Algae, shrimp grazing, and fecal pellets synergistically increase microbial activity and enhance N immobilization during Typha angustifolia leaf litter decomposition.

Algae play an important role in ecological processes of aquatic ecosystems. Understanding the interactive effects of algae with invertebrates in litter decomposition is important for predicting the effects of global change on aquatic ecosystems. We manipulated Typha angustifolia litter to control exposure to shrimp fecal pellets and/or grazing, and the green alga Chlorella vulgaris were added to test their interactive effects on T. angustifolia litter decomposition. Our results showed that algae largely shortened microbial conditioning time and improved litter palatability (increasing litter quality), resulting in greater decomposition and higher fecal pellet production. Fecal pellets enhanced grazing effects on decomposition by increasing litter ash content. The effects of algae and especially fecal pellets on decomposition were dependent on or mediated by grazing. Without grazing, algae slightly promoted decomposition and marginally offset the negative effect of fecal pellets on litter decomposition. Shrimp grazing dramatically decreased microbial activity (extracellular enzyme activity and microbial respiration) at microbial conditioning stage while enhanced microbial activity after 84 days especially with both algae and fecal pellets present. Algae significantly upregulated N- and P-acquiring and slightly downregulated C-acquiring enzyme activity. Fecal pellets significantly depressed recalcitrant C-decomposition enzyme activity. Nevertheless, the three factors synergistically and significantly increased C loss and most enzyme activities, microbial respiration, and N immobilization, resulting in the decrease of litter C:N. Our results reveal the synergistic action of different trophic levels (autotrophs, heterotrophs, and primary consumers) in the complicated nutrient pathways of litter decomposition and provide support for predicting the effects of global changes (e.g., N deposition and CO2 enrichment), which have dramatically effects on alga dynamics and on ecological processes in aquatic ecosystems.

Insight into nitrogen and phosphorus enrichment on cadmium phytoextraction of hydroponically grown Salix matsudana Koidz cuttings.

Cadmium (Cd) has already caused worldwide concern because of its high biotoxicity to human and plants. This study investigated how nitrogen (N) and phosphorus (P) enrichment alter the toxic morpho-physiological impacts of and accumulation of Cd in hydroponically grown Salix matsudana Koidz cuttings. Our results showed that Cd significantly depressed growth and induced a physiological response on S. matsudana cuttings, exhibiting by reduced biomass, decreased photosynthetic pigment concentrations, and increased soluble protein and peroxidase activity of shoots and roots. N and P enrichment alleviated the Cd toxic effects by increasing production of proline which prevented cuttings from damage by Cd-induced ROS, displaying with decreased malondialdehyde concentration, and stimulated overall Cd accumulation. Enrichment of N and P significantly decreased the upward Cd transfer, combing with enhanced root uptake (stimulated root activity) and retranslocation from stem, resulted in extensive Cd sequestration in S. matsudana roots. In both root and xylem, concentration of Cd is positively correlated with N and P. The improved phytoextraction potential by N and P enrichment was mainly via elevating Cd concentration in roots, probably by increased production of phytochelatins (e.g., proline) which form Cd chelates and help preventing damage from Cd-induced ROS. This study provides support for the application of S. matsudana in Cd phytoextraction even in eutrophic aquatic environments.

Secondary compounds of Pinus massoniana alter decomposers' effects on Quercus variabilis litter decomposition.

A major gap to understand the effects of plant secondary compounds on litter decomposition in the brown food web is lack of information about how these secondary compounds modify the activities of soil decomposers. To address this question, we conducted an experiment where aqueous extracts and tannins prepared from Pinus massoniana needles were added to soils collected either from P. massoniana (pine soil) or Quercus variabilis (oak soil). Our objective was to investigate the cascading effects of the two compounds on isopod (Armadillidium vulgare) activity and subsequent change in Q. variabilis litter decomposition. We found that in pine soil, both aqueous extracts and tannins (especially at high concentrations) had positive effects on litter decomposition rates when isopods were present. While without isopods, litter decomposition was enhanced only by high concentrations of aqueous extracts, and tannins had no significant effect on decomposition. In oak soil, high concentrations of aqueous extracts and tannins inhibited litter decomposition and soil microbial biomass, regardless of whether isopods were present or not. Low concentrations of aqueous extracts increased litter decomposition rates and soil microbial biomass in oak soil in the absence of isopods. Based on our results, we suggest that the high concentration of secondary compounds in P. massoniana is a key factor influencing the effects of decomposers on litter decomposition rates, and tannins form a major part of secondary compounds. These funding particularly provide insight into form- and concentration-oriented effects of secondary compounds and promote our understanding of litter decomposition and soil nutrient cycling in forest ecosystem.

Impact of vermiculite on ammonia emissions and organic matter decomposition of food waste during composting.

This study investigated the effects of adding vermiculite to the food waste composting process. Four treatments with varying vermiculite percent compositions, 0%, 5%, 10% and 15% (w/w, wet weight of food waste basis) mixed with initial food waste were designed and then composted for 42 days. Results show that adding vermiculite prolongs the thermophilic phase, speeds up the organic matter loss, reduces the NH3 emissions and electrical conductivity values. Compared to the control, the amount of nitrogen loss through NH3 emissions in the treatments of 5%, 10% and 15% vermiculite decreased by 9.89%, 26.39% and 18.65%, respectively. Finally this work suggests that vermiculite is a suitable additive for food waste composting, especially when the makeup of the compost is 10% vermiculite.

Effect of heavy metals combined stress on growth and metals accumulation of three Salix species with different cutting position.

This study aimed to compare growth performance and heavy metal (HM) accumulation at different cutting positions of Salix species grown in multi-metal culture. Three Salix species stems cut at different positions (apical to basal) were grown hydroponically for four weeks. The plants were then treated for three weeks with 0, 5, 10, and 20 µM Cd, Cu, Pb, and Zn, resulting in total metal concentrations of 0, 20, 40, and 80 µM. The growth parameters and HM content in shoots and initial cutting were measured. Results showed that, compared with S. fragilis, S. matsudana grew more poorly in uncontaminated condition but grew better and accumulated lower metal in shoots under mixed HM treatment. In addition, cuttings from apical parent stem position exhibited poorer growth performance before and after treatment, as well as greater metal content in shoots than base parts under the HM treatment. These results suggest that S. matsudana may undergo a special mechanism to hinder metals in the initial cutting, thus mitigating growth damage. The apical portion also showed poor resistance against the invasion of mixed HMs because of the immature structure. Therefore, in the selection of phytoremediation plants, metal accumulation ability is not proportional to growth performance.