Asymmetric pre-growing season warming may jeopardize seed reproduction of the sand-stabilizing shrub Caragana microphylla

Abstract

Our current understanding of the processes and mechanisms by which seasonal asymmetric warming affects seed reproduction in semiarid regions, which are essential in preserving the stability of both vegetation ecosystem structure and function, remains poorly understood. Here, we conducted a field warming experiment, including pre-growing season warming (W1), in-growing season warming (W2), and combined pre- and in-growing season warming (W3) treatments, to investigate the seed reproductive strategy of Caragana microphylla, an important sand-stabilizing shrub, from the perspective of reproductive phenology, reproductive effort, and reproductive success. Results show that the warming treatments advanced the initial stages of reproductive phenology, prolonged its duration, and decreased its synchrony (magnitude = W3 > W2 > W1). Additionally, flowering phenology was more sensitive to warming than podding phenology. The W1 treatment inclined seed reproduction towards the conservative strategy with low reproductive effort and success. The W3 treatment tended to increase seed reproductive effort and success. While the W2 treatment did not affect reproductive success, it did increase reproductive effort. Changes in reproductive phenology explained 20 % of the variation in reproductive effort and 38 % of the variation in reproductive success. However, these changes also directly hindered reproductive success (direct effect = −0.57) while indirectly promoting reproductive success (indirect effect = 0.27) by increasing reproductive efforts. Our results reveal that the seasonal asymmetry of warming altered the seed reproduction strategy of sand-stabilizing shrubs, with warmer winters and springs before the growing season decreasing seed fecundity.