Growing‐season temperature and precipitation are independent drivers of global variation in xylem hydraulic conductivity

Abstract

Stem xylem‐specific hydraulic conductivity (KS) represents the potential for plant water transport normalized by xylem cross section, length, and driving force. Variation in KS has implications for plant transpiration and photosynthesis, growth and survival, and also the geographic distribution of species. Clarifying the global‐scale patterns of KS and its major drivers is needed to achieve a better understanding of how plants adapt to different environmental conditions, particularly under climate change scenarios. Here, we compiled a xylem hydraulics dataset with 1,186 species‐at‐site combinations (975 woody species representing 146 families, from 199 sites worldwide), and investigated how KS varied with climatic variables, plant functional types, and biomes. Growing‐season temperature and growing‐season precipitation drove global variation in KS independently. Both the mean and the variation in KS were highest in the warm and wet tropical regions, and lower in cold and dry regions, such as tundra and desert biomes. Our results suggest that future warming and redistribution of seasonal precipitation may have a significant impact on species functional diversity, and is likely to be particularly important in regions becoming warmer or drier, such as high latitudes. This highlights an important role for KS in predicting shifts in community composition in the face of climate change.

Across climates and species, higher vapour pressure deficit is associated with wider vessels for plants of the same height

“…These results indicate that vessel diameter is predicted by precipitation only to the degree that plant height is predicted by precipitation, and that all else being equal similar-sized plants in areas of differing precipitation have similar mean vessel diameters (cf. He et al, 2019). They also indicate that vessel diameter is positively predicted by temperature even when standardizing for plant height.…”

“…That the results of our conductance-VPD estimates coincide strikingly with the predicted isometry does suggest that the role of conduit scaling with VPD is one worth exploring in more detail, especially because our analyses clearly reject the freezing hypothesis we tested. in freezing-prone localities as a result of narrow vessels better resisting freezing-induced embolism (He et al, 2019;Zanne et al, 2013Zanne et al, , 2018. If this were the case, then excluding freezingprone communities should have eliminated the VD stand -temperature relationship, but it persisted ( (Zanne et al, 2013).…”

“…Instead, recent studies (Morris et al, 2018;Olson et al, 2014Olson et al, , 2018) have shown the unexpected observation that, when taking conductive path length into account, mean annual temperature (MAT), not precipitation, is the variable examined explaining the most residual variation in the conduit diameter-stem length relationship (see also He et al, 2019). Because temperature is a fundamental driver of VPD (Eamus et al, 2013;Ficklin & Novick, 2017;Monteith & Unsworth, 2013;Wang, Dickinson, & Liang, 2012), these recent results point to the potential role of VPD in shaping plant conductive systems.…”

Adaptation and coordinated evolution of plant hydraulic traits

“…Xylem conductive capacity is another key determinant of hydraulic function, usually quantified as the maximum, stem‐specific hydraulic conductivity ( K s ). This property has been reported to be positively related to temperature and precipitation at a global scale (He et al ., 2020). Because the structural properties of xylem conduits and pit membranes associated with increased embolism resistance (quantified here as P50) are also expected to reduce conductive capacity, a trade‐off between P50 and K s has long been hypothesised (often referred to as the hydraulic safety‐efficiency trade‐off) (Tyree and Zimmermann, 2002).…”

Response of whole plant water use to limiting light and water conditions are independent of each other in seedlings of seasonally dry tropical forests

“…xylem vessels and transpiration loss through the stomata to the atmosphere. Studies of water use that have quantified stem xylem conductance (He et al 2020), leaf xylem conductance (Nardini and Luglio 2014), and leaf stomatal conductance (Cavaleri and Sack 2010) suggest that water use is important in understanding association with habitat specific water availability. However, inferences from these studies may be limited because quantification of water use is confined to scales that are smaller than the whole plant level (Meinzer et al 2010).…”