青藏高原高寒草甸门源草原毛虫取食偏好及其与植物C、N含量的关系

草食性昆虫对不同植物物种的取食存在偏好,这种取食偏好可能受其自身对蛋白质和碳水化合物的需求及二者平衡的调节。以青藏高原高寒矮嵩草草甸31种常见植物及门源草原毛虫为对象,通过饲喂实验,研究了草食性昆虫对不同物种和不同功能群植物的取食偏好,及其与植物叶片C、N含量和C∶N之间的关系。在31种植物中,门源草原毛虫对19种植物进行了取食,尤其对矮嵩草、红棕薹草、藏异燕麦和垂穗披碱草四种植物表现出强烈的取食偏好,而对另外12种植物未进行任何取食。在物种水平上,门源草原毛虫取食量与植物叶片N含量呈显著负相关,与叶片C∶N呈正相关。从功能群水平上看,门源草原毛虫对莎草类的取食偏好最大,而对豆科植物取食偏好最低;相应地,莎草类植物叶片N含量最低、C∶N最高,而豆科植物叶片N含量最高、C∶N最低。因此,即使在土壤有效氮匮乏、植物生长受氮素限制的高寒草甸生态系统,植物体内N含量的增加也可能不利于草食性昆虫的取食。门源草原毛虫对优势植物矮嵩草和垂穗披碱草的取食对高寒矮嵩草草甸物种共存和生物多样性维持可能具有重要的作用。

Feeding preference of Gynaephora menyuanensis and its relationships with plant carbon and nitrogen contents in an alpine meadow on the Tibetan plateau

Phytophagous insects show feeding preference for different plant species, and such preference may be regulated by their demands for proteins and carbohydrates and the balance between them. Therefore, feeding preference of phytophagous insects may be closely related to carbon (C) content, nitrogen (N) content, and the C:N ratio of plants. Although many studies have investigated feeding preference of phytophagous insects for different plant species, relatively few have examined how plant functional groups affect feeding preference of phytophagous insects and whether their leaf C and N content, and C:N ratio matter. To examine feeding preference of phytophagous insects for different plant species and for different functional groups and its relationships with leaf C, N, and the C:N ratio of plants and functional groups, we conducted a feeding experiment in which we fed the larvae of a phytophagous insect, Gynaephora menyuanensis (Lymantriidae), with leaves of 31 common herbaceous plant species of four functional groups (sedges, grasses, legumes and forbs) collected in an alpine meadow dominated by Kobresia humilis on the Tibetan plateau. Fresh leaves of the 31 plant species were cut into pieces of the similar area (about 0.5 cm²) and fixed randomly on the arenas made of foam boards installed at the inner bottoms of six glass boxes (each measuring 1 m long × 1 m wide × 0.25 m high). Each box was treated as a block, containing ten leaf pieces of each of the 31 plant species collected on the same day. We put on the arena of each box 20 larvae of G. menyuanensis that were collected in the same meadow and had been starved for 24 hours, and measured consumption of each leaf piece (i.e., the percentage of leaf area loss) after 72 hours. Leaf area consumed by the larvae was further transformed into dry mass based on the relationship between leaf area and dry mass of each plant species. Of the 31 plant species, 19 were consumed by the larvae to different degrees, but the other 12 were not. The larvae showed strong feeding preference only for four species, i.e., K. humilis, Carex przewalskii, Helictotrichon tibeticum and Elymus nutans. At the species level, leaf consumption by the larvae was significantly negatively related with plant leaf N content and significantly positively related with the leaf C:N ratio. At the functional-group level, the sedges had the highest leaf consumption by the larvae, the lowest leaf N content and the highest leaf C:N ratio, whereas the legumes had the lowest leaf consumption, the highest leaf N, and the lowest leaf C:N ratio. We conclude that increasing N content of plants may not increase the feeding preference of phytophagous insects even in alpine meadow ecosystems where plant growth is highly limited due to the lack of soil available N. Our results also suggest that the strong feeding preference of G. menyuanensis larvae for the dominant species K. humilis and E. nutans may help in maintaining species coexistence and biodiversity in the alpine meadow dominated by K. humilis.