Conversion of grassland to coniferous woodland has limited effects on soil nitrogen cycle processes

Influence of Tree Spacing on Soil Nitrogen Mineralization and Availability in Hybrid Poplar Plantations

“…In this study, the inorganic N contents in the growing season were higher than the non-growing season (Figure 3), possibly because of the higher microbial activity and nutrient turnover in the growing season [37,38]. However, inorganic N content in soils sampled in August 2012 under lower tree density was much lower than that of higher density treatments in the present study, confirming that available N in forest soils is often strongly influenced by N uptake by forest vegetation rather than microbial N mineralization and immobilization [39]. Our previous study indicated that understory Shannon index, understory biomass, and concentration of N, P, K, and Mg in understory were much greater in low density plantations (6 × 6 m and 4.5 × 8 m) than in high density stands (5 × 5 m and 3 × 8 m) during the growing season [9].…”

Water availability and abundance of microbial groups are key determinants of greenhouse gas fluxes in a dryland forest ecosystem

“…Our results are similar, with a significant reduction of CO 2 emissions under afforested soils. Moreover, it has been shown that the conversion of grasslands to woodlands can have limited effects on soil N processes (McKinley et al, 2008) and our study shows reduced effect of afforestation on inorganic N. This suggests that other environmental drivers can be affecting soil respiration, not to mention the contribution of grass root respiration not accounted for in our measurements. Water-filled pore space and soil temperature were significantly decreased under afforestation and also positively correlated to CO 2 , further supporting previous reports of water availability and soil temperature as a main driver of CO 2 emissions (Davidson et al, 2006).…”

Causes and consequences of woody plant encroachment into western North American grasslands

“…In new Juniperus woodlands, carbon and nitrogen stocks increased in plant biomass and soils with little change in availability of nitrogen (McKinley and Blair, 2008). Few changes in nitrogen cycle processes were detected in Juniperus woodlands recently converted from grasslands, including little change in microbiological activity (McKinley et al, 2008b). Soil temperatures were lower below the Juniperus canopies while soil moisture remained unchanged.…”