Interactive effects of photon fluence rates and drought on CAM-cycling in Delosperma tradescantioides (Mesembryanthemaceae)

Werner B Herppich; Guy F Midgley; Margaretha Herppich; Arnd Tüffers; Maik Veste; Dieter J Von Willert

doi:10.1034/j.1399-3054.1998.1020119.x

Interactive effects of photon fluence rates and drought on CAM-cycling in Delosperma tradescantioides (Mesembryanthemaceae)

Physiol Plant. 1998 Jan;102(1):148-154. doi: 10.1034/j.1399-3054.1998.1020119.x.

Authors

Werner B Herppich¹, Guy F Midgley¹, Margaretha Herppich¹, Arnd Tüffers¹, Maik Veste¹, Dieter J Von Willert¹

Affiliation

¹ W. B. Herppich (corresponding author, e-mail wherppich@atb.uni-potsdam.de), Inst. für Agrartechnik Bornim e. V., Abteilung Technik im Gartenbau, Max-Eyth-Allee 100, D-14469 Potsdam, Germany; G. F. Midgley, Ecology and Conservation, National Botanical Inst., Private Bag X 7, Claremont 7735, South Africa; M. Herppich, A. Tiffers and D. J. von Willert, Inst. für Ökologie der Pflanzen, Westfälische Wilhelms-Univ., Hindenburgplatz 55, D-48143 Münster, Germany; M. Veste, Abteilung für Ökologie, Univ. Bielefeld, Universitätsstraße 25, D-33615 Bielefeld, Germany.

PMID: 35359119
DOI: 10.1034/j.1399-3054.1998.1020119.x

Abstract

The ability of photosynthesis and CAM to acclimate to low (220 µmol m^-2 s^-1 ; LL) and relatively high (550 µmol m^-2 s^-1 ; HL) photosynthetic photon flux densities (PPFD) was investigated in the CAM-cycling species Delosperma tradescantioides by means of CO₂ gas exchange and chlorophyll fluorescence analysis. Furthermore, the influence of short-term drought on malic acid accumulation and the activity of photosystem II (PSII) was studied to assess the possible interactions between drought and the prevailing PPFD in this species. HL plants showed features of sun versus shade acclimation relative to LL plants. Nocturnal malic acid accumulation (Δ-malate) and leaf water content also tended to be higher in HL plants. Irrespective of the PPFD during growth, the weak Δ-malate doubled within 3 days of drought. Despite largely restricted CO₂ uptake, photosynthetic activity as estimated from fluorescence analysis declined only ca 5%. After 7 days of drought, when plants showed CAM-idling and Δ-malate had decreased again, potential carbon assimilation was still ca 84% of that in well-watered plants and remained relatively constant throughout the day. Decarboxylation of malic acid accounted for ca 23% of potential assimilation assuming total oxidation of a maximum portion of this organic acid. Drought did not affect predawn maximum photochemical efficiency (F_v /F_m ). Nonphotochemical quenching (qN) increased (24%) in response to desiccation and resulted in a more or less constant reduction state of PSII. This increase in qN resulted mainly from the change in its fast-relaxing component (qNF), while the slow component (qNS) was significant only at or above saturating PPFD in both HL and LL plants. The photon response characteristics of PSII, which differed between LL and HL plants, were unaffected by short-term drought. Photon harvesting and photon use were always adjusted to guarantee a low reduction state of PSII. Results suggest that in both LL and HL plants CAM-cycling may help to stabilize photosynthesis but to a large extent by other means than simply providing internally derived CO₂ .

Keywords: CAM-cycling; Crassulacean acid metabolism; Delosperma tradescantioides; drought stress; gas exchange; malic acid; photosynthetic electron transport.