Effects of potassium application on performance of photosystemⅡof various Bt cotton genotypes

Objectives The paper studied the fluorescence dynamics of functional leaves of Bt cotton genotypes under the condition of potash fertilization, to provide a scientific basis for K fertilizer application in Bt cottons.

Methods Field experiments were carried out at Shandong Agricultural University Experimental Station during 2016−2017. Three cotton genotypes, DP99B, L21 and J169 were chosen, and two treatments of no K fertilization (CK) and application of K₂SO₄ 240 kg/hm² (K) were used in the experiments. Samples of functional leaves were collected during the budding stage of cotton. The net photosynthetic rate (P_n), stomatal conductance (G_s) and chlorophyll content were measured using LI-6400XT potable photosynthesis system. The chlorophyll fluorescence transients were measured using multiple plant efficiency meter (M-PEA Hansatech), including the excitation energy of light absorbed by excited cross section of PSII reaction center (TR_o/CS_m), the number of active reaction centers (RC/CS_m), probability of an electron moving from Q_A to Q_B (Ψ_o) and the performance index of absorption basis (PI_abs). The related parameters of the dynamics of the photosystemⅡperformance (OJIP) were analyzed using JIP-test.

Results The basal application of K fertilizer significantly increased net photosynthetic rate (P_n), stomatal conductance (G_s), chlorophyll content, excitation energy of light absorbed by leaf area per PSII reaction center (TR_o/CS_m), number of active reaction centers (RC/CS_m), probability of an electron moving from Q_A to Q_B (Ψ_o), performance index of absorption basis (PI_abs). At the same time, application of K fertilizer significantly reduced the heat dissipation energy per unit reaction center (DI_o/RC), the ratio of a variable fluorescence F_k to the amplitude F_o-F_j (W_k) and the ratio of a variable fluorescence F_j to the amplitude F_o-F_p (V_j). After potassium fertilization, the net photosynthetic rate (P_n) was increased significantly by 9.60%, 19.84%, 11.85% in 2016 and by 9.14%, 18.48%, 9.60% in 2017, and the performance index (PI_abs) was also increased significantly by 10.79%, 17.93% and 14.04% for Bt cotton genotype DP99B, L21 and J169, respectively.

Conclusions Potassium fertilizer application is beneficial to improve the performances of electron donor and acceptor in PSII reaction center of various Bt cotton genotypes, and the performance of the electron transfer chain at the electron acceptor side of the PSII reaction center was also improved. Thus, potassium fertilizer application could effectively improve the overall performance of PSII and ultimately enhanced the photosynthetic capacity of different cotton genotypes. L21 showed better responsive effect to potassium fertilization than DP99B and J169. Thus, rational potassium fertilization in actual cotton production should consider the sensitivity of different genotypes to potassium fertilization.