Acidification alleviates the inhibition of hyposaline stress on physiological performance of tropical seagrass Thalassia hemprichii.

Since the Industrial Revolution, increasing atmospheric CO2 concentrations have had a substantial negative impact influence on coastal ecosystems because of direct effects including ocean acidification and indirect effects such as extreme rainfall events. Using a two-factor crossover indoor simulation experiment, this study examined the combined effects of acidification and hyposaline stress on Thalassia hemprichii. Seawater acidification increased the photosynthetic pigment content of T. hemprichii leaves and promoted seagrass growth rate. Hyposaline stress slowed down seagrass growth and had an impact on the osmotic potential and osmoregulatory substance content of seagrass leaves. Acidification and salinity reduction had significant interaction effects on the photosynthesis rate, photosynthetic pigment content, chlorophyll fluorescence parameters, and osmotic potential of T. hemprichii, but not on the growth rate. Overall, these findings have shown that the hyposaline stress inhibitory effect on the T. hemprichii physiological performance and growth may be reduced by acidification.

Succession of Bacteria Attached to Microplastics After Transferring from a Mariculture Area to a Seagrass Meadow.

Microplastics have been recognized as a novel niche for bacteria. However, studies have characterized the plastisphere microbial community in situ without exploring the microbial changes after transferring to other ecosystems. Here we focus on bacterial succession on typical microplastics (polypropylene and expanded polystyrene) and natural substrates (wood) after transferring from mariculture area to seagrass meadows system. Using high-throughput sequencing of 16 S rRNA, we found that alpha diversity significantly reduced after transferring and microplastics especially PP had significant separations on PCoA plots at different succession stages. The abundance and metabolic pathways of potential pathogen-associated microorganisms are significantly decreased. The relative abundance of xenobiotics biodegradation pathways was significantly lower and of energy metabolism pathways was significantly higher by comparing before and after transferring. Main environmental factors affecting microbial communities changed from nutrient characteristics to basic physicochemical properties after transferring. The succession times of the microbial communities of the three materials were different.

[Effects of fertilization on the P accumulation and leaching in vegetable greenhouse soil].

A packed soil column experiment was conducted to investigate the effect of different fertilization practices on phosphorus (P) accumulation and leaching potential in a vegetable greenhouse soil with different fertility levels. The results showed that the leaching loss of total P in the leachates elevated with the increment of leaching time while the accumulative leaching loss of total P was relatively low, indicating P was mainly accumulated in the soil instead of in the leachate. At the end of the leaching experiment, soil fertility and fertilization treatment affected the content of total phosphorus and Olsen-P significantly. Compared with the low-level-fertility soil, the contents of total P and Olsen-P increased by 14.3% and 12.2% in the medium-level-fertility soil, 33.3% and 37.7% in the high-level-fertility soil. Total P in the combined application of poultry manure and chemical fertilizer (M+NPK) was elevated by 5.7% and 4.3%, compared with the NPK and M treatment. Compared with NPK treatment, Olsen-P in M and M + NPK treatments augmented by 13.0% and 3.1%, respectively. Soil total P and Olsen-P mainly accumulated in the 0-10 cm and 10-20 cm soil layers, and much less in the 20-40 cm soil layer.

Phosphorus vertical migration in aquic brown soil and light chernozem under different phosphorous application rate: a soil column leaching experiment.

A soil column leaching experiment was conducted to study the vertical migration of phosphorus in aquic brown soil and light chernozem under different phosphorus fertilization rates. The results showed that total dissolved phosphorus concentration in the leachates from the two soils was nearly the same, but dissolved inorganic phosphorus concentration was obviously different. In all fertilization treatments, aquic brown soil had a higher content of phosphorus in calcium chloride extracts compared with light chernozem. But Olsen phosphorus content was higher at the soil depth beneath 0-20 cm, and increased with increasing phosphorus application rate.

[Simulation of relationship between dissoluble phosphorus loss and runoff time].

The environmental sensitive phosphorus point of a cinnamon fluvo-aquic soil was 69.4 mg/kg (Olsen-P) evaluated by fitting soil Olsen-P and CaCl2-P content using Heckrath split-line model. The relationship between dissoluble phosphorus (DP) lost from runoff in soils applied different P rate and runoff time was studied using circular water method. The first-order kinetics model was used to simulate the dynamics of DP transported from soil to water with time. The results indicated that this model could simulate the transport suitably. When the applied P less than 400 kg/hm2, the velocity constant K which is average 1.095 h(-1) unchanged; while when the applied P rates were 800 and 1600 kg/hm2, K decreased by 17.2% and 38.9%, respectively. The exponent function was used to simulate the velocity of DP from soil to water with time and the results showed that it was a suitable model. When the applied P less than 400 kg/hm2, the velocity constant K' which is average 1.037 h(-1) unchanged; while when the applied P rate was higher than 800 kg/hm2, a declining tendency was found for K'. There was significant relationship between soil Olsen-P or CaCl2-P content and soil DPLP or VP0 when surface runoff occurred. This result showed that soil Olsen-P or CaCl2-P content could be used to direct the runoff risk as a gist of estimate soil environment.

[Effects of P application on P concentrations in paddy soil and its surface water: a simulation test].

An anaerobic incubation test was conducted to study the effects of different P application rate on the P concentrations in paddy soil and its surface water. The results showed that soil available P (Olsen-P) decreased rapidly at the beginning, but approached to stable after 60 days of P application. Both Olsen-P and residual P increased with increasing P application rate, and Olsen-P had a positive correlation with P application rate, suggesting that the test soil had a strong P adsorption capacity. After P application, the total P (TP) in soil surface water increased rapidly, and then decreased slowly, showing that there was a P exchange between soil and its surface water. After 120 days of P application, there was an exponential relationship between soil surface water TP and P application. The TP in soil surface water increased rapidly when the P application rate was 400 - 800 kg x hm (-2) , and easy to be lost when the P application rate was higher than 800 kg x hm(-2). The simulation with split line model on the relationship between soil Olsen-P and soil surface water TP showed that the change point of soil Olsen-P, which induced a sharp increase of soil surface water TP concentration, was 82. 7 mg x kg( -l) , corresponding to a P application rate being about 712 x kg hm(-2). Soil Olsen-P could be a good indicator in forecasting the P loss from soil surface water.