Effects of temperature on the growth of spring ephemerals: Crocus vernus

Spring ephemerals of deciduous forests appear shortly after snow melt and senesce shortly after the overstorey canopy has closed. During this short period, they take advantage of the high light conditions, but also of the low‐temperature regime that favours growth in these species. This better growth at cooler temperatures has been attributed to longer leaf life duration. The objective of this study was to test if temperature effect on growth in spring ephemerals can be explained solely by the leaf life duration, or if there is also a direct temperature effect on the underground organ growth. Crocus vernus (L.) Hill was exposed to two temperature regimes, 12/8 and 18/14°C (day/night), for sequential harvests and to four differential air to soil temperature regimes: 12/12, 12/18, 18/12 and 18/18°C (air/soil temperature). Dry mass, leaf nitrogen, starch concentration and cell size of the new corm were determined. Final dry mass and cell size were higher at the lower temperature regime while leaf lasted longer than at the higher temperature regime. Although both air and soil temperatures had an impact on the different growth parameters measured, the impact of soil temperatures was greater and it also influenced leaf life duration. At higher temperature, corm growth stopped before the first visual sign of leaf senescence, suggesting that corm growth controls leaf life duration in C. vernus rather than the opposite and that crocus growth becomes rapidly sink limited at higher temperatures.