半干旱区沙质退化草地造林对土壤质量的影响

采用野外调查与室内培养相结合的方法,研究了我国北方半干旱区科尔沁沙地退化草地营造樟子松人工林32年后0～10 cm表层土壤理化性状、土壤碳氮矿化量、土壤微生物量以及土壤酶活性等的变化. 结果表明32年生樟子松人工林土壤有机碳、全氮和全磷等养分含量分别下降了21%、42%和45%;5月和11月樟子松人工林土壤NH4 -N显著高于草地(P=0.001;P=0.019),而5、8和11月草地土壤NO3--N含量显著高于樟子松人工林(P＜0.001;P=0.048;P=0.031);5、8和11月樟子松人工林土壤有机碳日矿化释放的CO2-C量均大于草地,而二者土壤氮矿化率差异不显著(P＞0.05);5和8月樟子松人工林土壤微生物量碳含量与草地相比差异不显著,11月则显著高于草地;土壤养分和水分含量是影响土壤微生物量碳含量的重要因素;与草地相比,樟子松人工林土壤脲酶和蔗糖酶活性降低,而土壤过氧化氢酶活性升高. 上述结果说明半干旱区沙质退化草地营造樟子松人工林32年后土壤质量出现一定程度的下降;由于植被的改变,樟子松人工林土壤理化性状和生物学性状等表现出与草地不同的季节动态特征.造林作为我国北方半干旱区沙地退化生态系统的一种恢复手段具有一定的局限性.

Effects of degraded sandy grassland afforestation on soil quality in semi-arid area of Northern China

By the methods of field survey and incubation test,this paper studied the effects of degraded sandy grassland afforestation with Mongolian pine on the soil physical,chemical and biological properties in 0-10 cm layer on Keerqin sandy land.The results showed that after 32 years afforestation,soil organic C,total N and total P decreased by 21%,42% and 45%,respectively.In May and November,soil NH4 -N content was significantly higher under Mongolian pine plantation than under grassland(P=0.001;P=0.019),but in May,August and November,soil NO3--N content was in adverse(P<0.001;P=0.048;P=0.031).In May,August and November,soil C mineralization rate was higher under Mongolian pine plantation than under grassland,but the difference in N mineralization rate was not significant(P>0.05).In May and August,soil microbial biomass C under Mongolian pine plantation and grassland had little difference,but in November,it was significantly higher under Mongolian pine plantation than under grassland.Soil nutrients-and moisture contents were the important factors affecting soil microbial biomass C.Soil urease and invertase activities decreased but catalase activity increased under Mongolian pine plantation,compared with those under grassland.It was suggested that 32 years afforestation of degraded sandy grassland with Mongolian pine on Keerqin sandy land led to a definite degradation of soil quality.Owing to the changes of vegetation,the test indicators of soil quality had different seasonal dynamic characteristics under Mongolian pine plantation and grassland.As a means of degraded ecosystem restoration in semi-arid area of Northern China,afforestation had its definite limitations.