Guihua Liu’s research while affiliated with Chinese Academy of Sciences and other places

Eutrophication of water bodies causes the disappearance of submerged macrophytes and frequent blooms of phytoplankton, which leads to changes in the underwater light environment in the aspect of light intensity and light quality. However, compared with underwater light intensity, only few studies have been concentrated in the effect of light quality on submerged macrophytes. The effect of light quality on plants is heterogeneous, and there are two absorption peaks in red and blue wavelengths. Thus, we carried out a mesocosm experiment to study the effects of a series of red and blue light ratios (red/blue light ratio = 1/8, 1/4, 1/1, 4/1, and 8/1) on two submerged macrophyte species, Hydrilla verticillata and Vallisneria natans. We hypothesized that functional traits (growth strategy, morphological, photosynthetic, and nutritional traits) of submerged macrophytes will be modified by different red/blue light ratios. With the increase of red/blue light ratio, plant height of the two submerged macrophytes decreased, while tillers number increased. We could not completely verify our hypothesis, but we found species-specific differences. The leaf area of H. verticillata under 8/1 red/blue light ratio was significantly higher than that under 1/8 red/blue light ratio, whereas the leaf area of V. natans under 4/1 red/blue light ratio was lower than that under 1/8 red/blue light ratio. Our results are helpful to understand the disappearance mechanism of submerged macrophytes in eutrophic lakes and devise more appropriate measures for the recovery of submerged macrophytes.

Currently, understanding of the variation and balance of multi-elements has mainly focused on terrestrial plants, however, only a few studies focused on aquatic plants in cold alpine wetlands. Here, we examined the pattern of concentrations and variations of 24 elements in wetland plants (including emerged, hydrophytic, and submerged macrophytes) across the Tibetan Plateau (China). The concentrations of these elements exhibit a wide extent by five orders of magnitude, besides, a significantly negative correlation is found between the average concentrations and their variations of each element, which means the macroelements are less variable than the microelements. The environmental factors, including the aqueous and edaphic properties and nutrient concentrations, drive the pattern of multi-element in wetland plants, while the spatial and climatic variables, along with the phylogenetic and taxonomic effects only provide modest contributions. Although human interference was not selected for the final best-fitting model, anthropogenic activities cannot be ignored. Our findings advance the knowledge about vegetal elements in high-altitude wetlands beyond the framework of carbon, nitrogen, and phosphorus, and facilitate the understanding of the multi-elemental model and the driving factors.

Microbial carbon use efficiency (CUE) is a key parameter for soil organic carbon (SOC) cycling. However, there is still lack of evidence for linkages between shifts in SOC stocks and altered microbial CUE under fertilization. Here, we conducted a meta-analysis to explore the effects of fertilization on microbial CUE and its relationships with SOC sequestration. We found that inorganic and combined inorganic-organic fertilization increased microbial CUE by 6.8% and 9.7%, respectively. These two types of fertilizer also increased SOC contents by 4.1% and 51.7%, respectively. Inorganic and combined inorganic-organic fertilization-induced increase in SOC content was positively associated with increased microbial CUE. Our result provided overwhelming evidence that the increase of microbial CUE induced by inorganic and combined inorganic-organic fertilization exerts important effect on SOC sequestration.

A R T I C L E I N F O Keywords: Carbon-degrading enzymes Detritus input manipulation treatment Microbial metabolic quotient (qCO 2) Recalcitrant index of soil organic carbon Specific soil enzyme activity A B S T R A C T Soil extracellular enzymes play a central role in mediating the decomposition of soil organic matter (SOM), and the activities of cellulase and ligninase therein quantify the preference of microbial carbon (C) utilization. However, the responses of cellulase and ligninase activities to plant detritus input change remain uncertain. Here, we investigated the activities of cellulase and ligninase after two years of detritus input manipulations (the detritus input and removal treatment (DIRT) include a control without litter manipulation, CK; double litter, DL; no litter, NL; no roots, NR; no litter and no roots, NRNL) in a coniferous forest in subtropical China. The litter removal treatments had negligible effect on cellulase activity, while the DL treatment significantly increased it by 55.7% compared to the CK treatment. The NL and NRNL treatments increased the activity of ligninase by 60.1% and 46.9%, respectively. However, the DL treatment did not significantly affect the activity of ligninase. Consequently, the ratio of ligninase to cellulase significantly increased under the litter removal treatments. Notably, the specific enzyme activity (the amount of enzyme produced per unit microbial biomass) increased under the litter removal treatment, but the DL treatment did not significantly affect it. The increased ratio of ligninase to cellulase under the litter removal treatments was primarily driven by the increased recalcitrance of substrates and higher proportion of fungal and gram-positive bacterial community. Moreover, the specific enzyme activity and ratio of ligninase to cellulase were positively correlated with microbial metabolic quotient (qCO 2). Overall, our results provided an empirical evidence that microorganisms could shift substrate-using strategy by upregulating the production of ligninase with the reduction of plant detritus input. More importantly , the enhanced activity or proportion of ligninase resulted in higher qCO 2 , and thereby can accelerate soil C loss once plant detritus input is decreased caused by some global change drivers.

Soil microorganisms are key regulators of soil carbon (C) and nutrients cycles in terrestrial ecosystems. However, it remains uncertain how the inter-annual variation in soil microbial community corresponds well with resource availability in the changing environment. Here, we investigated soil microbial community structure and abundance, as well as the associated environmental variables from 2015 to 2017 under different plant detritus input manipulation treatments in a coniferous (Platycladus orientalis (Linn.) Franco) plantation forest ecosystem in subtropical China. Our results showed that the inter-annual variation in soil microbial community was more visible than that caused by detritus input manipulations, owing to the temporal alterations in microclimates and substrate availability. Both aboveground litter removal and root exclusion had more negative effects on the bacterial PLFAs than fungi except half a year after detritus input manipulations. While, soil microbial abundance increased only after three years of litter addition compared to control. Litter removal, especially the no input treatment significantly increased the fungi to bacteria (F:B) and Gram-positive to Gram-negative bacteria (GP:GN) ratios after one and two years of detritus input manipulations. Whereas, the litter addition treatment had minor effects on these parameters. A clear discrimination of microbial community structure among the different detritus input manipulations appeared after two and three years. Both the F:B and GP:GN ratios were positively related to the carbon to nitrogen (C:N) ratio, recalcitrance index of carbon (RIC) and nitrogen (RIN). Overall, our results reveal that the inter-annual variations in soil microbial community are clearly differentiated by the environmental variables and substrate availability that occur in different years and detritus input manipulations. Our results also suggest that due to the vital role of microorganisms in biogeochemical cycling, shifts in the microbial community structure with altered plant detritus input could profoundly affect ecosystem processes in the long run.

Reactive nitrogen (N) addition may profoundly impact the global CH4 budget through its substantial effects on soil CH4 uptake and emission. However, the magnitude and direction of soil CH4 uptake and emission rates in response to N addition on a global scale are still unclear. Here, to investigate the effects of N addition on soil CH4 uptake and emission rates in various upland and wetland ecosystems, we synthesized a large dataset comprising 878 paired observations from 178 studies. Across these studies, we found that N addition significantly reduced soil CH4 uptake rate in upland ecosystems but significantly increased soil CH4 emission rate in wetland ecosystems. The magnitude of the effects was ecosystem-type dependent. Following N addition, reduction of soil CH4 uptake rate and increase in CH4 emission rate were significantly higher in natural ecosystems (with the exception of grassland ecosystems) than in agricultural ecosystems. However, reduction in soil CH4 uptake rate increased with N addition rate in only natural ecosystems. Moreover, the soil CH4 uptake rate in N-limited ecosystems (cold temperate zone and Tibet Plateau) was less sensitive to N addition compared to N-rich ecosystems (subtropical and tropical zones). Additionally, organic N addition had a lower reduction effect on soil CH4 uptake in upland ecosystems and a lower stimulatory effect on soil CH4 emission rate in wetland ecosystems compared to the addition of inorganic N forms. Overall, our results shed light on the magnitude and direction of the effect of N addition on soil CH4 uptake and emission rates in diverse upland and wetland ecosystems and will help improve ecosystem models for predicting soil CH4 flux caused by N addition.