增加而增加, 氮添加也促进了植物的生长, 当施氮量为10 g·m^-2·a^-1时植物产量达到最大。叶片C、N含量、净光合速率随种植密度增加而下降, 密度增加可以促进每盆的总生物量, 但对单个植株的生长有负效应。2)氮肥对根瘤形成有抑制作用, 但种植密度增加会缓解氮肥对生物固氮能力带来的“氮阻遏”。该实验条件下, 当施氮量为10 g·m^-2·a^-1, 种植密度为3 Ind.·pot^-1, 或施氮量为5 g·m^-2·a^-1, 种植密度为6 Ind.·pot^-1时, 能最大程度发挥“施氮增产”和种植密度缓解“氮阻遏”的作用。氮添加降低了达乌里胡枝子的根瘤生物量和对根瘤形成的投资(根瘤生物量占总生物量的比例), 从而抑制达乌里胡枝子的生物固氮。种植密度增加导致达乌里胡枝子因种内竞争增加而使资源获取受限, 从而增加对根瘤的投资和根瘤生物量来获得更多来自大气中的氮。3)结构方程结果显示, 氮肥和种植密度通过直接或间接作用, 解释了64%的达乌里胡枝子生物量变化和42%的根瘤生物量变化。上述结果表明合理优化豆科植物的施肥量和种植密度可能对人工草地种植以及退化草地恢复管理具有重要意义。     

Effects of light intensity variation on nitrogen and phosphorus contents,allocation and limitation in five shade-enduring plants

Aims To enhance the understanding on nitrogen (N) and phosphorus (P) physiological responses to different light environments in shade-enduring plants and provide references to improve the stand structure and ecosystem functions of plantation forests.Methods We selected seedlings of five shade-enduring species with high ecological and economic value in subtropical area of China to study the effects of light intensity on leaf N and P contents, allocation and nutrient limitation in shade-enduring plants. A light intensity gradient of five different levels was set to simulate the varying understory light environment.Important findings With decreasing light intensity, the total biomass and total N and P accumulation of five shade-enduring plants all showed a decreasing trend, but N, P contents in different organs increased. Among them, Gardenia jasminoides (GJ) had the highest while Illicium henryi (IH) had the lowest N content; The P contents of Quercus phillyraeoides (QP) and GJ were significantly higher than Elaeocarpus sylvestris (ES), Ardisia crenata (AC) and IH. QP and GJ had the highest N, P contents under extremely low light intensity (6% natural light intensity) condition (LIC), while AC and IH had the highest N and P contents in low (15% natural light intensity) and moderate (33% and 52% natural light intensity) LIC. ES demanded differently for LIC on N and P, which were 52% and 6% natural light intensity, respectively. N and P allocation of ES, AC and IH followed leaf > root > stem, but for QP and GJ were root > leaf > stem. Decreasing LIC significantly affected N and P allocation. N content variations shown good consistency among different organs under higher LIC (100% natural light intensity) while distinct variability under lower LIC (15% and 6% natural light intensity) in all five species. Phosphorus contents exhibited good consistency in IH, QP and GJ but varied in ES and AC. Decreasing LIC significantly affected organ N/P ratios of shade-enduring plants, but the fundamental growth restriction patterns remained. Light intensity variation and tree species co-regulated N, P utilization and allocation in shade-enduring plants, and then affected the total biomass and total N, P accumulation, which might result from the change of N and P utilization strategy. Therefore, light intensity preference and N, P nutrient balances in shade-enduring plants should be taken into account when constructing multiple layer and uneven-aged forests.     

青海森林生态系统中灌木层和土壤生态化学计量特征

灌木层作为森林生态系统的重要组成部分, 了解其生态化学计量特征将有助于揭示森林生态系统物质周转和养分循环等生态功能。该研究选取青海省7种主要优势林分——白桦(Betula platyphylla)林、毛白杨(Populus tomentosa)林、红桦(Betula albosinensis)林、青扦(Picea wilsonii)林、山杨(Populus davidiana)林、圆柏(Sabina chinensis)林、云杉(Picea asperata)林为研究对象, 采用野外取样和室内实验分析相结合的方法, 研究了不同林分林下灌木层不同器官(叶、枝干、根)及其表层(0-10 cm)土壤的碳(C)、氮(N)、磷(P)含量及其相关性。结果表明: 7种林分间灌木(叶、枝干、根) P含量、C:P均没有明显差异性; 山杨林、圆柏林、云杉林的林下灌木(叶、枝干、根) N含量、N:P高于白桦林、毛白杨林、红桦林和青扦林, C:N则相反。圆柏林的林下灌木生长受P限制, 其余6种林分的林下灌木生长受N限制。7种林分间土壤有机碳(SOC)和总氮(TN)含量呈现出明显差异性, 而总磷(TP)含量则差异不明显。相关性分析表明, 林下灌木(叶、枝干、根) N含量、C:N、N:P与土壤TN含量、C:N、N:P呈极显著相关性, 而P含量、C:P与土壤TP含量呈显著相关性。冗余分析表明, 林下灌木层植被C、N、P含量及生态化学计量特征受到土壤化学计量特征及各环境因子的共同影响, 其中土壤C:N、海拔、年平均气温、年降水量为主要影响因子。