Distinguish water utilization strategies of trees growing on earth‐rocky mountainous area with transpiration and water isotopes

Abstract

Water stress is regarded as a global challenge to forests. Unlike other water‐limited areas, the water use strategies of rocky mountainous forests, which play an important ecohydrological role, have not received sufficient attention. To prove our hypothesis that species adopt different water use strategies to avoid competition of limited water resources, we used site abiotic monitoring, sap flow and stable isotope method to study the biophysiological responses and water use preferences of two commonly distributed forest species, Pinus tabuliformis (Pt) and Quercus variabilis (Qv). The results showed that Pt transpired higher than Qv. Pt was also prone to adopt isohydric water use strategy as it demonstrated sensitive stomatal control over water loss through transpiration. Qv developed cavitation which was reflected by the dropping E c in response to high vapor pressure deficit, concentrated peak sap flux density (J s), and enlarged hysteresis loop. Considering the average soil depth of 52.8 cm on the site, a common strategy shared by both species was the ability to tap water from deep soil layers (below 40 cm) when soil water was limited, and this contributed to the whole growing season transpiration. The contribution of surface layer water to plant water use increased and became the main water source for transpiration after rainfall. Qv was more efficient at using water from surface layer than Pt due to the developed surface root system when soil water content was not stressed. Our study proves that different water‐using strategies of co‐occurring species may be conducive to avoid competition of limited water resources to guarantee their survival. Knowledge of water stress‐coping strategies of trees has implications for the understanding and prediction of vegetation composition in similar areas and can facilitate forest management criteria for plantations.

Roots‐Enhanced Preferential Flows in Deciduous and Coniferous Forest Soils Revealed by Dual‐Tracer Experiments

“…Thereafter, the dyed area was covered by a piece of canvas (2 m by 2 m) to prevent evaporation and rainfall infiltration. The maximum daily potential evapotranspiration is about 7 mm at the Mount Jiufeng forest sites (Jia et al, 2017), and the actual transpiration would be less than that as evaporation did not occur in the experimental plots. Thus, infiltration and redistribution (i.e., percolation) were considered to be the primary processes contributing to water flows in our experiments, whereas transpiration played a minor role (i.e., <17.5% of the applied 40‐mm water).…”

“…Mount Jiufeng has a maximum elevation of 1153 m and a minimum elevation of 60 m asl. This region is in a typical continental warm temperate zone and has a monsoon climate with a mean annual precipitation of 630 mm and an average annual temperature of 12.5°C, with a record maximum temperature of 41.6°C in July and a record minimum temperature of -19.6°C in January ( Jia et al, 2017). Mount Jiufeng has a vegetation cover of approximately 86%, and the majority of its existing forest was planted in the 1950s to the 1960s.…”

“…It was recognized that the staining of roots may also result from the uptake of dyed water due to transpiration. Given that transpiration was minor, as the maximum potential evapotranspiration (~7 mm) ( Jia et al, 2017) was <17.5% of the applied water (40 mm), it was reasonable to assume that the staining of roots largely resulted from the water percolation via preferential flow paths. Figure 2 illustrates typical stained soil profiles ( Fig.…”

“…In forest soils, these interrelationships are particularly important as root channels are considered to be primary preferential pathways (Elçi and Molz, 2009; Laine‐Kaulio et al, 2015; Zhang et al, 2016). Vegetation species in a forest can be diverse, including shrubs, coniferous and deciduous tree species, and so on (Jia et al, 2017). However, to date, little is known concerning how tree species (each with their unique root systems) may influence preferential flows in forest soils.…”

Depth distribution of soil water sourced by plants at the global scale: A new direct inference approach

“…Basically, this approach represents the plant root system as one unique root (Rothfuss & Javaux, 2017). IsoSource (Phillips & Gregg, 2003) is a widely used linear mixing model based on a mass balance equation (recent examples are Jia, Liu, Chen, & Yu, 2017;Zhu, Zhang, Gao, Qi, & Xu, 2016). Nowadays, statistical Bayesian mixing models such as SIAR (Parnell et al, 2013), MixSir, and MixSIAR (Moore & Semmens, 2008) are gaining popularity (e.g., Beyer, Hamutoko, Wanke, Gaj, & Koeniger, 2018).…”