Leaf dynamics and insect herbivory in a Eucalyptus camaldulensis forest under moisture stress

Abstract The influence of soil moisture content on leaf dynamics and insect herbivory was examined between September 1991 and March 1992 in a river red gum (Eucalyptus camaldulensis) forest in southern central New South Wales. Long-term observations of leaves were made in trees standing either within intermittently flooded waterways or at an average of 37. 5m from the edge of the waterways. The mean soil moisture content was significantly (P≤0.05) greater in the waterways than in the non-flooded areas. Trees in the higher soil moisture regime produced significantly larger basal area increments and increased canopy leaf area. This increase in canopy leaf area was achieved, in part, through a significant increase in leaf longevity and mean leaf size. Although a greater number of leaves was initiated and abscissed per shoot from the non-flooded trees, more leaves were collected from litter traps beneath the denser canopies of the flooded trees. Consumption of foliage by insects on the trees subjected to flooding compared to the non-flooded trees was not significantly different. However, the relative impact of insect herbivory was significantly greater on the non-flooded trees. Leaf chewing was the most common form of damage by insects, particularly Chryso-melidae and Curculionidae. No species was present in outbreak during this study. Leaf survival decreased as the per cent area eaten per leaf increased. In addition, irrespective of the level of herbivory, leaf abscission tended to be higher in E. camaldulensis under moisture deficit. The influence of soil moisture content on the balance between river red gum growth and insect herbivory is discussed.     

Contrasting foliar responses to drought in Quercus ilex and Phillyrea latifolia

Leaf morphology, longevity, and demography were examined in Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (northeast Spain). Four plots (10 × 15 m) of this forest were submitted to an experimental drought during three years (soil moisture was reduced about 15 %). Leaf area, thickness and leaf mass per area ratio (LMA) were measured in sun and shade leaves of both species. Leaf longevity, the mean number of current-year shoots produced per previous-year shoot (Sn/Sn-1), the mean number of current-year leaves per previous-year shoot (Ln/Sn-1), and the percentage of previous-year shoots that developed new ones were measured once a year, just after leaf flushing. LMA and leaf thickness increased since leaf unfolding except in summer periods, when stomatal closure imposed low photosynthetic rates and leaves consumed their reserves. LMA, leaf area, and leaf thickness were higher in Q. ilex than in P. latifolia, but leaf density was higher in the latter species. Drought reduced the leaf thickness and the LMA of both species ca. 2.5 %. Drought also increased leaf shedding up to ca. 20 % in Phillyrea latifolia and decreased it up to ca. 20 % in Q. ilex. In the later species, Sn/Sn-1 decreased by 32 %, Ln/Sn-1 by 41 %, percentage of shoots developed new ones by 26 %, and leaf area by 17 %. Thus the decrease of leaf number and area was stronger in the less drought-resistant Q. ilex, which, under increasingly drier conditions, might lose its current competitive advantage in these Mediterranean holm oak forests.     

Leaf life spans in wild perennial herbaceous plants: a survey and attempts at a functional interpretation

Summary Leaf longevity in 29 herbaceous plant species of Central Europe was studied by inspecting tagged leaves at weekly intervals. About half of the species are elements of the lowland meadow flora, the other half comprises a representative sample of species from the highest sites where vascular plants grow in the Alps. Shaded and water-stressed sites were avoided. Overall mean leaf longevity did not differ significantly between sites and amounted to 71±5 days at low and 68±4 days at high altitude. Leaf life spans ranged (with no clear altitudinal trend) from 41 to 95 days. Low-altitude forbs and grasses produced several leaf cohorts during their growth period, while most alpine species produced only one. Correlations were found between leaf duration and percent nitrogen content and carbon-cost/carbon-gain ratios, but not with leaf dry mass per unit leaf area and photosynthetic capacity alone. As leaf life spans increase, more C tends to be invested per unit CO₂ uptake and less N is invested per unit invested C. Thus, mass relationships rather than area relationships seem to be linked to leaf life span in these species, suggesting that leaf duration is associated with properties other than the efficiency of light utilization (e.g. mechanical strength, herbivory or pathogen resistance). It seems that the explanations of leaf duration that have been developed for evergreen/deciduous plants and for plants along steep light gradients do not apply to the variable life spans in leaves of perennial herbaceous plants of open habitats.     

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。     

Variability in leaf optical properties among 26 species from a broad range of habitats

Leaves from 26 species with growth forms from annual herbs to trees were collected from open, intermediate, and shaded understory habitats in Mississippi and Kansas, USA. Leaf optical properties including reflectance, transmittance, and absorptance in visible and near infrared (NIR) wavelengths were measured along with leaf thickness and specific leaf mass (SLM). These leaf properties and internal light scattering have been reported to vary with light availability in studies that have focused on a limited number of species. Our objective was to determine whether these patterns in leaf optics and light availability were consistent when a greater number of species were evaluated. Leaf thickness and SLM varied by tenfold among species sampled, but within-habitat variance was high. Although there was a strong trend toward thicker leaves in open habitats, only SLM was significantly greater in open vs. understory habitats. In contrast, leaf optical properties were strikingly similar among habitats. Reflectance and reflectance/transmittance in the NIR were used to estimate internal light scattering and there were strong relationships (r1 > 0.65) between these optical properties and leaf thickness. We concluded that leaf thickness, which did not vary consistently among habitats, was the best predictor of NIR reflectance and internal light scattering. However, because carbon allocation to leaves was lower in understory species (low SLM) yet gross optical properties were similar among all habitats, the energy investment by shade leaves required to achieve optical equivalence with sun leaves was lower. Differences in leaf longevity and growth form within a habitat may help explain the lack of consistent patterns in leaf optics as the number of species sampled increases.     

Is N‐resorption efficiency related to secondary compounds and leaf longevity in coexisting plant species of the arid Patagonian Monte,Argentina?

Leaf longevity and nutrient resorption efficiency are important strategies to conserve plant nutrients. Theory suggests a negative relationship between them and also proposes that high concentration of phenolics in long‐lived leaves may reduce nutrient resorption. In order to provide new evidence on these relationships, we explored whether N‐resorption efficiency is related to leaf longevity, secondary compounds and other leaf traits in coexisting plant species of different life forms in the arid Patagonian Monte, Argentina. We assessed N‐resorption efficiency, green leaf traits (leaf mass per area (LMA), leaf longevity and lignin, total soluble phenolics and N concentrations) and N concentration in senescent leaves of 12 species of different life forms (evergreen shrubs, deciduous shrubs and perennial grasses) with contrasting leaf traits. We found that leaf longevity was positively correlated to LMA and lignin, and negatively correlated to N concentration in green leaves. N concentrations both in green and senescent leaves were positively related. N‐resorption efficiency was not associated with the concentration of secondary compounds (total soluble phenolics and lignin) but it was negatively related to LMA and leaf longevity and positively related to N concentration in green leaves. Furthermore, leaf traits overlapped among life forms highlighting that life forms are not a good indicator of the functional properties (at least in relation to nutrient conservation) of species. In conclusion, our findings indicated that differences in N‐resorption efficiency among coexisting species were more related to N concentration in green leaves, leaf lifespan and LMA than to the presence of secondary compounds at least those assessed in our study (soluble phenolics and lignin). Accordingly, N‐resorption efficiency seems to be modulated, at least in part, by the productivity–persistence trade‐off.     

Variations of leaf longevity in tropical moist forests predicted by a trait‐driven carbon optimality model

Leaf longevity (LL) varies more than 20‐fold in tropical evergreen forests, but it remains unclear how to capture these variations using predictive models. Current theories of LL that are based on carbon optimisation principles are challenging to quantitatively assess because of uncertainty across species in the ‘ageing rate:’ the rate at which leaf photosynthetic capacity declines with age. Here, we present a meta‐analysis of 49 species across temperate and tropical biomes, demonstrating that the ageing rate of photosynthetic capacity is positively correlated with the mass‐based carboxylation rate of mature leaves. We assess an improved trait‐driven carbon optimality model with in situLL data for 105 species in two Panamanian forests. We show that our model explains over 40% of the cross‐species variation in LL under contrasting light environment. Collectively, our results reveal how variation in LL emerges from carbon optimisation constrained by both leaf structural traits and abiotic environment.     

Plant diversity patterns in semi-natural grasslands along an elevational gradient in southern Norway

Leaf demography and growth of six common, co-occurring woody plant species that varied in stature (tree vs. shrub) and leaf texture (sclerophyllous, coriaceous, malacophyllous) were examined in a subtropical savanna parkland in southern Texas, USA. We tested the hypotheses that, (a) leaves of plants with evergreen canopies would have longer life spans than those of deciduous species; (b) supplementation of soil moisture would decrease leaf life span in both evergreen and deciduous species; (c) species responses to increased soil moisture availability would be inversely related to leaf longevity; and (d) deciduous growth forms would exhibit a greater growth response to increased soil moisture availability than their evergreen counterparts.A variety of seasonal leaf habits (evergreen, winter-deciduous and summer-deciduous canopies) and leaf life spans (median = 66 to 283 days) were represented by the targeted species, but there was no clear relationship between seasonal leaf habit and leaf longevity. Among species with evergreen canopies, median leaf longevity ranged from short (Zanthoxylum fagara = 116 days; Condalia hookeri = 158 days) to long (Berberis trifoliolata = 283 days) but did not exceed 1 yr. In fact, leaf longevity in evergreen shrubs was often comparable to, or shorter than, that of species with deciduous canopies (Ziziphus obtusifolia = 66 days; Diospyros texana = 119 days; Prosopis glandulosa = 207 days). Augmentation of surface soil moisture had no detectable effect on median leaf life span in any species and there was no clear relationship between leaf longevity and species growth responses to irrigation. Contrary to expectations, species with evergreen canopies responded to irrigation by producing more leaf biomass, longer shoots and more leaf cohorts/year than did deciduous species.Species differences in the annual cycle of leaf initiation, leaf longevity and canopy development, combined with contrasts in root distributions and a highly variable climate, may allow for spatial and temporal partitioning of resources and hence, woody species coexistence and diversity in this system. However, the lack of expected relationships between leaf longevity, leaf habit and plant responses to resource enhancement suggests that structure-function relationships and functional groupings developed in strongly seasonal environments cannot be applied with confidence to these subtropical savannas and thorn woodlands.     

Leaf‐IT: An Android application for measuring leaf area

The use of plant functional traits has become increasingly popular in ecological studies because plant functional traits help to understand key ecological processes in plant species and communities. This also includes changes in diversity, inter‐ and intraspecific interactions, and relationships of species at different spatiotemporal scales. Leaf traits are among the most important traits as they describe key dimensions of a plant's life history strategy. Further, leaf area is a key parameter with relevance for other traits such as specific leaf area, which in turn correlates with leaf chemical composition, photosynthetic rate, leaf longevity, and carbon investment. Measuring leaf area usually involves the use of scanners and commercial software and can be difficult under field conditions. We present Leaf‐IT, a new smartphone application for measuring leaf area and other trait‐related areas. Leaf‐IT is free, designed for scientific purposes, and runs on Android 4 or higher. We tested the precision and accuracy using objects with standardized area and compared the area measurements of real leaves with the well‐established, commercial software WinFOLIA using the Altman–Bland method. Area measurements of standardized objects show that Leaf‐IT measures area with high accuracy and precision. Area measurements with Leaf‐IT of real leaves are comparable to those of WinFOLIA. Leaf‐IT is an easy‐to‐use application running on a wide range of smartphones. That increases the portability and use of Leaf‐IT and makes it possible to measure leaf area under field conditions typical for remote locations. Its high accuracy and precision are similar to WinFOLIA. Currently, its main limitation is margin detection of damaged leaves or complex leaf morphologies.     

Mistletoe host-resemblance: A study of herbivory,nitrogen and moisture in two Australian mistletoes and their host trees

Abstract For 150 years mistletoe host-resemblance has been an unsolved puzzle. Mimicry, camouflage, host protection and shape modification by the host tree have all been advanced as possible solutions. No extended examination of herbivory of host-parasite pairs has ever been done, however, to put these explanations to the test. The study was carried out in northeastern Australia from March to July 1994. Rates of leaf herbivory were estimated for seven individuals of Amyema biniflora Barlow (a cryptic mistletoe species), Dendrophthoe glabrescens (Blakely) Barlow (a non-cryptic mistletoe species) and their host trees (Eucalyptus tessellaris F. Muell. and Eucalyptus platyphylla F. Muell., respectively). In addition three measures of leaf palatability–nitrogen content, moisture content and toughness–were also assessed. Variability in mistletoe leaf shape was quantified by measuring the leaf widths of mistletoes on a variety of host tree species. Mistletoes sustained greater levels of herbivory compared to their host trees, but herbivory did not differ between mistletoe species. The non-cryptic mistletoe had lower levels of nitrogen compared to its host tree, but there was no difference in nitrogen levels between the cryptic mistletoe and its host. The moisture content of mistletoe leaves was greater than that of their hosts but not between mistletoe or host species. The mistletoe species had tougher leaves than their host trees. Leaf shape was different for one species of mistletoe growing on different host trees, but constant for another species of mistletoe. The results contradict, in some crucial aspect, all of the mimicry hypotheses currently on offer.     

Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70).     

Shoot growth phenology of co-existing evergreen and deciduous species in an oak forest

Shoot growth phenology was compared for the saplings of evergreen and deciduous woody species sharing the same microsite. Growth initiation occurred earlier in evergreens (among co-stratal species) while deciduous species completed their growth earlier. Shoot growth rate was significantly greater (P<0.01) for deciduous trees than evergreen trees. The amount of shoot elongations and shoot diameter was also significantly greater (P<0.01) for deciduous trees than evergreens. On the other hand, among shrubs the amount of shoot elongation and shoot diameter was greater for evergreens but the rate of elongation and diameter was more or less similar for both. The duration of shoot elongation and shoot diameter was significantly longer in evergreens than the deciduous species. Leaf packing (number of leaves per shoot) was significantly more dense in evergreen trees (P<0.01) than in deciduous tree species. Leaf packing was more dense in evergreen than deciduous shrubs but the difference was not significant. Leaf area (per individual leaf) at full expansion was significantly greater (P<0.01) in deciduous species. Leaf dry mass and specific leaf mass in the initial stage was significantly greater for evergreen species than for deciduous species. The number of buds/10 cm of shoot was higher in evergreens. However, the per cent mortality was also higher in them.     

Variation in leaf longevity of Pistacia lentiscus and its relationship to sex and drought stress inferred from leaf δ13C

1. Leaf formation, loss, retention, longevity and biomass on male branches of the evergreen mediterranean shrub Pistacia lentiscus , L. correlated strongly with water-use efficiency inferred from leaf δ¹³C across a gradient of precipitation on the island of Mallorca, Spain.
2. The correlations suggest that the leaf phenology is under control of drought-induced constraints on the carbon balance.
3. In fruiting female branches, the correlations between the inferred water-use efficiency and number of formed and retained leaves, leaf biomass and leaf longevity were non-significant. Leaf formation was strongly reduced by fruiting and the females compensated the reduced photosynthetic capacity by retaining older leaves for a longer time than male plants.
4. It is suggested that leaf longevity in females is under strong control of resource allocation to fruit formation which is 'overlaid' on the drought-induced carbon stress, which led to the observed longer leaf longevity in females than in males.     

Effect of leaf litter characteristics on leaf conditioning and on consumption by Gammarus pulex

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Differences in the structure, growth and survival of Parasenecio yatabei ramets with contrasting water relations on the slope of a stream bank

Parasenecio yatabei (Asteraceae), a summer-green perennial herb, is widely distributed on sloping mountain stream banks in cool-temperate zone forests of Japan. We investigated the growth pattern, leaf longevity and leaf water relations of vegetatively independent plants (ramets) growing in two contrasting soil water conditions, that is, upper and lower stream banks (U ramets and L ramets, respectively). The objective of the present study was to clarify the physiological and morphological responses of the ramets to soil water conditions. Dry matter allocation to subterranean parts was higher in U ramets than in L ramets. The U ramet leaves survived for approximately 2 months longer than L ramet leaves. The ratio of subterranean part to aerial part dry matter was greater in U ramets than L ramets. Leaf mass per leaf area (LMA) tended to be greater in U ramets than L ramets throughout the growing season. The leaf bulk modulus of elasticity at full hydration was significantly higher in U ramets. Thus, ramet growth patterns and morphological traits varied with changing soil water conditions. The greater longevity of U ramet leaves may play a role in compensating for the reduced annual net carbon gain caused by lower photosynthetic activity. U ramets growing in environments with less water availability achieved high water-use efficiency by a high passive water absorption capacity via a progressed root system and high productivity via longer leaf longevity with higher LMA and elasticity. Therefore, P. yatabei growing along mountain streams could have the ability to colonize the upper bank through higher survivorship based on these traits.     

Leaf Longevity,Construction, and Maintenance Costs of Three Mangrove Species Under Field Conditions

This study assessed the effect of leaf age on construction cost (CC) in the mangrove species Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle growing in their natural habitat. Leaf osmolality values were species-specific, the highest in A. germinans (1 693 mmol kg^–1) and the lowest in L. racemosa (1 270 mmol kg^–1). In the three species, contents of chlorophyll (a+b) (Chl_a+b) and nitrogen (N) per unit of leaf area were maximal in adult leaves and tended to decline with age. Leaf mass to leaf area ratio (LMA) and ash content increased during leaf ageing. Similarly, as leaves aged, a significant increase in leaf construction cost per leaf area (CC_a) was observed, while per leaf mass (CC_m) it remained almost constant, suggesting a sustained production of leaf compounds as leaves became older. CC was positively correlated with LMA and heat of combustion (Hc) per leaf area, suggesting differences among species in the quantity and composition of expensive compounds. Leaf half lifetime (t_0.5) showed contrasting values in the three mangrove species (60, 111, and 160 d in L. racemosa, R. mangle, and A. germinans, respectively). Overall, L. racemosa was the species with less expensive leaves to construct while leaves of A. germinans and R. mangle had the highest CC_m and CC_a, respectively. Leaf longevity was positively correlated with the ratio between CC and maximum photosynthetic rate (P _max), clearly showing the existence of a balance between leaf costs and benefits.     

The phenology of leaf quality and its within‐canopy variation is essential for accurate modeling of photosynthesis in tropical evergreen forests

Leaf quantity (i.e., canopy leaf area index, LAI), quality (i.e., per‐area photosynthetic capacity), and longevity all influence the photosynthetic seasonality of tropical evergreen forests. However, these components of tropical leaf phenology are poorly represented in most terrestrial biosphere models (TBMs). Here, we explored alternative options for the representation of leaf phenology effects in TBMs that employ the Farquahar, von Caemmerer & Berry (FvCB) representation of CO₂ assimilation. We developed a two‐fraction leaf (sun and shade), two‐layer canopy (upper and lower) photosynthesis model to evaluate different modeling approaches and assessed three components of phenological variations (i.e., leaf quantity, quality, and within‐canopy variation in leaf longevity). Our model was driven by the prescribed seasonality of leaf quantity and quality derived from ground‐based measurements within an Amazonian evergreen forest. Modeled photosynthetic seasonality was not sensitive to leaf quantity, but was highly sensitive to leaf quality and its vertical distribution within the canopy, with markedly more sensitivity to upper canopy leaf quality. This is because light absorption in tropical canopies is near maximal for the entire year, implying that seasonal changes in LAI have little impact on total canopy light absorption; and because leaf quality has a greater effect on photosynthesis of sunlit leaves than light limited, shade leaves and sunlit foliage are more abundant in the upper canopy. Our two‐fraction leaf, two‐layer canopy model, which accounted for all three phenological components, was able to simulate photosynthetic seasonality, explaining ~90% of the average seasonal variation in eddy covariance‐derived CO₂ assimilation. This work identifies a parsimonious approach for representing tropical evergreen forest photosynthetic seasonality in TBMs that utilize the FvCB model of CO₂ assimilation and highlights the importance of incorporating more realistic phenological mechanisms in models that seek to improve the projection of future carbon dynamics in tropical evergreen forests.     

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.     

Leaf economics and hydraulic traits are decoupled in five species‐rich tropical‐subtropical forests

Leaf economics and hydraulic traits are critical to leaf photosynthesis, yet it is debated whether these two sets of traits vary in a fully coordinated manner or there is room for independent variation. Here, we tested the relationship between leaf economics traits, including leaf nitrogen concentration and leaf dry mass per area, and leaf hydraulic traits including stomatal density and vein density in five tropical‐subtropical forests. Surprisingly, these two suites of traits were statistically decoupled. This decoupling suggests that independent trait dimensions exist within a leaf, with leaf economics dimension corresponding to light capture and tissue longevity, and the hydraulic dimension to water‐use and leaf temperature maintenance. Clearly, leaf economics and hydraulic traits can vary independently, thus allowing for more possible plant trait combinations. Compared with a single trait dimension, multiple trait dimensions may better enable species adaptations to multifarious niche dimensions, promote diverse plant strategies and facilitate species coexistence.     

南京地区落叶栎林木本植物叶物候研究

叶物候参数长期以来被认为与植物的碳获取的最大化有关,能反映物种的资源利用策略。温带地区因为寒冷冬天的限制,延长叶寿命成为一些物种进行生长发育和繁衍的基础。为探讨叶寿命延长的可能途径(早出叶、晚落叶,或两者兼有),该研究以南京地区两个落叶栎(Quercus spp.)林为研究对象,观测了其中木本植物的出叶物候、落叶物候,并分析了它们与叶寿命之间的关系。结果发现:1)不同物种的出叶开始时间相差较大,出叶早的物种早结束出叶过程;2)不同物种的落叶开始时间相差较大,早开始落叶的物种,落叶持续时间较长,落叶结束时间则相对集中。3)相关分析和回归分析都表明,叶寿命与出叶时间和落叶时间显著关联,但早出叶对叶寿命的延长可能更为重要,因为早出叶相对于晚落叶在物种资源利用上比较具有优势。4)不同物种的出叶时间和落叶时间没有显著相关,可能因为出叶过程和落叶过程是由不同的启动因子引起。这说明延长叶寿命不一定同时通过早出叶和晚落叶来达到。