Phosphorus limitation induced by nitrogen addition changed soil microbial community structure in a subtropical Pinus taiwanensis forest.

Soil microorganisms play an important role in the biogeochemical cycles of terrestrial ecosystems. How-ever, it is still unclear how the amount and duration of nitrogen (N) addition affect soil microbial community structure and whether there is a correlation between the changes in microbial community structure and their nutrient limi-tation status. In this study, we conducted an N addition experiment in a subtropical Pinus taiwanensis forest to simulate N deposition with three treatments: control (CK, 0 kg N·hm-2·a-1), low N (LN, 40 kg N·hm-2·a-1), and high N (HN, 80 kg N·hm-2·a-1). Basic soil physicochemical properties, phospholipid fatty acids content, and carbon (C), N and phosphorus (P) acquisition enzyme activities were measured after one and three years of N addition. The relative nutrient limitation status of soil microorganisms was analyzed using ecological enzyme stoichiometry. The results showed that one-year N addition did not affect soil microbial community structure. Three-year LN treatment significantly increased the contents of Gram-positive bacteria (G+), Gram-negative bacteria (G-), actinomycetes (ACT), and total phospholipid fatty acids (TPLFA), whereas three-year HN treatment did not significantly affect soil microbial community, indicating that bacteria and ACT might be more sensitive to N addition. Nitrogen addition exacerbated soil C and P limitation. Phosphorus limitation was the optimal explanatory factor for the changes in soil microbial community structure. It suggested that P limitation induced by N addition might be more beneficial for the growth of certain oligotrophic bacteria (e.g. G+) and the microorganisms participating in the P cycling (e.g. ACT), with consequences on soil microbial community structure of subtropical Pinus taiwanensis forest.

[Effects of different carbon addition modes on the soil priming effect of a subtropical Phyllostachys edulis forest under nitrogen deposition]. / æ°®æ²‰é™ä¸‹ä¸åŒç¢³æ·»åŠ æ¨¡å¼å¯¹äºšçƒ­å¸¦æ¯›ç«¹æž—åœŸå£¤æ¿€å‘æ•ˆåº”çš„å½±å“.

Priming effect (PE) plays an important role in regulating terrestrial soil carbon (C) cycling, but the impact of different C addition modes on the PE in subtropical forest ecosystems with increasing nitrogen (N) deposition is unclear. In this study, we investigated the effects of C addition patterns (single or repeated C addition) on soil PE by adding 13C-labeled glucose for 90 d in an incubation experiment with different levels of N application (0, 20, and 80 kg N·hm-2·a-1). The different patterns of glucose addition significantly increased soil organic C (SOC) mineralization and produced positive PE. Single glucose addition resulted in stronger PE than repeated addition. PE was significantly weakened with increasing N application levels, indicating that N deposition inhibited soil excitation in Phyllostachys edulis forests. The cumulative PE was significantly negatively correlated with ß-N-acetylaminoglucosidase (NAG) and peroxidase (PEO) activities, and was significantly positively correlated with microbial biomass P (MBP) and potential of hydrogen (pH). Our findings indicated that, when acting together on soil, N application and C addition could strongly affect soil C stocks by stimulating the mineralization of native soil organic matter in subtropical forests. The findings further indicated that single C addition model might overestimate the effect of exogenous readily decomposable organic C on PE and ignore the effect of N deposition on PE, which in turn would overestimate the mineralization loss of forest SOC.

Enzyme stoichiometry evidence revealed that five years nitrogen addition exacerbated the carbon and phosphorus limitation of soil microorganisms in a Phyllostachys pubescens forest.

The activity and stoichiometry of soil extracellular enzyme can provide a good indication for changes in soil nutrient availability and microbial demands for nutrients. However, it remains unclear how would nitrogen (N) deposition affect nutrient limitation of microbes in subtropical forest soils. We conducted a 5 years N addition experiment in a subtropical Phyllostachys pubescens forest. The soil nutrients and enzyme activities associated with carbon (C), N, and phosphorus (P) cycles were measured. We also examined the nutrient distribution of microorganisms using enzyme stoichiometry and vector analysis. The results showed that N addition significantly decreased the contents of soil soluble organic C and available P and increased that of available N. Furthermore, N addition significantly decreased ß-N-acetyl-glucosaminidase (NAG) activity and NAG/ microbial biomass carbon (MBC), and increased acid phosphatase (ACP) and ACP/MBC. The low and moderate N addition levels significantly increased enzyme C/P, vector length, and vector angle, but significantly decreased enzyme N/P. Results of redundancy analysis showed that the change in soil enzyme activity and enzymatic stoichiometry were mainly driven by soil available P content under N addition. In summary, N addition altered the microbial nutrient acquisition strategy, which increased nutrient allocation to P-acquiring enzyme production but reduced that to N-acquiring enzyme production. Moreover, N addition exacerbated the C and P limitation of soil microorganisms. Appropriate amount of P fertilizer could be applied to improve soil fertility of subtropical P. pubescens forest in the future.

Nutrient availability is a dominant predictor of soil bacterial and fungal community composition after nitrogen addition in subtropical acidic forests.

Nutrient addition to forest ecosystems significantly influences belowground microbial diversity, community structure, and ecosystem functioning. Nitrogen (N) addition in forests is common in China, especially in the southeast region. However, the influence of N addition on belowground soil microbial community diversity in subtropical forests remains unclear. In May 2018, we randomly selected 12 experimental plots in a Pinus taiwanensis forest within the Daiyun Mountain Nature Reserve, Fujian Province, China, and subjected them to N addition treatments for one year. We investigated the responses of the soil microbial communities and identified the major elements that influenced microbial community composition in the experimental plots. The present study included three N treatments, i.e., the control (CT), low N addition (LN, 40 kg N ha-1 yr-1), and high N addition (HN, 80 kg N ha-1 yr-1), and two depths, 0-10 cm (topsoil) and 10-20 cm (subsoil), which were all sampled in the growing season (May) of 2019. Soil microbial diversity and community composition in the topsoil and subsoil were investigated using high-throughput sequencing of bacterial 16S rDNA genes and fungal internal transcribed spacer sequences. According to our results, 1) soil dissolved organic carbon (DOC) significantly decreased after HN addition, and available nitrogen (AN) significantly declined after LN addition, 2) bacterial α-diversity in the subsoil significantly decreased with HN addition, which was affected significantly by the interaction between N addition and soil layer, and 3) soil DOC, rather than pH, was the dominant environmental factor influencing soil bacterial community composition, while AN and MBN were the best predictors of soil fungal community structure dynamics. Moreover, N addition influence both diversity and community composition of soil bacteria more than those of fungi in the subtropical forests. The results of the present study provide further evidence to support shifts in soil microbial community structure in acidic subtropical forests in response to increasing N deposition.

Sources and trends of oxidized and reduced nitrogen wet deposition in a typical medium-sized city of eastern China during 2010-2016.

Fluxes and composition dynamics of atmospheric nitrogen deposition play key roles in better balancing economic development and ecological environment. However, there are some knowledge gaps and difficulties in urban ecosystems, especially for small and medium-sized cities. In this study, both flux and composition (ratio of NH4+-N to NO3--N, RN) of wet-deposited dissolved inorganic nitrogen (DIN, sum of NO3--N and NH4+-N) were estimated and sources were identified at a long-term urban observation station in Tongling, a typical medium-sized city in eastern China during 2010-2016, respectively. Results showed that wet-deposited DIN fluxes were 33.20 and 28.15 kgN ha-1 yr-1 in Tongling city during 2010-2011 and 2015-2016, respectively. Compared to these two periods, both DIN and NO3--N fluxes decreased by 15.2% and 31.8% for a series of NOx abatement measures applied effectively, respectively. At the same time, the NH4+-N flux remained stable and ranged from 19.53 to 20.62 kgN ha-1 yr-1, and the RN increased from 1.7 to 2.2. Seasonally, winds from the southwest and west-southwest with higher frequencies and speeds in spring and summer brought more NH4+-N and DIN wet deposition from an ammonia plant, which could threaten the safety of regional hydrosphere ecosystems. On the whole, the wet-deposited NH4+-N was threatening regional ecosystems of both the hydrosphere and forest. The wet-deposited DIN including NH4+-N in Tongling city stemmed mainly from a combined source of coal combustion and dust from Cu extraction and smelting, ammonia production, and roads. Therefore, production lines should be updated for Cu extraction and smelting industries, thermal power generations and the ammonia plant, old vehicles should be eliminated, and the use of new energy vehicles should be promoted for regional sustainable development and human health in the medium-sized city.