川西北不同沙化程度草地植物功能性状及其驱动因子

以川西北不同沙化程度草地典型群落为研究对象,分析了不同沙化程度草地(未沙化草地、轻度沙化草地、中度沙化草地、重度沙化草地)植物功能性状之间的关系及其与地形和土壤因子的相关性,并对不同沙化程度草地植物功能性状进行了比较。结果发现:(1)从未沙化草地到重度沙化草地变化过程中,植物群落呈现出"湿生-中生-旱生"的演替格局,植物群落高度、盖度和物种丰富度随着沙化程度加剧而逐渐降低。(2)叶厚度(LT)、比叶面积(SLA)、叶组织密度(LD)、比根长(SRL)、根组织密度(RD)、叶氮含量(LN)、叶磷含量(LP)、根氮含量(RN)、根磷含量(RP)随着草地沙化程度的增加而降低。(3)未沙化地草本植物的植物功能性状最大,对资源的利用效率很高,其中SLA极差值最大(250.53),LT极差值最小(9.56),RD、SLA、RN、RP和LD具有较高的变异性,LT具有较低的变异系数,其保守性最高。(4)RN与所有的叶性状均有不同程度的相关性;SLA与LD呈极显著负相关关系,与RN呈显著正相关关系;SRL与LN呈极显著负相关关系,与RN呈显著负相关关系;LN与RN呈显著正相关关系。(5)逐步回归分析表明,功能性状与土壤因子间具有一定明显的相关性,可以通过土壤因子的定量分析来确定地上植物功能性状的变化趋势及可变范围。(6)灰色关联度分析发现,SLA、SRL、RD、LN、RP受海拔的影响较大,LT、LD、RN受坡向的影响最大,坡位对LP影响最大。研究表明,地形因子中海拔对植物功能性状影响较大,土壤因子中pH值对植物功能性状影响较大。     

放牧对草原植物功能性状及其权衡关系的调控

放牧是草原生态系统利用与管理的主要方式; 而过度放牧导致的草原退化和生产力衰减问题已成为当前生产及理论上的一个棘手难题。近年来, 植物功能性状及其权衡等新理论与方法的引入, 为解析放牧对草原的影响机制提供了新工具, 成为草原生态学的一个新兴领域, 但目前尚缺乏系统的回顾总结。该文综述了近年来国内外关于草原植物功能性状对放牧的响应及其权衡关系的研究进展, 综合分析了植物性状权衡变化的主要特征、成因与机制, 针对学界关于放牧下植物矮化型变机制的“避牧适应假说”与“生长受阻假说”的争论, 提出了下一步需重点关注的科学问题。     

Extensive Management Promotes Plant and Microbial Nitrogen Retention in Temperate Grassland

Leaching losses of nitrogen (N) from soil and atmospheric N deposition have led to widespread changes in plant community and microbial community composition, but our knowledge of the factors that determine ecosystem N retention is limited. A common feature of extensively managed, species-rich grasslands is that they have fungal-dominated microbial communities, which might reduce soil N losses and increase ecosystem N retention, which is pivotal for pollution mitigation and sustainable food production. However, the mechanisms that underpin improved N retention in extensively managed, species-rich grasslands are unclear. We combined a landscape-scale field study and glasshouse experiment to test how grassland management affects plant and soil N retention. Specifically, we hypothesised that extensively managed, species-rich grasslands of high conservation value would have lower N loss and greater N retention than intensively managed, species-poor grasslands, and that this would be due to a greater immobilisation of N by a more fungal-dominated microbial community. In the field study, we found that extensively managed, species-rich grasslands had lower N leaching losses. Soil inorganic N availability decreased with increasing abundance of fungi relative to bacteria, although the best predictor of soil N leaching was the C/N ratio of aboveground plant biomass. In the associated glasshouse experiment we found that retention of added ¹⁵N was greater in extensively than in intensively managed grasslands, which was attributed to a combination of greater root uptake and microbial immobilisation of ¹⁵N in the former, and that microbial immobilisation increased with increasing biomass and abundance of fungi. These findings show that grassland management affects mechanisms of N retention in soil through changes in root and microbial uptake of N. Moreover, they support the notion that microbial communities might be the key to improved N retention through tightening linkages between plants and microbes and reducing N availability.     

Plant Functional Traits Show Non-Linear Response to Grazing

The trait-based approach aims to detect functional patterns in vegetation beyond specific sites or taxa. In most cases, plant traits are assumed to be linearly related to environmental gradients such as grazing intensity. To generalize results beyond specific sites, it is important to know to which extent environment-trait relationships are non-linear. Non-linearity can be a source of inconsistency among different studies according to length and studied portion of a gradient. In this study, we test if and to what extent traits relate non-linearly to a grazing gradient using data from a grassland-matorral interface in the Mediterranean rangeland of “La Crau” (SE France). Because quantification of grazing by itinerant sheep flocks is difficult, we use a marker plant, Phillyrea angustifolia, and several independent pasture indicators to estimate grazing intensity. First, we related traits to grazing using a multivariate three-table ordination method (RLQ), which assumes linear reactions of traits. To evaluate the importance of non-linearity, we applied generalized additive models (GAMs) to our data. This revealed that a third of traits studied here showed non-linear relationships to grazing. These non-linear responses cover a large spectrum including seed mass, life form, phenology dispersal- and leaf traits. The high part of non-linear relations compromises a general assumption of linear trait-environment relationships. Future works should therefore more often consider non-linear relationships using methods with no constraints on shape of response, e.g., GAM in the analysis of functional trait studies. In this way, non-linear relationships can reveal new aspects of species and community response to global change and deepen our understanding of trait-environment relations.     

Functional Characterization of 14 Pht1 Family Genes in Yeast and Their Expressions in Response to Nutrient Starvation in Soybean

Background

Phosphorus (P) is essential for plant growth and development. Phosphate (Pi) transporter genes in the Pht1 family play important roles in Pi uptake and translocation in plants. Although Pht1 family genes have been well studied in model plants, little is known about their functions in soybean, an important legume crop worldwide.

Principal Findings

We identified and isolated a complete set of 14 Pi transporter genes (GmPT1-14) in the soybean genome and categorized them into two subfamilies based on phylogenetic analysis. Then, an experiment to elucidate Pi transport activity of the GmPTs was carried out using a yeast mutant defective in high-affinity Pi transport. Results showed that 12 of the 14 GmPTs were able to complement Pi uptake of the yeast mutant with Km values ranging from 25.7 to 116.3 µM, demonstrating that most of the GmPTs are high-affinity Pi transporters. Further results from qRT-PCR showed that the expressions of the 14 GmPTs differed not only in response to P availability in different tissues, but also to other nutrient stresses, including N, K and Fe deficiency, suggesting that besides functioning in Pi uptake and translocation, GmPTs might be involved in synergistic regulation of mineral nutrient homeostasis in soybean.

Conclusions

The comprehensive analysis of Pi transporter function in yeast and expression responses to nutrition starvation of Pht1 family genes in soybean revealed their involvement in other nutrient homeostasis besides P, which could help to better understand the regulation network among ion homeostasis in plants.     

围封与放牧对青藏高原草地生物量与功能群结构的影响

以青藏高原高寒草甸、高寒草原、温性荒漠草原的退化草地为基础,比较了5年围封样地与放牧样地的生物量和群落结构。结果表明:(1)围封后3类草地地上总生物量较放牧样地分别显著增加了48.1%、10.8%、34.5%;地下生物量对围封的响应与地上总生物量一致,且围封后高寒草原0~10cm土层根系生物量比例较放牧地显著下降。(2)围封显著降低了高寒草甸的根冠比,高寒草原和温性荒漠草原无显著变化。(3)与放牧地相比,围封显著增加了高寒草甸和高寒草原禾本科植物的生物量比例,高寒草甸杂类草显著降低,温性荒漠草原功能群生物量比例无显著差异。     

羊草草原植物-土壤之间主要营养元素动态的研究

羊草草原土壤中N、P、K含量的季节变化规律是生长季初期较高,6—8月生长旺季较低,生长季末再度升高。营养元素在植物体内的分配是地下部分大于地上部分。地下部分N的贮量为地上部分的3.6倍,K为2.9倍,P为2.8倍。地上部分3种元素含量的季节变化曲线呈单峰型,从生长初期开始上升,最大值出现在8月,生长末期逐渐下降。地下部分的季节变化规律,大体上在整个生长季内呈上升趋势,随着根系的生长,营养元素的积累量不断增加。对植物—土壤之间营养元素动态分析结果表明,随着时间的推移,N、P、K在各状态中的比例趋于恒定。在稳定状态下,3种元素在土壤中的比例逐渐减少,与初始量相比N、P、K的含量分别减少21.23%、5.14%和2.99%。在其它状态中,3种元素的含量均有提高,特别在枯枝落叶和死根中增加的幅度较大。     

Effects of Erosion from Mounds of Different Termite Genera on Distinct Functional Grassland Types in an African Savannah

A key aspect of savannah vegetation heterogeneity is mosaics formed by two functional grassland types, bunch grasslands, and grazing lawns. We investigated the role of termites, important ecosystem engineers, in creating high-nutrient patches in the form of grazing lawns. Some of the ways termites can contribute to grazing lawn development is through erosion of soil from aboveground mounds to the surrounding soil surface. This may alter the nutrient status of the surrounding soils. We hypothesize that the importance of this erosion varies with termite genera, depending on feeding strategy and mound type. To test this, we simulated erosion by applying mound soil from three termite genera (Macrotermes, Odontotermes, and Trinervitermes) in both a field experiment and a greenhouse experiment. In the greenhouse experiment, we found soils with the highest macro nutrient levels (formed by Trinervitermes) promoted the quality and biomass of both a lawn (Digitaria longiflora) and a bunch (Sporobolus pyramidalis) grass species. In the field we found that soils with the highest micro nutrient levels (formed by Macrotermes) showed the largest increase in cover of grazing lawn species. By linking the different nutrient availability of the mounds to the development of different grassland states, we conclude that the presence of termite mounds influences grassland mosaics, but that the type of mound plays a crucial role in determining the nature of the effects.     

植物蛋白磷酸酶及其在植物抗逆中的作用

随着多种蛋白磷酸酶在植物中的发现,可逆磷酸化作用在植物各种生理活动中的研究有许多重要的进展。本文概述了蛋白磷酸酶的类型与特点,并着重介绍近年来植物中多种磷酸酶的活性、基因、蛋白等各个水平上的鉴定工作。讨论了几类主要蛋白磷酸酶参与植物抵抗逆境胁迫的有关研究成果。     

ATP-dependent Proteases Differ Substantially in Their Ability to Unfold Globular Proteins

ATP-dependent proteases control the concentrations of hundreds of regulatory proteins and remove damaged or misfolded proteins from cells. They select their substrates primarily by recognizing sequence motifs or covalent modifications. Once a substrate is bound to the protease, it has to be unfolded and translocated into the proteolytic chamber to be degraded. Some proteases appear to be promiscuous, degrading substrates with poorly defined targeting signals, which suggests that selectivity may be controlled at additional levels. Here we compare the abilities of representatives from all classes of ATP-dependent proteases to unfold a model substrate protein and find that the unfolding abilities range over more than 2 orders of magnitude. We propose that these differences in unfolding abilities contribute to the fates of substrate proteins and may act as a further layer of selectivity during protein destruction.Energy-dependent proteolysis is responsible for more than 90% of the protein turnover inside the cell (1). This process both removes misfolded and aggregated proteins as part of the response of the cell to stress and controls the concentrations of regulatory proteins (2, 3). In prokaryotes and eukaryotic organelles, energy-dependent proteases fall into five classes as follows: ClpAP, ClpXP, Lon, HslUV (also referred to as ClpYQ), and HflB (also referred to as FtsH). In Archaea, analogous functions are performed by the archaebacterial proteasome, consisting of the proteasome-activating nucleotidase (PAN),³ working with the 20 S proteasome (4); in the cytoplasm and nucleus of eukaryotes, these same functions are performed by the 26 S proteasome (5). These different proteases show little sequence conservation outside the ATP-binding domains, but they share their overall architecture. They all form oligomeric, barrel-shaped complexes composed of one or more rings with the active sites of proteolysis sequestered inside a central degradation chamber (6). Access channels to these sites are narrow, and proteins have to be unfolded to gain entry (6). Regulatory particles belonging to the AAA family of molecular chaperones assemble on either end of the proteolytic chamber and recognize substrates destined for degradation. After recognition, the regulatory particles translocate the substrate through a central channel to the proteolytic chamber and in doing so unravel folded domains within the substrate. Translocation and unfolding are driven by ATP hydrolysis by the regulatory particles, with conformational changes in the protease transmitted to the substrate by conserved residues in the loops lining the channel (7–10).Protein degradation by AAA proteases is tightly regulated. Most proteins are targeted to ClpAP, ClpXP, HslUV, Lon, HflB, and PAN by sequence motifs in their primary structure (11–17). Sometimes adaptor proteins recognize and bind sequence elements in substrates and deliver them to the protease, and other times the protease recognizes sequence elements directly (18, 19). In contrast, proteins are typically targeted to the 26 S proteasome through the covalent attachment of polyubiquitin chains (20). Thus, substrates appear to be selected for degradation based on the presence of specific recognition elements in the protein substrates.However, other mechanisms may also affect the specificity of degradation by prokaryotic proteases. Individual proteases recognize a wide range of targeting signals (11, 16). (For example, Escherichia coli ClpXP recognizes sequences belonging to five distinct classes of consensus sequences (11), and ClpAP, Lon, and FtsH can bind to unstructured regions in proteins with a wide range of amino acid sequences (21–23).) One illustration of the loose specificity in targeting signals is the ability of a mitochondrial presequence to target proteins to the proteases ClpAP (24) and HslUV in vitro (see below). In addition, substrates are commonly acted upon by several different proteases in E. coli. For instance, proteins containing the 11-residue ssrA peptide at their C termini can be recognized by ClpAP, ClpXP, FtsH, Lon, and the archaebacterial proteasome (4, 25–27). Similarly, some substrates of Lon can be degraded by HslUV in vivo (28).It is not clear how degradation remains selective despite the loose specificity of targeting signals. We propose that the intrinsic protein unfolding ability of AAA proteases and the stabilities of substrates against unfolding play a role in determining the fate of cellular proteins. For example, ClpXP releases hard-to-unfold substrates when it encounters them and degrades destabilized titin variants 20-fold faster than wild type titin (29). The membrane-bound AAA protease FtsH has a weak unfolding ability, which allows this protease to act selectively on damaged and unfolded polypeptides (30). Here we find that the relative unfolding abilities of ATP-dependent proteases vary more than 100-fold and that the unfolding abilities of proteases belonging to the same class but originating from different species appear to be conserved. The unfolding abilities also seem to be intrinsic properties of the proteases themselves rather than other cytosolic factors, such as chaperones. Differences in protease unfolding abilities may contribute to substrate selectivity during protein degradation. For example, expression of a protease with a weak unfolding ability during a stress response could allow the selective elimination of unfolded, misfolded, or otherwise aberrant proteins and spare stable proteins from destruction (30).     

Short-Term Wavelike Dynamics of Bacterial Populations in Response to Nutrient Input from Fresh Plant Residues

The objectives of the research were to investigate short-term dynamics of bacterial populations in soil after a disturbance in the form of fresh organic matter incorporation and to investigate how these dynamics are linked to those of some environmental parameters. To reach these objectives, soil bacterial populations, mineral nitrogen, pH, and redox potential (ROP) were monitored daily for 1 month after incorporation of clover-grass (CG) plant material in microcosm experiments. Colony-forming units (CFUs) and direct microscopic counts of FDA-stained and FTTC-stained bacteria increased immediately after incorporation of the plant material, dropped within 2 days, and fluctuated thereafter. Harmonics analysis demonstrated that there were significant wavelike fluctuations with three or four significant peaks within 1 month after incorporation of clover-grass material. Peaks in CFUs were 1–2 days ahead of those in direct counts. Ammonium (NH₄) concentrations increased from the start of the experiments until nitrification commenced. Nitrate (NO₃) concentrations dropped immediately after plant incorporation, and then rose monotonically until the end of the experiments. There were no wavelike fluctuations in NH₄ and NO₃ concentrations, so that bacterial fluctuations could not be attributed to alternating mineral N shortages and sufficiencies. pH levels rose and declined with NH₄ levels. ROP dropped shortly before NH₄ concentrations rose, and increased before NH₄ concentrations decreased; there were no regular fluctuations in ROP, so that temporary oxygen shortages may not have been responsible for the observed fluctuations in bacterial populations. Thus, for the first time, regular wavelike dynamics were demonstrated for bacterial populations after perturbation by addition of fresh organic matter to soil, and several potential reasons for the death phase of the fluctuations could be excluded from further consideration.     

Plant Production Responses to Precipitation Differ Along an Elevation Gradient and Are Enhanced Under Extremes

Ecosystems - The sensitivity of plant production to precipitation underlies the functioning of ecosystems. Studies that relate long-term mean annual precipitation and production across multiple...     

Assessment of the Respiratory Costs of Adaptation in Plant Species That Differ in Their Responses to Insufficient and Excessive Mineral Nutrition

The effects of insufficient and excessive mineral nutrition on the relative growth rate (RGR); the rate of total dark respiration (R); gross photosynthesis (Pg); and the contents of endogenous IAA, ABA, and cytokinins (CK) were studied in 20–60-day-old seedlings of plant species that differed in their responses to these factors: beet root (Amaranthus retroflexusL.), orchard-grass (Dactylis glomerataL.), and common wheat (Triticum aestivumL.). The changes in the level of mineral nutrition lowered the RGR and Pgvalues and the IAA/ABA and CK/ABA ratios and increased the Rand R/Pgvalues and ABA content, especially in A. retroflexusand T. aestivum. The authors propose a new way to assess the respiratory cost of adaptation to stress based on the relation between the RGR and the R/Pgvalues. The adaptation component of Ris shown to relate to the ABA content.     

植物反转录转座子及其在功能基因组学中的应用

高等植物中的反转录转座子是构成植物基因组的重要成分之一.它分病毒家族和非病毒家族两类,病毒家族包括反转录病毒和类似于反转录病毒的非病毒转座子,病毒家族中的反转录转座子可再细分为Ty3-gypsy类和Ty1-copia类;非病毒家族可细分为LINE类和SINE类.正常情况下大部分反转录转座子不具有活性,某些生物或非生物因素胁迫可激活部分反转录转座子转座.反转录转座子自身编码反转录酶进行转录,以"拷贝-粘贴"的转座模式导致基因组扩增和进化.具有活性的反转录转座子通过插入产生新的突变,可作为一种基因标签技术,应用于功能基因组学研究,并成为研究植物基因功能和表达的重要技术平台.本文综述了近几年来在植物反转录转座子方面的研究进展,主要包括植物反转录转座子的结构、特征、活性及其对基因组的影响和它们在功能基因组学中的应用.     

植物抵御非生物胁迫的内源性保护物质及其作用机制

对几种主要的抵御非生物胁迫危害的内源性保护物质,包括热休克蛋白、LEA蛋白、脯氨酸,甜菜碱,多胺和糖类物质的作用及其机制作了介绍。     

不同降水条件下荒漠草原植物的养分含量及回收对增温和氮素添加的响应

为了探讨荒漠草原植物养分回收特征对长期增温和氮素添加的响应以及自然降水变异对其的调控作用,该研究依托实施12年的模拟增温和氮素添加实验平台,在相对多雨的2016年(超过长期均值52%)和相对少雨的2017年(低于长期均值16%),以常见C_3植物银灰旋花(Convolvulus ammannii)和C_4植物木地肤(Kochia prostrata)为研究对象,测定分析绿叶和枯叶的氮磷含量及回收效率。结果表明:(1)在相对多雨年(2016年),增温使2种植物的绿叶氮、枯叶氮、绿叶磷、枯叶磷含量分别增加了14.32%、25.45%、17.97%和46.47%,氮、磷回收效率分别显著减小了9.41%和16.99%(P0.05);氮素添加使2种植物的绿叶氮、枯叶氮、绿叶磷、枯叶磷含量分别提高了17.32%、25.62%、20.21%和51.41%,而氮、磷回收效率显著降低了9.33%和18.89%(P0.05);增温+氮素添加共同处理显著增加了植物氮磷含量、降低了氮磷回收效率。(2)在相对少雨年(2017年),增温、氮素添加、增温+氮素添加处理对植物叶片氮磷含量、回收效率均无显著影响。(3)叶片氮磷含量在物种间差异极显著(P0.000 1),而氮磷回收效率在物种间无显著差异。(4)回归分析表明,植物叶片氮磷含量随着土壤无机氮、有效磷及含水量的增加而增加,植物氮磷回收效率则随着土壤养分和水分的可利用性的增加而降低。研究认为,荒漠草原植物养分回收对全球变化的响应受自然降水变异的调控。     

Gene Expression Profiling of the Local Cecal Response of Genetic Chicken Lines That Differ in Their Susceptibility to Campylobacter jejuni Colonization

Campylobacter jejuni (C. jejuni) is one of the most common causes of human bacterial enteritis worldwide primarily due to contaminated poultry products. Previously, we found a significant difference in C. jejuni colonization in the ceca between two genetically distinct broiler lines (Line A (resistant) has less colony than line B (susceptible) on day 7 post inoculation). We hypothesize that different mechanisms between these two genetic lines may affect their ability to resist C. jejuni colonization in chickens. The molecular mechanisms of the local host response to C. jejuni colonization in chickens have not been well understood. In the present study, to profile the cecal gene expression in the response to C. jejuni colonization and to compare differences between two lines at the molecular level, RNA of ceca from two genetic lines of chickens (A and B) were applied to a chicken whole genome microarray for a pair-comparison between inoculated (I) and non-inoculated (N) chickens within each line and between lines. Our results demonstrated that metabolism process and insulin receptor signaling pathways are key contributors to the different response to C. jejuni colonization between lines A and B. With C. jejuni inoculation, lymphocyte activation and lymphoid organ development functions are important for line A host defenses, while cell differentiation, communication and signaling pathways are important for line B. Interestingly, circadian rhythm appears play a critical role in host response of the more resistant A line to C. jejuni colonization. A dramatic differential host response was observed between these two lines of chickens. The more susceptible line B chickens responded to C. jejuni inoculation with a dramatic up-regulation in lipid, glucose, and amino acid metabolism, which is undoubtedly for use in the response to the colonization with little or no change in immune host defenses. However, in more resistant line A birds the host defense responses were characterized by an up-regulation lymphocyte activation, probably by regulatory T cells and an increased expression of the NLR recognition receptor NALP1. To our knowledge, this is the first time each of these responses has been observed in the avian response to an intestinal bacterial pathogen.     

Deriving Plant Functional Types for Amazonian forests for use in vegetation dynamics models

Recent advances in our understanding of the linkages between plant physiological and morphological traits suggest a new means by which to define Plant Functional Types (Φ) for use in conceptual and mathematical models of vegetation dynamics. In this study we used data from the RAINFOR-network database, aiming to numerically derive Φ for tropical forest trees by jointly analysing an Amazon-wide dataset of (409) species abundance, species functional traits (10) and site edaphic and climatic conditions across 53 plots. We followed a stepwise procedure of numerical Φ definition with increasing complexity, starting from a simple PCA on species functional traits. We subsequently applied a three-table (RLQ) multivariate ordination method in two ways: with and without spatial autocorrelation between plots being taken into account. In all cases the environmental contribution to trait variation had been partialled out. Thus our results link species-specific “inherent” trait values with associated species abundances along environmental gradients. Our final classification of Amazonian tree species based on foliar dry leaf mass per area (M_A), leaf concentrations of C, N, P, Ca, K, Mg, carbon isotopic discrimination (Δ), branch xylem density (ρ_X) and maximum tree height (H_max) yielded four discrete Φ. These Φ were found to represent distinct life-history strategies and can be aligned with previous empirical definitions of tropical tree guilds. In particular, two ecological dimensions are identified: (1) a leaf deployment dimension which co-varies with soil fertility and (2) a stem deployment dimension which co-varies with soil texture. By analysing diameter growth rates of the same trees used to define the four Φ we found each Φ to have a different overall growth pattern. Furthermore, from a Basin-wide forest survey, differences in the relative abundance of the four Φ were related to stand level basal area growth and/or turnover rate variations. These new derived Φ should enhance our ability to better understand and model the dynamics of the Amazon forest, with the general procedure for plant functional trait definition described here potentially applicable to many other ecosystems.