Asymmetric Pre-Growing Season Warming Decreased Seed Fecundity of Sand-Stabilizing Shrub in Sandy Land of Northern China

Abstract

Asymmetric warming in semi-arid lands is affecting plant sexual reproduction, with implications for the stability of vegetation ecosystem structure and function. However, the merits and demerits of seasonal asymmetric warming on seed reproduction remain poorly understood. Therefore, we conducted a field simulated warming experiment including pre-growing-season warming (W1), growing-season warming (W2), and full-time warming (W3), and explored the seed reproductive strategy of sand-stabilizing shrub Caragana microphylla from the perspective of reproductive phenology (RP), reproductive effort (RE) and reproductive success (RS). The results showed that warming significantly advanced the initial stages of reproductive phenology, slightly delayed its end stages, significantly prolonged its duration, and significantly decreased its synchrony between flowering and podding, and these phenology changes were W3 > W2 > W1 in magnitude. Flowering phenology was more sensitive to warming than podding phenology. W1 inclined seed reproduction to a conservative strategy with low RE and low RS, but W3 tended to simultaneously increase its RE and RS. W2 did not significantly affect RS, but increased RE. PLS-SEM model showed that RP changes explained 20% of the variation in RE and 38% of the variation in RS. RP not only directly promoted RE (direct effect = 0.45) and hindered RS (direct effect = -0.57), but also indirectly promoted RS (indirect effect = 0.27) by affecting RE. Our study differentiates and quantifies the impact of seasonal asymmetric warming on sexual reproductive traits of sand-stabilizing shrub in the sandy land of northern China, and highlights that warmer winter and spring could decrease seed fecundity, although asymmetric climate warming overall favors seed reproduction.

Keywords: Asymmetric warming, Growing season, Sand-stabilizing shrub, Reproductive phenology, Seed reproduction