Mark Andrew Adams

Maintaining cellular hydration is essential for plant metabolic activity and carbon gain. Plants typically maintain hydration through efficiency of water transport networks, the ability to avoid network disruption, and retention of water via accumulation of osmotica. Given their global domain and their enduring presence across geological eras, plants have evolved with large variations in moisture supply across geographic and temporal space, notably via trait adaptation and plasticity. We quantified plastic and genetically fixed variation in 6 key hydraulic traits across 10 Eucalyptus species in 4 common gardens spanning a climatic relative‐moisture gradient in Victoria, Australia. These traits generally shift plastically within species across gardens while maintaining interspecific trends across species within gardens. Species grown at or originating from drier sites tend to have lower hydraulic conductivity, narrower xylem conduits, greater conduit density, greater bulk xylem density, greater fibre wall fraction, and more negative turgor loss point, consistent with expectations based on maximizing whole‐plant growth. Genetically fixed variation was usually greater than plastic variation, but some traits were more plastic in species native to moister areas. Variation in xylem anatomy largely explained variation in hydraulic conductivity and xylem density, notwithstanding idiosyncratic site and species effects.

Globally, rice cultivation consumes large amounts of fresh water, and urgent improvements in water use efficiency (WUE) are needed to ensure sustainable production, given increasing water scarcity. While stomatal traits have been a primary focus for enhancing WUE, complex interactions between stomatal and non-stomatal leaf traits remain poorly understood. In this review, we present an analysis of stomatal and non-stomatal leaf traits influencing WUE in rice. The data suggests that optimising stomatal density and size will be insufficient to maximise WUE because non-stomatal traits such as mesophyll conductance, leaf anatomy, and biochemical composition significantly modulate the relationship between stomatal conductance and the photosynthetic rate. Integrating recent advances in high-throughput phenotyping, multi-omics technologies, and crop modelling, we suggest that combinations of seemingly contradictory traits can enhance WUE without compromising yield potential. We propose a multi-trait breeding framework that leverages both stomatal and non-stomatal adaptations to develop rice varieties with superior WUE and climate resilience. This integrated approach provides a roadmap for accelerating the development of water-efficient rice cultivars, with broad implications for improving WUE in other crops.

Globally, rice cultivation consumes large amounts of fresh water and urgent improvements in water use efficiency (WUE) are needed to ensure sustainable production, given the increasing water scarcity. While stomatal traits have been a primary focus for enhancing WUE, complex interactions between stomatal and non-stomatal leaf traits remain poorly understood. In this review, we present an analysis of stomatal and non-stomatal leaf traits influencing WUE in rice. The data suggests that optimising stomatal density and size will be insufficient to maximise WUE because non-stomatal traits such as mesophyll conductance, leaf anatomy, and biochemical composition significantly modulate relationships between stomatal conductance and photosynthetic rate. Integrating recent advances in high-throughput phenotyping, multi-omics technologies, and crop modelling, we suggest that combinations of seemingly contradictory traits can enhance WUE without compromising yield potential. We propose a multi-trait breeding framework that leverages both stomatal and non-stomatal adaptations to develop rice varieties with superior WUE and climate resilience. This integrated approach provides a roadmap for accelerating the development of water-efficient rice cultivars, with broad implications for improving WUE in other crops.

The contributions of de novo synthesis to terpene emissions from Eucalyptus globulus subsp. globulus were determined by fumigating branchlets with ¹³CO₂ in a gas exchange system. Of more than thirty-four terpenes emitted by this species, only four, i.e., isoprene, iso-valeraldehyde, cis-ocimene, and trans-caryophyllene, incorporated ¹³C into the terpene carbon skeleton during the ~5–6 h experiment. ¹³C incorporation into isoprene and iso-valeraldehyde reached a maximum of ca. 82% of the carbon skeleton, similar to cis-ocimene, with a maximum of 77% ¹³C incorporation after ~2.5 h exposure to ¹³CO₂. Only ca. 20% of carbon was labelled in trans-caryophyllene after 5–6 h. the incorporation of ¹³C was observed only in compounds emitted from leaves, and was not detected in either individual oil glands or in bulk leaf tissue. The results suggest the de novo synthesis of some terpenes (isoprene, cis-ocimene, trans-caryophyllene, and iso-valeraldehyde) and their emission is independent of emissions of terpenes stored in oil glands.

Global climate change and land use change underlie a need to develop new crop breeding strategies, and crop wild relatives (CWR) have become an important potential source of new genetic material to improve breeding efforts. Many recent approaches assume adaptive trait variation increases towards the relative environmental extremes of a species range, potentially missing valuable trait variation in more moderate or typical climates. Here, we leveraged distinct genotypes of wild chickpea (Cicer reticulatum) that differ in their relative climates from moderate to more extreme and perform targeted assessments of drought and heat tolerance. We found significance variation in ecophysiological function and stress tolerance between genotypes but contrary to expectations and current paradigms, it was individuals from more moderate climates that exhibited greater capacity for stress tolerance than individuals from warmer and drier climates. These results indicate that wild germplasm collection efforts to identify adaptive variation should include the full range of environmental conditions and habitats instead of only environmental extremes, and that doing so may significantly enhance the success of breeding programs broadly.

Summary: Our ability to predict temperature responses of leaf respiration in light and darkness (R_L and R_Dk) is essential to models of global carbon dynamics. While many models rely on constant thermal sensitivity (characterized by Q₁₀), uncertainty remains as to whether Q₁₀ of R_L and R_Dk are actually similar. We measured short‐term temperature responses of R_L and R_Dk in immature and mature leaves of two evergreen tree species, Castanopsis carlesii and Ormosia henry in an open field. R_L was estimated by the Kok method, the Yin method and a newly developed Kok‐iterC_c method. When estimated by the Yin and Kok‐iterC_c methods, R_L and R_Dk had similar Q₁₀ (c. 2.5). The Kok method overestimated both Q₁₀ and the light inhibition of respiration. R_L/R_Dk was not affected by leaf temperature. Acclimation of respiration in summer was associated with a decline in basal respiration but not in Q₁₀ in both species, which was related to changes in leaf nitrogen content between seasons. Q₁₀ of R_L and R_Dk in mature leaves were 40% higher than in immature leaves. Our results suggest similar Q₁₀ values can be used to model R_L and R_Dk while leaf development‐associated changes in Q₁₀ require special consideration in future respiration models.

Tradeoffs between the energetic benefits and costs of traits can shape species and trait distributions along environmental gradients. Here we test predictions based on such tradeoffs using survival, growth, and 50 photosynthetic, hydraulic, and allocational traits of tenEucalyptusspecies grown in four common gardens along an 8-fold gradient in precipitation/pan evaporation (P/E_p) in Victoria, Australia. Phylogenetically structured tests show that most trait-environment relationships accord qualitatively with theory. Most traits appear adaptive across species within gardens (indicating fixed genetic differences) and within species across gardens (indicating plasticity). However, species from moister climates have lower stomatal conductance than others grown under the same conditions. Responses in stomatal conductance and five related traits appear to reflect greater mesophyll photosynthetic sensitivity of mesic species to lower leaf water potential. Our data support adaptive cross-over, with realized height growth of most species exceeding that of others in climates they dominate. Our findings show that pervasive physiological, hydraulic, and allocational adaptations shape the distributions of dominantEucalyptusspecies along a subcontinental climatic moisture gradient, driven by rapid divergence in speciesP/E_pand associated adaptations.