Phosphorus-fertilisation has differential effects on leaf growth and photosynthetic capacity of Arachis hypogaea L.

Abstract

The objectives of this study were to assess how Arachis hypogaea L. (peanut or groundnut) responds to different P supplies in terms of growth and photosynthesis, and to determine the optimum P supply and differential P stress thresholds. We investigated biomass production, leaf expansion, photosynthetic parameters, relative chlorophyll concentration, P700 parameters and chlorophyll fluorescence in a climate-controlled chamber at different P supplies (0.1, 0.5, 1, 1.5, 2 mM). Both deficient and excessive exogenous P supplies significantly reduced leaf growth, relative chlorophyll concentration and dry matter production in two high-yielding peanut cultivars. The optimum P range was 0.8–1.1 mM for peanut seedlings. Through principal component analysis (PCA) and data fitting, we found that the trade-off of the normalised actual quantum yield [Y(II)] and non-regulatory quantum yield [Y(NO)] in photosystem II (PSII) under light is one of the best proxies to determine the suboptimal, supraoptimal, deficient and toxic P supplies, because they are the two key factors with major positive and negative effects of PC1, accounting for 75.5% of the variability. The suboptimal P range was 0.41–0.8 mM and the supraoptimal P range was 1.1–1.72 mM. The suboptimal P supplies corresponded with a leaf P concentration range of 4.8–8.1 mg P g−1 DW, while the supraoptimal P supplies corresponded with a leaf P concentration range of 9.9–12.2 mg P g−1 DW. Both deficient and toxic P levels severely inhibited leaf growth and photosynthesis of peanut, and these unfavourable conditions were associated with significant reduction of biomass and photosynthesis, and photodamage extending beyond PSII. The trade-off of the normalised Y(II) and Y(NO) is a useful benchmark to demarcate deficient, suboptimal, supraoptimal and toxic P-fertilisations levels in A. hypogaea.