Differential responses of three coastal grassland species to seawater flooding

Aims Supratidal plant communities fulfil a vital role in coastal protec-tion,but despite an increased likelihood of seawater flooding resulting from anthropogenic climate change,we understand little about how tidal inundation affects these habitats or interactions between their component species.Our aim was to determine how three common coastal grassland species responded to simulated seawater flooding and how subsequent changes to their ecophysi-ology,growth and survival might affect plant-plant interactions in mixed assemblages.Methods Seeds of three widely distributed European coastal grassland species(Leontodon autumnalis Asteraceae,Plantago lanceo-lata Plantaginaceae and Trifolium pratense Fabaceae)were collected from a coastal grassland site in South West England.in Experiment 1,we quantified changes in leaf ion(K^(+),Na^(+),Cl^(−))concentrations as a response to short-duration(0,2,8 or 24 h)immersion in seawater of the root-zone before monitoring longer-term effects on plant survival and growth.in a second experiment,we examined community-level responses by subjecting mixed assemblages of all three species to seawater immersion for(0,12,24 or 96 h).Important Findings When grown individually,one species(Trifolium)had markedly reduced survival with increasing soil immersion time,but a con-sistent decline in plant growth for all species with flooding dura-tion was most likely linked to osmotic and ionic stresses caused by salt ion accumulation.in mixed assemblages,all species suffered increased mortality and reduced growth following seawater flood-ing,although the relative contribution of one species(Leontodon)to total biomass increased in flooded microcosms.We thus demon-strate a number of species-specific responses to simulated seawater flooding and show that when grown together,interactions between plants are altered as a consequence.We argue that variation in the responses of component plant species will dictate how coastal plant communities respond to,and recover from,expected changes in sea levels and transient floods following storm surge events.Such infor-mation is vital in order to predict future impacts of seawater floods on supratidal vegetation.

Climate variation, reproductive frequency and acorn yield in English Oaks

Aims Annually variable but synchronous production of large seed crops(‘masting’)is a widespread phenomenon in temperate trees.Mounting concerns about the impacts of anthropogenic climate change(ACC)on plant reproduction gives urgency to our need to understand better the role of climate on tree reproduction,and in particular,mast events.Unlike our understanding of reproductive phenology however,there is little consensus regarding how climate affects plant reproductive effort or indeed the actual environmental triggers that underpin masting behaviour.Methods We used a 27-year record of acorn yield from a population of 12 Quercus robur trees located in southern England to compare mast-ing frequency and post-dispersal acorn yield each year for each tree,with long-term weather data over the same period.We focussed on discrete or sequential climate cues(temperature,precipitation and frost days)as likely predictors of oak reproduction.Important Findings Annual post-dispersal acorn crop varied greatly;i.e.no acorns in 14 of the 27 years,but there was no sequential pattern of crop ver-sus non-crop years indicating that weather,rather than resource limitation alone,dictated the timing of reproduction.Crop years were instead most closely associated with relatively cool late sum-mer conditions in the preceding year,followed by anomalous sum-mer warmth within crop year.Acorn yield increased following dry April and above-average May and June temperatures within crop year.Although our results support a general association between warm late spring and summer conditions,and crop frequency and yield,respectively,the influence of cooler later summer conditions in the year prior to masting highlights how a combination of weather cues may dictate the occurrence of mast years.Consequently,our results corroborate not only the hypothesis that temperature differ-entials between consecutive years,not absolute temperatures,may be the better predictor of mast seeding events but lend support also to the suggestion that reproductive failure and resource accumu-lation resulting from a climate-linked environmental veto,drives future reproductive synchronization in temperate tree species.