Reproductive Shoots Research Articles

Increased Coastal Nutrient Loading Enhances Reproductive Intensity of Zostera marina: Implications for Seagrass Meadow Resilience

Because sexual reproduction is essential for the establishment and persistence of seagrass meadows, flowering intensity is an important trait that influences the resilience and stability of seagrass populations. Although the effects of excessive coastal nutrient loading on seagrass vegetative growth have been extensively documented, the effects on seagrass reproductive phenology and intensity remain unclear. To examine the reproductive responses of seagrass populations to increased coastal nutrient loading, the flowering phenology and intensity of Zostera marina were compared between sites with high-nutrient, low-light conditions (Deukryang Bay and Dongdae Bay) and low-nutrient, high-light conditions (Koje Bay) on the southern coast of Korea. Nutrient contents of the above- and below-ground tissues of Z. marina reflected in situ nutrient and light availability at the study sites. Reproductive shoot density and biomass, as well as flowering frequency and reproductive effort, were much higher (1.5–4.6-fold) at the high-nutrient, low-light study sites of Deukryang Bay and Dongdae Bay than at the low-nutrient, high-light site of Koje Bay. Consequently, potential seed production was higher in Deukryang Bay and Dongdae Bay than in Koje Bay. Chronic high-nutrient and low-light conditions significantly increased the reproductive intensity of Z. marina, supporting the persistence and resilience of Z. marina populations. The results of this study could provide insights into the conservation and management of seagrass meadows under increased coastal nutrient loading.

Detection of Management Practices and Cropping Phases in Wild Lowbush Blueberry Fields Using Multispectral UAV Data

Normalized difference vegetation index (NDVI) and normalized difference red-edge index (NDRE) are vegetation indices commonly used in agriculture to provide information on crop’s growth and health. Here, we investigated the sensitivity of both indices to management practices in lowbush blueberry fields. Images of the experimental plots were collected with a multispectral camera installed on an unmanned aerial vehicle. Both NDVI and NDRE values were significantly higher in fertilized plots than in controls (0.88 ± 0.03 vs. 0.79 ± 0.03 for NDVI, and 0.37 ± 0.01 vs. 0.33 ± 0.01 for NDRE) due to fertilization effect on vegetative growth. The increase was higher under mineral than organic fertilization during the two first phases of the cropping system (by ∼0.3 and ∼0.2 for NDVI and NDRE, respectively). NDRE was not affected by thermal pruning and fungicide application but was negatively correlated with Septoria infection level. NDVI was more strongly correlated with stem length than NDRE, but unlike NDRE, NDVI was not impacted by the development of reproductive shoots during the harvest phases. Overall, the results indicate that although both index values are correlated, their sensitivity to changes in canopy characteristics differs depending on the cropping phase. Further research must be conducted to relate these indices to blueberry’s nutrient status.

Effects of source-sink alteration by pruning on physiological parameters and fruit production of Rosa roxburghii Tratt. on the Yunnan-Guizhou Plateau in China

The formation of economic yield and fruit quality of Roxburgh rose (Rosa roxburghii Tratt.) depends essentially on its source-sink interaction. Thus, a pruning experiment was conducted to assess the effects of source-sink regulation on photosynthetic physiology and fruit yield of Roxburgh rose, which was of great significance to production. Cutting off vegetative branches reduced physiological fruit loss and malformed fruits but increased single fruit quality and yield. Results revealed that the stomatal characteristics, the composition of mesophyll tissue, and photosynthesis of leaves on reproductive branches were significantly affected by the ratio of the vegetative and reproductive shoots. Our data indicated that the source-sink ratio could reflect the balance between vegetative growth and reproductive growth of the tree during the whole fruit period. Fruit tree pruning had guiding significance for improving the fruit yield of Roxburgh rose.

Management of macro and micro nutrients to suppress flower yield fluctuations in productive clove

Yield fluctuations in cloves are still an unsolved problem. This study aimed to increase vegetative and reproductive shoots to stimulate flowering by applying macro and micronutrients using 30 years old clove-plant. The treatments tested were: (p0) control, (p1) NPKMg (4:1:3:0,4), (p2) NPKMg (4:1:3:0,4) + 30 g B + 30 g Zn, and (p3) NPKMg (4:1:3:0,4) + 60 g B + 60 g Zn. The dose of NPKMg given was adjusted to the plant-based on the SOP for fertilizing cloves aged 34 years, namely 8.4 kg (N=4 kg, P2O5=1 kg, K2O=3 kg, and MgO=0.4 kg per tree per year). The results showed that fertilizer application could improve canopy and branch conditions after a large harvest season and increase the number of shoots. Meanwhile, micro fertilizers B and Zn (p3) application during the small harvest season can increase the production of fresh flowers 303.27-516.67% higher than the control. During the medium harvest season, it is only 122.37%. In the large harvest season, macro fertilizer (p1) increased the production of fresh flowers by 135.53%, higher than the control. This study indicates that clove plants aged >30 years can still increase their productivity through macro and micronutrient management and suppress yield fluctuations.

О таксонах рода × Trisetokoeleria (Poaceae) в российской Арктике

An amplified description of the Siberian Arctic species × Trisetokoeleria taimyrica Tzvelev is compiled, based on the study and measurements of about 100 reproductive shoots (10 herbarium sheets) stored in the Herbarium of the Komarov Botanical Institute RAS (LE), including the neotype designated by the authors and 4 authentic herbarium specimens identified by N. N. Tzvelev. The main distinctive characters of the three species of the genus × Trisetokoeleria are given in the table, taking into account additional data on × T. taimyrica. The difficulty of recognizing the × Trisetokoeleria species in nature (the use of optics is necessary) is complicated by a weak difference in key features, primarily between T. gorodkowii (Roshev.) Tzvelev and T. taimyrica. The third species, namely T. jurtzevii Prob., clearly differs from the other two by pubescent (hairy) inflorescence branchlets and longer awns. × T. taimyrica differs from × T. gorodkowii by narrower, few-flowered panicles, glumes of slightly (vs. strongly) unequal length, and acuminate (vs. obtuse) lemma tips, and from × T. jurtzevii by glabrous stem, panicle branchlets and lemmas, as well as by shorter awns and narrower few-flowered panicles. Its differences from postulated parent species are as follows: from Koeleria asiatica Pers. — a short straight awn extending below the lemma tip (vs. extending from the very tip of the lemma, that is sometimes observed in K. asiatica), and glabrous stems and panicle branchlets; from Trisetum agrostideum (Laest.) Fr.) — a very short, straight awn extending slightly below the lemma tip (vs. twice articulated and extending slightly above ½ or at upper ⅓ of the lemma), as well as spike-like panicles. A map of the localities of the three × Trisetokoeleria species is compiled.

Evolution of Leaf Fusion in Honeysuckle (Periclymenum,Lonicera)

Premise of research. Fused or connate leaves are a well-known phenomenon observed across a limited number of angiosperm clades, and no study has attempted to examine this form of fusion from an evolutionary, morphometric, or functional perspective. We examined leaf fusion in honeysuckles, specifically the Periclymenum clade (∼22 species) of Lonicera (Caprifoliaceae, Dipsacales), which exhibits variation in leaf shape, degree of fusion, and the position of fused leaves. As fused leaves co-occurred with reproductive structures, evolutionary correlations between leaf fusion and inflorescence architecture were also examined.Methodology. Variation of leaf fusion was assessed using elliptical Fourier analysis, and multiple individuals of 19 of the 22 species of Periclymenum were sampled. As fused leaves occurred only on reproductive shoots, a suite of inflorescence characters were also studied. A phylogeny for Periclymenum was reconstructed using published sequence data, and this tree was used for ancestral character state reconstructions and correlation analyses.Pivotal results. Leaves directly subtending inflorescences of Periclymenum were free or fused but were rarely partially fused. Fused leaves were ancestral to Periclymenum and were lost in parallel. Leaf fusion was not correlated with inflorescence architecture features, yet inflorescence architecture has become more complex among Periclymenum species.Conclusions. While free leaves are the ancestral condition in the Dipsacales, fused leaves have been gained at least three times and lost at least twice. Given the proximity of fused leaves to reproductive structures, particularly in Lonicera, fused leaves may play a role in protection or in the discovery of flowers and fruits by pollinators and seed dispersers, respectively.

Reproductive ecology of Zostera marina L. (eelgrass) across varying environmental conditions

Sexual reproduction is critical to the resilience of seagrass beds impacted by habitat degradation or environmental changes, as robust seed banks allow new shoots to establish each year. Reproductive strategies of seagrass beds range on a continuum from strictly annual to perennial, driven by local environmental conditions. We examined the reproductive dynamics of Zostera marina beds at six sites on the Atlantic coast of Canada to characterize how life history strategies are shaped by the surrounding environment. Sites were categorized as wave protected and wave exposed, where protected sites were warm, shallow, with little water movement and muddy sediments, and exposed sites were either shallow or deep, with cooler water and sandy sediments. While mixed life history strategies were evident at all sites, protected eelgrass beds exhibited both the highest and lowest sexual reproductive effort relative to exposed beds. These beds regularly experienced thermal stress, with higher temperature range and extended warm water events relative to exposed beds. The development of reproductive shoots were similar across sites with comparable Growing Degree-days at the beginning and end of anthesis, but the First Flowering Date was earlier at the protected warmer sites relative to exposed sites. With different reproductive shoot density among sites, seed production, seed retention, and seedling recruitment also varied strongly. Only one site, located in a warm, shallow and protected lagoon, contained a mixed life history population with a high reproductive effort (33.7%), strong seed bank, and high seedling establishment. However, a primarily perennial population with the lowest reproductive effort (0.5%) was identified at the warmest site, suggesting that conditions here could not support high sexual reproduction. Robustness of seed banks was strongly linked to reproductive shoot density, although the role of seed retention, germination and seedling survival require further investigation. Our study provides insights into one key aspect of seagrass resilience, and suggests that resilience assessments should include reproductive shoot density to inform their management and conservation.

The use of plant ontologies in comparative and evolutionary studies should be flexible

The use of plant ontologies in comparative and evolutionary studies should be flexible

Integrated dominance mechanisms regulate reproductive architecture in Arabidopsis thaliana and Brassica napus.

The production of seed in flowering plants is complicated by the need to first invest in reproductive shoots, inflorescences, flowers, and fruit. Furthermore, in many species, it will be months between plants generating flowers and setting seed. How can plants therefore produce an optimal seed-set relative to environmental resources when the "reproductive architecture" that supports seed-set needs to be elaborated so far in advance? Here, we address this question by investigating the spatio-temporal control of reproductive architecture in Arabidopsis (Arabidopsis thaliana) and Brassica napus. We show that resource and resource-related signals such as substrate volume play a key role in determining the scale of reproductive effort, and that this is reflected in the earliest events in reproductive development, which broadly predict the subsequent reproductive effort. We show that a series of negative feedbacks both within and between developmental stages prevent plants from over-committing to early stages of development. These feedbacks create a highly plastic, homeostatic system in which additional organs can be produced in the case of reproductive failure elsewhere in the system. We propose that these feedbacks represent an "integrated dominance" mechanism that allows resource use to be correctly sequenced between developmental stages to optimize seed set.

Effect of depth gradient and temperature on Zostera marina vegetative and reproductive phenology in the first year of the 1997–1998 El Niño

Does Zostera marina exhibit phenotypic plasticity, maximizing fitness in traits responding to environmental factors, i.e., depth and temperature? We compared the vegetative and sexual phenology and reproductive effort of Z. marina by analyzing vegetative and reproductive shoot density, biomass, and reproductive stages to determine structural features of vegetative and reproductive shoots from subtidal and intertidal environments in San Quintín Bay, Baja California, a year before and after the 1997–1998 El Niño/Southern Oscillation (ENSO). We found significant differences in vegetative and reproductive biomass between intertidal and subtidal environments driven by temperature differences between ENSO and non-ENSO years. Subtidal plants had lower density of long reproductive shoots and a shorter reproductive cycle. Seed release occurred from May to October in the subtidal environment, and from May to November in the intertidal environment. Maximal recorded values were 219.5 (±45.8) seeds per reproductive shoot in the subtidal environment and 151.3 (±21.5) in the intertidal environment. We observed higher sexual activity and lower vegetative biomass in the intertidal environment, the most stressful environment. Both vegetative and reproductive biomass were affected by the increase in temperature during ENSO, but vegetative and reproductive shoot densities were not affected.

Phenology of Zostera caespitosa in Tongyeong on the coast of Korea

The variations of morphological features, density and biomass of vegetative shoots and characteristics of reproductive shoots of Zostera caespitosa were examined in Tongyeong, Korea. Morphological features such as leaf length, width and sheath length of Z. caespitosa showed significant seasonal variation (p < 0.001). The highest aboveground value was recorded in late spring to summer and the lowest value in winter. Density and biomass also showed seasonal variations. Annual average shoot density and biomass of Z. caespitosa were recorded as 1,223.4 leaf m−2 and 5,956.9 g w.w.m−2, respectively, and had the highest value in June and lowest values in November and January. Reproductive shoots were observed from April (13°C) to June (21°C). Pistils erected outside sheath, anther dehiscing and small embryos were found in April. Mature fruit and released seeds were found in May and June. These results suggest that this species had a high growth rate in late spring and early summer (15°C–20°C). Reproductive shoots of Z. caespitosa may initially appear at about 10°C in spring and seed have been released at about 20°C in fall.

Growth and reproductive responses of the seagrass Zostera marina to sediment nutrient enrichment

Abstract Nutrient loading into coastal sediments is increasing due to anthropogenic activity and climate change. We examined the effects of sediment nutrient enrichment on the growth and reproduction of Zostera marina by adding nitrogen (N) and phosphorus (P) fertilizers into sediments. Areal productivity and shoot density increased by ca. 60% in N and N + P enrichment plots and by ca. 20% in the P enrichment plots. Biomass and shoot height were also higher in the N and N + P enrichment plots than in the P enrichment and control plots. These results suggest that sediment N availability was more important than P availability in stimulating the vegetative growth of Z. marina . The density and morphology of reproductive shoots and seed production increased in only the N enrichment plots. The sediment N enrichment stimulated both the vegetative growth and sexual reproduction, improving the meadow resilience through both sexual and asexual mechanisms. The P enrichment slightly increased only the vegetative growth and might have limited influence on seagrass reproduction. According to these results, the alteration of the sediment nutrient regimes might shift the balance between the vegetative growth and sexual reproduction of Z. marina. These findings may have important implications for the management of seagrass meadows under fluctuations in sediment nutrients caused by anthropogenic activity and climate change.

Abiotic and Biotic Interactions Control Ruppia maritima Life History Development Within a Heterogeneous Coastal Landscape

Habitat-forming submerged aquatic vegetation (SAV) in estuaries increasingly depend on sexual recruitment from propagules for population sustainability under varying conditions from climate and human-induced changes. Seed recruitment requires successful transitions through multiple life history stages, but few studies have examined abiotic and interspecies interactions on multiple life stages in SAV. A series of field experiments in Florida Bay quantified impacts of abiotic (salinity, temperature, light, sediment nutrients) and biotic (interspecific SAV interactions) factors on seedlings, adult individuals (genets), and shoots (ramets) of the SAV Ruppia maritima. Five study sites were established at the Everglades-Florida Bay ecotone, where seed recruitment sustains R. maritima. Seedling survival was low (≤ 16%), and further reduced under low light, P-limitation and competition with the macroalga Chara hornemannii. Significantly high genet survival and vegetative and sexually reproductive shoot production (4400 m−2 and 300 m−2, respectively) were found at a site where nutrients (P) were sufficient, when C. hornemannii was absent and light levels were three-times higher during the dry season (~ 14000 lumens m−2; December–March) than any other time of year. At P-limited sites, vegetative shoot production occurred with adequate light (> 20,000 lumens m−2) at stable salinities (CV 0.5) where 30–45-day averages remained < 15. However, variable or elevated salinity delayed vegetative shoot production ~ 60 days, suggesting salinity stress limits asexual reproduction. Understanding how light and P-limitation, salinity stress, and competition controls R. maritima recruitment in the Everglades is essential to its management for restoration and climate change.

Managing flowering time in Miscanthus and sugarcane to facilitate intra- and intergeneric crosses.

Miscanthus is a close relative of Saccharum and a potentially valuable genetic resource for improving sugarcane. Differences in flowering time within and between Miscanthus and Saccharum hinders intra- and interspecific hybridizations. A series of greenhouse experiments were conducted over three years to determine how to synchronize flowering time of Saccharum and Miscanthus genotypes. We found that day length was an important factor influencing when Miscanthus and Saccharum flowered. Sugarcane could be induced to flower in a central Illinois greenhouse using supplemental lighting to reduce the rate at which days shortened during the autumn and winter to 1 min d-1, which allowed us to synchronize the flowering of some sugarcane genotypes with Miscanthus genotypes primarily from low latitudes. In a complementary growth chamber experiment, we evaluated 33 Miscanthus genotypes, including 28 M. sinensis, 2 M. floridulus, and 3 M. ×giganteus collected from 20.9° S to 44.9° N for response to three day lengths (10 h, 12.5 h, and 15 h). High latitude-adapted M. sinensis flowered mainly under 15 h days, but unexpectedly, short days resulted in short, stocky plants that did not flower; in some cases, flag leaves developed under short days but heading did not occur. In contrast, for M. sinensis and M. floridulus from low latitudes, shorter day lengths typically resulted in earlier flowering, and for some low latitude genotypes, 15 h days resulted in no flowering. However, the highest ratio of reproductive shoots to total number of culms was typically observed for 12.5 h or 15 h days. Latitude of origin was significantly associated with culm length, and the shorter the days, the stronger the relationship. Nearly all entries achieved maximal culm length under the 15 h treatment, but the nearer to the equator an accession originated, the less of a difference in culm length between the short-day treatments and the 15 h day treatment. Under short days, short culms for high-latitude accessions was achieved by different physiological mechanisms for M. sinensis genetic groups from the mainland in comparison to those from Japan; for mainland accessions, the mechanism was reduced internode length, whereas for Japanese accessions the phyllochron under short days was greater than under long days. Thus, for M. sinensis, short days typically hastened floral induction, consistent with the expectations for a facultative short-day plant. However, for high latitude accessions of M. sinensis, days less than 12.5 h also signaled that plants should prepare for winter by producing many short culms with limited elongation and development; moreover, this response was also epistatic to flowering. Thus, to flower M. sinensis that originates from high latitudes synchronously with sugarcane, the former needs day lengths >12.5 h (perhaps as high as 15 h), whereas that the latter needs day lengths <12.5 h.

Variability in fruit traits and anthocyanin content among and within populations of underutilized Patagonian species Berberis microphylla G. Forst.

BACKGROUND: The Berberis microphylla (calafate) is an evergreen shrub considered a non-timber product from the Patagonian forest, relevant for the diversification of agrifood production, particularly interesting since its black–blue fruits are extremely rich in phenolic compounds. OBJECTIVE: The main objectives were to: (1) quantify the variability of fruit traits, anthocyanin content, efficiency of the reproductive shoots and leaf nutrient content within the set of 34 B. microphylla wild accessions from Tierra del Fuego Island, Argentina, (2) calculate the coefficients of correlation between variables and (3) detect relationships between the genotypes. METHODS: Plants growing near Ushuaia city (n = 12), bordering Fagnano lake (n = 12) and central area of the Tierra del Fuego Island (n = 10) were selected. RESULTS: A significant variability in fruit traits, anthocyanin content and the efficiency of reproductive shoots among and within the three populations was assessed, a result with great relevance for breeding purposes. Phenotypic plasticity was related with the environmental conditions, i.e. air temperatures for each population during the three monitored growing seasons. CONCLUSIONS: Overall, results indicate that yearly environmental factors play a relevant role in phenotypic variation of both individual plants and populations, thus confirming the complexity of wild species evolution and domestication processes.

STATE OF COENOPOPULATIONS OF ORCHIDS IN THE MIDDLE-COURSE PECHORSKAYA PIZHMA RIVER CATCHMENT (PIZHEMSKIY NATURE RESERVE, KOMI REPUBLIC)

Nine species of Orchidaceae were studied through fieldwork in July 2018 in the integrated nature reserve Pizhemskiy (middle-course Pechorskaya Pizhma River catchment, Komi Republic): Coeloglossum viride (L.) Hartm., Corallorhiza trifida Châtel., Cypripedium calceolus L., C. guttatum Sw., Dactylorhiza fuchsii (Druce) Soó, Epipactis atrorubens (Hoffm.) Besser, Gymnadenia conopsea (L.) R. Br., Listera cordata (L.) R. Br., and L. ovata (L.) R. Br. Data on their distribution and phytocoenotic affiliations in this territory are provided. L. ovata was found in this protected area for the first time. Point maps of the orchids’ distribution in the surveyed part of the Middle Timan were compiled. Mostof the studied plant populations are confined to calcareous rock outcrops in the valley of the Pechorskaya Pizhma River. A total of 35 coenopopulations of seven orchid species were studied during the expedition. Orchids were found to be well adapted to the environmental conditions of the Middle Timan as evidenced by the relatively high abundance of the coenopopulations, successful reproduction, and conformance of ontogenetic spectra to specific biological characteristics. The main limiting factor for the reproduction of orchids is the short growing season. Early-summer frosts damage flower buds, especially in early flowering species (C. calceolus, C. guttatum), while late-summer frosts lead to the formation of damaged reproductive shoots in E. atrorubens. It can be concluded from the research results that the Pizhemskiy Nature Reserve is a unique area where habitats of such rare and vulnerable plants as orchids are preserved in their original state, offering good conditions for sustainable existence of their populations.

In situ Responses of the Eelgrass Zostera marina L. to Water Depth and Light Availability in the Context of Increasing Coastal Water Turbidity: Implications for Conservation and Restoration.

Accelerating losses of seagrass meadows has led to efforts to restore these highly productive and beneficial ecosystems globally. Depth and light availability are critical determinants of seagrass restoration success. Eelgrass (Zostera marina L.) is the dominant seagrass species in the temperate northern hemisphere, but its global distribution has reduced dramatically. The main aims of this study were to determine: (1) the depth limit for Z. marina survival in Ailian Bay, north China, and (2) how light availability affects the growth and recruitment of Z. marina as a basis for identifying a suitable depth range for successful restoration. To achieve these aims, Z. marina shoots were transplanted from a nearby donor site, Swan Lake, to an experimental site, Ailian Bay, and the temporal responses of Z. marina shoots to light availability at water depths ranging from 1 to 8 m were investigated using in situ suspended cultures. Four suspended shoot transplantation experiments were conducted in 4 years. The results showed that the transplanted Z. marina shoots could survive and branch during an annual growth cycle, permanently underwater, at a depth ≤3 m. Due to the local turbidity of the waters in Ailian Bay, a depth of 4 m led to sufficient light deprivation (reduced to 6.48–10.08% of surface irradiance) to negatively affect seagrass shoot density and clonal reproduction. In addition, reproductive shoot density also tended to decline with water depth and light deprivation. Our results indicated that Z. marina population recruitment, through sexual and asexual (clonal growth) reproduction, were negatively affected by increasing water depth and light deprivation. These findings may provide a suitable depth range for the successful restoration of Z. marina in local coastal waters. They may also be applied to the management and restoration of Z. marina globally.

Long-term seed storage for desiccation sensitive seeds in the marine foundation species Zostera marina L. (eelgrass)

Seagrass meadows are recognized as critical and among the most vulnerable habitats on the planet. There is an urgent need to develop techniques to restore and preserve these vital coastal ecosystems. So far little work has been done to develop effective long-term storage methods for desiccation sensitive seagrass seeds. In the present study, we developed a long-term seed storage method for desiccation sensitive seagrass seeds using Zostera marina L. as model species. During the storage, Z. marina seeds from the 0 °C treatments had lower seed loss percentages and high seed vigor, compared to the 4 °C treatments. Salinity significantly influenced seed vigor after storage. Seeds stored at a salinity of 40–50 psμ had the highest vigor. Wet storage at a salinity of 40–50 psμ and 0 °C was the optimal long-term storage condition, considering factors such as seed loss percentage, seed germination percentage, and seed germination value during or after the long-term storage. By controlling temperature and salinity, we could store Z. marina seeds for ca. 17 months because the collection of the seeds from reproductive shoots and maintain low seed losses and high seed vigor. The findings revealed the optimal conditions for long-term storage of desiccation sensitive Z. marina seeds and provided a useful reference for the establishment of Z. marina seed banks. Our results could also provide information to support Z. marina seagrass meadow restoration efforts using seeds.

Sonar and in situ surveys of eelgrass distribution, reproductive effort, and sexual recruitment contribution in a eutrophic bay with intensive human activities: Implication for seagrass conservation

Seagrass beds are recognized as pivotal and among the most vulnerable coastal marine ecosystems globally. The eelgrass Zostera marina L. is the most widely distributed seagrass species and dominates the temperate northern hemisphere. However, an alarming decline in seagrass has been occurring worldwide due to multiple stressors. Seagrass meadow degradation is particularly serious in the Bohai Sea, in temperate China; however, large areas (> 500 ha) of seagrass meadows and population recruitment have rarely been reported in this area. In the present study, we report on a large eelgrass bed in a eutrophic bay of the Bohai Sea. Sonar and field survey methods were used to investigate the distribution of seagrass and its population recruitment. We also analyzed the major threats to this large seagrass bed. Results showed that a large Z. marina bed with an area of 694.36 ha occurred in this area of the Bohai Sea, with a peripheral area of ~25 km2. Seagrass canopy height and plant coverage had a significant correlation with water depth. Asexual reproduction principally occurred in autumn and played a dominant role in population recruitment in vegetated areas, where no seedlings successfully colonized. In contrast, a considerable number of seedlings survived in the seagrass meadow gaps, and thus played a critical role in the recruitment in these areas. The maximum reproductive shoot densities were about 100 and 70 shoots m−2 at sampling site (S)-1 and S-2 in 2018, respectively, which was about two times more than in 2019 (50 and 20 reproductive shoots m−2 at S-1 and S-2, respectively). The potential seed output per unit area in 2019 was about 1020 seeds m−2 at S-1 and 830 seeds m−2 at S-2, and the seed output in the study area was at a low level compared with global values. Overall, high spring and summer water temperature appeared to induce sexual reproduction of Z. marina in the study area, including reproductive effort, reproductive investment, and seedling development. Furthermore, eelgrass height, aboveground biomass, and density were significantly related to water temperature. Among the potential threatening factors to seagrass in this area, the activities of clam harvesting were intense with daily clam catches >2000 kg, leading to patchy seagrass meadows, especially in the fringe areas. The seagrass bed was also threatened by marine pollution (nutrient loading) and land reclamation. Therefore, the protection and restoration of this seagrass bed are strongly recommended. Our study will provide fundamental information for the conservation and management strategies of large eelgrass beds in the Bohai Sea.

Floral structure inThismia(Thismiaceae: Dioscoreales): new insights from anatomy, vasculature and development

AbstractThismia is characterized by an exceptionally complicated floral morphology that is currently not understood properly. In the taxonomic literature, descriptive rather than morphological terms are often applied to parts of the flower in Thismia, relating to the general appearance of the floral organs instead of their precise homologies. Precise understanding of the floral structure is complicated by the rarity of Thismia spp. and the paucity of appropriate material. Here we provide a comprehensive study of reproductive organs of three Thismia spp. (T. annamensis, T. javanica and T. mucronata) including the first investigation of inflorescence architecture and early floral development in Thismiaceae. We found a hitherto unknown diversity of the reproductive shoots in the genus, manifested in the number of floral prophylls (two or three, in contrast to a single prophyll in the vast majority of monocots) and in the branching plane resulting in two distinct inflorescence types, a drepanium and a bostryx. We report the non-acropetal sequence of initiation of floral whorls (with stamens being the last elements to initiate), never previously described in monocots, and the gynoecium composed of completely plicate carpels, also a rare feature for monocots. Floral vasculature is relatively uniform in Thismia, but significant interspecific differences are found in tepal innervation, including the number of tepal traces; some of these differences are not immediately related to the external tepal morphology. We argue that the annulus, which acts as a roof of the hypanthium, possesses an androecium nature and represents congenitally fused bases of stamen filaments. We describe the stamens as laminar structures, which are also shortly tubular in the distal part of the supraconnective with the adaxial tubular side forming a skirt-like appendage. Finally, the placentas, which are column-like when mature, are initially parietal, becoming secondarily similar to free-central placentas through schizogenous separation from the ovary wall.