Plant functional types – a strategic perspective

Abstract. This paper discusses the use of Plant Functional Types to describe vegetation types – from plant communities to formations – in order to understand the ecological constraints of plants and plant communities on a higher level of abstraction. The terminology around plant functional types, traits and strategies is in need of further clarification and unification. The use of the term plant functional type is recommended. We are in need of a total environmental framework in which, hierarchically or reticulately, plant functional types can be compared and interpreted.     

Identifying plant functional types using floristic data bases: Ecological correlates of plant range size

Abstract. In an effort to identify ‘plant functional types’, the islands floras of Great Britain and Kríti (Crete, Greece) were examined separately for ecological correlates of plant range size. Plant functional types (PFTs) were defined here as categories into which plants could be grouped on the basis of attributes that predict greater or lesser sensitivity to ecological variability. Plant range size indicates commonness of a species and was assumed to be a proxy for ‘ecological flexibility’, i.e. species of larger range sizes can better withstand environmental change and differences than species of smaller range sizes. Using evolutionary comparative methods that account for the effect of taxonomic relatedness, both floras were investigated for the effects on range size of woodiness vs. non-woodiness, trees vs. shrubs, trees vs. herbs and shrubs vs. herbs. The British flora was examined additionally for the effects of wind- vs. non-wind-pollination, self vs. animal pollination and animal vs. non-animal fruit dispersal on range size. Two analyses showed significant effects on range size: for British species, trees had larger ranges than shrubs, and wind- pollinated species had larger ranges than non-wind-pollinated species. It is suggested that the lack of a similar pattern for shrubs and trees in Kríti is because the lower water availability of Kríti imbues shrubs with an ecophysiological advantage not relevant in plants of Great Britain. That trees have larger range sizes than shrubs in Great Britain is ascribed to the greater importance of competition for light when other factors are not at issue. The greater range of wind-pollinated than non-windpollinated species in Great Britain is postulated to be because both mutualists must be capable of invading new areas. This may be termed a ‘cost of mutualism’. In terms of PFTs, the results indicate that ‘life-form’ is too broad a classification category by which to differentiate relative sensitivity to environmental variability in Great Britain, in that there were significant differences in range size of trees and shrubs, but not between either of the two categories and herbs, or between woody and non-woody plants. Although pollination type may predict relative sensitivity to variation in Great Britain, dispersal type will not. Finally, differences between Great Britain and Kríti in relative range size patterns suggests that plant functional types may be specific to a region or set of conditions.     

Ecophysiological and bioclimatic foundations for a global plant functional classification

Question: What plant properties might define plant functional types (PFTs) for the analysis of global vegetation responses to climate change, and what aspects of the physical environment might be expected to predict the distributions of PFTs? Methods: We review principles to explain the distribution of key plant traits as a function of bioclimatic variables. We focus on those whole‐plant and leaf traits that are commonly used to define biomes and PFTs in global maps and models. Results: Raunkiær's plant life forms (underlying most later classifications) describe different adaptive strategies for surviving low temperature or drought, while satisfying requirements for reproduction and growth. Simple conceptual models and published observations are used to quantify the adaptive significance of leaf size for temperature regulation, leaf consistency for maintaining transpiration under drought, and phenology for the optimization of annual carbon balance. A new compilation of experimental data supports the functional definition of tropical, warm‐temperate, temperate and boreal phanerophytes based on mechanisms for withstanding low temperature extremes. Chilling requirements are less well quantified, but are a necessary adjunct to cold tolerance. Functional traits generally confer both advantages and restrictions; the existence of trade‐offs contributes to the diversity of plants along bioclimatic gradients. Conclusions: Quantitative analysis of plant trait distributions against bioclimatic variables is becoming possible; this opens up new opportunities for PFT classification. A PFT classification based on bioclimatic responses will need to be enhanced by information on traits related to competition, successional dynamics and disturbance.     

A hierarchical deductive approach for functional types in disturbed ecosystems

Abstract. We propose a hierarchical approach for plant functional classification in disturbed ecosystems to be used for vegetation modelling and global plant trait comparisons. Our framework is based on the persistence of plants at different levels of organization. We assume that the main parameters to determine persistence in chronically disturbed ecosystems are those related to: I ndividual‐persistence capacity, P ropagule‐persistence capacity (persistence at the population level), C ompetitive capacity (persistence at the community level) and D ispersal capacity (persistence at the landscape level). The IPCD approach is illustrated for fire‐prone and grazed ecosystems from the Mediterranean region and Australia and by assuming a binary classification of the four traits determining persistence which give a total 16 possible functional types. The IPCD framework provides a simple structured and synthetic view from which more elaborated schemes can be developed.     

Responses of plant functional types to an environmental gradient on the Northeast China Transect

The hypothesis that some plant traits such as life form are robust surrogates for plant functional type (PFT) has provoked an ongoing debate. Based on a dataset from the Northeast China Transect (NECT), we attempted to test the hypothesis by comparing an objective PFT identification framework in which large datasets of plant traits were considered with two subjective PFT frameworks in which only a few plant traits were involved. Additionally, we addressed the relations between the relative abundance of PFTs and the environmental gradient represented by actual evapotranspiration (AET) along the NECT. We also discuss the changes in ecosystem functioning associated with the PFT turnover along the environmental gradient. Based on an objective PFT classification, eight PFTs were identified: deciduous trees, shrubs, perennial forbs with lower net photosynthesis, perennial forbs with higher net photosynthesis, perennial bulb-grasses, perennial tiller-grasses, annual C₄ herbs and evergreen trees. Our results indicated that some plant traits, such as life form and photosynthesis pathway, are robust surrogates for PFTs, implying that subjective approaches to PFT classification are useful. Nonetheless, caution should be used during the classification of PFTs. The framework adopted for PFT classification should depend on the specific scientific issues being dealt with. It is therefore meaningless to pursue a general framework for the identification of PFTs even within given plant communities. On the other hand, our quantitative classification of PFTs confirmed recurrent patterns with respect to PFT turnover along an environmental gradient. Furthermore, with the turnover in PFT along the NECT from the west to the east, ecosystem properties such as productivity and carbon storage are predicted to decrease, while photosynthesis is predicted to increase, suggesting that PFT turnover would inevitably lead to changes in ecosystem functioning.     

An improved numerical method for the analysis of a floristic pasture survey

A classical ecologist is usually equally interested in groups of sites and groups of species, so that symmetrical numerical models are appropriate for the elucidation of floristic pattern. It is suggested that an agronomist is primarily interested in the pattern of site- (usually paddock-) groups, and is only interested in those species-groups whose members are present in sufficient abundance to be quickly recognizable, and which serve to discriminate clearly between the site-groups. An‘asymmetric inverse’model is defined for the purpose of extracting species-groups of this type, which can be combined with a site classification into a two-way table. The method is applied to a floristic survey carried out at the end of a grazing experiment, and is shown to produce meaningful and profitable results.     

An improved method for quantitative analysis of total fructans in plant tissues

Current methods for measuring fructan levels in plant tissues are time-consuming and costly. They often involve multiple or sequential extractions, enzymatic or acid hydrolysis of fructan polymers, and multiple HPLC runs to quantify fructan-derived hexoses. Here we describe a new method that requires a single extraction step, followed by selective precipitation of fructans by acetone, acid hydrolysis of the precipitate, and a short (10 min) HPLC run to complete the procedure. We used perennial ryegrass samples to show that the new method has similar sensitivity, but better reproducibility, than a more complex method that is widely used. We have used the new method to study developmentally related changes in fructan levels in glasshouse-grown perennial ryegrass plants.     

An improved optical technique for monitoring plant cell concentration

 An improved optical method was developed to determine cell weight concentrations using a micro-plate reader. Light absorbance was measured by a vertical light beam, which can minimize the cell settling effect found in traditional optical measurements with a horizontal light beam. The use of well plates not only requires very small sample sizes, but also handles a large number of samples at the same time. Absorbance measurements were linearly related to cell weight over the full range of batch culture growth. Received: 4 Jannuary 1999 / Revision received: 23 March 1999 / Accepted: 14 April 1999     

Response of plant functional types to changes in the fire regime in Mediterranean ecosystems: A simulation approach

Abstract. In the Mediterranean basin, the climate is predicted to be warmer and effectively drier, leading to changes in fuel conditions and fire regime. Land abandonment in the Mediterranean basin is also changing the fire regime through the increase in fuel loads. In the present study, two simulation models of vegetation dynamics were tested in order to predict changes in plant functional types due to changes in fire recurrence in eastern Spain. The two modelling approaches are the FATE-model (based on vital attributes) and the gap model BROLLA (based on the gap-phase theory). The models were arranged to simulate four functional types, based mainly on their regenerative strategies after disturbance: Quercus (resprouter), Pinus (non-resprouter with serotinous cones), Erica (resprouter), and Cistus (non-resprouter with germination stimulated by fire). The simulation results suggested a decrease in Quercus abundance, an increase in Cistus and Erica, and a maximum of Pinus at intermediate recurrence scenarios. Despite their different approaches, both models predicted a similar response to increased fire recurrence, and the results were consistent with field observations.     

An application of plant functional types to fire management in a conservation reserve in southeastern Australia

Abstract. The vital attribute system of Noble & Slatyer (1980) was used to classify the fire‐prone flora of Brisbane Water National Park (New South Wales, Australia) into plant functional types (PFTs), reflecting sensitivity to fire frequency (intervals between fire). A variety of information was used to assess the vital attributes of species in the predominant woodland/open‐forest vegetation within the Park. This was sufficient to allocate 54% of the species to functional types. Ca. 20% of the species belonged to PFTs defined as sensitive to either frequent or infrequent fire (e.g. obligate seeder types). Varied methods, based on the nature and quality of data were used to estimate juvenile periods and life spans among species in these types, however the estimates derived in each case were similar. On this basis, a domain of ‘acceptable’ fire intervals (7 to 30 yr) was derived for the woodland/open‐forest vegetation. Given the overall proportion of species considered, plus congruence between differing methods and sources of data, this domain was relatively robust. A landscape analysis using the domain indicated that the current trend in fire intervals, across the Park, may be adverse to floristic conservation.     

Pattern and process in Norwegian upland grasslands: a functional analysis

Abstract. Four classes of functional and morphological plant traits – established strategies (the CSR scheme sensu Grime 1979), life‐forms (sensu Raunkiaer 1934), morphology, and regenerative strategies – are used as tools for explaining vegetation gradients at summer farms in the mountains of western Norway. These farms are assembly points for free‐ranging domestic grazers, and differ floristically and ecologically from the surrounding heath or woodland vegetation. DCA and TWINSPAN are used to relate major gradients in a floristic data set from 12 summer farms to two sets of explanatory variables: (1) environmental variables representing physical factors, plot position, soils, and land use, and (2) the 4 classification schemes. The main floristic gradient parallels a spatial gradient from the centres of the farms to the surrounding vegetation. A functional interpretation based on the concurrent use of the 2 sets of explanatory variables suggests that the gradient is one of decreasing disturbance and increasing environmental stress caused by decreasing grazing and manure effects away from farms. Partial CCA is used to investigate the relationships between the 4 functional/morphological plant trait classes. The 4 classification schemes are partially redundant, and do not represent different trends of specialization within the landscape. There is no strong evidence for decoupling of the traits of the vegetative and regenerative phases within the data. The combination of general process‐based theories and specific plant attribute responses enhances the generality and interpretability of the study.     

Physiological and production responses of plant growth forms to increases in limiting resources in alpine tundra: implications for differential community response to environmental change

Physiological and growth measurements were made on forbs and graminoids following additions of water and N+water in a graminoid-dominated dry meadow and a forb-dominated moist meadow, to determine if the community-level response was related to differential responses between the growth forms. Graminoids had higher photosynthetic rates and lower transpiration rates and foliar N concentrations than forbs, and consequently maintained higher photosynthetic N- and water-use efficiencies. Photosynthetic rates, stomatal conductance, and transpiration rates increased significantly only in response to N fertilization and only in moist meadow species. The increase in photosynthetic rates was unrelated to variation in foliar N concentration, but instead correlated with variation in stomatal conductance. Growth based N-use efficiency was higher in moist meadow graminoids than in moist meadow forbs, but did not differ between the growth forms in the dry meadow. The moist meadow community had higher biomass and N standing crops, but the relative increase in these factors in response to N fertilization was greater in the dry meadow. Graminoids had a greater relative increase in biomass and N accumulation than forbs following N fertilization, but moist meadow graminoids exhibited a greater response than dry meadow graminoids. The difference in the growth response between the dry meadow and moist meadow graminoids to N fertilization was correlated with more conservative leaf gas exchange responses in dry meadow species, presumably related to a higher frequency of soil water deficits in this community. Community-level response to the resource additions was therefore mediated by the plant growth form response, corresponding with differences between the growth forms in physiological factors related to resource acquisition and use.     

A method for the study of fungal growth inhibition by plant proteins

A bioassay is described for the study of inhibitory activity of plant proteins on fungal growth. Fungal spores were germinated in liquid growth medium and pipetted into wells of a microtitre plate. Fungal growth was followed spectrophotometrically. The bioassay was tested using crude protein extracts from plant tissues known to have high activities of chitinase and beta-1,3-glucanase, and with purified enzymes. Crude protein preparations and combinations of the purified enzymes produced a temporary reduction of growth but no permanent growth inhibition.     

An improved approach for transformation of plant cells by microinjection: molecular and genetic analysis

A new culture method for the injection of tobacco mesophyll protoplasts has been established. The protoplasts are embedded in a thin layer of alginate and are nourished from the medium in the underlying basislayer. In the alginate layer the protoplasts regenerate to calli at a frequency of up to 80%. Embedded protoplasts can be selected either with 50 mg l⁻¹ kanamycin or 5 mg l⁻¹ paromomycin. Single resistant cells can be recovered from about 10 000 sensitive cells in one alginate layer. Injection of theneo gene (coding for neomycin phosphotransferase II) into protoplast derived single cells in the alginate layer results in kanamycin resistant colonies that can be regenerated to mature plants. These plants express the neomycin phosphotransferase as shown by enzyme activity assay. The integration of the transgene into the plant genome could be proved by Southern hybridization to high molecular weight DNA. With this culture method 100 cells can be injected per hour. Transformation frequencies range from 2 to 20%. In crossing experiments, it was shown that the foreign gene is transmitted to the next generation in a Mendelian fashion.     

An optimized protein in-gel digest method for reliable proteome characterization by MALDI-TOF-MS analysis

Human lung epithelial cells (A549) were used as a model to develop a reliable proteome characterization method by peptide mass fingerprinting (PMF). Lung cell lysate proteins and protein standards were separated by 2D-gel electrophoresis, stained with Coomassie blue, gel plugs were subjected to commonly adapted as well as optimized in-gel digestion/sample preparation methods. Samples were analyzed by MALDI-TOF-MS. Optimization parameters included, use of NH(4)OAc in destaining and in-gel digestion buffers, detergent/salt removal prior to in-gel digestion, use of solvents of varying polarities (0%, 30%, 60% ACN containing 0.1% TFA) to improve peptide recoveries, matrix composition (alpha-cyano-4-hydroxycinamic acid-organic solvent combinations) and on-target salt removal. This led to enhanced mass spectral information and a sensitivity gain in the order of 6-10 fold compared to that of common procedures, yielding reliable, unambiguous protein identification with femtomol protein sensitivity by Autoflex MALDI-TOF-MS. Triplicate analyses by two analysts revealed consistent, wide range m/z values including in < 1200Da region by relieving matrix-exerted signal suppression, requiring one trial to obtain a unique protein identification with superior PMF results for the optimized method. Analyses of ten A549 proteins in replicates using the optimized method yielded fast, reliable characterization, suggesting the potential application of this method in high-throughput protein identification by PMF.     

不同植茶年限土壤团聚体碳氮磷生态化学计量学特征

试验选取了四川雅安12～15年、20～22年、30～33年和>50年的茶园,研究其土壤团聚体有机碳、全氮、全磷的含量分布及其生态化学计量学特征,以阐明不同植茶年限土壤团聚体碳氮磷生态化学计量学特征的指示意义.结果表明: 0～20 cm和20～40 cm土层土壤有机碳、全氮和全磷含量的变异系数分别为17.5%、16.3%、9.4%和24.0%、21.0%、9.2%;全磷的空间变异性低于有机碳和全氮,但三者呈极显著的正相关关系.有机碳与全氮含量集中分布于小粒径团聚体中,且均在植茶50年后达到最大值,土壤全磷在各粒径团聚体中分布则较为均匀,在种植年限上的变化也不大;0～20 cm和20～40 cm土层土壤C/N、C/P和N/P的变异系数分别为9.4%、14.0%、14.8%和7.4%、24.9%、21.8%;土壤C/N的变异性较低,土壤C/P和N/P均在小粒径中较高,且在植茶50年后达到最大值. 土壤C/N、C/P和N/P对土壤有机碳储量具有良好的指示作用.
     

An improved numerical method for strong coupling of excitation and contraction models in the heart

Quantifying the interactions between excitation and contraction is fundamental to furthering our understanding of cardiac physiology. To date simulating these effects in strongly coupled excitation and contraction tissue models has proved computationally challenging. This is in part due to the numerical methods implemented to maintain numerical stability in previous simulations, which produced computationally intensive problems. In this study, we analytically identify and quantify the velocity and length dependent sources of instability in the current established coupling method and propose a new method which addresses these issues. Specifically, we account for the length and velocity dependence of active tension within the finite deformation equations, such that the active tension is updated at each intermediate Newton iteration, within the mechanics solution step. We then demonstrate that the model is stable and converges in a three-dimensional rod under isometric contraction. Subsequently, we show that the coupling method can produce stable solutions in a cube with many of the attributes present in the heart, including asymmetrical activation, an inhomogeneous fibre field and a nonlinear constitutive law. The results show no instabilities and quantify the error introduced by discrete length updates. This validates our proposed coupling framework, demonstrating significant improvement in the stability of excitation and contraction simulations.     

An improved method for analysis of biomass sugars and galacturonic acid by anion exchange chromatography

The most accurate analysis method for sugars in biomass, based on gas chromatography, requires a time consuming and laborious sample derivatation to trimethylsilanes or alditol acetates. In comparison, sample preparations for sugar analysis by liquid chromatography are simple water dilutions. However, HPLC methods either require long analysis times, use of expensive solvents, or do not give good resolution of sugars. A gradient method developed previously using a Dionex PA-1 column and pulsed-amperometric detection was modified to reduce analysis time from 75 to less than 40?min and provide good resolution of arabinose, rhamnose, galactose, xylose, glucose, fructose, sucrose, cellobiose, and galacturonic acid in both standards and hydrolyzed citrus waste biomass.