Acoustic Vulnerability, Hydraulic Capacitance, and Xylem Anatomy Determine Drought Response of Small Grain Cereals

Selection of high-yielding traits in cereal plants led to a continuous increase in productivity. However, less effort was made to select on adaptive traits, favorable in adverse and harsh environments. Under current climate change conditions and the knowledge that cereals are staple foods for people worldwide, it is highly important to shift focus to the selection of traits related to drought tolerance, and to evaluate new tools for efficient selection. Here, we explore the possibility to use vulnerability to drought-induced xylem embolism of wheat cultivars Excalibur and Hartog (Triticum aestivum L.), rye cultivar Duiker Max (Secale cereale L.), and triticale cultivars Dublet and US2014 (x Triticosecale Wittmack) as a proxy for their drought tolerance. Multiple techniques were combined to underpin this hypothesis. During bench-top dehydration experiments, acoustic emissions (AEs) produced by formation of air emboli were detected, and hydraulic capacitances quantified. By only looking at the AE50 values, one would classify wheat cultivar Excalibur as most tolerant and triticale cultivar Dublet as most vulnerable to drought-induced xylem embolism, though Dublet had significantly higher hydraulic capacitances, which are essential in terms of internal water storage to temporarily buffer or delay water shortage. In addition, xylem anatomical traits revealed that both cultivars have a contrasting trade-off between hydraulic safety and efficiency. This paper emphasizes the importance of including a cultivar’s hydraulic capacitance when evaluating its drought response and vulnerability to drought-induced xylem embolism, instead of relying on the AE50 as the one parameter.

Trade-offs between xylem water and carbohydrate storage among 24 coexisting subtropical understory shrub species spanning a spectrum of isohydry

Hydraulic capacitance and carbohydrate storage are two drought adaptation strategies of woody angiosperms. However, we currently lack information on their associations and how they are associated with species’ degree of isohydry. We measured total stem xylem nonstructural carbohydrate (NSC) concentration in the dry and wet seasons, xylem hydraulic capacitance, native leaf water potentials, pressure–volume curve parameters and photosynthetic performance in 24 woody understory species differing in their degree of isohydry. We found a trade-off between xylem water and carbohydrate storage both in storage capacitance and along a spectrum of isohydry. Species with higher hydraulic capacitance had lower native NSC storage. The less isohydric species tended to show greater NSC depletion in the dry season and have more drought-tolerant leaves. In contrast, the more isohydric species had higher hydraulic capacitance, which may enhance their drought avoidance capacity. In these species, leaf flushing in the wet season and higher photosynthetic rates in the dry season resulted in accumulation rather than depletion of NSC in the dry season. Our results provide new insights into the mechanisms through which xylem storage functions determine co-occurring species’ drought adaptation strategies and improve our capacity to predict community assembly processes under drought.

Growth patterns of Phragmites karka under saline conditions depend on the bulk elastic modulus

Salt stress is known to hamper steady-state water flow, which may reduce plant growth. This research was aimed to study the roles of leaf turgor, osmotic adjustment and cell wall elasticity under saline conditions which may reduce biomass production in Phragmites karka (Retz.) Trin, ex. Steud. (a marsh grass). Plants were grown in 0, 100 and 300 mM NaCl and harvested on 3, 7, 15 and 30 days to observe periodic changes in growth and water relations. Leaf number, relative growth rate, and relative elongation rates were higher in the non-saline control than in the plants grown under saline conditions. Plants showed a rapid decline in leaf growth rate (7–15 days) in 300 mM NaCl compared with a delayed response (15–30 days) in 100 mM NaCl. Leaf water potential decreased with increases in salinity after the third day of exposure whereas osmotic potential decreased after the fifteenth day. Low leaf turgor (Ψp) on the third day indicated an initial phase of osmotic stress under saline conditions. Plants maintained higher Ψp in 0 and 100 mM than in 300 mM NaCl. Differences between mid-day and pre-dawn water potential and water saturation deficit were higher in 300 mM NaCl than with other treatments. Water potential and hydraulic capacitance at turgor loss point decreased whereas bulk elastic modulus increased in 300 mM NaCl. Maintenance of turgor and growth at 100 mM NaCl could be related to efficient osmotic adjustment (use of K+ and Cl–), higher WUEi, and lower bulk elasticity whereas poor growth at 300 mM NaCl may have been a consequence of low turgor, decreased cell hydraulic capacitance and higher bulk elastic modulus.

The ratio of transpiration to evapotranspiration in a rainfed maize field on the Loess Plateau of China

Maize (Zea mays L.) is a major crop on the Loess Plateau, and calculating the ratio of transpiration to evapotranspiration (T/ET) of maize is important for estimating field water balance. In this study, the sap flow method was adopted to measure transpiration (T) characteristics of maize. In order to calibrate the sap flow gauge, the sap flow rate was compared to the leaf T determined by the weighing method. The sap flow value was measured per hour for 3 days and the mean of the hourly values for each day was taken as the daily value to avoid the influence of hydraulic capacitance. There was a significant linear relationship between leaf T and sap flow rate. The slope and intercept of linear regression were 0.764 and 4.944, with an R2 of 0.97 (p < 0.01). We also analyzed the T and ET of maize under field conditions. The T/ET of maize was 63.3% from July to September 2012. The T/ET and leaf area index had a good linear relationship. Partitioning of ET into soil evaporation (E) and T may have important implications for analyzing crop water use efficiency, evaluating the crop production potential of precipitation and optimizing field water management.

A Novel Approach to Measure the Hydraulic Capacitance of a Microfluidic Membrane Pump

A novel approach was proposed to measure the hydraulic capacitance of a microfluidic membrane pump. Membrane deflection equations were modified from various studies to propose six theoretical equations to estimate the hydraulic capacitance of a microfluidic membrane pump. Thus, measuring the center deflection of the membrane allows the corresponding pressure and hydraulic capacitance of the pump to be determined. This study also investigated how membrane thickness affected the Young’s modulus of a polydimethylsiloxane (PDMS) membrane. Based on the experimental results, a linear correlation was proposed to estimate the hydraulic capacitance. The measured hydraulic capacitance data and the proposed equations in the linear and nonlinear regions qualitatively exhibited good agreement.