Relationships of stable carbon isotopes, plant water potential and growth: an approach to asses water use efficiency and growth strategies of dry land agroforestry species

Abstract

The relationships between annual wood stable carbon isotope composition (d 13 C), dry season midday plant water potential, and annual growth rate were investigated to asses the ability of agroforestry species to adapt to climate changes. 6-8 stem disks from four co-occurring species (Acacia senegal, A. seyal, A. tortilis and Balanites aegyptiaca) were collected for radial growth measurements using tree-ring analysis spanning 1930-2003. Annual d 13 C was measured on three tree disks per species for the period 1970-2002. Midday plant water potential was measured during the dry season. Annual radial growth and midday plant water potential ranged from 0.27 to 9.12 mm and -1.0 to -5.0 MPa, respectively, with statistically significant differences. After correcting annual wood d 13 C for atmospheric changes in d 13 C, carbon isotopic composition ranged from -22.22 to -26.58%. Relationships between d 13 C, radial growth and plant water potentials revealed the interaction of water availability, stomatal conductance, d 13 C values and growth. Two contrasting water use strategies and competitive advantages can be distinguished. Species with lower mean d 13 C values (A. senegal and A. seyal) show high plant water potential and, hence, better growth during moist years. Thus, they indicate low water use efficiency (WUE) and opportunistic water use strategy. On the other hand, species with lower water potentials (A. tortilis and B. aegyptiaca) showed relative better growth performance and less increase in d 13 C in drought years, reflecting their high WUE and conservative water use strategy. These results suggest that d 13 C in tree rings can be useful in estimating historic changes in plant WUE and hence in screening drought tolerant species in the face of expected climate changes, as well as for assessing the functional diversity and risk reduction in mixed vegetation.

Dendrochronology in the dry tropics: the Ethiopian case

“…Most of the stem discs obtained from an enclosed ranch, where human disturbance is negligible, could be crossdated (Gebrekirstos et al 2008). Radial growth variations of crossdated trees studied at the Abernosa woodlands suggested that Acacia tortilis and Balanites aegyptiaca are more tolerant to drought, but less Trees vigorous under wetter conditions than Acacia senegal and Acacia seyal (Gebrekirstos et al 2008), supporting findings by Gebrekirstos et al (2006Gebrekirstos et al ( , 2010.…”

Baobabs on Kubu Island, Botswana – A dendrochronological multi-parameter study using ring width and stable isotopes (δ13C, δ18O)

“…Beside these exceptions (Bao9, Bao20), all sampled trees showed similar mean values for annual growth. Mean δ 13 C values varied about 1.8 per mille between trees, which is relatively little compared to 3 or up to 5 per mille stated for trees in other studies (loader et al 2003;skomarkova et al 2006;GeBrekirstos et al 2011). An increase in mean δ 13 C values was accompanied by decreasing variances most likely due to plant-physiological processes.…”

“…The resulting treering width time series were synchronized with TSAPWin (Time Series Analysis and Presentation for Dendrochronology and Related Applications;version 4.67c © 2002version 4.67c © -2011. The program allows visual and statistical crossdating by matching patterns of thin and wide rings (Fritts 1976) and illustrates discrepancies between the series. Areas of uncertain dating were reviewed in WinDENDRO TM and corrected if necessary.…”

Dendroecology in the tropics: a review

“…Information on d 13 C fractions can be used to estimate changes in water use efficiency or long-term changes in internal CO 2 concentration (C i ). For ten tropical tree species long-term trends in stable isotope levels have now been obtained (Hietz et al 2005;Gebrekirstos et al 2009;Nock et al 2010;Brienen et al 2010b;Gebrekirstos et al 2010). A decrease in d 13 C over time was reported, which led to an increase in intrinsic water use efficiency (iWUE) for six species (Hietz et al 2005;Nock et al 2010;Brienen et al 2010b).…”