Photochemical activity modulated by water, nitrogen, and phosphorus status in cactus pear

ABSTRACT This study aimed to evaluate the effects of nitrogen (N) and phosphorus (P) associated with dry and rainy seasons on the photochemical activity of Opuntia ficus-indica (L.) Mill. cv. Gigante. Combinations of N (10.0, 70.0, 100.0, 130.0, and 190.0 kg ha−1 yr−1) and P2O5 (10.0, 70.0, 100.0, 130.0, and 190.0 kg ha−1 yr−1) were evaluated in the dry and rainy seasons in semi-arid regions. A completely randomized block design with split-plot arrangement was adopted with four replications. In Quixadá, the maximum potential quantum efficiency of photosystem II (Fv/Fm) was 0.82, observed in third-order cladodes (rainy season and N/P 75.6/10.0 kg ha−1 yr−1), while in Tejuçuoca, the maximum Fv/Fm was 0.81, found in 2nd/3rd order cladodes (rainy season and N/P 10.0/190.0 kg ha−1 yr−1). In Quixadá, the maximum electron transport rate (ETR) was 31.6 μmol m−2 s−1 in 2nd/3rd order cladodes (rainy season and N/P 10.0/190.0 kg ha−1 yr−1), and in Tejuçuoca, the maximum ETR was 24.1 μmol m−2 s−1, in second-order cladodes (rainy season and N/P 110.1/10.0 kg ha−1 yr−1). In Quixadá and Tejuçuoca, higher values of Fv/Fm and ETR were observed in the rainy season. In Quixadá, the maximum fluorescence decrease ratio (FDR) was 4.04 in third-order cladodes (rainy season and N/P 10.0/114.8 kg ha−1 yr−1), while in Tejuçuoca, the maximum FDR was 6.93, found in 2nd/3rd order cladodes (rainy season and N/P 190.0/10.0 kg ha−1 yr−1). In Quixadá and Tejuçuoca, there was predominance of higher FDR values in the rainy season. Nitrogen, phosphorus, and water status modulate the photochemical efficiency of cladodes of cactus pear cv. Gigante in semi-arid regions.**摘要** 本研究旨在评估氮（N）、磷（P）配合旱季与雨季对梨果仙人掌（*Opuntia ficus-indica* (L.) Mill.）‘Gigante’（巨人）品种光化学活性的影响。在半干旱地区的旱季与雨季中，设置了梯度为10.0、70.0、100.0、130.0、190.0 kg·ha⁻¹·yr⁻¹的氮素与五氧化二磷（P₂O₅）组合处理，对二者的组合效应进行评估。本试验采用裂区排列的完全随机区组设计，设置4次重复。在基沙达（Quixadá），光系统II（Photosystem II）最大潜在量子效率（Fv/Fm）的最大值为0.82，出现在三级茎片（雨季、氮/磷配比75.6/10.0 kg·ha⁻¹·yr⁻¹）；而在特茹苏奥卡（Tejuçuoca），最大Fv/Fm为0.81，出现在2/3级茎片（雨季、氮/磷配比10.0/190.0 kg·ha⁻¹·yr⁻¹）。在基沙达，电子传递速率（ETR）的最大值为31.6 μmol·m⁻²·s⁻¹，出现在2/3级茎片（雨季、氮/磷配比10.0/190.0 kg·ha⁻¹·yr⁻¹）；在特茹苏奥卡，ETR最大值为24.1 μmol·m⁻²·s⁻¹，出现在二级茎片（雨季、氮/磷配比110.1/10.0 kg·ha⁻¹·yr⁻¹）。在基沙达与特茹苏奥卡两地，雨季的Fv/Fm与ETR值均更高。在基沙达，荧光下降比值（FDR）的最大值为4.04，出现在三级茎片（雨季、氮/磷配比10.0/114.8 kg·ha⁻¹·yr⁻¹）；而在特茹苏奥卡，最大FDR为6.93，出现在2/3级茎片（雨季、氮/磷配比190.0/10.0 kg·ha⁻¹·yr⁻¹）。两地均呈现雨季的FDR值占优的特征。氮、磷与水分状况可调控半干旱地区梨果仙人掌‘Gigante’（巨人）品种茎片的光化学效率。