Ferraz Tiago Massi, de Oliveira Maia Júnior Sebastião, de Souza Guilherme Augusto Rodrigues, Baroni Danilo Força, Rodrigues Weverton Pereira, de Sousa Elias Fernandes, Penchel Ricardo, Loos Rodolfo, de Assis Figueiredo Fábio Afonso Mazzei Moura, Rakocevic Miroslava, Campostrini Eliemar
Department of Zootechnics, State University of Maranhão, São Luís, MA, Brazil.
Plant Physiology Department, LMGV, Agricultural Science and Technology Center, State University of North Fluminense, Av. Alberto Lamego, 2000, Campos dos Goytacazes, RJ 28013-602, Brazil.
Tree Physiol. 2025 Jan 25;45(1). doi: 10.1093/treephys/tpae160.
Measuring ecophysiological responses of Eucalyptus clones grown under reduced water availability could assist in clonal selection for climate resilience. We hypothesized that clonal variation in chlorophyll a fluorescence was more readily detected than variations in leaf-level gas exchanges when 2-year-old Eucalyptus grandis W.Hill ex Maiden × Eucalyptus urophylla S.T. Blake hybrid clones (C1, C2, C3 and C4) grown under rainfed (RF) and water-restricted (WR) conditions were evaluated during dry and rainy seasons, in the morning and midday diurnal periods. The C2 clone was the most drought tolerant as it had a similar net CO2 assimilation rate (A) considering the RF and WR conditions at midday during the dry season, while C1, C3 and C4 CO2 assimilation rates (A) decreased by 29.1%, 28.3% and 13%, respectively. This response was associated with a reduction to a lesser extent in leaf water potential, stomatal conductance (gs) and transpiration rates (E) (ca 10%, 30% and 13% under WR, respectively), when compared with the other clones during the dry season at midday. The lower leaf to air vapor pressure deficit of C2 contributed to its greater water-use efficiency (WUE), resulting in greater total dry mass gain. C1, C3 and C4 were less drought tolerant, decreasing gs, E and especially A under WR, resulting in lower WUE and total dry mass gain. Chlorophyll a fluorescence indexes were better indicators of drought tolerance compared with gas exchange parameters in definition of drought tolerance of clonal Eucalyptus. Three drought-sensitive clones showed low photochemical efficiency under WR, with the electron transport rate being impaired between photosystems II and I, indicated by the greater changes in photosynthetic performance index (PIabs). Under WR conditions, Fv/Fm, Ψ0, ΦE0 and PIabs decreased in all clones while ΦD0 and DI0/CS0 increased, with C2 showing the most stable responses suggesting that the photochemical apparatus was the less damaged by drought. Thus, C2 was the best clone for regions with water scarcity.
测量在水分供应减少条件下生长的桉树无性系的生理生态响应，有助于进行适应气候变化的无性系选择。我们假设，当在旱季和雨季的上午和中午对2年生的巨桉（Eucalyptus grandis W.Hill ex Maiden）×尾叶桉（Eucalyptus urophylla S.T. Blake）杂交无性系（C1、C2、C3和C4）在雨养（RF）和水分受限（WR）条件下生长进行评估时，叶绿素a荧光的无性系变异比叶片水平气体交换的变异更容易被检测到。C2无性系是最耐旱的，因为在旱季中午，考虑到RF和WR条件，其净二氧化碳同化率（A）相似，而C1、C3和C4的二氧化碳同化率（A）分别下降了29.1%、28.3%和13%。与旱季中午的其他无性系相比，这种响应与叶片水势、气孔导度（gs）和蒸腾速率（E）在较小程度上的降低有关（WR条件下分别约为10%、30%和13%）。C2较低的叶-气蒸汽压差有助于其更高的水分利用效率（WUE），从而导致更大的总干物质积累。C1、C3和C4的耐旱性较差，在WR条件下gs、E尤其是A下降，导致WUE和总干物质积累较低。在定义无性系桉树的耐旱性方面，与气体交换参数相比，叶绿素a荧光指数是更好的耐旱性指标。三个干旱敏感无性系在WR条件下表现出低光化学效率，光合系统II和I之间的电子传递速率受损，光合性能指数（PIabs）变化更大表明了这一点。在WR条件下，所有无性系的Fv/Fm、Ψ0、ΦE0和PIabs均下降，而ΦD0和DI0/CS0增加，C2表现出最稳定的响应，表明光化学装置受干旱损害较小。因此，C2是缺水地区的最佳无性系。
