The effects of a 9-year nitrogen and water addition on soil aggregate phosphorus and sulfur availability in a semi-arid grassland

Abstract

14Previous studies have demonstrated that higher nitrogen (N) and water availability 15 affect both above-and below-ground communities, soil carbon and N pools, and 16 microbial activity in semi-arid grasslands of Inner Mongolia. However, how soil 17 phosphorus (P) and sulfur (S) pools, and related soil enzyme activities (as indicators 18 of P and S cycles) respond to long-term N and water addition has still remained 19 unclear. Since 2005, a field experiment with urea and water amendments has been 20 conducted to examine their effects on total and available P and S concentrations and 21 alkaline phosphomonoesterase (PME) and aryl-sulfatase (ArS) activities in three soil 22 3 soil structure, supplying available P and S, and maintaining the sustainability of this 36 semi-arid grassland. 37 38

Nitrogen addition alters elemental stoichiometry within soil aggregates in a temperate steppe

“…Our previous study suggested that microaggregates retained significantly higher inorganic N relative to large macroaggregates (Wang et al, 2015a). However, DOC and AP con- centrations showed no difference between large macroaggregates and microaggregates, as suggested by our previous studies (Wang et al, 2015b(Wang et al, , 2016a. In this context, microaggregates had significantly lower DOC : DIN ratios (Fig.…”

“…Our previous study suggested that N addition increased soil AP by 60.2 and 84.5 % within large macroaggregates and microaggregates, respectively (Wang et al, 2016a). Based on this, it was reasonable to detect a significant decrease in the ratio of DOC : AP within large macroaggregates and microaggregates (Fig.…”

“…A 7-year N field manipulation experiment has already shown significant aboveground changes in species turnover rates, plant community composition, and community stability (Xu et al, 2012). Microaggregates (< 250 µm) had the highest dissolved inorganic N (DIN) concentration as compared to large (> 2000 µm) and small (250-2000 µm; see Wang et al, 2015a) macroaggregates, which was not the case for both DOC (see Wang et al, 2015b) and AP (Wang et al, 2016a). Nitrogen addition significantly increased DIN (see Wang et al, 2015a) and available Fe and Mn but decreased exchangeable Ca and Mg across three soil fractions (not for Ca in microaggregates; Wang et al, 2016b).…”

“…2b). Soil acidification could enhance dissolution of phosphate from mineral-bound P pools, while this was not the case for DOC (Wang et al, 2016a). Thus, production of DOC might not keep up with continuous dissolution of AP, resulting in a lower DOC : AP ratio under N addition (Fig.…”

“…After being shaken at 180 rpm for 2 h, the extracts were filtered and available Fe and Mn concentrations in the filtration were determined by the AAS. Soil DOC and available nutrients of the control plot were listed in Table 1 (data from Wang et al, 2015a, b, and2016a). The concentrations of exchangeable Ca and Mg were represented as cmol per kg soil aggregate, and it was a mg per kg soil aggregate for available Fe and Mn.…”