摘要
Microbial activity and nutrient release are known to be influenced by organic matter properties,but it is difficult to separate the effect of C/N ratio from that of C/P ratio because in most plant residues both ratios are either high or low.An incubation experiment was conducted to investigate the effects of reducing the C/N and C/P ratios of slowly decomposable plant residues(young eucalyptus leaves,mature wheat straw,and sawdust) to those of rapidly decomposable residues(young kikuyu shoots) on soil respiration,microbial biomass,and N and P availability.The C/N and C/P ratios of the former were adjusted to 15 and 89,respectively,by adding N as(NH_4)_2SO_4,P as KH_2PO_4 or both and residues were added at 10 g C kg-1 to a silt loam.Soil respiration was measured over21 d;microbial biomass C(MBC) and available N and P were measured on days 0,7,and 21.Compared to the unamended soil,addition of kikuyu increased cumulative respiration 20-fold,MBC concentration 4 to 8-fold,and available P concentration up to4-fold,whereas the increase in available N concentration was small and transient.Cumulative respiration and MBC concentration were low in the sawdust-amended soil and were not influenced by reducing the C/N and C/P ratios.Cumulative respiration with original wheat and eucalyptus was 30%-40%of that with kikuyu.Reducing the C/N ratio alone or both C/N and C/P ratios increased cumulative respiration and MBC concentration 2-fold compared to the original wheat and eucalyptus,whereas reducing the C/P ratio had little effect.Throughout the experiment,the available N concentration after addition of residues with reduced C/N ratio increased in the following order of eucalyptus < wheat < sawdust.By independently lowering the C/N and C/P ratios,microbial activity was more limited by C and N than P.However,lowering the C/N ratio of very slowly decomposable sawdust had no effect on soil respiration and MBC concentration,suggesting that other properties such as concentration of poorly decomposable C compounds limited decompositio
Microbial activity and nutrient release are known to be influenced by organic matter properties, but it is difficult to separate the effect of C/N ratio from that of C/P ratio because in most plant residues both ratios are either high or low. An incubation experiment was conducted to investigate the effects of reducing the C/N and C/P ratios of slowly decomposable plant residues （young eucalyptus leaves, mature wheat straw, and sawdust） to those of rapidly decomposable residues （young kikuyu shoots） on soil respiration, microbial biomass, and N and P availability. The C/N and C/P ratios of the former were adjusted to 15 and 89, respectively, by adding N as （NH4）2SO4, P as KH2PO4 or both and residues were added at 10 g C kg-1 to a silt loam. Soil respiration was measured over 21 d; microbial biomass C （MBC） and available N and P were measured on days 0, 7, and 21. Compared to the unamended soil, addition of kikuyu increased cumulative respiration 20-fold, MBC concentration 4 to 8-fold, and available P concentration up to 4-fold, whereas the increase in available N concentration was small and transient. Cumulative respiration and MBC concentration were low in the sawdust-amended soil and were not influenced by reducing the C/N and C/P ratios. Cumulative respiration with original wheat and eucalyptus was 30% 40% of that with kikuyu. Reducing the C/N ratio alone or both C/N and C/P ratios increased cumulative respiration and MBC concentration 2-fold compared to the original wheat and eucalyptus, whereas reducing the C/P ratio had little effect. Throughout the experiment, the available N concentration after addition of residues with reduced C/N ratio increased in the following order of eucalyptus 〈 wheat 〈 sawdust. By independently lowering the C/N and C/P ratios, microbial activity was more limited by C and N than P. However, lowering the C/N ratio of very slowly decomposable sawdust had no effect on soil respiration and MBC concentration, suggesting that other properties such as concentration of
基金
supported by the Australian Research Council
