Hydrologic fragmentation-induced eutrophication in Dove Sound, Upper Florida Keys, USA

Anthropogenic impacts to island systems can have deleterious effects on coastal aquatic ecosystems. These effects can alter water quality, primary production as well as habitat. Land development often fragments hydrologic connectivity within aquatic ecosystems forcing alterations in nutrient transport and increases the potential for eutrophication. Dove Sound, a tidal lagoon located in the Upper Florida Keys on Key Largo, has been subjected to anthropogenic influences of land development during the last century. To investigate these influences a short sediment core was collected from within Dove Sound and investigated using 210Pb dating, stable isotopes of carbon and nitrogen, and sedimentary pigments. Results indicated that Dove Sound has undergone eutrophication and the primary producer community structure has shifted from dominantly macrophytic to a system that supports substantial algal production. While septic waste was a possible source for eutrophication, low δ15N did not support this conclusion. However, the timing of the shifts in Dove Sound along with indicators of anoxia leads to the conclusion that fragmentation caused by the construction of a railroad was the root cause. The hydrologic fragmentation reduced the flushing rates, thereby enhancing anoxic conditions in the system and increasing the internal nutrient loading

Changes in growth and soil microbial communities in reciprocal grafting clones between Populus deltoides males and females exposed to water deficit conditions

Key message. Our findings highlight that male-rooted clones (M/M and F/M) of Populus deltoides are more water-deficit tolerant than female-rooted clones (F/F and M/F), as shown by a smaller decrease in total biomass and net photosynthetic rate in the male-rooted clones. Context. It has been reported that graft clones (female scion and male rootstock) in poplars may be an option to mitigate the effects of water deficit on plants. However, the extent to which grafting mitigates the effect of soil water deficit on soil microorganisms remains poorly understood. Aims. The research was designed to investigate the effects of soil water deficit on plant growth, soil microbial communities, and soil enzymatic activities of the reciprocal graft clones of P. deltoides. Methods. Four different graft clones (female shoot scion and female rootstock, F/F; male shoot scion and female rootstock, M/F; male shoot scion and male rootstock scion, M/M; and female shoot scion and male rootstock, F/M) in P. deltoides were used. Two watering regimes, irrigation and soil water deficit (i.e., non-irrigation conditions, natural levels of precipitation) were included in the experiments. The microbial community structure was quantified using phospholipid fatty acid. Results. Under water deficit, the decreases in total biomass, net photosynthetic rates, and leaf nitrogen content were more evident in M/M and F/M than in F/F and M/F. Bacterial phospholipid fatty acids (PLFAs) and actinomycetal PLFAs remained unaffected in the four graft clones. In contrast, during soil water deficit, fungal PLFAs were higher in M/M and F/M soil coincided with higher extracellular activities of β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase. Conclusion. Male-rooted clones (M/M and F/M) are more tolerant to water deficit than female-rooted clones (F/F and M/F). It is possible that the better performance of M/M and F/M, when exposed to water deficit, is associated mainly with higher fine root activity, greater specific root length and root/shoot ratio as well as increased fungal PLFAs