Abstract
Higher plants have to cope with fluctuating mineral resource availability. However, strategies such as stimulation of root growth, increased transporter activities, and nutrient storage and remobilization have been mostly studied for only a few macronutrients. Leaves of cultivated crops (Zea mays, Brassica napus, Pisum sativum, Triticum aestivum, Hordeum vulgare) and tree species (Quercus robur, Populus nigra, Alnus glutinosa) grown under field conditions were harvested regularly during their life span and analyzed to evaluate the net mobilization of 13 nutrients during leaf senescence. While N was remobilized in all plant species with different efficiencies ranging from 40% (maize) to 90% (wheat), other macronutrients (K–P–S–Mg) were mobilized in most species. Ca and Mn, usually considered as having low phloem mobility were remobilized from leaves in wheat and barley. Leaf content of Cu–Mo–Ni–B–Fe–Zn decreased in some species, as a result of remobilization. Overall, wheat, barley and oak appeared to be the most efficient at remobilization while poplar and maize were the least efficient. Further experiments were performed with rapeseed plants subjected to individual nutrient deficiencies. Compared to field conditions, remobilization from leaves was similar (N–S–Cu) or increased by nutrient deficiency (K–P–Mg) while nutrient deficiency had no effect on Mo–Zn–B–Ca–Mn, which seemed to be non-mobile during leaf senescence under field conditions. However, Ca and Mn were largely mobilized from roots (-97 and -86% of their initial root contents, respectively) to shoots. Differences in remobilization between species and between nutrients are then discussed in relation to a range of putative mechanisms.
Highlights
IntroductionHigher plants have to cope with a permanently fluctuating availability of soil nutrients, both in space and time
As sessile organisms, higher plants have to cope with a permanently fluctuating availability of soil nutrients, both in space and time
Leaf life span was shorter for annual species (100, 95, 86, 94, and 67 days, respectively for B. napus, Z. mays, H. vulgare, T. aestivum, and P. sativum) than for tree species (218, 185, and 244 days, respectively for Q. robur, P. nigra, and A. glutinosa)
Summary
Higher plants have to cope with a permanently fluctuating availability of soil nutrients, both in space and time. Root exudation of organic compounds is the third process by which nutrient mobility and phytoavailability of some nutrients can be increased either directly or indirectly through stimulation of rhizobiont activity (Dakora and Phillips, 2002) These three first strategies may not be sufficient to buffer any reduction in soil mineral nutrient availability and maintain the plant growth rate under varying conditions. The fourth identified strategy has been less described and relies on the remobilization of short or mid-term storage of macro- and micronutrients within the plant, which may be used to buffer a transient lack of mineral uptake by roots This strategy occurs during vegetative growth when the availability of nutrients in soil is insufficient, mature leaves become sources to support the growth of news organs for example for N (Malagoli et al, 2005) or S (Abdallah et al, 2010)
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