杨树人工林品种更替连作与非更替连作根际效应的比较

采用空间位移法对杨树人工林更替连作和非更替连作两种经营模式下土壤养分、土壤酶活性和土壤微生物的根际效应进行了比较研究,以期探明不同连作经营模式对杨树人工林土壤生态环境的影响,探讨品种更替对杨树人工林地力维持的生态效果。研究结果表明,更替连作和非更替连作均导致杨树人工林土壤发生不同程度的衰退,非更替连作导致的林地土壤衰退现象更为严重。杨树根际和非根际土壤养分在非更替连作中下降最为显著,土壤有机质的根际效应显著大于更替连作,而土壤速效N、P、K的根际效应在更替连作中显著增大。非更替连作导致根际和非根际土壤中过氧化氢酶、脲酶和碱性磷酸酶活性发生较大幅度的下降,而多酚氧化酶和过氧化物酶活性较大幅度的上升;更替连作也导致土壤酶活性有类似的变化趋势,但下降(上升)幅度远小于非更替连作,土壤酶活性的根际效应总体呈现非更替连作变化幅度强于品种更替连作的趋势。两种连作模式下土壤中可培养土壤微生物的数量变化大致呈现一致趋势,连作将导致根际和非根际土壤微生物数量整体下降,其中土壤细菌比例有所降低,真菌比例上升,土壤呈现从细菌型向真菌型转化的特点,非更替连作对土壤微生物的根际效应明显大于更替连作。更替连作和非更替连作根际效应的差异可能由不同杨树品种根系分泌物的差异所导致。

Comparison on rhizosphere effect of cultivar alternation and non-alternation continuous cropping poplar(Populus deltoids) plantation

Rhizosphere is the important interface between plant roots and the soil environment. To detect the effects of cultivar alternation and continuous cropping on soil fertility maintenance and the soil environment of poplar (Populus deltoids) plantation, we compared soil nutrient, enzyme activity and microbe abundance of the rhizosphere and bulk soils from the poplar plantations under cultivar alternation continuous cropping (ACC) and non-alternation continuous cropping (NACC). The results showed that both ACC and NACC led to soil degradation, but the extent of NACC was higher than ACC. The nutrients in rhizosphere and bulk soils of NACC decreased significantly more than ACC. Rhizosphere effects of soil organic matter in NACC was significantly larger than ACC, In contrast, the rhizosphere effects of soil available N, P and K were significantly lower in NACC than ACC.. As for the soil enzyme activity, NACC led to a significant decline in catalase, urease and alkaline phosphatase activity while an increase in polyphenol oxidase and peroxidase activity in rhizosphere and bulk soils. The same pattern occurred in ACC, but the amplitude of decline or increase was much smaller. In addition, the rhizosphere effects of soil enzyme activity in NACC demonstrated the same pattern as that of ACC, but with a larger range of variation. For soil microbe abundance, the same patterns occurred in ACC and NACC. Both of the two continuous cropping models led to decrease of soil microbe abundance in rhizosphere and bulk soils. The percentage abundance of soil bacteria was decreased while that of fungi was increased indicating a transition from the bacterial functioning soil to the fungi functioning soil. The rhizosphere effects of soil microbes in NACC were significantly higher than ACC, which could be attributed to the difference of root exudates. We concluded that continuous cropping of poplar plantations would lead to soil degradation, possibly be mitigated by cultivar alternation, which should be considered in future managements.