The Phosphorus Economy of Mediterranean Oak Saplings Under Global Change

Abstract

While a severe decrease in phosphorus (P) availability is already taking place in a large number of ecosystems, drought and nitrogen (N) deposition will likely further decrease the availability of P under global change. Plants have developed physiological strategies to cope with decreasing P resources, but it is unclear how these strategies respond to elevated N deposition and summer droughts. We investigated the influence of N and P availability and soil drought on P uptake (H 3 33 PO 4 feeding experiment) and use efficiencies in young Quercus calliprinos Webb. trees. We hypothesized that (H1) the expected increases in soil N:P ratios will increase the efficiencies of P uptake and use of oak saplings but will decrease the efficiencies of N uptake and use, whereas (H2) drought will affect P uptake efficiency more than N uptake efficiency. In confirmation of (H1) we found that a sharp increase of the soil N:P ratio from 4 to 42 g g -1 significantly increased the instantaneous 33 P uptake efficiency ( 33 PUptakeE) by five-fold and long-term P uptake efficiency (PUptakeE) by six-fold, while it decreased N uptake efficiency (NUptakeE) and N use efficiency (NUE). In contradiction to (H1), P use efficiency (PUE) did not respond to the simulated extended gradient of soil N:P ratios but remained relatively constant. (H2) was only partially confirmed as soil drought reduced PUptakeE by up to a fourth at high soil N:P ratios but had no significant effect on NUptakeE. As a consequence, increasing summer droughts may decrease the response of PUptakeE to increasing P limitation, which – in the absence of adjustments of the efficiency of P use – can aggravate growth reductions in this eastern Mediterranean tree species under global change.

Influence of Soil Properties on P Pools and Its Effect on Forest Productivity in Mediterranean Calcareous Soils

“…Numerous studies have indicated that current climate change leads to an increase in N depositions and an increase in summer droughts causing nutritional imbalances and P deficiencies in ecosystems, making these changes more pronounced in the Mediterranean areas [18][19][20]. For this reason, and although general processes involved in the biochemistry and availability of P are well known, it is necessary to clarify which soil parameters mostly affect each process both in specific ecosystems, mainly in Mediterranean ones, and in different types of soil [21].…”

Drought Deteriorates the N Stoichiometry of Biomass Production in European Beech Saplings Under Global Change

“…In a comparison of the nutrient uptake efficiencies, drought had an even stronger effect on PUptakeE (as reported in Köhler et al, 2018) than on NUptakeE (cf. Dirks et al, 2019). Drought strongly decreased PUptakeE of beech saplings as a consequence of decreased ECMF colonization rate and the loss of ECMF with longdistance exploration.…”