Difference Of Water Use And Its Relationship With Nutrient In Pinus Yunnanensis Community In Karst Mountainous Area Of Eastern Yunnan

In order to research the differences of Water use resource and Water use efficiency（WUE）of pants and the relationship of nutrients in different communities of Pinus yunnanensis,the purpose of research is to explore the reasonable interspecific Configuration of plants,and to provide a scientific basis for the improvement and restoration of the fragile karst ecosystem.The researchers selected 3 Coniferous plant communities of Pinus yunnanensis,and 2 broad-leaved plant community of original forest and bush to investigate in the karst basin of eastern Yunnan--Natural secondary forest of Pinus yunnanensis,mixture plantation of Pinus yunnanensis,the artificial pure forest of Pinus yunnanensis,the original forest of Castanopsis orthacantha and bush of Myrsine africanna.Then the samples for dominant plant species in each community type were collected to study the different characteristics of water use and their responses to the changes of SOC,TN,TP,TK and etc.The main conclusions of this study are as follows:（1）For different plants communities,the water use sources of different plants communities were different,and the water competition in dry season was higher than that in rainy season as a whole.The plant stem’s ofδ¹⁸O value is mainly distributed between-13.09%and-2.58%.In terms of water use sources,the competition of water use of five plant communities decreased with the increase of forest age and restoration years.Because of the different community structure,the water use of each plant in the community is quite different.Among them,the water competition of Pinus yunnanensis artificial pure forest is the most intense in dry season.The water utilization ratio of Pinus yunnanensis in two different forest ages was almost similar,and the difference was no more than 2%.In the dry season,plants absorb more water from the lower layer,and use more karst water and 40～60cm deep soil water,which can reach more than 50%;With the increase of precipitation,the absorption of water by plants shifted to the upper layer in rainy season,and the absorption of precipitation,10-20cm shallow soil water and surface water increased.The contribution rate of the three water sources to the plants of Castanopsis orthacantha is 68%,and the contribution rate to the plants in the natural mixed forest of Pinus yunnanensis is more than50%.Due to the influence of surface lakes and rivers,the proportion of absorbing and utilizing water resources of Pinus yunnanensis mixture plantation,Pinus yunnanensis artificial pure gorest and bush of Myrsine africanna is more than 70%.Underground karst water can provide stable water source for plants in dry and rainy seasons.（2）WUE of plants in dry season was higher than that in rainy season,and that of Castanopsis fissa native forest was higher than that of other four plant communities.The range of WUE in March,May and August was respectively 63.69～66.87μmol·mol^-1,63.25～66.47μmol·mol^-1 and63.43～66.64μmol·mol^-1.With the increase of precipitation in the rainy season,the WUE in May and August is slightly lower than that in March in the dry season.The forest ages of the primary forest of Castanopsis variabilis,three Pinus yunnanensis and bush of Myrsine africanna were 100years,15-50 years and 10 years respectively.WUE decreased gradually with the decrease of plant community age.The WUE of Myrsine africanna bushes in karst area is relatively low due to its short recovery period.The variation range of Myrsine africanna bushes is the smallest in dry and rainy seasons,and the fluctuation is less than 0.2μmol·mol^-1.The WUE of interspecific combinations in different Pinus yunnanensis forests decreased with the increase of forest age in dry season.The WUE of Pinus yunnanensis natural mixed forest was the lowest,and its range was64.32～65.02μmol·mol^-1;The WUE about mixture plantation of Pinus yunnanensis was always high,with the range of 65.29～65.59μmol·mol^-1.Compared with the former two,WUE of Pinus yunnanensis’s artificial pure forest changed slightly with seasons,and it was 65.74μmol·mol^-1 in dry season and 63.78mol·mol^-1 in rainy season.The mixture plantation of Pinus yunnanensis is a better forest type for recovery.（3）All the five plant communities showed a lack of N content,and the nutrient content of the three Pinus yunnanensis communities was lower than that of the other two sample plots.Among the three plant communities of Pinus yunnanensis,TN and TP in natural mixture forest and pure plantation of Pinus yunnanensis were relatively deficient.TK content in the pure plantation of Pinus yunnanensis was the lowest,while SOC content was the highest.However,the contents of TN and TP in the mixture plantation of Pinus yunnanensis were relatively high,and the contents of SOC and TK in several vegetation types were also in the middle level.It can be seen that the mixed plantation of Pinus yunnanensis is better for improving the nutrient content.In the two broad-leaved plant communities,the content of SOC in Castanopsis orthacantha native forest was lower,the content of TP in the bush of Myrsine africanna was lower,and the other nutrient contents were higher than those in the Pinus yunnanensis community.（4）The correlation analysis between WUE of plant and nutrient indexes of leaf and soil showed some differences.Among all the nutrient indexes in leaves,only SOC had a significant correlation with WUE,while the correlation between other nutrient indexes and WUE was not obvious,so leaf SOC had a great influence on WUE.The contents of SOC,TN,TP,AN,AP and AK were positively correlated with WUE.In 0-20cm soil layer,the correlation between WUE and TN,TP,AP,AK was significant（P<0.05）;The correlation between WUE and SOC,TN,TP,AK in 20～60cm soil layer was significant（P<0.05）.In conclusion,increasing the contents of TN,TP and AK in the soil can improve the WUE of plants to a certain extent.Artificial mixture plantation of Pinus yunnanensis not only changed reasonably in the water use resources with the season,but also the water use efficiency and nutrient status were higher than the other five communities,which belongs to a better recovery in Pinus yunnanensis communities.Therefore,the Aritificial misture plantation of Pinus yunnanensis can be a better cultivation mode in Pinus yunnanensis community.Beside that,it is necessary to add N to each plant community.