Decomposition Characteristics Of Mixed Leaf Litter Of Acacia Melanoxylon And Acacia Cincinnata

Acacia cincinnata and melanoxylon are two kinds of introduced tree species with many excellent qualities.Their potential value（economic value and ecological value）needs to be developed urgently.Poor barren tolerance,nitrogen fixation and other excellent qualities have become the basis for the vigorous development and promotion of these two kinds of acacia Planting.At Present,most Acacia plantations are mainly pure forests,with a relatively single forest land structure and a single forest land landscape.This has been unable to meet the forest land construction needs of forest land ecological diversity and landscape diversity.So it is an urgent problem to select suitable tree species and mix proportion to create mixed forest in the process of plantation construction.The decomposition of litters is an important process of nutrient cycling in plantation,and the surface litters in mixed forest mainly exist in the form of mixed litters,which is bound to affect the decomposition rate and nutrient cycling rate of litters Therefore,in this study,the litter net bag decomposition method was adopted,with A.cincinnata litter leaf and A.melanoxylon litter leaf as the research objects,and seven mixed litter mixed decomposition tests were set under the A.cincinnata forest:Pure A.cincinnata litter（J-J）,pure A.melanoxylon litter（J-H）,A.cincinnata:A.melanoxylon=3:1（J-K1）,A.cincinnata:A.melanoxylon=2:1（J-K2）,A.cincinnata:A.melanoxylon=1:1（J-K3）,A.cincinnata:A.melanoxylon=1:2（J-K4）,A.cincinnata:A.melanoxylon=1:3（J-K5）;Under the A.melanoxylon forest,the same set of seven mixed litter decomposition tests:Pure A.cincinnata litter（H-J）,Pure A.melanoxylon litter（H-H）,A.cincinnata:A.melanoxylon=3:1（H-K1）,A.cincinnata:A.melanoxylon=2:1（H-K2）,A.cincinnata:A.melanoxylon=1:1（H-K3）,A.cincinnata:A.melanoxylon=1:2（H-K4）,A.cincinnata:A.melanoxylon=1:3（H-K5）.Through different treatments of the two forests,the litter dry weight residual rate,nutrient（C,N,P,K,Ca,Mg,Mn,Na,Fe）element release rule and cellulase enzyme activity,Polyphenol oxidase enzyme Monitor and analyze the dynamic changes of activity and acid phosphatase activity,and draw the following conclusions:（1）The annual litter amount of A.cincinnata is 12.25 t·hm^-2,and the annual litter amount of Acacia melanoxylon is 10.32 t·hm^-2.Both types of forest stands have double peaks,and the amount of litter in summer is significantly higher than that in winter.（2）The dry weight residual rate of litter with different proportions under the two forests decreased sharply within 0-90d during decomposition,and the dry weight residual rate of litter decreased gently within 90-270d,and the dry weight residual rate after decomposition after 270d was 25.10%-33.97%,the dry weight residual rate of litter of each ratio in the Olson index model is between 2.01-2.53 a^-1,the time required for T₅₀ is 0.25 a-0.32 a,and the time required for T₉₅ is 1.16 a-1.46 a.（3）In the home and away field experiment,the decomposition of pure A.cincinnata litter under the A.melanoxylon forest was 0.2928 a,and the decomposition T₉₅ was 1.3173 a;the decomposition of pure A.melanoxylon litter T₅₀ was 0.3088 a,and the decomposition T₉₅ was 1.3893a.The decomposition of pure A.cincinnata litter under the A.melanoxylon forest has a decomposition T₅₀ of 0.3214 a and a decomposition T₉₅ of1.4636 a;the decomposition of pure A.melanoxylon litter has a T₅₀ of0.3185 a and a decomposition T₉₅ of 1.4384 a.It can be seen that both types of acacia decompose T₅₀ and T₉₅under their own forest in the displacement experiment.（4）The proportion of litter under A.cincinnata has a very significant effect on the dry weight residual rate（P<0.01）,while the proportion of A.melanoxylon forest has no significant effect on the dry weight residual rate.A.cincinnata:A.melanoxylon=3:1 has the fastest rate of litter decomposition under two forest stands.（5）The difference in the release rule of the underground nutrient elements of the two forests coexisted with the same sex.Due to the forest land conditions and leaf physical and chemical properties of the two forest lands,the release rules of the elements are similar.The C element under the two forests showed a regular release pattern.The overall release rule of N element is release.The release rule of P element in the litter of different proportions under the two forests is release-enrichment.The release rule of K element is release-enrichment.Ca element is released first and then enriched.In the two forests,the Mg element of pure A.cincinnata litter was always higher than the Mg element content of other litter in 270 days of decomposition,while the Mg content of pure A.melanoxylon litter was significantly lower than the Mg content of other litter,Within 270 days of decomposition,the Mg element as a whole was released all the time.The change rule of Mn is similar to that of Mg,both of which are released first and then enriched.The overall release rule of Na element is release-enrichment-release.There was no obvious difference in nutrient release between mixed litters and single litters in each treatment.（6）In this study,the overall changes of the enzyme activities of different ratios in the two underground forests were similar,in which the cellulase enzyme activity increased first and then decreased within 0-270days of decomposition;the polyphenol oxidase enzyme activity has been increasing at an increasing rate fast first and then slow;the active leaves of acid phosphatase show first increase and then decrease.The difference between the same enzyme activity in different treatments in the same time period has diversity,and the same treatment in the same time period has significant and insignificant differences in enzyme activity between different stands.