Photosynthesis And Growth Responses Of Several Terraneous Plants In Three Gorges Reservoir Region As Affected By Simulated Flooding

Flooding changes a series of physical, chemical and biological factors in the soil, altering dramatically the environmental conditions for species growth. In plants, flooding affects different aspects of the physiology, morphology and anaomy depending on the species. Flooding reduces the photosynthetic rate of many plant species, particularly of flood-intolerant species. The main adverse effects of flooding are reduction in shoot and root growth, reduction in whole plant biomass, change in biomass partitioning and promotion of overall plant senescence and mortality. Complete submergence imposes considerable stress on plant functioning, predominantly by way of oxgen deprivation. Some of the species generally inhabit poorly drained habitats, where floodwater may remain stagnant for a substantial period of the growing season, and shoot elongation is at these sites an efficient solution to avoid oxygen deficiency. Many species, on the other hand, experience submerged conditions that too deep for the shoot to reach the surface. A straightforward way to reduce shortage of both oxygen and carbohydrates under such conditions would be the continuation of photosynthesis under water. As photosynthesis produces both oxygen and carbohydrates, it may alleviate stress considerably in completely submerged plants.To reveal the effects of flooding on the photosynthesis and growth of several riparian plant species in Three Gorges reservoir region, a flooding simulation experiment was conducted, the photosynthesis, chlorophyll fluorescence, growth and underwater photosynthesis of those plant species were analyzed. The results of the experiments showed that:Photosynthetic responses of riparian plant species Arundinella anomala Steud. and Salix variegata Franch. in Three Gorges Reservoir Region as affected by simulated flooding The results indicated that all photosynthetic characteristics were influenced by both the water depth and the duration of inundation, flooding didn’t have significant effects on photosynthetic characteristics of A.anomala and S. variegata exposed to inundation less than 60 days and the treatment effects varied with different flooding depths. After 20d of inundation, the aboveground half-submerged A. anomala had 16.1% higher Pn than control plants. After 60d inundation, Pn of A. anomala submerged with 0.5m water depth and plants submerged with 2m water depth were significantly lower than the Pn of control and aboveground half-submerged plants, the net photosynthetic rates of plants fully submerged decreased to 7.51μmol·m^-2·s^-1 and 9.15μmol·m^-2·s^-1. After 40 days inundation, the net photosynthetic rate of S. variegata was significantly higher than flood-intolerant species Salix babylonica L.. After 60 d and 90 d inundation, the photosynthetic capacity and Fv/Fm of wholly submerged plants decreased significantly as compared with the photosynthetic capacity and Fv/Fm of control and belowground-submerged plants, but the plants could still maintain high photosynthetic capacity. These results indicated that the net photosynthetic rate of A. anomala and S. variegata were much less affected by flooding than other flood-tolerant species and flood-intolerant species. The decrease of the net photosynthetic rate was mainly due to the damage of PSⅡ, and probably was also caused by the synthesis of photosynthetic pigment and the degradation of Rubisco, but for S. variegate, the decrease of Pn was probably caused by the degradation of Rubisco and the light utilization capacity. The results indicate that A. anomala and S. variegata can maintain high photosynthetic capacity after being inundated for 60 days and are promising species that can be applied in construction of riparian vegetations in the Three Gorge Reservoir Area.Photosynthesis of six kinds of terraneous plants in Three Gorges reservoir region as affected by simulated floodingPThe results showed that flooding did not have significant effects on net photosynthetic rate （Pn） of Acorus calamus L. Saccharum spontaneum L. Vetiveria zizanioides L. subjected to 30 days inundation, but after 30 days flooding Ficus tikoua Bur. died of inundation. After 60d inundation, Pn of Acorus calamus L., Saccharum spontaneum L., Phragmites communis（L.）Trin. and Hemarthris compressa （L. f.） R.Br. submerged with 2m water depth decreased to 75.1%, 80.5%, 40.7% and 55.7% of plants controlled, Pn of Vetiveria zizanioides L. submerged with 2m water depth contrarily had 16.9% higher Pn than controlled plants. After 90d inundation, All Phragmites communis （ L.） Trin. plants had no green leaves, 2/3 of total plants died of inundation, Pn of Acorus calamus L., Saccharum spontaneum L., Vetiveria zizanioides L. and Hemarthris compressa （L. f.） R.Br. submerged with 2m water depth decreased to 51.7%, 57.8%, 67.8% and 33.4% of controlled plants. After 60d inundation, Intercellular CO2 concentration（Ci） of Hemarthris compressa （L. f.） R.Br., Phragmites communis（L.）Trin., Acorus calamus L. and Saccharum spontaneum L. was significantly higher than plants controlled, stomatal limitation（Cs） of Hemarthris compressa （L.f.） R.Br., Phragmites communis （L.） Trin., Acorus calamus L., Saccharum spontaneum L. was significantly lower than plants controlled. After 90d inundation, Ci of all kinds of plants submerged with 2m water depth was significantly higher than plants controlled, Cs of these plants was significantly lower than plants controlled, so the dominant reason for inhibition of photosynthesis is non-stomatal inhibiting factor.Underwater photosynthesis of the riparian plant Salix variegata. Franch and Arundinella anomala Steud. in Three Gorges reservoir region as affected by simulated floodingIt was shown that before 40d inundation the underwater photosynthesis of S . variegata and A . anomala submerged with 2m water depth did not have significance lower than the underwater photosynthesis of control. After 5d and 15d inundation, the underwater photosynthesis of S . variegata and A . anomala submerged with 2m water depth was significantly higher than Cinnamomum camphora L. and Digitaia sanguinalis, respectively. After 60d inundation, the underwater photosynthesis of S. variegata and A . anomala controlled was significantly higher than plants submerged with 2m water depth, but they still had underwater photosynthesis and the underwater photosynthesis of S . variegate was higher than A . anomala. Our work shows that as regards underwater photosynthesis, S. variegata and A . anomala have high tolerance to inundation, they are promising species for revegetation of riparian area in Three Gorge reservoir region.Gowth of the riparian plant Salix variegata Franch. in Three Gorges Reservoir Region responding to simulated floodingThe results showed that during the 32 days flooding period, the number of adventitious roots of belowground-submerged plants was increasing with the duration of flooding, while the wholly submerged plants only had few adventitious roots. The belowground-submerged plants had higher increase in stem length, number of shoots, and newly generated leaves on stem, root biomass and total plant biomass than wholly submerged plants. During the flooding period, the stem length, number of shoots, and newly generated leaves on stem, root biomass and total plant biomass of wholly submerged plants increased, and the number of shed leaves of wholly submerged plants was higher than control and belowground-submerged plants. After 90d inundation, all belowground-submerged and wholly submerged S. variegata is 100 % survived. The results indicate that S. variegata shows high growth adaptability after an inundation of 90 days and is a promising species that can be applied in revegetation of riparian zone in Three Gorge reservoir region.In general, this paper: （1） studied the photosynthesis of several kinds of terraneous plants after different flooding treatments. It was found that the photosynthesis of these species（Salix variegata Franch., Arundinella anomala Steud., Acorus calamus L., Saccharum spontaneum L., Vetiveria zizanioides L., Phragmites communis （L.） Trin. ） was mildly affected by long-term inundation, but the photosynthesis of Ficus tikoua Bur .was obviously affected by long-term inundation. （2） Studied the chlorophyll fluorescence of S. variegata and A. anomala after different flooding treatments. The result showed that the chlorophyll fluorescence of S. variegata was not obviously affected by long-term inundation, but the chlorophyll fluorescence of A. anomala was greatly affected by long-term inundation. （3） Determined the underwater photosynthesis of S. variegata and A. anomala after different flooding treatments. It was found that the underwater photosynthesis （release of oxygen） of S . variegata and A . anomala was significantly higher than two kinds of typical terraneous, and after long-term inundation, S . variegata and A . anomala could maintain photosynthetic capacity. （4） Discussed the growth of S. variegata after different flooding treatments. It was found that plant would take different growth strategy under different inundation condition, plant belowground submerged was mildly affected, the growth indexes of the plant belowground submerged did not significantly decrease compared to the plants controlled. When whole plant was submerged, the growth rate would be slowed down, the shoot biomass and the root biomass would be reduced.