Litter Decomposition Processes And Their Microbiological Characteristics Under Different Land Use Types

Land use change greatly impacts the net primary productivity?NPP?and soil organic matter?SOM?,and also affects the soil properties indirectly.These changes potentially influence terrestrial ecosystem carbon?C?,nitrogen?N?,and phosphorus?P?cycling processes and microbial enzyme activities.However,the impact of different land use types on litter decomposition and microbial enzyme activities is not fully understand.Thus,in this study,the leaf litter and fine root of the dominant species?woodland:Platycladus orientalis?Linn.?Franco;shrubland:Sophora davidii?Franch.?Skeels;cropland:Zea mays?in Danjiangkou reservoir area were selected to study the litter decomposition process by in situ litterbag method.We aimed to reveal:?1?the litter decomposition processes and the related factors in different land use types;?2?the characteristics of microbial enzyme activities during litter decomposition and their interactions with litter decomposition processes including the decay rate of litters,the dynamics of nutrients release?C,N and P?and the degradation of refractory components?hemicellulose,cellulose and lignin?.The microbial enzyme activities during the decomposition were observed simultaneously.The results of this study were as follows:?1?The decomposition processes of different litter types?i.e.fine root and leaf litter?were significant different among land use types,and these differences were closely related to the quality and morphological characteristics of litters.During the784-day decomposition period,the leaf litter of shrubland had higher initial N content and N:P ratio,lower initial lignin concentration and C:N ratio,C:P ratio,with rapid decomposition(the decay rate was 0.57 yr^-1).By contrast,the leaf litter of woodland and cropland had slower decomposition(the decay rate were 0.32 yr^-11 and 0.31 yr^-1,respectively).The lower initial C concentration and root tissue density?RTD?together with higher special root length?SRL?led to a rapid decomposition in fine root of cropland(the decay rete was 0.89 yr^-1).However,the fine roots of woodland and shrubland were opposite,with decomposition rates of 0.25 yr^-1 and 0.12 yr^-1,respectively.?2?During litter decomposition,the loss rates of nutrient elements and refractory components were significantly affected by land use type,litter type and their interactions.The content of C,lignin,cellulose and hemicellulose generally showed release pattern during the 784-day decomposition period,while the N and P showed release or immobilization period depending on the land use types and litter types.The differences in litter decay rate,nutrient elements,refractory components and litter input in different land use types resulted in significantly higher soil organic carbon?SOC?stock in afforested land(woodland:1557.55±53.18 g m^-2,shrubland:1609.07±23.87 g m^-2)than cropland(734.42±56.36 g m^-2);as well as soil N stock in woodland(115.77±6.08 g m^-2)was higher than shrubland(94.37±3.38 g m^-2)and cropland(98.44±4.94 g m^-2);but soil P stock in woodland(5.16±0.34 g m^-2)was lower than shrubland(8.54±0.27 g m^-2)and cropland(8.27±0.31 g m^-2).?3?Microbial C-enzyme??-Glucosidase,BG?,N-enzyme?Leucine amino peptidase+N-acetyl-?-glucoasminidase,LAP+NAG?,and P-enzyme activities?Acid phosphatase,AP?greatly changed with land use type,litter type,decomposition time and their interactions during the 784-day field incubation,which resulted in a great changes in enzyme activities in the processes of decomposition.The linear regression analysis showed that there was a significant positive correlation between the activities of C-acquiring enzyme and N-acquiring enzyme,C-acquiring enzyme and P-acquiring enzyme,N-acquiring enzyme and P-acquiring enzyme.Due to impact of the stoichiometric ratio,environmental and microbial factors on the vector length of microbial enzyme activities,the vector length of leaf litter in afforested land increased gradually with the decomposition,while the cropland fluctuated up and down within a certain range.The vector length of fine root in woodland increased firstly,then decreased,and then increased with the decomposition,while it in the shrubland was rising all the time,and it in the cropland was rising first and then falling.Meanwhile,litter quality,stoichiometric ratio,environmental and microbial factors also had significant effects on the vector angle of microbial enzyme activity.For leaf litter decomposition,the vector angle of the woodland increased firstly and then decreased gradually,which was less than 45°;the vector angle of the shrubland raised sharply,but all of them were less than 45°;the vector angle of the cropland decreased steeply,and all of them were less than 45°except in the earlier decay stage.The vector angle of the fine root showed inconsistent changes,the vector angle of the fine root in afforested land increased firstly and then decreased;but it in woodland was more than 45°?except for the 784th-day decomposition?,it in the shrubland was less than 45°;it in cropland gradually increased,and all of them were more than 45°.In summary,land use change altered vegetation types,and thus altered litter decomposition due to the differences in litter quality,stoichiometric ratio and morphological characteristics.These changes could potentially influence SOC,N,P stock in different land use types.Thus,our results are helpful to evaluate the potential effects of land use change on soil C sequestration and nutrient cycling,and provide basic data for further understanding of the relevant research of material circulation and energy flow in ecosystems under land use change.