Non‐native tree in a dry coastal area in Hawai'i has high transpiration but restricts water use despite phreatophytic trait

Abstract

In arid systems, phreatophytes are often among the most effective invaders because of their capacity to access and exploit groundwater resources otherwise unavailable to native vegetation. On Hawai'i Island, a non-native phreatophyte, Prosopis pallida (kiawe), has invaded extensive dry lowland areas following its introduction in the 19th century. To better understand the influence of this invader on the host ecosystem, and vice versa, we determined transpiration characteristics of P. pallida by monitoring sap flux of mature individuals over an 18-month period on the arid leeward coast of Hawai'i Island. Daily sap flux increased with increasing atmospheric vapour pressure deficit (D) and exhibited no clear response related to rainfall events or prolonged drought. Annual transpiration (i.e. 308 mm) was 80% higher than rainfall. Stomatal conductance decreased with increasing vapour pressure deficits more slowly than the theoretical stomatal conductance-D relationship that assumes stomatal regulation of leaf water potential above a critical level. While daily peak stomatal conductance was relatively high, it nonetheless appeared limited by high intrinsic water use efficiency (net photosynthetic rate per stomatal conductance), suggesting a constraint to unlimited groundwater absorption. In this young volcanic environment where rainfall is low and quite episodic, the success of this species likely stems from its anisohydric strategy even at the risk of cavitation, and it is altering the hydrological cycling of the areas where it is dominant.where m is the slope ∂G s /∂lnD (mol kPa À1 m À2 s À1 ) and G sref is the intercept at D = 1 kPa (mol m À2 s À1 ). The ratio 1168 Y. MIYAZAWA ET AL.

Water sources for woody shrubs on hillslopes: An investigation using isotopic and sapflow methods

“…This analysis showed a significant reduction in sapflow when shallow soil layers became dry in mid-late summer ( Figure 6). Although our sapflow analysis does not rule out groundwater use by matagouri, it agrees with isotope results in that it indicates that matagouri plants did not take up sufficient groundwater to meet evaporative demand when shallow soil layers were very dry (Miyazawa et al, 2016).…”

Growth and physiological responses to successional water deficit and recovery in four warm‐temperate woody species

“…However, with respect to physiological drought responses, the eventual advantages of the isohydric versus the anisohydric strategy in native and invader species is not yet conclusive, with some studies indicating that invasive plants may be preferentially anisohydric (e.g. Cavaleri and Sack , Miyazawa et al ), while other studies propose isohydric behaviors for invaders (Savi et al ). Some other studies have even reported that invasive plants might shift their water use strategies under different water conditions (Kulmatiski et al ).…”

Transpiration of trees in a cool temperate forest on Mt. Aso, Japan: comparison of model simulation and measurements

“…Such unpredictable reduction in kE was not observed in Q. acutissima and A. hirsuta with low m, possibly because E was maintained at relatively low levels in these species and was able to be balanced by root water uptake even during rainless period (Katul et al 2003). The observed m values of these species were as low as m of trees in Mediterranean climate during the dry season (Baldocchi 1997), a phreatophyte with low leaf water potential in an arid area (Miyazawa et al 2016), and trees in a monsoon Southeast Asia forest during the dry season (Miyazawa et al 2014a). Increase in m and g sw could have allowed A. hirsuta to achieve higher A both at leaf-scale (Farquhar and Sharkey 1982) and standscale (Law et al 2000).…”

“…Leaf-level ecophysiological traits were periodically measured during the period August 2013-September 2014, using a portable photosynthesis measurement system (Li-6400, Li-cor, Lincoln, NE). The methods of the measurements are the same as those in Miyazawa et al (2016). The relationship between net photosynthetic rate (A, lmol m À2 s À1 ) and intercellular CO 2 concentration (C i , lmol mol À1 )( A-C i relationship) was obtained for intact leaves for Q. acutissima and A. hirsuta, and for leaves on excised branches for C. japonica, from the trees near the sap flux sample trees.…”