Water-nutrient management enhances root morpho-physiological functioning, phosphorus absorption, transportation and utilization of cotton in arid region

Phosphorus (P) plays a key role in regulating plants physio-biochemical processes of plants and is indispensable for cotton production. However, the mechanism how does root morpho-physiological characteristics can affect P uptake, assimilation and use efficiency in different soil layers at various fertigation depths have not been studied. To fill this knowledge gap, a two-year pot experiment under field conditions was conducted to evaluate the effects of two irrigation levels, i.e., presowing irrigation (W80, 0.28 m3 water equivalent to 80 ± 5 % field capacity) and no presowing irrigation (W0, no water applied to the entire depth of the tube), and two basal fertilization methods [surface application (F10) and deep application (F30)] on root physiology, biomass accumulation, P uptake, transportation, and distribution in the cotton crop. The W80 treatment had 2.4–11.1% lower soil available P content (SAP) in the 0−50 cm soil layer but 6.1–14.4% higher SAP in the 60−120 cm soil layer than those in the W0 treatment. In the fertilization treatments, F10 had 0.35–17.0% greater SAP content in the 0−20 cm soil layer than F30. The W80F10 combination resulted in higher root length (RL) in the 0−20 cm soil layer, higher root acid phosphatase activity (ACP) in the 0−40 cm and 60−80 cm soil layers, and increased root phosphorus content (RP) in the 0−60 cm soil profile. W80F10 increased sap flow (SF), dry matter, and P accumulation in the reproductive organs compared with those in the other treatments. P utilization was positively associated with RL and root ACP in the 0−40 cm soil layer. Root ACP RL in the 0−40 cm soil layer and root ACP in the 60−80 cm soil layer were also positively related with SF, but SF had a negative relationship with RP in the 0−60 cm soil layer. In conclusion, presowing irrigation in conjunction with basal surface fertilization can increase P absorption and translocation by improving RL and ACP in the 0−40 cm and 60−80 cm soil layers before the full flowering stage. This also improves the competitive ability of the reproductive organs to access RP in the 0−60 cm soil layer, leading to higher P utilization in cotton.