A new look at water transport regulation in plants

Martinez-Vilalta J., Poyatos R., Aguade D., Retana J., Mencuccini M. (2014) A new look at water transport regulation in plants. New Phytologist. : 0-0.
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Doi: 10.1111/nph.12912

Resum:

Plant function requires effective mechanisms to regulate water transport at a variety of scales. Here, we develop a new theoretical framework describing plant responses to drying soil, based on the relationship between midday and predawn leaf water potentials. The intercept of the relationship (Λ) characterizes the maximum transpiration rate per unit of hydraulic transport capacity, whereas the slope (σ) measures the relative sensitivity of the transpiration rate and plant hydraulic conductance to declining water availability. This framework was applied to a newly compiled global database of leaf water potentials to estimate the values of Λ and σ for 102 plant species. Our results show that our characterization of drought responses is largely consistent within species, and that the parameters Λ and σ show meaningful associations with climate across species. Parameter σ was ≤1 in most species, indicating a tight coordination between the gas and liquid phases of water transport, in which canopy transpiration tended to decline faster than hydraulic conductance during drought, thus reducing the pressure drop through the plant. The quantitative framework presented here offers a new way of characterizing water transport regulation in plants that can be used to assess their vulnerability to drought under current and future climatic conditions. © 2014 New Phytologist Trust.

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Interspecific variation in functional traits, not climatic differences among species ranges, determines demographic rates across 44 temperate and Mediterranean tree species

Martínez-Vilalta J., Mencuccini M., Vayreda J., Retana J. (2010) Interspecific variation in functional traits, not climatic differences among species ranges, determines demographic rates across 44 temperate and Mediterranean tree species. Journal of Ecology. 98: 1462-1475.
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Doi: 10.1111/j.1365-2745.2010.01718.x

Resum:

Surprisingly little is known about the relationship between functional traits and demographic rates of tree species under field conditions, particularly for non-tropical species. We studied the interspecific relationship between key functional traits (wood density (WD), maximum tree height, specific leaf area, nitrogen (N) content of leaves, leaf size and seed mass), demographic rates (relative growth rate (RGR) and mortality rate (MR)) and climatic niche for the 44 most abundant tree species in Spain. Demographic data were derived from the Spanish Forest Inventory, a repeated-measures scheme including c. 90 000 permanent plots spread over a territory of c. 500 000 km[TD-SUP-OPEN]2. Functional traits data came primarily from a more detailed forest inventory carried out in Catalonia, NE Spain. Our study region covers a wide range of climatic conditions and, not surprisingly, the studied species differed markedly in their climatic niche. Despite that fact, our results showed that the variability in demographic rates across species was much more related to differences in functional traits than to differences in the average climate among species. Maximum tree height and, particularly, WD, emerged as key functional traits, and were the best predictors of demographic rates in our study. These two variables also mediated the marginally significant relationship between RGR and MR, suggestive of a weak trade-off between growth and survival. The main aspects of our results were not altered by the explicit incorporation of phylogenetic effects, suggesting that the observed relationships are not due to divergences between a few major clades. Synthesis. Our study gives support to the notion that variation in functional traits across species allows them to perform largely independently of climatic conditions along environmental gradients. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.

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