Formation Mechanism Of Condensation Water And Its Ecological Effects Of Halostachys Caspica Community In Different Salinity Habitats

As one of the main water sources to maintain the food chain in arid area, condensation water has significance in conducting research on water balance in arid areas, and which play very important role in desert vegetation has been a focus problem to conduct research. This study take drought desert band in Ebinur Lake area as study area, and the salinity habitats as mainline, select Halostachys caspica community in mild, moderate and severe salinization soil, respectively (following abbreviation mild salt community, moderate salt community and severe salt community), conducting the field investigation, condensation water observation, plant physiological observation, and controlled test (salt stress and drought stress) and isotope experiment from August to October in2013. According to spatial and temporal heterogeneity characteristics of condensation water (soil condensation water and plant condensation water), analyze the environmental factors affecting the formation of condensation water, and carry out research on formation mechanism of condensation water in arid desert areas; Use isotopic techniques to analyze the source of plant to use condensation water and its percentage, study on migration paths of the condensation water in the plants, and explore the mechanism of plant uptake and utilization of condensation water. In addition, through the controlled experiment, further discuss the effect of condensation water on soil properties and plant physiology under different degree of salt stress and drought stress. This study aims to reveal formation mechanism of condensation water in arid areas and its ecological effect in Halostachys caspica communits in different salinity habitats, and provide scientific basis for guidance of vegetation restoration and condensation water resources utilization in arid area.The main results are as follows:Firstly, formation mechanism of condensation water of Halostachys caspica community in different salinity habitats.(1) Soil condensation water formation often occurs in the night, and the average duration time of soil condensation water are15.71h/d and18.50h/d in August and October, respectively. With increasing soil depth, times of soil condensation water start to form and the largest value appearance were delayed. Condensation water could supplement the evaporation of water consumption and other water sources in moderate salt community, while there are complementary difference in soil condensation water to supplement evaporation and others water source between soil under the crown and bare land, indicating that distance from water source and vegeration coverage has a certain impact on formation of soil condensatation water. Soil condensation water at4cm soil layer mainly comes from soil water below the4cm soil layer, and only a small portion comes from atmospheric water, as well as the source subject of soil condensation water underground section is soil pore water within0-20cm soil layers. The contribution of soil condensatation water at0-2cm,2-4cm and4-6cm soil layers to0-6cm soil condensation water reduced with vertical variation of soil profile in those three communities.(2) On the whole, formation of condensation water of Halostachys caspica canopy almost occur in the night in mild, moderate and severe salt community, with an average duration time is12h/d, maximum value of condensation water amount occurred around sunset, sunrise and early in the morning. Halostachys caspica canopy condensation water could complement evaporation consumption in moderate salt community in August, white Halostachys caspica must access to other water sources to meet their own growth in mild and severe salt community, except for condensation water. In October, canopy condensation water in those three communities all could complement evaporation consumption, and also supply plants to grow.(3) There are certain differences for correlation degree between environmental factors and soil condensation water under canopy and in bare land among communities in different salinity habitats. In General, there is very significant negative correlation between soil condensation water and solar radiation (PAR)(P<0.01), while shows very significant positive correlation with air relative humidity (P＜0.01). Impact of environmental factors on soil condensation water in October is higher than in August. Canopy condensation water and PAR is a significant negative correlation (P<0.05) in August, while shows very significant negative correlation (P<0.01) in October, while, canopy condensation water and environmental factors are not significant correlation (P>0.05) in other communities.Sencondly, estimation of condensation water ammount, and its contribution to growth of Halostachys caspica, and its migration path in plant bpdy.(1) Plant condensation water amount is greater than soil condensation water amount in three communities in different months, the amount are1.0412-3.1816mm/d and0.0137-0.0356mm/d, respectively; With the degree of salinity increase, condensation water amount increase, namely, severe, moderate and mild salt community are2.5426,1.4143,1.2702mm/d (in August) and3.2057,1.1020,1.0715mm/d (in October), respectively.(2) Scale-like leaves can absorb condensation water, the order of contribution of condensation water to plant growth in different salinity habitats are:salinity severe salinity>mild salinity>moderate salinity, the average contribution rate are11.13%,7.10%and3.79%, respectively.(3) Migration path of water movement in three community are two main ways:1) rainwater and condensation water recharge through soil to complement for groundwater, some groundwater complement for river water, partly return to atmosphere by soil evaporation and plant transpiration;2) rainwater and condensation water directly complement for the river, plant roots absorb river water, groundwater and soil water to grow. In mild salt communities, water movement path in plants: shallow rootâ†'stemâ†'branchesâ†'leaves; and shallow rootâ†'deep root exist water circuit; In moderate communities, stems as the bifurcation point, path of a part of water vapor is that:stemâ†'branchesâ†'leaves, another part:stemâ†'shallow rootâ†'deep root; In severe communities, water vapor path:deep rootâ†'shallow rootâ†'stemâ†'branchingâ†'leaves, and finally return to the atmosphere, while there exist water circuit from stem to shallow root.Thirdly, ecological effects of condensation water on Halostachys caspica and soil in natural condition.(1) In August, communities in different salinity habitats, there are different impacts of presence and absence condensation water on the Halostachys caspica leaf water potential; In October, condensation water during the night can increase plant leaf water potential in those three communities, while without condensation water would reduce the leaf water potential, and there are greatst influence of presence and no condensation water on leaves water potential. In mild, moderate and severe salt communities, leaf water absorption amount per unit area under no condensation water treatment is higher than presence condensation water trement, but the difference is not significant.(2) Condensation water can increase net photosynthetic rate (Pn) of Halostachys caspica leaf; No condensation water can increase plant water use efficiency (WUE) in daytime. In August, there are no significant difference for the minimum initial fluorescent (Fo), maximum fluorescent (Fm), and original light conversion efficiency in PS II reaction center (Fv/Fm), minimum fluorescent in light (Fo’), maximum fluorescent in light(Fm’), and steady-state fluorescent (Fs) between presence amd no condensation water treatment, and no condensation water could significantly reduce its maximum antenna efficiency (Fv’/Fm’), PhiPSâ…¡and electronic passed efficiency (ETR); In moderate salt community, there is no significant difference in Fo’and Fs between presence and no condensation water, no condensatation water could significantly reduce its Fo, Fm, Fv/Fm, Fm’. Fv’/Fm’, PhiPS â…¡ and ETR; In severe salt communities, there is no significant difference in Fo, Fm, Fv/Fm and Fo’between presence and no condensation water, while no condensatation water could significantly reduce its Fv’/Fm’, PhiPS â…¡ and ETR; In October, except no condensation water could significantly reduce Fo value in moderate salt community, three communities there are no significance diffenence for fluorescence parameter values between presence and no condensation water. Overall, effects of presence and no condensation water on fluorescence parameter of Halostachys caspica are greatest in moderate salt community.(3) Along with the salinity degree increases, soil respiration rate increase under the canopy in Halostachys caspica community, and the same to the order of condensation water amount among three communities, as follows:severe salt communities> moderate salt community>mild salt community.Fanally, ecological effects of condensation water on Halostachys caspica and soil under the salt stress and drought stree.(1) Under different degree of salt stress, supplement of condensation water can increase soil moisture, but reduce soil salinity and pH values; With the extension of processing time, condensation water can increase chlorophyll content of Halostachys caspica, while no condensataion water will reduce its content; under short-term salt stress, water condensation can significantly affect Pn, stomatal conductance (Gs), intercellular CO2concentration (Ci) and transpiration rate (Tr), while along with the extension of the processing time, Pn, Gs and Tr significantly reduced.(2) Halostachys caspica could tolerate mild and moderate salt stress, but condensation water amount increase could reduce the biological tolerance; In severe salt stress, condensation water amount increase will raise its salt tolerance and resistance. Short-term salt stress and condensation water treatment allow Fm have no significant changes, while long-term treatment reduce the Fm. Short-term salt stress and condensation water treatment could increase PS â…¡ activity, improving the original conversion efficiency of light energy, while long-term salt stress and condensation water could reduce its activity, and stress is not reversible. Overall, with the extension of processing time, no condensation water treament under mild salt stress, salt stress in small amounts of condensatation water treament in moderate salt stress and large amounts of condensation water treament in severe salt stress could better increase fluorescence parameter in light adaptation. With the stress extension, photosynthetic capacity (Fq’/Fm’) and heat dissipation capacity of the leaves (NPQ) could reduce.(3) In the different degree of drought stress, condensation water amount and duration could significantly affect soil moisture; Stress in the early, condensarion water can reduce soil salinity, different amounts of condensation water have significant different influence on soil salinity under long-term stress treatment; Stress in the early, a small amount of condensation water can lower the soil pH, and the reducing effect of large amount of condensation water is better under long-term stress treatment; Stress in the early, there are no significant differences in leaf chlorophyll content among different treatment, there are difference for influence of condensation water on chlorophyll content with different degree of drought stress under the long-term stress. Overall, stress in the early, condensation water can significantly increase Pn, while when the time and concentration of stress beyond the tolerance range of the plant, condensation water may inhibit their growth. Low concentation drought stress stimulate the Gs to increase, but high concentration of stress decrease the Gs, and condensation water could accelerate this process.In mild drought stress, a small amount of condensation water could increase Tr, while it could inhibits Tr in moderate and severe drought stress. Under the dual control of drought stress and condensation water, Tr may be affected by other factors. Stress in the early, WUE of Halostachys caspica increase, but it reduce under the long-term stress.(4)There is no obvious change of Fm in short-term drought stress, showed that Halostachys caspica can withstand mild, moderate and severe drought stress, while large amount of condensation water would increase drought tolerance and resistance, and improve Fm and PS II activity in leaves; However, under the long term treatment, Fo, Fm, PS II activity, photosynthetic capacity, as well as the NPQ reduced, but supplement of large condensation water amount would ease NPQ reduction degree.