A meta‐analysis of soil salinization effects on nitrogen pools, cycles and fluxes in coastal ecosystems

Abstract

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH (12%) and soil total N (210%), although it decreased soil NO (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N O fluxes as well as hydrological NH and NO fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen (DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized.

Stimulation of N2O emission by manure application to agricultural soils may largely offset carbon benefits: a global meta‐analysis

“…In addition to direct effects, manure application could indirectly regulate soil N 2 O emissions by changing soil aeration, specifically oxygen availability at microsites with the decomposition of organic matter (Xu et al ., ). Furthermore, manure application cannot only increase soil pH (Whalen et al ., ) but can also result in increased soil porosity, aggregation, and hydraulic conductivity (Haynes & Naidu, ), which can regulate various abiotic and biotic processes governing N 2 O production in agricultural soils (Butterbach‐Bahl et al ., ; Heil et al ., , Zhou et al ., ).…”

Xylem–phloem hydraulic coupling explains multiple osmoregulatory responses to salt stress

“…Over the last decades, soil salinization has grown at an unprecedented rate, becoming a global environmental issue (Datta & Jong, 2002;Schofield & Kirkby, 2003;Wicke et al, 2011;FAO, 2015), with substantial repercussions on both natural (Thomas & Middleton, 1993;Lombardini, 2006;Zhou et al, 2017) and managed ecosystems (Oldeman et al, 1990;Rohades et al, 1992;Jobb agy & Jackson, 2004;Marchesini et al, 2017). Out of the 1.5 billion ha in use for crop production world-wide, human-induced (secondary) salinity is now impacting some 0.3 billion ha and already represents a threat to the food security of arid regions, where irrigation is employed routinely (Ghassemi et al, 1995;Pitman & L€ auchli, 2002).…”

Effect of Salinity Stress and Microbial Inoculations on Glomalin Production and Plant Growth Parameters of Snap Bean (Phaseolus vulgaris)

“…In addition to that, secondary salinization, i.e., development of salinity due to human intervention, also affects 76 million ha of land area [1] worldwide. Ground water aquifers near coastal regions that are trapped under a permeable layer of rocks are susceptible to saltwater intrusion and degradation of water quality for agricultural use [3][4][5]. Typically, in South Florida, USA, sea level rise [6], saltwater intrusion, and high evaporation [7] results in high saline conditions, i.e., 40 to 60 PSU (practical salinity unit; g kg −1 ) [8], in the bay and agricultural area.…”