作 者 ：王春阳,周建斌*,董燕婕,陈兴丽,李婧
期 刊 ：生态学报 2010年 30卷 24期 页码：7092~7100
Keywords:the Loess Plateau, plant residues, soil microbial biomass carbon & nitrogen, C/N ratios,
摘 要 ：黄土高原丘陵沟壑区进行的以退耕还林还草为主的生态环境建设，使得进入土壤生态系统有机物的种类及数量发生变化，其对土壤微生物量碳、氮的影响是值得关注的问题。采用室内培养法研究了采自该区6种不同植物凋落物（碳氮比在15.1-50.7之间）及其与不同形态氮素（NH+4-N及NO-3-N）配合对土壤微生物量碳、氮及矿质态氮含量的影响。结果表明，加入不同凋落物均显著提高了土壤微生物量碳、氮含量，其中加入柠条、沙打旺等碳氮比低的凋落物在培养的一段时期内土壤微生物量碳、氮均高于碳氮比高的凋落物（刺槐、沙柳和长芒草）。在加入凋落物再施用NH+4或NO-3，也提高了土壤微生物量碳、氮含量，其中铵态氮处理土壤微生物量碳、氮含量的增加达显著水平，说明微生物更易利用铵态氮。加入C/N高的凋落物后土壤中的矿质氮发生固持，矿质态氮固持量与凋落物的C/N比呈显著的正相关关系。建议在黄土高原丘陵沟壑区植被恢复过程中，有必要考虑不同植物凋落物的碳、氮养分含量及转化特性，以协调土壤碳、氮转化过程。
Abstract:Both the quality and quantity of plant residues returned into the soil ecosystems in the gully and valley region of the Loess Plateau have been substantially changed with the returning of croplands to forests and grasslands since 1990 in Northwestern China. However, no study has reported if soil carbon (C) or nitrogen (N) has been increased after one decade of such a land use change. An important mechanism to understand these changes is to know if and how soil microbial biomass C and N (SMBC, SMBN) and mineral N have been altered in this region. We conducted a time course incubation experiment to study the effects of external addition of the sole plant residue and the dual residue plus inorganic nitrogen fertilizer on these three parameters to a Loess soil (similar to Ustochnept in the US or Calcic cambisol in FAO system) under laboratory conditions. Six local plant residues (Astragalus adsurgens Pall., Caragana Korshinskii Kom., Robinia pseudoacacia L., Salix psammophila Stipa bungeana Trin. and Ulmus pumila L., which were taken from the Loess Plateau with an average of 15.08-50.67 C/N ratio, as either a sole source (2.5 g organic C/kg DW soil) or with two inorganic N of (NH4)2SO4 and KNO3 (0.1 gN/kg DW soil), were mixed into 400 g dry soils (2 mm sieved) and incubated at (25±3)℃. A total of twenty-one treatments were designed with three replicates for each treatment. Both SMBC and SMBN in the incubated soils were analyzed at 0, 1, 7, 14, 28, 84 and 112 d, whilst mineral N was analyzed at 0, 0.5, 1, 3, 5, 7, 14, 21, 35, 70, 84, 98d and 112 d after the incubation. The moisture of incubated soils was maintained at 70% field water holding capacity by adding water once every two days. In general, the addition of the sole plant residue significantly increased the contents of SMBC and SMBN. The increasing rates of SMBC and SMBN were higher when the plant residues with low C/N ratios (e.g., A. adsurgens, C. Korshinskii,) than those with a higher C/N ratio (R. pseudoacacia, Salix psammophila, Stipa bungeana). The dual addition of plant residue and N fertilizer, either as NH+4-N or NO-3-N, also increased the contents of SMBC and SMBN, and the increasing rate was significant higher under the NH+4-N treatment, but not under the NH+4-N treatment, compared to the sole plant residue treatment. Our results thus indicated that microorganisms in this Losses soil may prefer to use NH+4-N rather than NO-3-N. In addition, the addition of plant residues with higher C/N ratios increased the immobilization of mineral N in the soil, and there was a positively significant relationship between the immobilized N and the C/N ratio in the plant residues. As a consequence, to adjust the processes of soil C and N transformations, our results suggested that both the characteristics of C and N in plant residues and the inorganic form of N fertilizer that applied to the soil should be considered for a better vegetation restoration in the gully and valley region in the Loess Plateau.
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