Water Adaptation Mechanism Of Plants In Limestone Mountain To Rainfall Pulses In Northwest Jiangxi Province

The theory of resource pluse is a successful paradigm to study the water adaptation mechanism of plants in arid and semi-arid areas.In the karst area of southern China,the soil moisture fluctuates strongly with frequent soil dry-wet alternation.Plants can not survive in the limestone habitats without a perfect adaptive mechanism for rainfall pulses.In this paper,the dominant species of Phyllostachys glauca,and two auxiliary species Lindera glauca and Camellia oleifera grown in limestone mountain area of northwest Jiangxi Province were selected as experimental objects.The leaf water potential and branch water conductivity were measured.The diurnal and periodical changes of water conductivity of sapwood and soil moisture content in high frequency precipitation period and low frequency precipitation period were analyzed,and the mechanism of water physiological regulation of limestone mountain plants to different rainfall pluses was analyzed.The main results of the study are as follows.（1）The fluctuation range of soil moisture content in limestone habitat is from 32.91±7.61 to±40.68±6.98%during the high frequency period of precipitation.Rainfall of 35.7mm increased soil moisture content by 8%in limestone habitat.In the low frequency period of precipitation,the heavy precipitation events（7.6 mm and 4.1 mm respectively）in the early stage increased the soil moisture content from 16.08±4.33%to 17.62±2.23%.The small precipitation event had no significant effect on soil moisture content,and the soil moisture content decreased to 8.58±2.62,and the soil moisture content decreased by 8%in this period.The soil moisture content in nonlimestone habitat was higher than that in limestone habitat in high-frequency precipitation period and low-frequency precipitation period.In high-frequency precipitation period,the difference of soil moisture content between non-limestone habitat and limestone habitat was 2%or 5%.In the low frequency period of precipitation,the soil moisture content of non-limestone habitat is higher than 20,and that of limestone habitat is lower than 20.Especially when there is a large precipitation of 4.1mm,the soil moisture content of nonlimestone habitat increases by about 16 times,which is more than 2 times of the accumulated amount of soil in limestone habitat.（2）The response of leaf water potential of different plants in limestone mountainous areas to precipitation was rapid,and the leaf water potential increased rapidly and approached to 0Bar in the precipitation high frequency period or precipitation low frequency period.During the continuous pulsating period of rainfall,the water potential of plant leaves was lower than that of-1 Bar.The water potential of leaves of plants showed U-shaped diurnal variation during the pulsating period of precipitation,the water potential of Phyllostachys glauca leaves was the lowest,the water potential of Lindera glauca was the second,and the water potential of Camellia oleifera was the highest.The water potential of Phyllostachys glauca in nonlimestone habitats is slightly higher than that in limestone habitats.Rain in the afternoon will quickly increase the leaf water potential from the lowest value to the early morning leaf water potential value or higher than the early morning leaf water potential value.Therefore,the precipitation will cause the increase of leaf water potential of limestone mountain plants.Among the three kinds of plants,Phyllostachys glauca is the most sensitive,Lindera glauca is the second,Camellia oleifera is the slowest.（3）The hydraulic conductance of plants in limestone mountainous areas is different in different periods,and the response of hydraulic conductance of different plants to precipitation pulsation is also different.The hydraulic conductivities of the three plants in the high frequency period of precipitation were higher than those of the plants in the period of low frequency precipitation,which were as low as 2 times and 10 times higher than those of the plants in the period of low frequency precipitation.During the pulsating interval of high frequency precipitation,the diurnal variation of water conductance of Phyllostachys glauca is U type,while the diurnal variation of water conductance of Phyllostachys glauca is U type in the pulsating interval of precipitation low frequency period.The pulsation interval of Lindera glauca increased first and then decreased,and the highest water conductivity was 8 o’clock in the morning.The diurnal variation of water conductivity of Camellia oleifera during pulsating interval is stable.During the continuous pulsating period of precipitation,the diurnal variation of water conductivity of Lindera glauca and Camellia oleifera varies greatly,while the water conductivity of Phyllostachys glauca first increases with the increase of precipitation,and the specific conductivity of their sapwood is more stable.In the period of afternoon rainfall,the water conductivity and sapwood specific conductivity of Phyllostachys glauca increased as a result of precipitation,but the water conductivity and sapwood specific conductivity of Camellia oleifera were not affected by rainfall.From the point of view of the variation of hydraulic conductance of plants at noon,during the high frequency period of precipitation,precipitation will cause the rapid increase of hydraulic conductivity of Phyllostachys glauca,the reaction of Camellia oleifera is slower than that of Phyllostachys glauca,and the reaction of Lindera glauca is the slowest.In the low frequency period of precipitation,the water conductivity of Lindera glauca and Camellia oleifera decreased gradually,while the specific conductivity of sapwood was stable,and the hydraulic conductivity of Camellia oleifera was higher than that of Lindera glauca.The water conductivity of Phyllostachys glauca and Camellia oleifera was increased by heavy precipitation 7.6mm,and the response of Lindera glauca was slow.The precipitation less than 5mm has no obvious change on the hydraulic conductivity of plants,and the small precipitation of many times will cause the hydraulic conductivity of plants to increase again.（4）The response of Phyllostachys glauca to precipitation in different habitats was the same,that is,the precipitation would increase the water potential and hydraulic conductivity of the leaves of Phyllostachys glauca.However,at the time of precipitation,the hydraulic conductivity of the Phyllostachys glauca in the limestone habitats is higher than that in the nonLimestone Habitats,especially in the pulsation period of the continuous rainfall.The Phyllostachys glauca hydraulic conductivity of the nonlimestone habitats is U-shaped,while the Phyllostachys glauca in the limestone habitat will increase because of the increase of precipitation intensity.In the low frequency period of precipitation,the hydraulic conductivity of the light bamboo in the limestone habitats is constantly fluctuating,while the nonlimestone habitats are more stable.In the period of the afternoon rainfall,the water conductivity of the light bamboo in the nonlimestone habitats is slightly fluctuating,and the variation range of the water conductivity is 0.11±0.09 to 0.22±0.18g·m·MPa^-1·min^-1.After precipitation,the increase of water conductivity is small.However,the water conductivity of Phyllostachys glauca in limestone habitat decreased from 0.86±0.34 g·m·MPa^-1·min^-1 to the lowest 0.11±0.15 g·m·MPa^-1·min^-1 at 14 o’clock,and then increased to 0.72±0.29 g·m·MPa^-1·min^-1 under the influence of precipitation.To sum up,the soil moisture fluctuates strongly in limestone mountain,especially in the low frequency period of precipitation,which makes plants in limestone habitat facing the threat of soil drought.Different plants have different physiological responses to different precipitation pulsation.Physiology of Phyllostachys glauca is more suitable for strong water pulse than other plants.It reduces water potential,water conductivity and specific conductivity of sapwood during interpulse phase.In the pluse phase,the response of leaves water potential is rapid,and Phyllostachys glauca is the most sensitive.Its hydraulic conductivity response is also the fastest,but the response of Lindera glauca is lagged,and the change of Camellia oleifera is not obvious.The mechanism of water physiological adaptation of Phyllostachys glauca in different habitats was different,and the hydraulic conductivity of Phyllostachys glauca in limestone habitats varied greatly,which reflected the physiological plasticity of Phyllostachys glauca which responses to precipitation pulsation.This is the physiological basis of Phyllostachys glauca as the dominant species in limestone mountain.