羊草的地上-地下功能性状对氮磷施肥梯度的响应及关联

羊草(Leymus chinensis)是我国北方典型草原群落的主要建群种和优势种, 由于长期的过度放牧, 羊草草原生态系统的结构和功能严重退化。养分添加作为恢复草地生态系统的一种管理措施, 其应用目前还处于实验性研究阶段。关于羊草的地上-地下功能性状对养分添加, 尤其是P添加的响应研究较少, 相关机制尚不十分清楚。为此, 该文以羊草为研究对象, 通过温室栽培进行N (50, 100, 250 mg N·kg^-1)和P (5, 10, 25 mg P·kg^-1)各3个水平的养分添加实验, 研究羊草的地上-地下功能性状对N、P添加的响应及适应机制。主要研究结果表明: 1)羊草的地上生物量和总生物量主要受N添加的影响, N添加显著提高了羊草的地上生物量, 而地下生物量主要受P添加的影响, 尤其在中N和高N水平, P添加显著降低了羊草的地下生物量。羊草的根冠比受N、P添加的共同影响, 随着N、P添加梯度加大, 根冠比显著降低, N、P添加促进了羊草生物量向地上部分的分配和N、P向叶片的分配。2)在低N和高N水平, 羊草对P添加的响应与适应机制不同。低N水平, 羊草主要通过增加光合速率和比根长(SRL), 提高光合能力和根系对N的获取能力促进地上部分的生长, 而根系对P的吸收有利于地下部分的生长; 在高N水平, P添加对羊草的个体生长无明显促进作用, 甚至地下生物量明显受到P素抑制, 羊草主要通过保持较高的比叶面积(SLA)和SRL, 提高对光资源的截获能力和根系对N的获取和吸收能力, 维持地上部分的生长。3)相对于地上性状, P添加对羊草的地下性状影响更大, 羊草的SLA与SRL呈较弱的正相关关系, 表明叶片与根系在资源获取和利用方面具有相对独立性。     

Relationships between soil nutrients and plant functional traits in different degradation stages of Leymus chinensis steppe in Nei Mongol,China

Aims Understanding ecological implications of plant functional traits is helpful in exploring community assembly under different environments of nature and human disturbances, and then to reveal the maintenance mechanism of the ecosystem services. By analyzing vegetation and soil data derived from field observations in Leymus chinensis steppe of Xilin River Basin in Nei Mongol, we aimed to explore the responses of plant functional traits to changing soil nutrients at different degradation stages. Methods We observed 69 plots for both plant community structure and soil attributes using quadrat and soil-drilling methods. Five plant functional traits, namely the specific leaf area (SLA), leaf dry matter content (LDMC), leaf carbon to nitrogen ratio (C:N), leaf lignin content (LLC), and maximum height (MH), were measured for each plot. We also tested soil attributes, such as total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), and organic carbon (OC). The sixty-nine communities were classified into four groups (undegraded L. chinensis + forbs, slightly degraded L. chinensis + Stipa sp., moderately degraded L. chinensis + Cleistogenes squarrosa, and heavily degraded L. chinensis + Artemisia frigida) using TWINSPAN software. The relationships between plant functional traits and soil nutrient variables were analyzed for the four community groups using the Pearson’s correlation test with SPSS 21.0 software. Important findings (1) The soil nutrients decreased with the grassland degradation process and there were significant differences in TN and TP between the undegraded L. chinensis + forbs and heavily degraded L. chinensis + A. frigida communities; (2) plant functional traits also showed strong differences between the degradation stages. MH and C:N decreased with degradation. A significant difference was observed in MH between the undegraded L. chinensis + forbs and slightly degraded L. chinensis + Stipa sp. communities. The difference in C:N was also significant between the undegraded L. chinensis + forbs and heavily degraded L. chinensis + A. frigida communities; (3) the effects of soil nutrients on plant functional traits changed with grassland degradation. AN was negatively correlated with MH, LLC, and C:N in the slightly degraded L. chinensis + Stipa sp. community. In the moderately degraded L. chinensis + C. squarrosa community, those three traits mentioned above showed significantly positive correlations with TP; (4) while analyzing the degraded grassland, different relationships between plant functional traits were found. In the slightly degraded L. chinensis + Stipa sp. community, LLC was positively correlated with all other traits. Moreover, positive correlations also occurred between C:N and MH, C:N and LDMC, and C:N and LLC. In the heavily degraded L. chinensis + A. frigida community, all traits demonstrated the most significantly positive correlations.     

水分和养分添加对羊草功能性状和地上生物量的影响

研究水分和养分添加对植物功能性状的影响, 对于揭示植物对环境变化的响应和适应规律至关重要。该文采用盆栽试验的方法, 进行不同水平水分处理(增水50%, 减水50%, 以498 mm降水量作为对照)和养分添加(无养分添加, 单施氮肥, 单施磷肥, 氮磷共施), 研究羊草(Leymus chinensis)的10种功能性状和地上生物量对水分和养分添加的响应。得出以下结论: (1)双因素方差分析结果表明, 水分主效应对羊草株高、分蘖数、茎生物量、叶生物量、叶面积、叶质量、净光合速率、蒸腾速率、水分利用效率存在显著影响; 养分主效应对羊草分蘖数、茎生物量、净光合速率、蒸腾速率、水分利用效率存在显著影响; 水分和养分的交互作用对羊草分蘖数、茎生物量、蒸腾速率、水分利用效率存在显著影响。(2)各功能性状对降水量的响应在不同养分添加水平是不同的, 分蘖数和叶面积在单施氮肥和氮磷共施条件下随降水量增加而增加, 而在无养分添加和单施磷肥条件下无显著变化; 茎生物量在无养分添加、单施氮肥和单施磷肥条件下随降水量增加而增加, 而在氮磷共施条件下无增加趋势; 比叶面积在单施氮肥条件下增水处理显著低于对照组, 而在其他养分添加条件下无明显变化。(3)短期氮磷处理显著影响羊草叶片光合生理性状, 而对叶形态性状影响不显著。(4)羊草地上生物量随降水量的增加呈现上升趋势, 并且在单施氮肥条件下, 增水处理使地上生物量达到最高, 为522.55 g·m ^-2。总之, 羊草的功能性状对降水量增加表现出明显的响应, 响应格局在不同养分条件下不同, 反映了其对水肥环境变化的适应。     

Phenotypic plasticity and genetic differentiation of quantitative traits in genotypes of Leymus chinensis

Aims Adaptation mechanisms of plants to environment can be classified as genetic differentiation and phenotypic plasticity (environmental modification). The strategy and mechanism of plant adaptation is a hot topic in the field of evolutionary ecology. Leymus chinensis is one of constructive species in the Nei Mongol grassland. Particularly, Leymus chinensis is a rhizomatous and clonally reproductive grass, a genotype that can play an important role in the community. In this study, we aimed to (1) investigate the phenotypic plasticity of L. chinensis under different conditions, and (2) test the genetic differentiation and reaction norms (the relationship between the environment and the phenotype of an individual or a group of individuals) under four environmental conditions among different genotypes of L. chinensis. Methods Ten genotypes of L. chinensis were randomly selected. Under the control condition, we studied the effects of genotype, defoliation, drought and their interactions on 11 quantitative traits of growth (8 traits including photochemical efficiency of photosystem II, maximum net photosynthetic rate, transpiration rate, specific leaf area, relative growth rate, the number of tillers increased, aboveground and underground biomass growth), defense (total phenol concentration of leaf) and tolerance (non-structural carbohydrate content of root, root/shoot ratio) of L. chinensis. We studied the phenotypic plasticity, genetic differentiation and reaction norms mainly through tested the effect of environment and genotype on these traits. Important findings First, all 11 traits showed obvious phenotypic plasticity (i.e., significant effect of drought, defoliation and their interactions). The expression of 10 genotypes of L. chinensis was divergent under different environmental conditions. Interactions of genotype and environment significantly affected the maximum net photosynthetic rate, transpiration rate, specific leaf area, relative growth rate, total phenolic concentration of leaf, and total non-structural carbohydrate content of root. This indicated that the phenotypic plasticity of these five traits exhibited genetic differentiation. Second, the increase of number of tillers, belowground biomass and non-structural carbohydrate content of root did not show genetic differentiation under the same condition. The other eight traits showed significantly genetic differentiation, and the heritabilities (H²) of six traits related to growth were higher than 0.5. The leaf total phenol concentration and root/shoot ratio showed genetically differentiation only under the drought and defoliation condition, with the heritabilities being 0.145 and 0.201, respectively. These results explained why L. chinensis widely distributed in the Nei Mongol grassland, and provided genetic and environmental basis for related application and species conservation in this grassland ecosystem.     

Plastic responses of stem and leaf functional traits in Leymus chinensis to long-term grazing in a meadow steppe

植物对不同功能性状进行权衡, 通过表型可塑性达到对异质生境的适应是植物的一种生态对策。羊草(Leymus chinensis)是欧亚温带草原东缘的主要优势植物, 研究其对放牧的表型反应对揭示草原生态系统的放牧响应机制具有代表意义。该文以内蒙古呼伦贝尔草甸草原为例, 通过设置不同放牧压力与围封的长期试验, 研究了羊草茎叶功能性状对放牧的可塑性响应模式。结果表明: 1)与长期围封相比, 长期放牧导致羊草茎叶性状显著小型化, 其中, 株高和个体地上生物量分别降低76.82%和89.88%, 但3年短期围封对茎性状影响不显著, 说明羊草表型矮小化现象具有一定的保守性; 2)通过排序构建羊草性状可塑性变化谱, 发现茎质量、总质量、茎高、株高、叶面积等为对放牧响应的敏感性状, 而叶片数、茎粗、叶宽等较为稳定, 为惰性性状; 3)放牧干扰下, 羊草性状可塑性程度与其变异性之间符合y = y₀ + ae^bx拟合关系, 随着植物性状的响应强度增大, 其变异性增强; 4)偏最小二乘法分析发现茎长、株高、叶面积、叶长等性状的投影重要性指标大于1, 对地上生物量变化的解释率为68.6%, 是导致长期放牧下羊草个体生物量降低的主要因子。研究认为, 矮化型变是羊草的避牧适应对策, 在亚稳态下, 通过不同性状的权衡, 充分利用环境资源完成其生活史。     

Effects of nitrogen addition on photosynthetic characteristics of Leymus chinensis in the temperate grassland of Nei Mongol,China

Aims The increased atmospheric nitrogen (N) deposition due to human activity and climate change greatly causes grassland ecosystems shifting from being naturally N-limited to N-eutrophic or N-saturated, and further affecting the growth of grass species. The aims of this study are: 1) to evaluate the effects of different N addition levels on morphology and photosynthetic characteristics of Leymus chinensis; 2) to determine the critical N level to facilitate L. chinensis growth.
Methods We conducted a different N addition levels experiment in dominant species in the temperate steppe of Nei Mongol. The aboveground biomass, morphological and leaf physiological traits, pigment contents, chlorophyll a fluorescence parameters and biochemical parameters of L. chinensis were investigated.
Important findings Our results showed that aboveground biomass first increased and then decreased with the increased N, having the highest values at the 10 g N·m^-2·a^?1 treatment, but the 25 g N·m^-2·a^?1 still significantly increased the aboveground biomass relative to 0 g N·m^-2·a^?1. Leymus chinensis accommodate low N situation through allocating less N to carboxylation system and decreasing leaf mass per area (LMA) in order to get more light energy. Moderate N addition captured more light energy through increasing total chlorophyll (Chl) contents and decreasing the ratio of Chl a/b. Moderate N addition increased LMA, carboxylation efficiency, maximum carboxylation rate (V_cmax), maximum electron transport rate (J_max) and decreased J_max/V_cmax, thus allocating more N to carboxylation system to enhance carboxylation capability. Moreover, the photochemical activity of PSII was increased through higher effective quantum yield of PSII photochemistry, electron transport rate and photochemical quenching coefficient. Excessive N addition had negative effects on physiological variables of L. chinensis due to lower carboxylation capability and photochemical activity of PSII, further leading to decreased net photosynthetic rate, whereas increased non-photochemical quenching coefficient and carotenoids played the role in the dissipation of excess excitation energy. Overall, moderate N addition facilitated the photosynthetic characteristics of dominant species, but excessive N addition inhibited photosynthetic characteristics. The most appropriate N addition for the growth of L. chinensis was 5-10 g N·m^-2·a^?1 in the temperate steppe of Nei Mongol, China.     

内蒙古羊草草原不同退化阶段土壤养分与植物功能性状的关系

深入认识植物功能性状的生态学含义, 对于阐明不同自然与人为干扰环境下的群落构建途径, 进一步揭示生态系统服务维持机制具有重要的理论意义。该文以内蒙古锡林河流域羊草(Leymus chinensis)草原不同退化演替阶段的群落为研究对象, 分析了土壤养分与植物功能性状的变化特征及两者之间的关系。结果表明: (1)退化导致土壤养分含量逐渐减少, 全氮和全磷在未退化的羊草+杂类草群落与严重退化的羊草+冷蒿(Artemisia frigida)群落之间差异显著; (2)随着退化演替的进程, 群落最大高度和叶片碳氮比减小, 群落最大高度在未退化的羊草+杂类草群落与轻度退化的羊草+针茅(Stipa sp.)群落之间差异显著, 碳氮比在未退化的羊草+杂类草群落与严重退化的羊草+冷蒿群落之间差异显著; (3)不同退化演替阶段的群落, 其土壤养分对植物功能性状的影响有所差异。在羊草+针茅群落, 速效氮与群落最大高度、叶片木质素含量和叶片碳氮比均呈显著负相关关系。而在羊草+糙隐子草(Cleistogenes squarrosa)群落中, 上述3种植物功能性状则表现为均与全磷含量显著正相关; (4)群落植物功能性状之间的关系也因退化阶段不同而有所不同。在轻度退化的羊草+针茅群落中, 叶片木质素含量与其他4个功能性状显著正相关, 叶片碳氮比与群落最大高度、叶干物质含量、木质素含量呈显著正相关关系。在严重退化的羊草+冷蒿群落中, 所有性状均呈极显著正相关关系。表明植物通过功能性状的协调或组合, 以适应贫瘠的土壤环境。上述结果深化了对典型草原退化演替的认识, 对退化草地的恢复与保护具有一定的指导意义。     

氮素和植物生长促进剂对羊草生长及竞争力的影响

选取羊草、斜茎黄芪、克氏针茅3种内蒙古典型草原常见植物,通过不同植物物种组合(单独种植或者羊草与其他两种混合种植)、施加不同剂量的氮素(0、0.1、0.2、0.4、0.8mg·g^-1)和植物生长促进剂——油菜素内酯(0.005 mg·g^-1)的温室盆栽试验,分析氮素和油菜素内酯对羊草生长及其与其他植物竞争力关系的影响.结果表明:添加氮素对羊草、斜茎黄芪的生物量影响显著,对克氏针茅的生物量影响较弱,并且氮素的影响因其伴生植物的不同而改变.氮素添加显著增加了羊草在单独种植和与斜茎黄芪混合种植时的地上生物量,但显著降低了与克氏针茅混合种植时的地下生物量.由于土壤可利用氮增加,羊草的地上与地下分配发生变化,表现为单独种植、与克氏针茅混合种植时,根冠比下降;与斜茎黄芪混合种植时,氮素添加对羊草根冠比的影响则不显著.油菜素内酯对植物生长的显著影响不普遍,仅显著降低了斜茎黄芪单独种植时的地下生物量;在羊草与斜茎黄芪混合种植时,显著增加了羊草地上生物量.油菜素内酯和氮适量联用可有效增加特定物种组合的生物量,从而在退化草地恢复中具有一定的应用前景.     

Plant leaf traits,height and biomass partitioning in typical ephemerals under different levels of snow cover thickness in an alpine meadow

Aims In the cold life zones, snow cover is a comprehensive environmental factor that directly influences soil temperature, soil water content, light and nutrient availability. Plants in these zones develop a series of unique mechanisms involving phenological characteristics, reproductive strategies, physiology and morphology to adapt to environmental changes. This paper is focused on the responses of plant leaf traits, height and biomass partitioning to variations in snow cover thickness, in order to better understand the responses of plant functional traits and specific adaptation strategies under global climate change scenarios. Methods Three transects were established along a gradient of snow cover in an alpine meadow of Mt. Kaka, in the eastern Qinghai-Xizang Plateau. Primula purdomii, Pedicularis kansuensis and Ranunculus tanguticus, which are three widely distributed and dominant ephemerals, were sampled and studied, particularly at their blooming stages. Plant height, specific leaf area (SLA) and biomass partitioning were measured accordingly. Important findings The values of SLA in Pedicularis kansuensis and R. tanguticus were relatively greater under better soil conditions; it was smaller in Primula purdomii with thick snow cover. The relationship between aboveground biomass and belowground biomass in Primula purdomii was allometric at sites with both thick and thin snow cover. No significant relationships were found between aboveground biomass and belowground biomass in Pedicularis kansuensis and R. tanguticus at some individual sites. However, when samples of the three species were pooled, the relationships between aboveground biomass and belowground biomass were allometric at all sites, which did not support isometric scaling hypothesis. In addition, on sites with either thick or thin snow cover, aboveground biomass had greater rate of accumulation than belowground biomass; whereas on sites with medium snow cover, the rate of biomass accumulation was greater for belowground component than aboveground component. Functional traits and biomass variables were better correlated in Primula purdomii and Pedicularis kansuensis than in R. tanguticus.     

Effects of dew on eco-physiological traits and leaf structures of Leymus chinensis and Agropyron cristatum grown under drought stress

Aims To investigate the effects of dew on plants, we conducted the experiment to determine the physiological characteristics and leaf structures of Leymus chinensis and Agropyron cristatum in response to increasing dew under drought stress.Methods Four treatments (no dew, three times dew and five times dew per week under drought stress, and well-watering) were designed to examine leaf relative water content, water potential, net photosynthetic rate, water use efficiency, biomass, and leaf structures of L. chinensis and A. cristatum. Important findings There was a significant increase in the relative water content and water potential by simulated dew increase for two plants species under drought stress (p < 0.05). For A. cristatum, simulated dew increase significantly enhanced the net photosynthetic rate, stomatal conductance, and transpiration rate of plants under drought stress (p < 0.05). On the other hand, there was no significant difference in the stomatal conductance and transpiration rate for L. chinensis among treatments. Simulated dew increase improved the aboveground biomass and root biomass of two species. The ratio of yellow leaves to the total leaves was decreased by simulated dew increase for two species. Dew increase also protected leaf structures against the drought stress, suggesting that the dew increase can slow down the death process of leaves resulted from drought stress. Therefore, the study demonstrated that dew increased the available water for the leaves of L. chinensis and A. cristatum grown in the drought stress and thus had positive effects on the photosynthesis, water physiology and plant development.     

Effects of nitrogen addition on leaf traits of common species in natural Pinus tabuliformis forests in Taiyue Mountain,Shanxi Province,China

Aims Our objectives were to explore the effects of simulated nitrogen deposition on leaf traits and ecological stoichiometry characteristics of common species in natural Pinus tabuliformis forests.
Methods We conducted the experiment of nitrogen (N) addition from 2009 to 2013 in the natural Pinus tabuliformis forests in Taiyue Mountain, Shanxi, China. The levels of N addition were 0 (control), 50 (low-N), 100 (medium-N) and 150 (high-N) kg·hm^-2·a^-1, respectively. Eleven common plant species in 12 20 m × 20 m plots were selected, including Pinus tabuliformis, Quercus mongolica, Acer ginnala, Corylus mandshurica, Cornus bretschneideri, Spiraea salicifolia, Lonicera maackii, Carex callitrichos, Diarrhena mandshurica, Anemone tomentosa, and Polygonatum odoratum. Nine leaf traits were measured, including leaf thickness (LT), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), and other four.
Important findings We found that: 1) LT and SLA of Polygonatum odoratum significantly differed among four levels of N addition. Leaf area (LA) and LDMC of several species, such as Spiraea salicifolia, had significant difference among the N addition concentration. LNC of all species, chlorophyll content (CC) and LPC of most species increased significantly with the addition of N. Leaf N:P of 9 species varied significantly, and leaves with different types and ages showed different responses to N addition. 2) Leaf traits were significantly correlated with each other. For instance, SLA was significantly positively correlated with LNC and LPC. In contrast LT was negatively connected with LNC and LPC. In addition, the degree of correlation changed with the level of N addition. 3) The pattern of species distribution in leaf trait space was consistent with the prediction from the theory of Leaf Economic Spectrum (LES). N addition drove species moving along axis 1 in the trait space, and propelled them towards different directions along axis 2, which indicated that these species tended to take the “fast investment-return” strategy. These results suggested that with the change of environmental conditions, plants changed their survival strategy and adjusted resource allocation to maintain the stability of communities. This is the inherent characteristic of plants, thus the formation of LES did not depend on the environment change.     

Responses of plant community biomass to nitrogen and phosphorus additions in natural and restored grasslands around Qinghai Lake Basin

Aims Plant biomass reflects the primary productivity of community vegetation, and is the main resource of carbon input in the terrestrial ecosystem. It is usually limited by nitrogen (N) and phosphorus (P) availability in the soil. Alpine grassland around Qinghai Lake Basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. In this experiment, two grassland types were chosen, natural alpine grassland (NG) and its adjacent restored grassland (RG), to determine the responses of plant community biomass to N and P additions with different land-use. Methods NH₄NO₃ and Ca(H₂PO₄)₂·H₂O were added in a completely randomized block design, with medium levels of 10 g N·m^-2 and 5 g P·m^-2. Soil NO₃^--N and available P contents, and the plant community biomass were measured in the two grasslands. Two-way ANOVA was used to determine the effects of nutrient additions on all measured indicators, and regression analysis was used to analyze the correlations between plant biomass and soil NO₃^--N and available P contents.Important findings Results showed: (1) N and P additions both increased grass biomass in the NG, and significantly elevated the total aboveground biomass, with the promoting effect of N addition higher than that of P addition; N addition significantly increased both grass and forb biomass in the RG, and markedly promoted the total aboveground biomass, while P addition had no effects on the functional groups and total aboveground biomass (p > 0.05). (2) N and P additions both had no effects on the belowground and total biomass in the NG, whereas N addition significantly increased the total biomass by 34% in the RG, which suggested that the effect of N limitation on the vegetation primary productivity was stronger in the RG at present stage. (3) The aboveground biomass in the NG increased with soil NO₃^--N content (p < 0.05), and the above- and below-ground as well as the total biomass were all positively correlated with soil NO₃^--N content in the RG (p < 0.01). These results indicated that the plant growth in alpine grassland around Qinghai Lake Basin was prone to N limitation, and the effect of P limitation changed with land-use. Soil available N might be the key limiting factor for vegetation restoration and reconstruction in the RG. The “Grain for Green” project (the land-use policy) and atmospheric N deposition are benefiting both plant growth and C accumulation in the alpine grassland ecosystem around Qinghai Lake Basin.     

草甸草原羊草茎叶功能性状对长期过度放牧的可塑性响应

植物对不同功能性状进行权衡, 通过表型可塑性达到对异质生境的适应是植物的一种生态对策。羊草(Leymus chinensis)是欧亚温带草原东缘的主要优势植物, 研究其对放牧的表型反应对揭示草原生态系统的放牧响应机制具有代表意义。该文以内蒙古呼伦贝尔草甸草原为例, 通过设置不同放牧压力与围封的长期试验, 研究了羊草茎叶功能性状对放牧的可塑性响应模式。结果表明: 1)与长期围封相比, 长期放牧导致羊草茎叶性状显著小型化, 其中, 株高和个体地上生物量分别降低76.82%和89.88%, 但3年短期围封对茎性状影响不显著, 说明羊草表型矮小化现象具有一定的保守性; 2)通过排序构建羊草性状可塑性变化谱, 发现茎质量、总质量、茎高、株高、叶面积等为对放牧响应的敏感性状, 而叶片数、茎粗、叶宽等较为稳定, 为惰性性状; 3)放牧干扰下, 羊草性状可塑性程度与其变异性之间符合y = y₀ + ae^bx拟合关系, 随着植物性状的响应强度增大, 其变异性增强; 4)偏最小二乘法分析发现茎长、株高、叶面积、叶长等性状的投影重要性指标大于1, 对地上生物量变化的解释率为68.6%, 是导致长期放牧下羊草个体生物量降低的主要因子。研究认为, 矮化型变是羊草的避牧适应对策, 在亚稳态下, 通过不同性状的权衡, 充分利用环境资源完成其生活史。     

Carbon,nitrogen and phosphorus stoichiometry of Myrica nana in Yunnan,China

Aims Carbon (C), nitrogen (N) and phosphorus (P) play important roles in plant growth and physiological functions. We aimed at exploring the intrinsic relationships of C, N and P in Myrica nana—a common shrub in Yunnan Province—as well as their relationships with pant biomass and soil nutrients.
Methods We measured the concentration of C, N and P of M. nana from 29 sites for their magnitudes and correlations with soil nutrients.
Important findings 1) The arithmetic mean value of C, N and P concentration in the roots, stems and leaves of M. nana was 45.94%, 0.54%, 0.03%, and 46.32%, 0.58%, 0.03%, and 49.05%, 1.70%, 0.06%, respectively. C, N and P concentrations in the leaves were significantly higher than those in the roots and the stems. The C:N:P in roots, stems and leaves was 1531:18:1, 1544:19:1, and 818:10:1, respectively. 2) The C concentration and N:P in leaves of M. nana decreased with the increase of biomass of M. nana; the leaf C concentration was significantly correlated with biomass (p < 0.01), while the correlation between N:P and biomass was not significant (p > 0.05). The leaf N increased with the increase of plant biomass, the P was significantly correlated with biomass (p < 0.05), but the correlation between N concentration and biomass was not significant (p > 0.05). N:P in leaves was 34.2, suggesting that plant growth was limited by P. 3) C, N and P concentration in the roots were significantly correlated with soil P (p < 0.05), with N, P concentrations correlated with soil P positively (p < 0.01) and C negatively (p < 0.05). C concentration in the stems was significantly and negatively correlated with soil C, N, with significant correlation with C, N, and P concentration (p < 0.01). P concentration in the stems was significantly and positively correlated with soil P concentration (p < 0.01), while leaf P significantly and positively correlated with soil C, N and P (p < 0.01); leaf C concentration was significantly and negatively correlated with soil P (p < 0.01).     

氮磷添加及林分密度对大叶相思林土壤化学性质的影响

大气氮(N)沉降随着人类的活动而日趋严重, 加上中国热带亚热带红壤普遍缺磷(P), 许多森林生态系统由于广泛使用磷肥而产生P富集, 直接影响了森林土壤化学特性。林分密度改变林地的光照、温度、湿度和凋落物持水量, 从而影响土壤特性。为了解外源性N和P添加与林分密度对大叶相思(Acacia auriculiformis)林地土壤化学性质的影响, 为大叶相思人工林的种植密度和土壤养分管理提供科学依据, 该研究于2013到2015年, 以4种不同密度(1 667、2 500、4 444和10 000 trees·hm ^-2)的10年生大叶相思人工林为研究对象, 分别进行添加N、P和N+P处理, 在试验结束时采集0-10 cm土壤, 对其pH、有机质含量、N含量、P含量和钾(K)含量进行了测定分析。结果表明: 施N和N+P均显著降低了土壤的pH和速效K含量, 显著提高了林地土壤的碱解N含量。施N还显著提高了林分土壤的全N含量, 施P显著提高了土壤pH, 降低了林分土壤的全N含量。施P和N+P显著提高了土壤有机质、全P和有效P含量。随着林分密度的增加, 各处理的土壤有机质、全N、碱解N、全P、有效P和速效K含量显著提高。N、P添加处理和密度处理对大叶相思林的土壤pH、有机质和N、P、K含量有显著的交互作用。总体来看, N添加、P添加、林分密度及其交互作用对大叶相思的土壤化学性质有显著影响。     

Foliar nitrogen and phosphorus stoichiometry of alien invasive plants and co-occurring natives in Xishuangbanna

Aims How alien invasive plants and co-occurring native plants utilize nutrients is one of major issues in invasion ecology. Foliar nitrogen (N) and phosphorus (P) contents and stoichiometry can elucidate the uptake ability and limitation status of nutrients in plants, which provides basic knowledge for understanding the invading ability and co-occurrence or disappearance of plants.
Methods Based on typical alien invasive plants (Chromolaena odorata, Ageratina adenophora) and native plants in southwestern China, this study focused on strategies of N and P utilization among invasive plants and native plants under different invasion conditions. The species compositions, aboveground biomass, leaf N and P contents and leaf N:P were investigated for plants in plots with no invasion and with different invasion extents (estimated by the plot-based percentage of invaders’ biomass in total community) at Mt. Kongming in Xishuangbanna region, Yunnan Province, China.
Important findings The species number decreased significantly with the invasion extent of both C. odorata and A. adenophora, although the aboveground biomass was greatly enhanced. Leaf N and P contents did not differ between the two studied invaders, but they showed significantly higher N and P levels than both co-occurring and only native species (p < 0.05). Besides, leaf N and P contents of invaders increased with the invasion extent, and leaf N of native plants also showed an increasing trend with the invasion extent. When the influence of invasion was checked for the same species, leaf P contents decreased, whereas leaf N and N:P increased for most native plants under invasion. Based on the absolute foliar N and P contents, N:P values, we inferred that native plants were still limited by N, although N availability might be enhanced by invasion. Both invasive plants had leaf N:P values lower than 10, suggesting a higher P uptake relative to N uptake. All above results highlighted a higher N and P uptake of typical alien invasive plants in southwestern China.     

不同雪被厚度下典型高山草地早春植物叶片性状、株高及生物量分配的研究

在高寒生命带, 雪被作为重要的综合环境因子, 影响着植物的生理生态特征、种群动态及群落演替等过程, 进而作用于生态系统的功能与服务。通过在青藏高原东缘高寒草甸设置厚雪、中雪和浅雪3个地段, 选取早春开花的常见种紫罗兰报春(Primula purdomii)、甘肃马先蒿(Pedicularis kansuensis)、高原毛茛(Ranunculus tanguticus), 研究了三种植物株高、叶片性状和生物量分配随雪被厚度的变化规律, 以及三者之间的关系。结果表明: 甘肃马先蒿和高原毛茛在生境状况较好的地段比叶面积相对较高, 紫罗兰报春由于具有根状茎和肉质根, 在厚雪地段比叶面积相对较小; 关于单个物种的地上-地下生物量的关系, 紫罗兰报春在厚雪和浅雪地段为完全一致的异速生长关系, 而甘肃马先蒿和高原毛茛在个别地段并无显著相关关系。总体而言, 三种植物整体样本的地上-地下生物量在不同雪被地段均为异速生长关系, 不支持等速生长假说, 并且地上生物量能够很好地解释地下生物量的变异; 功能性状和生物量指标间的相关性, 在紫罗兰报春和高原毛茛表现较好, 而在甘肃马先蒿表现较弱。植物对环境变化的适应具有一定的规律, 同时也表现出物种特异性。今后的研究中, 应注重构建植物适应环境变化的功能性状谱, 以更好地理解全球变化背景下植物功能性状的响应及其适应策略。     

Different responses of biomass allocation and leaf traits of Dodonaea viscosa to concentrations of nitrogen and phosphorus

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

环青海湖地区天然草地和退耕恢复草地植物群落生物量对氮、磷添加的响应

植物群落生物量反映了植被的初级生产能力, 是陆地生态系统碳(C)输入的最主要来源, 往往受到自然界中氮(N)、磷(P)元素供应的限制。该试验以青藏高原环青海湖地区的高寒草原为研究对象, 探讨了天然草地和退耕恢复草地植被群落生物量对N (10 g·m^-2)、P (5 g·m^-2)养分添加的响应。N、P添加显著增加了天然草地禾草的生物量, 进而促使地上总生物量显著提高。退耕恢复草地禾草和杂类草的生物量对N添加均有一致的正响应, 从而促使地上总生物量显著增加174%, 群落地上和地下总生物量显著增加34%; 而P添加对恢复草地生物量各项参数均无显著影响。回归分析显示: 天然草地植物群落地上生物量随土壤中NO₃^--N含量的增加而增加(p < 0.05), 退耕恢复草地植被地上、地下和总生物量均与土壤NO₃^--N含量显著正相关(p < 0.01), 说明环湖地区高寒草原植物生长主要受N供应的限制, P的限制作用随土地利用方式的转变和群落演替阶段的不同而变化; 相比天然草地, 恢复草地在现阶段植被初级生产力受N的限制作用更强烈, 土壤中可利用N含量是限制其植被自然恢复和重建的关键因子。     

毛乌素沙地油蒿叶建成成本及相关叶性状沿降水梯度的变化

干旱区植物在如何提高水分利用效率与降低叶建成成本之间可能存在一种权衡。我们假设: 与湿润区植物相比, 干旱区植物能通过调节叶功能性状之间的关系(如通过提高单位面积叶氮含量(N_area)), 实现在相同的叶建成成本下具有更高的水分利用效率。为了验证这一假设, 该研究以毛乌素沙地的广布物种油蒿(Artemisia ordosica)为研究对象, 分析了油蒿叶建成成本沿降水梯度的变化规律及其与比叶面积(SLA)、单位质量叶氮含量(N_mass)、N_area和叶碳稳定同位素比率(δ ¹³C)的关系。结果表明: 油蒿单位质量叶建成成本(CC_m)在不同降水条件下差异不显著, 而单位面积叶建成成本(CC_a)在不同降水条件下虽有显著差异, 但并未随降水减少而明显增加。油蒿CC_m与SLA无显著相关性, 与叶δ ¹³C值呈显著正相关关系。油蒿叶建成成本与N_area呈显著正相关关系, 但这种关系格局在低降水量(264 mm)区与高降水量(310-370 mm)区之间存在策略位移现象——即在相同叶建成成本下, 低降水量区植物比高降水量区植物具有更高的N_area。以上结果表明, 尽管高水分利用效率与高叶建成成本相关, 但与高降水量区植物相比, 低降水量区植物具有较高的N_area并没有导致其叶建成成本增加。