Warming results in advanced spring phenology, delayed leaf fall, and developed abnormal shoots in Pinus densiflora seedlings

Abstract

We investigated the effects of warming and precipitation manipulation on phenology (spring phenology, leaf fall, and abnormal shoot phenology) in Pinus densiflora, which is an evergreen species with fixed-growth. In an open-air nursery, 2-year-old P. densiflora seedlings were planted in April 2013 and treated with 6 treatments (n=3) [2 temperature levels: + 3 degrees C (TW) and control (TC); 3 precipitation levels: + 30% (PI), - 30% (PD), and control (PC)]. We observed spring and abnormal shoot phenology in 2014 and 2015, and measured dry weight of fallen leaves in 2015. Phenology was not changed by precipitation manipulation. In spring phenology, budburst was advanced by 9.4-9.6 days under warming, but timing of leaf appearance and growth did not changed. Cumulative weight of fallen leaves was 25.8-28.6% lower in TW plots than in TC plots between July and December 2015. There were no significant differences in occurrence rates of abnormal shoots among plots. 65.7-96.8% of abnormal shoots remained at the budburst stage in TC plots, while abnormal shoots in TW plots further developed to the leaf appearance and growth stages. Abnormal shoot development stopped 10.5-28.8 days later in TW plots than the TC plots in 2014 and 2015. Effects of warming were evident only in budburst, because leaf appearance and growth were affected by fixed-growth characteristics as well as warming. Decreased leaf fall and further developed abnormal shoots could be interpreted as delayed leaf senescence and extended growing season, respectively, for an evergreen species with fixed-growth.