RESUMO
Shrubs are the major components of vegetation in arid and semi-arid areas, and play a pivotal role in maintaining ecosystem stability and function. The nurse effects of shrubs can help with the regeneration of native target plant species by alleviating the adverse influences that limit their growth and reproduction in degraded habitats. We summarized the main research results and application of shrub nurse effects in the last 20 years. We discussed several facilitation mechanisms of nurse shrubs, including microhabitat amelioration, fertile island formation, defense and resistance against herbivores, introduction of beneficial microorganism and propagule propagation or preservation, as well as changes in the patterns of interspecific competitive networks. Key factors affecting nurse effects were analyzed, including abiotic environments, biological disturbances, plant life history as well as growth and reproductive strategies. Prospects for future research were also considered from the aspects of improving theore-tical mechanisms of nurse effects by shrubs and building models involved in multiple plant species interaction affec-ted by multifactors.
Assuntos
Ecossistema , Plantas , HerbivoriaRESUMO
The differences in the mechanism of cadmium (Cd) accumulation in the grains of different wheat (Triticum aestivum L.) cultivars remain unclear. Thus, we conducted a hydroponic experiment in a greenhouse to compare root surface adsorption, root uptake, subcellular distribution, and chemical forms of Cd between low- and high-Cd-accumulating wheat cultivars at seedling stage, to improve our understanding of the differences between cultivars. The results showed that Cd adsorbed on the root surface was mainly in a complexed form, and the total amount of Cd on the Yaomai16 (YM, high-Cd-accumulating genotypes) root surface was higher (p < 0.05) than that on Xinmai9817 (XM, low-Cd-accumulating genotypes). A large amount of Cd ions adsorbed on root surface would cause plant damage and inhibit growth. Comparing the root-to-shoot translocation factors of Cd, the transfer coefficients of YM were 1.017, 1.446, 1.464, and 1.030 times higher than those of XM under 5, 10, 50, and 100 µmol L-1 Cd treatments, respectively. The subcellular distribution of Cd under Cd exposure is mainly in the cell wall and soluble fraction. The proportions of Cd in YM shoot soluble fraction were higher than those in XM, which was the main detoxification mechanism limiting the activity of Cd and may be responsible for low Cd accumulation in grains, while the effects of the chemical forms of Cd on migration and detoxification were not found to be related to Cd accumulation in the kernels.