Acid rain remains a global environmental issue that can indirectly impact plant root growth and health by mediating soil acidification. The impact of acid rain on the roots of Jatropha curcas L., however, has not been thoroughly evaluated to date in soils with a range of buffering capacities. We, therefore, explored the ability of J. curcas roots to tolerate acid rain in a range of soil types by exposing samples to simulated acid rain (SAR) (pH2.5, pH3.5, pH4.5, pH5.6) and then examining the impact of such exposure on root morphology, relative growth rate (RGR(root)), nutrient absorption, enzymatic activity, and microbial biomass. Yellow-brown soil (YBS) and purple soil (PS) were found to be better able to buffer SAR-mediated acidification, thereby providing superior benefits to J. curcas root growth as compared to red soil (RS) and yellow soil (YS) under these experimental conditions. SAR (pH 4.5) significantly enhanced Ca, K, and Mg absorption by J. curcas roots, thereby improving their growth characteristics, whereas SAR (pH 2.5) impaired K and Mg absorption and thus suppressed root growth. K and Mg absorption characteristics were regulated by changes in plasma membrane H + -ATPase activity under these different SAR treatment conditions. Morphological and growth (RGR(root)) adaptations of J. curcas roots to SAR treatment were associated with superoxide dismutase activity levels therein. SAR (pH 4.5) was sufficient to bolster the rhizosphere microbial activity of J. curcas seedlings, and correlation analyses revealed that root growth was regulated by rhizosphere microbial biomass P content under SAR treatment conditions.
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