Perturbation in leaves of salt-treated Sorghum: elements for interpretation of the normal development as an adaptive response

Developmental windows are specific periods of sensitivity in which a perturbation may be adaptively integrated. In Sorghum bicolor , two developmental windows which enable adaptive adjustment to salinity (increase in tolerance) have been described during vegetative development. A third developmental window is open during the transition between vegetative and reproductive development. This third developmental window was analysed using morphological markers (specific malformations on leaves), and their relationship with vegetative and reproductive events. A positive link was observed between fertility and malformations on the last leaf. We concluded that this late window enables an adaptive adjustment of reproductive development, counteracting the negative effect of salt adaptation on fertility. Developmental windows open following rapid changes in growth of the different organs. They permit adaptive adjustments to emergence or senescence of various organs. This phenomenon is integrated within normal development, but developmental windows are enlarged for plants exposed to perturbation and for their progeny.     

Plant richness and blooming cover affect abundance of flower visitors and network structure in Colombian orchards

1. Pollination is essential to fruit production. How plant diversity and blooming events in and around orchards affect the pollinator community and the plant-flower-visitor network in neotropical systems remains largely unknown.
2. We surveyed the flower visitors in deciduous fruit trees and alternative blooming resources (other crops, hedgerows and weeds) in Colombia across 6 orchards over 12 months. We evaluated whether plant species richness and blooming cover influenced abundance and richness of flower visitors, as well as network-level connectance and specialization. We also assessed the role of alternative blooming resources for the flower visitors of deciduous fruit trees.
3. Overall, we found 66 taxa of flower visitors, 35 of which visited deciduous fruit trees. There was a greater abundance of flower visitors when there was higher richness of weedy species and greater blooming cover of deciduous fruit trees. Networks were less connected when there was lower crop and weedy species richness. Finally, flower visitor abundance and specialization increased when there were multiple hedgerow species in bloom with a high blooming cover.
4. We highlight the importance of maintaining alternative blooming resources in and around the orchards to support deciduous fruit tree pollinators and diversity in the plant flower-visitor network.

     

Will a large complex system be productive?

While the relationship between food web complexity and stability has been well documented, how complexity affects productivity remains elusive. In this study, we combine food web theory and a data set of 149 aquatic food webs to investigate the effect of complexity (i.e. species richness, connectance, and average interaction strength) on ecosystem productivity. We find that more complex ecosystems tend to be more productive, although different facets of complexity have contrasting effects. A higher species richness and/or average interaction strength increases productivity, whereas a higher connectance often decreases it. These patterns hold not only between realized complexity and productivity, but also characterize responses of productivity to simulated declines of complexity. Our model also predicts a negative association between productivity and stability along gradients of complexity. Empirical analyses support our predictions on positive complexity-productivity relationships and negative productivity-stability relationships. Our study provides a step forward towards reconciling ecosystem complexity, productivity and stability.     

Regulation of growth: the meristem network approach

Gibberellin (GA) and/or cytokinin (CK) supplied to the root medium modified the rate of growth of the shoot, the adventitious and seminal roots in young seedlings of Sorghum bicolor (L.) Moench. For each population submitted to a hormonal treatment, the link between the weight of these three organs was analysed. All these links build a network of relationships, also termed a meristem network. Treatments with 1–100 μ M CK modified the relative growth of these three organs, as well as the meristem network. Treatments with 1–100 μ M GA slightly modified the growth, but the meristem network was considerably changed. When GA and CK were applied simultaneously, the growth was similar to that of CK-treated plants, and the meristem network was similar to that of GA-treated plants. Similar experiments were performed on plants exposed to 150 m M NaCl. They showed that both growth and meristem networks are modified by salinity. Growth was unrelated to the network variations in non-salinized plants, while an optimal level of relationship for growth was observed in salinized plants. It is concluded that stress generates an imbalance between the self-stimulation of meristem activity and its regulation by the other organs. A definition of stress, independent from the rate of growth, is proposed.