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Does soil nitrogen availability mediate the response of grassland composition to water regime?
Author(s) -
Araya Yoseph N.,
Gowing David J.,
Dise N.
Publication year - 2013
Publication title -
journal of vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 115
eISSN - 1654-1103
pISSN - 1100-9233
DOI - 10.1111/j.1654-1103.2012.01481.x
Subject(s) - mineralization (soil science) , environmental science , dominance (genetics) , soil water , forb , plant community , nitrogen cycle , water table , ecology , agronomy , grassland , nitrogen , soil science , biology , chemistry , geology , species richness , biochemistry , geotechnical engineering , organic chemistry , gene , groundwater
Questions How is the composition of wet meadow plant communities influenced by water regime? What controls soil nitrogen ( N ) availability along a gentle soil water regime gradient? Is vegetation response to subtle changes in soil water regime mediated by N availability? Location Cricklade, W iltshire, southwest E ngland. Methods A field survey of community composition and soil N availability was conducted along a gentle gradient of water table depth (mean water table depth between 25 and 70 cm) at a species‐rich hay meadow in southwest E ngland. This study was complemented by a controlled mescosm study undertaken at water table depths between 5 and 45 cm, and a controlled laboratory N mineralization study with water tension varying between 0 and 100 cm (0–10 kPa), the latter augmented with a microbial community study. Results The field, mesocosm and laboratory studies showed that the soil N mineralization rate and N availability responded to water regime. In particular, the N mineralization rate strongly declined when the soil air‐filled pore space dropped below 10% of total soil volume. In the field, plant cover distribution (individual species as well as functional groups) correlated with increase in soil water table depth ( r = −0.86 and r = 0.89 for graminoids and forbs, respectively) and soil N availability ( r = 0.77 and r = −0.85, respectively). A switch in dominance between forbs and graminoids occurred at a mean water table depth of 55 cm and mean soil inorganic N of 20 mg·kg −1 ). Study of the soil microbial community composition in the mesocosms, using phospholipid fatty acid ( PLFA ) signatures, showed that microbial community composition was also significantly influenced by soil water status. Conclusions We show that soil moisture content and soil aeration control the availability of N , a limiting nutrient, in species‐rich wet meadows. The mechanism is linked to changes in suitability of the soil water regime for microbially mediated N mineralization. Maintaining the water regime is therefore critical because adjustment of the hydrological niche also conditions species' responses along the N availability gradient. This could subsequently prove a useful tool for conservation managers trying to sustain a target vegetation type.