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The photosynthetic physiological and ecological characteristics of plants are an important basis for the selection of plant species for restoration and reconstruction of degraded ecosystems. In order to study the photosynthetic physiological and ecological characteristics of different mangrove plants, from April to May in dry season and from July to September in rainy season of 2021, the LI-6400 photosynthetic measurement system was used to monitor the photosynthetic physiological parameters and main ecological factors of Kandelia obovata and Bruguiera sexangular in Dongzhaigang National Nature Reserve. The effects of major ecological factors on net photosynthetic rate were analyzed by using path analysis. The results were as follows: (1) The daily average net photosynthetic rate of Kandelia obovata in the dry season (8.43 μmol-2·s-1) was slightly lower than that in the rainy season (8.67 μmol-2·s-1), and the difference was not significant. In contrast, the rate of Bruguiera sexangular in the dry season (7.03 μmol-2·s-1) was significantly lower than that in the rainy season (9.41 μmol-2·s-1). The rate of Kandelia obovata was significantly higher than that of Bruguiera sexangular in dry season, while the rate of Kandelia obovata was significantly lower than that of Bruguiera sexangular in rainy season. (2) The daily average variations of transpiration rate, stomatal conductance and intercellular CO2 concentration of Kandelia obovata were smaller than those of Bruguiera sexangular and the water use efficiency was also lower than that of B. sexangular in dry and rainy seasons. (3) There was a phenomenon of “midday depression of photosynthesis” in both dry and rainy seasons of Kandelia obovata and Bruguiera sexangular. In dry season, the main reason for the phenomenon of Kandelia obovata might be due to non-stomatal limitation, while Bruguiera sexangular due to stomatal limitation. In rainy season, the phenomena of two mangrove plants were both mainly caused by stomatal limitation. (4) In the dry season, the main decision factor affecting the net photosynthetic rate of Kandelia obovata was photosynthetically active radiation, and the main limiting factor was relative humidity, while ecological factors played a limiting role on the net photosynthetic rate of Bruguiera sexangular of which saturated water vapor pressure difference was the main limiting factor. In the rainy season, the main decision factor was photosynthetically active radiation, and the main limiting factor was saturated water vapor pressure difference for both Kandelia obovata and Bruguiera sexangular. In summary, Kandelia obovata is more adaptable to habitat changes, and Bruguiera sexangular not only has better drought tolerance performance, but also more suitable for hot and rainy habitats, which will be the scientific reference for the selection of plant for restoration and reconstruction of degraded mangroves.

The photosynthetic physiological and ecological characteristics of plants are an important basis for the selection of plant species for restoration and reconstruction of degraded ecosystems. In order to study the photosynthetic physiological and ecological characteristics of different mangrove plants, from April to May in dry season and from July to September in rainy season of 2021, the LI-6400 photosynthetic measurement system was used to monitor the photosynthetic physiological parameters and main ecological factors of Kandelia obovata and Bruguiera sexangular in Dongzhaigang National Nature Reserve. The effects of major ecological factors on net photosynthetic rate were analyzed by using path analysis. The results were as follows:(1)The daily average net photosynthetic rate of Kandelia obovata in the dry season(8.43 μmol-2·s-1)was slightly lower than that in the rainy season(8.67 μmol-2·s-1), and the difference was not significant. In contrast, the rate of Bruguiera sexangular in the dry season(7.03 μmol-2·s-1)was significantly lower than that in the rainy season(9.41 μmol-2·s-1). The rate of Kandelia obovata was significantly higher than that of Bruguiera sexangular in dry season, while the rate of Kandelia obovata was significantly lower than that of Bruguiera sexangular in rainy season.(2)The daily average variations of transpiration rate, stomatal conductance and intercellular CO2 concentration of Kandelia obovata were smaller than those of Bruguiera sexangular and the water use efficiency was also lower than that of B. sexangular in dry and rainy seasons.(3)There was a phenomenon of “midday depression of photosynthesis” in both dry and rainy seasons of Kandelia obovata and Bruguiera sexangular. In dry season, the main reason for the phenomenon of Kandelia obovata might be due to non-stomatal limitation, while Bruguiera sexangular due to stomatal limitation. In rainy season, the phenomena of two mangrove plants were both mainly caused by stomatal limitation.(4)In the dry season, the main decision factor affecting the net photosynthetic rate of Kandelia obovata was photosynthetically active radiation, and the main limiting factor was relative humidity, while ecological factors played a limiting role on the net photosynthetic rate of Bruguiera sexangular of which saturated water vapor pressure difference was the main limiting factor. In the rainy season, the main decision factor was photosynthetically active radiation, and the main limiting factor was saturated water vapor pressure difference for both Kandelia obovata and Bruguiera sexangular. In summary, Kandelia obovata is more adaptable to habitat changes, and Bruguiera sexangular not only has better drought tolerance performance, but also more suitable for hot and rainy habitats, which will be the scientific reference for the selection of plant for restoration and reconstruction of degraded mangroves. [ABSTRACT FROM AUTHOR]

The photosynthetic characteristics of five mangrove tree species in Techeng Island of Zhanjiang City were measured by Li-6400 photosynthetic measurement system to explore the factors on diurnal course of photosynthesis and evaluate their photosynthetic carbon fixation capacity. The results showed that daily variation of net photosynthetic rate in leaves of Kandelia candel and Rhizophora stylosa presented a single-peak curve, however, Avicennia marina, Bruguiera gymnorhiza and Aegiceras corniculatum presented a double-peak curve and an obvious “midday depression” phenomenon occurred, with the peak values at 10:00 am and 14:00 pm. Among them, midday-depression of photosynthesis in Avicennia marina and Bruguiera gymnorhiza was affected by stomatal limitation, however, Aegiceras corniculatum was affected by non-stomatal limitation. By path analysis, photosynthetic active radiation(PAR)was the decision factors and vapor pressure deficit(VPD)was the main limiting factors which affecting the characteristic of net photosynthetic rate(Pn)of Avicennia marina and Aegiceras corniculatum. In contrast to the situation of Avicennia marina and Aegiceras corniculatum, leaf temperature(Tl)was the main limiting factor and stomatal conductance(Gs)was the decision factor which affected Pn of Rhizophora stylosa and Kandelia candel. Gs was also the decision factors which affected Pn of Bruguiera gymnorhiza. The daily net carbon fixation amount was significant different among the five mangrove trees based on the leaf net photosynthesis rate, of which Kandelia candel was the highest(13.83 g·m-2·d-1), followed by Avicennia marina and Aegiceras corniculatum (9.48 and 8.24 g·m-2·d-1, respectively), the lowest was Bruguiera gymnorhiza and Rhizophora stylosa(6.72 and 6.30 g·m-2·d-1, respectively). The light compensation point(LCP)values of five mangrove trees ranged from 28.3 to 37.0 μmol·m-2·s-1 which showed the typical properties of sun plants. The light saturation point(LSP)values range between 169.3 and 1 189.3 μmol·m-2·s-1 of which Aegiceras corniculatum was the largest but Rhizophora stylosa is minimal. There were significant differences among the five mangrove tree plants of apparent quantum yield(AQY)(P<0.01), of which Avicennia marina was up to 0.064 mol·mol-1 while Bruguiera gymnorhiza was the lowest 0.005 mol·mol-1. The magnitude on grey correlation degree between light response parameters and daily net photosynthetic carbon fixation in leaves of mangrove tree species was the maximum net photosynthetic rate(Pmax), LSP-LCP, AQY, LSP and LCP. [ABSTRACT FROM AUTHOR]