Leaf manganese and phenolics as proxies of soil acidification and phosphorus acquisition mechanisms in lentil cultivars on alkaline soil.

Leaf manganese (Mn) concentration has been used as a proxy for root exudation and phosphorus (P) uptake under controlled conditions, but there are limited field studies that confirm its validity. On an alkaline, P-poor soil, four lentil cultivars ('Samos', 'Thessaly', 'Flip', 'Algeria') received two P rates (0 and 26.2kgPha-1 ), for two growing seasons, to study whether aboveground assessments [leaf P, Mn, phenolic concentration (TPhe)] can approximate rhizosphere physiological traits related to P acquisition [soil acidification (ΔpH), arbuscular mycorrhizal fungi (AMF) colonisation, acid phosphatase activity (APase)]. Phosphorus addition had no effect on the determined traits. Cultivars differed in leaf P, Mn, TPhe and AMF, but there was no clear pattern relating aboveground traits to rhizosphere traits related to P acquisition, thus not confirming that leaf Mn can be a proxy of root exudation. Of three growth stages [V 7-8, R1 (first bloom), R4 (flat pod)], R1 seemed to be critical, showing the highest leaf P, ΔpH, AMF and TPhe. Precipitation and temperatures over the growing season were determinants of lentil responses affecting rhizosphere activity, soil P availability and finally leaf traits. In conclusion, in lentil on alkaline and P-limiting soils, high leaf Mn and phenolic concentration are not reliable indicators of rhizosphere P-acquiring mechanisms.

Phosphorus fertilisation may induce Zn deficiency in cotton (Gossypium hirsutum) on calcareous Mediterranean soils.

On a P-poor, calcareous soil, three upland cotton (Gossypium hirsutum L.) cultivars (ST 402, ST 405, Zeta 2) were tested for 2years under three P rates (0, 13.1, 26.2kgPha-1 ). Leaf traits (SPAD values; specific leaf area, SLA; carbon isotope discrimination, Δ; 15 N natural abundance, δ15 N) and elements (N, P, K, C, Na, Zn) along with arbuscular mycorrhizal (AM) colonisation were measured at first open flower, full bloom and first open boll stages. Phosphorus addition decreased yield, but had no effect on fibre quality, a response attributed to P-induced Zn deficiency, previously reported for cereals. The best-performing cv., ST 405, had high SPAD and SLA, but the lowest P, N and Zn concentrations, an indication of cultivar's high use efficiency for these nutrients. At full bloom, SPAD was lowest, while SLA was highest. AM increased gradually with growth stages, while N, P, K and Zn concentrations showed an opposite trend, possibly due to a dilution effect. On Mediterranean calcareous soils, P fertilisation should take into account soil Zn levels in order to avoid P-Zn antagonistic relationships, which could impact negatively on yield.