短期增温对贡嘎山峨眉冷杉幼苗生长及其CNP化学计量学特征的影响

2009年5月至10月,在中国科学院贡嘎山高山森林生态系统观测站附近,采用红外灯加热人工模拟气候变暖研究了增温对峨眉冷杉(Abies fabiri (Mast) Craib)幼苗生长和养分及其化学计量特征的影响。由于红外灯的增温作用,在幼苗的整个生长季节,增温样地地表下5 cm、10 cm、20 cm处土温平均高于对照样地5.04 ℃、4.81 ℃、4.35 ℃,而土壤含水量则分别降低了7.03%、6.10%、6.40%;地表20 cm处空气温度相比对照样地上升了1.12 ℃,而空气相对湿度则降低了6.30%。除茎重比外,增温处理降低了峨眉冷杉幼苗的根长、基径、株高、总生物量、根重比、叶重比、根冠比和比叶面积。经方差分析发现,增温处理后幼苗根、茎和叶的C平均含量与对照差异性均不显著(P>0.05),其中除茎的提高了2.76%外,根和叶分别降低了7.15%和2.29%;N平均含量除茎显著降低之外(P<0.05),根、叶分别提高了9.78%和5.70%;幼苗根、茎、叶的P平均含量均低于对照11.97%、10.69%和2.99%,并且根和茎与对照存在显著性差异(P<0.05)。增温处理后幼苗根、茎、叶各器官的C︰N、C︰P 、N︰P与对照均不存在显著性差异(P>0.05),其中C︰P均大于对照,而C︰N和N︰P与对照相比,均有不同程度的减小;C︰N、N︰P和C︰P的平均值(标准差)大小顺序依次为茎(92.594.92)>根(61.891.65)>叶(60.813.23)、叶(4.990.22)>根(4.440.58)>茎(3.640.10)和茎(336.358.70)>叶(302.854.49)>根(274.865.27)。实验结果表明：增温对幼苗生长和生物量积累具有明显的限制作用,对叶片生长的阻碍作用尤为突出;增温改变了幼苗根茎叶的CNP含量及其化学计量比格局;在养分供应上,增温和对照处理下幼苗生长均受N素限制。     

Early stages of root and leaf decomposition in Hawaiian forests: effects of nutrient availability

We examined the effects of soil nutrient availability and tissue chemistry on decomposition of both fine roots (<2 mm diameter) and leaves in three sites along a forest chronosequence in the Hawaiian Islands. These sites form a natural fertility gradient, with the youngest and oldest sites having lower nutrient availability than the intermediate-aged site. Nitrogen (N) limits aboveground net primary productivity (ANPP) in the youngest site, while phosphorus (P) limits ANPP in the oldest site. Both root and leaf litter decomposed most slowly in the 4.1-Myear-old site. We also investigated root decomposition in fertilized plots at the youngest and oldest sites; when roots were produced and decomposed in fertilized plots, root decomposition rates increased with N and P additions at the 4.1-Myear-old site. At the 300-year-old site, however, root decomposition rates did not respond to N or P additions. Roots decomposed faster than leaves at the more infertile sites, in part because of lower lignin-to-nitrogen ratios in roots than in leaf litter. Decomposing roots immobilized more nutrients than did decomposing leaves, and may serve an important role in retaining nutrients in these forests. Received: 30 November 1998 / Accepted: 12 August 1999     

Carbon and nitrogen allocation shifts in plants and soils along aridity and fertility gradients in grasslands of China

Plant carbon (C) and nitrogen (N) stoichiometry play an important role in the maintenance of ecosystem structure and function. To decipher the influence of changing environment on plant C and N stoichiometry at the subcontinental scale, we studied the shoot and root C and N stoichiometry in two widely distributed and dominant genera along a 2,200‐km climatic gradient in China's grasslands. Relationships between C and N concentrations and soil climatic variables factors were studied. In contrast to previous theory, plant C concentration and C:N ratios in both shoots and roots increased with increasing soil fertility and decreased with increasing aridity. Relative N allocation shifted from soils to plants and from roots to shoots with increasing aridity. Changes in the C:N ratio were associated with changes in N concentration. Dynamics of plant C concentration and C:N ratios were mainly caused by biomass reallocation and a nutrient dilution effect in the plant‐soil system. Our results suggest that the shifted allocation of C and N to different ecosystem compartments under a changing environment may change the overall use of these elements by the plant‐soil system.     

干旱胁迫下接种丛枝菌根真菌对七子花非结构性碳水化合物积累及C、N、P化学计量特征的影响

以濒危植物七子花二年生幼苗为研究材料,采用盆栽试验方法,研究干旱胁迫和接种丛枝菌根真菌(AMF)处理对幼苗不同器官C、N、P化学计量关系和非结构性碳水化合物(NSC)含量的影响。试验共设计4个处理:对照(CK)、干旱胁迫(D)、接种AMF(AMF)、干旱胁迫和接种AMF(D+AMF)。结果表明: 在干旱胁迫下七子花根系AMF的侵染率显著下降,但接种AMF处理植株的株高、叶片数显著高于未接种处理。接种AMF显著提高了干旱胁迫下植株根、叶可溶性糖和NSC含量及茎、叶淀粉含量,且茎和叶可溶性糖与淀粉比显著下降。干旱胁迫导致植株C含量在根和叶中显著增加,P含量在茎中显著减少;与干旱胁迫相比,胁迫下接种AMF植株根、茎、叶P含量及叶C含量显著提高,而根C、N含量及茎C含量显著降低。胁迫下接种AMF植株根、茎C∶N、C∶P、N∶P和叶N∶P均显著低于单一胁迫处理。NSC与C∶N∶P计量比的相关性分析表明,根、叶P含量与可溶性糖和NSC含量呈显著正相关,茎P含量与淀粉和NSC含量呈显著正相关,各器官N∶P与NSC含量呈显著负相关。综上,干旱胁迫显著抑制了七子花幼苗的生长,接种AMF通过提高植株根和叶的可溶性糖含量、根的可溶性糖/淀粉,增加地上部分淀粉含量,促进P元素吸收和降低各器官N∶P来增强植株耐旱性,从而提高七子花幼苗在干旱环境中的存活率。     

青藏高原东缘主要针叶树种叶片碳氮磷化学计量分布格局及其驱动因素

理解植物叶片化学计量特征及其驱动因素对认识植物种群分布规律及预测植物对环境变化响应具有重要意义。该研究采集了青藏高原东缘针叶林84个样点共29种主要针叶树种叶片, 探讨该区域常绿针叶树种叶片碳(C)、氮(N)、磷(P)化学计量特征和分布格局及其驱动因素。结果表明: (1)在科和属水平上, 不同针叶树种叶片C、N含量和C:N差异显著; 叶片N:P < 14, 表明该区域针叶树种主要受N限制。(2)叶片N、P含量在环境梯度上表现出一致的分布规律: 均呈现出随纬度和海拔增加而显著降低, 随年平均气温(MAT)和年降水量(MAP)增加而显著增加的趋势; 而叶片C含量与纬度、海拔、MAT和MAP均未表现出显著相关性。(3)叶片C:N、C:P呈现出与N、P含量变化相反的分布格局: 均随纬度和海拔增加而显著增加, 随MAT和MAP增加而显著降低; 而叶片N:P与海拔、MAT和MAP均无显著相关性。(4)进一步分析表明, 叶片C、N、P含量及其化学计量比的主要驱动因素不尽相同。具体而言: 土壤特性是叶片C含量和N:P变异的主要驱动因子, 而叶片N、P含量和C:N、C:P的变异主要由气候因素决定。总之, 该区域针叶树种叶片化学计量沿环境梯度的变异规律有力地支持了温度生物地球化学假说, 在一定程度上丰富了对环境变化下植物叶片化学计量分布格局及其驱动机制的认识。     

Variation in leaf nitrogen and phosphorus stoichiometry in the nitrogen-fixing Chinese sea-buckthorn (Hippophae rhamnoides L. subsp. sinensis Rousi) across northern China

Nitrogen (N) and phosphorus (P) concentrations and N:P ratios in terrestrial plants and their patterns of change along environmental gradients are important traits for plant adaptation to changes. We determined the leaf N and P concentrations of Chinese sea-buckthorn (Hippophae rhamnoides L. subsp. sinensis Rousi), a non-legume species with symbiotic N fixation (SNF), at 37 sites across northern China and explored their geographical patterns in relation to climate and soil factors. (1) The mean leaf N, P, and N:P ratio were 36.5, 2.1 mg g^?1, and 17.6, respectively, higher than the mean values of most shrub species in the region. (2) Leaf N was correlated with soil mineral N in cool areas (mean annual temperature MAT <3 °C) but with temperature in warm areas (MAT >3 °C). The high leaf N and divergent leaf N–soil N relationship suggested the importance of SNF in plant N uptake; SNF increases with temperature and is probably the major N source in warm areas. (3) Leaf P was positively related to mean annual precipitation. Leaf N:P ratio was primarily driven by changes in leaf P. The high leaf P reflected the greater requirements of the N-fixing species for P. Our results represent a major advance in understanding the elemental stoichiometry of non-legume N-fixing plants, indicating high P and N requirements and a shift in N source from SNF to soil as temperature declines. This knowledge will help in assessing the habitat suitability for the species and predicting the species dynamics under environmental changes.     

不同林龄和密度马尾松人工林针叶和根系的生态化学计量特征

为了解不同林龄和密度马尾松人工林针叶和根系的养分变化特征,该文在广西南宁市横县镇龙林场选择了四种林龄(幼龄林、中龄林、成熟林和过熟林)和四种密度(低密度林、中低密度林、中高密度林和高密度林)马尾松林共八种林分,分析了马尾松针叶和根系的C、N、P含量和比值及其与土壤养分的关系。结果表明:(1)所有龄林与密度林的马尾松针叶N∶P比值均大于16,表明该地区马尾松明显受P限制,幼龄林更加明显。(2)马尾松针叶C含量随着林龄增长逐渐增大后下降,N与P含量呈微弱下降趋势,导致C∶N比值、C∶P比值和N∶P比值呈微弱上升趋势,但没达到显著水平;根系C含量、P含量和C∶N比值逐渐增大,N含量、C∶P比值和N∶P比值呈U字型且都在幼龄林最大;针叶和根系在成熟林阶段均具有较高的P含量和最高的C含量。(3)中密度林的马尾松针叶的C和N含量较高且P含量最高,C∶N比值较低且C∶P比值和N∶P比值最低;根系的C、N和P含量较高,而C∶N比值、C∶P比值和N∶P比值较低。(4)马尾松的根系养分尤其是P含量在不同龄林和不同密度林之间的变化比针叶更加剧烈,且其与土壤养分之间的相关性比针叶更强。综上结果表明,马尾松人工林受P限制,在低龄林加强P肥管理和选择合适的林分密度(中等密度)则有利于缓解马尾松受P限制的状态。     

Variation of carbon and nitrogen stoichiometry along a chronosequence of natural temperate forest in northeastern China

Aims Carbon (C) and nitrogen (N) stoichiometry contributes to understanding elemental compositions and coupled biogeochemical cycles in ecosystems. However, we know little about the temporal patterns of C:N stoichiometry during forest development. The goal of this study is to explore the temporal patterns of intraspecific and ecosystem components' variations in C:N stoichiometry and the scaling relationships between C and N at different successional stages.Methods Along forest development in a natural temperate forest, northeastern China, four age gradients were categorized into ca. 10-, 30-, 70- and 200-year old, respectively, and three 20 m × 20 m plots were set up for each age class. Leaves, branches, fine roots and fresh litter of seven dominant species as well as mineral soil at depth of 0–10 cm were sampled. A Universal CHN Elemental Analyzer was used to determine the C and N concentrations in all samples.Important findings Intraspecific leaf C, N and C:N ratios remained stable along forest development regardless of tree species; while C, N concentrations and C:N ratios changed significantly either in branches or in fine roots, and they varied with tree species except Populus davidiana (P < 0.05). For ecosystem components, we discovered that leaf C:N ratios remained stable when stand age was below ca. 70 years and dominant tree species were light-demanding pioneers such as Betula platyphylla and Populus davidiana, while increased significantly at the age of ca. 200 years with Pinus koraiensis as the dominant species. C:N ratios in branches and fresh litter did not changed significantly along forest development stages. C concentrations scaled isometrically with respect to N concentrations in mineral soil but not in other ecosystem components. Our results indicate that, leaf has a higher intraspecific C:N stoichiometric stability compared to branch and fine root, whereas for ecosystem components, shifts in species composition mainly affect C:N ratios in leaves rather than other components. This study also demonstrated that C and N remain coupled in mineral soils but not in plant organs or fresh litter during forest development.     

Allocation strategies of carbon,nitrogen and phosphorus following a gradient of wildfire severities

植物碳、氮、磷在不同火烧强度下的分配策略 森林野火是影响北方针叶林演替过程中养分分配规律的重要因素。然而,植物叶片和细根之间 的碳(C)、氮(N)、磷(P)分配策略在不同强度森林野火后的研究尚不充分。本研究旨在探讨不同野火强度下叶片和细根间C、N、P的分配策略。运用化学计量学理论和异速生长方程,选取中国东北大兴安岭地区的4个不同火烧强度(未火烧、低、中、高)恢复10年后的火烧迹地为研究样地,比较不同火烧强 度下各物种叶片和细根的C、N、P含量。研究结果表明,与未受到火烧的样地相比,轻度火烧迹地的植物叶片和细根C浓度增加,重度火烧迹地植物叶片N浓度最高,但是细根N浓度最低。N:P比值的平均值大于16的结果表示植物养分利用策略在高火烧强度下趋于P限制。更重要的是,随着火烧严重程度的增加,细根与叶片间的C、N、P分配规律出现由异速生长向等速生长的转变,即随着火烧强度的增加,元素分配表现为对叶片的分配多于细根。这些结果表明,植物叶片和细根之间的元素分配策略在受到不同强度的野火干扰以后发生了失衡。本研究加深了我们对火后森林生态系统演替过程中植物与土壤养分动态的认识。     

Leaf-root-soil N:P stoichiometry of ephemeral plants in a temperate desert in Central Asia

Ephemeral plants are a crucial vegetation component in temperate deserts of Central Asia, and play an important role in biogeochemical cycle and biodiversity maintenance in desert ecosystems. However, the nitrogen (N) and phosphorus (P) status and interrelations of leaf-root-soil of ephemeral plants remain unclear. A total of 194 leaf-root-soil samples of eight ephemeral species at 37 sites in the Gurbantunggut Desert, China were collected, and then the corresponding N and P concentrations, and the N:P ratio were measured. Results showed that soil parameters presented no significant difference among the eight species. The total soil N:P was only 0.116 (geomean), indicating limited soil N, while the available soil N:P (4.896, geomean) was significantly larger than the total N:P. The leaf N (averagely 30.995 mg g^?1) and P (averagely 1.523 mg g^?1) concentrations were 2.64–8.46 and 0.93–3.99 times higher than the root N (averagely 8.014 mg g^?1) and P (averagely 0.802 mg g^?1) concentrations, respectively. Thus, leaf N:P (averagely 21.499) was 1.410–2.957 times higher than root N:P (averagely 11.803). Meanwhile, significant interspecific differences existed in plant stoichiometric traits. At the across-species level, N content scaled as the 3/4-power of P content in both leaves and roots. Leaf and root N:P ratios were mainly influenced by P; however, the leaf-to-root N or P ratio was dominated by roots. Leaf and root N, P contents and N:P were generally unrelated to soil nutrients, and the former presented lower variation than the latter, indicating a strong stoichiometric homeostasis for ephemerals. These results demonstrate that regardless of soil nutrient supply capacity in this region, the fast-growing ephemeral plants have formed a specific leaf-root-soil stoichiometric relation and nutrient use strategy adapting to the extreme desert environment.

     

Stoichiometry of Root and Leaf Nitrogen and Phosphorus in a Dry Alpine Steppe on the Northern Tibetan Plateau

Leaf nitrogen (N) and phosphorus (P) have been used widely in the ecological stoichiometry to understand nutrient limitation in plant. However,few studies have focused on the relationship between root nutrients and environmental factors. The main objective of this study was to clarify the pattern of root and leaf N and P concentrations and the relationships between plant nitrogen (N) and phosphorus (P) concentrations with climatic factors under low temperature conditions in the northern Tibetan Plateau of China. We conducted a systematic census of N and P concentrations, and the N∶P ratio in leaf and root for 139 plant samples, from 14 species and 7 families in a dry Stipa purpurea alpine steppe on the northern Tibetan Plateau of China. The results showed that the mean root N and P concentrations and the N∶P ratios across all species were 13.05 mg g⁻¹, 0.60 mg g⁻¹ and 23.40, respectively. The mean leaf N and P concentrations and the N∶P ratio were 23.20 mg g⁻¹, 1.38 mg g⁻¹, and 17.87, respectively. Compared to global plant nutrients concentrations, plants distributing in high altitude area have higher N concentrations and N∶P, but lower P concentrations, which could be used to explain normally-observed low growth rate of plant in the cold region. Plant N concentrations were unrelated to the mean annual temperature (MAT). The root and leaf P concentrations were negatively correlated with the MAT, but the N∶P ratios were positively correlated with the MAT. It is highly possible this region is not N limited, it is P limited, thus the temperature-biogeochemical hypothesis (TBH) can not be used to explain the relationship between plant N concentrations and MAT in alpine steppe. The results were valuable to understand the bio-geographic patterns of root and leaf nutrients traits and modeling ecosystem nutrient cycling in cold and dry environments.     

Effects of different nitrogen:phosphorus levels on the growth and ecological stoichiometry of Glycyrrhiza uralensis北大核心CSCD

Aims The increase in atmospheric nitrogen (N) deposition has accelerated N cycling of ecosystems, probably resulting in increases in phosphorus (P) demand of ecosystems. Studies on the effects of artificial N:P treatment on the growth and carbon (C), N, P ecological stoichiometry of desert steppe species could provide not only a new insight into the forecasting of how the interaction between soils and plants responses to long-term atmospheric N deposition increase, but also a scientific guidance for sustainable management of grassland in northern China under global climate change. Methods Based on a pot-cultured experiment conducted for Glycyrrhiza uralensis (an N-fixing species) during 2013 to 2014, we studied the effects of different N:P supply ratios (all pots were treated with the same amount of N but with different amounts of P) on aboveground biomass, root biomass, root/shoot ratio, and C:N:P ecological stoichiometry both in G. uralensis (leaves and roots) and in soils. Additionally, through the correlation analyses between biomass and C:N:P ecological stoichiometry in leaves, roots, and soils, we compared the differences among the C:N:P ecological stoichiometry of the three pools, and discussed the indication of C:N:P ecological stoichiometry in soils for the growth and nutrient uptake of G. uralensis. Important findings The results showed that, reducing N:P decreased C:P and N:P ratios both in G. uralensis (leaves and roots) and in soils but increased aboveground biomass and root biomass of G. uralensis, indicating that low to moderate P addition increased P availability of soils and P uptake of G. uralensis. However, excessive low N:P (high P addition) led to great decreases in soil C:P and N:P ratios, thus hindering N uptake and the growth of G. uralensis. C:N:P ratios in the two pools of G. uralensis (especially in leaves) had close correlations with soil C:N:P ratio, indicating that the change in soil C:N:P ratio would have a direct influence on plants. Our results suggest that, through regulating C:N:P ratio in leaves and soils, appropriate amounts of P addition could balance soil P supply and plant P demand and compensate the opposite influences of long-term atmospheric N deposition increase on the structure of desert steppe.     

Congeneric Serpentine and Nonserpentine Shrubs Differ More in Leaf Ca:Mg than in Tolerance of Low N, Low P, or Heavy Metals

Serpentine soils limit plant growth by NPK deficiencies, low Ca availability, excess Mg, and high heavy metal levels. In this study, three congeneric serpentine and nonserpentine evergreen shrub species pairs were grown in metalliferous serpentine soil with or without NPKCa fertilizer to test which soil factors most limit biomass production and mineral nutrition responses. Fertilization increased biomass production and allocation to leaves while decreasing allocation to roots in both serpentine and nonserpentine species. Simultaneous increases in biomass and leaf N:P ratios in fertilized plants of all six species suggest that N is more limiting than P in this serpentine soil. Neither N nor P concentrations, however, nor root to shoot translocation of these nutrients, differed significantly between serpentine and nonserpentine congeners. All six species growing in unfertilized serpentine soil translocated proportionately more P to leaves compared to fertilized plants, thus maintaining foliar P. Leaf Ca:Mg molar ratios of the nonserpentine species were generally equal to that of the soil. The serpentine species, however, maintained significantly higher leaf Ca:Mg than both their nonserpentine counterparts and the soil. Elevated leaf Ca:Mg in the serpentine species was achieved by selective Ca transport and/or Mg exclusion operating at the root-to-shoot translocation level, as root Ca and Mg concentrations did not differ between serpentine and nonserpentine congeners. All six species avoided shoot toxicity of heavy metals by root sequestration. The comparative data on nutrient deficiencies, leaf Ca:Mg, and heavy metal sequestration suggest that the ability to maintain high leaf Ca:Mg is a key evolutionary change needed for survival on serpentine soil and represents the physiological feature distinguishing the serpentine shrub species from their nonserpentine congeners. The results also suggest that high leaf Ca:Mg is achieved in these serpentine species by selective translocation of Ca and/or inhibited transport of Mg from roots, rather than by uptake/exclusion at root surfaces.     

Effects of artificial grassland establishment on soil nutrients and carbon properties in a black-soil-type degraded grassland

Despite a growing knowledge of nutrient limitation for mangrove species and how mangroves adapt to low nutrients, there is scant information about the relative importance of N:P ratio and leaf phenolics variability in determining nutrient conservation. In this study, we evaluated possible nutrient conservation strategies of a mangrove Rhizophora stylosa under nutrient limitation. 1. The leaf nutrient concentrations of R. stylosa changed with season, with the highest N concentration in winter and the highest P concentration in spring for both mature and senescent leaves. Leaf N and P concentrations decreased significantly during leaf senescence. Based on N:P ratios R. stylosa forest was N-limited. Accordingly, the nitrogen resorption efficiency (NRE) was significantly higher than phosphorus resorption efficiency (PRE) for the R. stylosa leaves during leaf senescence. The NRE and PRE both reached the highest in the autumn. Average N and P concentrations in the senescent leaves were 0.15% and 0.06% for R. stylosa, respectively, indicating a complete resorption of N and an incomplete resorption of P. There was a significant negative correlation between nitrogen resorption proficiency (NRP) and NRE, meanwhile phosphorus resorption proficiency (PRP) and PRE correlation was also highly significantly. 2. R. stylosa leaves contained relatively high tannin level. Total phenolics, extractable condensed tannins and total condensed tannins contents increased during leaf senescence, and changed between seasons. The lowest concentrations of total phenolics, extractable condensed tannins and total condensed tannins occurred in summer, total phenolics concentrations were inversely related to nitrogen or phosphorus concentrations. 3. Our results confirmed that resorption efficiency during leaf senescence depends on the type of nutrient limitation, and NRE was much higher than PRE under N-limited conditions. R. stylosa forest developed several nutrient conservation strategies in the intertidal coastline surroundings, including high nitrogen resorption efficiency, low nutrient losses and high tannins level.     

N limitation increases along a temperate forest succession: evidences from leaf stoichiometry and nutrient resorption

温带森林演替加剧了氮限制：来自叶片化学计量和养分重吸收的证据 森林生产力和碳汇功能在很大程度上取决于土壤氮和磷的有效性。然而,迄今为止,养分限制随森林演替的时间变化仍存在争议。叶片化学计量和养分重吸收是预测植物生长养分限制的重要指标。基于此,本研究测定了温带森林4个演替阶段所有木本植物叶片和凋落叶中氮和磷的含量,并分析了演替过程中非生物因子和生物因子如何影响叶片化学计量和养分重吸收。研究结果表明,在个体尺度上,叶片氮磷含量在演替末期显著增加,而叶片氮磷比无显著变化;氮的重吸收效率随演替显著增加,然而磷的重吸收效率先增加后减少;氮重吸收效率与磷重吸收效率的比值仅在演替末期显著增加。此外,植物氮素循环对土壤养分的响应比磷素循环更弱。在群落尺度上,叶片氮磷含量随森林演替呈现先降低后升高的趋势,主要受香农-维纳多样性指数和物种丰富度的影响;叶片氮磷比随演替而显著变化,主要由胸径的群落加权平均值决定;氮的重吸收效率增加,主要受物种丰富度和胸径的影响,而磷的重吸收效率相对稳定。因此,氮重吸收效率与磷重吸收效率的比值显著增加,表明随着温带森林演替,氮限制加剧。这些结果可能反映了较高生物多样性群落中物种间对有限资源的激烈竞争,强调了生物因子在驱动森林生态系统养分循环中的重要性,为中国温带和北方森林可持续经营的施肥管理提供了参考。     

干旱区湿地芦苇各器官生态化学计量对土壤因子的响应

了解植物养分浓度及其化学计量对土壤因子的响应,对预测脆弱而敏感生态系统对环境变化的响应至关重要。以敦煌阳关湿地优势种芦苇(Phragmites australis)为对象,通过野外调查与实验分析,研究芦苇不同器官生态化学计量特征及其影响因素。结果表明:芦苇各器官C、P含量为叶>根>茎,N含量及N∶P为叶>茎>根,C∶N为根>茎>叶,C∶P则为茎>根>叶。叶、根C含量显著高于茎(P<0.05),叶、根C含量之间无显著差异(P>0.05),根、茎和叶N、P含量及C∶N、C∶P和N∶P差异显著(P<0.05);芦苇根N∶P<14,叶片N∶P>16,茎N∶P介于14~16;C含量在各器官之间均无显著相关性(P>0.05),根与茎、叶N含量之间呈极显著正相关(P<0.01),根与茎P含量呈极显著正相关(P<0.01),茎与叶N含量呈显著正相关(P<0.05);土壤盐分与芦苇根和茎N含量呈极显著正相关(P<0.01),土壤P含量与茎P含量呈极显著正相关(P<0.01),土壤有效P与根、茎N含量呈极显著正相关(P<0.01);土壤P是影响芦苇根、茎化学计量的主要因素,土壤盐分是影响叶片化学计量的主要因素,芦苇趋向提高各器官N含量来应对高盐、低P的土壤环境。     

大兴安岭典型森林沼泽植物叶片和细根碳氮磷化学计量特征

探究大兴安岭典型森林沼泽不同植物叶片和细根生态化学计量特征,能够为进一步认识高纬度气候敏感生态系统养分利用策略和物质循环过程提供依据。对大兴安岭地区兴安落叶松-苔草、兴安落叶松-笃斯越桔-藓类和兴安落叶松-杜香-泥炭藓3种典型森林沼泽19种优势和亚优势维管植物叶片和细根碳氮磷计量特征(C∶N∶P)进行比较,分析不同森林沼泽类型、植物生长型和菌根类型叶片和细根C∶N∶P差异,通过标准化主轴回归分析叶片与细根C∶N∶P的关系。结果表明: 叶片C∶N∶P在种间水平具有最大的变异(42.5%～84.6%),且叶片和细根种间变异大小均为N∶P>C∶N>C∶P。土壤养分和水分含量较高的兴安落叶松-苔草沼泽叶片与细根C∶N和C∶P值较低,且3种森林沼泽植物叶片和细根N∶P均小于10,受N限制。草本植物叶片C∶P和细根C∶N、C∶P显著低于木本植物。外生菌根和杜鹃花类菌根植物叶片和细根C∶N和C∶P高于丛枝菌根和无菌根植物,且杜鹃花类菌根植物叶片和细根C∶P显著高于外生菌根植物。不同森林沼泽、生长型、菌根类型植物叶片和细根C∶N和C∶P差异明显,而N∶P相对稳定。森林沼泽植物叶片与细根C∶N、C∶P和N∶P呈线性正相关,植物地上与地下部分在生态化学计量特征上存在协同。     

亚热带不同林龄杉木林叶-根-土氮磷化学计量特征

以亚热带地区湖南会同5、10、15、20、25年生杉木(Cunninghamia lanceolata)人工林的针叶、细根及土壤(0—15、15—30、30—45 cm)为研究对象,在测定植物叶、细根、土壤中全N、全P含量的基础上,探讨杉木人工林全生命过程叶-根-土N、P化学计量特征的变化,为其经营过程提供基础数据。研究结果表明:(1)林龄对土壤N、P含量及N∶P具有极显著的影响(P0.01)。土层对土壤N含量影响显著(P0.01)。各层土壤N、P含量随林龄呈先减后升的趋势,变化显著(P0.05),土壤N、P含量的最大值分别出现在成熟林、幼龄林阶段,最小值出现在中龄林阶段。土壤N∶P随林龄呈增加趋势,但变化不显著。(2)林龄、器官均对植物N、P含量及N∶P具有极显著的影响(P0.01)。叶和细根的N、P含量随林龄呈"V"字型的变化趋势,且变化显著(P0.05),叶和细根N、P含量的最大值均出现在幼龄林、成熟林阶段,最小值出现在中龄林阶段。杉木叶的N∶P随林龄无显著变化,细根的N∶P随林龄显著增加(P0.05),杉木叶和细根N∶P变化范围分别为11.79—14.86,9.00—22.89。(3)5个林龄杉木叶、细根、土的N、P含量均表现为叶细根土,且差异显著(P0.05)。叶与细根的N、P含量及N∶P均显著正相关(P0.05)。0—15 cm土壤N与植物叶、细根N无显著相关性,15—30、30—45 cm土壤N与植物叶、细根N在5、10年生时存在显著相关性(P0.05)。5个林龄杉木叶、细根、土壤之间的P含量及N∶P均存在显著相关性。这些结果说明:在杉木的生长过程中,植物叶、细根以及土壤中养分不断变化,叶、细根、土之间的N、P化学计量特征显示出一定的相关关系。     

华北石质山地侧柏人工林C、N、P生态化学计量特征的季节变化

以北京九龙山自然保护区幼龄侧柏人工林为研究对象,对其不同生长季节叶、枝、根(0—10 cm、10—20 cm土层)的碳(C)、氮(N)、磷(P)含量及其生态化学计量学特征进行了分析,深入探讨了生长季节与器官以及两因素交互作用对以上特征的影响,研究有助于理解植物各性状之间的相互作用以及植物生长过程中资源的利用和分配状况。结果表明:1)不同器官间C含量为414.97—461.58 g/kg,枝最大,根(0—10 cm)最小;N含量为6.57—14.28 g/kg,叶最大,枝最小;P含量为0.39—1.28 g/kg,叶最大,根(10—20 cm)最小;C∶N为31.76—70.98,枝最大,叶最小;C∶P为369.93—1099.20,根(10—20 cm)最大,叶最小;N∶P为9.21—23.81,根(0—10 cm)最大,枝最小。整个生长季节中侧柏各器官C含量最稳定,变异系数均小于7%;P含量变异性最大,变异系数均超过15%,N含量变异性介于两者之间;各器官中C∶N和N∶P较C∶P更为稳定,C、N与P具有较好的耦合协同性,C∶P和N∶P的变化主要取决于P的变化。2)器官对C、N、P含量及其化学计量关系均存在显著影响,生长季节对N和P含量存在显著影响,两者交互作用只对P含量存在显著影响,器官对侧柏C、N、P含量及其化学计量变异的贡献大于生长季节。3)侧柏各器官间C、N、P含量及其化学计量比相关性多数未达到显著性水平,仅有叶与枝中的P及C∶P显著相关,说明侧柏器官分化过程中各器官对元素的吸收利用具有特异性。侧柏叶片N∶P14,说明生长季节里幼龄侧柏人工林更多受到N限制。     

Spatial changes and influencing factors of fine root carbon,nitrogen and phosphorus stoichiometry of plants in China

为了研究中国陆地植物细根碳(C)、氮(N)、磷(P)的空间变化模式,揭示细根在"温度-植物生理假说"及"生长速率假说"等方面的规律,该文收集已发表的有关中国陆地植物细根研究的文献,从中提取细根C、N、P元素含量及其相关数据,分析了细根C、N、P含量及其比例与经纬度之间的关系。结果表明:细根N、P元素含量均随纬度增加而增加,P含量随经度增加而降低,N:P随经度增加而增加。细根N、P含量与年平均气温、年降水量均呈负相关关系,与土壤养分呈正相关关系。在土壤养分、温度、降水量3个非生物因素中,土壤养分对细根N、P含量的影响最大。该文中细根和粗根的C:P、N:P差异变化不完全支持"生长速率假说"。根系和叶片一样,N、P含量与纬度呈正相关关系,支持"温度-植物生理假说",反映了植物对自然环境的适应策略。