Longevity, lignin content and construction cost of the assimilatory organs of Nepenthes species

Background and Aims

This study examined level of causal relationships amongst functional traits in leaves and conjoint pitcher cups of the carnivorous Nepenthes species.

Methods

Physico-chemical properties, especially lignin content, construction costs, and longevity of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, northern Borneo were determined.

Key Results

Longevity of these assimilatory organs was linked significantly to construction cost, lignin content and structural trait of tissue density, but these effects are non-additive. Nitrogen and phosphorus contents (indicators of Rubisco and other photosynthetic proteins), were poor predictors of organ longevity and construction cost, suggesting that a substantial allocation of biomass of the assimilatory organs in Nepenethes is to structural material optimized for prey capture, rigidity and escape from biotic and abiotic stresses rather than to light interception. Leaf payback time – a measure of net carbon revenue – was estimated to be 48–60 d. This is in line with the onset of substantial mortality by 2–3 months of tagged leaves in many of the Nepenthes species examined. However, this is a high ratio (i.e. a longer minimum payback time) compared with what is known for terrestrial, non-carnivorous plants in general (5–30 d).

Conclusions

It is concluded that the leaf trait bivariate relationships within the Nepenthes genus, as in other carnivorous species (e.g. Sarraceniaceae), is substantially different from the global relationship documented in the Global Plant Trait Network.Key words: Botanical carnivory, carbon gain, functional traits, leaf chemistry, leaf lifespan, leaf mass per unit area, Nepenthes, pitcher, payback time     

Construction costs and physico-chemical properties of the assimilatory organs of Nepenthes species in Northern Borneo

BACKGROUND AND AIMS: Species of the Nepenthaceae family are under-represented in studies of leaf traits and the consequent view of mineral nutrition and limitation in carnivorous plants. This study is aimed to complement existing data on leaf traits of carnivorous plants. METHODS: Physico-chemical properties, including construction costs (CC), of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, Northern Borneo were determined. KEY RESULTS: Stoichiometry analyses indicate that Nepenthes species are nitrogen limited. Most traits vary appreciably across species, but greater variations exist between the assimilatory organs. Organ mass per unit area, dry matter tissue concentration (density), nitrogen (N), phosphorus (P), carbon, heat of combustion (H(c)) and CC values were higher in the leaf relative to the pitcher, while organ thickness, potassium (K) and ash showed the opposite trend. Cross-species correlations indicate that joint rather than individual consideration of the leaf and the pitcher give better predictive relationships between variables, signalling tight coupling and functional interdependence of the two assimilatory organs. Across species, mass-based CC did not vary with N or P, but increases significantly with tissue density, carbon and H(c), and decreases with K and ash contents. Area-based CC gave the same trends (though weaker in strength) in addition to a significant positive correlation with tissue mass per unit area. CONCLUSIONS: The lower CC value for the pitcher is in agreement with the concept of low marginal cost for carnivory relative to conventional autotrophy. The poor explanatory power of N, P or N : P ratio with CC suggests that factors other than production of expensive photosynthetic machinery (which calls for a high N input), including concentrations of lignin, wax/lipids or osmoregulatory ions like K(+), may give a better explanation of the CC variation across Nepenthes species.     

A novel insight into the cost–benefit model for the evolution of botanical carnivory

Background The cost–benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (A_N) in the microsites inhabited by carnivorous plants.Scope This review summarizes results from the classical interpretation of the cost–benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost–benefit model.Conclusions Traps of carnivorous plants have lower A_N than leaves, and the leaves have higher A_N after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, R_D) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted.     

Energetics and the evolution of carnivorous plants--Darwin's 'most wonderful plants in the world'

Carnivory has evolved independently at least six times in fiveangiosperm orders. In spite of these independent origins, thereis a remarkable morphological convergence of carnivorous planttraps and physiological convergence of mechanisms for digestingand assimilating prey. These convergent traits have made carnivorousplants model systems for addressing questions in plant moleculargenetics, physiology, and evolutionary ecology. New data showthat carnivorous plant genera with morphologically complex trapshave higher relative rates of gene substitutions than do thosewith simple sticky traps. This observation suggests two alternativemechanisms for the evolution and diversification of carnivorousplant lineages. The ‘energetics hypothesis’ positsrapid morphological evolution resulting from a few changes inregulatory genes responsible for meeting the high energeticdemands of active traps. The ‘predictable prey capturehypothesis’ further posits that complex traps yield morepredictable and frequent prey captures. To evaluate these hypotheses,available data on the tempo and mode of carnivorous plant evolutionwere reviewed; patterns of prey capture by carnivorous plantswere analysed; and the energetic costs and benefits of botanicalcarnivory were re-evaluated. Collectively, the data are moresupportive of the energetics hypothesis than the predictableprey capture hypothesis. The energetics hypothesis is consistentwith a phenomenological cost–benefit model for the evolutionof botanical carnivory, and also accounts for data suggestingthat carnivorous plants have leaf construction costs and scalingrelationships among leaf traits that are substantially differentfrom those of non-carnivorous plants. Key words: Carnivorous plants, competition, construction costs, cost–benefit model, Darwin, energetics, niche overlap, phylogeny, prey capture, universal spectrum of leaf traits Received 6 May 2008; Revised 5 June 2008 Accepted 16 June 2008     

A cost-benefit analysis of acclimation to low irradiance in tropical rainforest tree seedlings: leaf life span and payback time for leaf deployment

The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity.     

Construction costs, chemical composition and payback time of high- and low-irradiance leaves

The effect of irradiance on leaf construction costs, chemical composition, and on the payback time of leaves was investigated. To enable more generalized conclusions, three different systems were studied: top and the most-shaded leaves of 10 adult tree species in a European mixed forest, top leaves of sub-dominant trees of two evergreen species growing in small gaps or below the canopy in an Amazonian rainforest, and plants of six herbaceous and four woody species grown hydroponically at low or high irradiance in growth cabinets. Daily photon irradiance varied 3-6-fold between low- and high-light leaves. Specific leaf area (SLA) was 30-130% higher at low light. Construction costs, on the other hand, were 1-5% lower for low-irradiance leaves, mainly because low-irradiance leaves had lower concentrations of soluble phenolics. Photosynthetic capacity and respiration, expressed per unit leaf mass, were hardly different for the low- and high-light leaves. Estimates of payback times of the high-irradiance leaves ranged from 2-4 d in the growth cabinets, to 15-20 d for the adult tree species in the European forest. Low-irradiance leaves had payback times that were 2-3 times larger, ranging from 4 d in the growth cabinets to 20-80 d at the most shaded part of the canopy of the mixed forest. In all cases, estimated payback times were less than half the life span of the leaves, suggesting that even at time-integrated irradiances lower than 5% of the total seasonal value, investment in leaves is still fruitful from a carbon-economy point of view. A sensitivity analysis showed that increased SLA of low-irradiance leaves was the main factor constraining payback times. Acclimation in the other five factors determining payback time, namely construction costs, photosynthetic capacity per unit leaf mass, respiration per unit leaf mass, apparent quantum yield, and curvature of the photosynthetic light-response-curve, were unimportant when the observed variation in each factor was examined.     

Recent ecophysiological,biochemical and evolutional insights into plant carnivory

BackgroundCarnivorous plants are an ecological group of approx. 810 vascular species which capture and digest animal prey, absorb prey-derived nutrients and utilize them to enhance their growth and development. Extant carnivorous plants have evolved in at least ten independent lineages, and their adaptive traits represent an example of structural and functional convergence. Plant carnivory is a result of complex adaptations to mostly nutrient-poor, wet and sunny habitats when the benefits of carnivory exceed the costs. With a boost in interest and extensive research in recent years, many aspects of these adaptations have been clarified (at least partly), but many remain unknown.ScopeWe provide some of the most recent insights into substantial ecophysiological, biochemical and evolutional particulars of plant carnivory from the functional viewpoint. We focus on those processes and traits in carnivorous plants associated with their ecological characterization, mineral nutrition, cost–benefit relationships, functioning of digestive enzymes and regulation of the hunting cycle in traps. We elucidate mechanisms by which uptake of prey-derived nutrients leads to stimulation of photosynthesis and root nutrient uptake.ConclusionsUtilization of prey-derived mineral (mainly N and P) and organic nutrients is highly beneficial for plants and increases the photosynthetic rate in leaves as a prerequisite for faster plant growth. Whole-genome and tandem gene duplications brought gene material for diversification into carnivorous functions and enabled recruitment of defence-related genes. Possible mechanisms for the evolution of digestive enzymes are summarized, and a comprehensive picture on the biochemistry and regulation of prey decomposition and prey-derived nutrient uptake is provided.     

叶物候、构建消耗和偿还时间对入侵植物碳积累的影响

随着全球经济一体化进程的深入,生物入侵已成为严重的全球性问题之一.外来种入侵打破了物种生存的自然平衡,导致生态系统趋于均质化,并给社会经济发展和人类健康造成了无法估量的损失.然而,目前人们对外来种的入侵机理仍不十分清楚.叶物候如叶片发生时间、凋落时间、及由二者决定的叶寿命和叶片发育进程是植物在季节和非季节性变化的环境中为了获得碳收益所采取的适应策略.叶构建消耗是植物碳收获过程中必要的成本投入,反映了植物在叶片水平上的能量分配策略.偿还时间能在一定程度上反映叶片碳的积累情况.从叶物候、构建消耗和偿还时间入手,分析了入侵植物的资源捕获能力和成本对其碳积累的影响,并提出了今后的研究方向.     

Carnivorous syndrome in Asian pitcher plants of the genus Nepenthes

BACKGROUND AND AIMS: Pitcher plants Nepenthes alata and N. mirabilis are carnivorous species with leaves composed of a photosynthetic part (lamina) and a pitcher trap. This characteristic permitted direct physiological and anatomical comparison between these two distinct parts of the leaves to determine those features involved in the 'carnivorous syndrome', which include low net photosynthetic assimilation rate (A(N)) and low photosynthetic nitrogen use efficiency (PNUE). METHODS: Photosynthetic rate (A(N)) and respiration rate (R(d)) were measured gasometrically, chlorophyll concentration was determined spectrophotometrically and nitrogen concentration was determined using a CHN elemental analyser in lamina and trap separately. Anatomy of N. alata was observed using light, fluorescence and transmission electron microscopy. A(N), foliar nitrogen and chlorophyll concentration were also compared with values for other carnivorous plant species (genera Sarracenia, Drosera) that combine both autotrophic and carnivorous functions into the same physical organ. KEY RESULTS: It was found that the A(N) in Nepenthes lamina was low and PNUE was only slightly higher or similar in comparison with other carnivorous plants. It was not observed that the pitcher had a higher R(d) than the lamina, but A(N) in the pitcher was significantly lower than in the lamina. Nepenthes possesses a cluster of characters that could result in reduced photosynthesis in the pitcher and be responsible for carnivorous function of the leaf: replacement of chlorophyll-containing cells with digestive glands, low chlorophyll and nitrogen concentration, compact mesophyll with a small portion of intercellular spaces, absence of palisade parenchyma and low stomatal density. CONCLUSION: Low photosynthetic capacity, nitrogen efficiency, chlorophyll and nitrogen concentration of Nepenthes pitchers was found, together with a set of features that characterized the carnivorous syndrome. Dual use of leaves for photosynthesis and nutrient gain can decrease photosynthetic efficiency in carnivorous plants in general.     

Do bryophyte shoot systems function like vascular plant leaves or canopies? Functional trait relationships in Sphagnum mosses (Sphagnaceae)

Vascular plant leaf traits that influence photosynthetic function form the basis of mechanistic models of carbon exchange. Given their unique tissue organization, bryophytes may not express similar patterns. We investigated relationships among tissue, shoot, and canopy traits, and their associations with photosynthetic characteristics in 10 Sphagnum species. Trait relationships were organized around a primary dimension accounting for 43% of variation in 12 traits. There was no significant relationship between nitrogen content of shoot systems and maximum photosynthesis expressed on mass (A(mass)) or area (A(area)) bases due to nitrogen sequestration and storage within the canopy interior. This pattern differs from the distribution of nitrogen in vascular plant canopies. Thus, nitrogen and its relationship to carbon uptake in Sphagnum shoots does not conform to patterns of either vascular plant leaves or canopies. Species that concentrate biomass and nitrogen in the capitulum have enhanced rates of A(mass) and A(area). Consequently, A(area) was positively associated with N(area) of the capitulum only. Overall, water content and carotenoid concentration were the strongest predictors of both A(mass) and A(area) and these were expressed as inverse relationships. The relationships of plant traits in Sphagnum defines a principal trade-off between species that tolerate environmental stress and those that maximize carbon assimilation.     

The cost of carnivory for Darlingtonia californica (Sarraceniaceae): evidence from relationships among leaf traits

Scaling relationships among photosynthetic rate, foliar nutrient concentration, and leaf mass per unit area (LMA) have been observed for a broad range of plants. Leaf traits of the carnivorous pitcher plant Darlingtonia californica, endemic to southern Oregon and northern California, USA, differ substantially from the predictions of these general scaling relationships; net photosynthetic rates of Darlingtonia are much lower than predicted by general scaling relationships given observed foliar nitrogen (N) and phosphorus (P) concentrations and LMA. At five sites in the center of its range, leaf traits of Darlingtonia were strongly correlated with elevation and differed with soil calcium availability and bedrock type. The mean foliar N : P of 25.2 ± 15.4 of Darlingtonia suggested that these plants were P-limited, although N concentration in the substrate also was extremely low and prey capture was uncommon. Foliar N : P stoichiometry and the observed deviation of Darlingtonia leaf traits from predictions of general scaling relationships permit an initial assessment of the "cost of carnivory" in this species. Carnivory in plants is thought to have evolved in response to N limitation, but for Darlingtonia, carnivory is an evolutionary last resort when both N and P are severely limiting and photosynthesis is greatly reduced.     

Functional analysis of the relative growth rate, chemical composition, construction and maintenance costs, and the payback time of Coffea arabica L. leaves in response to light and water availability

In this study, the combined effects of light and water availability on the functional relationships of the relative growth rate (RGR), leaf chemical composition, construction and maintenance costs, and benefits in terms of payback time for Coffea arabica are presented. Coffee plants were grown for 8 months in 100% or 15% full sunlight and then a four-month water shortage was implemented. Plants grown under full sunlight were also transferred to shade and vice versa. Overall, most of the traits assessed were much more responsive to the availability of light than to the water supply. Larger construction costs (12%), primarily associated with elevated phenol and alkaloid pools, were found under full sunlight. There was a positive correlation between these compounds and the RGR, the mass-based net carbon assimilation rate and the carbon isotope composition ratio, which, in turn, correlated negatively with the specific leaf area. The payback time was remarkably lower in the sun than in shade leaves and increased greatly in water-deprived plants. The differences in maintenance costs among the treatments were narrow, with no significant impact on the RGR, and there was no apparent trade-off in resource allocation between growth and defence. The current irradiance during leaf bud formation affected both the specific leaf area and leaf physiology upon transferring the plants from low to high light and vice versa. In summary, sun-grown plants fixed more carbon for growth and secondary metabolism, with the net effect of an increased RGR.     

Photosynthetic light response in three carnivorous plant species: <Emphasis Type="Italic">Drosera rotundifolia,D. capensis and Sarracenia leucophylla</Emphasis>

Photosynthetic properties of carnivorous plants have not been well characterized and the extent to which photosynthesis contributes to carbon gain in most carnivorous plants is also largely unknown. We investigated the photosynthetic light response in three carnivorous plant species, Drosera rotundifolia L. (sundew; circumpolar and native to northern British Columbia, Canada), Sarracenia leucophylla Rafin. (‘pitcher-plant’; S.E. United States), and D. capensis L. (sundew; Cape Peninsula, South Africa), using portable gas-exchange systems to explore the capacity for photosynthetic carbon gain in carnivorous plant species. Maximal photosynthetic rates (1.32–2.22 μmol m⁻² s⁻¹ on a leaf area basis) and saturating light intensities (100 to 200 μmol PAR m⁻² s⁻¹) were both low in all species and comparable to shade plants. Field or greenhouse-grown D. rotundifolia had the highest rates of photosynthesis among the three species examined. Dark respiration, ranging from −1.44 (S. leucophylla) to −3.32 (D. rotundifolia) μmol m⁻² s⁻¹ was high in comparison to photosynthesis in the species examined. Across greenhouse-grown plants, photosynthetic light compensation points scaled with light-saturated photosynthetic rates. An analysis of gas-exchange and growth data for greenhouse-grown D. capensis plants suggests that photosynthesis can account for all plant carbon gain in this species.     

Mineral cost of carnivory in aquatic carnivorous plants

Tissue N, P, K, Ca, and Mg content was estimated in traps and photosynthetic and carnivorous shoots in five aquatic carnivorous plant species from an outdoor culture: Aldrovanda vesiculosa, Utricularia vulgaris, U. reflexa, U. intermedia, and U. stygia, for the determination of the mineral cost of carnivory. In three species with monomorphic shoots (A. vesiculosa, U. vulgaris, U. reflexa), tissue P and K content in traps was significantly higher than that in their photosynthetic shoots, whereas N content was about the same. In U. stygia and U. intermedia with dimorphic shoots, tissue N and P content was markedly the highest in photosynthetic shoots followed by traps, while it was lowest in carnivorous shoots. In all five species, trap K content was significantly (2–4 times) higher than that in photosynthetic and carnivorous shoots. In all species, the values of the mineral cost of carnivory – the proportion of mineral nutrient amount contained in traps or carnivorous shoots to that in the total plant biomass – were within 19–61% for N, 33–76% P, 51–78% K, 26–70% Ca, and 34% for Mg. A new concept of the ecological cost-benefit relationships of plant carnivory, based on the mineral benefit of prey capture and mineral costs associated with trap production, is introduced for aquatic carnivorous plants. The evolution of this plant group is considered to show the optimization of these mineral cost-benefit relationships.     

Biomass allocation patterns in terrestrial, epiphytic and aquatic species of Utricularia (Lentibulariaceae)

Utricularia forms the largest genus of carnivorous plants and is characterized by the possession of typical traps (“bladders”). Total biomass allocation was examined in three aquatic, six terrestrial and one epiphytic species of Utricularia from natural habitats in West Africa and from the Botanical Gardens, Bonn. Total biomass of aquatic species was considerably higher than that of terrestrial or epiphytic species. Epiphytic Utricularia accumulate about 35% of their biomass in green leaves, in contrast to 65% of nearly chlorophylless reproductive structures and traps. Aquatic species allocated more than 85% of their total biomass to stolons, leaves and traps, but only 10–13% to reproductive structures. This is in stark contrast to the allocation patterns of terrestrial bladderworts. These species allocate nearly 90% of their total biomass in reproductive structures, and only about 10% to stolons, leaves and traps. This reduction of photosynthetically active plant tissue strongly suggests that as a consequence of the alternative resource of chemical energy, the carnivorous habit might have partly replaced autotrophy in certain terrestrial Utricularia species, especially in some smaller ones.     

An experimental test of the defensive role of sticky traps in the carnivorous plant Pinguicula moranensis (Lentibulariaceae)

It has been sustained that the sticky traps present in some carnivorous plants could have evolved from ancestor species bearing leaves covered with secreting glands formerly associated with a defensive function. In this study, we evaluated the interaction of the carnivorous plant Pinguicula moranensis with its insect herbivores to assess the defensive role of the glandular trichomes. Firstly, we estimated the standing levels of insect herbivory in field conditions. We also evaluated the response of herbivore insects to the removal of the secreting glands from the leaves of P. moranensis in field and laboratory conditions. The mean damage was 1.61%, and half of the sampled plants showed no damage. The low level of herbivory in the field suggests that P. moranensis has an efficient defense ability. In the field experiment, after 25 d of exposure to natural damage, treated glandless plants received 18 times more damage than control plants. In the laboratory, the consumption of glandless tissue was three times higher during a 6 h evaluation period. Overall, our results provide evidence that secreting trichomes in Pinguicula are not only associated with prey capture but also have a defensive role. The defensive function could have favored the evolution of the sticky traps, the most extended prey‐capture strategy among carnivorous plants.     

Dark respiration of leaves and traps of terrestrial carnivorous plants: are there greater energetic costs in traps?

In this study, O₂-based dark respiration rate (R_D) in leaf and trap cuttings was compared in 9 terrestrial carnivorous plant species of 5 genera to decide whether traps represent a greater energetic (maintanence) cost than leaves or photosynthetic parts of traps. R_D values of cut strips of traps or leaves of terrestrial carnivorous plants submerged in water ranged between 2.2 and 8.4 nmol g⁻¹ s⁻¹ (per unit dry weight) in pitcher traps of the genera Sarracenia, Nepenthes, and Cephalotus, while between 7.2 and 25 nmol g⁻¹ _DW s⁻¹ in fly-paper or snapping traps or leaves of Dionaea and Drosera. No clear relationship between R_D values of traps (or pitcher walls) and leaves (or pitcher wings or petioles) was found. However, RD values of separated Drosera prolifera tentacles exceeded those of leaf lamina 7.3 times.     

Construction cost and invasive potential: comparing Lythrum salicaria (Lythraceae) with co-occurring native species along pond banks

Lythrum salicaria (purple loosestrife) is a nonindigenous invasive species characterized by prolific growth and abundance in marshy and riparian habitats across North America. Given its invasive success, we hypothesized this species may require less energy and/or use energy more efficiently for biomass construction than co-occurring noninvasive plant species. We measured leaf construction cost (CC), leaf mass per unit area (LMA), and leaf organic nitrogen and carbon content of L. salicaria and the five most abundant co-occurring species, Parthenocissus quinquefolia, Erigeron philadelphicus, Asclepias syriaca, Spiraea latifolia, and Solidago graminifolia, along dammed ponds in the Black Rock Forest, Cornwall, New York, USA. Lythrum salicaria, which was highly abundant (2.52 individuals/m(2)), exhibited significantly lower area-based leaf CC (44.47 ± 4.24 g glucose/m(2) leaf) than relatively less abundant species, suggesting energetics may influence its invasive success. Conversely, least abundant Solidago graminifolia (0.67 individuals/m(2)) exhibited the significantly highest leaf CC per unit leaf area (141.87 ± 39.21 g glucose/m(2) leaf). Overall, a negative correlation between species abundance and area-based leaf CC (r(2) = 0.73) indicated low energy requirements and/or high energy efficiency may influence relative abundance in the plant species studied. As it correlates with species abundance in this study, CC may be a useful tool for evaluating invasive potential.     

Increase in leaf organic acids to enhance adaptability of dominant plant species in karst habitats

Estimation of leaf nutrient composition of dominant plant species from contrasting habitats (i.e., karst and nonkarst forests) provides an opportunity to understand how plants are adapted to karst habitats from the perspective of leaf traits. Here, we measured leaf traits—specific leaf area (SLA), concentrations of total carbon ([TC]), nitrogen ([TN]), phosphorus ([TP]), calcium ([Ca]), magnesium ([Mg]), manganese ([Mn]), minerals ([Min]), soluble sugars, soluble phenolics, lipids, and organic acids ([OA])—and calculated water‐use efficiency (WUE), construction costs (CC), and N/P ratios, and searched for correlations between these traits of 18 abundant plant species in karst and nonkarst forests in southwestern China. Variation in leaf traits within and across the abundant species was both divergent and convergent. Leaf [TC], [Ca], [Min], [OA], and CC were habitat‐dependent, while the others were not habitat‐ but species‐specific. The correlations among [TN], [TP], SLA, [TC], CC, [Min], WUE, [OA], and CC were habitat‐independent, and inherently associated with plant growth and carbon allocation; those between [CC] and [Lip], between [Ca] and [Mg], and between [Mg] and [WUE] were habitat‐dependent. Habitat significantly affected leaf [Ca] and thus indirectly affected leaf [OA], [Min], and CC. Our results indicate that plants may regulate leaf [Ca] to moderate levels via adjusting leaf [OA] under both high and low soil Ca availability, and offer new insights into the abundance of common plant species in contrasting habitats.     

Leaf age effects on photosynthetic rate, transpiration rate and nitrogen content in a tropical dry forest

This study examines the effect of leaf age on photosynthesis, transpiration and nitrogen concentration in four deciduous (DC) and two evergreen (EG) species coexisting in a tropical dry forest of Venezuela. Leaf age was characterized on the basis of leaf chorophyll, nitrogen content, and construction and maintenance costs. The mean leaf area-based nitrogen concentration (N) in EG was about twice that in DC species. A leaf age effect was observed in both DC and EG species, with largest N concentration in mature leaves. Fractional leaf N allocation to chlorophyll was higher in the DC than in the EG species. Differences in the construction costs of leaf mass between the youngest and the oldest leaves averaged from 2.14 to 1.55 g glucose g⁻¹ dry weight. Although variation in area-based leaf maintenance and construction costs between DC and EG species existed, they were, nevertheless, positively correlated. Individual data sets, for each species, indicated that leaf N and maximum rate of photosynthesis (A_max) were linearly related. Nitrogen use efficiency (NUE) and water use efficiency (WUE) tended to be higher in mature leaves than in expanding and old leaves. Moreover, DC species always had higher NUE than EG species. Intercellular to ambient pressures of CO₂ (P_i/P_a) were related to WUE in a negative manner. Higher P_i/P_a values were observed in expanding and old leaves. Leaf age effect on photosynthesis was, therefore, due to greater decline of carbon fixation capacity by mesophyll tissue relative to the decline in stomatal conductance in youngest and oldest leaves.