Low sink demand caused net photosynthetic rate decrease is closely related to the irrecoverable damage of...

Source sink balance is one of the major determinants of carbon partitioning in plants. However, its effects on photosynthesis in fruit trees are largely unknown. In this work, the effects of low sink demand on net photosynthetic rate (P_n) and chlorophyll fluorescence after fruit removal (-fruit) in peach (Prunus persica (L.) Batsch cv. 'Zaojiubao') trees were investigated. The stepwise energy flow through photosystem II (PSII) at the reaction center (RC) was analyzed with quantitative analyses of fluorescence transient, also called JIP-test. We found that P_n was significantly lower and closely correlated to the leaf stomatal conductance (G_s) of -fruit trees than that of fruit retained (+fruit) trees. Leaf temperature (T_leaf) of -fruit trees was remarkably higher than that of +fruit trees. Day-time-period assays of chlorophyll (Chl) fluorescence revealed that, in the leaves of -fruit trees, the fluorescence parameters, such as NPQ (non-photochemical quenching coefficient) and ΦD₀ (maximum quantum yield of non-photochemical de-excitation), decreased in the morning and recovered to the normal level in the afternoon, whereas other parameters, such as ΦE₀ (quantum yield for electron transport at t = 0), Ψ₀ (probability that a trapped exciton moves an electron to Q_A pool), F₀ (minimum fluorescence, when all PSII RCs are open) and W_k (relative variable fluorescence at 300 μs of the chlorophyll fluorescence transient), did not. These results suggest that OEC complex and Q_A pool were irreversibly affected by low sink demand, whereas light harvest antenna and PSII potential efficiency retained a strong ability to recover.