Quantifying atmospheric N deposition in dryland ecosystems: A test of the Integrated Total Nitrogen Input (ITNI) method

Abstract

Estimating nitrogen (N) deposition to terrestrial ecosystems is complicated by the multiple forms and routes of N loading from the atmosphere. We used the integrated total nitrogen input (ITNI) method, which is based on the principle of isotope dilution within a plant-liquid-sand system, to quantify N inputs to coastal sage scrub ecosystems in Riverside, California. Using the ITNI method, we measured atmospheric N deposition of 29.3 kg N ha yr over a range of aboveground plant biomass of 228 to 424 g m. From 85 to 96% of the atmospheric N inputs were taken up by plants in the ITNI modules with most of the assimilation mediated by, and stored in, aboveground biomass. Parallel measurements using conventional approaches yielded deposition rates of 25.2 kg N ha yr when using the inferential method and 4.8 kg N ha yr using throughfall collectors. The relatively low throughfall estimates were attributed to canopy retention of inorganic N, low rainfall, and to the fact that the throughfall flux data did not include organic N and stomatal uptake of N gases. Also, during dry periods, frequent watering of ITNI modules may have increased stomatal conductance and led to overestimates of N deposition. Across published studies that used the ITNI method, areal N deposition rates varied by ~40-fold, were positively correlated with plant biomass and 90% of the variability in measured deposition rates can be explained by plant biomass production. The ITNI method offers a holistic approach to measuring atmospheric N deposition in arid ecosystems, although more study is needed to understand how watering rates effect N deposition measurements.

Nutrients cause grassland biomass to outpace herbivory

“…However, with nutrient addition at larger spatial scales, only if herbivore population growth is limited by the nutritional quality of resources in dry sites could this effect amplify with time. While population dynamics of herbivores in some low precipitation systems can vary with the quality of their resources 45 , elevated nitrogen inputs can lead to increased standing biomass even in dryland systems 46 , suggesting that this preference response in low precipitation regions may be weaker at the landscape scale. However, while decreased fertilization effects on biomass production in arid systems are often attributed to nutrient immobilization or water resource limitation 47 , these results suggest that herbivory also may play a role.…”

Direct Canopy Uptake of Atmospheric Reactive Nitrogen: A Significant Pathway for Airborne Nitrogen Input into Rice Paddy Ecosystems

“…Although we employed methods such as wrapping the rice-growing boxes, the use of ultra-pure water, using similar fertilizer N rates in the rice-growing boxes and in the rice fields, covering the boxes during rainfall events, and collecting every wilted leaf during the experiments, our study has some limitations. Canopy uptake of ARN has been reported to be affected by plant biomass, , and it is likely that the canopy ARN uptake in our study may have been overestimated to some extent. For example, after the elongation stage, the fresh weights of rice plants grown in the water-culture boxes were significantly higher than those of a hill of rice plants in the nearby rice fields (Figure S2).…”

“…19,20 Canopy absorption has been considered to be an important pathway through which forests acquire N. 21 In addition, using micrometeorological techniques, deposition of NH 3 , NO x , or HNO 3 on forest, 22 grassland, 23 and cropland 24 soil-plant systems has been detected in open fields where the ARN compounds were present at low concentrations. Furthermore, using sand-culture combined with a 15 N dilution technique, the estimated total airborne N inputs (wet and dry N deposition, including direct canopy uptake of ARN) of some dryland substrate-plant systems 8,25 were found to be much higher than the wet-only or bulk N deposition over the same period, indicating that a certain portion of the total N deposition originated from direct canopy uptake of ARN.…”

Atmospheric Organic Nitrogen Deposition in Strategic Water Sources of China after COVID-19 Lockdown

“…The total N deposition was estimated at 80–100 kg N · ha −1 · yr −1 for a maize-wheat cropping system in the North China Plain, China (He et al, 2007, 2010 [ 38 ]), and 29.3 kg N · ha −1 · yr −1 in coastal sage scrub ecosystems in Riverside, California (Sickman et al) [ 39 ].…”