Supplementary Information for Online Publication Only

Retention of dissolved inorganic nitrogen by foliage and twigs of four temperate tree species

Sandy Adriaenssens, Jeroen Staelens, Karen Wuyts, Roeland Samson, Kris Verheyen, Pascal Boeckx

1. Supplementary experiment

1.1. Aims and description

Because during the experiment conducted in 2008 a large amount of the applied 15NH4+ could not be retrieved in throughfall water and plant material (see Water Samples in the main paper), the 15N spraying experiment was repeated on beech twigs only in June 2010. The aim of this experiment was to assess (i) if the “lost 15NH4+” could be attributed to the rinsing of leaves and twigs after the experiment and (ii) if this rinsing loss is affected by the type of rinsing solution, that is, distilled water, KCl or a non-labelled rainwater solution.

For this experiment 3-year-old beech saplings were used of the same provenance as in 2008. They were planted on 16 March 2010 in a 1:1 mixture of river sand (1-5mm) and sandy soil from a mature Corsican pine stand (20-100 cm depth). The saplings were also placed at a wind sheltered location in the close vicinity of the laboratory near Ghent (north of Belgium, approximately 60 km from the North Sea in the prevailing wind direction; 50°58 N, 3°49 E).

Similar to the experiment conducted in 2008, twelve foliated beech twigs were selected and sprayed with the low NO3-to NH4+ratio treatment (only 15N-labeled NH4+), after which the throughfall solution was collected. After harvesting, one-third of the treated beech twigs was rinsed with deionized water, one-third with 0.05 M KCl and one-third with an unlabeled artificial rainwater solution and subsequently the rinsing solution was collected. Plant material and water samples were analyzed as described in Materials and Methods.

1.2. Results

Foliar 15NH4+ retention did not differ between the three different rinsing methods (results not shown; p = 0.22). Average NH4+-N concentrations of the rinsing water collected in 2010 were 1.22 ± 3.15 µg N g-1 DM for deionized water, 10.40 ± 7.74 µg N g-1 DMfor KCl and 32.24 ± 4.08 µg N g-1 DMfor the artificial rainwater solution, with an average 15N enrichment of 8.24, 4.29 and 1.45 atom %, respectively. This resulted in an average 15N recovery of 0.5, 1.3 and 1.8 % for deionizedwater, KCl and artificial rainwater, respectively (Figure S1). No significant differences in 15NH4+ concentration were found between the three different rinsing methods (p= 0.966).

Fig. S1 Average 15NH4+ (µg N g DM-1) retrieved in leaves + twigs, throughfall water and rinsing water compared with the 15NH4+ applied to foliated beech twigs.

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Table S1 Mean Net Throughfall Fluxes (NTF, µmolc g-1 DM) for All Major Ions per Tree Species and Phenological Stage.

Tree species / Season / NH4+ / NO3- / H+ / SO42- / Na+ / Cl- / K+ / Ca2+ / Mg2+ / WA
Birch / Developing / 0.23 (2.54) / 0.59 (0.56) / 1.55 (0.78) / 0.88 (0.50) / 0.53 (1.08) / -0.33 (0.33) / 1.71 (0.78) / 2.04 (1.08) / 0.62 (0.30) / 5.31 (2.57)
Fully leafed / -1.18 (1.84) / -0.03 (0.12) / -0.17 (0.05) / 0.37 (0.49) / 0.60 (0.71) / -0.43 (1.10) / 0.90 (0.59) / 3.18 (1.48) / 0.47 (0.26) / 3.76 (1.59)
Senescing / 5.20 (7.09) / 0.44 (1.05) / -0.05 (0.24) / 0.48 (0.28) / 0.14 (0.67) / 0.36 (0.89) / 0.92 (0.56) / 1.15 (0.45) / 0.39 (0.31) / 6.30 (7.41)
Leafless / 0.01 (0.98) / 0.22 (0.17) / -0.25 (0.14) / 1.29 (0.81) / 1.07 (0.54) / 0.63 (1.01) / 0.45 (0.26) / 1.08 (0.49) / 0.35 (0.09) / 0.30 (1.32)
Beech / Developing / -3.90 (1.82) / -2.07 (2.27) / -0.20 (0.07) / 0.41 (0.41) / -0.20 (0.64) / 0.09 (0.46) / 7.72 (5.80) / 2.07 (1.16) / 1.22 (0.76) / 8.29 (7.16)
Fully leafed / -0.71 (1.75) / 0.06 (1.09) / -0.12 (0.06) / 0.49 (0.43) / 0.22 (1.11) / -0.13 (1.21) / 0.85 (0.42) / 2.24 (0.54) / 0.49 (0.33) / 2.46 (0.73)
Senescing / 0.18 (0.54) / 0.43 (0.25) / -0.16 (0.05) / 1.70 (0.33) / 0.31 (0.22) / 0.70 (0.34) / 1.46 (0.74) / 1.95 (0.63) / 0.35 (0.16) / 1.17 (1.04)
Leafless / 1.12 (0.79) / 0.33 (0.14) / -0.08 (0.03) / 2.09 (0.44) / 0.78 (0.22) / 1.40 (1.55) / 0.70 (0.14) / 1.22 (0.33) / 0.94 (0.23) / 0.30 (1.78)
Oak / Developing / -1.49 (1.08) / 0.02 (0.73) / -0.20 (0.09) / 0.46 (0.57) / -0.04 (0.66) / 0.09 (0.57) / 3.61 (2.87) / 1.60 (0.84) / 1.14 (0.85) / 3.97 (2.81)
Fully leafed / -0.31 (0.56) / 0.08 (0.11) / -0.10 (0.05) / 0.40 (0.17) / 0.24 (0.22) / 0.05 (0.35) / 1.68 (0.93) / 2.28 (0.89) / 0.94 (0.46) / 3.82 (0.97)
Senescing / 0.19 (0.63) / 0.53 (0.58) / -0.15 (0.10) / 0.83 (0.24) / 0.40 (0.43) / 1.11 (1.01) / 1.70 (1.38) / 1.68 (0.83) / 0.71 (0.37) / 1.67 (1.54)
Leafless / 0.10 (1.66) / 0.10 (1.67) / -0.22 (0.10) / 0.97 (1.46) / 0.73 (1.63) / 0.67 (2.28) / 0.95 (0.40) / 1.46 (0.83) / 0.36 (0.51) / 1.00 (1.75)
Pine / Developing / 0.03 (0.75) / 0.31 (0.16) / 0.12 (0.29) / 0.17 (0.08) / 0.04 (0.06) / 0.07 (0.11) / 0.79 (0.33) / 0.26 (0.21) / 0.08 (0.06) / 0.72 (0.40)
Fully leafed / -0.04 (0.35) / 0.02 (0.09) / -0.05 (0.03) / 0.09 (0.12) / 0.30 (0.17) / 0.07 (0.29) / 0.43 (0.18) / 0.88 (0.33) / 0.16 (0.06) / 1.49 (0.76)
Senescing / 1.16 (2.04) / 0.21 (0.14) / 0.02 (0.10) / 0.35 (0.07) / -0.02 (0.09) / 0.06 (0.14) / 0.44 (0.18) / 0.38 (0.09) / 0.08 (0.04) / 1.44 (2.07)
Leafless / 0.54 (0.35) / 0.25 (0.09) / -0.05 (0.02) / 1.12 (0.20) / 0.79 (0.25) / 0.70 (0.28) / 0.50 (0.14) / 0.75 (0.32) / 0.33 (0.09) / 0.47 (0.45)

Standard deviation is given in parentheses

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