Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems.

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Differential responses of arbuscular mycorrhizal fungal communities to mineral and organic fertilization.

Agricultural fertilization is used extensively to increase soil fertility and maximize crop yield. Despite numerous studies on how fertilization influences plant and bacterial communities, little is known about the roles of long-term application of different fertilizers in shaping arbuscular mycorrhizal fungal (AMF) community structures in a comparative manner. The response of AMF community to 28 years of chemical and organic fertilization was investigated using the Illumina Mi-Seq platform. Soil AMF community composition showed significant and differential responses to long-term fertilization. Changes in available phosphorus (AP) content were the primary driver shaping AMF community composition. Chemical fertilization significantly decreased AMF alpha-diversity, whereas the alpha-diversity remained equally high in organic fertilization treatment as in the control. In addition, soil AMF alpha-diversity was negatively and positively correlated with elevated soil nutrient level following chemical and organic fertilization, respectively. Plants could directly acquire sufficient nutrients without their AMF partners after chemical fertilization, while plants might rely on AMF to facilitate the transformation of organic matter following organic fertilization, indicating that chemical fertilization might reduce the reliance of plants on AMF symbioses while organic fertilization strengthened the symbiotic relationship between plants and their AMF partners in agricultural ecosystems. This study demonstrated that AMF communities responded differently to long-term chemical and organic fertilization, indicating that organic fertilization might activate belowground AMF function to maintain soil nutrients and benefit the sustainable development of agriculture.

[Abundance of Toxic and Non-toxic Microcystis sp. in Lake Hongze and Its Correlation with Environmental Factors].

In the present study, the eutrophic level of 30 water samples collected from Lake hongze in August 2014 were analyzed, and the abundance of toxic and non-toxic Microcystis sp., together with their spatial distribution, was investigated by quantitative real-time PCR techniques. The results showed that the average concentrations of total nitrogen and total phosphorus were 1.63 and 0.11 mg x L(-1), respectively. The trophic state index ( TSI) ranged from 58.1 to 73.6, and the water quality was in the state of eutrophication based on TSI. Toxic Microcystis was widely distributed in Lake Hongze, and its abundance varied sharply, from 1. 13 x 10(4) to 3.51 x 10(6) copies x mL(-1), and the abundance of total Microcystis ranged from 1.06 x 10(5) to 1.10 x 10(7) copies x m(-1), meanwhile, the proportion of toxic Microcystis in the total Microcystis ranged from 8.5% to 38.5%, with the average value of 23.6%. Correlation analysis indicated that there was a significant positive correlation among total Mirocystis, toxic Microcystis and the toxic proportion (P < 0.01). The abundance of total and toxic Microcystis was significantly positively correlated to chlorophyll a ( Chl-a) concentrations and TSI (P < 0.01), but was negatively correlated to transparency (SD) (P < 0.01). The ratio of toxic Microcystis to total Microcystis was significantly positively correlated to Chl-a, TN, TP and TSI (P < 0.01), but significantly negatively correlated to the ratio of TN to TP and SD (P < 0.01). Therefore, reducing total nitrogen and phosphorus concentrations could not only lower the eutrophication level of Lake Hongze, but also inhibit the competition advantage of the toxic Microcystis over non-toxic Microcystis.

The dynamics of toxic and nontoxic Microcystis during bloom in the large shallow lake, Lake Taihu, China.

Lake Taihu is a large shallow freshwater lake (surface area 2,338 km(2), mean depth 1.9 m) in China, which has experienced toxic cyanobacterial bloom dominated by Microcystis annually during the last few decades. In the present study, the dynamics of toxic and nontoxic Microcystis in three sampling stations (Meiliang Bay (site N2), Gonghu Bay (site N4), and the lake center area (site S4)) were quantified using quantitative real-time PCR (qPCR) during bloom periods from April to September, 2010. Our data showed that the abundance of toxic Microcystis and the toxic proportion gradually increased from April to August in water samples and reached the peak in August. During the study period, toxic Microcystis genotypes comprised between 26.2 and 64.3, between 4.4 and 22.1, and between 10.4 and 20.6 % of the total Microcystis populations in the three sampling sites, respectively. Correlation analysis suggested that there was a strong positive relationship between total Microcystis, toxic Microcystis and the toxic proportion. Chlorophyll a, total phosphorus, and water temperature were positively correlated with the abundances of total Microcystis and toxic Microcystis. Furthermore, the toxic proportion was positively correlated with total phosphorus (P < 0.05) and water temperature (P < 0.01), showing that global warming together with eutrophication could promote more frequent toxic blooms.