Plants have evolved photoprotective mechanisms in order to counteract the damaging effects of excess light in hyper-arid desert environments. We evaluated the impact of surface canopy positions on the photosynthetic adjustments and chlorophyll fluorescence attributes (photosystem II photochemistry, quantum yield, fluorescence quenching, and photon energy dissipation), leaf biomass and nutrient content of sun-exposed leaves at the south east (SE canopy position) and shaded-leaves at the north west (NW canopy position) in the invasive Prosopis juliflora and native Prosopis cineraria in the extreme environment (hyper-arid desert area, United Arab Emirates (UAE)). The main aim of this research was to study the photoprotection mechanism in invasive and native Prosopis congeners via the safe removal—as thermal energy—of excess solar energy absorbed by the light collecting system, which counteracts the formation of reactive oxygen species. Maximum photosynthetic efficiency (F_v/F_m) from dark-adapted leaves in P. juliflora and P. cineraria was higher on NW than SE canopy position while insignificant difference was observed within the two Prosopis congeners. Greater quantum yield was observed in P. juliflora than P. cineraria on the NW canopy position than SE. With the change of canopy positions from NW to SE, the reduction of the PSII reaction center activity in the leaves of both Prosopis congeners was accelerated. On the SE canopy position, a significant decline in the electron transport rate (ETR) of in the leaves of both Prosopis congeners occurred, which might be due to the blockage of electron transfer from QA to QB on the PSII acceptor side. On the SE canopy position; Prosopis leaves dissipated excess light energy by increasing non-photochemical quenching (NPQ). However, in P. cineraria, the protective ability of NPQ decreased, which led to the accumulation of excess excitation energy (1 − qP)/NPQ and the aggravation of photoinhibition. The results also explain the role of different physiological attributes contributing to invasiveness of P. juliflora and to evaluate its liaison between plasticity of these characters and invasiveness.

中文翻译：

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表面冠层的位置决定了阿联酋沙迦沙漠中入侵和原生Prosopis同系动物的Photosystem II光化学

植物已经进化出光保护机制，以抵消在超干旱沙漠环境中过量光的破坏作用。我们评估了表面冠层位置对东南部（SE冠层）光合调节和叶绿素荧光属性（光系统II光化学，量子产率，荧光猝灭和光子能量耗散），叶片生物量和营养成分的影响。极端环境（阿拉伯联合酋长国（阿拉伯联合酋长国）的高干旱沙漠地区）的侵入性Prosopis juliflora和原生Prosopis cineraria中西北的阴影叶子（NW树冠位置）。这项研究的主要目的是研究侵入性和天然的光保护机制。Prosopis可以通过安全地去除集光系统吸收的多余太阳能（作为热能）而产生热量，从而抵消了活性氧的形成。最大的光合效率（F _v / F_米从在暗适应叶）P. juliflora和P.瓜叶菊上NW比SE篷位置较高而被两个内观察到差异不显着牧豆同源。在西北冠层位置，在胡桃李上观察到的瓜产量比在瓜胡瓜上更大。随着冠层位置从西北向SE的变化，两个Prosopis叶片中PSII反应中心活性的降低同族人被加速。在SE冠层位置，两个Prosopis同系物的叶片中的电子传输速率（ETR）发生了显着下降，这可能是由于PSII受体一侧从Q A到Q B的电子转移受阻。在SE天篷位置；Prosopis叶片通过增加非光化学猝灭（NPQ）消散了多余的光能。然而，在灰霉病中，NPQ的保护能力降低，这导致过量的激发能（1-qP）/ NPQ的积累和光抑制的加剧。结果还解释了不同生理特性对胡桃李侵袭性的作用。 并评估其在这些特征的可塑性与侵袭性之间的联系。