In this study, we conducted a 14-month investigation in Daya Bay, southern China to understand the effects of oyster farming on phytoplankton community and biomass by using size-fractionated phytopigments. Results proved the filtering effects of oysters on phytoplankton biomass. During the oyster culture period, the average concentration of total chlorophyll a (sum of size-fractionated Chl a) within the farming area was approximately 60% lower than that at the reference site. Phytoplankton depletion in the aquaculture zone mainly occurred in micro-sized fractions (>20 μm) of Chl a, fucoxanthin, and peridinin. The influence of oyster filtration on nano-sized (2.7–20 μm) pigments seemed less than that on micro-sized ones. The depletion of peridinin and 19′-hex-fucoxanthin in aquaculture zone was higher than those of the other pigments, which indicated that flagellated cells might be selectively filtered by oysters and could be more easily influenced by oyster aquaculture. The pico-sized Chl a (<2.7 μm) comprised 24% of total Chl a on the average in the aquaculture zone during the cultural period compared to 6% in the reference site. Picoeukaryote abundance, which was determined via flow cytometry, was significantly higher in the aquaculture zone than in the non-aquaculture areas. The abundance of picoeukaryote is significantly and positively correlated with the concentrations of pico-sized prasinoxanthin, violaxanthin, and neoxanthin, indicating that picoeukaryote is dominated by those in prasinophyte. The results suggest that oyster aquaculture might stimulate the growth of prasinophyte, although the seasonal variations are mainly controlled by the water temperature in the study area. This research highlights the successful use of size-fractionated phytopigments to estimate size-specific phytoplankton biomass and community, which can be applied as a routine method to monitor the environmental effect and food resources of bivalve aquaculture.

High O3 levels, driving uptake and challenging defense, prevail on the Canary Islands, being associated with the hot and dry summers of the Mediterranean-type climate. Pinus canariensis is an endemic conifer species that forms forests across these islands. We investigated the effects of ozone on photosynthesis and biochemical parameters of P. canariensis seedlings exposed to free-air O3 fumigation at Kranzberg Forest, Germany, where ambient O3 levels were similar to those at forest sites in the Canary Islands. The twice-ambient O3 regime (2xO3) neither caused visible injury-like chlorotic or necrotic spots in the needles nor significantly affected violaxanthin, antheraxanthin and zeaxanthin levels and the de-epoxidation state of the xanthophyll cycle. In parallel, stomatal conductance for water vapour, net photosynthesis, intercellular CO2 concentration, chlorophyll fluorescence parameters, as well as antioxidant levels were hardly affected. It is concluded that presently prevailing O3 levels do not impose severe stress on P. canariensis seedlings.

A dose–response study was performed in four commercial clones, Baldo (Populus deltoides), Jean Pourtet (Populus nigra), I-214 (Populus x euramericana) and Villafranca (Populus alba), to investigate the best performing species in terms of metal content and high metal resistance (absence of symptoms) useful in biomass production on contaminated water/land by zinc. Zinc (1 μM as control and 1 mM) was applied for 4 weeks in a hydroponic system. Clone Villafranca was the least damaged, while the most sensitive was clone I-214. The highest zinc concentration in all different parts of plants analysed was recorded in Villafranca > I-214 > Baldo > Jean Pourtet. The higher translocation factor was seen in Baldo, the lowest in Villafranca. Analyses of leaf damage showed a reduction on Chl a in young leaves (96 %) in I-214 stressed plants, whereas in Villafranca, Chl a was about double compared to the control. Regarding other photosynthetic pigments, violaxanthin was significantly correlated to zinc concentration in old leaves. The responses of clones to zinc (Zn) stress were specific: Villafranca was the most resistant, while I-214 showed the highest biomass production under Zn excess. Since these two clones have useful and complementary traits for uptake and detoxification while maintaining high biomass production under Zn excess, they are interesting candidates for understanding the key resistance mechanisms.