残落物添加对农林复合系统土壤有机碳矿化和土壤微生物量的影响

Influence of residue composition and addition frequencies on carbon mineralization and microbial biomass in the soils of agroforestry systems

采用室内培养研究了黏壤土和粉砂质壤土条件下杨树叶和小麦秸秆混合以及改变杨树叶添加频次对土壤有机碳矿化及土壤微生物量的影响。结果表明:(1)添加各残落物后,25℃时土壤呼吸速率高于15℃,粉砂质壤土高于黏壤土(P<0.05)。分4次添加杨树叶处理(P2、P2-W)的呼吸速率在1—7d较小,第8天后高于其他处理(P<0.05),且在9、17、25d会出现峰值。(2)培养初期,混合物对有机碳矿化的促进作用不明显,培养结束时表现出促进作用(P<0.05)。分4次添加杨树叶最终的有机碳净矿化累积量高于一次添加处理(P<0.05)。(3)和单一处理相比,杨树叶-小麦秸秆混合后的土壤微生物量碳、氮显著提高(P<0.05),而分4次添加杨树叶的土壤微生物量碳、氮高于一次性添加处理(P<0.05)。添加残落物处理均降低了土壤矿质态氮含量,且这种现象在混合处理(P1-W,P2-W)中更为明显(P<0.05)。说明残落物混合及添加频次增加能有效调节碳动态及氮供应,这对深入了解农林复合系统碳氮循环具有一定的现实意义。

The forest litter and crop straw residues are important components in the agroforestry system and play a key role in ecosystem carbon and nutrient cycle.During decomposition,to a great extent,the carbon mineralization is controlled by soil microorganisms.However,the quality of mixtures with various compositions is different due to difference in chemical compositions and physical structure from single component.Moreover,frequent addition of residues is reported to be able to keep the easily available compounds in soils in a high level.All the factors mentioned above were considered to have important effects on soil microbial activity.However,the effects of residue composition and addition frequencies on carbon mineralization,microbial biomass carbon and nitrogen have been seldom reported in the soil of agroforestry system.Poplars are the major tree component of traditional agroforestry systems throughout the south temperate central area of China.In this paper,an experiment was designed to study the influnce of different residue compositions and addition frequencies on carbon mineralization,microbial biomass carbon and nitrogen in the soil of poplar-wheat agroforestry system.The clay loam and silty loam in the experiment were collected from Sihong and Dafeng County of northern Jiangsu Province.The six treatments in the experiment were W： 16 g/kg（soil） wheat straw residue;P1： 16 g/kg（soil） poplar leaf litter;P1-W： 16 g/kg（soil） mixture of poplar leaf and wheat straw residue with 1 ∶1;P2： adding 4 g/kg（soil） poplar leaf litter every 8 days;P2-W： adding 2 g/kg（soil） poplar leaf litter every 8 days and 8 g/kg（soil） wheat straw residue at the first day,and CK： the control（without any addition）.The soils with different treatments were incubated under the temperature of 25℃ at daytime and 15℃ at night for 31 days.The results showed that,for all the residue addition treatments,the carbon mineralization rates were higher in the daytime with the temperature of 25℃ than those in the night with 15℃（P〈0.05）.For the soils,the silty loam showed higher carbon mineralization rates than clay loam（P〈0.05）.After 8 days of incubation,the treatment P2 and P2-W showed higher carbon mineralization rates than the other treatments（p0.05）,and the peak values occurred at 9,17,25 days.Mixed residues of poplar leaf and wheat straw could promote the cumulated carbon mineralization at the end of incubation,and the cumulated carbon mineralization was significantly higher in the treatment of adding poplar leaf litter serially（P2） than that of adding all at the first day（P1）（P〈0.05）.Compared to the treatments of poplar leaf litter（P1） and wheat straw residues（W）,mixed residues of poplar leaf and wheat straw significantly increased microbial biomass carbon and nitrogen in soil（P〈0.05）.Furthermore,the microbial biomass carbon and nitrogen were significantly higher in the treatment of adding poplar leaf litter serially（P2） than that of adding all at the first day（P1）.However,compared to the CK,the content of soil inorganic nitrogen decreased significantly for all the residue addition treatments,especially in the mixed residues treatments（P1-W and P2-W）.The results from this study suggested that residue composition and addition frequencies could enhance the decomposition process,and regulate carbon dynamic and nitrogen supply.Such study would provide an important information for a deeper understanding of the carbon and nitrogen cycle in agroforestry systems.