Herbivore resistance of invasive <Emphasis Type="Italic">Fallopia</Emphasis> species and their hybrids

Hybridization has been proposed as a mechanism by which exotic plants can increase their invasiveness. By generating novel recombinants, hybridization may result in phenotypes that are better adapted to the new environment than their parental species. We experimentally assessed the resistance of five exotic Fallopia taxa, F. japonica var. japonica, F. sachalinensis and F. baldschuanica, the two hybrids F. × bohemica and F. × conollyana, and the common European plants Rumex obtusifolius and Taraxacum officinale to four native European herbivores, the slug Arion lusitanicus, the moth Noctua pronuba, the grasshopper Metrioptera roeselii and the beetle Gastrophysa viridula. Leaf area consumed and relative growth rate of the herbivores differed significantly between the Fallopia taxa and the native species, as well as among the Fallopia taxa, and was partly influenced by interspecific variation in leaf morphology and physiology. Fallopia japonica, the most abundant Fallopia taxon in Europe, showed the highest level of resistance against all herbivores tested. The level of resistance of the hybrids compared to that of their parental species varied depending on hybrid taxon and herbivore species. Genotypes of the hybrid F. × bohemica varied significantly in herbivore resistance, but no evidence was found that hybridization has generated novel recombinants that are inherently better defended against resident herbivores than their parental species, thereby increasing the hybrid’s invasion success. In general, exotic Fallopia taxa showed higher levels of herbivore resistance than the two native plant species, suggesting that both parental and hybrid Fallopia taxa largely escape from herbivory in Europe.     

温带针阔混交林叶片性状随树冠垂直高度的变化规律

自然界中,森林植物叶片的生长随树冠高度呈现明显的垂直分布现象;然而,有关叶片性状随着树冠垂直高度增加的变化规律仍不清楚。为了更好地揭示植物叶片对光环境变化的适应策略以及对资源的利用能力,有必要深入探讨叶片性状与冠层高度的定量关系及其内在调控机制。以中国广泛分布的温带针阔混交林为对象,选取8种主要树种为研究对象(白桦、蒙古栎、水曲柳、大青杨、色木槭、千金榆、核桃楸和红松),通过测定这些物种9个冠层高度的叶片比叶面积(SLA)、叶片干物质含量(LDMC)、叶片氮含量(N)、叶片磷含量(P)、氮磷比(N∶P)和叶绿素含量(Chl)等属性,探讨了针阔混交林叶片性状的差异以及各性状之间的相关关系,进而揭示叶片性状随树冠垂直高度的变化规律。实验结果表明:1)温带针阔混交林内优势树种的部分叶片性状在不同冠层高度之间差异显著。2)随着树冠垂直高度的增加,SLA、LDMC、N、P、N∶P和Chl呈现不同的变化趋势。其中,阔叶树种SLA随着树冠垂直高度的增加而减小;所有树种的LDMC随着树冠垂直高度的增加而增加;不同树种的N、P、N∶P和Chl随着树冠垂直高度的变化规律存在差异。3)对于温带针阔混交林冠层中,SLA与N、P、N∶P均存在显著的正相关关系,高SLA伴随着高的N、P、N∶P,表明植物通过SLA与N、P等性状的协同来提高叶片的光合作用(或对光热资源的利用效率)。本研究通过定量分析探讨温带针阔混交林叶片性状随冠层高度的变化规律,一定程度地揭示了树木对光、热和水资源竞争的适应机制,以及植物叶片的资源利用和分配策略,不仅拓展了传统性状研究的范畴,其相关研究结论也有助于树木生长模型的构建和优化。     

Effects of nutrient addition on leaf chemistry,morphology, and photosynthetic capacity of three bog shrubs

Plants in nutrient-poor environments typically have low foliar nitrogen (N) concentrations, long-lived tissues with leaf traits designed to use nutrients efficiently, and low rates of photosynthesis. We postulated that increasing N availability due to atmospheric deposition would increase photosynthetic capacity, foliar N, and specific leaf area (SLA) of bog shrubs. We measured photosynthesis, foliar chemistry and leaf morphology in three ericaceous shrubs (Vaccinium myrtilloides, Ledum groenlandicum and Chamaedaphne calyculata) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada, with a background deposition of 0.8 g N m⁻² a⁻¹. While biomass and chlorophyll concentrations increased in the highest nutrient treatment for C. calyculata, we found no change in the rates of light-saturated photosynthesis (A _max), carboxylation (V _cmax)_, or SLA with nutrient (N with and without PK) addition, with the exception of a weak positive correlation between foliar N and A _max for C. calyculata, and higher V _cmax in L. groenlandicum with low nutrient addition. We found negative correlations between photosynthetic N use efficiency (PNUE) and foliar N, accompanied by a species-specific increase in one or more amino acids, which may be a sign of excess N availability and/or a mechanism to reduce ammonium (NH₄) toxicity. We also observed a decrease in foliar soluble Ca and Mg concentrations, essential minerals for plant growth, but no change in polyamines, indicators of physiological stress under conditions of high N accumulation. These results suggest that plants adapted to low-nutrient environments do not shift their resource allocation to photosynthetic processes, even after reaching N sufficiency, but instead store the excess N in organic compounds for future use. In the long term, bog species may not be able to take advantage of elevated nutrients, resulting in them being replaced by species that are better adapted to a higher nutrient environment.     

Predicting competitive interactions between pioneer plant species by using plant traits

Abstract. A competitive effect hierarchy for 15 Namaqualand pioneer plant species was established by using the mean mass of the phytometer (Dimorphotheca sinuata) when grown in combination with itself and 14 other species. There were no clear groupings of species in the hierarchy. This competitive hierarchy (gradient) indicated which species are strong competitors (resulting in a low phytometer mass) with D. sinuata and which species are weak competitors (resulting in a high phytometer mass). Each plant species has a certain combination of plant traits which determines its life history strategy and competitive ability. Regressions of various plant traits (measured on plants grown singly) against phytometer biomass indicated which traits were significantly correlated. The traits, most being size-related, were: maximum shoot mass, total mass, stem mass, reproductive mass, leaf area, stem allocation, specific leaf area (SLA), vegetative height × diameter, leaf area ratio (LAR); and mean number of days to flower initiation. A forward stepwise multiple regression of the significant traits was used to determine an equation to predict competitive effect.     

Light and VPD gradients drive foliar nitrogen partitioning and photosynthesis in the canopy of European beech and silver fir

While foliar photosynthetic relationships with light, nitrogen, and water availability have been well described, environmental factors driving vertical gradients of foliar traits within forest canopies are still not well understood. We, therefore, examined how light availability and vapour pressure deficit (VPD) co-determine vertical gradients (between 12 and 42 m and in the understorey) of foliar photosynthetic capacity (Amax), 13C fractionation (∆), specific leaf area (SLA), chlorophyll (Chl), and nitrogen (N) concentrations in canopies of Fagus sylvatica and Abies alba growing in a mixed forest in Switzerland in spring and summer 2017. Both species showed lower Chl/N and lower SLA with higher light availability and VPD at the top canopy. Despite these biochemical and morphological acclimations, Amax during summer remained relatively constant and the photosynthetic N-use efficiency (PNUE) decreased with higher light availability for both species, suggesting suboptimal N allocation within the canopy. ∆ of both species were lower at the canopy top compared to the bottom, indicating high water-use efficiency (WUE). VPD gradients strongly co-determined the vertical distribution of Chl, N, and PNUE in F. sylvatica, suggesting stomatal limitation of photosynthesis in the top canopy, whereas these traits were only related to light availability in A. alba. Lower PNUE in F. sylvatica with higher WUE clearly indicated a trade-off in water vs. N use, limiting foliar acclimation to high light and VPD at the top canopy. Species-specific trade-offs in foliar acclimation to environmental canopy gradients may thus be considered for scaling photosynthesis from leaf to canopy to landscape levels.     

An intraspecific application of the leaf‐height‐seed ecology strategy scheme to forest herbs along a latitudinal gradient

We applied the leaf‐height‐seed (LHS) ecology strategy scheme (a combination of three ecologically important traits: specific leaf area (SLA), seed mass and plant height) intraspecifically to two widespread European forest herbs along a latitudinal gradient. The aims of this study were to quantify LHS trait variation, disentangle the environmental factors affecting these traits and compare the within‐species LHS trait relationships with latitude to previously established cross‐species comparisons. We measured LHS traits in 41 Anemone nemorosa and 44 Milium effusum populations along a 1900–2300 km latitudinal gradient from N France to N Sweden. We then applied multilevel models to identify the effects of regional (temperature, latitude) and local (soil fertility and acidity, overstorey canopy cover) environmental factors on LHS traits. Both species displayed a significant 4% increase in plant height with every degree northward shift (almost a two‐fold plant height difference between the southernmost and northernmost populations). Neither seed mass nor SLA showed a significant latitudinal cline. Temperature had a large effect on the three LHS traits of Anemone. Latitude, canopy cover and soil nutrients were related to the SLA and plant height of Milium. None of the investigated variables appeared to be related to the seed mass of Milium. The variation in LHS traits indicates that the ecological strategy determined by the position of each population in this three‐factor triangle is not constant along the latitudinal gradient. The significant increase in plant height suggests greater competitive abilities for both species in the northernmost populations. We also found that the studied environmental factors affected the LHS traits of the two species on various scales: spring‐flowering Anemone was affected more by temperature, whereas early‐summer flowering Milium was affected more by local and other latitude‐related factors. Finally, previously reported cross‐species correlations between LHS traits and latitude were generally unsupported by our within‐species approach.     

井冈山鹿角杜鹃群落灌木层植物叶功能性状对海拔梯度的响应

为揭示鹿角杜鹃(Rhododendron latoucheae)群落灌木层植物叶功能性状及其对环境变化的响应趋势,对分布于井冈山不同海拔梯度鹿角杜鹃群落灌木层植物的叶功能性状进行了研究。结果表明,海拔梯度对灌木植物的叶功能性状有显著影响。随海拔的升高,叶片的干物质含量(LDMC)、厚度(LT)、氮含量(LNC)、磷含量(LPC)呈显著上升趋势,比叶面积(SLA)和N/P呈显著下降趋势,而叶大小(LS)呈先上升后下降的变化趋势;灌木植物叶片的LDMC与SLA、LS呈负相关,与LT、LNC、LPC呈正相关;SLA与LT、LNC呈负相关;LS与LT呈负相关;LNC与LPC呈正相关;N/P与LPC呈负相关;环境因子对灌木植物叶功能性状有重要影响,除受海拔的影响外,LPC、N/P还受坡位的影响,LS、LNC则分别还受到坡向和坡度的影响。因此,井冈山地区鹿角杜鹃群落灌木层植物通过改变叶功能性状来适应海拔和其它环境因子的变化。     

Competitive ability of two Brassica varieties in relation to biomass allocation and morphological plasticity under varying nutrient availability

Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.     

Coordinated changes in photosynthesis,water relations and leaf nutritional traits of canopy trees along a precipitation gradient in lowland tropical forest

We investigated leaf physiological traits of dominant canopy trees in four lowland Panamanian forests with contrasting mean annual precipitation (1,800, 2,300, 3,100 and 3,500 mm). There was near complete turn-over of dominant canopy tree species among sites, resulting in greater dominance of evergreen species with long-lived leaves as precipitation increased. Mean structural and physiological traits changed along this gradient as predicted by cost–benefit theories of leaf life span. Nitrogen content per unit mass (N_mass) and light- and CO₂-saturated photosynthetic rates per unit mass (P_mass) of upper canopy leaves decreased with annual precipitation, and these changes were partially explained by increasing leaf thickness and decreasing specific leaf area (SLA). Comparison of 1,800 mm and 3,100 mm sites, where canopy access was available through the use of construction cranes, revealed an association among extended leaf longevity, greater structural defense, higher midday leaf water potential, and lower P_mass, N_mass, and SLA at wetter sites. Shorter leaf life spans and more enriched foliar ¹⁵N values in drier sites suggest greater resorption and re-metabolism of leaf N in drier forest. Greater dominance of short-lived leaves with relatively high P_mass in drier sites reflects a strategy to maximize photosynthesis when water is available and to minimize water loss and respiration costs during rainless periods. Overall, our study links coordinated change in leaf functional traits that affect productivity and nutrient cycling to seasonality in lowland tropical forests.     

闽楠叶片功能性状及表型可塑性对其与杉木混交的响应

慢生（闽楠）与速生（杉木）树种混交后,植物是如何改变功能性状来适应环境,在资源获取与分配权衡中来实现共存？是人工林精准提质改造过程中的关键问题,研究了闽楠（Phoebe bournei）与杉木（Cunninghamia lanceolate）混交后,其叶厚（LT）、叶面积（LA）、比叶面积（SLA）、碳含量（LC）、氮含量（LN）、磷含量（LP）和氮磷比（N：P）7项性状指标的差异,探讨其各性状间的变异大小及其相关关系。结果表明：（1）与闽楠纯林相比,混交林闽楠叶片叶面积、比叶面积、叶碳含量、叶氮含量和氮磷比分别增加了16.78%、8.50%、3.12%、21.38%和17.61%,而叶厚与叶磷含量减少了8.80%和25.87%,除叶碳含量差异不显著,其他6项功能性状差异性均达到显著（P<0.05）。（2）混交使闽楠叶LC、LN、LP含量与LT、LA、SLA相关性均发生明显的变化,对其叶厚、叶面积、比叶面积及其交互作用对叶片C：N、C：P、N：P产生一定的影响,表明混交闽楠叶功能性状间的相关关系发生了适应性调整;（3）闽楠主要叶片功能性状的表型可塑性指数分布在0.04-0.33之间,叶厚、叶面积、比叶面积和氮磷比的可塑性变化不敏感（PPI<0.20）,叶氮含量、磷含量的可塑性变化较敏感（PPI>0.20）,其大小排序为LP > LN > N：P > LA > SLA > LT > LC。以上结果表明了闽楠杉木混交造林模式对闽楠叶形态性状可塑性变化影响较小,没有受到生长空间和光资源的限制,混交是一种较好的造林模式。但闽楠叶氮、磷含量可塑性变化在混交模式中十分敏感,表明生长过程中可能会受到N、P的限制,在培育过程中应注意N肥和P肥的及时补充。这一研究结果,将为今后速生树种与珍贵树种混交造林模式研究提供理论与数据支撑。     

The effects of clipping and soil moisture on leaf and root morphology and root respiration in two temperate and two tropical grasses

Numerous studies have explored the effect of environmental conditions on a number of plant physiological and structural traits, such as photosynthetic rate, shoot versus root biomass allocation, and leaf and root morphology. In contrast, there have been a few investigations of how those conditions may influence root respiration, even though this flux can represent a major component of carbon (C) pathway in plants. In this study, we examined the response of mass-specific root respiration (μmol CO₂ g⁻¹ s⁻¹), shoot and root biomass, and leaf photosynthesis to clipping and variable soil moisture in two C₃ (Festuca idahoensis Elmer., Poa pratensis L.) and two C₄ (Andropogon greenwayi Napper, and Sporobolus kentrophyllus K. Schum.) grass species. The C₃ and C₄ grasses were collected in Yellowstone National Park, USA and the Serengeti ecosystem, Africa, respectively, where they evolved under temporally variable soil moisture conditions and were exposed to frequent, often intense grazing. We also measured the influence of clipping and soil moisture on specific leaf area (SLA), a trait associated with moisture conservation, and specific root length (SRL), a trait associated with efficiency per unit mass of soil resource uptake. Clipping did not influence any plant trait, with the exception that it reduced the root to shoot ratio (R:S) and increased SRL in P. pratensis. In contrast to the null effect of clipping on specific root respiration, reduced soil moisture lowered specific root respiration in all four species. In addition, species differed in how leaf and root structural traits responded to lower available soil moisture. P. pratensis and A. greenwayi increased SLA, by 23% and 33%, respectively, and did not alter SRL. Conversely, S. kentrophyllus increased SRL by 42% and did not alter SLA. F. idahoensis responded to lower available soil moisture by increasing both SLA and SRL by 38% and 33%, respectively. These responses were species-specific strategies that did not coincide with photosynthetic pathway (C₃/C₄) or growth form. Thus, mass-specific root respiration responded uniformly among these four grass species to clipping (no effect) and increased soil moisture stress (decline), whereas the responses of other traits (i.e., R:S ratio, SLA, SRL) to the treatments, especially moisture availability, were species-specific. Consequently, the effects of either clipping or variation in soil moisture on the C budget of these four different grasses species were driven primarily by the plasticity of R:S ratios and the structural leaf and root traits of individual species, rather than variation in the response of mass-specific root respiration.     

Low genetic variation of invasive Fallopia spp. in their northernmost European distribution range

Knowledge about the reproduction strategies of invasive species is fundamental for effective control. The invasive Fallopia taxa (Japanese knotweed s.l.) reproduce mainly clonally in Europe, and preventing spread of vegetative fragments is the most important control measure. However, high levels of genetic variation within the hybrid F. × bohemica indicate that hybridization and seed dispersal could be important. In Norway in northern Europe, it is assumed that these taxa do not reproduce sexually due to low temperatures in the autumn when the plants are flowering. The main objective of this study was to examine the genetic variation of invasive Fallopia taxa in selected areas in Norway in order to evaluate whether the taxa may reproduce by seeds in their most northerly distribution range in Europe. Fallopia stands from different localities in Norway were analyzed with respect to prevalence of taxa, and genetic variation within and between taxa was studied using amplified fragment length polymorphism (AFLP). Taxonomic identification based on morphology corresponded with identification based on simple sequence repeats (SSR) and DNA ploidy levels (8× F. japonica, 6× F. × bohemica and 4× F. sachalinensis). No genetic variation within F. japonica was detected. All F. × bohemica samples belonged to a single AFLP genotype, but one sample had a different SSR genotype. Two SSR genotypes of F. sachalinensis were also detected. Extremely low genetic variation within the invasive Fallopia taxa indicates that these taxa do not reproduce sexually in the region, suggesting that control efforts can be focused on preventing clonal spread. Climate warming may increase sexual reproduction of invasive Fallopia taxa in northern regions. The hermaphrodite F. × bohemica is a potential pollen source for the male‐sterile parental species. Targeted eradication of the hybrid can therefore reduce the risk of increased sexual reproduction under future warmer climate.     

Taller and larger: shifts in Arctic tundra leaf traits after 16 years of experimental warming

Understanding plant trait responses to elevated temperatures in the Arctic is critical in light of recent and continuing climate change, especially because these traits act as key mechanisms in climate‐vegetation feedbacks. Since 1992, we have artificially warmed three plant communities at Alexandra Fiord, Nunavut, Canada (79°N). In each of the communities, we used open‐top chambers (OTCs) to passively warm vegetation by 1–2 °C. In the summer of 2008, we investigated the intraspecific trait responses of five key species to 16 years of continuous warming. We examined eight traits that quantify different aspects of plant performance: leaf size, specific leaf area (SLA), leaf dry matter content (LDMC), plant height, leaf carbon concentration, leaf nitrogen concentration, leaf carbon isotope discrimination (LCID), and leaf δ¹⁵N. Long‐term artificial warming affected five traits, including at least one trait in every species studied. The evergreen shrub Cassiope tetragona responded most frequently (increased leaf size and plant height/decreased SLA, leaf carbon concentration, and LCID), followed by the deciduous shrub Salix arctica (increased leaf size and plant height/decreased SLA) and the evergreen shrub Dryas integrifolia (increased leaf size and plant height/decreased LCID), the forb Oxyria digyna (increased leaf size and plant height), and the sedge Eriophorum angustifolium spp. triste (decreased leaf carbon concentration). Warming did not affect δ¹⁵N, leaf nitrogen concentration, or LDMC. Overall, growth traits were more sensitive to warming than leaf chemistry traits. Notably, we found that responses to warming were sustained, even after many years of treatment. Our work suggests that tundra plants in the High Arctic will show a multifaceted response to warming, often including taller shoots with larger leaves.     

Stem diameter growth rates in a fire‐prone savanna correlate with photosynthetic rate and branch‐scale biomass allocation,but not specific leaf area

Plant growth rates strongly determine ecosystem productivity and are a central element of plant ecological strategies. For laboratory and glasshouse‐grown seedlings, specific leaf area (SLA; ratio of leaf area to mass) is a key driver of interspecific variation in growth rate (GR). Consequently, SLA is often assumed to drive GR variation in field‐grown adult plants. However, there is an increasing evidence that this is not the general case. This suggests that GR – SLA relationships (and perhaps those for other traits) may vary depending on the age or size of the plants being studied. Here we investigated GR – trait relationships and their size dependence among 17 woody species from an open‐canopy, fire‐prone savanna in northern Australia. We tested the predictions that SLA and stem diameter growth rate would be positively correlated in saplings but unrelated in adults while, in both age classes, faster‐GR species would have higher light‐saturated photosynthetic rate (A_sat), higher leaf nutrient concentrations, higher branch‐scale biomass allocation to leaf versus stem tissues and lower wood density (WD). SLA showed no relationship to stem diameter GR, even in saplings, and the same was true of leaf N and P concentrations, and WD. However, branch‐scale leaf:stem allocation was strongly related to GR in both age groups, as was A_sat. Together, these two traits accounted for up to 80% of interspecific variation in adult GR, and 41% of sapling GR. A_sat is rarely measured in field‐based GR studies, and this is the first report of branch‐scale leaf:stem allocation (analogous to a benefit:cost ratio) in relation to plant growth rate. Our results suggest that we may yet find general trait‐drivers of field growth rates, but SLA will not be one.     

引种期同质园翅荚木主要叶功能性状与种源地环境关系

从比叶面积(SLA)、叶片相对含水量(LRWC)、叶组织密度(LTD)、叶片干物质含量(LDMC)、叶片碳(C)氮(N)磷(P)含量及其化学计量比等方面对在引种期同质园的广西桂林市(GGL)、广西靖西市(GJX)、湖南江华县(HJH)、湖南通道市县(HTD)、广东英德市(GYD)等5翅荚木种源叶片主要功能性状进行差异分析及相关性分析,并研究翅荚木叶功能性状与种源地环境因子的关系。结果显示,(1)不同种源间叶片C、N含量及C/N差异显著,5种源间叶片C含量GYD最高、GGL最低,N含量GJX最高、GYD最低,C/N为GYD最高、GJX最低。(2)比叶面积与叶组织密度呈显著负相关;叶片N含量与C/N和C/P呈显著负相关,与N/P呈显著正相关;C/P与P含量呈显著负相关,与C/N呈显著正相关;C/N与N/P呈显著负相关。(3)翅荚木叶功能性状主要受七月均温、年均温和相对湿度等地理环境因子影响。七月均温与C/P、比叶面积呈正相关,与叶片N含量、叶片干物质含量、叶组织密度呈负相关;年均温与C/N呈正相关,与N/P呈负相关;相对湿度与叶片P含量、叶组织密度呈正相关,与C/P、比叶面积呈负相关。研究结果有助于理解翅荚木对引种区的环境适应特征及其在引种期的生长与生存策略,对探究翅荚木的养分利用策略、揭示其对环境变化的响应机制等具有重要意义,并为相关部门选择适宜的翅荚木引种栽培种源及开展其优良种源的遗传改良等提供理论指导与决策参考。     

Trait‐abundance relation in response to nutrient addition in a Tibetan alpine meadow: The importance of species trade‐off in resource conservation and acquisition

In competition‐dominated communities, traits promoting resource conservation and competitive ability are expected to have an important influence on species relative abundance (SRA). Yet, few studies have tested the trait‐abundance relations in the line of species trade‐off in resource conservation versus acquisition, indicating by multiple traits coordination. We measured SRA and key functional traits involving leaf economic spectrum (SLA, specific leaf area; LDMC, leaf dry matter content; LCC, leaf carbon concentration; LNC, leaf nitrogen concentration; LPC, leaf phosphorus concentration; Hs, mature height) for ten common species in all plots subjected to addition of nitrogen fertilizer (N), phosphorus fertilizer (P), or both of them (NP) in a Tibetan alpine meadow. We test whether SRA is positively related with traits promoting plant resource conservation, while negatively correlated with traits promoting plant growth and resource acquisition. We found that species were primarily differentiated along a trade‐off axis involving traits promoting nutrient acquisition and fast growth (e.g., LPC and SLA) versus traits promoting resource conservation and competition ability (e.g., large LDMC). We further found that SRA was positively correlated with plant height, LDMC, and LCC, but negatively associated with SLA and leaf nutrient concentration irrespective of fertilization. A stronger positive height‐SRA was found in NP‐fertilized plots than in other plots, while negative correlations between SRA and SLA and LPC were found in N or P fertilized plots. The results indicate that species trade‐off in nutrient acquisition and resource conservation was a key driver of SRA in competition‐dominated communities following fertilization, with the linkage between SRA and traits depending on plant competition for specific soil nutrient and/or light availability. The results highlight the importance of competitive exclusion in plant community assembly following fertilization and suggest that abundant species in local communities become dominated at expense of growth while infrequent species hold an advantage in fast growth and dispersals to neighbor meta‐communities.     

Hydraulic limitation not declining nitrogen availability causes the age‐related photosynthetic decline in loblolly pine (Pinus taeda L.)

Declining net primary production (NPP) with forest age is often attributed to a corresponding decline in gross primary production (GPP). We tested two hypotheses explaining the decline of GPP in ageing stands (14–115 years old) of Pinus taeda L.: (1) increasing N limitation limits photosynthetic capacity and thus decreases GPP with increasing age; and (2) hydraulic limitations increasingly induce stomatal closure, reducing GPP with increasing age. We tested these hypotheses using measurements of foliar nitrogen, photosynthesis, sap‐flow and dendroclimatological techniques. Hypothesis (1) was not supported; foliar N retranslocation did not increase and declines were not observed in foliar N, leaf area per tree or photosynthetic capacity. Hypothesis (2) was supported; declines were observed in light‐saturated photosynthesis, leaf‐ and canopy‐level stomatal conductance, concentration of CO₂ inside leaf air‐spaces (corroborated by an increase in wood δ¹³C) and specific leaf area (SLA), while stomatal limitation and the ratio of sapwood area (SA) to leaf area increased. The sensitivity of radial growth to inter‐annual variation in temperature and drought decreased with age, suggesting that tree water use becomes increasingly conservative with age. We conclude that hydraulic limitation increasingly limits the photosynthetic rates of ageing loblolly pine trees, possibly explaining the observed reduction of NPP.     

基于地理种源的刨花楠苗木比叶面积与叶片化学计量学关系

探讨植物比叶面积(SLA)与叶片碳(C)、氮(N)、磷(P)化学计量学关系,能够反映植物为获取最大光合生产所采取的内部调控机制,共同体现植物的适应策略。利用生长于同一土壤与气候环境中培育的刨花楠(Machilus pauhoi)1年生苗木,对其SLA与叶片C、N、P含量进行测定,并对SLA与叶片C、N、P化学计量学特征及其与种源地环境因子的关系进行分析。结果表明:(1)叶片养分含量的变异系数大小排序为CNP;SLA与叶片N、P含量呈显著的正相关,与叶片C∶N及C∶P呈极显著的负相关。(2)SLA与经度、年均温、年降水量呈显著负相关;叶片C、N、P含量也受种源地环境因子影响,其中以海拔最为重要。研究结果有助于理解刨花楠苗木的生存适应对策,对探究刨花楠对养分的资源利用效率等具有重要意义。     

Leaf area index (LAI) map of a protected area within the caldera of Vico Lake (Italy)

ABSTRACT

Structural traits of the vegetation types and plantations occurring in a protected area within the caldera of Vico Lake (Italy) were analysed. There were significant correlations among structural traits, at leaf and stand level. Leaf area index (LAI) and specific leaf area (SLA) were the most significantly correlated traits. LAI rose according to stand plant density, tree size and SLA; the highest LAI value monitored in the Fagus sylvatica L. forest was justified by the largest tree size (28.9±2.8 m height and 53±15 cm diameter) and the highest SLA (212±23 cm² g^-1). The main traits determining the variations in leaf structure among species were analysed by Principal Component Analysis (PCA). The LAI values were used to realise a map allowing us to delimit high LAI values (4.1–5.0), corresponding to the F. sylvatica forest and to the F. sylvatica forest with the sporadic presence of Quercus cerris L. and Castanea sativa Miller, mean LAI values (classes 3.1–4.0) corresponding to Corylus avellana L. plantations and to the Phragmites australis (Cav.) Trin. vegetation type, low LAI values (classes 2.6–3.0) corresponding to Q. cerris forests and C. sativa plantations.     

Important foliar traits depend on species-grouping: analysis of a remnant temperate forest at the Keerqin Sandy Lands, China

Foliar traits are often interpreted to reflect strategies for coping with water and nutrient supply limitations. In this study, we measured several important leaf traits for 147 species sampled from a remnant, temperate deciduous broad-leaved forest in Keerqin Sandy Lands, Northeast China to test whether these traits are ‘invariant’ or dependent on water supply limitations. Our data show that average specific leaf area (SLA), nitrogen (N) and phosphorus (P) concentrations, leaf C/N, C/P and N/P were 273 cm²?g^?1, 18.1 mg?g^?1, 1.60 mg?g^?1, 28.2, 343 and 12.4, respectively. However, most of these traits were significantly different (P?<?0.05) for different species groupings based on growth forms, phylogenetic history, photosynthetic pathways, or habitats. SLA was positively correlated with leaf P concentration across the broad spectrum of 118 species and most species functional groupings. However, SLA was not correlated with N concentration across all species or within each species functional group. SLA and N and P concentrations in dry habitats were lower than those in wet habitats, whereas leaf C/N, C/P, and N/P had the opposite trend both across all species and within major species functional groupings (herb, monocots and C3 species). Our data indicate that SLA vs. leaf N and SLA vs. P relationships may be regulated differentially for different species functional groupings and that water limitation may have a greater influence than nutrient limitation for plant growth.