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Autophagy (self-eating), a conserved pathway in eukaryotes, which is designed to handle cytoplasmic material in bulk and plays an important role in the remobilization of nutrient, such as nitrogen (N) under suboptimal nutrient conditions. Here, we identified a core component of an autophagy gene in rice ( ), , with increased expression levels under N starvation conditions. Overexpression of significantly enhanced the level of autophagy and the number of effective tillers in the transgenic rice. In addition, the transgenic lines accumulated more N in grains than in the dry remains and the yield was significantly increased under normal N conditions. Further N allocation studies revealed that the nitrogen uptake efficiency (NUpE) and nitrogen use efficiency (NUE) significantly increased. Otherwise, under suboptimal N conditions, overexpression of did not seem to have any effect on yield and NUE, but NUpE was still improved significantly. Based on our findings, we consider to be a great candidate gene to increase NUE and yield.

Autophagy, a conserved cellular process in eukaryotes, has evolved to a sophisticated process to dispose of intracellular constituents and plays important roles in plant development, metabolism, and efficient nutrients remobilization under suboptimal nutrients conditions. Here, we show that OsATG8b , an AUTOPHAGY-RELATED8 ( ATG8 ) gene in rice, was highly induced by nitrogen (N) starvation. Elevated expression of OsATG8b significantly increased ATG8 lipidation, autophagic flux, and grain yield in rice under both sufficient and deficient N conditions. Overexpressing of OsATG8b could greatly increase the activities of enzymes related to N metabolism. Intriguingly, the 15 N-labeling assay further revealed that more N was remobilized to seeds in OsATG8b -overexpressing rice, which significantly increased the N remobilization efficiency (NRE), N harvest index, N utilization efficiency (NUE), and N uptake efficiency (NUpE). Conversely, the osatg8b knock-out mutants had the opposite results on these characters. The substantial transcriptional changes of the overexpressed transgenic lines indicated the presence of complex signaling to developmental, metabolic process, and hormone, etc. Excitingly, the transgenic rice under different backgrounds all similarly be boosted in yield and NUE with OsATG8b overexpression. This work provides an excellent candidate gene for improving N remobilization, utilization, and yield in crops simultaneously.

Small fish are highly associated with submerged macrophytes but may potentially hamper their growth due to nutrient excretion that stimulate growth of phytoplankton and periphyton growth. We conducted a mesocosm experiment to elucidate the effects of the small omnivore Chinese bitterling Acheilognathus macropterus on the growth of phytoplankton, periphyton and the submerged macrophyte Vallisneria denseserrulata. The treatments were fishless as well as low (LF) and high (HF) fish density. We found that the concentrations of nutrients and the phytoplankton biomass increased substantially in both fish treatments, leading to a significantly higher light attenuation compared with the control. Moreover, bitterling substantially enhanced the biomass of periphyton on plant leaves. Consequently, the relative growth rate (RGR) of V. denseserrulata was significantly suppressed in HF, while RGR in the LF treatment did not differ significantly from the controls. However, the bitterling also stimulated the ramet production of V. denseserrulata, significantly. Our results indicate that Chinese bitterling reduce the RGR of V. denseserrulata under high fish density condition. Therefore, the density of Chinese bitterling should be kept low in order to reduce the negative effects of the fish on the RGR of submerged macrophytes (e.g. V. denseserrulata), when restoring lakes by plant transplantation.

Small omnivorous fish often dominate in subtropical shallow lakes, and they may affect the community structure of aquatic organisms on at least two trophic levels. However, in the study of aquatic food webs in subtropical lakes, most ecologists have focused on the effects of large-sized omnivorous species (e.g. common carp), studies of small-sized species being scarce. We conducted a mesocosm experiment with two treatments (fish presence and absence) to examine the effects of a small-sized omnivore, bitterling ( Acheilognathus macropterus ), on phytoplankton, zooplankton and benthic macroinvertebrates. Our results showed that bitterling presence significantly increased the chlorophyll a concentration and biomass of phytoplankton, which became dominated by cyanobacteria (mainly Aphanizomenon spp.) that accounted for >99% of both total phytoplankton abundance and biomass. Both the abundance and biomass of zooplankton were also higher in the fish-present treatment, but small rotifers became dominant, and the zooplankton:phytoplankton biomass ratio decreased, indicating less grazing on phytoplankton. Moreover, both the abundance and biomass of benthic macroinvertebrates (tubificids) were higher in the bitterling-present treatment than in the controls, which is opposite to the situation found when omni-benthivorous fish (e.g. crucian carp) dominate. Higher biomass of tubificids may, in turn, result in higher sediment nutrient release. Our study suggests that A. macropterus , and maybe also other bitterling species, can alter both pelagic and benthic assemblages via both top-down and bottom-up control effects and lead to more turbid water in eutrophic lakes. Thus, more attention should be paid to these small omnivorous species in the restoration and management of shallow subtropical lakes.

Lake restoration, achieved through a combination of biomanipulation and the recovery of submerged macrophytes, can effectively reduce nutrient concentrations, thereby suppressing phytoplankton biomass. Nevertheless, there is limited knowledge regarding the impact of nutrient limitation in phytoplankton biomass on lake restoration efforts. We compared the changes in nutrient levels and phytoplankton biomass (measured by chlorophyll a, Chl a) between restored and unrestored areas of a subtropical shallow Lake Yiai. Furthermore, we assessed the nutrient limitation patterns in these two areas through field nutrient addition experiments conducted during the summer. Monitoring results indicated that mean concentrations of Chl a and nutrients were significantly lower (t-test p < 0.0001) in the restored area compared to the unrestored area. In the nutrient addition experiment, phytoplankton biomass was nitrogen-limited in the unrestored part, whereas it was co-limited by both nitrogen and phosphorus in the restored area. These findings suggest that nutrient limitation may serve as a crucial mechanism in sustaining low phytoplankton biomass following the restoration of shallow lakes, particularly during the summer season, with the recovery of submerged macrophytes.

Shallow lakes are dominated by small omnivorous fish, but the roles of these small fish in aquatic ecosystems are not well-known. A small omnivorous bitterling (Acheilognathus macropterus) has been found to be dominant after lake restoration in shallow lakes. We conducted a mesocosm experiment to examine the effects of bitterling on water quality and plankton communities. Bitterling significantly increased the concentrations of nutrients, chlorophyll a (Chla) and suspended solids (TSS), and decreased the light intensity. The abundance and biomass of phytoplankton in the fish-present treatment were significantly higher than the controls, with Microcystis spp. and Dolichospermum spp. dominating the phytoplankton community. However, bitterling did not significantly affect the abundance and biomass of zooplankton, although the presence of bitterling shifted the community structure to dominance by small-sized species. Density-dependent effects of bitterling were observed on the concentrations of nutrient, TSS, organic suspended solids and Chla and on light intensity, but were not found for plankton and ratio of zooplankton to phytoplankton biomass. Our study indicates that A. macropterus can negatively affect water quality and facilitate the dominance of cyanobacteria. Therefore, monitoring and control of these small omnivorous species should be emphasized when restoring or managing shallow lakes.

How fish communities change with eutrophication in temperate lakes is well documented, while only a few studies are available from subtropical lakes. We investigate the fish community structure in 36 lakes located in the Yangtze River basin, covering a wide nutrient gradient. We found that fish species richness and total fish catch per unit effort (CPUE) increased significantly with chlorophyll a (Chla). Among the different feeding types, the proportion of zooplanktivores increased significantly with Chla, while the percentage of omnibenthivores showed no obvious changes; the CPUE of piscivorous Culter spp. increased with Chla, while their proportion of total catch decreased pronouncedly. Based on the index of relative importance (IRI), the most important and dominant fish species was the zooplanktivorous Sijiao (Toxabramis swinhonis), followed by the omniplanktivorous sharpbelly (Hemiculter leucisculus) and the omnibenthivorous crucian carp (Carassius carassius), a small-sized species belonging to the Cyprinidae family. The CPUE of these three species increased significantly with Chla. The focus has, so far, been directed at large fish, but as emphasized by our results, the abundant small fish species were dominant in our subtropical study lakes even in terms of biomass, and, accordingly, we recommend that more attention be paid to the population dynamics of these species in the future.

Thermokarst lakes play a critical role in global biogeochemistry. Here we delved into nutrient stoichiometry and its cascading effects on plankton communities across thermokarst lakes on the Qinghai-Tibet Plateau. Our findings revealed significant variability in nutrient concentrations and stoichiometric ratios in both water and seston, indicating heterogeneous nature of thermokarst lakes. Phytoplankton communities were dominated by cyanobacteria. Zooplankton communities, though simple, varied significantly and responded distinctly to the prevailing nutrient stoichiometry, and particularly shown competitive interactions between copepods and Cladocera. Structural Equation Modeling revealed a complex web of interactions, underscoring the bottom-up influences from nutrient stoichiometry in water to phytoplankton/seston, and finally to zooplankton, although there were no direct relationships between phytoplankton and zooplankton communities. Water nutrient stoichiometry positively affected eukaryotic algae but negatively impacted seston stoichiometry, which. had a negative influence on copepods. Our study highlighted the intertwined relationships between nutrient stoichiometry and plankton communities within thermokarst lakes. Direct sampling of 68 thermokarst lakes across the Qinghai-Tibet Plateau, China suggests significant variability in nutrient concentrations and stoichiometry, as well as complex relationships with plankton communities

Parrot feather (Myriophyllum aquaticum) is an introduced, noninvasive amphibious plant found in coastal provinces, but it has the potential to become an invasive species in China. The plant is heterophyllous, with both emergent (aerial) and submerged (aquatic) leaves, and has two distinct root types: aquatic (adventitious) and edaphic (sediment) root systems. This morphological plasticity allows M. aquaticum to effectively absorb nutrients from different layers of the environment, making it a suitable model plant for exploring nutrient dynamics in both water and soil systems and investigating how wetland plants respond to cultural eutrophication. We designed an outdoor mesocosm experiment to assess plant growth traits and root topological indices in response to different nitrogen (N) and phosphorus (P) concentrations. The results indicated that the plant has a high tolerance to N loading. In contrast, the P content had greater impacts than the N content on plant growth and root topological indices, indicating that the P content was the main influencing factor affecting and suppressing the development of M. aquaticum. The aquatic or edaphic root branching did not change, but the aquatic root topology of M. aquaticum exhibited similar stable trends with increasing P concentration, indicating typical herringbone branching; additionally, its edaphic roots exhibited decreasing topological indices, indicating more typical dichotomous branching with increasing P concentration. The plant has a high tolerance to N, and it may become invasive following the current trend of increasing cultural eutrophication.

Submerged macrophytes play a pivotal role in the restoration of shallow lakes. Compared to meadow-forming Vallisneria, canopy-forming Myriophyllum spicatum exhibits characteristics that may render it the dominant species. However, M. spicatum may hamper recreational and commercial activities. Herbivorous fish may potentially regulate the biomass and interspecific competition between the two plant species. We conducted an enclosure experiment to elucidate the effects of grass carp (Ctenopharyngodon idella) and Wuchang bream (Megalobrama amblycephala) on the biomass ratio and morphological traits of M. spicatum and V. denseserrulata. Grass carp significantly reduced the biomass, density, and relative growth rate of both plant species, while Wuchang bream had no significant effect on any of these variables. Accordingly, the biomass ratio of M. spicatum to V. denseserrulata was significantly lower in the grass carp treatment than in both the fish-free controls and the Wuchang bream treatment. Wuchang bream significantly decreased the individual height of V. denseserrulata, whereas grass carp substantially reduced the height of both plant species. Our findings suggest that Wuchang bream may be more appropriate for maintaining meadow-forming species such as Vallisneria than grass carp, though it faces challenges in controlling both the biomass and height of canopy-forming species like M. spicatum.