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Root Foraging Behavior of Two Agronomical Herbs Subjected to Heterogeneous P Pattern and High Ca Stress

Ecosystems are vulnerable to large areas of rocky desertification, which results in patchy soils and stone-inlaid soils. Karst landforms are typically characterized by heterogeneous phosphorus (P) distributions in soils at high calcium (Ca), but root foraging behavior has not been fully documented in agronomical plants. In this study, Bidens pilosa L. and Plantago asiatica L. were raised in pots in a simulated soil environment with sands at high Ca (2 g kg−1) and low Ca (0.63 g kg−1) levels. Inner spaces were divided into four sections to receive P in homogeneous (Homo.) (four quarters: 2 mg P kg−1) or heterogenous (Hete.) (one quarter: 8 mg P kg−1; three quarters: no-P input) patterns. Both species had longer roots in high P sections compared to no P sections. Foraging scale (highest length or surface-area(SA)) was higher in P. asiatica plants subjected to the Hete. pattern than to the Homo. pattern in low Ca pots. Foraging precision (length or SA differences between P patches as a proportion of the total) was also higher for P. asiatica subjected to the Hete. pattern but did not change in response to Ca level or P placement pattern. Overall, P. asiatica has a higher foraging ability than B. pilosa because of higher levels of foraging scale and precision from high-P (8 mg kg−1) patches in soils subjected to low Ca (0.63 g kg−1).