Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. It is difficult to partition ecosystem-scale evapotranspiration (ET) measurements into E and T, which makes it difficult to validate satellite data and land surface models. Here, we review current progress in partitioning E and T and provide a prospectus for how to improve theory and observations going forward. Recent advancements in analytical techniques create new opportunities for partitioning E and T at the ecosystem scale, but their assumptions have yet to be fully tested. For example, many approaches to partition E and T rely on the notion that plant canopy conductance and ecosystem water use efficiency exhibit optimal responses to atmospheric vapor pressure deficit (D). We use observations from 240 eddy covariance flux towers to demonstrate that optimal ecosystem response to D is a reasonable assumption, in agreement with recent studies, but more analysis is necessary to determine the conditions for which this assumption holds. Another critical assumption for many partitioning approaches is that ET can be approximated as T during ideal transpiring conditions, which has been challenged by observational studies. We demonstrate that T can exceed 95 % of ET from certain ecosystems, but other ecosystems do not appear to reach this value, which suggests that this assumption is ecosystem-dependent with implications for partitioning. It is important to further improve approaches for partitioning E and T, yet few multi-method comparisons have been undertaken to date. Advances in our understanding of carbon–water coupling at the stomatal, leaf, and canopy level open new perspectives on how to quantify T via its strong coupling with photosynthesis. Photosynthesis can be constrained at the ecosystem and global scales with emerging data sources including solar-induced fluorescence, carbonyl sulfide flux measurements, thermography, and more. Such comparisons would improve our mechanistic understanding of ecosystem water fluxes and provide the observations necessary to validate remote sensing algorithms and land surface models to understand the changing global water cycle.

Summary: Sun‐induced fluorescence (SIF) in the far‐red region provides a new noninvasive measurement approach that has the potential to quantify dynamic changes in light‐use efficiency and gross primary production (GPP). However, the mechanistic link between GPP and SIF is not completely understood. We analyzed the structural and functional factors controlling the emission of SIF at 760 nm (F₇₆₀) in a Mediterranean grassland manipulated with nutrient addition of nitrogen (N), phosphorous (P) or nitrogen–phosphorous (NP). Using the soil–canopy observation of photosynthesis and energy (SCOPE) model, we investigated how nutrient‐induced changes in canopy structure (i.e. changes in plant forms abundance that influence leaf inclination distribution function, LIDF) and functional traits (e.g. N content in dry mass of leaves, N%, Chlorophyll a+b concentration (Cab) and maximum carboxylation capacity (V_cmax)) affected the observed linear relationship between F₇₆₀ and GPP. We conclude that the addition of nutrients imposed a change in the abundance of different plant forms and biochemistry of the canopy that controls F₇₆₀. Changes in canopy structure mainly control the GPP–F₇₆₀ relationship, with a secondary effect of Cab and V_cmax. In order to exploit F₇₆₀ data to model GPP at the global/regional scale, canopy structural variability, biodiversity and functional traits are important factors that have to be considered.

Sufficient flower number and quality is a prerequisite for subsequent fruit set, and, in the case of commercial fruit crops, for fruit production. In the olive tree, Olea europaea L., flower development constitutes an extensive process which requires two to three months and includes the elongation and branching of the inflorescence axis and the formation of the individual flowers. We applied controlled water deficit to young olive trees in successive periods from winter dormancy until flowering and initial fruit set, and determined inflorescence, flower, ovary and ovule development and final fruit yield at both morphological and histological levels. Water deficit during winter dormancy had no effect on either flowering or fruiting parameters. Fruit production was reduced in all other treatments, but due to different timing-related causes. Deficit during inflorescence development reduced many different flowering parameters, including inflorescence number, flower number, perfect flower number and percentage, and ovule development. When applied two weeks prior to bloom little change was noted in floral development, but ovary and ovule starch content were reduced as was fruit set. Finally, deficit during bloom-initial fruit set produced a drastic effect in which many flowers remained closed and fertilization was prevented. Overall the results indicated developmental plasticity and compensation among flowering and fruiting parameters, and high sink priority for the ovary tissues. © 2011 Elsevier B.V.This study was financed by ERDF co-financed Spanish Ministry of Science and Innovation grants AGL2008-02570 and AGL2009-07248, and Andalusian Excellence grantPO6-AGR-01791.Peer Reviewe