Variation in nitrogen supply changes water-use efficiency of Pseudotsuga menziesii and Populus x euroamericana; a comparison of three approaches to determine water-use efficiency

Abstract

We studied the effects of three nitrogen (N) supply rates (low, intermediate and high) on Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings and poplar clone "I-214" (Populus x euroamericana (Dole) Guinier) cuttings growing in mini-stands. Our specific objectives were to: (1) evaluate the effects of N supply on water-use efficiency (WUE) and biomass production; (2) determine if N affects WUE through control of carbon assimilation rates or through stomatal control of water loss; and (3) compare three methods of estimating WUE: one short-term method (WUE(i), based on gas exchange measurements) and two long-term methods (WUE(T), based on the ratio between biomass production and transpired water, and Delta, based on leaf carbon isotope discrimination tested as a proxy of WUE). In both species, biomass production, WUE(i) and WUE(T) increased with increasing N supply, but there was no effect of N supply on either transpiration or stomatal conductance and Delta was negatively related to leaf N concentration. Plots of Delta versus both WUE(i) and WUE(T) revealed negative trends, but the regression between WUE(i) and Delta was significant only for Douglas-fir, and the regression between WUE(T) and Delta was significant only for poplar. Thus, the mechanisms underlying the response of WUE to N supply were mainly related to a positive effect of N supply on photosynthetic rates. The data confirm that carbon isotope discrimination may be a useful proxy of WUE. The finding that N availability enhances both biomass production and WUE may have practical implications in regions where these factors impose constraints on forest productivity.

Effect of fertigation with potassium and nitrogen on gas exchange and biomass accumulation in eggplant1

“…The N doses that maximized the water-use efficiency and total dry weight (250 kg ha -1 and 215 kg ha -1 , respectively) were close, indicating that the total dry weight (carbon isotope) is a useful proxy of water-use efficiency (Ripullone et al 2004).…”

“…When the water-use efficiency was evaluated in other crops, similar results were obtained for N application, if compared to eggplant. Using a fertilizer solution, Ripullone et al (2004) applied N in low, medium and high amounts on two forest species seedlings, and concluded that the high N supply increased the biomass production and water-use efficiency. The water-use efficiency was influenced by the positive effect of N on the net photosynthesis rates, since stomatal conductance and transpiration were not affected by N application.…”

The Response of Soil CO2 Efflux to Water Limitation Is Not Merely a Climatic Issue: The Role of Substrate Availability

“…This can be attributed to the different water use efficiency of the two species. In fact, poplar is a winter deciduous plant; it boosts its assimilation rates, at the expense of water control, during the more favourable period [49,50]. Differently, C. monspeliensis, a summer deciduous Mediterranean species, taking advantage of the autumn period to extend the growing season after the summer drought, adopts more constant and lower assimilation rates in order to minimize both water loss throughout the year and the unit cost of leaf production [51,52].…”

13C abundance, water-soluble and microbial biomass carbon as potential indicators of soil organic carbon dynamics in subtropical forests at different successional stages and subject to different nitrogen loads

“…In the N-unsaturated disturbed and rehabilitated forests, foliar C isotopic discrimination decreased with the increase of foliar N concentration (Fig. 2), which indicated that N availability had a positive effect on photosynthesis when foliar N was below the threshold (Sparks and Ehleringer 1997;Ripullone et al 2004). Brown et al (1996) reported that the photosynthetic rate of seedlings of Picea sitchensis, Thuja plicata and Tsuga heterophylla decreased when foliar N exceeded 21 mg g −1 .…”

“…One of our previous studies also indicated that litter decomposition rates were stimulated by N addition in the disturbed and rehabilitated forests limited by N ). At the plant species level, the foliar C isotopic discrimination value(Δ)could reflect water use efficiency (WUE) during photosynthesis (Ripullone et al 2004), and δ 13 C of foliar tissues could represent integrated effects of exchange between plant and atmosphere during plant growing period of the year. The plant species studies were representative within their forests.…”