Water Response Strategies Of Several Quercus Species In Warm-Temperate Zone

Under the background of climate change,the global precipitation pattern has changed.Frequent extreme climate and uneven precipitation lead to seasonal drought and local heavy precipitation.So forests are facing more complex moisture conditions.Soil moisture condition plays a key role in forest vegetation change and stand regeneration.The change of precipitation pattern will lead to the change of forest soil moisture availability,affect the physiological characteristics and growth status of plants,and then drive the dynamic change of forest plant species composition,affect the biodiversity and stability of forest ecosystem.Quercus species is one of the most widely distributed forest plants in the world.It plays an important role in forest community function maintenance and vegetation restoration,and has high ecological and application value.Among them,deciduous Quercus species is the main component of global warm-temperate zone forest.It often appears as the dominant species and constructive species in the forest,and has a high dominant position in the warm temperate forest.In China,many native Quercus species with good ecological characteristics are often used in forest vegetation restoration,while some exotic Quercus plants also have strong tolerance and adaptability.Although they are introduced and planted in many places,they are rarely used in vegetation restoration and afforestation.So it is urgent to strengthen the research on tolerance difference of environmental factors between native and exotic Quercus species.In this study,some common Quercus species in warm temperate-zone were selected as the research objects.Through the combination of greenhouse control experiment and field experiment,the water response strategies of exotic and local common Quercus species were explored.This study provides a theoretical basis for predicting the dynamic changes of Quercus species in warm temperate-zone forests and species selection in forest vegetation restoration,and provides scientific guidance for stand management and tending of warm temperate Quercus forests.In the greenhouse control experiment,the soil moisture conditions(95%,75%,55%,35%and 15%soil field capacity)that may be produced by different precipitation patterns were simulated.The growth indexes,such as plant height,basal diameter,biomass and distribution,and physiological indexes,such as gas exchange parameters,chlorophyll fluorescence parameters,leaf photosynthetic pigment content,hydraulic traits,leaf chemometric characteristics,were measured.The difference of response mode of Q.rubra,Q.robur,Q.acutissima and Q.serrata var.brevipetiolata seedlings to different soil moisture conditions in growth and physiology was studied.The results showed that:(1)When the soil moisture content decreased,the Quercus seedlings showed a similar change trend,that is,they had the best physiological and growth conditions at the highest 95%soil moisture content.With the decrease of soil moisture content,the growth and physiology of seedlings were adversely affected.When the soil moisture content was 35%and 15%,the growth and physiology of seedlings were severely restricted,and even many deaths occurred;(2)Compared with the other two Quercus species,the exotic species Q.robur and Q.acutisima seedlings have better physiological and growth conditions when the soil moisture is sufficient,and they are suitable for vegetation restoration in warm-temperate zone forests as the preferred species.However,they have poor drought tolerance and poor survival rate and growth condition in drought,while the native species of Q.serrata var.brevipetiolata seedlings can maintain a higher survival rate in drought,which is suitable for vegetation restoration in poor moisture condition.The field experiments were conducted on the perennial seedlings of Q.rubra,Q.robur,Q.palustris and Q.dentata.The gas exchange parameters,such as transpiration rate,net photosynthetic rate,stomatal conductance and water use efficiency,and the related parameters of pressure volume(P-V)curve and other hydraulic characteristics such as plant water potential were compared to reveal the differences of photosynthetic capacity and hydraulic characteristics among those species.The results showed that in the field environment with abundant resources,the alien species of Q.palustris and Q.robur had stronger photosynthesis and growth ability,while the alien species of Q.rubra and native species of Q.dentata had relatively weaker growth ability.However,the water use efficiency and drought tolerance of Q.palustris are relatively poor,so it is necessary to ensure that the growth environment of has sufficient water.The growth ability of Q.robur is similar to that of Q.palustris,but it has stronger drought tolerance than Q.palustris,and it is more likely to be dominant in the field environment when moisture is insufficient.In general,there are differences in growth ability and drought tolerance among Quercus species.The seedlings and perennial seedlings of Q.robur have strong growth ability and excellent ecological characteristics under the condition of sufficient water.It is a potential species for vegetation restoration in warm-temperate zone of China.The soil moisture condition is closely related to the growth of seedlings of four Quercus species.The decrease of soil moisture contents limits the growth and normal physiological activities of seedlings.Therefore,it is very important to maintain good soil moisture conditions for the realization of vegetation restoration effect of oak forest.