Light intensity influence maize adaptation to low P stress by altering root morphology

Abstract

Soil phosphorus (P) availability, as well as shoot P status, may alter root morphology. However, how root morphological traits to light intensity under various P environments remains unknown. Maize (Zea mays L.) cultivar CD418 grew under nine P application rates (ranged from 0 to 300 mg P kg−1 soil, supplied as KH2PO4) under natural light intensity (NL) and low light intensity (LL, 40% of natural light intensity) in a naturally-lit rain-shed. Plant growth, P uptake, and responses of root morphological traits (i.e. total root length, root surface area, and proportion of <0.2 mm diameter fine root) in the light and P treatments were assessed after 36 d of growth (five-leaf stage). Shoot and root dry weights increased under the natural light intensity in all P treatments. The ratio of root to shoot dry weight increased under NL when the soil Olsen-P was below 15.9 mg kg−1. At relatively low soil P availability (6.7 to 15.9 mg kg−1), total root length, root surface area, and fine root percentage were enhanced with increases in light intensity from LL to NL. These effects diminished in soil with either severely low P (2.6 mg kg−1) or excess P (above 20.6 mg kg−1). Express of the low P-tolerance transcription factor ZmPTF1 (that influences root growth by regulating carbon metabolism in leaves and roots), P uptake, and fertilizer P use efficiency were higher under NL than LL, especially under low P conditions (Olsen-P 6.7–15.9 mg kg−1). Increased responses of root morphological traits to low P conditions were associated with relatively low P concentrations in the leaves and high sucrose concentrations in the roots. Compared to LL, under P deficiency and NL conditions, maize allocated more photosynthates to roots as sucrose, which acts as a low-P signal; in addition, sucrose as a carbon and energy source stimulated root growth and, consequently, adaptation of maize to low P stress.