[Response of root dynamics to nitrogen addition and the influencing factors in a Tibetan alpine steppe, China]. / é’è—é«˜åŽŸé«˜å¯’è‰åŽŸæ ¹ç³»åŠ¨æ€å¯¹æ°®æ·»åŠ çš„å“åº”åŠå ¶è°ƒæŽ§å› ç´ .

A field manipulative experiment was carried out during 2015 and 2016 to examine the changes and influencing factors of root production, turnover rate, and standing crop under different nitrogen (N) addition levels, i.e., 0, 1, 2, 4, 8 and 16 g N·m-2·a-1, in a Tibetan alpine steppe. The results showed that root production and standing crop decreased linearly or exponentially with increasing N addition rates. Compared with control, 16 g N·m-2·a-1 significantly reduced the two-year average root production and standing crop by 43.0% and 45.7%, respectively. Root turnover rate increased first and then decreased along the N addition gradient, with the maximum appearing under 2 and 4 g N·m-2·a-1 treatments for 2015 and 2016, respectively. Results from linear mixed-effects models showed that root starch content was the main factor modulating the N-induced changes in root production and turnover rate, explaining 21.7% and 25.4% of their variations. Root protein content mainly contributed to the variations in standing crop, with an explanation of 20.8% of its variance. Overall, N addition had negative effect on root production and standing crop, and low N promoted while high N inhibited root turnover rate. Root metabolic parameters were the main factors modulating the N-induced changes in root dynamics.

Distinct microbial communities in the active and permafrost layers on the Tibetan Plateau.

Permafrost represents an important understudied genetic resource. Soil microorganisms play important roles in regulating biogeochemical cycles and maintaining ecosystem function. However, our knowledge of patterns and drivers of permafrost microbial communities is limited over broad geographic scales. Using high-throughput Illumina sequencing, this study compared soil bacterial, archaeal and fungal communities between the active and permafrost layers on the Tibetan Plateau. Our results indicated that microbial alpha diversity was significantly higher in the active layer than in the permafrost layer with the exception of fungal Shannon-Wiener index and Simpson's diversity index, and microbial community structures were significantly different between the two layers. Our results also revealed that environmental factors such as soil fertility (soil organic carbon, dissolved organic carbon and total nitrogen contents) were the primary drivers of the beta diversity of bacterial, archaeal and fungal communities in the active layer. In contrast, environmental variables such as the mean annual precipitation and total phosphorus played dominant roles in driving the microbial beta diversity in the permafrost layer. Spatial distance was important for predicting the bacterial and archaeal beta diversity in both the active and permafrost layers, but not for fungal communities. Collectively, these results demonstrated different driving factors of microbial beta diversity between the active layer and permafrost layer, implying that the drivers of the microbial beta diversity observed in the active layer cannot be used to predict the biogeographic patterns of the microbial beta diversity in the permafrost layer.

[Survey on intestinal nematode infections among school students in Tengchong County].

One primary school and one middle school were selected from Gudong Town, Tengyue Town and Puchuan Township of Tengchong County, respectively, by using the lamination stochastic group sampling method. The intestinal parasite infections were investigated with the iodine-stained direct smear method and modified Kato-Katz thick smears method. A total of 1 134 students were investigated and the total infection rate of intestinal nematodes was 12.4% (141/1 134). The infection rate of Ascaris lumbricoides, Trichuris trichura, and hookworm was 9.4% (106/1 134), 2.8% (32/1 134), and 0.3% (3/1 134), respectively. The prevalence of intestinal nematodes among the students of urban (2.2%, 8/363) was lower than those of rural (17.3%, 133/771) (P < 0.01). The infection rate in students from Gudong Town was higher than those of Tengyue (2.2%, 8/363) and Puchuan County (2.3%, 8/35) (P < 0.01), whereas the economy level of Gudong Town (29.9%, 123/412) was the best in the three towns. After all, the infection rate of the middle school students (13.7%, 59/432) was higher than that of pupils (11.7%, 82/702) (P < 0.01). Compared with 2003, the prevalence of nematode infection among the school students in Tengchong County decreased significantly in 2013.