Coupling N Cycling and N Productivity in Relation to Seasonal Stress in Quercus Pyrenaica Willd. Saplings

Abstract

The N economy of saplings of the Mediterranean Quercus pyrenaica Willd. species was analysed at wholeplant level. The amount and timing of N cycling were determined by strong seasonality in N productivity, which peaked in late spring. Most leaf N was allocated to a main first flush of leaves in early spring, and a minor second flush during early summer or autumn. After peak of N productivity, the allocation of biomass production and N resources was mainly switched to lignotuber and coarse roots. Q. pyrenaica displayed a non-conservative pattern of N use as compared with other co-occurring Quercus species. Potential leaf N-resorption efficiency was moderate, but N proficiency was low, which contributed to high losses of N throughout leaf litter and to short mean residence times of N (MRT N ). Additionally, summer water stress reduced foliar area, producing leaf litter with a high N concentration due to almost negligible resorption efficiency, and in some cases, the loss of the whole above-ground fraction. A large investment of plant resources to the root system appeared as a key trait in the N economy and plant fitness of young Q. pyrenaica saplings, allowing them: (1) to counteract N losses and to maintain a positive N balance, (2) to access deep soil resources (water and nutrients), and (3) to 'safe'-store N for coupling supply and demand processes during spring growth or sprouting after a strong summer drought.

Soil properties and understory herbaceous biomass in forests of three species of Quercus in Northeast Portugal

“…This could explain the fact that the total soil N found in this study was higher than the levels reported by Silla & Escudero (2006) and Turrión et al (2009) in Q. pyrenaica forests developed over granites. In the case of Q. rotundifolia and Q. suber, total soil N contents were between the range obtained by Canadell and Vilá (1992) for Q. ilex forests studied in Spain & Otieno et al (2011) for Q. suber forests in Southern Portugal.…”

Effects of simulated herbivory on photosynthesis and N resorption efficiency in Quercus pyrenaica Willd. saplings

“…We chose the plants randomly, although those severely damaged or visually infested with Malacosoma neustrium caterpillars were excluded. Previous work had shown that the generalist M. neutrium was the main herbivore species of Q. pyrenaica at the study site (Silla and Escudero 2006). Although the population density of M. neustrium was low during 2003, this species is a tent caterpillar exhibiting gregarious behaviour and some individual plants were severely defoliated.…”

“…Thus, around &13 and &26% of the leaf area in the selected stem was removed in the low and high treatments, respectively. These treatments intended to represent the frequent but low-moderate damage (1-20% of leaf area loss at whole plant-level) and the scarce but intense damage (21-60%) that was found previously in saplings of this study area (Silla and Escudero 2006). However, we mimicked the scale of damage only at stem level, as we want to study if the responses to damage were induced locally or at whole plant-level (Meyer and Whitlow 1992;Retuerto et al 2004).…”

“…Folivory by outbreaks of caterpillars produces significant damage in Quercus reforestations in the Iberian Peninsula (Silla 2001). In Q. pyrenaica plantations, the generalist caterpillar Malacosoma neustrium L. causes significant leaf area losses (Silla and Escudero 2006). We set out to test two main hypothesis: (a) leaf damage induced compensatory photosynthesis responses (the CO 2 assimilation rate, conductance and PNUE) at stem level (damaged versus intact leaves in treated plants) and plant level (damaged and intact leaves in treated plants versus intact leaves in control plants), and (b) leaf damage affected N resorption efficiency and proficiency through changes in N leaf content during leaf senescence and abscission at stem and plant level.…”

Estimation of tree water stress from stem and soil water monitoring with time‐domain reflectometry in two small forested basins in Spain

“…This species is well adapted to surviving summer water deficits while maintaining photosynthetic production (Gallego et al, 1994;Rico et al, 1996). Q. pyrenaica has been poorly studied in relation to other Mediterranean Quercus species (Silla and Escudero, 2006).…”