城乡交错带土壤氮素空间分布及其影响因素

城乡交错带土壤氮素是城乡生态系统中最重要的氮源与氮汇,但是城市化下的土壤氮素分布及其影响机制还不清楚,基于3S平台研究了土壤氮素在成都西郊城乡交错带的空间分布特征及城市化对土壤氮素的影响。结果表明,研究区内土壤全氮(STN)、硝态氮(NO_3~--N)和铵态氮(NH_4~+-N)含量均值分别为(1.46±0.06)g/kg、(50.04±3.59)mg/kg和(6.72±0.53)mg/kg。区内土壤氮素含量从近郊向远郊逐渐增高,STN和NO_3~--N含量为中部高于南北部,NH_4~+-N含量则由西北部和东南部向中部递增。方差分析表明,区内不同土地利用方式下STN、NO_3~--N和NH_4~+-N含量差异显著(P0.05)。回归分析显示STN含量与建筑密度(BD)、道路密度(RD)均呈现显著线性负相关(P0.05),NO_3~--N含量与道路密度呈极显著线性负相关(P=0.001),与建筑密度关系不明显(P=0.217)。土壤NH_4~+-N与建筑密度呈显著负线性相关(P=0.001),与道路密度呈显著指数相关关系(P=0.021)。研究结果显示城市发展使得城乡交错带土壤氮素含量降低,这种影响伴随着建筑面积的增加,道路长度的增加而加强。

Spatial distribution of soil nitrogen in an urban-rural fringe and its influencing factors

Urban-rural fringe is a special zone that evolved from the suburbanization accompanying intensified land use changes from agricultural to non-agricultural land. Nitrogen in the soil of urban-rural fringe is an important nitrogen source and sink for urban and suburban ecosystems. The nitrogen content changes not only affect greenhouse gas emissions, but also threaten plant nitrogen supply and water ecosystems. However, in suburb urbanization, the proportion of non-agricultural land, construction land, and road land exhibited a successive increase. Currently, the mechanism of spatial distribution of soil nitrogen, caused by an increase in non-agricultural land, remains unclear. In the present study, the 3S platform was used to investigate the spatial distribution of soil nitrogen and its influencing factors in the urban-rural fringe of the western suburbs of Chengdu. Results showed that the average contents of soil total nitrogen (STN), nitrate (NO₃^--N), and ammonium (NH₄⁺-N) were (1.46±0.06) g/kg, (50.04±3.59) and (6.72±0.53) mg/kg, respectively. In the investigated region, average content of soil nitrogen gradually increased from the inner to the outer suburbs. The STN and NO₃^--N distribution in the inner suburbs were higher than those of the northern and southern areas. High STN(>1.5 g/kg) and soil NO₃^--N(> 62.2 mg/kg) values presented mass distribution in the eastern suburbs. In addition, NH₄⁺-N in soil gradually increased from the northwest or southeast to the center, and the high values(> 8.5 mg/kg) presented irregular piece distribution in the eastern suburbs. Analysis of variance (ANOVA) showed that the difference of STN, NO₃-N, and NH₄⁺-N contents were significant under different land use patterns (P < 0.01). The STN content in vegetable fields was the highest (> 1.8 g/kg), followed by rape fields, gardens, and woodland (1.5-1.8 g/kg). Garlic fields and idle land were relatively moderate (1.0-1.5 g/kg), and residential land and urban green land were relatively low (< 1.0 g/kg). NO₃^--N content was ranked as residential land > vegetable field > garlic field > garden > rape field > idle field > woodland > urban green land. NH₄⁺-N content was ranked as vegetable field > woodland > garden > rape field > garlic field > residential land > idle field > urban green land. Correlation analysis indicated that average STN content and building density (BD) showed a negative linear correlation (P <0.05), and similar linear correlation was also observed between STN and road density (RD) (P < 0.05). NO₃^--N content in soil and road density showed a negative correlation (P = 0.001). However, the correlation was not significant between NO₃^--N and the building density (P = 0.217) after being analyzed using different curve models. NH₄⁺-N content and building density showed a significant negative linear correlation (P = 0.001), and a significant exponential correlation existed in NH₄⁺-N content and the road density (P = 0.021). Therefore, a significant effect on the development of urban distribution of soil nitrogen was observed, that was potentially strengthened by increasing road lengths and building areas. It can be suggested that the monitoring and management of soil nitrogen should be enhanced, and the cycling of soil nitrogen, atmospheric nitrogen, and water nitrogen should be investigated in future studies.