Nitrogen acquisition by plants and microorganisms in a temperate grassland.

Qianyuan Liu,Hua Ouyang,Na Qiao,Xiaoping Xin,Xingliang Xu,Yakov Kuzyakov,Jessie Yc Han,Yuqiang Tian

doi:10.1038/srep22642

Abstract

Nitrogen (N) limitation is common in most terrestrial ecosystems, often leading to strong competition between microorganisms and plants. The mechanisms of niche differentiation to reduce this competition remain unclear. Short-term 15N experiments with NH4+, NO3−, and glycine were conducted in July, August and September in a temperate grassland to evaluate the chemical, spatial and temporal niche differentiation by competition between plants and microorganisms for N. Microorganisms preferred NH4+ and NO3−, while plants preferred NO3−. Both plants and microorganisms acquired more N in August and September than in July. The soil depth had no significant effects on microbial uptake, but significantly affected plant N uptake. Plants acquired 67% of their N from the 0–5 cm soil layer and 33% from the 5–15 cm layer. The amount of N taken up by microorganisms was at least seven times than plants. Although microorganisms efficiently compete for N with plants, the competition is alleviated through chemical partitioning mainly in deeper soil layer. In the upper soil layer, neither chemical nor temporal niche separation is realized leading to strong competition between plants and microorganisms that modifies N dynamics in grasslands.

Highlights

Plants and microorganisms compete for the same soil resources, but they are mutually dependent on each other[1]
The microbial N pool was the largest in August, but its size in July and September relied on soil depth. It was larger in the upper soil layer (0–5 cm) than the deeper soil layer (5–15 cm) in all three months (Table 1)
Both NO3− and NH4+ pools showed a similar spatio-temporal pattern. Their size was the largest in August but the smallest in July in the upper soil layer, while it increased from July to September in the deeper soil layer (Table 1)

Summary

Introduction

Plants and microorganisms compete for the same soil resources, but they are mutually dependent on each other[1]. Understanding how plants and microorganisms acquire limited nutrients from soils is essential for understanding carbon (C) and nitrogen (N) cycles. Nitrogen is a fundamental nutrient for plant growth and metabolism but limited in most terrestrial ecosystems[7], causing strong competition for available N between roots and soil microorganisms[8,9]. Studies have explored plant-microbial competition for N to understand the mechanisms responsible for plant productivity[6], species coexistence[10,11], and ecological consequences of this competition in various terrestrial ecosystems. The consequences of competition often lead to: i) limitation on plant growth, ii) reduced microbial mineralization, and iii) increased competition for N between coexisting plant species. The old paradigm for terrestrial N cycling assumed that plants were only capable of using inorganic N (i.e., NH4+ and NO3−), mineralized by microorganisms from organic N forms. Similar patterns were observed in montane heath communities in Scotland, where microbial N was greater in autumn, after plant senescence, than early in the growing season, when microorganisms were strongly N limited[26]

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