Trade-off between leaf size and vein density of Achnatherum splendens in Zhangye wetland

Aims Trade-offs between leaf size and vein density are the basis of the theory of leaf economics spectrum, and are to understand the relationship between the physical build and physiological metabolism of plant leaves under different degrees of competition for resources. Our objective was to study the changes in the relationship between leaf size and vein density (leaf dry biomass and leaf area) in Achnatherum splendens populations with four plant bundle densities located in the flood plain wetland of Zhangye. Methods The study site was located at floodplain wetlands of Zhangye, Gansu Province, China. Survey and sampling were carried out in the communities that A. splendens dominated. According to the plant bundle density, the A. splendens communities were divided into four density gradients with “bundle” for the sampling units, high density (I, > 12 bundle·m^-2), medium density (II, 8-12 bundle·m^-2), medium density (III, 4-8 bundle·m^-2) and Low density (IV, <4 bundle·m^-2). According to the density of each combination, we chose seven (5 m × 5 m) A. splendens samples, resulting in a total of 28 samples (4 × 7). The soil physical and chemical properties of four density gradients were investigated and six samples of A. splendens were used to measure the leaf area, leaf dry biomass and vein density in laboratory, and biomass of different organs was measured after being dried at 85 °C in an oven. 28 plots were categorized into three groups: high, medium and low density, and the standardized major axis (SMA) estimation method was used to examine the allometric relationships between leaf area, leaf dry biomass and vein density. Important findings The results showed that with the population density changed from high, medium, to low, the soil moisture decreased, and soil electric conductivityincreased. The leaf area, leaf biomass and height of A. splendens decreased, and the vein density, specific leaf area and photosynthetically active radiation (PAR) increased gradually. In addition, leaf net photosynthetic rate (P_n), transpiration rate (T_r) and twig number firstly increased then decreased. There was a highly significantly negative correlation (p < 0.01) between the leaf size and vein density on the high- and low-level densities (I, IV), whereas less significant (p < 0.05) on the level of medium density (II, III). The SMA slope of regression equation in the scaling relationships between leaf size and vein density was significantly smaller than -1 (p < 0.05).     

Trade-off relationship between vein density and vein diameter of Achnatherum splendens in response to habitat changes in Zhangye wetland

Aims The coevolution between vein traits has influences on water use strategies of plant and the formation of leaf economic spectrum, and therefore is important for understanding the trade-off between carbon input in leaf vein construction and the functional feedback from leaf veins. Our aim is to study the allometric relationship between vein density and vein diameter of Achnatherum splendens populations at three natural microhabitats (subcanopy, transitional and open areas) in Zhangye wetland. Methods According to the shade condition of the arbor canopy and the distance to arbor, the A. splendens community were divided into three microenvironments: subcanopy, transitional and open areas. We sampled 10 (4 m × 4 m) A. splendens plots from each microenvironment and investigate the biological characteristics of the plots and leaf traits of the plants within the plots. Then the soil physical and chemical properties, and community photosynthetically active radiation (PAR) were investigated at three gradients. Six individual of A. splendens were selected in each plot and the leaf length, leaf width, vein density and vein diameter of two or three healthy and complete leaves from four directions of each individual were measured in laboratory. The SMA estimation method and correlation analysis were then used to examine the allometric relationship between vein density and vein diameter. Important findings Along the gradient from subcanopy, transitional zone to open areas, soil moisture displayed a pattern of initial decrease of plant community, and soil electric conductivity displayed increase changing trends. Photosynthetically active radiation (PAR), vapor pressure deficit (VPD), vein density (1.28-1.59 mm·mm^-2), leaf width and water use efficiency (WUE) increase gradually, while the leaf length, vein diameter (0.21-0.16 mm) of A. splendens decrease. The average value of plasticity indexes of leaf characteristics was 0.19. Leaf net photosynthetic rate (P_n), transpiration rate (T_r) and bundle density increase first and them decrease. The vein density and vein diameter of A. splendens were negatively correlated with each other in subcanopy environment (p < 0.01), transitional and open areas (p < 0.05). The SMA (0.54-1.50) slope of regression equation in the scaling relationships between vein density and vein diameter decrease gradually from subcanopy to open areas.     

张掖湿地芨芨草叶大小和叶脉密度的权衡关系

叶大小-叶脉密度的权衡关系是植物叶经济谱理论的基础, 对理解资源竞争条件下植物叶片的物理构建与生理代谢的关系具有重要的意义。该文采用标准化主轴估计(standardized major axis estimation, SMA)的方法, 按芨芨草(Achnatherum splendens)株丛密度设置I (>12丛·m^-2)、II (8-12丛·m^-2)、III (4-8丛·m^-2)和IV (<4丛·m^-2) 4个密度梯度, 以叶面积和叶干质量分别表示叶大小, 对张掖洪泛平原湿地不同密度条件下芨芨草种群的叶大小和叶脉密度的关系进行研究。结果表明: 随着芨芨草株丛密度的降低, 湿地群落的土壤含水量逐渐减小、土壤电导率逐渐增加, 芨芨草的净光合速率(P_n)、蒸腾速率(T_r)和分枝数呈先增大后减小的趋势, 叶面积、叶干质量、比叶面积和株高呈逐渐减小趋势、光合有效辐射(PAR)和叶脉密度呈逐渐增加趋势; 芨芨草叶大小和叶脉密度在高密度(I)和低密度(IV)样地均呈极显著负相关关系(p < 0.01), 中密度(II、III)样地二者呈显著负相关关系(p < 0.05); 叶大小和叶脉密度回归方程的SMA斜率在不同密度样地均显著小于-1 (p < 0.05), 即芨芨草叶大小和叶脉密度呈“此消彼长”的权衡关系。在高密度湿地群落芨芨草倾向于大叶片低叶脉密度的叶片构建模式, 在低密度湿地群落选择小叶片高叶脉密度的异速生长模式, 体现了密度制约下湿地植物的生物量分配格局和资源利用对策。     

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.     

天童山阔叶木本植物叶片大小与叶脉密度及单位叶脉长度细胞壁干质量的关系

叶片大小是植物生态策略中的一个关键性状, 而叶脉是叶内主要的支撑和输导结构, 对叶片的生长发育具有重要的影响。该研究以天童山38种阔叶木本植物为研究对象, 以叶片面积、干质量和周长表征叶片大小, 采用标准化主轴估计(SMA)方法和系统发育独立比较(PIC)分析主脉密度、细脉密度和总叶脉密度, 以及各级叶脉单位长度的细胞壁干质量与叶片大小之间的关系, 拟从叶片内部结构和资源分配策略的角度探明叶片大小与叶脉结构之间的变化关系及生态学意义。研究结果显示: (1)叶片大小与主脉密度极显著负相关, 细脉密度以及总叶脉密度与叶片大小关系不显著, 表明叶片越小, 主脉密度越高, 而细脉密度与叶片大小无关; (2)单位主脉长度的细胞壁干质量与叶片大小极显著正相关, 单位细脉和总叶脉长度的细胞壁干质量与叶片大小的相关性均不显著, 表明随着叶片的增大, 单位主脉长度的细胞壁干质量显著增加, 而细脉的细胞壁干质量与叶片大小无关; (3)主脉密度与单位主脉长度的细胞壁干质量之间是斜率显著大于-1的负异速生长关系, 表明主脉密度随单位主脉长度的细胞壁干质量增加而显著下降, 两者之间存在权衡关系, 而单位细脉长度的细胞壁干质量与细脉密度关系不显著。上述结果表明, 与大叶片相比, 小叶中通常具有较高的主脉密度, 这不仅是叶片发育过程中叶形变化调控的结果, 也是单位叶脉长度的细胞壁干质量调控的结果, 单位叶脉长度的细胞壁干质量是导致叶片大小与主、细脉密度之间不同变化关系的直接因素。该研究结果为我们理解全球范围内叶片大小变化的生物地理分布模式以及植物对环境的适应策略提供了参考。     

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.     

呼伦贝尔草原辉河湿地不同淹水状态的土壤碳氮磷特征比较

碳(C)、氮(N)、磷(P)生态化学计量比是生态系统过程及其功能的重要特征。为了比较不同淹水状态下草原区河岸湿地土壤生态化学计量特征差异,探讨用土壤生态化学计量特征来表征草原河岸湿地的退化状态,以呼伦贝尔草原辉河河岸湿地为研究对象,分别选择完全退化和未退化河岸湿地,从中选取常年淹水区域(W)、年际干湿交替区域(WD)以及河岸带边缘多年未曾淹没的干燥区域(D)为观测样地,对比研究退化与未退化草原河岸湿地土壤C、N、P化学计量比在不同淹水状态下的表征。结果表明:(1)随着淹水状态的改变,不论是退化河岸湿地还是未退化河岸湿地,不同淹水状态下的土壤C/N、C/P、N/P均差异显著(P0.05);(2)退化河岸湿地的C/N、C/P和N/P的平均值分别为9.05、273.08和28.25,与未退化河岸湿地相比(7.85、95.48、11.41)值显著升高;(3)相关性分析结果显示,土壤总磷与有机碳、全氮显著正相关,与C/N、C/P、N/P负相关,这可能是限制退化河岸湿地土壤养分元素循环的主要因素。研究结果表明:呼伦贝尔草原辉河河岸湿地不同淹水状态的土壤碳、氮、磷特征差异明显(P0.05),尤其是土壤C/P和N/P。与未退化河岸湿地相比,退化河岸湿地的C/N、C/P、N/P均明显高于未退化河岸湿地(P0.05),因此可以将土壤碳、氮、磷化学计量比特征作为草原区河岸湿地退化的评价指标。     

张掖湿地旱柳叶水势与中脉性状的关联性

植物叶水势和中脉性状是反映叶片水力特性的主要参数,二者之间的关联性对理解植物水分供需平衡的生态适应策略具有重要意义。选择张掖市黑河干流边缘的洪泛平原湿地为实验地,以河岸为起点沿平行河岸线的方向依次设置近水区(样地Ⅰ)、中水区(样地Ⅱ)和远水区(样地Ⅲ)3个水分梯度样地,采用标准化主轴估计方法(standardized major axis estimation,SMA),研究了对水分影响下旱柳(Salix matsudana)叶水势与中脉性状之间的关系。结果表明:随着土壤含水量减少,旱柳林的高度、密度和郁闭度均持续降低,旱柳叶片的中脉密度、净光合速率(Pn)、蒸腾速率(Tr)、光合有效辐射(PAR)和叶片温度(Tleaf)逐渐增加,中脉直径、比叶面积及叶水势、叶绿素含量逐渐减少;不同土壤含水量样地旱柳叶水势与中脉性状间的相关性存在差异(P0.05),在样地Ⅰ和样地Ⅲ叶水势与中脉密度呈极显著负相关关系(P0.01),在样地Ⅱ两者之间呈显著负相关关系(P0.05);旱柳叶水势与中脉直径在3个水分梯度样地均呈显著正相关关系(P0.05)。随着湿地土壤含水量减少,旱柳采取降低叶水势、增加中脉密度并减少中脉直径的资源投资策略,反映了该物种在异质生境中具有较强的叶片性状可塑性,从而有利于其适应特殊的湿地生境。     

黑河中游典型土地利用方式下土壤有机碳与活性和非活性组分的关系

以黑河中游7种典型土地利用方式(水田、旱地、中覆盖度草地、盐碱地、裸土地、戈壁和沙地)为对象,分析土壤有机碳含量及其组分的关系.结果表明:在0 ～100 cm土壤中,随土层深度增加,土壤总有机碳(TOC)、活性有机碳(AOC)和非活性有机碳(NOC)含量逐渐降低.中覆盖度草地、盐碱地、裸土地、戈壁、沙地、水田和旱地中的TOC、AOC、NOC含量不同,土地利用方式的改变将引起土壤有机碳的增减,水田耕作是提高绿洲土壤有机碳的有效途径.当土地利用方式变化后,NOC对TOC含量的贡献大于AOC.同一种土地利用类型中,随TOC含量的增加,AOC、NOC含量也呈增加趋势,且NOC的增幅高于AOC.AOC、NOC变化趋势线的交叉点对应的TOC含量可作为土壤中TOC易积累或易损失的分界点,AOC、NOC的饱和容量可通过其变化趋势线来确定.