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.

[Responses of soil microbial carbon use efficiency to short-term nitrogen addition in Castanopsis fabri forest]. / ç½—æµ®æ ²æž—åœŸå£¤å¾®ç”Ÿç‰©ç¢³åˆ©ç”¨æ•ˆçŽ‡å¯¹çŸ­æœŸæ°®æ·»åŠ çš„å“åº”.

As an important parameter regulating soil carbon mineralization, microbial carbon use efficiency (CUE) is essential for the understanding of carbon (C) cycle in terrestrial ecosystems. Three nitrogen supplemental levels, including control (0 kg N·hm-2·a-1), low nitrogen (40 kg N·hm-2·a-1), and high nitrogen (80 kg N·hm-2·a-1), were set up in a Castanopsis fabri forest in the Daiyun Mountain. The basic physical and chemical properties, organic carbon fractions, microbial biomass, and enzyme activities of the soil surface layer (0-10 cm) were measured. To examine the effects of increasing N deposition on microbial CUE and its influencing factors, soil microbial CUE was measured by the 18O-labelled-water approach. The results showed that short-term N addition significantly reduced microbial respiration rate and the activities of C and N acquisition enzymes, but significantly increased soil microbial CUE. ß-N-acetyl amino acid glucosidase (NAG)/microbial biomass carbon (MBC), microbial respiration rate, ß-glucosidase (BG)/MBC, cellulose hydrolase (CBH)/MBC, and soil organic carbon content were the main factors affecting CUE. Moreover, CUE significantly and negatively correlated with NAG/MBC, microbial respiration rate, BG/MBC, and CBH/MBC, but significantly and positively correlated with soil organic carbon. In summary, short-term N addition reduced the cost of soil microbial acquisition of C and N and microbial respiration, and thus increased soil microbial CUE, which would increase soil carbon sequestration potential of the C. fabri forest.

[Isolation of endophytic fungi from Macleaya cordata and screening of sanguinarine-producing strains].

Endophytic fungi were isolated from Macleaya cordata growing in Dabie Mountain by agar-block method, and then the endophytic fungi were grouped into different types based on their morphological characteristics, and thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) were employed to determine whether the metabolic substances contained sanguinarine or not, and then preliminarily identified by morphological method. The results showed that the leaves hosted the largest number of endophytes (96 isolates) followed by the stems (57 isolates) and finally the roots (28 isolates), respectively. Based on morphological characteristics the endophytic fungi were grouped into 26 types in our study. TLC and HPLC results showed that there was sanguinarine in the metabolic substances of BLH 51 strain. According to the morphological characteristic, the BLH 51 strain was identified as Fusarium proliferatum. All these indicated that the medicinal plant M. cordata harbors abundant endophytes, which could be a new source for the search of active secondary metabolites.