UC Santa Cruz

As climate conditions become warmer and drier, there is an increased threat to agricultural productivity. Increased temperatures and reduced water availability can impede crop performance and reduce yields. However, the relative effects of drought on different crops and the consequences for yield is less well understood, specifically, the physiological and structural principles that underpin crop performance under water deficit. Understanding the limits of economically important crops, especially as growers transition towards more sustainable forms of agriculture, is critical. In order for these transitions to occur, it is useful to identify the crop varieties and the suite of traits that will allow them to thrive under limited resources. To identify these suite of traits that allow crops to survive under water deficit, I studied a combination of physiological, anatomical, and morphological traits in strawberries, tomatoes, and beans, grown under well-watered and water-deficit conditions. In the first chapter titled “Physiological and yield tradeoffs among ten strawberry (Fragaria x ananasssa Duch.) cultivars under reduced irrigation frequency”, I hypothesized that strawberry cultivars subjected to reduced water availability would have a variety of physiological traits that would lead to tradeoffs in drought resistance and hydraulic efficiency. To test this hypothesis, I compared physiological traits among 10 different cultivars of strawberries that were commercially grown at Driscoll’s Berries facilities under regular irrigation and a 50% decline in irrigation. I found that water stress consistently increased leaf thickness and fruit soluble solids (°Brix) while reducing stomatal conductance, phloem fraction, and fruit size, revealing trade-offs between water conservation and yield. In Chapter 2, “The structure-function tradeoffs of the dry-farm adapted, heirloom tomato Solanum lycopersicum L., var. Dirty Girl”, I build upon the results of Chapter 1 in a different system of sustainable agriculture called dry-farming. Dry-farming is a method for growing crops under little to no irrigation. I hypothesized that dry-farm adapted varieties of tomatoes have adapted to mitigate drought stress under minimal water input through a variety of physiological traits, such as increased resistance to embolism. To test this hypothesis, I compared two popular California varieties of organic tomatoes, the dry-farm-adapted Dirty Girl and the non-adapted Cherokee Purple, under irrigated and dry-farm conditions. I observed that dry-farming conditions reduced individual plant yield by 35.32% in Dirty Girl and 59.91% in Slicer, indicating a stronger decline in Slicer, although this difference is not statically supported by significant interaction dry-farmed. This result is bolstered by enhanced carbon acquisition traits in Dirty Girls, including greater plant height, which was supported by increased leaf vein density, and root vessel diameters, two proxies pointing to greater hydraulic conductance.. Concurrently, these plants expressed drought-tolerant traits such as a safer xylem network (smaller stem vessel diameters), increased leaf thickness (leaf mass per area), increased resistance to leaf wilting (lower water potential at turgor loss point), and increased embolism resistance in stems. To expand on the novel research of dry-farming, Chapter 3, “The physiological tradeoffs of dry-farm adapted Phaseolus vulgaris L. (common bean) varieties”, further investigates the traits I observed in Chapter 2. However, this study focuses on a two-year experiment with three varieties of common bean, which rely on water to form below ground associations with nitrogen-fixing bacteria. Like Chapter 2, I grew different bean varieties (Hopi, Black, and Green) under irrigated and dry-farmed conditions to test the hypothesis that dry-farm adapted varieties have adapted to mitigate drought stress through a variety of physiological traits. Across both years, dry-farming significantly reduced yield in all varieties despite shifts in anatomical traits associated with drought tolerance, with more pronounced effects in 2024, a warmer growing season. However, Hopi beans invested more carbon resources toward reproductive output, resulting in the highest dry mass per pod across all varieties, treatments, and years. Overall, this work explores the importance of studying physiology, morphology, anatomy, and soil traits of multiple crop varieties in the context of sustainable agriculture. The information obtained in this project is essential for informing future breeding work and farming management.