Westudied tree water uptake patterns, tested for complementary water use among species and analysed controlling factors in a tropical tree diversity experiment. The water uptake depth of five species was investigated across seasons and diversity levels using the natural abundance of water isotopes (δ2H, δ18O) and modelling. Three distinct water acquisition strategies were found for trees growing inmonocultures during the dry season: strong reliance (>70%) on soil water fromthe upper layer (0–30 cm) (Cedrela odorata), uptake from the upper and deeper layers (>30cm) in equal proportions (Hura crepitans, Anacardium excelsum and Luehea seemannii) and water uptake predominately from deeper layers (Tabebuia rosea). Seasonal shifts in water uptake were most pronounced for T. rosea. The water uptake pattern of a given species was independent of the diversity level underlining the importance of species identity and species characteristics in spatial and temporal tree water use. Statistics did not show a significant effect of diversity on source water fractions, but we did see some evidence for complementary water resource utilization in mixed species plots, especially in the dry season. Our results also demonstrated that the depth of soil water uptake was related to leaf phenology and tree transpiration rates. A higher proportion of water obtained from deeper soil layers was associated with a high percentage foliage cover in the dry season, which explained the higher transpiration rates

The ear, together with the flag leaf, is believed to play a major role as a source of assimilates during grain filling in C 3 cereals. However, the intrusive nature of most of the available methodologies prevents reaching conclusive results in this regard. This study compares the carbon isotope composition (d 13 C) in its natural abundance in the watersoluble fractions of the flag leaf blade and the ear with the d 13 Cof mature kernels to assess the relative contribution of both organs to grain filling in durum wheat (Triticum turgidum L. var. durum). The relative contribution of the ear was higher in landraces compared to modern cultivars, as well as in response to nitrogen fertilization and water stress. Such genotypic and environmentally driven differences were associated with changes in harvest index (HI), with the relative contribution of the ear being negatively associated with HI. In the case of the genotypic differences, the lower relative contribution of the ear in modern cultivars compared with landraces is probably associated with the appearance in the former of a certain amount of source limitation driven by a higher HI. In fact, the relative contribution of the ear was far more responsive to changes in HI in modern cultivars compared with landraces.Keywords: Carbon isotope discrimination; ear; flag leaf; grain filling; harvest index; photosynthesis Citation: Sanchez-Bragado R, Elazab A, Zhou B, Serret MD, Bort J, Nieto-Taladriz MT, Araus JL (2014) Contribution of the ear and the flag leaf to grain filling in durum wheat inferred from the carbon isotope signature: Genotypic and growing conditions effects.

SummaryWe present a non-intrusive method to quantify the relative contribution of different photosynthetic organs to grain filling in cereals based on their discrimination among isotopes of carbon fixed, highlighting the key role of the ear.

HighlightThis study proves the key role of the ear as a source of assimilates for grain filling under good agronomical conditions and compares different methodologies of phenotyping.

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