Abstract

Climate warming is occurring asymmetrically in the Northern Hemisphere, with more warming in winter than summer. This asymmetric warming may have profound impacts on plant phenology and reproduction, particularly in cold regions. Caragana microphylla, a sand-stabilizing shrub widely distributed in semi-arid regions of northern China, is highly sensitive to temperature changes. To understand how asymmetric warming affects the seed reproduction of C. microphylla, we conducted a three-year field experiment with warming treatments applied during different seasons (winter warming, summer warming, and uniform warming). Our results showed that asymmetric warming significantly altered the phenology and reproductive traits of C. microphylla. Winter warming advanced flowering and fruiting time, increased fruit set and seed production, and accelerated seed germination. In contrast, summer warming delayed flowering and fruiting time, reduced fruit set and seed production, and slowed down seed germination. Uniform warming had intermediate effects on the phenology and reproductive traits of C. microphylla. Our findings suggest that asymmetric warming may have significant implications for the reproductive success and population dynamics of C. microphylla, with winter warming potentially promoting its growth and reproduction, while summer warming may have negative impacts. These findings highlight the importance of considering the seasonal specificity of warming when predicting the impacts of climate change on plant reproduction and ecosystem dynamics in cold regions.

Keywords: Asymmetric warming; Caragana microphylla; Climate change; Phenology; Reproductive traits; Seed reproduction.