Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing, China.
PeerJ. 2023 Jan 27;11:e14790. doi: 10.7717/peerj.14790. eCollection 2023.
Secondary succession after agricultural land abandonment generally affects nitrogen (N) cycle processes and ecosystem N status. However, changes in soil N availability and NO loss potential following secondary succession are not well understood in karst ecosystems.
In the Karst Critical Zone Observatory (KCZO) of Southwest China, croplands, shrub-grass lands, and secondary forest lands were selected to represent the three stages of secondary succession after agricultural land abandonment by using a space-for-time substitution approach. The contents and N natural abundance ( N) of leaves, soils, and different-sized aggregates at the three stages of secondary succession were analyzed. The N compositions of soil organic nitrogen (SON) in aggregates and soil to plant N enrichment factor ( = N - N), combined with soil inorganic N contents and N compositions were used to indicate the alterations of soil N availability and NO loss potential following secondary succession.
Leaf N content and SON content significantly increased following secondary succession, indicating N accumulation in the soil and plant. The N values of SON also significantly decreased, mainly affected by plant N composition and N mineralization. SON content in macro-aggregates and soil NH content significantly increased while N values of NH decreased, implying increases in SON stabilization and improved soil N availability following secondary succession. Leaf N values, the values, and the (NO -N)/(NH -N) ratio gradually decreased, indicating reduced NO loss following secondary succession.
Soil N availability improves and NO leaching loss reduces following secondary succession after agricultural land abandonment in the KCZO.
农业用地废弃后的次生演替通常会影响氮（N）循环过程和生态系统的 N 状况。然而，在喀斯特生态系统中，对于次生演替后土壤 N 有效性和 NO3-流失潜力的变化还了解甚少。
在中国西南喀斯特关键带观测站（KCZO），采用时空替代法，选择耕地、灌草丛和次生林地来代表农业用地废弃后的三个次生演替阶段。分析了三个次生演替阶段的叶片、土壤和不同粒径团聚体的含量和 N 自然丰度（δ15N）。土壤有机氮（SON）在团聚体中的δ15N 组成和土壤与植物的 N 富集因子（EN = δ15N-δ15N），结合土壤无机 N 含量和δ15N 组成，用于指示次生演替后土壤 N 有效性和 NO3-流失潜力的变化。
次生演替后，叶片 N 含量和 SON 含量显著增加，表明土壤和植物中 N 的积累。SON 的δ15N 值也显著降低，主要受植物 N 组成和 N 矿化的影响。大团聚体中的 SON 含量和土壤 NH4+含量显著增加，而 NH4+的δ15N 值降低，表明 SON 的稳定性增加，土壤 N 有效性提高。次生演替后，叶片的δ15N 值、EN 值和（NO3--N/ NH4+-N）比值逐渐降低，表明 NO3-流失减少。
KCZO 农业用地废弃后的次生演替后，土壤 N 有效性提高，NO3-淋失减少。
