A new life table of leaves ofPhaseolus vulgris L. in relation to their position within the canopy and plant density

In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy. The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about 20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about 10 days after emergence. Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival period. For the total foliage, the summed value of accumulated surplus production during the survival period was about five times as large as the summed value of the dry weight of the dead leaves, regardless of planting density. The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production.     

芭蕉芋叶片结构特征及其与抗旱性的关系

运用石蜡切片法和指甲油印迹法,对3个芭蕉芋品种的叶片解剖结构——叶片厚度、叶肉厚度、上表皮厚度、下表皮厚度、气孔密度、气孔长度及宽度、长细胞长度及宽度、短细胞长度及宽度等10项相关指标进行测定,分析芭蕉芋抗旱性与叶片结构之间的关系。结果表明:(1)芭蕉芋的表皮结构与抗旱性有一定的关系,表现为抗旱性强的品种气孔密度大,且长、短细胞体积小、排列紧密。(2)芭蕉芋叶片、叶肉、上下表皮厚度与抗旱性关系在不同品种间差异不显著。(3)芭蕉芋叶肉及上、下表皮占叶片横切面的比例与抗旱性存在显著相关关系。(4)芭蕉芋叶片保水能力与叶肉比例呈极显著负相关关系,与上表皮比例呈极显著正相关关系。     

Responses of four succession tree species in low subtropics to enhanced UV-B radiation in the field

The tested tree species included pioneer species Acacia mangium, early succession stage species Schima superba, mesophyte intermediate-succession species Machilus chinensis, and shade-tolerant plant or late-succession species Cryptocarya concinna which occur in the lower subtropical forest community. A comparison with the current ambient level of UV-B radiation (UV-B) showed the leaf net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) of the four species ranged from significantly decreased to no significant change. Additionally, the thickness of palisade and mesophyll in leaves of four tree species were decreased sharply by enhanced UV-B. The thickness of spongy parenchyma in leaves was also decreased except for M. chinensis. UV-B increased the leaf width of A. mangium but its leaf length, leaf thickness, and dry mass per unit area were not affected. Significantly increased stomata width was observed in A. mangium leaf epidermis in response to UV-B. Significantly decreased stomata width and significantly increased stomata density of leaf abaxial epidermis in M. chinensis were also observed. The stomata density of abaxial epidermis of C. concinna was remarkably increased by enhanced UV-B. The height and branch biomass of A. mangium and the height of S. superba were reduced visibly by enhanced UV-B. The four plant species could be classified into three groups of UV-B sensitiveness by hierarchical cluster analysis. A. mangium was sensitive to enhanced UV-B, while C. concinna showed more tolerance.     

Survival curves and longevity of the leaves of Alnus japonica var. arguta in Kushiro Marsh

The seasonal changes in leaf emergence and leaf-fall in a Japanese alder stand of the fen in Kushiro Marsh were studied, and survival curves for the leaves were drawn. Leaves collected in litter traps were dried and weighed to study the seasonal changes, peaks in mid-August and late September to October suggested a bimodal annual curve. Study of the seasonal changes in the number of emerged and fallen leaves per shoot revealed a third peak about one month before the August peak, showing a trimodal annual curve. First and second leaves had a longevity of about 40 and 50–60 days, respectively. The longevity increased until the fifth leaf. With the sixth and following leaves, longevity decreased. Leaf size increased with leaf rank, with the first leaf being the smallest. The first leaf had only about 10% and the second leaf only 20% of the area of the fifth leaf. On this basis, the early to mid-July peak in number of fallen leaves was composed of first and second leaves which were smaller and short-lived. The early August and September/October peaks were high in both number and mass of fallen leaves. Compared to reports on Japanese alder of other mountainous districts in Hokkaido, the alder trees of Kushiro Marsh had about the same number of leaves per shoot, but had a season of leaf emergence which was about 6 weeks shorter. In addition, the longevity of the longest-lived fifth leaf was about 30–40 days shorter. The short life span of the leaves could be considered as an adaptive strategy of this species to environmental constraints of its habitat.     

罗汉松雌雄株叶形态结构的比较研究

该研究以雌雄异株植物罗汉松(Podocarpus macrophyllus)成熟叶为研究材料,采用光学显微镜、扫描电镜和透射电镜观察比较罗汉松雌、雄植株叶在形态、显微结构和超显微结构的差异,以明确罗汉松雌、雄株在进化过程中叶对环境功能的适应性。结果显示:(1)罗汉松雌株的叶片大于雄株,且两者的叶长、叶宽和叶柄长差异极显著,而叶柄厚、叶面积、叶体积、叶质量、比叶重(SLW)、面积与体积之比(A/V)等性状无显著差异。(2)雌株叶片的气孔相对较大,密度较高,且雌株气孔宽度极显著大于雄株;雌株叶片的上表皮长细胞宽度和下表皮短细胞宽度均显著大于雄株,但雌株叶片的上表皮长细胞和短细胞的长度则显著小于雄株。(3)罗汉松雌株叶片的栅栏组织厚度、海绵组织厚度、传输组织长度和宽度、上下角质层厚度、维管束厚度、叶片紧密度(CTR)及疏松度(SR)均极显著大于雄株,而雌株的下表皮厚度极显著小于雄株,但雌雄株叶片的上表皮细胞厚度和栅海比差异不显著;雌株叶片的栅栏组织细胞、叶绿体和线粒体均较雄株的长而细,且雌株的线粒体宽度极显著小于雄株。(4)罗汉松雌株叶片上表皮蜡质饰纹、下表皮角质层纹饰、气孔外拱盖纹饰及内缘类型等4个微形态特征与雄株差异明显。(5)叶表皮蜡质层能谱分析表明,罗汉松雌株叶片含有9种元素,而雄株叶片仅有8种(缺少K元素);且雌株的Si元素含量高于雄株,而雄株的C、O、Na、Mg、Al、Ca和Au元素含量均高于雌株。研究表明,罗汉松雌、雄植株之间存在明显的第二性征,雌株叶片结构有助于提高光合等性能以满足生殖需求;罗汉松雌、雄株叶形态结构的差异是其长期进化形成的有利于物种繁衍的适应策略。     

Mutual shading and the photosynthetic capacity of exposed leaves of field grown soybeans

Light-saturated photosynthetic rates at air levels of carbon dioxide were measured about weekly in upper canopy leaves of two soybean cultivars grown at stand densities of 40 and 100 plants per square meter. Early in the season, when leaf area indices differed between stand densities, plants of both cultivars grown at high stand density had photosynthetic rates which averaged 23% lower than plants at low stand density. Later in the season, when there were no differences in leaf area index between stand densities, there were no differences in photosynthetic rates in the cultivar Kent, but rate differences of about 14% persisted in the cultivar Williams. In Williams mainstem leaves emerged into full sunlight later in their development at high than at low stand density. In both cultivars the oldest fully exposed leaves were photosynthetically immature for much of the season, as higher rates could be achieved by lower leaves which were shaded in situ. The results identify shading of young developing leaves and photosynthetic immaturity of fully exposed leaves as factors limiting canopy photosynthesis in soybeans, and indicate cultivar differences in how much high stand density reduces photosynthetic capacity.     

Leafing patterns and leaf traits of four evergreen shrubs in the Patagonian Monte, Argentina

We assessed leafing patterns (rate, timing, and duration of leafing) and leaf traits (leaf longevity, leaf mass per area and leaf-chemistry) in four co-occurring evergreen shrubs of the genus Larrea and Chuquiraga (each having two species) in the arid Patagonian Monte of Argentina. We asked whether species with leaves well-defended against water shortage (high LMA, leaf longevity, and lignin concentration, and low N concentration) have lower leaf production, duration of the leafing period, and inter-annual variation of leafing than species with the opposite traits. We observed two distinctive leafing patterns each related to one genus. Chuquiraga species produced new leaves concentrated in a massive short leafing event (5–48 days) while new leaves of Larrea species emerged gradually (128–258 days). Observed leafing patterns were consistent with simultaneous and successive leafing types previously described for woody plants. The peak of leaf production occurred earlier in Chuquiraga species (mid September) than in Larrea species (mid October–late November). Moreover, Chuquiraga species displayed leaves with the longest leaf lifespan, while leaves of Larrea species had the lowest LMA and the highest N and soluble phenolics concentrations. We also observed that only the leaf production of Larrea species increased in humid years. We concluded that co-occurring evergreen species in the Patagonian Monte displayed different leafing patterns, which were associated with some relevant leaf traits acting as plant defenses against water stress and herbivores. Differences in leafing patterns could provide evidence of ecological differentiation among coexisting species of the same life form.     

Water relations,chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence,and contents of saccharides in tree species of a tropical forest in response to flood

We studied the seasonal changes in water relations, chlorophyll a fluorescence, and leaf saccharide contents of the tropical flood-tolerant trees Acosmium nitens, Campsiandra laurifolia, Eschweilera tenuifolia, Symmeria paniculata, and Psidium ovatifolium. Xylem water potential increased with flooding to a larger extent than leaf sap osmotic potential in all the species, and soluble sugars contributed up to 66 % of osmotic potential at maximum flooding. Starch was accumulated in leaves. Maximum quantum yield of photosystem 2 decreased in emerged leaves, values being always higher than 0.76. Daily maximum net photosynthetic rate and leaf conductance decreased in all the species. This reduction was associated in all the species but S. paniculata with the absence of a compensatory increase in non-photochemical quenching.This research was financially supported by CONICIT grant S1-96001345. E. Rengifo was funded by a CONICIT scholarship.     

Leaf dynamics,self-shading and carbon gain in seedlings of a tropical pioneer tree

We examined leaf dynamics and leaf age gradients of photosynthetic capacity and nitrogen concentration in seedlings of the tropical pioneer tree, Heliocarpus appendiculatus, grown in a factorial design under controlled conditions with two levels each of nutrients, ambient light (light levels incident above the canopy), and self-shading (the gradient of light levels from upper to lower leaves on the shoot). Correlations among these parameters were examined in order to determine the influence of self-shading, and the regulation of standing leaf numbers, on leaf longevity and its association with leaf photosynthetic capacity. Leaf longevity and the number of leaves on the main shoot were both reduced in high light, while in the low light environment, they were reduced in the steeper self-shading gradient. In high nutrients, leaf longevity was reduced whereas leaf number increased. Leaf initiation rates were higher in the high nutrient treatment but were not influenced by either light treatment. Maximum-light saturated photosynthetic rate, on an area basis, was greater in the high light and nutrient treatments, while the decline in photosynthetic capacity in realtion to leaf position on the shoot was more rapid in high light and in low nutrients. Leaf longevity was negatively correlated among treatments with initial photosynthetic capacity. The leaf position at which photosynthetic capacity was predicted to reach zero was positively correlated with the number of leaves on the shoot, supporting the hypothesis that leaf numbers are regulated by patterns of self-shading. The negative association of longevity and initial photosynthetic capacity apparently arises from different associations among gradients of photosynthetic capacity, leaf numbers and leaf initiation rates in relation to light and nutrient availability. The simultaneous consideration of age and position of leaves illuminates the role of self-shading as an important factor influencing leaf senescence and canopy structure and dynamics.     

Toward synthesis of relationships among leaf longevity, instantaneous photosynthetic rate, lifetime leaf carbon gain, and the gross primary production of forests

The assimilation of carbon by plant communities (gross primary production [GPP]) is a central concern in plant ecology as well as for our understanding of global climate change. As an alternative to traditional methods involving destructive harvests or time-consuming measurements, we present a simple, general model for GPP as the product of the lifetime carbon gain by a single leaf, the daily leaf production rate, and the length of the favorable period for photosynthesis. To test the model, we estimated leaf lifetime carbon gain for 26 species using the concept of mean labor time for leaves (the part of each day the leaf functions to full capacity), average potential photosynthetic capacity over the leaf lifetime, and functional leaf longevity (leaf longevity discounted for periods within a year wholly unfavorable for photosynthesis). We found that the lifetime carbon gain of leaves was rather constant across species. Moreover, when foliar biomass was regressed against functional leaf longevity, aseasonal and seasonal forests fell on a single line, suggesting that the leaf production rate during favorable periods is not substantially different among forests in the world. The gross production of forest ecosystems then can be predicted to a first approximation simply by the annual duration of the period favorable for photosynthetic activity in any given region.     

Phytochrome effects on leaf growth and chlorophyll content in Petunia axilaris

Abstract Changes in the phytochrome status at the end of the daily photosynthetic period result in several plant responses. To understand the causal relations among these responses it is useful to investigate species or experimental conditions where the most common correlations among responses are broken. A step in this direction is presented here with Petunia axilaris, where FR-treated plants showed low chlorophyll content and erect leaves, but- contrary to other species-higher leaf area and plant dry weight. Differences in area expansion were related to the late phase of leaf growth and were due, at least in part, to larger cells in FR-treated plants. Effects on length/width ratio, specific leaf area, net assimilation rate, shoot/root ratio and leaf number were small or non-existent. It is suggested that the lower chlorophyll content in FR-treated plants was not a consequence of scarcity of assimilates.     

Leaf development and photosynthetic properties of three tropical tree species with delayed greening

Leaf developmental patterns were characterized for three tropical tree species with delayed greening. Changes in the pigment contents, photosynthetic capacity, stomata development, photosystem 2 efficiency, rate of energy dissipation, and the activity of partial protective enzymes were followed in developing leaves in an attempt to elucidate the relative importance of various photoprotective mechanisms during leaf ontogeny. Big leaves of Anthocephalus chinensis, a fast-growing light demanding species, expanded following an exponential pattern, while relatively small leaves of two shade-tolerant species Litsea pierrei and Litsea dilleniifolia followed a sigmoidal pattern. The juvenile leaves of A. chinensis and L. pierrei contained anthocyanin located below the upper epidermis, while L. dilleniifolia did not contain anthocyanin. Leaves of A. chinensis required about 12 d for full leaf expansion (FLE) and photosynthetic development was delayed 4 d, while L. pierrei and L. dilleniifolia required 18 or 25 d for FLE and photosynthetic development was delayed 10 or 15 d, respectively. During the leaf development the increase in maximum net photosynthetic rate was significantly related to changes in stomatal conductance and the leaf maturation period was positively related to the steady-state leaf dry mass per area for the three studied species. Dark respiration rate of leaves at developing stages was greater, and pre-dawn initial photochemical efficiency was lower than that of mature leaves. Young leaves displayed greater energy dissipation than mature leaves, but nevertheless, the diurnal photoinhibition of young L. dilleniifolia leaves was higher than that of mature leaves. The young red leaves of A. chinensis and L. pierrei with high anthocyanin contents and similar diurnal photoinhibition contained more protective enzymes (superoxide dismutase, ascorbate peroxidase) than mature leaves. Consequently, red leaves may have higher antioxidant ability.     

Linking leaf and root trait syndromes among 39 grassland and savannah species

Here, we tested hypothesized relationships among leaf and fine root traits of grass, forb, legume, and woody plant species of a savannah community. CO2 exchange rates, structural traits, chemistry, and longevity were measured in tissues of 39 species grown in long-term monocultures. Across species, respiration rates of leaves and fine roots exhibited a common regression relationship with tissue nitrogen (N) concentration, although legumes had lower rates at comparable N concentrations. Respiration rates and N concentration declined with increasing longevity of leaves and roots. Species rankings of leaf and fine-root N and longevity were correlated, but not specific leaf area and specific root length. The C3 and C4 grasses had lower N concentrations than forbs and legumes, but higher photosynthesis rates across a similar range of leaf N. Despite contrasting photosynthetic pathways and N2-fixing ability among these species, concordance in above- and below-ground traits was evident in comparable rankings in leaf and root longevity, N and respiration rates, which is evidence of a common leaf and root trait syndrome linking traits to effects on plant and ecosystem processes.     

Phenological and growth patterns of the Mediterranean oak Quercus suber L.

The phenology of Quercus suber L., a dominant species of the montados in the Iberian Peninsula, was studied for 2 years in southwest Portugal. The seasonal progression of phenological events was analyzed in seven trees. Selected branches were examined monthly for shoot elongation, leaf number, branching, flowering, and fruiting. Radial stem growth and specific leaf weight were also studied. Active growth was observed from early spring to early summer. Reserves accumulated during winter and high photosynthetic activity in early spring apparently supported this strong development. The growth flush started with stem radial increment, which seemed to be impaired by spring rainfall. Male inflorescence production was the next phenological event. Old leaves were shed during new twig and leaf emergence. Shoot elongation and the number of new leaves produced were well correlated with the previous-year shoot's length, and were not clearly related to climatic factors. Radial growth resumed in autumn at a lower rate than in the previous spring, a possible consequence of a reserve depletion due to lower photosynthetic production in summer and investment on fruit maturation, which was complete by late autumn. Premature and excessive new leaf production were apparently subjected to self-pruning strategies related to the development of each tree's crown. Younger cork-oaks produced shorter and fewer shoots per module, and more sclerophyllous leaves than the older ones. A high intra-specific variability was observed in all the results.     

Seasonal changes in photosynthesis of four understory herbs in deciduous forests

Seasonal patterns of photosynthesis and respiration of single leaves of four understory perennial herbs in deciduous forests were investigated in relation to their leaf growth and light conditions on the forest floor.Anemone flaccida shows rapid growth of leaf area and high rates of gross photosynthesis at light saturation (Psat) in its early stage of development. Its photosynthetic activity is restricted to a brief period of high light intensity before the closure of overstory canopies.Disporum smilacinum possesses light-photosynthesis curves of the shade-leaf type throughout its whole growing period. A shading experiment has shown that this plant is low-light adapted and can utilize weak light efficiently. The light-photosynthesis curve ofSyneilesis palmata shifts from the sun-leaf type to the shade-leaf type in response to the seasonal change of light regime on the forest floor. Evergreen leaves ofPyrola japonica have three year longevity, and light-photosynthesis curves of the shade-leaf type. They maintain some photosynthetic activity even in late autumn and winter.     

枫香变红过程中叶片组织结构、光合特性及色素含量变化研究

枫香(Liquidambar formosana)因其叶片入秋后逐渐变红而极具观赏价值,是优良的景观生态树种。为了解枫香叶片结构变化与叶色的关系,该文通过连续监测枫香叶片变红过程中组织结构、光合特性及色素含量的变化,分析叶片结构与其光合特性和色素的关系。结果表明：(1)叶片变色过程中,表皮细胞均为椭圆形,紧密排列,未观察到明显的细胞变异,表面未附着绒毛和蜡质,且上表皮细胞与栅栏组织细胞间排列紧密,未出现较大的气室。(2)随着叶片逐渐变红,叶片结构变化显著,其中叶片、上表皮、栅栏组织和海绵组织厚度及气孔开度均逐渐减小,而气孔器长和宽、单个气孔器面积则逐渐增大。(3)随着叶片结构的变化,其叶绿素含量逐渐减少,致使净光合速率逐渐减小,在出现光破坏时,叶片通过在栅栏组织细胞液泡内合成花色苷来自我保护,而大量的花色苷致使叶片表面呈现红色。综上认为,叶绿素含量降低,花色素苷大量积累是导致枫香叶片变红的直接原因,而枫香叶色变红则是其一系列生理结构特征综合作用的结果。     

不同类型土壤栽培对苦丁茶树叶片生长和光合特性的影响

研究苦丁茶树叶片生长与光合特性对不同类型土壤栽培的响应特征,确定最适苦丁茶栽培的土壤类型,可为高产优质化的苦丁茶种植业及其规模化生产基地的建立提供科学依据。通过土壤栽培实验研究了不同类型的土壤对苦丁茶树叶片生长、叶片解剖结构、叶绿素含量和光合特性的影响。结果表明:石灰岩土壤栽培条件下,苦丁茶叶长和叶面积比其他6种土壤栽培下的显著提高了34%—57%和43%—68%,叶绿素总量显著增加9%—33%,叶片、上下表皮、海绵组织和栅栏组织的厚度均显著高于其他6种土壤栽培。不同类型土壤栽培下苦丁茶净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和饱和蒸气压亏缺(Vpdl)的日变化趋势均呈单峰型,日均Pn和Tr值大小依次为:石灰岩石英砂岩玄武岩长石石英砂岩第四纪红色黏土变余砂岩煤系砂页岩,其中石灰岩土壤栽培下的日均Pn值相比其他6种土壤下的显著提高了13%—45%,且叶片最大净光合速率、表观量子效率、暗呼吸速率、光补偿点(LCP)和光饱和点(LSP)也最大,而煤系砂页岩栽培时最低,其LSP和LCP较石灰岩栽培的分别显著下降了40%和46%。综上,在7种类型的土壤中,石灰岩土壤栽培最有利于苦丁茶树叶片的生长发育、并促进叶绿素的合成和加强对光能的吸收利用,最终提高其叶片光合能力,其次为玄武岩土壤,而煤系砂页岩土壤是最不利于苦丁茶树叶片生长发育和光合作用。建议在苦丁茶种植业的发展和规模化生产基地建立时因选择由石灰岩性母岩发育的土壤进行栽培,从而提高苦丁茶的产量和品质。     

Differences in response to simulated herbivory between <Emphasis Type="Italic">Quercus crispula</Emphasis> and <Emphasis Type="Italic">Quercus dentata</Emphasis>

To evaluate the responses of Quercus crispula and Quercus dentata to herbivory, their leaves were subjected to simulated herbivory in early spring and examined for the subsequent changes in leaf traits and attacks by chewing herbivores in mid summer. In Quercus crispula, nitrogen content per area was higher in artificially damaged leaves than in control leaves. This species is assumed to increase the photosynthetic rate per area by increasing nitrogen content per area to compensate leaf area loss. In Quercus dentata, nitrogen content per area did not differ between artificially damaged and control leaves, while nitrogen content per mass was slightly lower in artificially damaged leaves. The difference in their responses can be attributable to the difference in the architecture of their leaves and/or the severeness of herbivory. The development of leaf area from early spring to mid summer was larger in artificially damaged leaves than in control leaves in both species, suggesting the compensatory response to leaf area loss. Leaf dry mass per unit area was also larger in artificially damaged leaves in both species, but the adaptive significance of this change is not clear. In spite of such changes in leaf traits, no difference was detected in the degree of damage by chewing herbivores between artificially damaged and controlled leaves in both species.     

冠层高度对毛竹叶片光合生理特性的影响

借助LI-6400便携式光合作用系统,研究了冠层高度对不同林龄毛竹(Phyllostachys pubescens)叶片光合生理特性和水分利用效率(WUE)的季节性影响,为促进毛竹林碳汇能力和生产力提升的林分结构调整等可持续栽培技术提供理论依据。结果表明:(1)出笋期,不同竹龄毛竹叶片净光合速率(Pn)和蒸腾速率(Tr)的日均值呈现出冠层上部小于冠层下部的梯度变化趋势,且2a生毛竹不同冠层Pn日均值大于3a生毛竹;孕笋行鞭期,不同林龄毛竹各时间点Pn值和日均值、以及2年生毛竹各时间点的Tr值均为冠层上部大于冠层下部。各生长季节,不同林龄毛竹个体叶片的气孔导度(Gs)均与Tr的变化趋势一致。(2)2年生毛竹各季节仅冠层上部叶片会出现"光合午休",而3年生毛竹仅于出笋期时各冠层叶片出现"光合午休"现象。(3)出笋期毛竹叶片WUE日均值随着冠层高度增加而增加,这种变化趋势不受竹龄影响;而孕笋行鞭期,仅2年生毛竹叶片WUE日均值随着冠层高度增加而下降。不同冠层高度的孕笋行鞭期毛竹叶片WUE日均值都显著高于出笋期;冠层高度对毛竹叶片气体交换特性和WUE的影响受生长发育关键期的季节因素影响,且毛竹叶片WUE与Gs之间存在负相关关系,其不受毛竹个体年龄和叶片冠层高度影响。(4)不同生长季节各冠层叶绿素a/b值均随着冠层高度下降而降低,不同林龄毛竹叶片叶绿素含量基本随着冠层自上而下呈逐渐增加的趋势。各生长季节,不同林龄个体叶片氮素含量、比叶重随冠层高度垂直变化趋势与叶片Pn日均值的垂直变化趋势一致。研究认为,毛竹不同冠层部位叶片通过改变形态、氮素含量来适应不同生长季节生长环境的变化,以便充分利用光能提高光合能力。     

Herbivory pattern and induced responses to simulated herbivory inQuercus mongolica var.grosseserrata

Seasonal changes in leaf traits and the herbivory pattern ofQuercus mongolica var.grosseserrata were studied, and simulated herbivory experiments were carried out in order to evaluate leaf trait responses. Leaves ofQ. mongolica emerged simultaneously in spring and most were retained until autumn. Nitrogen concentration was highest when leaves first emerged and decreased rapidly with leaf age. Leaf mass per area (LMA) increased with leaf age. Herbivore attack was concentrated in the first 20 days after bud-break, which corresponded to the high nutritional value of the leaves for herbivores at this time. Simulated herbivory experiments indicated that LMA increased with artificial leaf damage, suggesting an increase in leaf toughness, and that nitrogen concentration decreased later in the season in comparison with intact leaves. As a result, herbivore attack following artificial leaf damage decreased with increasing initial leaf damage. However, leaf longevity was not affected by initial leaf damage. These responses were considered to be a strategy to disperse herbivory damage among leaves.