Rhododendron Lapponicum Research Articles

The expansion of evergreen and deciduous shrubs changed the chemical characteristics and biological community of alpine meadows soil

Global warming drives shrubs expansion. However, it is unclear how shrubs expansion affect the nutrients cycling, decomposer diversity and activity of alpine meadows. We selected two dominant shrub species in an alpine forest-Tundra ecotone on the eastern Tibetan Plateau: Rhododendron lapponicum (evergreen shrubs), and Sorbus rufopilosa (deciduous shrubs), the shrub-free tundra site as the control site. The fauna community diversity, microbial biomass, extracellular enzyme activity and enzyme stoichiometry of organic soil and mineral soil layer were determined to explore the effects of shrubs expansion. The soil total nitrogen, microbial biomass carbon and nitrogen, and some extracellular enzyme activity of the two shrubs were higher than those in CK. In addition, deciduous shrub expansion had a stronger effect on meadows ecosystem process than evergreen shrub expansion. However, both of them may alleviate the limitation of nitrogen and phosphorus in alpine meadows ecosystem, and the expansion of evergreen shrubs may also contribute to the accumulation of particulate organic matter. It is of great significance to probe the biogeochemical cycle of alpine meadows ecosystems under climate change.

Cover: Journal of Basic Microbiology. 8/2022

Journal of Basic MicrobiologyVolume 62, Issue 8 p. 887-887 COVER PICTUREFree Access Cover: Journal of Basic Microbiology. 8/2022 First published: 01 August 2022 https://doi.org/10.1002/jobm.202270015AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Cover illustration: Pathogenicity of Phytophthora cinnamomi Pci-1 on Rhododendron lapponicum and 14 different possible host displaying plant leaves. The diseased leaves showed brown color and decayed eventually. (Photo: Yinglong Liu, State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan Agricultural University, Kunming, Yunnan, China) Volume62, Issue8August 2022Pages 887-887 RelatedInformation

Phytophthora cinnamomi causing root rot on Rhododendron lapponicum and control it using potential biocontrol agents.

Rhododendron lapponicum (R. lapponicum) is a dwarf Rhododendron species, which is severely infected with root rot and wilt in Yunnan province, China. However, the causal agent causing these symptoms was unknown. An isolate, Pci-1 was identified as Phytophthora cinnamomi, based on its morphology and the sequences of β-tubulin, internal transcribed spacer, and Ypt1 genes and verified according to the Koch's postulate. We found that this pathogen could infect 14 species of plants, including Althaea rosea, Viburnum cylindricum, and Brassica napus. Strain Pci-1 could cause R. lapponicum to wither and die; and it grows best in an oat medium with pH 7.0 - 8.0 and an optimum temperature of 27°C. We suggest that the rhizosphere of R. lapponicum treated with biocontrol strains Paenibacillus polymyxoides P2-5 and Trichoderma asperellum Tv-1 showed a significant inhibitory effect on pathogen Pci-1. The inhibitory effect of 70% dimethomorph + cymoxanil was significantly higher with EC50 and EC90 values of 0.1894 and 0.3618 a.i. µg/ml, respectively. Greenhouse experiments revealed that the pathogen load is decreased in the presence of potential antagonists. This study provides fundamentals on risk assessment and theoretical support for the management of P. cinnamomi pathogen and contributes significantly to the planting of forest and horticultural crops in a disease-free environment.

Analysis of Transcriptome Sequencing and MYB Transcription Factor Family in <i>Rhododendron lapponicum</i>

MYB transcription factor is the largest family of transcription factors in plants, and they are involved in the regulation of plant growth and development, secondary metabolism, adversity stress and other biological processes. So far, there is no the study on the MYB transcription factor of  Rhododendron lapponicum . In this study, the  Rhododendron lapponicum  variety ‘Fuli Jinling’ transcriptome was generated by SMRT sequencing technology. A total of 15.37 Gb data was obtained, and 75 002 transcript sequences were obtained by removing redundancy. 71 155, 33 653 and 30 359 transcripts were assigned to the Nr, GO and COG databases, respectively. Based on the transcriptome sequencing data, 64 transcription factor gene families were identified, including 220 MYB genes. According to the structural characteristics, the MYB gene is divided into four categories, including 1R-MYB, R2R3-MYB, R1R2R3-MYB and 4R-MYB. The amino acid sequence of MYB transcription factor contains 20 conserved elements. Phylogenetic analysis showed that the MYB genes of  Rhododendron lapponicum  could be divided into 28 subclasses. In this study, we first used SMRT sequencing technology to generate the  Rhododendron lapponicum  transcriptome. In this study, single molecule real time (SMRT) technology was used to sequence the transcriptome of the  Rhododendron lapponicum  variety 'Fuli Jinling', and the obtained transcript sequences were functionally annotated and classified, and 220  MYB  genes for bioinformatics analysis, these related results have certain reference significance.

Volatile organic compound emission in tundra shrubs – Dependence on species characteristics and the near-surface environment

Temperature is one of the key abiotic factors during the life of plants, especially in the Arctic region which is currently experiencing rapid climate change. We evaluated plant traits and environmental variables determining leaf temperature in tundra shrubs and volatile organic compound (VOC) emissions with field measurements on deciduous tundra shrubs, Salix myrsinites and Betula nana, and evergreen Cassiope tetragona and Rhododendron lapponicum. Higher leaf-to-air temperature difference was observed in evergreen, compared to deciduous shrubs. Evergreen shrubs also showed continuously increasing photosynthesis with increasing temperature, suggesting high thermal tolerance. For the deciduous species, the optimum temperature for net photosynthesis was between our measurement temperatures of 24 °C and 38 °C. Air temperature and vapor pressure deficit were the most important variables influencing leaf temperature and VOC emissions in all the studied plants, along with stomatal density and specific leaf area in the deciduous shrubs. Using climate data and emission factors from our measurements, we modelled total seasonal tundra shrub VOC emissions of 0.3–2.3 g m−2 over the main growing season. Our results showed higher-than-expected temperature optima for photosynthesis and VOC emission and demonstrated the relative importance of plant traits and local environments in determining leaf temperature and VOC emissions in a subarctic tundra.

Seasonal dynamics of organic components in fresh foliar litters at different gap positions in an alpine forest on the eastern Tibetan Plateau

The organic components in fresh litters are important chemical traits for evaluating the initial quality that controls decomposition of plant litter. This study aimed to assess the seasonal dynamics and drivers of organic components in four dominant fresh litters and their variations at different gap positions in an alpine forest on the eastern Tibetan Plateau. We measured the water- (WSE), organic- (OSE), acid-soluble extractables (ASE) and acid-unhydrolyzable residues (AUR) in fresh litters of fir (Abies faxoniana), cypress (Sabina saltuaria), azalea (Rhododendron lapponicum), and cherry (Cerasus duclouxii) at the gap center, gap edge, and under the closed canopy over 1 year in an alpine forest. The contents of organic components significantly varied among litter species and collecting time, and the ASE content also showed significant variations among gap positions. Manganese (Mn) was negatively related to the OSE content, and dissolved organic carbon (DOC) was the most significant factor affecting WSE and AUR contents. Magnesium (Mg) was the factor of great magnitude that significantly influenced the ASE content, and the correlation coefficient between Mg and ASE in the gap center was higher than that in other gap positions. The contents of organic components were markedly controlled by litter species over time, and ASE content varied significantly after gap formation. The seasonal dynamics of these organic components were strongly mediated by litter nutrients, such as Mg, Mn, calcium (Ca), and nitrogen (N), while DOC was a significant factor controlling WSE and AUR contents in fresh litters in this alpine forest.

Effects of Litter Quality Diminish and Effects of Vegetation Type Develop During Litter Decomposition of Two Shrub Species in an Alpine Treeline Ecotone

Because climate change is predicted to have a strong impact on high-altitude ecosystems, a better knowledge of litter decomposition in alpine ecosystems is critical to improve our predictions of the effect of climate change on ecosystem processes and services such as nutrient cycling, carbon sequestration, and below-ground biodiversity. To evaluate the effects of vegetation types [alpine shrubland (AS) and alpine meadow (AM)] and litter quality on litter decomposition and related biochemical processes, the decomposition of leaf litter of two dominant shrub species, Sorbus rufopilosa (SR, high quality) and Rhododendron lapponicum (RL, low quality), was studied using the litterbag method in an alpine treeline ecotone on the eastern Tibetan Plateau. After 1 year of decomposition, cellulolytic enzyme activities and gram-negative bacterial biomass were higher in shrubland than in meadow. However, higher fungal biomass, fungal/bacteria ratio and ligninolytic activity were observed in meadow than in shrubland after 2 years of decomposition. During the first year of decomposition, litter decomposition was faster in shrubland than in meadow probably due to the home-field advantage (HFA) effect and the bacteria-dominated decomposition, whereas in later decomposition stages, litter decomposition was faster in meadow than in shrubland, as the HFA effect diminished and fungal-dominated decomposition of recalcitrant components took over. These results indicated that litter quality effects were generally strongest in the first year and diminished in later stages when the effect of vegetation type in incubation sites developed.

Single-molecule long-read sequencing of the full-length transcriptome of Rhododendron lapponicum L.

Rhododendron lapponicum L. is a familiar ornamental plant worldwide with important ornamental and economic value. However, a full-length R. lapponicum transcriptome is still lacking. In the present study, we used the Pacific Biosciences single-molecule real-time sequencing technology to generate the R. lapponicum transcriptome. A total of 346,270 full-length non-chimeric reads were generated, from which we obtained 75,002 high-quality full-length transcripts. We identified 55,255 complete open reading frames, 7,140 alternative splicing events and 2,011 long non-coding RNAs. In gene annotation analyses, 71,155, 33,653, 30,359 and 31,749 transcripts were assigned to the Nr, GO, COG and KEGG databases, respectively. Additionally, 3,150 transcription factors were detected. KEGG pathway analysis showed that 96 transcripts were identified coding for the enzymes associated with anthocyanin synthesis. Furthermore, we identified 64,327 simple sequence repeats from 45,319 sequences, and 150 pairs of primers were randomly selected to develop SSR markers. This study provides a large number of full-length transcripts, which will facilitate the further study of the genetics of R. lapponicum.

Litter chemical quality strongly affects forest floor microbial groups and ecoenzymatic stoichiometry in the subalpine forest

Litter chemical quality regulates the distinct composition of the main microbial groups and ecoenzymatic stoichiometry. Microbes in spruce ( Picea asperata Mast.) and fir ( Abies faxoniana Rehd.) rather than birch ( Betula platyphylla Suk.) and rhododendron ( Rhododendron lapponicum (L.) Wahl.) can more easily adjust their physiological metabolism to acclimate to low N resources. Litter decomposition is the main pathway of nutrient cycling that bridges aboveground and underground material circulation and energy flow. Microorganisms are essential for the regulation of organic carbon decomposition and nutrient cycling. We sought to reveal whether litter chemical quality predominates forest floor microbial structure and function in different species and how their characteristics vary with litter decomposition stages. We measured litter substrate quality, microbial community structure, microbial biomass carbon (MBC) and nitrogen (MBN), extracellular enzyme activities and stoichiometric homeostasis of fresh litter (L), and fermentative (F) and humus (H) layers for these tree species. Overall, the enzyme activities and microbial biomass of birch and rhododendron were greater than those of spruce and fir. The microbial abundances of birch and rhododendron decreased with decomposition. Forest floor microbial nutrient limitation is generally restricted by N in subalpine forests, and ecoenzymatic stoichiometry is affected mainly by dissolved C/N/P stoichiometry. Stronger microbial C:N homeostasis (H′) was observed for spruce (5.56) and fir (4.17) than that for birch (1.82) and rhododendron (1.33). We conclude that litter chemical quality led to the disparity in forest floor microbial groups and ecoenzymatic stoichiometry for different tree species.

Higher soil fauna abundance accelerates litter carbon release across an alpine forest-tundra ecotone

Upward shifts of alpine treelines and shrub expansion are occurring under climate change, and Abies faxoniana (AF) and Rhododendron lapponicum (RL) may become distributed at higher altitudes. How do abiotic factors and litter quality modulate the effects of soil fauna on carbon release in this context? A field decomposition experiment involving the foliar litter of AF and RL was conducted along an elevation gradient encompassing coniferous forest, alpine shrubland and alpine meadow by using litterbags with different mesh sizes (3 and 0.04 mm). The objective was to determine the influences of soil fauna, litter quality and abiotic factors on species-specific carbon release and their contributions during litter decomposition. Our findings demonstrated that higher soil fauna abundance and diversity facilitated litter carbon release. The contribution rates of soil fauna to carbon release (Cfau) decreased with elevation increasing and decomposition time. Cfau are influenced by soil faunal diversity, dominant fauna groups (Collembola, Oribatida, Mesostigmata), and abiotic factors (temperature). Soil fauna significantly and directly regulated carbon release, abiotic factors indirectly regulated carbon release via altering soil fauna community composition and litter quality. This study improve our understanding in the mechanisms of decomposer contributions to carbon cycling in the context of global climate change.

Impacts of soil fauna on lignin and cellulose degradation in litter decomposition across an alpine forest-tundra ecotone

The degradation of lignin and cellulose is the primary ecological process in terrestrial ecosystems; these chemical changes have been associated with the subsequent colonization and activity of decomposer flora and fauna. To evaluate the contribution of soil fauna on lignin and cellulose degradation during litter decomposition, we conducted a field experiment along an elevation gradient: coniferous forest, alpine timberline and alpine meadow, and monitored Abies faxoniana and Rhododendron lapponicum foliar litter decomposition with litterbags of different mesh sizes. We observed soil fauna significantly accelerated litter decay. Soil fauna effect on cellulose degradation rate was significantly accelerated in the snowing period (213-320d), which were 19.3%, 12.36%, 27.96% in A. faxoniana litter and 9.2%, 32.65%, 22.11% in R. lapponicum litter in the coniferous forest, alpine timberline and alpine meadow, respectively. By contrast, lignin degradation rates by soil fauna were higher in the later stages (321-554d). In addition, the average monthly contribution of soil fauna effect on cellulose degradation rate mainly occurred during the first year. However, the contribution of lignin degradation by soil fauna was higher in coniferous forest and alpine meadow, where they were 13.84% and 18.06% in A. faxoniana, and 14.5% and 10.1% in R. lapponicum litter. Elevation gradient and seasonal dynamics will influence on activity of soil fauna, which may modify the impacts of soil fauna on lignin and cellulose degradation during litter decomposition. Elucidating the role of soil fauna in litter decomposition is important for understanding the formation of soil organic matter in alpine ecosystems.

The losses of condensed tannins in six foliar litters vary with gap position and season in an alpine forest

Condensed tannins (CTs) have been considered to be intrinsic variables that determine litter decomposition. Forest gaps and the surrounding crown canopies may locally influence the microenvironmental factors, thus affecting the losses of CTs from litter. However, little information is available about the dynamics of CTs loss in forest gaps. In this study, litterbags containing foliar litter of Minjiang fir (Abies faxoniana), red birch (Betula albosinensis), Masters larch (Larix mastersiana), cypress (Sabina saltuaria), Kangding willow (Salix paraplesia), and Lapland azalea (Rhododendron lapponicum), were placed on the forest floor at differet positions from the gap center to the closed canopy in the alpine Minjiang fir forest located in the upper reaches of the Yangtze River and the eastern Tibetan Plateau (China). The samples were retrieved during the periods of snow formation, snow cover, snow melt and in the growing season, and the CTs content was measured at each time point. During the first year, all six types of foliar litter experienced high losses of CTs with values ranging from 70.18% to 96.67%. Forest gaps accelerated litter CTs losses in the winter but inhibited CTs losses in the growing season, which demonstrated significant seasonal differences. Additionally, the litter of conifers exhibited greater CTs losses in the winter, especially during the snow formation period, whereas the litter of broadleaved trees showed greater CTs losses during the growing season. These results indicate that the predicted reductions in snow depth resulting from future winter warming and the loss of forest gaps due to forest regeneration will inhibit the decomposition of CTs in the litter of alpine forest ecosystems, which will slow soil carbon sequestration from foliar litter in cold biomes.

Contribution of soil fauna to litter decomposition of Abies faxoniana and Rhododendron lapponicum across an alpine timberline ecotone in Western Sichuan, China.

Soil fauna is an important biological factor in regulation litter decomposition. In order to quantify the contributions of soil fauna to the mass losses of litter of two dominant species fir (Abies faxoniana) and rhododendron (Rhododendron lapponicum) in the alpine timberline ecotone (coniferous forest-timberline-alpine meadow) of western Sichuan, China, a field litterbag experiment was conducted from May 2013 to November 2014. Samples of air-dried leaf litter were placed in nylon litterbags of two different mesh sizes, i.e. 3.00 mm (with the soil animals) and 0.04 mm (excluded the soil animals). The results showed that the decomposition rate of A. faxoniana (k: 0.209-0.243) was higher than that of R. lapponicum (k: 0.173-0.189) across the timberline ecotone. Soil fauna had significant contributions to litter decomposition of two species, the contributions of soil fauna to mass loss showed a decreasing trend with increasing altitude. From the coniferous forest to the alpine meadow, the mass losses caused by soil fauna for the fir litter accounted for 15.2%, 13.2% and 9.8%, respectively and that for the rhododendron litter accounted for 20.1%, 17.5% and 12.4%, respectively. Meanwhile, the daily average contributions caused by soil fauna for the fir and rhododendron litter decomposition accounted for 0.17%, 0.13%, 0.12% and 0.26%, 0.25%, 0.23%, respectively. Relatively, soil fauna had more influence on alpine rhododendron decomposition. Two-way ANOVA showed that species, altitude and their interaction had significant impact on the litter mass loss and decomposition rate caused by soil fauna. The daily average contribution caused by soil fauna for the fir and rhododendron litter decomposition accounted for 0.25% and 0.44% in the first growing season, then 0.10% and 0.19% in the second growing season, both were higher than that of snow-covered season (0.07% and 0.12%). Regression analysis showed that the environmental factors (daily average temperature, freezing and thawing cycles and snow thickness) explained 42.7% and 50.9% in the mass loss as well as 43.2% and 55.6% in the contribution rate of fir and rhododendron litter decomposition. These results suggest that soil fauna contributes strongly to litter decomposition in the alpine ecosystem, and it is of great significance to thorough understanding and recognizing material cycle through the role of soil fauna in the litter decomposition.

Degradation of lignin and cellulose during foliar litter decomposition in an alpine forest river

AbstractLignin and cellulose are thought to be critical factors that affect the rate of litter decomposition; however, few data are available on their degradation dynamics during litter decomposition in lotic ecosystems, such as forest rivers, where litter can decompose much more rapidly than in terrestrial ecosystems. We studied the degradation of lignin and cellulose in the foliar litter of four dominant riparian species (willow:Salix paraplesia; azalea:Rhododendron lapponicum; cypress:Sabina saltuaria; and larch:Larix mastersiana) in an alpine forest river. Over an entire year's incubation, litter lignin and cellulose degraded by 14.7–100% and 57.7–100% of their initial masses, respectively, depending on litter species. Strong degradations of lignin and cellulose occurred in the prefreezing period (i.e., the first 41 d) during litter decomposition, and the degradation rate was the highest among all the decomposition periods regardless of litter species. Litter species, decomposition period, and environmental factors such as temperature and nutrient availability showed significant influences on lignin and cellulose degradation rates. Compared with previously reported data regarding the dynamics of lignin and cellulose during litter decomposition in terrestrial ecosystems, our results suggest that lignin and cellulose can be degraded much more rapidly in lotic ecosystems, indicating that the traditionally used two‐phased model for the dynamics of lignin in decomposing litter may not be suitable in lotic ecosystems.

Cellulose Dynamics during Foliar Litter Decomposition in an Alpine Forest Meta-Ecosystem

To investigate the dynamics and relative drivers of cellulose degradation during litter decomposition, a field experiment was conducted in three individual ecosystems (i.e., forest floor, stream, and riparian zone) of an alpine forest meta-ecosystem on the eastern Tibetan Plateau. Four litter species (i.e., willow: Salix paraplesia, azalea: Rhododendron lapponicum, cypress: Sabina saltuaria, and larch: Larix mastersiana) that had varying initial litter chemical traits were placed separately in litterbags and then incubated on the soil surface of forest floor plots or in the water of the stream and riparian zone plots. Litterbags were retrieved five times each year during the two-year experiment, with nine replicates each time for each treatment. The results suggested that foliar litter lost 32.2%–89.2% of the initial dry mass depending on litter species and ecosystem type after two-year’s incubation. The cellulose lost 60.1%–96.8% of the initial mass with degradation rate in the order of stream > riparian zone > forest floor. Substantial cellulose degradation occurred at the very beginning (i.e., in the first pre-freezing period) of litter decomposition. Litter initial concentrations of phosphorus (P) and lignin were found to be the dominant chemical traits controlling cellulose degradation regardless of ecosystems type. The local-scale environmental factors such as temperature, pH, and nutrient availability were important moderators of cellulose degradation rate. Although the effects of common litter chemical traits (e.g., P and lignin concentrations) on cellulose degradation across different individual ecosystems were identified, local-scale environmental factors such as temperature and nutrient availability were found to be of great importance for cellulose degradation. These results indicated that local-scale environmental factors should be considered apart from litter quality for generating a reliable predictive framework for the drivers of cellulose degradation and further on litter decomposition at a global scale.

Foliar litter decomposition in an alpine forest meta-ecosystem on the eastern Tibetan Plateau

Litter decomposition is a biological process fundamental to element cycling and a main nutrient source within forest meta-ecosystems, but few studies have looked into this process simultaneously in individual ecosystems, where environmental factors can vary substantially. A two-year field study conducted in an alpine forest meta-ecosystem with four litter species (i.e., willow: Salix paraplesia, azalea: Rhododendron lapponicum, cypress: Sabina saltuaria, and larch: Larix mastersiana) that varied widely in chemical traits showed that both litter species and ecosystem type (i.e., forest floor, stream and riparian zone) are important factors affecting litter decomposition, and their effects can be moderated by local-scale environmental factors such as temperature and nutrient availability. Litter decomposed fastest in the streams followed by the riparian zone and forest floor regardless of species. For a given litter species, both the k value and limit value varied significantly among ecosystems, indicating that the litter decomposition rate and extent (i.e., reaching a limit value) can be substantially affected by ecosystem type and the local-scale environmental factors. Apart from litter initial acid unhydrolyzable residue (AUR) concentration and its ratio to nitrogen concentration (i.e., AUR/N ratio), the initial nutrient concentrations of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were also important litter traits that affected decomposition depending on the ecosystem type.

Chromium, Cadmium, and Lead Dynamics During Winter Foliar Litter Decomposition in an Alpine Forest River

ABSTRACTLittle information is currently available about heavy metal dynamics during litter decomposition in areas receiving few inputs of exotic metals. A field litter decomposition experiment was conducted during the winter in an alpine forest river on the eastern Tibetan Plateau. Concentrations, release rates, and release rate per day of chromium (Cr), cadmium (Cd), and lead (Pb) were investigated in the foliar litter of willow (Salix paraplesia), azalea (Rhododendron lapponicum), cypress (Sabina saltuaria), and larch (Larix mastersiana) during the prefreezing, freezing, and thawing periods. Concentrations of Cr in willow, cypress, and larch; Cd in all foliar litter types; and Pb in azalea foliar litter increased following incubation over an entire winter. Both Cr and Pb showed patterns of accumulation during the prefreezing period and patterns of release in the freezing and thawing periods, but Cd showed accumulation in all three periods. Water temperature, pH, flow velocity, conductivity, and nutrient availability in the river were significantly related to the dynamics of these heavy metals in the decomposing foliar litter. The heavy metal accumulation pattern in running water suggested an absolute increase in metal mass, indicating that litter may act as an efficient metal “cleaner” and contribute to an ecosystem’s capacity for self-purification.

Copper and zinc dynamics in foliar litter during decomposition from gap center to closed canopy in an alpine forest

ABSTRACTForest gap in alpine forests may redistribute the hydrothermal conditions in winter and growing season, which may affect the releases of copper and zinc in foliar litter during decomposition. However, the details of this process are largely unknown. Foliar litters of willow (Salix paraplesia), larch (Larix mastersiana), fir (Abies faxoniana), azalea (Rhododendron lapponicum), birch (Betula albosinensis) and cypress (Sabina saltuaria) were selected in an alpine forest of eastern Tibetan Plateau. The litterbags were placed on the forest floor from gap center, canopy gap edge and expanded gap edge to closed canopy. Zinc and copper contents were studied as litter decomposition proceeded. After one year of decomposition, zinc accumulated in all foliar litters regardless of gap positions, but copper accumulated in the litters of fir, azalea and cypress. Separately, copper was released from all foliar litters in winter, whereas zinc in litters of larch, azalea, birch and cypress was released in winter. Moreover, both copper and zinc accumulated during the growing season regardless of litter species. Nevertheless, higher accumulation rates were observed under closed canopy compared with other gap positions. These results suggest that forest gap slows the releases of copper and zinc in foliar litter during forest regeneration in these cold biomes.

Forest Gaps Inhibit Foliar Litter Pb and Cd Release in Winter and Inhibit Pb and Cd Accumulation in Growing Season in an Alpine Forest.

AimsThe release of heavy metals (such as Pb and Cd) from foliar litter play an important role in element cycling in alpine forest ecosystems. Although natural forest gaps could play important roles in the release of heavy metals from foliar litter by affecting the snow cover during the winter and solar irradiation during the growing season, few studies have examined these potential roles. The objectives of this study were to document changes in Pb and Cd dynamics during litter decomposition in the center of gaps and under closed canopies and to investigate the factors that controlled these changes during the winter and growing seasons.MethodsSenesced foliar litter from six dominant species, including Kangding willow (Salix paraplesia), Masters larch (Larix mastersiana), Mingjiang fir (Abies faxoniana), Alpine azalea (Rhododendron lapponicum), Red birch (Betula albosinensis) and Mourning cypress (Sabina saltuaria), was placed in litterbags and incubated between the gap center and closed canopy conditions in an alpine forest in the eastern region of the Tibetan Plateau. The litterbags were sampled at the snow formation stage, snow coverage stage, snow melt stage and during the growing season. The Pb and Cd concentrations in the sampled foliar litter were determined by acid digestion (HNO3/HClO4).Important findingsOver one year of decomposition, Pb accumulation and Cd release from the foliar litter occurred, regardless of the foliar litter species. However, Pb and Cd were both released from the foliar litter during the winter and accumulated during the growing season. Compared with the gap center and the canopy gap edge, the extended gap edge and the closed canopy showed higher Pb and Cd release rates in winter and higher Pb and Cd accumulation rates during the growing season, respectively. Statistical analyses indicate that the dynamics of Pb were significantly influenced by frequent freeze–thaw cycles in winter and appropriate hydrothermal conditions during the growing season, the dynamics of Cd were strongly influenced by species and the presence of a forest gap at different decomposition stages. These results show that forest gaps could inhibit Pb and Cd release from foliar litter in the alpine forest of western Sichuan. In addition, a decrease in the snow depth in the winter warming scenario would promote the release of Pb during foliar litter decomposition. There exist some difference that may be influenced by litter quality, microenvironment and microtopography during litter decomposition.

Temperature and delayed snowmelt jointly affect the vegetative and reproductive phenologies of four sub-Arctic plants

Over the coming decades, the Arctic is expected to experience warming temperatures and variable changes in the timing of snowmelt. Both temperature and the timing of snowmelt are important drivers of phenology and reproduction on the tundra. However, few studies have considered their combined effects, making it difficult to predict the direction and magnitude of Arctic plant responses to changing climates. In this 1-year study, we examine how temperature and delayed snowmelt jointly impact the phenology and reproductive effort/success of four common heath tundra species: Empetrum nigrum L., Rhododendron lapponicum (L.) Wahlenb., Dryas integrifolia Vahl, and Arctostaphylos rubra Fernald. We erected snow fences during the winter to increase snowpack on six plots (paired with six control plots), resulting in a consistent 10-day delay in the timing of snowmelt. During the subsequent growing season, we tracked how temperature and the delayed snowmelt on the treatment plots affected the day of onset of species’ phenophases, as well as their ability to flower and set fruit. Both temperature and snow addition were significant drivers of phenological onset in these species, though species showed different sensitivities to these factors, possibly as a result of differences in life history strategies. In addition, two of the four species responded positively to snow addition in terms of reproductive effort. Our results emphasize the importance of considering the simultaneous effects of the multiple drivers of Arctic plant phenology.