Effects of Water Level Fluctuations on the Growth Characteristics and Community Succession of Submerged Macrophytes: A Case Study of Yilong Lake, China

Water level fluctuation (WLF) has a significant effect on aquatic macrophytes, but few experimental studies have examined the effect of WLF on submerged community succession, especially from a large-scale perspective. In this study, field monitoring of WLF and submerged macrophytes was conducted in Yilong Lake (SE China) over two years, and the impacts of WLF on the growth characteristics and the community structure of submerged macrophytes were determined. The results show that the biomass of submerged macrophytes decreased significantly after the water level increased and submerged macrophytes could cope with the adverse environment by adjusting their growth posture, for example, increasing plant length and reducing branch number. However, different submerged plants have different regulatory abilities, which leads to a change in the community structure. Myriophyllum spicatum, Stuckenia pectinata, and Najas marina had better adaptation abilities to WLF than Najas minor and Utricularia vulgaris. Changes in water depth, dissolved oxygen, and transparency significantly contribute to the effect of WLF on submerged plant communities. Therefore, when determining the range of WLF, the above three critical factors and submerged plant species should be considered. WLF changed the spatial distribution of the aquatic plant community. When water levels rose, the density of the submerged macrophyte community in the original growth region reduced as the emergent plants migrated to shallower water, and the seed bank germination was aided by transparent water produced among emergent plants. This can be used as a pioneering measure to restore submerged plants in eutrophic lakes with low transparency. In addition, a suitable water depth created by WLF was conducive to activating the seed bank and improving the diversity of aquatic plants. Finally, a distribution map of aquatic plants in Yilong Lake is drawn.

Responses of morphological and physiological traits to herbivory by snails of three invasive and native submerged plants

Aims The submerged plant species Carolina fanwort (Cabomba caroliniana) has become a dominant invasive aquatic plant in the Lake Taihu Basin (LTB) in China. Introduced species may escape their original specialist enemies and encounter fewer enemies in their new environment. They were assumed to have suffered less herbivory than native species as they are relatively unpalatable (the enemy release hypothesis (ERH)). The objective of this study was to compare the responses of C. caroliniana with those of co-occurring native species to herbivory from native herbivores. Methods We conducted a mesocosm experiment to record the responses of C. caroliniana and two commonly co-occurring native submerged plant counterparts, water thyme (Hydrilla verticillata) and Eurasian watermilfoil (Myriophyllum spicatum), to herbivory by two native generalist gastropod snails, Radix swinhoei and Sinotaia quadrata. Plant morphological traits (total biomass, shoot/root (S/R) biomass ratio and relative growth rate (RGR)) and physiological traits (leaf total nonstructural carbohydrate (TNC), lignin, and cellulose) were recorded. Important Findings The snail S. quadrata rarely influenced the plant traits of the three submerged plants. With the increasing numbers of R. swinhoei treatments, most of the plant traits of H. verticillata and M. spicatum changed, while those of C. caroliniana showed a relatively stable fluctuation. This result indicates that C. caroliniana is more resistant to herbivory by the snail R. swinhoei, which is consistent with the ERH hypothesis. This finding indicates that herbivorous snail species contributes to the invasion of C. caroliniana, which potentially alters the species composition of submerged plants in the plant community.

Snail communities improve submerged macrophytes growth by graze epiphytic algae and phytoplankton in a mesocosm experiment

The relationship between producers (e.g., macrophyte, phytoplankton and epiphytic algae) and snails plays an important role in maintaining the function and stability of the shallow ecosystems. A complex relationship exists among macrophytes, epiphytic algae, phytoplankton and snails. An outdoor mesocosm experiment with two-way factorials was carried out, three species submerged macrophytes (Hydrilla verticillate, Vallisneria natans or one exotic submerged plant Elodea nuttallii) and two grazing treatments (4 snail species present or absent) to elucidate those relationships. The results showed that the snail communities reducing the biomass of phytoplankton and epiphytic algae indirect then enhanced the growth of the submerged macrophytes. The macrophyte with complex architecture supported more snail and epiphytic algae, and snails preferred to feed on native plants. Competition drove snails change the grazing preferences to achieve coexistence, so that led to the assembling of snail communities towards the direction of highest resource utilization.

Quantitative indicators and trophic structure of zooplankton in different types of shallow water zone in Meshinsky Bay (Kuibyshev Reservoir)

The trophic structure and quantitative characteristics of zooplankton in four shallow water areas of Meshinsky Bay of Kuibyshev Reservoir were studied in the summer and autumn seasons. The sites differed in their protection from wind and wave impacts, and in intensity of macrophyte overgrowth. The maximum species richness of zooplankters feeding in the water column was observed in open and vegetation-free shallow water and foraging from the surface of the substrate in closed areas, overgrown mainly with one type of submerged plant. The highest quantitative indicators of zooplankton in all areas were observed in summer. Regardless of the season, the maximum abundance and biomass of communities was observed in protected shallow water in thickets of Potamogeton lucens L. This is associated with the density of vegetation cover protecting invertebrates from predation by fish.

ISOLATION AND IDENTIFICATION OF FUNGI FROM SUBMERGED PLANTS DEBRIS IN AQUATIC HABITATS IN MISAN PROVINCE

Forty-eight taxa of saprophytes fungi were isolated and identified from submerged plant debris samples collected from different sites in Misan province, southern Iraq, which are Maymouna, Al-Salam, Majar Al-Kabir, and Amara. Among them, 24 species belonged to Ascomycota (six of which are sexual state), 19 species to hyphomycetes (anamorphic fungi), 4 to Zygomycota, and one to Oomycetes. Six species were isolated and newly recorded from Iraq, which are Aniptodera margaration, Cirrenalia iberica, Cordana lignicola, Cordana verruculosa, Pseudoacrodictys appendiculata, and Scytalidium thermophilum. However, in the evaluation of both moist chamber and direct culture methods, 34 species were isolated by the first method and 27 species by the second method, meantime, 13 species (9 belonged to Ascomycota, 2 to hyphomycetes, and 2 to Zygomycetes) were recovered by both methods. Aspergillus terrus was appeared in highest frequency and occurrence (11.76%, 42.55%, respectively), followed by Aspergillus horti (10%, 36.17%, respectively), and then A. niger with a frequency and occurrence of 5.29% and 19.14%, respectively, while 17 species were appeared lowest frequency and occurrence to reach 0.58%, 2.12%, respectively, for all. One hundred and seven isolates have been recovered from all study sites. Meantime, sixty-four isolates have been reported from Majar Al-Kabir, as compared with other sites, followed by Amara (43 isolates), while 39 isolates have been isolated from the Maymouna, and 24 isolates from Al-Salam. The biodiversity of fungi isolated from submerged plant debris was compared with previous studies. Brief descriptions of the new recorded fungi were given.