We suggest that the increased rooting depth and the decreased DOC concentration in the root uptake zone resulting from progressively thawing soil lead to heavy isotopes becoming more and more available for the larch roots in the course of the vegetative season.
Moreover, recent studies showed the important role of the DEEPER ROOTING 1 (DRO1) mutation in rice, which increased rooting depth (>2-fold in Dro1-NIL compared with its genetic background, IR64) and conferred drought tolerance (Uga et al., 2013).
Cortical cell file number, which is correlated with the number of cortical cells, has been shown to improve drought tolerance of maize by reducing root respiration, increasing rooting depth and thereby improving water capture (Chimungu et al. 2014).
Root ideotypes that have been suggested to improve rice performance under drought include increased root growth at depth (Nicou et al. [1970]; O'Toole and Chang [1978]) and coarse axial roots to increase the ability to penetrate hardpans (Hasegawa et al. [1985]).
In pot experiments, von Felten and Schmid [48] found that mixtures of grass species increased root biomass in deeper soil depths than monocultures.
Moreover, green manures increased roots dry weight.
At times of water stress, plants can decrease their above-ground surface area and eventually biomass, thereby reducing water loss, or increase their rooting depth, thereby increasing water uptake.
Recent studies in rice have shown that an increase in root depth leads to an increase in water uptake, which is translated into higher grain yield under rain-fed conditions [ 29].
For all seed lots combined, the mean maximum root depth increased significantly between years from 0.96 m in year 1 (SE = 0.03) to 2.81 m (SE = 0.05) in year 4 (Additional file 10).
Furthermore, alterations in root morphology, quantity of root exudates and increases in rooting depth may be observed in an elevated [CO2] environment (Rogers et al. 1992; Nie et al. 2013).
