四种不同生活型植物幼苗对喀斯特生境干旱的生理生态适应性

喀斯特石漠化是我国西南喀斯特地区最严重的生态环境问题, 生境干旱是限制该地区植物生长的主要因素之一, 掌握喀斯特植被不同演替阶段不同生活型植物对干旱胁迫的适应策略有助于提高植被恢复的成功率。通过人工模拟4种干旱强度, 测定叶片水势、气体交换、叶绿素荧光、光合色素含量、渗透调节物质浓度、抗氧化酶活性以及生物量, 研究了喀斯特地区4种不同生活型植物幼苗对干旱胁迫的适应策略。这4种植物为常绿灌木火棘(Pyracantha fortuneana)、落叶灌木小果蔷薇(Rosa cymosa)、常绿乔木猴樟(Cinnamomum bodinieri)和落叶乔木圆果化香树(Platycarya longipes)。结果表明: 随着干旱程度的加深, 4种植物幼苗的叶片水势、光合能力、叶绿素含量、生物量增长、叶重比(LMR)、叶面积比(LAR)和比叶面积(SLA)逐渐下降, 而热耗散(NPQ)、类胡萝卜素与叶绿素含量比值、丙二醛含量和根重比(RMR)逐渐上升; 圆果化香树和猴樟的水分利用效率(A_n/g_s)、渗透调节物质浓度和抗氧化酶活性呈先升高后降低的趋势, 而火棘和小果蔷薇的A_n/g_s、脯氨酸含量和超氧化物歧化酶活性呈上升趋势。严重干旱下, 火棘和小果蔷薇幼苗的叶片水势和叶绿素含量下降较少, 具有较高的光合能力和生物量增长, 这主要是由于它们具有较低的SLA和LAR、较高的NPQ和A_n/g_s以及较高的渗透调节能力和抗氧化保护能力。中度干旱下, 猴樟幼苗叶片水势下降很少, LMR和LAR也较高, 脯氨酸含量和抗氧化酶活性非常高。但在严重干旱下, 其叶片水势、LMR、LAR和生物量增长大幅度下降, 最大光化学效率和光合速率也非常低, 渗透调节能力与抗氧化酶活性大幅度下降至正常水平以下。水分好的条件下, 圆果化香树幼苗具有较高的RMR以吸收充足的水分, 具有较高的LAR和叶绿素含量, 保证了生物量的大量积累。然而, 干旱胁迫致使其生物量大幅度下降, 主要是由于LMR、LAR、气体交换和叶绿素含量的大量下降以减少蒸腾面积、水分散失和对光能的吸收。研究结果表明, 火棘、小果蔷薇和猴樟幼苗主要采用耐旱策略, 其中猴樟抗严重干旱的能力较弱; 圆果化香树幼苗对干旱胁迫更为敏感, 主要采取避旱策略。     

Growth analysis of UV-B-irradiated cucumber seedlings as influenced by photosynthetic photon flux source and cultivar

A growth analysis was made of ultraviolet-B (UV-B)-sensitive (Poinsett) and insensitive (Ashley) cultivars of Cucuumis satives L. grown in growth chambers at 600 μmol m⁻² s⁻¹ of photosynthetic photon flux (PPF) provided by red- and far-red-deficient metal halide (MH) or blue- and UV-A-deficient high pressure sodium/deluxe f HPS/DX) lamps. Plants were irradiated 6 h daiiy with 0.2 f-UV-B) or 18.2 C+UV-B) kJ m⁻² day⁻¹ of biologically effective UV-B for 8 or 15 days from time of seeding. In general, plants given supplemental UV-B for 15 days showed lower leaf area ratio (LARs, and higher specific leaf mass (SLM) mean relative growth rate (MRGR) and net assimilation rate (NAR) than that of control plants, but they showed no difference in leaf mass ratio (LMR), Plants grown under HPS/DX lamps vs MH lamps showed higher SLM and NAR. lower LAR and LMR. hut no difference in MRGR. LMR was the only growth parameter affected by cultivar: at 15 days, it was slightly greater in Poinsett than in Ashley. There were no interactive effects of UV-B. PPF source or cultivar on any of the growth parameters determined, indicating that the choice of either HPS/DX or MH lamps should not affect growth response to UV-B radiation. This was true even though leaves of UV-B-irradiated plants grown under HPS/DX lamps have been shown to have greater chlorosis than those grown under MH lamps.     

Leaf traits as indicators of limiting growing conditions for lettuce (Lactuca sativa)

Lettuce growth under unstressed conditions was compared to growth under four limiting conditions, i.e. no phosphorus fertilization (0_P), no nitrogen fertilization (0_N), low light (LR) and water stress (WR) over two different growing periods. We investigated the adaptive changes in terms of the morphological and physiological leaf traits, identifying stress‐specific and ‘stable’ indicators suitable for use in breeding programmes. The plants subjected to the WR treatments had lower leaf expansion and specific leaf area (SLA), as well as lower soil–plant analysis development (SPAD) values, stomatal conductance (POR), water index (WI) and leaf temperature (TIR) compared with plants in the unstressed CONTROL. Low light increased the leaf area (LA), SLA and leaf mass ratio (LMR). The 0_N treatment induced a general reduction in the normalised difference vegetation index (NDVI) values, as well as strong changes in LMR and SLA. In general, 0_P induced less pronounced effects than the other treatments. Principal component analysis indicated that the stable and suitable selection indicators of adaptive changes for low nitrogen and low light conditions were LA, SLA, leaf area per unit total plant mass (LAR), LMR, SPAD and POR, while SPAD, POR, TIR and WI were suitable indicators for drought.     

Chemical and mechanical changes during leaf expansion of four woody species of dry Restinga woodland

Young leaves are preferential targets for herbivores, and plants have developed different strategies to protect them. This study aimed to evaluate different leaf attributes of presumed relevance in protection against herbivory in four woody species (Erythroxylum argentinum, Lithrea brasiliensis, Myrciaria cuspidata, and Myrsine umbellata), growing in a dry restinga woodland in southern Brazil. Evaluation of leaf parameters was made through single-point sampling of leaves (leaf mass per area and leaf contents of nitrogen, carbon, and pigments) at three developmental stages and through time-course sampling of expanding leaves (area and strength). Leaves of M. umbellata showed the highest leaf mass per area (LMA), the largest area, and the longest expansion period. On the other extreme, Myrc. cuspidata had the smallest LMA and leaf size, and the shortest expansion period. Similarly to L. brasiliensis, it displayed red young leaves. None of the species showed delayed-greening, which might be related to the high-irradiance growth conditions. Nitrogen contents reduced with leaf maturity and reached the highest values in the young leaves of E. argentinum and Myrc. cuspidata and the lowest in M. umbellata. Each species seems to present a different set of protective attributes during leaf expansion. Myrciaria cuspidata appears to rely mostly on chemical defences to protect its soft leaves, and anthocyanins might play this role at leaf youth, while M. umbellata seems to invest more on mechanical defences, even at early stages of leaf growth, as well as on a low allocation of nitrogen to the leaves. The other species display intermediate characteristics.     

Leaves of Lianas and Self-Supporting Plants Differ in Mass per Unit Area and in Nitrogen Content

Abstract: The aim of this study was to test the hypothesis that the reduction in supporting tissues in climbers compared to self-supporting plants is also true for their leaves, and that climbers generally require higher leaf nitrogen than self-supporting plants to accomplish fast growth. This hypothesis was tested using paired samples of both growth forms with assessment of leaf area index above the sampled plants (LAI_a) in a tropical rain forest in Gabon. The sampling protocol ensured that within a highly fluctuating low canopy environment, the growth conditions were identical for each pair sampled. The results confirmed the hypothesis. Lianas had significantly lower leaf mass per unit leaf area (LMA) than their supporters. Liana leaves also contained significantly more nitrogen than host tree leaves. The differences in nitrogen concentration between liana and tree leaves reversed for the most shaded sites, when nitrogen was expressed on a leaf area base (N_area). Significant regression between leaf nitrogen and LAI_a was found for the climbers on the shaded sites but not for their supporters. This indicated better acclimation of climbers to prevailing light conditions. Better nitrogen allocation at low LMA, together with lower carbon costs for building supporting tissues, makes lianas highly competitive, especially where high nitrogen availability is assured.     

狭叶红景天幼苗对水分及遮阴的生长及生理生化响应

研究植物对水分和遮阴胁迫的响应及其生理机制对制定合理的栽培管理措施十分必要。以红景天属植物为研究对象,设置土壤含水量分别为田间持水量的80%(过湿水分)、70%(正常水分)、60%(轻度干旱)、40%(中度干旱)、20%(重度干旱)5个水分梯度;设置2个遮阴处理,以全光照(遮阴率为0)为对照、黑色遮阴网遮阴(遮阴率为85%),研究狭叶红景天生长及生理生化指标的变化特征。结果表明:在不同水分处理下,与对照相比,叶绿素含量、茎干重和茎重比(SMR)显著增加(P0.05),株高、总生物量、叶面积、叶干重、叶重比(LMR)、比叶面积(SLA)、叶面积比(LAR)和叶面积根干重比(LARMR)增加,根冠比和根重比(RMR)减少;随着干旱程度加剧,丙二醛(MDA)、脯氨酸(Pro)和可溶性糖(Ss)含量增加,超氧化物歧化酶(SOD)活性总体呈先增加后减小的趋势。在遮阴处理下,株高、SMR、SLA、LAR和LARMR显著增加(P0.05),叶绿素SPAD值和叶面积增加,总生物量、根干重、根冠比和LMR显著减少(P0.05),茎干重和叶干重减少,MDA含量显著增加,Pro含量略有下降,Ss含量减少。在水分胁迫下,狭叶红景天中度干旱时通过增加酶活性抵御伤害,重度干旱超过其阈值,SOD活性下降,植物体受到伤害,Ss可能是主要的渗透调节物质。在遮阴处理下,狭叶红景天通过增加SLA避免遮阴伤害。狭叶红景天在受到环境胁迫时会通过形态改变、调节MDA含量、抗氧化酶活性和渗透调节物质来保证自身正常的生长发育。     

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.     

Photosynthetic acclimation to light in woody and herbaceous species: a comparison of leaf structure, pigment content and chlorophyll fluorescence characteristics measured in the field

Acclimation of foliage photosynthetic properties occurs with varying time kinetics, but structural, chemical and physiological factors controlling the kinetics of acclimation are poorly understood, especially in field environments. We measured chlorophyll fluorescence characteristics, leaf total carotenoid (Car), chlorophyll (Chl) and nitrogen (N) content and leaf dry mass per area (LMA) along vertical light gradients in natural canopies of the herb species, Inula salicina and Centaurea jacea, and tree species, Populus tremula and Tilia cordata, in the middle of the growing season. Presence of stress was assessed on the basis of night measurements of chlorophyll fluorescence. Our aim was to compare the light acclimation of leaf traits, which respond to light availability at long (LMA and N), medium (Chl a/b ratio, Car/Chl ratio) and short time scales (fluorescence characteristics). We found that light acclimation of nitrogen content per unit leaf area (N(area)), chlorophyll content per unit dry mass (Chl(mass)) and Chl/N ratio were related to modifications in LMA. The maximum PSII quantum yield (F(v) /F(m)) increased with increasing growth irradiance in I. salicina and P. tremula but decreased in T. cordata. Leaf growth irradiance, N content and plant species explained the majority of variability in chlorophyll fluorescence characteristics, up to 90% for steady-state fluorescence yield, while the contribution of leaf total carotenoid content was generally not significant. Chlorophyll fluorescence characteristics did not differ strongly between growth forms, but differed among species within a given growth form. These data highlight that foliage acclimation to light is driven by interactions between traits with varying time kinetics.     

Leaf age and season influence the relationships between leaf nitrogen, leaf mass per area and photosynthesis in maple and oak trees

Abstract. Seasonal changes in photosynthesis, leaf nitrogen (N) contents and leaf mass per area (LMA) were observed over three growing seasons in open-grown sun-lit leaves of red maple ( Acer rubrum ), sugar maple ( A. sacchamm ) and northern pin oak ( Quereus ellipsoidalis ) trees in southern Wisconsin. Net photosynthesis and leaf N were highly linearly correlated on both mass and area bases within all species from late spring until leaf senescence in fall. Very early in the growing season leaves had high N concentrations, but low photosynthetic rates per unit leaf N, suggesting that leaves were not fully functionally developed at that time. Leaf N per unit area and LMA had nonparallel seasonal patterns, resulting in differing relationships between leaf N/area and LMA in the "early versus late growing season. As a result of differences in seasonal patterns between leaf N/area and LMA, net photosynthesis/area was higher for a given LMA in the spring than fall, and the overall relationships between these two parameters were poor.     

Changes of Leaf Morphological, Anatomical Structure and Carbon Isotope Ratio with the Height of the Wangtian Tree （Parashorea chinensis） in Xishuangbanna, China

Leaf morphological and anatomical structure and carbon isotope ratio （δ^13C） change with increasing tree height. To determine how tree height affects leaf characteristics, we measured the leaf area, specific leaf mass （ratio of leaf mass to leaf area [LMA]）, thickness of the total leaf, cuticle, epidermis, palisade and sponge mesophyll, stomata traits and δ^13C at different heights of Parashorea chinensis with methods of light and scanning electron microscopy （SEM） and isotope-ratio mass spectrometry. The correlation and stepwise regression between tree height and leaf structure traits were carried out with SPSS software. The results showed that leaf structures and δ^13C differed significantly along the tree height gradient. The leaf area, thickness of sponge mesophyll and size of stomata decreased with increasing height, whereas the thickness of lamina, palisade mesophyll, epidermis, and cuticle, ratios of palisade to spongy thickness, density of stomata and vascular bundles, LMA and δ^13C increased with tree height. Tree height showed a significant relationship with all leaf indices and the most significant relationship was with epidermis thickness, leaf area, cuticle thickness, δ^13C. The δ^13C value showed a significantly positive relationship with LMA （R = 0.934）. Our results supported the hypothesis that the leaf structures exhibited more xeromorphic characteristics with the increasing gradient of tree height.     

Comparative ecophysiological responses to drought of two shrub and four tree species from karst habitats of southwestern China

Drought stress is one of the most important factors in limiting the survival and growth of plants in the harsh karst habitats of southwestern China, especially at the seedling establishment stage. The ecophysiological response to drought stress of native plants with different growth forms is useful for re-vegetation programs. Two shrub and four tree species were studied, including Pyracantha fortuneana (evergreen shrub), Rosa cymosa (deciduous shrub), Cinnamomum bodinieri (evergreen tree), and other three deciduous trees, Broussonetia papyrifera, Platycarya longipes, and Pteroceltis tatarinowii. The seedlings were randomly assigned to four drought treatments, i.e., well-watered, mild drought stress, moderate drought stress, and severe drought stress. Leaf water relations, gas exchange, chlorophyll fluorescence, and growth of the seedlings were investigated. Under severe drought stress, the two shrubs with low leaf area ratio (LAR) maintained higher water status, higher photosynthetic capacity, and larger percent biomass increase than the most of the trees. The two shrubs also had lower specific leaf area, greater intrinsic water use efficiency, and thermal dissipation than the trees. This suggested that the two shrubs had high tolerance to severe drought and were suitable for re-vegetation in harsh habitats. The evergreen C. bodinieri exhibited higher leaf mass ratio (LMR) and LAR than the deciduous species under mild and moderate stress. However, the low maximum quantum efficiency of PSII photochemistry (F _v/F _m) and net assimilation rate, and the sharp decreases of water potential, LMR, LAR, and biomass under severe stress indicated C. bodinieri’s weak tolerance to severe drought. In response to drought stress, the three deciduous trees revealed sharp reductions of biomass due to the large drought-induced decreases of gas exchange, LAR, and LMR. Under drought conditions, the deciduous trees minimized water loss by stomatal closure and by reducing transpiration leaf area and light harvesting through shedding leaves. This suggested that the three deciduous trees were more sensitive to water availability than the shrubs and used avoidance strategies against drought stress. However, the better growth performance of the deciduous trees than that of the shrubs under favorable conditions suggested that deciduous trees could be suitable for habitats with mild and temporary drought stress.     

Salt effects on functional traits in model and in economically important Lotus species

A common stress on plants is NaCl‐derived soil salinity. Genus Lotus comprises model and economically important species, which have been studied regarding physiological responses to salinity. Leaf area ratio (LAR), root length ratio (RLR) and their components, specific leaf area (SLA) and leaf mass fraction (LMF) and specific root length (SRL) and root mass fraction (RMF) might be affected by high soil salinity. We characterised L. tenuis, L. corniculatus, L. filicaulis, L. creticus, L. burtii and L. japonicus grown under different salt concentrations (0, 50, 100 and 150 mm NaCl) on the basis of SLA, LMF, SRL and RMF using PCA. We also assessed effects of different salt concentrations on LAR and RLR in each species, and explored whether changes in these traits provide fitness benefit. Salinity (150 mm NaCl) increased LAR in L. burtii and L. corniculatus, but not in the remaining species. The highest salt concentration caused a decrease of RLR in L. japonicus Gifu, but not in the remaining species. Changes in LAR and RLR would not be adaptive, according to adaptiveness analysis, with the exception of SLA changes in L. corniculatus. PCA revealed that under favourable conditions plants optimise surfaces for light and nutrient acquisition (SLA and SRL), whereas at higher salt concentrations they favour carbon allocation to leaves and roots (LMF and RMF) in detriment to their surfaces. PCA also showed that L. creticus subjected to saline treatment was distinguished from the remaining Lotus species. We suggest that augmented carbon partitioning to leaves and roots could constitute a salt‐alleviating mechanism through toxic ion dilution.     

A Comparison of Photosynthesis in Endangered and Non-Endangered Plants Changium smyrnioides and Anthriscus sylvestris

Changium smyrnioides Wolff. and Anthriscus sylvestris (L.) Hoffm. have similar photosynthetic characters; they use radiant energy in winter and early spring effectively, but cannot take full advantage of higher irradiance after spring. The specific leaf area (SLA), leaf area ratio (LAR), and leaf mass ratio (LMR) of C. smyrnioides were lower than those of A. sylvestris. The photosynthetic period of C smyrnioides was about 160 d shorter than that of A. sylvestris, causing the total photosynthetic production of C. smyrnioides to be lower than that of A. sylvestris. Hence if C. smyrnioides is disturbed, it could not recover within a short period.     

Long-term drought modifies the fundamental relationships between light exposure, leaf nitrogen content and photosynthetic capacity in leaves of the lychee tree (Litchi chinensis)

Drought has dramatic negative effects on plants' growth and crop productivity. Although some of the responses and underlying mechanisms are still poorly understood, there is increasing evidence that drought may have a negative effect on photosynthetic capacity. Biochemical models of leaf photosynthesis coupled with models of radiation transfer have been widely used in ecophysiological studies, and, more recently, in global change modeling. They are based on two fundamental relationships at the scale of the leaf: (i) nitrogen content-light exposure and (ii) photosynthetic capacity-nitrogen content. Although drought is expected to increase in many places across the world, such models are not adapted to drought conditions. More specifically, the effects of drought on the two fundamental relationships are not well documented. The objective of our study was to investigate the effects of a long-term drought imposed slowly on the nitrogen content and photosynthetic capacity of leaves similarly exposed to light, from 3-year-old lychee trees cv. Kwa? Mi. Leaf nitrogen and non-structural carbohydrate concentrations were measured along with gas exchanges and the light-saturated rate of photosynthetic electron transport (J(max)) after a 5.5-month-long period of drought. Leaf nitrogen content on a mass basis remained stable, while the leaf mass-to-area ratio (LMA) increased with increasing water stress. Consequently, the leaf nitrogen content on an area basis (N(a)) increased in a non-linear fashion. The starch content decreased, while the soluble sugar content increased. Stomata closed and net assimilation decreased to zero, while J(max) and the ratio J(max)/N(a) decreased with increasing water stress. The drought-associated decrease in photosynthetic capacity can be attributed to downregulation of photosynthetic electron transport and to reallocation of leaf nitrogen content. It is concluded that modeling photosynthesis in drought conditions will require, first, the modeling of the effect of drought on LMA and J(max).     

Examining variation in the leaf mass per area of dominant species across two contrasting tropical gradients in light of community assembly

Understanding variation in key functional traits across gradients in high diversity systems and the ecology of community changes along gradients in these systems is crucial in light of conservation and climate change. We examined inter‐ and intraspecific variation in leaf mass per area (LMA) of sun and shade leaves along a 3330‐m elevation gradient in Peru, and in sun leaves across a forest–savanna vegetation gradient in Brazil. We also compared LMA variance ratios (T‐statistics metrics) to null models to explore internal (i.e., abiotic) and environmental filtering on community structure along the gradients. Community‐weighted LMA increased with decreasing forest cover in Brazil, likely due to increased light availability and water stress, and increased with elevation in Peru, consistent with the leaf economic spectrum strategy expected in colder, less productive environments. A very high species turnover was observed along both environmental gradients, and consequently, the first source of variation in LMA was species turnover. Variation in LMA at the genus or family levels was greater in Peru than in Brazil. Using dominant trees to examine possible filters on community assembly, we found that in Brazil, internal filtering was strongest in the forest, while environmental filtering was observed in the dry savanna. In Peru, internal filtering was observed along 80% of the gradient, perhaps due to variation in taxa or interspecific competition. Environmental filtering was observed at cloud zone edges and in lowlands, possibly due to water and nutrient availability, respectively. These results related to variation in LMA indicate that biodiversity in species rich tropical assemblages may be structured by differential niche‐based processes. In the future, specific mechanisms generating these patterns of variation in leaf functional traits across tropical environmental gradients should be explored.     

Effects of Manganese in Solution Culture on the Growth of Five Deciduous Broad-Leaved Tree Species with Different Successional Characters from Northern Japan

The effects of four manganese (Mn) concentrations (1, 10, 50, and 100 g m^-3 = Mn₁, Mn₁₀, Mn₅₀, Mn₁₀₀) in solution culture on growth variables were studied for seedlings of five deciduous broad-leaved trees with different successional characteristics and shoot development patterns in northern Japan. The five species were: Betula ermanii, Betula platyphylla var. japonica, and Alnus hirsuta (early-successional species with continuous leaf development), Ulmus davidiana var. japonica (mid-successional species with flush and continuous leaf development), and Acer mono (late-successional species with a flush type leaf development). In plants grown in the Mn environment for about 45 d, relative growth rate (RGR) decreased with increasing Mn supply. Between the 1 and 100 g(Mn) m^-3, RGR decreased by 20 % for B. ermanii and B. platyphylla, by 40 % for A. hirsuta and A. mono, and by 80 % for U. davidiana. Specific leaf area (SLA) and leaf mass ratio (LMR) of all species were little affected by high Mn supply. In U. davidiana, however, there was a 67 % decrease in LMR in Mn₁₀₀ plants. Leaf area ratio (LAR) was higher in early-successional species than in mid- and late-successional ones but differed little among Mn treatments within species, except for U. davidiana where LAR declined substantially with increased Mn supply. While LAR, which represents the relative size of assimilatory apparatus, was little affected, net photosynthetic rate (P_N) saturated with radiant energy decreased with increasing Mn supply in all species. Thus P_N was adversely affected by high accumulation of Mn in leaves, which resulted in an overall reduction in biomass production. However, the proportional allocation of photosynthates to the assimilatory apparatus was not affected by different Mn toxicity in hardwood tree seedlings. This revised version was published online in September 2006 with corrections to the Cover Date.     

Are correlations among foliar traits in ferns consistent with those in the seed plants?

Broad-based studies of gymnosperms and angiosperms reveal consistent and functionally significant correlations among foliar traits such as leaf mass per area (LMA), maximum photosynthetic rate (A(area)), foliar nitrogen (N(area)), foliar chlorophyll (Chl) and leaf longevity. To assess the generality of these relationships, we studied 20 fern species growing in the understorey of a temperate deciduous forest. We found that foliar N(area) increases with LMA, and that foliar N(area) and A(area) are positively correlated with one another, as are foliar N(area) and Chl. The ferns in general have very low LMA compared with most seed plants; A(area), N(area) and Chl are below median values for seed plants but are not extreme. Species with overwintering fronds have significantly higher LMA than species with fronds that senesce at the end of the growing season, as well as a significantly higher C : N ratio in frond tissue and relatively high foliar N on an areal basis. Correlations among foliar traits associated with gas exchange in these forest understorey ferns are in accordance with patterns reported for seed plants, suggesting a high degree of functional constraint on the interrelationships among key elements in foliar design.     

Changes in the chlorophyll and carotenoid contents in the leaves of steppe plants along a latitudinal gradient in South Ural

We studied the content of chlorophylls and carotenoids in the leaves of steppe plants of South Ural growing along a latitudinal gradient from southern steppe to forest-steppe. The content of chlorophylls (a + b) was 5–6 mg per 1 g of the leaf dry weight and did not depend on the latitude, whereas the content of carotenoids in the leaves increased northward from 1.0 to 1.5 mg/g dry wt. At the same time, the greatest changes occurred in the ratios between the forms of pigments: the chlorophyll a/b ratio increased from 1.8 to 2.8, and the chlorophyll/carotenoid ratio decreased from 5.6 to 3.5. The obtained results indicate that adaptation of the pigment apparatus of steppe plants growing along the latitudinal gradient occurs due to the transformation of the light-harvesting complex.     

Optimisation of spatial allocation patterns in lianas compared to trees used for support

There are only limited possibilities to study the competition between trees and lianas in the top canopy of tropical rain forests. Furthermore, the important question how the leaf traits are related to twig support is rarely studied, especially regarding growing space partitioning between the self-supporting and the climbing growth form. Our study used the hot-air balloon within the “Operation Canopee” in the Masoala National Park, Madagascar, to test the differences in spatial allocation patterns of leaves and twigs in lianas and tree parts used for support. The sampling design emphasised to obtain a common assembly of twigs and leaves from both, trees and lianas. The results from the top canopy were compared to the data from the understorey regarding biomass and nutrients in leaves and distal twigs. In the understorey the reduction in structural investment was much stronger in lianas than in trees. The results showed that lianas reduced carbon investment per volume, but increased leaf nitrogen concentration and leaf area ratio (LAR), the latter driven by a reduction in leaf mass per area (LMA). In the top canopy, lianas contributed about one third of the leaf area density of 3 m² m⁻³. For distal twigs, no relationship was found between twig biomass per volume and leaf area density for trees, but lianas balanced both structural parameters closely. The climbers benefit from the external support provided by the trees and optimise the area of assimilation tissue at low per volume investment for mechanical stability. Several traits such as low LMA and high leaf nitrogen concentrations together with higher LAR and optimised spatial investment advantage the climbing growth form and enable a fast acquisition of growing space. The results emphasize the necessity to consider spatial and structural features of growing space acquisition when dealing with plant competition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Trends in Biomass Fractionation in Wheat and Barley from Wild Ancestors to Modern Cultivars

Abstract: We tested the hypothesis that cultivar selection during the process of domestication in cereal plants led to a change in dry mass allocation, e.g., less root mass and more leaf mass or more leaf area per unit leaf mass. We divided 24 varieties of diploid, tetraploid and hexaploid winter wheat and two-rowed winter barley into three categories of domestication levels (wild species, old landraces and modern cultivars) and compared the patterns of dry matter fractionation at the time of anthesis under standardized outdoor growth conditions. In both cereals, total biomass per individual increased significantly with domestication level but, to our surprise, we found no significant change in dry matter investment between domestication levels: neither the dry mass fraction of leaves increased, nor was there a trend of reduced investment in stems and roots, contrary to what we expected. Specific leaf area (SLA) and leaf area ratio (LAR) of modern wheat and barley cultivars were significantly lower compared to wild varieties. Major differences in both cereals were of a purely morphological nature, namely a decrease in the number of stems and ears from wild species to domesticated varieties, along with more synchronous tiller development and therefore similar tiller size. Fertilizer increased total biomass in all domestication levels in both cereals, but influenced the dry matter fractionation only in barley. Tissue nitrogen concentration was unresponsive to both domestication and fertilization. The expected shift in functional traits, conventionally considered to determine plant growth, was not found. Indeed, dry matter fractionation among the major plant biomass components seems to be very conservative.