Litter decomposition and N release are the key processes that strongly determine the nutrient cycling at the soil–plant interface; however, how these processes are affected by grazing or grazing exclusion in the alpine grassland ecosystems on the Qinghai-Tibetan Plateau (QTP) is poorly understood. So far few studies have simultaneously investigated the influence of both litter quality and incubation site on litter decomposition and N release. Moreover, previous studies on the QTP investigating how grazing exclusion influences plant abundance and biodiversity usually lasted for many years, and the short-term effects have rarely been reported. This work studied the short-term (6 months) effects of grazing and grazing exclusion on plant community composition (i.e., plant species presented) and litter quality and long-term (27–33 months) effects on soil chemical characteristics and mixed litter decomposition and N release on the QTP. Our results demonstrate that (1) shorter-term grazing exclusion had no effect on plant community composition but increased plant palatability and total litter biomass; (2) grazing resulted in higher N and C content in litter; and (3) grazing accelerated litter decomposition, while grazing exclusion promoted N release from litter and increased soil organic carbon. In addition, incubation site had significantly more impact than litter quality on litter decomposition and N release, while litter quality affected decomposition in the early stages. This study provides insights into the mechanisms behind the nutrient cycling in alpine ecosystems. We suggest that periodic grazing and grazing exclusion is beneficial in grassland management on the QTP.

Exploring the pathogenicity of a new fungus strain to non-target host pests can provide essential information on a large scale for potential application in pest control. In this study, we tested the pathogenicity of Beauveria bassiana PfBb on the important agricultural pest Spodoptera frugiperda (Lepidoptera: Noctuidae) by determining the relative activities of protective enzymes and detoxifying enzymes in different larval instars. Our results show that the B. bassiana PfBb strain could infect all six larval instars of S. frugiperda, and its virulence to S. frugiperda larvae gradually increased with an increase in spore concentration. Seven days after inoculation, the LC₅₀ of B. bassiana PfBb was 7.7 × 10⁵, 5.5 × 10⁶, 2.2 × 10⁷, 3.1 × 10⁸, 9.6 × 10⁸, and 2.5 × 10¹¹ spores/mL for first to sixth instars of S. frugiperda, respectively, and the LC₅₀ and LC₉₀ of B. bassiana PfBb for each S. frugiperda instar decreased with infection time, indicating a significant dose effect. Furthermore, the virulence of B. bassiana PfBb to S. frugiperda larvae gradually decreased with an increase in larval instar. The activities of protective enzymes (i.e., catalase, peroxidase, and superoxide dismutase) and detoxifying enzymes (i.e., glutathione S-transferases, carboxylesterase, and cytochrome P450) in S. frugiperda larvae of the first three instars infected with B. bassiana PfBb changed significantly with infection time, but such variations were not obvious in the fifth and sixth instars. Additionally, after being infected with B. bassiana PfBb, the activities of protective enzymes and detoxification enzymes in S. frugiperda larvae usually lasted from 12 to 48 h, which was significantly longer than the control. These results indicate that the pathogenicity of B. bassiana PfBb on the non-target host S. frugiperda was significant but depended on the instar stage. Therefore, the findings of this study suggest that B. bassiana PfBb can be used as a bio-insecticide to control young larvae of S. frugiperda in an integrated pest management program.

SUMMARY: A simulated grazing system was set up in Huanxian County, Gansu province, on the Loess Plateau of Northwest China, involving the purchase of 18-month-old wether lambs in June of each year atc. 20 kg body weight (BW) and sale 6 months later atc. 35 kg BW. Three stocking rate (SR) treatments of 2·7, 5·3 and 8·7 wether lambs/ha were evaluated on geographically separated warm season (WS) and cold season (CS) paddocksc. 1 km apart; 3 years' data are reported (2004–2006). The metabolizable energy (ME) yield of the grazing system, calculated from the weight of animals fed and their weight gain, averaged 1·7, 3·3 and 4·7 GJ/ha/year for 2004, 2005 and 2006, respectively, in the WS and 0·9, 1·9, and 2·7 GJ/ha/year, respectively, in the CS for SR of 2·7, 5·3 and 8·7 animals/ha. Detailed grazing behaviour records were kept in order to elucidate intake dynamics. In these grazing systems, bite weight was typicallyc. 0·04 g/bite, lower than for temperate grazing systems at comparable herbage mass. A hypothesis for further study is proposed that this may relate to the distribution of a similar herbage mass over a greater sward height range in steppe vegetation than in temperate grass pasture. Sheep increased their bite rate (bites/min) and the number of steps/min at higher SR to compensate, such that intake/animal was reduced by not more than 10% with a threefold increase in SR. At higher SR, herbage ground cover on grazed plots was still lower than on ungrazed plots, 1 year after a 90-day summer grazing period or a 48-day winter grazing period. The significance of the findings for management of these systems is briefly discussed.