Application of leaf size and leafing intensity scaling across subtropical trees

Understanding the scaling between leaf size and leafing intensity (leaf number per stem size) is crucial for comprehending theories about the leaf costs and benefits in the leaf size–twig size spectrum. However, the scaling scope of leaf size versus leafing intensity changes along the twig leaf size variation in different leaf habit species remains elusive. Here, we hypothesize that the numerical value of scaling exponent for leaf mass versus leafing intensity in twig is governed by the minimum leaf mass versus maximum leaf mass (M _min versus M _max) and constrained to be ≤−1.0. We tested this hypothesis by analyzing the twigs of 123 species datasets compiled in the subtropical mountain forest. The standardized major axis regression (SMA) analyses showed the M _min scaled as the 1.19 power of M _max and the ‐α (−1.19) were not statistically different from the exponents of M _min versus leafing intensity in whole data. Across leaf habit groups, the M _max scaled negatively and isometrically with respect to leafing intensity. The pooled data''s scaling exponents ranged from −1.14 to −0.96 for M _min and M _max versus the leafing intensity based on stem volume (LIV). In the case of M _min and M _max versus the leafing intensity based on stem mass (LIM), the scaling exponents ranged from −1.24 to −1.04. Our hypothesis successfully predicts that the scaling relationship between leaf mass and leafing intensity is constrained to be ≤−1.0. More importantly, the lower limit to scaling of leaf mass and leafing intensity may be closely correlated with M _min versus M _max. Besides, constrained by the maximum leaf mass expansion, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest.     

Incidence of Alternaria Species Associated with Watermelon Leaf Blight in Korea

Alternaria leaf blight is one of the most common diseases in watermelon worldwide. In Korea, however, the Alternaria species causing the watermelon leaf blight have not been investigated thoroughly. A total of 16 Alternaria isolates was recovered from diseased watermelon leaves with leaf blight symptoms, which were collected from 14 fields in Korea. Analysis of internal transcribed spacer (ITS) region, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and RNA polymerase II second largest subunit (RPB2) were not competent to differentiate the Alternaria isolates. On the contrary, analysis of amplicon size of the histone H3 (HIS3) gene successfully differentiated the isolates into three Alternaria subgroups, and further sequence analysis of them identified three Alternaria spp. Alternaria tenuissima, A. gaisen, and A. alternata. Representative Alternaria isolates from three species induced dark brown leaf spot lesions on detached watermelon leaves, indicating that A. tenuissima, A. gaisen, and A. alternata are all causal agents of Alternaria leaf blight. Our results indicate that the Alternaria species associated watermelon leaf blight in Korea is more complex than reported previously. This is the first report regarding the population structure of Alternaria species causing watermelon leaf blight in Korea.     

华南地区6种阔叶幼苗叶片形态特征的季节变化

对山杜英、米老排、樟树、海南红豆、红花油茶和红锥6种幼苗叶长和叶宽的相关性和叶片的比叶重变化进行了研究,结果表明：幼苗各月份的叶长和叶宽呈极显著正相关。根据相关系数把6种幼苗分为：a),叶长和叶宽的相关性随季节变化型,包括山杜英、红花油茶、海南红豆、红锥;b),叶长和叶宽的相关性稳定型,有樟树和米老排。6种幼苗叶片的比叶重随幼苗种类和季节而变化,新叶的比叶重上半年比下半年变化大,老叶全年变化较小,上半年新叶的比叶重比老叶低,下半年两者相近。红花油茶新叶和老叶的平均比叶重明显大于其余5种幼苗。     

The relationship of leaf photosynthetic traits – Vcmax and Jmax – to leaf nitrogen,leaf phosphorus,and specific leaf area: a meta‐analysis and modeling study

Great uncertainty exists in the global exchange of carbon between the atmosphere and the terrestrial biosphere. An important source of this uncertainty lies in the dependency of photosynthesis on the maximum rate of carboxylation (V_cmax) and the maximum rate of electron transport (J_max). Understanding and making accurate prediction of C fluxes thus requires accurate characterization of these rates and their relationship with plant nutrient status over large geographic scales. Plant nutrient status is indicated by the traits: leaf nitrogen (N), leaf phosphorus (P), and specific leaf area (SLA). Correlations between V_cmax and J_max and leaf nitrogen (N) are typically derived from local to global scales, while correlations with leaf phosphorus (P) and specific leaf area (SLA) have typically been derived at a local scale. Thus, there is no global-scale relationship between V_cmax and J_max and P or SLA limiting the ability of global-scale carbon flux models do not account for P or SLA. We gathered published data from 24 studies to reveal global relationships of V_cmax and J_max with leaf N, P, and SLA. V_cmax was strongly related to leaf N, and increasing leaf P substantially increased the sensitivity of V_cmax to leaf N. J_max was strongly related to V_cmax, and neither leaf N, P, or SLA had a substantial impact on the relationship. Although more data are needed to expand the applicability of the relationship, we show leaf P is a globally important determinant of photosynthetic rates. In a model of photosynthesis, we showed that at high leaf N (3 gm⁻²), increasing leaf P from 0.05 to 0.22 gm⁻² nearly doubled assimilation rates. Finally, we show that plants may employ a conservative strategy of J_max to V_cmax coordination that restricts photoinhibition when carboxylation is limiting at the expense of maximizing photosynthetic rates when light is limiting.     

Validation of leaf undulation traits in the taxonomy of Epipactis muelleri Godfery, 1921 (Orchidaceae,Neottieae)

Leaf undulation is used as a diagnostic feature in the taxonomy of different taxa of the Epipactis (Orchidaceae) genus. It is considered a specifically important trait, apart from the column (gynostemium) structure, in the identification of E. muelleri. However, leaf undulation is a common developmental phenomenon in various plants, including orchids, thus the main goal of the research presented was to validate the usefulness of this feature in Epipactis taxonomy. In the course of this study, the leaf structure of six Epipactis species was analyzed, i.e., E. albensis, E. atrorubens, E. helleborine, E. muelleri, E. palustris and E. purpurata. The leaf margin outline and the cellular pattern of the leaf surface, as well as the presence of papillae, were examined in detail. The results obtained showed that in all taxa analyzed, representing different groups of the Epipactis genus, leaf undulation was present. The phenomenon was related to leaf blade development and the local differential growth of leaf sectors rather than to the taxonomic position of the species. Therefore, leaf undulation studied in Helleborines does not have a diagnostic value as a non-programmed intrinsic feature and should not be applied to taxa identification. The valid trait in Epipactis classification (including E. muelleri) is the column structure.     

Co-ordination between leaf biomechanical resistance and hydraulic safety across 30 sub-tropical woody species

Background and AimsLeaf biomechanical resistance protects leaves from biotic and abiotic damage. Previous studies have revealed that enhancing leaf biomechanical resistance is costly for plant species and leads to an increase in leaf drought tolerance. We thus predicted that there is a functional correlation between leaf hydraulic safety and biomechanical characteristics.MethodsWe measured leaf morphological and anatomical traits, pressure–volume parameters, maximum leaf hydraulic conductance (K_leaf-max), leaf water potential at 50 % loss of hydraulic conductance (P50_leaf), leaf hydraulic safety margin (SM_leaf), and leaf force to tear (F_t) and punch (F_p) of 30 co-occurring woody species in a sub-tropical evergreen broadleaved forest. Linear regression analysis was performed to examine the relationships between biomechanical resistance and other leaf hydraulic traits.Key ResultsWe found that higher F_t and F_p values were significantly associated with a lower (more negative) P50_leaf and a larger SM_leaf, thereby confirming the correlation between leaf biomechanical resistance and hydraulic safety. However, leaf biomechanical resistance showed no correlation with K_leaf-max, although it was significantly and negatively correlated with leaf outside-xylem hydraulic conductance. In addition, we also found that there was a significant correlation between biomechanical resistance and the modulus of elasticity by excluding an outlier.ConclusionsThe findings of this study reveal leaf biomechanical–hydraulic safety correlation in sub-tropical woody species.     

Optimizing nitrogen economy under drought: increased leaf nitrogen is an acclimation to water stress in willow (Salix spp.)

Background and Aims

The major objective was to identify plant traits functionally important for optimization of shoot growth and nitrogen (N) economy under drought. Although increased leaf N content (area basis) has been observed in dry environments and theory predicts increased leaf N to be an acclimation to drought, experimental evidence for the prediction is rare.

Methods

A pedigree of 200 full-sibling hybrid willows was pot-grown in a glasshouse in three replicate blocks and exposed to two water regimes for 3 weeks. Drought conditions were simulated as repeated periods of water shortage. The total leaf mass and area, leaf area efficiency (shoot growth per unit leaf area, E_A), area-based leaf N content (N_A), total leaf N pool (N_L) and leaf N efficiency (shoot growth per unit leaf N, E_N) were assessed.

Key Results

In the water-stress treatment, shoot biomass growth was N limited in the genotypes with low N_L, but increasingly limited by other factors in the genotypes with greatest N_L. The N_A was increased by drought, and drought-induced shift in N_A varied between genotypes (significant G × E). Judged from the E_A–N_A relationship, optimal N_A was 16 % higher in the water-stress compared with the well-watered treatment. Biomass allocation to leaves and shoots varied between treatments, but the treatment response of the leaf : shoot ratio was similar across all genotypes.

Conclusions

It is concluded that N-uptake efficiency and leaf N efficiency are important traits to improve growth under drought. Increased leaf N content (area basis) is an acclimation to optimize N economy under drought. The leaf N content is an interesting trait for breeding of willow bioenergy crops in a climate change future. In contrast, leaf biomass allocation is a less interesting breeding target to improve yield under drought.     

Leaf shape evolution has a similar genetic architecture in three edaphic specialists within the Mimulus guttatus species complex

Background and Aims The genetic basis of leaf shape has long interested botanists because leaf shape varies extensively across the plant kingdom and this variation is probably adaptive. However, knowledge of the genetic architecture of leaf shape variation in natural populations remains limited. This study examined the genetic architecture of leaf shape diversification among three edaphic specialists in the Mimulus guttatus species complex. Lobed and narrow leaves have evolved from the entire, round leaves of M. guttatus in M. laciniatus, M. nudatus and a polymorphic serpentine M. guttatus population (M2L).Methods Bulk segregant analysis and next-generation sequencing were used to map quantitative trait loci (QTLs) that underlie leaf shape in an M. laciniatus × M. guttatus F₂ population. To determine whether the same QTLs contribute to leaf shape variation in M. nudatus and M2L, F₂s from M. guttatus × M. nudatus and lobed M2L × unlobed M. guttatus crosses were genotyped at QTLs from the bulk segregant analysis.Key Results Narrow and lobed leaf shapes in M. laciniatus, M. nudatus and M. guttatus are controlled by overlapping genetic regions. Several promising leaf shape candidate genes were found under each QTL.Conclusions The evolution of divergent leaf shape has taken place multiple times in the M. guttatus species complex and is associated with the occupation of dry, rocky environments. The genetic architecture of elongated and lobed leaves is similar across three species in this group. This may indicate that parallel genetic evolution from standing variation or new mutations is responsible for the putatively adaptive leaf shape variation in Mimulus.     

Leaf paraheliotropism in Styrax camporum confers increased light use efficiency and advantageous photosynthetic responses rather than photoprotection

Styrax caporum is a native shrub from the Brazilian savanna. Most of its leaves are diaheliotropic, whereas some are paraheliotropic, mainly at noon. A previous study of this species revealed higher stomatal conductance (gs) and transpiration rates (E) in para- compared to diaheliotropic leaves, and a rise in CO₂ assimilation rates (A) with an increase of irradiance for paraheliotropic leaves. We hypothesized that this species exploits the paraheliotropism to enhance the light use efficiency, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. Gas exchange was measured with devices that enabled light interception on only one of the leaf surfaces and with devices that enabled light interception by both leaf surfaces. Water relations, relative reflected light intensity, leaf temperature (T_l), and leaf anatomical analyses were also performed. When both leaf surfaces were illuminated, a higher A, E, and gs were observed in para- compared to diaheliotropic leaves; however, A did not depend on gs, which did not influence CO₂ accumulation in the stomatal cavity (Ci). When only the adaxial leaf surface was illuminated, a greater A was detected for para- than for diaheliotropic leaves only at 11:00 h; no differences in T_l were observed between leaf types. Light curves revealed that under non-saturating light the adaxial side of paraheliotropic leaves had higher A than the abaxial side, but they showed similar values under saturating light. Although the abaxial leaf side was highly reflective, both surfaces presented the same response pattern for green light reflection, which can be explained by the compact spongy parenchyma observed in the leaves, increasing light use efficiency in terms of CO₂ consumption for paraheliotropic leaves. We propose that paraheliotropism in S. camporum is not related to leaf heat avoidance or photoprotection.     

黄土高原樟子松和落叶松与其他树种枯落叶混合分解对土壤的影响

通过采集树木枯落叶与土壤进行室内混合分解培养试验,研究了黄土高原常见的樟子松和落叶松与其他树种枯落叶混合分解对土壤性质的影响及存在的相互作用,从而为不同树木种间关系的探索和该地区人工纯林的混交改造提供科学指导。结果表明:12种枯落叶单一分解均明显提高了土壤脲酶(54%—110%)、脱氢酶(85%—288%)和磷酸酶(81%—301%)活性以及有机质(29%—55%)和碱解N(12%—49%)含量,但对土壤速效P含量和CEC的影响存在较大差异。综合而言,樟子松分别与白桦、刺槐、白榆、柠条和落叶松枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与小叶杨、沙棘、紫穗槐、侧柏和辽东栎枯落叶混合分解在对土壤性质的影响中存在相互抑制作用;落叶松分别与刺槐、白桦、小叶杨和紫穗槐枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与柠条、侧柏、辽东栎、沙棘、油松和白榆枯落叶混合分解在对土壤性质的影响中存在相互抑制作用。     

Differences in leaf nitrogen content, photosynthesis, and resource-use efficiency between Eichhornia crassipes and a native plant Monochoria vaginalis in response to altered sediment nutrient levels

Eichhornia crassipes is one of the world’s most prevalent invasive aquatic plants, causing significant ecological and socio-economic impacts in introduced areas. In this study, we compared the leaf resource capture- and use-related traits of E. crassipes with its confamilial native aquatic plant Monochoria vaginalis at three nutrient levels. Our results showed that leaf nitrogen content based on mass, leaf nitrogen content based on area, N:C, photosynthetic rate, specific leaf area, and leaf construction cost of E. crassipes increased significantly with increasing levels of nutrition, the mean values of these traits increased 0.55, 0.35, 0.51, 0.43, 0.21, and 0.07 times from low nutrient level to high, respectively. These traits (except for the leaf construction cost) in M. vaginalis remained unchanged. At low nutrient level, M. vaginalis had a higher leaf nitrogen content, N:C, photosynthetic rate, specific leaf area, and water-use efficiency than E. crassipes. At high nutrient level, E. crassipes had a higher photosynthetic rate and photosynthetic nitrogen-use efficiency than M. vaginalis, suggesting that the invasiveness of E. crassipes was dependent on the availability of resources in environment. In addition, our results supported the fluctuating resources hypothesis, indicating that an increased level of nutrients in the environment will increase the invasiveness of E. crassipes.     

Is expression of aquaporins (plasma membrane intrinsic protein 2s, PIP2s) associated with thermonasty (leaf-curling) in Rhododendron?

It is postulated that leaf thermonasty (leaf curling) in rhododendrons under sub-freezing temperatures is caused by water redistribution due to extracellular freezing. We hypothesize that aquaporins (AQPs), the transmembrane water-channels, may be involved in regulating water redistribution and thus leaf curling. Our experimental system includes two Rhododendron species with contrasting leaf curling behavior whereby it was observed in R. catawbiense but not in R. ponticum. We compared leaf movements and the expression of two AQPs, i.e. R. catawbiense/ponticum plasma-membrane intrinsic protein 2 (Rc/RpPIP2;1 and Rc/RpPIP2;2), in the two species under freezing–rewarming and dehydration–rehydration cycles. To determine the relationship between extracellular freezing and leaf-curling, we monitored leaf-curling in R. catawbiense with or without controlled ice-nucleation. Our data indicate that extracellular freezing may be required for leaf curling. Moreover, in both species, PIP2s were up-regulated at temperatures that fell in ice-nucleation temperature range. Such up-regulation could be associated with the bulk-water efflux caused by extracellular freezing. When leaves were frozen beyond the ice-nucleation temperature range, PIP2s were continuously down-regulated in R. catawbiense along with the progressive leaf curling, as also observed for RcPIP2;2 in dehydrated leaves; as leaves uncurled during re-warming/rehydration, RcPIP2 expression was restored. On the other hand, R. ponticum, a non-curling species, exhibited substantial up-regulation of RpPIP2s during freezing/dehydration. Taken together, our data suggest that RcPIP2 down-regulation was associated with leaf curling. Moreover, the contrasting PIP2 expression patterns combined with leaf behavior of R. catawbiense and R. ponticum under these two cycles may reflect different strategies employed by these two species to tolerate/resist cellular dehydration.     

The ADAXIALIZED LEAF1 gene functions in leaf and embryonic pattern formation in rice

The adaxial-abaxial axis in leaf primordia is thought to be established first and is necessary for the expansion of the leaf lamina along the mediolateral axis. To understand axis information in leaf development, we isolated the adaxialized leaf1 (adl1) mutant in rice, which forms abaxially rolled leaves. adl1 leaves are covered with bulliform-like cells, which are normally distributed only on the adaxial surface. An adl1 double mutant with the adaxially snowy leaf mutant, which has albino cells that specifically appear in the abaxial mesophyll tissue, indicated that adl1 leaves show adaxialization in both epidermal and mesophyll tissues. The expression of HD-ZIPIII genes in adl1 mutant increased in mature leaves, but not in the young primordia or the SAM. This indicated that ADL1 may not be directly involved in determining initial leaf polarity, but rather is associated with the maintenance of axis information. ADL1 encodes a plant-specific calpain-like cysteine proteinase orthologous to maize DEFECTIVE KERNEL1. Furthermore, we identified intermediate and strong alleles of the adl1 mutant that generate shootless embryos and globular-arrested embryos with aleurone layer loss, respectively. We propose that ADL1 plays an important role in pattern formation of the leaf and embryo by promoting proper epidermal development.     

Leaf nitrogen distribution in relation to crown architecture in the tall canopy species,Fagus crenata

The theory of optimal leaf N distribution predicts that the C gain of plants is maximized when the N content per unit area (N _area) scales with light availability, but most previous studies have demonstrated that the N distribution is not proportional to light availability. In tall trees, the leaves are often clustered on twigs (leaf cluster) and not evenly distributed within the crowns. Thus, we hypothesized that the suboptimal N distribution is partly caused by the limited capacity to translocate N between leaf clusters, and consequently, the relationship between light and N _area differs for leaves in different clusters. We investigated the light availability and N content of all individual leaves within several leaf clusters on tall trees of a deciduous canopy species Fagus crenata in Japan. We observed that the within-cluster leaf N distribution patterns differed from the between-cluster patterns and the slopes of the relationships between light and N _area were lower within clusters than between clusters. According to the detailed analysis of the N distribution within leaf clusters, N _area was greater for current-year shoots with greater light availability or a larger total leaf area. The latter pattern was probably caused by the greater sink strength of the current-year shoots with a larger leaf area. These N distribution patterns suggest that leaf clusters are fairly independent with respect to their N use, and the productivity of real F. crenata crowns may be less than optimal.