Scaling sun and shade photosynthetic acclimation of Alocasia macrorrhiza to whole-plant performance – I. Carbon balance and allocation at different daily photon flux densities

We determined the carbon allocation patterns and construction costs of Alocasia macrorrhiza plants grown at different photon flux densities (PFD) as well as the whole-plant carbon gain of these plants at different daily PFDs. Growth at high PFD resulted in thicker leaves with a higher leaf mass per unit area, and increased biomass allocation to petioles and roots, as compared to growth at low PFD. Increased allocation to petioles may have been necessary to support the heavier leaves, whereas increased allocation to roots may have been necessary to supply sufficient water for the higher transpiration rates in high PFD. Root biomass was highly correlated with the daily, whole-plant transpiration rate. Tissue construction costs per unit dry mass were unchanged by acclimation, but, since the mass per unit areas of leaves, roots and petioles all increased, construction costs per unit leaf area were much higher for plants grown at high PFD. On a per unit leaf area basis, daily whole-plant carbon gain measured at high daily PFD was higher in high- than in low-PFD-grown plants. However, on a per unit leaf mass basis, low-PFD-grown plants had a daily carbon gain at least as high as that of high-PFD-grown plants at high daily PFD. At low daily PFD, low-PFD-grown plants maintained an advantage over high-PFD-grown plants in terms of carbon gain because of their larger leaf area ratios. Thus, in terms of carbon gain, low-PFD-grown plants performed better than sun plants at low PFD and as well as high-PFD-grown plants at high PFD, despite their lower photosynthetic capacities per unit area. For high-PFD-grown plants, the higher construction costs per unit leaf area resulted in lower leaf area ratios, which counteracted the advantage of higher photosynthetic rates per unit leaf area.     

Contrasting patterns of diameter and biomass increment across tree functional groups in Amazonian forests

Species' functional traits may help determine rates of carbon gain, with physiological and morphological trade-offs relating to shade tolerance affecting photosynthetic capacity and carbon allocation strategies. However, few studies have examined these trade-offs from the perspective of whole-plant biomass gain of adult trees. We compared tree-level annual diameter increments and annual above-ground biomass (AGB) increments in eight long-term plots in hyper-diverse northwest Amazonia to wood density (rho; a proxy for shade tolerance), whilst also controlling for resource supply (light and soil fertility). rho and annual diameter increment were negatively related, confirming expected differences in allocation associated with shade tolerance, such that light-demanding species allocate a greater proportion of carbon to diameter gain at the expense of woody tissue density. However, contrary to expectations, we found a positive relationship between rho and annual AGB increment in more fertile sites, although AGB gain did not differ significantly with rho class on low-fertility sites. Whole-plant carbon gain may be greater in shade-tolerant species due to higher total leaf area, despite lower leaf-level carbon assimilation rates. Alternatively, rates of carbon loss may be higher in more light-demanding species: higher rates of litterfall, respiration or allocation to roots, are all plausible mechanisms. However, the relationships between rho and AGB and diameter increments were weak; resource availability always exerted a stronger influence on tree growth rates.     

Heteroblastic development and the optimal partitioning of traits among contrasting environments in Acacia implexa

Background and Aims: Optimal partitioning theory (OPT) predicts plants will allocatebiomass to organs where resources are limiting. Studies of OPTfocus on root, stem and leaf mass ratios where roots and stemsare often further sub-divided into organs such as fine roots/taproots or branches/main stem. Leaves, however, are rarely sub-dividedinto different organs. Heteroblastic species develop juvenileand adult foliage and provide an opportunity of sub-dividingleaf mass ratio into distinct organs. Acacia implexa (Mimosaceae)is a heteroblastic species that develops compound (juvenile),transitional and phyllode (adult) leaves that differ dramaticallyin form and function. The aims of the present study were togrow A. implexa to examine patterns of plastic development ofwhole-plant and leaf traits under the OPT framework. Methods: Plants were grown in a glasshouse under contrasting nutrient,light and water environments in a full factorial design. Allocationto whole-plant and leaf-level traits was measured and analysedwith multivariate statistics. Key Results: Whole-plant traits strongly followed patterns predicted by OPT.Leaf-level traits showed a more complex pattern in responseto experimental treatments. Compound leaves on low nutrientplants had significantly lower specific leaf area (SLA) andwere retained for longer as quantified by a significantly greatercompound leaf mass ratio after 120 d. There was no significantdifference in SLA of compound leaves in the light treatment,yet transitional SLA was significantly higher under the lowlight treatment. The timing of heteroblastic shift from compoundto transitional leaves was significantly delayed only in thelow light treatment. Therefore, plants in the light treatmentresponded at the whole-plant level by adjusting allocation toproductive compound leaves and at the leaf-level by adjustingSLA. There were no significant SLA differences in the watertreatment despite strong trends at the whole-plant level. Conclusion: Explicitly sub-dividing leaves into different types providedgreater insights into OPT.     

性别和发育阶段对绒毛白蜡光合特征及叶功能性状的影响

雌雄异株植物资源分配模式上往往表现出显著的性别二态性,但在叶片光合及功能性状上是否有差异目前仍未有定论,且与发育阶段的关系尚不明确。阐明上述问题,能够进一步了解雌雄异株植物的生理生态特征,并为理解性别对性二态植物生长发育的影响机制提供理论依据。以雌雄异株绒毛白蜡(Fraxinus velutina Torr.)为研究对象,针对不同发育阶段不同性别植株进行光合特征及叶功能性状测定,采用双因素方差分析了不同发育阶段下雌雄植株光合能力及叶功能性状的性别间差异,采用Pearson检验了雌雄植株各叶功能性状之间的相关性,并采用标准化主轴分析(Standardized major axis regression, SMA)分析不同性别植株净光合速率与叶功能性状的相关性。结果表明性别和发育阶段显著影响植物个体的光合能力和叶功能性状。总体而言,雄树在坐果期和果实成熟期均表现出更强的净光合速率(Pn)、更高的比叶面积(SLA)、叶绿素含量(Chl)和叶氮含量(LNC);而雌树在果实膨大期表现出更强Pn、SLA和Chl。雌雄性别内Pn与SLA、Chl和LNC间均呈显著正相关(P<0.05),雄树的S...     

Sex-specific physiology and source-sink relations in the dioecious plant Silene latifolia

Differences in reproductive demands between the sexes of dioecious plants could cause divergence in physiology between the sexes. We found that the reproductive effort of female Silene latifolia plants increased to more than twice that of male plants or female plants that were prevented from setting fruit by lack of pollination after 4 weeks of flowering. Whole-plant source/sink ratios of pollinated females were significantly lower than those of males or unpollinated females because of investment in fruit. We hypothesized that these differences in source/sink ratio between the sexes and within females, depending on pollination, would lead to differences in leaf photosynthetic rates. Within females, we found that photosynthetic capacity was consistent with measurement of whole-plant source/sink ratio. Females that were setting fruit had 30% higher light-saturated photosynthetic rates by 28 days after flowering than females that were not setting fruit. Males, however, had consistently higher photosynthetic rates than females from 10 days after flowering onwards. Males also had approximately twice the dark respiration rates of fruiting females. We found that female reproductive structures are longer-lived and contribute more carbon to their own support than male reproductive structures. Despite the higher rates of leaf dark respiration and lower calyx photosynthetic rates, males fix more carbon than do females. We conclude that females have a sink-regulated mechanism of photosynthesis that allows them to respond to variations in fruit set. This mechanism is not, however, sufficient to explain why male S. latifolia plants have higher rates of photosynthesis, higher source/sink ratios, and lower reproductive allocation, but fail to grow larger than female plants.     

Physiological and morphological correlates of whole-plant light compensation point in temperate deciduous tree seedlings

A range of traits, including metabolic costs, biomass allocation and seed reserves, may contribute to interspecific variation in the shade tolerance of tree seedlings. In addition, shade tolerance may be affected by differential responses of species to soil resource availability at low light. We used a custom-built whole-plant gas-exchange chamber to quantify instantaneous whole-plant light compensation point (WPLCP) and to parameterize whole-plant daily C gain models for seedlings of eight temperate deciduous tree species. We examined the relationship of WPLCP to growth, biomass allocation and gas-exchange under high and low light and nutrient availabilities and compared it to WPCLP of naturally recruited saplings. For species showing a response, both increased light and nutrient availability resulted in increased WPLCP. However, species’ responses to resource availability did not correspond closely with shade tolerance as has generally been predicted. Variation in WPLCP within species was best predicted by whole-plant dark respiration rates, leaf-level light compensation point and leaf mass per area. Among species, seed size was a strong negative correlate of WPLCP, explaining 66% of the variation. Species with the lowest WPLCP maintained lower growth rates across treatments but greater biomass in the low-light treatment compared with more light-demanding species. These data suggest that a number of traits, in particular metabolic costs and seed size, contribute to WPLCP. However, gas-exchange-based WPLCP was 1.5–3.5 times lower than corresponding growth-based field estimates of WPLCP, suggesting that other factors such as biotic interactions or ontogenetic shifts in whole-plant light requirements may substantially increase species’ WPLCP under natural conditions.     

Optimal nitrogen allocation controls tree responses to elevated CO2

Despite the abundance of experimental data, understanding of forest responses to elevated CO2 is limited. Here I show that a key to previously unexplained production and leaf area responses lies in the interplay between whole-plant nitrogen (N) allocation and leaf photosynthesis. A simple tree growth model, controlled by net growth maximization through optimization of leaf area index (LAI) and plant N, is used to analyse CO2 responses in both young, expanding and closed, steady-state canopies. The responses are sensitive to only two independent parameters, the photosynthetic capacity per leaf N (a) and the fine-root N:leaf N ratio. The model explains observed CO2 responses of photosynthesis, production and LAI in four forest free air CO2 enrichment (FACE) experiments. Insensitivity of LAI except at low LAI, increase in light-use efficiency, and photosynthetic down-regulation (as a result of reduced leaf N per area) at elevated CO2 are all explained through the combined effects on a and leaf quantum efficiency. The model bridges the gap between the understanding of leaf-level and plant-level responses and provides a transparent framework for interpreting and linking structural (LAI) and functional (net primary production (NPP):gross primary production (GPP) ratio, light-use efficiency, photosynthetic down-regulation) responses to elevated CO2.     

Effects of light and soil water availability on leaf photosynthesis and growth of Arisaema heterophyllum,a riparian forest understorey plant

The effects of soil-water availability on leaf light acclimation and whole-plant carbon gain were examined in Arisaema heterophyllum Blume, a riparian deciduous forest understorey plant. Photosynthesis, above-ground morphology and ramet biomass accumulation (relative growth rate: RGR of a corm for a full leaf life-span) were measured on plants raised under three light treatments combined with two soil water conditions. The two higher light treatments during growth (high: max. 550 μmol photons m^–2 s^–1; medium: 150 μmol photons m^–2 s^–1) resulted in a twofold increase in RGRs, 30% higher photosynthetic capacities and 20% less photosynthetic low-light use efficiency than those under a low light condition (50 μmol photons m^–2 s^–1). Leaf area was the smallest and leaf mass area ratio was the largest under the high light treatment. Water stress decreased both photosynthetic rate and leaf area and, hence, RGR in all the light regimes. However, water stress did not alter the general patterns of physiological and morphological responses to different light regimes. We estimated that higher photosynthetic low-light use efficiency and larger leaf area in the low light leaf would lead to a threefold carbon gain as compared with the high light leaf under simulated low light conditions. Both experimental and simulation results suggest that the physiological and morphological acclimations tend to be beneficial to carbon gain when light availability is low, whereas they favor increased water use efficiency when light availability is sufficiently high. Electronic Publication     

雌雄异株的大戟科植物中叶片大小和形状的性别差异

雌雄异株的大戟科植物中叶片大小和形状的性别差异 作为自然选择的对象,叶片大小和形状能够发挥适应性作用,并且随叶龄而改变。在雌雄异株的植物中,叶片大小和形状因性别而不同,在大多数情况下,雌性的叶片较大。以往研究表明,Adriana tomentosa在叶裂方面存在性别差异。在本研究中,我们探讨了在叶片大小、形状和生理生态等方面是否存在其他性别差异,以及这些差异是否与A. tomentosa的性别适应性和繁殖作用有关。我们测定了生 长在澳大利亚东部的两个不连续种群的雌性和雄性植物的幼叶和老叶的物理化学特征,主要包括：叶面积、周长、锯齿、圆形度、长宽比、圆度以及生态生理指标,包括SLA、干物质质量、叶片水分、RWC、δ ¹³C、δ ¹⁵N同位素比、碳氮含量和碳氮比。同时还测定了叶裂、叶片损伤程度和光合色素含量。在这两个种群中,植物性别显著影响几乎所有与叶片形态相关的参数,如面积、周长、圆形度、长宽比和圆度。与预期相反,我们发现两个种群的雄性具有较大的叶面积且与叶龄无关。雄叶裂片较多,周长较长,但它们较少伸长且锯齿较少。雌性和雄性叶片的生理生态指标差异不大。叶片损伤程度因性别而异,但也因种群而异。叶面积和叶形在性别间的差异不能被生理生态因素所补偿。然而,叶面积可能由其他与叶片形态相关的生理生态机制补偿,因为与雄性相比,雌性的叶面积较小,但叶片锯齿较大。     

Canopy dynamics and carbon gain in response to soil water availability in Encelia frutescens gray,a drought-deciduous shrub

Summary The production and longevity of leaves of Encelia frutescens Gray, a drought-deciduous subshrub of the Mohave and Sonoran Deserts, were followed during the summer and fall of 1983 in an experimental field garden. The relationships between seasonally changing plant water status, extent of canopy development, and photosynthetic capacity per unit leaf area were determined. Maximum leaf life spans during a summer activity period were between 3 and 4 months, with the great majority living between 1 and 3 months. Leaf production occurred synchronously in well defined cohorts triggered by precipitation events. Extensive leaf turnover occurred during the summer period even though the plants remained in continuous leaf. Turnover was most pronounced when precipitation triggered the production of new leaf cohorts.Five weeks were required for plants to reach maximum canopy development when renewed soil-water availability followed a prolonged drought. Photosynthetic capacity per unit leaf area recovered much sooner than total leaf area, and submaximal leaf area development was the major factor limiting whole-plant carbon gain during a leaf-flushing period lasting several weeks. As the soil began to dry out, physiological capacity declined more rapidly than leaf area, and became the primary limiting factor to whole plant carbon gain.     

Does leaf shedding increase the whole-plant carbon gain despite some nitrogen being lost with shedding?

When old leaves are shed, part of the nitrogen in the leaf is retranslocated to new leaves. This retranslocation will increase the whole-plant carbon gain when daily C gain : leaf N ratio (daily photosynthetic N-use efficiency, NUE) in the old leaf, expressed as a fraction of NUE in the new leaf, becomes lower than the fraction of leaf N that is resorbed before shedding (R(N)). We examined whether plants shed their leaves to increase the whole-plant C gain in accord with this criterion in a dense stand of an annual herb, Xanthium canadense, grown under high (HN) and low (LN) nitrogen availability. The NUE of a leaf at shedding expressed as a fraction of NUE in a new leaf was nearly equal to the R(N) in the LN stand, but significantly lower than the R(N) in the HN stand. Thus shedding of old leaves occurred as expected in the LN stand, whereas in the HN stand, shedding occurred later than expected. Sensitivity analyses showed that the decline in NUE of a leaf resulted primarily from a reduction in irradiance in the HN stand. On the other hand, it resulted from a reduction in irradiance and also in light-saturated photosynthesis : leaf N content ratio (potential photosynthetic NUE) in the LN stand.     

Sex-different response in growth traits to resource heterogeneity explains male-biased sex ratio

In dioecious plants, differences in growth traits between sexes in a response to micro-environmental heterogeneity may affect sex ratio bias and spatial distributions. Here, we examined sex ratios, stem growth traits and spatial distribution patterns in the dioecious clonal shrub Aucuba japonica var. borealis, in stands with varying light intensities. We found that male stems were significantly more decumbent (lower height/length ratio) but female stems were upright (higher height/length ratio). Moreover, we found sex-different response in stem density (no. of stems per unit area) along a light intensity gradient; in males the stem density increased with increases in canopy openness, but not in females. The higher sensitivity of males in increasing stem density to light intensity correlated with male-biased sex ratio; fine-scale sex ratio was strongly male-biased as canopy openness increased. There were also differences between sexes in spatial distributions of stems. Spatial segregation of sexes and male patches occupying larger areas than female patches might result from vigorous growth of males under well-lit environments. In summary, females and males showed different growth responses to environmental variation, and this seemed to be one of possible causes for the sex-differential spatial distributions and locally biased sex ratios.     

Leaf physiological aspects of nitrogen-use efficiency in Brassica campestris L.: quantitative genetic variation across nutrient treatments

Summary Quantitative genetic parameters for leaf physiological and whole-plant aspects of nitrogen-use efficiency in Brassica camprestris L. were estimated in three nutrient treatments in the greenhouse. Narrow-sense heritabilities and genetic correlations varied across treatments for some traits. Sire effects were significant for leaf nitrogen content in near-optimal and super-optimal, but not in suboptimal nutrient treatments. Additive genetic variation for two estimates of leaf physiological nitrogen-use efficiency (nitrogen-based photosynthetic capacity and leaf carbon: nitrogen ratio) was significant only in the suboptimal nutrient treatment. Area-based photosynthetic capacity, on the other hand, exhibited no heritable variation in any nutrient treatment. Heritability estimates of aboveground biomass and flower production were greatest in sub- and super-optimal treatments, respectively. Negative genetic correlations between leaf nitrogen content and both estimates of leaf nitrogen-use efficiency were evident in the super-optimal treatment. Aboveground biomass and leaf nitrogen-use efficiency were positively correlated in the suboptimal treatment, suggesting that growth differences were due in part to the efficiency with which nitrogen was utilized in physiological processes. Although implications for breeding may differ for different sources of germ plasm or different measures of performance or yield, selection for improved whole-plant performance through increased nitrogen-use efficiency should proceed best in suboptimal nutrient treatments.     

Contrasting modes of light acclimation in two species of the rainforest understory

In tropical rainforests, the increased light associated with the formation of treefall gaps can have a critical impact on the growth and survivorship of understory plants. Here we examine both leaf-level and whole-plant responses to simulated light gap formation by two common shade-tolerant shrubs, Hybanthus prunifolius and Ouratea lucens. The species were chosen because they differed in leaf lifespans, a trait that has been correlated with a number of leaf- and plant-level processes. Ouratea leaves typically live about 5 years, while Hybanthus leaves live less than 1 year. Potted plants were placed in the understory shade for 2 years before transfer to a light gap. After 2 days in high light, leaves of both species showed substantial photoinhibition, including reduced CO₂ fixation, F _v/F _m and light use efficiency, although photoinhibition was most severe in Hybanthus. After 17 days in high light, leaves of both species were no longer photoinhibited. In response to increased light, Ouratea made very few new leaves, but retained most of its old leaves which increased photosynthetic capacity by 50%. Within a few weeks of transfer to high light, Hybanthus had dropped nearly all of its shade leaves and made new leaves that had a 2.5-fold greater light-saturated photosynthetic rate. At 80 days after transfer, the number of new leaves was 4.9-fold the initial leaf number. After 80 days in high light, Hybanthus had approximately tenfold greater productivity than Ouratea when leaf area, photosynthetic capacity, and leaf dark respiration rate were all taken into account. Although both species are considered shade tolerant, we found that their growth responses were quite different following transfer from low to high light. The short-lived Hybanthus leaves were quickly dropped, and a new canopy of sun leaves was produced. In contrast, Ouratea showed little growth response at the whole-plant level, but a greater ability to tolerate light stress and acclimate at the leaf level. These differences are consistent with predictions based on leaf lifespan and are discussed within the context of other traits associated with shade-tolerant syndromes. Received: 25 March 1999 / Accepted: 16 August 1999     

Morning vs afternoon sun patches in experimental forest gaps: consequences of temporal incongruency of resources to birch regeneration

We investigated whether the timing of high light availability as sun patches within forest gaps, independent of total or peak photosynthetic photon flux (PPF), influences the physiology and growth of four coexisting birch species (Betula alleghaniensis, B. lenta, B. papyrifera, and B. populifolia). Birch seedlings were grown for two years along either the east or west sides of experimental gap structures and at two moisture levels. Seedlings positioned in the west received sun patches earlier in the day than those in the east, and environmental conditions for carbon gain were generally more favorable during the earlier sunpatches in the west; air and leaf temperatures were lower, and relative humidity higher, relative to conditions during sun patches in the cats, simulating patterns observed in natural forest gaps. Seedlings positioned along the west edges of gaps fixed more carbon earlier in the day than those in the east, and in many cases, peak net photosynthetic rates were greater for west positioned seedlings. In year two, leaf-level integrated daily carbon gain was greater for west- than eastpositioned plants, and for the most pioneer species, B. populifolia, differences between west and east seedlings were greatest at lower soil moisture levels. Despite some small effects on leaf gas exchange, the timing of high light availability, and its temporal congruence with other factors critical to carbon gain, had no significant effects on first or second year seedling biomass. The responses of birch seedlings to controlled variations in the timing of high light availability were generally much smaller than birch seedling responses to variations in other components of daily light regimes such as total integrated and peak PPF.     

Responses of the functional traits in Cleistogenes squarrosa to nitrogen addition and drought

植物功能性状被广泛地用于研究植物对环境变化的响应。糙隐子草(Cleistogenes squarrosa)是内蒙古草原重要的C4物种,其功能性状是如何对水氮环境的变化做出响应的,还不十分清楚。该文采用盆栽实验的方法,进行氮添加(0,10.5,35.0和56.0 g·m–2·a–1)和降水(自然降水和70%平均月降水量)处理,研究糙隐子草整株性状、叶形态性状和叶生理性状对氮添加和干旱的响应。结果表明,氮添加显著影响了糙隐子草的整株性状,氮、水处理及它们的交互作用显著影响了糙隐子草的叶形态性状和叶生理性状。各功能性状对氮添加的响应格局在自然降水和干旱处理下是不同的。根深、茎生物量和茎叶比在干旱条件下低和中氮添加处理中较高,而在自然降水下无明显变化;比叶面积在干旱条件下随氮添加量的增加而增加,而在自然降水下无增加趋势;自然降水下,高氮添加显著刺激了光合速率和蒸腾速率,增加了水分利用效率,而在干旱条件下氮添加对它们没有显著影响;叶片单位面积的氮含量在自然降水下随氮添加量的增加有增加趋势,而在干旱条件下显著降低。在自然降水下,氮添加主要影响糙隐子草的叶形态和生理性状,而在干旱条件下,氮添加主要影响糙隐子草的整株性状和形态性状。总之,糙隐子草的功能性状对氮添加表现出明显的响应,响应格局在不同的水分条件下不同,反映了其对氮水环境变化的弹性适应。     

Leaf size in three generations of a dioecious tropical tree, Ocotea tenera (Lauraceae): Sexual dimorphism and changes with age

? Premise of the study: In dioecious species, selection should favor different leaf sizes in males and females whenever the sexes experience distinct environments or constraints such as different costs of reproduction. We took advantage of a long-term experimental study of Ocotea tenera (Lauraceae), a dioecious understory tree in Monteverde, Costa Rica, to explore leaf size differences between genders and age classes across generations. ? Methods: We measured leaf size in adult trees in a natural population, in their adult F(1) offspring in two experimental populations, and in their F(2) offspring at the seedling stage. Individual trees were measured at various times over 20 yr. ? Results: Leaves of female trees averaged 8% longer and 12% greater in area than those of males. Leaves were sexually dimorphic at reproductive maturity. Leaf size declined during the lifetime of most trees. Heritability estimates for leaf length were positive although not statistically significant (h(2) = 0.63, SE = 0.48, P = 0.095). ? Conclusions: We ruled out the ecological causation hypothesis for sexual dimorphism in leaf size because male and female trees co-occurred in the same habitats. Sexual dimorphism appeared not to result from genetic or phenotypic correlations with other traits such as height or flower size. Rather, females appear to compensate for higher costs of reproduction and diminished photosynthetic capacity by producing larger leaves. Additive genetic variance in leaf size, a prerequisite for an evolutionary response to selection for sexual dimorphism, was suggested by positive (although only marginally significant) heritability estimates.     

Productive leaf functional traits of Chinese savanna species

The river valleys in Southwest China are characterized by a dry?Chot climate and relatively rich soils, and host valley-type savannas that are dominated by deciduous species. However, little is known about the ecological adaptations of Chinese savanna plants to the local environments. We hypothesize that Chinese savanna species mainly possess a drought-avoiding strategy by having a deciduous leaf habit and have productive leaf traits. To test this hypothesis, we measured 26 anatomical, morphological, physiological, and chemical traits for 33 woody species from a valley savanna in Southwest China and compared them with the literature data of other dry and wet tropical tree species and a global dataset. We found that Chinese savanna species showed drought avoidance adaptations and exhibited productive leaf traits, such as thin and dense leaves with high ratio of palisade to spongy mesophyll, leaf nutrient concentrations and photosynthetic capacity. Correlations of photosynthetic capacity with N, P, and stomatal conductance across Chinese savanna species were consistent with global patterns reported for seed plants. However, the Chinese savanna species had consistently greater carbon gain at a given specific leaf area, N, P, and stomatal conductance, suggesting higher nutrient- and intrinsic water use efficiencies. These results suggest that paradoxically, Chinese savanna species are adapted to the stressful dry?Chot valley habitat by having productive leaves.     

Leaf expansion,net CO2 uptake,Rubisco activity,and efficiency of long-term biomass gain for the common desert subshrub Encelia farinosa

Encelia farinosa is one of the most abundant and highly studied species of the Sonoran Desert, yet characteristics of its leaf development and long-term photosynthetic capacity are relatively unknown. The net CO₂ uptake rate and the Rubisco activity per unit leaf area for E. farinosa in a glasshouse increased in parallel for about 18 days after leaf emergence (leaf area was then 5 cm²), after which both were constant, suggesting that Rubisco levels controlled net CO₂ uptake. Instantaneous net CO₂ uptake rates at noon for well-watered E. farinosa in the glasshouse at different temperatures and light levels correctly predicted differences in daily net CO₂ uptake at four seasonally diverse times for transplanted plants under irrigated conditions in the field but overpredicted the daily means by 13%. After this correction, seasonally adjusted net CO₂ uptake per unit leaf area multiplied by the estimated monthly leaf area predicted that 42% of the net carbon gain was incorporated into plant dry weight over a 17-month period. The ecological success of E. farinosa apparently reflects an inherently high daily net CO₂ uptake and retention of a substantial fraction of its leaf carbon gain.     

Sex-specific physiological, allocation and growth responses to water availability in the subdioecious plant Honckenya peploides

The gender of dimorphic plant species is often affected by ecophysiological variables. Differences have been interpreted as a response of the sexes to meet specific resource demands associated with reproduction. This study investigated whether sex‐specific variations in ecophysiological traits in response to water availability determine the performance of each sex in different habitats, and therefore promote extreme spatial segregation of the sexes in the subdioecious plant, Honckenya peploides. Twenty‐seven plants of each sex were individually potted in dune sand and assigned randomly to one of three water treatments. Well‐watered plants were watered daily to field capacity, whereas plants in the moderate and high‐water stress treatments received 40% and 20%, respectively, of the water given to well‐watered plants. Photochemical efficiency, leaf spectral properties and components of relative growth rate (leaf area ratio and net assimilation rate) were measured. Photochemical efficiencies integrated over time were higher in male than in female plants. Water deficit decreased maximum quantum yield in female plants more rapidly than in male plants, but female plants (unlike male plants) had recovered to initial values by the end of the experiment. Maximum quantum yield in male plants was more affected by water stress than in female plants, indicating that male plants were more susceptible to photoinhibition. The two sexes did not differ in growth rate, but male plants invested a higher proportion of their biomass in leaves, had a higher leaf area per unit biomass and lower net assimilation rate relative to female plants. Female plants had a higher water content and succulence than male plants. Differences in stomatal density between the sexes depended on water availability. The results suggest that the two sexes of H. peploides have different strategies for coping with water stress. The study also provides evidence of sex differences in allocation traits. We conclude that between‐sex differences in ecophysiological and allocation traits may contribute to explain habitat‐related between‐sex differences in performance and, therefore, the spatial segregation of the sexes.