Nitrogen accumulation and distribution in Danthonia richardsonii swards in response to CO₂ and nitrogen supply over four years of growth

Abstract

Nitrogen-stressed microcosms of the C3 grass Danthonia richardsonii gained nitrogen from the environment when grown under ambient or enriched (359,`amb' or 719 mL L ±1 enr', respectively) atmospheric CO 2 concentrations over a 4-y period. This gain was apparent at all rates of supplied mineral N (2.2, 6.7 or 19.8 g N m ±2 y ±1 ± low-N, mid-N or high-N), although it was small at high-N. Small losses of N occurred from the microcosm as leachate, while gaseous losses of N were estimated to be between 10% and 25% of applied mineral N. Losses of applied mineral N were slightly lower under CO 2 enrichment only at the highest rate of mineral N supply. Levels of 15 N natural abundance in green leaf (d 15 N) of ±2½ (amb low-N) and of below ±4½ (enr low-& mid-N) suggest that absorption of atmospheric NH 3 may have been a source of some of the extra N in the low and mid-N treatments. Biological N 2 ®xation, of up to 2 g m ±2 y ±1 was hypothesized to form the remainder of the environmental N source. Microcosm C:N ratio was higher under CO 2 enrichment. Nitrogen productivity of microcosm carbon gain (g C accumulated g ±1 leaf N day ±1 ) was increased (up to 100%) by CO 2 enrichment at all rates of mineral N supply. Green leaf %N was reduced by CO 2 enrichment, and there was less nitrogen in the green leaf pool under CO 2 enrichment. Less, or the same amount of nitrogen was present in senesced leaf, surface litter and root under CO 2 enrichment while more nitrogen was present in the soil in organic forms, and as NH 4 + at the highest rate of mineral N supply.

Dynamics of nitrifying activities, denitrifying activities and nitrogen in grassland mesocosms as altered by elevated CO2

“…Soil water content has generally been found to increase at elevated CO 2 due to reduced stomatal conductance (Knapp et al ., 1996; Hungate et al ., 1997; Arnone & Bohlen, 1998; Lutze & Gifford, 1998; Niklaus et al ., 1998b; Hungate et al ., 2002), and occurs even in some situations where leaf area index is increased at elevated CO 2 (Li et al ., 2003). Our measurements of soil water content are consistent with these previous studies, since soil water content was generally increased at elevated CO 2 for both Holcus and Festuca mesocosms.…”

Patterns of soil nitrogen storage in China

“…The productivity and dynamics of many natural and managed terrestrial ecosystems, including most agricultural and managed-forest ecosystems, are limited by the supply of biologically available N [Vitousek and Howarth, 1991;McGuire et al, 1995;Melillo, 1996;Tian et al, 1999;Galloway et al, 2004]. The enrichment experiments of carbon dioxide further indicate that N limitation directly influences carbon sequestration of terrestrial ecosystems [Lutze and Gifford, 2000;Oren et al, 2001;Hu et al, 2001;Schlesinger and Lichter, 2001]. Increased nitrogen availability increases productivity and biomass accumulation substantially, at least for the short-term [Vitousek and Howarth, 1991].…”

Modeling Vegetation as a Dynamic Component in Soil‐vegetation‐atmosphere Transfer Schemes and Hydrological Models

“…A decrease in transpiration and an increase in carbon uptake (in elevated CO 2 conditions) imply increased water use efficiency and increased soil moisture. A number of studies have reported higher soil moisture under conditions of elevated CO 2 [e.g., Knapp et al ., 1996; Fredeen et al ., 1997; Lutze and Gifford , 1998; Morgan et al ., 1998; Volk et al ., 2000]. However, hydrological models, which are used to study the impact of climate change on hydrology and water resources, rarely consider the effects of changes in LAI and stomatal conductance (associated with a change in climate and CO 2 concentration), the resulting changes in soil moisture, and the effect on evapotranspiration and runoff.…”