Physiological responses of the beet crop under agricultural environment and saline stress

Abstract The deleterious effects of salts on plants exposed to high solar radiation tend to be more accelerated due to the increase of toxic ions in the aerial plant part. Consequently, the physiological and biochemical processes will be affected. These effects can be minimized, however, with the use of management strategies, such as the use of a shading screen and a protected environment. In this sense, the objective of this work was to evaluate the physiological responses of sugar beet cultivated in different environments and irrigated with saline water. The experiment was conducted in an experimental design entirely randomized, using the factorial scheme 3 × 2, equivalent to three environments (FS = full sun; SSOS = shading screen open on the sides and PE = protected environment) and two electrical conductivities of the irrigation water (0.5 and 6.2 dS m-1), with four repetitions. At 45 days after sowing (DAS) the following variables were analyzed: stomatal conductance, liquid photosynthesis, transpiration, internal CO2 concentration, leaf temperature, instantaneous water use efficiency, instantaneous carboxylation efficiency, intrinsic water use efficiency, and relative chlorophyll index. Irrigation with water of higher salinity negatively affected stomatal conductance, net photosynthesis, leaf temperature and instantaneous water use efficiency of sugar beet plants grown in a full sun environment. The protected environment and open shading on the sides partially mitigated the deleterious effects of salinity.

**摘要** 当植物地上部分的有毒离子含量升高时，盐分对处于强太阳辐射环境下植物的有害影响会进一步加剧，进而干扰其生理与生化过程。不过通过遮阳网覆盖、保护性栽培环境等管理策略，可将此类负面影响降至最低。本研究旨在评估不同栽培环境下、经盐水灌溉的甜菜的生理响应。试验采用完全随机设计的3×2因子方案，设置3种栽培环境：全光照（Full Sun, FS）、侧边开放式遮阳网（Shading Screen Open on the Sides, SSOS）以及保护性栽培环境（Protected Environment, PE），同时设置2个灌溉水电导率梯度（0.5与6.2 dS·m⁻¹），每组设置4次重复。于播种后45天（Days After Sowing, DAS）测定以下生理指标：气孔导度、净光合速率（原表述为liquid photosynthesis，结合学术规范修正为标准术语）、蒸腾速率、胞间CO₂浓度、叶温、瞬时水分利用效率、瞬时羧化效率、内在水分利用效率以及相对叶绿素指数。结果表明，在全光照环境中，高盐度灌溉会对甜菜的气孔导度、净光合速率、叶温及瞬时水分利用效率产生显著抑制作用；而保护性栽培环境与侧边开放式遮阳网可部分缓解盐胁迫带来的有害影响。