Diatom cell-size composition as a novel tool for quantitative estimates of the water table in peatlands.

Diatom cell-size composition is an indicator of aquatic environmental changes but has been rarely investigated, especially in semi-terrestrial peatlands. In this study, both taxonomic composition and cell-size composition of diatoms were analysed in 41 samples from two montane peatlands, northeastern China. Redundancy analyses revealed that diatom taxonomic composition was significantly related to the depth to the water table (DWT) and Ca2+, while cell-size composition was significantly associated with DWT and Si. DWT was the most important factor and its sole effect explained 26.2% and 17.9% of the total variance in taxonomic composition and cell-size composition, respectively. Accordingly, diatom-based water-table transfer functions were developed based on taxonomic composition and cell-size composition, respectively. The maximum-likelihood (ML) model based on diatom taxonomic composition had the best performance, with a correlation coefficient value (R2) of 0.78 and the root mean squared error of prediction (RMSEP) of 6.66 cm. The ML model based on cell-size composition had similar performance, with an R2 of 0.78 and the RMSEP of 6.87 cm, suggesting that diatom cell-size composition can be a new quantitative means to track past water-table changes. This method requires further appraisal with palaeoecological data but offers a new option that deserves exploration.

Smoke promotes germination of peatland bryophyte spores.

Northern peatlands are globally important carbon stores. With increasing fire frequency, the re-establishment of bryophytes becomes crucial for their carbon sequestration. Smoke-responsive germination is a common trait of seeds in fire-prone ecosystems but has not been demonstrated in bryophytes. To investigate the potential role of smoke in post-fire peatland recovery, we tested the germination of spores of 15 bryophyte species after treatment with smoke-water. The smoke responsiveness of spores with different laboratory storage times and burial depths/age (3-200 years) was subsequently tested. Smoke increased the germination percentage for 10 of the species and the germination speed for four of these. Smoke responsiveness increased along the fire frequency gradient from open expanse to forest margin, consistent with the theory that this selects for the maintenance of fire-adapted traits. Smoke enhanced the germinability of 1-year but not 4-year laboratory-stored spores, and considerably increased the germinability of spores naturally buried in peat for up to ~200 years. The effect of fire may be overlooked in non-fire-prone ecosystems, such as those in which wetland bryophytes dominate. Our study reveals a mechanism by which an increase in fire frequency may lead to shifts in species dominance, which may affect long-term carbon sequestration in peatlands.

Induced defense and its cost in two bryophyte species.

PREMISE: Current knowledge about defense strategies in plants under herbivore pressure is predominantly based on vascular plants. Bryophytes are rarely consumed by herbivores since they have ample secondary metabolites. However, it is unknown whether bryophytes have induced defenses against herbivory and whether there is a trade-off between growth and defense in bryophytes. METHODS: In an experiment with two peatland bryophytes, Sphagnum magellanicum Brid. and S. fuscum (Schimp.) H. Klinggr., two kinds of herbivory, clipping with scissors and grazing by mealworms (Tenebrio molitor L.) were simulated. At the end of the experiment, we measured growth traits, carbon-based defense compounds (total phenolics and cellulose) and storage compounds (total nonstructural carbohydrates) of these two Sphagnum species. RESULTS: Grazing but not clipping increased total phenolics and C:N ratio and reduced biomass production and height increment. A negative relationship between biomass production and total phenolics was found in S. magellanicum but not in S. fuscum, indicating a growth-defense trade-off that is species-specific. Grazing reduced the sugar starch content of S. magellanicum and the sugar of S. fuscum. Either clipping or grazing had no effect on chlorophyll fluorescence (including actual and maximum photochemical efficiency of photosystem II) except that a significant effect of clipping on actual photochemical efficiency in S. fuscum was observed. CONCLUSIONS: Our results suggest that Sphagnum can have induced defense against herbivory and that this defense can come at a cost of growth. These findings advance our knowledge about induced defense in bryophytes, the earliest land plants.

Estimating Chlorophyll Content of Leafy Green Vegetables from Adaxial and Abaxial Reflectance.

As a primary pigment of leafy green vegetables, chlorophyll plays a major role in indicating vegetable growth status. The application of hyperspectral remote sensing reflectance offers a quick and nondestructive method to estimate the chlorophyll content of vegetables. Reflectance of adaxial and abaxial leaf surfaces from three common leafy green vegetables: Pakchoi var. Shanghai Qing (Brassica chinensis L. var. Shanghai Qing), Chinese white cabbage (Brassica campestris L. ssp. Chinensis Makino var. communis Tsen et Lee), and Romaine lettuce (Lactuca sativa var longifoliaf. Lam) were measured to estimate the leaf chlorophyll content. Modeling based on spectral indices and the partial least squares regression (PLS) was tested using the reflectance data from the two surfaces (adaxial and abaxial) of leaves in the datasets of each individual vegetable and the three vegetables combined. The PLS regression model showed the highest accuracy in estimating leaf chlorophyll content of pakchoi var. Shanghai Qing (R2 = 0.809, RMSE = 62.44 mg m-2), Chinese white cabbage (R2 = 0.891, RMSE = 45.18 mg m-2) and Romaine lettuce (R2 = 0.834, RMSE = 38.58 mg m-2) individually as well as of the three vegetables combined (R2 = 0.811, RMSE = 55.59 mg m-2). The good predictability of the PLS regression model is considered to be due to the contribution of more spectral bands applied in it than that in the spectral indices. In addition, both the uninformative variable elimination PLS (UVE-PLS) technique and the best performed spectral index: MDATT, showed that the red-edge region (680-750 nm) was effective in estimating the chlorophyll content of vegetables with reflectance from two leaf surfaces. The combination of the PLS regression model and the red-edge region are insensitive to the difference between the adaxial and abaxial leaf structure and can be used for estimating the chlorophyll content of leafy green vegetables accurately.

Seed dormancy types and germination response of 15 plant species in temperate montane peatlands.

Despite their crucial role in determining the fate of seeds, the type and breaking mode of seed dormancy in peatland plants in temperate Asia with a continental monsoon climate are rarely known. Fifteen common peatland plant species were used to test their seed germination response to various dormancy-breaking treatments, including dry storage (D), gibberellin acid soaking (GA), cold stratification (CS), warm followed cold stratification (WCS), GA soaking + cold stratification (GA + CS) and GA soaking + warm followed cold stratification (GA + WCS). Germination experiment, viability and imbibition test, and morphological observation of embryos were conducted. Of the 15 species, nine showed physiological dormancy (PD), with non-deep PD being the dominant type. Four species, Angelica pubescens, Cicuta virosa, Iris laevigata, and Iris setosa exhibited morphophysiological dormancy. Two species, Lycopus uniflorus and Spiraea salicifolia, demonstrated nondormancy. Overall, the effect hierarchy of dormancy-breaking is: CS > GA > WCS > GA + CS > D > GA + WCS. Principal component analysis demonstrated that seed traits, including embryo length: seed length ratio, seed size, and monocot/eudicot divergence, are more likely to influence seed dormancy than environmental factors. Our study suggests that nearly 90% of the tested peatland plant species in the Changbai Mountains demonstrated seed dormancy, and seed traits (e.g. embryo-to-seed ratio and seed size) and abiotic environmental factors (e.g. pH and temperature seasonality) are related to germination behavior, suggesting seed dormancy being a common adaptation strategy for the peatland plants in the temperate montane environment.

The Response of Spore Germination of Sphagnum Mosses to Single and Combined Fire-Related Cues.

Plants in flammable ecosystems have different response strategies to fire, such as increasing germination after exposure to smoke and break of dormancy through heat shock. Peatlands are ecosystems that are more likely to be disturbed by fire with increasing temperatures, but it is not clear how fire affects spore germination of Sphagnum, the dominant plants in peatlands. Here, we hypothesize that Sphagnum spores respond positively to single and combined treatments of moderate heat and smoke (by increased germinability), while spore germinability decreases in response to high temperature. We exposed the Sphagnum spores of four selected species (S. angustifolium, S. fuscum, S. magellanicum and S. squarrosum) collected from peatlands in the Changbai Mountains to heat (40, 60 and 100 °C), on its own and combined with smoke-water treatments. Our results showed that a heat of 100 °C inhibited the spore germination or even killed spores of all species, while spore germination of three (Sphagnumangustifolium, S. fuscum and S. squarrosum) of the four species was promoted by 40 and 60 °C heat compared to the control (20 °C). Hollow species (S. angustifolium and S. squarrosum) showed a stronger positive responsive to heat than hummock species (S. fuscum and S. magellanicum). Sphagnumfuscum spores responded positively to the combined heat and smoke treatment while the other species did not. For the first time, we demonstrate the positive effects of heat on its own and in combination with smoke on spore germination in wetland mosses, which may be important for the establishment and persistence of peatmoss populations after fire.

Does Shift in Vegetation Abundance After Nitrogen and Phosphorus Additions Play a Key Role in Regulating Fungal Community Structure in a Northern Peatland?

Soil fungal communities are key players in biogeochemical processes of peatlands, which are important carbon stocks globally. Although it has been elucidated that fungi are susceptible to environmental changes, little is known about the intricate and interactive effect of long-term nitrogen (N) and phosphorus (P) enrichment on fungal community structure in northern peatlands. In this study, we compared a short- (2 years) with a long-term (10 years) fertilization experiment in a peatland complex in northeastern China to assess how N and/or P additions influence fungal community structure. The results showed that fungal community composition and diversity were altered by N addition, without a significant interactive effect with P addition. Not only the long-term but also the short-term nutrient addition could change the abundance of different plant functional types. However, there were no strong cascading effects on the fungal community in any of the fertilization experiments. Long-term nutrient addition showed a stronger effect on the relative abundance of different fungal functional guilds; an increase in the relative abundance of saprotrophs after fertilization did not jeopardize mycorrhizal fungi. Moreover, the decline in Sphagnum cover after long-term N addition did not parallel changes in the relative abundance of Sphagnum-associated fungi (Clavaria sphagnicola, Galerina tibiicystis, G. sphagnicola, and G. paludosa). Given that short- and long-term fertilization showed strongly contrasting effects on fungal community structure, our study highlights the necessity of assessing the long-term effects of nutrient enrichment on the association between vegetation and fungal community in peatland ecosystems. Future research priorities should emphasize the connection between the community structure of fungal functional guilds and their functionality, which is of paramount importance to better understand their influences on C storage in the face of uncertain N and P deposition regimes.

Direct and interaction-mediated effects of environmental changes on peatland bryophytes.

Ecosystem processes of northern peatlands are largely governed by the vitality and species composition in the bryophyte layer, and may be affected by global warming and eutrophication. In a factorial experiment in northeast China, we tested the effects of raised levels of nitrogen (0, 1 and 2 g m(-2) year(-1)), phosphorus (0, 0.1 and 0.2 g m(-2) year(-1)) and temperature (ambient and +3°C) on Polytrichum strictum, Sphagnum magellanicum and S. palustre, to see if the effects could be altered by inter-specific interactions. In all species, growth declined with nitrogen addition and increased with phosphorus addition, but only P. strictum responded to raised temperature with increased production of side-shoots (branching). In Sphagnum, growth and branching changed in the same direction, but in Polytrichum, the two responses were uncoupled: with nitrogen addition there was a decrease in growth (smaller than in Sphagnum) but an increase in branching; with phosphorus addition growth increased but branching was unaffected. There were no two-way interactions among the P, N and T treatments. With increasing temperature, our results indicate that S. palustre should decrease relative to P. strictum (Polytrichum increased its branching and had a negative neighbor effect on S. palustre). With a slight increase in phosphorus availability, the increase in length growth and production of side-shoots in P. strictum and S. magellanicum may give them a competitive superiority over S. palustre. The negative response in Sphagnum to nitrogen could favor the expansion of vascular plants, but P. strictum may endure thanks to its increased branching.

Hydrological variation recorded in a subalpine peatland of Northeast Asia since the Little Ice Age and its possible driving mechanisms.

Hydrological characteristics since the Little Ice Age (LIA) could provide a good reference for current climate analysis and future climate prediction. However, the hydrological variation since the LIA and its driving mechanisms in Northeast Asia remain unclear, which has severely restricted our understanding on the past, present and future hydroclimate changes in these regions. Here we reconstruct the hydrological dynamics over the past 700 years using samples from the Hani peatland a subalpine peatland of Changbai Mountains to reveal these issues. The analytical results from plant macrofossil and grain-size of the HN-1 core and the integrated moisture/precipitation records across the entire Northeast Asia indicate that the hydrological environments in Northeast Asia were wetter conditions during the period of 1300-1700 AD, dry conditions during the period of 1700-1850 AD, and wet conditions during the period of 1850-2018 AD, respectively. The possible driving mechanisms for the hydrological variations in Northeast Asia since the LIA can be divided into three models. La Niña-like conditions induced wetter conditions in Northeast Asia from 1300 to 1700 AD. From 1700 to 1850 AD, strong volcanic aerosol effects superimposed on weaker La Niña-like conditions, resulting in dry conditions in Northeast Asia. However, El Niño-like conditions induced wet conditions in Northeast Asia from 1850 to 2018 AD. These driving models suggest that the teleconnected influence of solar activity/sunspot could control the hydrological dynamics in Northeast Asia on a decadal-centennial scale through the ENSO activities and Walker Circulation changes since the LIA. Based on the periodicity relationship between hydrological conditions and sunspot, it can be predicted that the moisutre conditions in Northeast Asia would gradually decrease from 2030 to 2085 AD, and gradually increase from 2085 to 2140 AD.

The variations of surface wetness recorded by multi-proxies in Yuanchi peatland of the Changbai Mountains from 1962 to 2008.

Surface wetness of Yuanchi peatland in the Changbai Mountains were reconstructed by comprehensive analysis on plant residue, testate amoeba and humification, using the age-depth model established with AMS 14C and 137Cs dating methods. The response of surface wetness to climate change was addressed. Results showed that plant residues in the top 50 cm of peat sequence were dominated by mosses. Detrended correspondence analysis (DCA) of plant residue revealed that axis 1 of DCA biplot might represent mire surface wetness (MSW). MSW from 1962 to 2008 as indicated by axis 1 scores of DCA on plant residue were compared with depths to water table derived by testate amoebae-DWT transfer function and humification measurements, and the results showed that the trends of MSW reconstructed by three proxies were largely consistent. They were wetter MSW from 40-50 cm (1962 to 1975), 27-40 cm (fluctuating from wet to dry from 1975 to 1987), and 0-27 cm (drier from 1987 to 2008). Compared with instrumental data from nearby Erdao weather station, the reconstructed MSW was basically consistent with temperature change in this period. The decreases of MSW occurred when mean summer temperature and mean annual temperature were higher than long-term mean value. Our results suggest that the variability in MSW in the recent 46 years predominantly responded weakening of effective precipitation induced by increasing temperature.

Inhibition or Facilitation? Contrasted Inter-Specific Interactions in Sphagnum under Laboratory and Field Conditions.

In a natural environment, plants usually interact with their neighbors predominantly through resource competition, allelopathy, and facilitation. The occurrence of the positive effect of allelopathy between peat mosses (Sphagnum L.) is rare, but it has been observed in a field experiment. It is unclear whether the stability of the water table level in peat induces positive vs. negative effects of allelopathy and how that is related to phenolic allelochemical production in Sphagnum. Based on field experiment data, we established a laboratory experiment with three neighborhood treatments to measure inter-specific interactions between Sphagnum angustifolium (Russ.) C. Jens and Sphagnum magellanicum Brid. We found that the two species were strongly suppressed by the allelopathic effects of each other. S. magellanicum allelopathically facilitated S. angustifolium in the field but inhibited it in the laboratory, and relative allelopathy intensity appeared to be positively related to the content of released phenolics. We conclude that the interaction type and intensity between plants are dependent on environmental conditions. The concentration of phenolics alone may not explain the type and relative intensity of allelopathy. Carefully designed combined field and laboratory experiments are necessary to reveal the mechanism of species interactions in natural communities.

[Responses of the germinability of Sphagnum spores in peat to drainage in Baijianghe Peatland, China]. / 白江河泥炭地泥炭藓孢子萌发力对排水的响应.

Drainage severely changes the environment and ecological process in peatlands, but how does it affect the germinability of Sphagnum spores in peat remains unclear. In this study, we took two peat cores from a near-pristine stand dominated by Sphagnum and a drained stand dominated by dwarf shrubs in Baijianghe Peatland in the Changbai Mountains as experimental materials. Those peat cores were cut into slices. Physicochemical characteristics were measured while Sphagnum spores from each slice were extracted to count spore density and test spore germinability. After dating and determining relationship between peat depth and age, we tried to figure out the mechanism underlying the responses of Sphagnum spore germinability to drainage. The average number of spores in the near-pristine stand was slightly higher than that in the drained stand. There was no difference in average spore germinability between the two stands. The drained stand showed higher peat bulk density, total carbon and total nitrogen relative to the near-pristine stand. Upper peat core showed no significant difference in spore accumulation rate between the two stands after drainage (in 1987), with lower average spore germinability (34%) in the near-pristine stand relative to the drained stand (72%). For the whole peat cores, C/N was positively correlated with spore ger-minability in the near-pristine stand while total carbon, pH and burial time were negatively correlated with spore germinability in the drained stand. The drainage 30 years ago had limited effect on spore accumulation, but improved germinability of spores in shallow peat by changing physicochemical properties of peat due to accelerating decomposition, and thus reduced the persistence of spore bank. This may reduce the persistent regeneration potential of Sphagnum after catastrophic distur-bances.

Diatom-based water-table reconstruction in Sphagnum peatlands of northeastern China.

Peatlands are important ecosystems for biodiversity conservation, global carbon cycling and water storage. Hydrological changes due to climate variability have accelerated the degradation of global and regional ecosystem services of peatlands. Diatoms are important producers and bioindicators in wetlands, but comprehensive diatom-based inference models for palaeoenvironmental reconstruction in peatlands are scarce. To explore the use of diatoms for investigating peatland hydrological change, this study established a training set consisting of diatom composition and twelve environmental factors from 105 surface samples collected from five Sphagnum peatlands in northeastern China. Diatom communities were dominated by Eunotia species. Ordination analyses showed that depth to the water table (DWT) was the most important factor influencing diatom distribution, independently accounting for 4.99% of total variance in diatom data. Accordingly, a diatom-based DWT transfer function was developed and thoroughly tested. The results revealed that the best-performing model was based on weighted averaging with inverse deshrinking (R2 = 0.66, RMSEP = 8.8 cm with leave-one-out cross validation). Quantitative reconstruction of DWT on a short peat core collected from the Aershan Peatland (Inner Mongolia) recorded climate-mediated hydrological changes over the last two centuries. This study presents the first diatom-water table transfer function in Sphagnum peatlands, and highlights the potential of diatoms as a powerful tool to assess the magnitude of past hydrological changes in peatlands of northeastern China, as well as similar peaty environments worldwide.

[Simulated study on the effects of smoke on Sphagnum spore germination]. / çƒŸæ°”å¯¹æ³¥ç‚­è—“å­¢å­èŒå‘å½±å“çš„æ¨¡æ‹Ÿç ”ç©¶.

Moderate smoke could facilitate seed germination, but its effects on bryophyte spore germination is still unknown. Here, we analyzed the effects of smoke, capsule size and storage time on the spore germination of Sphagnum squarrosum and S. magellanicum, with the capsules of which being collected from two peatlands of the Changbai Mountains. The smoke solution prepared by burning peatland plants was combined with the capsules with different sizes (large, 2.10-2.50 mm in diameter; small, 1.50-1.90 mm in diameter) and storage time (old, being stored for 4.3 or 6.3 a; new, being stored for 0.3 a) to conduct a factorial experiment. The spores were soaked with smoke solution for different durations and then cultured for germination. The results showed that smoke solution affected spore germination. After 10 d cultivation, germination rate of spores soaking with smoke solution for all duration was increased by more than 5-fold, with the small spores having higher germination rate. After 21 d cultivation, the facilitative effect was only observed in moderate soaking (3 d), and spore size showed no effect on germination. Smoke solution could not increase the germination of spores from the capsules with long storage time (4.3 and 6.3 a). Our results indicated that moderate smoke solution soaking might accelerate germination of Sphagnum spores including small pores. In the ecosystems with casual fire disturbance such as peatlands, similar with its effects on the seed plants, smoke might play a key role in the regeneration and persistence of bryophyte population.

The development of Hani peatland in the Changbai mountains (NE China) and its response to the variations of the East Asian summer monsoon.

The past ecosystem responses to climate variability makes it possible to view the sensitivity of ecosystems to climate-forced state shifts. To test the hypothesis that the development of peatland in the Changbai Mountains responds to the variability of the East Asian summer monsoon (EASM), the developmental history of the Hani peatland was investigated based on peat basal ages. It can be concluded that the development of Hani peatland is the paludification. The development of the northern region started 13,685 cal. yr BP, while that of the southern region was initiated 7705 cal. yr BP. In addition, the moisture changes and development of the Hani peatland can be divided into three periods. From 16 to 7 ka cal. BP, the increase in the EASM was induced by the lower sea level and southward displacement of the Western Pacific Subtropical High (WPSH), resulting in increasing moisture in the Hani peatland. Peat was gradually established in the northern region. From 7 to 2 ka cal. BP, the increased relative sea level and northward displacement of the WPSH induced the maximum EASM. The EASM and Northeast Monsoon (NEM) induced the maximum moisture in the Hani peatland. Both the northern and southern regions were covered with peat during this period. Since 2 ka cal. BP, the decreasing EASM might be related to the seasonal decrease in the Northern Hemisphere summer insolation and ENSO intensity. Thus, the decreasing EASM induced the decrease in the moisture in the Hani peatland. Peat further accumulated in both the northern and southern regions. This study will help to understand the future EASM behavior in NE China and the development of similar peatlands in response to ongoing and future climatic change.

Degradation of polycyclic aromatic hydrocarbons (PAHs) during Sphagnum litters decay.

The dynamics of polycyclic aromatic hydrocarbon (PAH) degradation in Sphagnum litters and the decomposition of the litters were investigated. PAH concentration decreased to approximately half of the initial concentration as Sphagnum litters decayed. The initial PAH concentration was 489.2 ± 72.2 ng g-1, and the concentration after 120 days of incubation was 233.0 ± 5.8 ng g-1. The different PAH compositions changed concentrations at different times. The low-molecular-weight (LMW) and high-molecular-weight (HMW) PAHs started to be degraded after incubation and after 40 days of incubation, respectively. PAH concentrations in the Sphagnum litters correlated with the total organic carbon (TOC) content (p < 0.05), indicating that PAHs were associated with the TOC of the Sphagnum litters and were degraded as organic matter decayed. The positive relationship between LMW PAH concentration and the soluble carbohydrate content (p < 0.05) indicated that LMW PAHs and the readily decomposed organic carbon fractions were cometabolized, or that LMW PAHs were mainly absorbed by soluble carbohydrate. The weak negative correlation between fulvic acid (FA) and PAH concentrations (p < 0.1) indicated that FA may enhance PAH degradation. Redundancy analysis suggested that the contents of both soluble carbohydrate and cellulose significantly affected the changes in PAH concentrations (p < 0.05), and that FA content and C/N ratios may also contribute to the changes in PAH concentrations (p < 0.1). However, the polyphenol that was related to microbial activities was not associated with changes in PAH concentrations. These results suggested that litter quality is more important than microbial activities in PAH degradation in Sphagnum litters.

Mercury and arsenic in the surface peat soils of the Changbai Mountains, northeastern China: distribution, environmental controls, sources, and ecological risk assessment.

The potential toxic risk of mercury (Hg) and arsenic (As) in the soils of mining regions and other artificially disturbed lands receives considerable research attention. However, limited investigation has been conducted into the surface soils of natural globally distributed ecosystems, for example peatlands. In this study, we examine the distribution, controlling factors, sources, and potential ecological risks of Hg and As in 96 samples from 42 peatlands in the Changbai Mountains of northeastern China. The results showed that average concentrations (dry weight) of Hg and As at the samples sites were 169.1 ± 0.1 µg kg-1 and 13.0 ± 7.7 mg kg-1, respectively. The distribution of Hg is largely determined by latitude and altitude, while As is controlled more by pH, total organic carbon (TOC), and ratio of TOC and nitrogen (C/N) at the regional scale. Variations in TOC, C/N ratio, and redox conditions contribute to determining the distribution of Hg, while TOC and redox conditions mainly affected the distribution of Arsenic at the local scale. Mercury mostly comes from regional atmospheric wet deposition, whereas elevated concentrations of As are related to local anthropogenic activities. Overall, Hg and As in the peatlands of the Changbai Mountains pose a moderate level of potential risk to ecological health.

Variations in diatom communities at genus and species levels in peatlands (central China) linked to microhabitats and environmental factors.

Peatlands are a specialized type of organic wetlands, fulfilling essential roles as global carbon sinks, headwaters of rivers and biodiversity hotspots. Despite their importance, peatlands are being lost at an alarming rate due to human disturbance and climatic variability. Both the scientific and regulatory communities have focused considerable attention on developing tools for assessing environmental changes in peatlands. Diatoms are widely used in biomonitoring studies of lakes, rivers and streams as they have high abundance, specific ecological preferences and can respond rapidly to environmental change. However, diatom-based assessment studies in peatlands remain limited. The aims of this study were to identify indicator species and genus for three types of habitats (hummocks, hollows and ditch edges) in peatlands (central China), to examine the effects of physiochemical factors on diatom composition at genus and species levels, and to compare the efficiency of species- and genus-level identification in environmental assessment. Our results revealed that hummocks were characterized by drought-tolerant diatoms, while hollows were dominated by species and genus preferring wet conditions. Ditch edges were characterized by diatoms with different life strategies. Depth to water table, redox potential, conductivity and calcium were significant predictors of both genus- and species-level composition. According to ordination analyses, pH was not correlated with species composition while it was a significant factor associated with genus-level composition. Genus-level composition outperformed species composition in describing the response of diatoms to environmental variables. Our results indicate that diatoms can be useful environmental indicators of peatlands, and show that genus-level taxonomic analysis can be a potential tool for assessing environmental change in peatlands.

Is there 'anther-anther interference' within a flower? Evidences from one-by-one stamen movement in an insect-pollinated plant.

The selective pressure imposed by maximizing male fitness (pollen dispersal) in shaping floral structures is increasingly recognized and emphasized in current plant sciences. To maximize male fitness, many flowers bear a group of stamens with temporally separated anther dehiscence that prolongs presentation of pollen grains. Such an advantage, however, may come with a cost resulting from interference of pollen removal by the dehisced anthers. This interference between dehisced and dehiscing anthers has received little attention and few experimental tests to date. Here, using one-by-one stamen movement in the generalist-pollinated Parnassia palustris, we test this hypothesis by manipulation experiments in two years. Under natural conditions, the five fertile stamens in P. palustris flowers elongate their filaments individually, and anthers dehisce successively one-by-one. More importantly, the anther-dehisced stamen bends out of the floral center by filament deflexion before the next stamen's anther dehiscence. Experimental manipulations show that flowers with dehisced anther remaining at the floral center experience shorter (1/3-1/2 less) visit durations by pollen-collecting insects (mainly hoverflies and wasps) because these 'hungry' insects are discouraged by the scant and non-fresh pollen in the dehisced anther. Furthermore, the dehisced anther blocks the dehiscing anther's access to floral visitors, resulting in a nearly one third decrease in their contact frequency. As a result, pollen removal of the dehiscing anther decreases dramatically. These results provide the first direct experimental evidence that anther-anther interference is possible in a flower, and that the selection to reduce such interferences can be a strong force in floral evolution. We also propose that some other floral traits, usually interpreted as pollen dispensing mechanisms, may function, at least partially, as mechanisms to promote pollen dispersal by reducing interferences between dehisced and dehiscing anthers.