The iso/anisohydric continuum describes how plants regulate leaf water potential and is commonly used to classify species drought response strategies. However, drought response strategies comprise more than just this continuum, incorporating a suite of stomatal and hydraulic traits. Using a common garden experiment, we compared and contrasted four metrics commonly used to describe water use strategy during drought in 10 eucalyptus species comprising four major ecosystems in eastern Australia. We examined the degree to which these metrics were aligned with key stomatal and hydraulic traits related to plant water use and drought tolerance. Species rankings of water use strategy were inconsistent across four metrics. A newer metric (Hydroscape) was strongly linked to various plant traits, including the leaf turgor loss (TLP), water potential at stomatal closure (Pgs90), leaf and stem hydraulic vulnerability to embolism (PL50 and Px50), safety margin of hydraulic segmentation (HSMHS), maximum stomatal conductance (gsmax) and Huber value (HV). In addition, Hydroscape was correlated with climatic variables representing the water availability at the seed source site. Along the continuum of water regulation strategy, species with narrow Hydroscapes tended to occupy mesic regions and exhibit high TLP, PL50 and Px50 values and narrow HSMHS. High gsmax recorded in species with broad hydroscapes was also associated with high HV. Despite a fourfold difference in Hydroscape area, all species closed their stomata prior to the onset of hydraulic dysfunction, suggesting a common stomatal response across species that minimizes embolism risk during drought. Hydroscape area is useful in bridging stomatal regulation, hydraulic architecture and species drought tolerance, thus providing insight into species water use strategies. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13320/suppinfo is available for this article.

Background and Aims Plant hydraulic traits influence the capacity of species to grow and survive in waterlimited environments, but their comparative study at a common site has been limited. The primary aim of this study was to determine whether selective pressures on species originating in drought-prone environments constrain hydraulic traits among related species grown under common conditions. Methods Leaf tissue water relations, xylem anatomy, stomatal behaviour and vulnerability to drought-induced embolism were measured on six Eucalyptus species growing in a common garden to determine whether these traits were related to current species climate range and to understand linkages between the traits. Key Results Hydraulically weighted xylem vessel diameter, leaf turgor loss point, the water potential at stomatal closure and vulnerability to drought-induced embolism were significantly (P < 0Á05) correlated with climate parameters from the species range. There was a coordination between stem and leaf parameters with the water potential at turgor loss, 12 % loss of conductivity and the point of stomatal closure significantly correlated. Conclusions The correlation of hydraulic, stomatal and anatomical traits with climate variables from the species' original ranges suggests that these traits are genetically constrained. The conservative nature of xylem traits in Eucalyptus trees has important implications for the limits of species responses to changing environmental conditions and thus for species survival and distribution into the future, and yields new information for physiological models.

Globally, forests are facing an increasing risk of mass tree mortality events associated with extreme droughts and higher temperatures. Hydraulic dysfunction is considered a key mechanism of drought‐triggered dieback. By leveraging the climate breadth of the Australian landscape and a national network of research sites (Terrestrial Ecosystem Research Network), we conducted a continental‐scale study of physiological and hydraulic traits of 33 native tree species from contrasting environments to disentangle the complexities of plant response to drought across communities. We found strong relationships between key plant hydraulic traits and site aridity. Leaf turgor loss point and xylem embolism resistance were correlated with minimum water potential experienced by each species. Across the data set, there was a strong coordination between hydraulic traits, including those linked to hydraulic safety, stomatal regulation and the cost of carbon investment into woody tissue. These results illustrate that aridity has acted as a strong selective pressure, shaping hydraulic traits of tree species across the Australian landscape. Hydraulic safety margins were constrained across sites, with species from wetter sites tending to have smaller safety margin compared with species at drier sites, suggesting trees are operating close to their hydraulic thresholds and forest biomes across the spectrum may be susceptible to shifts in climate that result in the intensification of drought.

Land-use intensification is a central element in proposed strategies to address global food security. One rationale for accepting the negative consequences of land-use intensification for farmland biodiversity is that it could ‘spare’ further expansion of agriculture into remaining natural habitats. However, in many regions of the world the only natural habitats that can be spared are fragments within landscapes dominated by agriculture. Therefore, land-sparing arguments hinge on land-use intensification having low spillover effects into adjacent protected areas, otherwise net conservation gains will diminish with increasing intensification. We test, for the first time, whether the degree of spillover from farmland into adjacent natural habitats scales in magnitude with increasing land-use intensity. We identified a continuous land-use intensity gradient across pastoral farming systems in New Zealand (based on 13 components of farmer input and soil biogeochemistry variables), and measured cumulative off-site spillover effects of fertilisers and livestock on soil biogeochemistry in 21 adjacent forest remnants. Ten of 11 measured soil properties differed significantly between remnants and intact-forest reference sites, for both fenced and unfenced remnants, at both edge and interior. For seven variables, the magnitude of effects scaled significantly with magnitude of surrounding land-use intensity, through complex interactions with fencing and edge effects. In particular, total C, total N, δ15N, total P and heavy-metal contaminants of phosphate fertilizers (Cd and U) increased significantly within remnants in response to increasing land-use intensity, and these effects were exacerbated in unfenced relative to fenced remnants. This suggests movement of livestock into surrounding natural habitats is a significant component of agricultural spillover, but pervasive changes in soil biogeochemistry still occur through nutrient spillover channels alone, even in fenced remnants set aside for conservation. These results have important implications for the viability of land-sparing as a strategy for balancing landscape-level conservation and production goals in agricultural landscapes.

X-ray microtomography (microCT) is becoming a valuable noninvasive tool for advancing our understanding of plant-water relations. Laboratory-based microCT systems are becoming more affordable and provide better access than synchrotron facilities. However, some systems come at the cost of comparably lower signal quality and spatial resolution than synchrotron facilities. In this study, we evaluated laboratory-based X-ray microCT imaging as a tool to nondestructively analyse hydraulic vulnerability to drought-induced embolism in a woody plant species. We analysed the vulnerability to drought-induced embolism of benchtop-dehydrated Eucalyptus camaldulensis plants using microCT and hydraulic flow measurements on the same sample material, allowing us to directly compare the two methods. Additionally, we developed a quantitative procedure to improve microCT image analysis at limited resolution and accurately measure vessel lumens. Hydraulic measurements matched closely with microCT imaging of the current-year growth ring, with similar hydraulic conductivity and loss of conductivity due to xylem embolism. Optimized thresholding of vessel lumens during image analysis, based on a physiologically meaningful parameter (theoretical conductivity), allowed us to overcome common potential constraints of some lab-based systems. Our results indicate that estimates of vulnerability to embolism provided by microCT visualization agree well with those obtained from hydraulic measurements on the same sample material.