Effects Of Simulated Karst Fissure Habitat On Growth,Physiology And Non-Structural Carbohydrates Of Phoebe Zhennan Seedlings

Karst is widely distributed in China,the ecosystem is fragile,vegetation degradation is serious,rocky desertification is prominent.How to effectively carry out vegetation restoration has become one of the hot spots in karst ecological research.Influenced by its geological background and water chemical dissolution,a large number of karst fissures are formed on the surface of karst,which is considered as an important reason for water shortage in karst areas.Under the global climate change,the rainfall in karst areas in southwest China is decreasing,which will aggravate the drought in karst areas.Recent studies have shown that plants may be able to make full use of water in karst fissures to adapt to karst drought.It is also possible to adjust the spatial distribution and functional traits of underground roots,plant photosynthesis and non-structural carbohydrates to adapt to the karst fissure water shortage habitat.At the same time,the field investigation found that the rare and unique tree species Phoebe zhennan well in karst areas,with the characteristics of taking root and breaking rock.Therefore,in this study,P.zhennan seedlings were used as experimental materials to set up karst fissure habitats with different soil amounts and fissure sizes(pure soil without fissure S group,soil-filled fissure SF group:SF_Smalland SF_Big,soil-filled fissure F group:F_Smalland F_Big)and different precipitation treatments(normal precipitation W_100%,drought W_30%)to explore whether plants can utilize karst fissure water（that is,whether karst fissure has habitat function）.Whether we can adapt to karst fissure habitat by changing biomass accumulation and allocation,adjusting root spatial distribution,regulating photosynthetic physiology and non-structural carbohydrate.The main results are as follows:（1）The biomass and root spatial distribution of P.zhennan seedlings were affected by different karst fissure.Under the control and drought conditions,the total biomass of P.zhennan seedlings was inhibited in the group without soil filling fissure,but not in the group with soil filling fissure.Under dry water,the distribution of root length,root surface area and root volume of fissure layer increased with or without fissure group.In different karst fissure habitats,large karst fissure promoted the increase of root biomass,root length,root surface area and root volume,but each habitat group chose different root spatial distribution strategies to increase the spatial distribution of root in the fissure layer or soil layer.In SF habitat,the root biomass of fissure layer was mainly increased under sufficient water condition,while that of soil layer was mainly increased under water deficiency condition.In the habitats of group F,the response of roots in the fissured layer was more sensitive under water deficit condition.Therefore,only the root length,root surface area and root volume of coarse roots in the soil layer increased under sufficient water.However,water deficit not only increased the root length,root surface area and root volume of fine roots in fissured layer,but also increased the biomass of coarse roots and fine roots in the fissured layer.（2）Different karst fissures affected photosynthesis and leaf functional traits of P.zhennan seedlings.Different from the change of biomass,the net photosynthetic rate,stomatal conductance and transpiration rate of P.zhennan seedlings were promoted in the group with soil filling fissure under control water,and the net photosynthetic rate,stomatal conductance and transpiration rate of P.zhennan seedlings were the highest in the group without soil filling fissure under drought water.In the habitats with different karst fissure sizes,P.zhennan seedlings would choose to close stomata or improve water use efficiency to regulate photosynthesis.Leaf water content,leaf dry matter content,specific leaf area and leaf area ratio remained stable all the time,but had smaller specific leaf area and larger leaf dry matter content.（3）Different karst fissures could affect the content of non-structural carbohydrates in P.zhennan seedlings.Under the control and drought conditions,the soluble sugar content of each component was inhibited by the existence of karst fissure,but the soluble sugar content of fine roots and leaves was not inhibited by the soil fissure group.The existence of karst fissure can increase the average starch content and NSC content of the whole plant,but too large karst fissure can inhibit the average starch content and NSC content of the whole plant.The starch content of each component was inhibited in both control and drought conditions in the habitat with or without karst fissure,but increased in the habitat with soil filling（especially in the fine roots with fissure layer）.Different karst fissure size habitats,soil fill a fissure in the group,big in karst fissure of frame nan seedling root showed inhibitory effect on the soluble sugar content and starch content,without soil filling fissure in the group,only a leaf in the control of karst fissure water starch content was suppressed,mainly inhibit the stem under drought,water starch content.In a word,the soil existing in karst fissure is no longer just a channel for water loss,but also a"container"for plant root growth,alleviating the negative effect of surface drought and water shortage in karst areas.At the same time,P.zhennan adapted to karst habitat by regulating growth,photosynthetic physiology and non-structural carbohydrates,but compared with other organs of P.zhennan,roots were the most sensitive to karst fissure habitat.The results can provide a theoretical basis for predicting the future dynamic change of forest ecosystem and vegetation restoration in karst region under climate change.