Senescent Leaf Research Articles

Effects of climate, soil, and leaf traits on nutrient resorption efficiency and proficiency of different plant functional types across arid and semiarid regions of northwest China

BackgroundPlant nutrient resorption is crucial for the efficient conservation of nutrients. However, the mechanisms through which abiotic and biotic factors control nutrient resorption remain controversial. We investigated leaf nitrogen (N) and phosphorus (P) resorption efficiency (NRE and PRE) and resorption proficiency, as well as the underlying mechanisms for each plant functional type (PFT: non-legume herbs, non-legume shrubs, and legumes) by collecting green and senescent leaves of 59 species covering 106 sites from arid and semiarid regions of northwest China.ResultsLegumes had much lower leaf NRE and much higher senesced leaf N than the other two PFTs; they had similar leaf PRE to non-legume shrubs. Non-legume herbs exhibited the highest leaf P resorption. Climate, particularly temperature, increased leaf N resorption in non-legume herbs; however, climate, particularly decreasing precipitation, decreased leaf P resorption in legumes. Leaf nutrient resorption in non-legume shrubs decreased with increasing soil fertility, but leaf NRE in legumes increased. Leaf traits contributed more to leaf N and P resorption than climate and soil. Senesced leaf N and P concentrations increased along the resource-conservative to resource-acquisitive strategy axis. There were strong negative relationships between leaf NRE and senesced leaf N concentration and between leaf PRE and senesced leaf P concentration, in which legumes had a lower slope than non-legumes.ConclusionsThese findings suggest that ecological strategies and N-fixing plant types modulate nutrient resorption. Plants with the resource-conservative strategy are highly proficient in nutrient resorption. We highlight the importance of leaf economics traits and spectrum in regulating leaf nutrient resorption in drylands in the context of global climate change, potentially modulating plant traits and community composition. The higher proficient and efficient N and P resorption of plant species suggests the crucial importance of nutrient resorption in the nutrient cycling of harsh drylands.

Genetic Analysis and Fine Mapping of a New Rice Mutant, Leaf Tip Senescence 2.

Premature leaf senescence significantly reduces rice yields. Despite identifying numerous factors influencing these processes, the intricate genetic regulatory networks governing leaf senescence demand further exploration. We report the characterization of a stably inherited, ethyl methanesulfonate(EMS)-induced rice mutant with wilted leaf tips from seedling till harvesting, designated lts2. This mutant exhibits dwarfism and early senescence at the leaf tips and margins from the seedling stage when compared to the wild type. Furthermore, lts2 displays a substantial decline in both photosynthetic activity and chlorophyll content. Transmission electron microscopy revealed the presence of numerous osmiophilic granules in chloroplast cells near the senescent leaf tips, indicative of advanced cellular senescence. There was also a significant accumulation of H2O2, alongside the up-regulation of senescence-associated genes within the leaf tissues. Genetic mapping situated lts2 between SSR markers Q1 and L12, covering a physical distance of approximately 212 kb in chr.1. No similar genes controlling a premature senescence leaf phenotype have been identified in the region, and subsequent DNA and bulk segregant analysis (BSA) sequencing analyses only identified a single nucleotide substitution (C-T) in the exon of LOC_Os01g35860. These findings position the lts2 mutant as a valuable genetic model for elucidating chlorophyll metabolism and for further functional analysis of the gene in rice.

Substantial variation of the two‐dimensional spectrum of senescent leaf in subalpine forest along elevational gradients

AbstractLeaf senescence have shed light on its contribution to the recovery of nutrients and signaling of the transition from the active to the dormant stage in winter. The manner by which climatic and edaphic factors and plant phylogeny affect the senescent leaf economics spectrum (more mineral elements included) of different growth habits along elevational gradients in mountain ecosystems is highly uncertain. To fill this knowledge gap, we examined 15 representative subalpine forest species' senescent leaf functional traits (i.e., specific leaf area [SLA], leaf dry matter content [DMC], pH, carbon [C], nitrogen [N], phosphorus [P], potassium [K], calcium [Ca], sodium [Na], magnesium [Mg], manganese [Mn], aluminum [Al], iron [Fe], C:N, N:P, and C:P ratios) to determine the senescent leaf economics spectrum along elevational gradients in the Hengduan Mountains, China. Our results demonstrate that all the functional traits of senescent leaf showed strong correlations with one another, and K was observed as the hub for the leaf economics spectrum. Irrespective of the difference among growth habits (arbor vs. shrub), leaf habits (deciduous vs. evergreen), and leaf types (broad vs. needle), the variations in the two‐dimensional spectrum of the senescent leaf trait exhibited uniformly positive associations with elevation, primarily attributed to climatic drivers. However, the modulation of the senescent leaf economics spectrum by soil properties and plant phylogeny was surprisingly modest. Collectively, our results revealed that the resource trade‐off of senescent leaf showed a trend from acquisition to conservation along elevational gradients, which could broaden the plant economics spectrum to include senescent leaf.

Linkages among leaf nutrient concentration, resorption efficiency, litter decomposition and their stoichiometry to canopy nitrogen addition and understory removal in subtropical plantation

BackgroundThe prevalence of understory removal and anthropogenic nitrogen (N) deposition has significantly altered the ecological processes of forest ecosystems at both regional and global scales. However, it remains a pressing challenge to understand how N deposition and understory removal affect leaf nutrient dynamics, nutrient resorption, litter decomposition, and their linkages for better managing forest ecosystems under nutrient imbalances induced by N enrichment. To address this research gap, a field manipulation experiment was carried out in a subtropical Cunninghamia lanceolata plantation with four treatments including: control (CK), canopy N addition (CN), understory removal (UR), and canopy N addition plus understory removal (CN × UR). Green and senesced leaf N and phosphorus (P) concentrations, N and P resorption efficiencies, litter decomposition, and their correlations were measured.ResultsThe results revealed that the average N concentrations of green early and late leaves in UR were increased by 6.61 and 18.89% compared to CK. UR had the highest whereas CN had the lowest P concentrations in green leaves across the two sampling seasons. Following this, UR, leaf type, season, and their interactions significantly affected leaf N, P, and N:P (P < 0.05). The highest leaf N resorption (32.68%) and P resorption efficiencies (63.96%) were recorded in UR. Litter decomposition was significantly retarded in UR (P < 0.01) relative to CN. The regression analysis demonstrated that leaf nutrient status was significantly interconnected with leaf nutrient resorption efficiencies. In addition, leaf nutrient dynamics were strongly correlated with litter nutrients, indicating that both were coupled.ConclusionThese findings can deepen our knowledge of biogeochemical cycling and reveal contrasting nutrient-acquisition strategies on N and P limitation in response to UR and CN. Considering the P limitation, it is important to note that P was resorbed more efficiently, illustrating a remarkable nutrient preservation approach for nutrient-limitations. Resorption may be a crucial mechanism for keeping nutrients in these forests, so better understory management practices are required to prevent reliance on external nutrient pools. Overall, this study sheds meaningful insights into the ability of forest adaptation in response to global climatic change.

Legacy effects of long‐term autumn leaf litter removal slow decomposition rates and reduce soil carbon in suburban yards

Societal Impact StatementAs cities grow, it is essential to understand how landscape management decisions in urban spaces alter ecosystem function. This study demonstrates that the ubiquitous practice of long‐term leaf litter removal in suburbs, even in relatively small patches of a yard, reduces the soil's ability to cycle nutrients in plant litter and results in lower amounts of carbon stored in the soil. Even two years of retaining leaves where they previously were removed is insufficient to restore decomposition rates or carbon pools. This research is an important step in creating best practices for litter management to maintain essential ecosystem functions, like carbon sequestration, water holding capacity, and soil fertility.Summary Seasonal senesced leaf litter removal eliminates considerable organic material from suburban soils annually. We test if this disturbance alters decomposition and carbon cycles and depletes soils of organic matter over time, creating persistent legacy effects. We used a factorial experimental design to implement 1–2 years of current leaf litter manipulations (remove or retain fallen leaves) within historically raked and unraked areas in suburban Maryland yards. We then compared total organic soil carbon and decomposition using a standardized substrate decomposition methodology (Tea Bag Index) across treatment plots. Long‐term litter removal in suburban yards reduced decomposition rates by 17% and total soil organic carbon concentration by up to 24% compared to areas where leaf litter was retained in situ. In contrast, short‐term management changes (1–2 years) did not significantly impact decomposition rates or total organic soil carbon concentrations. Our findings suggest that long‐term suburban litter raking creates legacy effects that alter decomposition and carbon storage process trajectories that are not easily reversed. This is important in understanding urban ecosystem function and sustainable management.

Coexisting superhydrophobicity and superadhesion features of Ziziphus mauritiana abaxial leaf surface with possibility of biomimicking using electrospun microfibers

The coexistence of superhydrophobicity and superadhesion features is being reported for the abaxial leaf of Indian jujube (Ziziphus mauritiana) possessing hairy, matted surface texture with fiber dia ranging ∼ 5.6–7.1 μm. Very high-water contact angle (WCA &amp;gt; 143°) and high contact angle hysteresis (CAH ∼ 30°–46°) were observed and compared for the tender, mature, and senescent leaf states. The tender leaf exhibits a maximal superhydrophobicity with WCA as high as ∼151° and an increased roll-off angle from ∼21° to 33°. Conversely, next two leaf states are characterized by excellent adhesion even up to a base tilting of 90° without any tendency to roll-off. An attempt has also been made for biomimicking the leaf's hairy fiber microstructure with polyvinylidene fluoride (PVDF) by employing an electrospinning setup, with adjustable control parameters. The fabricated ∼4.3-μm-dia PVDF-based nonwoven fibers were seen to be replicated at par with excellent superhydrophobicity and high adhesion features. The WCA and CAH of artificially grown fibers were estimated to be ∼145.7° and 49.4°. The nonwoven, yarn-like surface construct of microfibers fits well in worm-like chain model, which considers a normal distribution of segments described through discrete jointed length, persistent length, and bending angle between successive segments.

Substantial variation of the two-dimensional spectrum of senescent leaf in subalpine forest along elevational gradients

Substantial variation of the two-dimensional spectrum of senescent leaf in subalpine forest along elevational gradients

Analysis of Nitrogen Dynamics and Transcriptomic Activity Revealed a Pivotal Role of Some Amino Acid Transporters in Nitrogen Remobilization in Poplar Senescing Leaves.

Leaf senescence is an important developmental process for deciduous trees during which part of leaf nitrogen is remobilized to branches, thus being beneficial for nitrogen conservation. However, the associated regulatory mechanism remains largely unknown in deciduous trees. In this study, nitrogen dynamics and transcriptomic activity in senescing leaves were measured during autumnal senescence in hybrid poplar. Both concentrations of leaf total nitrogen (N) and amine compounds were found to decline from the pre-senescence (PRE) to the middle-senescence (MS) stage. Although the total N concentration decreased further from MS to the late-senescence (LS) and leveled off to abscission (ABS) stage, amine compound concentration increased continuously from MS to ABS, suggesting that translocation of amine compounds underperformed production of amine compounds in leaves during this period. L-glutamate, L-glutamine and α-aminoadipic acid were the top three amine compounds accumulated in senescent leaves. RNA-Seq profiling identified thousands of differentially expressed genes (DEGs) with functional association with a metabolic transition towards disassimilation. Many genes encoding amino acid metabolism enzymes and amino acid transporters (AATs) were up-regulated. Comparison of expression trend with leaf N dynamics and phylogenetic analysis identified several PtAATs which exhibited down-regulation from MS to LS stage and putatively limited leaf N remobilization. This study can serve as a primary basis to further elucidate the molecular mechanisms of nitrogen remobilization in poplar senescing leaves.

Altitudinal Patterns of Foliar Nutrients in Dominant Tree Species: Are Central Himalayan Forests Nutrient Stressed?

In forest ecosystems nutrient availability is one of the most important drivers of tree growth and ecosystem function. We studied changes in soil and foliar nutrients (N, P &amp; K) and leaf N and P stoichiometry in eight dominant canopy and sub-canopy forest tree species of Central Himalayan forests occurring between 300 and 2200 m asl. Nutrient (N, P &amp; K) concentration in leaves at bud break, mature and senescent stage varied significantly across the tree species. The nutrient resorption efficiency (NRE) varied significantly across the species and found ranging for N from 48.7 - 76.8%. Both the nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE) increased linearly with altitude (R2= 0.647 for NRE significant at p&lt; 0.05; and R2 for PRE= 0.525; NS) pointing out that trees growing in temperate climate conserve nutrients more efficiently to withstand the slow mineralization due to cold climate. With the increasing altitude leaf life-span increases significantly (R2= 0.0025; p&lt; 0.0074). ANOVA indicates that the foliar N and P and altitude were unrelated. The low N: P ratio, a measure of nutrient status of forest ecosystems at senescent leaf stage, found ranging from 9.97 in Q. floribunda to 18.8 in P. roxburghii points out that forests of the study region are nutrient stressed, partly due to low P mineralization in temperate climate, leaching of nutrients due to heavy monsoon rain, and poorly developed underlying geology. Thus, the Central Himalayan forests are characterized by high NRE and low growth rate with increasing altitude. Winter season warming might help improve the nutrient availability in the forest floor and nutrient uptake to enhance nutrient cycling and biomass productivity in these forests.

Nutrient content and resorption efficiency of leaves of broad-leaved trees along altitudes in Wuyi Mountains, China.

To reveal the variation of leaf nutrient utilization strategies with altitude gradient in subtropical mountain broadleaved trees, 44 species of broadleaved trees at different altitudes (1400, 1600 and 1800 m) in Wuyi Mountains were selected to measure nutrient content, stoichiometric ratio, and nutrient resorption efficiency of green and senescent leaves, and analyzed their allometric growth relationships. The results showed that nitrogen (N) and phosphorus (P) contents in green leaves were significantly higher than those in senescent leaves, which increased with the increases of altitude. The average values of phosphorus resorption efficiency (PRE) and nitrogen resorption efficiency (NRE) were 48.3% and 34.9%, respectively. PRE was significantly higher than NRE. There was no significant difference in nutrient resorption efficiency with altitude. NRE had positive isokinetic growth with and mature leaf N content at low altitude (1400 m) and negative allometry growth with senescent leaf N content at high altitude (1800 m). PRE and N and P contents of senescent leaves had negative isokinetic growth at low altitude (1400 m) and negative allometry growth at high altitudes (1600 and 1800 m). PRE-NRE allometric growth index was 0.95 at each altitude. The nutrient contents of green and senescent leaves increased with the increases of altitude, but altitude did not affect nutrient resorption efficiency. Plants preferred to re-absorbed P from senescent leaves. Nutrient resorption efficiency of leaves at high altitude affected the nutrient status of senescent leaves.

Less is more: partial larvicidal efficacy of plant leachate leads to larger Aedes aegypti mosquitoes.

Major efforts to control the population of Aedes aegypti mosquitoes involve the use of synthetic insecticides, which can be harmful to the environment. Most plant compounds are eco-friendly and some of them have biocontrol potential, whereas a fraction of these compounds is released into the environment through the leaf-leaching process. We evaluated the effects of secondary compounds from Ateleia glazioviana and Eucalyptus grandis senescent leaf leachates on Ae. aegypti larval mortality, adult emergence time, and wing size using a microcosm approach. The microcosms consisted of 10 larvae kept in water (control) and under four treatments with leachates from a combination of plant species and leaching time (7 or 14 days). Chemical analyses of the leachates showed the presence of carboxaldehyde and Heptatriocotanol, which have antimicrobial properties, potentially reducing the food available for larvae. β-Sitosterol, Stigmasterol, α-Amyrin, and Lupeol are compounds with inhibitory, neurotoxic, and larvicidal effects. Both plant species' leachates increased larval mortality and decreased emergence time due to the presence of compounds toxic to the larvae. Larger organisms emerged in treatments with 7-days leachates, likely due to the high concentration of dissolved organic matter in the leachates. The higher mortality in 7-days leachates may also increase the organic matter from co-specific decomposition, improving adult size. Therefore, if the mosquito population is not locally extinct, compounds present in leaf leachates may act as a resource enhancing larvae growth, potentially increasing survivors' fitness. In conclusion, biocontrol attempts using urban green spaces may have unexpected outcomes, such as resulting in larger pest organisms.

Influence of Mycorrhiza on C:N:P Stoichiometry in Senesced Leaves.

Senesced leaves play a vital role in nutrient cycles in the terrestrial ecosystem. The carbon (C), nitrogen (N) and phosphorus (P) stoichiometries in senesced leaves have been reported, which are influenced by biotic and abiotic factors, such as climate variables and plant functional groups. It is well known that mycorrhizal types are one of the most important functional characteristics of plants that affect leaf C:N:P stoichiometry. While green leaves' traits have been widely reported based on the different mycorrhiza types, the senesced leaves' C:N:P stoichiometries among mycorrhizal types are rarely investigated. Here, the patterns in senesced leaves' C:N:P stoichiometry among plants associated with arbuscular mycorrhizal (AM), ectomycorrhizal (ECM), or AM + ECM fungi were explored. Overall, the senesced leaves' C, with 446.8 mg/g in AM plants, was significantly lower than that in AM + ECM and ECM species, being 493.1 and 501.4 mg/g, respectively, which was mainly caused by boreal biomes. The 8.9 mg/g senesced leaves' N in ECM plants was significantly lower than in AM (10.4 mg/g) or AM + ECM taxa (10.9 mg/g). Meanwhile, the senesced leaves' P presented no difference in plant associations with AM, AM + ECM and ECM. The senesced leaves' C and N presented contrary trends with the changes in mean annual temperature (MAT) and mean annual precipitation (MAP) in ECM or AM + ECM plants. The differences in senesced leaves' C and N may be more easily influenced by the plant mycorrhizal types, but not P and stoichiometric ratios of C, N and P. Our results suggest that senesced leaves' C:N:P stoichiometries depend on mycorrhizal types, which supports the hypothesis that mycorrhizal type is linked to the evolution of carbon-nutrient cycle interactions in the ecosystem.

Effect of shrub encroachment on leaf nutrient resorption in temperate wetlands in the Sanjiang Plain of Northeast China

BackgroundNutrient resorption is an important plant nutrient conservation strategy in wetlands. However, how shrub encroachment alters plant nutrient resorption processes is unclear in temperate wetlands. Here, we collected green and senesced leaves of common sedge, grass, and shrub species in wetlands with high (50–65%) and low (20–35%) shrub covers in the Sanjiang Plain of Northeast China, and assessed the impact of shrub encroachment on leaf nitrogen (N) and phosphorus (P) resorption efficiency and proficiency at both plant growth form and community levels.ResultsThe effects of shrub cover on leaf nutrient resorption efficiency and proficiency were identical among shrubs, grasses, and sedges. Irrespective of plant growth forms, increased shrub cover reduced leaf N resorption efficiency and proficiency, but did not alter leaf P resorption efficiency and proficiency. However, the effect of shrub cover on leaf nutrient resorption efficiency and proficiency differed between plant growth form and community levels. At the community level, leaf N and P resorption efficiency decreased with increasing shrub cover because of increased dominance of shrubs with lower leaf nutrient resorption efficiency over grasses and sedges. Accordingly, community-level senesced leaf N and P concentrations increased with elevating shrub cover, showing a decline in leaf N and P resorption proficiency. Moreover, the significant relationships between leaf nutrient resorption efficiency and proficiency indicate that shrub encroachment increased senesced leaf nutrient concentrations by decreasing nutrient resorption efficiency.ConclusionsThese observations suggest that shrub encroachment reduces community-level leaf nutrient resorption efficiency and proficiency and highlight that the effect of altered plant composition on leaf nutrient resorption should be assessed at the community level in temperate wetlands.

Nitrogen and Carbon Mineralization from Green and Senesced Leaf Litter Differ between Cycad and Angiosperm Trees.

Plant leaf litter decomposition is directly influenced by the identity of the source plants and the leaf age. Defoliation of forests by tropical cyclones (TC) transfers copious amounts of high-quality green leaf litter to soils. We used a soil amendment approach with the incubated buried bag method to compare carbon (C) and nitrogen (N) mineralization dynamics of green and senesced leaf litter from cycad Cycas micronesica and angiosperm Morinda citrifolia trees on the island of Guam. Soil priming increased the decomposition of pre-existing organic C, and were greater for green leaf litter additions than senesced leaf litter additions. Available N content increased by day 14 and remained elevated for the entire 117-d incubation for soils amended with green M. citrifolia litter. In contrast, available N content increased above those in control soils by day 90 and above those in soils amended with senesced litter by day 117 for green C. micronesica litter. The net N mineralization rate was higher than control soils by 120% for the senesced litter treatments and 420% for the green litter treatments. The results reveal a complex but predictable interplay between TC defoliation and litter quality as defined by tree identity. We have illuminated one means by which increased frequency of intense TCs due to climate change may alter the global C and N cycles.

Towards quantifying microbial dispersal in the environment.

Towards quantifying microbial dispersal in the environment.

Transcriptomic analysis of ncRNA and mRNA interactions during leaf senescence in tomato

An increasing number of non-coding RNAs (ncRNAs) have been discovered recently with the advance of RNA-seq. Nevertheless, the function of ncRNAs in leaf senescence was not fully elucidated. In this study, the whole transcriptome sequencing was employed to characterize the expression profiles of mRNA, lncRNA and miRNA during leaf senescence. A total of 2774 mRNAs, 160 lncRNAs and 117 miRNAs were identified to be significantly differentially expressed between the senescent and the young leaves. Co-expression analysis showed that 160 differential expressing (DE) lncRNAs potentially regulated 946 protein-coding genes in trans, but only 32 targeted protein-coding genes were predicated to be regulated by 30 lncRNAs in cis. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of these trans- and cis-target genes revealed that the DE lncRNAs participated in pathways, such as photosynthesis, transporters and circadian rhythm. Furthermore, virus-induced gene silencing (VIGS) was employed to illuminate the role of lncRNAs. The silence of MSTRG.16920 and MSTRG.7613, two intergenic lncRNAs, significantly inhibited leaf senescence induced by darkness, presumably attributed to the downregulated expression of their corresponding target genes Solyc02g069960 and Solyc06g050440, respectively. Notably, Solyc02g069960 and Solyc06g050440 encoding senescence-related NAC transcription factor and reactive oxygen species (ROS)-related peroxidase, respectively, served as positive regulators of leaf senescence. Collectively, our study provides a comprehensive expression profile of lncRNAs in senescent leaf with the concurrent integrated expression of mRNAs and miRNAs.

Behavior of Photosystems II and I Is Modulated Depending on N Partitioning to Rubisco in Mature Leaves Acclimated to Low N Levels and Senescent Leaves in Rice.

In mature leaves acclimated to low N levels and in senescent leaves, photosystems II and I (PSII and PSI, respectively) show typical responses to excess light energy. As CO2 assimilation is not transiently suppressed in these situations, the behavior of PSII and PSI is likely caused by endogenous biochemical changes in photosynthesis. In this study, this subject was studied in rice (Oryza sativa L.). Analysis was performed on mature and senescent leaves of control and N-deficient plants. Total leaf-N, Rubisco and chlorophyll (Chl) levels and their ratios were determined as biochemical parameters of photosynthesis. Total leaf-N, Rubisco and Chl levels decreased in the mature leaves of N-deficient plants and senescent leaves. The percentage of Rubisco-N in the total leaf-N decreased in these leaves, whereas that of Chl-N tended to remain almost constant in mature leaves but increased in senescent leaves. Changes in PSII and PSI parameters were best accounted for by the Rubisco-N percentage, strongly suggesting that the behavior of PSII and PSI is modulated depending on changes in N partitioning to Rubisco in mature leaves acclimated to low N levels and in senescent leaves. It is likely that a decrease in N partitioning to Rubisco leads to a decrease in Rubisco capacity relative to other photosynthetic capacities that inevitably generate excess light energy and that the operation of PSII and PSI is modulated in such situations.

Structural similarity versus secretion composition in colleters of congeneric species of Prepusa (Gentianaceae)

Although the Atlantic Forest is considered a humid environment, plants that grow on rock outcrops present adaptive strategies, which correlate with tolerance to desiccation. Colleters are secretory structures that protect meristems and developing organs from dehydration and attack by herbivores or pathogens. Colleters are common in Gentianaceae; however, there is little research from an anatomical perspective. This study evaluated three Prepusa species (P. connata, P. hookeriana, and P. viridiflora) that are endemic to rock outcrops associated with the Atlantic Forest to investigate the distribution, anatomy, and histochemical composition of secretion of the their colleter throughout leaf growth and maturation. Samples of young, mature, and senescent leaf bases were collected, fixed, and processed following routine techniques in anatomical and micromorphological studies. In the three species, the colleters are located at the base of the leaves, on the adaxial surface. They are non-vascularized and have a short peduncle and a multicellular secretory portion coated by the cuticle. They develop asynchronously, as they are active in young leaves, and cease their activity in fully expanded leaves, but they are not deciduous. They have intercellular spaces, in which polysaccharide and protein secretions accumulate. Moreover, lipids were observed only in P. hookeriana and P. connata. Phenolic compounds are common and occur during colleter senescence, which is characterized by total cell collapse. Even though this study examined congeneric species from similar environments, the results confirm alterations in secretion composition and structural and chemical changes throughout leaf growth and maturation.

Polyamines-a novel molecular coordinator of nitro oxidative signaling in barley senescing leaf

Polyamines-a novel molecular coordinator of nitro oxidative signaling in barley senescing leaf

Nutrient resorption responses of plant life forms to nitrogen addition in temperate shrublands

AbstractAtmospheric nitrogen (N) deposition has significantly altered nutrient availability in most terrestrial ecosystems, which may affect plant nutrient resorption and hence change nutrient cycling and community composition. Although studies on the effects of changed soil nutrients on leaf nutrient resorption have been extensively reported in forests and grasslands, much less known about how plants in temperate shrublands respond to nitrogen deposition across the world. A 4‐year N addition experiment in Vitex negundo and Spiraea trilobata shrublands was conducted to investigate the potential impacts of N deposition on nutrient resorption in two life forms. The green and senesced leaf N ([N]g and [N]s) and phosphorus ([P]g and [P]s) concentrations were measured in four shrubs and two graminoids to calculate N (NRE) and P (PRE) resorption efficiency. We found markedly lower NRE and PRE in shrubs than in graminoids, implying that shrubs probably have a higher capability of acquiring nutrients from soil, whereas graminoids rely on acquiring more nutrients via resorption. N addition increased the [N]g, [N]s, and N:P ratios ([N:P]) and decreased the [P]g of shrubs and all species, whereas it only increased [N]s but had negligible effects on the [N]g, [P]g, and [N:P] of graminoids. The [P]s, NRE, and PRE did not change in either life form or all species combined after N fertilization. Our results suggest that shrubs increase N uptake but do not alter internal N cycling (i.e., nutrient resorption), whereas graminoids do not change N acquisition strategies, in response to increased N supply from the soil. Continuous N addition exacerbated the P limitation of the shrub plants. Both shrubs and graminoids were more likely to adopt nearly complete utilization of P from the soil and senesced leaves under P deficiency, leading to a noneffect of N addition on leaf PRE. Our findings also suggest that the [N]g and [P]g responses to N addition are life‐form specific, implying that N addition may affect ecosystem carbon (C) and nutrient cycles by altering the dominance values of the two life forms and community composition.