Search

Nonstructural carbohydrates (NSCs) reflect the carbon balance in trees and play a central role in their responses to environmental stresses. However, our understanding of tree NSC storage dynamics under environmental stress is unclear. Here, we quantified the deciduous conifer Larix principis-rupprechtii at five altitudes on Luya Mountain, North-Central China. We measured NSCs in different organs and simultaneously monitored environmental variables during the growing seasons in 2018 and 2019. The results showed that temperature was the main environmental factor affecting tree NSCs. Furthermore, as the soil–atmosphere temperature gradient decreased, the concentrations of soluble sugars in the needles increased while their starch decreased, as well as the concentrations of starch in the shoots, stems, and roots increased. These results may indicate that temperature gradients may assist carbohydrate allocation within individual trees. The NSCs, especially starch, in the needles increased with lower soil moisture, and the soluble sugars and starch in the needles and shoots increased with a higher vapor pressure deficit. The soluble sugars in the stems were significantly affected by soil moisture, and the NSCs in the roots were mainly affected by temperature. These results provide new insights to improve our understanding of the environmental stress effects on future forest C balances. [ABSTRACT FROM AUTHOR]

Quantifying the effects of environmental variables on radial growth has real significance for reasonably predicting the impacts of environmental changes on tree dynamics. This study used Picea crassifolia , a widely distributed dominant evergreen coniferous tree species found on the north-eastern fringe of the Tibetan Plateau, as a case study to analyse the associations of radial growth with environmental variables during 1960–2018 using a correlation analysis and sliding correlation analysis. The responses of radial growth to different moisture conditions were further quantitatively evaluated through the generalised linear model and relative dominance analysis. The results show that the radial growth of P. crassifolia is mainly influenced by moisture conditions in the study area. Specifically, the response times of P. crassifolia radial growth to soil moisture and precipitation differ, as radial growth has a significant positive correlation with precipitation in the early growth period. Notably, radial growth has a remarkable and stable correlation with soil moisture in the autumn and winter seasons of the previous year. This study provides a theoretical foundation and scientific grounds for analysing the response of Tibetan Plateau forests to climate change and can act as a reference for future research on the response of radial growth to soil moisture in alpine regions. • Soil moisture impacts the growth of P. crassifolia on the northeast edge of the Tibetan Plateau. • The response time of P. crassifolia to soil moisture is more stable. • Precipitation in May and June promotes the growth of P. crassifolia. • Soil moisture of the previous year is used for tree growth at the beginning of the growing season. • The response of radial growth to soil moisture is positive and stable from 1960 to 2018. [ABSTRACT FROM AUTHOR]

• P.meyeri tends to increase soluble sugars and starch under low soil moisture conditions. • Needle soluble sugars were more sensitive to air temperature than other organs. • NSCs in the shoots and stems were affected by both soil moisture and atmospheric factors. • Stem soluble sugars had a different response to soil moisture and vapor pressure deficit. • Root NSC reserves may be important for P.meyeri to respond to low soil moisture. Nonstructural carbohydrate (NSC) dynamics have been suggested to be an important trait reflecting carbon balance under environmental changes. However, our understanding of NSC storage dynamics, their controls, and their responses to environmental factors remain unclear. In this study, we selected the evergreen conifer Picea meyeri at five altitudes (2040 m, 2260 m, 2440 m, 2600 m, and 2740 m a.s.l.) on Luya Mountain, North-central China. NSC concentrations in the needles, shoots, stems, and roots were measured, and the environmental variables were monitored during the growing seasons in 2018 and 2019. The results showed that the NSCs first decreased slightly and then increased gradually as altitude increased in the needles, shoots, stems, and roots. The NSC concentrations with the highest levels occurring in the needles and the lowest in the stems, whereas the shoots and roots showed intermediate concentrations. Moreover, soil moisture was the major factor influencing the dynamics of NSC storage in P. meyeri. The concentrations of soluble sugars and starch in all four organs increased with decreasing soil moisture, except for needle starch. In particular, the soluble sugars in the needles were significantly negatively correlated with air temperature, and those in the stems had a different response to soil moisture and vapor pressure deficit (VPD). Furthermore, root NSCs reserves may be important for P. meyeri to respond to low soil moisture. These findings provide new insights for understanding tree NSC allocation and the mechanism of stress resistance. [ABSTRACT FROM AUTHOR]

• The magnitude and duration of tree water deficit were combined to study drought intensity. • Larch showed less limited stem water and a greater increment rate than spruce. • Interspecific differences in annual growth declined in dry years. • Species-specific responses of stem increment to the drought intensity. The heterogeneous responses of mixed forests to climate change are integral to the promotion of the resilience and resistance of forest ecosystems, yet the hydraulic and growth sensitivity of mixed tree species to environmental drivers remain largely unexplored. In this study, stem radial variations in larch (Larix principis-rupprechtii) and spruce (Picea meyeri) were monitored using high-resolution point dendrometers over six years (2014–2019) in a mixed coniferous stand in semi-humid China. The extracted hourly tree water deficit-induced stem shrinkage (TWD) and stem radial increment (SRI) were compared between tree species and among years, and the species-specific responses of the daily maximum TWD and cumulative SRI to environmental variables were fitted by linear mixed models. Averagely, larch had a lower TWD and greater SRI rate than spruce in all six growing seasons. The interspecific differences in the TWD (length, magnitude, and intensity) were significant in dry years, while significant differences in the SRI rates were in wet years. The SRI rate of larch showed a more rapid decrease than that of spruce with increasing intensity of TWD. Furthermore, the TWD of both species was mainly regulated by vapor pressure deficit (VPD) and soil water content (SWC). The TWD of larch had a stronger and earlier response to VPD, while TWD of spruce was more affected by SWC (10 cm depth). The daily SRI of larch was more significantly related to all the measured environmental variables, indicating a more sensitive response to environmental drivers than that of spruce. We identified a shift in competitive advantage from sensitive L. principis-rupprechtii to conservative P. meyeri under extreme drought conditions, providing deep insights into species‐specific water and carbon dynamics in mixed forests. [ABSTRACT FROM AUTHOR]