Abstract
The impact of (long-term) drought acclimation and (short-term) heat stress and their combination on fast chlorophyll fluorescence induction curves (OJIP) and grain yield was tested using pot-grown plants of wild barley (Hordeum spontaneum) originating from Northern Egypt. Concerning agronomic traits, the main effect of drought was decreased biomass accumulation and grain yield, while heat specifically affected floral development. The treatments caused specific inhibitions of photosystem II (PSII) functionality. While heat stressed plants showed a reduction of maximum quantum efficiency of PSII (φP0), an indication of effects on oxygen evolving complex (OEC) functionality, and the connectivity of PSII units, these features were entirely missing in drought acclimated plants. Drought caused a reduction of the Performance Index (PIabs) and of the relative amplitude of the IP-phase of the OJIP induction curve (ΔVIP). Individuals suffering from a combination of drought and heat showed a better ability to recover photosynthetic electron transport after the relief of stress in comparison to heat stressed plants. However, this improved capacity to recover was not accompanied by an increased grain yield. Thus, we conclude that chlorophyll fluorescence measurements provide valuable physiological data; however, their use in agronomic studies for the prediction of agronomic traits should be done with some precaution.
Highlights
During the forthcoming decades, global agriculture will have to face dramatic climatic changes [1, 2]
Measurements of fast chlorophyll fluorescence induction curves revealed a characteristic pattern of inhibitions of the photosynthetic electron transport
In the case of longterm drought treatment, fluorescence data could be used for estimating productivity, as the reduced yield was directly related to photosynthetic limitations
Summary
During the forthcoming decades, global agriculture will have to face dramatic climatic changes [1, 2]. Water availability will be a limiting factor for agricultural activities in arid and semiarid regions. Drought and heat are two main factors limiting plant productivity, and in the natural environment these two abiotic stresses often occur simultaneously. H. spontaneum is self-pollinating annual grass, interfertile with cultivated barley, and mainly distributed in the Mediterranean and Irano-Turanian regions [4], the “Fertile Crescent,” and eastward to Central Asia [5]. It is considered a beneficial source for the inbreeding of tolerance genes against biotic and abiotic stresses into cultivated barley [6]
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