Land-use change (LUC) in the tropics, such as the exponential rate of conversion of natural habitats into intense monocultures focusing on cash-crop cultivation, is a major causal factor of global environmental change. To understand the effects of LUC on soil organic matter (SOM) stability and the dynamics of C and N within SOM fractions, we measured the C and N content and δ¹³C and δ¹⁵N in fractions of different aggregate- and density-size of acric ferralsols in tropical rainforests and rubber plantations. The proportion of macroaggregates, heavy and light fractions significantly decreased after LUC. The results showed that, in general, conversion of tropical rainforest to rubber plantation significantly decreased the C and N content in bulk soil and the aggregate- and density-size to 20 cm soil depth. The decrease in C and N content in bulk soil was mainly driven by decreasing C and N associated with macroaggregates and light fractions, which accounted for > 50%. We found significant correlations among mean weight diameter, aggregate-, and density-size fractions C, N, and C/N ratios. The conversion of tropical rainforest to rubber plantation significantly enriched soil δ¹³C while depleting δ¹⁵N. Enrichment of δ¹³C in rubber plantations could be explained by the mixing of old and fresh C. We conclude that, C and N dynamics within SOM fractions were greatly affected by LUC and the δ¹³C and δ¹⁵N signature confirms the changes in SOM stability after forest conversion. We suggest that planting intercrops within rubber monocultures may improve SOM accumulation, soil aggregation, and C and N sequestration.

热带地区的土地利用变化（LUC），例如自然栖息地向以现金作物种植为重点的密集单一文化转化的指数速率，是全球环境变化的主要成因。为了理解LUC对土壤有机质（SOM）的稳定性和影响C和N的SOM馏分内的动力学，我们测量了C和N含量和δ ¹³ C和δ ¹⁵在热带雨林和橡胶园中，不同浓度和密度的丙烯酸铁醛溶胶的氮含量不同。LUC后，大型集料，重质和轻质组分的比例显着降低。结果表明，总的来说，热带雨林向橡胶林的转化显着降低了散装土壤中的碳和氮含量，降低了20cm土壤深度的集料和密度大小。散装土壤中碳和氮含量的下降主要是由与大骨料和轻质组分相关的碳和氮含量下降所致，其含量> 50％。我们发现平均重量直径，集料和密度尺寸分数C，N和C / N之比之间存在显着相关性。热带雨林到橡胶种植显著富集土壤转换δ ¹³C，而消耗δ ¹⁵ N.富集的δ ¹³在橡胶种植园C可通过旧和新的C.我们得出结论，混合来解释，SOM馏分内的C和N动力学受到极大LUC和δ的影响¹³ C和δ ¹⁵ N签名确认了林转换后SOM稳定性的变化。我们建议在橡胶单一栽培中种植间作可能改善SOM积累，土壤聚集以及C和N的固存。