Effects of nitrogen inputs and mowing on the abundance and species richness of herbivorous insects in a meadow steppe.

To reveal the effects of nitrogen (N) inputs and mowing on the abundance and richness of insect community in meadow steppe, we investigated the abundance and diversity of herbivorous insects under four treatments in Inner Mongolia meadow steppe in August 2022, including control, N addition, mowing, and combined N addition and mowing. At a long-term control experimental platform, we collected insects using the vacuum sampling method. The results showed that N addition significantly increased the abundance of herbivorous insects, and mowing significantly decreased the abundance of herbivorous insects. Nitrogen addition significantly increased insect abundance in unmown condition but not in the mown condition. The responses of insect abundance at the community level to N addition were mainly driven by the dominant groups, Cicadellidae and Lygaeidae, which was affected by the abundance of Gramineae species. In contrast, their responses to mowing were the opposite. Both N addition and mowing did not affect the diversity of herbivorous insects. Our results indicated that the responses of herbivorous insect abundance to N inputs and mowing were directly regulated by food resources. With increasing food resource availability, the abundance but not the diversity of herbivorous insects increased, with stronger responses of dominant groups than subordinate ones.

[Effects of nitrogen and phosphorus inputs on soil nematode community in a degraded grassland.] / æ°®ç£·è¾“å ¥å¯¹è¿‡åº¦æ”¾ç‰§é€€åŒ–è‰åŽŸåœŸå£¤çº¿è™«ç¾¤è½çš„å½±å“.

Nematodes, occupying multiple trophic levels in the food web, play important roles in energy flow and nutrient cycling. Most of Chinese natural grasslands have been degraded due to long-term unreasonable utilization, such as over-grazing. External nutrient input is an important way to restore the ecological function of degraded grasslands. The main and intertative effects of nitrogen and phosphorus inputs on soil nematode abundance, trophic group composition and community structure were studied in the grasslands in Xilingol League of Inner Mongolia. Totally, 38 genera of nematodes were recorded. Tylencholaimus, Aphelenchoides, Thonus, and Scutylenchus were dominant genera in this degraded grassland. Nitrogen input decreased total abundances of soil nematodes, and that of omnivores-carnivorous nematodes and plant-feeding nematodes. Phosphorus input increased total abundances of soil nematodes, and that of fungal-feeding nematodes, omnivores-carnivorous nematodes, and plant-feeding nematodes. Nitrogen input inhibited the positive effects of phosphorus input on the abundances of total nematodes, omnivores-carnivorous nematodes and plant-feeding nematodes. Nutrient inputs had no effect on nematode diversity, which would be resulted from the stable plant community. Nitrogen input significantly increased nematode maturity index, decreased plant parasitic nematode maturity index (PPI), and greatly alleviated the negative effects of phosphorus input on PPI and Wasilewska index, indicating that nitrogen input could improve soil health condition and the stability of nematodes community. Our results would help improve our understanding of the effects of nutrient inputs on degraded grassland ecosystem from a soil biotic perspective.

The relative contributions of intra- and inter-specific variation in driving community stoichiometric responses to nitrogen deposition and mowing in a grassland.

AIMS: The stoichiometric characteristics of plant communities are important controller for several fundamental ecological processes. The effects of environmental changes on community stoichiometric characteristics are driven by intra- and inter-specific variation. However, the relative importance of both pathways has seldom been empirically examined. METHODS: We quantified the relative contribution of intra- and inter-specific variation to the changes of community nitrogen (N) and phosphorus (P) concentrations after seven-year factorial N addition and mowing treatments in a semi-arid grassland of northern China. RESULTS: Nitrogen addition significantly increased community N and P concentrations and N:P ratio. Mowing significantly increased community N concentration and N:P. Intra-specific variation contributed more than inter-specific variation to the total variability of all the nutritional and stoichiometric characteristics, with intra-specific variation accounting for 68%, 70%, and 75% of the total variation in community-level N, P, and N:P, respectively. Negative covariations between the contribution of intra- and inter-specific variation occurred for community N and P concentrations. Further, N addition and mowing interacted to affect the impacts of intra- and inter-specific variation on community N concentration and N:P stoichiometry. CONCLUSIONS: Our results highlight different ways of trait selection for N addition and mowing treatments. Interactions between those two factors make it more difficult to accurately predict the responses of plant-mediated biogeochemical cycles under co-occurrence of environmental changes.

Diversity and composition of understory vegetation in the tropical seasonal rain forest of Xishuangbanna, SW China.

Tropical forests vegetation and community research have tended to focus on the tree component, and limited attention has been paid to understory vegetation. Species diversity and composition of the understory of tropical seasonal rain forest were inventoried in a 625 m2 area (for sapling layer) and a 100 m2 area (for herb/seedling layer) in three 1 ha plots. We found 3068 individuals belonging to 309 species, 192 genera and 89 families. The most important family as determined by the Family Importance Value (FIV) was Rubiaceae in both sapling and herb/seedling layers. In terms of Importance Value Index (IVI), the shrub Mycetia gracilis (Rubiaceae) was the most important species in the sapling layer and the pteridophyte Selaginella delicatula (Selaginellaceae) was the most ecological significant species in the herb/seedling layer. Much more vascular plant species were registered in the understory than in the tree layer totaled among the three plots. The species diversity did not differ significantly among the tree layer, sapling layer and herb/seedling layer. Given that we still know little about the understory plant community for growth forms other than trees, the results from the present study indicate that more attention should be paid to the understory vegetation during the decision-making process for biodiversity conservation in the tropical forests.