Topsoil Stockpiling in Restoration: Impact of Storage Time on Plant Growth and Symbiotic Soil Biota


Addressing plant-soil relationships within restoration science may improve success and reduce costs. Here we assess the question of topsoil storage time: how does stockpile age impact plant biomass and soil microbial activity, particularly root symbionts such as rhizobia and arbuscular mycorrhizal fungi (AMF)? Working in Western Australia and in sandy soils, we grew a legume species Acacia saligna (Fabaceae) in one-, two-, three-, five- and ten-year-old stockpile soils under controlled glasshouse conditions. We assessed whether plant biomass, specific root length, and root diameter decreased with stockpile age. Further, we investigated how stockpile age affected the distribution and the number of effective nodules, nodule biomass and AMF colonization in roots. These above and belowground traits were chosen because they reflect the A. saligna response to growing in soils stockpiled for 1–10 years. We hypothesised that in older stockpiles there would be fewer rhizobial and AMF propagules which would constrain A. saligna growth, whereas in younger stockpiles there would be more rhizobial and AMF propagules, and A. saligna growth would be facilitated via these root symbionts. Using generalized linear mixed models, we found that total plant biomass was the lowest but AMF percent colonization was the highest when A. saligna was grown in ten-year-old soils, suggesting that AMF spores and hyphae are present in old stockpiles. Our results demonstrate that AMF communities may be initially disrupted by soil disturbance and storage, and then begin to re-establish between 5–10 years after stockpiling. However, other soil microbial communities, such as fungal pathogens that were not assessed in this study may have been responsible for decreased A. saligna biomass in older soils. Further research, particularly on other soil microbial communities, is needed to understand restoration success using stockpiled soil older than ten years.

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