Field Crop 2025, Vol.8, No.3, 126-138 http://cropscipublisher.com/index.php/fc 127 sativum), and mung beans (Vigna radiata). Their respective distributions also have some differences: soybeans and peanuts are more commonly grown in rain-grown areas in northern China, while peas and mung beans are more frequently found in dryland systems in Northwest and North China. When evaluating drought tolerance, it is not just about looking at one aspect, but taking into account the entire growth process from seed germination to flowering and podding to observe the overall impact of drought on phenotypes and yields (Ali et al., 2018). As for the experimental environment, all the selected ones were typical rain-fed farmlands, which have distinct characteristics-little rainfall, uneven rainfall, light soil and high evaporation. For instance, in the Horqin Sandy Land of Inner Mongolia, the climate is a typical temperate continental monsoon: summers are short and hot with scarce rainfall, and spring and autumn are dry and windy. Such an environment is precisely the touchstone to test whether beans can withstand drought (Zhang et al., 2012). The research adopts multi-point experiments. In other words, it covers different ecological conditions to clearly see whether the drought tolerance of each variety is stable and adaptable under the interaction of genotype and environment (Yan et al., 2015). In rain-fed environments, the differences in drought resistance among legume varieties can be seen at a glance. Some can still maintain their output during water shortages and perform quite steadily, but there are also many varieties that fail as soon as there is a drought. Generally speaking, drought-tolerant plants often have more advantages in water retention, photosynthetic efficiency or antioxidant reactions, but this is not an absolute rule. In the research, some quantitative indicators were attempted to make judgments, such as drought resistance index and yield stability parameters, etc. However, after comparison, it was found that the results of several methods did not always match (sometimes the differences were quite significant). One more point that is easily overlooked is that the interaction between the environment and genotypes is sometimes more prominent than the main effect of the variety itself. This means that when promoting, merely focusing on the variety name is unreliable; different ecological regions require a different approach. Overall, these findings, on the one hand, explain the physiological and ecological reasons behind the differences, and on the other hand, provide some practical references for drought-resistant breeding and the management of arid areas. 2 Theoretical and Conceptual Framework 2.1 Drought tolerance mechanism and physiological and ecological basis The drought tolerance of leguminous crops is not the result of a single link, but rather the accumulation of multiple levels of action: the adjustment of morphological structure, the regulation of physiological state, and the coordination of molecular and biochemical mechanisms. First, let's look at the shape. Drought-tolerant varieties usually have more developed root systems that can penetrate deep into the soil to absorb water. Their leaves are often smaller, with thicker cuticle layers, and thus less transpiration. Studies have found that the root cap of drought-resistant types is generally higher than that of sensitive varieties, and their root systems are more capable of exploring downward during droughts (Vadez et al., 2008). Looking at the physiological responses, the common ones are stomata and osmotic regulation. During droughts, some varieties will partially close their stomata earlier to control water loss while still maintaining a relatively high water use efficiency (WUE). Some will adopt a "throttling" strategy when the atmosphere is particularly dry. Stomata are more sensitive to vapor pressure loss. By moderately reducing the rate of light formation, soil moisture can be saved in exchange for future use. Meanwhile, osmotic regulation is also at work. Small molecules such as proline and soluble sugars accumulate, reducing the water potential of cells and helping to maintain a relatively high water content (Zhang and Shi, 2018). Finally, at the biochemical level, the efficiency of the antioxidant enzyme system is often higher in drought-tolerant varieties, such as superoxide dismutase (SOD) and peroxidase (POD), which can eliminate excessive reactive oxygen species (ROS) produced under drought conditions, thereby reducing the peroxidation damage of membrane lipids (Ahmad et al., 2022). 2.2 Key evaluation indicators and index system Evaluating the drought tolerance of legume varieties cannot rely on a single indicator; usually, a relatively comprehensive system needs to be established. Common practices can be divided into two categories: yield type and physiological and ecological type. Output types include relative output, reduction rate, drought resistance coefficient, etc. Among them, the drought resistance coefficient measures the degree of reduction by the ratio of
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