水田和旱地土壤有机碳周转对水分的响应

Response of the Turnover of Soil Organic Carbon to the Soil Moisture in Paddy and Upland Soil

【目的】研究土壤含水量对水田和旱地土壤中可溶性有机碳和微生物量碳含量以及有机碳矿化的影响,以探明水田和旱地有机碳周转差异的来源。【方法】在标准培养条件下(25℃,100%空气湿度)培养100 d,研究了5个水分梯度下(45%、60%、75%、90%、105%WHC,WHC为土壤饱和持水量)水田和旱地土壤有机碳的矿化特征,并测定了培养期内3个水分梯度下(45%、75%、105%WHC)土壤的可溶性有机碳(DOC)和微生物量碳(MBC)含量。【结果】土壤含水量、土地利用方式(水田和旱地)及两者的交互作用对土壤有机碳的矿化、DOC和MBC均有显著影响。水田(45%—90%WHC)和旱地(45%—75%WHC)土壤有机碳的累积矿化率(量)随含水量增高而增高,有机碳的周转半衰期随含水量的增高而缩短(水田为5.23—7.57 a,旱地为6.79—12.87 a)。100 d的培养期内,水田和旱地土壤分别有2.33%—3.94%和1.66%—3.33%的有机碳参与了矿化。淹水条件下,水田和旱地土壤的有机碳矿化速率均高于好气条件。同时,淹水条件还使水田土壤的DOC、MBC含量显著降低,对旱地则无影响。【结论】在一定水分范围内(水田:45%—90%WHC;旱地:45%—75%WHC),提高含水量可以促进水田和旱地土壤有机碳的矿化,有利于养分的释放,但对土壤活性有机碳(DOC和MBC)无促进甚至有抑制作用。土壤有机碳的矿化速率和累积矿化率(量),在淹水条件下和水田土壤中比在好气条件和旱地土壤中高,其原因之一可能是取样制样过程中土样经历的干湿交替过程促进了有机碳的降解。

【Objective】To ascertain the difference of the accumulation of soil organic carbon（SOC） in paddy and upland soil,the mineralization,dissolved organic carbon（DOC） and microbial biomass carbon（MBC） in soil under different soil moisture conditions were determined.【Method】 In laboratory,one portion of paddy and upland soil was incubated under 45%,60%,75%,90% and 105% water holding capacity（WHC） to measure the mineralization of SOC.The other portion was incubated under 45%,75% and 105%WHC to measure the DOC and MBC content in soil.All the soils were placed at 25℃,100% air humidity for 100 days.【Result】The soil moisture,land use（paddy and upland） and the interactions of them all had significant effects on the mineralization of SOC,content of soil DOC and MBC.The accumulative mineralized proportion（amount） of SOC increased as moisture content increased from 45% to 90%WHC in paddy soil and from 45% to 75%WHC in upland soil.Meanwhile,the half decay time of SOC（paddy,5.23-7.57 age;upland,6.79-12.87 age） decreased as moisture content increased.During 100 d incubation period,the equivalent of 2.33%-3.94% and 1.66%-3.33% of SOC in paddy and upland soil respectively,were mineralized.Both the mineralization rate of SOC in paddy and upland soil were greater under flooding condition than under aerobic condition.However,the content of DOC and MBC in paddy soil were lower under flooding condition.【Conclusion】Along with the increasing of soil moisture content,from 45%-90%WHC in paddy soil and from 45%-75%WHC in upland soil,the mineralization of SOC will be accelerated,thereby the soil nutrient release will be expedited.Nevertheless,the increase in soil moisture has no positive-effects on the DOC and MBC content of soil.The reasons,why the mineralization rate and the accumulative mineralization proportion（amount） of SOC were higher under flooding condition or in paddy soil than under aerobic condition or in upland soil,may be that the decomposition of SOC be accelerated by the alternation of drying and wetting of soil,and the priming effects of the alternation of drying and wetting on the paddy soil are greater than that on the upland soil.