Abstract

CORREA-DIAZ, Arian et al. Physiological response of Taxodium mucronatum Ten. to the increases of atmospheric CO₂ and temperature in the last century. Agrociencia [online]. 2018, vol.52, n.1, pp.129-149. ISSN 2521-9766.

The increase of atmospheric CO2 can influence the growth of vegetation causing stomatal closure, changes in the wateruse efficiency, or a fertilization effect that leads to greater growth. However, the response of vegetation depends on the environmental conditions and physiology of each species. The objective of this study was to evaluate the composition of carbon and oxygen isotopes (δ13C and δ18O) the net discrimination of 13C (Δ13C), the growth rate in basal area (IAB) and the intrinsic water-use efficiency (iWUE) of Taxodium mucronatum Ten. (Montezuma baldcypress) over the last 100 years in three regions of central Mexico. The hypotheses were: 1) the physiological response of T. mucronatum Ten. to climatic variation is different among regions; 2) changes in the growth rate in basal area and physiological variables of the Montezuma baldcypress tree suggest that fertilization effects took place in the last century. The regions under study were: Estado de México (MEX), Querétaro (QRO), and Morelos (MOR), with 600, 750, and 1038 mm rainfall. Nine trees per site were sampled to build a common chronology. In the growth rings, δ13C and δ18O were analyzed to estimate discrimination (Δ13C), internal CO2 concentration (Ci), and iWUE in the last century. The data were analyzed as samples repeated over time with variable spacing. The difference between sites was tested with a multivariate analysis of variance (MANOVA) and contrasts tests. The δ13C on wood and Ci varied according to the moisture regime in MEX and MOR. In the past five decades, δ18O increased by 4 ‰ and the average annual temperature (AAT) increased from 1.2 to 1.4 °C. Since 1950, Δ13C decreased by 1.1 ‰ and iWUE increased by 50 %. The increase in Ca, iWUE, and AAT was related to the IAB decrease in MEX site, and a slight IAB increase in QRO and MOR, indicating a different CO2 fertilization effect depending on the moisture gradient.

Keywords : Montezuma baldcypress; hydric stress; stable isotopes; climate change.

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