Effects Of Water Addition On Aboveground And Below-ground Primary Productivity And Species Composition Of Typical Steppe In Inner Mongolia During Freezing-thawing Period

Typical steppe in Inner Mongolia is an important part of Eurasian steppe and the most important ecological barrier in north China.However,in recent decades,due to climate drought,overgrazing and other reasons,the grassland has been seriously degraded.Water is the main limiting factor of productivity of typical steppe in Inner Mongolia.Water during freezing-thawing period is a precious water resource in arid and semi-arid regions,which is beneficial to the plant growth in spring.However,there are few reports on the effects of water change during freezingthawing period on aboveground and belowground primary productivity and species change in Inner Mongolia grassland.In this paper,a degraded field in typical grassland was selected and enclosed in 2019 in Inner Mongolia,three water treatments were designed: 1)natural recovery without water addition（W0）,2)20mm water addition before freezing in autumn（W1）,3)20mm water addition before freezing + 20 mm snow addition before melting in spring（W2）.The effects of water addition during freezing-thawing period on above-and below-ground primary productivity and species composition were analyzed in typical steppe in Inner Mongolia.The main results are as follows:（1）Compared with no water treatment,above-ground biomass was significantly increased by20-40 mm water addition during freezing-thawing period in the second year of the experiment.（2）Compared with no water treatment,the aboveground biomass of shrubs and semi-shrubs increased significantly with water addition during freeze-thaw period.The aboveground biomass and relative abundance of Artemisia frigida,the main species,increased significantly.（3）Compared with no water treatment,the total root length of 0-70 cm soil layer increased significantly after water input before freezing.In the vertical distribution of 0-70 cm soil layer,the total root length,root surface area and total fine root length at 10-30 cm depth were significantly higher in water treatment than those in the control,but there were no significant treatments differences in other soil layers.（4）Compared with no water treatment,the total root length of 0-70 cm soil layer treated with water before freezing increased significantly;In the longitudinal distribution of 0-70 cm soil layer,the total root length and root surface area at the depth of 10-30 cm were significantly higher than those of the control,and there was no significant difference in other soil layers.The increase of water input in the freeze-thaw period mainly increased the coarse root length of 0-10 cm soil layer >2mm diameter and the fine root length of 10-30 cm soil layer <0.5mm.（5）Endogenous root bag method showed: compared with W0,the new roots biomass in 0-70 cm soil layer was significantly increased by adding water in W2 treatment,which was mainly caused by the increasement in 10-50 cm soil layer.The new root biomass was not significantly higher than that of no water treatment in W1 treatment.（6）The endogenous root bag method showed: compared with no water treatment,the total root length increased significantly in 50-70 cm soil layer after water addition during freezingthawing period,but there was no significant difference in other soil layers.,The root length of<1mm fine roots increased significantly in 30-70 cm soil layer after water addition during freezethaw period.In conclusion,20-40 mm water addition during freezing-thawing period significantly increased the total aboveground biomass,aboveground biomass and relative abundance of Artemisia frigida,increased the belowground biomass of 0-50 cm soil layer.increased the subsoil（30-50-70cm）<1mm new fine root length,and increased the soil water content of 50-70 cm layer.