| Eucalyptus spp.is the third dominant tree species in China’s artificial forests.While making great contributions to the regional economy,it also brings some controversial ecological problems,such as the decline of soil fertility,the decrease of biodiversity and the increase of diseases and pests.Constructing artificial mixed forest can effectively promote resource utilization,reduce interspecific competition,improve undergrowth light transmittance and environmental heterogeneity due to niche differentiation among tree species,complementary canopy structure and heterogeneity of stand structure.Litter decomposition is very important in nutrient cycle of forest ecosystem.In the natural state,litters often exist in mixed form.After litters are mixed,mixed effects can be produced due to potential nutrient transfer,and different mixed effects can be produced due to different types of litters.However,the underlying mechanism under the decomposition characteristics of mixed litter is still unclear.Therefore,in this study,the defoliation of E grandis mixed forest with three common tree species(E-B,mixed stand of E.grandis and Betula luminifera;E-C,mixed stand of E.grandis and Cunninghamia lanceolata;E-P,mixed stand of E.grandis and Pinus massoniana)in Danling County,Sichuan Province was taken as the research object,and the defoliation of 4-year-old and 8-year-old E grandis pure forest was taken as the control,and 5 ratios(3 mixed ratios + 2 single ratios)were set in each of the three mixed forests,and a total of 17 treatments were used for field decomposition experiments.By comparing the decomposition characteristics of litter leaves under different treatments and the differences in quality,carbon,nitrogen,phosphorus,lignin and cellulose between different treatments,the best companion tree species and mixing ratio of E.grandis were found,so as to provide scientific basis and technical support for the selection,scientific management and operation of companion tree species in eucalyptus artificial mixed forest.The main conclusions are as follows;(1)The initial nutrient content of single giant eucalyptus litter in the three mixed forests was different,and the manifestations were as follows: E-B> E-C> E-P.The N content of leaf litter of E-B single giant eucalyptus was significantly higher than that of the other two stands,but the C content,cellulose content and carbon-nitrogen ratio were lower than those of the other two mixed stands.8E initial nutrients are better than 4E.(2)During the early decomposition stage,the decomposition of 3 mixed forests and 2pure forests has a faster decomposition,while the later decomposition phase becomes slower,95%of the time required for decomposition is 5.97 required for 50%.-7.06 times.The E-C forest in a single giant eucalyptus deciduous has the highest decomposition coefficient(1.103),and the E-B forest in the single E.grandis deciduous lobe has the lowest decomposition factor(0.304).Compared with the mixed deciduous leaves in the rest of the forest,the highly decomposed coefficient of the mixed deciduous deciduous deciduous and the quality loss rate in the E-B forest alone is high and the quality loss rate of the decomposition coefficient of a single E.grandis leaf in the forest.During the decomposition of the decoction of the decoction,the proportion of non-increase in the quality loss rate of mixed deciduous lobe accounted for 37.78%,while the synergy effect accounted for 20.00%.Among the three mixed forest points,the E-B forest points compared to the remaining two forest points,the proportion of the collaborative effect of quality loss rates is high,and the maximum value(6.67%)is reached at 7: 3 ratio.(3)The release mode of the release of different elemental nutrients in 3 mixed forests and two pure forests is different.The C element is a direct release mode,the P element is released-enrichment-release mode,and the N element is the enrichment-release mode.At the end of the final stage,the release rate of mixed deciduous elements from low to high is P,N,C.Compared with the forest points,overall,the elements of the E-C forest points are released faster,E-B secondary,E-P is the slowest.The release rate of each element is expressed as non-addition and effects in the mixed effect most of the time.For elements,non-addition and effects from large to small order N > C > p,while the synergy effect is C > N > P.The hybrid effect of the release rate of C is mostly non-added and effect,with a total of 60.00%of the three forest scores.Among them,the highest proportion of synergistic effects is E-B(24.44%),followed by E-C(22.22%)..In E-B,5: 3 and 3: 7 accounted for a high percentage,both of which were 8.89%.N’s hybrid effects of release rates 64.44% are presented as nonaddition and effects,of which 37.78% are manifested as synergistic effects.In terms of 3forest points,the proportion of the coordination effect of the N release rate is E-P(11.11%)and E-B(8.89%).In the E-C mixed ratio,7: 3 accounts for 8.89%.The hybrid effect of the release rate of P element has 51.11% of non-additional effects,of which 15.55% are manifested as synergistic effects.E-C(11.11%)has the highest proportion of synergy effects,E-B(4.44%)secondary,while E-P has no synergy effect.In E-C,the synergy effect is relatively high in 7: 3 and 3: 7,and the proportion is 4.44%.On the whole,the average value of the release rate of each element of E-B forests is higher than that of the other two mixed forests,14.10%,and E-C and E-P are 11.11%.In E-B,the synergy effect of 5: 5 is the highest,which is 5.93%.(4)The concentrations and residual amounts of three mixed forests and 2 mixed forests and two pure forests are different.The end-stage cellulose content range is between 42.10-178.27 g/kg,while the concentration of lignin is between 46.80-330.45 g/kg.In the final decomposition stage,the residual rate of lignin was 6.91-83.92%,while the cellulose residual rate was 21.52-136.97%.In general,the release mode of lignin and cellulose is roughly the same,but when it is decomposed to 362 d,the release rate of lignin began to change from slowly to fast,while cellulose has changed from release to enrichment state.The average value of non-addition and effects in the mixed effects in the three mixed forest cellulose degradation is 60.66%.Among the three forest points,E-B’s synergy effect is the largest,accounting for 40.00%,followed by E-C(11.11%),and finally E-P(6.67%).In E-B,the highest proportion of synergy effect appears in the ratio of 3: 7(8.89%).Among the hybrid effects of lignin degradation rate,66.67%of the effect of non-addition and effect,46.67%of which are synergistic effects.Among the three forest points,the proportion of the synergy effect of lignin degradation rate is E-B,E-C,and E-P from high to low.In E-B,the proportion of the most synergistic effect of lignin degradation rate is 5: 5(26.70%).The relationship between the synergy of cellulose degradation rate is E-C> E-B> E-P.In the EB mixed forest,the proportion of the highest synergy effect of cellulose degradation rate is3: 7(26.70%).The average proportion of synergy effects of lignin and cellulose appeared in5: 5(23.3%)in E-B(63.30%).In order to improve the quality of E.grandis artificial forests,you can choose Betula luminifera to mix with E.grandis,try to avoid the Pinus massoniana.,and set an appropriate proportion.Because the best proportion of this study is 7: 3 and 5: 5,this is only the proportion of withered leaves,not the proportion of the number of tree species.Therefore,when formulating a planting plan,it is necessary to consider factors such as the annual fidelity and afforestation density of different tree species in combination with the actual situation. |
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