Linking reliance on deep soil water to resource economy strategies and abundance among coexisting understorey shrub species in subtropical pine plantations

Abstract

Summary Strategies for deep soil water acquisition (WAdeep) are critical to a species’ adaptation to drought. However, it is unknown how WAdeep determines the abundance and resource economy strategies of understorey shrub species. With data from 13 understorey shrub species in subtropical coniferous plantations, we investigated associations between the magnitude of WAdeep, the seasonal plasticity of WAdeep, midday leaf water potential (Ψmd), species abundance and resource economic traits across organs. Higher capacity for WAdeep was associated with higher intrinsic water use efficiency, but was not necessary for maintaining higher Ψmd in the dry season nor was it an ubiquitous trait possessed by the most common shrub species. Species with higher seasonal plasticity of WAdeep had lower wood density, indicating that fast species had higher plasticity in deep soil resource acquisition. However, the magnitude and plasticity of WAdeep were not related to shallow fine root economy traits, suggesting independent dimensions of soil resource acquisition between deep and shallow soil. Our results provide new insights into the mechanisms through which the magnitude and plasticity of WAdeep interact with shallow soil and aboveground resource acquisition traits to integrate the whole‐plant economic spectrum and, thus, community assembly processes.

Below‐ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations

“…This may be a result of the quantification of isohydry being based on the variation of midday leaf water potential in the dry season, and that deep water storage was greater than shallow water storage during the dry season (Fig. S3; Yang et al , 2015; Jiang et al , 2020).…”

“…Plant relative reliance on soil water sources at different depths was calculated using the IsoSource model (the multisource mass balance approach, http://www.epa.gov/wed/pages/models/stableIsotopes/isosource/isosource.htm) (Phillips et al , 2005). Based on root vertical distribution and soil water δ 18 O variation along the profile, we defined the deep soil layer as the layer below 60 cm (Jiang et al , 2020). Light‐saturated photosynthetic rate ( A max ) for the 24 study species was measured using a portable photosynthesis system (Li‐6400XT; Li‐Cor, Lincoln, NE, USA) in August 2016.…”

“…Light‐saturated photosynthetic rate ( A max ) for the 24 study species was measured using a portable photosynthesis system (Li‐6400XT; Li‐Cor, Lincoln, NE, USA) in August 2016. Procedures for sampling, isotope data analysis for deep water utilisation, and environmental conditions during A max measurements are described in detail by Jiang et al (2020).…”

Insights into the isotopic mismatch between bulk soil water and <i>Salix matsudana</i> Koidz trunk water from root water stable isotope measurements

“…One possibility is that trees preferentially use much deeper soil water and groundwater than fluctuating shallow soil water, which is a less stable and reliable water source because it is subject to rapid evaporation and seasonal precipitation (Zhao and Wang, 2018). Deep soil water can make a significant contribution to drought avoidance during dry periods (Yang et al, 2017), and an increasing capacity for deep soil water utilization was positively correlated with intrinsic water use efficiency (Jiang et al, 2020). Moreover, the deep water use strategy of S. matsudana may provide favourable water conditions for shallow-rooted herbaceous species, facilitating stable coexistence.…”

Water Use by Chinese Pine Is Less Conservative but More Closely Regulated Than in Mongolian Scots Pine in a Plantation Forest, on Sandy Soil, in a Semi-Arid Climate

“…The ability of roots to access deep soil water has been found to be crucial to a species' adaptation to drought (Jiang et al, 2020). Although the roots of larger diameter generally account for a greater proportion of root biomass, approximately 92% of the mineral nutrients and 75% of the water that supports growth is absorbed by fine roots in lateral roots rather than by taproots (Makkonen and Helmisaari, 2001;Epron and Osawa, 2017).…”