Leaf gas films,underwater photosynthesis and plant species distributions in a flood gradient

Traits for survival during flooding of terrestrial plants include stimulation or inhibition of shoot elongation, aerenchyma formation and efficient gas exchange. Leaf gas films form on superhydrophobic cuticles during submergence and enhance underwater gas exchange. The main hypothesis tested was that the presence of leaf gas films influences the distribution of plant species along a natural flood gradient. We conducted laboratory experiments and field observations on species distributed along a natural flood gradient. We measured presence or absence of leaf gas films and specific leaf area of 95 species. We also measured, gas film retention time during submergence and underwater net photosynthesis and dark respiration of 25 target species. The presence of a leaf gas film was inversely correlated to flood frequency and duration and reached a maximum value of 80% of the species in the rarely flooded locations. This relationship was primarily driven by grasses that all, independently of their field location along the flood gradient, possess gas films when submerged. Although the present study and earlier experiments have shown that leaf gas films enhance gas exchange of submerged plants, the ability of species to form leaf gas films did not show the hypothesized relationship with species composition along the flood gradient.     

Altitudinal Change in LAI and Stand Leaf Biomass in Tropical Montane Forests: a Transect Study in Ecuador and a Pan-Tropical Meta-Analysis

Abstract Leaf area index (LAI) is a key parameter controlling plant productivity and biogeochemical fluxes between vegetation and the atmosphere. Tropical forests are thought to have comparably high LAIs; however, precise data are scarce and environmental controls of leaf area in tropical forests are not understood. We studied LAI and stand leaf biomass by optical and leaf mass-related approaches in five tropical montane forests along an elevational transect (1,050–3,060 m a.s.l.) in South Ecuador, and conducted a meta-analysis of LAI and leaf biomass data from tropical montane forests around the globe. Study aims were (1) to assess the applicability of indirect and direct approaches of LAI determination in tropical montane forests, (2) to analyze elevation effects on leaf area, leaf mass, SLA, and leaf lifespan, and (3) to assess the possible consequences of leaf area change with elevation for montane forest productivity. Indirect optical methods of LAI determination appeared to be less reliable in the complex canopies than direct leaf mass-related approaches based on litter trapping and a thorough analysis of leaf lifespan. LAI decreased by 40–60% between 1,000 and 3,000 m in the Ecuador transect and also in the pan-tropical data set. This decrease indicates that canopy carbon gain, that is, carbon source strength, decreases with elevation in tropical montane forests. Average SLA decreased from 88 to 61 cm² g⁻¹ whereas leaf lifespan increased from 16 to 25 mo between 1,050 and 3,060 m in the Ecuador transect. In contrast, stand leaf biomass was much less influenced by elevation. We conclude that elevation has a large influence not only on the leaf traits of trees but also on the LAI of tropical montane forests with soil N (nitrogen) supply presumably being the main controlling factor.     

Consequences of phenotypic plasticity vs. interspecific differences in leaf and root traits for acquisition of aboveground and belowground resources

Trade-offs between acquisition capacities for aboveground and belowground resources were investigated by studying the phenotypic plasticity of leaf and root traits in response to different irradiance levels at low nutrient supply. Two congeneric grasses with contrasting light requirements, Dactylis glomerata and D. polygama, were used. The aim was to analyze phenotypic covariation in components of leaf area and root length in response to above- and belowground resource limitation and the consequences of this variation for resource acquisition and plant growth. At intermediate shading (30 and 20% of full sunlight) the plants were able to maintain their total root length, despite a strongly increased total leaf area and a reduced biomass allocation to roots. This was associated with an unaltered or slightly increased nutrient uptake and growth. At 5.5% relative irradiance, growth was severely reduced, especially in the shade-tolerant D. polygama. The results show that constraints on acquisition capacities for aboveground and belowground resources, caused by biomass allocation, may be alleviated by plasticity in other traits such as tissue-mass density and thickness of roots and leaves. The results also suggest different adaptive constraints for phenotypic plasticity and for genetically determined interspecific variation. Phenotypic plasticity tends to maximize resource acquisition and growth rate in the short term, whereas the higher tissue-mass density and the longer leaf life-span of shade-tolerant species indicate reduced loss rates as a more advantageous species-specific adaptation to shade in the long term.     

Three-year field response of young olive trees (Olea europaea L., cv. Arbequina) to soil salinity: Trunk growth and leaf ion accumulation

Irrigated olive is rapidly increasing in arid and semiarid areas, many of which may be negatively affected by soil salinity. We evaluated changes in trunk growth and leaf Cl^–, Na⁺ and K⁺ concentrations in young Arbequina olives (Olea europaea L.) grown in a saline-sodic field over a three-year period. The trunk diameter was measured at the beginning and the end of the 1999 (70 trees), 2000 (59 trees) and 2001 (42 trees) growing periods. Leaves, sampled in August of each year, were analyzed for Cl^–, Na⁺ and K⁺ concentrations. Soil salinity (apparent electrical conductivity, ECa) of each monitored tree was measured 14 times during the 1999–2001 experimental period with an electromagnetic sensor and converted to root zone electrical conductivity of the soil saturation extract (ECe) based on ECa–ECe calibration curves. Salinity tolerance was determined using the Maas and Hoffman threshold–slope response model. Based on salinity thresholds (ECe_thr), the tolerance of olive in terms of trunk growth was high in 1999 (ECe_thr = 6.7 dS m^–1), but declined with age and time of exposure to salts by 30% in 2000 (ECe_thr = 4.7 dS m^–1) and by 55% in 2001 (ECe_thr = 3.0 dS m^–1). Based on the high absolute slopes obtained in all years (values between 16% and 23% dS^–1 m), olive was classified as very sensitive to ECe values above the threshold. Trunk growth thresholds based on leaf ion concentrations varied, depending on years, between 2.6 and 4.0 mg g^–1 (Cl_thr) and between 1.0 and 1.2 mg g^–1 (Na_thr), indicating that Arbequina olive was less sensitive to leaf Cl^– and much more sensitive to leaf Na⁺ than values reported as toxic in greenhouse studies. Leaf K⁺ slightly decreased with increasing salinity, whereas the K⁺/Na⁺ ratio sharply decreased with increasing salinity. We concluded that the initial salinity tolerance of olive was high, but declined sharply with time of exposure to salts and became quite sensitive due primarily to increasing toxic concentrations of Na⁺ in the leaves.     

Salinity and flooding level as determinants of soil solution composition and nutrient content inPanicum hemitomum

A greenhouse experiment was conducted to examine the effects of salinity and flooding level on interstitial solute speciation and solute uptake byPanicum hemitomum grown on intact marsh substrates. The experimental set-up consisted of a factorial arrangement of treatments (5 salinity levels×3 flooding levels) with 4 replications.Salinity treatments with the addition of salt (Instant Ocean^r) successfully increased interstitial pore water conductivities and resulted in significantly different treatment means. Redox potentials and proton activities were significantly higher in the drained treatment, with only minor differences between the two flooded treatments. There was not a significant pH effect due to salinity, although a significant interaction between salinity and flooding level was observed. Analysis of variance suggested that electro-chemical and interstitial solute behaviour could significantly be described by salinity and flooding treatments.GEOCHEM calculations were performed in order to relate leaf concentrations to ion activities in interstitial soil solutions. Leaf contents of Mg, Ca, K, Mn, and Cu were significantly correlated with the activities of corresponding ions in the interstitial pore water. However, most of the variabilitiy in leaf metal content could be accounted for by treatment effects. Regression analysis showed that the ion activities explained less than 25% of the variability in leaf metal content.     

呼伦贝尔草原植物叶片大小与数量的权衡关系及其内在机制

叶片大小与数量的权衡关系是植物生长策略的基础,研究叶片大小与数量权衡关系的内在机制对于深刻理解植物生长策略具有重要意义.本研究以单个叶片干重表示叶大小,以单位茎上的叶片数量表示出叶强度,采用标准主轴回归分析方法研究呼伦贝尔草原植物叶片大小与数量的权衡关系以及内在机制.结果表明:陈旗嵯岗(典型草原)和陈旗八一(草甸草原)...     

Biomass estimation models and allocation patterns of 14 shrub species in Mountain Luya,Shanxi, China

Aims Shrub species have evolved specific strategies to regulate biomass allocation among various organs or between above- and belowground biomass and shrub biomass model is an important approach to estimate biomass allocation among different shrub species. This study was designed to establish the optimal estimation models for each organ (leaf, stem, and root), aboveground and total biomass of 14 common shrub species in Mountain Luya, Shanxi Province, China. Furthermore, we explored biomass allocation characteristics of these shrub species by using the index of leaf biomass fraction (leaf to total biomass), stem biomass fraction (stem to total biomass), root biomass fraction (root to total biomass), and root to shoot mass ratio (R/S) (belowground to aboveground biomass).
Methods We used plant height, basal diameter, canopy diameter and their combination as variables to establish the optimal biomass estimation models for each shrub species. In addition, we used the ratios of leaf, stem, root to total biomass, and belowground to aboveground biomass to explore the difference of biomass allocation patterns of 14 shrub species.
Important findings Most of biomass estimation models could be well expressed by the exponential and linear functions. Biomass for shorter shrub species with more stems could be better estimated by canopy area; biomass for taller shrub species with less stems could be better estimated by the sum of the square of total base diameter multiply stem height; and biomass for the rest shrub species could be better estimated by canopy volume. The averaged value for these shrub species was 0.61, 0.17, 0.48, and 0.35 for R/S, leaf biomass fraction, stem biomass fraction, and root biomass fraction, respectively. Except for leaf biomass fraction, R/S, stem biomass fraction, and root biomass fraction for shrubs with thorn was significantly greater than that for shrubs without thorn.     

Nitrogen addition promotes terrestrial plants to allocate more biomass to aboveground organs: A global meta-analysis

A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m⁻² year⁻¹) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%–32.1%) and 14.7% (11.6%–17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.     

The effect of allometric partitioning on herbivory tolerance in four species in South China

Herbivory tolerance can offset the negative effects of herbivory on plants and plays an important role in both immigration and population establishment. Biomass reallocation is an important potential mechanism of herbivory tolerance. To understand how biomass allocation affects plant herbivory tolerance, it is necessary to distinguish the biomass allocations resulting from environmental gradients or plant growth. There is generally a tight balance between the amounts of biomass invested in different organs, which must be analyzed by means of an allometric model. The allometric exponent is not affected by individual growth and can reflect the changes in biomass allocation patterns of different parts. Therefore, the allometric exponent was chosen to study the relationship between biomass allocation pattern and herbivory tolerance. We selected four species (Wedelia chinensis, Wedelia trilobata, Merremia hederacea, and Mikania micrantha), two of which are invasive species and two of which are accompanying native species, and established three herbivory levels (0%, 25% and 50%) to compare differences in allometry. The biomass allocation in stems was negatively correlated with herbivory tolerance, while that in leaves was positively correlated with herbivory tolerance. Furthermore, the stability of the allometric exponent was related to tolerance, indicating that plants with the ability to maintain their biomass allocation patterns are more tolerant than those without this ability, and the tendency to allocate biomass to leaves rather than to stems or roots helps increase this tolerance. The allometric exponent was used to remove the effects of individual development on allocation pattern, allowing the relationship between biomass allocation and herbivory tolerance to be more accurately explored. This research used an allometric model to fit the nonlinear process of biomass partitioning during the growth and development of plants and provides a new understanding of the relationship between biomass allocation and herbivory tolerance.     

Complex combination of seed dormancy and seedling development determine emergence of Viburnum tinus (Caprifoliaceae)

BACKGROUND AND AIMS: The shrub Viburnum tinus is widely distributed in mattoral vegetation of the Mediterranean basin. The purpose of the present study was to classify the seed dormancy type and examine the requirements for embryo growth, root protrusion and shoot emergence. METHODS: Overwintered fruits were collected in western Spain in April 2001 and prepared in three ways: entire pericarp was removed, exocarp and mesocarp were removed or fruits were left intact. Fruits treated in these three ways were subjected to artificial annual temperature cycles or to constant temperature regimes for 1.5 years. KEY RESULTS: Removal of exocarp and mesocarp was necessary for embryo growth and germination. High temperature favoured dormancy alleviation and embryo growth, intermediate to low temperatures favoured root protrusion, and intermediate temperature shoot emergence. There was substantial germination at constant temperature regimes, indicating an overlap between temperature intervals suitable for the different stages of embryo and seedling development. Functionally, V. tinus has the same root and shoot emergence pattern that is described for other Viburnum species considered to have epicotyl dormancy. However, the requirement for high and low temperatures for radicle protrusion and epicotyl emergence, respectively, was missing in V. tinus; these characters are the foundation for the epicotyl dormancy classification. CONCLUSIONS: It is concluded that V. tinus does not have epicotyl dormancy. Instead, there is a combination of a weak morphophysiological dormancy and a slow germination process, where different temperatures during an annual cycle favour different development stages. The present study suggests that the first complete seedlings would emerge in the field 1.5 years after fruit maturation in October, i.e. seed dispersal during winter, embryo growth during the first summer, root protrusion and establishment during the second autumn and winter, and cotyledon emergence during the second spring.     

基于森林群落和光谱曲线特征分异的福建省森林生物量遥感反演

基于福建省Landsat8 OLI影像,利用混合像元分解模型筛选出"纯净"的植被像元,提取296个调查样地对应植被像元的红光和近红外波段的中心波长(分别CWR和CWNIR)及其对应的反射率(分别R和NIR),构建以(NIR-R)/(CWNIR-CWR)为特征指数的叶生物量回归模型。然后根据针叶林、阔叶林及针阔混交林叶生物量与干、枝、叶所组成的地上生物量的关系方程,结合福建省植被覆盖分类数据,估测了整个福建省针叶林、阔叶林、混交林的地上生物量,并绘制了福建省地上生物量分布图。结果表明:红光和近红外两个波段反射率和其中心波长所组成的斜率与叶生物量相关性显著,与针叶林、阔叶林、混交林叶生物量的精度分别达到70.55%、68.89%、51.75%,采用这种方法对福建省叶生物量和地上总生物量进行估算,并进行精度验证,其中,针叶林、阔叶林、混交林叶物量的模型误差(RMSE)分别达到29.2467 t/hm~2(R~2=66.64%)、14.0258 t/hm~2(R~2=61.13%)、10.1788 t/hm~2(R~2=55.43%),地上总生物量的模型精度分别达到49.8315 t/hm~2(R~2=54.65%)、45.1820 t/hm~2(R~2=49.01%)、41.5131 t/hm~2(R~2=38.79%),这说明,采用红光波段和近红外波段与其中心波长所组成的斜率估测森林叶生物量,进而估算其地上总生物量的方法是可行的。     

Effect of Radiation Quality on Growth and Photosynthesis of Acacia mangium Seedlings

Radiation quality was an important environmental cue to stimulate seed germination in Acacia mangium. The photo-synthetic CO₂ assimilation rate, dark respiration rate, total biomass, and relative growth rate of seedlings grown under monochromatic radiation were significantly lower than those of seedlings grown under full spectrum radiation. Blue and red radiation induced shade-avoidance and shade-tolerant responses of A. mangium seedlings, respectively.     

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。     

江西千烟洲人工针叶林下狗脊蕨群落生物量

 根据野外调查和实验分析研究了江西省千烟洲人工针叶林下狗脊蕨（Woodwardia japonica）群落的生物量、细根生物量、净初级生产力(Net primary productivity, NPP)、 比叶面积（Specific leaf area, SLA） 和叶面积指数（Leaf area index, LAI）等。通过叶片参数和地上生 物量的相关关系建立了狗脊蕨单株地上生物量估算模型,分别 为W1=0.021H^1.545（R²=0.790）和W1=2.518（D²H）^{0 .616}（R²=0.894;H为株高 ,D为地径）。人工针叶林下灌草层地上生物量为367.8 g&;#8226;m^－2（52～932 g&;#8226;m^－2）,凋落物为1 631 g&;#8226;m^－2（672～2 763 g&;#8226;m^－2）,分别占 乔木层地上生物量的4.7%（1.55%～13.2%）和20.7%（7.6%～32.1%）。狗脊蕨群落地上生物量和NPP分别为266.6 g&;#8226;m^－2和88.67 g&;#8226;m^－2&;#8226;a ^-1 ,其中狗脊蕨种群占73.7%;地下生物量为212.6 g&;#8226;m^－2。狗脊蕨的SLA和叶干物质含量（Leaves day mutter content, LDMC）分别为144.0 cm²&;#8226;g^-1和31.99%,二者之间呈显著负相关;最佳叶面积估算模型为S=21.922 6-0.152L²+0.000 9L³（9.0≤L（叶片长度）≤23.5;1.4≤W （ 叶片宽度）≤5.9）。狗脊蕨种群的LAI为1.8。土壤含水量对狗脊蕨生物量有显著影响。群落生物量与土壤有机质和全氮含量正相关     

从叶内生物量分配策略的角度理解叶大小的优化

叶大小的变化是许多因素综合作用的结果, 对叶大小优化机制的研究有助于我们更好地理解植物的适应进化和生活史策略。该研究通过对浙江省清凉峰常绿阔叶混交林中的19个常绿阔叶物种和30个落叶阔叶物种叶水平上的相关性状进行分析, 探讨叶内生物量分配策略对叶大小优化的限制性影响。研究结果显示: 无论叶大小用面积还是质量表示, 常绿物种和落叶物种均呈现出叶内生物量分配到支撑结构的比例随着叶大小的增加而增加的规律, 这主要是由叶柄大小与叶片大小之间显著的异速生长关系导致的。这种异速生长关系在常绿物种和落叶物种中普遍存在。然而, 由于常绿物种对叶柄具有较高的机械以及抵抗冰冻栓塞等不利环境的需求, 在某一给定的叶面积下, 常绿物种比落叶物种具有更高的叶柄生物量投资。这些结果表明: 作为整个植株支撑投资的一个重要组成部分, 叶内支撑投资所占的生物量比例对叶大小的优化具有一定的限制性影响。