Light-induced Stomatal Dynamics Of Typical Tree Species In Huanglong Mountain Forest Region Under Shading And Drought

Stomata control CO₂ absorption and water loss in photosynthesis and transpiration,which are important regulatory targets to improve carbon assimilation and optimize water use（WUE）.Light and water are the main factors affecting plant succession and water use in the Loess Plateau.It is unclear whether the high water use efficiency in early succession and exotic species is related to their rapid light-induced stomatal dynamics.Therefore,three independent pot experiments were used to study the relationship between light-induced stomatal dynamics and leaf water use efficiency in different succession tree species（Populus davidiana,B.platyphylla and Quercus liaotungensis）,the effects of shading and drought on stomatal dynamics of native species of Betula platyphylla and exotic species of Robinia pseudoacacia,and its relationship with stomatal anatomical characteristics,growth and water use,and the physiological mechanism of stomatal dynamics under progressive drought.The main results are as follows:（1）Among three different succession tree species,the early succession species P.davidiana and B.platyphylla had higher photosynthetic capacity and leaf intrinsic water use efficiency,and were faster during stomatal opening than the late succession species Q.liaotungensis,suggesting higher photosynthetic capacity and WUE in early succession species may be related with their rapid stomal opening.The time constant during stomatal opening in P.davidiana and B.platyphylla was shorter than in Q.liaotungensis,but time constant during stomatal closing in P.davidiana and B.platyphylla was longer than Q. liaotungensis,suggesting the early succession species P.davidiana and B.platyphylla were faster during stomatal opening,Q.liaotungensis was faster during stomatal closing.The time constant ratio of stomatal closing and opening in P.davidiana and B.platyphylla is close to 1,showing a symmetrical response,while the ratio in Q.liaotungensis is far less than 1,showing an obvious asymmetric response.Among three species,Q.liaotungensis had the largest stomatal density,smallest stomata size and biggest stomatal index, indicating the stomatal anatomy is hard to explain the slow stomatal opening in Q. liaotungensis.P.davidiana and B.platyphylla had higher photosynthetic rate,maximum carboxylation velocity and maximum electron transport rate and WUE,possibly be related to its rapid stomatal opening.（2）Shading and drought significantly affect the stomatal dynamic parameters,these stomatal dynamics parameters affected the whole plant growth of B.platyphylla and R.pseudoacacia seedlings to a certain extent,but they had no significant correlation with water use efficiency.Shading significantly prolonged the lag time and response time of B.platyphylla during stomatal opening,significantly shortened the lag time of R. pseudoacacia during stomatal closing,and significantly reduced the response speed and amplitude of the two tree species during both stomatal opening and closing.Drought significantly slowed down the response speed during stomatal closing in two tree species,and response amplitude of B.platyphylla during stomatal opening was significantly reduced.The effect of shading on stomatal dynamics parameters was greater than that of drought in two species.The stomatal density and index of the two tree species decreased significantly under shading,while the stomatal size（stomatal length,width and area）did not change significantly.Drought had no significant effect on the stomatal anatomical traits of B.platyphylla,while led to a significant increase in the stomatal density of R. pseudoacacia.The response speed of B.platyphylla during stomatal closing was significantly positively correlated with stomatal density and stomatal index,and there was no significant correlation between all stomatal dynamic parameters and stomatal anatomical characteristics of R.pseudoacacia.For B.platyphylla seedlings,only response speed during stomatal closing was positively correlated with whole-plant biomass and water use,whereas for R.pseudoacacia,both response speed and amplitude during stomatal opening and closing were positively related with whole-plant biomass and water use.（3）The progressive drought had different effects on stomatal dynamic in the two species,the effects were closely related with stomatal antomy,leaf water potential and leaf abscisic acid content（ABA）.In the process of progressive drought,mild drought had little effect on stomatal dynamic parameters of the two tree species.Under severe and extreme drought,the response amplitude of B.platyphylla during stomatal opening and closing was significantly reduced,and its response time was shortened during stomatal closing;but the stomatal response speed and amplitude of R.pseudoacacia during stomatal opening and closing were significantly reduced.With the decrease of soil moisture,the stomatal density and index of the two tree species showed a trend of increasing first and then decreasing. Under extreme drought,the stomatal length,width and area of B.platyphylla were significantly higher than those of the control,while the stomatal width and area of R. pseudoacacia were significantly lower than those of the control.The response speed of B.platyphylla during stomatal closing was significantly positively correlated with stomatal density and stomatal index,and the lag time of R.pseudoacacia during stomatal closing was significantly positively correlated with stomatal width and stomatal area.The response time and amplitude during stomatal opening in B.platyphylla are mainly regulated by leaf water potential,and its response time and amplitude during stomatal closing are simultaneously regulated by ABA and leaf water potential;the response speed during stomatal opening and amplitude during stomatal closing in R.pseudoacacia are mainly affected by leaf water potential,while its speed during stomatal closing and amplitude during stomatal opening were affected by both ABA content and leaf water potential.