Stem Circadian Phenology of Four Pine Species in Naturally Contrasting Climates from Sky-Island Forests of the Western USA

Abstract

We identified intra-annual climatic drivers of stem water relationships and growth in foundation conifers at a subalpine site in the Great Basin Desert and at a montane site in the Mojave Desert (Nevada, USA). Sites were instrumented to represent naturally different levels of heat and drought stress as part of NevCAN (the Nevada Climate and ecohydrological Assessment Network). We analyzed three years (2013-2015) of sub-hourly dendrometer records for limber (Pinus flexilis) and bristlecone pine (Pinus longaeva) at the subalpine site, and for ponderosa (Pinus ponderosa) and pinyon pine (Pinus monophylla) at the montane site. Multiple logistic regression was used to identify relationships with environmental variables measured in-situ. At both sites, stem expansion occurred during the early morning and late afternoon, and irreversible stem increment was concentrated in the early morning hours. In subalpine species, stem growth started in late spring and continued until August, while at the montane site stem growth was episodic, peaking during summer monsoonal rainstorms. Circadian maximum and minimum stem size during the growing season were reversed during the dormant season at the colder/wetter subalpine site but not at the warmer/drier montane one. Knowledge of intra-annual tree-water relationships and stem growth helps understand how sky island forests grow under highly diverse climatic conditions, including severe drought and heat stress.

Reduction in lumen area is associated with the δ18O exchange between sugars and source water during cellulose synthesis

“…While Pinus ponderosa and Pseudotsuga menziesii can co‐exist, Pinus ponderosa tends to grow in more xeric locations compared to Pseudotsuga menziesii and the two species have different strategies to deal with drought stress (e.g. sensitivity in stomatal conductance, rooting depth, ratio of leaf area to sapwood area, hydraulic conductivity, xylem phenology) (Burns & Honkala, ; Stout & Sala, ; Domec et al , ; Martin et al , ; Ziaco & Biondi, ; Ziaco et al , ). Thus, we chose to examine both species to account for any physiological differences.…”

Why trees grow at night

“…Such data are often coarse and are obtained typically with an annual resolution of the underlying tree ring samples (Schweingruber, 1996 ; Babst et␣al ., 2018 ) or, in less frequent cases, small wood samples obtained at (bi‐)weekly intervals (Zweifel et␣al ., 2006 ; Delpierre et␣al ., 2016 ; Huang et␣al ., 2020 ; Peters et␣al ., 2021 ). Daily or even hourly‐resolved growth responses of mature forest trees have been rarely recorded (Schurr et␣al ., 2006 ), most data covers only short periods and were monitored in single stands (Ziaco & Biondi, 2018 ; Knüsel et␣al ., 2019 ; Güney et␣al ., 2020 ).…”

Seasonal Drought Effects on Intra-Annual Stem Growth of Taiwan Pine along an Elevational Gradient in Subtropical China

“…While wood anatomical methods allow for an accurate description of wood formation at the cellular level through weekly sampling micro-cores, dendrometer-based stem radial variation can provide detail tree physiological reactions at higher temporal resolutions (sub-hourly and daily) without wounding the cambium. Importantly, dendrometer-derived diurnal stem radial variations consist not only of irreversible radial growth of new xylem cells but also of reversible stem shrinking and swelling (reflecting water storage dynamics in tree stems), thereby providing continuous information on tree water status and further facilitating the physiological interpretation of stem growth under drought stress [14,15,19,20]. Despite this, intra-annual stem growth dynamics and its response to regional climate are still very scarce in subtropical China, among which most studies focused on a single site with limited observation years [21][22][23].…”