Distribution Of Litter And Soil Organic Carbon And Nitrogen In Four Subtropical Forests In Central Southern China

Litter and soil are the important components in forest ecosystems and play critical roles in nutrient cycling and energy flow as well as soil fertility maintenance. Litter biomass and corresponding carbon and nitrogen concentration, storage and distribution and soil organic carbon (SOC) and nitrogen (N) concentration, storage and distribution in soil profile were investigated in four subtropical forests in hilly area of central Hunan Province, China. The four subtropical forests were Cunninghamia lanceolata plantation, Pinus massoniana and Lithocarpus glaber mixed forest, Choerospondias axillaris forest, and Cyclobalanopsis glauca and L. glaber mixed forest. The main results are listed as followed:(1) Litter biomass in the four forests varied from the highest in Cyclobalanopsis glauca and L. glaber mixed forest (CG)(12.04±3.60t·hm-2), through Pinus massoniana and Lithocarpus glaber mixed forest (PM)(11.65±2.15t-hm-2), and Choerospondias axillaris forest (CA)(9.12±2.30t·hm-2), to the lowest in Cunninghamia lanceolata plantation (CL)(8.92±1.80t·hm-2). The leaves litter consisted of the largest proportion of the litter layer, and the fruits were the smallest proportion of the total litter, less than5%. There were no significant differences in the litter amount of decomposition degree (p <0.0001). Carbon concentration of the litter in the four forests ranged from177.90to581.34g·kg-1, and N concentration varied from5.18to15.48g·kg-1. Carbon concentration decreased with the degree of litter decomposition. The proportion of semi-decomposed litter and decomposed litter showed a negative correlation with C/N. Litter C storage in the four forests ranged from3.37to5.69t-hm-2while litter N storage varied from81.52to152.18kg·hm-2PM mixed forest had the highest C storage and N storage because of the low litter decomposition rate and high litter amount.(2) SOC and N concentration and storage differed significantly among the four forests and soil depth (p<0.05). In general, SOC and N concentration in the four forests decreased with soil depth, ranging from8.66to22.96g-kg-1for CL plantation, from13.33to37.50g-kg-1for PM mixed forest, from13.78to43.58g-kg-1for CA forest, and from13.33to36.87g-kg-1for CG mixed forest. Soil N concentration varied from1.37to2.29g-kg-1for CL plantation, from1.29to2.65g-kg-1PM mixed forest, from1.69to3.96g-kg-1CA forest, and from1.23to3.26g-kg-1CG mixed forest. Differences in SOC concentration among four forests varied with soil depths. For example, a great significant difference among forests was observed at the0-10cm soil depth (p=0.0083), while no significant difference for the10-20cm soil depth (p=0.2292), marginal significant difference for the20-30cm soil depth (p=0.0467). Soil total N concentration showed great significant difference at the0-10cm depth (p=0.0062), significant difference at10-20cm depth (p=0.0204), no significant difference at the20-30cm depth (p=0.0805). Four forests had no significant difference in SOC storage (p=0.1776), but showed significant difference for total N storage (p=0.0007). SOC concentration was positively correlated with total N concentration (p<0.01), and had a significant correlation with C/N (p<0.01) with exception of CG mixed forest. Soil N concentration significantly correlated with C/N for PM mixed forest (p<0.01) and CA forest (p<0.05), but correlation was insignificant for CL plantation and CG mixed forest (p>0.05).(3) Litter biomass, soil porosity were higher and soil bulk density was lower in CG mixed forest and PM, and litter biomass, soil porosity were lower and soil bulk density was higher in CA. The smaller soil bulk density was and the larger soil porosity was, the better soil structure was. The Litter biomass was less, but the soil bulk density was low, the soil porosity was high in CL, mainly due to people's activities make the soil was loose and the permeability was good. Overall, the SOC content was not strictly correspond to the C content of litter, this may be affected by other factors, but the PM broad-leaved mixed forest litter and SOC content were the highest, which might be associated with forest density, site condition and other related. Litter N content and soil N content had significant mutual feedback effect, when the litter N content was high, the soil N content was low, when the litter N content is low, the soil of high content of N, vice versa. But the CL Litter and soil N content were the lowest, did not show the mutual feedback mechanism. Litter biomass and the content and storage of SOC had positive linear correlation, but the thread affinity R2was small (R2=0.0757; R2=0.0273), the correlation was no significant. Litter biomass the content and storage of soil N had negative linear relation, but the thread affinity R2was small (R2=0.0022; R2=0.0337), the correlation was no significant. SOC content and the content and storage of litter C, N had a significant positive correlation (p <0.01), in addition, the soil porosity and soil N content were positively correlated with the litter biomass, soil C, N content and storage. Soil bulk density and soil C storage were negatively correlated with the litter biomass, soil C, N content and storage, but there were no significant correlation (p>0.05).