Drought-induced mortality selectively affects Scots pine trees that show limited intrinsic water-use efficiency responsiveness to raising atmospheric CO2

Heres A.-M., Voltas J., Lopez B.C., Martinez-Vilalta J. (2014) Drought-induced mortality selectively affects Scots pine trees that show limited intrinsic water-use efficiency responsiveness to raising atmospheric CO2. Functional Plant Biology. 41: 244-256.
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Doi: 10.1071/FP13067

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Widespread drought-induced tree mortality has been documented around the world, and could increase in frequency and intensity under warmer and drier conditions. Ecophysiological differences between dying and surviving trees might underlie predispositions to mortality, but are poorly documented. Here we report a study of Scots pines (Pinus sylvestris L.) from two sites located in north-eastern Iberian Peninsula where drought-associated mortality episodes were registered during the last few decades. Time trends of discrimination against 13C (Δ13C) and intrinsic water-use efficiency (WUEi) in tree rings at an annual resolution and for a 34 year period were used to compare co-occurring now-dead and surviving pines. Results indicate that both surviving and now-dead pines significantly increased their WUEi over time, although this increase was significantly lower for now-dead individuals. These differential WUEi trends corresponded to different scenarios describing how plant gas exchange responds to increasing atmospheric CO2 (Ca): the estimated intercellular CO2 concentration was nearly constant in surviving pines but tended to increase proportionally to Ca in now-dead trees. Concurrently, the WUEi increase was not paralleled by a growth enhancement, regardless of tree state, suggesting that in water-limited areas like the Mediterranean, it cannot overcome the impact of an increasingly warmer and drier climate on tree growth. © 2014 CSIRO.

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Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality

Hereş A.-M., Camarero J.J., López B.C., Martínez-Vilalta J. (2014) Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality. Trees - Structure and Function. 28: 1737-1750.
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Doi: 10.1007/s00468-014-1081-3

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Key message: The retrospective analysis of wood anatomical features evidences how a long-term deterioration of hydraulic performance and carbon use portend drought-induced mortality in Scots pine.Abstract: Widespread episodes of drought-induced tree mortality are predicted to become more frequent as climate becomes warmer and drier. Nevertheless, growth trends and their links to changes in wood anatomy before tree dies are still poorly understood. Wood anatomical features provide valuable information that can be extracted to infer the mechanisms leading to tree death. In this study, we characterize drought-induced mortality affecting two Scots pine (Pinus sylvestris) sites (Prades and Arcalís) located in the North Eastern Iberian Peninsula. Co-occurring now-dead and living Scots pine trees were sampled and their wood anatomical features were measured and compared. We aimed to detect differences in anatomical features between living and dead trees, and to infer past physiological performances that might have determined their subsequent death or survival. Now-dead trees showed lower tracheid and resin duct production, and smaller radial lumen diameters than co-occurring living trees. At the more xeric Prades site, these anatomical differences were larger and chronic, i.e. were observed over the three studied decades, whilst they were less pronounced at the other, more mesic Arcalís site, where tree mortality episodes were more recent. This indicates that dead trees’ hydraulic conductivity was severely affected and that carbon investment in xylem formation and resin duct production was constrained prior to tree death. Our findings show that both hydraulic deterioration and low carbon allocation to xylem formation were associated to drought-induced mortality in Scots pine. Nevertheless, the temporal dynamics of these processes differed between populations as a function of site climatic conditions. © 2014, Springer-Verlag Berlin Heidelberg.

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