Context-dependent plant responses to soil conditioning and irradiation across contrasting land-use legacies in an Atlantic Forest–Cerrado ecotone

Plant responses to prior soil conditioning depend on plant identity and soil context, yet how these responses vary among soils with contrasting land-use soil histories remains uncertain. We tested how experimental soil pool, plant conditioning, and gamma irradiation affected plant biomass, foliar chemistry, and microbial gene-copy abundance in soils from an Atlantic Forest–Cerrado ecotone. Two greenhouse experiments used one composite soil pool from each of three land-use histories: primary forest, secondary forest, and long-term pasture. In Experiment 1, soils were conditioned by Cecropia pachystachya , Cedrela fissilis , or Copaifera langsdorffii , and C. fissilis was then used as the phytometer. In Experiment 2, irradiated and non-irradiated soils were conditioned with Urochloa brizantha cv. Piatã before the three native tree species were grown. Biomass, foliar nutrients, and qPCR gene-copy abundances for archaeal and bacterial 16S rRNA and phoD genes and fungal ITS region based on genomic soil DNA were analyzed using factorial models and planned contrasts. In Experiment 1, biomass varied among soil pools and conditioning species, but none of six heterospecific-versus-conspecific conditioning contrasts was significant after multiplicity adjustment. In Experiment 2, U. brizantha biomass was greater in irradiated soil, whereas native-tree responses depended on experimental pool, irradiation, and species; in pasture-derived soil, all three native species produced more biomass in non-irradiated soil. Foliar nutrient profiles showed supported pairwise interactions, while molecular soil microbial results were interpreted cautiously because of persistent non-detections after repeat qPCR assays and influential observations. Plant responses to conditioning and irradiation were context dependent and plant specific. The results support treatment-level differences within the three experimental soil pools but not general land-use effects or microbial causation.