The Characteristics Of Stomatal Response To Environmental Factors In Mangrove Forest

The coordination between plant photosynthesis and water status is maintained by the open and closure of stomata.The opening and closing of stomata is influenced by environmental factors and the water status of plants.Mangroves grow in special circumstances with high salinity and high light density.It is hardly understood how their stomata respond to environmental factors and the regulation mechanisms of their stomatal movement.In this study,nine mangrove species in a mangrove forest in Hainan were measured for their stomatal density(SD),stomatal length(SL),vein density(VD),diurnal variation of stomatal conductance(Gs)and response curves of Gs to different transient light densities and vapor pressure deficit(VPD),predawn leaf water potentials(?pd),midday minimum leaf water potentials(?min)and leaf hydraulic conductance(Kleaf).In addition,in order to explore the relationship of stomatal movement with leaf water potential(?leaf)and abscisic acid(ABA),we carried out drought stress experiments on potted saplings of Kandelia candel and Bruguiera gymnorrhiza.The results showed that VD was positively correlated with SD,but negatively correlated with SL,and there was also a negative correlation between SD and SL in mangrove plants.SL and VD both did not show significant correlation with the daily maximum stomatal conductance(Gmax).The Gs of the mangrove plants increased linearly with the increase of light intensity in order to maximize photosynthesis,and the sentivity of stomatal response to light was correlated with ?pd.Moreover,there were three different modes of stomatal response to transient increase of VPD:(1)initially increase then decrease to a very low value;(2)decrease of Gs until a very low value;(3)continuously increase until to a stable value.These different stomatal response modes might be related to leaf anatomical structure(with or without aquiferous tissue)and water use strategies.We also found that there were significant linear correlations between the ?pd,?min of the leaves and maximum stomatal conductance in a day(Gmax).This indicates that good water potential status could help plants to achieve higher stomatal opening and photosynthetic rate.Moreover,we also found that there was significant positive correlation between mangroves' Kleaf and daily maximum photosynthetic rate(Amax),Gmax,indicating the coordination between photosynthesis and stomatal behaviors and hydraulic functions in mangrove plants.We found that during the proloned drought treatment Gs of both Kandelia candel and Bruguiera gymnorrhiza gradually decreased and eventually closed with the decrease of ?leaf and accumulation of ABA in the leaves.The present study showed the diverse stomatal behaviors in response to the fluctuation of ambint environmental factors and coordination between stomatal behaviors and leaf hydraulic traits,and provides novel knowledge on stomatal regulation behavior of plants.