Age‐mediation of tree‐growth responses to experimental warming in the northeastern Tibetan Plateau

Abstract

The trajectory of tree‐growth response to climate warming may be related to attributes like tree age. However, age‐mediation of temperature sensitivity of tree growth has received little attention. This study aimed to determine how age affects tree growth in a future warmer world. In a 2‐year ecosystem warming experiment in the northeastern Tibetan Plateau of China, we explored the response of Qinghai spruce saplings at two life stages to two warming levels. Our results indicated a significant interaction between warming and age for sapling growth of Qinghai spruce. In high‐level warming scenario, the experiment increased growing season air temperatures by approximately 1.0°C and annual growing degree‐days by 38%. In response, warmed saplings lengthened the growing season by 10 days on average and increased the final shoot length to a maximum of 104% compared to control groups. Comparison of age classes revealed that old saplings exhibited significantly higher temperature sensitivity than young saplings. This performance may be caused by the differences in adaptive strategy to the asymmetric warming occurring during the whole day. Increased daytime temperature was expected to significantly enhance leaf photosynthesis, whereas lack of obvious nighttime warming would effectively restrict autotrophic respiration, thus resulting in the higher growth rate of old saplings compared with young saplings. Moreover, lack of nighttime warming rendered young saplings to be still in high stresses of freezing injury at low temperatures. These findings highlight the need for additional research on the effects of further climate anomalies on tree species during their ontogenetic processes.

Planting long‐lived trees in a warming climate: Theory shows the importance of stage‐dependent climatic tolerance

“…Long‐term provenance trials, where different seed sources are planted on multiple sites, are invaluable for assessing the risks and benefits of assisted gene flow. While there are older trials for some common species (e.g., Carter, 1996 ; Rehfeldt et al., 1999 ; Schmidtling, 1994 ; St. Clair et al., 2022 ), establishing new common gardens, with responses to climate changes in mind (such as Du et al., 2019 ; Kueppers et al., 2017 ; Munier et al., 2010 ), should be a priority. Another approach is the analysis of tree rings in regards to past climate change.…”

“…Only a few recent models have, however, begun to investigate how different assisted gene flow strategies can accelerate adaptation (DeFilippo et al., 2022 ; Grummer et al., 2022 ; Quigley et al., 2019 ), and even fewer have attempted to quantify the demographic consequences of assisted gene flow and its impact on population persistence and function (e.g., Bay et al., 2017 ; Kelly & Phillips, 2019 ; Kuparinen & Uusi‐Heikkilä, 2020 ). Many organisms targeted for assisted gene flow, such as trees or corals, are long‐lived and have complex life cycles: life cycle stages (e.g., seed, seedling, sapling, pole, mature tree and senescent stages) differ in their tolerance to climatic variables (Du et al., 2019 ; Mašek et al., 2021 ; Pompa‐Garcıa & Hadad, 2016 ), and different individuals may spend different amounts of time in each stage before growing to the next (Jackson et al., 2009 ). Yet, we have little insight into how complex life cycles may affect optimal assisted gene flow strategies.…”

Growing‐season frost is a better predictor of tree growth than mean annual temperature in boreal mixedwood forest plantations

“…Near‐ground radiative growing‐season frosts have already been identified as important ecological and evolutional drivers of subalpine trees and of trees growing at the treeline (Li et al., 2017; Wang et al., 2019). Moreover, frost occurring during the opening of buds seems to better explain the altitudinal and latitudinal range limit of tree species compared to mean annual temperature (Du et al., 2019; Kollas, Körner, & Randin, 2014; Körner et al., 2016; Vitra, Lenz, & Vitasse, 2017). Even though growing‐season frost was an important factor driving tree growth at northern latitudes and at high altitudes, growing‐season frosts was seldom considered important in forestry and forest management disciplines where near‐ground radiative growing‐season frosts are less frequent.…”

Influence of Anthropogenic Activities on Elevation‐Dependent Weakening of Annual Temperature Cycle Amplitude Over the Tibetan Plateau

“…Variables related to temperature seasonality seem to be more important than variables related to mean temperature for distinguishing biomes (Silva de Miranda et al., 2018). Compared to the mean annual temperature, frost, which is correlated with temperature seasonality (Hänninen, 2016), is identified as a more important driver of tree growth (Marquis et al., 2020), and seems to better explain the altitudinal and latitudinal range limits of tree species (Du et al., 2019; Kollas et al., 2014; Körner et al., 2016; Vitra et al., 2017). Therefore, knowledge of not only changes in mean temperatures but also changes in temperature variation is required to reasonably understand and predict the biological consequences of climate change (Karl et al., 1995).…”