杨树采伐剩余物施用对土壤养分和二氧化碳释放的影响

  目的  探索施用杨树Populus采伐剩余物对土壤养分和二氧化碳(CO₂)释放的影响，为其潜在利用提供参考。  方法  以杨树树枝、树皮、树叶和水稻Oryza sativa秸秆等4种农林废弃物为生物质原料，根据杨树人工林单位面积凋落物量，以2%质量分数(以烘干土质量计)均匀混入新鲜土壤，25 ℃恒温培养箱中暗培养180 d。控制培养期间土壤含水量为田间持水量的60%。测定不同处理下土壤微生物生物量碳(MBC)、微生物生物量氮(MBN)、无机氮铵态氮(NH₄ +-N)和硝态氮(NO₃ ?-N)]、有效磷(AP)、速效钾(AK)等质量分数以及CO₂日释放速率和累积释放量。  结果  ① 4种生物质原料施用显著影响土壤微生物生物量及土壤氮磷钾的有效性(P＜0.05)。相比对照，杨树树枝、树皮、树叶和水稻秸秆处理的土壤MBC质量分数分别增加了50%、31%、80%和109%，土壤MBN质量分数分别增加了54%、40%、72%和203%。施用杨树树皮和树枝土壤的NH₄ +-N质量分数从大到小依次为对照、秸秆处理、树叶处理、树皮处理、树枝处理。土壤AP质量分数以树枝处理最高，AK质量分数以秸秆处理最高。②不同处理的土壤CO₂日释放速率均表现为初期较快，中期逐渐减缓，后期趋于稳定。培养期间，秸秆处理的土壤CO₂累积释放量最高，显著高于其他处理(P＜0.05)，其次为杨树树叶，不同处理间差异显著(P＜0.05)。③相关性分析表明:生物质原料的性质与土壤微生物生物量、土壤养分和CO₂释放量存在显著相关性。其中土壤微生物生物量与生物质原料的全氮、全磷、全钾显著正相关(P＜0.05)，与全碳和碳氮比显著负相关(P＜0.05)；土壤CO₂日释放速率与土壤MBC、MBN、NH₄ +-N、AP和AK均显著正相关(P＜0.05)，但与NO₃ ?-N呈极显著负相关(P＜0.01)。  结论  从土壤养分和环境效应综合考量，杨树采伐剩余物的施用能提高土壤有效态的氮磷钾等养分，相对减少碳排放。图3表3参47

Impacts of poplar harvesting residue additions on soil nutrients and CO2 emission

  Objective  Impacts of the addition of poplar harvesting residues on soil nutrients and CO₂ emission were investigated in controlled conditions to provide a reference for its potential utilization.  Method  The indoor incubation experiment was carried out by selecting logging residues of twigs, barks, and leaves from a poplar plantation and the rice straw as research materials. Based on the litter amount in the unit area of the poplar plantation, the fresh soil equivalent to 100 g of dry soil weight and biomass materials equivalent to 2% of dry soil weight were mixed evenly. Then the mixed soils were loaded into a homemade polyethylene plastic box, and incubated in a constant temperature incubator at 25℃ for 180 days in darkness. During the culture period, the soil moisture content was controlled to 60% of the field moisture capacity. Dynamic variations in microbial biomass carbon (MBC) and nitrogen (MBN), inorganic nitrogen (NH₄ +-N and NO₃ ?-N), available phosphorus (AP) and available potassium (AK) as well as CO₂ in the soil were measured.  Result  (1) The addition of all four residue biomass significantly affected microbial biomass and nutrient availability in the soil (P＜0.05). Compared with the control, the soil MBC contents treated by the residue biomass of poplar twigs, barks, leaves and straw increased by 50%, 31%, 80% and 109% respectively, while the soil MBN contents increased by 54%, 40%, 72% and 203%, respectively. The contents of NH₄ +-N in the soil treated with bark and twigs residues were higher than those in the control and rice straw treatments, whereas the NO₃ ?-N content in the soil was in the order of control>rice straw>leaf residue>bark residue>twig residue treatments. The highest AP content was observed in the soil treated with twigs, while the AK content in the soil treated with rice straw was higher than that treated with other biomass residues. (2) After adding biomass residues into the soil, the daily release rate of CO₂ from the soil showed a tendency with being relatively fast in the initial period, gradually slowing down in the middle stage, and tending to be stable in the later stage of the incubation. After 180 days of indoor incubation, the cumulative CO₂ emission from the soil treated with rice straw was significantly higher than that of the other treatments (P＜0.05), followed by the soil treated with poplar leaves. (3) Correlation analysis showed that microbial biomass, nutrient contents and CO₂ daily release rate in the soil were obviously correlated to the properties of biomass residues. Of them, a significantly positive correlation of soil microbial biomass to the contents of total nitrogen, total phosphorus and total potassium but a significantly negative correlation to the total carbon content and C/N ratio in the biomass residues were detected (P＜0.05). Meanwhile, the CO₂ daily emission rate was positively correlated to the contents of MBC, MBN, NH₄ +-N, AP and AK in the soil (P＜0.05), whereas a significantly negative correlation of the CO₂ daily emission rate to the contents of NO₃ ?-N was observed (P＜0.01).  Conclusion  From the views of soil nutrients and environmental effects, application of poplar harvesting residues not only can increase the contents of soil available nutrients, but also relatively reduce carbon emissions compared with the rice straw. Ch, 3 fig. 3 tab. 47 ref.]