RESUMO
Collembola are among the most abundant and integral group in soil decomposers. They channel C and nutrients from basic food resources to higher trophic levels, and therefore play an irreplaceable role in the underground food web. Collembola community would be altered dramatically by increasing N and P deposition. However, we still know little about how Collembola respond to N and P inputs, which will largely retard our steps to understand the ecological functions of collembolans, material circulation and energy flow of the underground food web, and even C cycling in terrestrial ecosystem. The different classification rules for Collembola functional groups have led to poor comparability of research results in the literature. This review proposed three taxonomic criteria of Collembola and four common research means on trophic relationships, summarized the mechanisms underlying the responses of Collembola to N and P addition alone and coadded. Overall, Collembola generally shows a negative response to N addition namely community density decreases, while a positive response to P addition in most ecosystems. The situation was more complicated under the combined N and P application. In the future, the research of Collembola response to N and P deposition should focus on the scientific taxa of Collembola functional groups, improving the research methods of trophic structure of Collembola, and the mechanism underlying the impacts of N and P interaction on Collembola community.
Assuntos
Artrópodes , Solo , Animais , Ecossistema , Nitrogênio , FósforoRESUMO
To explore the influencing factors of understory plant species diversity of Eucalyptus grandis, we examined understory plant species diversity and phenolic allelochemicals in the rhizosphere soils of four-year-old and eight-year-old E. grandis plantations with different densities (1200, 1600, 2000 ind·hm-2) in Danling County of Sichuan Province. The results showed that a total of 45 plant species were recorded, belonging to 33 families and 44 genera. With the increases of stand age and decreases of stand density, plant species richness increased and their importance values were evenly distributed. Phanerophytes was the dominant life form across all stands. Shannon index and Margalef index of shrub in the four-year-old E. grandis plantations increased significantly at the density of 1600 ind·hm-2. All herbage plant diversity index except for Margalef index in four-year-old ones and Pielou index in eight-year-old plantations increased significantly with the decreases of density. Shannon index and Margalef index of shrub in 1200 ind·hm-2 were significantly higher in eight-year-old E. grandis stands than those in four-year-old ones. Five phenolic allelochemicals in the rhizosphere soils of E. grandis plantations were identified. In four-year-old stands, salicylic acid concentrations decreased significantly at the density of 1600 ind·hm-2. The concentrations of chrysin in four-year-old stands reduced significantly with the decreases of density. The concentrations of salicylic acid in eight-year-old stands increased significantly with the decreases of tree density. Salicylic acid concentrations in 2000 ind·hm-2 were significantly higher in four-year-old stands than that in eight-year-old ones, but the result was opposite in stands with density of 1600 ind·hm-2. The concentrations of chrysin in stand with density of 1200 ind·hm-2 were significantly higher in eight-year-old stands than that in four-year-old ones. Rundancy analysis (RDA) result showed that soil pH, bulk density, and the concentrations of soil organic matter, total nitrogen, total phospho-rus, and allelochemicals were the main environmental factors influencing understory plant species diversity. Therefore, prolonging rotation period and reducing stand density would improve micro-environmental condition of forests and buffer the allelopathy of E. grandis, which could facilitate the development of understory vegetation.
