A simulation study on CO_2 assimilation and crop growth in agroforest ecosystems in the East China Plain

ＡｓｉｍｕｌａｔｉｏｎｓｔｕｄｙｏｎＣＯ２ａｓｉｍｉｌａｔｉｏｎａｎｄｃｒｏｐｇｒｏｗｔｈｉｎａｇｒｏｆｏｒｅｓｔｅｃｏｓｙｓｔｅｍｓｉｎｔｈｅＥａｓｔＣｈｉｎａＰｌａｉｎＺｈｏｕＬｉｎ，ＷａｎｇＨａｎｊｉｅＥｃｏＥｎｖｉｒｏｎｍｅｎｔａｌＲｅｓｅ...

Short-term responses to salinity of seabuckthorn (Hippophae rhamnoides L.) seedlings in the extremely cold and saline Qinghai region of China

The investigation of the mechanisms of plant adaptation to stressor action is one of the leading directions of current biological studies. To understand the mechanism of salt tolerance of seabuckthom （Hippophae rhamnoides L.） and identify its ability to cope with the salinity effect in the saline and extremely cold region of Qinghai, China, a test was conducted with two-year-old seedlings subjected to 0, 200, 400 and 600 mmol·L^-1 NaClsolutions for 30 d. The results show that with an increase in salinity, the biomass of H. rhamnoides seedlings clearly decreased. Leaf water potential （ψw） and relative water content （RWC） were significantly reduced under salinity, with severe water shortages appearing in leaves. At the same time, the total chlorophyll content declined markedly. When salinity increased and stress time prolonged, the net CO2 assimilation rate （A） significantly declined. Intercellular CO2 concentration （Ci） declined at first and was then followed by an increase over the stress time. We conclude that H. rhamnoides grown in the extremely cold and saline region of Qinghai has a certain resistance to salt, which can be planted at appropriate salinity levels.

Ecophysiological responses and carbon distribution of Pinus koraiensis seedlings to elevated carbon dioxide

The net CO2 assimilation rate, stomatal conductance, RuBPcase (ribulose 1,5-biphosphate carboxylose) activity, dry weight of aboveground and belowgroud part, plant height, the length and diameter of taproot ofPinus koraiensis seedlings were measured and analyzed after six-week exposure to elevated CO2 in an open-top chamber in Changbai Mountain of China from May to Oct. 1999. Seedlings were planted in four different conditions: on an open site, control chamber, 500 μL·L?1 and 700 μL·L?1 CO2 chambers. The results showed that the total biomass of the seedlings increased whereas stomatal conductance decreased. The physiological responses and growth to 500 μL·L?1 and 700 μL·L?1 CO2 varied greatly. The acclimation of photosynthesis was downward to 700 μL·L?1 CO2 but upward to 500 μL·L?1 CO2. The RuBPcase activity, chlorophyll and soluble sugar contents of the seedlings grown at 500 μL·L?1 CO2 were higher than that at 700 μL·L?1 CO2. The concentration 500 μL·L?1 CO2 enhanced the growth of aboveground part whereas 700 μL·L?1 CO2 allocated more carbon to belowground part. Elevated CO2 changed the carbon distribution pattern. The ecophysiological responses were significantly different between plants grown under 500 μL·L?1 CO2 and 700 μL·L?1 CO2.

Mitochondrial GPX1 silencing triggers differential photosynthesis impairment in response to salinity in rice plants

The physiological role of plant mitochondrial glutathione peroxidases is scarcely known. This study attempted to elucidate the role of a rice mitochondrial isoform（GPX1） in photosynthesis under normal growth and salinity conditions. GPX1 knockdown rice lines（GPX1s） were tested in absence and presence of 100 mM NaCl for 6 d.Growth reduction of GPX1 s line under non-stressful conditions, compared with non-transformed（NT） plants occurred in parallel to increased H_2O_2 and decreased GSH contents. These changes occurred concurrently with photosynthesis impairment, particularly in Calvin cycle＇s reactions, since photochemical efficiency did not change.Thus, GPX1 silencing and downstream molecular/metabolic changes modulated photosynthesis differentially. In contrast, salinity induced reduction in both phases of photosynthesis, which were more impaired in silenced plants.These changes were associated with root morphology alterations but not shoot growth. Both studied lines displayed increased GPX activity but H_2O_2 content did not change in response to salinity. Transformed plants exhibited lower photorespiration, water use efficiency and root growth, indicating that GPX1 could be important to salt tolerance. Growth reduction of GPX1 s line might be related to photosynthesis impairment, which in turn could have involved a cross talk mechanism between mitochondria and chloroplast originated from redox changes due to GPX1 deficiency.