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

Authors: HE, PENGCHENG - CHINESE ACADEMY OF SCIENCES; Gleason, Sean; WRIGHT, IAN - MACQUARIE UNIVERSITY; WENG, ENSHENG - Columbia University; LIU, HUI - CHINESE ACADEMY OF SCIENCES; ZHU, SHIDAN - GUANGXI UNIVERSITY; LU, MINGZHEN - PRINCETON UNIVERSITY; LUO, QI - INSTITUTE OF GEOGRAPHIC SCIENCES AND NATURAL RESOURCES; LI, RONGHUA - SOUTH CHINA AGRICULTURAL UNIVERSITY; WU, GUILIN - CHINESE ACADEMY OF SCIENCES; YAN, ENRONG - EAST CHINA UNIVERSITY OF SCIENCE AND TECHNOLOGY; SONG, YANJUN - EAST CHINA UNIVERSITY OF SCIENCE AND TECHNOLOGY; MI, XIANGCHENG - CHINESE ACADEMY OF SCIENCES; HAO, GUANGYOU - CHINESE ACADEMY OF SCIENCES; REICH, PETER - UNIVERSITY OF MINNESOTA; WANG, YINGPING - COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION (CSIRO); ELLSWORTH, DAVID - WESTERN SYDNEY UNIVERSITY; YE, QING - CHINESE ACADEMY OF SCIENCES

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2019
Publication Date: 12/10/2019
Citation: He, P., Gleason, S.M., Wright, I., Weng, E., Liu, H., Zhu, S., Lu, M., Luo, Q., Li, R., Wu, G., Yan, E., Song, Y., Mi, X., Hao, G., Reich, P.B., Wang, Y., Ellsworth, D.S., Ye, Q. 2019. Growing-season temperature and precipitation are independent drivers of global variation in xylem hydraulic conductivity. Global Change Biology. 00:1-9. https://doi.org/10.1111/gcb.14929.
DOI: https://doi.org/10.1111/gcb.14929

Interpretive Summary: Vascular plant species must transport water from the soil to the sites of evaporation and photosynthesis in the leaves. The capacity of the water-conducting tissues (xylem) to transport water has therefore been under strong selection over the past 400+ million years of evolution. The cost and functional significance of this tissue is evident in its large variation across species (> 2 orders of magnitude). However, it remains an important and relevant question what selection pressures (e.g., temperature, precipitation, evaporation) have "tuned" xylem tissue, and therefore, the likely suitability of different xylem "designs" for different ecological and agricultural settings. We gathered together a database of hydraulic capacity measurements, representing 975 species, 149 families, and across 199 different sites sampled from every vegetated biome on earth. Growing-season temperature and growing-season precipitation drove global variation in xylem hydraulic capacity, with each of these climate variables explaining 23% and 15% of the variation, respectively. The hydraulic capacity of xylem was both highest and most variable in the warm and wet tropical regions, and lowest in the cold or dry regions, such as tundra and desert biomes. Our results suggest that future warming and redistribution of seasonal precipitation may have significant impact on species functional diversity or community species composition.

Technical Abstract: Stem xylem-specific hydraulic conductivity (KS) represents the potential for plant water transport per unit 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 are needed for a better understanding of how plants adapt water transport to different environmental conditions, particularly under global climate change scenarios. Here, we compiled a xylem hydraulics dataset with 1315 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 (Tgs) and growing-season precipitation (Pgs) drove global variation in KS independently with Tgs and Pgs explaining 23% and 15% of the variation in KS, respectively. Both the mean and variations of KS were highest in the warm and wet tropical region, and lowest in the cold or dry regions, such as tundra and desert biomes. Our results suggest that future warming and redistribution of seasonal precipitation may have significant impact on species functional diversity or community species composition, depending on whether the sensitivities of KS to Tgs or Pgs are predominantly influenced by genotypic or phenotypic variations, particularly at high latitudes where it is projected that wet areas will get wetter and dry regions will become drier. Our results also highlight an important role for KS in predicting changes in plant hydraulic diversity and community species composition under global climate change.